Molecular-Level Organic-Inorganic Hybrid Solid State Electrolyte

Abstract

All-solid-state batteries (ASSB) are of great interest due to their unique chemical/physical properties, such as non-flammability, no liquid leakage and gas generation, and a broad operating temperature range. Solid state electrolyte (SSE) can be divided into two categories: solid inorganic and polymer electrolytes. Inorganic electrolytes possess high ionic conductivities but are generally brittle and difficult to process. In contrast, polymer electrolytes are inherently flexible and easy to process but their ionic conductivities are generally low. Thus, extensive research has been devoted to combining the inorganic electrolyte and polymer electrolyte to achieve a balance in ionic conductivity and mechanical flexibility. The mechanical flexibility also enables hybrid solid electrolyte (HSE) to achieve an intimate contact/ improved interface with solid-state electrode. HSE has so far been fabricated by mechanical mixing of inorganic and polymeric materials which result in a heterogeneous mixture. It is often observed that interfacial issues between the components result in ionic conductivities far less than the values estimated from volume fractions and pure material performance. Here we report the synthesis of a sulfide based HSE via an in-situ polymerization reaction. An inorganic Li-P-S electrolyte is used to trigger the polymerization of a sulfur containing precursor. As a result, the resultant composite achieved molecular bonding at the interface between the inorganic and the polymeric electrolytes. The interfacial structure was confirmed by the cryogenic-transmission electron microscopy and cryogenic-scanning transmission electron microscopy-energy-dispersive X-ray spectroscopy. Owing to this molecular level interaction, the ionic conductivity of this HSE is as high as 2.91*10-5 S cm-1 at room temperature, which is very close to the value expected from the volume fractions of the components. An ASSB fabricated with the HSE along with LiNi0.80Co0.15Al0.05O2 as the cathode and Li-In alloy as the anode demonstrated stable cycling shown in Figure 1. Our work shows that molecular engineering at the interface is a promising approach to fabricate flexible HSEs with high ionic conductivity for ASSBs. Figure 1