Garnet-type solid-state electrolytes (SSEs) have great potential to be applied in all-solid-state lithium batteries (ASSLBs) due to their high ionic conductivity and excellent electrochemical stability with Li metal. However, the poor interface contact and the high electronic conductivity issues resulting in lithium dendrites growth remain challenging. Herein, we constructed a multifunctional interlayer LiF/Li-Ag alloy (LFA) in situ on the surface of garnet-type Li6.5La3Zr1.5Ta0.5O12 (LLZTO) to suppress Li dendrite growth. The matrix of the interlayer is a three-dimensional porous structure LiF and it is filled with Li-Ag alloy. The LiF blocks electron access to the LLZTO and the Li-Ag alloy ensures a good interface contact during cycling. The Li/LFA-LLZTO/Li symmetrical cells exhibit an ultralow interfacial resistance of 1.8 Ω cm2, a high critical current density of 1.1 mA cm-2 and outstanding galvanostatic cycling stability at 0.2 mA cm-2 for 2000 h. Moreover, the LiFePO4/LFA -LLZTO/Li full cell delivers a high discharge capacity of 155 mAh g-1 at 0.1 C with a capacity retention of 93% after 100 cycles.
Li7La3Zr2O12 (LLZO) is considered as a promising solid-state electrolyte due to its high ionic conductivity, wide electrochemical window, and excellent electrochemical stability. However, its application in solid-state lithium metal batteries (SSLMBs) is impeded by the growth of lithium dendrites in LLZO due to some reasons such as its high electronic conductivity. In this study, lithium fluoride (LiF) was introduced into Ta-doped LLZO (LLZTO) to modify its grain boundaries to enhance the performance of SSLMBs. A nanoscale LiF layer was uniformly coated on the LLZTO grains, creating a three-dimensional continuous electron-blocking network at the grain boundaries. Benefiting from the electronic insulator LiF and the special structure of the modified LLZTO, the symmetric cells based on LLZO achieved a high critical current density (CCD) of 1.1 mA cm-2 (in capacity-constant mode) and maintained stability over 2000 h at 0.3 mA cm-2. Moreover, the full cells combined with a LiFePO4 (LFP) cathode, demonstrated excellent cycling performance, retaining 97.1% of capacity retention after 500 cycles at 0.5 C. Therefore, this work provides a facile and effective approach for preparing a modified electrolyte suitable for high-performance SSLMBs.
Carbonyl-containing polymers have been considered promising candidates as hosts in solid polymer electrolytes (SPEs) due to the reasonable chelating coordination with Li+, better antioxidation for high-voltage cathodes, and higher ion transference number compared with polyether SPEs. In this work, four polyesters of poly(octamethylene succinate), poly(hexmethylene succinate) (PHS), poly(butylene succinate), and polycaprolactone were investigated. In these SPEs with different −C═O/–CH2– ratios, PHS had the highest conductivity (σ) of 1.24 × 10–4 S/cm because of the excellent ability to deionize bis(trifluoromethane)sulfonimide (LiTFSI) up to 88.3 ± 3.2% at 70 °C and the lowest activation energy of Li+ ionic conduction. The effect of Li+/–C═O ratios (r) on the ionic conductivity can be clarified into low-, middle-, and high-concentrated regions. The decrease of PHS crystallinity due to LiTFSI solvation provided ion transport paths and mainly contributed to the improvement of ionic conductivity in the middle-concentrated region, while the solvation degree dominantly facilitated ionic conduction in the high-concentrated region and at higher temperatures. By combining the DFT simulation and polymer thermal analysis, we found the transition of Li+ coordination from multichain to single-chain bindings provided more flexible segment movement. It also proved that the sequence design of active groups in a polymer chain would be a promising strategy for stable and high-performance SPEs.
Abstract Li 7 La 3 Zr 2 O 12 is a promising material used as solid electrolyte in all‐solid‐state lithium batteries. However, the lithium ionic conductivity of LLZO is limited, and the cycling stability of lithium symmetric battery based on LLZO is not good. In this research, different Ga‐doped LLZO samples were prepared by adding different excess amounts of Li 2 O, and the effect of excess amount of Li 2 O on the structure and performance of LLZO have been researched. The results show that with the rise of the amount of Li 2 O, the lithium ionic concentration increases gradually, and the lithium ionic conductivity and the ratio of grain resistance to total resistance rise first and then drop. When the excess amount of Li 2 O is 10 wt.%, the sample exhibits the highest lithium ionic conductivity of 1.36 mS/cm, and the lithium symmetric battery exhibits the most stable operation.
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