Relevance between the Bulk Density and Li+-Ion Conductivity in a Porous Electrolyte: The Case of Li[Li1/3Ti5/3]O-4

摘要

The Li+-ion conductivity (sigma(Li)) in an electrolyte is an important parameter with respect to the performance of all-solid-state lithium-ion batteries (LIBs). However, little is known about how sigma(Li) in a porous electrolyte differs from that in a highly dense electrolyte. In this study, the relationship between the bulk density (d(bulk)) and apparent sigma(Li) (sigma(app)(Li)) in a porous electrolyte of Li[Li1/3Ti5/3]O-4 (LTO) was examined by theoretical and experimental approaches. The theoretical calculations demonstrated that d(bulk) and sigma(Li) have a simple relationship irrespective of the radius of the spherical pores in the electrolyte; i.e., sigma(Li) increases almost linearly with increasing zeta, where zeta is the ratio of d(bulk) to the theoretical density. In fact, the observed sigma(app)(Li) of LTO, which was determined by four-probe alternating-current impedance measurements, increased with increasing zeta. Hence, with this relationship, sigma(app)(Li) can be estimated by zeta and intrinsic sigma(Li) (sigma(int)(Li)) and vice versa; such estimations provide critical information for determining the optimum compositions of composite electrodes for all-solid-state LIBs. The temperature dependence of of sigma(app)(Li) in LTO and differences between the calculated and experimental results are also discussed.