A Carbon-coated And Doped Binary Nickel-manganese-lithium Battery Positive Electrode Material Was Prepared By Spray-thermochemical Reaction

Lithium-ion battery（LIB）has been widely used as a power source for the new electronic products,such as unmanned aerial vehicles（UAV）,smart glasses,VR and so on.There is a great need to develop excellent cathode materials with their good safety,high discharge specific capacity,high energy density and better cycle performance.The lithium-ion Li_1.2Ni_0.2Mn_0.6O₂ cathode material has attracted more and more attention because of its high energy density.However,Li_1.2Ni_0.2Mn_0.6O₂ exhibits some drawbacks,such as poor rate capability and bad cycle performance.In this thesis,Li_1.2Ni_0.2Mn_0.6O₂ was synthesized by pressure spray-drying technology.The electrochemical properties of Li_1.2Ni_0.2Mn_0.6O₂ was improved by means of elemental doping and surface modification with different substance.The details are as follows:1.The Li_1.2Ni_0.2Mn_0.6O₂ was synthesized by pressure spray-drying technology,optimizing the different conditions.Influence of lithium content,the inlet air temperature and equipment pressure,structure and electrochemical performance of prepared materials were discussed.The electrochemical performance shows that product which uses Li OH as Li source exhibits the highest capacity at 0.1C,after 50 cycles among different Li sources（Li OH,Li2CO3,LiNO3）.Secondly,when the lithium content is 1.00mol（stoichiometric ratio）and the air inlet temperature is about 170℃,the comprehensive performances of the material are the best.The nano-structured Li_1.2Ni_0.2Mn_0.6O₂ material is obtained by adjusting the pressure of the sprayer.When the pressure of spray-drying technology is 0.6 MPa and the sample size is between 150²00 nm,the discharge capacity is 153.4 mAh/g after 50 cycle at 2.5⁴.8 V,0.1C.The performance of Li_1.2Ni_0.2Mn_0.6O₂ was optimized under the above reaction conditions.On voltage range of 2.5⁴.8 V,a discharge capacity of 227 mAh/g has been measured after 50 cycles at 0.1C and discharge capacity is 160.1 mAh/g after 100 cycles at 1C.Moreover,a discharge capacity of 231.4 mAh/g has been obtained after 50 cycles at 0.1C and discharge capacity is 166.4 mAh/g after 100 cycles at 1 C,on voltage range of 2.0⁴.8 V.2.By doping a minor mount of Co to replace Ni and Mn,Li_1.2Ni_0.2Mn_0.6O₂ electrochemical performance has been enhanced.A certain extent Co-doped Li1.2Ni0.2-x/2Mn0.6-x/2CoxO₂ ruduces Li+/Ni²⁺ replacement ration.With the increase of Co doping amount,all the samples are layered structure and the crystallinity of the materials increase.When the amount of Co doping increases,the hexagonal structure is better,which is beneficial to Li1.2Ni0.2-x/2Mn0.6-x/2CoxO₂ electrochemical performance.Li1.2Ni0.17Mn0.57Co0.06O₂ can reach 256.1 mAh/g and the capacity retention is close to 92.4% after 50 cycles at 0.1C,and 179 mAh/g after 100 cycles at 1C on voltage range of 2.0⁴.8 V.3.Li_1.2Ni_0.2Mn_0.6O₂ coated by different content of Al₂O₃ can effectively avoid side effects between the electrolyte and the cathode material.The discharge capacity of cell maded of 3wt.% Al₂O₃-coated Li_1.2Ni_0.2Mn_0.6O₂ can reach 263mAh/g and the capacity retention is 89.5% at 0.1C after 50 cycles,and 185.5 mAh/g after 100 cycles at 1C on voltage range of 2.0⁴.8 V.Li-rich oxide Li_1.2Ni_0.2Mn_0.6O₂ is modified with LPAN as grapheme-like carbon which presents lower surface resistance and increase the cycle stability of the materials under high voltage range discharge capacity.The discharge capacity of cell made of 20 wt.% LPAN-coated Li_1.2Ni_0.2Mn_0.6O₂ can reach 262.5 mAh/g and the capacity still retention is close to 98.3% at 0.1 C after 50 cycles,and 177.5 mAh/g after 100 cycles at 1C on voltage range of 2.0⁴.8 V.LPAN-coated Li_1.2Ni_0.2Mn_0.6O₂ can effectively protect the cathode directly contact with the electrolyte to avoid side effects.Moreover 20 wt.% LPAN-coated Li_1.2Ni_0.2Mn_0.6O₂ achieves 290.5 mAh/g on wide voltage window range of 1.5⁴.8 V and the capacity still retention is close to 85.8% at 0.1 C after 50 cycles.