Electrolyte engineering and solid electrolyte strategies for enabling lithium-metal batteries

RWTH Publications (RWTH Aachen)

Abstract

Batteries with high energy density are urgently needed to meet the growing demand for electric vehicles (EVs) and humanoid robotic applications. Li-metal batteries (LMBs) are considered as a promising candidate with the potential to achieve energy density exceeding 500Wh∙kg-1. However, the use of Li-metal is hampered by many challenges, such as its side reaction with electrolyte to form solid electrolyte interphase (SEI) layer, formation of harmful Li-dendrites, and large volume change of Li-anode. This dissertation aims to resolve these problems and improve the performance of LMBs by different strategies.The first part describes four strategies to overcome the challenges encountered in LMBs mentioned above: (a) liquid electrolyte engineering by adjusting the composition of the electrolyte to improve the performance of the battery; (b) surface coating to modify the interface between electrolyte and Li-anode to reduce Li-dendrite formation; (c) use solid electrolyte to increase safety of LMB due to its intrinsic nonflammability when compared to liquid electrolyte; (d) anode structure design to limits the volume changes of Li-metal and promotes uniform Li deposition. Here, liquid electrolyte engineering and solid electrolyte strategies were used to improve the performance of LMBs.In the second part, electrolyte engineering is applied to improve the cycling stability of high voltage LMBs with high current density. A dual-salt electrolyte using the concept of local-high-concentration-electrolyte (LHCE) with additive is developed, which not only largely reduces Li-dendrites on the anode surface but also protects the microstructure of cathode. Its excellent performance is attributed to the formation of beneficial SEI and cathode electrolyte interphase (CEI) by carefully design of solvation structure, i.e. through selection of Li-salts, solvent and additive. In the third part, the sintering process of LiCoO2/Li7La3Zr2O12 (LCO/LLZO) composite positive electrodes (CPEs) is optimized to improve the performance of LLZO-based all-solid-state Li-metal batteries (ASSLMBs). It is concluded that sintering temperature has both positive and negative influence on the CPEs. When sintering atmosphere is considered, an oxygen sintering atmosphere only brings drawbacks than advantages compared to an air sintering atmosphere. The degradation mechanisms of ASSLMBs are also investigated. It is found that except form microstructure degradation, the ASSLMBs also suffer from LLZO electrochemical degradation at high voltage.

Authors 1

1. Zhizhen Qin corresponding Aachen

   RWTH Aachen University

   Affiliation as printed

   RWTH Aachen