Positive electrode material, preparation method thereof, and lithium ion battery

Abstract

The present application provides a positive electrode material, a preparation method thereof, and a lithium-ion battery, and relates to the field of battery material technology. The positive electrode material comprises: a base material containing a lithium nickel transition metal composite oxide and a coating layer at least partially located on the surface of the base material, the coating layer comprising an Al-containing compound and a Co-containing compound. The preparation method of the positive electrode material comprises: mixing a nickel-containing transition metal composite precursor, a lithium salt, and a dopant, and performing a first sintering to obtain a base material; mixing the base material, aluminum stearate, and cobalt stearate, and performing a second sintering after heat treatment to obtain the positive electrode material. The positive electrode material adopts a reactive coating, does not require water washing, can greatly reduce the residual alkali on the surface of the high-nickel ternary positive electrode material, and improve the rate and cycle performance of the lithium battery.

Description

Technical Field

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

[0002] High nickel ternary cathode materials (Ni content ≥ 80%) have gradually become the development trend of cathode materials due to their high energy density. They meet the requirements of electric vehicles for long driving range and reduce the dependence on high-cost Co. However, as the Ni content increases, the average valence of Ni in the ternary material increases from +2 to +3. Ni 3+ Unstable, easily spontaneously reduced to Ni 2+ , resulting in an increase in Li / Ni mixing and accompanied by Li precipitation. The precipitated lithium further forms LiOH and Li2CO3 on the surface of the particles. In addition, during the synthesis of positive electrode materials, in order to compensate for the volatilization of lithium at high temperatures, excess lithium salts are usually added. Therefore, a small amount of Li2O will remain on the surface after sintering. Li2O can adsorb H2O and CO2 in the air to form LiOH and Li2CO3. Alkaline substances on the surface of high-nickel ternary materials will increase the pH of the material and affect the processing performance of the material; in addition, alkaline substances on the surface of high-nickel ternary materials are the key factor leading to rapid capacity decay.

[0003] At present, water washing is generally used in industry to reduce the residual alkali on the surface of high nickel ternary cathode materials. During the water washing process, LiOH and Li2CO3 will dissolve in water and then be removed by filtration. However, the water washing process has its inherent disadvantages. First, the Li + Will and H + First, replacement occurs, resulting in the loss of surface Li; second, it aggravates Li / Ni mixing and forms a NiO-like rock salt phase on the surface, affecting the rate performance; third, the water washing process increases the complexity of the process and produces a large amount of alkaline wastewater.

[0004] Therefore, providing a method for preparing a high-nickel ternary positive electrode material with low residual alkali without water washing has become a technical problem that needs to be solved urgently in this field. Summary of the Invention

[0005] In view of this, the present application provides a positive electrode material and a preparation method thereof, and a lithium-ion battery. The positive electrode material does not require water washing and can take into account both the rate performance and cycle performance of the positive electrode material.

[0006] To achieve the above objectives, the technical solutions of this application are as follows:

[0007] In a first aspect, the present application provides a positive electrode material, comprising a base material containing a lithium nickel transition metal composite oxide and a coating layer at least partially located on the surface of the base material, wherein the coating layer comprises an Al-containing compound and a Co-containing compound.

[0008] In combination with the first aspect, in a feasible embodiment, the positive electrode material satisfies at least one of the following conditions an:

[0009] a. The ratio of the Li content on the surface of the positive electrode material to the Li content in the bulk phase is P, 0.8≤P≤1.0;

[0010] b. The ratio of the Ni content on the surface of the positive electrode material to the Ni content in the bulk phase is Q, Q≤0.9;

[0011] c. The specific surface area of the positive electrode material is ≤ 0.5m 2 / g;

[0012] d. The surface free lithium content of the positive electrode material is ≤0.25wt%;

[0013] e. pH of the cathode material ≤ 11.8;

[0014] f. The particles of the cathode material are spherical or spherical;

[0015] g. D50 of the positive electrode material is 3-20 μm;

[0016] h. The powder particle strength of the positive electrode material is ≥50MPa;

[0017] i. The tap density of the positive electrode material is ≥ 0.2 g / cm 3 ;

[0018] j. The compaction density of the positive electrode material is ≥3g / cm 3 ;

[0019] k. The half-peak width of the (003) crystal plane of the positive electrode material is R, 0.150≤R≤0.175;

[0020] l. The XPS spectrum of the positive electrode material is in the range of 850eV-870eV, Ni 2+ The peak area is S1, Ni 3+ The peak area is S2, and S1 and S2 satisfy the following relationship: S2 / (S1+S2)≥0.70;

[0021] m. The positive electrode material relative to Li / Li + At 25°C and 3.0-4.3V, the ratio of the discharge capacity at 0.1C to the charge capacity at 0.1C is ≥91.0%, and the ratio of the discharge capacity at 0.5C to the discharge capacity at 0.1C is ≥92.5%;

[0022] n. The cathode material relative to Li / Li +At 25°C, 3.0-4.3V, and 1C rate, the capacity decay is less than 5% after 50 cycles.

[0023] In combination with the first aspect, in a feasible embodiment, the positive electrode material satisfies at least one of the following conditions ot:

[0024] o. The positive electrode material comprises a plurality of secondary particles composed of primary particles, wherein the coating layer is located on the surface of the secondary particles, the surface of the primary particles and at least one position in the gaps of the primary particles;

[0025] p. The mass ratio of the Al element, the Co element and the base material in the coating layer is (0.0005-0.005): (0.001-0.02): 1;

[0026] q. the Al-containing compound in the coating layer includes Al metal oxide and / or LiAlO2;

[0027] r. The Co-containing compound in the coating layer includes a Co metal oxide and / or LiCoO2;

[0028] s. The thickness of the coating layer is 1-50nm;

[0029] t. The coating layer further comprises a boron-containing compound, the boron-containing compound comprising B2O3, H3BO3, Li2O-B2O3, Li3BO3, Li2B4O7, Li2B2O7 and Li2B8O 13 At least one of .

[0030] In combination with the first aspect, in a feasible embodiment, the chemical formula of the lithium nickel transition metal composite oxide is Li a Ni x M y N 1-x-y O2;

[0031] Among them, 0.98≤a≤1.05, 0.80≤x<1, 0<y≤0.2, 0≤1-xy≤0.05;

[0032] M includes at least one of Co, Mn, and Al;

[0033] N includes at least one of Ti, Zr, Mg, Sr, Ba, Nb, W, and Y.

[0034] In a second aspect, the present application provides a method for preparing a positive electrode material, comprising:

[0035] Mixing a nickel-containing transition metal composite precursor, a lithium salt, and a dopant, and performing a first sintering to obtain a matrix material;

[0036] The base material, aluminum stearate and cobalt stearate are mixed, heat treated, and then sintered for a second time to obtain the positive electrode material.

[0037] In conjunction with the second aspect, in a feasible embodiment, the preparation method satisfies at least one of the following conditions AC:

[0038] A. The chemical formula of the nickel-containing transition metal composite precursor is Ni x Co t M 1-x-t (OH)2, wherein 0.80≤x<1.00, 0<t<0.2, and M comprises at least one of Mn and Al;

[0039] B. the lithium salt comprises at least one of lithium carbonate, lithium hydroxide, lithium acetate, lithium nitrate and lithium oxalate;

[0040] C. The dopant includes a compound containing at least one element of Ti, Zr, Mg, Sr, Ba, Nb, W and Y.

[0041] In conjunction with the second aspect, in a feasible embodiment, the preparation method satisfies at least one of the following conditions DF:

[0042] D. The molar ratio of the lithium element in the lithium salt to the total metal elements in the nickel-containing transition metal composite precursor and the dopant is (0.98-1.05):1;

[0043] E. The molar ratio of the metal element in the dopant to the total metal elements in the nickel-containing transition metal composite precursor and the dopant is (0-0.05):1;

[0044] F. The mass ratio of the aluminum stearate, the cobalt stearate and the matrix material is (0.015-0.15):(0.01-0.2):1.

[0045] In conjunction with the second aspect, in a feasible embodiment, the preparation method satisfies at least one of the following conditions GI:

[0046] G. The sintering atmosphere of the first sintering is oxygen, the temperature of the first sintering is 600-800°C, and the time is 3-15h;

[0047] H. The heat treatment needs to be carried out under vacuum conditions, the heat treatment temperature is 120-150°C, and the time is 3-8h;

[0048] I. The sintering atmosphere of the second sintering is oxygen, the temperature of the second sintering is 600-800°C, and the time is 3-15 hours.

[0049] In conjunction with the second aspect, in a feasible embodiment, after the second sintering, the method further includes: mixing the product of the second sintering with boric acid and performing a third sintering to obtain the positive electrode material;

[0050] The sintering atmosphere of the third sintering is oxygen, the temperature of the third sintering is 300-500° C., and the time is 3-8 hours.

[0051] In a third aspect, the present application provides a lithium-ion battery, which comprises the positive electrode material of the first aspect or the positive electrode material prepared by the preparation method described in the second aspect.

[0052] Beneficial effects of this application:

[0053] The coating material of the positive electrode material provided in this application can react with alkaline substances such as LiOH and Li2CO3 on the surface of the positive electrode material, thereby significantly reducing the residual alkali on the surface of the positive electrode material and improving the processing performance of the positive electrode material. Furthermore, since the water washing process is eliminated, there is no loss of Li on the surface of the positive electrode material (manifested as no significant difference in Li concentration between the surface Li and the bulk phase), and there is less rock salt phase (manifested as Ni 2+ The content is small, that is, S2 / (S1+S2)≥0.7), so the impedance is low and the rate performance is good; the positive electrode material has a small specific surface area, and the coating material can isolate the positive electrode material from the electrolyte, reducing the side reaction with the electrolyte, and during the coating process, part of the Co will diffuse into the surface material lattice, resulting in a decrease in the surface Ni content, so the positive electrode material exhibits excellent cycle performance.

[0054] The cathode material preparation method provided by the present application is simple in process, greatly improves production efficiency, eliminates the water washing process, and avoids the generation of wastewater. Among them, when aluminum stearate and cobalt stearate are used to coat the matrix material, the heat treatment process can melt the aluminum stearate and cobalt stearate, penetrate through the gaps between the primary particles to the surface of the primary particles, and form a preliminary coating. Then, when a second sintering is performed, the molten aluminum stearate and cobalt stearate can be decomposed to form a coating of aluminum oxide and cobalt oxide, which can further react with the residual alkali on the surface of the material to finally prepare the cathode material. DETAILED DESCRIPTION

[0055] As used herein:

[0056] "Prepared from" is synonymous with "comprising." As used herein, the terms "comprising," "including," "having," "containing," or any other variations thereof, are intended to cover a non-exclusive inclusion. For example, a composition, process, method, article, or apparatus that comprises the listed elements is not necessarily limited to only those elements but may include other elements not expressly listed or inherent to such composition, process, method, article, or apparatus.

[0057] The conjunction "consisting of" excludes any unspecified element, step, or component. If used in a claim, this phrase renders the claim closed, excluding materials other than those described, except for conventional impurities associated therewith. When the phrase "consisting of" appears in a clause of the body of a claim, rather than immediately following the subject matter, it limits only the elements described in that clause; other elements are not excluded from the claim as a whole.

[0058] When an amount, concentration, or other value or parameter is expressed as a range, a preferred range, or a range defined by a series of upper preferred values and lower preferred values, this should be understood as specifically disclosing all ranges formed by any pairing of any range upper limit or preferred value with any range lower limit or preferred value, regardless of whether the range is disclosed alone. For example, when a range of "1 to 5" is disclosed, the described range should be interpreted as including the range "1 to 4", "1 to 3", "1 to 2", "1 to 2 and 4 to 5", "1 to 3 and 5", etc. When a numerical range is described herein, unless otherwise stated, the range is intended to include its end values and all integers and fractions within the range.

[0059] In these examples, parts and percentages are by mass unless otherwise indicated.

[0060] "Parts by mass" refers to the basic unit of measurement used to express the mass ratio of multiple components. One part can represent any unit of mass, such as 1g or 2.689g. If we say that the mass of component A is a parts and the mass of component B is b parts, this means the ratio of the mass of component A to the mass of component B is a:b. Alternatively, we could say that the mass of component A is aK and the mass of component B is bK (K is an arbitrary number representing a multiplication factor). It's important to note that, unlike parts by mass, the sum of the mass of all components is not limited to 100 parts.

[0061] "And / or" is used to indicate that one or both of the stated situations may occur, for example, A and / or B includes (A and B) and (A or B).

[0062] At present, water washing is the most effective method in the industry to remove residual alkali on the surface of high nickel ternary cathode materials. However, water washing will increase the complexity of the process, reduce production efficiency, and produce a large amount of wastewater during the water washing process. Water washing will also have an adverse effect on the performance of the material: (1) Li in the material during the water washing process + Will and H + (1) Water washing can cause the surface Li to be replaced, resulting in the loss of surface Li; (2) Water washing can destroy the surface structure of the material and form a NiO-like salt rock phase, resulting in increased impedance and decreased rate and cycle performance; (3) Water washing can increase the specific surface area and cause a decrease in cycle stability. Therefore, this application proposes a positive electrode material that does not require water washing and has excellent performance and a preparation method thereof.

[0063] In a first aspect, the present application provides a positive electrode material comprising a base material containing a lithium nickel transition metal composite oxide and a coating layer at least partially located on the surface of the base material, wherein the coating layer comprises metal oxides of Al and Co and / or a lithium ion conductor compound.

[0064] As an optional technical solution of this application, the chemical formula of the lithium nickel transition metal composite oxide is Li a Ni x M y N 1-x-y O2, wherein 0.98≤a≤1.05, 0.80≤x<1, 0<y≤0.2, 0≤1-xy≤0.05, M includes at least one of Co, Mn, and Al, and N is a doping element including at least one of Ti, Zr, Mg, Sr, Ba, Nb, W, and Y. When 1-xy=0, this indicates that no doping element is present in the lithium-nickel transition metal composite oxide.

[0065] As an optional technical solution of the present application, the present application uses TOF-SIM to perform in-depth analysis of the positive electrode material. The ratio of the Li content on the surface of the positive electrode material to the Li content in the bulk phase is P, 0.8≤P≤1.0, for example, it can be 0.82, 0.85, 0.88, 0.9, 0.93, 0.95, 0.97 or other values within the above range, which are not limited here.

[0066] It should be noted that the Li content on the surface of the positive electrode material refers to the Li content within a depth of 2 nm from the surface of the positive electrode material particles, while the Li content in the bulk refers to the Li content within a depth of 50 nm from the surface of the positive electrode material particles. A P value within this range indicates that there is no significant difference between the Li content on the surface of the positive electrode material and the Li content in the bulk. This further indicates that since the water washing process is omitted, there is no significant Li loss from the surface of the positive electrode material, and this does not significantly affect the battery rate.

[0067] As an optional technical solution of the present application, the ratio of the Ni content on the surface of the positive electrode material to the Ni content in the bulk phase is Q, Q≤0.9, for example, it can be 0.2, 0.4, 0.6, 0.8 or other values within the above range, which is not limited here.

[0068] It can be understood that the Ni content on the surface of the positive electrode material refers to the Ni content within the range from the surface of the positive electrode material particles to a depth of 2nm, while the Ni content in the bulk phase refers to the Ni content within the range from the surface of the positive electrode material particles to a depth of 50nm. The value of Q within the above range indicates that the Ni content on the surface of the positive electrode material is lower than the Ni content in the bulk phase, which further indicates that the lower Ni content on the surface of the positive electrode material is conducive to improving the cycling performance of the material.

[0069] As an optional technical solution of this application, the specific surface area of the positive electrode material is ≤0.5m 2 / g, for example, it can be 0.1m 2 / g, 0.2m 2 / g, 0.3m 2 / g, 0.4m 2 / g or other values within the above range, which are not limited here, and more preferably ≤0.35m 2 / g.

[0070] As an optional technical solution of the present application, the surface free lithium content in the positive electrode material is ≤0.25wt%, for example, it can be 0.05wt%, 0.1wt%, 0.15wt%, 0.2wt% or other values within the above range, which are not limited here, and is more preferably ≤0.18wt%.

[0071] It is understood that the surface free lithium content in the positive electrode material refers to the free lithium content within a range from the surface of the positive electrode material particles to a depth of 2nm. If the free lithium content is too high, excess residual alkali will form on the surface of the positive electrode material particles. This will affect battery performance by increasing irreversible capacity loss and deteriorating cycle performance. It will also affect the processing performance of the positive electrode material, which is reflected in the easy formation of jelly during the preparation of the slurry, affecting the coating effect.

[0072] As an optional technical solution of the present application, the pH value of the positive electrode material is ≤11.8, for example, it can be 7, 9, 11 or other values within the above range, which is not limited here.

[0073] As an optional technical solution of the present application, the particles of the positive electrode material are spherical or quasi-spherical.

[0074] As an optional technical solution of the present application, the D50 of the positive electrode material is 3-20 μm, for example, it can be 3 μm, 5 μm, 10 μm, 15 μm, 20 μm or any value between 3-20 μm, which is not limited here.

[0075] As an optional technical solution of the present application, the powder particle strength of the positive electrode material is ≥50 MPa, for example, it can be 50 MPa, 52 MPa, 55 MPa, 60 MPa or other values within the above range, which are not limited here.

[0076] As an optional technical solution of this application, the tap density of the positive electrode material is ≥0.2g / cm 3 , for example, it can be 0.2g / cm 3 , 0.25g / cm 3 , 0.3g / cm 3 , 0.35g / cm 3 Or other values within the above range, which are not limited here.

[0077] As an optional technical solution of this application, the compaction density of the positive electrode material is ≥3g / cm 3 , for example, it can be 3g / cm 3 , 4g / cm 3 , 4.5g / cm 3 , 5g / cm 3 Or other values within the above range, which are not limited here.

[0078] It can be understood that through the reasonable selection of the pH value, particle shape, average particle size, powder particle strength, tap density and compaction density of the positive electrode material, the positive electrode material has excellent electrochemical properties and meets the needs of battery use. It also has excellent processing performance, preventing the slurry from being too viscous or even forming a jelly-like state during the processing process, making it difficult to coat.

[0079] As an optional technical solution of the present application, the half-peak width of the (003) crystal plane of the positive electrode material is R, 0.150≤R≤0.175, for example, it can be 0.155, 0.16, 0.165, 0.17 or other values within the above range, which are not limited here.

[0080] As an optional technical solution of this application, the XPS spectrum of the positive electrode material is in the range of 850eV-870eV, Ni 2+ The peak area is S1, Ni 3+The peak area is S2, and S1 and S2 satisfy the following relationship: S2 / (S1+S2)≥0.70, for example, it can be 0.70, 0.75, 0.8, 0.85, 0.9, 0.95 or other values within the above range, which are not limited here.

[0081] It should be noted that, due to Ni 2+ The ionic radius is 0.069nm and Li + The ionic radius of Li is similar to 0.076nm, Ni will occupy the 3a position of Li, and Li will occupy the 3b position of Ni. + Ni in the layer 2+ The greater the concentration, the more serious the Li / Ni mixing is, which leads to Li + The more difficult it is to deintercalate, the worse the electrochemical performance. Therefore, the XRD or XPS test results reflect the degree of Li / Ni mixing to a certain extent. When the test results are within the above range, it indicates that the Li / Ni mixing of the positive electrode material is small.

[0082] As an optional technical solution of this application, the positive electrode material is relatively Li / Li + At 25°C and 3.0-4.3V, the ratio of the discharge capacity at 0.1C to the charge capacity at 0.1C is ≥91.0%, for example, 91%, 91.2%, 91.5%, 91.7%, 91.9%, or other values within the above range, which are not limited here; the ratio of the discharge capacity at 0.5C to the discharge capacity at 0.1C is ≥92.5%, for example, 92.8%, 93%, 93.3%, 93.5%, or other values within the above range, which are not limited here. These ratios indicate that the positive electrode material of the present application can improve the rate performance during charge and discharge.

[0083] As an optional technical solution of the present application, the positive electrode material has a capacity decay of <5% after 50 cycles at 25°C, 3.0-4.3V, and 1C rate, which also shows that the positive electrode material of the present application can improve the cycle performance.

[0084] As an optional technical solution of the present application, the positive electrode material includes secondary particles composed of multiple primary particles, and the coating layer is located at at least one position on the surface of the secondary particles, the surface of the primary particles, and the gaps between the primary particles.

[0085] As an optional technical solution of the present application, the mass ratio of the Al element and the Co element in the coating layer to the base material is (0.0005-0.005): (0.001-0.02):1, for example, it can be 0.0005:0.001:1, 0.001:0.001:1, 0.002:0.005:1, 0.003:0.01:1, 0.005:0.0.2:1 or other values within the above range, which are not limited here.

[0086] As an optional technical solution of the present application, the Al-containing compound in the coating layer includes Al metal oxide and / or LiAlO2.

[0087] As an optional technical solution of the present application, the Co-containing compound in the coating layer includes Co metal oxide and / or LiCoO2.

[0088] It should be noted that LiAlO2 and LiCoO2 are substances generated by the further reaction of metal oxides of Al and Co with the residual alkali on the surface of the positive electrode material. They are lithium ion conductor compounds with certain electrical conductivity.

[0089] As an optional technical solution of the present application, the thickness of the coating layer is 1-50 nm, for example, it can be 1 nm, 5 nm, 10 nm, 20 nm, 30 nm, 40 nm, 50 nm or any value between 1-50 nm, which is not limited here.

[0090] As an optional technical solution of the present application, the coating layer further includes a boron-containing compound, which includes B2O3, H3BO3, Li2O-B2O3, Li3BO3, Li2B4O7, Li2B2O7 and Li2B8O 13 At least one of .

[0091] In a second aspect, the present application also provides a method for preparing a positive electrode material, comprising: mixing a nickel-containing transition metal composite precursor, a lithium salt and a dopant, and performing a first sintering to obtain a base material; mixing the base material, aluminum stearate and cobalt stearate, performing a heat treatment, and performing a second sintering to obtain the positive electrode material.

[0092] The positive electrode material of the present application adopts a reactive coating, and aluminum stearate and cobalt stearate are used as raw materials, because: the reaction between the compounds of Al and Co and the residual alkali on the surface of the positive electrode material is a solid phase reaction. The solid phase reaction mainly occurs at the interface between the two phases, so the degree of reaction between the coating material and the residual alkali is greatly affected by the contact between the two. Conventional aluminum oxide and cobalt oxide have very high melting points. When used as coating materials, they are always in a solid state, so they can often only contact and react with the residual alkali on the surface of the secondary particles of the positive electrode material, and cannot reduce the residual alkali on the surface of the primary particles. Therefore, conventional aluminum oxide and cobalt oxide coatings are not significantly effective in reducing the residual alkali on the surface of polycrystalline materials. Aluminum stearate and cobalt stearate have low melting points (about 120°C). When heat treated under vacuum, aluminum stearate and cobalt stearate begin to melt and penetrate the gaps between the primary particles to the surface of the primary particles. After high-temperature sintering, aluminum stearate and cobalt stearate decompose to form aluminum oxide and cobalt oxide. Aluminum oxide and cobalt oxide further react with LiOH and Li2CO3 to reduce the residual alkali on the surface of the material. Therefore, using aluminum stearate and cobalt stearate as coating materials can not only reduce the residual alkali on the surface of secondary particles, but also reduce the residual alkali on the surface of primary particles, making the material better meet processing requirements.

[0093] As an optional technical solution of the present application, the chemical formula of the nickel-containing transition metal composite precursor is Ni x Co t M 1-x-t (OH)2, wherein 0.80≤x<1.00, 0<t<0.2, and M includes at least one of Mn and Al.

[0094] As an optional technical solution of the present application, the lithium salt includes at least one of lithium carbonate, lithium hydroxide, lithium acetate, lithium nitrate and lithium oxalate.

[0095] As an optional technical solution of the present application, the dopant includes a compound containing at least one element of Ti, Zr, Mg, Sr, Ba, Nb, W and Y.

[0096] As an optional technical solution of the present application, the molar ratio of the lithium element in the lithium salt to the total metal elements in the nickel-containing transition metal composite precursor and the dopant is (0.98-1.05):1, for example, it can be 0.98:1, 1:1, 1.02:1, 1.03:1, 1.05:1 or any value between (0.98-1.05):1, which is not limited here.

[0097] As an optional technical solution of the present application, the molar ratio of the metal element in the dopant to the total metal elements in the nickel-containing transition metal composite precursor and the dopant is (0-0.05):1, for example, it can be 0:1, 0.01:1, 0.03:1, 0.05:1 or any value between (0-0.05):1, and is not limited here. Among them, when the molar ratio is 0:1, it indicates that no dopant is added, and the matrix material can be prepared using only the precursor and the lithium salt.

[0098] As an optional technical solution of the present application, the mass ratio of the aluminum stearate, the cobalt stearate and the matrix material is (0.015-0.15): (0.01-0.2): 1, for example, it can be 0.015:0.01:1, 0.02:0.05:1, 0.05:0.08:1, 0.1:0.1:1, 0.12:0.15:1, 0.15:0.5:1 or any value between (0.015-0.15): (0.01-0.2): 1, which is not limited here.

[0099] As an optional technical solution of the present application, the sintering atmosphere of the first sintering is air, the temperature of the first sintering is 600-800°C, for example, it can be 600°C, 650°C, 700°C, 750°C, 800°C or any value between 600-800°C, and the time of the first sintering is 3-15h, for example, it can be 3h, 5h, 8h, 10h, 12h, 15h or any value between 3-15h, which is not limited here.

[0100] As an optional technical solution of the present application, the heat treatment needs to be carried out under vacuum conditions, the heat treatment temperature is 120-150°C, for example, it can be 120°C, 130°C, 140°C, 150°C or any value between 120-150°C, and the heat treatment time is 3-8h, for example, it can be 3h, 4h, 5h, 6h, 7h, 8h or any value between 3-8h, which is not limited here.

[0101] It should be noted that heat treatment at a low temperature of 120-150°C can melt aluminum stearate and cobalt stearate, and penetrate into the surface of the primary particles through the gaps between the primary particles, fully infiltrating the positive electrode material and increasing the contact between the coating substance and the material.

[0102] As an optional technical solution of the present application, the sintering atmosphere of the second sintering is oxygen, the temperature of the second sintering is 600-800°C, for example, it can be 600°C, 650°C, 700°C, 750°C, 800°C or any value between 600-800°C, and the time of the second sintering is 3-15h, for example, it can be 3h, 5h, 8h, 10h, 12h, 15h or any value between 3-15h, which is not limited here.

[0103] As an optional technical solution of the present application, after the second sintering, the method further includes: mixing the product of the second sintering with boric acid, and performing a third sintering to obtain the positive electrode material.

[0104] It should be noted that the present application prepares a coating layer containing Al and Co on the surface of the base material, and then further reacts it with boric acid to prepare a coating layer containing a boron compound. This can further improve the ionic conductivity of the coating layer and reduce the electronic conductivity. The lower electronic conductivity can prevent electron transitions at the positive electrode / electrolyte interface, making it have good resistance to electrolyte decomposition. The higher ionic conductivity is conducive to improving the electrical performance of the positive electrode material. At the same time, the introduction of boron can form a more stable SEI film on the surface of the positive electrode material, which helps to improve the thermal stability of the positive electrode material.

[0105] Further preferably, the sintering atmosphere of the third sintering is oxygen, the temperature of the third sintering is 300-500°C, for example, it can be 300°C, 350°C, 400°C, 450°C, 500°C or any value between 300-500°C, and the time of the third sintering is 3-8h, for example, it can be 3h, 4h, 5h, 6h, 7h, 8h or any value between 3-8h, which is not limited here.

[0106] In a third aspect, an embodiment of the present application further provides a lithium-ion battery, comprising the above-mentioned positive electrode material or the positive electrode material prepared by the above-mentioned preparation method.

[0107] The embodiments of the present invention will be described in detail below with reference to specific examples, but those skilled in the art will appreciate that the following examples are intended only to illustrate the present invention and should not be construed as limiting the scope of the present invention. Where specific conditions are not specified in the examples, the methods were performed according to conventional conditions or the conditions recommended by the manufacturer. Where the manufacturers of the reagents or instruments are not specified, they are all conventional products that can be purchased commercially.

[0108] Example 1

[0109] The method for preparing the positive electrode material of this embodiment includes:

[0110] ① Weigh 300g of ternary precursor Ni0.90 Co 0.05 Mn 0.05 (OH)2 and 135.3 g of lithium hydroxide monohydrate were mixed evenly and sintered at 750°C for 12 h in an oxygen atmosphere to obtain an active material matrix.

[0111] ② Weigh 300g of active substance matrix, 9.8g of aluminum stearate, and 6.4g of cobalt stearate, mix thoroughly, place in a vacuum oven, keep warm at 140°C for 5h, and cool to room temperature.

[0112] ③ Transfer the above materials to an atmosphere furnace and sinter at 750℃ for 10h in an oxygen atmosphere.

[0113] The above preparation method is used to prepare a positive electrode material whose surface is coated with Al compounds (Al2O3, LiAlO2) and Co compounds (Co3O4, LiCoO2), wherein the mass of Al elements and Co elements in the positive electrode material coating layer are 0.1% and 0.2% of the mass of the positive electrode base material, respectively.

[0114] Example 2

[0115] The method for preparing the positive electrode material of this embodiment includes:

[0116] ① Weigh 300g of ternary precursor Ni 0.90 Co 0.05 Mn 0.05 (OH)2 and 135.3 g of lithium hydroxide monohydrate were mixed evenly and sintered at 750°C for 12 h in an oxygen atmosphere to obtain an active material matrix.

[0117] ② Weigh 300g of active substance matrix, 9.8g of aluminum stearate, and 12.8g of cobalt stearate, mix thoroughly, place in a vacuum oven, keep warm at 140°C for 5h, and cool to room temperature.

[0118] ③ Transfer the above materials to an atmosphere furnace and sinter at 750℃ for 10h in an oxygen atmosphere.

[0119] The above preparation method is used to prepare a positive electrode material whose surface is coated with Al compounds (Al2O3, LiAlO2) and Co compounds (Co3O4, LiCoO2), wherein the mass of Al elements and Co elements in the positive electrode material coating layer are 0.1% and 0.4% of the mass of the positive electrode base material, respectively.

[0120] Example 3

[0121] The method for preparing the positive electrode material of this embodiment includes:

[0122] ① Weigh 300g of ternary precursor Ni 0.90 Co 0.05Mn 0.05 (OH)2 and 135.3 g of lithium hydroxide monohydrate were mixed evenly and sintered at 750°C for 12 h in an oxygen atmosphere to obtain an active material matrix.

[0123] ② Weigh 300g of active substance matrix, 19.6g of aluminum stearate, and 6.4g of cobalt stearate, mix thoroughly, place in a vacuum oven, keep warm at 140°C for 5h, and cool to room temperature.

[0124] ③ Transfer the above materials to an atmosphere furnace and sinter at 750℃ for 10h in an oxygen atmosphere.

[0125] The above preparation method is used to prepare a positive electrode material whose surface is coated with Al compounds (Al2O3, LiAlO2) and Co compounds (Co3O4, LiCoO2). The mass of Al elements and Co elements in the positive electrode material coating layer are 0.2% and 0.2% of the mass of the positive electrode base material, respectively.

[0126] Example 4

[0127] The method for preparing the positive electrode material of this embodiment includes:

[0128] ① Weigh 300g of ternary precursor Ni 0.90 Co 0.05 Mn 0.05 (OH)2 and 135.3 g of lithium hydroxide monohydrate were mixed evenly and sintered at 750°C for 12 h in an oxygen atmosphere to obtain an active material matrix.

[0129] ② Weigh 300g of active substance matrix, 9.8g of aluminum stearate, and 6.4g of cobalt stearate, mix thoroughly, place in a vacuum oven, keep warm at 140°C for 5h, and cool to room temperature.

[0130] ③ Transfer the above materials to an atmosphere furnace and sinter at 750℃ for 10h in an oxygen atmosphere.

[0131] ④ The material obtained in step ③ was mixed evenly with 1.5 g of boric acid, and then transferred to an atmosphere furnace and sintered at 500°C for 5 h in an oxygen atmosphere.

[0132] The above preparation method produces a positive electrode material having a substrate coated with an Al compound (Al2O3, LiAlO2), a Co compound (Co3O4, LiCoO2), and a B compound (B2O3, Li3BO3, etc.). The Al, Co, and B elements in the coating layer are 0.1%, 0.2%, and 0.087% of the positive electrode substrate mass, respectively.

[0133] Example 5

[0134] The method for preparing the positive electrode material of this embodiment includes:

[0135] ① Weigh 300g of ternary precursor Ni 0.90 Co 0.05 Mn 0.05 (OH)2, 135.3g lithium hydroxide monohydrate, and 7.5g tungsten oxide were mixed evenly and sintered at 750°C for 12h in an oxygen atmosphere to obtain a tungsten-doped active material matrix.

[0136] ② Weigh 300 g of tungsten-doped active material matrix, 19.6 g of aluminum stearate, and 6.4 g of cobalt stearate, mix thoroughly, place in a vacuum oven, keep warm at 140°C for 5 h, and cool to room temperature.

[0137] ③ Transfer the above materials to an atmosphere furnace and sinter at 750℃ for 10h in an oxygen atmosphere.

[0138] The above preparation method produces a tungsten-doped positive electrode material coated with an Al compound (Al2O3, LiAlO2) and a Co compound (Co3O4, LiCoO2). The Al and Co elements in the coating layer are 0.2% and 0.2% of the mass of the tungsten-doped base material, respectively.

[0139] Example 6

[0140] The method for preparing the positive electrode material of this embodiment includes:

[0141] ① Weigh 300g of ternary precursor Ni 0.80 Co 0.15 Mn 0.05 (OH)2 and 135.3 g of lithium hydroxide monohydrate were mixed evenly and sintered at 800 °C for 15 h in an oxygen atmosphere to obtain an active material matrix.

[0142] ② Weigh 300g of active substance matrix, 19.6g of aluminum stearate, and 6.4g of cobalt stearate, mix thoroughly, place in a vacuum oven, keep warm at 150°C for 3h, and cool to room temperature.

[0143] ③ Transfer the above materials to an atmosphere furnace and sinter at 700℃ for 3h in an oxygen atmosphere.

[0144] The positive electrode material whose surface is coated with Al-containing compounds (Al2O3, LiAlO2) and Co-containing compounds (Co3O4, LiCoO2) is prepared by the above preparation method.

[0145] Example 7

[0146] The method for preparing the positive electrode material of this embodiment includes:

[0147] ① Weigh 300g of ternary precursor Ni 0.98 Co 0.02 (OH)2 and 135.3 g of lithium hydroxide monohydrate were mixed evenly and sintered at 600 °C for 12 h in an oxygen atmosphere to obtain an active material matrix.

[0148] ② Weigh 300g of active substance matrix, 19.6g of aluminum stearate, and 6.4g of cobalt stearate, mix thoroughly, place in a vacuum oven, keep warm at 150°C for 3h, and cool to room temperature.

[0149] ③ Transfer the above materials to an atmosphere furnace and sinter at 600℃ for 10h in an oxygen atmosphere.

[0150] The positive electrode material whose surface is coated with Al-containing compounds (Al2O3, LiAlO2) and Co-containing compounds (Co3O4, LiCoO2) is prepared by the above preparation method.

[0151] Comparative Example 1

[0152] The positive electrode material of this comparative example is prepared using a common water washing process, which includes:

[0153] ① Weigh 300g of ternary precursor Ni 0.90 Co 0.05 Mn 0.05 (OH)2 and 135.3 g of lithium hydroxide monohydrate were mixed evenly and then heat-treated at 780°C in an oxygen atmosphere for 12 h to obtain an active material matrix.

[0154] ② The above active substance matrix was mixed with water in a mass ratio of 1:1, stirred for 10 minutes, and then filtered and dried.

[0155] ③ The dried sample was transferred to an atmosphere furnace and heat treated at 750°C for 10 h in an oxygen atmosphere, and then naturally cooled to room temperature to prepare the positive electrode material.

[0156] Comparative Example 2

[0157] The positive electrode material of this comparative example is prepared by a wet coating process containing Al and Co, and the preparation method comprises:

[0158] ① Weigh 300g of ternary precursor Ni 0.90 Co 0.05 Mn 0.05 (OH)2 and 135.3 g of lithium hydroxide monohydrate were mixed evenly and then heat-treated at 750°C for 12 h in an oxygen atmosphere to obtain an active material matrix.

[0159] ② Take 2.37g of aluminum nitrate and 1.86g of cobalt nitrate, dissolve them in 30g of water to prepare an aqueous solution containing aluminum and cobalt.

[0160] ③ Take 300g of active material matrix, place it in a disperser, stir it, and slowly add the above-mentioned aqueous solution containing aluminum and cobalt. Continue stirring for 30 minutes after the addition. Then transfer the above sample to an atmosphere furnace and heat treat it at 750℃ for 10 hours in an oxygen atmosphere.

[0161] In this comparative example, a positive electrode material with Al and Co coated on the surface is obtained, wherein the contents of Al and Co on the surface are 0.1% and 0.2% respectively.

[0162] Comparative Example 3

[0163] The positive electrode material of this comparative example is obtained by conventional Al2O3+Co3O4 coating, and the preparation method includes:

[0164] ① Weigh 300g of ternary precursor Ni 0.90 Co 0.05 Mn 0.05 (OH)2 and 135.3 g of lithium hydroxide monohydrate were mixed evenly and then heat-treated at 750°C for 12 h in an oxygen atmosphere to obtain an active material matrix.

[0165] ② Weigh 300g of active material matrix, 0.57g of aluminum oxide, and 0.82g of cobalt trioxide, mix thoroughly, place in a vacuum oven, keep warm at 140℃ for 5h, and then cool to room temperature.

[0166] ③ The above materials were transferred to an atmosphere furnace and heat treated at 750°C for 10 hours under an oxygen atmosphere to obtain a positive electrode material coated with Al and Co, wherein the surface Al and Co contents were 0.1% and 0.2%, respectively.

[0167] In this comparative example, a positive electrode material with Al and Co coated on the surface is obtained, wherein the contents of Al and Co on the surface are 0.1% and 0.2% respectively.

[0168] Comparative Example 4

[0169] The positive electrode material of this comparative example is obtained by a one-step sintering method, which comprises:

[0170] ① Weigh 300g of ternary precursor Ni 0.90 Co 0.05 Mn 0.05 (OH)2 and 135.3 g of lithium hydroxide monohydrate were mixed evenly and then heat-treated at 750°C for 12 h in an oxygen atmosphere to obtain an active material matrix.

[0171] ② Weigh 300g of active material matrix, 9.8g of aluminum stearate, and 6.4g of cobalt stearate, mix thoroughly, and then transfer directly to an atmosphere furnace for heat treatment at 750°C for 10h under an oxygen atmosphere.

[0172] In this comparative example, a positive electrode material with Al and Co coated on the surface is obtained, wherein the contents of Al and Co on the surface are 0.1% and 0.2% respectively.

[0173] Comparative Example 5

[0174] The positive electrode material of this comparative example is obtained by using aluminum stearate alone, and the preparation method includes:

[0175] ① Weigh 300g of ternary precursor Ni 0.90 Co 0.05 Mn 0.05 (OH)2 and 135.3 g of lithium hydroxide monohydrate were mixed evenly and then heat-treated at 750°C for 12 h in an oxygen atmosphere to obtain an active material matrix.

[0176] ② Weigh 300g of active substance matrix and 9.8g of aluminum stearate, mix thoroughly, place in a vacuum oven, keep warm at 140℃ for 5h, and then cool to room temperature.

[0177] ③ Transfer the above materials to an atmosphere furnace and heat treat them at 750℃ for 10h in an oxygen atmosphere.

[0178] In this comparative example, a positive electrode material with Al coated on the surface was obtained, wherein the content of Al on the surface was 0.1%.

[0179] Comparative Example 6

[0180] The positive electrode material of this comparative example is obtained by using cobalt stearate alone, and the preparation method includes:

[0181] ① Weigh 300g of ternary precursor Ni 0.90 Co 0.05 Mn 0.05 (OH)2 and 135.3 g of lithium hydroxide monohydrate were mixed evenly and then heat-treated at 750°C for 12 h in an oxygen atmosphere to obtain an active material matrix.

[0182] ② Weigh 300g of active substance matrix and 6.4g of cobalt stearate, mix thoroughly, place in a vacuum oven, keep warm at 140℃ for 5h, and then cool to room temperature.

[0183] ③ Transfer the above materials to an atmosphere furnace and heat treat them at 750℃ for 10h in an oxygen atmosphere.

[0184] In this comparative example, a positive electrode material with a surface coated with Co was obtained, wherein the content of surface Co was 0.2%.

[0185] Comparative Example 7

[0186] The positive electrode material of this comparative example is obtained by using cobalt stearate + TiO2, and the preparation method includes:

[0187] ① Weigh 300g of ternary precursor Ni 0.90 Co 0.05 Mn 0.05 (OH)2 and 135.3 g of lithium hydroxide monohydrate were mixed evenly and then heat-treated at 750°C for 12 h in an oxygen atmosphere to obtain an active material matrix.

[0188] ② Weigh 300g of active material matrix, 9.8g of aluminum stearate, and 4.27g of tetrabutyl titanate, mix thoroughly, place in a vacuum oven, keep warm at 140°C for 5h, and then cool to room temperature.

[0189] ③ Transfer the above materials to an atmosphere furnace and heat treat them at 750℃ for 10h in an oxygen atmosphere.

[0190] In this comparative example, a positive electrode material with Al and Ti coated on the surface is obtained, wherein the contents of Al and Ti on the surface are 0.1% and 0.2% respectively.

[0191] Comparative Example 8

[0192] The positive electrode material of this comparative example is obtained by using a combination of cobalt stearate and magnesium stearate, and the preparation method includes:

[0193] ① Weigh 300g of ternary precursor Ni 0.90 Co 0.05 Mn 0.05 (OH)2 and 135.3 g of lithium hydroxide monohydrate were mixed evenly and then heat-treated at 750°C for 12 h in an oxygen atmosphere to obtain an active material matrix.

[0194] ② Weigh 300g of active substance matrix, 6.4g of cobalt stearate, and 7.30g of magnesium stearate, mix thoroughly, place in a vacuum oven, keep warm at 140°C for 5h, and then cool to room temperature.

[0195] ③ Transfer the above materials to an atmosphere furnace and heat treat them at 750℃ for 10h in an oxygen atmosphere.

[0196] In this comparative example, a positive electrode material with Mg and Co coated on the surface is obtained, wherein the contents of Mg and Co on the surface are 0.1% and 0.2% respectively.

[0197] Comparative Example 9

[0198] The positive electrode material of this comparative example is not coated, and the preparation method includes:

[0199] ① Weigh 300g of ternary precursor Ni 0.90 Co 0.05 Mn 0.05 (OH)2 and 135.3 g of lithium hydroxide monohydrate were mixed evenly and then heat-treated at 750°C for 12 h in an oxygen atmosphere to obtain an active material matrix.

[0200] ② Weigh 300g of active material matrix, place it in a vacuum oven, keep it at 140℃ for 5h, and then cool it to room temperature.

[0201] ③ Transfer the above materials to an atmosphere furnace and heat treat them at 750℃ for 10h in an oxygen atmosphere.

[0202] This comparative example obtains a positive electrode material whose surface is not coated with Al and Co.

[0203] The present application conducted the following performance tests on the above Examples 1-3 and Comparative Examples 1-9:

[0204] A potentiometric titrator was used to measure the residual alkali on the surface of the material. The specific method was as follows: 5 g of sample and 100 mL of water were weighed, placed in a beaker, and the beaker was sealed with a sealing film. After stirring at 450 rpm for 15 minutes, the mixture was filtered. 10 mL of the filtrate was taken with a pipette, diluted to 40 mL with pure water, and then titrated with a standard hydrochloric acid solution on an automatic potentiometric titrator using an equivalence point titration method. Two inflection points appeared during the test, and the volumes of hydrochloric acid consumed corresponding to the two inflection points were V1 and V2. The residual carbonate and hydroxide contents in the sample were calculated based on the amount of standard hydrochloric acid solution consumed.

[0205]

[0206]

[0207]

[0208] c(HCl)——concentration of hydrochloric acid standard titration solution, mol / L;

[0209] V1——the volume of hydrochloric acid standard titrant consumed in titration to the first sudden jump point, mL;

[0210] V2 is the volume of the hydrochloric acid standard titrant consumed from the first sudden jump point to the second sudden jump point, mL;

[0211] V3——the volume of the filtrate, here V3=10mL;

[0212] V4——Filtrate is fixed to a certain volume, here V4=100mL;

[0213] m——mass of the sample, g.

[0214] The pH of the material was tested using a pH meter. The procedure was as follows: 5g of sample and 45ml of deionized water were placed in a 100ml beaker. Ultrasonic cleaning was performed for 5 minutes. The sample was then removed and allowed to stand for 10 minutes before filtering. The pH of the filtered solution was then tested using a Mettler-Toledo laboratory pH meter.

[0215] The electrochemical performance of the material was evaluated using a coin-shaped half-cell. The following steps were used: the positive electrode material, conductive carbon black, and PVDF were weighed in a 93:5:2 mass ratio. N-methyl-2-pyrrolidone (NMP) was added to a 50% solids content. The mixture was then dispersed in a high-speed disperser to form a viscous slurry. The slurry was evenly coated onto aluminum foil using a spatula. After drying in an 80°C oven, the slurry was rolled and cut into 14mm diameter positive electrode sheets. A 16mm lithium sheet was used as the negative electrode, a Celgard polypropylene film as the separator, and a 1 mol / L LiPF6 carbonate solution as the electrolyte. The coin-shaped half-cell was assembled in an argon-filled glove box. Capacity and cycling performance were tested at 25°C and 45°C, respectively, at 3.0-4.3V using a LAND battery testing system. The nominal capacity at 1C was set to 220 mAh / g.

[0216] XPS test of high nickel positive electrode material: X-ray photoelectron spectroscopy (XPS) can analyze the depth range from the surface of the material to about 5nm to 10nm, so the concentration and valence state of each element in the surface area can be quantitatively analyzed. XPS can be performed using ULVAC-PHI X-ray photoelectron spectroscopy (model: QuanteraII). X-ray source: Al monochromatic 100μm, 25W, 15kV; no surface etching; photoelectron extraction angle: 45°; bonding energy correction: set the CC peak of the C1s spectrum to 284.6eV; XPS is measured on the high nickel material of the present invention, and according to the obtained XPS spectrum, the peak Ni2P of the Ni bonding part appearing at the binding energy of 850eV to 870eV is 3 / 2 Perform peak separation and curve fitting to obtain Ni 2+ Peak area and Ni 3+ Peak area.

[0217] Characterization of the spatial distribution of Ni and Li in high nickel cathode materials: A time-of-flight secondary ion mass spectrometer (TOF-SIMS 4, IONTOF) was used to collect high spatial resolution TOF-SIMS depth profiles. + The peak intensity of the fragment represents the content of Ni, 7Li + The fragment peak intensity represents the Li content. The sputtering depth is 50nm. The ratio of the surface Ni content of the material to the Ni content in the bulk can be approximated by the top layer (sputtering depth < 2nm) 58Ni + The peak intensity of the fragments and the sputtering depth of 58Ni at 50nm + Similarly, the ratio of the Li content on the surface of the material to the Li content in the bulk phase can be approximated by the topmost layer (sputtering depth < 2nm) 7Li + The peak intensity of the fragments and the sputtering depth of 7Li at 50nm +It is expressed as the ratio of the peak intensities of the fragments.

[0218] Test of the specific surface area of the high nickel cathode material: Using the nitrogen physical adsorption method, the sample tube was installed on a specific surface area tester (model: Micromeritics Tristar II 3020) for testing.

[0219] Test of particle size D50 of high nickel cathode material: The cathode material was uniformly dispersed in an aqueous solution and then tested using a laser particle size analyzer (model: Malvern Instruments Ltd MASTERSIZER3000).

[0220] Powder Particle Strength Test Method for High-Nickel Cathode Material: The particle strength of the cathode material was measured using a dynamic ultramicrohardness tester (model: DUH-211S). Each sample was measured 15 times and the average value was calculated.

[0221] The tap density test method of nickel positive electrode material is as follows: the positive electrode material is placed in the steel cylinder of the tap density tester. After vibrating for 10 minutes, the depth of the material is tested. The volume after vibration is calculated by the depth of the test. The weight of the positive electrode material is then divided by the volume after vibration to obtain the tap density.

[0222] The compaction density test method for high-nickel cathode materials is as follows: The cathode material is prepared as a slurry and applied to aluminum foil. After drying, it is rolled to form a plate. A plate is cut with a circular cutter and its thickness and weight are measured. The cathode material is then washed off, air-dried, and the remaining aluminum foil is weighed and weighed. Areal density = (weight after rolling - aluminum foil weight) / cut area; compaction density = areal density / (thickness after rolling - aluminum foil thickness).

[0223] The performance results of Examples 1-6 and Comparative Examples 1-9 are shown in Table 1 and Table 2.

[0224] Table 1

[0225]

[0226]

[0227]

[0228] Table 2

[0229]

[0230]

[0231] According to the results in Table 1 and Table 2, by comparing Example 1 with Comparative Examples 1 and 2, it can be seen that: although conventional water washing process or wet coating can reduce the residual alkali of the material, water will destroy the surface structure of the positive electrode material during the material preparation process, resulting in material performance degradation. Specifically, it increases the specific surface area and reduces the particle strength, thereby aggravating the capacity decay during the cycle; on the other hand, it causes the loss of surface Li and Ni. 2+ The content increases and a rock salt phase is formed, so the impedance of the prepared material is large, which is manifested as a low first efficiency and poor rate performance.

[0232] By comparing Example 1 with Example 4, it can be seen that the present application can further reduce the residual alkali and improve the electrochemical performance by continuing to coat the boron-containing compound on the Al / Co coating layer; by comparing Example 1 with Example 5, it can be seen that the present application significantly improves the cycle stability of the positive electrode material by adding a dopant (such as tungsten) to the base material of the positive electrode, and the 50-cycle capacity attenuation is greatly reduced.

[0233] By comparing Example 1 with Comparative Example 3, it can be seen that the conventional coating using Al and Co oxides is not as effective in reducing residual alkali as Example 1. The free lithium content of the final material is greater than 0.25, and the pH is greater than 11.8, which easily causes the slurry to gel during processing. In addition, the Al and Co coating layers only exist on the surface of the secondary particles, and the surface of the primary particles is not coated. Therefore, the capacity decay is aggravated during the cycle process, and the capacity decay reaches 7.0% after 50 cycles.

[0234] Comparing Example 1 with Comparative Example 4, it can be seen that: in Comparative Example 4, after the coating material is mixed with the matrix, it is directly subjected to high-temperature sintering treatment. The aluminum stearate and cobalt stearate have no time to penetrate into the gaps between the primary particles before they are decomposed into corresponding oxides, so the effect is similar to that of Comparative Example 3. This also shows that the low-temperature heat treatment in the preparation method of the present application is very necessary, and the low-temperature heat treatment followed by high-temperature sintering can not only reduce the residual alkali on the surface of the secondary particles, but also reduce the residual alkali on the surface of the primary particles. Moreover, since the coating is more uniform and complete, the material exhibits excellent cyclic stability.

[0235] Comparing Example 1 with Comparative Examples 5 and 6, it can be seen that the effect of using Al or Co alone in reducing residual alkali is not as good as Al / Co co-coating. Further analysis found that Al is more effective than Co in removing Li2CO3, while Co is more effective than Al in removing LiOH. Therefore, Al / Co co-coating is more effective in reducing residual alkali than Al or Co coating alone. In addition, although Al coating alone can reduce the attenuation of capacity during the cycle, it will increase impedance and reduce the first effect (Comparative Example 5); although Co coating alone improves the first effect and rate performance, the cycle performance is poor. Therefore, Al / Co co-coating has better comprehensive electrochemical performance (Comparative Example 6).

[0236] Comparing Example 1 with Comparative Examples 7 and 8, it can be seen that in Comparative Examples 7 and 8, Al / Ti coating and Mg / Co coating were used respectively, and their residual alkali was higher than that of Example 1, and their electrochemical performance was not as good as that of Example 1, which shows that Al / Co co-coating can better reduce the surface residual alkali.

[0237] By comparing Example 1 with Comparative Example 9, it can be seen that the Al / Co coating method adopted in the present application can improve the performance of the material, which is specifically manifested as follows: 1. Al / Co coating reduces the residual alkali on the surface, reducing the free lithium from 0.31% to 0.23%, and the pH from 12.05 to 11.79, meeting the processing requirements; 2. Part of the Co will diffuse into the lattice on the surface of the material, reducing the Ni content on the surface of the material, and the Al / Co coating can isolate the material from contact with the electrolyte, so that the capacity attenuation during the cycle is greatly reduced.

[0238] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, rather than to limit it. Although the present invention has been described in detail with reference to the above embodiments, those skilled in the art should understand that they can still modify the technical solutions described in the above embodiments, or replace some or all of the technical features therein with equivalents. However, these modifications or replacements do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments of the present invention.

[0239] Furthermore, those skilled in the art will appreciate that although some embodiments herein include certain features included in other embodiments but not others, combinations of features from different embodiments are intended to be within the scope of the present invention and to form different embodiments. For example, in the claims above, any of the claimed embodiments may be used in any combination. The information disclosed in this background section is intended solely to enhance understanding of the overall background of the present invention and should not be construed as an admission or any form of implication that such information constitutes prior art known to those skilled in the art.

Claims

1. A positive electrode material, characterized in that It comprises a base material containing a lithium nickel transition metal composite oxide and a coating layer at least partially located on the surface of the base material, wherein the coating layer comprises an Al-containing compound and a Co-containing compound; The XPS spectrum of the positive electrode material is in the range of 850eV-870eV, Ni 2+ The peak area is S1, Ni 3+ The peak area is S2, and S1 and S2 satisfy the following relationship: S2 / (S1+S2)≥0.70; The surface free lithium content in the positive electrode material is ≤0.25 wt %, and the ratio of the Li content on the surface of the positive electrode material to the Li content in the bulk phase is P, 0.8≤P≤1.0; The Al-containing compound includes Al metal oxide and / or LiAlO2; The Co-containing compound includes Co metal oxide and / or LiCoO2; The base material, aluminum stearate and cobalt stearate are mixed, heat treated, and then sintered for a second time to obtain the positive electrode material.

2. The positive electrode material according to claim 1, wherein It satisfies at least one of the following conditions ak: a. The ratio of the Ni content on the surface of the positive electrode material to the Ni content in the bulk phase is Q, Q≤0.9; b. The specific surface area of the positive electrode material is ≤ 0.5m 2 / g; c. pH of the cathode material ≤ 11.8; d. The particles of the positive electrode material are spherical or spherical; e. D of the positive electrode material 50 3-20μm; f. The powder particle strength of the positive electrode material is ≥50MPa; g. The tap density of the positive electrode material is ≥0.2g / cm 3 ; h. The compaction density of the positive electrode material is ≥3g / cm 3 ; i. The half-peak width of the (003) crystal plane of the positive electrode material is R, 0.150≤R≤0.175; j. The positive electrode material relative to Li / Li + At 25°C and 3.0-4.3V, the ratio of 0.1C discharge capacity to 0.1C charge capacity is ≥91.0%, and the ratio of 0.5C discharge capacity to 0.1C discharge capacity is ≥92.5%; k. The positive electrode material relative to Li / Li + At 25°C, 3.0-4.3V, and 1C rate, the capacity decay is less than 5% after 50 cycles.

3. The positive electrode material according to claim 1, wherein It meets at least one of the following conditions ot: o. The positive electrode material comprises a plurality of secondary particles composed of primary particles, wherein the coating layer is located on the surface of the secondary particles, the surface of the primary particles and at least one position in the gaps of the primary particles; p. The mass ratio of the Al element, the Co element and the base material in the coating layer is (0.0005-0.005): (0.001-0.02): 1; s. The thickness of the coating layer is 1-50nm; t. The coating layer further comprises a boron-containing compound, the boron-containing compound comprising B2O3, H3BO3, Li2O-B2O3, Li3BO3, Li2B4O7, Li2B2O7 and Li2B8O 13 At least one of .

4. The positive electrode material according to any one of claims 1 to 3, characterized in that The general chemical formula of the lithium nickel transition metal composite oxide is Li a Ni x M y N 1-x-y O2; Among them, 0.98≤a≤1.05, 0.80≤x<1, 0<y≤0.2, 0≤1-xy≤0.05; M includes at least one of Co, Mn, and Al; N includes at least one of Ti, Zr, Mg, Sr, Ba, Nb, W, and Y.

5. A method for preparing the positive electrode material according to any one of claims 1 to 4, characterized in that: include: Mixing a nickel-containing transition metal composite precursor, a lithium salt, and a dopant, and performing a first sintering to obtain a matrix material; The base material, aluminum stearate and cobalt stearate are mixed, heat treated, and then sintered for a second time to obtain the positive electrode material; Among them, the XPS spectrum of the positive electrode material is in the range of 850eV-870eV, Ni 2+ The peak area is S1, Ni 3+ The peak area is S2, and S1 and S2 satisfy the following relationship: S2 / (S1+S2)≥0.

70.

6. The preparation method according to claim 5, wherein It meets at least one of the following conditions AC: A. The chemical formula of the nickel-containing transition metal composite precursor is Ni x Co t M 1-x-t (OH)2, wherein 0.80≤x<1.00, 0<t<0.2, and M comprises at least one of Mn and Al; B. the lithium salt comprises at least one of lithium carbonate, lithium hydroxide, lithium acetate, lithium nitrate and lithium oxalate; C. The dopant includes a compound containing at least one element of Ti, Zr, Mg, Sr, Ba, Nb, W and Y.

7. The preparation method according to claim 5, wherein It satisfies at least one of the following conditions DF: D. The molar ratio of the lithium element in the lithium salt to the total metal elements in the nickel-containing transition metal composite precursor and the dopant is (0.98-1.05):1; E. The molar ratio of the metal element in the dopant to the nickel-containing transition metal composite precursor and the total metal element in the dopant is (0-0.05): 1; F. The mass ratio of the aluminum stearate, the cobalt stearate and the matrix material is (0.015-0.15): (0.01-0.2):

1.

8. The preparation method according to claim 5, wherein It meets at least one of the following GI conditions: G. The sintering atmosphere of the first sintering is oxygen, the temperature of the first sintering is 600-800°C, and the time is 3-15h; H. The heat treatment needs to be carried out under vacuum conditions, the heat treatment temperature is 120-150°C, and the time is 3-8h; I. The sintering atmosphere of the second sintering is oxygen, the temperature of the second sintering is 600-800°C, and the time is 3-15 hours.

9. The preparation method according to any one of claims 5 to 8, characterized in that After the second sintering, the method further includes: mixing the product of the second sintering with boric acid and performing a third sintering to obtain the positive electrode material; The sintering atmosphere of the third sintering is oxygen, the temperature of the third sintering is 300-500° C., and the time is 3-8 hours.

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

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