Room temperature Na-ion batteries (NIBs) hold great promises in grid-scale electric energy storage1. An in-depth and fundamental understanding of the structure-property relationship in the electrode materials is pivotal to the rational design of electrodes and batteries with improved performance. As a group of promising cathode materials for NIBs, P2-NaxFeyMn1-yO2 typically undergo a phase transition from P2 to O2 or OP4 phases with a highly disordered crystalline nature, upon sodium extraction up to 4.2 V2-4 , and can evolved into a distorted orthorhombic P’2 phase on sodium insertion at below 2 V5-6. Such phase transitions greatly hinders the kinetics of sodium insertion/extraction and leads to poor cycling stability.<br/>We report the design, synthesis and electrochemical testing of Li-doped P2 cathodes and the positivity effects of Li-doping in the transition metal (TM) layer on the electrochemical property and structural stability. Synchrotron X-ray and neutron diffraction, and solid-state nuclear magnetic resonance (NMR) were used to characterize the long range and local structure of the materials, respectively. It is demonstrated with in situ XRD that Li doping leads to favorable single-phase evolution within a wide potential range during cycling, which is essentially beneficial for the significantly improved capacity and capacity retention. The Li doped cathode material delivers a high capacity of 214 mAh g-1 for the first cycle and a remarkable high capacity retention of ~87% is obtained after 80 cycles. The fate of the Li in the local structure as well as the structural transformation during the long-term cycles are investigated by NMR and X-ray diffraction. The strategy for the design of high performance Li-doped cathode materials will be discussed.

High performance Li-doped cathode materials for Na-ion battery: Insights from electrochemistry, diffraction and NMR investigations

255th National Meeting (2018)

The official archive and repository for all ACS Meetings & Expositions abstracts and select posters or presentations.