Pan Hui,Wang Lei,Shi Yu,Sheng Chuanchao,Yang Sixie,He Ping,Zhou Haoshen
Applying high stack pressure (often up to tens of megapascals) to solid-state Li-ion batteries is primarily done to address the issues of internal voids formation and subsequent Li-ion transport blockage within the solid electrode due to volume changes. Whereas, redundant pressurizing devices lower the energy density of batteries and raise the cost. Herein, a mechanical optimization strategy involving elastic electrolyte is proposed for SSBs operating without external pressurizing, but relying solely on the built-in pressure of cells. We combine soft-rigid dual monomer copolymer with deep eutectic mixture to design an elastic solid electrolyte, which exhibits not only high stretchability and deformation recovery capability but also high room-temperature Li-ion conductivity of 2×10 −3 S cm −1 and nonflammability. The micron-sized Si anode without additional stack pressure, paired with the elastic electrolyte, exhibits exceptional stability for 300 cycles with 90.8% capacity retention. Furthermore, the solid Li/elastic electrolyte/LiFePO 4 battery delivers 143.3 mAh g −1 after 400 cycles. Finally, the micron-sized Si/elastic electrolyte/LiFePO 4 full cell operates stably for 100 cycles in the absence of any additional pressure, maintaining a capacity retention rate of 98.3%. This significantly advances the practical applications of solid-state batteries.
Sulfide electrolytes show great potential as solid electrolytes for all-solid-state batteries due to their high ionic conductivity and low interfacial resistance toward electrode materials. The structure of the P–S framework in the composition of sulfides plays a crucial role in the conductivity. Introducing LiI in the Li3PS4 structure can tailor the P–S frameworks and thus achieve high ionic conductivities. Herein, the dopant of LiI is optimized by high-rotation milling, followed by a sintering route to achieve the highest Li-ion conductivity of 2.3 mS cm–1 for the Li3PS4-50% LiI electrolyte (also denoted as Li7P2S8I) among different compositions. The phase variations and structure evolution of the P–S frameworks in the LiI-doped Li3PS4 electrolytes are carefully investigated in a combination of X-ray diffraction and Raman spectra. All-solid-state Li–S batteries using the prepared Li7P2S8I electrolyte combined with a nano Li2S cathode and a Li–In anode deliver a high initial discharge capacity of 739.7 mA h g–1 and sustain a discharge capacity of 517.7 mA h g–1 after 60 cycles with a capacity retention of 70.0% at 0.13 mA cm–2 at room temperature. When the operating temperature rises to 60 °C, it shows a higher discharge capacity of 862.8 mA h g–1 with fast capacity decay. However, it exhibits stable capacities and superior cycling performance under 0 °C over 70 cycles. Electrochemical impedance spectroscopy and in situ stack-pressure results find that the electrochemical performance differences of the assembled battery at different operating temperatures are associated with the interfacial resistance caused by volume changes. This work provides the strategy to obtain highly conductive sulfide electrolytes for SSBs and unravels the temperature effects on the electrochemical performance of all-solid-state Li–S batteries.
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