Study On The Synthesis And Surface Modification Of Ni-Based Layered Cathode Materials For Lithium-Ion Batteries

Nickel-rich layered cathode material(LiNi_1-x-yCo_xMn_yO₂and LiNi_1-x-yCo_xAl_yO₂)for lithium-ion batteries have been widely studied and applied due to its high energy density,low cost and easy synthesis,especially in the field of power batteries.However,it suffers from unstable surface properties,poor thermal stability,and low reversibility of high-voltage phase transition,so there are certain drawbacks involving its cycling stability and safety performance,which limit its wider application.In this paper,aiming at the drawbacks of the material’s structural stability,surface stability and thermal stability,the synthesis and modification of LiNi_1-xMe_xO₂ cathode material were studied basing on co-precipitation and solid-phase sintering method,which is widely used in the industry.The main results are as follows:（1）LiNi_0.90Co_0.03Mn_0.04Al_0.03O₂ cathode material（NCMA90）with low cobalt content was synthesized by co-precipitation and solid-state sintering process.Reduced Co³⁺content makes the material more economical.The material has an initial discharge capacity of 193.4 m Ah g^-1 at 1 C,2.8-4.3V,the capacity retention rate after 100 cycles reaches 91.37%.The characterization results of XPS and XRD before and after cycling show that the introduction of Co³⁺,Mn⁴⁺,Al³⁺doping ions reduces the cation mixing and suppress the structural degradation of the material.（2）The cg-NCM83 cathode material with TM ions concentration gradient along the secondary particles was synthesized through a co-precipitation and solid-state sintering method.The outer surface of cg-NCM83 secondary particles is relatively robust.The material sintered at750°C maintains the concentration gradient of the Mn and Co contents along the secondary particles.Cg-NCM83 has an initial discharge specific capacity of 178.5 m Ah g^-1 at 1 C,2.8-4.3 V,after 100 cycles,the capacity retention reaches 96.86%.Discharge capacity at high current density of 10C reaches 155.3 m Ah g^-1.The higher surface Mn content further dilutes the surface Ni concentration.Compared with commercial NCM83 cathode material（C-NCM83）,the cycle stability,surface stability and thermal stability of cg-NCM83 have been significantly improved.（3）CeP₂O₇ was used as coating layer for LiNi_0.83Co_0.12Mn_0.05O₂cathode material（LNCM83）.1.0 wt.%CPPO coated LNCM83 via solid process shows the best electrochemical performance.The LNCM83 was then subjected to a simultaneous water washing and surface coating treatment with CeP₂O₇（CPPO）,and the modified sample（Aq-LNCM83@CPPO）was compared with the untreated sample（P-LNCM83）and the water-washed sample（W-LNCM83）in a series of properties.A series of characterization results show suppressed side-reaction,improved thermal and unit cell stability.After cycling,the formation of strain microcracks on the surface of the material is effectively suppressed.After200 cycles of charge and discharge at 1 C and 2.8-4.4 V,it maintained 80.54%of the initial capacity,which was also much higher than that of the water-washed and untreated samples.49 pictures,19 tables,162 references included...