From metal to cathode material: in situ formation of LiCoO2 with enhanced cycling performance and suppressed phase transition

Abstract

LiCoO₂ (LCO) has attracted wide attention due to its high energy density, whose synthesis relies on the cobalt oxide precursor. The conventional synthetic method features a low yield. What is even worse, order–disorder phase transition of LCO occurs above 4.2 V, leading to structural instability and rapid capacity decay. To tackle these problems, a new synthetic method is proposed in this work, where LiCoO₂ is in situ formed using cobalt metal as the precursor. M-LCO-850 °C (cobalt metal used as the precursor) exhibits a better cycle performance and faster Li⁺ diffusion rate than C-LCO (commercial synthesis method). The stable cycling performance is associated with the suppression of the order–disorder phase transition, which is attributed to the Co²⁺ “pillar” effect. Co²⁺ occupies the Li layer in the charge and discharge process, which acts as a “pillar” to support the CoO₂ layer to inhibit order–disorder phase transition during the cycle, reducing the polarization and promoting the insertion/de-insertion reaction of Li⁺. Meanwhile, the synthesis yield and compacted density of M-LCO-850 °C are improved by 18.8% and 11.89%, respectively, compared to C-LCO. This method provides a new strategy for the in situ synthesis of cathode materials for lithium-ion batteries.