This capacity limit has led to a number of other layered LiCoO2 oxides being investigated over the years, driving the substitution of cobalt with manganese and nickel for NMC cathodes. However, despite good electrochemical performance, the practical capacity of LiCoO2 is limited to around 140 mAh/g, says Professor Arumugam Manthiram, Chair in Engineering at the Walker Department of Mechanical Engineering at the University of Texas and developer of the polyanion oxide technology. As well as the higher voltage, it allows a lithium-free anode using materials such as graphite or silicon to be paired with LiCoO2 to give the modern-day lithium-ion cell that was pioneered by Sony in 1991. The LiCoO2 cathode solved two major challenges associated with the sulphide cathodes. That means LiCoO2 remains one of the best cathodes to date, thanks to its 4 V operating voltage. The large charge and size differences between Li+ and Co3+ ions lead to good ordering of the ions, which is critical to support fast 2D lithium-ion diffusion and conductivity. This enabled a substantial increase in the operating voltage from less than 2.5 V from earlier sulphide cathodes to around 4 V, allowing a cell to be assembled without having to use a metallic lithium anode, with fast charge/discharge characteristics and good reversibility. The first layered oxide cathode used lithium cobalt dioxide (LiCoO2), where Li+ and trivalent Co3+ ions are ordered on the alternate planes with a cubic close-packed array of oxide ion. Principally, the cathode types are layered oxides with nickel, manganese and cobalt (NMC), and spinel and polyanion oxides such as lithium iron phosphate (LFP). There are however also many different approaches to constructing cathodes, using different chemical compositions, crystal structures and methods of high-volume manufacturing. There are three main types lithium-ion batteries for e-mobility, all with different balances of energy capacity, charging rate and long-term stability. Researchers have been announcing advances in lithium-ion cathode materials and their manufacture, as Nick Flaherty reports Materials for cathodes in lithium-ion batteries include this layered oxide sheet
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