A sandwich-type composite polymer electrolyte for all-solid-state lithium metal batteries with high areal capacity and cycling stability

Abstract Development of solid electrolytes with fast ion conductivity, high electrochemical and thermal stability, and excellent compatibility with electrodes is the crucial issue for high-performance all-solid-state lithium metal batteries (ASSLMBs). In this work, a flexible and stable composite polymer electrolyte (CPE) composed of poly(vinylidene fluoride-hexafluoropropylene) (PVDF-HFP)-Li6.4La3Zr1.4Ta0.6O12 (LLZTO) sandwiched by PEO-lithium bis(trifluoromethylsulfonyl)imide (LiTFSI) polymer skin layers in two sides (denoted as sandwich-type CPE) was fabricated and applied for the ASSLMBs. In such a CPE film, the PEO-LiTFSI polymer layers not only ameliorated the ion conductivity of PVDF-HFP-LLZTO, but also improved the intimate contact with the electrodes. Meanwhile, the crystallinity of PEO as well as the PVDF-HFP polymer matrix was significantly reduced owing to the cross-linking of them at the interfacial sections so that the obtained CPE membrane had faster Li+ ions transportation ability. Assembled with this sandwich-type CPE, the all-solid-state LiFePO4 (areal capacity: 1.5 mAh cm−2) |Li-metal battery exhibited excellent rate performance and cycle stability with a discharge capacity of 120.01 mAh g−1 even after 300 cycles at 40 °C. Also, other two all-solid-state LiCoO2|Li-metal and LiNi1/3Mn1/3Co1/3O2|Li-metal batteries showed high voltage stability along with the satisfied energy density as well as excellent cycle performance. Moreover, the fabricated flexible pouch cell exhibited outstanding performance, indicating its feasibility for the next-generation of flexible ASSLMBs.