Constructing stable surface structures enabling fast charging for Li-rich layered oxide cathodes

Li-rich Mn-based layered oxides (LLOs) exhibiting ultrahigh specific capacity larger than 250 mAh g⁻¹ have become the most promising cathode candidate for high energy density lithium-ions batteries (LIBs). Fast charging capability and cycling stability are highly desirable for LIBs so as to satisfy specific application scenarios such as electric vehicles. However, stable cycling and fast charging properties are severely hindered by obstacles including irreversible oxygen release, structural degradation and poor reaction kinetics. In this work, an integrative and facile surface structures constructing strategy to achieve stable cycling and fast charging in LLOs was provided. Oxygen vacancies and double coating layers including lithium phosphate layer and spinel layer were constructed on the surface through ammonium dihydrogen phosphate (NH₄H₂PO₄) pretreatment. The designed material with induced stable bi-phase coating layers delivers a high discharge specific capacity of 284.6 mAh g⁻¹ at 0.1 C with an ultrahigh initial coulombic efficiency of 95.3% and excellent rate performance of 132.2 mAh g⁻¹ at 10 C. Even after 100 cycles, it can display a remarkable capacity of 215.8 mAh g⁻¹ under 1 C/1 C and 205.1 mAh g⁻¹ under 3 C/1 C. The excellent fast charging performance and cycling stability can be attributed to accelerated Li⁺ transportation rate due to its surface ion conductive layer and surface spinel phase layer, as well as suppressed oxygen release, transition metals dissolution and electrolyte attack resulting from surface oxygen vacancies and dual protective layers.