3-V Full Cell Performance of Anode Framework TiNb2O7/Spinel LiNi_(0.5)Mn_(1.5)O4

摘要

The rechargeable lithium-ion batteries now widely used in cell phones, laptop computers, and digital cameras generally use a graphitic carbon as the anode and lithiated transitional-metal oxide cathodes, for example, LiCo_(1/3)Ni_(1/3)Mn_(1/3)O_2 LiCoO_2 and LiFePO4, because graphite is inexpensive and has better safety characteristics and a longer cycle life compared with a lithium—metal anode. However, like lithium, a charged carbon anode has its electrochemical potential (Fermi energy) poorly matched to the LUMO of the organic liquid-carbonate electrolyte, which is about 1 eV below the Fermi energy of lithium. Therefore, a passivating solid—electrolyte interface (SEI) layer is formed on the carbon to prevent further reduction of the electrolyte. In the case of a carbon anode, a charging voltage V_(ch) electroplates lithium on the SEI layer during a fast charge. On subsequent repeated charges, lithium dendrites extend from the lithium layer; dendrite growth across the electrolyte short-circuits the battery to fire the flammable electrolyte. However, a carbon-buffered alloy having a displacement reaction at a V ≈ 0.8 V versus Li~+/Li~0 can allow a fast charge. Nevertheless, the formation of a Li~+-permeable passivating SEI layer on the anode increases the impedance of the anode and robs Li from the cathode irreversibly on the initial charge to reduce the limiting capacity of a cell. ' Therefore, there is motivation to identify a large-capacity insertion-compound anode having a voltage range of 1.0 < V ≤ 1.5 V versus Li~+/Li~0.