Development of advanced solid-state electrolytes and interfaces for high-performance sulfide-based all-solid-state lithium batteries

Feipeng Zhao, The University of Western Ontario

Abstract

All-solid-state lithium batteries (ASSLBs) have become increasingly attractive due to the demand of high-energy-density and high-safety lithium-ion batteries for electric vehicles (EVs). As the core component of ASSLBs, solid-state electrolytes (SSEs) are regarded as essential to determine the electrochemical performance of ASSLBs. The inorganic SSEs is one of the most important categories in all developed SSEs, representing the advance of superionic lithium conductors as well as the cornerstone to construct flexible polymer/inorganic composite SSEs. The sulfide-based inorganic SSE is one of the most promising SSEs that is receiving a lot of attentions, because only sulfide SSEs can show ultrahigh ionic conductivity (up to 10^-2 S cm^-1) at room temperature (RT) that can be comparable to conventional liquid electrolytes. However, sulfide SSEs are suffering interfacial instability at both anode and cathode sides, as well as poor air stability. These drawbacks are hindering the commercialization of ASSLBs using sulfide as the SSE.

In this thesis, first, from the point view of electrolyte synthesis, strategies of element substitution are rationally developed to realize good Li anode compatibility or (and) air stability. It is noted that these strategies are on the premise to achieve decent or improved ionic conductivity for the parent sulfide SSEs. Specifically, replacing Cl partially with F in the Argyrodite sulfide Li₆PS₅Cl SSEs can trigger to generate LiF-rich Li anode interface, which can realize ultrastable Li plating and stripping. Additionally, Sn-substituted Argyrodite Li₆PS₅I and Li₃PS₄ glass-ceramic sulfide SSEs are developed, respectively. The versatile Sn is verified to improve the air stability, ionic conductivity, and Li anode compatibility, simultaneously. The mechanism of multi-functionality obtained from Sn substitution has been well explored. Overall, these novel sulfide SSEs can be viewed as new choices for developing all-solid-state Li metal batteries with high energy densities. Second, atomic layer deposition is used to design new lithium zirconium oxides (LZO) as the interfacial buffer layer to alleviate the cathode interface problems (slow Li⁺ transport and side reaction) between Li₆PS₅Cl sulfide SSEs and LiCoO₂ cathode materials. These works focusing on the synthesis of new sulfide SSEs and the interface engineering pave the way to achieve high-performance sulfide-based ASSLBs.