Development of High Performance Cathodes: From Liquid to Solid-State Batteries

Sixu Deng, The University of Western Ontario

Abstract

Lithium-ion batteries (LIBs) are critical for the development of electric vehicles (EVs) because of their higher operating voltages compared to other energy storage technologies. However, the development of start-of-the-art LIBs touched the ceiling because of three main challenges: safety risks, limited energy density, and high cost. Accordingly, all-solid-state lithium-ion batteries (ASSLIBs) have recently emerged as promising alternative batteries for next-generation EVs because of their ability to overcome the drawbacks of conventional LIBs. Whether in conventional liquid LIBs or ASSLIBs, cathode materials are crucial in determining the overall performance. Hence, this thesis focuses on understanding the degradation mechanism of cathode interfaces and developing novel interfacial strategies in both liquid LIBs and ASSLIBs.

The first work in this thesis develops a hybrid Li₃PO₄-TiO₂ coating layer by atomic layer deposition (ALD) to improve both interfacial ionic/electronic conductivities and stability for high-voltage LiNi_0.5Mn_1.5O₄ (LNMO) cathode in liquid LIBs.

In the second work, a dual-functional Li₃PO₄ (LPO) modification is designed for Ni-rich layered oxide cathodes, aiming to address both the interfacial side reactions and the microstructural cracks in sulfide-based ASSLIBs.

In the third work, the origin of cathode interface degradation in sulfide-based ASSLIBs is unveiled by the X-ray and electrochemical analyses. Residual lithium compounds on the surface of Ni-rich layered cathodes are proved as the main reason that triggers the oxidation of sulfide solid-state electrolytes (SSEs), therefore inducing severe side reactions at cathode interface and structural degradation of Ni-rich cathodes.

The fourth wok for the first time reports a controllable semi-conductive additive, poly(3,4-ethylenedioxythiophene) (PEDOT), in sulfide-based ASSLIBs, therefore realizing effective electron transfer at the cathode/SSE/additive three-phase interface along with a competitive rate capacity.

To realize fast-charging ASSLIBs, the fifth work investigates the interfacial evolution of Al foil current collector in all-climate environment. At room temperature, side reactions are the main challenge for interfacial stability. At low temperature, the low Li⁺ and electron transfer kinetics along with side reactions are the key limitations for rate capability. The challenges at both room temperature and low temperature can be addressed by the graphene modification on Al foil.