Study On The Modification Of Nickel-Cobalt-Manganese Ternary Cathode Material For Lithium Ion Batteries

With the rapid development of electric vehicle industry and large-scale energy storage in the power gird,lithium-ion batteries are required to meet the demand of higher energy density and longer cycle life.At present,the layered nickel-cobalt-manganese ternary cathode materials has been successfully applied in the electric vehicles filed,due to its high energy density,high specific capacity,low cost.However,there are irreversible phase transition and some side reactions such like transition metal dissolution between the surface of the cathode and the electrolyte,which can lead to an increase in impedance of electrode reaction and significant deterioration of the cycling performance and rate capability.To solve the above problems,we have investigated the surface modification on the LiNi1/3Mn1/3Co1/3O2 and Li1.14Ni0.133Co0.133Mn0.544O2 cathode materials for lithium ion batteries.The main research contents are as follows:(1)Tungsten-modified LiNi1/3Co1/3Mn1/3O2(NMC)cathode material was synthesized by a facile cost-effective ball-milling and annealing process.This modification method can retard the cathode/electrolyte interfacial reactions and enhance the electrode surface stability,which can improve the cycling performance of NMC.Under the high operating voltage range(3-4.5 V),the W-modified NMC(NMC-3%W)delivered a discharge capacity of 150.5 mAh g-1(representing a 27%increase from that of the standard NMC)after 150 cycles at 1C,with a capacity retention of 87.5%.This modification method also can decrease the charge transfer resistance and facilitate the Li-ion diffusion,which can improved the rate capability.With the W-modification,the discharge capacity at 10 C rate was increased from 78 to 162 mAh g-1(by 57.6%).(2)Graphite fluoride modifided Li 1.14Ni0.133Co0.133Mn0.544O2(LRCM)cathode material was synthesized by a facile mild and solvent evaporating method.This modification method can form a graphite fluoride(CF)on the surface of LRCM,which can compensates the capacity loss with the productions of LiF and carbon during the first discharging to significantly improve initial coulombic efficiency.The LiF@carbon layer on the surface of the cathode can decreases the interfacial reactions,which can enhance the cycling performance and the rate capability.Under the high operating voltage range(3-4.5 V),LRNCM showed the discharge capacity of 180 mAh g-1 after 100 cycles at 1C.After modification,the discharge capacity for LRNCM@10%CF was increased to 203 mAh g-1(by 12.7%).The discharge capacity at 2 C rate was increased from 140 to 177 mAh g-1(by 13%).