A positive electrode material, a preparation method thereof, and a battery

Abstract

The application provides a positive electrode material and a preparation method and a battery. The positive electrode material comprises an active substance, a first shell layer coated on the surface of the active substance, and a second shell layer coated on the surface of the first shell layer. The active substance comprises a transition metal. The first shell layer comprises a first polymer, and the first polymer has a fluorine-substituted aromatic group. The second shell layer comprises a second polymer, and the second polymer has at least one group selected from an amino group, an acyl group or an amide group. The first polymer has good conductivity and can inhibit the elution of the transition metal. The functional groups in the second polymer can capture transition metal ions, thereby further inhibiting the elution of the transition metal. The double-coating structure of the combination of the first shell layer and the second shell layer can improve the overall conductivity of the positive electrode material and reduce the problems of voltage attenuation and cycle deterioration caused by metal elution.

Description

Technical Field

[0001] This application belongs to the field of battery materials technology, specifically relating to a cathode material and its preparation method, and a battery. Background Technology

[0002] With the rapid development of electric vehicles and energy storage facilities, the demand for high-energy-density lithium-ion batteries is increasing. Transition metal oxides are a new type of lithium battery cathode material that can undergo reversible redox reactions between anions and cations, and have great potential in the development of high-energy-density lithium batteries.

[0003] However, transition metal oxides have low electronic conductivity, and the dissolution of transition metals greatly affects electrochemical rate performance. Low-rate cycling leads to gradient dissolution of transition metals and severe structural degradation within secondary particles, resulting in a large number of microcracks. This causes rapid decay of capacity and voltage, making it difficult to commercialize some transition metal materials.

[0004] Therefore, improving the electrochemical performance of transition metal materials is a problem that needs to be solved. Summary of the Invention

[0005] This application provides a cathode material, a preparation method, and a battery, aiming to solve the problem of unsatisfactory cycle performance of batteries made from existing transition metal materials.

[0006] The first embodiment of this application provides a positive electrode material, including an active material, a first shell layer coated on the surface of the active material, and a second shell layer coated on the surface of the first shell layer; the active material includes a transition metal; the first shell layer includes a first polymer having a fluorine-substituted aromatic group; the second shell layer includes a second polymer having at least one group selected from amino, acyl, or amide.

[0007] In some embodiments, the mass ratio of the active substance, the first polymer, and the second polymer is 220–250: 1000–5000: 40–400.

[0008] In some embodiments, the molecular weight of the first polymer is 1000 to 5000.

[0009] In some embodiments, the molecular weight of the second polymer is 40 to 400.

[0010] In some embodiments, the amount of metal leached from the cathode material after cycling is 0 to 400 ppm.

[0011] In some embodiments, the particle size of the active substance is 4000–10000 nm.

[0012] In some embodiments, the thickness of the first shell layer is 150–400 nm.

[0013] In some embodiments, the thickness of the second shell layer is 50–200 nm.

[0014] In some embodiments, the active material includes any one of lithium-rich manganese-based layered oxides, lithium nickel manganese oxide, lithium manganese oxide, lithium nickel cobalt manganese oxide, or lithium cobalt oxide.

[0015] In some embodiments, the first polymer includes at least one of poly3-fluorothiophene and poly3,4-difluorothiophene.

[0016] In some embodiments, the second polymer includes at least one of polyethyleneimine and polypropyleneimine.

[0017] The second embodiment of this application provides a method for preparing a cathode material, used to prepare the cathode material in any of the above embodiments, comprising the following steps:

[0018] The active material is mixed with the first monomer and subjected to a polymerization reaction to obtain the active material with a first shell coating, wherein the first monomer contains a fluorine-substituted aromatic group.

[0019] The active material coated by the first shell is mixed with the second polymer and dispersed to obtain the positive electrode material.

[0020] In some embodiments, the mass ratio of the active substance to the first monomer is 220–250:80–120.

[0021] In some embodiments, the mass ratio of the active substance coated by the first shell to the second polymer is 220-250:40-400.

[0022] In some embodiments, the first monomer includes at least one of 3-fluorothiophene and 3,4-difluorothiophene.

[0023] In some embodiments, the polymerization reaction is carried out in a first solution, wherein the first monomer has a mass percentage of 0.8 to 1.6 wt% in the first solution.

[0024] In some embodiments, the polymerization reaction takes 12 to 24 hours.

[0025] In some embodiments, the dispersion step is carried out in a second solution, wherein the second polymer comprises 1 to 5 wt% of the second solution by mass.

[0026] In some embodiments, the dispersion time is 10 to 60 minutes.

[0027] The third embodiment of this application provides a battery including a positive electrode sheet, wherein the positive electrode sheet includes the positive electrode material in any of the above embodiments.

[0028] This application provides a cathode material, comprising an active material, a first shell coating the surface of the active material, and a second shell coating the surface of the first shell. The active material includes a transition metal. The first shell includes a first polymer having fluorine-substituted aromatic groups. The second shell includes a second polymer having at least one group selected from amino, acyl, or amide groups. The first polymer contains fluorine-substituted aromatic groups, which provides both good conductivity and inhibits the dissolution of the transition metal. The functional groups in the second polymer can interact with the transition metal ions through electrostatic interactions, coordination bonds, or hydrogen bonds, capturing the transition metal ions and further inhibiting their dissolution. This dual-coating structure combining the first and second shells improves the overall conductivity of the cathode material and reduces voltage decay and cycle degradation caused by metal dissolution. Detailed Implementation

[0029] The technical solutions in the embodiments of this application will be clearly and completely described below. Obviously, the described embodiments are only a part of the embodiments of this application, and not all of them. All other embodiments obtained by those skilled in the art based on the embodiments of this application without creative effort are within the scope of protection of this application.

[0030] In the description of this application, it should be noted that, unless otherwise expressly specified and limited, the terms "connected" and "linked" should be interpreted broadly. For example, they can refer to a fixed connection, a detachable connection, or an integral connection; they can refer to a mechanical connection, an electrical connection, or a connection that allows for mutual communication; they can refer to a direct connection, an indirect connection through an intermediate medium, or an indirect connection through a pipe or conduit; they can refer to the internal communication of two components or the interaction between two components. Those skilled in the art can understand the specific meaning of the above terms in this application according to the specific circumstances. In the description of this application, "multiple" means two or more, unless otherwise expressly and specifically limited. Furthermore, 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 indicated technical features. Thus, features defined with "first" and "second" may explicitly or implicitly include one or more features.

[0031] The first embodiment of this application provides a positive electrode material, including an active material, a first shell layer coated on the surface of the active material, and a second shell layer coated on the surface of the first shell layer; the active material includes a transition metal; the first shell layer includes a first polymer having a fluorine-substituted aromatic group; the second shell layer includes a second polymer having at least one group selected from amino, acyl, or amide.

[0032] Transition metals such as cobalt, nickel, and manganese possess high charge density and electron affinity. Aromatic groups, by forming coordinate bonds with transition metal ions, can influence the chemical properties and reactivity of these ions. Fluorine atoms, with their high electronegativity and strong electron attraction, introduce more electrons into the aromatic ring when fluorine replaces hydrogen atoms in the aromatic group, increasing the electron density on the aromatic group and enabling more effective adsorption of transition metal ions. This, in turn, suppresses transition metal dissolution during battery charging and discharging. Furthermore, polymers containing fluorine-substituted aromatic groups also exhibit good conductivity, maintaining good conductivity while coating the active material. The functional groups in the second polymer can interact with transition metal ions through electrostatic interactions, coordinate bonds, or hydrogen bonds, capturing them and further suppressing their dissolution. This dual-shell structure, combining the first and second shells, improves the overall conductivity of the cathode material and reduces voltage decay and cycle degradation caused by metal dissolution.

[0033] In some embodiments, the mass ratio of the active substance, the first polymer, and the second polymer is 220–250: 1000–5000: 40–400.

[0034] When the mass ratio of the active material, the first polymer, and the second polymer meets the above-mentioned range, it can ensure that the formed cathode material has ideal conductivity, while the two coating layers can effectively suppress the dissolution of transition metals.

[0035] In some embodiments, the molecular weight of the first polymer is 1000 to 5000.

[0036] Understandably, the molecular weight of the first polymer can be any value or a range between any two of 1000, 2000, 3000, 4000, and 5000. The molecular weight of the first polymer is positively correlated with the length of its molecular chain. If the molecular chain is too short, the coordination bonds between the functional groups and transition metal ions may weaken, reducing the adsorption capacity of the shell for transition metals. Conversely, if the molecular chain is too long, it will affect the conductivity of the active material. When the molecular weight of the first polymer meets the above-mentioned range, the first shell can effectively adsorb metal ions while also possessing ideal conductivity.

[0037] In some embodiments, the molecular weight of the second polymer is 40 to 400.

[0038] It is understandable that the molecular weight of the second polymer can be any value or a range between any two of the following: 40, 100, 150, 200, 250, 300, 350, and 400. Based on the same principle, when the molecular weight of the second polymer meets the above-mentioned range, the second shell can effectively adsorb metal ions while also possessing ideal electrical conductivity.

[0039] In some embodiments, the amount of metal leached from the cathode material after cycling is 0 to 400 ppm.

[0040] In this application, the post-cycle metal leaching amount refers to the amount of metal elements in the positive electrode material that dissolve in ionic form and detach from the electrode into the electrolyte or other media inside the battery after the single cell formed by the positive electrode material is cycled 100 times at 25°C. It is understood that the value (unit: ppm) of the post-cycle metal leaching amount of the positive electrode material can be any value or a range between any two of the following: 0, 50, 100, 150, 200, 250, 300, 350, 400. When the post-cycle metal leaching amount of the first and second shells meets the above-mentioned value range, it can be ensured that the cell formed by the positive electrode material still has good capacity after multiple cycles.

[0041] In some embodiments, the particle size of the active material is 4000–10000 nm.

[0042] It is understandable that the particle size (unit: nm) of the active material can be any value or a range between any two of the following: 4000, 5000, 6000, 7000, 8000, 9000, and 10000. As the core of the cathode material, the particle size of the active material affects the diffusion of lithium ions within the cathode material. Smaller particle sizes result in shorter diffusion paths and lower diffusion resistance for lithium ions, which is beneficial for increasing the diffusion rate of lithium ions and thus improving the rate performance of the material. However, excessively small particle sizes may lead to decreased structural stability of the material, making it prone to agglomeration during charge and discharge, thereby reducing the electrical performance of the cathode material. When the particle size of the active material meets the above-mentioned range, the core of the cathode material can have a stable structure and ideal electrical performance.

[0043] In some embodiments, the thickness of the first shell layer is 150–400 nm.

[0044] It can be understood that the value of the thickness of the first shell layer (unit: nm) can be any value among 150, 200, 250, 300, 350, 400 or the range between any two values. When the thickness of the first shell layer meets the above value range, the first polymer containing fluorine-substituted aromatic groups can effectively adsorb transition metal ions, enhance the interfacial stability between the active material and the electrolyte, reduce the dissolution of transition metal, thereby improving the cycle stability of the positive electrode material; at the same time, it can also ensure the transport efficiency of lithium ions on the surface of the electrode material and improve the rate performance of the battery.

[0045] In some embodiments, the thickness of the second shell layer is 50 - 200 nm.

[0046] It can be understood that the value of the thickness of the second shell layer (unit: nm) can be any value among 50, 90, 130, 170, 200 or the range between any two values. When the thickness of the second shell layer meets the above value, on the one hand, groups such as amino, acyl or amide contained in it can effectively capture transition metal ions, thereby further inhibiting the dissolution of transition metal; on the other hand, it ensures the overall conductivity of the positive electrode material, reduces the structural change during charge and discharge, and prolongs the cycle life of the battery.

[0047] In some embodiments, the active material includes any one of lithium-rich manganese-based layered oxides (LLOs), lithium nickel manganate, lithium manganate, lithium nickel cobalt manganate or lithium cobaltate, and is further preferably LLOs. The chemical formula of LLOs is nLi2MnO3·(1 - n)LiNi x Mn (1-x-y) Co y O2, 0.1 < n < 1, 0 < x ≤ 0.3, 0 ≤ y ≤ 0.1. LLOs can undergo reversible redox reactions of anions and cations, and the specific capacity can reach more than 200 mAh / g, which is higher than materials such as lithium nickel manganate and lithium manganate, and can provide higher energy density, thereby being able to improve the overall performance and endurance of the battery under the same volume.

[0048] In some embodiments, the first polymer includes at least one of poly(3-fluorothiophene) and poly(3,4-difluorothiophene).

[0049] In some embodiments, the second polymer includes at least one of polyethyleneimine and polypropyleneimine.

[0050] The second embodiment of the present application provides a preparation method of a positive electrode material for preparing the positive electrode material in any of the above embodiments, including the following steps:

[0051] Mix the active material with the first monomer and carry out a polymerization reaction to obtain the active material coated with the first shell layer, wherein the first monomer contains a fluorine-substituted aromatic group;

[0052] The active material coated with the first shell is mixed with the second polymer and dispersed to obtain the positive electrode material.

[0053] Specifically, the method for preparing the cathode material in the above embodiments can be achieved through the following steps:

[0054] S1. Place the active substance powder into the initiator solution, add the first monomer under mechanical stirring, then sonicate, and continue stirring for a certain time to allow the first monomer to undergo a polymerization reaction on the surface of the active substance.

[0055] S2. Filter the product, wash it three times with ethanol and filter it again. The filtered filter cake is kept at high temperature in a vacuum drying oven for a certain period of time to obtain the active substance coated with the first shell layer.

[0056] S3. Take a certain amount of the active substance coated by the first shell and soak it in a second polymer aqueous solution of a certain concentration. Stir to disperse the reactant powder and continue for a certain period of time.

[0057] S4. Filter the product, and keep the filtered cake at a constant temperature in a vacuum drying oven for a certain period of time to obtain the positive electrode material.

[0058] In some embodiments, the initiator can be LiClO4 / PTSA (p-toluenesulfonic acid). LiClO4 provides an ion-conducting environment for the polymerization of the first monomer, while PTSA, as a strong organic acid, can donate protons, enabling the first monomer to form an active intermediate, thereby lowering the activation energy of the reaction and accelerating the polymerization rate. The method for preparing the cathode material provided in this application involves polymerizing the first monomer under the action of an initiator to form a first shell, followed by a direct reaction with a second polymer to form a second shell. The reaction can be carried out at room temperature, under mild conditions, and with a simple process.

[0059] In some embodiments, the mass ratio of the active substance to the first monomer is 220–250:80–120.

[0060] It is understandable that when the mass ratio of the active material to the first monomer meets the above-mentioned range, the first shell formed after the polymerization of the first monomer has a reasonable particle size / thickness ratio with the core formed by the active material, thereby ensuring the efficient transport of lithium ions on the electrode material surface while the first shell effectively adsorbs transition metal ions.

[0061] In some embodiments, the mass ratio of the active substance coated by the first shell to the second polymer is 220–250:40–400.

[0062] It is understandable that when the mass ratio of the active material coated by the first shell to the second polymer meets the above-mentioned range, there is a reasonable thickness ratio between the second shell and the first shell, thereby enabling the second shell to effectively inhibit the dissolution of transition metals and have ideal structural strength.

[0063] In some embodiments, the first monomer includes at least one of 3-fluorothiophene and 3,4-difluorothiophene.

[0064] In some embodiments, the polymerization reaction is carried out in a first solution, wherein the mass percentage of the first monomer in the first solution is 0.8 to 1.6 wt%.

[0065] It is understood that the mass percentage of the first monomer in the first solution can be any value or a range between any two of 0.8 wt%, 1.0 wt%, 1.2 wt%, 1.4 wt%, and 1.6 wt%. When the mass percentage of the first monomer in the first solution meets the above range, a coating layer with good uniformity and conductivity can be formed.

[0066] In some embodiments, the polymerization reaction takes 10 to 24 hours.

[0067] It is understandable that the polymerization reaction time (in hours) can be any value from 10, 12, 16, 20, and 24, or any range between two values. When the polymerization reaction time meets the above range, it can effectively form a coating, reduce the residual monomer concentration, and reduce the side reactions of the later electrochemical cycle.

[0068] In some embodiments, the dispersion step is carried out in a second solution, wherein the mass percentage of the second polymer in the second solution is 1 to 5 wt%.

[0069] It is understood that the mass percentage of the second polymer in the second solution can be any value or a range between any two of 1 wt%, 2 wt%, 3 wt%, 4 wt%, and 5 wt%. When the mass percentage of the second polymer in the second solution meets the above-mentioned range, it can form a complete and uniform coating, thereby improving the capture rate of transition metal elements.

[0070] In some embodiments, the dispersion time is 10 to 60 minutes.

[0071] It is understandable that the dispersion time (in minutes) can be any value from 10, 20, 30, 40, 50, 60, or any range between two values. When the dispersion time meets the above range, a coating layer with good uniformity can be formed.

[0072] The third embodiment of this application provides a battery including a positive electrode sheet, which includes the positive electrode material in any of the above embodiments.

[0073] The following description, in conjunction with specific embodiments, illustrates the cathode material, preparation method, and battery provided in this application:

[0074] Example 1

[0075] Example 1 provides a cathode material prepared in the following manner:

[0076] S1. Lithium-rich manganese-based powder was placed in a LiClO4 / PTSA solution, and 0.8 wt% of 3-fluorothiophene was added under mechanical stirring. The mixture was then sonicated for 30 min and stirred for 10 h to allow 3-fluorothiophene to polymerize on the surface of the lithium-rich manganese-based material. The reaction principle is as follows:

[0077]

[0078] S2. Filter the product and wash it three times with ethanol and filter it again. The filtered filter cake is kept at 120°C for 12 hours in a vacuum drying oven to obtain the lithium-rich manganese-based material with the first shell layer.

[0079] S3. Take the active material coated by the first shell layer and soak it in a 4wt% polyethyleneimine aqueous solution. Stir to disperse the reactant powder and continue for a certain period of time.

[0080] S4. Filter the product and keep the filtered cake at 120°C for 6 hours in a vacuum drying oven to obtain the positive electrode material.

[0081] Example 1 also provides a battery prepared in the following manner:

[0082] The positive electrode material powder prepared in the above steps is thoroughly mixed with conductive carbon black, polyvinylidene fluoride (PVDF) and a small amount of N-methylpyrrolidone (NMP) to form a uniform slurry, which is then coated onto an aluminum foil substrate as a test positive electrode.

[0083] The negative electrode graphite powder is thoroughly mixed with conductive carbon black, sodium carboxymethyl cellulose (CMC), and styrene-butadiene rubber solution (SBR) to form a uniform slurry, which is then coated onto a copper foil substrate to serve as the test negative electrode.

[0084] The cycle efficiency and electrochemical performance were recorded after a single cell was cycled 100 times at 25°C.

[0085] Examples 2-19

[0086] The preparation methods of the cathode materials and batteries provided in Examples 2 to 19 are the same as those in Example 1, except that the process parameters are adjusted, as detailed in Table 1.

[0087] Comparative Examples 1-3

[0088] The preparation methods of the cathode materials and batteries provided in Comparative Examples 1 to 3 are the same as those in Example 1, except that the process parameters are adjusted, as detailed in Table 1.

[0089] Table 1

[0090]

[0091] The electrical performance of the batteries provided in the above embodiments and comparative examples was tested, and the results are shown in Figure 2.

[0092] Table 2

[0093]

[0094]

[0095] As shown in Table 1, the cathode material obtained by the preparation method provided in this application, within the scope of protection of this application, can achieve the effect of reducing metal dissolution by adjusting the process parameters and material parameters, and exhibits a relatively ideal capacity retention rate in battery cycle testing. Comparative Example 1 shows that an excessively low concentration of the first monomer leads to a small molecular weight of the first polymer, resulting in insufficient adsorption of manganese metal. Comparative Examples 2 and 3 show that while excessive amounts of the first monomer or the second polymer can inhibit metal dissolution, the resulting shell thickness is too large, also leading to less than ideal battery cycle performance.

[0096] The foregoing has provided a detailed description of a positive electrode material, its preparation method, and the battery provided in the embodiments of this application. Specific examples have been used in this application to illustrate the principles and implementation methods of this application. The descriptions of the above embodiments are only for the purpose of helping to understand the technical solutions and core ideas of this application. Those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some of the technical features. These modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments of this application.

Claims

1. A positive electrode material, characterized in that, It includes an active substance, a first shell layer covering the surface of the active substance, and a second shell layer covering the surface of the first shell layer; The active material includes any one of lithium-rich manganese-based layered oxides, lithium nickel manganese oxide, lithium manganese oxide, lithium nickel cobalt manganese oxide, or lithium cobalt oxide. The first shell layer includes a first polymer, which includes at least one of poly3-fluorothiophene and poly3,4-difluorothiophene. The second shell layer comprises a second polymer, which comprises at least one of polyethyleneimine and polypropyleneimine.

2. The cathode material according to claim 1, characterized in that, The mass ratio of the active substance, the first polymer, and the second polymer is 220~250:1000~5000:40~400.

3. The positive electrode material according to claim 1, characterized in that, The molecular weight of the first polymer is 1000~5000; and / or, The molecular weight of the second polymer is 40 to 400.

4. The positive electrode material according to claim 1, characterized in that, The metal leaching amount of the cathode material after cycling is 0~400ppm.

5. The positive electrode material according to claim 1, characterized in that, The particle size of the active substance is 4000~10000 nm; and / or, The thickness of the first shell layer is 150~400 nm; and / or, The thickness of the second shell is 50~200nm.

6. A method for preparing a positive electrode material as described in any one of claims 1 to 5, characterized in that, Includes the following steps: The active material is mixed with the first monomer and subjected to a polymerization reaction to obtain the active material with a first shell coating, wherein the first monomer contains a fluorine-substituted aromatic group. The active material coated by the first shell is mixed with the second polymer and dispersed to obtain the positive electrode material.

7. The method for preparing a positive electrode material according to claim 6, characterized in that, The mass ratio of the active substance to the first monomer is 220~250:80~120; and / or, The mass ratio of the active substance coated by the first shell to the second polymer is 220~250:40~400; and / or, The first monomer includes at least one of 3-fluorothiophene and 3,4-difluorothiophene.

8. The method for preparing a positive electrode material according to claim 6, characterized in that, The polymerization reaction is carried out in a first solution, wherein the first monomer has a mass percentage of 0.8~1.6 wt% in the first solution; and / or, The polymerization reaction takes 10-24 hours; and / or, The dispersion step is carried out in a second solution, wherein the second polymer comprises 1-5 wt% by mass in the second solution; and / or, The dispersion time is 10~60 minutes.

9. A battery, comprising a positive electrode, characterized in that, The positive electrode sheet includes the positive electrode material as described in any one of claims 1 to 5 or the positive electrode material prepared by the preparation method as described in any one of claims 6 to 8.

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