Li-ion Battery LiNi_0.815Co_0.15Al_0.035O₂The Mechanism Of Metal Ion Dissolution In Water Washing And Surface Modification Of Cathode Material Sexual Research

Since the commercialization of lithium ion batteries（LIBs）,they have become the widely used energy storage system due to their advantages of high energy density,environmental friendliness and relatively low cost.Because of the rapid development of green energy storage and electric vehicle industry,Nickel-Rich cathode materials are considered to be the most potential lithium-ion power battery materials.However,the cathode materials with nickel content higher than 80%still have some problems,such as air s ensitivity,poor thermal stability and cycle performance,which limit their large-scale commercial application of NCA materials.Among them,the air sensitive effect will lead to a large number of lithium residues（Li₂CO₃ and Li OH）remain on the particle surface,which will reduce the discharge capacity,and destroy safety performance and cycle stability of the material.Water washing is one of the most effective methods to remove lithium residue.At the same time,water washing technology will lead to the dissolution of Li⁺and Al³⁺in the material,which restricts the effect of water washing modification.In this paper,the influence of the amount of lithium on the migration of metal ions in the process of sintering and washing is studied systematically.The ammonium fluoride additi ves are used to deeply remove lithium residues,and build a high stability fluoride coating on the surface of the material to improve the electrochemical stability and structural stability of the material.The conclusions are as follows:In this paper,LiNi_0.815Co_0.15Al_0.035O₂（NCA）is taken as the research object,and the influence of the amount of lithium excess on the metal ion loss in the process of water washing is systematically studied.Multiple characterizations including inductive coupled plasma atomic emission spectrometry（ICP-AES）,scanning electron microscopy（SEM）,and X-ray photoelectron spectroscopy（XPS）depth profiles show that certain amount of Li⁺and Al³⁺are lost from the near-surface of NCA during washing process,which is one of the key issues that lead washed samples suffer from poor electrochemical performance and structural stability.The excess Li OH·H₂O ratio in mixing and high temperature sintering during NCA synthesis has a remarkable effect on the Al³⁺dissolution ratio,and t he loss rate of Al³⁺is as high as23.14%for lithium excess ratio up to 10 at.%.Characterization analyses of the electrochemical performance,structure,morphology and elemental chemical state of the samples demonstrate that the Li⁺and Al³⁺on the surface of the material are lost first in the process of water washing,and the lack of Li⁺and Al³⁺surface structure is an important reason for deterioration of the material’s air storage performance,electrochemical performance,structural stability and thermal stability.After the damage mechanism of material washed by water is proved,a solution is put forward,the NH₄F assisted water wash Li Ni_0.815Co_0.15Al_0.035O₂.The results show that a layer of about 5nm fluoride can be coated on the surface of NCA with the right feeding method,and the phase gradient doping of fluorine can be formed in the area of 1μm below the surface of NCA particles.In terms of electrochemical properties,the first cycle coulomb efficiency of NCAF material washed with NH₄F is 91.63%,the initial discharge capacity is 180.3 mAhg^-1,and the capacity retention rate after 50 cycles is 98.1%.