Succinonitrile-Lithium Salt Composite As a Solid Catholyte for Llzo-Based All-Solid-State Batteries

Abstract

All-solid-state batteries (ASSB) have come into the spotlight as next-generation batteries because of their potential high energy density and low flammability. LLZO (Li7La3Zr2O12) is a prominent solid electrolyte material for ASSBs due to its high ionic conductivity (>1 x 10-4 S/cm at room temperature) and compatibility with Li metal. However, for its use in ASSBs, there are challenges including forming intimate contact with the active electrode material. Because both LLZO and the cathode active material are rigid, employing a soft solid catholyte between them can be a solution to ensure intimate contact. The solid catholyte must be ionically conductive, and stable against oxidation (> 4.5 V vs. Li/Li+).Organic Ionic Plastic Crystals (OIPC) are a class of materials that is soft and waxy at room temperature. When the OIPC is mixed with Li salts, the mixture has high ionic conductivity and a wide electrochemical window. Succinonitrile (SN) is an OIPC material, and SN with Li salts are reported to have high ionic conductivities (> 1x10-4 S/cm), good oxidation stability (>5 V vs. Li/Li+), and low flammability as well [1][2]. Despite the favorable properties of the SN-Li salt composite, poor chemical stability with Li metal makes it difficult to use it alone as a solid electrolyte [1]. For its use as a solid catholyte, chemical stability with Li metal is not an issue, making it a prominent candidate material. However, studies for its use as a solid catholyte with LLZO are limited.In this talk, we describe the properties of Succinonitrile-Lithium salt composites focusing on their suitability as solid catholytes in LLZO-based ASSBs. SN is mixed with different kinds of Li salts including LiTFSI and LiBOB to form composites. Their electrochemical properties are compared and the contact between the composite and LLZO is observed. The performance of all-solid-state cells with the mixtures will also be evaluated at room temperature. It is hoped that this work can motivate efforts toward developing LLZO cells using OIPC materials.[1] Alarco P.J, et al Nat. Mater., 3, 476 (2004)[2] Effat M.B, et al J. Power Sources, 226802, 436 (2019)