Synthesis And Properties Of Modified LiNi_1/3Co_1/3Mn_1/3O₂ Cathode Materials

Lithium-ion batteries (LIBs) have a wide application in the information industry, transportation, national defense and other fields due to their advantages of high specific energy, no memory effect and no environmental pollution. The cathode material is an important component of lithium-ion batteries. Notably, LiNil/3Co1/3Mn1/3O2 (NCM), which integrates the good electrochemical performance of LiCoO2, high capacity of LiNiO2, high security and low cost of LiMnO2, has aroused broad concern.In this dissertation, the LiNi1/3Co1/3Mn1/3O2 cathode material and its modified materials were synthesized by the method of high-temperature solid state assisted with ball milling. Meanwhile, the results of the synthesis process, element doping (Mg-ion, Fe-ion) and compound (Cu(Ac)2, SnO2, Fe (NO3)3·9H2O) were analyzed and discussed.The main results are as follows:1. Through the analysis of structure and properties of the LiNi1/3Co1/3Mn1/3O2 materials, the optimal synthesis process was pre-calcining at 500℃ for 6h and calcining at 800℃ for 15h in the air atmosphere, in which the material had perfect crystal shape and splited obviously. The initial discharge capacity of the product was 149.3 mAh/g at 0.2C between 2.5-4.3V. LiNi1/3Co1/3Mn1/3O2 samples had good properties, which LA2CO3 was used as raw materials.2. Li (Ni1/3Co1/3Mn1/3)i-xMgxO2 was synthesized by solid phase synthesis method under the optimized conditions, the effects of Mg doping on the structure and properties were researched. The results showed that Mg-doping did not change the layer structure of LiNi1/3Co1/3Mn1/3O2 material, which had high crystallinity and purity. The initial discharge capacity of Li (Ni1/3Co1/3Mn1/3)i-0.03Mg0.03O2 was 158.5mAh/g at 0.2C between 2.5-4.3V, and the discharge capacity retention ratio was 89.7% after 20 cycles. Based on Mg-doping, Li(Ni1/3Co1/3Mn1/3)i-0.03Mg0.03O2 mixed with 8wt% Cu(Ac)2 was treated at low temperature. The initial discharge capacity of the composite cathode material reached 167.4 mAh/g at 0.2C between 2.5-4.3V, the retention ratio of discharge capacity was more than 90.3% after 20 cycles.3. The effects of SnO2-mixed on the structure and electrochemical performance of LiNi1/3Co1/3Mn1/3O2 were studied. The results indicated that SnO2-mixed did not change the layer structure. When mixed with 4wt% SnO2, the composite cathode material had the best electrochemical performance and the initial discharge capacity reached 158.9mAh/g at 0.2C between 2.5-4.3V, and the retention ratio of discharge capacity was 90.1% after 20 cycles. It had great performance in high rate condition, which had wide application prospect in the power battery.4. LiNi1/3Co1/3Mn1/3O2 materials were doped by Fe-ion and mixed with Fe(NO3)3·9H2O. The results showed that LiNi1/3Co1/3Mn1/3O2 material had a single layered structure after Fe-doping.The effects of Fe(NO3)3·9H2O on the structure and electrochemical performance were studied. Li(Ni1/3Co1/3Mn1/3)i-o.o3Feo.o302 had the best electrochemical performance and the initial discharge capacity of the composite cathode material reached 155.9mAh/g at 0.2C between 2.5-4.3V, and the retention ratio of discharge capacity was 89.6% after 20 cycles. Fe-doping could reduce the cation mixing and increase the electronic conductivity and diffusion coefficient. The discharge capacity of LiNi1/3Co1/3Mm/3O2 material mixed with Fe(NO3)3-9H2O decreased gradually, while the capacity retention rate was improved.