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Relevance between the Bulk Density and Li+-Ion Conductivity in a Porous Electrolyte: The Case of Li[Li1/3Ti5/3]O4

Mukai, Kazuhiko, Nunotani, Naoyoshi, Moriyasu, Ryuta
ACS Applied Materials & Interfaces 2015 v.7 no.36 pp. 20314-20321
bulk density, electrodes, electrolytes, impedance, lithium batteries, temperature
The Li⁺-ion conductivity (σLᵢ) 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 σLᵢ in a porous electrolyte differs from that in a highly dense electrolyte. In this study, the relationship between the bulk density (dbᵤₗₖ) and apparent σLᵢ (σLᵢᵃᵖᵖ) in a porous electrolyte of Li[Li₁/₃Ti₅/₃]O₄ (LTO) was examined by theoretical and experimental approaches. The theoretical calculations demonstrated that dbᵤₗₖ and σLᵢ have a simple relationship irrespective of the radius of the spherical pores in the electrolyte; i.e., σLᵢ increases almost linearly with increasing ζ, where ζ is the ratio of dbᵤₗₖ to the theoretical density. In fact, the observed σLᵢᵃᵖᵖ of LTO, which was determined by four-probe alternating-current impedance measurements, increased with increasing ζ. Hence, with this relationship, σLᵢᵃᵖᵖ can be estimated by ζ and intrinsic σLᵢ (σLᵢⁱⁿᵗ) 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 σLᵢᵃᵖᵖ in LTO and differences between the calculated and experimental results are also discussed.