Strategy to Increase Energy Density and Improve Stability of LiMPO4 (M=Co, Ni) Cathodes for All-Solid-State Li-Ion Batteries

正极材料对锂离子电池的能量密度和寿命周期起着至关重要的作用。它的热力学稳定性取决于本征电压极限，而本征电压极限是由相关材料内阴离子的固有氧化极限决定的。整个电池的外在稳定性还受到电解液氧化还原电位和阴极/电解液界面的化学相容性的影响。功率能力取决于锂离子和/或电子通过大块阴极材料和跨相边界阴极/电解质的转移速率。因此，为了从本质上提高能量密度和功率密度，同时保持电池的高稳定性，必须解决以下关键问题：a)电池在高压充电状态下的化学相容性和热力学稳定性；b) Li+离子通过相和跨相边界的高迁移率；C)电极的高电子导电性。我们项目的目的是制备和研究新型5V固态电池。我们专注于LiMPO4 （M=Co, Ni）橄榄石基材料，其中通过与另一种具有更高氧化电位的聚磷酸盐相的材料设计，在完全稀薄状态下实现了高结构稳定性。应解决以下科学问题：a)所设计的阴极材料显示的异常高电子导电性的来源是什么？B)电池的能量密度能否通过多磷酸盐相参与氧化还原反应而本质上提高？c)橄榄石基材料是否与高Li+离子导电性固体电解质化学相容？d)电池芯充放电时，阴极/电解质界面是否稳定，Li+离子是否导电？薄膜阴极材料及其界面将在特高压条件下制备，其电子和结构性质将主要通过原位电子能谱、操作电子能谱、HRTEM/STEM和XRD进行研究，并结合电子和结构性质建模。通过这种新颖的方法，我们将通过监测电池运行过程中物理化学性质的演变来解决离子导体及其界面的内在和外在稳定范围。

The cathode material plays a key role in the energy density and life cycle of Lithium Ion Batteries (LIB). Its thermodynamic stability depends on the intrinsic voltage limit which is defined by the inherent oxidation limit of the anions within the relevant material. The extrinsic stability of the whole battery cell is additionally influenced by the redox potential of the electrolyte and by the chemical compatibility of the cathode/electrolyte interface. Power capability depends on the Li+ and/or electron transfer rates through the bulk cathode material and across the phase boundary cathode/electrolyte. Thus, to increase essentially the energy density and the power density, whilst maintaining a high battery stability, the following key issues have to be solved: a) chemical compatibility and thermodynamic stability of the battery cell operated at a high voltage charged state; b) high migration rate of Li+ ions through the phases and across the phase boundaries; c) high electronic conductivity in the electrode. The aim of our project is the preparation and investigation of novel 5V solid-state batteries. We focus on the LiMPO4 (M=Co, Ni) olivine-based material in which a high structural stability in the fully delithiated state is achieved via the material design with another polyphosphate phase of higher oxidation potential. The following scientific problems shall be addressed: a) what is the origin of unusually high electronic conductivity revealed for the designed cathode material? b) can the energy density of the battery be essentially increased via the involvement of the polyphosphate phase into the redox reaction? c) are the olivine-based materials chemically compatible with highly Li+ ion conductive solid electrolyte? d) is the cathode/electrolyte interface stable and Li+ ion conducting upon the charging/discharging of the battery cell? The film cathode materials and their interfaces will be prepared under UHV condition and their electronic and structural properties will be studied mostly by in situ and operando electron spectroscopy, HRTEM/STEM and XRD combined with the modelling of electronic and structural properties. With such a novel approach, we will address the intrinsic and extrinsic stability range of ion conductors and their interfaces by monitoring the evolution of the physicochemical properties during operation of the battery cell.