Positive electrode material, preparation method and battery

Abstract

The invention provides a positive electrode material, a preparation method and a battery. The positive electrode material comprises an active substance, a first shell layer coating the surface of the active substance and a second shell layer coating the surface of the first shell layer, the active substance comprises transition metal; the first shell layer comprises a first polymer, and the first polymer has a fluorine-substituted aryl group; the second shell layer includes a second polymer having at least one group selected from an amino group, an acyl group, or an amide. The first polymer not only has good conductivity, but also can inhibit the dissolution of transition metal; functional groups in the second polymer can capture transition metal ions, so that the dissolution of transition metal is further inhibited. The first shell layer and the second shell layer are combined to form a dual-coating structure, so that the overall conductivity of the positive electrode material can be improved, and the problems of voltage attenuation and cycle deterioration caused by metal dissolution are reduced.

Description

Technical Field

[0001] This application belongs to the technical field of battery materials, and particularly relates to a cathode material, a preparation method thereof, and a battery. Background Art

[0002] With the rapid development of power equipment such as electric vehicles and energy storage facilities, the demand for lithium-ion batteries with high energy density is increasing day by day. Transition metal oxides are a new type of lithium battery cathode material, which can undergo reversible oxidation-reduction reactions of anions and cations, and have extremely high potential in the development of high energy density lithium batteries.

[0003] However, the electronic conductivity of transition metal oxides is relatively low, and the dissolution of transition metals greatly affects the electrochemical rate performance. Low-rate cycling will lead to the gradient dissolution of transition metals and serious structural degradation inside secondary particles, generating a large number of microcracks, resulting in rapid attenuation of capacity and voltage, making the commercial application of some transition metal materials difficult.

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

[0005] This application provides a cathode material, a preparation method thereof, and a battery, aiming to solve the problem that the cycle performance of the battery made of existing transition metal materials is not ideal.

[0006] The first embodiment of this application provides a cathode material, which includes 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 includes transition metals; the first shell layer includes a first polymer, and the first polymer has a fluorine-substituted aromatic group; the second shell layer includes a second polymer, and the second polymer has 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 1000-5000.

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

[0010] In some embodiments, the amount of metal dissolution after cycling of the cathode material is 0-400 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 oxide, 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 poly(3-fluorothiophene) and poly(3,4-difluorothiophene).

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

[0017] The second embodiment of the present application provides a method for preparing a cathode material for preparing the cathode material in any of the above embodiments, including the following steps:

[0018] 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;

[0019] Mix the active material coated with the first shell layer with the second polymer and carry out dispersion to obtain the cathode material.

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

[0021] In some embodiments, the mass ratio of the active material coated with the first shell layer 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 step is carried out in a first solution, and the mass percentage of the first monomer in the first solution is 0.8 - 1.6 wt%.

[0024] In some embodiments, the polymerization reaction time is 12 - 24 h.

[0025] In some embodiments, the dispersion step is carried out in a second solution, and the mass percentage of the second polymer in the second solution is 1 - 5 wt%.

[0026] In some embodiments, the dispersion time is 10 - 60 min.

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

[0028] The present 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 transition metals; 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 group, acyl group or amide group. The first polymer contains a fluorine-substituted aromatic group, which has good electrical conductivity and can inhibit the dissolution of transition metals; the functional groups in the second polymer can interact with transition metal ions through electrostatic interaction, coordination bond or hydrogen bond with transition metal ions, capture transition metal ions, and thus further inhibit the dissolution of transition metals. The double coating structure formed by the combination of the first shell layer and the second shell layer can improve the overall electrical conductivity of the positive electrode material and reduce the problems of voltage decay and cycle deterioration caused by metal dissolution. Detailed implementation manners

[0029] The technical solutions in the embodiments of the present application will be clearly and completely described below. Obviously, the described embodiments are only a part of the embodiments of the present application, rather than all the embodiments. Based on the embodiments in the present application, all other embodiments obtained by those skilled in the art without creative efforts shall fall within the protection scope of the present application.

[0030] In the description of the present application, it should be noted that, unless otherwise clearly defined and limited, the terms "connected" and "coupled" should be understood in a broad sense. For example, it may be a fixed connection, a detachable connection, or an integral connection; it may be a mechanical connection, an electrical connection, or a communication with each other; it may be directly connected, or indirectly connected through an intermediate medium, or indirectly connected through a pipeline or a conduit, and it may be the internal communication of two components or the interaction relationship between two components. For those of ordinary skill in the art, the specific meanings of the above terms in the present application can be understood according to specific situations. In the description of the present application, "a plurality of" means two or more, unless otherwise clearly and specifically defined. In addition, the terms "first" and "second" are only used for descriptive purposes and cannot be understood as indicating or implying relative importance or implicitly indicating the number of the indicated technical features. Thus, the features defined with "first" and "second" may explicitly or implicitly include one or more features.

[0031] The first embodiment of the present application provides a cathode material, which includes 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 transition metals; the first shell layer includes a first polymer, and the first polymer has a fluorine-substituted aromatic group; the second shell layer includes a second polymer, and the second polymer has at least one group selected from amino group, acyl group or amide group.

[0032] Transition metals such as cobalt, nickel, manganese and other elements have relatively high charge density and electron affinity. The aromatic group can affect the chemical properties and reactivity of transition metal ions by forming coordination bonds with transition metal ions. Fluorine atoms have relatively high electronegativity and strong electron-attracting ability. When fluorine atoms replace hydrogen atoms in the aromatic group, they introduce more electron density into the aromatic ring, increasing the electron density on the aromatic group, which can more effectively adsorb transition metal ions, thereby inhibiting the dissolution of transition metals during the charge and discharge process of the battery; in addition, the polymer containing fluorine-substituted aromatic groups also has good conductivity and can maintain good conductivity while coating the active material. The functional groups in the second polymer can interact with transition metal ions through electrostatic interaction, coordination bond or hydrogen bond with transition metal ions, capture transition metal ions, and further inhibit the dissolution of transition metals. The double coating structure formed by the combination of the first shell layer and the second shell layer can improve the overall conductivity of the cathode material and reduce the problems of voltage attenuation and cycle deterioration caused by metal dissolution.

[0033] In some embodiments, the mass ratio of the active material, 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 satisfies the above value range, it can ensure that the formed cathode material has ideal conductivity, and at the same time, the two coating layers can effectively inhibit the dissolution of transition metals.

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

[0036] It can be understood that the value of the molecular weight of the first polymer can be any value among 1000, 2000, 3000, 4000, 5000 or the range between any two values. The molecular weight of the first polymer is positively correlated with the length of its molecular chain. When the length of the molecular chain of the first polymer is too short, it may lead to the weakening of the coordination bond formed between the functional group and the transition metal ion, resulting in a decrease in the adsorption ability of the shell layer to transition metals. When the length of the molecular chain of the first polymer is too long, it will affect the conductivity of the active material. When the molecular weight of the first polymer satisfies the above value range, it can enable the first shell layer to effectively adsorb metal ions and have ideal conductivity.

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

[0038] It can be understood that the value of the molecular weight of the second polymer can be any value among 40, 100, 150, 200, 250, 300, 350, 400 or the range between any two values. Based on the same principle, when the molecular weight of the second polymer meets the above value range, the second shell layer can not only effectively adsorb metal ions but also have ideal conductivity.

[0039] In some embodiments, the metal dissolution amount of the positive electrode material after cycling is 0 to 400 ppm.

[0040] The metal dissolution amount after cycling in this application refers to the amount of metal elements in the positive electrode material dissolved in the form of ions and separated from the electrode into the electrolyte and other media inside the battery after a single-piece battery cell formed by the positive electrode material is cycled 100 times at 25°C. It can be understood that the value of the metal dissolution amount of the positive electrode material after cycling (unit: ppm) can be any value among 0, 50, 100, 150, 200, 250, 300, 350, 400 or the range between any two values. When the metal dissolution amounts of the first shell layer and the second shell layer after cycling meet the above value range, it can ensure that the battery 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 to 10000 nm.

[0042] It can be understood that the value of the particle size of the active material (unit: nm) can be any value among 4000, 5000, 6000, 7000, 8000, 9000, 10000 or the range between any two values. As the core of the positive electrode material, the particle size of the active material affects the diffusion of lithium ions in the positive electrode material. The diffusion path of lithium ions inside the active material with a smaller particle size is shorter, and the diffusion resistance is smaller, which is beneficial to improving the diffusion rate of lithium ions and thus improving the rate performance of the material. However, too small a particle size may lead to a decrease in the structural stability of the material, and it is easy to agglomerate during charge and discharge, reducing the electrical performance of the positive electrode material. When the particle size of the active material meets the above value range, the core of the positive electrode material can have a stable structure and ideal electrical performance at the same time.

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

[0044] It is understandable 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 metals, thereby improving the cycle stability of the cathode 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 is understandable 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 values, on the one hand, groups such as amino, acyl or amide contained therein can effectively capture transition metal ions, thereby further inhibiting the dissolution of transition metals, and on the other hand, ensuring the overall conductivity of the cathode material, while reducing the structural changes during charge and discharge and prolonging 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 nLi 2 MnO 3 ·(1 - n)LiNi x Mn (1-x-y) Co y O 2 , 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 a 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 cathode material for preparing the cathode 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] Mix the active material coated with the first shell layer with the second polymer and disperse them to obtain the positive electrode material.

[0053] Specifically, the preparation method of the positive electrode material in the above embodiments can be realized through the following steps:

[0054] S1. Put the active material powder into the initiator solution, add the first monomer under mechanical stirring, then perform ultrasonic treatment, and continue stirring for a certain time to cause the first monomer to polymerize on the surface of the active material;

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

[0056] S3. Take a certain amount of the active material coated with the first shell layer and soak it in an aqueous solution of the second polymer with a certain concentration, stir to disperse the reactant powder and continue for a certain time;

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

[0058] In some embodiments, the initiator can be LiClO 4 / PTSA (p-toluenesulfonic acid), LiClO 4 can provide an ionic conduction environment for the polymerization of the first monomer, and PTSA, as an organic strong acid, can provide protons to cause the first monomer to form an active intermediate, thereby reducing the activation energy of the reaction and accelerating the polymerization reaction rate. The preparation method of the positive electrode material provided in this application forms the first shell layer by polymerizing the first monomer under the action of the initiator, and then directly reacts with the second polymer to form the second shell layer. The reaction can be carried out at room temperature, with mild conditions and simple process.

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

[0060] It can be understood that when the mass ratio of the active material to the first monomer satisfies the above value range, there is a reasonable particle size / thickness ratio between the first shell layer formed after the polymerization of the first monomer and the inner core formed by the active material, so that the first shell layer can effectively adsorb transition metal ions while ensuring the transport efficiency of lithium ions on the surface of the electrode material.

[0061] In some embodiments, the mass ratio of the active material coated with the first shell layer 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 layer to the second polymer satisfies the above value range, a reasonable thickness ratio exists between the second shell layer and the first shell layer, so that the second shell layer can effectively inhibit the dissolution of transition metals and has an 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 step is carried out in a first solution, and the mass percentage of the first monomer in the first solution is 0.8-1.6 wt%.

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

[0066] In some embodiments, the polymerization reaction time is 10-24 h.

[0067] It is understandable that the value of the polymerization reaction time (unit: h) can be any value among 10, 12, 16, 20, 24 or the range between any two values. When the polymerization reaction time satisfies the above value range, a coating can be effectively formed, the residual monomer concentration can be reduced, and the side reactions in the later electrochemical cycle can be reduced.

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

[0069] It is understandable that the value of the mass percentage of the second polymer in the second solution can be any value among 1 wt%, 2 wt%, 3 wt%, 4 wt%, 5 wt% or the range between any two values. When the mass percentage of the second polymer in the second solution satisfies the above value range, a complete and uniform coating can be formed, and the capture rate of transition metal elements can be improved.

[0070] In some embodiments, the dispersion time is 10-60 min.

[0071] It is understandable that the value of the dispersion time (unit: min) can be any value among 10, 20, 30, 40, 50, 60 or the range between any two values. When the dispersion time satisfies the above value range, a coating layer with better uniformity can be formed.

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

[0073] The following is an explanation of the positive electrode material, preparation method, and battery provided by the present application in combination with specific embodiments:

[0074] Example 1

[0075] Example 1 provides a positive electrode material, which is prepared by the following method:

[0076] S1. Take the lithium-rich manganese-based powder and place it into the LiClO 4 / PTSA solution, add 0.8 wt% of 3-fluorothiophene under mechanical stirring, then perform ultrasonic treatment for 30 min, and continue stirring for 10 h to cause a polymerization reaction of 3-fluorothiophene on the surface of the lithium-rich manganese-based material. The reaction principle is as follows:

[0077]

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

[0079] S3. Take the active substance coated with the first shell layer and soak it in a 4 wt% aqueous solution of polyethyleneimine, and stir to disperse the reactant powder for a certain period of time;

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

[0081] Example 1 also provides a battery, which is prepared by the following method:

[0082] Mix the positive electrode material powder prepared in the above steps with conductive carbon black, polyvinylidene fluoride (PVDF), and a small amount of N-methylpyrrolidone (NMP) to form a uniform slurry, and coat it on an aluminum foil substrate as a test positive electrode.

[0083] Mix the negative electrode graphite powder with conductive carbon black, sodium carboxymethyl cellulose (CMC), and styrene-butadiene rubber solution (SBR) to form a uniform slurry, and coat it on a copper foil substrate as a test negative electrode.

[0084] Record the cyclic efficiency electrochemical performance after 100 cycles of a single-cell battery at 25 °C.

[0085] Examples 2 - 19

[0086] The preparation methods of the positive electrode materials and batteries provided in Examples 2 - 19 are the same as those in Example 1, except that the process parameters are adjusted. For details, see Table 1.

[0087] Comparative Examples 1-3

[0088] The preparation methods of the positive electrode materials and batteries provided in Comparative Examples 1-3 are the same as those in Example 1, except that the process parameters are adjusted. See Table 1 for details.

[0089] Table 1

[0090]

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

[0092] Table 2

[0093]

[0094]

[0095] As can be seen from Table 1, for the positive electrode material obtained by the preparation method provided in this application, adjusting the process parameters and material parameters within the scope protected by this application can achieve the effect of reducing the metal dissolution amount, and has an ideal capacity retention rate in the battery cycle test. As can be seen from Comparative Example 1, too low concentration of the first monomer will lead to a relatively small molecular weight of the first polymer, resulting in insufficient adsorption effect on manganese metal; as can be seen from Comparative Examples 2 and 3, although excessive first monomer or second polymer can inhibit the dissolution of metal, the formed shell thickness is too large, which also leads to unsatisfactory cycle performance of the battery.

[0096] The above has introduced in detail a positive electrode material, its preparation method, and a battery provided in the embodiments of the present application. Specific examples are used in the present application to elaborate on the principle and implementation manner of the present application. The description of the above embodiments is only used to help understand the technical solution and its core idea of the present application; those of ordinary skill in the art should understand that they can still modify the technical solutions recorded in the foregoing embodiments, or perform equivalent replacements on some of the technical features; and these modifications or replacements do not make the essence of the corresponding technical solutions deviate from the scope of the technical solutions of the embodiments of the present application.

Claims

1. A positive electrode material, characterized in that: It includes 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 includes a transition metal; the first shell layer includes a first polymer, and the first polymer has a fluorine-substituted aromatic group; the second shell layer includes a second polymer, and the second polymer has at least one group selected from amino, acyl or amide.

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

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

4. A positive electrode material according to claim 1, characterized in that: The metal dissolution amount of the positive electrode material after circulation is 0 to 400 ppm.

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

6. A positive electrode material according to claim 1, characterized in that: The active material comprises any one of lithium-rich manganese-based layered oxide, lithium nickel manganese oxide, lithium manganese oxide, lithium nickel cobalt manganese oxide or lithium cobalt oxide; and / or, The first polymer includes at least one of poly 3-fluorothiophene and poly 3,4-difluorothiophene; and / or, The second polymer includes at least one of polyethyleneimine and polypropyleneimine.

7. A method for preparing a positive electrode material according to any one of claims 1 to 6, characterized in that: The steps include: The active material is mixed with a first monomer and subjected to a polymerization reaction to obtain the active material coated with a first shell layer, wherein the first monomer contains a fluorine-substituted aromatic group; The active material coated with the first shell layer is mixed with the second polymer and dispersed to obtain the positive electrode material.

8. The method for preparing a positive electrode material according to claim 7, 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 layer 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.

9. The method for preparing a positive electrode material according to claim 7, characterized in that: The polymerization step is carried out in the first solution, and the mass percentage of the first monomer in the first solution is 0.8-1.6 wt %; and / or, The polymerization reaction time is 10 to 24 hours; and / or, The dispersing step is performed in the second solution, and the mass percentage of the second polymer in the second solution is 1 to 5 wt %; and / or, The dispersion time is 10 to 60 minutes.

10. A battery comprising a positive electrode sheet, characterized in that: The positive electrode sheet comprises the positive electrode material as described in any one of claims 1 to 6 or comprises the positive electrode material prepared by the preparation method as described in any one of claims 7 to 9.

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