Research On The Synthesis And Modification Of LiNi_0.8Co_0.15Al_0.05O₂ As Cathode For Lithium-Ion Batteries

Energy keeps the society function well,but the overuse of fossil fuels now causes heavy energy shortage and environmental problems,so it is necessary to use more clean renewable energy.Nevertheless,clean renewable energy such as solar energy is not evenly distributed in time and space,making it impossible to be used for all humans.Thus,we should develop energy storage technology to store renewable energy for all humans.With all technology,Lithium-ion battery has been widely used in portable electronics such as mobile phones for high voltage and high energy density.However,popular Lithium-ion cathode,LiCoO₂ cannot be used in electric vehicles for its low capacity,high cost and toxicity.Among all alternatives,LiNiO₂ has attracted much attention for high capacity,low cost and low toxicity.Nevertheless,the structure of LiNiO₂ is unstable and may transform to other structure in long cycles and high temperature.Therefore,we dope Co³⁺ to improve cycle stability and Al³⁺ to improve thermal stability,making LiNi_0.8Co_0.15Al_0.05O₂（NCA）,On the side,NCA has bad surface stability,reacting with H₂O and CO₂ to generate LiOH and Li2CO3 which may affect coating film.NCA also may react with electrolyte during long-time cycles,producing by-products on the electrode to decrease cycle and rate capacities.So,this article does research on the effect of the adding rate of Na₂S₂O₈ on Ni_0.8C_o.15Al_0.05OOH and NCA,the effect of the weight of LiOH·H₂O and temperature of pre-calcination on NCA,the effect of the coating weight of AIPO₄ on AIPO₄-coated NCA.First,this article prepares Ni_0.8Co_0.15Al_0.05OOH,the precursor of NCA through Co-oxidation-precipitation and NCA through calcination of LiOH·H₂O.And this article does research on the effect of adding rate of Na₂S₂O₈ on the structure of Ni0.8Co0.15sAl0.05OOH and NCA.The experiment shows that,when the adding rate of Na₂S₂O₈ rises,the percentage of Ni（OH）₂ in Ni_0.8Co_0.15Al_0.05OOH drops,the percentage of a-Ni（OH）₂ rises,the color of precursor turns yellow from green,the discharge capacity of NCA in 1st cycle rises,the coulombic effiency in 1st cycle rise and the cycle stability rises first and drops after.When the adding rate of Na₂S₂O₈ is 20 mL/min,NCA performs best.The discharge capacity of NCA in 1st cycle is 150.1 mAh/g,the coulombic effiency in 1st cycle is 92.3%,the discharge capacity after 50 cycles is 133.6 mAh/g,the capacity retention is 89%and the capacity decreases only 0.22%per cycle.Second,this article prepares NCA through solid-state method,which mixes the precursor of NCA with LiOH·H₂O and calcines at high temperature.This article does research on the effect of the weight of LiOH·H₂O and the temperature of pre-calcination on the properties of NCA.When the weight of LiOH H₂O rises,the discharge capacity of NCA in 1st cycle rises,the coulombic effiency in 1St cycle rises and the cycle stability rises first and drops after.When the weight of LiOH H₂O is 3%excess in weight,NCA performs best.The discharge capacity of NCA in 1st cycle is 176.1 mAh/g,the coulombic effiency in 1st cycle is 97.7%,the discharge capacity after 50 cycles is 172.2 mAh/g,the capacity retention is 97.7%and the capacity decreases only 0.05%per cycle.When the temperature of pre-calcination rises,the discharge capacity of NCA in 1st cycle rises,the coulombic effiency in 1st cycle rises.When the temperature of pre-calcination is 750℃,NCA performs best.The discharge capacity of NCA in 1st cycle is 202.5 mAh/g,the coulombic effiency in 1st cycle is 97.7%.Third,this article prepares AlPO₄-coated NCA through liquid method.This article does research on the effect of the weight of AlPO₄ on the properties of NCA.When the weight of AIPO₄ rises,the discharge capacity of NCA in 1st cycle drops,the coulombic effiency in 1st cycle drops and the cycle stability and rate capacity rise first and drops after.When the weight of AIPO₄ is 1%in weight,AlPO₄-coated NCA performs best.The discharge capacity of NCA in 1st cycle is 192.1 mAh/g,the coulombic effiency in 1st cycle is 86.3%,the discharge capacity after 100 cycles is 174.4 mAh/g,the capacity retention is 92.1%,the capacity decreases only 0.08%per cycle and the rate capacity of 10C is 110 mAh/g.Above all,this article does systematical research on the synthesis of the precursor of NCA,the calcination of NCA and surface coating,which making the foundation of synthesis and modification of NCA in the future.