A solid-state surface-to-bulk modification with a multifunctional modified layer for 4.6 V LiCoO2

Abstract

With the attempts of more than 30 years, the current commercial LiCoO2 (LCO) offers a reversible capacity of 185 mAh g−1 with a cut-off voltage of 4.5 V vs. Li+/Li. Further increasing the cut-off voltage, more lithium-ions can extract, deeply enhancing the capacity and energy density. However, it results in numerous side reactions and a significant decay in battery cycle performance. To address these issues, Nano-LiNbO3 as a coating agency is introduced by a solid-state surface-to-bulk modification process. To avoid the agglomeration and achieve uneven coating of Nano-LiNbO3 in the solid-state reaction, polyvinylpyrrolidone (PVP) is introduced as a dispersant, which effectively ensures the uniform and smooth coating along with the carbonization process. The modified LCO sample presents a specific reversible capacity of 215.5 mAh g−1 in the initial cycle and a capacity retention rate of 90 % after 100 cycles at 3–4.6 V and 0.5 C. Further analysis demonstrate that the LiNbO3 surface coating layer and the element gradient doping layer provide LCO a stable structure and an inert surface, which improves the surface stability, suppresses the oxygen release and ensures the enhanced electrochemical performance.