Abstract

LiCoO2 (LCO) is one of the most promising cathode materials for Li ion batteries (LIBs). However, LCO shows a rate-limiting step of Li+ migration between electrode and electrolyte interfaces, requiring LIBs to be charged under low-current conditions. For next generation batteries, it will be necessary to meet the demand for a shorter charging-time. We investigated a support method for the LCO surface to improve high C-rate performance, and revealed that the Li+ intercalation/de-intercalation reaction into/from LCO was accelerated by the introduction of a BaTiO3-LCO-electrolyte interface (triple-phase interface; TPI), due to the electric field concentration near the TPI. In this report, we investigate the dependence of high C-rate performance on the density of surface BaTiO3 nanodots using epitaxial LiCoO2 thin films created via pulsed laser deposition (PLD). As the number of nanodots increased, so did discharge capacity at 50C, becoming saturated at surface coverage over 22%. However, at 100C, the discharge capacity decreased at surface coverage over 40%. These results indicate that coalescence of nanodots reduces not only the TPI length but also the electrochemically active range at quite high C-rate. Therefore, we infer that optimal surface coverage should be varied depending on the C-rate.

Highlights

  • Li ion batteries (LIBs) [1,2] have been commercialized worldwide as a portable electric storage device because of superior properties such as high working voltage and large specific capacity

  • We investigated the mechanism of a method to support the surface using BaTiO3 (BTO) nanodots deposited on a LCO epitaxial thin film, and revealed that Li+ migration could be accelerated near the BTO-LCO-electrolyte caused by the electric field concentration [11,12]

  • To observe the BTO nanodots, scanning electron microscopy (SEM) measurements were carried out using Hitachi S-4800

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Summary

Introduction

Li ion batteries (LIBs) [1,2] have been commercialized worldwide as a portable electric storage device because of superior properties such as high working voltage and large specific capacity. We investigated the mechanism of a method to support the surface using BaTiO3 (BTO) nanodots deposited on a LCO epitaxial thin film, and revealed that Li+ migration could be accelerated near the BTO-LCO-electrolyte (triple-phase interface, TPI) caused by the electric field concentration [11,12]. Based on this finding, we expected that we could vary the enhancement of high C-rate performance by altering the surface coverage of supporting material. The finite element method for calculation of a surface electric field was carried out using ANSYS-HFSS ver. 18.1

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