Hydrothermal Growth Kinetics Of Li₂FeSiO₄ Cathode Material For Lithium Ion Batteries

Cathode material is a key factor that restricts the specific capacities of lithium ion batteries（LIBs）,which are currently used as power sources for portable electric power tools and other electronic products.Lithium iron silicate,Li₂FeSiO₄ is a polyanion-type cathode material that has a super-high theoretical capacity(332 mAh·g^-1)and has attracted much attention because it is low cost,safe,and environmentally friendly.Nanoscale Li₂FeSiO₄cathode material is successfully prepared using a ball-milling assisted hydrothermal method with inorganic precursors.The growth,crystallinity,nucleation rate,growth rate,activation energy and electrochemical properties of Li₂FeSiO₄ crystals were systematically studied in this paper.The main contents are as follows::1.Nanoscale Li₂FeSiO₄ cathode material is successfully prepared using a ball-milling assisted hydrothermal method with inorganic precursors.Structures,morphologies,and thermal stabilities of the samples are characterized using X-ray diffraction（XRD）,scanning electron microscopy（SEM）,transmission electron microscopy（TEM）.The prepared Li₂FeSiO₄ samples are well crystallized and have an irregular cuboid morphology with particle sizes in the range of 50–300 nm.The crystal structure of pure Li₂FeSiO₄ is stable in air at room temperature,and no distinct new phase is observed for the sample annealed at300°C in argon.The effect of growth conditions on the synthesis of Li₂FeSiO₄ cathode materials was further investigated.The results showed that the alkaline solution was conducive to the growth of Li₂FeSiO₄,and the grain size of Li₂FeSiO₄ increased with the increase of reaction time,reaction temperature and precursor concentration.2.Under hydrothermal conditions,the crystallinity of Li₂FeSiO₄ increases with the increase of temperature and the reaction time.By analyzing the crystallization curves of different hydrothermal temperatures,it was found that a higher reaction temperature is favorable to increase the nucleation rate Vn and the growth rate Vk.Experimentally measured apparent activation energy of the nucleation En is 58.10 kJ·mol-1,the apparent activation energy Ek to grow 27.26kJ·mol-1.3.Electrochemical analysis of Li₂FeSiO₄ material showed that the first charge and discharge capacity remain 137mAh/g and 134mAh/g at 0.1C rate,and the Coulomb efficiency is 97.8%.After 50 cycles,the discharge capacity of charge and discharge is 118mAh/g and116mAh/g respectively,and Coulomb efficiency is 98.3%.Li₂FeSiO₄ has a stable structure during charge and discharge.The material still maintains high specific capacity after multiple cycles at different rates.The intrinsic ionic conductivity,electronic conductivity and lithium ion diffusion coefficient of Li₂FeSiO₄ at 0-60°C were measured by AC impedance spectroscopy,At a temperature of 20°C,the ionic conductivity and electronic conductivity are only 1.32×10^-8S/cm and 2.8×10^-88 S/cm,respectively,and the diffusion coefficient of lithium ion is 2.3×10^-12 cm²s^-1.