Compared with traditional lithium–sulfur batteries, all-solid-state lithium–sulfur batteries assembled with inorganic solid electrolytes can not only effectively eliminate the shuttle effect but also drastically improve the safety performance. Due to the low ionic conductivity of the active materials, the construction of the interface between the active materials and the solid electrolytes in the composite cathode is crucial to the performance of the battery. Herein, Li 2 S– Li 3 PS 4 (LPS) composite materials are prepared by the in situ growth of solid electrolytes on the surface of the active material Li 2 S through the method of liquid-phase shaking. After heat treatment at 320 °C for 1 h, the 45Li 2 S–55LPS-320 exhibits a high ionic conductivity of 1.11 × 10 −4 S cm −1 , much higher than that of commercial Li 2 S. Without additional electrolytes, the Li 2 S–LPS composite mixed with a conductive agent is directly used as the cathode material. The composite cathode with high active material Li 2 S, whose content is up to 50%, delivers a discharge specific capacity of 674.3 mAh g −1 after 30 cycles at a current density of 0.2 mA cm −2 at 60 °C, with Coulombic efficiency being 100%.
All-solid-state lithium–sulfur batteries (ASSLSBs) are considered to be a promising solution for the next generation of energy storage systems due to their high theoretical energy density and improved safety. However, the practical application of ASSLSBs is hindered by several critical challenges, including the poor electrode/electrolyte interface, sluggish electrochemical kinetics of solid–solid conversion between S and Li2S in the cathode, and big volume changes during cycling. Herein, the 85(92Li2S-8P2S5)-15AB composite cathode featuring an integrated structure of a Li2S active material and Li3PS4 solid electrolyte is developed by in situ generating a Li3PS4 glassy electrolyte on Li2S active materials, resulting from a reaction between Li2S and P2S5. The well-established composite cathode structure with an enhanced electrode/electrolyte interfacial contact and highly efficient ion/electron transport networks enables a significant enhancement of redox kinetics and an areal Li2S loading for ASSLSBs. The 85(92Li2S-8P2S5)-15AB composite demonstrates superior electrochemical performance, exhibiting 98% high utilization of Li2S (1141.7 mAh g(Li2S)–1) with both a high Li2S active material content of 44 wt % and corresponding areal loading of 6 mg cm–2. Moreover, the excellent electrochemical activity can be maintained even at an ultrahigh areal Li2S loading of 12 mg cm–2 with a high reversible capacity of 880.3 mAh g–1, corresponding to an areal capacity of 10.6 mAh cm–2. This study provides a simple and facile strategy to a rational design for the composite cathode structure achieving fast Li–S reaction kinetics for high-performance ASSLSBs.
The fast Li-ion pathways in crystals contribute to superionic conductivity—extraordinarily high ionic conductivity—of the Li10GeP2S12 (LGPS) structure. Composition tuning is expected to improve the conductivity. The phase behavior, microstructure, and ion dynamics of a series of solid solutions of xLi4GeS4–yLi3PS4 (4/1 ≥ x/y ≥ 1/2) were studied by multiple 7Li and 31P solid-state NMR methods. Li10GeP2S12 (Ge/P = x/y = 1/2) is the smallest x/y of the disordered LGPS structure. When the Ge/P ratio increases, the room-temperature Li ionic conductivity first increases to a maximum around x/y = 1/1.2 and then decreases. Meanwhile, a disordered LGPS structure transforms into an ordered LGPS′ structure synchronously with conductivity reduction. The Li4GeS4–Li3PS4 phase diagram with the order–disorder structure transition was reconstructed accordingly. Both ordered LGPS′ and disordered LGPS exhibit similar two-dimensional (2D) and one-dimensional (1D) Li diffusion paths. But the disordered LGPS structure is conducive to fast ionic conductivity, rooted in its fast 2D Li+ diffusion in the ab-plane rather than 1D diffusion along the c-axis. Two high-temperature relaxation processes are observed in the LGPS′ structure, suggesting heterogeneous 2D jumps of rapid and slow rates, whereas only a single homogeneous 2D jump process was found in the LGPS structure. Our findings provide insight into understanding the relationship between structure order (or disorder) and ionic conductivity of superionic materials, offering guidelines for optimizing ionic conductivity for extensive solid electrolyte materials rather than LGPS materials.
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