Enhancing the Stability of 4.6 V LiCoO Cathode Material via Gradient Doping.

LiCoO (LCO) can deliver ultrahigh discharge capacities as a cathode material for Li-ion batteries when the charging voltage reaches 4.6 V. However, establishing a stable LCO cathode at a high cut-off voltage is a challenge in terms of bulk and surface structural transformation. O release, irreversible structural transformation, and interfacial side reactions cause LCO to experience severe capacity degradation and safety problems. To solve these issues, a strategy of gradient Ta doping is proposed to stabilize LCO against structural degradation. Additionally, Ta-LCO that was tuned with 1.0 mol% Ta doping demonstrated outstanding cycling stability and rate performance. This effect was explained by the strong Ta-O bonds maintaining the lattice oxygen and the increased interlayer spacing enhancing Li conductivity. This work offers a practical method for high-energy Li-ion battery cathode material stabilization through the gradient doping of high-valence elements.