Secondary lithium battery and positive electrode material thereof, and positive electrode material preparation method

Abstract

The present invention provides a positive active material for use in a lithium ion battery, a method for preparing the positive active material and a lithium ion battery containing the positive active material. The positive active material includes a core of lithium containing transition metal oxide represented by Formula LixMyN1-yO2-αAβ and a coating layer of lithium containing transition metal phosphate represented by Formula LiaMbN′1-bPO4-λBζ in situ formed on the core, wherein 0.9≰x≰1.2, 0.6≰y≰1.0, 0.9≰a≰1.1, 0.6≰b≰1.0, 0≰α≰0.2, 0≰β≰0.4, 0≰λ≰0.5, 0≰ζ≰0.5. The positive active material for use in a lithium ion battery according to the present invention has high capacity, desirable cycling performance and safety performance, as well as desirable thermal stability.

Description

technical field [0001] The invention belongs to the technical field of secondary lithium batteries. More specifically, the invention relates to a secondary lithium battery cathode material with excellent performance and a preparation method thereof. Background technique [0002] At present, there are mainly three types of positive electrode materials used in secondary lithium batteries: spinel structure LiM 2 o 4 (M is Co, Ni, Mn, etc.); layered lithium-containing transition metal oxide LiMO 2 (M is Mn, Co, Ni, etc.); lithium phosphate LiMPO with olivine structure 4 (M is Fe, Mn, Co, Ni, etc.). Among them, the layered lithium-containing transition metal oxide LiCoO 2 It is currently the most widely used cathode material in commercialization, and has the advantages of simple synthesis process and mature application technology; however, LiCoO 2 Cobalt in LiCoO is expensive, highly toxic, and has poor safety performance, so that it is difficult to meet the application need...

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Problems solved by technology

However, this material also has some problems, such as bulging under high battery voltage, easy pulverization of the material after multiple cycles, safety problems when the battery is overcharged or thermal runaway, etc.

In order to solve the above problems, it was proposed to coat lithium metal phosphate (LiMPO) on the surface of nickel-based oxide cathode materials. 4 ) and metal phosphates (M 3 (PO4) 2 ) compound, thereby improving the safety performance of the battery by improving the thermal stability of the material; but this scheme still has the following disadvantages: one is the formed M 3 (PO 4 ) 2 Difficult to convert to LiMPO 4 ; Second is M 3 (PO 4 ) 2 and LiMPO 4 The proportion of Li is difficult to control; the third is that the scheme requires that the content of Li on the surface of the nickel-based oxide must be higher than that of the main material, which increases the requirements for the base material, thus limiting the scope of application; the fourth is that the coating material is deposited on the surface of the base It is obtained after post-calcination, so it is difficult to form a complete and dense coating layer. The electrolyte and the HF in the electrolyte can react after touching the uncoated position, and the physical adhesion between the coating material and the main material is the basis. Mainly, it is easy to fall off after a long-term cycle, and it cannot protect the main material in the later stage of the cycle.

However, because the coated metal oxides are all non-electrochemically active materials and have poor lithium-ion conductivity, the actual improvement effect is very limited, and some even bring negative effects.

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