Cobalt hydroxide and preparation method therefor, positive electrode material, battery and electrical equipment

Abstract

The present disclosure belongs to the field of batteries, and particularly relates to cobalt hydroxide and a preparation method therefor, a positive electrode material, a battery and electrical equipment. Provided in the present disclosure is cobalt hydroxide, the particles of which are in the shape of a sheet and have an average thickness of 10-20 nm. The cobalt hydroxide of the present disclosure is nanosheets having an extremely small average thickness and a larger surface area, which can thus improve the coating effect thereof on a positive electrode material, thereby effectively inhibiting the formation of a nickel oxide rock salt-like phase in the positive electrode material, reducing the concentration of residual lithium on the surface of the positive electrode material and enabling lithium ions to be quickly deintercalated / intercalated; therefore, the electrical properties of the positive electrode material prepared therefrom can be significantly improved.

Description

Cobalt hydroxide, preparation method thereof, positive electrode material, battery and electrical equipment

[0001] Cross-reference to related applications

[0002] The present disclosure claims priority to the Chinese patent application No. 2024104680101, filed on April 18, 2024, entitled "Cobalt hydroxide, preparation method thereof, positive electrode material, battery and electrical equipment", the entire content of which is incorporated herein by reference. TECHNICAL FIELD

[0003] The present disclosure belongs to the field of batteries, and particularly relates to a cobalt hydroxide, a preparation method thereof, a positive electrode material, a battery and an electrical equipment. BACKGROUND

[0004] As an important component of lithium batteries, the positive electrode material is mainly used to complete the conversion of electric energy by embedding or removing lithium ions into or out of the electrode structure during the charging and discharging process. During the charging and discharging process, nickel ions are prone to migrate to the lithium layer during the removal of lithium ions, thereby forming a nickel oxide-like rock salt phase and surface residual lithium, resulting in poor battery stability. Therefore, in the related art, the surface of the nickel-based positive electrode material is generally coated to inhibit the formation of the rock salt phase and lithium leaching. SUMMARY

[0005] The present disclosure provides a cobalt hydroxide, a preparation method thereof, a positive electrode material and a battery, aiming to solve or at least alleviate the defects existing in the prior art.

[0006] One aspect of the present disclosure provides a cobalt hydroxide, wherein the particles of the cobalt hydroxide are in a sheet shape, and the average thickness thereof is 10-20 nm.

[0007] The cobalt hydroxide provided by the present disclosure can be used as a coating material of the positive electrode material to generate lithium cobaltate with ion conductivity on the surface of the positive electrode material. During the charging and discharging process, the lithium cobaltate not only consumes the residual lithium compounds on the surface of the positive electrode material, but also reduces the nickel concentration on the surface of the positive electrode material, thereby inhibiting the formation of the nickel oxide-like rock salt phase. When applied to a battery, the cobalt hydroxide can improve the charging and discharging efficiency and the cycle life of the battery.

[0008] It is particularly crucial that the cobalt hydroxide in the present disclosure is in a sheet shape and has a thickness of 10-20 nm, which is extremely thin. The cobalt hydroxide with an extremely thin thickness is conducive to the close adsorption of the particles on the surface of the positive electrode material, shortens the electron transmission path, improves the ion migration rate, further facilitates the rapid extraction / insertion of lithium ions, and ultimately improves the rate performance of the battery. In addition, the cobalt hydroxide in a sheet shape and with an extremely thin thickness has a larger surface area, and after the particles are coated on the positive electrode material, the positive electrode material has more contact surfaces with the positive electrode material, so that the coverage rate of the surface of the positive electrode material is improved, which is conducive to promoting the reaction and consumption of the coating material and the residual lithium on the surface, reducing the residual lithium concentration on the surface of the positive electrode material, and thus improving the cycle performance of the battery.

[0009] In some embodiments, the cobalt hydroxide satisfies at least one of the following conditions A-H:

[0010] A. The peak intensity ratio I(001) / I(100) in the XRD pattern of the cobalt hydroxide is greater than 7.5, and optionally I(001) / I(100) is greater than or equal to 9;

[0011] B. The loose bulk density of the cobalt hydroxide is 0.08-0.40 g / cm 3 , and optionally 0.10-0.20 g / cm 3 ;

[0012] C. The average particle size D50 of the cobalt hydroxide is less than or equal to 0.2 μm, and optionally 0.05-0.20 μm;

[0013] D. The maximum particle size Dmax of the cobalt hydroxide is less than or equal to 1.5 μm;

[0014] E. The particle size distribution (D90-D10) / D50 of the cobalt hydroxide is less than or equal to 4.0;

[0015] F. The average width of the cobalt hydroxide is 220-400 nm, and the average length of the cobalt hydroxide is 300-500 nm;

[0016] G. The specific surface area of the cobalt hydroxide is 10-80 m 2 / g, and optionally 15-40 m 2 / g;

[0017] H. The chemical formula of the cobalt hydroxide is Co a A b (OH)2, wherein 0.6≤a≤1.0 and 0≤b≤0.4, and A comprises one or more of Al, Mg, Mn, Ni, La, Ti, Y, and Er.

[0018] The second aspect of the present disclosure provides a preparation method of the cobalt hydroxide as described above, comprising:

[0019] The synthetic process comprises: adding a cobalt salt solution, a base solution and an antioxidant into a bottom solution containing an antioxidant; performing a synthetic reaction to obtain a cobalt hydroxide slurry;

[0020] The post-processing process comprises: performing washing, pressure filtration, drying and crushing on the cobalt hydroxide slurry to obtain the cobalt hydroxide.

[0021] In the synthetic process, the pH of the bottom solution is 4.0-8.5.

[0022] In some embodiments, in the synthetic process, during the synthetic reaction, the flow rate ratio of the cobalt salt solution, the base solution and the antioxidant is 1:(0.35-0.45):(0.05-0.20).

[0023] In some embodiments, in the synthetic process, the volume ratio of the bottom solution to the cobalt salt solution is (0.5-2):1; and / or, the volume ratio of the bottom solution to the base solution is (1-5):1; and / or, the volume ratio of the bottom solution to the antioxidant is (2.5-40):1.

[0024] In some embodiments, the post-processing process specifically comprises: performing washing, pressure filtration, drying and crushing on the cobalt hydroxide slurry to obtain the cobalt hydroxide.

[0025] In some embodiments, the cobalt salt solution comprises at least one of cobalt chloride, cobalt sulfate or cobalt nitrate; and / or, the base solution comprises at least one of sodium hydroxide or potassium hydroxide; and / or, the antioxidant comprises at least one of citric acid, hydrazine hydrate, sodium borohydride, ascorbic acid, sodium ascorbate or carbohydrazide; and / or, the synthetic process is performed in a protective atmosphere, and the protective atmosphere is at least one of nitrogen, helium or argon.

[0026] In some embodiments, stirring is performed during the synthetic reaction and after the reaction, and the stirring rate is controlled to be 400 r / min-1000 r / min; and / or, the temperature of the synthetic reaction is controlled to be 35℃-50℃; and / or, in the post-processing process, when the drying treatment is performed, the temperature is controlled to be 80℃-150℃; and / or, in the post-processing process, when the drying treatment is performed, the time is controlled to be 10 h-20 h.

[0027] A third aspect of the present disclosure provides a positive electrode material, and a raw material of a coating material of the positive electrode material, comprising the cobalt hydroxide as described above or the cobalt hydroxide prepared by the preparation method as described above.

[0028] A fourth aspect of the present disclosure provides a battery, comprising a positive electrode made of the positive electrode material as described above.

[0029] A fifth aspect of the present disclosure provides an electrical equipment, comprising the battery as described above. BRIEF DESCRIPTION OF DRAWINGS

[0030] In order to more clearly illustrate the technical solutions in the specific embodiments of the present disclosure or the prior art, the accompanying drawings required by the specific embodiments or prior art description will be briefly introduced. Obviously, the accompanying drawings in the following description are some embodiments of the present disclosure, and other drawings can be obtained by a person of ordinary skill in the art without creative effort.

[0031] FIG. 1 is an SEM image of cobalt hydroxide prepared in Example 2 of the present disclosure (10000x);

[0032] FIG. 2 is an SEM image of cobalt hydroxide of a test thickness provided in an example of the present disclosure (50000x);

[0033] FIG. 3 is an ImageJ interface diagram of cobalt hydroxide of a test thickness provided in an example of the present disclosure;

[0034] FIG. 4 is an SEM image of the length and width of cobalt hydroxide provided in an example of the present disclosure (50000x);

[0035] FIG. 5 is an SEM image of cobalt hydroxide prepared in Comparative Example 1 of the present disclosure (10000x);

[0036] FIG. 6 is an SEM image of cobalt hydroxide prepared in Comparative Example 2 of the present disclosure (10000x);

[0037] FIG. 7 is an XRD diagram of cobalt hydroxide prepared in Example 1, 2 and Comparative Example 1, 2 of the present disclosure;

[0038] FIG. 8 is an SEM image of a positive electrode material prepared from cobalt hydroxide of Example 2 of the present disclosure;

[0039] FIG. 9 is an EDS characterization test diagram of a positive electrode material prepared from cobalt hydroxide of Example 2 of the present disclosure;

[0040] FIG. 10 is a Co element distribution diagram obtained from EDS characterization test of a positive electrode material prepared from cobalt hydroxide of Example 2 of the present disclosure;

[0041] FIG. 11 is a diagram showing the distribution of Ni, Co, and Mn elements obtained from EDS characterization test of a positive electrode material prepared from cobalt hydroxide of Example 2 of the present disclosure;

[0042] FIG. 12 is an SEM image of a positive electrode material prepared from cobalt hydroxide of Comparative Example 2 of the present disclosure;

[0043] FIG. 13 is an SEM image of an uncoated nickel-based positive electrode material of the present disclosure;

[0044] FIG14 is a graph showing the direct current resistance (DCR) of button-type batteries made from the positive electrode materials of Examples 1 to 3 of the present disclosure, Comparative Examples 1 to 2, and the uncoated nickel-based positive electrode material of the control group. DETAILED DESCRIPTION

[0045] " scope " disclosed in the present disclosure is limited in the form of lower limit and upper limit, and given range is limited by selecting a lower limit and an upper limit, and selected lower limit and upper limit define the boundary of special scope.The scope that this mode limits can be to include end value or not include end value, and can be combined arbitrarily, and promptly any lower limit can form a scope with any upper limit combination.For example, if the scope of 60-120 and 80-110 is listed for specific parameter, it is understood that the scope of 60-110 and 80-120 is also expected.In addition, if the minimum range value 1 and 2 listed, and if the maximum range value 3,4 and 5 listed, then the following scope can all be expected: 1-3, 1-4, 1-5, 2-3, 2-4 and 2-5.In the present disclosure, unless otherwise specified, numerical range " ab " represents the abbreviation of any real number combination between a and b, and wherein a and b are all real numbers. For example, a numerical range of "0-5" indicates that all real numbers between "0-5" are listed herein, and "0-5" is simply an abbreviation for these numerical combinations. Furthermore, when a parameter is expressed as an integer ≥ 2, this is equivalent to disclosing that the parameter is, for example, an integer of 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, etc.

[0046] Unless otherwise specified, all embodiments and optional embodiments of the present disclosure can be combined with each other to form new technical solutions.

[0047] Unless otherwise specified, all technical features and optional technical features disclosed herein can be combined with each other to form a new technical solution.

[0048] Unless otherwise specified, all steps of the present disclosure may be performed sequentially, randomly, or optionally sequentially. For example, the method includes steps (a) and (b), which indicates that the method may include steps (a) and (b) performed sequentially, or may include steps (b) and (a) performed sequentially. For example, the method may further include step (c), which indicates that step (c) may be added to the method in any order, for example, the method may include steps (a), (b), and (c), or may include steps (a), (c), and (b), or may include steps (c), (a), and (b), etc.

[0049] If not specifically stated, the "include" and "contain" mentioned in the present disclosure represent open type, and can also be closed type. For example, the "include" and "contain" can represent that other components not listed can also be included or contained, or can only include or contain the listed components.

[0050] If not specifically stated, in the present disclosure, the term "or" is inclusive. For example, the phrase "A or B" means "A, B, or both A and B". More specifically, either of the following conditions satisfies the condition "A or B": A is true (or exists) and B is false (or does not exist); A is false (or does not exist) and B is true (or exists); or A and B are both true (or exist).

[0051] It should be noted that the sheet shape in the embodiments of the present disclosure means that the particles have a flat, thin and large shape, similar to a sheet; in three-dimensional space, the sheet-shaped particles have a large extension in two dimensions, and are relatively small in the other dimension, so as to obtain more surface area.

[0052] As described above, in order to improve the adsorption of the coating material to the positive electrode material and the surface coverage, improve the coating effect, and strengthen the performance of the lithium battery, one embodiment of the present disclosure provides a cobalt hydroxide, the particles of the cobalt hydroxide are in a sheet shape, and the average thickness thereof is 10-20 nm.

[0053] It can be understood that the rock salt phase of the nickel-based positive electrode material is mainly due to the similar ionic radius of Li + and Ni 2+ , and the irreversible migration of Ni 2+ to the lithium layer during the Li + extraction process, thereby forming a rock salt phase structure; the formation of the rock salt phase will further cause the formation of Li2O on the surface of the positive electrode material, and the adsorption of Li2O by CO2 and H2O in the air will form residual lithium compounds on the surface of the positive electrode material.

[0054] The conventional cobalt hydroxide has poor adsorption to the positive electrode material, low surface coverage on the positive electrode material, and is difficult to effectively consume the surface residual lithium, so the coating effect is poor, and the coating on the surface of the positive electrode material often causes the electronic transmission path to be too long, which is not conducive to the rapid extraction / insertion of lithium ions, and further causes the poor performance of the lithium battery.

[0055] The cobalt hydroxide provided by the embodiment of the present disclosure is in a sheet shape, and has a thickness of 10-20 nm. The cobalt hydroxide has an extremely thin thickness, which is conducive to obtaining more surface area, so as to be closely adsorbed on the surface of the positive electrode material, effectively improve the surface coverage, and then improve the coating effect. The cobalt hydroxide provided by the embodiment is applied to a coating material of the positive electrode material, has more excellent coating effect, can generate LiCoO2 with ion conductivity on the surface of the positive electrode material, the LiCoO2 can not only effectively consume the residual lithium content on the surface of the positive electrode material, but also effectively reduce the Ni concentration on the surface of the material, inhibit the formation of rock salt phase and the leaching of lithium, thereby improving the charge-discharge efficiency and cycle life of the lithium battery. Moreover, the sheet-shaped cobalt hydroxide with an extremely thin thickness coated on the surface of the positive electrode material is also conducive to shortening the electron transport path, improving the ion migration rate, enabling the lithium ion to be quickly inserted and extracted, and improving the rate performance of the battery. If the thickness of the cobalt hydroxide is too small, the LiCoO2 coating layer formed on the secondary surface of the positive electrode material after secondary sintering is too thin in part, which may not effectively isolate the side reaction of the electrolyte and the core material, leading to the dissolution of transition metals in the positive electrode material of the battery or the intensification of the interface side reaction, affecting the conductivity of the material.

[0056] It should be noted that the cobalt hydroxide in the embodiment of the present disclosure can be in a regular or irregular sheet shape. When the cobalt hydroxide is in a regular sheet shape, it has clear boundaries and regular shapes, and the surface is flat and the edges are neat, and the whole presents a clear geometric shape, such as a square sheet shape, a rectangular sheet shape or a circular sheet shape. When the cobalt hydroxide is in an irregular sheet shape, it does not have a clear regular shape, and the boundaries are irregular, and presents various irregular shapes, and the surface can be uneven or irregular.

[0057] It should be noted that the thickness of the sheet-shaped cobalt hydroxide in the embodiment of the present disclosure is 10-20 nm, and can be 10 nm, 11 nm, 12 nm, 13 nm, 14 nm, 15 nm, 16 nm, 17 nm, 18 nm, 19 nm, 20 nm or any thickness value and any thickness range value in the range of 10-20 nm, which can effectively improve the adsorption of the positive electrode material and the surface coverage, so as to promote the significant improvement of the coating effect.

[0058] It is necessary to clarify that, with reference to FIGS. 2 and 3, the test method for the thickness of the flaky cobalt hydroxide in the present disclosure is as follows: the SEM picture of the cobalt hydroxide is imported into the ImageJ software, the scale is set, and the thickness of the side of a single flaky cobalt hydroxide particle is measured. The side is rectangular or rectangular-like, and has two substantially parallel long sides. The thickness is defined as follows: a vertical line is drawn from any point on one long side to the opposite side, and the vertical distance is the thickness. Since the single cobalt hydroxide particle is flaky, the thicknesses of different positions of the side are relatively small, but in order to more clearly define the thickness, the present disclosure selects the thickest region (the maximum vertical distance) of the side of a single flaky cobalt hydroxide particle as the thickness, then randomly selects 2-3 regions, measures the thickness of several (such as 8-12) flakes in each region, obtains a plurality of thickness values, and further obtains the average value of the plurality of thickness values to obtain the thickness of the flaky cobalt hydroxide.

[0059] In some embodiments, the peak intensity ratio I(001) / I(100) in the XRD pattern of the cobalt hydroxide is > 7.5, and optionally ≥ 9. Further, I(001) / I(100) = 9-11.

[0060] It is necessary to clarify that I(001) / I(100) in the present embodiment refers to the ratio of the (001) crystal plane diffraction intensity to the (100) crystal plane diffraction intensity of the cobalt hydroxide, which reflects the ratio of the exposed areas of the (001) crystal plane and the (100) crystal plane of the cobalt hydroxide. To some extent, it can be understood that the larger the I(001) / I(100) ratio, the larger the surface area of the cobalt hydroxide, and the more active sites exposed, which is more conducive to being dispersed and covered on the surface of the positive electrode material, and improves the overall coating effect of the positive electrode material.

[0061] The value of the peak intensity ratio I(001) / I(100) in the XRD pattern of the cobalt hydroxide in the present disclosure is large, which means that the cobalt hydroxide is thin and has a large surface area. It is relatively difficult to obtain a cobalt hydroxide that is both thin and has a large surface area. The cobalt hydroxide that is thin and has a large surface area can obtain more contact area with the positive electrode material, thereby improving the coverage on the surface of the positive electrode material, making it better react with the residual lithium compound, consuming the surface residual lithium, and further effectively reducing the residual lithium concentration on the surface of the positive electrode material and improving the cycle performance of the battery.

[0062] In some embodiments, the bulk density of the cobalt hydroxide is 0.08-0.40 g / cm 3 , and optionally 0.10-0.20 g / cm 3, which indicates that the cobalt hydroxide particles are in a fluffy state when freely accumulated, and have good dispersibility, so as to facilitate more uniform dispersion and loading of the particles on the surface of the positive electrode material, thereby effectively improving the uniformity of the coating. The uniform coating layer helps to isolate the positive electrode material from the electrolyte, protects the positive electrode material from electrolyte corrosion, inhibits the generation of side reactions, thereby improving the surface stability of the positive electrode material and enhancing the electrochemical performance of the positive electrode material.

[0063] It should be noted that the bulk density in the embodiments of the present disclosure is the density range in a loose state formed by free accumulation of cobalt hydroxide particles without external constraints or compression.

[0064] In some embodiments, the average particle size D50 of the cobalt hydroxide is ≤0.2 μm, and the maximum particle size Dmax of the cobalt hydroxide is ≤1.5 μm, which indicates that the particle size of the cobalt hydroxide particles is small, so as to facilitate the formation of a more uniform coating layer, further improve the coating effect, and promote the improvement of the electrochemical performance of the positive electrode material.

[0065] In some embodiments, the particle size distribution (D90-D10) / D50 of the cobalt hydroxide is ≤4.0, and optionally, (D90-D10) / D50 = 1.0-3.5. The particle size distribution of the cobalt hydroxide is relatively narrow, and the difference in the particle size of the cobalt hydroxide is relatively small, so as to facilitate more uniform coating on the surface of the positive electrode material, form a stable and uniform coating layer, and improve the electrochemical performance of the positive electrode material.

[0066] In some embodiments, the average width of the particles of the cobalt hydroxide is 220-400 nm, and the average length of the particles of the cobalt hydroxide is 300-500 nm. It can be understood that, since the nanosheet of the cobalt hydroxide is extremely thin, within the above-mentioned average width and average length range, the particles have a larger surface area, and the contact surface between the cobalt hydroxide and the positive electrode material is larger, so as to further improve the coverage on the surface of the positive electrode material and enhance the coating effect, thereby promoting the improvement of the electrochemical performance of the positive electrode material.

[0067] It should be noted that, as shown in Figure 4, the test method for the width mean and length mean of the particles of cobalt hydroxide is: select multiple flaky cobalt hydroxides in the SEM image of cobalt hydroxide, measure the length and width values ​​of each flaky cobalt hydroxide respectively, and then calculate the length mean and width mean. The length and width test method of the particles of a single cobalt hydroxide is: use ImageJ software to measure, and take the dimension in the direction of the longest axis of the single flaky cobalt hydroxide particle as the length, and the dimension perpendicular to the midpoint direction of the longest axis as the width. More specifically, among the selected flaky cobalt hydroxide particles, select a side with a relatively large area and a small difference in length and width ratio to test its length and width. In the above measurement, if there is a situation where the particles are blocked, the unblocked part is assumed to be a complete particle for measurement. Exemplary, the magnification of the surface SEM photo can be 50.0K, etc.

[0068] In some embodiments, the specific surface area of ​​cobalt hydroxide is 10-80 m 2 / g, optional 15~40m 2 / g, a larger specific surface area can provide more electrochemical active sites to better adsorb on the surface of the matrix positive electrode material, thereby improving the coating effect and thus improving the electrochemical performance of the positive electrode material.

[0069] In some embodiments, the chemical formula of cobalt hydroxide is Co a A b (OH)2, wherein 0.6≤a≤1.0, 0≤b≤0.4, and A includes one or more of Al, Mg, Mn, Ni, La, Ti, Y, and Er; it can be understood that the cobalt hydroxide in this embodiment can be Co(OH) 2， That is, pure phase cobalt hydroxide can also be doped cobalt hydroxide containing one or more elements of Al, Mg, Mn, Ni, La, Ti, Y, and Er. By doping with different elements, the crystal structure and properties of cobalt hydroxide can be changed, thereby achieving the regulation of the properties of the coating material and making the application of cobalt hydroxide more flexible.

[0070] Therefore, the embodiment of the present disclosure designs the morphology of cobalt hydroxide, so that cobalt hydroxide has an extremely thin thickness, a large specific surface area and good dispersibility, which can effectively improve the adsorption of the positive electrode material, increase the coverage of the positive electrode material, and form a more uniform coating layer, thereby effectively improving the electrochemical performance of the positive electrode material, and significantly improving the battery's charge and discharge efficiency, cycle life and cycle performance.

[0071] In order to prepare cobalt hydroxide having the above morphological characteristics and performance advantages, another embodiment of the present disclosure provides a method for preparing cobalt hydroxide, comprising:

[0072] Synthesis process: adding cobalt salt solution, alkali solution and antioxidant into the base solution containing antioxidant; performing synthesis reaction to obtain cobalt hydroxide slurry;

[0073] Post-processing process: post-processing the cobalt hydroxide slurry to obtain cobalt hydroxide;

[0074] In the synthesis process, the pH of the base solution is 4.0-8.5.

[0075] It can be understood that in the synthesis process of the embodiment, the cobalt salt solution in the base solution is in contact with the alkali solution and the antioxidant, the alkali solution continuously reacts with the cobalt salt to generate cobalt hydroxide, and the antioxidant can prevent the cobalt in the reaction system from being oxidized to trivalent, so that the cobalt in the reaction system can remain divalent, so as to obtain the cobalt hydroxide slurry; wherein the pH of the base solution is maintained at an appropriate level, which can promote the generation of a large amount of nanosheets with thin thickness and large surface area, and then obtain the cobalt hydroxide slurry containing cobalt hydroxide with extremely thin thickness; after the cobalt hydroxide slurry is post-processed, cobalt hydroxide is obtained.

[0076] It should be noted that in the synthesis process, the pH of the base solution is mainly controlled by the content of the antioxidant in the base solution. If the pH of the base solution is higher than 8.5, the reaction system will have a high initial supersaturation (reaction concentration), which will lead to the generation of sheet-shaped cobalt hydroxide with small surface area and thicker thickness, and the generated nanosheet-shaped cobalt hydroxide is more prone to agglomeration, with poor dispersibility, so that the cobalt hydroxide in the embodiment cannot be obtained.

[0077] In some embodiments, in the synthesis process, during the synthesis reaction: the flow rate ratio of the cobalt salt solution, the alkali solution and the antioxidant is 1:(0.35-0.45):(0.05-0.20).

[0078] It should be understood that when the three are added in parallel, the flow rate ratio of the cobalt salt solution, the alkali solution and the antioxidant is a volume ratio. During the synthesis reaction, if the volume flow rate of the alkali solution and the antioxidant is too high compared with the volume amount of the cobalt salt solution, the supersaturation of the reaction system will be too strong, which will lead to the generation of nanosheets with thicker thickness and smaller surface area, and will also greatly increase the particle agglomeration and increase the impurity level, which is not conducive to post-processing. In addition, if the volume flow rate of the alkali solution and the antioxidant is too low compared with the volume amount of the cobalt salt solution, the supersaturation of the reaction system will be weak, which will lead to the rapid growth of the nanosheets, the large particle size, and will also lead to insufficient morphology induction, affecting the quality of the prepared cobalt hydroxide. Therefore, in the embodiment, during the synthesis reaction, by adjusting the flow rate ratio of the cobalt salt solution, the alkali solution and the antioxidant added in the base solution to be 1:(0.35-0.45):(0.05-0.20), the morphology of the sheet-shaped cobalt hydroxide can be further controlled, which is conducive to promoting the generation of sheet-shaped cobalt hydroxide with thinner thickness and larger surface area, so as to obtain the cobalt hydroxide in the embodiment.

[0079] Therefore, in the synthesis process, by controlling the pH of the bottom solution to be 4.0-8.5, and controlling the feeding flow rate ratio of the cobalt salt solution, the alkali solution and the antioxidant to be 1:(0.35-0.45):(0.05-0.20) during the synthesis reaction process, the morphology of the cobalt hydroxide can be effectively and synergistically controlled, so as to facilitate the preparation of cobalt hydroxide with an extremely thin thickness.

[0080] In some embodiments, in the synthesis process, the volume ratio of the amount of the bottom solution to the amount of the cobalt salt solution is (0.5-2):1; and / or, the volume ratio of the amount of the bottom solution to the amount of the alkali solution is (1-5):1; and / or, the volume ratio of the amount of the bottom solution to the amount of the antioxidant is (2.5-40):1. By designing the volume ratio of the amount of the bottom solution and the cobalt salt solution, the alkali solution and the antioxidant to be within the above range, respectively, the reaction conditions can be optimized during the reaction process, the full mixing of the components in the reaction system and the reaction efficiency can be ensured, and the generated cobalt hydroxide has a morphology feature of being thinner and having a larger surface area.

[0081] In some embodiments, the post-processing process specifically includes: sequentially performing washing, pressure filtration, drying and crushing treatment on the cobalt hydroxide slurry to obtain the cobalt hydroxide.

[0082] In the post-processing process of the present embodiment, by washing the cobalt hydroxide slurry, the residual impurities on the surface of the particles can be removed, and after washing, the solid-liquid separation of the cobalt hydroxide and the solvent can be realized through pressure filtration, and after further drying and crushing, the cobalt hydroxide of the present embodiment can be obtained.

[0083] In some embodiments, the cobalt salt solution includes at least one of cobalt chloride, cobalt sulfate or cobalt nitrate; the above substances as the cobalt salt solution can all perform a synthesis reaction with the alkali solution in the bottom solution, provide a cobalt source for the synthesis of cobalt hydroxide, and facilitate the preparation of flaky cobalt hydroxide with an extremely thin thickness.

[0084] In some embodiments, the alkali solution includes at least one of sodium hydroxide or potassium hydroxide; the above substances as the alkali solution can perform a synthesis reaction with the cobalt salt solution in the bottom solution, provide hydroxyl ions for the synthesis of cobalt hydroxide, and facilitate the preparation of flaky cobalt hydroxide with an extremely thin thickness.

[0085] In some embodiments, the antioxidant includes at least one of citric acid, hydrazine hydrate, sodium borohydride, ascorbic acid, sodium ascorbate or carbohydrazide; the above substances can all inhibit the oxidation of cobalt in the bottom solution, and facilitate the synthesis of flaky cobalt hydroxide with an extremely thin thickness.

[0086] In some embodiments, to avoid the bivalent cobalt ions being oxidized during the reaction process, the synthesis process is carried out in a protective atmosphere, the protective atmosphere is at least one of inert gases such as nitrogen, helium or argon, so that the cobalt ions can remain bivalent to facilitate the synthesis of the extremely thin thickness cobalt hydroxide sheet.

[0087] In some embodiments, the synthesis reaction process and after the reaction are stirred, and the stirring rate is controlled to be 400 r / min-1000 r / min, which is beneficial to the mixing of the cobalt salt solution, the lye and the antioxidant, avoids the local aggregation of the reactants, and makes the obtained cobalt hydroxide have more excellent uniformity.

[0088] In some embodiments, the temperature of the synthesis reaction is controlled to be 35-50℃, which is beneficial to the control of the growth morphology of the cobalt hydroxide, so as to obtain the cobalt hydroxide with extremely thin thickness.

[0089] In some embodiments, the time of the synthesis reaction is controlled to be 1-4h, which is helpful to the control of the growth morphology of the cobalt hydroxide, and then the cobalt hydroxide with extremely thin thickness is obtained.

[0090] In some embodiments, when the drying treatment is carried out in the post-processing process, the temperature is controlled to be 80℃-150℃, and the time is controlled to be 10h-20h, so as to improve the drying efficiency and make the cobalt hydroxide fully dry.

[0091] Another embodiment of the present disclosure provides a positive electrode material, and the raw material of the positive electrode material or the coating material of the positive electrode material comprises the cobalt hydroxide as above or the cobalt hydroxide prepared by the preparation method as above.

[0092] In some embodiments, the positive electrode material is prepared by mixing and sintering the nickel-based positive electrode material and the cobalt hydroxide; wherein the nickel-based positive electrode material comprises at least one of lithium nickel cobalt manganese oxide, lithium nickel cobalt aluminate, lithium nickel cobalt manganese titanate and nickel hydride. For example, the above-mentioned cobalt hydroxide is mixed with the nickel-based positive electrode material after one-time sintering, and then secondary sintering treatment is carried out in air or oxygen atmosphere, and the product obtained by the sintering treatment is cooled to room temperature, and then crushed and sieved to obtain the positive electrode material.

[0093] In this embodiment, the positive electrode material is prepared by sintering the nickel-based positive electrode material and the cobalt hydroxide, the cobalt hydroxide is in sheet shape and has extremely thin thickness, and the cobalt hydroxide is closely adsorbed on the surface of the nickel-based positive electrode material, so as to improve the surface loading rate of the positive electrode material, effectively improve the coating effect, and improve the electrochemical performance of the positive electrode material, so as to effectively improve the electrical performance of the lithium battery.

[0094] The nickel-based positive electrode material in the embodiment includes at least one of lithium nickel cobalt manganese oxide, lithium nickel cobalt aluminum oxide, lithium nickel cobalt manganese titanium oxide, and nickel hydride, and is more preferably lithium nickel cobalt manganese oxide with a nickel content greater than 60%. The lithium nickel cobalt manganese oxide with a high nickel content has poor surface properties and is more likely to form a nickel oxide-like rock salt phase and surface residual lithium. The coating of the cobalt hydroxide in the embodiment can effectively inhibit the rock salt phase and consume the surface residual lithium, form a uniform coating layer, isolate the positive electrode material from the electrolyte, shorten the electron transport path, improve the ion migration rate, enable lithium ions to be quickly inserted and extracted, and thus improve the electrochemical performance of the positive electrode material.

[0095] Another embodiment of the present disclosure provides a battery including a positive electrode made of the positive electrode material as above. For example, the positive electrode material, conductive carbon black, and a binder are mixed and coated on an aluminum foil to form a positive electrode sheet; and a battery case, the positive electrode sheet, a negative electrode sheet, a separator, a spring, and a gasket are assembled into a battery.

[0096] Another embodiment of the present disclosure provides an electrical equipment including the battery as above.

[0097] The following embodiments more specifically describe the disclosure of the present disclosure, which are merely used for illustrative explanation, and various modifications and changes within the scope of the disclosure of the present disclosure are obvious to those skilled in the art. Unless otherwise stated, all reagents and raw materials used in the embodiments are commercially available or synthesized according to conventional methods, and the instruments used in the embodiments are commercially available.

[0098] Embodiment 1

[0099] Synthesis process: a mixed solution of pure water and an antioxidant (citric acid) solution is used as a base solution, and the pH of the base solution is controlled to be 4.0; the base solution is added to a reaction container, and a cobalt chloride solution (1.8 mol / L), a sodium hydroxide solution (8 mol / L), and a hydrazine hydrate solution (80 wt%) are added to the base solution in parallel under nitrogen protection conditions, and a synthesis reaction is performed under stirring, wherein the temperature of the synthesis reaction is controlled to be 35°C, the time of the synthesis reaction is controlled to be 2 h, the flow rate of the cobalt chloride solution is 15% of the volume of the reaction kettle per hour, the volume ratio of the flow rates of the cobalt chloride solution, the sodium hydroxide solution, and the hydrazine hydrate solution (i.e., the flow rate ratio of the feedstocks) is 1:0.45:0.05, the stirring speed is 700 r / min, and the volume ratio of the base solution to the cobalt salt solution is 1:1; after the reaction is completed, the stirring speed is kept unchanged, and the obtained cobalt hydroxide slurry is stirred at a constant temperature for 0.5 h.

[0100] Post-treatment process: the cobalt hydroxide slurry is washed for 3 times and then pressure-filtered to obtain a material after pressure filtration, and the material is dried at a temperature of 100-120°C for 15-18 h to obtain a dried material; and the dried material is crushed to obtain cobalt hydroxide.

[0101] Example 2

[0102] Synthesis process: the mixed solution of pure water and antioxidant (sodium ascorbate) solution is used as the bottom solution, and the pH of the bottom solution is controlled to be 7.1; the bottom solution is added into a reaction container, and under the condition of nitrogen protection, a cobalt chloride solution (2.0 mol / L), a sodium hydroxide solution (11 mol / L), and a hydrazine hydrate solution (80 wt%) are added into the bottom solution in parallel flow, and a synthesis reaction is carried out under stirring, wherein the temperature of the synthesis reaction is controlled to be 40°C, the time of the synthesis reaction is controlled to be 2 h, the flow rate of the cobalt chloride solution is 22% of the volume of the reaction kettle per hour, the volume ratio of the flow rates of the cobalt chloride solution, the sodium hydroxide solution, and the hydrazine hydrate solution is 1:0.38:0.10, the stirring speed is 700 r / min, and the volume ratio of the dosages of the bottom solution and the cobalt salt solution is 1:1; after the reaction is completed, the stirring speed is maintained unchanged, and the obtained cobalt hydroxide slurry is stirred at constant temperature for 0.5 h.

[0103] Post-treatment process: the cobalt hydroxide slurry is washed for 3 times, and then is subjected to pressure filtration, and the obtained material after pressure filtration is dried at a temperature of 100-120°C for 15-18 h to obtain dried material; and then the dried material is subjected to crushing treatment to obtain cobalt hydroxide.

[0104] Example 3

[0105] Synthesis process: the mixed solution of pure water and antioxidant (sodium ascorbate) solution is used as the bottom solution, and the pH of the bottom solution is controlled to be 7.1; the bottom solution is added into a reaction container, and under the condition of nitrogen protection, a cobalt chloride solution (2.0 mol / L), a sodium hydroxide solution (11 mol / L), and a hydrazine hydrate solution (80 wt%) are added into the bottom solution in parallel flow, and a synthesis reaction is carried out under stirring, wherein the temperature of the synthesis reaction is controlled to be 40°C, the time of the synthesis reaction is controlled to be 2 h, the flow rate of the cobalt chloride solution is 22% of the volume of the reaction kettle per hour, the volume ratio of the flow rates of the cobalt chloride solution, the sodium hydroxide solution, and the hydrazine hydrate solution is 1:0.38:0.10, the stirring speed is 700 r / min, and the volume ratio of the dosages of the bottom solution and the cobalt salt solution is 1:1; after the reaction is completed, the stirring speed is maintained unchanged, and the obtained cobalt hydroxide slurry is stirred at constant temperature for 0.5 h.

[0106] Post-treatment process: the cobalt hydroxide slurry is washed for 3 times, and then is subjected to pressure filtration, and the obtained material after pressure filtration is dried at a temperature of 100-120°C for 15-18 h to obtain dried material; and then the dried material is subjected to crushing treatment to obtain cobalt hydroxide.

[0107] Example 4

[0108] Synthesis procedure: using the mixed solution of pure water and antioxidant (ascorbic acid and sodium ascorbate) solution as the bottom solution, the pH of the bottom solution is controlled to be 6.0; the bottom solution is added into a reaction container, under the condition of nitrogen protection, a cobalt chloride solution (1.5 mol / L), a sodium hydroxide solution (8 mol / L) and a hydrazine hydrate solution (80 wt%) are added into the bottom solution in parallel flow, and the synthesis reaction is carried out under stirring, wherein the temperature of the synthesis reaction is controlled to be 35°C, the time of the synthesis reaction is controlled to be 1 h, the flow rate of the cobalt chloride solution is 30% of the volume of the reaction kettle per hour, the volume ratio of the cobalt chloride solution, the sodium hydroxide solution and the hydrazine hydrate solution is 1:0.40:0.15, the stirring speed is 700 r / min, and the volume ratio of the bottom solution and the cobalt salt solution is 1:1; after the reaction is completed, the stirring speed is kept unchanged, and the constant temperature stirring is carried out for 0.5 h, and then the cobalt hydroxide slurry is obtained.

[0109] Post-processing procedure: the cobalt hydroxide slurry is washed for 3 times, and then is subjected to pressure filtration, the post-filtration material is dried at a temperature of 100-120°C for 15-18 h, and then the dried material is obtained; the dried material is subjected to crushing treatment, and then the cobalt hydroxide is obtained.

[0110] Example 5

[0111] Synthesis procedure: using the mixed solution of pure water and antioxidant (sodium borohydride) solution as the bottom solution, the pH of the bottom solution is controlled to be 8.0; the bottom solution is added into a reaction container, under the condition of nitrogen protection, a mixed solution of cobalt chloride and aluminum sulfate (aluminum content 0.3 wt%, 1.8 mol / L), a sodium hydroxide solution (8 mol / L) and a hydrazine hydrate solution (80 wt%) are added into the bottom solution in parallel flow, and the synthesis reaction is carried out under stirring, wherein the temperature of the synthesis reaction is controlled to be 35°C, the time of the synthesis reaction is controlled to be 2.5 h, the flow rate of the cobalt chloride solution is 12% of the volume of the reaction kettle per hour, the volume ratio of the cobalt chloride solution, the sodium hydroxide solution and the hydrazine hydrate solution is 1:0.42:0.10, the stirring speed is 700 r / min, and the volume ratio of the bottom solution and the cobalt salt solution is 1:1; after the reaction is completed, the stirring speed is kept unchanged, and the constant temperature stirring is carried out for 0.5 h, and then the cobalt hydroxide slurry is obtained.

[0112] Post-processing procedure: the cobalt hydroxide slurry is washed for 3 times, and then is subjected to pressure filtration, the post-filtration material is dried at a temperature of 100-120°C for 15-18 h, and then the dried material is obtained; the dried material is subjected to crushing treatment, and then the cobalt hydroxide is obtained.

[0113] Example 6

[0114] Synthesis process: using a mixed solution of pure water and antioxidant solution (hydrazine hydrate and sodium ascorbate) as the bottom solution, controlling the pH of the bottom solution to be 8.2; the bottom solution is added into a reaction container, under the condition of nitrogen protection, a cobalt chloride solution (2.2 mol / L), a sodium hydroxide solution (10 mol / L), and a hydrazine hydrate solution (80 wt%) are added into the bottom solution in parallel flow, and the synthesis reaction is carried out under stirring, wherein the temperature of the synthesis reaction is controlled to be 50°C, the time of the synthesis reaction is controlled to be 3.5 h, the flow rate of the cobalt chloride solution is 10% of the volume of the reaction kettle per hour, the volume ratio of the cobalt chloride solution, the sodium hydroxide solution, and the hydrazine hydrate solution is 1:0.36:0.18, the stirring speed is 700 r / min, and the volume ratio of the bottom solution and the cobalt salt solution is 1:1; after the reaction is completed, the stirring speed is kept unchanged, and the constant-temperature stirring is carried out for 0.5 h, and then the cobalt hydroxide slurry is obtained.

[0115] Post-treatment process: the cobalt hydroxide slurry is washed for 3 times, and then pressure filtration is carried out, the obtained material after pressure filtration is dried at a temperature of 100-120°C for 15-18 h, and then dry material is obtained; the dry material is subjected to crushing treatment, and then the cobalt hydroxide is obtained.

[0116] Comparative example 1

[0117] Synthesis process: using a mixed solution of pure water and antioxidant solution (hydrazine hydrate and sodium ascorbate) as the bottom solution, controlling the pH of the bottom solution to be 8.2; the bottom solution is added into a reaction container, under the condition of nitrogen protection, a cobalt chloride solution (2.2 mol / L), a sodium hydroxide solution (10 mol / L), and a hydrazine hydrate solution (80 wt%) are added into the bottom solution in parallel flow, and the synthesis reaction is carried out under stirring, wherein the temperature of the synthesis reaction is controlled to be 50°C, the time of the synthesis reaction is controlled to be 3.5 h, the flow rate of the cobalt chloride solution is 10% of the volume of the reaction kettle per hour, the volume ratio of the cobalt chloride solution, the sodium hydroxide solution, and the hydrazine hydrate solution is 1:0.36:0.18, the stirring speed is 700 r / min, and the volume ratio of the bottom solution and the cobalt salt solution is 1:1; after the reaction is completed, the stirring speed is kept unchanged, and the constant-temperature stirring is carried out for 0.5 h, and then the cobalt hydroxide slurry is obtained.

[0118] Post-treatment process: the cobalt hydroxide slurry is washed for 3 times, and then pressure filtration is carried out, the obtained material after pressure filtration is dried at a temperature of 100-120°C for 15-18 h, and then dry material is obtained; the dry material is subjected to crushing treatment, and then the cobalt hydroxide is obtained.

[0119] Comparative example 2

[0120] Synthesis process: using the mixed solution of pure water and antioxidant (hydrazine hydrate) solution as the bottom solution, controlling the pH of the bottom solution to be 9.5; the bottom solution is added into a reaction container, under the condition of nitrogen protection, a cobalt chloride solution (1.8 mol / L), a sodium hydroxide solution (8 mol / L) and a hydrazine hydrate solution (80 wt%) are added into the bottom solution in parallel flow, and the synthesis reaction is carried out under stirring, wherein the temperature of the synthesis reaction is controlled to be 45℃, the time of the synthesis reaction is controlled to be 2h, the flow rate of the cobalt chloride solution is 15% of the volume of the reaction kettle per hour, the volume ratio of the cobalt chloride solution, the sodium hydroxide solution and the hydrazine hydrate solution is 1:0.50:0.25, the stirring speed is 700 r / min, and the volume ratio of the bottom solution and the cobalt salt solution is 1:1; after the reaction is completed, the stirring speed is kept unchanged, and the constant temperature stirring is carried out for 0.5h, and then the cobalt hydroxide slurry is obtained.

[0121] Post-treatment process: the cobalt hydroxide slurry is washed for 3 times, and then is subjected to pressure filtration, the post-filtration material is dried at a temperature of 100-120℃ for 15-18h to obtain dried material; and then the dried material is subjected to crushing treatment to obtain cobalt hydroxide.

[0122] Comparative example 3

[0123] Synthesis process: 238 mg (1.0 mmol) of cobalt chloride hexahydrate and 1206 mg (9.0 mmol) of sodium oxalate are mixed in 20 mL of ethylene glycol solvent, stirred at a speed of 700 r / min at room temperature for 2h to obtain solution A; 60 mg of sodium hydroxide is added into 10 mL of ethylene glycol solution, stirred at a speed of 700 r / min at room temperature for 2h to obtain solution B; solution A and solution B are mixed, and ultrasonic treatment is carried out for 0.5h to obtain solution C; solution C is subjected to solvothermal reaction at 200℃ for 16h in a 50 mL closed polytetrafluoroethylene hydrothermal kettle, and then is naturally cooled to room temperature;

[0124] Post-treatment process: the reaction material is washed for 3 times, and then is dried at a temperature of 60℃ for 15-18h to obtain dried material; and then the dried material is subjected to crushing treatment to obtain cobalt hydroxide.

[0125] Comparative example 4

[0126] Synthesis process: pure water is used as the bottom liquid, and under the condition of nitrogen protection, cobalt chloride solution (1.8 mol / L) and sodium hydroxide solution (11 mol / L) are added into the bottom liquid in parallel flow, and the synthesis reaction is carried out under stirring, wherein the temperature of the synthesis reaction is controlled at 50℃, the time of the synthesis reaction is controlled at 2h, the flow rate of the cobalt chloride solution is 15% of the volume of the reactor per hour, the volume ratio of the cobalt chloride solution to the sodium hydroxide solution is 1:0.51, the stirring speed is 700r / min, and the volume ratio of the bottom liquid to the cobalt salt solution is 1:1; after the reaction is completed, the stirring speed is kept unchanged, and the constant temperature stirring is maintained for 0.5h, and then the cobalt hydroxide slurry is obtained.

[0127] Post-treatment process: the cobalt hydroxide slurry is washed for 3 times, and then pressure filtration is carried out, and the obtained material after pressure filtration is dried at a temperature of 100-120℃ for 15-18h to obtain dry material; and then the dry material is crushed to obtain cobalt hydroxide.

[0128] Comparative Example 5

[0129] Synthesis process: pure water is used as the bottom liquid, and cobalt chloride solution (1.8 mol / L) is added into the bottom liquid, and under the condition of nitrogen protection, cobalt chloride solution (1.8 mol / L) and sodium hydroxide solution (10 mol / L) are added into the bottom liquid in parallel flow, and the synthesis reaction is carried out under stirring, wherein the temperature of the synthesis reaction is controlled at 45℃, the time of the synthesis reaction is controlled at 1h, the flow rate of the cobalt chloride solution is 20% of the volume of the reactor per hour, the volume ratio of the cobalt chloride solution to the sodium hydroxide solution is 1:0.36, the stirring speed is 700r / min, and the volume ratio of the bottom liquid to the cobalt salt solution is 1:1; after the reaction is completed, the stirring speed is kept unchanged, and the constant temperature stirring is maintained for 0.5h, and then the cobalt hydroxide slurry is obtained.

[0130] Post-treatment process: the cobalt hydroxide slurry is washed for 3 times, and then pressure filtration is carried out, and the obtained material after pressure filtration is dried at a temperature of 100-120℃ for 15-18h to obtain dry material; and then the dry material is crushed to obtain cobalt hydroxide.

[0131] The cobalt hydroxide obtained in the above Examples 1-6 and Comparative Examples 1-5 is tested and characterized, and the test data of the cobalt hydroxide is obtained, and the statistical data is shown in Table 1 and Figures 1-7:

[0132] Table 1: Physical and chemical data table of cobalt hydroxide Note: In the above Table 1, "BET" represents specific surface area; "width a" and "length b" represent the average width and length of the cobalt hydroxide, respectively.

[0133] In addition, “Intensity (counts)” in FIG. 7 represents the diffraction intensity, and “Two-Theta (deg)” represents the double Theta angle, ie, the 2θ angle, which is the angle between the incident X-ray and the normal line of the sample surface.

[0134] Furthermore, the cobalt hydroxide prepared in Examples 1 to 6 and Comparative Examples 1 to 5 was coated on the surface of the positive electrode material to prepare the positive electrode material. The preparation process was as follows:

[0135] The cobalt hydroxide prepared in Examples 1 to 6 and Comparative Examples 1 to 5 was mixed with the nickel-based positive electrode material LiNi prepared once at a mass ratio of 1%. 0.9 Co 0.06 Mn 0.04 The mixture was mixed at high speed with O2 for 60 minutes, and then the mixture was heated to 700°C at a heating rate of 3°C / min for a second firing, and the firing time was 10 hours. The fired materials obtained by the second firing were cooled and sieved in turn to obtain positive electrode materials made of cobalt hydroxide.

[0136] The positive electrode materials prepared from cobalt hydroxide in Example 2 and Comparative Example 2, and the nickel-based positive electrode material in the control group were characterized under a scanning electron microscope, and the obtained SEM images are shown in Figures 8, 12 and 13, respectively.

[0137] The positive electrode material prepared from cobalt hydroxide in Example 2 was characterized by EDS spectrometer, and the obtained element distribution diagrams are shown in Figures 9 to 11.

[0138] It can be seen from Figures 8, 12 and 13 that the surface of the secondary particles of the nickel-based positive electrode material in the control group in Figure 13 (nickel-based positive electrode material not coated with cobalt hydroxide) is smooth; the surface of the secondary particles of the positive electrode material prepared by cobalt hydroxide in Example 2 in Figure 8 is relatively smooth, with only a very small amount of small particles attached; the surface of the secondary particles of the positive electrode material prepared by cobalt hydroxide in Comparative Example 2 in Figure 12 is uneven, with a large amount of small particles attached.

[0139] It can be found in combination with FIGS. 8, 12 and 13 that on the positive electrode material prepared from the cobalt hydroxide in Example 2, the cobalt hydroxide is closely adsorbed on the surface of the nickel-based positive electrode material, the cobalt hydroxide has a high coverage on the surface of the nickel-based positive electrode material, and is uniformly distributed, forming a more uniform coating layer, which exhibits a good coating effect on the nickel-based positive electrode material, and after secondary sintering, the cobalt hydroxide can be melted on the surface of the secondary particles; on the positive electrode material prepared from the cobalt hydroxide in Comparative Example 2, the cobalt hydroxide is accumulated on the surface of the nickel-based positive electrode material in a large amount, and is not uniformly distributed, has a poor adsorption on the surface of the nickel-based positive electrode material, has a low coverage on the surface of the nickel-based positive electrode material, and forms a coating layer with poor uniformity, which has a poor coating effect on the nickel-based positive electrode material, and after secondary sintering, a large amount of the cobalt hydroxide fails to be melted on the surface of the secondary particles, and small particles are formed on the surface.

[0140] As can be seen from FIGS. 9-11, in FIG. 9, the abscissa represents the length corresponding to different positions in the cross-sectional secondary particles of the positive electrode material prepared from the cobalt hydroxide in Example 2, and the ordinate represents the element content corresponding to different positions in the cross-sectional secondary particles thereof; the yellow line represents the nickel content of the cross-sectional secondary particles thereof at different positions, the green line represents the cobalt content of the cross-sectional secondary particles thereof at different positions, and the purple-red line represents the manganese content of the cross-sectional secondary particles thereof at different positions; from inside to outside along the radial direction near the surface of the secondary particles, the yellow line shows a sharp downward trend, the green line shows an upward trend, and the purple-red line shows a small downward trend; in FIG. 10, the green dots represent the Co element of the cross-sectional secondary particles thereof, which are gathered on the surface of the secondary particles and are uniformly distributed inside; in FIG. 10, the yellow dots represent the Ni element of the cross-sectional secondary particles thereof, the green dots represent the Co element of the cross-sectional secondary particles thereof, and the purple-red dots represent the Mn element of the cross-sectional secondary particles thereof; the green dots are gathered on the surface of the secondary particles and are uniformly distributed inside, and the yellow dots and the purple-red dots are less distributed on the surface of the secondary particles and are uniformly distributed inside.

[0141] It can be further found in combination with FIGS. 9-11 that in the positive electrode material prepared from the cobalt hydroxide in Example 2, from inside to outside along the radial direction near the surface of the secondary particles, the concentrations of the nickel element and the manganese element in the particles gradually decrease, while the concentration of the cobalt element gradually increases, the concentration of the cobalt element on the surface of the particles is high and is uniformly distributed, forming a uniform coating layer, which indicates that the cobalt hydroxide prepared in Example 2 can be closely adsorbed on the surface of the nickel-based positive electrode material, has a high coverage on the surface of the nickel-based positive electrode material, and is uniformly distributed, forming a more uniform coating layer, which exhibits a good coating effect on the nickel-based positive electrode material.

[0142] To verify the influence of the cobalt hydroxide prepared in each example and comparative example on the residual lithium on the surface of the positive electrode material, a control group is set, and the control group is the above uncoated nickel-based positive electrode material LiNi 0.9 Co 0.06 Mn 0.04O2, the positive electrode material prepared from the cobalt hydroxide in the above Examples 1-6 and Comparative Examples 1-5 and the nickel-based positive electrode material in the control group were subjected to surface residual lithium testing, and the data are shown in Table 2 below,

[0143] Table 2: Positive electrode material surface residual lithium data table Note: The calculation formula of residual alkali change rate is:

[0144] For example, taking Example 1 as an example, the residual alkali of the positive electrode material prepared from the cobalt hydroxide in Example 1 is 2800 ppm in terms of Li2CO3 and 3100 ppm in terms of LiOH; the residual alkali of the uncoated positive electrode material in the control group is 4300 ppm in terms of Li2CO3 and 3700 ppm in terms of LiOH, and the residual alkali change rate of the positive electrode material prepared from the cobalt hydroxide in Example 1 is:

[0145] In order to verify the influence of cobalt hydroxide on the electrical performance of the battery, the positive electrode materials prepared from the cobalt hydroxide in the above Examples 1-6 and Comparative Examples 1-5, and the uncoated nickel-based positive electrode material in the control group were respectively assembled into button cells, and the electrical performance was tested. The button cell preparation process and test conditions are as follows:

[0146] The positive electrode materials prepared from the cobalt hydroxide in the above Examples 1-6 and Comparative Examples 1-5, and the nickel-based positive electrode material in the control group were respectively mixed with a conductive agent and a binder PVDF in a mass ratio of 96.5:1.5:2 to form a slurry, which was coated on an aluminum foil to form a positive electrode sheet. A metal lithium sheet was used as a negative electrode sheet, and a 1 mol / L LiPF6 / EC:DMC (volume ratio 1:1) electrolyte was used. The battery shell, positive and negative electrode sheets, separator, spring, and gasket were assembled into a button cell in a vacuum glove box.

[0147] The button cells prepared above were subjected to electrochemical performance testing using a blue light testing system. The test temperature was 25°C, the test voltage range was 3.0-4.3V, and 1C=210 mAh / g. The test results obtained are shown in Tables 3, 4, 5 and Figure 14 below:

[0148] Table 3: Cycle performance data statistics table

[0149] Table 4: Direct current internal resistance (DCR) data statistics table under different SOC states

[0150] It should be noted that DCR (Direct Current Resistance) in Table 4 is the direct current resistance, i.e. the internal resistance Ω; and SOC (State of Charge) refers to the ratio between the current capacity and the maximum capacity of the battery.

[0151] Table 5: Rate performance data statistics

[0152] The advantages of the embodiments of the present disclosure are analyzed below in combination with Tables 1-5 and Figures 1-14.

[0153] Referring to Table 1, compared with Example 1, the average thickness of the cobalt hydroxide prepared in Comparative Example 1 is too large, the aspect ratio (the ratio of I(001) / I(100)) of the flaky particles is slightly low, the peak intensity ratio I(001) / I(100) in the XRD pattern is less than 7.5, the surface area of the cobalt hydroxide is low, and the coating effect on the nickel-based positive electrode material is poor. On the contrary, the average thickness of the cobalt hydroxide prepared in Example 1 is thinner than that in Comparative Example 1, the peak intensity ratio I(001) / I(100) in the XRD pattern is much higher than 7.5, the surface area of the cobalt hydroxide is high, and the coating effect on the nickel-based positive electrode material is better.

[0154] Further referring to Table 2, the residual Li2CO3 on the surface of the positive electrode material prepared from the cobalt hydroxide in Comparative Example 1 is 3400 ppm, and the residual LiOH is 2700 ppm, both of which are much higher than those in Example 1. At the same time, the residual alkali change rate of Comparative Example 1 is 23.75%, which is lower than that of Example 1, indicating that the cobalt hydroxide in Comparative Example 1 is not good at consuming the residual lithium on the surface of the nickel-based positive electrode material. The residual Li2CO3 on the surface of the positive electrode material prepared from the cobalt hydroxide in Example 1 is 2800 ppm, the residual LiOH is 3100 ppm, and the residual alkali change rate is 26.25%, which has a significant inhibitory effect on the residual alkali on the surface of the nickel-based positive electrode material.

[0155] Further referring to Tables 3-5 and Figure 14, the battery prepared from the positive electrode material group of Comparative Example 1 has lower capacity retention rate after 50 cycles at 1C and lower discharge median voltage retention rate after 50 cycles at 1C than the battery prepared from the positive electrode material group of Example 1, has higher direct current resistance under different SOC states than the corresponding Example 1, and has lower discharge specific capacity under 0.2C, 0.5C, 1C, 2C and 4C than Example 1. It can be seen that, due to the poor coating effect of the cobalt hydroxide on the positive electrode material, the battery rate performance and cycle performance of Comparative Example 1 are not significantly improved. The battery prepared from the positive electrode material group of Example 1 has significantly improved cycle performance at 1C, and the direct current resistance under different SOC states is also lower than the corresponding Comparative Example 1 and far lower than the control group. Moreover, the discharge specific capacity under 0.2C, 0.5C, 1C, 2C and 4C is much higher than that of Comparative Example 1, and the battery rate performance is effectively improved.

[0156] With reference to Table 1, FIG. 1, FIG. 6, FIG. 7, FIG. 8 and FIG. 12, the average thickness of the cobalt hydroxide in Comparative Example 2 is significantly thicker than that in Example 2, resulting in a significant decrease in the specific surface area and the surface area, and a poor coating effect on the nickel-based positive electrode material (as shown in FIG. 12); in contrast, the average thickness of the cobalt hydroxide prepared in Example 2 is thinner than that in Comparative Example 2, the peak intensity ratio I(001) / I(100) in the XRD pattern is much higher than 7.5, the surface area of the cobalt hydroxide is higher, and the cobalt hydroxide has a better coating effect on the nickel-based positive electrode material (as shown in FIG. 8).

[0157] With further reference to Table 2, the residual Li2CO3 on the surface of the positive electrode material prepared from the cobalt hydroxide in Comparative Example 2 is 3600 ppm, and the residual LiOH is 2800 ppm, both of which are much higher than those in Example 2. Meanwhile, the residual alkali change rate of Comparative Example 2 is 20%, which is lower than that of Example 2, indicating that the cobalt hydroxide in Comparative Example 2 is not good at consuming the residual lithium on the surface of the nickel-based positive electrode material; while the residual Li2CO3 on the surface of the positive electrode material prepared from the cobalt hydroxide in Example 2 is 2600 ppm, the residual LiOH is 3300 ppm, and the residual alkali change rate is 26.25%, indicating that the cobalt hydroxide in Example 2 has a significant inhibitory effect on the residual alkali on the surface of the nickel-based positive electrode material.

[0158] With further reference to Tables 3-5 and FIG. 14, the capacity retention rate at 1C after 50 cycles and the discharge median voltage retention rate at 1C after 50 cycles of the battery prepared from the positive electrode material group of Comparative Example 2 are both lower than those of the battery prepared from the positive electrode material group of Example 2, the direct current resistance under different SOC states is higher than that of Example 2, and the discharge specific capacity under 0.2C, 0.5C, 1C, 2C and 4C is lower than that of Example 2; it can be seen that, due to the poor coating effect of the cobalt hydroxide on the positive electrode material, the rate performance and the cycle performance of the battery of Comparative Example 2 are not significantly improved; while the cycle performance of the battery prepared from the positive electrode material group of Example 2 is significantly improved, the direct current resistance under different SOC states is lower than that of Comparative Example 2, and is much lower than that of the control group, and the discharge specific capacity under 0.2C, 0.5C, 1C, 2C and 4C is much higher than that of Comparative Example 2, especially the discharge specific capacity under 4C can reach 174.2 mAh / g, and the rate performance of the battery is effectively improved.

[0159] Compared with Example 1, the battery prepared by using other processes in Comparative Example 3 has poor electrochemical performance, and the possible reason is that the thickness of the cobalt hydroxide is 8 nm, which is too thin, resulting in a locally thin coating layer on the surface of the secondary particles after the secondary firing, which may not effectively isolate the side reaction between the electrolyte and the core material, leading to the dissolution of transition metals in the positive electrode material of the battery or the intensification of the interface side reaction, affecting the conductivity of the material.

[0160] Compared with Example 1, the battery prepared by Comparative Example 4 using nitrogen protection instead of the added antioxidant has poor electrochemical performance, and the possible reason is that the structure of the product obtained by different processes is changed, showing that the thickness, D50, Dmax, etc. are too large, and I(001) / I(100) is too small.

[0161] Compared with Example 1, the battery prepared by Comparative Example 5 without adding an antioxidant has poor electrochemical performance, and the possible reason is that the structure of the product obtained by different processes is changed, showing that the thickness, D50, Dmax, etc. are too large, and I(001) / I(100) is too small.

[0162] Through comprehensive analysis of Examples 1-6 and Comparative Examples 1-5, the disclosed embodiment can control the pH of the bottom solution to be 4.0-8.5 in the synthesis process, and control the flow rate ratio of the added cobalt salt solution, alkali solution and antioxidant to be 1:(0.35-0.45):(0.05-0.20) during the synthesis reaction process, so as to regulate the specific surface area and morphology of the cobalt hydroxide, and obtain cobalt hydroxide with an average thickness of 10-20 nm, which is beneficial to improve the adsorption and surface coverage of the nickel-based positive electrode material, effectively improve the coating effect, and thus effectively improve the cycle performance and rate performance of the battery.

[0163] In summary, the disclosed embodiment designs the structure and preparation method of cobalt hydroxide to prepare cobalt hydroxide with an extremely thin average thickness and a large surface area, so as to improve the coating effect of the nickel-based positive electrode material, and then effectively inhibit the formation of nickel oxide rock salt phase in the positive electrode material and reduce the residual lithium concentration on the surface of the positive electrode material, so that lithium ions can be quickly deintercalated, and finally the electrical performance of the lithium battery is significantly improved.

[0164] The above-described technical features can be combined in any manner. Although not all possible combinations of the technical features are described, any combination of the technical features should be considered to be covered by the present disclosure, as long as such a combination does not contradict.

[0165] Finally, it should be noted that: the above embodiments are only used to illustrate the technical solutions of the present disclosure, and not to limit them; although the present disclosure has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that they can still modify the technical solutions described in the foregoing embodiments, or make equivalent replacements to some or all of the technical features; and such modifications or replacements do not make the essence of the corresponding technical solutions deviate from the scope of the technical solutions of the embodiments of the present disclosure. Industrial applicability

[0166] The cobalt hydroxide particle of the present disclosure is in a sheet shape, and the average thickness thereof is 10-20 nm. As a coating material of the positive electrode material, the cobalt hydroxide particle can improve the coating effect on the positive electrode material, can generate lithium cobalt oxide with ion conductivity on the surface of the positive electrode material, effectively inhibit the formation of nickel oxide rock salt phase of the positive electrode material, reduce the residual lithium concentration on the surface of the positive electrode material, enable the lithium ion to be quickly extracted / inserted, and promote the significant improvement of the electrical performance of the positive electrode material made therefrom.

Claims

1. Cobalt hydroxide, characterized in that, The cobalt hydroxide particles are in a flaky shape, and the average thickness thereof is 10-20 nm.

2. Cobalt hydroxide according to claim 1, characterized in that The cobalt hydroxide satisfies at least one of the following conditions A-H: A. The peak intensity ratio I(001) / I(100) in the XRD pattern of the cobalt hydroxide is greater than 7.5, and optionally, I(001) / I(100) is greater than or equal to 9; B. the bulk density of the cobalt hydroxide is 0.08-0.40 g / cm 3 , optionally 0.10-0.20 g / cm 3 ; C. The average particle size D50 of the cobalt hydroxide is less than or equal to 0.2 μm, and optionally, 0.05-0.2 μm; D. The maximum particle size Dmax of the cobalt hydroxide is less than or equal to 1.5 μm; E. The particle size distribution (D90-D10) / D50 of the cobalt hydroxide is less than or equal to 4.0; F. The average width of the particles of the cobalt hydroxide is 220-400 nm, and the average length of the particles of the cobalt hydroxide is 300-500 nm. G. the specific surface area of the cobalt hydroxide is 10-80 m 2 / g, optionally 15-40 m 2 / g; H, the cobalt hydroxide has a chemical formula of Co a A b (OH)2, wherein 0.6≤a≤1.0, 0≤b≤0.4, and A includes one or more of Al, Mg, Mn, Ni, La, Ti, Y, and Er.

3. A process for the preparation of cobalt hydroxide according to any one of claims 1 to 2, characterized in that, The method comprises: a synthesis step of adding a cobalt salt solution, a base solution and an antioxidant to a base solution containing an antioxidant, and performing a synthesis reaction to obtain a cobalt hydroxide slurry; a post-treatment step of post-treating the cobalt hydroxide slurry to obtain a cobalt hydroxide; In the synthesis step, the pH of the base solution is 4.0-8.

5.

4. The method for preparing cobalt hydroxide according to claim 3, wherein In the synthesis step, during the synthesis reaction: The feed flow rate ratio of the cobalt salt solution, the base solution and the antioxidant is 1:(0.35-0.45):(0.05-0.20).

5. The method for preparing cobalt hydroxide according to claim 3, wherein In the synthesis step, the volume ratio of the base solution to the cobalt salt solution is (0.5-2):1; and / or, the volume ratio of the base solution to the base solution is (1-5):1; and / or, the volume ratio of the base solution to the antioxidant is (2.5-40):

1.

6. The method of claim 3, wherein: The cobalt salt solution comprises at least one of cobalt chloride, cobalt sulfate or cobalt nitrate; and / or, the base solution comprises at least one of sodium hydroxide or potassium hydroxide; and / or, the antioxidant comprises at least one of citric acid, hydrazine hydrate, sodium borohydride, ascorbic acid, sodium ascorbate or carbohydrazide; and / or, the synthesis step is performed in a protective atmosphere comprising at least one of nitrogen, helium or argon.

7. The method of claim 3, wherein: During the synthesis reaction and after the reaction, stirring is performed, and the stirring rate is controlled to be 400 r / min-1000 r / min; and / or, the temperature of the synthesis reaction is controlled to be 35-50°C; and / or, the time of the synthesis reaction is controlled to be 1-4 h; and / or, in the post-treatment step, when drying is performed, the temperature is controlled to be 80°C-150°C; and / or, in the post-treatment step, when drying is performed, the time is controlled to be 10 h-20 h.

8. A positive electrode material, characterized by, The raw material of the positive electrode material or the coating material of the positive electrode material comprises the cobalt hydroxide of any one of claims 1-2 or the cobalt hydroxide prepared by the method of any one of claims 3-7.

9. A battery, characterized by The battery comprises a positive electrode made of the positive electrode material of claim 8.

10. An electrical device, comprising: The electrical equipment comprises the battery of claim 9.

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