Utilizing Li4Ti5O12 as multifunctional filler in composite solid electrolyte for all-solid-state lithium metal battery

Abstract

Developing solid-state electrolytes (SSEs) with superior electrochemical performance that are compatible with lithium metal is one of the most promising strategies for solid-state lithium metal batteries (SSLMBs). The widely used polyethylene oxide (PEO)-based solid-state electrolyte is compatible with lithium metal. However, the ionic conductivity of PEO is unsatisfactory, and the poor mechanical performance is not ideal in suppressing lithium dendrites. The bare ether oxygen also causes decomposition under high voltage. Many filler strategies to address these issues have been studied, but the mixed ionic/electronic conductors (MIECs) with electrochemical activity have rarely been investigated due to their fatal electronic conductivity and redox behavior. Herein, a composite solid electrolyte incorporating Li₄Ti₅O₁₂ (LTO), which is used as an electrochemically active anode for lithium-ion batteries, into PEO was studied and optimized for the electrochemical stable window (ESW), ionic conductivity, interface dynamics and lithium deposition. It is noteworthy that PEO with 60 wt% LTO shows faster ionic transport with a wider ESW. The lithiophilic layer on the surface induces a dendrite-free anode with lower lithium nucleation energy and interface impedance, realizing a much longer stable cycling of Li/Li symmetric cells. The Li/LiFePO₄ button cells present a specific discharge capacity of 154.1 mA h g⁻¹ at 0.5C with the retention of 79.1% after 600 cycles. The Li/LiMn_0.6Fe_0.4PO₄ button and pouch cells also show superior electrochemical behavior. This work confirms the multiple improvements of LTO filler in composite solid electrolytes (CSEs) and demonstrates the potential application value of LTO, providing a novel direction for selecting fillers for CSEs.