Facile in-Situ Polymerized Polymer Electrolytes in All Solid-State Lithium-Ion Batteries

Abstract

With the push towards renewable energy sources and “green” technologies, lithium-ion batteries (LIBs) have proven to be necessary across multiple technological realms, the biggest of which is currently the electric vehicle (EV) and grid storage markets. But the popular choice of liquid organic electrolytes in LIBs suffers from safety concerns, which motivated significant innovations in safer solid-state electrolytes. Among them, solid polymer electrolytes (SPEs) have shown great potential due to their processability, flexibility and tunability of physical properties. The past decade has seen rapid evolution in the development of SPE LIBs, but most of them still stand inadequate. SPEs are typically processed either by using solvents, or by using them in their solid state, to blend with the active electrode materials. While these systems are often subject to additional compression to promote continuous electrolyte-electrode interface, they still suffer from the almost unavoidable formations of voids, and inhomogeneous contact between the active materials and the SPEs. Furthermore, most of these processes require excessive amounts of SPEs, and yet result in a large interfacial resistance.Here we introduce a novel one-step manufacturing strategy for polymer electrolytes in solvent-free SPE LIBs. The process involves in-situ polymerization of a liquid-monomer precursor directly infiltrated into a dry jelly roll or individual electrodes to form SPE cells. Our microscopy and FIB experiments confirmed a near-perfect polymer infiltration in porous cathodes, while electro-chemical tests confirmed excellent characteristics of cathode-electrolyte interfaces. The cycling performance of lithium iron phosphate (LFP) half cells using thus produced and infiltrated SPE showed very good stability and columbic efficiency. In addition to single-ion conductive SPEs, we tested hybrid SPE systems where Li salts were added into the single-ion conductive SPEs to improve rate and capacity utilization.