Preparation And Modification Of Ni-Rich Ternary Layered Oxides

From portable device power to electric vehicle power batteries,lithium-ion batteries are widely used and have attracted much attention.With the improvement of people’s demand,its performance requirements are also getting higher and higher.It is urgent to increase the strength of further research and development of lithium-ion batteries,especially the development of cathode materials.High nickel ternary cathode material is considered to be the most promising cathode material for power batteries in the future.However,the capacity reduction caused by lithium residue and the phase transition and crystal structure collapse caused by the increase of nickel content are the main factors limiting its industrial application.Therefore,based on the industrial demand,this paper studies the problems of high lithium residue and structural stability.Firstly,the relationship between different mixed lithium ratio and lithium residue is discussed.Then,the high nickel ternary cathode material is modified by sintering doping and precursor doping to improve the electrochemical performance of the material.The research contents and results are as follows:（1）Aiming at the problems of serious cation mixing,high lithium residue and poor electrochemical performance of high nickel ternary cathode materials,the lithium residue under different lithium to transition metal ratios（Li:TM）was quantitatively analyzed by potentiometric titration to explore the effect of Li:TM on lithium residue and electrochemical performance of high nickel ternary cathode materials.Li Ni_0.9Co_0.05Mn_0.05O₂ cathode materials with different Li:TM were prepared by high temperature solid state method using Li OH·H₂O as lithium source.The lithium residue was determined and the electrochemical performance was tested.The results show that when the mixing ratio of precursor and Li OH·H₂O is 1.03:1（NCM90-1.03）,the lithium residue is 17189.959 ppm,and the total alkalinity is 4196.896 ppm.The prepared NCM90-1.03 exhibits low cation mixing degree and good cycle stability.The secondary particles of NCM90-1.03 have regular morphology,good crystallinity,low cation mixing degree and wide Li layer.Under the cut-off voltage of 2.7-4.3 V,the discharge specific capacity at 0.1 C is 205.74 m Ah g^-1,and the discharge specific capacity at 1 C is 184.1 m Ah g^-1,and the capacity retention rate is 89%after 100 cycles.By studying the effects of different lithium mixing ratios and lithium residues on NCM90,it provides a definite direction for improving the deficiencies in subsequent materials.（2）Aiming at the problem of poor cycle stability and rate performance of high nickel cathode materials,Nb⁵⁺doping was carried out to explore the effect of Nb⁵⁺on the morphology and electrochemical properties of high nickel ternary cathode materials.Nb⁵⁺doped Li Ni_0.88Co_0.05Mn_0.07O₂ cathode material was prepared by high temperature solid state method.Nb⁵⁺doping does not change the original crystal structure of the material,but changes the morphology of the primary particles,making it a slender rod-like structure and distributed along the radial direction,which can effectively inhibit the anisotropic volume change caused by long-term cycle and increase the cycle stability of the material.At a cut-off voltage of 2.7-4.3 V,the discharge specific capacity at 0.1 C is 203.7 m Ah g^-1,and the discharge specific capacity at 1 C is 185.3 m Ah g^-1;at1 C,the capacity retention rate is 96.7%after 100 cycles.At a high voltage of 2.7-4.5 V,the discharge specific capacity at 0.1 C is 224.4 m Ah g^-1,and the discharge specific capacity at 1 C is 200.3 m Ah g^-1.At 1 C,the capacity retention rate after 100 high voltage cycles is still 92.9%.The improvement of cycle stability is mainly due to the fact that Nb⁵⁺doping changes the morphology of primary particles and inhibits the generation of microcracks.At the same time,the introduction of Nb⁵⁺in the lattice can prevent the collapse of the material structure under complete discharge.（3）Aiming at the problem that the high nickel content in ultra-high nickel（Ni≥95%）leads to the deformation of primary particles during the cycle,Nb⁵⁺was introduced into the precursor by co-precipitation method for in-situ doping,and the effect of Nb⁵⁺on the cycle stability of ultra-high nickel ternary cathode materials was investigated.By characterizing the prepared Ni_0.95Co_0.01Mn_0.04（OH）₂ and[(Ni_0.95Co_0.01Mn_0.04)_0.99Nb_0.01]（OH）₂,it was found that the doping in the precursor did not change the crystal structure of the material,but the introduction of Nb⁵⁺changed the compactness inside the secondary particles of the precursor.Then,Li Ni_0.95Co_0.01Mn_0.04O₂ and Li[(Ni_0.95Co_0.01Mn_0.04)_0.99Nb_0.01]O₂ were prepared by high temperature solid state method.The primary particles of Li[(Ni_0.95Co_0.01Mn_0.04)_0.99Nb_0.01]O₂ showed a slender rod-like structure and distributed along the radial direction.At the cut-off voltage of 2.7-4.3 V,the discharge specific capacity at 0.1 C was 226.2 m Ah g^-1,and the discharge specific capacity at 1 C was209.3 m Ah g^-1.At 1 C,the capacity retention rate is 95.2%after 100 cycles of charge and discharge cycles.This is mainly due to the introduction of Nb⁵⁺in the precursor,which changes the morphology of the primary particles,inhibits the change of the anisotropic volume during the cycle of ultra-high nickel materials,reduces the occurrence of micro-cracks,reduces the immersion of the electrolyte into the interior of the secondary particles,thereby reducing the occurrence of side reactions and improving the cyclic stability of the materials.