Preparation And Modification Of Lithium Titanate Nanosheets And Their Application In Anode Materials Of Lithium Ion Batteries

Spinel lithium titanate (Li4Ti5O12,LTO) has attracted considerable attention because of its intrinsic characteristics, such as high structural stability and long cyclic life. Furthermore,LTO exhibits an extremely flat charge-discharge plateau, which makes it safe by avoiding the solid electrolyte interface (SEI) film formation. In addition, spinel LTO is a zero-strain insertion material due to the negligible volume change in the charge-discharge process. However, the main disadvantage that restricts the application of LTO is an almost insulating material having low electronic conductivity and lithium diffusion coefficient, resulting in poor rate capability of the lithium ion batteries. In this paper, we have successfully synthesized LTO NSs to increase the contact area with the electrolyte material. LTO NSs/CNTs (carbon nanotubes) composites were synthesized by the introduction of electronic conductor CNTs. Lithium fluoride used as a fluorine source wae doped in LTO to improve the electrochemical performance of LTO NSs.(1) We have successfully synthesized LTO NSs with a thickness of 20 nm and diameter of 300 nm. The sheet-like structure greatly increases the surface area of the material and the contact area with the electrolyte, resulting in larger diffusion coefficient of Li+ and shorter the transmission path of Li+ to improve the electrochemical performance. LTO NSs show the high reversible capacity of 106 mAh·g-1 at a current density of 2 A·g-1 with good cycling performance,retaining 98.1% of its initial capacity after 100 cycles with a capacity retention of 104 mAh·g-1.LTO NSs exhibit good rate capability and cycling performance. At the highest rate of 5 A·g-1,LTO NSs electrode still have a capacity retention of 61 mAh·g-1.(2) LTO NSs/CNTs composites are synthesized using a facile hydrothermal method. The incorporation of CNTs into the LTO NSs forms a delicate conductive network for rapid electron and lithium ions transport, resulting in excellent rate performance and superior cycling performance. LTO NSs/CNTs composites show the lower polarization of potential difference,the larger difffusion coefficient of lithium ion and smaller charge-transfer resistance than pure LTO NSs. LTO NSs/7.5%-CNTs composites show the highest reversible capacity at a current density of 2 A·g-1 with good cycling performance, retaining 93.1% of its initial capacity after 1000 cycles with a capacity retention of 135 mAh·g-1. At the highest rate of 5 A·g-1, LTO NSs/7.5%-CNTs composites still manitian the specific capacity of 105 mAh·g-1.(3) F doped LTO (F-LTO) composites are synthesized using a step hydrothermal method.From the characterization resutls. it is found that F atoms can enter the lattice structure and did not affect its structure. A fluoride ion (F-) doping technique might that partially substitute O with F forming Ti-F bond in the LTO spinel, which induced the Ti4+ formation of charge compensating Ti3+ to increase conductivity. F-LTO composites show the lower polarization of potential difference, the higher lithium storage performance and larger diffusion coefficient of lithium ion because of Ti3+ conductivity than Ti4+ than pure LTO NSs. At the highest rate of 5 A·g-1, F-LTO composites still diaplay a capacity retention of 101 mAh·g-1. F-LTO composites show excellent rate performance and superior cycling performance with the high reversible capacity at a current density of 2 A·g-1 with good cycling performance, retaining 86.2% of its initial capacity after 1000 cycles with a capacity retention of 119 mAh·g-1.