Interface engineering of high voltage cathode for poly(ethylene oxide) based all-solid-state Li battery

Abstract

It is in the objective of current research to obtain a high energy density next-generation lithium-ion battery (LIB). Extensive studies have therefore been carried out on cathode materials with high capacity and high voltage as well as anode materials with high capacity. Also, the safety of the next-generation high energy density LIBs is of utmost importance. In particular, the application of conventional flammable liquid electrolytes in traditional LIBs involves the risk of thermal runaways and other safety hazards. Solid electrolytes have a higher flash point compared to flammable liquid organic electrolytes. Hence, the application of solid electrolytes can improve the thermal stability of LIBs and are therefore expected to play a key role in next-generation high energy density LIBs.

Polymer electrolytes, such as poly(ethylene oxide) are reported as possible solid electrolyte candidate due to their thermal and electrochemical stability. However, the poor interfacial stability of poly(ethylene oxide) with high voltage cathode materials, such as $LiNi_{0.6}Mn_{0.2}Co_{0.2}O_2$, limits the application of poly(ethylene oxide) as solid electrolyte for higher energy density LIB fabrication. In particular, the surface catalytic effect of high voltage cathode materials leads to a decomposition of poly(ethylene oxide).

This thesis is focused on coating the $LiNi_{0.6}Mn_{0.2}Co_{0.2}O_2$ cathode material with chemically stable Li3PO4 by sol-gel method to increase the interfacial stability between the cathode and the poly(ethylene oxide) solid electrolyte. The successful coating of the $LiNi_{0.6}Mn_{0.2}Co_{0.2}O_2$ surface is demonstrated by scanning electron microscope analysis. An improved electrochemical performance was achieved, showing a discharge capacity decay of 6 % after 66 cycles for the coated material compared to 31.8 % after 66 cycles for pristine $LiNi_{0.6}Mn_{0.2}Co_{0.2}O_2$ at 0.2 C. In addition, potential experimental conditions are identified to operate cells with an increased active material loading to demonstrate more practical battery cycling results.