Positive electrode material and preparation method thereof, positive electrode plate and secondary battery

Abstract

The invention relates to the technical field of batteries, and provides a positive electrode material and a preparation method thereof, a positive electrode plate and a secondary battery, the positive electrode material comprises an inner core and a coating layer coating at least part of the surface of the inner core; the inner core comprises a material with a chemical formula of LiCoxQ1-xO2-yZy, the element Q comprises at least one of Mg, Al, Ti, La, Y, Zr, Ni, Mn, Ce, Sc, W, Nb and V, the element Z comprises at least one of S, F and Cl, x is greater than or equal to 0.9 and less than or equal to 1, and y is greater than or equal to 0 and less than or equal to 0.1; and the material of the coating layer comprises organic acid metal salt. The positive electrode material has the characteristics of good conductivity, good structural stability and the like.

Description

Technical Field

[0001] The present application relates to the field of battery technology, and in particular to a positive electrode material and a preparation method thereof, a positive electrode plate and a secondary battery. Background Art

[0002] Lithium cobalt oxide materials have the characteristics of high energy density and high compaction density. In order to further improve the compaction density of lithium cobalt oxide materials, traditional technology improves the structural stability of lithium cobalt oxide materials by coating them with inert oxides. However, the conductivity of inert oxides is poor, which affects the cycle performance of the battery. Summary of the invention

[0003] Based on this, an embodiment of the present application provides a positive electrode material with good conductivity and good structural stability, a preparation method thereof, a positive electrode plate and a secondary battery.

[0004] In a first aspect, the present application provides a positive electrode material, the positive electrode material comprising a core and a coating layer coated on at least a portion of the surface of the core; the core comprises a chemical formula of LiCo x Q 1-x O 2-y Z y A material, wherein the Q element includes at least one of Mg, Al, Ti, La, Y, Zr, Ni, Mn, Ce, Sc, W, Nb and V, the Z element includes at least one of S, F and Cl, 0.9≤x≤1, 0≤y≤0.1;

[0005] The material of the coating layer includes organic acid metal salt.

[0006] In some embodiments, the organic acid group of the organic acid metal salt contains 1 to 6 carbon atoms.

[0007] In some embodiments, the organic acid group of the organic acid metal salt further contains at least one of the B element, the F element, the S element and the N element.

[0008] In some embodiments, the mass of the coating layer is 300ppm~6000ppm of the mass of the core.

[0009] In some embodiments, the volume average particle size Dv50 of the positive electrode material is 15.0 μm to 17.0 μm.

[0010] In some embodiments, the compaction density of the positive electrode material at 200 MPa is ≥ 4.17 g / cm 3 .

[0011] In a second aspect, the present application provides a method for preparing a positive electrode material, the method for preparing a positive electrode material comprising:

[0012] Provided is a LiCo x Q 1-x O 2-y Z y The core of the material is a material of the present invention, wherein the Q element includes at least one of Mg, Al, Ti, La, Y, Zr, Ni, Mn, Ce, Sc, W, Nb and V, the Z element includes at least one of S, F and Cl, 0.9≤x≤1, 0≤y≤0.1;

[0013] A mixture comprising the core, a metal source, an organic acid and an organic solvent is formed, and the mixture is dried and then calcined to form a coating layer comprising an organic acid metal salt on at least a portion of the surface of the core.

[0014] In some embodiments, the drying process is carried out at a temperature of 50° C. to 100° C. and for a time of 6 h to 10 h.

[0015] In some embodiments, the calcination temperature is 200° C. to 550° C., the calcination time is 4 h to 8 h, and the atmosphere is an inert atmosphere.

[0016] In some embodiments, the volume average particle size Dv50 of the core is 14.0 μm to 16.0 μm.

[0017] In some embodiments, the number of carbon atoms in the organic acid is 1 to 6.

[0018] In some embodiments, the organic acid further contains at least one of the B element, the F element, the S element and the N element.

[0019] In some embodiments, the organic acid includes at least one of n-propylboric acid, boron trifluoride acetic acid, and trifluoromethanesulfonic acid.

[0020] In a third aspect, the present application provides a positive electrode plate, comprising at least one of the positive electrode material as described in the first aspect and the positive electrode material prepared by the preparation method as described in the second aspect.

[0021] In a fourth aspect, the present application provides a secondary battery, comprising the positive electrode plate as described in the third aspect.

[0022] Compared with the traditional technology, this application has at least the following beneficial effects:

[0023] The present application uses a coating layer containing an organic acid metal salt to coat the core material, which can not only protect the integrity of the core material bulk structure, but also reduce the content of inert substances on the surface of the positive electrode material and improve the conductivity of the interface. In addition, the organic acid metal salt of the present application maintains the original organic structure in the coating layer, which can improve the compatibility with the electrolyte. Therefore, the positive electrode material of the present application has good structural stability and good conductivity. BRIEF DESCRIPTION OF THE DRAWINGS

[0024] Figure 1 This is a SEM image of the positive electrode material prepared in Example 1 of the present application;

[0025] Figure 2 This is another SEM image of the positive electrode material prepared in Example 1 of the present application;

[0026] Figure 3 This is a SEM image of the positive electrode material prepared in Example 2 of the present application;

[0027] Figure 4 This is another SEM image of the positive electrode material prepared in Example 2 of the present application;

[0028] Figure 5 This is a SEM image of the positive electrode material prepared in Example 3 of the present application;

[0029] Figure 6 This is another SEM image of the positive electrode material prepared in Example 3 of the present application;

[0030] Figure 7 This is a SEM image of the positive electrode material prepared in Example 4 of the present application;

[0031] Figure 8 This is another SEM image of the positive electrode material prepared in Example 4 of the present application;

[0032] Fig. 9 This is a SEM image of the positive electrode material in Comparative Example 1 of the present application;

[0033] Fig.10 This is another SEM image of the positive electrode material in Comparative Example 1 of the present application;

[0034] Fig.11 Graph showing the relationship between specific capacity and voltage of Example 4 and Comparative Example 1 of the present application;

[0035] Fig.12 Graph showing the relationship between the number of cycles and the cycle retention rate of Example 4 and Comparative Example 1 of the present application;

[0036] Fig.13 This is a relationship diagram between pressure and compaction density of Example 4 of the present application and Comparative Example 1. DETAILED DESCRIPTION

[0037] Below in conjunction with the embodiments and examples, the present application is further described in detail. These embodiments and examples are only used to illustrate the present application and are not used to limit the scope of the present application. The purpose of providing these embodiments and examples is to make the understanding of the disclosure of the present application more thorough and comprehensive. It should also be understood that the present application can be implemented in many different forms, and is not limited to the embodiments and examples described herein. Those skilled in the art can make various changes or modifications without violating the connotation of the present application, and the equivalent form obtained also falls within the protection scope of the present application. In addition, in the description below, a large number of specific details are given in order to provide a more comprehensive understanding of the present application. It should be understood that the present application can be implemented without one or more of these details.

[0038] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as those commonly understood by those skilled in the art to which this application belongs. The terms used herein in the specification of this application are only for the purpose of describing specific embodiments and are not intended to limit this application.

[0039] In this application, "optionally", "optional", and "optional" mean optional or dispensable, that is, any one of the two parallel schemes of "yes" or "no". If multiple "options" appear in a technical solution, unless otherwise specified and there is no contradiction or mutual restriction, each "optional" is independent.

[0040] In this application, the terms "first", "second", etc. in "the first aspect", "the second aspect", etc. are used only for descriptive purposes and cannot be understood as indicating or implying relative importance or quantity, nor can they be understood as implicitly indicating the importance or quantity of the indicated technical features. Moreover, "first", "second", etc. only serve the purpose of non-exhaustive enumeration and description, and it should be understood that they do not constitute a closed limitation on quantity.

[0041] In the present application, the technical features described in an open manner include closed technical solutions composed of the listed features, and also include open technical solutions containing the listed features.

[0042] In the present application, when it comes to a numerical interval (i.e., a numerical range), unless otherwise specified, the distribution of the optional numerical values ​​in the numerical interval is considered to be continuous, and includes the two numerical endpoints (i.e., the minimum and maximum values) of the numerical interval, and each numerical value between the two numerical endpoints. Unless otherwise specified, when the numerical interval only refers to an integer in the numerical interval, it includes the two endpoint integers of the numerical range, and each integer between the two endpoints, which is equivalent to directly listing each integer. When multiple numerical ranges are provided to describe features or characteristics, these numerical ranges can be combined. In other words, unless otherwise specified, the numerical range disclosed in the present application should be understood to include any and all sub-ranges included therein. The "numerical value" in the numerical interval can be any quantitative value, such as a number, a percentage, a ratio, etc. "Numerical interval" allows for a broad range of quantitative intervals such as percentage intervals, ratio intervals, and ratio intervals.

[0043] All documents mentioned in this application are cited as references in this application, just as each document is cited as reference separately. Unless they conflict with the application purpose and / or technical solution of this application, the cited documents involved in this application are cited with all contents and all purposes. When the cited documents are involved in this application, the definitions of relevant technical features, terms, nouns, phrases, etc. in the cited documents are also cited. When the cited documents are involved in this application, the examples and preferred methods of the cited relevant technical features can also be incorporated into this application as references, but are limited to the implementation of this application. It should be understood that when the cited content conflicts with the description in this application, the present application shall prevail or be modified adaptively according to the description of this application.

[0044] In traditional technology, inert oxides (such as aluminum oxide, yttrium oxide, zirconium oxide or titanium dioxide) are used to solid-phase coat lithium cobalt oxide materials. The process mainly involves mechanically mixing the lithium cobalt oxide material and the coating and then sintering them, which can easily cause an uneven coating layer (such as forming an island-shaped coating). The use of inert oxides not only reduces conductivity and increases the risk of element enrichment, but also has a high sintering temperature.

[0045] In a first aspect, the present application provides a positive electrode material, the positive electrode material comprising a core and a coating layer coated on at least a portion of the surface of the core; the core comprises a LiCo x Q 1-x O 2-y Z y A material, wherein the Q element includes at least one of Mg, Al, Ti, La, Y, Zr, Ni, Mn, Ce, Sc, W, Nb and V, the Z element includes at least one of S, F and Cl, 0.9≤x≤1, 0≤y≤0.1;

[0046] The material of the coating layer includes organic acid metal salt.

[0047] The present application uses a coating layer containing an organic acid metal salt to coat the core material, which can not only protect the core material, but also reduce the content of inert substances on the surface of the positive electrode material and improve the conductivity of the interface. In addition, the organic acid metal salt of the present application maintains the original organic structure in the coating layer, which can improve the compatibility with the electrolyte. Therefore, the positive electrode material of the present application has good structural stability and good conductivity.

[0048] Compared with inert oxides, the organic acid metal salt in the present application has a faster lithium ion conduction rate and better compatibility with the electrolyte, which is beneficial to improving the battery performance.

[0049] In some embodiments, the organic acid group of the organic acid metal salt contains 1 to 6 carbon atoms, for example, 1, 2, 3, 4, 5 or 6. The present application selects the number of carbon atoms in the organic acid group as above, so that the volatilization point of the organic acid metal salt is relatively high (the volatilization temperature is greater than 200°C), ensuring the coating effect; and avoiding too high carbon atom weight, the organic acid metal salt exhibits more organic properties, affecting the conductivity of the organic acid metal salt.

[0050] In some embodiments, the organic acid group of the organic acid metal salt further contains at least one of element B, element F, element S and element N. The organic acid group of the present application contains the above elements, which can coordinate with the core material to further improve the surface structure stability of the positive electrode material.

[0051] In some embodiments, the metal element in the organic acid metal salt includes at least one of Li, Co and Q element.

[0052] In some embodiments, the mass of the coating layer is 300ppm to 6000ppm of the mass of the core, for example, 300ppm, 400ppm, 600ppm, 800ppm, 1000ppm, 1200ppm, 1400ppm, 1600ppm, 1800ppm, 2000ppm, 3000ppm, 4000ppm, 5000ppm or 6000ppm. The present application selects the coating amount of the coating layer as above, so as to improve the conductivity and structural stability of the positive electrode material and improve the electrochemical performance of the battery.

[0053] In some embodiments, the volume average particle size Dv50 of the positive electrode material is 15.0 μm to 17.0 μm, for example, it can be 15.0 μm, 15.2 μm, 15.4 μm, 15.6 μm, 15.8 μm, 16.0 μm, 16.2 μm, 16.4 μm, 16.6 μm, 16.8 μm or 17.0 μm.

[0054] In some embodiments, the compaction density of the positive electrode material at 200 MPa is ≥ 4.17 g / cm 3 .

[0055] The second aspect of the present application provides a method for preparing a positive electrode material, the method for preparing a positive electrode material comprising:

[0056] Provided is a LiCo x Q 1-x O 2-y Z y The core of the material is a material of the present invention, wherein the Q element includes at least one of Mg, Al, Ti, La, Y, Zr, Ni, Mn, Ce, Sc, W, Nb and V, the Z element includes at least one of S, F and Cl, 0.9≤x≤1, 0≤y≤0.1;

[0057] A mixture comprising the core, a metal source, an organic acid and an organic solvent is formed, and the mixture is dried and then calcined to form a coating layer comprising an organic acid metal salt on at least a portion of the surface of the core.

[0058] The present application prepares the positive electrode material as above, and improves the uniformity of the surface coating of the positive electrode material by liquid phase coating, thereby improving the protective effect of the material on the interior. In addition, a coating layer containing an organic acid metal salt is formed, which reduces the content of inert substances on the outer surface of the positive electrode material and improves the conductivity of the interface. Furthermore, the present application can enable part of the organic acid metal salt to maintain the original organic structure during the calcination process, thereby improving the compatibility with the electrolyte. Therefore, the positive electrode material prepared in the present application has good structural stability and good conductivity.

[0059] It is understood that in the present application, the metal source and the organic acid can react to form an organic acid metal salt. For example, when the metal source is lithium hydroxide and the organic acid is n-propyl boric acid, n-propyl lithium borate can be formed during the mixing process.

[0060] In some embodiments, the drying temperature is 50°C to 100°C, for example, 50°C, 55°C, 60°C, 65°C, 70°C, 75°C, 80°C, 85°C, 90°C, 95°C or 100°C.

[0061] In some embodiments, the drying time is 6 h to 10 h, for example, 6.0 h, 6.5 h, 7.0 h, 7.5 h, 8.0 h, 8.5 h, 9.0 h, 9.5 h or 10.0 h.

[0062] The present application selects the drying treatment temperature as above, so that the metal source and the organic acid react fully and form an organic acid metal salt in situ on the surface of the inner core, thereby improving the coating effect and improving the structural stability and conductivity of the positive electrode material.

[0063] In some embodiments, the calcination temperature is 200°C to 550°C, for example, 200°C, 220°C, 240°C, 260°C, 280°C, 300°C, 320°C, 340°C, 360°C, 380°C, 400°C, 420°C, 440°C, 460°C, 480°C, 500°C, 520°C, 540°C or 550°C. The present application selects the calcination temperature as above to achieve the effect of low-temperature coating, which can not only ensure that the organic acid reacts with the lithium salt, but also achieve heat treatment of the surface of the lithium cobalt oxide. It can effectively avoid the volatilization of the organic acid at high temperature or the decomposition of the formed organic acid salt.

[0064] In some embodiments, the calcination time is 4 h to 8 h, for example, 4.0 h, 4.5 h, 5.0 h, 5.5 h, 6.0 h, 6.5 h, 7.0 h, 7.5 h or 8.0 h.

[0065] In some embodiments, the calcination atmosphere is an inert atmosphere. It is understood that the inert atmosphere refers to a gas that does not react with the raw material during the calcination process, for example, it can be an inert gas or nitrogen, wherein the inert gas can be argon.

[0066] In some embodiments, the volume average particle size Dv50 of the core is 14.0 μm to 16.0 μm, for example, 14.0 μm, 14.5 μm, 15.0 μm, 15.5 μm or 16.0 μm.

[0067] In some embodiments, the number of carbon atoms in the organic acid is 1 to 6, for example, 1, 2, 3, 4, 5 or 6.

[0068] In some embodiments, the organic acid further contains at least one of the B element, the F element, the S element and the N element.

[0069] In some embodiments, the organic acid includes at least one of n-propylboric acid, boron trifluoride acetic acid, and trifluoromethanesulfonic acid.

[0070] In some embodiments, the metal source may be at least one of metal carbonate, metal hydroxide, metal chloride, and metal nitrate, etc. Taking Li as an example, the metal element in the metal source may include at least one of lithium carbonate, lithium hydroxide, lithium chloride, and lithium nitrate, etc.

[0071] In some embodiments, the organic solvent can at least dissolve organic acid. Optionally, the organic solvent includes at least one of an alcohol solvent, an amide solvent, and a sulfoxide solvent. For example, it can be ethanol.

[0072] In some embodiments, the mass ratio of the metal source to the organic acid is (0.95-1.1):1, for example, 0.95:1, 0.96:1, 0.98:1, 1.00:1, 1.02:1, 1.04:1, 1.06:1, 1.08:1 or 1.10:1.

[0073] In some embodiments, the mass proportion of the organic solvent in the mixture is 25% to 60%, for example, it can be 25%, 30%, 35%, 40%, 42%, 44%, 46%, 48%, 50%, 52%, 54%, 56%, 58% or 60%.

[0074] In some embodiments, the method for preparing the mixture comprises:

[0075] The core, the metal source, the organic acid and the organic solvent are ball-milled and mixed to obtain the mixture.

[0076] Optionally, the ball mill has a rotation speed of 20 rpm to 300 rpm and a time of 4 h to 8 h.

[0077] In some embodiments, the core is directly made of existing materials, or is obtained by mixed sintering of a lithium source, a cobalt source, a compound containing the Q element, and a compound containing the Z element.

[0078] Exemplarily, a method for preparing the above-mentioned positive electrode material is provided, comprising the following steps:

[0079] Provided is a LiCo x Q 1-x O 2-y Z y The core of the material, wherein the Q element includes at least one of Mg, Al, Ti, La, Y, Zr, Ni, Mn, Ce, Sc, W, Nb and V, the Z element includes at least one of S, F and Cl, 0.9≤x≤1, 0≤y≤0.1, and the volume average particle size Dv50 of the core is 14.0μm~16.0μm;

[0080] The core, the metal source, the organic acid and the organic solvent are ball-milled at 20 rpm to 300 rpm for 4 h to 8 h to obtain a mixture;

[0081] The mixture is dried at 50°C to 100°C for 6h to 10h, and then the dried mixture is calcined at 300°C to 550°C for 4h to 8h to form a coating layer containing an organic acid metal salt on at least a portion of the surface of the inner core to obtain the positive electrode material.

[0082] A third aspect of the present application provides a positive electrode plate, comprising at least one of the positive electrode material as described in the first aspect and the positive electrode material prepared by the preparation method as described in the second aspect.

[0083] The positive electrode sheet comprises a positive electrode current collector and a positive electrode active material layer located on at least one side of the positive electrode current collector, wherein the positive electrode active material layer comprises a positive electrode active material, a conductive agent and a binder. The positive electrode active material comprises at least one of the positive electrode material or the positive electrode material prepared by the preparation method, and the conductive agent and the binder may be conductive agents and binders commonly used in the technical field.

[0084] A fourth aspect of the present application provides a secondary battery, comprising the positive electrode sheet as described in the third aspect.

[0085] The above-mentioned secondary battery may, for example, include the above-mentioned positive electrode sheet, negative electrode sheet, electrolyte and diaphragm of the present application. The diaphragm is arranged between the positive electrode sheet and the negative electrode sheet, and mainly plays the role of preventing the positive and negative electrodes from short-circuiting, while allowing active ions to pass through. The electrolyte plays the role of conducting active ions between the positive electrode sheet and the negative electrode sheet. During the charging and discharging process of the secondary battery, the active ions are embedded and released back and forth between the positive electrode sheet and the negative electrode sheet. The present application has no special restrictions on the negative electrode sheet, electrolyte and diaphragm, and the negative electrode sheet, electrolyte and diaphragm prepared by the preparation method commonly used in the technical field, or the negative electrode sheet, electrolyte and diaphragm commonly used in the art can be used. Optionally, the above-mentioned secondary battery includes a lithium-ion battery.

[0086] Furthermore, another embodiment of the present application also provides an electrical device, including the above-mentioned battery of the present application.

[0087] The above-mentioned electrical devices may include any equipment or devices that use secondary batteries as driving sources, such as mobile phones, laptop computers, electric vehicles, ships, satellites, energy storage devices, smart home appliances, etc., but are not limited thereto.

[0088] The embodiments of the present application will be described in detail below in conjunction with examples. It should be understood that these examples are only used to illustrate the present application and are not intended to limit the scope of the present application. The experimental methods for which specific conditions are not specified in the following examples are preferably referred to the guidance provided in the present application, and can also be based on the experimental manual or normal conditions in this area, can also be based on the conditions recommended by the manufacturer, or refer to experimental methods known in the art.

[0089] Example 1

[0090] Provides LiCo with an average particle size Dv50 of 15.0μm 0.995 Mg 0.002 Al 0.003 O 1.9997 F 0.0003 As the core of

[0091] 200g of LiCo 0.995 Mg 0.002 Al 0.003 O 1.9997 F 0.0003 , 0.05 g of lithium hydroxide, 0.05 g of n-propylboric acid and 100 mL of ethanol were ball-milled at 200 rpm for 6 h to obtain a mixture;

[0092] The mixture was dried at 60°C for 10 h, and then calcined at 250°C for 6 h in a nitrogen atmosphere. 0.995 Mg 0.002 Al 0.003 O 1.9997 F 0.0003 A coating layer containing n-propyl lithium borate is formed on the surface of the calcined material, and the calcined material is cooled to room temperature and then sieved to remove magnetism to obtain the following Figure 1 and Figure 2 The positive electrode material shown.

[0093] Example 2

[0094] Provides LiCo with an average particle size Dv50 of 14.5μm 0.993 Mg 0.002 Al 0.003 Y 0.002 O2 is the core;

[0095] 200g of LiCo 0.993 Mg 0.002 Al 0.003 Y 0.002 O2, 0.101 g of lithium hydroxide, 0.099 g of boron trifluoride acetic acid and 100 mL of ethanol were ball-milled at 200 rpm for 6 h to obtain a mixture;

[0096] The mixture was dried at 60°C for 10 h, and then calcined at 300°C for 6 h in a nitrogen atmosphere. 0.993 Mg 0.002 Al 0.003 Y 0.002 A coating layer containing lithium boron trifluoride acetate is formed on the surface of O2. The calcined material is cooled to room temperature and then sieved to remove magnetism to obtain Figure 3 and Figure 4 The positive electrode material shown.

[0097] Example 3

[0098] Provides LiCo with an average particle size Dv50 of 15.8μm 0.994 Mg 0.002 Al 0.003Ti0.001 O 1.9998 F 0.0002 As the core of

[0099] 200g of LiCo 0.994 Mg 0.002 Al 0.003Ti0.001 O 1.9998 F 0.0002 , 0.51 g of lithium hydroxide, 0.49 g of trifluoromethanesulfonic acid and 100 mL of ethanol were ball-milled at 200 rpm for 6 h to obtain a mixture;

[0100] The mixture was dried at 60°C for 10 h, and then calcined at 300°C for 6 h in a nitrogen atmosphere. 0.994 Mg 0.002 Al 0.003Ti0.001 O 1.9998 F 0.0002 The surface of the calcined material is cooled to room temperature and then sieved to remove the magnetism to obtain the following Figure 5 and Figure 6 The positive electrode material shown.

[0101] Example 4

[0102] Providing LiCoO2 with an average particle size Dv50 of 14.9 μm as a core;

[0103] 200 g of LiCoO2, 0.77 g of lithium hydroxide, 0.73 g of boron trifluoride acetic acid and 100 mL of ethanol were ball-milled at 200 rpm for 6 h to obtain a mixture;

[0104] The mixture was dried at 60°C for 10 hours, and then calcined at 350°C for 6 hours in a nitrogen atmosphere to form a coating layer containing lithium boron trifluoride acetate on the surface of LiCoO2. The calcined material was cooled to room temperature and then sieved to remove magnetism to obtain Figure 7 and Figure 8 The positive electrode material shown.

[0105] Example 5

[0106] The positive electrode material was prepared according to the method of Example 3, except that trifluoromethanesulfonic acid was replaced by methanesulfonic acid.

[0107] Example 6

[0108] The positive electrode material was prepared according to the method of Example 1, except that n-propylboric acid was replaced by n-acetic acid.

[0109] Example 7

[0110] The positive electrode material was prepared according to the method of Example 1, except that the calcination temperature was 150°C.

[0111] Example 8

[0112] The positive electrode material was prepared according to the method of Example 1, except that the calcination temperature was 600°C.

[0113] Comparative Example 1

[0114] LiCoO2 with an average particle size Dv50 of 14.9 μm is directly used as the positive electrode material. The SEM image of the positive electrode material is shown in Fig. 9 and Fig.10 shown.

[0115] Comparative Example 2

[0116] Providing LiCoO2 with an average particle size Dv50 of 14.9 μm as a core;

[0117] 200 g of LiCoO2 and 0.5 g of aluminum oxide were mixed to obtain a mixture;

[0118] The mixture is calcined at 900° C. for 8 h in a nitrogen atmosphere to form a coating layer containing aluminum oxide on the surface of LiCoO2. The calcined material is cooled to room temperature and then sieved for demagnetization to obtain the positive electrode material.

[0119] The positive electrode materials prepared in the above embodiments and comparative examples are used to assemble button-type lithium-ion half-cells, including:

[0120] The positive electrode materials prepared in the examples and comparative examples were made into positive electrode sheets, which were prepared according to the mass ratio of positive electrode material: conductive agent super carbon black: PVDF (polyvinylidene fluoride) = 96.5:2:1.5. The positive electrode sheets were assembled into button batteries of model LR2032.

[0121] The above assembled battery is subjected to performance testing, and the testing method includes:

[0122] Capacity performance: constant current constant voltage charge and discharge mode is adopted, the charge and discharge voltage range is 3V~4.6V, the charge and discharge times are first 0.1C charge and then 0.1C discharge, and the charge specific capacity, discharge specific capacity, first efficiency and median voltage are obtained. The test results are shown in Table 1. The relationship between the specific capacity and voltage of Example 4 and Comparative Example 1 is shown in Fig.11 As shown;

[0123] Cycle performance: The charge and discharge voltage range is 3V~4.62V. The charge and discharge cycle test is carried out at 45℃ and 1C rate to obtain a 30-cycle cycle retention rate. The test results are shown in Table 1. The relationship between the number of cycles and the cycle retention rate of Example 4 and Comparative Example 1 is shown in Fig.12 As shown;

[0124] The compaction density is obtained by testing the powder resistivity & compaction density instrument. The relationship between the pressure and compaction density of Example 4 and Comparative Example 1 is shown in the figure below: Fig.13 shown.

[0125] Table 1

[0126]

[0127] From the above table we can see that:

[0128] (1) Compared with Examples 5-6, it can be seen that the organic acid metal salt of the present application contains B element, F element, S element and N element, which can coordinate with the core, improve the surface structure stability, and effectively improve the battery cycle performance.

[0129] (2) Compared with Examples 7-8, it can be seen that the calcination temperature selected in the present application as above can achieve the effect of low-temperature coating, which can not only ensure the reaction between the organic acid and the lithium salt, but also achieve heat treatment of the surface of the lithium cobalt oxide. It can effectively avoid the volatilization of the organic acid at high temperature or the decomposition of the formed organic acid salt.

[0130] (3) Example 4 Compared with Comparative Examples 1-2, it can be seen that the present application uses a coating layer containing an organic acid metal salt to coat the core material, which can not only protect the core material, but also reduce the content of inert substances on the surface of the positive electrode material and improve the conductivity of the interface. In addition, the organic acid metal salt of the present application maintains the original organic structure in the coating layer, which can improve the compatibility with the electrolyte. Therefore, the positive electrode material of the present application has good structural stability and good cycle performance.

[0131] In summary, the present application uses liquid phase coating, and the coating is in situ wrapped on the surface of the inner core, thereby improving the uniformity of the surface coating and forming a continuous and uniform coating layer. Moreover, the coating temperature of the present application is low relative to that of solid phase coating, and the structure of the organic acid metal salt can be maintained, and the compatibility of the positive electrode material and the electrolyte can be increased. While improving the electrochemical performance, the surface of the material is modified, the content of the surface inert substances is reduced, and the conductivity of the interface is improved. In addition, the organic acid metal salt contains elements such as B, F, N and S, which can coordinate with the inner core, improve the surface structure stability, improve the compaction density of the powder, and improve the protective effect of the material on the interior.

[0132] The technical features of the above-described embodiments may be arbitrarily combined. To make the description concise, not all possible combinations of the technical features in the above-described embodiments are described. However, as long as there is no contradiction in the combination of these technical features, they should be considered to be within the scope of this specification.

[0133] The above-described embodiments only express several implementation methods of the present application, and the descriptions thereof are relatively specific and detailed, but they cannot be construed as limiting the scope of the application. It should be noted that, for a person of ordinary skill in the art, several modifications and improvements can be made without departing from the concept of the present application, and these all belong to the protection scope of the present application. Therefore, the protection scope of the present application shall be subject to the attached claims.

Claims

1. A positive electrode material, characterized in that: The positive electrode material comprises a core and a coating layer coated on at least a portion of the surface of the core; the core comprises a LiCo x Q 1-x O 2-y Z y A material, wherein the Q element includes at least one of Mg, Al, Ti, La, Y, Zr, Ni, Mn, Ce, Sc, W, Nb and V, the Z element includes at least one of S, F and Cl, 0.9≤x≤1, 0≤y≤0.1; The material of the coating layer includes organic acid metal salt.

2. The positive electrode material according to claim 1, characterized in that The organic acid group of the organic acid metal salt contains 1 to 6 carbon atoms.

3. The positive electrode material according to claim 1, characterized in that The organic acid group of the organic acid metal salt further contains at least one of the B element, the F element, the S element and the N element.

4. The positive electrode material according to any one of claims 1 to 3, characterized in that The positive electrode material also satisfies at least one of the following conditions: (1) The mass of the coating layer is 300ppm to 6000ppm of the mass of the core; (2) The volume average particle size Dv50 of the positive electrode material is 15.0 μm to 17.0 μm; (3) The compaction density of the positive electrode material at 200 MPa is ≥ 4.17 g / cm 3 .

5. A method for preparing a positive electrode material, characterized in that: The preparation method of the positive electrode material comprises: Provided is a LiCo x Q 1-x O 2-y Z y The core of the material is a material of the present invention, wherein the Q element includes at least one of Mg, Al, Ti, La, Y, Zr, Ni, Mn, Ce, Sc, W, Nb and V, the Z element includes at least one of S, F and Cl, 0.9≤x≤1, 0≤y≤0.1; A mixture comprising the core, a metal source, an organic acid and an organic solvent is formed, and the mixture is dried and then calcined to form a coating layer comprising an organic acid metal salt on at least a portion of the surface of the core.

6. The preparation method according to claim 5, characterized in that: The drying process is carried out at a temperature of 50°C to 100°C and for a time of 6h to 10h.

7. The preparation method according to claim 5, characterized in that: The calcination temperature is 200° C. to 550° C., the calcination time is 4 h to 8 h, and the atmosphere is an inert atmosphere.

8. The preparation method according to any one of claims 5 to 7, characterized in that: The preparation method satisfies at least one of the following conditions: (1) The volume average particle size Dv50 of the core is 14.0 μm to 16.0 μm; (2) The number of carbon atoms in the organic acid is 1 to 6; (3) The organic acid contains at least one of the elements B, F, S and N; (4) The organic acid includes at least one of n-propylboric acid, boron trifluoride acetic acid and trifluoromethanesulfonic acid.

9. A positive electrode sheet, characterized in that: The invention comprises at least one of the positive electrode material described in any one of claims 1 to 4 and the positive electrode material prepared by the preparation method described in any one of claims 5 to 8.

10. A secondary battery, characterized in that: Including the positive electrode sheet as described in claim 9.

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