Jingxian Zhang,Ning Zhao,Miao Zhang,Yiqiu Li,Paul K. Chu,Xiangxin Guo,Zengfeng Di,Xi Wang,Hong Li
Solid-state electrolytes with high ionic conductivity , large electrochemical window, good mechanical properties , and easy processability are needed for high-energy solid-state lithium batteries . In this work, composite membranes consisting of lithium garnet (i.e. Li 6.4 La 3 Zr 1.4 Ta 0.6 O 12 , LLZTO) particles and Li-salt-free polyethylene oxides (PEOs) are produced as solid-state electrolytes. Li-ion-conducting particles in nano-scale are crucial for the enhancement of conductivity and the membranes containing ~40 nm LLZTO particles exhibit conductivities nearly two orders of magnitude larger than those with the micro-scale ones, which is attributed to the difference in specific surface area related to the percolation effect. Compared to the conventional PEO doped with lithium salt, the insulating PEO in PEO:LLZTO membrane electrolyte is conducive to the suppression of lithium dendrite growth owing to prohibition of current flow. With PEO:LLZTO membrane electrolytes in conductivity of 2.1×10 −4 S cm −1 at 30 °C and 5.6×10 −4 S cm −1 at 60 °C, the solid-state LiFePO 4 /PEO:LLZTO/Li and LiFe 0.15 Mn 0.85 PO 4 /PEO:LLZTO/Li cells deliver energy densities of 345 Wh kg −1 (662 Wh L −1 ) and 405 Wh kg −1 (700 Wh L −1 ) (without the package weight or volume) with good rate capability and cycling performance. This study suggests that the conjunction of nano-scale Li-ion-conducting particles and an insulating polymer provides a promising solution to produce powerful solid-state electrolytes for high-performance solid-state lithium batteries .
Lithium metal batteries based on solid electrolytes are considered as promising candidates with high energy density and safety. However, the weak solid-solid contact between electrolyte and electrode can easily lead to interface instability and lithium ions discontinuous migration, which seriously reduces the electrochemical performance of the battery. Herein, we construct a soft gel interfacial layer to improve the stability of the solid-solid interface between electrolyte and electrode by means of polyester-based monomers and imidazole-based ionic liquids. Based on this, garnet-type Li 6.4 La 3 Zr 1.4 Ta 0.6 O 12 (LLZTO) particles as inorganic ceramic filler were introduced in the layer to obtain composite electrolytes with high ionic conductivity (up to 1.1 × 10 −3 S/cm at 25 °C). As a result, the assembled lithium symmetric battery of Li|THCE-15%LLZTO|Li suggests excellent cycling stability with 700 h at 0.1 mA/cm 2 at 50 °C, and the lithium metal batteries of LFP|THCE-15%LLZTO|Li delivers high initial discharge capacity of 128.2 mA ·h/g with capacity retain of 75.48% after 150 cycles at 2 C. This work paves a new route to build safe and stable lithium metal batteries with synergistic introduction of composite electrolytes between electrolyte and electrode using soft gel interfacial layer and inorganic filler.
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 .
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