Modified positive electrode material, preparation method thereof and lithium ion battery

Abstract

The application relates to the field of lithium ion battery materials, and discloses a modified positive electrode material, a preparation method thereof and a lithium ion battery. The preparation comprises the following steps: (1) carrying out a co-precipitation reaction of a Ni-containing salt and an element M-containing salt on the surface of a nickel-based precursor to obtain a nickel-based precursor containing a coating layer, and carrying out first sintering of the nickel-based precursor containing the coating layer and a first lithium salt to obtain a nickel-based positive electrode material matrix; (2) carrying out second sintering of the nickel-based positive electrode material matrix, a second lithium salt and a modification aid to obtain a secondary lithium intercalation modification product; and (3) carrying out surface coating treatment of the secondary lithium intercalation modification product by using a metal element-containing solution and a phosphate-containing solution, and then carrying out third sintering to obtain the modified positive electrode material. The prepared modified positive electrode material has a multilayer structure, the surface Ni content is lower than that of the matrix, the NiO impurity phase is less, the surface residual alkali content is low, the surface structure is stable, and the cycle stability is excellent.

Description

Technical Field

[0001] This invention relates to the field of lithium-ion battery materials, specifically to a modified cathode material, its preparation method, and a lithium-ion battery. Background Technology

[0002] With the pursuit of high energy density, high-nickel cathode materials are being used more and more widely. However, as the Ni content increases, high-nickel cathode materials still have certain drawbacks: compared with medium and low-nickel cathode materials, firstly, high-nickel cathode materials have high residual alkali on the surface and a certain amount of NiO rock salt phase, resulting in high electrochemical impedance; secondly, in the high delithiation state, the surface Ni of high-nickel cathode materials... 4+ The proportion is large, while Ni 4+ Easily reduced to Ni 2+ The formation of NiO rock salt phase and O2 promotes electrolyte decomposition and gas production, and the formation of NiO rock salt phase blocks Li + The migration path leads to a further increase in impedance.

[0003] Therefore, it is urgent to solve the problems of high-nickel cathode materials, such as high surface Ni content, high surface residual alkali content, high DC internal resistance, unsatisfactory surface structure stability, and the need to improve cycle performance. Summary of the Invention

[0004] This invention addresses the problems of high residual alkali content on the surface, rapid increase in DC internal resistance, unsatisfactory surface structure stability, and the need to improve cycle performance of existing high-nickel cathode materials by providing a modified cathode material, its preparation method, and a lithium-ion battery.

[0005] To achieve the above objectives, a first aspect of the present invention provides a method for preparing a modified cathode material, comprising:

[0006] (1) A co-precipitation reaction is carried out on the surface of a nickel-based precursor containing element M salt and optional Ni salt to obtain a nickel-based precursor with a coating layer, and the nickel-based precursor with the coating layer and a first lithium salt are subjected to a first sintering to obtain a nickel-based cathode material matrix.

[0007] (2) The nickel-based cathode material matrix, the second lithium salt, and the modifying agent are subjected to a second sintering to obtain a secondary lithium intercalation modified product;

[0008] (3) The secondary lithium intercalation modified product is surface coated with a solution containing metal elements and a solution containing phosphate, and then a third sintering is performed to obtain the modified cathode material.

[0009] In the nickel-based precursor containing the coating layer, the chemical composition of the coating layer satisfies the chemical formula Ni x M y(OH)2, wherein element M is selected from at least one of Mn, Ti, Zr, Co, Al, Mg, Sr, Ca, Ba, Y, W, La, Mo and Nb; x+y=1, 0≤x≤0.7.

[0010] The second aspect of the present invention provides a modified cathode material prepared by the method described in the first aspect above.

[0011] A third aspect of the present invention provides a lithium-ion battery comprising the modified cathode material described in the aforementioned third aspect.

[0012] The modified cathode material prepared by this invention has a multilayer structure, with a lower Ni content on the surface than the matrix, fewer NiO impurities, and low residual alkali content, resulting in a slow increase in DC internal resistance during charge and discharge. Furthermore, the modified cathode material prepared by this method exhibits a stable surface structure, fewer side reactions with the electrolyte, and excellent cycle stability. Attached Figure Description

[0013] The accompanying drawings are provided to further illustrate the invention and form part of the specification. They are used together with the following detailed description to explain the invention, but do not constitute a limitation thereof. In the drawings:

[0014] Figure 1 The graph shows the capacity retention test results of lithium-ion batteries assembled using the cathode materials prepared in Examples 1, 4, 5, Comparative Example 1, and Comparative Example 2, respectively, during cycling at 25°C. Detailed Implementation

[0015] The endpoints and any values ​​of the ranges disclosed herein are not limited to the precise ranges or values, and these ranges or values ​​should be understood to include values ​​close to these ranges or values. For numerical ranges, the endpoint values ​​of the various ranges, the endpoint values ​​of the various ranges and individual point values, and individual point values ​​can be combined with each other to obtain one or more new numerical ranges, which should be considered as specifically disclosed herein.

[0016] The first aspect of this invention provides a method for preparing a modified cathode material, comprising:

[0017] (1) A co-precipitation reaction is carried out on the surface of a nickel-based precursor containing element M salt and optional Ni salt to obtain a nickel-based precursor with a coating layer, and the nickel-based precursor with the coating layer and a first lithium salt are subjected to a first sintering to obtain a nickel-based cathode material matrix.

[0018] (2) The nickel-based cathode material matrix, the second lithium salt, and the modifying agent are subjected to a second sintering to obtain a secondary lithium intercalation modified product;

[0019] (3) The secondary lithium intercalation modified product is surface coated with a solution containing metal elements and a solution containing phosphate, and then a third sintering is performed to obtain the modified cathode material.

[0020] In the nickel-based precursor containing the coating layer, the chemical composition of the coating layer satisfies the chemical formula Ni x M y (OH)2, wherein element M is selected from at least one of Mn, Ti, Zr, Co, Al, Mg, Sr, Ca, Ba, Y, W, La, Mo and Nb; x+y=1, 0≤x≤0.7.

[0021] According to the present invention, in the preparation method of the modified cathode material, in step (1), the nickel-based precursor may be selected from at least one of Ni-containing hydroxides, Ni-containing hydroxyoxides, and Ni-containing oxides. Preferably, the nickel-based precursor may be selected from Ni... a R b (OH)2, Ni a R b O(OH) and Ni a R b At least one of O2; wherein element R may be selected from at least one of Mn, Ti, Zr, Co, Al and W; a+b=1, 0.8≤a<1. When the nickel-based precursor has the above chemical composition, it can form a structurally stable layered oxide.

[0022] In this invention, the nickel-based precursor, having the above-mentioned chemical composition, preferably has R selected from at least one of Al, Co, W and Mn, a+b=1, and 0.9≤a<1, which can enable the prepared modified cathode material to have higher energy density and cycle life.

[0023] In this invention, the source of the nickel-based precursor is broadly defined. It can be obtained in-house by methods known in the art, such as co-precipitation, or it can be obtained through commercial channels, as long as the above-mentioned chemical composition requirements are met.

[0024] According to the present invention, in the preparation method of the modified cathode material, in step (1), the element M can be selected from at least one of Mn, Ti, Zr, Co, Al, Mg, Sr, Y, W, La and Mo, preferably at least one of Co, Mn and Al, which can improve the surface stability of the prepared cathode material and improve the cycle life of the cathode material.

[0025] According to the present invention, in the preparation method of the modified cathode material, in step (1), the Ni-containing salt can preferably be a Ni sulfate and / or nitrate, and the element M-containing salt can preferably be an element M sulfate and / or nitrate.

[0026] According to the present invention, in the preparation method of the modified cathode material, the method and parameters used for the coprecipitation reaction in step (1) are relatively broadly defined, and methods and parameters known in the art for coprecipitation reactions using metal salts in alkaline solutions can be used. According to a preferred embodiment of the present invention, a dispersion containing the nickel-based precursor is first placed in a reaction vessel, then a solution containing the elemental M salt, optionally containing a Ni salt, is added, along with NaOH solution and ammonia water, to carry out the coprecipitation reaction. After the reaction is completed, the solid product is washed and dried to obtain the nickel-based precursor with the coating layer.

[0027] According to the present invention, preferably, the conditions for the coprecipitation reaction include: a pH value of 10-13 and a temperature of 40-80°C.

[0028] According to the present invention, in the preparation method of the modified cathode material, in step (1), the above-mentioned coating layer is formed by co-precipitation on the surface of the nickel-based precursor, which can protect the material structure within the coating layer and improve the overall structural stability of the material. Preferably, the ratio of Ni content (weight percentage) in the nickel-based precursor containing the coating layer to the total Ni content (weight percentage) in the nickel-based precursor is (0.5-0.97):1, which can reduce the Ni content on the material surface, reduce the formation of NiO phase during sintering, and improve the cycle life of the obtained cathode material.

[0029] According to the present invention, in the preparation method of the modified cathode material, in step (1), the weight ratio of the first lithium salt to the nickel-based precursor with the coating layer is (40-65):100, preferably (45-55):100.

[0030] According to the present invention, in the preparation method of the modified cathode material, in step (1), the conditions for the first sintering include: a temperature of 600-900℃, preferably 600-800℃; and a constant temperature time of 4-20h, preferably 6-15h.

[0031] According to the present invention, in the preparation method of the modified cathode material, in step (2), the modifying agent can be selected from at least one of the oxides, hydroxides, and phosphates of the modifying element, wherein the modifying element can be selected from at least one of Mn, Ti, Zr, Zn, Co, Al, Mg, Ce, Sr, Ca, Ba, Y, W, La, Mo, Sn, Se, and Nb. Preferably, the modifying element can be selected from at least one of W, Sr, Zr, and Al. In the present invention, the modifying agent can promote uniform lithium intercalation and reduce the sintering temperature.

[0032] According to the present invention, in the preparation method of the modified cathode material, in step (2), the weight ratio of the modified additive to the nickel-based cathode material matrix, based on the metal elements contained, is (0.01-2):100, preferably (0.02-0.2):100. The amount of the modified additive fed within the above range can better promote uniform lithium intercalation and sintering, and save costs.

[0033] According to the present invention, in the preparation method of the modified cathode material, in step (2), the weight ratio of the second lithium salt to the nickel-based cathode material matrix, calculated as Li element, is (0.01-0.5):100, preferably (0.03-0.2):100.

[0034] In this invention, the first lithium salt and the second lithium salt are broadly defined, and can be any conventional lithium source used in the preparation of cathode materials in the art, including but not limited to at least one of lithium carbonate, lithium hydroxide, lithium nitrate, lithium phosphate, lithium fluoride and lithium sulfate, with lithium carbonate and / or lithium hydroxide being preferred.

[0035] According to the present invention, in the preparation method of the modified cathode material, in step (2), the nickel-based cathode material matrix, the second lithium salt, and the modifying agent are sintered together in a second sintering process. The modifying agent reacts with the second lithium salt on the surface of the nickel-based cathode material matrix to form lithium oxide, which can improve the surface stability of the material and promote the uniform diffusion of the second lithium salt into the interior of the nickel-based cathode material matrix, improve the internal structure of the material, and further enhance the overall structural stability of the material.

[0036] According to the present invention, the conditions for the second sintering include: a temperature of 500-850°C, preferably 500-750°C; and a holding time of 2-15 hours, preferably 4-10 hours.

[0037] According to the present invention, the second sintering is carried out in an oxidizing atmosphere, preferably, the oxidizing atmosphere having an O2 content of 20.0-99.5% by volume.

[0038] According to the present invention, in the preparation method of the modified cathode material, in step (3), the metal element in the metal-containing solution can react with phosphate and element Li to generate lithium oxide containing phosphate. Further, the metal element in the metal-containing solution can be selected from at least one of Al, Ti, La, Zr, Cr, Fe, Nb, Co, Ge, and Sn, preferably at least one of Al, Zr, Ti, Co, and Ge, which can improve the surface chemical composition of the material and increase the lithium-ion diffusion rate on the material surface.

[0039] According to the present invention, in the preparation method of the modified cathode material, in step (3), the metal element in the solution containing the metal element can be added in the form of a soluble metal salt, including but not limited to nitrates, organic salts, chlorates or chlorides of the metal element.

[0040] According to the present invention, in the preparation method of the modified cathode material, in step (3), the phosphate is preferably selected from at least one of ammonium dihydrogen phosphate, ammonium hydrogen phosphate and triammonium phosphate.

[0041] According to the present invention, in the preparation method of the modified cathode material, in step (3), the weight ratio of metal element in the solution containing metal element to secondary lithium intercalation modification product is (0.01-0.9):100, preferably (0.1-0.4):100. The amount of metal element in the solution containing metal element meets the above range, which is beneficial to the formation of lithium oxide with stable phase structure.

[0042] According to the present invention, in the preparation method of the modified cathode material, in step (3), the molar ratio of the metal element in the solution containing the metal element to the phosphate in the solution containing the phosphate is (0.1-2):1, which is conducive to the formation of a structurally stable lithium oxide with phosphate ions, improving the structural stability of the outer layer of the material, and increasing the lithium ion diffusion rate of the outer layer of the material.

[0043] In this invention, the concentration of the metal element in the solution containing the metal element is preferably 0.01-0.5 mol / L.

[0044] In this invention, the concentration of phosphate in the phosphate-containing solution is preferably 0.01-0.5 mol / L.

[0045] According to the present invention, in the preparation method of the modified cathode material, in step (3), the surface coating treatment of the secondary lithium intercalation modified product using a solution containing metal elements and a solution containing phosphate is preferably carried out by spray drying. This allows the solution containing metal elements and the solution containing phosphate to be spray-coated onto the surface of the secondary lithium intercalation modified product while simultaneously drying. In the present invention, the order in which the solution containing metal elements and the solution containing phosphate are added during the coating treatment is not particularly limited. For example, one method can be used: first, spray the solution containing metal elements onto the surface of the secondary lithium intercalation modified product and dry it simultaneously; then, spray the solution containing phosphates onto the product and dry it simultaneously. Another method can be used: first, spray the solution containing phosphates onto the surface of the secondary lithium intercalation modified product and dry it simultaneously; then, spray the solution containing metal elements onto the product and dry it simultaneously. Yet another method can be used: mix the solution containing metal elements and the solution containing phosphates, feed them together, spray the mixture onto the surface of the secondary lithium intercalation modified product, and dry it simultaneously.

[0046] According to the present invention, in the preparation method of the modified cathode material, in step (3), the metal elements and phosphates are uniformly coated on the surface of the secondary lithium intercalation modified product through the coating treatment. Preferably, the conditions for the coating treatment include: a temperature of 70-180℃, a vacuum degree of -60 to -90 kPa, and a time of 10-120 min.

[0047] According to a preferred embodiment of the present invention, the surface coating treatment is performed in a vacuum spray mixer. Preferably, the secondary lithium intercalation modified product is placed in the mixing vessel of the vacuum spray mixer, and stirring is started (stirring rate is 10-500 rpm). The secondary lithium intercalation modified product is subjected to a first spray drying using the solution containing metal elements (temperature is 70-180℃, vacuum degree is -60 to -90 kPa, stirring time is 5-60 min), and then stirring is continued (stirring rate is 100-600 rpm). Then, a second spray drying is performed using the solution containing phosphates (temperature is 70-180℃, vacuum degree is -60 to -90 kPa, stirring time is 5-60 min). The resulting coated product is discharged from the vacuum spray mixer and then subjected to a third sintering to obtain the modified cathode material.

[0048] According to the present invention, in the preparation method of the modified cathode material, in step (3), a lithium oxide with phosphate groups can be formed through the third sintering. This oxide has a stable structure, is not easily reacted with the electrolyte, and has a high lithium-ion diffusion rate, which can improve the stability of the outer layer structure of the material and reduce the increase in internal resistance of the material. Preferably, the conditions for the third sintering include: a temperature of 250-750℃ and a holding time of 2-10h.

[0049] According to the present invention, in the preparation method of the modified cathode material, step (3) further includes washing and drying the product obtained by the third sintering to obtain the modified cathode material product.

[0050] The modified cathode material preparation method provided by the present invention produces a modified cathode material with a multilayer structure, a lower Ni content on the surface than the matrix, less NiO impurity phase, low residual alkali content on the surface, slow DC internal resistance growth during charge and discharge, and stable surface structure with few side reactions with the electrolyte, resulting in excellent cycle stability and thus improving the electrical performance of lithium-ion batteries.

[0051] The second aspect of the present invention provides a modified cathode material prepared by the method described in the first aspect above.

[0052] The modified cathode material provided by the present invention has a multilayer structure, including a nickel-based oxide core, a nickel-based metal lithium compound layer and an outermost lithium oxide layer distributed from the inside to the outside.

[0053] According to the present invention, the residual alkali content of the modified cathode material is ≤0.5wt%, preferably 0.15-0.25wt%.

[0054] In this invention, the residual alkali content of the cathode material refers to the percentage of the total weight of Li2CO3 and LiOH on the surface of the cathode material to the total weight of the cathode material.

[0055] The modified cathode material provided by this invention has a low surface Ni content, few NiO impurities, low surface residual alkali, slow DC internal resistance growth during charge and discharge, stable surface structure, few side reactions with electrolyte, and excellent cycle stability.

[0056] A third aspect of the present invention provides a lithium-ion battery comprising the modified cathode material described in the second aspect above.

[0057] The lithium-ion battery provided by this invention uses a modified cathode material prepared by the method provided by this invention, and has a low DCR growth rate and excellent cycle stability.

[0058] The present invention will be described in detail below through examples. Unless otherwise specified, the following examples and comparative examples are all conventional methods; the reagents and materials mentioned are commercially available unless otherwise specified.

[0059] Example 1

[0060] The chemical composition of the nickel-based precursor used meets the requirements of the chemical formula Ni. 0.88 Co 0.06 Mn 0.06 (OH)2

[0061] (1) The above-mentioned nickel-based precursor was placed in a reaction vessel at a certain concentration (solid content 300 g / L); a mixed solution was prepared using nickel sulfate, cobalt sulfate, manganese sulfate and water (the molar ratio of Ni:Co:Mn in the mixed solution was 6:2:2), and the mixed solution was pumped into the reaction vessel. Nitrogen gas was introduced into the reaction vessel, and NaOH solution and ammonia water were pumped in simultaneously to carry out a co-precipitation reaction (the pH value of the reaction system was maintained at 11-12, and the reaction temperature was 50℃). After the reaction was completed, the solid product was washed and dried to obtain a nickel-based precursor with a coating layer (wherein, the chemical composition of the coating layer satisfies the chemical formula Ni). 0.6 Co 0.2 Mn 0.2 (OH)2; The ratio of Ni content in the above-mentioned coated nickel-based precursor to Ni content in the raw nickel-based precursor is 0.96:1;

[0062] The above-mentioned nickel-based precursor with coating layer is thoroughly and uniformly mixed with the first lithium source (LiOH) (the first lithium salt is 47 wt% of the weight of the nickel-based precursor with coating layer), and then subjected to the first sintering (sintering temperature is 780℃, and the isothermal time is 8h) to obtain the nickel-based cathode material matrix.

[0063] (2) The above-mentioned nickel-based cathode material matrix, modifying agent (zirconia accounting for 0.12 wt% of the weight of the nickel-based cathode material matrix, tungsten trioxide accounting for 0.09 wt% of the weight of the nickel-based cathode material matrix), and second lithium source (lithium carbonate, the second lithium salt accounting for 0.08 wt% of the weight of the nickel-based cathode material matrix based on Li element) are thoroughly and uniformly mixed, and then subjected to a second sintering (carried out in an oxidizing atmosphere with an O2 content of 85% by volume, a sintering temperature of 600℃, and a holding time of 4.5h) to obtain a secondary lithium intercalation modified product;

[0064] (3) Prepare a solution containing metal elements (the concentration of element Al is 0.025 wt% of the weight of the above-mentioned secondary lithium intercalation modified product), titanium nitrate (the concentration of element Ti is 0.15 wt% of the weight of the above-mentioned secondary lithium intercalation modified product), and water to form a solution containing metal elements (the concentration of element Al is 0.05 mol / L and the concentration of element Ti is 0.17 mol / L), and prepare an aqueous solution of ammonium dihydrogen phosphate with a concentration of 0.5 mol / L (the molar ratio of metal elements (Al and Ti) in the above-mentioned solution containing metal elements to ammonium dihydrogen phosphate in the aqueous solution of ammonium dihydrogen phosphate is 0.67:1);

[0065] The above-mentioned secondary lithium intercalation modified product was placed in the mixing tank of a vacuum spray mixer. The vacuum degree was set to -65 kPa, and stirring was started (stirring speed of 400 rpm). The secondary lithium intercalation modified product was subjected to a first spray drying using the above-mentioned solution containing metal elements (spraying temperature of 150°C) for 30 min. Then, stirring was continued under a vacuum degree of -65 kPa (stirring speed of 600 rpm). The product of the first spray drying was subjected to a second spray drying using the above-mentioned ammonium dihydrogen phosphate aqueous solution (spraying temperature of 120°C) for 40 min. After the spray drying was completed, stirring was stopped. The obtained coated product was discharged from the vacuum spray mixer and then subjected to a third sintering (sintering temperature of 500°C, isothermal time of 6 h). The sintered product was washed and dried to obtain the modified cathode material (denoted as S1).

[0066] Example 2

[0067] The chemical composition of the nickel-based precursor used meets the requirements of the chemical formula Ni. 0.94 Co 0.03 Mn 0.03 (OH)2

[0068] (1) The above-mentioned nickel-based precursor was placed in a reaction vessel at a certain concentration (solid content 450 g / L); a mixed solution was prepared using cobalt sulfate and water, and the mixed solution was pumped into the reaction vessel. Nitrogen gas was introduced into the reaction vessel, and NaOH solution and ammonia water were pumped in at the same time to carry out a co-precipitation reaction (the pH value of the reaction system was maintained at 11-12, and the reaction temperature was 45℃). After the reaction was completed, the solid product was washed and dried to obtain a nickel-based precursor with a coating layer (wherein, the chemical composition of the coating layer satisfies the chemical formula Co(OH)2); the ratio of the Ni content in the nickel-based precursor with the coating layer to the Ni content in the raw nickel-based precursor was 0.95:1.

[0069] The above-mentioned nickel-based precursor with coating layer is thoroughly and uniformly mixed with the first lithium source (LiOH) (the first lithium salt is 46 wt% of the weight of the nickel-based precursor with coating layer), and then subjected to the first sintering (sintering temperature is 700℃, and the isothermal time is 7h) to obtain the nickel-based cathode material matrix.

[0070] (2) The above nickel-based cathode material matrix, the modifying agent (alumina accounting for 0.4 wt% of the weight of the nickel-based cathode material matrix) and the second lithium source (lithium carbonate, the second lithium salt accounting for 0.1 wt% of the weight of the nickel-based cathode material matrix) are thoroughly and uniformly mixed, and then a second sintering is carried out (in an oxidizing atmosphere, the O2 content in the oxidizing atmosphere is 70% by volume, the sintering temperature is 550℃, and the isothermal time is 7h) to obtain the secondary lithium intercalation modified product;

[0071] (3) Prepare a solution containing a metal element (the concentration of element Zr is 0.12 wt% of the weight of the above-mentioned secondary lithium intercalation modified product) and water, and prepare an aqueous solution of ammonium dihydrogen phosphate with a concentration of 0.35 mol / L (the molar ratio of metal element Zr in the above-mentioned solution containing a metal element to ammonium dihydrogen phosphate in the aqueous solution of ammonium dihydrogen phosphate is 0.6:1);

[0072] The above-mentioned secondary lithium intercalation modified product was placed in the mixing tank of a vacuum spray mixer. The vacuum degree was set to -60 kPa, and stirring was started (stirring speed of 200 rpm). The secondary lithium intercalation modified product was subjected to a first spray drying using the above-mentioned solution containing metal elements (spraying temperature of 170°C) for 45 min. Then, stirring was continued under a vacuum degree of -60 kPa (stirring speed of 300 rpm). The product obtained from the first spray drying was subjected to a second spray drying using the above-mentioned ammonium dihydrogen phosphate aqueous solution (spraying temperature of 170°C) for 45 min. After the spray drying was completed, stirring was stopped. The obtained coated product was discharged from the vacuum spray mixer and then subjected to a third sintering (sintering temperature of 500°C, isothermal time of 6 h). The sintered product was washed and dried to obtain the modified cathode material (denoted as S2).

[0073] Example 3

[0074] The chemical composition of the nickel-based precursor used meets the requirements of the chemical formula Ni. 0.88 Co 0.06 Mn 0.06 (OH)2

[0075] (1) The above-mentioned nickel-based precursor was placed in a reaction vessel at a certain concentration (solid content 480 g / L); a mixed solution was prepared using nickel sulfate, cobalt sulfate, manganese sulfate and water (the molar ratio of Ni:Co:Mn in the mixed solution was 6:2:2), and the mixed solution was pumped into the reaction vessel. Nitrogen gas was introduced into the reaction vessel, and NaOH solution and ammonia water were pumped in simultaneously to carry out a co-precipitation reaction (the pH value of the reaction system was maintained at 12-13, and the reaction temperature was 40℃). After the reaction was completed, the solid product was washed and dried to obtain a nickel-based precursor with a coating layer (wherein, the chemical composition of the coating layer satisfies the chemical formula Ni). 0.6 Co 0.2 Mn 0.2 (OH)2); The ratio of Ni content in the above-mentioned coated nickel-based precursor to Ni content in the raw nickel-based precursor is 0.94:1;

[0076] The above-mentioned nickel-based precursor with coating layer is thoroughly and uniformly mixed with the first lithium source (LiOH) (the first lithium salt is 45 wt% of the weight of the nickel-based precursor with coating layer), and then subjected to the first sintering (sintering temperature is 750℃, and the isothermal time is 6h) to obtain the nickel-based cathode material matrix.

[0077] (2) The above nickel-based cathode material matrix, the modifying agent (niobium pentoxide accounting for 0.6 wt% of the weight of the nickel-based cathode material matrix) and the second lithium source (lithium carbonate, the second lithium salt accounting for 0.1 wt% of the weight of the nickel-based cathode material matrix) are thoroughly and uniformly mixed, and then subjected to a second sintering (air atmosphere, sintering temperature of 650℃, and constant temperature time of 6h) to obtain the secondary lithium intercalation modified product.

[0078] (3) Lanthanum nitrate (wherein element La is 0.15 wt% of the weight of the above-mentioned secondary lithium intercalation modified product) and water are prepared into a solution containing metal element (the concentration of element La is 0.12 mol / L), and an aqueous solution of ammonium dihydrogen phosphate with a concentration of 0.3 mol / L is prepared (the molar ratio of metal element La in the above-mentioned solution containing metal element to ammonium dihydrogen phosphate in the aqueous solution of ammonium dihydrogen phosphate is 0.4:1);

[0079] The above-mentioned secondary lithium intercalation modified product was placed in the mixing tank of a vacuum spray mixer. The vacuum degree was set to -70 kPa, and stirring was started (stirring speed of 200 rpm). The secondary lithium intercalation modified product was subjected to a first spray drying using the above-mentioned solution containing metal elements (spraying temperature of 130°C) for 45 min. Then, stirring was continued under a vacuum degree of -70 kPa (stirring speed of 300 rpm). The product obtained from the first spray drying was subjected to a second spray drying using the above-mentioned ammonium dihydrogen phosphate aqueous solution (spraying temperature of 130°C) for 45 min. After the spray drying was completed, stirring was stopped. The obtained coated product was discharged from the vacuum spray mixer and then subjected to a third sintering (sintering temperature of 550°C, isothermal time of 7 h). The sintered product was washed and dried to obtain the modified cathode material (denoted as S3).

[0080] Example 4

[0081] The chemical composition of the nickel-based precursor used meets the requirements of the chemical formula Ni. 0.88 Co 0.06 Mn 0.06 (OH)2

[0082] (1) The above-mentioned nickel-based precursor was placed in a reaction vessel at a certain concentration (solid content 480 g / L); a mixed solution was prepared using nickel sulfate, cobalt sulfate and water (the molar ratio of element Ni:Co in the mixed solution was 7:3), and the mixed solution was pumped into the reaction vessel. Nitrogen gas was introduced into the reaction vessel, and NaOH solution and ammonia water were pumped in simultaneously to carry out a co-precipitation reaction (the pH value of the reaction system was maintained at 12-13, and the reaction temperature was 40℃). After the reaction was completed, the solid product was washed and dried to obtain a nickel-based precursor with a coating layer (wherein, the chemical composition of the coating layer satisfies the chemical formula Ni). 0.7 Co 0.3 (OH)2); The ratio of Ni content in the above-mentioned coated nickel-based precursor to Ni content in the raw nickel-based precursor is 0.94:1;

[0083] The above-mentioned nickel-based precursor with coating layer is thoroughly and uniformly mixed with the first lithium source (LiOH) (the first lithium salt is 45 wt% of the weight of the nickel-based precursor with coating layer), and then subjected to the first sintering (sintering temperature is 750℃, and the isothermal time is 6h) to obtain the nickel-based cathode material matrix.

[0084] Steps (2) and (3) are exactly the same as in Example 3, and the modified cathode material (denoted as S4) is obtained.

[0085] Example 5

[0086] The chemical composition of the nickel-based precursor used meets the requirements of the chemical formula Ni. 0.88 Co0.06 Mn 0.06 (OH)2

[0087] The method of Example 3 is followed, except that in step (2), the nickel-based cathode material matrix, the modifying agent (cobalt hydroxide accounting for 0.6 wt% of the weight of the nickel-based cathode material matrix and aluminum oxide accounting for 0.15 wt% of the weight of the nickel-based cathode material matrix), and the second lithium source (lithium carbonate, the second lithium salt being 0.1 wt% of the weight of the nickel-based cathode material matrix) are thoroughly and uniformly mixed, and then subjected to a second sintering (carried out in an oxidizing atmosphere with an O2 content of 80% by volume, a sintering temperature of 650°C, and a holding time of 6 hours) to obtain a secondary lithium intercalation modified product. Other steps and conditions are the same as in Example 3, and the modified cathode material (denoted as S5) is obtained.

[0088] Example 6

[0089] The chemical composition of the nickel-based precursor used meets the requirements of the chemical formula Ni. 0.88 Co 0.06 Mn 0.06 (OH)2

[0090] Steps (1) and (2) are performed according to the method and parameters of Example 3, with the only difference being that in step (3), the secondary lithium intercalation modified product is placed in the mixing tank of a vacuum spray mixer, the vacuum degree is set to -70 kPa, stirring is started (stirring speed is 300 rpm), and the secondary lithium intercalation modified product is spray-dried for the first time using ammonium dihydrogen phosphate aqueous solution (spraying temperature is 130°C, stirring time is 45 min). Then, under a vacuum degree of -70 kPa, stirring is continued (stirring speed is 200 rpm), and the product spray-dried for the first time is spray-dried for the second time using a solution containing metal elements (spraying temperature is 130°C, stirring time is 45 min). After the spray drying is completed, stirring is stopped. The obtained coated product is discharged from the vacuum spray mixer, and then a third sintering is performed (sintering temperature is 550°C, constant temperature time is 7 h). The sintered product is washed and dried to obtain the modified cathode material (denoted as S6).

[0091] Comparative Example 1

[0092] The method of Example 4 is followed, except that step (1) is adjusted as follows: the nickel-based precursor and the first lithium source (LiOH) are thoroughly and uniformly mixed (the first lithium salt is 46.5 wt% of the weight of the nickel-based precursor), and then a first sintering is performed (sintering temperature is 730°C, and the isothermal time is 8 h) to obtain the nickel-based cathode material matrix. Other steps and conditions are the same as in Example 4 to obtain the cathode material (denoted as D1).

[0093] Comparative Example 2

[0094] The method of Example 4 is followed, except that the process of preparing the nickel-based precursor with coating in step (1) is adjusted as follows: the raw nickel-based precursor is placed in a reaction vessel at a certain concentration (solid content 480 g / L); a mixed solution is prepared using nickel sulfate, calcium nitrate and water (the molar ratio of element Ni:Ca in the mixed solution is 7:3), and the above mixed solution is pumped into the above reaction vessel. Nitrogen gas is introduced into the reaction vessel, and NaOH solution and ammonia water are pumped in at the same time to carry out a co-precipitation reaction (the pH value of the reaction system is maintained at 12-13, and the reaction temperature is 40℃). After the reaction is completed, the solid product is washed and dried to obtain the nickel-based precursor with coating (wherein, the chemical composition of the coating satisfies the chemical formula Ni). 0.7 Ca 0.3 (OH)2); the ratio of Ni content in the coated nickel-based precursor to Ni content in the raw nickel-based precursor is 0.94:1; the coated nickel-based precursor is thoroughly and uniformly mixed with the first lithium source (LiOH) (the first lithium salt is 45 wt% of the weight of the coated nickel-based precursor), and then subjected to a first sintering (sintering temperature is 750℃, and the isothermal time is 6h) to obtain a nickel-based cathode material matrix. Other steps and conditions are the same as in Example 4 to obtain the cathode material (denoted as D2).

[0095] Comparative Example 3

[0096] The method of Example 4 was followed, except that no modifying agent was added in step (2). All other steps and conditions were the same as in Example 4, and the positive electrode material (denoted as D3) was obtained.

[0097] Comparative Example 4

[0098] The method of Example 4 is followed, except that step (3) is omitted, and the secondary lithium intercalation modified product obtained in step (2) is used as the final cathode material product. The other steps and conditions are the same as in Example 4, and the cathode material (denoted as D4) is obtained.

[0099] Test case

[0100] 1. Surface residual alkali test

[0101] The surface residual alkali content of the above-mentioned cathode materials S1-S6 and D1-D4 was tested according to the method specified in GB / T 41704-2022, and the results are shown in Table 1.

[0102] Table 1

[0103] S1 1025 2036 782 S2 1134 2337 889 S3 1355 2612 1006 S4 1416 2432 970 S5 1512 2512 1011 S6 1422 2602 1020 D1 1750 3320 1289 D2 2230 2700 1200 D3 2355 3230 1377 D4 3400 5320 2178

[0104] Note: In Table 1, the total lithium content is the sum of lithium elements in Li₂CO₃ and LiOH.

[0105] As shown in Table 1, the modified cathode material prepared by the method of the present invention has a low surface residual alkali content, which can reduce the products after side reaction with electrolyte to a certain extent, and is more conducive to improving the cycle life of battery.

[0106] 2. DCR performance test, cycle performance test

[0107] Lithium-ion batteries were fabricated using the aforementioned cathode materials S1-S6 and D1-D4. The fabrication process is as follows:

[0108] The positive electrode materials (S1-S6, D1-D4), SP (carbon black), and PVDF (polyvinylidene fluoride) were dissolved in NMP (N-methylpyrrolidone) at a weight ratio of 95:2.5:2.5 to obtain a slurry (solid content 55% by weight). After uniform stirring, the slurry was coated onto aluminum foil and dried in a vacuum drying oven at 150°C for 8 hours. Following drying, the foil was rolled to ensure a compaction density of 3.1-3.4 g / cm³. 3 Then, the positive electrode sheet is stamped in a drying chamber with dew point control to obtain a positive electrode sheet with a diameter of 12mm.

[0109] Using the above-mentioned positive electrode as the positive electrode, the lithium metal sheet as the negative electrode, the polyethylene membrane as the separator, and a 1 mol / L LiPF6 electrolyte solution (wherein the solvent is a mixture of ethylene carbonate and dimethyl carbonate in a volume ratio of 1:1, and the lithium salt is LiPF6) as the electrolyte, the cells were assembled into a coin cell in the following order: positive electrode shell, positive electrode, separator, electrolyte, lithium sheet, gasket, spring, and negative electrode shell. Finally, the cells were packaged to obtain the test cells (denoted as B1-B6 and DB1-DB4, respectively).

[0110] DCR performance tests were performed on the above-mentioned test batteries B1-B6 and DB1-DB4, where:

[0111] (1) DCR performance test: According to the HPPC test method in the American Freedom CAR Battery Test Manual, the battery DCR was tested at different SOC (90%, 70%, 50%, 30%, 10%) with a discharge pulse of 0.2C for 10s. The results are shown in Table 2. The DCR growth after 50 cycles at 25℃ and 45℃ was tested. The results are shown in Table 3.

[0112] (2) The capacity retention rate of batteries B1, B4, B5, DB1, and DB2 was tested under the conditions of 25℃, 3.0-4.2V, and constant current 1C charging / discharging to evaluate their cycle performance. The results are shown in [Figure number missing]. Figure 1 .

[0113] Table 2

[0114]

[0115] Table 3

[0116]

[0117] As can be seen from the data in Tables 2 and 3, the modified cathode materials S1-S6 prepared using the method of this invention, compared with the cathode materials D1-D4 prepared in the comparative example, exhibit lower DC internal resistance and lower DCR growth rate before and after high and low temperature cycling during the charge and discharge processes of the battery at different SOCs. Figure 1 It is evident that the cycle capacity retention rates of batteries B1, B4, and B5 are significantly higher than those of DB1 and DB2, indicating superior cycle performance.

[0118] The preferred embodiments of the present invention have been described in detail above; however, the present invention is not limited thereto. Within the scope of the inventive concept, various simple modifications can be made to the technical solutions of the present invention, including combinations of various technical features in any other suitable manner. These simple modifications and combinations should also be considered as the content disclosed in the present invention and are all within the protection scope of the present invention.

Claims

1. A method for preparing a modified cathode material, characterized in that, include: (1) A co-precipitation reaction is carried out on the surface of a nickel-based precursor containing element M salt and optional Ni salt to obtain a nickel-based precursor with a coating layer, and the nickel-based precursor with the coating layer and a first lithium salt are subjected to a first sintering to obtain a nickel-based cathode material matrix. (2) The nickel-based cathode material matrix, the second lithium salt, and the modifying agent are subjected to a second sintering to obtain a secondary lithium intercalation modified product; In step (2), the modifying agent is selected from at least one of the oxides of the modifying element, the hydroxides of the modifying element, and the phosphates of the modifying element, and the modifying element is selected from at least one of W, Sr, Zr and Al; the weight ratio of the second lithium salt to the nickel-based cathode material matrix, calculated as Li, is (0.01-0.5):

100. (3) The secondary lithium intercalation modified product is surface coated with a solution containing metal elements and a solution containing phosphate, and then subjected to a third sintering to obtain a modified cathode material; the weight ratio of the metal element in the solution containing metal elements to the secondary lithium intercalation modified product is (0.1-0.4):100; the surface coating treatment includes: spray drying, first spray coating the surface of the secondary lithium intercalation modified product with the solution containing metal elements and drying it at the same time, and then spray coating with the solution containing phosphate and drying it at the same time; the metal element in the solution containing metal elements is selected from at least one of Al, Ti, La, Zr, Cr, Fe, Nb, Co, Ge and Sn; In the nickel-based precursor containing the coating layer, the chemical composition of the coating layer satisfies the chemical formula Ni x M y (OH)₂, wherein element M is selected from at least one of Mn, Co, and Al; x + y = 1, 0 ≤ x ≤ 0.7; the nickel-based precursor is selected from Ni. a R b (OH)2, Ni a R b O(OH) and Ni a R b At least one of O2; wherein element R is selected from at least one of Mn, Ti, Zr, Co, Al and W; a+b=1, 0.8≤a<1.

2. The method according to claim 1, wherein, The conditions for the coprecipitation reaction include: a pH of 10-13 and a temperature of 40-80℃.

3. The method according to claim 1 or 2, wherein, The weight ratio of the first lithium salt to the nickel-based precursor with the coating layer is (40-65):100; And / or, the conditions for the first sintering include: a temperature of 600-900℃ and a holding time of 4-20h.

4. The method according to claim 3, wherein, The weight ratio of the first lithium salt to the nickel-based precursor with the coating layer is (45-55):

100.

5. The method according to claim 1 or 2, wherein, In step (2), the weight ratio of the modified additive to the nickel-based cathode material matrix, based on the metal elements contained, is (0.01-2):

100.

6. The method according to claim 5, wherein, In step (2), the weight ratio of the modified additive to the nickel-based cathode material matrix, based on the metal elements contained, is (0.02-0.2):

100.

7. The method according to claim 1, wherein, The weight ratio of the second lithium salt to the nickel-based cathode material matrix, calculated as Li, is (0.03-0.2):

100. And / or, the conditions for the second sintering include: a temperature of 500-850℃ and a holding time of 2-15h.

8. The method according to claim 1 or 2, wherein, The phosphate is selected from at least one of ammonium dihydrogen phosphate, ammonium hydrogen phosphate, and triammonium phosphate; And / or, the molar ratio of the metal element in the solution containing the metal element to the phosphate in the solution containing the phosphate is (0.1-2):

1.

9. The method according to claim 8, wherein, In step (3), the metal element in the solution containing the metal element is selected from at least one of Al, Zr, Ti, Co and Ge.

10. The method according to claim 1 or 2, wherein, In step (3), the surface coating treatment conditions include: temperature of 70-180℃, vacuum degree of -60 to -90 kPa, and time of 10-120 min; And / or, the conditions for the third sintering include: a temperature of 250-750℃ and a holding time of 2-10h.

11. A modified cathode material prepared by the method of any one of claims 1-10.

12. The modified cathode material according to claim 11, wherein, The surface residual alkali content of the modified cathode material is ≤0.5wt%.

13. A lithium-ion battery comprising the modified cathode material as described in claim 11 or 12.

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