Mechanisms of the decrease in low-temperature electrochemical performance of Li4Ti5O12-based anode materials

Qian Huang,Zhen Yang,Jian Mao

doi:10.1038/s41598-017-15504-4

Abstract

The electrochemical performances of Li4Ti5O12 (LTO) and Li4Ti5O12-rutile TiO2 (LTO–RTO) composite electrodes at low temperatures were evaluated. The electrochemical performance of both electrodes decreased at low temperatures; regardless, the LTO–RTO electrode performed better than the LTO electrode. First, high viscosity and low ion conductivity of liquid electrolytes at low temperatures significantly reduce electrochemical performance. Second, cycling at low temperatures changes the crystal structure of LTO–based electrodes, impeding lithium ion diffusion and even causing the diffusion path to change from easy to difficult. However, changes in the crystal structure of the LTO–RTO electrode were not sufficient to change this path; thus, diffusion continued along the 8a-16c-8a pathway. Finally, from the perspective of dynamics, aggravation of a side reaction, increase in charge transfer resistance and polarization, and decrease in lithium ion diffusion at low temperatures reduce the electrochemical performance of LTO–based anode materials. However, the activation energy based on lithium ion diffusion is lower in the LTO–RTO electrode than the LTO electrode. The results confirmed that the electrochemical performance of the LTO–RTO electrode was better than that of the LTO electrode at low temperatures.

Highlights

Fossil fuel has started to diminish, and air pollution has escalated in severity; clean and renewable energy sources are urgently needed
The patterns suggest that all diffraction peaks of LTO are in accordance with a cubic spinel structure with the Fd-3 m space group (JCPDS: 49–0207); some weak diffraction peaks in the pattern of Li4Ti5O12-rutile TiO2 (LTO–RTO) were detected at 27.5°, 36.1°, 54.3°, which correspond to rutile-TiO2 (JCPDS: 21–1276)
The results showed that the RTO content in the LTO–RTO powder was 3.257 wt%

Summary

Introduction

Fossil fuel has started to diminish, and air pollution has escalated in severity; clean and renewable energy sources are urgently needed. Li4Ti5O12 (LTO) is indisputably a high-potential anode material because of its distinct features, including the following: “zero-strain” structure during charge/discharge, which ensures a long cycling life[4,5]; high charge/discharge platform, which can avoid the deposition of lithium metal on the electrode surface and the formation of lithium dendrites during charge/discharge at high rates or low temperatures, thereby strengthening safety[6]; and 2-phase electrochemical reaction mechanism. References[9,15,16,17,18,19] indicated that the appropriate particle size, large specific surface area, fewer contact points between particles, and high electrode conductivity could effectively enhance the low-temperature electrochemical performance to a certain extent. In the current study, the low-temperature electrochemical performance of LTO and LTO–RTO anode materials was investigated, and its mechanisms were explored by analyzing the influence www.nature.com/scientificreports/. The improved methods were presented by reducing the melting point of the liquid electrolyte or by coating an RTO layer on the surface of the LTO nanosheet

Methods

Results

Conclusion