Improving the high-rate performance of LCO cathode by metal oxide coating: Evaluation using single particle measurement

Abstract

Surface coating is a key approach for lithium-ion batteries (LIBs) to improve the high-rate performance and stability of batteries. LiCoO2 (LCO) has been one of the promising cathode materials in LIBs due to its high theoretical capacity of 274 mAh/g and high theoretical density (5.1 g cm−3) of material. However, the capacity used is only 140 mAh/g (∼50 % of theoretical capacity) under the voltage condition limited to 4.2 V. Increasing the operation voltage is the prime way to increase the energy density of the LCO electrode. In this study, we synthesize the pristine and Al-Ti oxide coated LCO materials by simple, cost-effective and eco-friendly sol–gel method and its intrinsic parameters are measured by single particle measurement (SPM) technique. A quantitative evaluation of the electrochemical properties of the active material shows a clear difference between pristine LCO and Al-Ti@ LCO. The measured rate characteristics show that Al-Ti@ LCO has higher discharge capacity under the same current rate condition and stable cycling ability. The high voltage rate capability of LCO is exponentially increased with Al-Ti oxide coating with the highest retention of 96 % after 50 cycles within 3.0–4.5 V at 4.2C. From Tafel plot analysis the charge transfer resistance (RCT) of Al-Ti@ LCO was lower in all DOD states than pristine LCO. Also, to investigate mass transfer properties, GITT was carried out. The Al-Ti oxide coating is believed to make the LCO electrode more resistant to interfacial side reactions and fast structural degradation at high voltage and thus reduce the degradation of active material within long cycling. This result shows Al-Ti oxide coating layer contributes to the enhancement of electrochemical performance without interfering with lithium-ion diffusion.