Cathode material and preparation method thereof, and lithium ion battery

Abstract

The application relates to a positive electrode material and a preparation method thereof, and a lithium ion battery, and the positive electrode material comprises: a base material, the base material is a lithium transition metal composite oxide; a transition layer located on the surface of the base material, the transition layer comprises an oxide of an M1 doped element, the M1 doped element comprises Nb and / or Ta, and the transition layer has oxygen defect sites; and a lithium-rich oxide coating layer located on the surface of the transition layer, the chemical general formula of the lithium-rich oxide coating layer is Li 1+a M1 b M2 c O2, wherein a+b+c=1, 0 The positive electrode material disclosed by the application has a uniform coating layer on the surface, and the electrochemical performance and safety performance of the positive electrode material can be improved.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of positive electrode materials, in particular to a positive electrode material, a preparation method thereof and a lithium ion battery. BACKGROUND

[0002] High-nickel positive electrode materials have the advantages of low cost, high energy density and superior rate performance, and thus are high-energy-density lithium ion battery positive electrode materials with great development potential. Research has found that the energy density of high-nickel positive electrode materials can be improved by increasing the Ni content, however, the structural stability of the positive electrode material is destroyed when the Ni content is too high; and the cycle stability of the material is also deteriorated due to the continuous side reaction between the electrolyte and the surface of the positive electrode material during charging and discharging.

[0003] At present, the surface of the material is modified by a dry coating process in the industry to improve the electrochemical performance and stability of the positive electrode material. However, the process has very strict requirements for the particle size and purity of the coating raw material, and also has very high requirements for the performance of the coating equipment.

[0004] In addition, due to the difference in the active sites (surface defect sites) on the surface of the positive electrode material, the coating layer of the positive electrode material is prone to uneven coating and uncontrollable thickness, which can easily deteriorate the electrochemical performance of the positive electrode material. SUMMARY

[0005] The purpose of the present application is to provide a positive electrode material, a preparation method thereof and a lithium ion battery, the positive electrode material has a uniform coating layer on the surface, and can improve the electrochemical performance and safety performance of the positive electrode material.

[0006] In a first aspect, the present application provides a positive electrode material, which comprises:

[0007] a base material, the base material being a lithium transition metal composite oxide;

[0008] a transition layer on the surface of the base material, the transition layer comprising an oxide of M1 doping elements, the M1 doping elements comprising Nb and / or Ta, and the transition layer having oxygen defect sites; and

[0009] a lithium-rich oxide coating layer on the surface of the transition layer, the lithium-rich oxide coating layer having a general formula of Li 1+a M1 b M2 c O2, wherein a+b+c=1, 0

[0010] In some embodiments, the base material has a general formula of Li n1Ni x1 Co y1 A z1 O2, wherein, 0.95≤n1≤1.2, 0.6≤x1<1, 0

[0011] In some embodiments, the transition layer has a chemical formula of Li n2 Ni x2 Co y2 A z2 M1 w2 O 2-σ , wherein, 0.95≤n2≤1.2, 0.6≤x2<1, 0

[0012] In some embodiments, the transition metal M2 element includes at least one of Ni, Co, Mn, Mo and Cr.

[0013] In some embodiments, the base material has a median particle size of 3 μm to 15 μm.

[0014] In some embodiments, the transition layer has a thickness of 5 nm to 3 μm.

[0015] In some embodiments, the lithium-rich oxide coating layer has a thickness of 5 nm to 2 μm.

[0016] In some embodiments, the lithium-rich oxide coating layer has a cubic crystal structure of Fd-3m rock salt crystalline phase.

[0017] In some embodiments, the lithium-rich oxide coating layer has an amorphous crystal structure.

[0018] In some embodiments, the M1 doping element has a doping depth of 5 nm to 5 μm.

[0019] In some embodiments, the transition layer has a higher content of M1 doping element near the surface of the lithium-rich oxide coating layer than near the surface of the base material.

[0020] In some embodiments, the positive electrode material is measured by powder XPS using Al-Kα rays, and the transition layer has more oxygen defect sites near the surface of the lithium-rich oxide coating layer than near the surface of the base material.

[0021] In some embodiments, the thickness uniformity of the lithium-rich oxide coating layer is ≥ 90%.

[0022] In some embodiments, the mass content of the lithium-rich oxide coating layer is 0.5% to 5% based on 100% of the mass of the base material.

[0023] In some embodiments, the median particle size D50 of the positive electrode material is 3 μm to 17 μm.

[0024] In some embodiments, the specific surface area of the positive electrode material is 0.1 m 2 / g to 3 m 2 / g.

[0025] In a second aspect, the present application provides a preparation method of a positive electrode material, comprising the following steps:

[0026] dispersing the base material in a weak acid solution to perform a replacement reaction, and performing solid-liquid separation to obtain a precursor, the base material being a lithium-transition metal composite oxide;

[0027] performing a stepwise temperature sintering treatment on a mixture containing the precursor, a dopant containing a doping element M1, an additive containing a transition metal M2, and a lithium compound under a protective atmosphere to obtain a positive electrode material, the doping element M1 including Nb and / or Ta.

[0028] In some embodiments, the base material has a general chemical formula of Li n1 Ni x1 Co y1 A z1 O2, wherein 0.95≤n1≤1.2, 0.6≤x1<1, 0

[0029] In some embodiments, the base material has a median particle size of 3 μm to 15 μm.

[0030] In some embodiments, the weak acid solution includes at least one of acetic acid, citric acid, phosphoric acid, sulfurous acid, sulfuric acid, and hydrochloric acid.

[0031] In some embodiments, the pH value of the weak acid solution is 4 to 6.

[0032] In some embodiments, the weak acid solution further includes water.

[0033] In some embodiments, the temperature of the replacement reaction is 10°C to 70°C.

[0034] In some embodiments, the time of the displacement reaction is 2 min to 30 min.

[0035] In some embodiments, the solid-liquid separation comprises at least one of filtration separation and centrifugal separation.

[0036] In some embodiments, the method further comprises drying the solid obtained from the solid-liquid separation, and the drying temperature is 80°C to 110°C.

[0037] In some embodiments, the dopant comprises at least one of a Nb salt, a Nb oxide, a Ta salt, and a Ta oxide.

[0038] In some embodiments, the transition metal M2 comprises at least one of Ni, Co, Mn, Mo, and Cr.

[0039] In some embodiments, the additive containing the transition metal M2 comprises at least one of a carbonate of M2, a hydroxide of M2, an acetate of M2, an oxalate of M2, a sulfate of M2, a chloride of M2, and a nitrate of M2.

[0040] In some embodiments, the lithium-containing compound comprises at least one of lithium hydroxide, lithium carbonate, lithium nitrate, lithium acetate, lithium sulfate, lithium oxalate, and lithium chloride.

[0041] In some embodiments, the additive containing the dopant element M1, the additive containing the transition metal M2, and the lithium-containing compound are added in amounts satisfying the ratio of the total moles of M1 and M2 to the moles of Li being (0.2-0.5):(0.25-0.6):1.

[0042] In some embodiments, the mixing condition for obtaining the mixture is solid-phase mixing at 10°C to 50°C for 0.3 h to 2 h.

[0043] In some embodiments, the mass content of the lithium-rich oxide coating layer formed by sintering the mixture is 0.5% to 5% based on 100% of the mass of the base material.

[0044] In some embodiments, the median particle size of the dopant, the additive, and the lithium-containing compound is 0.005 μm to 5 μm.

[0045] In some embodiments, the protective atmosphere comprises at least one of nitrogen, helium, neon, and argon.

[0046] In some embodiments, the stepwise temperature increase sintering process comprises sintering the mixture at 200°C to 400°C for 1 h to 10 h, and then increasing the temperature to 500°C to 800°C for 2 h to 20 h.

[0047] In some embodiments, the preparation method further comprises cooling, shaping and sieving the product after sintering.

[0048] In some embodiments, the preparation method further comprises cooling, shaping and sieving the product after sintering, wherein the shaping comprises at least one of crushing, grinding, ball milling or air crushing.

[0049] In a third aspect, the present application provides a lithium ion battery comprising the positive electrode material of the first aspect or the positive electrode material prepared by the method of the second aspect.

[0050] Compared with the prior art, the present application has at least the following beneficial effects:

[0051] The positive electrode material provided by the present application comprises a base material, a transition layer on the surface of the base material, and the transition layer has uniformly distributed oxygen defect sites on the surface, which can inhibit oxygen release and crystal structure phase transition; the transition layer contains Nb and / or Ta doping elements, which can make the crystal structure of the lithium-rich oxide coating layer formed on the surface of the base material more stable, and is conducive to stabilizing the crystal structure of the base material itself; in addition, the Li ions in the lithium-rich oxide coating layer and the M1 and M2 ions are mutually occupied (i.e. Li ions will occupy the positions of transition metals M1 and M2, and transition metals M1 and M2 will also occupy Li positions), so that the lithium-rich oxide coating layer has more lithium intercalation sites, and the lithium-rich oxide coating layer has a more stable structure during charging and discharging, and the changes in the lattice parameters and the lattice volume of the coating layer are very small. In the repeated charging and discharging process, the coating layer has good structural stability and is not easy to break or fall off, etc., which can better protect the base material and the transition layer; in addition, the stacking mode of the lithium-rich oxide coating layer and the oxygen atoms in the base material is consistent, which is cubic close packing and has better compatibility with the base material. In addition, the transition layer and the lithium-rich oxide coating layer have a good synergistic effect, the surface of the transition layer has uniform active sites due to the uniform oxygen defect sites on the surface, and the lithium-rich oxide coating layer can uniformly crystallize and grow at the active sites, thereby forming a coating layer with uniform thickness, so that the coating layer and the base material can be more closely combined, and the side reactions between the base material and the electrolyte are inhibited, improving the structural stability of the entire positive electrode material, thereby greatly improving the electrochemical performance and safety performance of the positive electrode material.

[0052] The preparation method of the positive electrode material provided by the present application can displace the Li + and H + on the surface layer of the base material by dispersing the base material in a weak acid solution to carry out a displacement reaction, so that the Li +The crystal structure in the surface layer of the base material is left, and then the mixture containing the precursor, the dopant containing the doping element M1, the additive containing the transition metal M2 and the lithium-containing compound is subjected to a stepwise temperature sintering treatment under a protective atmosphere. During the sintering treatment, H + is removed from the crystal structure in the surface layer of the base material in the form of H2O, so that the surface layer of the base material is partially deoxidized to form uniformly distributed oxygen defect sites. These oxygen defect sites have high activity, so that the lithium-rich oxide formed during the sintering process can uniformly grow at these oxygen defect sites to form a lithium-rich oxide coating layer with uniform thickness. During the sintering process, the Nb and / or Ta elements in the dopant are doped into the crystal structure of the surface layer of the base material to form a transition layer with more stable crystal structure, so that the coating layer can be tightly combined with the base material through the transition layer, inhibit the occurrence of side reactions between the electrolyte and the base material, and improve the structural stability of the positive electrode material, thereby greatly improving the electrochemical performance and safety performance of the positive electrode material. Moreover, the preparation method is simple and controllable, and can reduce production cost. BRIEF DESCRIPTION OF DRAWINGS

[0053] The application will be further described below in combination with the drawings and examples.

[0054] Figure 1 The structure schematic diagram of the positive electrode material provided for the embodiments of the present application is shown in the figure.

[0055] Figure 2 The flow schematic diagram of the preparation method of the positive electrode material provided for the embodiments of the present application is shown in the figure.

[0056] In the Figure 1 , the positive electrode material comprises:

[0057] 1-base material;

[0058] 2-transition layer;

[0059] 3-lithium-rich oxide coating layer. DETAILED DESCRIPTION

[0060] In order to better understand the technical solutions of the present application, the embodiments of the present application will be described in detail below in combination with the drawings.

[0061] It should be clear that the described embodiments are only a part of the embodiments of the present application, not all the embodiments. Based on the embodiments in the present application, all other embodiments obtained by those skilled in the art without creative labor fall within the scope of protection of the present application.

[0062] The terminology used in the description of the application herein is for the purpose of describing particular embodiments only and is not intended to be limiting of the application. As used in the description of the application and the appended claims, the singular forms "a", "an" and "the" are intended to include the plural forms as well, unless the context clearly indicates otherwise.

[0063] It should be understood that the term "and / or" as used herein merely describes associated objects with a cohesive relationship, which means that there can be three relationships, for example, A and / or B, which can represent the following three cases: A exists alone, A and B exist together, and B exists alone. In addition, the character " / " in this paper generally represents that the front and rear associated objects are a "or" relationship.

[0064] The present application provides a positive electrode material, such as Figure 1 As shown in the figure, the positive electrode material comprises:

[0065] A base material 1, which is a lithium transition metal composite oxide;

[0066] A transition layer 2 located on the surface of the base material 1, the transition layer 2 comprising an oxide of M1 doping elements, the M1 doping elements comprising Nb and / or Ta, and the transition layer 2 having oxygen defect sites; and

[0067] A lithium-rich oxide coating layer 3 located on the surface of the transition layer 2, the lithium-rich oxide coating layer 3 having a chemical formula of Li 1+a M1 b M2 c O2, wherein a+b+c=1, 0

[0068] The positive electrode material provided in the present application comprises a base material, a transition layer on the surface of the base material, and the transition layer has uniformly distributed oxygen defect sites on the surface, which can inhibit oxygen release and crystal structure phase transition; the transition layer contains Nb and / or Ta doping elements, which can make the crystal structure of the lithium-rich oxide coating layer formed on the surface of the base material more stable, and is conducive to stabilizing the crystal structure of the base material itself; in addition, the Li ions in the lithium-rich oxide coating layer and the M1 and M2 ions are mutually occupied (i.e. the Li ions will occupy the positions of the transition metals M1 and M2, and the transition metals M1 and M2 will also occupy the Li positions), so that the lithium-rich oxide coating layer has more lithium intercalation sites, and the lithium-rich oxide coating layer has a more stable structure during charging and discharging, and the changes in the lattice parameters and the lattice volume of the coating layer are very small, and the coating layer has good stability during repeated charging and discharging, and is not easy to break and fall off, etc., which can better protect the base material and the transition layer; in addition, the stacking mode of the lithium-rich oxide coating layer and the oxygen atoms in the base material is consistent, which is cubic close packing, and has better matching with the base material. In addition, the transition layer and the lithium-rich oxide coating layer have a good synergistic effect, the transition layer has uniform active sites on the surface of the base material due to the oxygen defect sites, and the lithium-rich oxide coating layer can uniformly crystallize and grow at the active sites, thereby forming a coating layer with uniform thickness, so that the coating layer and the base material can be more closely combined, and the occurrence of side reactions between the base material and the electrolyte can be inhibited, and the structural stability of the entire positive electrode material is improved, thereby greatly improving the electrochemical performance and safety performance of the positive electrode material.

[0069] In some embodiments, the base material has a chemical formula of Li n1 Ni x1 Co y1 A z1 O2, wherein 0.95≤n1≤1.2, 0.6≤x1<1, 0

[0070] In some embodiments, the value of n1 can be 0.95, 0.96, 0.97, 0.98, 0.99, 1.0, 1.03, 1.05, 1.15, or 1.2, etc., the value of x1 can be 0.6, 0.65, 0.7, 0.75, 0.8, 0.85, 0.9, 0.95, 0.96, 0.97, 0.98, or 0.99, etc., the value of y1 can be 0.01, 0.05, 0.07, 0.09, 0.1, 0.15, 0.17, 0.19, or 0.2, etc., and the value of z1 can be 0, 0.05, 0.1, 0.15, 0.5, 0.25, 0.27, or 0.3, etc., and of course it can also be other values within the above range, which are not limited herein.

[0071] In some embodiments, the median particle size of the base material is 3 μm to 15 μm, specifically can be 3 μm, 4 μm, 5 μm, 6 μm, 7 μm, 8 μm, 9 μm, 10 μm, 11 μm, 12 μm, 13 μm, 14 μm or 15 μm, and of course can be other values within the above range, which are not limited herein.

[0072] In some embodiments, the base material is a lithium transition metal composite oxide, specifically can be a high-nickel ternary material, a lithium-rich material, etc.

[0073] In some embodiments, the crystal structure of the base material belongs to hexagonal system.

[0074] In some embodiments, the chemical formula of the transition layer is Li n2 Ni x2 Co y2 A z2 M1 w2 O 2-σ , wherein 0.95≤n2≤1.2, 0.6≤x2<1, 0

[0075] Specifically, the value of n2 can be 0.95, 0.96, 0.97, 0.98, 0.99, 1.0, 1.03, 1.05, 1.15 or 1.2, etc., the value of x2 can be 0.6, 0.65, 0.7, 0.75, 0.8, 0.85, 0.9, 0.95, 0.96, 0.97, 0.98 or 0.99, etc., the value of y2 can be 0.01, 0.05, 0.07, 0.09, 0.1, 0.15, 0.17, 0.19 or 0.2, etc., the value of z2 can be 0, 0.05, 0.1, 0.15, 0.5, 0.25, 0.27 or 0.3, etc., the value of w2 can be 0.01, 0.03, 0.05, 0.06, 0.07, 0.09 or 0.1, etc., the value of σ can be 0.001, 0.01, 0.09, 0.1, 0.2, 0.3, 0.4 or 0.5, etc., and of course can be other values within the above range, which are not limited herein.

[0076] In some embodiments, the thickness of the transition layer is 5 nm to 3 μm, specifically, 5 nm, 10 nm, 50 nm, 80 nm, 100 nm, 200 nm, 300 nm, 400 nm, 500 nm, 600 nm, 700 nm, 800 nm, 1 μm or 3 μm, or other values within the above range, which are not limited herein.

[0077] In some embodiments, the crystal structure of the transition layer belongs to at least one of hexagonal system, cubic system or hexagonal system / cubic system mixed phase.

[0078] In some embodiments, the content of M1 doping element near the side surface of the transition layer close to the lithium-rich oxide coating layer is higher than the content of M1 doping element near the side surface of the transition layer close to the base material.

[0079] In some embodiments, the positive electrode material is measured by powder XPS using Al-Ka ray, and the number of oxygen defect sites near the side surface of the transition layer close to the lithium-rich oxide coating layer is more than the number of oxygen defect sites near the side surface of the transition layer close to the base material.

[0080] In some embodiments, the thickness of the lithium-rich oxide coating layer is 5 nm to 2 μm, specifically, 5 nm, 10 nm, 50 nm, 80 nm, 100 nm, 200 nm, 300 nm, 400 nm, 500 nm, 600 nm, 700 nm, 800 nm, 900 nm, 1 μm or 2 μm, or other values within the above range, which are not limited herein.

[0081] In some embodiments, the thickness uniformity of the lithium-rich oxide coating layer is ≥ 90%, specifically, 90%, 91%, 92%, 93%, 95%, or the like, which are not limited herein. It can be understood that, due to the uniformly distributed oxygen defect sites (active sites) of the transition layer on the surface of the base material, the lithium-rich oxide coating layer can uniformly crystallize at the active sites, thereby forming a coating layer with uniform thickness, so that the coating layer and the base material can be more closely combined. In this embodiment, the thickness uniformity of the lithium-rich oxide coating layer is calculated as follows:

[0082] The cross-section of 10 randomly sampled positive electrode material particles is processed by FIB-TEM equipment, and the maximum thickness (D max ) and the minimum thickness (D min ) of the lithium-rich oxide coating layer are measured from 10 samples, and the uniformity of the coating layer is calculated as follows: Ψ = 100% - (D max -D min ) / Dmax .

[0083] In some embodiments, the transition metal M2 element comprises at least one of Ni, Co, Mn, Mo and Cr.

[0084] In some embodiments, the crystal structure of the lithium-rich oxide coating layer is a cubic crystal system Fd-3m rock salt crystalline phase.

[0085] In some embodiments, the crystal structure of the lithium-rich oxide coating layer is amorphous.

[0086] In some embodiments, the doping depth of the M1 doping element is 5 nm to 5 μm, and specifically can be 5 nm, 10 nm, 30 nm, 80 nm, 100 nm, 200 nm, 300 nm, 400 nm, 500 nm, 600 nm, 700 nm, 800 nm, 1 μm, 3 μm or 5 μm, and of course can also be other values within the above range, which are not limited herein. The doping depth refers to the thickness of the doping element that can be detected from the surface of the transition layer to the inside by cutting the particle and detecting the cut surface.

[0087] In some embodiments, the mass content of the lithium-rich oxide coating layer is 0.5% to 5% based on 100% of the mass of the base material, and specifically can be 0.5%, 1%, 1.5%, 2%, 2.5%, 3%, 3.5%, 4%, 4.5% or 5%, and of course can also be other values within the above range, which are not limited herein.

[0088] In some embodiments, the median particle size D50 of the positive electrode material is 3 μm to 17 μm, and specifically can be 3 μm, 3.5 μm, 4 μm, 4.5 μm, 6 μm, 7 μm, 8 μm, 9 μm, 10 μm, 11 μm, 12 μm, 13 μm, 14 μm, 15 μm, 16 μm or 17 μm, and of course can also be other values within the above range, which are not limited herein.

[0089] In some embodiments, the specific surface area of the positive electrode material is 0.1 m 2 / g to 3 m 2 / g, and specifically can be 0.1 m 2 / g, 0.5 m 2 / g, 0.7 m 2 / g, 0.9 m 2 / g, 1 m 2 / g, 1.5 m 2 / g, 1.7 m 2 / g, 1.9 m 2 / g, 2 m 2 / g, 2.5 m 2 / g, 2.7 m 2 / g, 2.9 m 2 / g or 3 m 2 / g, etc., of course, other values within the above range are also possible, which are not limited herein.

[0090] In a second aspect, the application provides a preparation method of a positive electrode material, as shown in the following formula: Figure 2 The preparation method of the positive electrode material comprises the following steps:

[0091] S100: dispersing a base material in a weak acid solution to perform a displacement reaction, and performing solid-liquid separation to obtain a precursor, wherein the base material is a lithium transition metal composite oxide;

[0092] S200: performing a stepwise temperature sintering treatment on a mixture containing the precursor, a dopant containing a doping element M1, an additive containing a transition metal M2, and a lithium compound under a protective atmosphere to obtain a positive electrode material, wherein the doping element M1 includes Nb and / or Ta.

[0093] In the above preparation method of the positive electrode material, by dispersing the base material in the weak acid solution to perform the displacement reaction, Li + in the surface layer of the base material is displaced by H + , and H + is left in the crystal structure of the surface layer of the base material, and then the mixture containing the precursor, the dopant containing the doping element M1, the additive containing the transition metal M2, and the lithium compound is subjected to the stepwise temperature sintering treatment under the protective atmosphere, in the sintering process, H + in the crystal structure of the surface layer of the base material is removed in the form of H2O, so that the surface layer of the base material is partially deoxidized to form uniformly distributed oxygen defect sites, and these oxygen defect sites have high activity, so that the lithium-rich oxide formed in the sintering process can uniformly grow at these oxygen defect sites to form a lithium-rich oxide coating layer with uniform thickness; in the sintering process, the Nb and / or Ta elements in the dopant are doped into the crystal structure of the surface layer of the base material to form a transition layer with more stable crystal structure, so that the coating layer can be tightly combined with the base material through the transition layer, inhibit the side reaction of the electrolyte with the base material, and improve the structural stability of the positive electrode material, thereby greatly improving the electrochemical performance and safety performance of the positive electrode material. And the preparation method is simple and controllable, and can reduce the production cost.

[0094] The preparation method of the application will be specifically described below in combination with examples:

[0095] S100: dispersing the base material in a weak acid solution to perform a replacement reaction, and performing solid-liquid separation to obtain a precursor, wherein the base material is a lithium-transition metal composite oxide.

[0096] In some embodiments, the base material has a chemical formula of Li n1 Ni x1 Co y1 A z1 O2, wherein 0.95≤n1≤1.2, 0.6≤x1<1, 0

[0097] In some embodiments, the base material has a median particle size of 3 μm to 15 μm, and specifically can be 3 μm, 4 μm, 5 μm, 6 μm, 7 μm, 8 μm, 9 μm, 10 μm, 11 μm, 12 μm, 13 μm, 14 μm, or 15 μm, and of course can be other values within the above range, which are not limited herein.

[0098] In some embodiments, the base material can be prepared by sintering a lithium source, a nickel source, a cobalt source, and an A source, or can be purchased as a ready-made base material, which are not limited herein.

[0099] In some embodiments, the weak acid solution includes at least one of acetic acid, citric acid, phosphoric acid, sulfurous acid, sulfuric acid, and hydrochloric acid.

[0100] In some embodiments, the weak acid solution has a pH value of 4 to 6, and specifically can be 4, 4.1, 4.3, 4.5, 4.7, 4.9, 5, 5.1, 5.3, 5.5, 5.7, 5.9, or 6, and of course can be other values within the above range, which are not limited herein. Preferably, the weak acid solution has a pH value of 5 to 6. Controlling the pH value of the weak acid solution within the above range is beneficial to controlling the replacement rate of hydrogen ions and lithium ions in the crystal lattice of the base material, so that the hydrogen-lithium replacement rate is neither too fast to be out of control nor too slow to be ineffective.

[0101] In some embodiments, the weak acid solution further includes water.

[0102] In some embodiments, the replacement reaction has a temperature of 10°C to 70°C, and specifically can be 10°C, 15°C, 20°C, 25°C, 30°C, 40°C, 50°C, 60°C, or 70°C, and of course can be other values within the above range, which are not limited herein.

[0103] In some embodiments, the time of the displacement reaction is 2 min to 30 min, specifically, 2 min, 3 min, 4 min, 5 min, 6 min, 7 min, 8 min, 9 min, 10 min, 11 min, 15 min, 20 min, 25 min, 27 min or 30 min, and the like, and of course, other values within the above range are also possible, which are not limited herein. Preferably, the time of the displacement reaction is 10 min to 20 min.

[0104] The time for drying is not limited herein, as long as the solvent in the precursor is removed.

[0105] S200: performing a stepwise temperature sintering treatment on the mixture containing the precursor, the dopant containing the doping element M1, the additive containing the transition metal M2 and the lithium-containing compound under a protective atmosphere, to obtain a positive electrode material, wherein the doping element M1 includes Nb and / or Ta.

[0106] In some embodiments, the protective atmosphere includes at least one of nitrogen, helium, neon, argon.

[0107] In some embodiments, the dopant includes at least one of a Nb salt, a Nb oxide, a Ta salt and a Ta oxide.

[0108] In some embodiments, the transition metal M2 includes at least one of Ni, Co, Mn, Mo and Cr.

[0109] In some embodiments, the additive containing the transition metal M2 includes at least one of a carbonate of M2, a hydroxide of M2, an acetate of M2, an oxalate of M2, a sulfate of M2, a chloride of M2, a nitrate of M2.

[0110] In some embodiments, the lithium-containing compound includes at least one of lithium hydroxide, lithium carbonate, lithium nitrate, lithium acetate, lithium sulfate, lithium oxalate and lithium chloride.

[0111] In some embodiments, the additive amount of the dopant containing the doping element M1, the additive containing the transition metal M2 and the lithium-containing compound satisfies the ratio of the molar amount of M1, the molar amount of M2 and the molar amount of Li as (0.2-0.5):(0.25-0.6):1, specifically, 0.2:0.25:1, 0.3:0.3:1, 0.35:0.35:1, 0.4:0.4:1, 0.5:0.5:1, 0.5:0.6:1, and the like, and of course, other values within the above range are also possible, which are not limited herein.

[0112] In some embodiments, the median particle size of the dopant, additive and lithium-containing compound is 0.005 μm to 5 μm, and can be 0.005 μm, 0.05 μm, 0.1 μm, 0.5 μm, 0.8 μm, 1 μm, 2 μm, 3 μm, 4 μm or 5 μm, or other values within the above range, which are not limited herein. Controlling the particle size of the above raw material components is conducive to improving the uniformity of solid-phase mixing and the uniformity of doping.

[0113] In some embodiments, the mixing conditions for obtaining the mixture are as follows: solid-phase mixing at 10°C to 50°C for 0.3 h to 2 h. Specifically, the temperature for solid-phase mixing can be 10°C, 15°C, 20°C, 25°C, 30°C, 35°C, 40°C, 45°C or 50°C, and the time for solid-phase mixing can be 0.3 h, 0.4 h, 0.5 h, 0.6 h, 0.7 h, 0.8 h, 0.9 h, 1 h, 1.5 h or 2 h, or other values within the above range, which are not limited herein.

[0114] In some embodiments, the method for solid-phase mixing can be dry grinding or ball milling, which are not limited herein as long as the components are uniformly mixed.

[0115] In some embodiments, the mixing device can be at least one of a ball mill, a three-dimensional mixer, a high-speed mixer and a VC mixer.

[0116] In some embodiments, the stepwise temperature sintering process comprises sintering the mixture at 200°C to 400°C for 1 h to 10 h, and then sintering at 500°C to 800°C for 2 h to 20 h. It can be understood that the stepwise temperature sintering process is divided into a low-temperature sintering stage and a high-temperature sintering stage. Specifically, the temperature for low-temperature sintering can be 200°C, 210°C, 220°C, 230°C, 240°C, 250°C, 260°C, 270°C, 288°C, 290°C, 300°C, 330°C, 350°C, 370°C or 400°C, or other values within the above range, which are not limited herein. The time for low-temperature sintering can be 1 h, 2 h, 3 h, 4 h, 5 h, 6 h, 7 h, 8 h, 9 h or 10 h, or other values within the above range, which are not limited herein. Preferably, the time for low-temperature sintering is 3 h to 6 h.

[0117] The high-temperature sintering temperature can be 500℃, 530℃, 550℃, 570℃, 600℃, 630℃, 650℃, 670℃, 700℃, 730℃, 750℃, 770℃, or 800℃, etc. The high-temperature sintering time can be 2 h, 3 h, 4 h, 5 h, 6 h, 7 h, 8 h, 9 h, 10 h, 13 h, 15 h, 17 h, 19 h, or 20 h, etc., or other values ​​within the above range, which are not limited here. Preferably, the high-temperature sintering time is 5 h to 10 h. During the high-temperature sintering process, lithium interacts with M1 and / or M2.

[0118] In some embodiments, the preparation method further includes cooling, shaping, and sieving the sintered product;

[0119] In some embodiments, the preparation method further includes cooling, shaping, and sieving the sintered product, wherein the shaping includes at least one of crushing, grinding, ball milling, or air crushing.

[0120] Thirdly, this application provides a lithium-ion battery comprising the above-described positive electrode material or the positive electrode material prepared by the above-described preparation method.

[0121] The above are merely preferred embodiments of the present invention and are not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the scope of protection of the present invention.

[0122] Example 1

[0123] (1) Weigh 10g of matrix material (LiNi) 0.95 Co 0.025 Mn 0.025 O2, D 50 =10.23μm), was transferred to an acetic acid solution with pH 6 under stirring at room temperature for a displacement reaction for 10 min, then filtered and dried at 100℃ to obtain the precursor.

[0124] (2) Using the sintered product Li 1.3 Nb 0.3 Mn 0.4 Based on an O2 content of 0.5% in the matrix material, niobium oxide (D2) is weighed according to a molar ratio (Nb:Mn:Li=0.3:0.4:1.3). 50 =1.5μm), manganese carbonate (D 50 =1.5μm) and lithium hydroxide (D 50 =2μm), and then transferred to a three-dimensional mixer to be mixed evenly with the precursor to obtain a mixture.

[0125] (3) The mixture is transferred into a muffle furnace, nitrogen is introduced, and sintering is first carried out at 300°C for 5h, and then sintering is continued at 700°C for 10h.

[0126] (4) The sintered product is cooled, shaped and sieved to obtain the positive electrode material.

[0127] The positive electrode material prepared in the embodiment comprises a base material, a transition layer on the surface of the base material and a lithium-rich oxide coating layer on the surface of the transition layer, the base material has a general formula of LiNi 0.95 Co 0.025 Mn 0.025 O2, the transition layer has a general formula of Li(Ni 0.95 Co 0.025 Mn 0.025 ) 0.995 Nb 0.005 O 2-σ , σ is 0.02, and the lithium-rich oxide coating layer has a general formula of Li 1.3 Nb 0.3 Mn 0.4 O2; the specific surface area of the positive electrode material is 0.42m 2 / g, and the median particle size D 50 is 10.25μm.

[0128] The thickness of the transition layer is 2.1μm, the thickness of the lithium-rich oxide coating layer is 20nm, the thickness uniformity of the lithium-rich oxide coating layer is 93.2%, the crystal structure of the coating layer is rock salt crystalline phase, and the doping depth of Nb is 2.0μm.

[0129] Example 2

[0130] Different from Example 1 is that:

[0131] (1) 10g of base material (LiNi 0.95 Co 0.025 Mn 0.025 O2, D 50 =10.52μm) is transferred into a citric acid solution with a pH of 5 under stirring at room temperature for displacement reaction for 10min, and then filtered and dried at 100°C to obtain a precursor.

[0132] The positive electrode material prepared in the embodiment comprises a base material, a transition layer on the surface of the base material and a lithium-rich oxide coating layer on the surface of the transition layer, the base material has a general formula of LiNi 0.95 Co 0.025 Mn 0.025 O2, the transition layer has a general formula of Li(Ni 0.95 Co 0.025 Mn 0.025 )0.997 Nb 0.003 O 2-σ , σ is 0.06, the lithium-rich oxide coating layer is Li 1.3 Nb 0.3 Mn 0.4 O2; the specific surface area of the positive electrode material is 0.48 m 2 / g, and the median particle size D 50 is 10.63 μm.

[0133] The thickness of the transition layer is 2.3 μm, the thickness of the lithium-rich oxide coating layer is 19 μm, the thickness uniformity of the lithium-rich oxide coating layer is 93.5%, the crystal structure of the coating layer is rock salt crystalline phase, and the doping depth of Nb is 1.9 μm.

[0134] Example 3

[0135] Different from Example 1 is that:

[0136] (1) 10 g of the base material (LiNi 0.95 Co 0.025 Mn 0.025 O2, D 50 = 10.67 μm) is weighed and transferred to an acetic acid solution with a pH of 6.5 under stirring at room temperature for displacement reaction for 10 min, and then filtered and dried at 100°C to obtain a precursor.

[0137] The positive electrode material prepared in this example comprises a base material, a transition layer on the surface of the base material, and a lithium-rich oxide coating layer on the surface of the transition layer. The general formula of the base material is LiNi 0.95 Co 0.025 Mn 0.025 O2, the transition layer is Li(Ni 0.95 Co 0.025 Mn 0.025 ) 0.998 Nb 0.002 O 2-σ , σ is 0.08, the lithium-rich oxide coating layer is Li 1.3 Nb 0.3 Mn 0.4 O2; the specific surface area of the positive electrode material is 0.52 m 2 / g, and the median particle size D 50 is 10.78 μm.

[0138] The thickness of the transition layer is 1.7 μm, the thickness of the lithium-rich oxide coating layer is 25 nm, the thickness uniformity of the lithium-rich oxide coating layer is 92.5%, the crystal structure of the coating layer is rock salt crystalline phase, and the doping depth of Nb is 2.1 μm.

[0139] Example 4

[0140] Different from Example 1 is that:

[0141] (1) 10 g of the base material (LiNi 0.95 Co 0.025 Mn 0.025 O2, D 50 = 10.83 μm) is transferred to an acetic acid solution with pH of 6 under stirring at room temperature for displacement reaction for 10 min, then filtered and dried at 100°C to obtain the precursor.

[0142] The positive electrode material prepared in this example comprises a base material, a transition layer on the surface of the base material, and a lithium-rich oxide coating layer on the surface of the transition layer, the base material has a general formula of LiNi 0.95 Co 0.025 Mn 0.025 O2, the transition layer has a general formula of Li(Ni 0.95 Co 0.025 Mn 0.025 ) 0.998 Nb 0.002 O 2-σ , σ is 0.06, and the lithium-rich oxide coating layer has a general formula of Li 1.3 Nb 0.3 Mn 0.4 O2; the specific surface area of the positive electrode material is 0.47 m 2 / g, and the median particle size D 50 is 10.85 μm.

[0143] The thickness of the transition layer is 2.7 μm, the thickness of the lithium-rich oxide coating layer is 18.9 nm, the thickness uniformity of the lithium-rich oxide coating layer is 93.7%, the crystal structure of the coating layer is rock salt crystalline phase, and the doping depth of Nb is 1.8 μm.

[0144] Example 5

[0145] Different from Example 1 is that:

[0146] (1) 10 g of the base material (LiNi 0.98 Co 0.02 O2, D 50 = 10.24 μm) is transferred to an acetic acid solution with pH of 6 under stirring at room temperature for displacement reaction for 10 min, then filtered and dried at 100°C to obtain the precursor.

[0147] The positive electrode material prepared in this example comprises a base material, a transition layer on the surface of the base material, and a lithium-rich oxide coating layer on the surface of the transition layer, the base material has a general formula of LiNi 0.98 Co0.02 O2, the transition layer is Li(Ni 0.98 Co 0.02 ) 0.997 Nb 0.003 O 2-σ , σ is 0.05, the lithium-rich oxide coating layer is Li 1.3 Nb 0.3 Mn 0.4 O2; the specific surface area of the positive electrode material is 0.51 m 2 / g, and the median particle size D 50 is 10.38 μm.

[0148] The thickness of the transition layer is 2.1 μm, the thickness of the lithium-rich oxide coating layer is 18.7 nm, the thickness uniformity of the lithium-rich oxide coating layer is 93.1%, the crystal structure of the coating layer is rock salt crystalline phase, and the doping depth of Nb is 2.1 μm.

[0149] Example 6

[0150] Different from Example 1 is that:

[0151] (3) The mixture is transferred into a muffle furnace, nitrogen is introduced, and sintering is first performed at 300°C for 5 h, and then sintering is continued at 600°C for 10 h.

[0152] The positive electrode material prepared in the example includes a base material, a transition layer on the surface of the base material, and a lithium-rich oxide coating layer on the surface of the transition layer. The base material has a general formula of LiNi 0.95 Co 0.025 Mn 0.025 O2, the transition layer is Li(Ni 0.95 Co 0.025 Mn 0.025 ) 0.999 Nb 0.001 O 2-σ , σ is 0.09, the lithium-rich oxide coating layer is Li 1.3 Nb 0.3 Mn 0.4 O2; the specific surface area of the positive electrode material is 0.58 m 2 / g, and the median particle size D 50 is 10.45 μm.

[0153] The thickness of the transition layer is 2.0 μm, the thickness of the lithium-rich oxide coating layer is 22.1 nm, the thickness uniformity of the lithium-rich oxide coating layer is 92.9%, the crystal structure of the coating layer is rock salt crystalline phase, and the doping depth of Nb is 1.5 μm.

[0154] Example 7

[0155] Different from example 1 is that:

[0156] (3) The mixture is transferred into a muffle furnace, nitrogen is introduced, and sintering is first carried out at 300 DEG C for 5h, and then sintering is carried out at 800 DEG C for 10h.

[0157] The positive electrode material prepared in the example comprises a base material, a transition layer on the surface of the base material, and a lithium-rich oxide coating layer on the surface of the transition layer, the base material has a general formula of LiNi 0.95 Co 0.025 Mn 0.025 O2, the transition layer has a general formula of Li(Ni 0.95 Co 0.025 Mn 0.025 ) 0.994 Nb 0.006 O 2-σ , sigma is 0.08, and the lithium-rich oxide coating layer has a general formula of Li 1.3 Nb 0.3 Mn 0.4 O2; the specific surface area of the positive electrode material is 0.37m 2 / g, and the median particle size D 50 is 10.67 mu m.

[0158] The thickness of the transition layer is 2.2 mu m, the thickness of the lithium-rich oxide coating layer is 18.9 nm, the thickness uniformity of the lithium-rich oxide coating layer is 93.6%, the crystal structure of the coating layer is rock salt crystalline phase, and the doping depth of Nb is 3.2 mu m.

[0159] Example 8

[0160] Different from example 1 is that the replacement reaction time in step (1) is 30 min.

[0161] The subsequent operations are the same as those in example 1.

[0162] The positive electrode material prepared in the example comprises a base material, a transition layer on the surface of the base material, and a lithium-rich oxide coating layer on the surface of the transition layer, the base material has a general formula of LiNi 0.95 Co 0.025 Mn 0.025 O2, the transition layer has a general formula of Li(Ni 0.95 Co 0.025 Mn 0.025 ) 0.998 Nb 0.002 O 2-σ , sigma is 0.1, and the lithium-rich oxide coating layer has a general formula of Li 1.3 Nb 0.3 Mn 0.4 O2; the specific surface area of the positive electrode material is 0.46m 2 / g, the median particle size D 50 was 10.35 pm.

[0163] The thickness of the transition layer was 1.9 pm, the thickness of the lithium-rich oxide coating layer was 19.5 nm, the thickness uniformity of the lithium-rich oxide coating layer was 93.3%, the crystal structure of the coating layer was rock salt crystalline phase, and the doping depth of Ta was 1.8 pm.

[0164] Example 9

[0165] Different from Example 1 is that:

[0166] Step (2) uses the sintered product Li 1.3 Ta 0.3 Mn 0.4 O2is 5%, according to the molar ratio (Ta:Mn:Li=0.3:0.4:1.3), tantalum dioxide (500 nm), manganese carbonate (1 pm) and lithium carbonate (1 pm) are weighed, and then transferred to the three-dimensional mixer together with the precursor to mix uniformly, and the mixture is obtained.

[0167] The subsequent operation is the same as Example 1.

[0168] The positive electrode material prepared in this example includes a base material, a transition layer on the surface of the base material, and a lithium-rich oxide coating layer on the surface of the transition layer. The general formula of the base material is LiNi 0.95 Co 0.025 Mn 0.025 O2, the transition layer is Li(Ni 0.95 Co 0.025 Mn 0.025 0.998 Ta 0.002 O 2-σ , and the lithium-rich oxide coating layer is Li 1.3 Ta 0.3 Mn 0.4 O2; the specific surface area of the positive electrode material is 0.45 m 2 / g, the median particle size D 50 was 10.21 pm.

[0169] The thickness of the transition layer was 1.9 pm, the thickness of the lithium-rich oxide coating layer was 19.5 nm, the thickness uniformity of the lithium-rich oxide coating layer was 93.3%, the crystal structure of the coating layer was rock salt crystalline phase, and the doping depth of Ta was 1.8 pm.

[0170] Example 10

[0171] Different from Example 1 is that:

[0172] ​The base material in step (1) is LiNi 0.95 Co 0.025 Mn 0.025 O2, which is replaced by LiNi 0.95 Co 0.025 Al 0.025 O2.

[0173] The subsequent operations are the same as in Example 1.

[0174] The positive electrode material prepared in this example comprises a base material, a transition layer on the surface of the base material, and a lithium-rich oxide coating layer on the surface of the transition layer. The base material has a general formula of LiNi 0.95 Co 0.025 Al 0.025 O2, the transition layer is Li(Ni 0.95 Co 0.025 Al 0.025 ) 0.997 Nb 0.003 O 2-σ , σ is 0.08, and the lithium-rich oxide coating layer is Li 1.3 Nb 0.3 Mn 0.4 O2. The specific surface area of the positive electrode material is 0.52 m 2 / g, and the median particle size D 50 is 10.24 μm.

[0175] The thickness of the transition layer is 2.3 μm, the thickness of the lithium-rich oxide coating layer is 18.9 nm, the thickness uniformity of the lithium-rich oxide coating layer is 93%, the crystal structure of the coating layer is rock salt crystalline phase, and the doping depth of Nb is 2.2 μm.

[0176] Comparative Example 1

[0177] The difference between this example and Example 1 is that:

[0178] (1) 10 g of base material (LiNi 0.95 Co 0.025 Mn 0.025 O2, D 50 = 10.25 μm) is weighed and transferred to an alkaline solution with a pH of 7.5 under stirring for displacement reaction for 10 min, then filtered and dried at 100°C to obtain a precursor.

[0179] The positive electrode material prepared in this example comprises a base material, a transition layer on the surface of the base material, and a lithium-rich oxide coating layer on the surface of the transition layer. The base material has a general formula of LiNi 0.95 Co 0.025 Mn 0.025 O2, the transition layer is Li(Ni0.95 Co 0.025 Mn 0.025 ) 0.997 Nb 0.003 O2, the lithium-rich oxide coating layer is Li 1.3 Nb 0.3 Mn 0.4 O2; the specific surface area of the positive electrode material is 0.43 m 2 / g, and the median particle size D 50 is 10.38 μm.

[0180] The thickness of the transition layer is 0.8 μm, the thickness of the lithium-rich oxide coating layer is 23 nm, the thickness uniformity of the lithium-rich oxide coating layer is 60.5%, the crystal structure of the coating layer is rock salt crystalline phase, and the doping depth of Nb is 1.9 μm.

[0181] Comparative Example 2

[0182] Different from Example 1 is that:

[0183] (3) The mixture is transferred to a muffle furnace, and first sintered at 300°C for 5 h, and then heated to 700°C for continuous sintering for 10 h under an air atmosphere.

[0184] The positive electrode material prepared in the present comparative example comprises a base material, a transition layer on the surface of the base material, and a lithium-rich oxide coating layer on the surface of the transition layer. The general formula of the base material is LiNi 0.95 Co 0.025 Mn 0.025 O2, the transition layer is Li(Ni 0.95 Co 0.025 Mn 0.025 ) 0.996 Nb 0.004 O 2-σ , σ is 0.01, and the lithium-rich oxide coating layer is Li 1.3 Nb 0.3 Mn 0.4 O2; the specific surface area of the positive electrode material is 0.38 m 2 / g, and the median particle size D 50 is 10.34 μm.

[0185] The thickness of the transition layer is 0.03 μm, the thickness of the lithium-rich oxide coating layer is 23 nm, the thickness uniformity of the lithium-rich oxide coating layer is 65%, the crystal structure of the coating layer is rock salt crystalline phase, and the doping depth of Nb is 1.9 μm.

[0186] Comparative Example 3

[0187] Different from Example 1 is that:

[0188] The precursor after the displacement reaction is directly sintered without step (2).

[0189] The positive electrode material prepared in the present comparative example comprises a base material and a transition layer on the surface of the base material, the base material has a general formula of LiNi 0.95 Co 0.025 Mn 0.025 O2, and the transition layer has a general formula of LiNi 0.95 Co 0.025 Mn 0.025 O 2-σ 2, and σ is 0.02; the specific surface area of the positive electrode material is 0.52 m 2 / g, and the median particle size D 50 is 10.24 μm.

[0190] The thickness of the transition layer is 2.2 μm.

[0191] Comparative Example 4

[0192] (1) 10 g of the base material (LiNi 0.95 Co 0.025 Mn 0.025 O2, D 50 = 10.25 μm) was weighed, and the sintered product Li 1.3 Nb 0.3 Mn 0.4 O2 was obtained, wherein the mass content of the base material was 0.5%; the niobium oxide (D 50 = 1.5 μm), manganese carbonate (D 50 = 1.5 μm) and lithium hydroxide (D 50 = 2 μm) were weighed according to the molar ratio (Nb:Mn:Li = 0.3:0.4:1.3), and then the base material and the weighed materials were transferred to a three-dimensional mixer to mix uniformly to obtain a mixture.

[0193] (2) The mixture was transferred to a muffle furnace, and nitrogen was introduced; the mixture was first sintered at 300°C for 5 h, and then the temperature was increased to 700°C for further sintering for 10 h.

[0194] (3) The sintered product was cooled, shaped and sieved to obtain the positive electrode material.

[0195] The positive electrode material prepared in the present comparative example comprises a base material and a lithium-rich oxide coating layer on the surface of the base material, the base material has a general formula of LiNi 0.95 Co 0.025 Mn 0.025 O2, and the lithium-rich oxide coating layer has a general formula of LiNi 1.3 Nb 0.3 Mn 0.4 O2; the specific surface area of the positive electrode material is 0.46 m2 / g, the median particle size D 50 was 10.48 μm.

[0196] The thickness of the lithium-rich oxide coating layer was 23 nm, the thickness uniformity of the lithium-rich oxide coating layer was 47%, the crystal structure of the coating layer was rock salt crystalline phase, and the doping depth of Nb was 2.3 μm.

[0197] Comparative Example 5

[0198] (1) 10 g of the base material (LiNi 0.95 Co 0.025 Mn 0.025 O2, D50=10.27 μm) was transferred to an acetic acid solution (hydrogen ion concentration of 10 -6 mol / L) with a pH of 6 under stirring at room temperature for displacement reaction for 10 min, and then filtered and dried at 100°C to obtain a precursor.

[0199] (2) The sintered product Li 1.3 Mn 0.7 O2 was taken as the base material with a mass content of 0.5%, and manganese carbonate (D 50 =1.5 μm) and lithium hydroxide (D 50 =2 μm) were weighed according to the molar ratio (Mn:Li=0.7:1.3), and then transferred to a three-dimensional mixer together with the precursor to obtain a mixture.

[0200] (3) The mixture was transferred to a muffle furnace, nitrogen was introduced, and then sintered at 300°C for 5 h, and then sintered at 700°C for 10 h.

[0201] (4) The sintered product was cooled, shaped and sieved to obtain a positive electrode material.

[0202] The positive electrode material prepared in the comparative example comprises a base material, a transition layer on the surface of the base material, and a lithium-rich oxide coating layer on the surface of the transition layer, the general formula of the base material is LiNi 0.95 Co 0.025 Mn 0.025 O2, the transition layer is LiNi 0.95 Co 0.025 Mn 0.025 O 2-σ , σ is 0.001, and the lithium-rich oxide coating layer is Li 1.3 Mn 0.7 O2; the specific surface area of the positive electrode material is 0.53 m 2 / g, the median particle size D 50 is 10.32 μm.

[0203] The thickness of the transition layer is 1.9 μm, the thickness of the lithium oxide-rich coating layer is 25 nm, the thickness uniformity of the lithium oxide-rich coating layer is 85.1%, and the crystal structure of the coating layer is monoclinic.

[0204] Comparative Example 6

[0205] Unlike Example 1, the base material (LiNi 0.95 Co 0.025 Mn 0.025 O2) was directly used as the positive electrode material.

[0206] The positive electrode material in the present comparative example includes a base material, and the general formula of the base material is LiNi 0.95 Co 0.025 Mn 0.025 O2. The specific surface area of the positive electrode material is 0.45 m 2 / g, and the median particle size D 50 is 10.35 μm.

[0207] Test method:

[0208] (1) Test method for particle size of positive electrode material:

[0209] The particle size distribution range of the positive electrode material was tested by a Malvern laser particle size analyzer.

[0210] (2) Test method for specific surface area of positive electrode material:

[0211] A dynamic specific surface area rapid tester JW-DX from Beijing Jingmi Gaobote Science and Technology Co., Ltd. was used for testing, and the unit was m 2 / g.

[0212] (3) Test method for SEM of positive electrode material:

[0213] The scanning electron microscope characterization was performed on a transmission electron microscope, and the operating voltage was 200 kV. The structure of the positive electrode material was observed.

[0214] (4) Test method for thickness and thickness uniformity Ψ of lithium oxide-rich coating layer:

[0215] The cross-section of 10 randomly sampled positive electrode material particles was processed by a FIB-TEM device. The average thickness (D0), the maximum thickness (D max ), and the minimum thickness (D min ) of the lithium oxide-rich coating layer were measured from 10 samples. The average thickness was taken as the thickness of the coating layer, and the uniformity Ψ of the coating layer was calculated as Ψ=100%- (D max -D min ) / D max。

[0216] (5) XPS test of the positive electrode material

[0217] X-ray photoelectron spectroscopy was used to study the oxygen defect sites and their content on the surface of the positive electrode material. The instrument model was ESCALAB 250Xi.

[0218] (6) Electrochemical performance test

[0219] The positive electrode materials obtained in Examples 1-10 and Comparative Examples 1-6 were assembled into button cells: the positive electrode material, conductive carbon, and polyvinylidene fluoride (PVDF) were added into N-methyl-2-pyrrolidone (NMP) at a mass ratio of 96:2:2, uniformly mixed to prepare a positive electrode slurry, and coated on a positive electrode current collector to form a positive electrode sheet (the sheet compaction density was 2.8 g / cm 3 ) after vacuum drying, with lithium sheet as the negative electrode, to assemble into 2016 button cells in a glove box.

[0220] In the discharge interval of 3.0-4.3 V, under the condition of 1C theoretical capacity of 250 mAh / g, the CT2001A battery detection system of Wuhan Blue Electronic Co., Ltd. was used for testing, and the test results are shown in Table 1.

[0221] Table 1 Electrochemical performance of the materials of the comparative examples and the examples

[0222]

[0223] As can be seen from Examples 1-10 in Table 1, the substrate material surface has a transition layer and a lithium-rich oxide coating layer, the transition layer has uniformly distributed oxygen defect sites, which can inhibit oxygen release and crystal structure phase transition; the transition layer contains Nb and / or Ta doping elements, which can make the crystal structure of the lithium-rich oxide coating layer more stable, which is conducive to stabilizing the crystal structure of the substrate material itself; the discharge specific capacity, the first coulombic efficiency, and the capacity retention rate of the positive electrode material are all improved, indicating that the presence of the transition layer and the lithium-rich oxide coating layer reduces the direct contact of the substrate material with the electrolyte and inhibits the occurrence of side reactions between the substrate material and the electrolyte, so that the electrochemical performance and safety performance of the positive electrode material are improved.

[0224] According to the test data of Example 1 and Comparative Example 1, it can be seen that the alkaline solution is difficult to undergo displacement reaction with lithium ions in the lattice of the substrate material, i.e., the transition layer on the surface of the substrate material cannot form uniformly distributed and abundant oxygen defect sites, so that the lithium-rich oxide coating layer on the surface of the transition layer is not uniform enough, and the electrochemical performance of the positive electrode material is deteriorated.

[0225] In Comparative Example 2, the substrate material surface was sintered in air, and the oxygen defect sites were difficult to maintain, most of which were lost, so that the lithium-rich oxide coating layer on the surface of the transition layer was not uniform enough, and the electrochemical performance of the positive electrode material was deteriorated.

[0226] Comparative Example 3 only has a transition layer, because only oxygen defect sites exist, and there is no Ta / Nb doping, so the structural stability of the transition layer itself will be poor. In addition, the surface of the transition layer is not protected by the coating layer, which makes the electrochemical performance of the positive electrode material deteriorate.

[0227] Comparative Example 4 only has a lithium-rich oxide coating layer, and the positive electrode material does not contain a transition layer with oxygen defect sites, so during the calcination process, the lithium-rich oxide coating layer is not evenly coated, and the electrochemical performance of the positive electrode material is limitedly improved, which is worse than the examples.

[0228] Comparative Example 5 does not have Nb or Ta doping, and it does not contain Ta / Nb elements. During high-temperature calcination, Mn elements diffuse into the transition layer, but the bond strength of Mn-O bond is much smaller than that of Ta / Nb-O bond. The crystal phase of the coating layer is monoclinic, and serious phase change occurs during charging and discharging, so the structural stability of the coating layer and the transition layer is poor, and the electrochemical performance of the positive electrode material is worse than that of Example 1.

[0229] Comparative Example 6 has no any treatment, and the direct contact between the base material and the electrolyte causes serious side reactions, and the surface structure of the base material is destroyed, which makes the electrochemical performance of the positive electrode material deteriorate.

[0230] The above only describes the preferred embodiments of the present application and is not intended to limit the present application. Those skilled in the art can make various modifications and changes to the present application. Any modification, equivalent replacement, improvement, etc. within the spirit and principles of the present application shall be included in the protection scope of the present application.

Claims

1. A positive electrode material, characterized by, The positive electrode material comprises: a base material, the base material being a lithium transition metal composite oxide; a transition layer on the surface of the base material, the transition layer comprising an oxide of M1 doping elements, the M1 doping elements comprising Nb and / or Ta, and the transition layer having oxygen defect sites, the transition layer having a general chemical formula of Li n2 Ni x2 Co y2 A z2 M1 w2 O 2-σ wherein 0.95≤n2≤1.2, 0.6≤x2<1, 0 A elements comprising at least one of Mn, Al, Zr, Mg and Ti; and A lithium-rich oxide coating layer on the surface of the transition layer, the chemical general formula of the lithium-rich oxide coating layer is Li 1+ a M1 b M2 c O2, wherein a+b+c=1, 0 M2 is a transition metal, and in the lithium-rich oxide coating layer, Li ions and M1 ions and / or M2 ions are mutually occupied.

2. The positive electrode material of claim 1, wherein, The positive electrode material comprises at least one of the following characteristics (1)~(2): (1) the chemical general formula of the base material is Li n1 Ni x1 Co y1 A z1 O2, wherein, 0.95≤n1≤1.2, 0.6≤x1<1, 0 y1≤0.2, 0≤z1≤0.3, x1+y1+z1=1, the A element includes at least one of Mn, Al, Zr, Mg and Ti; (2) the transition metal M2 element comprises at least one of Ni, Co, Mn, Mo and Cr.

3. The positive electrode material according to any one of claims 1-2, characterized in that, The positive electrode material comprises at least one of the following characteristics (1)~(10): (1) the median particle size of the base material is 3μm~15μm; (2) the thickness of the transition layer is 5nm~3μm; (3) the thickness of the lithium-rich oxide coating layer is 5nm~2μm; (4) the crystal structure of the lithium-rich oxide coating layer is cubic Fd-3m rock salt crystalline phase; (5) the crystal structure of the lithium-rich oxide coating layer is amorphous; (6) the doping depth of the M1 doping element is 5nm~5μm; (7) the content of the M1 doping element on the side surface of the transition layer close to the lithium-rich oxide coating layer is higher than that on the side surface of the transition layer close to the base material; (8) the positive electrode material is measured by powder XPS with Al-Kα ray, and the oxygen defect sites on the side surface of the transition layer close to the lithium-rich oxide coating layer are more than those on the side surface of the transition layer close to the base material; (9) the mass content of the lithium-rich oxide coating layer is 0.5%~5% based on 100% of the mass of the base material; (10) the thickness uniformity of the lithium-rich oxide coating layer is ≥90%.

4. The positive electrode material according to claim 3, characterized in that, The positive electrode material comprises at least one of the following characteristics (1)~(2): (1) the median particle size D50 of the positive electrode material is 3 μm to 17 μm; 50 3 μm to 17 μm; (2) the specific surface area of the positive electrode material is 0.1 m 2 / g~3m 2 / g.

5. A method for producing the positive electrode material according to any one of claims 1 to 4, characterized by, The preparation steps comprise: dispersing the base material in a weak acid solution to carry out a replacement reaction, and solid-liquid separation to obtain a precursor, the base material being a lithium transition metal composite oxide; under a protective atmosphere, a mixture containing the precursor, a dopant containing a doping element M1, an additive containing a transition metal M2, and a lithium compound is subjected to stepwise temperature sintering treatment to obtain a positive electrode material, the doping element M1 comprising Nb and / or Ta.

6. The preparation method according to claim 5, characterized in that, The method comprises at least one of the following characteristics (1)~(8): (1) the chemical general formula of the base material is Li n1 Ni x1 Co y1 A z1 O2, wherein, 0.95≤n1≤1.2, 0.6≤x1<1, 0 y1≤0.2, 0≤z1≤0.3, x1+y1+z1=1, the A element includes at least one of Mn, Al, Zr, Mg and Ti; (2) the median particle size of the base material is 3μm~15μm; (3) the weak acid solution comprises at least one of acetic acid, citric acid, phosphoric acid, and sulfurous acid; (4) the pH value of the weak acid solution is 4~6; (5) the weak acid solution further comprises water; (6) the temperature of the replacement reaction is 10℃~70℃; (7) the time of the replacement reaction is 2min~30min; (8) the solid-liquid separation comprises at least one of filtration separation and centrifugal separation.

7. The preparation method according to claim 6, characterized in that, The method further comprises: drying the solid obtained by solid-liquid separation, and the drying temperature is 80℃~110℃.

8. The production method according to claim 5 or 6, characterized by, The method comprises at least one of the following characteristics (1)~(8): (1) the dopant comprises at least one of Nb salt, Nb oxide, Ta salt and Ta oxide; (2) the transition metal M2 comprises at least one of Ni, Co, Mn, Mo and Cr. (3) the transition metal M2-containing additive comprises at least one of a carbonate of M2, a hydroxide of M2, an acetate of M2, an oxalate of M2, a sulfate of M2, a chloride of M2, a nitrate of M2; (4) the lithium-containing compound comprises at least one of lithium hydroxide, lithium carbonate, lithium nitrate, lithium acetate, lithium sulfate, lithium oxalate and lithium chloride; (5) the additive amount of the dopant containing the doping element M1, the transition metal M2-containing additive and the lithium-containing compound satisfies that the ratio of the molar amount of M1, the molar amount of M2 and the molar amount of Li is (0.2-0.5):(0.25-0.6):1; (6) the mixing condition for obtaining the mixture is that solid-phase mixing is performed at 10-50℃ for 0.3-2h; (7) the mass content of the lithium oxide-rich coating layer formed by sintering the mixture is 0.5-5% based on 100% of the mass of the base material; (8) the median particle size of the dopant, the additive and the lithium-containing compound is 0.005-5μm.

9. The production method according to claim 8, characterized by, The method comprises at least one of the following features (1)-(3): (1) the protective atmosphere comprises at least one of nitrogen, helium, neon, argon; (2) the stepwise sintering treatment comprises sintering the mixture at 200-400℃ for 1-10h, and then sintering at 500-800℃ for 2-20h; (3) the preparation method further comprises cooling, shaping and sieving the sintered product, and the shaping comprises at least one of crushing, grinding, ball milling or air crushing.

10. A lithium-ion battery, characterized by, The lithium ion battery comprises the positive electrode material of any one of claims 1-4 or the positive electrode material prepared by the method of any one of claims 5-9.

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