Preparation of Amorphous SiO2 Coated Li4Ti5O12 Anode and Their High Cycleability
Authors: Nomura Ryota , Kobayashi Yoshinao , Yasui Shintaro 
Published: December 2024

In recent years, lithium-ion batteries (LIBs) have been commonly used in batteries for electric vehicles and smartphones because of their higher capacity, higher energy density, and longer life than other rechargeable batteries. The viewpoint of longer life in LIBs, Li4Ti5O12 (LTO) oxide anode is one of the possible alternative materials. LTO possesses less than 1% volume change property during charging and discharging, which prevents poor contact with active materials due to less cracking. Furthermore, LTO is operated at a high voltage of 1.55 V vs Li/Li+, so metallic Li dendrites do not grow. However, it is well known that side reactions such as SEI formation and gas generation are caused at the interface between the electrolyte and LTO. Therefore, in this study, in order to reduce side reactions at the interface, the LTO surface was coated with amorphous SiO2, which is electrochemically stable and inexpensive, to improve the rate and cycle characteristics.

An amorphous SiO2-coated LTO (coated-LTO) was prepared by a sol-gel method using TEOS as the starting material. 5wt% and 10wt% of TEOS vs LTO were used to prepare coated LTO with different coating thicknesses. The obtained powders were analyzed by XRD, SEM/EDS, XPS, and AES for crystal structure and surface conditions. A 2032-type coin cell was fabricated for battery characterization. Li foil was used as the counter electrode and LiPF6 EC:DEC (3:7 vol%) as the liquid electrolyte. Charge-discharge measurements were carried out using CC-mode under a measured voltage range of 1.0 V to 3.0 V and a theoretical capacity of 175 mAh/g. To evaluate the C-rate performance of LIBs using coated-LTO, the C-rate was varied from 0.1C to 40C. In the cycle test, 1000 charge-discharge cycles were conducted at 3C, with 1 hour of OCV after charge and discharge in all cycles. EIS measurements were taken before and after charging and discharging to evaluate interfaces caused by side reactions.

The results of the XRD analysis showed that the crystal structure was not disturbed by the coating, meaning that the coating did not destroy the LTO through the coating process. The average thickness of the SiO2 layer was 1-3 nm and 2-4 nm for the sample coated with TEOS at a concentration of 5wt% and 10wt% vs LTO, respectively. The C-rate performance of the charge-discharge test shows that the discharge capacity slightly decreased at low C-rate operation due to the coating, meaning that SiO2 should be a resistance of Li-ion migration at the interface. On the other hand, at high rates exceeding 2.0C, the discharge capacity of coated-LTO was higher than that of pure LTO. At 40C, the discharge capacity was approximately 80 mAh/g, suppressing energy loss at high C-rate operation. In the cycling test at 3C, only the sample coated with 10wt% coated-LTO achieved 1000 reversible cycles, and the capacity retention after 1000 cycles was 93.3%.(show in figure) The electrochemical impedance spectroscopy results should suggest that part of the improvement in battery properties was due to the prevention of SEI formation.