Applications of metal nitride nanostructures in stabilising high energy and high capacity battery systems

Abstract

Applications of metal nitride nanostructures in stabilising high energy and high capacity battery systems were investigated. Sol-gel synthesis routes using tetrakis(dimethylamido)titanium(IV) and a propylamine or ammonia cross linking agent, followed by thermal treatment under NH3 or H2+N2,were developed to produce TiN powders of small crystallite size (<10 nm). The TiN with good conductivity were coated on LiFePO4 cathodes in lithium-ion batteries, which exhibited significantly improved electrochemical performance with a discharge capacity of 159 mA h g-1 at 0.1 C, that is~93% of the theoretical capacity. A literature review of various synthetic routes such as solid-state reactions, hydrothermal/solvothermal synthesis and sol-gel process to produce LiCoPO4 was performed, and various strategies such as surface modification, ion doping, size reduction and morphology control to improve the electrochemical performance of LiCoPO4 were summarised. Olivine-structured LiCoPO4 was prepared via a facile solvothermal synthesis, using various ratios of water/diethylene glycol co-solvent, followed by thermal treatment under Ar, air, 5%H2/N2 or NH3.The LiCoPO4 prepared after heating in Ar exhibited high initial discharge capacity of 147 mA h g-1 at0.1 C with capacity retention of 70% after 40 cycles. This is attributed to the enhanced electronic conductivity of LiCoPO4 due to the presence of Co2P after firing under Ar. In addition, Li4Ti5O12 synthesized via solid-state reaction with 2% Li excesses were found to have minimum TiO2 impurities, which delivered an initial capacity of 165 mA h g-1. TiN were coated onto Li4Ti5O12 anodes in lithium-ion batteries, which exhibited improved initial capacity of 174 mA h g-1. Finally, nanostructured TiN were prepared by a cross-linked sol-gel method with HDA or P123 as a surfactant, or evaporation induced self-assembly method with PEO-b-PS as a surfactant, and heated under NH3 at a variety of processing conditions. Mesoporous TiN with worm-like morphology and pore size of ~20 nm were obtained, and selected TiN samples have been used as host materials for sulfur cathodes in lithium-sulfur batteries.

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ORCID for Andrew L. Hector: orcid.org/0000-0002-9964-2163

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