P2 - Type Na0.67Mn0.8Cu0.1Mg0.1O2 as a New Cathode Material for Sodium-Ion Batteries: Insights of the Synergetic Effects of Multi-Metal Substitution and Electrolyte Optimization

摘要

Sodium-ion batteries (SIBs), as a complementary system to lithium-ion batteries (LIBs), have received significant attention owing to the cost-effective and relatively abundant sodium resource and the possibility to use an Al current collector at the anode rather than Cu, especially for large-scale energy storage. However, due to the low specific capacity and capacity-detrimental phase transition during cycling, low energy density and poor cycling performance of cathode materials are the main barriers for the development of SIBs. Sodium layered oxides NaxTMO2 (TM: transition metal) are one of the most promising cathode materials as they generally have empty layers allowing for two-dimensional Na-ion diffusion, in addition to their easy synthesis. In this work, a P2-type Na0.67Mn0.8Cu0.1Mg0.1O2 has been synthesized as a cathode material for sodium ion batteries. By utilizing the synergetic effects of Cu and Mg substitution, the prepared material delivers a discharge capacity of 84 mAh g-1 at 180 mA g-1, with a superior capacity retention of 93 % after 500 cycles. The Mn, Cu and Mg ions are located in the transition metal sites, and a good structural reversibility during the charge and discharge process has been confirmed. In addition, the electrolyte additive fluoroethylene carbonate is shown to be effective for the formation of passivation layer at the electrode/electrolyte interface and improve the long-term cycling performance of the Na0.67Mn0.8Cu0.1Mg0.1O2 cathode material using a 1 M NaPF6 in ethylene carbonate and dimethyl carbonate electrolyte.