Composite positive electrode material and preparation method therefor, positive electrode sheet, and secondary battery

Abstract

The present application provides a composite positive electrode material and a preparation method therefor, a positive electrode sheet, and a secondary battery. The composite positive electrode material comprises a shell layer and a core material, wherein the chemical formula of the core material is LiNiaCobMn1-a-b-c-dMecBdO2; the shell layer is a boride, and the chemical formula of the shell layer is MepBq; and the Me comprises at least one of Mn, Co, Ni, Fe, Al, Cu, Ti, Cr, Zr, Zn, Mg and W. Compared with the prior art, the composite positive electrode material provided by the present application has the advantage that by means of the cooperation between the doping of the core material with metal ions and boron and the coating of the shell layer with a boride, the particle size of the material is increased, and the standard deviation of the particle size distribution thereof is reduced; therefore, the chemical stability and electrochemical performance of the positive electrode material are improved, and the cycling stability of a battery under a high voltage is maintained.

Description

A composite cathode material and its preparation method, cathode sheet and secondary battery Technical Field

[0001] This application relates to the field of secondary battery technology, specifically to a composite cathode material and its preparation method, cathode sheet and secondary battery. Background Technology

[0002] Since their commercialization in the 1990s, lithium-ion batteries have been widely used in consumer electronics, aerospace, military equipment, power tools, and electric vehicles due to their high energy density, high charge / discharge efficiency, low self-discharge rate, long lifespan, and environmental friendliness, becoming one of the key technologies for energy storage and conversion in modern society. With continuous technological development and the diversification of application scenarios, the performance requirements for lithium-ion batteries are also increasing. Among these, battery range has become a core concern for users, and improving the energy density of lithium-ion batteries is one of the key paths to meeting this demand.

[0003] Improving the energy density of lithium-ion batteries can be approached from two main aspects: first, by developing high-specific-capacity cathode and anode materials to enhance the battery's storage capacity; and second, by increasing the charge and discharge voltage of lithium-ion batteries, thereby improving both mass energy density and volumetric energy density. In particular, increasing the charge and discharge voltage can significantly optimize the structural design of lithium-ion batteries and further reduce the production cost per unit of energy, thus becoming a hot research topic in the current lithium-ion battery field.

[0004] In recent years, single-crystal cathode materials have gradually become a key research and application focus for high-energy-density lithium-ion battery cathode materials due to their advantages such as high crystal structure integrity, good stability, and long cycle life. However, under high-voltage conditions, single-crystal cathode materials still face problems such as poor electrochemical stability, intensified interfacial side reactions, and crystal structure damage, which seriously affect their performance and lifespan extension. Therefore, in order to meet the requirements of high-voltage applications for cathode materials, it is urgent to develop a single-crystal cathode material with excellent chemical stability and electrochemical performance, so as to improve the charge and discharge voltage while ensuring the long-term stability of the material and the overall performance of the battery. Summary of the Invention

[0005] One of the objectives of this application is to provide a composite cathode material to address the shortcomings of existing technologies and improve the performance instability of current ternary single-crystal cathode materials under high voltage.

[0006] To achieve the above objectives, this application adopts the following technical solution:

[0007] A composite cathode material includes an outer shell layer and a core material; wherein the core material has the chemical formula LiNi. a Cob Mn 1-a-b-c-d Me c B d O2, 0≤a≤1, 0≤b≤1, 0≤c≤0.1, 0≤d≤0.1, a+b+c+d>0; the outer shell is a boride, and the chemical formula of the outer shell is Me. p B q , 1≤p≤3, 1≤q≤3; the Me includes at least one of Mn, Co, Ni, Fe, Al, Cu, Ti, Cr, Zr, Zn, Mg and W.

[0008] Preferably, the mass ratio of the outer shell layer to the core material is (0.01-0.5):100.

[0009] Preferably, the standard deviation σ of the particle size distribution of the composite cathode material particles and the Dv10 particle size r of the composite cathode material particles satisfy the following relationship: 0.001≤σ / r≤0.5, where 0.01≤σ≤5, and the unit of r is μm.

[0010] Preferably, the Dv10 particle size r of the composite cathode material particles is 5-25 μm.

[0011] Preferably, the standard deviation σ of the particle size distribution of the composite cathode material particles and the mass ratio w of the outer shell layer satisfy the following relationship: 10≤σ / w≤1000, wherein the mass ratio of the outer shell layer is the mass ratio of the outer shell layer to the core material.

[0012] The second objective of this application is to provide a method for preparing a composite cathode material, comprising the following steps:

[0013] S1. After uniformly mixing lithium compound, nickel-cobalt-manganese ternary precursor and Me-containing borate, the first stage of sintering is carried out in air atmosphere, and then the temperature is increased to carry out the second stage of sintering. After holding at the temperature and cooling, the product is ground in an inert atmosphere to obtain the pre-sintered product.

[0014] S2. Add a boride containing Me element to the pre-sintered product, mix thoroughly, sinter under a protective atmosphere, keep warm, cool, and grind in an inert atmosphere to finally obtain the boride-modified composite cathode material.

[0015] Preferably, the molar ratio of the lithium compound, the nickel-cobalt-manganese ternary precursor, and the Me-containing borate is Li:(Ni+Co+Mn):Me=(1.01-1.10):1:(0.005-0.2).

[0016] Preferably, the molar ratio of the lithium compound, the nickel-cobalt-manganese ternary precursor, and the Me-containing borate is Li:(Ni+Co+Mn):Me=1.05:1:(0.01-0.1).

[0017] Preferably, in step S1, the sintering temperature of the first stage is 700-900℃, the heating rate is 1-5℃ / min, and the sintering time is 6-8h.

[0018] The second stage sintering temperature is 1200-1400℃, the heating rate is 5-10℃ / min, the sintering time is 4-6h, the holding temperature is 300-500℃, and the holding time is 5-9h.

[0019] In step S2, the sintering temperature is 1000-1200℃, the heating rate is 1-5℃ / min, and the sintering time is 8-12h; the holding temperature is 400-600℃, and the holding time is 4-6h.

[0020] The third objective of this application is to provide a positive electrode sheet comprising the positive electrode material described in any of the preceding paragraphs.

[0021] The fourth objective of this application is to provide a secondary battery, including a positive electrode, a negative electrode, and a separator spaced between the positive electrode and the negative electrode, wherein the positive electrode is the aforementioned positive electrode.

[0022] Compared with the prior art, the beneficial effects of this application are as follows: The composite cathode material provided by this application, through the doping of metal ions and boron elements in the core material and the coating of the outer shell with borides, the two work together to improve the particle size of the material and reduce the standard deviation of its particle size distribution, thereby improving the chemical stability of the cathode material and enhancing the electrochemical performance of the cathode material, maintaining the cycle stability of the battery under high voltage. Attached Figure Description

[0023] Figure 1 is a SEM image of a composite cathode material according to an embodiment of this application. Detailed Implementation

[0024] To make the technical solution and advantages of this application clearer, the application and its beneficial effects will be described in more detail below in conjunction with specific embodiments, but the embodiments of this application are not limited thereto.

[0025] The terms "first" and "second" are used for descriptive purposes only and should not be construed as indicating or implying relative importance or implicitly specifying the number of technical features indicated. Therefore, a feature defined as "first" or "second" may explicitly or implicitly include one or more of that feature. In the description of this application, "multiple" means two or more, unless otherwise explicitly specified.

[0026] 1. Cathode material

[0027] In a first aspect, this application provides a composite cathode material, comprising an outer shell layer and a core material; wherein the core material has the chemical formula LiNi. a Co b Mn 1-a-b-c-d Me c B d O2, 0≤a≤1, 0≤b≤1, 0≤c≤0.1, 0≤d≤0.1, a+b+c+d>0; the outer shell is a boride, and the chemical formula of the outer shell is Me. p B q , 1≤p≤3, 1≤q≤3; the Me includes at least one of Mn, Co, Ni, Fe, Al, Cu, Ti, Cr, Zr, Zn, Mg and W.

[0028] Borides, used as outer shell coating materials for the core, can reduce side reactions between the core material and the electrolyte, improving the battery's cycle stability and electrochemical performance. Simultaneously, borides can enhance the material's thermal stability, suppress oxygen release, and improve battery safety.

[0029] In this application, by doping the core material with metal cations and boron, the particle size of the ternary cathode material is increased and the standard deviation of its particle size distribution is reduced, thereby improving the overall uniformity of the material. The doping of metal cations can induce the formation of oxygen vacancies and metal atom vacancies, increase active sites, form an atomic-level conductive network, and ultimately enhance lithium storage performance. Furthermore, the doping of metal cations can improve the stability of the material structure, thereby significantly improving the cycle stability of the battery material.

[0030] In some embodiments, the mass ratio of the outer shell layer to the core material is (0.01-0.5):100. Specifically, it can be 0.01:100, 0.05:100, 0.1:100, 0.2:100, 0.3:100, 0.4:100, 0.5:100, and may include, but is not limited to, the values ​​listed above.

[0031] In some embodiments, the standard deviation σ of the particle size distribution of the composite cathode material particles and the Dv10 particle size r of the composite cathode material particles satisfy the following relationship: 0.001≤σ / r≤0.5, where 0.01≤σ≤5, and the unit of r is μm. Preferably, 0.004≤σ / r≤0.12.

[0032] The smaller the ratio of standard deviation σ to particle size r, the smaller the corresponding standard deviation or the larger the particle size for the same particle size or standard deviation. A smaller standard deviation indicates more uniform particle size, better material consistency, and more stable performance; conversely, a larger particle size indicates better material stability. This means that a smaller ratio of standard deviation σ to particle size r generally indicates better material performance. However, since standard deviation σ cannot be infinitely small, there is a lower limit; a larger standard deviation σ indicates poorer material consistency, hence an upper limit. Exceeding this range will significantly deteriorate material performance.

[0033] In some embodiments, the Dv10 particle size r of the composite cathode material particles is 5-25 μm.

[0034] Within the particle size range r, the smaller the particle size, the worse the material stability, so a lower limit is set; however, due to process limitations, it is difficult to achieve a particularly large single crystal particle size, so there is an upper limit. Exceeding this range will significantly deteriorate the material properties.

[0035] In some embodiments, the standard deviation σ of the particle size distribution of the composite cathode material particles and the mass ratio w of the outer shell layer satisfy the following relationship: 10 ≤ σ / w ≤ 1000, where the mass ratio of the outer shell layer is the mass ratio of the outer shell layer to the core material. Preferably, 20 ≤ σ / w ≤ 800. The smaller the ratio of the standard deviation σ to the mass of the outer shell layer, the smaller the corresponding standard deviation or the larger the particle size for the same mass or standard deviation of the outer shell layer. A smaller standard deviation indicates more uniform particle size, better material consistency, and more stable performance; a larger outer shell layer mass indicates better material stability. This means that a smaller ratio of the standard deviation σ to the mass of the outer shell layer results in better material performance, hence an upper limit is set; however, since the standard deviation σ cannot be infinitely small, there is a lower limit. Exceeding this range will significantly deteriorate the material performance.

[0036] A second aspect of this application provides a method for preparing the above-mentioned composite cathode material, comprising the following steps:

[0037] S1. After uniformly mixing lithium compound, nickel-cobalt-manganese ternary precursor and Me-containing borate, the first stage of sintering is carried out in air atmosphere, and then the temperature is increased to carry out the second stage of sintering. After holding at the temperature and cooling, the product is ground in an inert atmosphere to obtain the pre-sintered product.

[0038] S2. Add a boride containing Me element to the pre-sintered product, mix thoroughly, sinter under a protective atmosphere, keep warm, cool, and grind in an inert atmosphere to finally obtain the boride-modified composite cathode material.

[0039] In some embodiments, the molar ratio of the lithium compound, the nickel-cobalt-manganese ternary precursor, and the Me-containing borate is Li:(Ni+Co+Mn):Me=(1.01-1.10):1:(0.005-0.2). The preferred ratio is Li:(Ni+Co+Mn):Me = 1.05:1:0.01-0.1, specifically 1.05:1:0.01, 1.05:1:0.01, 1.05:1:0.02, 1.05:1:0.03, 1.05:1:0.04, 1.05:1:0.05, 1.05:1:0.06, 1.05:1:0.07, 1.05:1:0.08, 1.05:1:0.09, 1.05:1:0.1, and may include, but is not limited to, the values ​​listed above, with 1.05:1:0.05 being more preferred.

[0040] In the embodiments of this application, in step S1, the first sintering temperature is 700-900℃, the heating rate is 1-5℃ / min, and the sintering time is 6-8h.

[0041] The second sintering temperature is 1200-1400℃, the heating rate is 5-10℃ / min, the sintering time is 4-6h, the holding temperature is 300-500℃, and the holding time is 5-9h.

[0042] In this embodiment of the application, in step S2, the sintering temperature is 1000-1200℃, the heating rate is 1-5℃ / min, and the sintering time is 8-12h; the holding temperature is 400-600℃, and the holding time is 4-6h.

[0043] This application employs multiple segmented sintering processes and uses borides to coat the material. Combined with reasonable temperature and time control, it improves the morphological stability of the ternary material surface and enhances the particle size and standard deviation of its particle size distribution, making the outer shell coating more consistent, reducing material variability, and thus improving chemical resistance.

[0044] 2. Positive electrode plate

[0045] A third aspect of this application provides a positive electrode sheet comprising the composite positive electrode material described above, specifically comprising a positive electrode current collector and a positive electrode active material layer coated on at least one surface of the positive electrode current collector, wherein the positive electrode active material is the positive electrode material described in this application.

[0046] The positive electrode current collector can be any material suitable for use as a positive electrode current collector in the field. For example, the positive electrode current collector can be, but is not limited to, metal foil, and more specifically, aluminum foil.

[0047] 3. Secondary battery

[0048] A fourth aspect of this application aims to provide a secondary battery, including a positive electrode, a negative electrode, and a separator spaced between the positive electrode and the negative electrode, wherein the positive electrode is the positive electrode described above.

[0049] The negative electrode includes a negative current collector and a negative active material layer coated on at least one surface of the negative current collector. The negative active material layer can be one or more of the following, including but not limited to graphite, soft carbon, hard carbon, carbon fiber, mesophase carbon microspheres, silicon-based materials, tin-based materials, lithium titanate, or other metals that can form alloys with lithium. Specifically, the graphite can be selected from one or more of artificial graphite, natural graphite, and modified graphite; the silicon-based material can be selected from one or more of elemental silicon, silicon oxide compounds, silicon-carbon composites, and silicon alloys; and the tin-based material can be selected from one or more of elemental tin, tin oxide compounds, and tin alloys. The negative current collector is typically a structure or component that collects current. The negative current collector can be any material suitable for use as a negative current collector in lithium-ion batteries, for example, it can be, but is not limited to, metal foil, and more specifically, copper foil.

[0050] The separator can be any material suitable for lithium-ion battery separators in the art, for example, it can be one or more of the following: polyethylene, polypropylene, polyvinylidene fluoride, aramid, polyethylene terephthalate, polytetrafluoroethylene, polyacrylonitrile, polyimide, polyamide, polyester and natural fibers.

[0051] The secondary battery also includes an electrolyte, which comprises an organic solvent, an electrolyte lithium salt, and additives. The electrolyte lithium salt can be LiPF6 and / or LiBOB used in high-temperature electrolytes; it can also be at least one of LiBF4, LiBOB, and LiPF6 used in low-temperature electrolytes; it can also be at least one of LiBF4, LiBOB, LiPF6, and LiTFSI used in overcharge-resistant electrolytes; or it can be at least one of LiClO4, LiAsF6, LiCF3SO3, and LiN(CF3SO2)2. The organic solvent can be a cyclic carbonate, including PC and EC; it can also be a chain carbonate, including DFC, DMC, or EMC; or it can be a carboxylic acid ester, including MF, MA, EA, MP, etc. The additives include, but are not limited to, at least one of film-forming additives, conductive additives, flame-retardant additives, overcharge-resistant additives, additives for controlling the H2O and HF content in the electrolyte, additives for improving low-temperature performance, and multifunctional additives.

[0052] To make the technical solution and advantages of this application clearer, the application and its beneficial effects will be described in more detail below in conjunction with specific embodiments, but the embodiments of this application are not limited thereto.

[0053] Example 1

[0054] The preparation method of the composite cathode material in this embodiment is as follows:

[0055] Step S1: Lithium carbonate, nickel-cobalt-manganese ternary cathode precursor, and titanium borate are thoroughly mixed in a stoichiometric ratio of Li:(Ni+Co+Mn):Ti=1.05:1:0.05. The mixture is then sintered at 800℃ for 7 hours in air at a heating rate of 1-5℃ / min. The temperature is then increased to 1300℃ for 5 hours at a heating rate of 5-10℃ / min. The mixture is then held at 400℃ for 7 hours. After cooling, the mixture is ground in a nitrogen atmosphere to obtain the pre-sintered product.

[0056] Step S2: Add titanium boride to the pre-sintered product, then mix thoroughly by ball milling, sinter at 1100℃ for 10h under a nitrogen atmosphere with a heating rate of 1-5℃ / min, hold at 500℃ for 5h, cool, and then grind under a nitrogen atmosphere to obtain the ternary single-crystal composite cathode material. The mass ratio of the titanium boride outer shell to the core material is 0.25:100.

[0057] Examples 2-3

[0058] The difference between this embodiment and Embodiment 1 is that the stoichiometric ratio of titanium borate in step S1 is detailed in Table 1.

[0059] The rest is the same as in Example 1, and will not be repeated here.

[0060] Examples 4-5

[0061] The difference between this embodiment and Embodiment 1 is the sintering temperature and holding temperature in step S1; see Table 1 for details.

[0062] The rest is the same as in Example 1, and will not be repeated here.

[0063] Examples 6-7

[0064] The difference between this embodiment and Embodiment 1 is the sintering time in step S1; see Table 1 for details.

[0065] The rest is the same as in Example 1, and will not be repeated here.

[0066] Examples 8-9

[0067] The difference between this embodiment and Embodiment 1 is that titanium boride with different mass ratios is added in step S2; see Table 2 for details.

[0068] The rest is the same as in Example 1, and will not be repeated here.

[0069] Examples 10-11

[0070] The difference between this embodiment and Embodiment 1 lies in the sintering temperature and holding temperature in step S2; see Table 2 for details.

[0071] The rest is the same as in Example 1, and will not be repeated here.

[0072] Examples 12-13

[0073] The difference between this embodiment and Embodiment 1 is the sintering time in step S2; see Table 2 for details.

[0074] The rest is the same as in Example 1, and will not be repeated here.

[0075] Comparative Example 1

[0076] After thoroughly mixing lithium carbonate and nickel-cobalt-manganese ternary precursors at a stoichiometric ratio of Li:(Ni+Co+Mn)=1.05:1, the mixture was sintered at 800℃ for 7h in air atmosphere with a heating rate of 1~5℃ / min. Then, it was held at 400℃ for 7h, cooled, and ground in an inert atmosphere to obtain a ternary material sintered in one step.

[0077] Comparative Example 2

[0078] The difference between this comparative example and Comparative Example 1 is that the ternary material obtained by one sintering is subjected to a second calcination, as detailed in Tables 1 and 2.

[0079] The rest are the same as in Example 1, and will not be repeated here.

[0080] Comparative Example 3

[0081] The difference between this comparative example and Example 1 is that step S2 is omitted.

[0082] The rest is the same as in Example 1, and will not be repeated here.

[0083] Comparative Example 4

[0084] The difference between this comparative example and Example 1 is that there is no second stage of heating and sintering in step S1.

[0085] The rest is the same as in Example 1, and will not be repeated here.

[0086] Comparative Example 5

[0087] The difference between this comparative example and Example 1 is that titanium borate is not added in step S1.

[0088] The rest is the same as in Example 1, and will not be repeated here.

[0089] Comparative Example 6

[0090] The difference between this comparative example and Example 1 is that titanium boride is not added in step S2.

[0091] The rest is the same as in Example 1, and will not be repeated here.

[0092] The specific preparation parameters of the above embodiments and comparative examples are summarized in Tables 1 and 2.

[0093] Table 1

[0094] Table 2

[0095] The cathode materials prepared in Examples 1-13 and Comparative Examples 1-6 were assembled into lithium-ion coin cells, and their electrical performance was tested at room temperature under a charge / discharge condition of 0.5C and a charge / discharge range of 3.0V-4.60V. The test results are summarized in Tables 3 and 4.

[0096] Table 3 Electrical performance test results

[0097] Particle size measurement method: The weighed positive electrode material is added to the particle size analyzer. The dispersant in the instrument is pure water. The speed of the stirrer is 3000 rpm. By adjusting the refractive index, the test cycle is repeated 3 times. Finally, the particle size data of the particle size analyzer Dv10 is read, which is the particle size r.

[0098] Standard deviation calculation method: Calculate the standard deviation using the particle size measurements Dv10, Dv50, and Dv90 according to the standard deviation calculation formula. Where Dv10, Dv50, and Dv90 are xi, μ is the average value of Dv10, Dv50, and Dv90, and n = 3.

[0099] Table 4. Test results of particle size and standard deviation

[0100] The test results above show that doping with metal ions and boron in ternary cathode materials, combined with the use of boride coating in the outer shell, can improve the particle size and reduce the standard deviation of the particle size distribution, thereby improving the chemical stability of the cathode material and enhancing its electrochemical performance, thus maintaining the cycle stability of the battery under high voltage.

[0101] Based on the disclosure and teachings of the foregoing specification, those skilled in the art can make changes and modifications to the above embodiments. Therefore, this application is not limited to the specific embodiments described above, and any obvious improvements, substitutions, or modifications made by those skilled in the art based on this application are within the scope of protection of this application. Furthermore, although some specific terms are used in this specification, these terms are only for convenience of explanation and do not constitute any limitation on this application.

Claims

1. A composite cathode material, comprising an outer shell layer and a core material; wherein, The core material has the chemical formula LiNi. a Co b Mn 1-a-b-c-d Me c B d O2, 0≤a≤1, 0≤b≤1, 0≤c≤0.1, 0≤d≤0.1, a+b+c+d>0; the outer shell is a boride, and the chemical formula of the outer shell is Me. p B q , 1≤p≤3, 1≤q≤3; the Me includes at least one of Mn, Co, Ni, Fe, Al, Cu, Ti, Cr, Zr, Zn, Mg and W.

2. The composite cathode material according to claim 1, wherein, The mass ratio of the outer shell layer to the core material is (0.01-0.5):

100.

3. The composite cathode material according to claim 1, wherein, The standard deviation σ of the particle size distribution of the composite cathode material particles and the Dv10 particle size r of the composite cathode material particles satisfy the following relationship: 0.001≤σ / r≤0.5, where 0.01≤σ≤5, and the unit of r is μm.

4. The composite cathode material according to claim 3, wherein, The composite cathode material particles have a Dv10 particle size r of 5-25 μm.

5. The composite cathode material according to claim 1, wherein, The standard deviation σ of the particle size distribution of the composite cathode material particles and the mass ratio w of the outer shell layer satisfy the following relationship: 10≤σ / w≤1000, where the mass ratio of the outer shell layer is the mass ratio of the outer shell layer to the core material.

6. A method for preparing a composite cathode material according to any one of claims 1-5, comprising the following steps: S1. After uniformly mixing lithium compound, nickel-cobalt-manganese ternary precursor and Me-containing borate, the first stage of sintering is carried out in air atmosphere, and then the temperature is increased to carry out the second stage of sintering. After holding at the temperature and cooling, the product is ground in an inert atmosphere to obtain the pre-sintered product. S2. Add a boride containing Me element to the pre-sintered product, mix thoroughly, sinter under a protective atmosphere, keep warm, cool, and grind in an inert atmosphere to finally obtain the boride-modified composite cathode material.

7. The method for preparing a composite cathode material according to claim 6, wherein, The molar ratio of the lithium compound, the nickel-cobalt-manganese ternary precursor, and the Me-containing borate is Li:(Ni+Co+Mn):Me=(1.01-1.10):1:(0.005-0.2).

8. The method for preparing a composite cathode material according to claim 6, wherein, In step S1, the first sintering temperature is 700-900℃, the heating rate is 1-5℃ / min, and the sintering time is 6-8h; the second sintering temperature is 1200-1400℃, the heating rate is 5-10℃ / min, the sintering time is 4-6h, the holding temperature is 300-500℃, and the holding time is 5-9h. In step S2, the sintering temperature is 1000-1200℃, the heating rate is 1-5℃ / min, and the sintering time is 8-12h; the holding temperature is 400-600℃, and the holding time is 4-6h.

9. A positive electrode sheet comprising the composite positive electrode material according to any one of claims 1 to 5.

10. A secondary battery, comprising a positive electrode, a negative electrode, and a separator spaced between the positive electrode and the negative electrode, wherein, The positive electrode is the positive electrode as described in claim 9.

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