镍富集层状正极材料在锂离子电池中的基本降解机制：

Increasing of the Ni fraction increase the discharge capacity of the cathode but decreases the ability to retain its original capacity during cycling. The relatively inferior cycling stability of NCM with x > 0.8 is attributed to the phase transition near the charge-end. Stress stemming from the H2 to H3 phase transition destabilized the internal microcracks and allowed the microcracks to propagate to the surface, providing channels for electrolyte penetration and subsequent degradation of the exposed internal surfaces.

镍含量增加可以提高正极的放电容量，但其在循环过程中保持原始容量的能力会降低。x>0.8的NCM在循环稳定性上相对较差，原因在于在充电结束时发生了阶段转变。来自H2到H3相变的应力不稳定化了内部微裂缝，并允许微裂缝传播到表面，为电解质渗透提供了通道，并导致内部表面的降解。

Concentration gradient cathode materials for advanced lithium-ion batteries

梯度浓度正极材料用于高级锂离子电池

NCM cathodes with concentration gradients represent a viable solution that simultaneously addresses the specific energy density, cycling and chemical stability, and safety issues of Ni-enriched NCM cathodes. Currently, concentration gradient cathode with extremely high Ni content has been developed by X-doping. Interdiffusion and coarsening in the X-doped CG cathode were suppressed by the segregation of X at the grain boundary and particle surfaces, which also provided a protective coating layer that lowered the surface reactivity.

梯度浓度的NCM正极材料是同时解决Ni浓度较高的NCM正极材料的比能量密度、循环和化学稳定性以及安全问题的可行解决方案。目前，通过X掺杂已经开发出了具有极高Ni含量的梯度浓度正极材料。在X掺杂的CG正极材料中，通过X在晶界及粒子表面的分离抑制了扩散和粗化，同时提供了一层保护性涂层，降低了表面反应性。

Microstructurally modified cathodes by high valence electron elements doping

高价电子元素掺杂改性的正极材料：

Specific dopants, especially high-valence elements can change the morphology of primary particles in Ni-rich cathode materials. The introduction of a high- valence element during calcination effectively reduces the size of the grains and refines the morphology of primary particles into rod-shaped ones by inhibiting the coarsening of particles. The superior cycling stability clearly indicates the importance of the particle microstructure (i.e., particle size, particle shape, and crystallographic orientation) in mitigating the abrupt internal strain caused by phase transitions in the deeply charged state, which occur in Ni-rich layered cathodes.某些特定掺杂剂，尤其是高价元素，可以改变Ni富集的正极材料的初级颗粒形态。在煅烧过程中引入高价元素可以有效减小晶粒尺寸，并通过抑制颗粒的粗化将初级颗粒的形态细化为棒状，并在深度充电状态下缓解突然的内部应变所带来的影响，进而提高优异的循环稳定性。

Effects of low valence elements excess doping in microstructure

低价元素超量掺杂的正极材料的微观结构变化：

The grain size refinement can be achieved by the introduction of an excess amount of Al doping, which inhibits particle coarsening by segregating Al ions at the particle boundaries. A highly aligned microstructure is achieved by doping 4 mol% of Al, which can allow uniform contraction of the primary particles in the deeply charged state, preventing the formation of local stress concentrations, and deflecting the propagation of microcracks. The proposed Al 4mol%-doped NCA cathode represents a new breed of a Ni-rich NCA cathode that can meet the energy density required for the next-generation EVs without compromising the battery life and safety.通过引入过量的Al掺杂可以获得晶粒尺寸的细化，同时通过将Al离子分离到颗粒边界处，从而抑制颗粒的粗化。掺杂4mol% Al可以实现高度对齐的微观结构，并允许初级颗粒在深度充电状态下实现均匀收缩，防止局部应力集中并缓解微裂缝的扩展。提出的掺杂4mol% Al的NCA正极材料代表了一种新型的Ni富集NCA正极材料，能够满足下一代电动汽车所需的能量密度，同时不会损害电池寿命和安全性。

Advanced Co-free cathode

Co-free正极材料的先进结构：

The elimination of Co from Ni-rich layered cathodes is considered a priority to reduce their material cost and for sustainable development of Li-ion batteries (LIBs) as Co is becoming increasingly scarce. In the Co-free cathode, the H2-H3 phase transition occurring near the charge end is shifted to a high voltage, so the capacity is lower than that of the NCM cathode at the standard operating voltage (4.3V). However, when operated at high voltage(4.4V), it shows improved thermal stability and cycling stability due to high Mn contents, while exhibiting capacity similar to that of NCM cathode.

减少材料成本和可持续性发展是将Co从Ni富集的层状正极材料中淘汰的优先事项，因为Co越来越稀缺。Co-free正极材料中，在电荷端附近发生的H2-H3相变发生了向高电压的转变，因此其在标准工作电压(4.3V)下的容量低于NCM正极材料。然而，在高电压(4.4V)下操作时，由于Mn含量高，具有更好的热稳定性和循环稳定性，并且显示出与NCM正极材料相似的容量。

Introducing High-Valence Elements into Co-free NM Cathodes(micro-, nano- structure enegineering

将高价元素引入Co-free NM正极材料中的结构工程：

By doping high-valence elements into the Co-free cathodes, the electrochemical performances of the cathodes can be further extended. The grain size refinement achieved by X-doping (X=high-valence element) dissipates the deleterious strain from abrupt lattice contraction through fracture toughening and the removal of local compositional inhomogeneities. Also, the unique structure induced by the presence of X stabilizes the delithiated structure through a pillar effect. The X-doped NM90 cathode can deliver a high capacity with cycling stability, and is suitable for the electric vehicles with long service life at a reduced material cost.

通过向Co-free正极材料中掺杂高价元素可以进一步提高正极材料的电化学性能。通过非常高的X掺杂(X=高价元素)实现的晶粒细化，通过断口增强和去除局部成分不均匀性消除了由于晶格收缩而产生的有害应变。此外，由于存在X而引起的独特结构通过柱状效应稳定了脱锂结构。掺杂X的NM90正极材料可以提供具有循环稳定性的高容量，适用于具有降低材料成本的长寿命电动汽车。

资料来源：

http://escml.hanyang.ac.kr/sub/sub01_02.php