Abstract:

The increasing development of society has resulted in the ever-growing demand for energy storage devices. To satisfy this demand, both energy density and safety performance of lithium batteries must be improved, which is challenging. Solid-state lithium batteries are promising in this regard because of their safe operation and high electrochemical performance. In recent years, intense effort has been devoted toward the exploration of materials with high ionic conductivity for room-temperature solid-state batteries. Among several types of solid-state electrolytes, Li_1.5Al_0.5Ge_1.5(PO₄)₃ (LAGP), an inorganic NASICON-type electrolyte, has drawn considerable attention because of its high ionic conductivity, wide electrochemical window, and environmental stability. However, the formation of lithium-ion-conducting networks within the electrode and between the electrode-LAGP interface is limited because of high interfacial resistance caused by the direct contact and volume expansion between the electrode and electrolyte. Thus, the application of LAGP in the fabrication of solid-state batteries is limited. Moreover, the occurrence of the unavoidable side reaction because of the direct contact of LAGP with the lithium metal anode shortens battery life. In addition, the rigid brittle nature of the LAGP electrolyte leads to the limits the facile fabrication of solid-state batteries. To overcome these limitations, herein, a novel strategy based on in situ polymerization of a vinylene carbonate solid polymer electrolyte (PVC-SPE) was proposed. The in situ formed PVC-SPE can effectively construct ion-conducting pathways within the cathode and on the interfaces of the LAGP electrolyte and electrodes. Furthermore, the PVC-SPE can significantly inhibit the side reaction between the lithium anode and LAGP electrolyte. The electrochemical performances of Li | LAGP | Li and Li | LAGP | Li with in situ PVC-SPE modified interface symmetrical solid-state batteries were compared. The in situ modified Li | LAGP | Li symmetrical solid-state battery exhibited stability toward plating and stripping for over 2700 h and a low overpotential (34 mV) at room temperature. Moreover, a Li | LAGP | LiFePO₄ solid-state battery exhibited a capacity retention of 94% at 0.2 C after 200 cycles with a capacity of 158 mAh·g^-1. In addition, high rate capability (72.4% capacity retention at 3 C) was achieved at room temperature. Therefore, the proposed in situ modification strategy was found to resolve the interface-related problem and facilitated the construction of the ion-conducting network within the electrode; thus, it can be a promising approach for the fabrication of high-performance solid batteries.

Key words: Ion network, Interface, In situ polymerization, Solid-state battery