Positive electrode material, positive electrode plate and secondary battery

Abstract

The invention provides a positive electrode material, a positive electrode plate and a secondary battery, and belongs to the technical field of batteries. The doping elements with specific types and contents are introduced into the positive electrode material, so that the structural stability of the positive electrode material is improved, when the positive electrode material is applied to the secondary battery, an ideal capacity effect can be exerted, the structural stability is excellent, and excellent cycle performance can be realized at high temperature.

Description

Technical Field

[0001] This application relates to the field of battery technology, specifically to a positive electrode material, a positive electrode sheet, and a secondary battery. Background Technology

[0002] In the development of modern lithium-ion batteries, ternary cathode materials have attracted widespread attention due to their excellent specific capacity and energy density. In recent years, increasing the nickel content has been considered a significant way to enhance battery energy density, a crucial direction for improving battery performance. However, increasing the nickel content also brings a series of technical and material challenges, mainly including reduced thermal stability, instability in redox reactions, and structural collapse during cycling. To address these challenges, researchers have gradually realized that cation doping strategies can mitigate these adverse effects to some extent.

[0003] The stronger bond energy between doped cations and anions results in higher stability, thus improving the stability of ternary cathode materials and enhancing cycle capacity retention. Doped ions can also introduce vacancies, improving kinetics to some extent. However, their high stability means that excessively high doping levels can degrade the specific capacity. In practical applications, considering that the specific capacity cannot deteriorate too much, the cation doping level cannot be too high, and the improvement in cycle capacity retention cannot meet the requirements. Summary of the Invention

[0004] The purpose of this application is to overcome the shortcomings of the prior art and provide a positive electrode material, a positive electrode sheet, and a secondary battery.

[0005] To achieve the above objectives, the technical solution adopted in this application is as follows: Firstly, a cathode material is provided, wherein the cathode material has the structural formula LiNi. x Co y Mn z A k O2, where 0.5≤x≤0.7, 0≤y≤0.30, 0≤z≤0.30, 0.006≤k≤0.09, x+y+z+k=1, and element A is at least one of Na, K, Ba, Ca, La, Y, Cu, Ce, Ru, Rb, Sn, Zr, Bi, Pb, Ag, Cr, Sr, and W; The average particle size of the cathode material is Dv50 = 0.25-20 μm, satisfying the following relationship: 0.3 ≤ 10 * Dv50 * k ≤ 5.1.

[0006] In some embodiments, the cathode material satisfies the following relationship: 0.1 ≤ 10 * k / x ≤ 1.

[0007] In some embodiments, the elemental concentration of the A element decreases in a gradient from the surface of the primary particles of the cathode material towards the center of the primary particles of the cathode material.

[0008] In some embodiments, the radius of the primary particles of the cathode material is a. The primary particles of the cathode material are divided into regions. The region where the distance L from the center of the primary particles of the cathode material satisfies 0 ≤ L ≤ 0.6a is the first region, and the region where the distance L from the center of the primary particles of the cathode material satisfies 0.6a < L ≤ a is the second region; the mass percentage concentration of the A element in the first region is kn%, and the mass percentage concentration of the A element in the second region is kw%, where 2 ≤ kw / kn ≤ 10.

[0009] In a second aspect, a method for preparing the cathode material is provided, including the following steps: Prepare a mixed salt solution by mixing nickel salts, optionally cobalt salts, and optionally manganese salts according to a molar ratio; prepare a dopant solution containing element A as a doped element A solution; prepare a complexing agent solution with a complexing agent; prepare a precipitating agent solution with a precipitating agent; Add the mixed salt solution, the precipitating agent solution, the complexing agent solution, and optionally the doped element A solution into a reaction kettle for coprecipitation reaction. After aging, filtration, washing, and drying, a cathode material precursor is obtained; Mix and sinter a Li source and the cathode material precursor to obtain the cathode material.

[0010] In some embodiments, the pH of the coprecipitation reaction is 10 - 12; In some embodiments, the temperature of the coprecipitation reaction is 50 - 60 °C; In some embodiments, the stirring speed of the coprecipitation reaction is 300 - 1000 rpm; In some embodiments, the time of the coprecipitation reaction is 6 - 12 h; In some embodiments, the coprecipitation reaction is carried out in the presence of an inert gas; In some embodiments, the doped element A solution is added in one portion or in portions; In some embodiments, the rotation speed of the mixing is 300 - 500 rpm, and the time is 2 - 4 h; In some embodiments, the sintering includes first sintering and second sintering. The temperature of the first sintering is 400 - 500 °C, and the time is 4 - 6 h. The temperature of the second sintering is 750 - 900 °C, and the time is 10 - 20 h.

[0011] In a third aspect, a positive electrode sheet is provided, including the cathode material.

[0012] Fourthly, a secondary battery is provided, including the aforementioned positive electrode, negative electrode, a separator spaced between the positive electrode and the negative electrode, and an electrolyte; The electrolyte comprises lithium difluorooxalate borate and adiponitrile; the mass ratio of lithium difluorooxalate borate to adiponitrile is m, wherein when 1≤kw / kn<5, m=0.5-0.8; when 5≤kw / kn≤10, m=0.8-1.2.

[0013] In some embodiments, the lithium difluorooxalate borate has a mass fraction of m1 in the electrolyte, where m1 = 0.1%-3%, and an adiponitrile content of m2, where m2 = 0.25%-5%.

[0014] Fifthly, an electrical device is provided, including the aforementioned secondary battery, which serves as the power supply for the electrical device.

[0015] Compared with existing technologies, the beneficial effects of this application are as follows: Introducing element A into the cathode material not only forms a stable protective layer on the surface of the cathode material, inhibiting nickel dissolution and migration, but also enhances the mechanical strength and toughness of the cathode material, thereby improving its stability under high temperature and high voltage. In terms of tensile strength, element A can effectively isolate external heat sources, reduce the rate of heat diffusion, and improve the stability of the cathode material. In terms of affinity, element A can increase the affinity of the electrode for lithium ions, thereby promoting smooth lithium ion insertion / extraction, reducing resistance to ion migration, and improving the overall performance of the battery. Furthermore, it enables the cathode material to meet the requirement of 0.3≤10*Dv50*k≤5.1, which is beneficial for improving the cycle stability of the cathode material. Detailed Implementation

[0016] To facilitate understanding of this application, a more complete description will be provided below. However, this application can be implemented in many different forms and is not limited to the embodiments described herein. Rather, these embodiments are provided to provide a more thorough and complete understanding of the disclosure of this application.

[0017] As used in this article: "Prepared from" is synonymous with "comprising". The terms "comprising", "including", "having", "containing", or any other variations thereof as used herein are intended to cover non-exclusive inclusion. For example, a composition, step, method, article, or apparatus that includes the listed elements is not necessarily limited to those elements, but may include other elements not expressly listed or elements inherent to such composition, step, method, article, or apparatus.

[0018] The conjunction "composed of..." excludes any unspecified elements, steps, or components. If used in a claim, this phrase makes the claim closed, excluding materials other than those described, except for associated conventional impurities. When the phrase "composed of..." appears in a clause of the body of a claim rather than immediately following it, it limits only the elements described in that clause; other elements are not excluded from the claim as a whole.

[0019] When a quantity, concentration, or other value or parameter is expressed as a range, a preferred range, or a range defined by a series of upper and lower preferred values, this should be understood as specifically disclosing all ranges formed by any pair of any upper or preferred value with any lower or preferred value, regardless of whether the range is disclosed individually. For example, when the range “1-5” is disclosed, the described range should be interpreted as including ranges “1-4”, “1-3”, “1-2”, “1-2 and 4-5”, “1-3 and 5”, etc. When numerical ranges are described herein, unless otherwise stated, the range is intended to include its endpoints and all integers and fractions within that range.

[0020] In these embodiments, unless otherwise specified, the portions and percentages are all by weight.

[0021] "Parts by mass" refers to the basic unit of measurement that expresses the mass ratio of multiple components. One part can represent any unit mass, such as 1g or 2.689g. If we say that component A has "a" parts by mass and component B has "b" parts by mass, it means the ratio of the mass of component A to the mass of component B is a:b. Alternatively, it can mean that the mass of component A is aK and the mass of component B is bK (K is any number representing a multiplier). It is important to understand that, unlike the number of parts by mass, the sum of the mass parts of all components is not limited to 100 parts.

[0022] "And / or" is used to indicate that one or both of the described situations may occur, for example, A and / or B includes (A and B) and (A or B).

[0023] The present application is further illustrated below with specific embodiments: In a first aspect, embodiments of this application provide a cathode material, the cathode material having the structural formula LiNi. x Co y Mn z A kO2, wherein 0.5≤x≤0.7, 0≤y≤0.30, 0≤z≤0.30, 0.006≤k≤0.09, x+y+z+k=1, and element A is at least one of Na, K, Mg, Ba, Ca, La, Y, Cu, Ce, Ru, Rb, Sn, Zr, Bi, Pb, Ag, Cr, Sr, and W; preferably at least one of Na, Mg, and Zr. The average particle size of the cathode material is Dv50 = 0.25-20 μm, satisfying the following relationship: 0.3 ≤ 10 * Dv50 * k ≤ 5.1.

[0024] This application introduces element A into the cathode material, which not only forms a stable protective layer on the surface of the cathode material, inhibiting the dissolution and migration of nickel, but also enhances the mechanical strength and toughness of the cathode material, thereby improving its stability under high temperature and high voltage. In terms of tensile strength, element A can effectively isolate external heat sources, reduce the rate of thermal diffusion, and improve the stability of the cathode material. Regarding affinity, element A can increase the electrode's affinity for lithium ions, thereby promoting smooth lithium ion insertion and extraction, reducing resistance to ion migration, and improving the overall performance of the secondary battery. Furthermore, it enables the cathode material to meet the properties 0.3 ≤ 10 * Dv50 * k ≤ 4.5, which is beneficial for improving the cycle stability of the cathode material.

[0025] Specifically, Dv50 can be a range of values ​​consisting of one or any two of the following: 0.25μm, 0.5μm, 1μm, 3μm, 5μm, 8μm, 10μm, 12μm, 15μm, 17μm, and 20μm.

[0026] Specifically, 10*Dv50*k can be a range of values ​​consisting of one or any two of the following: 0.3, 0.6, 0.9, 1.2, 1.5, 1.8, 2, 2.2, 2.5, 2.7, 3, 3.3, 3.5, 3.8, 4, 4.3, 4.5, 4.7, 4.9, and 5.1; preferably, it is between 0.3 and 4.5.

[0027] In some embodiments, the cathode material satisfies the following relationship: 0.1 ≤ 10 * k / x ≤ 1.

[0028] The amount of element A added is positively correlated with the content of nickel, and satisfies 0.1≤10*k / x≤1. Within this range, the amount of element A added can effectively stabilize the material structure and broaden the lithium-ion transport channel without excessively affecting the proportion of active elements in the material. As a result, the cycle performance and safety of the secondary battery containing this cathode material are improved without sacrificing capacity.

[0029] Specifically, 10*k / x can be one of 0.1, 0.2, 0.6, 0.4, 0.5, 0.6, 0.7, 0.8, 0.9, 1 or a range value composed of any two of them.

[0030] In some embodiments, the element concentration of the A element decreases in a gradient from the surface of the primary particles of the cathode material to the center of the primary particles of the cathode material.

[0031] In some embodiments, the radius of the primary particles of the cathode material is a. The primary particles of the cathode material are divided into regions. The region where the distance from the center of the primary particles of the cathode material is 0≤L≤0.6a is the first region, and the region where the distance from the center of the primary particles of the cathode material is 0.6a<L≤a is the second region; the mass percentage concentration of the A element in the first region is kn%, and the mass percentage concentration of the A element in the second region is kw%, where 2≤kw / kn≤10.

[0032] In this application, the electrolyte is in contact with the surface of the cathode material. The gradient distribution of the A element can optimize the ionic conductivity and interface stability of the cathode material, thereby enhancing the corrosion resistance and mechanical strength of the cathode material; when T of the cathode material is within the above range, the cycle stability of the cathode material is higher.

[0033] When the k content is the same, if T is too large, it will cause a low element concentration of the A element inside the cathode material, reduce the stability of the first region of the cathode material, and thus cause the cycle stability of the cathode material to deteriorate.

[0034] Specifically, kw / kn can be one of 2, 3, 4, 5, 6, 7, 8, 9, 10 or a range value composed of any two of them; preferably 5-10.

[0035] a is the particle size of the primary particles of the ternary material, with the unit of μm, and the range is 0.1-20 μm.

[0036] Determination of kw%: Use 500 ml of dilute acid (such as 1 mol / L dilute nitric acid) to dissolve 1 g of the cathode material and control the dissolution time to dissolve about 40% (mass ratio) of the material. Take out the powder and test the concentration of the A element in the dissolution, which is kw. Completely dissolve the remaining cathode material with 500 ml of the same acid to obtain the concentration of the A element in the remaining solution, which is kn. In a second aspect, a preparation method of the cathode material described above is provided, including the following steps: S1: Prepare a mixed salt solution by mixing nickel salt, optionally cobalt salt, and optionally manganese salt according to a molar ratio; prepare a doping element A solution with a dopant containing element A; prepare a complexing agent solution with a complexing agent; prepare a precipitating agent solution with a precipitating agent; In this application, there is no particular limitation on the types of nickel salts and cobalt salts, which can be conventional nickel salts and cobalt salts in the art. For example, the nickel salt is selected from at least one of nickel sulfate, nickel nitrate and nickel chloride; and the cobalt salt is selected from at least one of cobalt sulfate, cobalt nitrate and cobalt chloride.

[0037] In this application, there is no particular limitation on the types of complexing agents and precipitants. Conventional complexing agents and precipitants in the art can be used. For example, the precipitant is an alkaline solution, preferably a sodium hydroxide solution; and the complexing agent is ammonia.

[0038] Specifically, the molar ratio of nickel salt, cobalt salt and manganese salt is n(Ni):n(Co):n(M)=x:y:z, where 0.5≤x≤0.99, 0≤y≤0.20, and 0≤z≤0.20.

[0039] Specifically, the dopant containing element A is one or more of oxides, hydroxides, fluorides, nitrates, phosphates, carbonates, oxalates, carboxylates, or sulfates containing element A; preferably, it is a sulfate, such as at least one of Na2SO4, MgSO4, and Zr(SO4)2.

[0040] S2: The mixed salt solution, precipitant solution, complexing agent solution and optional dopant element A solution are added to the reactor to carry out a co-precipitation reaction. After aging, filtration, washing and drying, the cathode material precursor is obtained. In some embodiments, the pH of the coprecipitation reaction is 10-12, for example, but not limited to 10, 10.2, 10.4, 10.6, 10.8, 11, 11.2, 11.4, 11.6, 11.8, 12; In some embodiments, the temperature of the coprecipitation reaction is 50-60°C, for example, but not limited to 50°C, 51°C, 52°C, 53°C, 54°C, 55°C, 56°C, 57°C, 58°C, 59°C, and 60°C.

[0041] In some embodiments, the stirring speed of the coprecipitation reaction is 300-1000 rpm, for example, but not limited to 300 rpm, 400 rpm, 600 rpm, 800 rpm, 900 rpm, or 1000 rpm.

[0042] In some embodiments, the coprecipitation reaction takes 6-12 hours, for example, but not limited to 6 hours, 7 hours, 8 hours, 9 hours, 10 hours, 11 hours, or 12 hours.

[0043] In some embodiments, the coprecipitation reaction is carried out in the presence of an inert gas.

[0044] Specifically, the inert gas can be at least one of nitrogen and argon.

[0045] In some embodiments, the solution of dopant element A is added either all at once or in multiple stages.

[0046] In this application, by adjusting the above-mentioned process conditions of the co-precipitation reaction, cathode materials with different particle sizes (Dv50), different doping elements, and different doping concentrations are obtained. Specifically, by controlling the addition of the doping element A solution to be done in stages, cathode materials with a gradient distribution can be prepared, which significantly improves the structural stability of the cathode material and ultimately significantly improves the cycle performance and safety of lithium-ion batteries containing this cathode material.

[0047] S3: Mix the Li source and the cathode material precursor and sinter them to obtain the cathode material.

[0048] In this application, there is no particular limitation on the type of Li source, which can be a conventional Li source in the art, such as at least one of lithium hydroxide, lithium carbonate, lithium acetate, lithium oxalate, lithium sulfate, lithium chloride and lithium nitrate; preferably lithium hydroxide.

[0049] Specifically, the molar ratio of the cathode material precursor to the Li source is Li / (Ni+Co+Mn+A)=1.05-1.20.

[0050] Specifically, the mixing method is not specifically limited in this application, and can adopt the milding methods commonly used in the art, such as ball milling, shear dispersion, etc., with ball milling being preferred.

[0051] In some embodiments, the mixing speed is 300-500 rpm, for example, but not limited to 300 rpm, 350 rpm, 400 rpm, 450 rpm, 500 rpm; the time is 2-4 h, for example, but not limited to 2 h, 2.5 h, 3 h, 4 h.

[0052] In some embodiments, the sintering includes a first sintering and a second sintering, wherein the temperature of the first sintering is 400-500℃ and the time is 4-6h, and the temperature of the second sintering is 750-900℃ and the time is 10-20h.

[0053] Specifically, the temperature of the first sintering can be, but is not limited to, 400℃, 420℃, 450℃, 480℃, or 500℃; and the time can be, but is not limited to, 4 h, 4.5 h, 5 h, 5.5 h, or 6 h.

[0054] Specifically, the temperature of the second sintering can be, but is not limited to, 750℃, 770℃, 800℃, 830℃, 850℃, 880℃, or 900℃; and the time can be, but is not limited to, 10 h, 12 h, 14 h, 16 h, 18 h, or 20 h.

[0055] Specifically, the first sintering is carried out in an air atmosphere; the second sintering is carried out in an oxygen atmosphere.

[0056] In this application, the first sintering can remove bound water from nickel salts, cobalt salts and manganese salts, as well as sulfate ions from sulfates containing element A, thereby reducing the influence of impurities and improving the stability of the cathode material; the second sintering can enable the cathode material precursor to form a cathode material with a layered structure, while simultaneously dissolving and ionizing the dopant element A, which diffuses into the crystal structure of the cathode material, providing a stable and orderly environment for the growth of the cathode material.

[0057] Specifically, in step S2, after sintering, the sintered product is cooled to room temperature at a cooling rate of 2-5°C / min. At this cooling rate, thermal stress can be avoided from causing cracks in the cathode material.

[0058] In one specific embodiment of this application, the positive electrode material is prepared according to the following steps: A mixed salt solution was prepared by mixing nickel salt, cobalt salt, and manganese salt in a specific molar ratio; a dopant containing element A was prepared into a solution containing dopant element A; a complexing agent was prepared into a complexing agent solution; and a precipitant was prepared into a precipitant solution. Under a nitrogen atmosphere and with a stirring speed of 300-1000 rpm, the complexing agent solution and the precipitant solution are added to the reactor. After adjusting the pH of the reactor to 10-12, the mixed salt solution, the precipitant solution, the complexing agent solution, and optionally the dopant element A solution are added to the reactor. A co-precipitation reaction is carried out at pH 10-12 and a temperature of 50-60°C for 6-12 hours. The precursor material is then obtained by aging, filtration, washing, and drying. The cathode material precursor and Li source are added to a ball mill jar and ball milled at 300-500 rpm for 2-4 hours. The ball-milled product is then sintered at 400-500℃ for 4-6 hours, followed by sintering at 750-900℃ for 10-20 hours. Finally, it is cooled to room temperature at a cooling rate of 2-5℃ / min to obtain the cathode material.

[0059] Thirdly, a positive electrode sheet is provided, comprising the aforementioned positive electrode material.

[0060] In some embodiments, the positive electrode sheet includes a positive current collector and a positive active layer located on at least one surface of the positive current collector, wherein the positive active layer includes the positive electrode material described above or the positive electrode material obtained by the preparation method described above.

[0061] In some embodiments, the positive electrode active layer may optionally include a positive electrode conductive agent. This application does not have any particular limitation on the type of positive electrode conductive agent. As an example, the positive electrode conductive agent includes at least one of superconducting carbon, conductive graphite, acetylene black, carbon black, Ketjen black, carbon dots, carbon nanotubes, graphene, and carbon nanofibers.

[0062] In some embodiments, the positive electrode active layer may optionally include an adhesive. This application does not have any particular limitation on the type of positive electrode adhesive. As an example, the positive electrode adhesive may include at least one of the following: polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), ethylene-tetrafluoroethylene-propylene terpolymer, ethylene-hexafluoropropylene-tetrafluoroethylene terpolymer, tetrafluoroethylene-hexafluoropropylene copolymer, fluorinated acrylate resin, styrene-butadiene rubber (SBR), water-soluble unsaturated resin (SR-1B), waterborne acrylic resin (e.g., polyacrylic acid PAA, polymethacrylic acid PMAA, sodium polyacrylate PAAS), polyacrylamide (PAM), polyvinyl alcohol (PVA), sodium alginate (SA), and carboxymethyl chitosan (CMCS).

[0063] In some embodiments, the positive current collector may be a metal foil or a composite current collector. An example of a metal foil is aluminum foil. The composite current collector may include a polymer substrate and a metal layer formed on at least one surface of the polymer substrate. An example of a metal material may be at least one of aluminum, aluminum alloy, nickel, nickel alloy, titanium, titanium alloy, silver, and silver alloy. An example of a polymer substrate may be polypropylene (PP), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polystyrene (PS), polyethylene (PE), etc.

[0064] The positive electrode active layer is typically formed by coating a positive electrode slurry onto a positive electrode current collector, followed by drying and cold pressing. The positive electrode slurry is usually formed by dispersing the positive electrode material, optional conductive agent, optional binder, and any other components in a solvent and stirring until homogeneous. The solvent can be N-methylpyrrolidone (NMP), but is not limited to it.

[0065] Fourthly, a secondary battery is provided, including the aforementioned positive electrode, negative electrode, a separator spaced between the positive electrode and the negative electrode, and an electrolyte.

[0066] During the charging and discharging process of a battery, lithium ions are inserted and extracted back and forth between the positive and negative electrode plates, while the electrolyte plays a role in conducting lithium ions between the positive and negative electrode plates.

[0067] In some embodiments, the electrolyte comprises lithium difluorooxalate borate and adiponitrile; the mass ratio of lithium difluorooxalate borate to adiponitrile is m, wherein when 2≤kw / kn<5, m=0.5-0.8; and when 5≤kw / kn≤10, m=0.8-1.2.

[0068] In some embodiments, the lithium difluorooxalate borate has a mass fraction of m1 in the electrolyte, where m1 = 0.1%-3%, and an adiponitrile content of m2, where m2 = 0.25%-5%.

[0069] Specifically, the mass ratio of lithium difluorooxalate-borate to adiponitrile in the electrolyte is controlled in relation to the concentration gradient ratio of element A in the cathode material (T=kW / kn). Lithium difluorooxalate-borate helps form a CEI film, avoids side reactions, and improves cycle stability. Adiponitrile can couple easily soluble ions such as Ni, preventing surface metal dissolution from deteriorating kinetics and cycle stability. When 10 ≥ T ≥ 5 (significant surface A enrichment), the structure is stable and ion dissolution is low. Limiting m to 0.8~1.2, lithium difluorooxalate-borate preferentially decomposes on highly active surfaces to form a dense CEI film, suppressing side reactions between the material and the electrolyte and improving cycle stability. When 1 ≤ T < 5 (insufficient surface A concentration), controlling m to 0.5~0.8 utilizes adiponitrile's preferential coupling with Ni ions to suppress transition metal migration to the anode and improve cycle stability. However, excessively high m will worsen the specific capacity, as film formation consumes active lithium; excessively low m will cause metal ions to dissolve and migrate to the anode, worsening anode kinetics and specific capacity.

[0070] Specifically, m can be a range of values ​​consisting of one or any two of the following: 0.5, 0.55, 0.6, 0.65, 0.7, 0.75, 0.8, 0.85, 0.9, 0.95, 1.0, 1.05, 1.1, 1.15, and 1.2.

[0071] Specifically, m1 can be a range of values ​​consisting of one or any two of the following: 0.1%, 0.3%, 0.5%, 0.7%, 0.9%, 1.2%, 1.5%, 1.8%, 2%, 2.2%, 2.4%, 2.6%, 2.8%, and 3%.

[0072] Specifically, m2 can be a range of values ​​consisting of one or any two of the following: 0.25%, 0.5%, 0.7%, 1%, 1.3%, 1.5%, 1.8%, 2%, 2.2%, 2.5%, 2.7%, 3%, 3.3%, 3.5%, 3.8%, 4%, 4.2%, 4.5%, 4.7%, and 5%.

[0073] Fifthly, an electrical device is provided, including the aforementioned secondary battery, which serves as the power supply for the electrical device.

[0074] For example, the aforementioned electrical devices may include mobile devices (such as mobile phones, laptops, etc.), electric vehicles (such as pure electric vehicles, hybrid electric vehicles, plug-in hybrid electric vehicles, electric bicycles, electric scooters, electric golf carts, electric trucks, etc.), electric trains, ships, satellites, energy storage systems, etc., but are not limited thereto.

[0075] The present invention is further illustrated below with specific embodiments, which should not be construed as limiting the scope of protection claimed by the present invention: Example 1 Preparation of cathode materials: S1: Weigh NiSO4·6H2O, CoSO4·7H2O, MnSO4·H2O, and NaSO4 according to the molar ratio of Ni:Co:Mn:Na = 0.6:0.2:0.194:0.006; add NiSO4·6H2O, CoSO4·7H2O, and MnSO4·H2O to deionized water to prepare a mixed salt solution; add NaSO4 to deionized water to prepare a NaSO4 solution; prepare an 8% (v / v) ammonia solution; prepare a 3 mol / L sodium hydroxide solution. S2: Under a nitrogen atmosphere and stirring speed of 600 rpm, ammonia solution and sodium hydroxide solution were added to the reactor. After adjusting the pH of the reactor to 11, the mixed salt solution, ammonia solution, sodium hydroxide solution and NaSO4 solution were directly added to the reactor. Co-precipitation reaction was carried out at pH=11 and temperature of 55℃ for 10 hours. Then, the precursor of the positive electrode material was obtained by aging, filtration, washing and drying. S3: The Li source and the cathode material precursor were added to a ball mill jar at a molar ratio of Li / (Ni+Co+Mn+A)=1.1 and ball milled for 3 hours at a speed of 400 rpm. The ball-milled product was sintered at 450℃ for 5 hours, then sintered at 800℃ for 15 hours, and then cooled to room temperature at a cooling rate of 3℃ / min to obtain the cathode material.

[0076] In the process of preparing cathode materials, by controlling the timing of adding the solution of dopant element A and the above parameters, cathode materials with different performance parameters can be obtained. The physicochemical properties of the obtained cathode materials are shown in Table 1.

[0077] Preparation of the positive electrode sheet: The positive electrode material, conductive agent acetylene black, and binder polyvinylidene fluoride (PVDF) are thoroughly mixed in an N-methylpyrrolidone solvent system at a mass ratio of 95:3:2. The mixture is then coated onto the positive electrode current collector Al foil, dried, cold-pressed, and slit to obtain the positive electrode sheet.

[0078] Preparation of negative electrode sheet: The negative electrode active material artificial graphite, conductive agent acetylene black, binder styrene-butadiene rubber (SBR), and thickener sodium carboxymethyl cellulose (CMC) are thoroughly mixed in a deionized water solvent system at a mass ratio of 96:1:1.5:1.5. The mixture is then coated onto the negative electrode current collector Cu foil, dried, cold-pressed, and slit to obtain the negative electrode sheet.

[0079] Electrolyte preparation: At room temperature, in an argon-filled glove box (H2O < 1 ppm, O2 < 1 ppm), ethylene carbonate (EC), diethyl carbonate (DEC), propylene carbonate (PC), propyl propionate (PP), and vinylene carbonate (VC) were mixed uniformly at a mass ratio of EC:DEC:PC:PP:VC = 20:30:20:28:2 to obtain the first solvent. Lithium difluorooxalate borate (LIDFOB) and adiponitrile (ADN) were added to the first solvent, mixed thoroughly, and water was removed using a 4Å molecular sieve to obtain a non-aqueous organic solvent. The lithium salt LiPF6 was mixed evenly with a non-aqueous organic solvent to obtain the electrolyte; The electrolyte comprises the following components by mass percentage: 2% LIDFOB, 2.5% ADN, 10% LiPF6, with the first solvent as the balance.

[0080] Preparation of secondary batteries: Using a porous polyethylene (PE) polymer film as a separator, the positive electrode, separator, and negative electrode are stacked in sequence, with the separator positioned between the positive and negative electrodes. After winding, hot pressing and shaping, and electrode tab welding, a bare cell is obtained. The bare cell is placed in an outer packaging aluminum-plastic film and baked in an oven at 85±10℃ for 24 hours. Electrolyte is injected into the dried battery, and the battery is allowed to stand, form, and be capacity tested to complete the preparation of the lithium-ion secondary battery.

[0081] Example 2 The difference between this embodiment and Embodiment 1 is that step S1 for preparing the cathode material is different. Step S1 for preparing the cathode material in this embodiment is as follows: Weigh NiSO4·6H2O, CoSO4·7H2O, MnSO4·H2O, and NaSO4 according to the molar ratio of Ni:Co:Mn:Na = 0.6:0.2:0.14:0.06; add NiSO4·6H2O, CoSO4·7H2O, and MnSO4·H2O to deionized water to prepare a mixed salt solution; add NaSO4 to deionized water to prepare a NaSO4 solution; prepare an 8% (v / v) ammonia solution; and prepare a 3 mol / L sodium hydroxide solution.

[0082] Example 3 The difference between this embodiment and Embodiment 1 is that step S1 for preparing the cathode material is different. Step S1 for preparing the cathode material in this embodiment is as follows: Weigh NiSO4·6H2O, CoSO4·7H2O, MnSO4·H2O, and NaSO4 according to the molar ratio of Ni:Co:Mn:Na = 0.6:0.2:0.11:0.09; add NiSO4·6H2O, CoSO4·7H2O, and MnSO4·H2O to deionized water to prepare a mixed salt solution; add NaSO4 to deionized water to prepare a NaSO4 solution; prepare an 8% (v / v) ammonia solution; and prepare a 3 mol / L sodium hydroxide solution.

[0083] Example 4 The difference between this embodiment and Embodiment 2 is that step S2 in preparing the cathode material is different. Step S2 in this embodiment is as follows: Under a nitrogen atmosphere and with a stirring speed of 600 rpm, ammonia solution and sodium hydroxide solution were added to the reactor. After adjusting the pH of the reactor to 11, the mixed salt solution, ammonia solution, and sodium hydroxide solution were directly added to the reactor. The NaSO4 solution was divided into two portions and added to the reactor at 0h and 2h, respectively. The co-precipitation reaction was carried out at pH=11 and temperature of 55℃ for 10h. Then, the precursor of the positive electrode material was obtained by aging, filtration, washing, and drying.

[0084] Example 5 The difference between this embodiment and Embodiment 2 is that step S2 in preparing the cathode material is different. Step S2 in this embodiment is as follows: Under a nitrogen atmosphere and with a stirring speed of 600 rpm, ammonia solution and sodium hydroxide solution were added to the reactor. After adjusting the pH of the reactor to 11, the mixed salt solution, ammonia solution, and sodium hydroxide solution were directly added to the reactor. The NaSO4 solution was divided into two portions and added to the reactor at 0h and 3h, respectively. The co-precipitation reaction was carried out at pH=11 and temperature of 55℃ for 10h. Then, the precursor of the positive electrode material was obtained by aging, filtration, washing, and drying.

[0085] Example 6 The difference between this embodiment and Embodiment 2 is that step S2 in preparing the cathode material is different. Step S2 in this embodiment is as follows: Under a nitrogen atmosphere and with a stirring speed of 600 rpm, ammonia solution and sodium hydroxide solution were added to the reactor. After adjusting the pH of the reactor to 11, the mixed salt solution, ammonia solution, and sodium hydroxide solution were directly added to the reactor. The NaSO4 solution was divided into three portions and added to the reactor at 0h, 3h, and 4h, respectively. The co-precipitation reaction was carried out at pH=11 and temperature of 55℃ for 10h. Then, the precursor of the positive electrode material was obtained by aging, filtration, washing, and drying.

[0086] Example 7 The difference between this embodiment and Embodiment 2 is that step S2 in preparing the cathode material is different. Step S2 in this embodiment is as follows: Under a nitrogen atmosphere and with a stirring speed of 600 rpm, ammonia solution and sodium hydroxide solution were added to the reactor. After adjusting the pH of the reactor to 11, the mixed salt solution, ammonia solution, and sodium hydroxide solution were directly added to the reactor. The NaSO4 solution was divided into three portions and added to the reactor at 0h, 3h, and 6h, respectively. The co-precipitation reaction was carried out at pH=11 and temperature of 55℃ for 10h. Then, the precursor of the cathode material was obtained by aging, filtration, washing, and drying.

[0087] Example 8 The difference between this embodiment and Embodiment 2 is that step S2 in preparing the cathode material is different. Step S2 in this embodiment is as follows: Under a nitrogen atmosphere and with a stirring speed of 600 rpm, ammonia solution and sodium hydroxide solution were added to the reactor. After adjusting the pH of the reactor to 11, the mixed salt solution, ammonia solution, and sodium hydroxide solution were directly added to the reactor. The NaSO4 solution was divided into three portions and added to the reactor at 0 h and 6 h, respectively. The co-precipitation reaction was carried out at pH=11 and temperature of 55℃ for 10 h. Then, the precursor of the positive electrode material was obtained by aging, filtration, washing, and drying.

[0088] Example 9 The difference between this embodiment and Embodiment 6 is that step S2 in preparing the cathode material is different. In this embodiment, step S2 in preparing the cathode material is as follows: Under a nitrogen atmosphere and with a stirring speed of 1000 rpm, ammonia solution and sodium hydroxide solution were added to the reactor. After adjusting the pH of the reactor to 11, the mixed salt solution, ammonia solution, and sodium hydroxide solution were directly added to the reactor. The NaSO4 solution was divided into three portions and added to the reactor at 0 h and 6 h, respectively. The co-precipitation reaction was carried out at pH=11 and temperature of 55℃ for 10 h. Then, the precursor of the positive electrode material was obtained by aging, filtration, washing, and drying.

[0089] Example 10 The difference between this embodiment and Embodiment 6 is that step S2 in preparing the cathode material is different. In this embodiment, step S2 in preparing the cathode material is as follows: Under a nitrogen atmosphere and with a stirring speed of 800 rpm, ammonia solution and sodium hydroxide solution were added to the reactor. After adjusting the pH of the reactor to 11, the mixed salt solution, ammonia solution, and sodium hydroxide solution were directly added to the reactor. The NaSO4 solution was divided into three portions and added to the reactor at 0 h and 6 h, respectively. The co-precipitation reaction was carried out at pH=11 and temperature of 55℃ for 10 h. Then, the precursor of the positive electrode material was obtained by aging, filtration, washing, and drying.

[0090] Example 11 The difference between this embodiment and Embodiment 6 is that step S2 in preparing the cathode material is different. In this embodiment, step S2 in preparing the cathode material is as follows: Under a nitrogen atmosphere and with a stirring speed of 500 rpm, ammonia solution and sodium hydroxide solution were added to the reactor. After adjusting the pH of the reactor to 11, the mixed salt solution, ammonia solution, and sodium hydroxide solution were directly added to the reactor. The NaSO4 solution was divided into three portions and added to the reactor at 0 h and 6 h, respectively. The co-precipitation reaction was carried out at pH=11 and temperature of 55℃ for 10 h. Then, the precursor of the positive electrode material was obtained by aging, filtration, washing, and drying.

[0091] Example 12 The difference between this embodiment and Embodiment 6 is that step S2 in preparing the cathode material is different. In this embodiment, step S2 in preparing the cathode material is as follows: Under a nitrogen atmosphere and with a stirring speed of 580 rpm, ammonia solution and sodium hydroxide solution were added to the reactor. After adjusting the pH of the reactor to 11, the mixed salt solution, ammonia solution, and sodium hydroxide solution were directly added to the reactor. The NaSO4 solution was divided into three portions and added to the reactor at 0 h and 6 h, respectively. The co-precipitation reaction was carried out at pH=11 and temperature of 55℃ for 10 h. Then, the precursor of the positive electrode material was obtained by aging, filtration, washing, and drying.

[0092] Example 13 The difference between this embodiment and Embodiment 6 is that the composition of the electrolyte is different. In this embodiment, the electrolyte has the following components by mass percentage: 2% LIDFOB, 1.67% ADN, 10% LiPF6, and the balance of the first solvent.

[0093] Example 14 The difference between this embodiment and Embodiment 6 is that the composition of the electrolyte is different. In this embodiment, the electrolyte has the following components by mass percentage: 2.5% LIDFOB, 1.67% ADN, 10% LiPF6, and the balance being the first solvent.

[0094] Example 15 The difference between this embodiment and Embodiment 6 is that the composition of the electrolyte is different. In this embodiment, the electrolyte has the following components by mass percentage: 1.5% LIDFOB, 2.5% ADN, 10% LiPF6, and the balance being the first solvent.

[0095] Example 16 The difference between this embodiment and Embodiment 4 is that the composition of the electrolyte is different. In this embodiment, the electrolyte has the following components by mass percentage: 2.1% LIDFOB, 4.2% ADN, 10% LiPF6, and the balance being the first solvent.

[0096] Example 17 The difference between this embodiment and Embodiment 4 is that the composition of the electrolyte is different. In this embodiment, the electrolyte has the following components by mass percentage: 2.3% LIDFOB, 2.3% ADN, 10% LiPF6, and the balance being the first solvent.

[0097] Example 18 The difference between this embodiment and Embodiment 4 is that the composition of the electrolyte is different. In this embodiment, the electrolyte has the following components by mass percentage: 1.8% LIDFOB, 6.0% ADN, 10% LiPF6, and the balance being the first solvent.

[0098] Example 19 The difference between this embodiment and Embodiment 6 is that magnesium sulfate is used to replace sodium sulfate in the preparation of the cathode material.

[0099] Example 20 The difference between this embodiment and Embodiment 6 is that zirconium sulfate is used to replace sodium sulfate in the preparation of the cathode material.

[0100] Example 21 The difference between this embodiment and Embodiment 6 is that the composition of the electrolyte is different. In this embodiment, the electrolyte has the following components by mass percentage: 0.08% LIDFOB, 0.1% ADN, 10% LiPF6, and the balance being the first solvent.

[0101] Example 22 The difference between this embodiment and Embodiment 6 is that the composition of the electrolyte is different. In this embodiment, the electrolyte has the following components by mass percentage: 3.2% LIDFOB, 4% ADN, 10% LiPF6, and the balance being the first solvent.

[0102] Example 23 The difference between this embodiment and Embodiment 6 is that the composition of the electrolyte is different. In this embodiment, the electrolyte has the following components by mass percentage: 0.15% LIDFOB, 0.19% ADN, 10% LiPF6, and the balance being the first solvent.

[0103] Example 24 The difference between this embodiment and Embodiment 6 is that the composition of the electrolyte is different. In this embodiment, the electrolyte has the following components by mass percentage: 4.1% LIDFOB, 5.13% ADN, 10% LiPF6, and the balance being the first solvent.

[0104] Comparative Example 1 The difference between this comparative example and Example 6 is that step S1 in preparing the cathode material is different. The step S1 in this comparative example for preparing the cathode material is as follows: Weigh NiSO4·6H2O, CoSO4·7H2O, and MnSO4·H2O according to the molar ratio of Ni:Co:Mn = 0.6:0.2:0.2; add NiSO4·6H2O, CoSO4·7H2O, and MnSO4·H2O to deionized water to prepare a mixed salt solution; prepare an 8% (v / v) ammonia solution; and prepare a 3 mol / L sodium hydroxide solution.

[0105] Comparative Example 2 The difference between this comparative example and Example 6 is that step S2 in preparing the cathode material is different. Step S2 in this comparative example is as follows: Under a nitrogen atmosphere and with a stirring speed of 1200 rpm, ammonia solution and sodium hydroxide solution were added to the reactor. After adjusting the pH of the reactor to 11, the mixed salt solution, ammonia solution, and sodium hydroxide solution were directly added to the reactor. The NaSO4 solution was divided into three portions and added to the reactor at 0h and 6h, respectively. The co-precipitation reaction was carried out at pH=11 and temperature of 55℃ for 10h. Then, the precursor of the positive electrode material was obtained by aging, filtration, washing, and drying.

[0106] Comparative Example 3 The difference between this comparative example and Example 6 is that step S2 in preparing the cathode material is different. Step S2 in this comparative example is as follows: Under a nitrogen atmosphere and with a stirring speed of 460 rpm, ammonia solution and sodium hydroxide solution were added to the reactor. After adjusting the pH of the reactor to 11, the mixed salt solution, ammonia solution, and sodium hydroxide solution were directly added to the reactor. The NaSO4 solution was divided into three portions and added to the reactor at 0 h and 6 h, respectively. The co-precipitation reaction was carried out at pH=11 and temperature of 55℃ for 10 h. Then, the precursor of the positive electrode material was obtained by aging, filtration, washing, and drying.

[0107] Performance testing The secondary batteries obtained in the above embodiments and comparative examples were subjected to the following performance tests: (1) Quantity test: At 25±2℃, each secondary soft pack battery was charged to 4.6V at a rate of 0.1C, then charged at 4.6V until the current rate was less than 0.05C, and then discharged at a constant current rate of 0.1C to 2.5V.

[0108] (2) Cyclic performance test: At 45±2℃, each secondary soft-pack battery was subjected to charge-discharge cycle test at a charge-discharge rate of 0.1C / 1C within the range of 2.5-4.2V, and the discharge specific capacity of the battery in the first cycle and the discharge specific capacity after 500 cycles were recorded. The capacity retention rate after 500 cycles (C500 / %) was calculated as: discharge specific capacity after 500 cycles / discharge specific capacity in the first cycle × 100%.

[0109] The test results are recorded in Tables 1 and 2.

[0110] Table 1: Performance parameters of cathode materials in the examples and comparative examples Table 2: Performance parameters and battery performance test results of cathode materials in the examples and comparative examples As can be seen from the experimental data in Table 1, the cathode material of this application can enable the secondary battery to have good cycle performance during use.

[0111] Finally, it should be noted that the above embodiments are used to illustrate the technical solutions of this application and not to limit the scope of protection of this application. Although this application has been described in detail with reference to preferred embodiments, those skilled in the art should understand that modifications or equivalent substitutions can be made to the technical solutions of this application without departing from the substance and scope of the technical solutions of this application.

Claims

1. A positive electrode material, characterized in that, The structural formula of the cathode material includes LiNi. x Co y Mn z A k O2, where 0.5≤x≤0.7, 0≤y≤0.30, 0≤z≤0.30, 0.006≤k≤0.09, x+y+z+k=1, and element A is at least one of Na, K, Mg, Ba, Ca, La, Y, Cu, Ce, Ru, Rb, Sn, Zr, Bi, Pb, Ag, Cr, Sr, and W; The average particle size of the positive electrode material is Dv50 = 0.25 - 20 μm, satisfying the following relationship: 0.3 ≤ 10 * Dv50 * k ≤ 5.

1.

2. The cathode material as described in claim 1, characterized in that, The positive electrode material satisfies the following relationship: 0.1 ≤ 10 * k / x ≤ 1.

3. The positive electrode material as described in claim 1, characterized in that, The mass percentage concentration of the element A decreases in a gradient from the surface of the primary particle of the positive electrode material to the center of the primary particle of the positive electrode material.

4. The cathode material as described in claim 3, characterized in that, The radius of the primary particle of the positive electrode material is a. The primary particle of the positive electrode material is divided into regions. The region where the distance from the center of the primary particle of the positive electrode material is 0 ≤ L ≤ 0.6a is the first region, and the region where the distance from the center of the primary particle of the positive electrode material is 0.6a < L ≤ a is the second region; the mass percentage concentration of the element A in the first region is kn%, and the mass percentage concentration of the element A in the second region is kw%, where 2 ≤ kw / kn ≤ 10.

5. A method for preparing a positive electrode material as described in any one of claims 1-4, characterized in that, It includes the following steps: Prepare a mixed salt solution by mixing nickel salts, cobalt salts and / or manganese salts according to a molar ratio; prepare a doping element A solution with a dopant containing element A; prepare a complexing agent solution with a complexing agent; Prepare a precipitant solution with a precipitant. Add the mixed salt solution, the precipitant solution, the complexing agent solution, and the doping element A solution into a reaction kettle for coprecipitation reaction. After aging, filtration, washing, and drying, a positive electrode material precursor is obtained. Mix and sinter the Li source and the positive electrode material precursor to obtain the positive electrode material.

6. The method for preparing the cathode material as described in claim 5, characterized in that, The pH of the coprecipitation reaction is 10 - 12; and / or, the temperature of the coprecipitation reaction is 50 - 60 °C; and / or, the stirring speed of the coprecipitation reaction is 300 - 1000 rpm; and / or, the time of the coprecipitation reaction is 6 - 12 h; and / or, the coprecipitation reaction is carried out in the presence of an inert gas; and / or, the doping element A solution is added in one portion or in portions; and / or, the rotation speed of the mixing is 300 - 500 rpm, and the time is 2 - 4 h; and / or, the sintering includes first sintering and second sintering. The temperature of the first sintering is 400 - 500 °C, and the time is 4 - 6 h. The temperature of the second sintering is 750 - 900 °C, and the time is 10 - 20 h.

7. A positive electrode sheet, characterized in that, It includes the positive electrode material as described in any one of claims 1 - 4.

8. A secondary battery, characterized in that, It includes the positive electrode plate as described in claim 7, and also includes a negative electrode plate, an electrolyte, and a separator disposed between the positive electrode plate and the negative electrode plate at intervals; The electrolyte includes lithium difluorooxalate borate and adiponitrile; the mass ratio of lithium difluorooxalate borate to adiponitrile is m, where when 1 ≤ kw / kn < 5, m = 0.5 - 0.8; when 5 ≤ kw / kn ≤ 10, m = 0.8 - 1.

2.

9. The secondary battery as described in claim 8, characterized in that, The mass fraction of lithium difluorooxalate borate in the electrolyte is m1, m1 = 0.1% - 3%, and the fraction of adiponitrile is m2, m2 = 0.25% - 5%.

10. An electrical device, characterized in that, It includes the secondary battery as described in any one of claims 8 - 9, and the secondary battery is used as the power supply of the electrical device.

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