Tuning Phase Structures of In-Situ Polymerized Elastomeric Electrolyte via Monomer Structure Engineering for Achieving High Stability in Solid-State Lithium Metal Batteries

Abstract

To achieve high-performance solid-state lithium (Li) metal batteries (LMBs), both the Li-ion conductivity and mechanical robustness of the polymeric electrolyte are crucial. Herein, we develop a series of elastomeric electrolytes with different phase structures to optimize their Li-ion conductivity and mechanical properties. The phase structures are controlled by modifying the side alkyl chain length of the acrylate monomer during the in-situ polymerization process. Specifically, when using short alkyl chain monomers such as methyl and ethyl, a homogeneous phase of the electrolyte was generated after the in-situ polymerization. On the other hand, longer-chain monomers like butyl and hexyl result in bicontinuous and macrophase-separated structures, respectively. Among these different structures, the elastomeric electrolyte based on butyl acrylate (BA) and succinonitrile (SN), denoted as BA-SPE, exhibits excellent ionic conductivity (>1 mS cm-1) and high mechanical extensibility due to its bicontinuous structure. The BA-SPE also demonstrates stable operation when used in a Li/LiNi0.8Co0.1Mn0.1O2 (NCM811) full cell. To further enhance the performance of the BA-SPE, we introduced a dual salt system comprising lithium bis(trifluoromethane sulfonyl)imide (LiTFSI) and lithium difluoro(oxalato)borate (LiDFOB). This modification resulted in superior full cell performance, with 88% capacity retention after 100 cycles under a current density of 0.5 mA cm-2, using a 40 µm-Li anode and high-loading NCM811 cathode (>10 mg cm-2).