Optimized amounts of excess Li in cation-disordered rocksalt cathodes assisted by carbon nanotubes

Abstract

Cation-disordered rocksalt (DRX) has been studied for high-energy density cathodes for lithium ion batteries (LIBs). In this study, the effect of Li-deficiency and Li-excess in the DRX structure was investigated. Different capacity behaviors during long-term cycling for 30 cycles were observed depending on the content of lithium ions. The capacity of the stoichiometric Li-excess DRX cathode of Li_1.2Mn_0.5Ti_0.3O₂ was increased by contributions from both oxygen redox (O²⁻/O⁻) and Mn³⁺/Mn⁴⁺ redox reactions, but it exhibited low capacity retention (79.6%) at 10 mA g⁻¹ after 30 cycles with a first discharge capacity of 260 mAh g⁻¹. On the other hand, the Li-deficient sample showed an increase in capacity retention of 102.8% after 30 cycles with a first discharge capacity of 150 mAh g⁻¹ at 10 mA g⁻¹. Also, multi-wall CNTs (MWCNTs) were used as a conductive agent in the DRX electrode. With the aid of highly conductive MWCNTs, a high rate capability (∼100 mAh g⁻¹ at 500 mA g⁻¹) can be achieved with stoichiometric Li-rich DRX cathodes. This study demonstrated the behavior of DRX cathodes depending on the amounts of lithium ions and the type of conductive agent used such as carbon black and MWCNTs.