Influences of Microstructures of the Cathode/Electrolyte Interface on the Electrochemical Properties of All Solid-State
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0972-AA13-05
Influences of Microstructures of the Cathode/Electrolyte Interface on the Electrochemical Properties of All Solid-State Li-ion Batteries Kyosuke Kishida1, Naoyuki Wada1, Yuji Yamaguchi1, Katsushi Tanaka1, Yasutoshi Iriyama2, Zempachi Ogumi2, and Haruyuki Inui1 1 Department of Materials Science and Engineering, Kyoto University, Sakyo-ku, Kyoto, 6068501, Japan 2 Department of Energy and Hydrocarbon Chemistry, Kyoto University, Nishikyo-ku, Kyoto, 615-8510, Japan
ABSTRACT Two types of samples containing different La2/3-xLi3xTiO3 (LLT) solid electrolyte /LiCoO2 cathode interfaces were prepared by depositing LiCoO2 on polycrystalline LLT with two different surface finishes: cleaved and polished surfaces. Electrochemical properties of the samples were analyzed by cyclic voltammetry (CV). Microstructures of the LLT/LiCoO2 interfaces were investigated by scanning electron microscopy and transmission electron microscopy. Cyclic voltammograms of the cleaved sample show that the anodic and cathodic peaks respectively shift to higher and lower potential with the number of cycles, while those for the polished samples do not change much during cycles of potential sweeps, indicating the higher stability for the polished samples upon insertion and extraction of lithium ion. The LiCoO2 thin-film cathode is epitaxially deposited with the orientation relationships: {110}LLT//{11¯20}LiCoO2 and LLT// LiCoO2 for both samples with different geometric configurations of the interfaces to the Li layers in the LiCoO2. Amorphous regions are observed to exist in places at the interface only in the polished samples. The geometric configuration of the interface and the existence of the amorphous regions are considered to have great influences on the stability of the LLT/LiCoO2 interfaces upon charge / discharge operations. INTRODUCTION Lithium lanthanum titanate (LLT: general formula La2/3-xLi3xTiO3) with a perovskitebased structure has received considerable attentions as a solid-state electrolyte for all solid-state lithium rechargeable batteries since it possesses very high Li-ion conductivity and hightemperature stability [1,2]. Extensive studies have revealed its compositional range, crystal structure variations and electrical properties [2]. In the case of the all solid-state systems, interfaces between electrodes and a solid-state electrolyte should have great influences on the battery performance such as interface resistivity and structural stability upon charging and discharging. However, the relationship between the solid-state-electrolyte/electrode interface structure and electrochemical properties has not been studied in detail. In the present study, we prepared two different types of solid electrolyte/electrode interfaces composed of LLT and HT-LiCoO2 cathode with a layered rock-salt type rhombohedral structure (space group: R¯3m) and investigated the evolution of microstructures and electrochemical properties of the cells upon charging and discharging operations.
EXPERIMENTAL PROCEDURE Polycrystalline samples of LLT
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