Paramount attention has been paid on solid polymer electrolytes due to their potential in enhancement of energy density as well as improvement of safety. Herein, the composite electrolytes consisting of Li-salt-free polyethylene oxides and 200 nm-sized Li 6.4 La 3 Zr 1.4 Ta 0.6 O 12 particles interfacially wetted by [BMIM]TF 2 N of 1.8 μL cm −2 have been prepared. Such wetted ionic liquid remains the solid state of membrane electrolytes and decreases the interface impedance between the electrodes and the electrolytes. There is no release of the liquid phase from the PEO matrix when the pressure of 5.0 × 10 4 Pa being applied for 24 h. The interfacially wetted membrane electrolytes show the conductivity of 2.2 × 10 −4 S cm −1 at 20 °C, which is one order of magnitude greater than that of the membranes without the wetted ionic liquids. The conduction mechanism is related to a large number of lithium ions releasing from Li 6.4 La 3 Zr 1.4 Ta 0.6 O 12 particles and the improved conductive paths along the ion-liquid-wetted interfaces between the polymer matrix and ceramic grains. When the membranes being used in the solid-state LiFePO 4 /Li and LiFe 0.15 Mn 0.85 PO 4 /Li cells at 25 °C, the excellent rate capability and superior cycle stability has been shown. The results provide a new prospect for solid polymer electrolytes used for room-temperature solid-state lithium batteries .
Li 7 La 3 Zr 2 O 12 (LLZO) with cubic phase structure is a kind of lithium-ion-conducting nanoparticles. According to the previous studies, incorporation of c-LLZO can improve electrochemical properties of PEO-based composite polymer electrolytes (CPEs). Therefore, in our study, we synthesized a kind of room-temperature-stable cubic phase LLZAO (Li 6.25 La 3 Zr 2 Al 0.25 O 12 ) nanofibers, and we aimed to confirm the optimal content of LLZAO nanofibers in PEO-based CPEs. With the incorporating 10 wt% LLZAO nanofibers, ionic conductivity of CPEs are 9.87×10 −5 S cm −1 at 30 °C and 8.66×10 −4 S cm −1 at 60 °C. The Li/CPE incorporating 10 wt% LLZAO nanofibers/Li symmetric cell exhibits little voltage fluctuation in 1000 cycles under a current density of 0.5 mA cm −2 , demonstrating better cycling stability with long cycle life. The LiFePO 4 /CPE incorporating 10 wt% LLZAO nanofibers/Li cell has a high initial discharge-specific capacity of 155.6 mAh g −1 under 0.1 C rate at 60 °C and remains 94.5% of capacity after 100 cycles. This cell also has great cycling performance under 0.2 C and 0.5 C rate, indicating good rate performance. Our work indicates that incorporation of LLZAO nanofibers enhances electrochemical properties and cycling stability of PEO-based all-solid-state lithium-ion batteries.
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