Composite Electrolytes Prepared by Improving the Interfacial Compatibility of Organic–Inorganic Electrolytes for Dendrite-Free, Long-Life All-Solid Lithium Metal Batteries

Abstract

Compared with simplex ceramic or polymer solid electrolytes, composite solid electrolyte (CSE) is more promising for its better interfacial compatibility to electrode and high ionic conductivity simultaneously. Further, the interfacial compatibility within ceramic and polymer is considered to be more and more critical to the overall performance of solid-state batteries. Avoiding the agglomeration of ceramic particles at high loadings can improve the whole intrinsic characteristic and electrochemical performance of CSEs. Herein, we designed a CSE (EO@LLZTO–PEO), which consists of composite particles (EO@LLZTO) as a filler and polyethylene oxide (PEO) as polymer matrix. EO@LLZTO was prepared by chemically grafting polyethylene glycol monomethyl ether methacrylate (MPEG-MAA) on the micro-sized Li_6.4La₃Zr_1.4Ta_0.6O₁₂ (LLZTO) particles. By introducing of polymer containing EO segments onto LLZTO, the interfacial compatibility between LLZTO and PEO matrix is highly enhanced, and the intrinsic Li⁺ complexation capability of MPEG-MAA is improved, even at the high loading of garnet. EO@LLZTO–PEO shows a high ionic conductivity (1.91 mS cm^–1), a broad electrochemical window (～5.2 V vs Li/Li⁺), and a high lithium ion transference number (0.72). The Li/EO@LLZTO–PEO/Li battery also exhibits a long cycle stability (over 1200 h of cycling). Moreover, all-solid-state batteries with LiFePO₄ and LiNi_0.8Co_0.1Mn_0.1O₂ (NCM811) cathodes exhibit excellent cycling stability and rate performance. Consequently, enhancing the interfacial compatibility between organic and inorganic electrolytes is identified to be one of the crucial strategies for commercial solid-state lithium batteries.