Preparation And Modification Of LiNi_1/3Co_1/3Mn_1/3O₂Cathode Material For Li-ion Batteries

LiCoO2is one of the most widely used commercial cathode materials in the current lithium ion batterymarket. However, Further application of LiCoO2is restricted due to high cost of Co, unfriendly to theenvironment. NCM is becoming the new generation cathode material for lithium ion battery.Firstly, we synthesised NCM cathode material by traditional high temperature solid state reactionmethod and studied the effect of synthesis parameters on the property, such as sintering temperature, rawmaterials and ball-milling speed. The optimal synthesis conditions are: Co3O4(1) as Co source, theball-milling speed of300r/min, presintered at600℃for5h and sintered at950℃for20h.Secondly, the NCM cathode material was prepared from nickel-cobalt-manganese hydroxide precursors(Ni1/3Co1/3Mn1/3(OH)2and LiNO3. Ball-milling and annealing process were used to modify the NCMcathode material. And the discharge capacity of NCM with post-annealing at800℃was116.6mAh g-1at5C rate in liquid lithium ion battery. But the discharge capacity of NCM without annealing process was just81mAh g-1. This indicated that annealing process has enhanced the electrochemical properties of NCMcathode material.Furthermore, Al2O3-coated NCM was synthesised by sol-gel method and solvothermal method,respectively. XRD and SEM were used to characterize the structure and morphology of Al2O3-coated NCM.The results showed that Al2O3coated layer has no influence on the structure of NCM material, but thepartical size was larger than uncoated NCM. Charge-discharge performance was measured by aLAND-CT2001battery test system and the electrochemical impedance spectroscopy (EIS) analysis wascarried out by using a Solartron1470E multi-channel potentiostat electrochemical workstation. The resultsshowed that the performance of NCM had improved by Al2O3layer. The cycle performance and rateproperty of Al2O3-coated NCM prepared by sol-gel method was the best. On the basis of above, we studiedthe influence of sintering temperature and the amount of Al2O3coating on performances of NCM. NCMcoated with2wt%Al2O3and sintered at500℃exhibits the best electrochemical performances, and thecapacity retention ratio reaches97.4%after50cycles in a high voltage range of2.8-4.5V. The high ratecapacity was151.5mAh g-1even at5C.Finally, performances of NCM cathode material synthesis by high temperature solid state reaction,annealing process and surface modification were studied in the all-solid-state lithium battery with thesulfide as the solid state electrolyte respectively. The interfacial compatibility of NCM cathode material andsulfide solid state electrolyte was analysised. The results showed that NCM prepared by high temperaturesolid state method had small capacity in all-solid-state lithium battery. The impedance was about severalthousand. This could be due to serious particle agglomeration. After annealing treatment at800℃, the firstdischarge capacity of NCM cathode material was more than114.5mAh g-1while the capacity of NCMwithout annealing treatment was just76.4mAh g-1. This indicated that improvement of the interfacebetween the cathode material and sulfide solid state electrolyte was very important to enhance theperformance of all-solid-state lithium battery. On the other hand, the charge-discharge capacity ofAl2O3-coated NCM almost was no improved, probably the coated layer was too thick or the Al2O3layer hadbad compatibility with sulfide solid state electrolyte.