Highly conductive ceramic-in-polymer composite electrolyte enabling superior electrochemical performance for all-solid-state lithium batteries

In the present work, poly (vinylidene fluoride-co-hexafluoropropylene) [P(VDF-HFP)] and various amounts of NASICON-type LiZr1.5Sn0.5(PO4)3 (LZSP) as the active filler were used to fabricate composite solid electrolytes (CSEs) by solution-casting method and their structural and electrochemical behaviour were studied. The X-ray diffraction (XRD) data showed the compatibility of the rhombohedral LZSP with P(VDF-HFP). A uniform distribution of ceramic particles in the polymer was observed from scanning electron microscopy (SEM) images and energy X-ray dispersive maps. The addition of 15% wt. ceramic filler to the polymer matrix enhanced the room temperature ionic conductivity (σ ∼ 2.87 × 10−5 S/cm), lithium-ion transference number (tLi+ ∼ 0.55), and electrochemical stability window (∼4.87 V). The reversibility and endurance of lithium-ion conduction across the composite electrolyte at various current densities were confirmed through galvanostatic charge-discharge measurements on a symmetric lithium cell for more than 500 h. A full cell fabricated using a commercial grade LiMn2O4 cathode and the optimized CSE electrolyte showed excellent rate performance at room temperature. The cell delivered a discharge capacity of 105 mAh/g with a nominal voltage of 4.0 V and retained 93% of its initial capacity after 100 cycles at a current density of 0.1 mA/cm2.