Lithium-Ion Dynamic Interface Engineering of Nano-Charged Composite Polymer Electrolytes for Solid-State Lithium-Metal Batteries

Composite polymer electrolytes (CPEs) offer a promising solution for all-solid-state lithium-metal batteries (ASSLMBs). However, conventional nanofillers with Lewis-acid-base surfaces make limited contribution to improving the overall performance of CPEs due to their difficulty in achieving robust electrochemical and mechanical interfaces simultaneously. Here, by regulating the surface charge characteristics of halloysite nanotube (HNT), we propose a concept of lithium-ion dynamic interface (Li⁺-DI) engineering in nano-charged CPE (NCCPE). Results show that the surface charge characteristics of HNTs fundamentally change the Li⁺-DI, and thereof the mechanical and ion-conduction behaviors of the NCCPEs. Particularly, the HNTs with positively charged surface (HNTs⁺) lead to a higher Li⁺ transference number (0.86) than that of HNTs^- (0.73), but a lower toughness (102.13 MJ m^-3 for HNTs⁺ and 159.69 MJ m^-3 for HNTs^-). Meanwhile, a strong interface compatibilization effect by Li⁺ is observed for especially the HNTs⁺-involved Li⁺-DI, which improves the toughness by 2000% compared with the control. Moreover, HNTs⁺ are more effective to weaken the Li⁺-solvation strength and facilitate the formation of LiF-rich solid-electrolyte interphase of Li metal compared to HNTs^-. The resultant Li|NCCPE|LiFePO₄ cell delivers a capacity of 144.9 mAh g^-1 after 400 cycles at 0.5 C and a capacity retention of 78.6%. This study provides deep insights into understanding the roles of surface charges of nanofillers in regulating the mechanical and electrochemical interfaces in ASSLMBs.