An ultra-thin polymer electrolyte for 4.5 V high voltage LiCoO2 quasi-solid-state battery

To achieve safe and high energy density solid-state batteries (SSBs), the weight of solid-state electrolyte (SSE) should be minimized and a high voltage and high specific capacity cathode should be used. Polyethylene oxide (PEO)-based polymer electrolytes (PEs) has been identified as the optimal SSE for SSBs owing to their versatile advantages. However, fabricating ultra-thin and high voltage stable PEO-based PEs is still challenging. Herein, an ultra-thin (8.1 mu m) blending polymer electrolyte (BPE) is designed through blending PEO, Polymethyl methac-rylate (PMMA) and Poly(vinylidene fluoride-hexafluoropropylene) (PVDF-HFP), and complexing with Succino-nitrile (SN), Fluoroethylene carbonate (FEC) and LiTFSI plasticizers. Based on this design, Li|BPE|LiFePO4 quasi-solid-state battery (QSSB) can operate for 250 cycles with a capacity retention of 92.8%, 4.5 V high voltage Li| BPE|LiCoO2 QSSB exhibits 87% capacity retention after 80 cycles, with an average Coulombic efficiency >= 99.8%, which is much superior than 4.5 V Li|PEO|LiCoO2 SSB, whose capacity rapidly decays to 0 mAh/g after a dezen of cycles. DFT calculation suggests that blending PEO, PMMA and PVDF-HFP increase the electro-chemical oxidation tolerance. Interface study by TEM and XPS discloses PEO-LiTFSI/LiCoO2 interface is unstable with a big amount of decomposed products from PEO-LiTFSI and from LiCoO2, while BPE/LiCoO2 interface is more stable without obvious decomposition, indicating the promising application of BPE for high energy density QSSBs.

Automated summary

To achieve safe and high energy density solid-state batteries (SSBs), minimizing the weight of solid-state electrolyte (SSE) and using a high voltage and high specific capacity cathode are crucial. An ultra-thin blending polymer electrolyte (BPE) is designed by blending PEO, PMMA, and PVDF-HFP, and complexing with SN, FEC, and LiTFSI plasticizers. The BPE shows superior performance in terms of capacity retention, stability, and Coulombic efficiency, indicating its promising application in high energy density quasi-solid-state batteries (QSSBs).