Enabling 4.5 V Solid Polymer Batteries through a 10 µm, Crosslinked Polyether Electrolyte

Abstract The implementation of solid polymer electrolytes (SPEs) in energy‐dense batteries faces severe challenges including sluggish ionic diffusion, oxidation tendency at the cathode interface, dendrite protrusion from the metallic anode, as well as the technological incompatibility with the layer stack‐up cell assembly. Herein, an in‐situ polymerization strategy is presented to deal with above dilemma for the solid battery prototyping. The in situ cross‐linked poly(ethylene glycol) diglycidyl ether is embedded within the nanocellulose framework, endowing SPE membrane with the reinforced mechanical strength (11.31 MPa) at the thickness of 10 µm as well as superior ionic conductance (150 mS). After a rigorous selection, the sacrificial triphenylphosphine additive preferentially oxidizes on the LiNi 0.8 Mn 0.1 Co 0.1 O 2 (NCM811) cathode to form the cathode electrolyte interface during the formation charging. Concurrently, the solvated zinc(II) bis(trifluoromethylsulfonyl)imide constructs the polyether/LiZn mosaic layer on the Li foil, which effectively promotes interfacial cation diffusion and horizontal deposits propagation. By pairing the polymerized SPE with the thin‐layer Li foil (50 µm) and the NCM811 cathode (25 mg cm −2 ), the 94 mAh pouch‐format cell can realize a gravimetric/volumetric energy density of 397.5 Wh kg −1 and 1197.6 Wh L −1 , high‐voltage tolerance till 4.5 V, and robust cyclability (95.1% capacity retention for 200 cycles).