| As the new type of environmental-friendly energy storage device,Lithium-ion batteries(LIB)are expected to have huge development prospect.Meanwhile,Ni-rich ternary cathode materials attract wildly consideration in recent years due to their high capacity,low cost,little consumption and so on.However,there still are some shortcomings of Ni-rich ternary materials such as short cycle life,poor stability of structure,poor thermal stability and low initial Coulombic Efficiency,which severely limits their application.To this end,we synthesized the stable L1Ni0.8Co0.1Mn0.1O2(NCM811)cathode material with sol-gel method and explored some modifications thorough controlling structure and surface coating,the main contents are as follows:First of all,we synthesized NCM811 materials coated with LiAlO2 in different proportions.It was found that the coating has almost no effect on the size and morphology of NCM811 particles,but would increase the lattice parameters of the material,decrease the degree of cations mixing and increase the proportion of surface Ni3+.By adjusting the LiAlO2 coating amount,the lithium ion diffusion coefficient of the cathode material could be optimized.Compared with the pristine NCM,the specific capacities of 3 wt%LiAlO2 coated material at 1 C,5 C and 10C are 182.1 mAh g-1,152.6 mAh g-1 and 137.2 mAh g-1,respectively.After 50 cycles at room temperature 25 0C of 1 C,the capacity retention is about 83.9%,and the cycling stability increased with the increase of the amount of coating materials.In addition,NCM811 materials with different coating amounts of Li2ZrO3 were synthesized.Li2rO3 is a good conductor of lithium ions.The modified materials exhibit excellent rate and cycle performance,especially in the case of high rate,such as 15C,the discharge specific capacity of 1 wt%Li2ZrO3 modified sample could reach 107 mAh g-1,while the bare sample is only 87 mAh g-1.After 100 times cycle at room temperature 25? of 1 C,the capacity retention of the bare NCM811 is 61.6%,and that of 1 wt%,3 wt%,5 wt%Li2ZrO3 coated samples are 65.8%,66.8%and 70.9%,respectively.The Li2ZrO3 coating layers not only serve for protective effect,but also maintain the structure stability of the base material NCM811 and promote the lithium ionic diffusion,all of these factors lead to the excellent performance of lithium ion batteries.Finally,nano-scale TiO2 was used as raw material to prepare monoclinic Li2TiO3 particles of small size by calcining at high temperature,and then coated on the surface of NCM811 materials in collaboration with PANI,a kind of conductive polymer.The coating layers make no difference on the morphology of the pristine material.The thickness of the double coating layer of 3 wt%Li2TiO3-3 wt%PANI coated sample was about 25-30 nm,which was relatively uniform.The amorphous substance in the coating layer is PANI and the grain is Li2TiO3.From the perspective of electrochemical properties,the 0.1 C initial discharge specific capacity of NCM811 is 196 mAh g-1,while the modified sample could reach 214 mAh g-1,and the high rate performance has also been improved to a certain extent.The discharge capacity of the modified sample at 10 C could reach 143 mAh g-1,while that of the pristine sample is only 136 mAh g-1.In addition,the Li2TiO3-PANI double-coated samples have excellent structural and thermal stability.After 100 cycles of 1 C at the room tempperature 25 ?,the capacity retention of 3 wt%Li2TiO3-5 wt%PANI coated sample is about 90%,while that of the bare NCM811 is only 69.5%.After 200 cycles of 1C at high temperature 50?,the capacity retention of bare NCM811 is about 53.3%,while that of the 3 wt%Li2TiO3-5 wt%PANI coated NCM811 could reach 64.8%.Reasons of the improvement of cycle stability and thermal stability is that PANI as a kind of organic polymer has certain thermal stability,at the same time the double coating layer could inhibit side reactions accored on the NCM811 surface,hence Li2TiO3-PANI double-coated materials exhibit more stable electrochemical performance. |
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