Regulation of surface oxygen activity in Li-rich layered cathodes using band alignment of vanadium phosphate surface coatings

Abstract

With a specific energy density >250 mA h g⁻¹, Li-rich layered transition metal oxides (LLOs) are one of the most promising cathode materials for commercial higher energy density lithium-ion batteries (LIBs). However, oxygen release, voltage fade and active material decomposition in electrolyte due to the gradual layered-to-spinel transition leads to increasing interfacial resistances and impaired electrochemical performance over long-term cycling. The structural transformation is widely recognized as a surface-propagating phenomenon so surface modification has become a primary remedying approach. Electronic band structure compatibility at the interface between surface-modifier (i.e. coating) and the bulk cathode is a less investigated but potentially pivotal aspect for mixed anionic/cationic charge transfer and structural stability in LLOs during cycling. In this study, we characterise and investigate the utility of electroactive Li₃V₂(PO₄)₃ (LVP) and Na₃V₂(PO₄)₃ (NVP) materials as band-aligned surface coatings for LLO cathode materials. In practice, we find VP-coated LLOs exhibit far better capacity and voltage retention than pristine LLO samples with up to 90% capacity retention and a −0.315 V median voltage fade after 250 cycles. These results indicate that coating design protocols which consider interfacial electronic compatibility between surface modification agents and battery cathode materials can deliver practical utility in rechargeable battery performance. In addition to current structural considerations, electronic band alignment proves beneficial for reducing charge transfer hysteresis and alleviating structural deterioration in high energy Li-rich layered cathode materials for Li-ion batteries.