Development of Ceramic-Polymer Composite Electrolyte for All-Solid Lithium Ion Batteries

In recent years, research on all-solid lithium ion batteries (LIBs) has increased considerably due to raised concerns relating to safety hazards such as the solvent leakage and flammability of liquid electrolytes used in commercial LIBs. All-solid LIBs use fast Li ion conducting solid electrolytes that do not carry the safety burdens of liquid electrolytes and are more effective. In addition, all-solid LIBs can increase the energy density of the entire battery pack by reducing the need for auxiliary systems such as safety monitoring systems. However, even with the highly ionic conductive solid electrolytes, it has been a struggle for a solid electrolyte LIBs to obtain similar specific capacity, rate capability, and cycle life to those of a liquid electrolyte LIBs. Studies conclude that these issues arise from the solid electrolyte’s inability to interface with the solid electrodes mainly due to the volume change of electrode materials during charge and discharge processes (1). In addition, it is difficult to manufacture on large scale the ceramic solid electrolyte LIBs, because the ceramic type solid electrolyte materials are hard and brittle.  

 To overcome this problem, a composite electrolyte was designed and fabricated using the combination of ceramic solid electrolyte and Li ion conducting organic polymer. The flexible polymer electrolyte can improve the interface stability and processibility for large cells. In this study, NASICON-type Li_1.3Al_0.3Ti_1.7 (PO₄)₃ (LATP) was used as the solid electrolyte, which offers chemical stability and high conductivity at room temperature (2). Poly(ethylene oxide) (PEO) was used as the Li ion conducting polymer. The composite electrolyte was prepared by mixing LATP powders and the PEO binder with lithium salt (lithium bis(trifluoromethanesulfonyl)imide) (LITFSI). The conductivity of the composite electrolyte was studied by varying the composition at different temperatures. As shown in Fig.1, a stable composite film with good conductivity and flexibility was achieved with an optimum ratio of 75:25 of the LATP and the PEO binder. By using the composite electrolyte, all-solid LIBs were fabricated and studied. An initial discharge capacity of 92 mAh/g was achieved with 0.1 C rate at 60 °C. The detailed fabrication processes and charge-discharge characteristics of the all-solid LIBs will be reported.

Acknowledgments: This work was supported by US National Science Foundation under Grant No. 1335850.

References:

1.             N. M. Asl, J. Keith, C. Lim, L. K. Zhu and Y. Kim, Electrochimica Acta, 79, 8 (2012).

2.             H. Aono, E. Sugimoto, Y. Sadaoka, N. Imanaka and G. Adachi, Journal of the Electrochemical Society, 137, 1023 (1990).