Freestanding Trilayer Hybrid Solid Electrolyte with Electrospun Interconnected Al-LLZO Nanofibers for Solid-State Lithium-Metal Batteries

Energy storage devices that are safe to use and thermally stable and have a wide working electrochemical window and high specific capacity would be a boon to modern society. All-solid-state lithium-metal batteries (ASSLMBs) are promising devices for energy storage because they fulfill these requirements. In this study, we used a solution-casting method to synthesize a freestanding trilayer hybrid solid-state electrolyte (Tri-HSE) membrane from a suspension of interconnected Li6.28La3Zr2Al0.24O12 (Al-LLZO, as the filler), poly(vinylidene fluoride)/poly(ethylene carbonate) (PVDF/PEC, as the blended polymer), lithium bis(trifluoromethanesulfonyl)imide (LiTFSI, as the salt), and succinonitrile (SN, as the plasticizer). The as-prepared Tri-HSE membrane exhibited a high ionic conductivity (ca. 3.91 × 10–4 S cm–1 at 25 °C), a high Li transference number (ca. 0.78), and a high tensile strength (ca. 11.36 MPa). The symmetric cell (Li/Tri-HSE/Li) was stable during Li plating/stripping cycles for 470 h without any short-circuiting. The assembled NCM811/Tri-HSE/Li full cell operated between 2.6 and 4.2 V cut-off voltages, displaying a high initial discharge capacity (162.59 mAh g–1) and a high capacity retention (92.41%) after 100 cycles at a rate of 0.1C. Also, at a rate of 0.2C, it displayed admirable capacity retentions and average Coulombic efficiencies of 87.52, 83.40 and 99.21, 99.47%, after 450 and 250 cycles, at 4.2 and 4.3 V cut-off voltages, respectively. Moreover, the 5 × 3 cm2 dimensional pouch cell assembled using the same membrane reveals an average Coulombic efficiency and capacity retention of 99.53 and 95.58% after 30 cycles, respectively. Therefore, this as-synthesized Tri-HSE membrane─characterized by high flexibility, ionic conductivity, mechanical strength, wide electrochemical window, and low in situ heat generation─appears to be a promising solid-state electrolyte for upcoming generations of lithium-metal batteries operated at room temperature.