Revealing Lithium Configuration in Aged Layered Oxides for Effective Regeneration

Layered oxides LiNi_xCo_yMn_zO₂ are widely used as the main cathode material for high-energy lithium-ion batteries. Over long-term cycling, irreversible phase transformations in layered oxides usually occur along with the loss of active lithium, which directly reflects in the sharp decrease of capacity. However, it is difficult to accurately and rapidly determine lithium content in aged materials, raising extreme impediments in the direct recycling of layered oxides. Herein, we propose a facile method for quick and accurate calculation of the residual lithium content through the developed relationship of shear strain and the states of charge. Based on this recognization, a discharge capacity close to the original capacity of the pristine material is achieved in the regenerated material by combining a hydrothermal method with annealing treatment. The recycled material demonstrates a dramatic improvement in electrochemical properties, especially the high rate performance. This method not only effectively realizes the quantitative regeneration of cathode materials but also provides a possible strategy for the future development of direct regeneration.