Tailoring the ionic conductivity of composite electrolyte by La-doping regulated Li4Ti5O12 for solid state lithium metal batteries

Abstract

It is urgently required that polyethylene oxide (PEO) based electrolytes exhibit high Li⁺ conductivity and exceptional interfacial compatibility at wide temperature. In this study, La-doped two-dimensional (2D) Li₄Ti₅O₁₂ nanosheets (La-LTO NSs) are firstly introduced into PEO (La-LTO/PL) to achieve composite polymer electrolytes (CPEs). The La-doping regulated Li₄Ti₅O₁₂ with high aspect ratio and rich oxygen vacancy can significantly enhance the amorphous region and anchor adequate TFSI⁻. Furthermore, the DFT calculation reveals that enrichment of charge density gather around La element and oxygen vacancies, indicating the stronger interaction between La-LTO NSs and PEO/TFSI⁻. Therefore, the CPEs deliver multiple ion-transport channels including the interface between the La-LTO NSs and PEO, PEO chains and La-LTO NSs, enabling fast Li-ion transport and highly stable interface. As a result, the CPEs exhibit impressive ionic conductivity (2 × 10⁻⁴ S cm⁻¹ under 30 °C, 1 × 10⁻³ S cm⁻¹ under 60 °C) and steady electrochemical impedance value during 22 days. While the all-solid-state Li|LiFePO₄ (Li|LFP) cells deliver remarkable cycle stability for 400 cycles with 80 % capacity retention at 0.2 C under 30 °C. Moreover, the pouch cell of Li|LFP maintains approximately 92.0 % capacity retention after 200 cycles. This work promotes the applications of CPEs in high-performance solid-state Li batteries.