Synthesis And Modification Of Nicke Rich Concentration Gradient Cathode Materials

Since its commercialization 30 years ago,lithium-ion batteries have been widely used in military and civilian applications.However,Industry must meet demand for durable and inexpensive lithium-ion batteries.One way manufacturers are seeking to meet this growing demand is to use nickel-rich Li Ni_xMn1-x-y Co_yO₂ as a cathode material.High nickel type NCM ternary cathode material has significant advantages in material cost,thermodynamic stability and cycling performance compared with the traditional material.Due to the high nickel content,it is easy to undergo phase change and release oxygen,which not only leads to cycle degradation but also raises many safety issues as a result.Conventional modifications do not fundamentally solve the structural problems.In this paper,the influence of the co-precipitation preparation process of concentration gradient precursors on the material properties is investigated,and the optimal synthesis process is proposed.On this basis,the materials were subjected to single-crystallization modification,W-element coating,and Nb-element doping experiments,and the materials were characterized before and after modification by physical means to analyze the effects of modification on the electrochemical properties of the materials.Firstly,the co-precipitation preparation process of concentration gradient pre cursors was optimized.The effects of improved stirring mode,reaction p H and reaction duration on the morphology of precursor materials and electrochemical properties of electrode materials were investigated.The synthesized ternary mate rials have dense surface,high sphericity,good laminar integrity and low lithium-nickel mixing.Among them,materials with a nickel-cobalt-manganese ratio of8:1:1 are fed by a concentration gradient,which improves the structural stabi lity of the material and achieves a long cycle life of the material.The material with the nickel-cobalt-manganese ratio of 83:12:5 has the best electrochemic al performance when 3%manganese sulfate solution is prepared alone.It is fou nd that manganese enhances the stability of the transition metal layer.Secondly,in order to improve the stability and cycling stability of the material,a single crystal material with the nickel-cobalt-manganese ratio of 6:2:2 was synthesized,and the effect of tungsten elemental cladding on the electrochemical performance was investigated.The WO₃ films were deposited directly on the single crystal particles by atomic layer deposition,and investigate the atomic-to-microscopic structures in detail via advanced characterization techniques,such as Cs-corrected scanning transmission electron microscopy.The results reveal that coated tungsten is predominately accumulated on the（003）facet of NCM,with the migration of a small amount of W⁶⁺into this facet,resulting in a reduction of Ni³⁺to Ni²⁺and the formation of a rock-salt-like structure on the surface.It is proved that the tungsten coating can alleviate the structural distortion of the layered high-nickel material during cycling to a certain extent,significantly improved the stability of the NCM cathode material,and slowed down the particle breakage during the cycling process.Finally,based on the fabricated NCM precursors,the doping of Nb elements was explored to investigate the effects of Nb elements on particle size,doping amount and cycling performance,and to study its doping principle.The doping by solid-phase calcination method,the size of primary particles becomes smaller after doping,and the XRD and cross-sectional EDS analysis proves that Nb elements are doped into the inner lattice of the material and distributed uniformly in the particles.The electrochemical properties of the Nb element doped materials were analyzed at different ratios,and the 1%Nb doping was found to improve the cycle retention while taking into account the discharge specific capacity.the best doping content of Nb element doped NCM was 1%.In summary,the high nickel ternary material adopts the concentration gradient feeding method to improve the structural stability of the material.Using tungsten to coat and modify the high nickel ternary material,it is found that the tungsten mainly aggregates on the（003）surface,which slows down the particle breakage during the cycle.The Nb-doped high-nickel ternary material significantly reduces the particle size,and proper doping can improve the cycle stability.