Achievement of Compatibility of Electrochemical Performances in P-Type Semiconducting Lithium-Rich Oxides

Abstract

Owing to anionic redox, lithium rich oxides (LROs), which are a new class of semiconductor compounds, are promising for fabrication of cathode materials for next-generation lithium-ion batteries (LIBs) with large energy density (>500 Wh·kg-1) and long lifespan. However, it is challenging to simultaneously realize good electrochemical performances in different aspects. From the band structure, this is explained to result from a trade-off with the relative position of the Fermi level. In this work, we demonstrate that the electrochemical performances are compatible with an overall improvement through an increase of mobility of charge carriers (approximately one order of magnitude from 69 cm2/V·s to 789 cm2/V·s) in LRO semiconductor nanocrystals via partial element substitution, without significant shifting of the Fermi level by carrier concentration. Cycling stability of the LRO cathode material is further shown to be enhanced via treatment at the LRO/electrolyte interface. As a result, a large discharge capacity of 303.7 mAh·g-1 (0.1C, RT, 2.0-4.8 V) is realized with a large capacity retention of 97.16% after 400 cycles at 1C, in addition to an excellent 5C rate capability of 147.76 mAh·g-1. More importantly, we for the first time report that LRO nanocrystals are an intrinsic p-type semiconductor with a bandgap of ~1.0 eV. Our work lays a solid foundation for achieving good performances in LIB cathode materials with materials design and synthesis using a top-down approach that is simple, facile at low costs.

Keywords: Lithium ion batteries, Lithium rich oxides, Cathode materials, Cycling stability, Charge transport