Method for coating nickel-cobalt lithium manganate and obtained nickel-cobalt lithium manganate material

Abstract

The invention discloses a method for coating nickel-cobalt lithium manganate. A nickel-cobalt lithium manganate material with high nickel content is coated by a nickel-cobalt lithium manganate material with low nickel content. The invention also discloses a nickel-cobalt lithium manganate prepared by the method. A nickel-cobalt lithium manganate surface is coated and modified, thus, relatively high initial capacity of nickel-cobalt lithium manganate is maintained, the cycle performance is greatly improved, the capacity attenuation of a battery after circulation for many times is obviously reduced under high temperature and high rate, side reaction between an electrolyte and an electrode material is reduced, dissolving of metal ions of Ni<2+>, Co<3+> and Mn<4+> is prevented, so that the impedance of the battery is reduced, and the electrochemical performance of the material is greatly improved; and meanwhile, the nickel-cobalt lithium manganate material is coated by a ternary material with low nickel, and the defects of high phase surface impedance, low Li<+> migration rate, poor power performance of the material and the like caused by coating of a conventional oxide are overcome.

Description

technical field [0001] The invention relates to the technical field of lithium ion battery electrode materials, in particular to a method for coating nickel-cobalt lithium manganese oxide and the obtained nickel-cobalt lithium manganese oxide material. Background technique [0002] Ternary layered Li[Ni-Co-Mn]O 2 Lithium-ion battery cathode material, with LiCoO 2 , LiNiO 2 , LiMnO 2 The advantages of the three materials: Co element can stabilize the layered structure, which can effectively reduce the phenomenon of cation mixing (Cation Mixing); Ni element can improve the gram capacity of the material; Mn element can improve the safety and stability of the material, and Low cost; due to its high energy density, good safety performance, low toxicity and low price, the ternary nickel-cobalt lithium manganese oxide material is now widely used in the positive electrode of lithium-ion batteries, and because the market is demanding high-energy-density materials There will be a ...

AI Technical Summary

Problems solved by technology

[0003] Due to the requirement of energy density, Li[Ni-Co-Mn]O 2 The proportion of Ni element in the medium is getting higher and higher, and the increase of Ni content will make the rate and cycle performance of the material worse. The chemical formula of high-nickel ternary NMC can be seen. In order to balance the valence, Ni in the high-nickel ternary has + 2 and +3 valence, and the higher the nickel content, the more +3 valence Ni, so the high-nickel ternary crystal structure is not as stable as the symmetrical ternary material; the Li structure is hexagonal α-NaFeO 2 Layered, lithium ions occupy the 3a position of the (111) surface, nickel, cobalt, and manganese ions occupy the 3b position, and oxygen occupies the 6c position. During charging and discharging, lithium ions can be formed in the (Ni x co y mn 1-x-y o 2 ) Intercalation and extraction between layers; Since the radius of divalent nickel ions is close to that of lithium ions, nickel ions may occupy the 3a position of lithium ions, resulting in mixed cation occupancy, resulting in a decrease in the electrochemical performance of the material; and Ni + Unstable, easy to react with the electrolyte in the electrolyte, not only the structure is destroyed, resulting in a decrease in cycle, but also the interfacial impedance reduces the cycle performance

[0004] At present, the ratio improvement methods are mainly doping and coating. This method mainly considers the coating improvement, and the Li[Ni-Co-Mn]O is modified by coating. 2 surface, maintaining Li[Ni-Co-Mn]O 2 With its high initial capacity, the cycle performance has been greatly improved, especially at high temperature and high rate, the capacity fading of the battery after multiple cycles is significantly reduced, which is due to the use of LiPF 6 When the electrolyte is in the electrolyte, the presence of the coating layer inhibits the corrosion of the electrode material by HF during the cycle, reduces the side reaction between the electrolyte and the electrode material, and prevents the Ni 2+ ,Co 3+ ,Mn 4+ The dissolution of metal ions reduces the impedance of the battery and greatly improves the electrochemical performance of the material; however, conventional oxides (Al 2 o 3 , ZrO 2 、TiO 2 , MgO and ZnO 2 etc.) cladding may cause the phase impedance of the material, making Li + The migration rate is reduced, reducing the power performance of the material, and there is no significant improvement in the electrochemical performance of the high-nickel material itself

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