(Invited) High-Energy and Safe Lithium-Ion Batteries Using Layered Oxides Cathodes

Abstract

Ni-rich layered lithium transition metal oxides have been considered as one of the key cathode materials for next-generation lithium-ion batteries for electric vehicle applications due to their high specific capacity of >200 mAh/g and low cost. However, they suffer from crystal and interfacial structural instability under aggressive electrochemical and thermal driving forces, leading to rapid performance degradation and severe safety concerns.In this talk, we will first discuss the fundamental role of Co and Mn in determining the thermal stability of layered cathode materials. By using in situ synchrotron X-ray diffraction and X-ray absorption spectroscopy, we revealed that Co4+ reduces prior to the reduction of Ni4+ and could thus prolong the Ni migration by occupying the tetrahedra sites and, hence, postpone the oxygen release and thermal failure. In contrast, the Mn itself is stable, but barely stabilizes the Ni4+.[1] We will then introduce a transformative approach using an oxidative chemical vapour deposition technique to build a protective conductive polymer (poly(3,4-ethylenedioxythiophene)) skin on layered oxide cathode materials. The ultraconformal poly(3,4-ethylenedioxythiophene) skin facilitates the transport of lithium ions and electrons, significantly suppresses the undesired layered to spinel/rock-salt phase transformation and the associated oxygen loss, mitigates intergranular and intragranular mechanical cracking, and effectively stabilizes the cathode–electrolyte interface. This approach remarkably enhances the capacity and thermal stability under high-voltage operation.[2][1] Building ultraconformal protective layers on both secondary and primary particles of layered lithium transition metal oxide cathodes. Nature Energy, 2019, 4, 484-494.[2] Probing the Thermal-Driven Structural and Chemical Degradation of Ni-rich Layered Cathodes by Co/Mn Exchange J. Am. Chem. Soc. 2020, 142, 19745-19753.