Fast Li-ion conductor Li1+yTi2-yAly(PO4)3 modified Li1.2[Mn0.54Ni0.13Co0.13]O2 as high performance cathode material for Li-ion battery

In the material of xLi₂MnO₃ ·(1-x) LiMO₂ (0 < x < 1), the Li₂MnO₃ component is used to stabilize the layered LiMO₂ structure. However, the electrochemical inactive Li₂MnO₃ makes Li-ion diffusion difficult, leading to a sluggish rate capability. In this work, Li_1.3Ti_1.7Al_0.3(PO₄)₃ (LTA0.3), a NASICON-type Li-ion conductor, is applied to modified Li_1.2Mn_0.54Ni_0.13Co_0.13O₂ to overcome the above shortcoming. Additionally, the Li-ion conductivity of LiTi₂(PO₄)₃ can be improved effectively by replacing tetravalent cation Ti⁴⁺ with trivalent Al³⁺ at the optimal ratio. At 1C rate, the LR cathode with 3 wt% LTA0.3 delivers 200 mAh g^?1 after 170 cycles and maintains 140 mAh g^?1 after 500 cycles. Moreover, the modified cathode shows an enhanced rate performance of 169.7 mAh g^?1 at 5C. Enhanced cycle durability and rate capability are aroused by the 3D skeletal framework of LTA0.3, which is suitable for Li-ion diffusion. The LTA0.3 coating layer displays a robust shell which not only avoids the corrosion of electrode materials but also effectively facilitates Li-ion diffusion.     

Enhanced electrochemical performance of ZrO2 modified LiNi0.6Co0.2Mn0.2O2 cathode material for lithium ion batteries

LiNi_0.6Co_0.2Mn_0.2O₂ (NCM622) cathode has been modified by incorporating ZrO₂ nanoparticles to improve its electrochemical performance. Compared to the pristine electrode, the cycling stability and rate capability of 0.5 wt% ZrO₂ modified-NCM622 have been improved significantly. The 0.5 wt% ZrO₂ modified-NCM622 cathode shows a capacity retention of 83.8% after 100 cycles at 0.1 C between 2.8 and 4.3 V, while that of the pristine NCM622 electrode is only 75.6%. When the current rate is set as 5C, the capacity retention of the 0.5 wt% ZrO₂-modified NCM622 is 10% higher than that of the pristine NCM622. Also, the rate capability of 0.5 wt% ZrO₂-modified NCM622 is better than that of the pristine NCM622 at various C-rates in a voltage range of 2.8–4.3 V. The enhanced electrochemical performances of the ZrO₂-modified NCM622 cathodes can be attributed to their high Li-ion conductivity and structural stability.     

Nano-Y2O3-coated LiNi0.5Co0.2Mn0.3O2 cathodes with enhanced electrochemical stability under high cut-off voltage and high temperature

LiNi_0.5Co_0.2Mn_0.3O₂ (523) coated with ~ 20 nm thick Y₂O₃ nano-membrane is prepared via a sol-type chemical precipitation process based on electrostatic attraction between the materials. The nano-Y₂O₃-coated 523 cathode can deliver 160.3 mA h g⁻¹ (87.8% of its initial discharge capacity) after 50 cycles at 1 C (180 mA g⁻¹) between 3.0 and 4.6 V by coin cell testing, while the pristine 523 keeps only 146.2 mA h g⁻¹ with 78.6% capacity retention left. The capacity retention rate increases from 50% to 86.7% after 150 cycles at 1 C in 3.0–4.35 V by soft package testing under 45 °C. Through this novel Y₂O₃ coating operation, both the charge transfer resistance and the electrode polarization of the 523 electrode have been suppressed, and its structure stability is also improved.     

WO3 membrane-encapsulated layered LiNi0.6Co0.2Mn0.2O2 cathode material for advanced Li-ion batteries

Despite Nickel-rich materials have all the advantages of high capacity, long cycle life and low cost, there is still a disadvantage that the capacity decreases rapidly as the number of cycles increases. In order to solve this problem, WO₃ was uniformly coated on the surface of LiNi_0.6Co_0.2Mn_0.2O₂ cathode materials by wet coating, and its cycling performance was greatly improved with the higher capacity. The coated materials were analyzed by X-ray diffraction(XRD), Scanning electron microscope (SEM), high resolution Transmission electron microscopy (TEM) and X-ray photoelectron spectroscopy(XPS). The results showed that the coating thickness was around 3.15?nm, and some tungsten ions were doped into the lattice of the near surface area of the LiNi_0.6Co_0.2Mn_0.2O₂ material. In addition, the results of charge-discharge test showed that 1?wt%WO₃ coating LiNi_0.6Co_0.2Mn_0.2O₂ had the best performance, and delivered a discharge capacity of 140 mAh g^?1 (the capacity retention rate is 84.8%) in the potential interval of 2.8–4.3?V at 1?C (1?C?=?165?mA?g^?1) after 200 cycles, while the bare cathode material only delivered a discharge capacity of 120 mAhg^?1 (the capacity retention rate is 75%). The phenomenon indicates that the WO₃ coating plays a role in inhibiting the harmful side reactions between the cathode material and the electrolyte, improving the electrochemical and structure stability of LiNi_0.6Co_0.2Mn_0.2O₂ cathode materials.     

Highly enhanced electrochemical performances of LiNi0.815Co0.15Al0.035O2 by coating via conductively LiTiO2 for lithium-ion batteries

LiTiO₂ film-coated layered LiNi_0.815Co_0.15Al_0.035O₂ (NCA) material was successfully synthesised through in situ hydrolysis–lithiation to improve electrochemical properties. Herein, NCA was synthesised using solid state reaction, coated by hydrolysis of tetrabutyl titanate and subjected to lithiation process. The optimal molar ratio (LiTiO₂: NCA) was found to be 1.0 mol%, and the thickness of LiTiO₂ film coated on the surface of NCA of 18 nm was observed through HRTEM images. Compared with pristine NCA, 1.0 mol% LiTiO₂-coated NCA demonstrated better electrochemical performance with larger capacity of 20 mAh g⁻¹ under 1 C after 100 cycles. Its related capacity retention was 90.8%. The 1.0 mol% LiTiO₂-coated sample exhibited high discharge capacity of 157.6 mAh g⁻¹ at a current rate of 10 C, whereas the pristine sample only presented 145.3 mAh g⁻¹. The considerably improvement of the rate and cycling properties of the NCA cathode material is achieved using LiTiO₂ as a Li⁺-conductive coating layer. These new findings contribute towards the design of a stable-structured Ni-rich material for lithium-ion batteries.     

Influence of lithium difluorophosphate additive on the high voltage LiNi0.8Co0.1Mn0.1O2/graphite battery

Lithium-ion batteries (LIBs) possessing high energy densities are driven by the growing demands of electric vehicles (EVs) and hybrid electric vehicles (HEVs). One of the most effective strategies to improve the energy density of LIBs is to enlarge the charge cut-off voltage via a lithium salt additive for the conventional electrolyte system. Herein, lithium difluorophosphate (LIDFP) is employed to optimize and reconstruct the composition of the structure and interface for both cathode and anode, which can effectively restrain the oxidation decomposition of electrolyte as well as refrain the dissolve out of transition metals. The LiNi_0.8Co_0.1Mn_0.1O₂ (LNCM811)/graphite pouch cell with 1 wt% LIDFP in electrolyte delivers a discharge capacity retention of 91.3% at a high voltage of 4.4 V over 100 cycles, which is higher than the 82.0% of that without LIDFP additive. Additionally, the remaining capacity of LNCM811/C battery with 1 wt% LIDFP additive which is left at 60 °C for 14 days is 85.2%, and the recovery capacity is 93.3%. The LIDFP-containing electrolyte demonstrates a great application future for the LiBs operating under the high-voltage condition and high-temperature storage performance.     

Preparation of LiNi1/3Co1/3Mn1/3O2/polytriphenylamine cathode composites with enhanced electrochemical performances towards reversible lithium storage

A series of LiNi_1/3Co_1/3Mn_1/3O₂/polytriphenylamine composites were successfully synthesized by ultrasound dispersion method. LiNi_1/3Co_1/3Mn_1/3O₂/polytriphenylamine (5.0?wt%) composite with small and homogeneous particle size exhibited excellent electrochemical performance, which delivered an initial discharge capacity of 223.7?mAh g^?1 with a capacity retention of 84.39% after 100 cycles in the voltage range of 2.5–4.5?V and at a current density of 0.2C. Moreover, an excellent specific discharge capacity of 127.3?mAh g^?1 at a current density 5C indicates a superior rate performance of the LiNi_1/3Co_1/3Mn_1/3O₂/polytriphenylamine (5.0?wt%) composite. The good electrochemical performances of the composite can be attributed to the introduction of polytriphenylamine, which increased electrical conductivity, decreased charge transfer resistance and increased Li⁺ ion diffusion ability. These noteworthy results demonstrated that LiNi_1/3Co_1/3Mn_1/3O₂/polytriphenylamine composites might be potential cathode materials for lithium ion batteries.     

Effect of niobium doping on the structure and electrochemical performance of LiNi0.5Co0.2Mn0.3O2 cathode materials for lithium ion batteries

Key issues including poor rate capability and limited cycle life span should be addressed for the extended application of LiNi_0.5Co_0.2Mn_0.3O₂ cathode. The suppressed Li⁺/Ni²⁺ site exchange, enlarged LiO₂ inter-slab space and reduced impedance, which could facilitate the structure stability, were achieved by controlled Niobium (Nb) doping and contributed to enhanced performance even at elevated temperature (55 °C). The detailed role of the doped Nb was investigated thoroughly and systematically with the help of XRD, SEM, XPS and related electrochemical tests. The full and accurate results demonstrate that the Li(Ni_0.5Co_0.2Mn_0.3)_0.99Nb_0.01O₂ sample with appropriate Nb doping amount possess high capacity retention of 93.77% after 100 cycles at 1.0 C and improved rate performance with 125.5 mA h g⁻¹ at 5.0 C, which are much better than that of the LiNi_0.5Co_0.2Mn_0.3O₂. Moreover, at high temperature of 55 °C, Nb doping shows more remarkable effect on stabilizing the structure and 88.63% of the initial reversible capacity could be retained, which is ~20% higher than the LiNi_0.5Co_0.2Mn_0.3O₂. This study intensively determines that controlled Nb doping could be effectively maintain the structure stability of advanced LiNi_0.5Co_0.2Mn_0.3O₂ cathode and promote the development of high energy density lithium ion batteries.     

硼高效掺杂LiNi0.5Co0.2Mn0.3O2正极材料及其性能提升机制

高键能异质原子的高效掺杂是稳定高电压LiNi_0.5Co_0.2Mn_0.3O₂（NCM）三元正极材料并提升其电化学性能的有效策略。借助含硼前体在二次颗粒表面富集及随后高温煅烧强化B³⁺体相扩散的策略,构建了硼离子高效掺杂NCM正极材料（NCM-B）。引入B—O键（键能：809 kJ·mol^-1）抑制了电化学反应过程中晶格氧析出,进而稳定材料的氧离子框架;此外,表面残余的高锂离子导体Li₂O-B₂O₃包覆层可以在一定程度上稳定电极-电解液界面。与改性前NCM相比,改性后的NCM-B正极材料在3.0~4.5 V电压区间的可逆比电容量可以达到193.7 mA·h·g^-1,在10 C大功率下,比电容量仍保持120 mA·h·g^-1（NCM仅为78.2 mA·h·g^-1）。1 C下连续循环100圈后,比电容量保持率从73%提升到90%。表面富集和扩散强化的思想也有望实现其他正极材料的高效掺杂。     

Impact of coatings on the electrochemical performance of LiNi0.5Mn1.5O4 cathode materials: A focused review

The application of Lithium-ion batteries (LIBs) in portable electronics and electric vehicles (EVs) has increased in the past decade. Extended commercialization of LIBs for advanced applications requires the development of high-performance electrode materials. LiNi_0.5Mn_1.5O₄ (Lithium Nickel Manganese Oxide referred to as LNMO) has attracted much attention as a cathode material due to its high voltage and energy density, lower cost, and environmental friendliness. However, LNMO cathodes are currently suffering from poor cyclability and capacity degradation at elevated temperatures. Many strategies have been suggested in the literature to address the challenges associated with numerous families of cathode materials. Among those, surface modification techniques like surface coatings have proven to be promising. Surface coatings have a good effect on the electrochemical performance of LNMO, as these result in increasing electronic and ionic conductivity, fast ions mobility and high diffusivity. Towards this direction, a systematic review of research progress carried out in the area of coated LNMO has been summarized. More precisely, the impact of numerous coating materials in improving cyclability and capacity retention at elevated temperatures of LNMO has been discussed along with a variety of coating synthesis technologies.     

Ultrathin-Y2O3-coated LiNi0.8Co0.1Mn0.1O2 as cathode materials for Li-ion batteries: Synthesis,performance and reversibility

Nickel-rich lithium material LiNi_xCo_yMn_1-x-yO₂(x > 0.6) becomes a new research focus for the next-generation lithium-ion batteries owing to their high operating voltage and high reversible capacity. However, the rate performance and cycling stability of these cathode materials are not satisfactory. Inspired by the characteristics of Y₂O₃ production, a new cathode material with ultrathin-Y₂O₃ coating was introduced to improve the electrochemical performance and storage properties of LiNi_0.8Co_0.1Mn_0.1O₂ for the first time. XRD, scanning electron microscopy (SEM), high-resolution transmission electron microscopy (HRTEM), energy dispersive spectroscopy (EDS) and XPS were used to mirror the crystal and surface of LiNi_0.8Co_0.1Mn_0.1O₂ particles, results i that a uniform interface formed on as-prepared material. The impacts on the electrochemical properties with or without Y₂O₃ coating are discussed in detail. Notably, galvanostatic discharge-charge tests appear that Y₂O_3-coated sample especially 3% coating displayed a better capacity retention rate of 91.45% after 100 cycles than the bare one of 85.07%.     

A green and economical route to the precursor for the synthesis of single crystal LiNi0.5Co0.2Mn0.3O2

Single crystal LiNi_1-x-yCo_xMn_yO₂(NCM) cathode materials are typically synthesized using spherical polycrystalline hydroxides which are often prepared via coprecipitation reactions. However, the spherical morphology of polycrystalline hydroxides is not essential for the precursor in the synthesis of single crystal NCM, and also the coprecipitation process is not environmentally friendly and cost-effective enough. Herein a new process based on room-temperature solid-state metathesis reactions is developed to prepare the precursor for the synthesis of single crystal LiNi_0.5Co_0.2Mn_0.3O₂(NCM523). The whole process is free of any undesirable chemicals, and the resulting nanosize precursor can facilitate the synthesis of micron-level single crystal NCM523 at relatively lower sintering temperatures with less lithium excess. Moreover, the obtained single crystal NCM523 can exhibit comparable reversible capacities as compared with that synthesized from the coprecipitated spherical polycrystalline hydroxides. This work demonstrates a green and economical route to the precursor for the synthesis of single crystal NCM.     

Synthesis of LiNi1/3Mn1/3Co1/3O2@graphene for lithium-ion batteries via self-assembled polyelectrolyte layers

LiNi_1/3Co_1/3Mn_1/3O₂ cathode coated with a thin layer of graphene (~8 nm) is successfully synthesized by self-assembly and pyrolysis of polyelectrolyte layers on the surface of NMC particles. The graphene coated NMCs still possess a layered structure with good crystallinity and demonstrate a superior electrochemical performance (e.g., rate capability and cycling stability). The best graphene coated NMC cathode is prepared at a calcination temperature of 800 °C, exhibiting a capacity retention of ~90% vs. 78% for pristine NMC @ cycle 100 and 1 C rate. The improvement in cycling performance is further enlarged after 500 cycles (74% vs. 51%). This can be attributed to the dual functions of graphene coating in enhancing electronic conductivity and protecting NMC surface from the contact with electrolyte during the electrochemical reaction.     

Enhancing electrochemical performance and structural stability of LiNi0.5Mn1.5O4 cathode material for rechargeable lithium-ion batteries by boron doping

LiNi_0.5Mn_1.5O₄ cathode materials with a range of boron doping contents were successfully synthesized via an in situ solid-state method. The structures and grain morphologies were examined to elucidate the effect of boron doping on the electrochemical performance of LiNi_0.5Mn_1.5O₄. Scanning electron microscopy images show that the particle sizes of boron-doped LiNi_0.5-x/2B_xMn_1.5-x/2O₄ samples increase compared with those of pure LiNi_0.5Mn_1.5O₄. Characterization results confirm that boron doping could create more Mn³⁺ ions and increase the Mn³⁺ ions contents in LiNi_0.5-x/2B_xMn_1.5-x/2O₄ samples with increasing boron doping content. A greater number of Mn³⁺ ions could enhance the cationic disorder degree, thereby resulting in high electronic conductivities of LiNi_0.5-x/2B_xMn_1.5-x/2O₄ samples. Charge-discharge tests reveal that improvements in the electrochemical performance are achieved in LiNi_0.5-x/2B_xMn_1.5-x/2O₄ samples compared with that of pure LiNi_0.5Mn_1.5O₄. The boron-doped LiNi_0.495B_0.01Mn_1.495O₄ (denoted as LNMO-B0.01) cathode exhibits an excellent cycling stability with a capacity retention of 83.3% after 500 cycles at 3 C. Moreover, it also displays an optimal rate capability with discharge capacities of 136.1, 135.7, 130.3, 126.2, 123.1, 114.5, 104.5, and 82.9 mA h g^?1 at 0.2, 0.5, 1, 2, 3, 5, 7, and 10 C, respectively. The highest Li⁺ diffusion coefficient of LNMO-B0.01 determined from cyclic voltammetry tests indicates that an appropriate amount of boron doping could accelerate the Li⁺ diffusion in LNMO-B0.01. The lowest charge-transfer resistance obtained from the impedance spectra suggests that boron doping could promote kinetic charge transfer. As a result, this modification strategy can be utilized to enhance the electrochemical performance of LiNi_0.5Mn_1.5O₄ material.     

A nest-like hierarchical porous V2O5 as a high-performance cathode material for Li-ion batteries

In this article, V₂O₅ with a novel nest-like hierarchical porous structure has been synthesized by a facile solvothermal method and investigated as cathode material for lithium-ion batteries. The nest-like V₂O₅ with a diameter of about 1.5 µm, was composed of interconnected nanosheets with a highly porous structure. Without other modification, the as-prepared V₂O₅ electrode exhibited superior capacity. An initial discharge capacity of 330 mAh g⁻¹ (at a current density of 100 mA g⁻¹) could be delivered and a stable discharge capacity of 240 mAh g⁻¹ after 50 cycles is maintained. The excellent performance was attributed to the hierarchical porous structure that could buffer against the local volume change and shorten the lithium-ions diffusion distance.     

Optimized synthesis of Na2/3Ni1/3Mn2/3O2 as cathode for sodium-ion batteries by rapid microwave calcination

Microwave calcination is proposed as an alternative route to conventional heating to prepare layered P2–Na_2/3Ni_1/3Mn_2/3O₂ as a positive electrode for sodium-ion batteries. The sample obtained by the fastest conditions, with a heating ramp of 20 °C min⁻¹ for only 2 h, showed well-crystallized rounded particles. Cyclic voltammetry and impedance spectroscopy evidenced a low internal cell resistance, and high diffusion coefficients, which justify its capability to sustain the highest capacity at 1 C and retain the discharge capacity for at least two hundred cycles.     

Direct regeneration of LiNi0.5Co0.2Mn0.3O2 cathode material from spent lithium-ion batteries

At present, metal ions from spent lithium-ion batteries are mostly recovered by the acid leaching procedure, which unavoidably introduces potential pollutants to the environment. Therefore, it is necessary to develop more direct and effective green recycling methods. In this research, a method for the direct regeneration of anode materials is reported, which includes the particles size reduction of recovered raw materials by jet milling and ball milling, followed by calcination at high temperature after lithium supplementation. The regenerated LiNi_0.5Co_0.2Mn_0.3O₂ single-crystal cathode material possessed a relatively ideal layered structure and a complete surface morphology when the lithium content was n(Ni + Co + Mn):n(Li) = 1:1.10 at a sintering temperature of 920 ℃, and a sintering time of 12 h. The first discharge specific capacity was 154.87 mA·h·g^-1 between 2.75 V and 4.2 V, with a capacity retention rate of 90% after 100 cycles.     

MgF2包覆对正极材料LiNi1/3Co1/3Mn1/3O2性能的影响

通过浸渍法在正极材料LiNi1/3Co1/3Mn1/3O2的表面包覆MgF2,通过XRD、SEM、交流阻抗（EIS）分析、充放电测试研究了不同量MgF2包覆对LiNi1/3Co1/3Mn1/3O2正极材料的结构与电化学性能的影响。结果表明,MgF2以非晶态形式包覆于LiNi1/3Co1/3Mn1/3O2材料颗粒的表面,当包覆量为3%（物质的量分数,下同）时,三元正极材料具有优良的电化学性能,在3.0~4.6 V充放电范围内0.1C充放电倍率下,首次放电比容量为196.3 mA·h/g,1C循环50次后容量保持率为95.7%,55 ℃高温下1C循环50次后容量保持率为93.3%。     

锂离子电池正极材料LiNi1/3Co1/3Mn1/3O2研究进展

层状结构材料LiNi1/3Co1/3Mn1/3O2具有高比容量、高循环性能、低成本和环保等优点,有望取代LiCoO2成为新一代锂离子电池正极材料。在介绍LiNi1/3Co1/3Mn1/3O2的结构特点和电化学反应特性的基础上,对其主要合成方法进行了详细评述,总结了该正极材料的阴阳离子掺杂、复合离子掺杂以及表面包覆改性等技术,指出国内外目前锂离子电池材料研究中存在的问题和未来的发展方向。