表面尖晶石修饰的层状高镍正极材料界面结构调控及储锂机制研究

The inherent structural instability of the high-energy-density layered nickel-rich oxide (LiNi0.8Co0.1Mn0.1O2, NCM-811) would restrict its large-scale application in power battery. To solve this key issue of sluggish charge transfer caused by the surface structure degradation of NCM-811, this project proposed the idea about "fabrication of stable fast-ion-transport layers on its surface". The stable-structure, fast-ionic-conductor, electro-active LiMn2O4 was in-situ fabricated on NCM-811. Furthermore, the heterogeneous interfacial compatibility and interfacial structure of NCM-811 and LiMn2O4 were regulated through driving controllable diffusion of transition metal ions at the interface under accelerated temperature. This research will be mainly focused on the following contents: exploring the regulation mechanism of the layered structure of NCM-811 and the relationship model of structure order and lithium storage; confirming the diffusion law of transition-metal ions at heterogeneous interface, the coupling effect of interface phase, and the regulation mechanism of interfacial structure; revealing the influence of the interfacial structure on the charge transfer and ion transport kinetics; clarifying the synergetic mechanism of the layered-spinel composite on electrochemical lithium storage. This proposal will be expected to provide the theoretical basis for the rational design of the high-energy-density cathode materials and its large-scale application in the power battery.

高能量密度的层状高镍氧化物LiNi0.8Co0.1Mn0.1O2（NCM-811）结构不稳定限制了其在动力电池领域的规模化应用。针对NCM-811表面结构衰变引起电荷传输迟缓这个问题，本项目提出“构建表面结构稳定的快离子传输层”的设计思路，在NCM-811表面原位生长结构稳定、离子传导快、电化学活性高的LiMn2O4尖晶石包覆层，通过升温诱导NCM-811和LiMn2O4两相界面过渡金属离子的可控扩散，实现对异质界面兼容性和界面结构调控。探索NCM-811结构有序度的调控机理及储锂的构效关系；明确异相界面过渡金属离子的扩散规律、界面耦合作用及界面结构调控机制；揭示界面结构对电荷转移和离子传输动力学的影响规律；阐明层状尖晶石复合结构电化学协同储锂机制。本项目的研究有望为高能量密度正极材料的设计及其在动力电池中规模化应用提供理论依据。

高能量密度的层状高镍正极材料LiNi0.8Co0.1Mn0.1O2（NCM-811）在动力电池领域具有潜在的应用前景。然而，严重的表面结构衰变会引起电荷传输迟缓，从而限制了其实际应用。为此，本项目提出“构建表面结构稳定的快离子传输层”的设计思路，在NCM-811表面构建高电压下稳定的包覆层，通过升温诱导NCM-811和包覆层两相界面金属离子的可控扩散，实现对异质界面兼容性和界面结构调控。研究了尖晶石包覆层（LiMn2O4和LiNi0.5Mn1.5O4）对NCM-811晶体结构、高电压循环稳定性和电荷传输速率的影响规律；研究了Li2GeO3包覆的NCM-811异相界面金属离子的扩散规律、界面耦合作用，揭示了界面结构对相变过程以及离子扩散行为的作用机制；研究了尖晶石-层状复合结构在反应过程中相变行为和电荷传输机制。结果表明，尖晶石包覆层可有效提升NCM-811高电压循环稳定性，其特殊的三维离子通道有助于Li+快速传输；升温诱导下Li2GeO3包覆层中Ge4+会在界面呈梯度扩散，有助于降低材料体相阳离子混排，提高层状有序度；结合电化学动力学和理论计算结果验证了Ge4+梯度掺杂可降低Li+扩散能垒和提高相变能垒，从而提升离子扩散动力学速率和结构稳定性；建立了相变路径与离子扩散速率的强依赖关系；明确了尖晶石-层状共生结构在电化学反应中晶体结构演化过程及电荷传输过程。本项目的研究结果有望为高能量密度正极材料的设计提供理论依据。