Polymeric gel electrolytes reinforced with glass-fibre cloth for lithium secondary batteries

Polymeric gel electrolytes (PGE), based on polyacrylonitrile blended with poly(vinylidene fluoride-co-hexafluoropropylene) (P(VdF-co-HFP)), which are reinforced with glass-fibre cloth (GFC) to increase the mechanical strength, are prepared for the practical use in lithium secondary batteries. The resulting electrolytes exhibit electrochemical stability at 4.5 V against lithium metal and a conductivity value of (2.0–2.1)×10⁻³ S cm⁻¹ at room temperature. The GFC–PGE electrolytes show excellent strength and flexibility when used in batteries even if they contain a plasticiser. A test cell with LiCoO₂ as a positive electrode and mesophase pich-based carbon fibre (MCF) as a negative electrode display a capacity of 110 mAh g⁻¹ based on the positive electrode weight at the 0.2 C rate at room temperature. Over 80% of the initial capacity is retained after 400 cycles. This indicates that GFC is suitable as a reinforcing material to increase the mechanical strength of gel-based electrolytes for lithium secondary batteries.