High Temperature Properties of LiNi0.5Mn1.5O4 as Cathode Materials for High Voltage Lithium-Ion Batteries

Jinhuo Gao; Jiafeng Ruan; Yuepeng Pang; Hao Sun; Junhe Yang; Shiyou Zheng

doi:10.7536/PC200773

Progress in Chemistry ›› 2021, Vol. 33 ›› Issue (8) : 1390-1403 DOI: 10.7536/PC200773

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High Temperature Properties of LiNi_0.5Mn_1.5O₄ as Cathode Materials for High Voltage Lithium-Ion Batteries

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Abstract

The rapid development of electric vehicles and large-scale energy storage systems have created a huge demand for high energy density and power density lithium-ion batteries in the market. Because of the advantages such as high voltage(4.7 V vs. Li/Li⁺), high energy density and power density, abundant resources and low cost, LiNi_0.5Mn_1.5O₄ is considered as one of the most promising lithium-ion battery cathode materials. However, the severe undesirable side reactions between LiNi_0.5Mn_1.5O₄ and electrolyte at elevated temperature leads to worse cycling performance, which limits its commercial application. Therefore, improving the high-temperature performance of LiNi_0.5Mn_1.5O₄ has become one of the research hotspots in the field of lithium-ion batteries. In this paper, the main achievements of recent researches on LiNi_0.5Mn_1.5O₄ materials are reviewed. Starting with the basic characteristics and existing challenges of LiNi_0.5Mn_1.5O₄, strategies such as ion doping, surface coating and surface doping are focused on improving the high-temperature performance. In addition, suggestions and prospects are put forward for subsequent research.

Contents

1 Introduction

2 Structure of LiNi_0.5Mn_1.5O₄cathode material

3 Synthesis of LiNi_0.5Mn_1.5O₄cathode material

4 Challenges of LiNi_0.5Mn_1.5O₄cathode material

5 Modification of LiNi_0.5Mn_1.5O₄cathode material at high temperature

5.1 Bulk ion doping

5.2 Surface coating

5.3 Surface ion doping

6 Conclusion and outlook

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Keywords

lithium-ion batteries / LiNi_0.5Mn_1.5O₄ / bulk ion doping / surface ion doping / surface coating / high temperature properties

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Jinhuo Gao, Jiafeng Ruan, Yuepeng Pang, Hao Sun, Junhe Yang, Shiyou Zheng. High Temperature Properties of LiNi_0.5Mn_1.5O₄ as Cathode Materials for High Voltage Lithium-Ion Batteries. Progress in Chemistry, 2021, 33(8): 1390-1403 DOI:10.7536/PC200773

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1 Introduction

With the change of the world energy structure, governments have greatly increased their support for the new energy industry. Energy-saving and environmentally friendly pure electric vehicles and hybrid electric vehicles have become the main direction of the development of the automotive industry in the 21st century^[1]. Lithium-ion battery has become the most potential power battery for electric vehicles because of its high energy density, long cycle life and environmental friendliness^[2⇓~4]. The anode material of commercial lithium-ion batteries generally uses graphite with much higher capacity than the cathode material, and the process is relatively mature, so the cathode material has become the key to the breakthrough of power batteries. At present, the main commercial cathode materials are lithium iron phosphate (LiFePO₄), lithium manganate (LiMn₂O₄) and ternary materials (LiNi_xCo_yM_1-_x_-_yO₂,M=Mn/Al,0<x,y,z<1), but their discharge plateau is generally lower than 4 V. To obtain a high voltage, the number of single batteries is relatively large when grouped, which occupies a large space, thus limiting the range of electric vehicles^[5]. In order to obtain higher energy density and power density to meet the performance requirements of lithium-ion batteries for electric vehicles, it is necessary to develop new high-voltage cathode materials.

Lithium nickel manganate (LiNi_0.5Mn_1.5O₄) is a spinel cathode material with a three-dimensional lithium ion diffusion channel, a voltage plateau up to 4. 7 V, a theoretical specific capacity of 146.7 mAh·g^-1, high energy density (650 Wh·kg^-1) and power density, low cost, abundant raw materials and environmental friendliness, which is considered as one of the preferred cathode materials for the next generation of power lithium-ion batteries^[6⇓~8]. However, the serious interfacial side reaction between the LiNi_0.5Mn_1.5O₄ material and the electrolyte occurs at high voltage, which leads to the decomposition of the electrolyte and the formation of SEI film, and the dissolution of transition metal ions, resulting in the capacity attenuation during cycling^[9,10]. In addition, the side reaction between LiNi_0.5Mn_1.5O₄ and electrolyte is more intense at high temperature, and the thickness of SEI film is increasing, which seriously affects its cycle performance, which has become a major factor restricting its commercialization^[11,12].

In this paper, the research progress of improving the high-temperature properties of LiNi_0.5Mn_1.5O₄ by ion doping, surface coating and surface doping is reviewed, and the future research directions are prospected according to the current development status.

2 Structure of the LiNi_0.5Mn_1.5O₄.

The LiNi_0.5Mn_1.5O₄ is a spinel material with a more stable structure obtained by substituting 0.5 mol of Ni for Mn in the LiMn₂O₄. As shown in fig. 1, the LiNi_0.5Mn_1.5O₄ has two structures, one is the same as the LiMn₂O₄ structure, which is the Fd3m space group, and the other is the P4₃32 space group^[13]. The Fd3m space group is a Ni/Mn disordered structure, in which Ni atoms randomly replace some Mn atoms and occupy 16d sites, and O atoms occupy 32e sites. There are some Mn³⁺ in the crystal, which is caused by the lack of O in the material calcined at high temperature. The space group of the P4₃32 is an ordered Ni/Mn structure, in which Ni orderly replaces part of Mn atoms, Ni and Mn occupy 4A and 12d sites of 16d sites, respectively, and O occupies 8C and 24e sites. The stoichiometry of Li, Ni, Mn and O is satisfied, and the valence of Mn in the crystal is + 4. During the preparation process, when the calcination temperature is lower than 700 ℃, the LiNi_0.5Mn_1.5O₄ material has an P4₃32 type ordered structure, and when the calcination temperature is higher than 700 ℃, the LiNi_0.5Mn_1.5O₄ material has an Fd3m type disordered structure^[14]. If the Fd3m type structure LiNi_0.5Mn_1.5O₄ material is subjected to heat treatment at a temperature lower than 700 deg C, the disordered structure is converted into the ordered structure. Due to the presence of the Mn³⁺, the Fd3m space group has higher ion and electron transport rates, and thus exhibits better rate capability^[15]. Yang et al. studied the thermal stability of two structures of LiNi_0.5Mn_1.5O₄ materials, and found that the ordering of Ni/Mn increases the energy barrier of ion migration, and thermal decomposition can only occur at a higher temperature, that is, the LiNi_0.5Mn_1.5O₄ with P4₃32 structure has better thermal stability^[16].

3 Method for preparing LiNi_0.5Mn_1.5O₄

There are many methods to prepare spinel LiNi_0.5Mn_1.5O₄, such as solid phase method, sol-gel method and co-precipitation method, and hydrothermal method, molten salt method, spray drying method, electrospinning method, template method and combustion method^[17,18]^[19,20]^[21,22]^[23]^[24]^[25]^[26]^[27]^[28]. Solid-state method is the most commonly used industrial preparation method of LiNi_0.5Mn_1.5O₄ because of its simple process, low cost and suitable for large-scale production. In the solid phase method, the stoichiometric lithium source, nickel source and manganese source are directly mixed and ball-milled, and then calcined at a high temperature of 600 to 1000 deg C to obtain the LiNi_0.5Mn_1.5O₄. However, the LiNi_0.5Mn_1.5O₄ materials prepared by solid phase method have some disadvantages, such as large particle size, poor uniformity, more impurities and high energy consumption. Sol-gel method can be used to prepare LiNi_0.5Mn_1.5O₄ materials with small particle size, uniform size and good crystallization, which is a common preparation method in the laboratory. Sol-gel method is generally to dissolve soluble salt in deionized water in stoichiometric ratio, add chelating agent, form high-viscosity gel through condensation and hydrolysis reaction, and calcine at high temperature after drying to obtain the final product. However, the sol-gel method is difficult to achieve industrial production because of its complex process and high cost. Coprecipitation method is a common method to prepare high performance LiNi_0.5Mn_1.5O₄ materials in industry because of its simple process and good uniformity. The coprecipitation method generally comprises the following steps of: mixing and stirring soluble salts in a stoichiometric ratio, adding a precipitant to precipitate all metal salts to form a composite precipitate, and then calcining the dried precipitate at high temperature to obtain the LiNi_0.5Mn_1.5O₄ material. Although the quality of LiNi_0.5Mn_1.5O₄ prepared by co-precipitation method is better, its cost is higher than that of solid phase method, so it is relatively less used in industrial production.

4 Problems in the LiNi_0.5Mn_1.5O₄.

(1)Li_xNi_1-_xO halite impurity facies

In the preparation process, when the calcination temperature is higher than 700 deg C, the LiNi_0.5Mn_1.5O₄ with a P4₃32structure is easy to lose oxygen and form oxygen defects, so that the Mn⁴⁺ is reduced to the Mn³⁺, and the Li_xNi_1-_xO rock salt impurity phase is generated^[29]^[30].

LiNi_0.5Mn_1.5O₄→qLi_xNi_1-_xO+rLiNi_0.5-_wMn_1.5+_wO₄+sO₂ 。

(2) Formation of SEI Film

In the process of charge and discharge, the highest voltage is close to 5 V. The electrolyte on the electrode surface is easily decomposed by the strong oxidizing Ni⁴⁺ in the charged state, and the decomposition products deposit on the electrode surface to form SEI film, which hinders the transmission of lithium ions and electrons and causes capacity attenuation^[21]. At high temperature, the decomposition of the electrolyte is more serious, and the SEI film becomes thicker and thicker, which seriously affects the cycle performance of the LiNi_0.5Mn_1.5O₄^[11].

(3) Dissolution of Transition Metal Ion

Due to the existence of trace water, water reacts with the electrolyte to produce a small amount of HF, which reacts with the LiNi_0.5Mn_1.5O₄ to dissolve the transition metal ions. The specific reaction equation is:^[14]

2LiNi_0.5Mn_1.5O₄+4HF→3Ni_0.25Mn_0.75O₂+0.25NiF₂+0.75MnF₂+2LiF+2H₂O 。

In addition, for the Fd3m disordered LiNi_0.5Mn_1.5O₄ material, the disproportionation reaction of the Mn³⁺ and the 2Mn³⁺→Mn⁴⁺+Mn²⁺ will make the Mn²⁺ dissolve in the electrolyte and reduce the stability of the material structure^[31].

5 Study on Modification of LiNi_0.5Mn_1.5O₄ at High Temperature

At high temperature, the poor electrochemical performance of LiNi_0.5Mn_1.5O₄ is caused by serious interfacial side reactions with electrolyte, which seriously affects its commercialization process. In order to solve this problem, researchers have done a lot of research, mainly focusing on ion doping and surface coating, in which ion doping is divided into two parts: bulk doping and surface doping.

5.1 Bulk doping

In order to improve the high temperature performance of the LiNi_0.5Mn_1.5O₄,The bulk doping modification mainly includes single cation doping (Al³⁺,Cu²⁺ 、Co³⁺ 、Ti⁴⁺ 、Zn²⁺ 、Ga³⁺ 、Fe³⁺ 、Cr³⁺ 、Ce³⁺ 、UY³⁺ UNNa⁺ NKMg²⁺Anion doping (F^-, UCl^-, and multiple ion co-doping)^[32~34]^[35~38]^[39]^[40,41]^[42,43]^[44~46]^[45,47]^[45,48,49]^[50]^[51]^[52,53]^[54,55]^[56,57]^[58]^{[59⇓⇓~62]}.

5.1.1 Cation doping

Al is a common metal in daily life. Compared with other transition metals, Al has the advantages of light weight, low cost and non-toxicity. Chen et Al introduced Al into the LiNi_0.5Mn_1.5O₄ by thermal polymerization, and prepared the LiNi_0.5-_xAl₂_xMn_1.5-_xO₄(0≤2x≤0.6),Al, which significantly improved the high temperature cycle stability of the LiNi_0.5Mn_1.5O₄^[32]. After 100 cycles at 1 C rate and 55 ℃, the capacity retention of Al-doped material is more than 95%, while the capacity retention of undoped material is only 74. 7%. This is mainly because the bond energy of Al-O bond (511 kJ·mol^-1) is larger than that of Ni-O bond (382 kJ·mol^-1) and Mn-O bond (402 kJ·mol^-1), which improves the structural stability of LiNi_0.5Mn_1.5O₄. In addition, they found that Al doping can improve the thermal stability and safety of LiNi_0.5Mn_1.5O₄. Xu et Al. Studied the optimal Al doping amount for different sites of Al-doped LiNi_0.5Mn_1.5O₄, and the results showed that 5 wt% Al-doped Ni site, 3 wt% Al-doped Mn site and 5 wt% Al doped Ni/Mn site had the best high-temperature cycling performance, with capacity retention of 90.1%, 88.8% and 88.7%, respectively, after 50 cycles at 55 ℃, while the undoped material was only 44.0%^[33]. Cu is also a common metal in daily life, and has higher conductivity compared with other transition metals. Meng et al. Proved by first-principles calculation that Cu ion doping LiNi_0.5Mn_1.5O₄ can reduce the barrier of lithium ion migration and improve the conductivity^[35]. Xu et al. Prepared Cu²⁺ doped LiNi_0.5Mn_1.5O₄ materials by sol-gel method, and achieved good high temperature cycle performance and rate capability^[36]. After 100 cycles at 5 C rate and 55 ℃, the initial capacity retention of the LiNi_0.45Cu_0.05Mn_1.5O₄ is as high as 98%, while that of the undoped material is only 86.2%. The initial discharge specific capacity of the material is 114.2 mAh·g^-1 at 20 C rate, and the capacity retention rate is as high as 95. 7% after 150 cycles at room temperature. They point out that Cu²⁺ doping improves the transport rate of lithium ions and reduces the accumulation of lithium ions on the surface of particles, thus reducing polarization and stabilizing the crystal structure. Liu et al. Also achieved good high temperature performance and rate capability by doping LiNi_0.5Mn_1.5O₄ materials with Cu²⁺^[37]. Kim et al. Showed through the density functional theory calculation that when a small amount of Cu²⁺ replaces the Mn site, the formation of Mn³⁺ will be inhibited, the dissolution of Mn²⁺ will be reduced, and the LiNi_0.5Mn_1.5O₄ material will change from Fd3m structure to P4₃32 structure^[38]. When the doping amount of the Cu²⁺ is increased, the material keeps the original Fd3m structure.

Cr, Ga and Fe are common doping elements for LiNi_0.5Mn_1.5O₄. In 2011, Manthiram et al. Found that the Ga³⁺ will segregate to the surface of the LiNi_0.5Mn_1.5O₄, thus forming a stable interface with the electrolyte, inhibiting the formation of SEI film and the dissolution of Mn ions, greatly improving the high temperature performance^[44]. Subsequently, they used the same method to prepare Cr, Fe and Ga-doped LiNi_0.5Mn_1.5o₄ respectively. The research shows that Cr, Fe and Ga will segregate to the surface to form a stable interface between the cathode material and the electrolyte, which inhibits harmful interfacial side reactions and improves the cycle performance of the material at room temperature and high temperature^[45]. In 2018, Li et al. Pointed out that Ga-doped LiNi_0.5Mn_1.5O₄ materials inhibit the formation of Li_xNi_1-_xO impurity phase and improve the transport rate of lithium ions^[46]. The results show that the capacity retention of the LiNi_0.5-_xGa_0.06Mn_1.5O₄ is 98. 4% after 50 cycles at 1 C rate and 55 ℃, while that of the undoped material is only 74. 0%. As shown in Figure 2 (a ~ d), Zhang et al. synthesized Cr-doped LiNi_0.5Mn_1.5O₄ material by liquid phase method. The material has a high proportion of (100) crystal face, and the (100) crystal face has better structural stability than the (111) crystal face, which can better inhibit the side reaction between the material and the electrolyte, thus improving the long cycle performance of the material at 25 ℃ and 55 ℃^[48]. The XRD results show that the Cr doping effectively inhibits the formation of the impurity phase in the Li_xNi_1-_xO. They point out that this is because the bond between Cr and O is very strong, which inhibits the loss of oxygen during high temperature calcination. In 2012, Yang et al. Used the first-principles calculation method to deeply analyze the reason why Cr doping improves the electrochemical performance of LiNi_0.5Mn_1.5O₄ materials^[49]. It is found that after doping Cr, the volume change rate of the material during charge and discharge is lower (Fig. 2e), indicating that doping Cr improves the structural stability of the material; The Cr³⁺ tends to replace the Ni²⁺, so that the Mn⁴⁺ is reduced to the Mn³⁺ and the bond length of the Li — O bond is prolonged, so that the Li migration energy barrier and the lithium vacancy formation energy of the material are reduced (Fig. 2F), thereby improving the lithium ion transport rate.

Cation doping generally introduces cations to replace the Ni and Mn sites of the LiNi_0.5Mn_1.5O₄, and the metal ions replacing the Li site are less. Zhao et al. used Na to replace the Li site in the LiNi_0.5Mn_1.5O₄, and found that Na ion doping increased the disorder degree of Ni/Mn, and added two additional electron transition channels, which accelerated the transmission rate of electrons and lithium ions, thus improving the cycle performance and rate capability of the material^[52]. After 400 cycles at 55 ℃ and 5 C rate, the 5% Na-doped material has a 97.6 mAh·g^-1 discharge capacity, which is higher than the 87.6 mAh·g^-1 of undoped material. Wang et al. Used Na-doped LiNi_0.5Mn_1.5O₄ materials, through XRD characterization, found that Na ions broadened the transport channel of lithium ions and improved the transport rate of lithium ions^[53]. At the same time, Na occupies the tetrahedral 8A site of Li, which makes Li migrate to the octahedral 16d site and reduces the stability of the material structure, so the cycle performance of Na-doped materials is not significantly improved.

5.1.2 Anion doping

In addition to cations, many researchers have also done corresponding research on anion-doped LiNi_0.5Mn_1.5O₄ materials. The electronegativity of F is large, and its ability to adsorb electrons is strong, which is conducive to improving the structural stability, so many researchers use F to replace O in the LiNi_0.5Mn_1.5O₄. Sun et al. prepared F-doped LiNi_0.5Mn_1.5O₄ by spray pyrolysis. They pointed out that F-doping increased the particle size and reduced the contact area between the LiNi_0.5Mn_1.5O₄ and the electrolyte, resulting in better thermal stability of the material, and predicted that F-doped materials had better high-temperature cycle performance^[56]. Xie et al. Prepared the LiNi_0.5Mn_1.5O₄ with F gradient doping, and confirmed that F doping can improve its high temperature performance^[57]. After 100 cycles at 1 C rate at 55 ℃, the capacity of undoped LiNi_0.5Mn_1.5O₄ decays sharply, while the capacity retention of F-doped sample is as high as 92. 1%. TEM observation shows that after 150 cycles at room temperature and 5 C rate, the SEI film on the surface of F-doped material is uniform and flat, with a thickness of 5 nm, while the surface of LiNi_0.5Mn_1.5O₄ material is uneven, with an average thickness of about 2 times that of F-doped LiNi_0.5Mn_1.5O₄. They pointed out that HF could not destroy the M-F bond, and the F-rich surface could slow down the side reaction between the cathode material and the electrolyte, inhibit the formation of SEI film, and thus improve its cycle performance. In the periodic table of elements, Cl, which is in the same main group as F, also has strong electronegativity. Kwon et al. Used Cl-doped LiNi_0.5Mn_1.5O₄ materials to effectively improve the high temperature cycle performance and rate performance^[58]. Through X-ray photoelectron spectroscopy (XPS) characterization, they found that the binding force of Cl with Ni and Mn was stronger than that of O, so Cl doping improved the structural stability of the material. In addition, the constant current intermittent titration (GITT) test results show that the lithium ion transport rate of Cl-doped materials is twice that of undoped materials. They point out that this is because the ionic radius of Cl is larger than that of O, which increases the lattice constant and broadens the transport channel of lithium ions.

5.1.3 Multi-ion co-doping

The effect of single ion doping is limited, while multi-ion co-doping can coordinate the advantages of each ion, so that the material has better comprehensive electrochemical properties^{[63⇓⇓~66]}. Ma et Al. Prepared Al, Cr, F co-doped LiNi_0.5Mn_1.5O₄ material LiNi_0.475Al_0.01Cr_0.04Mn_1.475O_3.95F_0.05 by sol-gel method. The results of infrared spectroscopy (FTIR) test showed that multi-element doping changed the structure of LiNi_0.5Mn_1.5O₄ from ordered P4₃32 space group to Fd3m space group with higher ionic conductivity and electronic conductivity.At the same time, the co-doping improves the structural stability of the material, thereby significantly improving the cycle performance and rate performance of the LiNi_0.5Mn_1.5O₄, and the capacity retention rate of the material is improved from 67.6% to 95.6% after 100 cycles at 10 C rate and high temperature of 55 deg C^[59]. Yan et al. Doped Li⁺ and F^- in the LiNi_0.5Mn_1.5O₄ material by solid phase method. They pointed out that the co-doping of Li and F increased the disorder degree of Ni/Mn, slowed down the interfacial side reaction, and thus improved the cycle performance of the material at high temperature^[60].

Ion doping can effectively improve the high temperature properties of LiNi_0.5Mn_1.5O₄ materials. The main reasons are summarized as follows: (1) The bond energy between the doped metal ions and oxygen is larger than that between Ni — O and Mn — O, which improves the structural stability of LiNi_0.5Mn_1.5O₄ materials; (2) Increasing the disorder of Ni/Mn and increasing the content of Mn³⁺ can improve the transport rate of lithium ions and electrons. (3) the generation of the impurity phase of the Li_xNi_1-_xO is inhibited, and the discharge specific capacity and the lithium ion transmission rate are improved. (4) Cr, Fe and Ga ions will segregate to the surface of the LiNi_0.5Mn_1.5O₄ automatically, while the gradient doping will enrich the ions on the surface of the material, both of which can form a stable interface with the electrolyte, inhibit the formation of SEI film and the dissolution of Mn ions.

5.2 Surface coating

Surface coating is a common high-temperature modification method, which can alleviate the interfacial side reaction between the electrolyte and the LiNi_0.5Mn_1.5O₄ and effectively reduce the capacity loss.

Shirakata et al. Coated the LiNi_0.5Mn_1.5-_xTi_xO₄ with Bi₂O₃, which effectively improved the high temperature cycle stability, and the capacity retention rate reached 70% after 500 cycles at 45 ℃^[67]. They pointed out that the decomposition of electrolyte would lead to the dissolution of transition metal ions, while the Bi₂O₃ coating physically isolated the contact between cathode materials and electrolyte, inhibited the decomposition of electrolyte, and thus reduced the dissolution of Mn, Ni and Ti elements by 40%. Amin et al. Prepared the LiNi_0.5Mn_1.5O₄ material coated with ZrO₂ by a simple solid phase method, and achieved excellent cycle performance and rate performance. After 120 cycles at 40 C rate and 55 ℃, the capacity retention of the 2 wt%ZrO₂ coated material was 76%, while that of the uncoated material was only 25%^[68]. Huang et al. found through the spherical aberration correction scanning transmission electron microscopy that the Mn²⁺ on the surface of the LiNi_0.5Mn_1.5O₄ material will migrate to the Li tetrahedral site and the empty octahedral site in the cycling process, so that the surface and subsurface spinel structures will be transformed into Mn₃O₄-type spinel structure and salt rock structure respectively, thus reducing the electrochemical performance of the material^[69]. Zhou et al. Prepared the LiNi_0.5Mn_1.5O₄ material coated with Al₂O₃ by atomic layer deposition (ALD), and the results of scanning transmission electron microscopy and electron energy loss spectroscopy (STEM-EELS) showed that the coating of Al₂O₃ could reduce the content of Mn²⁺ on the surface of the LiNi_0.5Mn_1.5O₄ material, thereby inhibiting the transformation of the surface structure of the material and improving the electrochemical performance^[70]. Rare earth oxides (La₂O₃, CeO₂, Sm₂O₃, etc.) Have good stability under high temperature, high pressure and acidic conditions^{[71⇓⇓~74]}. Therefore, our research group used La₂O₃ to coat the LiNi_0.5Mn_1.5O₄ material. As shown in the figure, 3(a~d),La₂O₃ coating not only alleviated the capacity fading during cycling, but also inhibited the decline of the voltage platform. After 50 cycles at 1 C rate and 55 ℃, 2 wt%La₂O₃ coating reduced the voltage drop of the material from 62. 0 mV to 3. 8 mV^[75]. Through SEM, TEM and EIS studies after cycling, it is found that the coated La₂O₃ can effectively alleviate the side reaction between the cathode material and the electrolyte, thereby inhibiting the formation of SEI film and improving the structural stability and lithium ion transport rate of the material (Figure 3I).

In 2002, Amine et al. First proposed that ZnO coating could reduce the HF content in the electrolyte, thus alleviating the corrosion of HF to the LiNi_0.5Mn_1.5O₄, but they did not explain the reaction mechanism of ZnO coating to reduce HF in the electrolyte^[76]. In 2010, Morales et al. Pointed out that ZnO is an amphoteric oxide, which is more likely to react with HF in the electrolyte, thus reducing the content of HF in the electrolyte^[77]. Wang et al. Used SiO₂ to coat LiNi_0.5Mn_1.5O₄ materials, and after 100 cycles at 0.5 C rate and 55 ℃, the capacity retention rate of uncoated LiNi_0.5Mn_1.5O₄ was only 59%, while that of 3.0 wt%SiO₂ coated materials was 87%^[78]. They point out that this is because the SiO₂ coating reduces the amount of HF in the electrolyte, and the specific reaction formula is

SiO₂+4HF→SiF₄+2H₂O 。

In 2018, Huang et al. Studied the HF corrosion resistance of a series of oxide Ta₂O₅, Al₂O₃, TiO₂ and Nb₂O₅.After soaking in 20% HF for 7 days, the Ta₂O₅ was hardly dissolved, the Nb₂O₅ was partially dissolved, and the TiO₂ and Al₂O₃ were completely dissolved^[79]. The change of capacity in the voltage window of 3.5-4.3 V can reflect the transition of oxygen and the structural stability of the material^[80]. As shown in Figure 3 (e ~ H), the specific capacity variation of the Ta₂O₅ coated material is lower than that of the uncoated material at 3.5 ~ 4.3 V at both room temperature and high temperature, which indicates that the Ta₂O₅ coating reduces the oxygen loss and improves the structural stability of the material. Through the comparative experiments of coating LiNi_0.5Mn_1.5O₄ materials with Ta₂O₅ and Al₂O₃ respectively, they found that the coating materials with good HF tolerance could maintain stable surface structure before and after high temperature cycling, while the coating materials which were easy to react with HF would dissolve in the electrolyte, resulting in surface structure instability (Fig. 3j, K).

Oxides as the coating of LiNi_0.5Mn_1.5O₄ may react with HF at the same time, resulting in the loss of the coating, so some researchers have used phosphates and fluorides which are more stable than oxides to coat the LiNi_0.5Mn_1.5O₄. Yi et al. Used AlPO₄ coating to improve the high-temperature cycling performance of LiNi_0.5Mn_1.5O₄ materials. They pointed out that the AlPO₄ coating has an activation process. At the beginning, the coating hinders the intercalation and deintercalation of lithium ions. With the increase of cycling times, the coating is activated, and lithium ions can be easily transported freely on the interface^[81]. Wang et al. prepared the AlPO₄ coated LiNi_0.5Mn_1.5O₄ material by ALD method, and through the characterization of X-ray absorption near edge structure spectroscopy (XANES) and differential scanning calorimetry (DSC), it was proved that the AlPO₄ coating inhibited the interfacial side reaction, reduced the Mn³⁺ on the surface of the material, and improved the structural stability, thus significantly improving the thermal stability and safety of the LiNi_0.5Mn_1.5O₄^[82]. They pointed out that the AlPO₄ is not only a separation layer between the cathode material and the electrolyte, but also can be converted into a stable SEI film to maintain the stability of the interface, thereby improving the cycle performance. Tong et al. Coated the LiNi_0.5Mn_1.5O₄ with GaF₃, and the coated material showed excellent high temperature performance and thermal stability, with a capacity retention of 82.9% after 300 cycles at 1 C rate of 60 ℃^[83]. LiF is a kind of lithium salt which is the decomposition product of electrolyte. It has good chemical stability and high voltage stability. Tiurin et al. Prepared LiF-coated LiNi_0.5Mn_1.5O₄ materials by ALD method using TiF₄ and Hfac as raw materials respectively, both of which greatly reduced the dissolution of transition metal ions and improved the high-temperature storage performance of the materials^[84]. In addition, through ICP and TOP-SIMS characterization, they found that LiF (Hfac) coated LiNi_0.5Mn_1.5O₄ increased the content of lithium ions in the material, while LiF(TiF₄) coated LiNi_0.5Mn_1.5O₄ decreased the content of lithium ions in the surface of the material, so the former showed better electrochemical performance. Lin et al. Used AlF₃ to coat LiNi_0.5Mn_1.5O₄ materials and achieved good high temperature cycle performance^[85]. According to previous reports, transition metal ions will deposit on the surface of the negative electrode material of the whole battery after dissolving in the electrolyte. They analyzed the whole battery after high temperature cycle by X-ray fluorescence spectrometer and found that the deposition of transition metal elements on the surface of the negative electrode of LiNi_0.5Mn_1.5O₄@AlF₃//Li₄Ti₅O₁₂ was much less than that of the whole battery of LiNi_0.5Mn_1.5O₄//Li₄Ti₅O₁₂.

Oxides, fluorides and phosphates can effectively alleviate the side reactions between LiNi_0.5Mn_1.5O₄ and electrolyte, improve the structural stability, inhibit the formation of SEI film and reduce the dissolution of transition metal ions, but these coating materials are often poor conductors of lithium ions and electrons, which is not conducive to the transport of lithium ions and electrons at the interface^[86]. The coating of LiNi_0.5Mn_1.5O₄ with fast ionic conductors or materials with high electronic conductivity is beneficial to the rapid transport of lithium ions and electrons at the interface, which can effectively reduce polarization and improve high temperature performance, so it is favored by researchers.

At present, the fast ion conductor materials used for coating the LiNi_0.5Mn_1.5O₄ include LiNbO₃,Li₂ZrO₃ 、Li₂TiO₃ 、Li₄Ti₅O₁₂ 、LiAlO₂ 、LiSiO₃ 、Li₄SiO₄ 、LiAlSiO₄ 、YBa₂Cu₃O₇ 、ULi₃V₂(PO₄)₃Li_6.4La₃Al_0.2Zr₂O₁₂ 、PI、ULi₃PO₄ UNLi₄P₂O₇ NKLi₂SnO₃^[87,88]^[89]^[90]^[91,92]^[93,94]^[95]^[96]^[97]^[98]^[99]^[100]^[101]^[102,103]^[104]^[105] Choi et al. prepared a LiNbO₃ coated LiNi_0.5Mn_1.5O₄ material by pre-coating, as shown in Figure 4A. First, the Ni_0.25Mn_0.75(OH)₂ precursor was coated with Nb-containing citrate.And then LiOH·H₂O is added, mixed and calcined, so that the coating layer and the main body material are doped with lithium synchronously, and the LiNbO₃ coated LiNi_0.5Mn_1.5O₄ material is obtained^[87]. The rate capability (100 mAh·g^-1 discharge capacity at 10 C rate) and high temperature cycling performance (90% capacity retention at 60 ℃ after 100 cycles) of the material were significantly improved by LiNbO₃ coating. The action principle diagram of the LiNbO₃ coating LiNi_0.5Mn_1.5O₄ material is shown in fig. 4 (B, C), and the specific mechanism can be attributed to the following three points: (1) in the high-temperature calcination process,A part of Nb⁵⁺ is doped into the bulk of the LiNi_0.5Mn_1.5O₄, so that the Mn⁴⁺ is reduced to Mn³⁺, and a Mn³⁺ rich region appears in the near-surface layer, thereby improving the transport rate of lithium ions and electrons in the surface layer; (2) The bond energy of Nb — O is larger than that of Ni — O and Mn — O, which can improve the structural stability and thermal stability of LiNi_0.5Mn_1.5O₄; The (3)LiNbO₃ material is a fast ion conductor, which not only inhibits the side reaction at the interface between the LiNi_0.5Mn_1.5O₄ and the electrolyte, but also improves the transport rate of lithium ions at the interface. Shao et al. Used Li₂ZrO₃ to coat LiNi_0.5Mn_1.5O₄ materials, which also showed the above three effects, and greatly improved the high temperature cycle performance of the materials^[89]. Zhang et al. Coated the LiNi_0.5Mn_1.5O₄ material with Li₂TiO₃. After 50 cycles at 1 C rate and 55 ℃, the capacity retention rate of the material was increased from 77.1% to 94.1% by 5 wt%Li₂TiO₃ coating^[90]. Kim et al. Prepared LiNi_0.5Mn_1.5O₄ materials coated with Al₂O₃ and LiAl₂O₃ by ALD method^[93]. The lithium ion transport rate of the LiAlO₂ is several orders of magnitude higher than that of the Al₂O₃, so the material coated with the LiAlO₂ has better high-temperature performance. From room temperature to 50℃,Al₂O₃, the coulombic efficiency of both coated and uncoated materials decreased significantly, while the coulombic efficiency of LiAlO₂ coated materials increased slightly. They pointed out that the Coulomb efficiency macroscopically reflects the intensity of the interfacial side reaction between the active material and the electrolyte, that is, the LiAlO₂ coating can effectively inhibit the interfacial side reaction. The Li₄SiO₄ has 1.2×10^-8S·cm^-1 lithium ion transmission rate and 3.36×10^-6S·cm^-1 conductivity, can reduce the content of HF in the electrolyte, and is suitable for being used as a coating material of the LiNi_0.5Mn_1.5O₄. Zhao et al. Coated the LiNi_0.5Mn_1.5O_3.98F_0.02 material with Li₄SiO₄ and achieved excellent high temperature cycle performance and rate performance. After 150 cycles at 5 C rate and 55 ℃, the capacity retention of the Li₄SiO₄ coated material was as high as 94.2%, while that of the uncoated material was only 54.9%^[96].

In recent years, fast ionic conductors, such as electrode materials for lithium ion batteries, solid electrolytes and separator materials, have also been applied to the coating modification of LiNi_0.5Mn_1.5O₄. Bai et al. Prepared LiNi_0.5Mn_1.5O₄ materials coated with Li₃V₂(PO₄)₃ as cathode materials for lithium-ion batteries by sol-gel method^[99]. As shown in Fig. 4 (e-i), a uniform coating layer of 2 nm is formed on the surface of the LiNi_0.5Mn_1.5O₄ material, and a part of V⁵⁺ is doped into the surface structure of the material in a gradient manner to form a Li-Ni-Mn-V-O solid solution transition layer, which tightly combines the coating layer with the bulk material. The electrochemical results show that the Li₃V₂(PO₄)₃ coating can effectively improve the high temperature cycle performance, rate capability and storage performance of the LiNi_0.5Mn_1.5O₄. As shown in fig. 4D, the action principle diagram of the Li₃V₂(PO₄)₃ coating LiNi_0.5Mn_1.5O₄ is shown, and the specific mechanism can be attributed to two points: on the one hand, the fast ion conductor Li₃V₂(PO₄)₃ coating layer and the Li-Ni-Mn-V-O solid solution transition layer reduce the corrosion of HF and the dissolution of transition metal ions,The formation of the SEI film at the interface is inhibited, the structural stability of the material is improved, and on the other hand, the kinetics of lithium ion and electron transfer at the interface of the electrode material and the electrolyte is accelerated. Yu et al. First used the precursor of solid electrolyte material Li_6.4La₃Al_0.2Zr₂O₁₂(LLAZO) to coat the precursor of LiNi_0.5Mn_1.5O₄, and then obtained the LLAZO coated LiNi_0.5Mn_1.5O₄ material by high temperature calcination^[100]. The LLAZO coating greatly improved the cycling performance and rate capability of the LiNi_0.5Mn_1.5O₄ material.The capacity retention of 1 wt% LLAZO coated material was 74. 4% after 100 cycles at 0. 1 C rate at 55 ℃, while the capacity retention of the uncoated material was only 24. 4%. They pointed out that LLAZO precursor was coated on the surface of LiNi_0.5Mn_1.5O₄ precursor in the form of network structure, which inhibited the growth of particles, shortened the path of lithium ion transport and improved the kinetics of electrochemical reaction. Lee et al. Coated the surface of the LiNi_0.5Mn_1.5O₄ with a layer of polyimide (PI) separator material, which effectively improved the high temperature performance. After 50 cycles at 55 ℃, the specific discharge capacity of the material increased from 98 mAh·g^-1 to 120 mAh·g^-1^[101]. They point out that the PI coating is highly continuous and has good ionic conductivity compared to the metal oxide and phosphate coatings, so the coating effect is better.

In addition to fast ionic conductors, high conductivity materials as coating materials of LiNi_0.5Mn_1.5O₄ also have a good effect on improving their high temperature performance. Huang et al. Used La_0.7Sr_0.3MnO₃ with high conductivity to coat the LiNi_0.5Mn_1.5O₄ material^[106]. The La_0.7Sr_0.3MnO₃ coating not only increases the capacity retention from 41% to 90% after 100 cycles at 60 ℃, but also improves the high temperature rate capability and storage performance. There are three main reasons for the improvement of high temperature performance of La_0.7Sr_0.3MnO₃ coating materials: :(1)La_0.7Sr_0.3MnO₃ has high conductivity, which reduces the interface impedance and polarization; The chemical reaction between the (2)La_0.7Sr_0.3MnO₃ and HF alleviates the corrosion of HF to the LiNi_0.5Mn_1.5O₄ and improves the structural stability of the material; The (3)La_0.7Sr_0.3MnO₃ coating alleviates the side reaction of the electrolyte and the LiNi_0.5Mn_1.5O₄, and inhibits the formation of the SEI film. Carbon materials are often used as coating materials for LiNi_0.5Mn_1.5O₄ because of their excellent electrical conductivity. Graphene is often used to modify electrode materials because of its excellent electrical and thermal conductivity, mechanical properties and chemical stability^[107]. Liu et al. Prepared graphene-coated LiNi_0.5Mn_1.5O₄ materials by self-assembly method, and achieved excellent high-temperature cycle performance^[108]. After 100 cycles at 2 C rate and 55 ℃, the graphene-coated material still has a 83.8 mAh·g^-1 discharge capacity, which is much higher than the 36.0 mAh·g^-1 of the uncoated material. They used in-situ XRD characterization to find that graphene-coated materials have smaller lattice strain, larger proportion of solid solution reaction and smaller proportion of two-phase transformation during charging and discharging, so they have better structural stability and higher specific discharge capacity. Conductive polymers have good conductivity and are also suitable for coating cathode materials. Wang et al. Coated a layer of 3 nm polypyrrole (PPY) on the surface of LiNi_0.5Mn_1.5O₄, which improved the high temperature cycling performance and increased the coulombic efficiency from 90% to 92%^[11]. They pointed out that the coulombic efficiency was related to the thickness of the SEI film on the surface of the material, and PPY coating inhibited the decomposition of the electrolyte, reduced the thickness of the SEI film, and thus had a higher coulombic efficiency. Yang et al. Used polyaniline (PANI) to modify the surface of LiNi_0.5Mn_1.5O₄ materials, and increased the capacity retention of the materials from 13.0% to 94.5% after 100 cycles at 55 ℃^[109]. Lin et al. Coated the LiNi_0.5Mn_1.5O₄ material with semiconductor material LaFeO₃, and achieved good high temperature cycle performance. After 100 cycles at 1 C rate of 55 ℃, the capacity retention rate of the 2 wt%LaFeO₃ coated material was as high as 93.3%, while that of the uncoated material was only 69.6%^[110]. Through the microscopic morphology after cycling, they found that the uncoated material had obvious cracks due to the erosion of HF, while the LaFeO₃ coated material still maintained a stable and complete morphology. Choi et al. Coated the surface of the LiNi_0.5Mn_1.5O₄ with a composite material of fast ion conductor Li₂O-2B₂O₃ and conductive carbon, which improved the lithium ion and electron transport rate of the material, accelerated the electrochemical reaction kinetics, and effectively improved the electrochemical performance^[111].

The surface coating can effectively improve the high-temperature performance of the LiNi_0.5Mn_1.5O₄, and the main reasons are summarized as follows: (1) the coating layer physically isolates the contact between the electrolyte and the LiNi_0.5Mn_1.5O₄, and inhibits the oxidation of the electrolyte by a strong oxidizing Ni⁴⁺, thereby inhibiting the formation of a SEI film; (2) The coating layer can protect the LiNi_0.5Mn_1.5O₄ from the erosion of HF and inhibit the dissolution of transition metal ions, thus improving the structural stability. (3) for coat materials such as ZnO, SiO₂ and La_0.7Sr_0.3MnO₃, that content of HF is reduce through chemical reaction, thereby reducing the dissolution of transition metal ions; (4) For fast ionic conductors and high conductivity materials, the transport of lithium ions or electrons at the interface is accelerated and the polarization is reduced; (5) In the coating process of some coating materials (such as Ta₂O₅, LiNbO₃, Li₃V₂(PO₄)₃), some ions are doped into the crystal structure, so that the LiNi_0.5Mn_1.5O₄ material has the effect of surface coating and ion doping at the same time, which effectively improves the comprehensive electrochemical performance.

5.3 Surface doping

Ion doping is helpful to improve the structural stability of LiNi_0.5Mn_1.5O₄ materials, but has limited effect on the interfacial side reactions between electrode materials and electrolyte. The surface coating can effectively inhibit the interfacial side reactions, while the non-electrochemically active coating hinders the transport of lithium ions and electrons, and may fall off during long cycles. Pure ion doping and surface coating both have their limitations, if we can combine them organically and give full play to their advantages, it is bound to achieve better modification effect. In 2014, Lu et al. Proposed the concept of surface doping, that is, first coating the surface of the material, and then doping ions into the surface structure of the material by high temperature calcination^[112]. The surface doping can improve the stability of the surface structure of the material and inhibit the corrosion of HF to the material, and the surface structure of the material is electrochemically active and does not hinder the transmission of lithium ions and electrons, thereby effectively improving the cycle performance of the material.

Park et al. First mixed tetrabutyl titanate with LiNi_0.5Mn_1.5O₄ materials, stirred and evaporated to dryness, and then calcined at 500 ℃ under argon to prepare Ti-doped LiNi_0.5Mn_1.5O₄ materials^[113]. Based on the first-principles calculations and experimental results, it is concluded that the doping of Ti surface retains the characteristics of strong oxidation state, so that more electrons can be accommodated around O, the bond energy of TM — O on the material surface is improved, and the dissolution of transition metal ions is effectively inhibited, thus improving the cycle performance of the material at room temperature and high temperature. Wan et Al. First coated a layer of AlPO₄ on the surface of the LiNi_0.5Mn_1.5O₄ material, and then decomposed the 2 h,AlPO₄ after calcination at 700 ℃ to form the Al-doped LiNi_0.5Mn_1.5O₄ material^[114]. The theoretical calculation and experimental results show that the octahedral 16c vacancy of transition metal ions is occupied by Al³⁺, which reduces the migration of transition metal ions and inhibits the structural degradation of the material during cycling. At the same time, the doping of appropriate amount of Al³⁺ does not affect the lithium ion transport rate. The electrochemical test results show that the Al-doped LiNi_0.5Mn_1.5O₄ material exhibits good cycling performance at high temperature. Subsequently, they prepared Zn-doped LiNi_0.5Mn_1.5O₄ materials by a similar method, as shown in Figure 5 (a ~ e). During the high temperature calcination process, ZnO reacted with the LiNi_0.5Mn_1.5O₄ materials in a solid phase to form a 30 nm shell on the surface of the materials, which contained rock salt structure and layered structure^[115]. They pointed out that the rock salt structure is non-electrochemically active, which is conducive to improving the stability of the material surface, while the layered structure can ensure the electrochemical activity of the material surface. As shown in Figure 5F, the surface structure of the material is closely related to the content of Zn²⁺. When the Zn²⁺ increases gradually, the surface of the material changes from spinel structure to layered structure, and the layered structure further changes to rock salt structure. The stability of the surface structure of the material is enhanced, and the transmission rate of lithium ions is reduced. Liang et al. First prepared the LiNi_0.5Mn_1.5O₄ materials with synergistic modification of FeO_x coating and Fe ion surface doping by ALD method^[116]. Subsequently, they calcined the coated material at 700 ℃ to obtain a LiNi_0.5Mn_1.5O₄ material with complete surface doping of Fe ions^[117]. STEM-EELS and XPS studies show that the surface of the material is rich in Mn⁴⁺, which is beneficial to inhibit the dissolution of Mn and form a stable electrode-electrolyte interface. The material is rich in Mn³⁺, which can accelerate the transmission of lithium ions, thus significantly improving the high temperature cycle performance of the material. After 500 cycles at 1 C rate and 55 ℃, the initial discharge capacity of the LiNi_0.5Mn_1.5O₄ was increased from 116 mAh·g^-1 to 122 mAh·g^-1, and the capacity retention was increased from 26. 7% to 86. 1%. Sun et al. First coated a layer of TiO₂ on the LiNi_0.5Mn_1.5O₄ material by ALD method, and then prepared the Ti-doped LiNi_0.5Mn_1.5O₄ material by high temperature calcination^[118]. It is found that the substitution of Ti for Li in the surface layer of the material results in the formation of TiMn₂O₄ spinel phase, which inhibits the transformation of the surface layer structure to salt rock phase. Ti doped in the deeper region replaces the Ni/Mn sites; The combined effect of the two results in the formation of a SEI film with more Li₂CO₃ on the surface of the material (Li₂CO₃ is helpful to form a strong and dense SEI film), which strengthens the Ni — O bond and inhibits the dissolution of Mn, thus improving the electrochemical performance.

However, Huang et al studied the Ti/Ta surface doped LiNi_0.5Mn_1.5O₄ material by using the density functional theory based on the first-principles calculation, and came to the opposite conclusion: Ti/Ta surface doping reduces the migration energy barrier of Ni/Mn on the material surface, promotes the formation of the surface rock salt phase, and inhibits the loss of O by forming stronger TM — O bonds, thus improving the stability of the material surface structure^[119]. In addition, Ti/Ta surface doping reduces the valence state of Ni in the deep charge state, thus inhibiting the oxidative decomposition of the electrolyte. Wang et al. First coated the LiNi_0.5Mn_1.5O₄ material with Co(NO₃)₂, and then calcined it at 700 ℃ to form Co-doped LiNi_0.5Mn_1.5O₄ material^[120]. The XPS and XANES results show that Co doping reduces the content of Ni and Mn³⁺ on the surface of the material, which inhibits the decomposition of electrolyte and the dissolution of Mn. As shown in fig. 6, Co surface doping significantly improves the electrochemical performance of the LiNi_0.5Mn_1.5O₄ material. After 200 cycles at 1 C rate and 55 ℃, Co surface doping improves the capacity retention of the LiNi_0.5Mn_1.5O₄ from 82% to 93%.

Surface doping can inhibit the dissolution of transition metal ions, form a more stable structure at the material interface, inhibit the decomposition of electrolyte, and ultimately improve the stability of the interface between LiNi_0.5Mn_1.5O₄ and electrolyte, inhibit the occurrence of side reactions at the interface, and thus improve the cycle performance.

In this paper, the representative work on the modification of LiNi_0.5Mn_1.5O₄ in recent years and the high-temperature properties of related materials are summarized in Table 1.

6 Conclusion and prospect

As the most expensive core component of new energy electric vehicles, lithium-ion batteries show broad market prospects. LiNi_0.5Mn_1.5O₄ has become one of the preferred cathode materials for power lithium-ion batteries because of its high voltage platform, high energy density and power density, low cost and abundant raw materials. In the environment of "de-cobaltization" of power lithium-ion batteries, the advantages of cobalt-free material LiNi_0.5Mn_1.5O₄ are further highlighted. Due to the high temperature performance constraints on the commercialization of LiNi_0.5Mn_1.5O₄ materials, in recent years, researchers have paid more and more attention to the electrochemical performance and related mechanisms of LiNi_0.5Mn_1.5O₄ at high temperatures. The research on high temperature modification of LiNi_0.5Mn_1.5O₄ is mainly divided into three aspects: bulk ion doping, surface ion doping and surface coating. Among them, bulk ion doping is mainly to improve the stability of the bulk crystal structure of the LiNi_0.5Mn_1.5O₄ material, while surface coating and surface doping focus on improving the stability of the interface between the LiNi_0.5Mn_1.5O₄ and the electrolyte, which is more conducive to improving the cycle performance.

Although LiNi_0.5Mn_1.5O₄ materials have achieved good electrochemical performance through a variety of modification methods, the high temperature performance is still facing serious challenges. According to the current research status of LiNi_0.5Mn_1.5O₄, the future development trends are prospected as follows: (1) The combined modification of ion doping and surface coating, such as surface doping, can synergize the advantages of both, and achieve better modification effect. How to simplify the operation process and accurately control the ratio of doping and coating is the key issue to be studied. (2) The coating layer may fall off due to the volume expansion and contraction of the electrode material during the intercalation and deintercalation of lithium ions, thus affecting the coating effect. Therefore, how to improve the stability of the coating layer needs to be further improved. (3) The cycle performance can be effectively improved by precisely controlling the doping sites, such as doping at the tetrahedral 8A and octahedral 16c sites of the LiNi_0.5Mn_1.5O₄ of the Fd3m structure. (4) The development of high voltage electrolyte matched with LiNi_0.5Mn_1.5O₄ materials can significantly alleviate the side reactions at the interface, which is an important direction for the wide commercialization of materials. (5) The development of solid electrolyte can greatly reduce the interfacial side reactions between electrode materials and electrolytes, and improve the safety of batteries, which is also an important direction for future development. (6) In practical applications, the cathode materials of LiNi_0.5Mn_1.5O₄ are generally used together with the anode materials of Li₄Ti₅O₁₂, so the development of high-performance Li₄Ti₅O₁₂ materials is of great significance for the commercial application of LiNi_0.5Mn_1.5O₄.

References

Publishing order | Descend order by publishing year | Descend order by cited within

[1]	Wang J, Liao H Y, Li B C, Yang G, Wang L, Meng R. Chem. Reag., 2009, 31(11): 948.

[2]	(王健, 廖红英, 李冰川, 杨光, 王磊, 孟蓉. 化学试剂, 2009, 31(11): 948.)

[3]	Ruan J F, Pang Y P, Luo S N, Yuan T, Peng C X, Yang J H, Zheng S Y. J. Mater. Chem. A, 2018, 6(42): 20804.

[4]	Ding L. Chin. J. Power Sources, 2015, 39(8): 1780.

[5]	(丁玲. 电源技术, 2015, 39(8): 1780.)

[6]	Li M, Wang Y L, Wu X Y, Duan L, Zhang C M, He D N. Prog. Chem., 2017, 29(12): 1526.

[7]	(李敏, 王艳丽, 吴晓燕, 段磊, 张春明, 何丹农. 化学进展, 2017, 29(12): 1526.)

[8]	Zhang K Q, Ling Z, Wang L Z. Battery Bimon., 2013, 43(4): 235.

[9]	(张凯庆, 凌泽, 王力臻. 电池, 2013, 43(4): 235.)

[10]	Chang Q, Wei A J, Li W, Bai X, Zhang L H, He R, Liu Z F. Ceram. Int., 2019, 45(4): 5100.

[11]	Ulvestad A, Singer A, Clark J N, Cho H M, Kim J W, Harder R, Maser J, Meng Y S, Shpyrko O G. Science, 2015, 348(6241): 1344.

[12]	Jung H G, Jang M W, Hassoun J, Sun Y K, Scrosati B. Nat. Commun., 2011, 2(1): 1527.

[13]	Li W D, Dolocan A, Oh P, Celio H, Park S, Cho J, Manthiram A. Nat. Commun., 2017, 8(1): 14589.

[14]	Madsen K E, Wade K A, Haasch R T, Buchholz D B, Bassett K L, Nicolau B G, Gewirth A A. ACS Appl. Mater. Interfaces, 2019, 11(43): 39890.

[15]	Gao X W, Deng Y F, Wexler D, Chen G H, Chou S L, Liu H K, Shi Z C, Wang J Z. J. Mater. Chem. A, 2015, 3(1): 404.

[16]	Kim J H, Pieczonka N P W, Yang L. ChemPhysChem, 2014, 15(10): 1940.

[17]	Zhang X L, Cheng F Y, Zhang K, Liang Y L, Yang S Q, Liang J, Chen J. RSC Adv., 2012, 2(13): 5669.

[18]	Yi T F, Mei J, Zhu Y R. J. Power Sources, 2016, 316: 85.

[19]	Luo Y. Doctoral Dissertation of Harbin University of Industry, 2017.

[20]	(罗英. 哈尔滨工业大学博士论文, 2017.).

[21]	Hu E Y, Bak S M, Liu J, Yu X Q, Zhou Y N, Ehrlich S N, Yang X Q, Nam K W. Chem. Mater., 2014, 26(2): 1108.

[22]	Gao Z G, Sun K, Cong L N, Zhang Y H, Zhao Q, Wang R S, Xie H M, Sun L Q, Su Z M. J. Alloys Compd., 2016, 654: 257.

[23]	Betz J, Nowak L, Brinkmann J P, Bärmann P, Diehl M, Winter M, Placke T, Schmuch R. Electrochimica Acta, 2019, 325: 134901.

[24]	Lin H B, Zhang Y M, Hu J N, Wang Y T, Xing L D, Xu M Q, Li X P, Li W S. J. Power Sources, 2014, 257: 37.

[25]	Lobo L S, Kumar A R. J. Sol Gel Sci. Technol., 2016, 80(3): 821.

[26]	Song Y M, Han J G, Park S, Lee K T, Choi N S. J. Mater. Chem. A, 2014, 2(25): 9506.

[27]	Li Y, Wang J, Zhou Z, Yao Q, Wang Z, Zhou H, Deng J. Int. J. Electrochem. Sci., 2019, 2822.

[28]	Zhao E Q, Wei L, Guo Y D, Xu Y J, Yan W C, Sun D Y, Jin Y C. J. Alloys Compd., 2017, 695: 3393.

[29]	Mokhtar N, Idris N H, Din M F M. Int. J. Electrochem. Sci., 2018, 13(11): 10113.

[30]	Hallot M, Demortière A, Roussel P, Lethien C. Energy Storage Mater., 2018, 15: 396.

[31]	Xu R, Zhang X F, Chamoun R, Shui J L, Li J C M, Lu J, Amine K, Belharouak I. Nano Energy, 2015, 15: 616.

[32]	Shu Y, Xie Y, Yan W C, Meng S, Sun D Y, Jin Y C, He K. J. Power Sources, 2019, 433: 226708.

[33]	Shirazi moghadam Y, Masoudpanah S M, Alamolhoda S, Daneshtalab R. Adv. Powder Technol., 2020, 31(2): 639.

[34]	Liu G Q, Zhang J Y, Zhang X H, Du Y L, Zhang K, Li G C, Yu H, Li C W, Li Z Y, Sun Q, Wen L. J. Alloys Compd., 2017, 725: 580.

[35]	Chen Y Y, Sun Y, Huang X J. Comput. Mater. Sci., 2016, 115: 109.

[36]	Ulu Okudur F, D'Haen J, Vranken T, de Sloovere D, Verheijen M, Karakulina O M, Abakumov A M, Hadermann J, van Bael M K, Hardy A. RSC Adv., 2018, 8(13): 7287.

[37]	Zhong G B, Wang Y Y, Zhao X J, Wang Q S, Yu Y, Chen C H. J. Power Sources, 2012, 216: 368.

[38]	Chen A Y, Kong L L, Shu Y, Yan W C, Wu W, Xu Y J, Gao H T, Jin Y C. RSC Adv., 2019, 9(22): 12656.

[39]	Luo Y, Lu T L, Zhang Y X, Yan L Q, Mao S S, Xie J Y. J. Alloys Compd., 2017, 703: 289.

[40]	Yang M C, Xu B, Cheng J H, Pan C J, Hwang B J, Meng Y S. Chem. Mater., 2011, 23(11): 2832.

[41]	Sha O, Qiao Z, Wang S L, Tang Z Y, Wang H, Zhang X H, Xu Q. Mater. Res. Bull., 2013, 48(4): 1606.

[42]	Sun H Y, Kong X, Wang B S, Luo T B, Liu G Y. Ceram. Int., 2018, 44(5): 4603.

[43]	Shiiba H, Zettsu N, Kida S, Kim D W, Teshima K. J. Mater. Chem. A, 2018, 6(45): 22749.

[44]	Ito A, Li D C, Lee Y, Kobayakawa K, Sato Y. J. Power Sources, 2008, 185(2): 1429.

[45]	Jin Y Z, Lv Y Z, Xue Y, Wu J, Zhang X G, Wang Z B. RSC Adv., 2014, 4(100): 57041.

[46]	Lin M, Wang S H, Gong Z L, Huang X K, Yang Y. J. Electrochem. Soc., 2013, 160(5): A3036.

[47]	Sun H, Kong X, Wang B, Luo T, Liu G. Int. J. Electrochem. Sci., 2017, 8609.

[48]	Chemelewski K R, Manthiram A. J. Phys. Chem. C, 2013, 117(24): 12465.

[49]	Shin D W, Manthiram A. Electrochem. Commun., 2011, 13(11): 1213.

[50]	Shin D W, Bridges C A, Huq A, Paranthaman M P, Manthiram A. Chem. Mater., 2012, 24(19): 3720.

[51]	Lan L F, Li S, Li J, Lu L, Lu Y, Huang S, Xu S J, Pan C Y, Zhao F H. Nanoscale Res. Lett., 2018, 13(1): 251.

[52]	Kiziltas-Yavuz N, Yavuz M, Indris S, Bramnik N N, Knapp M, Dolotko O, Das B, Ehrenberg H, Bhaskar A. J. Power Sources, 2016, 327: 507.

[53]	Wang J, Nie P, Xu G Y, Jiang J M, Wu Y T, Fu R R, Dou H, Zhang X G. Adv. Funct. Mater., 2018, 28(4): 1704808.

[54]	Li F, Ma J N, Lin J Y, Zhang X H, Yu H, Yang G C. Phys. Chem. Chem. Phys., 2020, 22(7): 3831.

[55]	Li S, Lan L F, Lu L, Lu Y, Li S F, Li J, Pan C Y, Zhao F H. AIP Adv., 2019, 9(2): 025210.

[56]	Wu W, Guo J L, Qin X, Bi C B, Wang J F, Wang L, Liang G C. J. Alloys Compd., 2017, 721: 721.

[57]	Wang J, Lin W Q, Wu B H, Zhao J B. Electrochimica Acta, 2014, 145: 245.

[58]	Wang J F, Chen D, Wu W, Wang L, Liang G C. Trans. Nonferrous Met. Soc. China, 2017, 27(10): 2239.

[59]	Deng M M, Zou B K, Shao Y, Tang Z F, Chen C H. J. Solid State Electrochem., 2017, 21(6): 1733.

[60]	Liang G M, Wu Z B, Didier C, Zhang W C, Cuan J, Li B H, Ko K Y, Hung P Y, Lu C Z, Chen Y Z, Leniec G, Kaczmarek S M, Johannessen B, Thomsen L, Peterson V K, Pang W K, Guo Z P. Angew. Chem. Int. Ed., 2020, 59(26): 10594.

[61]	Oh S W, Park S H, Kim J H, Bae Y C, Sun Y K. J. Power Sources, 2006, 157(1): 464.

[62]	Luo Y, Li H Y, Lu T L, Zhang Y X, Mao S S, Liu Z, Wen W, Xie J Y, Yan L Q. Electrochimica Acta, 2017, 238: 237.

[63]	Kim W K, Han D W, Ryu W H, Lim S J, Eom J Y, Kwon H S. J. Alloys Compd., 2014, 592: 48.

[64]	Sha O, Tang Z Y, Wang S L, Yuan W, Qiao Z, Xu Q, Ma L. Electrochimica Acta, 2012, 77: 250.

[65]	Li H Y, Luo Y, Xie J Y, Zhang Q S, Yan L Q. J. Alloys Compd., 2015, 639: 346.

[66]	Chao M, Luo L, Li K, Zhou B, Shi Q. Int. J. Electrochem. Sci., 2019, 7643.

[67]	Gu T T, Wang J, Tian J H, Zheng X J, Lu K W, Xin Y, Wang H B, Yang R Z. ChemElectroChem, 2019, 6(8): 2224.

[68]	Zheng X Y, Liu W J, Qu Q T, Zheng H H, Huang Y H. J. Materiomics, 2019, 5(2): 156.

[69]	Höweling A, Stoll A, Schmidt D O, Geßwein H, Simon U, Binder J R. J. Electrochem. Soc., 2017, 164(1): A6349.

[70]	Liu J H, Sun Z Q, Xie J N, Chen H Y, Wu N N, Wu B R. J. Power Sources, 2013, 240: 95.

[71]	Choi S, Kim M C, Moon S H, Kim H, Park K W. Electrochimica Acta, 2019, 326: 135015.

[72]	Noguchi T, Yamazaki I, Numata T, Shirakata M. J. Power Sources, 2007, 174(2): 359.

[73]	Nisar U, Amin R, Essehli R, Shakoor R A, Kahraman R, Kim D K, Khaleel M A, Belharouak I. J. Power Sources, 2018, 396: 774.

[74]	Lin M, Ben L, Yang S, Hao W, Huang X. Chem. Mater., 2015, 27(1): 292.

[75]	Fang X, Lin F, Nordlund D, Mecklenburg M, Ge M Y, Rong J P, Zhang A Y, Shen C F, Liu Y H, Cao Y, Doeff M M, Zhou C W. Adv. Funct. Mater., 2017, 27(7): 1602873.

[76]	Fey G T K, Muralidharan P, Lu C Z, Cho Y D. Electrochimica Acta, 2006, 51(23): 4850.

[77]	Yuan W, Zhang H Z, Liu Q, Li G R, Gao X P. Electrochimica Acta, 2014, 135: 199.

[78]	Shi S J, Tu J P, Zhang Y J, Zhang Y D, Zhao X Y, Wang X L, Gu C D. Electrochimica Acta, 2013, 108: 441.

[79]	Luo X Y, Liao Y H, Zhu Y M, Li M S, Chen F B, Huang Q M, Li W S. J. Power Sources, 2017, 348: 229.

[80]	Gao J H, Yuan T, Luo S N, Ruan J F, Sun H, Yang J H, Zheng S Y. J. Colloid Interface Sci., 2020, 570: 153.

[81]	Sun Y K, Lee Y S, Yoshio M, Amine K. Electrochem. Solid-State Lett., 2002, 5(5): A99.

[82]	Arrebola J C, Caballero A, Hernán L, Morales J. J. Power Sources, 2010, 195(13): 4278.

[83]	Fan Y K, Wang J M, Tang Z, He W C, Zhang J Q. Electrochimica Acta, 2007, 52(11): 3870.

[84]	Ben L, Yu H, Wu Y, Chen B, Zhao W, Huang X. ACS Appl. Energy Mater., 2018, 1(10): 5589.

[85]	Luo K, Roberts M R, Hao R, Guerrini N, Pickup D M, Liu Y S, Edström K, Guo J H, Chadwick A V, Duda L C, Bruce P G. Nat. Chem., 2016, 8(7): 684.

[86]	Shi J Y, Yi C W, Kim K. J. Power Sources, 2010, 195(19): 6860.

[87]	Deng S X, Xiao B W, Wang B Q, Li X, Kaliyappan K, Zhao Y, Lushington A, Li R Y, Sham T K, Wang H, Sun X L. Nano Energy, 2017, 38: 19.

[88]	Huang Y Y, Zeng X L, Zhou C, Wu P, Tong D G. J. Mater. Sci., 2013, 48(2): 625.

[89]	Tiurin O, Solomatin N, Auinat M, Ein-Eli Y. J. Power Sources, 2020, 448: 227373.

[90]	Chu C T, Mondal A, Kosova N V, Lin J Y. Appl. Surf. Sci., 2020, 530: 147169.

[91]	Deng H F, Nie P, Shen L F, Luo H F, Zhang X G. Prog. Chem., 2014, 26(6): 939.

[92]	(邓海福, 聂平, 申来法, 罗海峰, 张校刚. 化学进展, 2014, 26(6): 939.)

[93]	Kim H, Byun D, Chang W, Jung H G, Choi W. J. Mater. Chem. A, 2017, 5(47): 25077.

[94]	Gabrielli G, Axmann P, Diemant T, Behm R J, Wohlfahrt-Mehrens M. ChemSusChem, 2016, 9(13): 1670.

[95]	Zhang J N, Sun G, Han Y, Yu F D, Qin X J, Shao G J, Wang Z B. Electrochimica Acta, 2020, 343: 136105.

[96]	Deng H F, Nie P, Luo H F, Zhang Y, Wang J, Zhang X G. J. Mater. Chem. A, 2014, 2(43): 18256.

[97]	Zhao J Z, Liu Y R, He Y, Lu K. J. Alloys Compd., 2019, 779: 978.

[98]	Wu Q, Xue K, Zhang X H, Xie X S, Wang H Q, Zhang J J, Li Q Y. Ceram. Int., 2019, 45(4): 5072.

[99]	Park J S, Meng X B, Elam J W, Hao S Q, Wolverton C, Kim C, Cabana J. Chem. Mater., 2014, 26(10): 3128.

[100]

Cheng F Q, Xin Y L, Huang Y Y, Chen J T, Zhou H H, Zhang X X. J. Power Sources, 2013, 239: 181.

[101]

Deng Y L, He L H, Ren J, Zheng Q J, Xu C G, Lin D M. Mater. Res. Bull., 2018, 100: 333.

[102]

Xu Y H, Zhao S X, Deng Y F, Deng H, Nan C W. J. Materiomics, 2016, 2(3): 265.

[103]

Deng J C, Xu Y L, Li L, Feng T Y, Li L. J. Mater. Chem. A, 2016, 4(17): 6561.

[104]

Lin Y B, Yang Y M, Yu R B, Lai H, Huang Z G. J. Power Sources, 2014, 259: 188.

[105]

Zhao R, Li L, Xu T H, Wang D D, Pan D, He G J, Zhao H L, Bai Y. ACS Appl. Mater. Interfaces, 2019, 11(17): 16233.

[106]

Li L, Zhao R, Pan D, Yi S H, Gao L F, He G J, Zhao H L, Yu C Y, Bai Y. J. Power Sources, 2020, 450: 227677.

[107]

Cho J H, Park J H, Lee M H, Song H K, Lee S Y. Energy Environ. Sci., 2012, 5(5): 7124.

[108]

Chong J, Xun S D, Zhang J P, Song X Y, Xie H M, Battaglia V, Wang R S. Chem. Eur. J., 2014, 20(24): 7479.

[109]

Konishi H, Suzuki K, Taminato S, Kim K, Zheng Y M, Kim S, Lim J, Hirayama M, Son J Y, Cui Y T, Kanno R. J. Power Sources, 2014, 269: 293.

[110]

Chong J, Xun S D, Song X Y, Liu G, Battaglia V S. Nano Energy, 2013, 2(2): 283.

[111]

Mou J R, Deng Y L, Song Z C, Zheng Q J, Lam K H, Lin D M. Dalton Trans., 2018, 47(20): 7020.

[112]

Zhao G Y, Lin Y B, Zhou T, Lin Y, Huang Y D, Huang Z G. J. Power Sources, 2012, 215: 63.

[113]

Liang G M, Peterson V K, See K W, Guo Z P, Pang W K. J. Mater. Chem. A, 2020, 8(31): 15373.

[114]

Gao C, Liu H P, Bi S F, Fan S S, Meng X H, Li Q Y, Luo C X. J. Materiomics, 2020, 6(4): 712.

[115]

Dong H Y, Zhang Y J, Zhang S Q, Tang P P, Xiao X L, Ma M Y, Zhang H S, Yin Y H, Wang D, Yang S T. ACS Omega, 2019, 4(1): 185.

[116]

Mou J R, Deng Y L, He L H, Zheng Q J, Jiang N, Lin D. Electrochimica Acta, 2018, 260: 101.

[117]

Lee K, Yang G J, Kim H, Kim T, Lee S S, Choi S Y, Choi S, Kim Y. J. Power Sources, 2017, 365: 249.

[118]

Lu J, Zhan C, Wu T P, Wen J G, Lei Y, Kropf A J, Wu H M, Miller D J, Elam J W, Sun Y K, Qiu X P, Amine K. Nat. Commun., 2014, 5(1): 5693.

[119]

Lim J M, Oh R G, Kim D, Cho W, Cho K, Cho M, Park M S. ChemSusChem, 2016, 9(20): 2967.

[120]

Piao J Y, Sun Y G, Duan S Y, Cao A M, Wang X L, Xiao R J, Yu X Q, Gong Y, Gu L, Li Y T, Liu Z J, Peng Z Q, Qiao R M, Yang W L, Yang X Q, Goodenough J B, Wan L J. Chem, 2018, 4(7): 1685.

[121]

Piao J Y, Gu L, Wei Z X, Ma J M, Wu J P, Yang W L, Gong Y, Sun Y G, Duan S Y, Tao X S, Bin D S, Cao A M, Wan L J. J. Am. Chem. Soc., 2019, 141(12): 4900.

[122]

Patel R L, Jiang Y B, Choudhury A, Liang X H. Sci. Rep., 2016, 6(1): 25293.

[123]

Gao Y, He X Q, Ma L, Wu T P, Park J, Liang X H. Electrochimica Acta, 2020, 340: 135951.

[124]

Xiao B W, Liu H S, Liu J, Sun Q, Wang B Q, Kaliyappan K, Zhao Y, Banis M N, Liu Y L, Li R Y, Sham T K, Botton G A, Cai M, Sun X L. Adv. Mater., 2017, 29(47): 1703764.