Positive electrode material and preparation method thereof, positive electrode sheet, secondary battery and electronic device

Abstract

The present application provides a positive electrode material and a preparation method thereof, a positive electrode plate, a secondary battery and an electronic device. The preparation method of the positive electrode material comprises: providing a ternary positive electrode material matrix; wet coating the ternary positive electrode material matrix with a nitride nanoparticle coating agent and an organic combustion aid to prepare a pre-coated material; sintering the pre-coated material to form a nitride coating layer on the surface of the ternary positive electrode material matrix. The preparation method of the positive electrode material provided in the present application can improve the high temperature storage and cycle performance of the secondary battery.

Description

Technical Field

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

[0002] Secondary batteries represented by lithium-ion batteries have the advantages of high operating voltage, high energy density, good safety and no memory effect, and have achieved great success in portable electronic devices, electric vehicles and hybrid vehicles. At present, in traditional secondary batteries, ternary materials such as nickel, cobalt and manganese are widely used as positive electrode materials due to their advantages such as high capacity and energy density. However, secondary batteries containing ternary positive electrode materials such as nickel, cobalt and manganese usually have poor high-temperature storage and cycle performance. Summary of the invention

[0003] Based on this, the present application provides a positive electrode material and a preparation method thereof, a positive electrode plate, a secondary battery and an electronic device, aiming to improve the high temperature storage and cycle performance of the secondary battery.

[0004] The first aspect of the present application provides a method for preparing a positive electrode material, comprising:

[0005] Providing a ternary cathode material matrix;

[0006] The ternary cathode material matrix is ​​wet coated by using a nitride nanoparticle coating agent and an organic combustion aid to prepare a pre-coated material;

[0007] The pre-coated material is sintered to form a nitride coating layer on the surface of the ternary positive electrode material matrix.

[0008] According to any embodiment of the first aspect of the present application, wet coating treatment of the ternary cathode material matrix using a nitride nanoparticle coating agent and an organic combustion aid comprises:

[0009] The ternary cathode material matrix, the nitride nanoparticle coating agent and the organic combustion aid are contacted and mixed in a dispersant to obtain a mixed slurry;

[0010] The mixed slurry is ball-milled and dried to obtain a pre-coated material.

[0011] According to any embodiment of the first aspect of the present application, the preparation method satisfies at least one of the following conditions:

[0012] (1) The average particle size of the nitride nanoparticle coating agent is 10 to 2000 nm, preferably 10 nm to 500 nm;

[0013] (2) The nitride nanoparticle coating agent includes one or more of TiN, AlN, Si3N4, and BN;

[0014] (3) Organic combustion aids include one or more of urea, glucose, melamine, phenolic resin and urea-ammonia resin;

[0015] (4) The dispersant includes one or more of deionized water, ethanol, isopropanol and acetone.

[0016] According to any embodiment of the first aspect of the present application, the mass ratio of the ternary positive electrode material matrix, the nitride nanoparticle coating agent, the organic combustion aid and the dispersant is 1: (0.001~0.05): (0.01~1.0): (0.2~2.0).

[0017] According to any embodiment of the first aspect of the present application, the preparation method satisfies at least one of the following conditions:

[0018] (1) The sintering temperature is 200°C to 400°C, preferably 250°C to 350°C;

[0019] (2) The sintering time is 5 h to 20 h, preferably 10 h to 15 h;

[0020] (3) The thickness of the nitride coating is 10nm~100nm.

[0021] According to any implementation of the first aspect of the present application, providing a ternary cathode material matrix includes:

[0022] The ternary cathode precursor is brought into contact with and mixed with a lithium source to obtain a mixed material;

[0023] The mixed material is sintered.

[0024] According to any implementation of the first aspect of the present application, sintering the mixed material includes:

[0025] The mixed material is sintered at 300°C to 1000°C, preferably at 350°C to 950°C, for 10h to 30h, preferably for 15h to 25h.

[0026] According to any implementation of the first aspect of the present application, the preparation process of the ternary positive electrode material matrix satisfies at least one of the following conditions:

[0027] (1) The molecular formula of the ternary cathode precursor is Ni x Co y Mn 1-x-y (OH)2, where 0.33≤x≤0.95, 0.05≤y≤0.77;

[0028] (2) The lithium source includes one or more of lithium carbonate, lithium hydroxide, lithium nitrate and lithium acetate;

[0029] (3) The molar ratio of the lithium element in the lithium source to the sum of the metal elements in the ternary positive electrode precursor is (1.0~1.1):1.

[0030] According to any embodiment of the first aspect of the present application, the preparation method satisfies at least one of the following conditions:

[0031] The molecular formula of the ternary cathode material matrix is ​​LiNi x Co y Mn 1-x-y O2, where 0.33≤x≤0.95, 0.05≤y≤0.77;

[0032] The matrix of the ternary positive electrode material is micron particles, and the average particle size of the micron particles is 3μm~20μm, preferably 5μm~18μm.

[0033] The second aspect of the present application provides a positive electrode material, which is prepared using the preparation method provided according to the first aspect of the present application.

[0034] The third aspect of the present application provides a positive electrode plate, comprising a positive electrode material prepared by the preparation method provided by the first aspect of the present application or a positive electrode material provided by the second aspect of the present application.

[0035] The fourth aspect of the present application provides a secondary battery, comprising the positive electrode plate provided in the third aspect of the present application.

[0036] The fifth aspect of the present application provides an electronic device, comprising the secondary battery provided by the fourth aspect of the present application.

[0037] The electronic device of the present application includes the secondary battery provided by the present application, and thus has at least the same advantages as the secondary battery.

[0038] In the preparation method of the positive electrode material provided in the present application, by wet-coating the ternary positive electrode material matrix with a nitride nanoparticle coating agent and an organic combustion aid and then performing a sintering treatment, a high-conductivity nitride coating layer can be uniformly coated on the surface of the ternary positive electrode material matrix. The coating layer can reduce the powder resistance of the ternary positive electrode material, reduce the resistance of active ions (such as lithium ions) in the positive electrode of the secondary battery during the embedding and release process at the electrode / electrolyte interface, reduce the polarization of the secondary battery during a long cycle, and thus improve the cycle performance of the secondary battery.

[0039] In addition, the addition of organic combustion aids during the sintering process is beneficial to lowering the sintering temperature, allowing the sintering process to be carried out at a lower temperature. This can to a certain extent avoid the titanium and nitrogen elements entering the material's crystal lattice due to traditional high-temperature sintering, which in turn leads to incomplete growth and uneven thickness of the formed coating layer, thereby enhancing the uniformity and mechanical strength of the nitride coating layer, thereby improving the stability of the electrode / electrolyte interface of the secondary battery's ternary positive electrode, which is beneficial to improving the high-temperature storage performance of the secondary battery.

[0040] Furthermore, the organic combustion aid can act as a cross-linking agent to consolidate the bonding force between the nitride nanoparticle coating agent and the surface of the ternary cathode material matrix at the initial stage of sintering treatment, which helps to form a dense nitride coating layer and improve the stability and mechanical strength of the coating layer structure. The dense and stable nitride coating layer can effectively stabilize the electrode / electrolyte interface of the secondary battery cathode, isolate the reaction path between the transition metal elements in the high oxidation state of the ternary cathode material and the electrolyte, thereby reducing the formation of hydrofluoric acid, reducing the dissolution of transition metal elements caused by hydrofluoric acid corrosion on the surface of the ternary cathode material, and reducing the distortion of the surface structure of the ternary cathode material caused by the dissolution of transition metal elements, thereby further improving the interface stability of the ternary cathode of the secondary battery and improving the cycle performance of the secondary battery. BRIEF DESCRIPTION OF THE DRAWINGS

[0041] Figure 1 The XRD diagrams of the positive electrode materials prepared in Example 1 and Comparative Examples 1-4 are shown.

[0042] Figure 2 The polarization curves of the positive electrode materials prepared in Example 2 and Comparative Example 2.

[0043] Figure 3 This is the SEM image of the positive electrode material prepared in Example 1.

[0044] Figure 4 This is a test diagram of the high temperature cycle performance of the positive electrode materials prepared in Examples 1-2 and Comparative Examples 1-2. DETAILED DESCRIPTION

[0045] In order to facilitate the understanding of the present application, the present application will be described more fully below with reference to the relevant drawings. The preferred embodiments of the present application are given in the drawings. However, the present application can be implemented in many different forms and is not limited to the embodiments described herein. On the contrary, the purpose of providing these embodiments is to make the understanding of the disclosure of the present application more thorough and comprehensive.

[0046] For simplicity, this application only explicitly discloses some numerical ranges. However, any lower limit can be combined with any upper limit to form an unclearly recorded range; and any lower limit can be combined with other lower limits to form an unclearly recorded range, and any upper limit can be combined with any other upper limit to form an unclearly recorded range. In addition, although not clearly recorded, each point or single value between the range endpoints is included in the range. Thus, each point or single value can be combined with any other point or single value as its own lower limit or upper limit or with other lower limits or upper limits to form an unclearly recorded range.

[0047] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as those generally understood by those skilled in the art to which this application belongs. The terms used herein in the specification of this application are for the purpose of describing specific embodiments only and are not intended to limit this application. It should be noted that, unless otherwise specified, the term "and / or" used herein includes any and all combinations of one or more related listed items, and "above" and "below" are inclusive of the number, and the meaning of "multiple" in "one or more" is more than two.

[0048] The above application content of the present application is not intended to describe each disclosed embodiment or each implementation in the present application. The following description more specifically illustrates exemplary embodiments. In many places throughout the application, guidance is provided by a series of examples, which can be used in various combinations. In each example, enumeration is only used as a representative group and should not be interpreted as exhaustive.

[0049] During the research process, the inventors found that during high-temperature storage and cycling of secondary batteries containing ternary positive electrode materials such as nickel, cobalt and manganese, the highly oxidized metal elements in the positive electrode materials are easily reacted with lithium hexafluorophosphate and carbonate solvents in the electrolyte. On the one hand, hydrofluoric acid that is corrosive to the electrode / electrolyte interface will be produced in the electrolyte, resulting in the dissolution of transition metal elements such as nickel, cobalt and manganese in the positive electrode material; on the other hand, a high-impedance solid electrolyte interface film will be generated at the electrode / electrolyte interface, resulting in an unstable electrode / electrolyte interface of the positive electrode of the secondary battery during high-temperature storage and cycling, resulting in poor high-temperature storage and cycling performance of the secondary battery.

[0050] In order to solve the above technical problems, the traditional method is to use inorganic metal oxides, such as aluminum oxide, magnesium oxide, titanium oxide and boron oxide, as coating agents to coat and modify the ternary positive electrode materials, thereby avoiding direct contact between the ternary positive electrode materials and the electrolyte to a certain extent, reducing the dissolution of transition metal elements, and thus improving the high-temperature storage and cycle performance of secondary batteries to a certain extent.

[0051] However, after further research, the inventors found that the ternary positive electrode material will have two adverse effects after being coated with inorganic metal oxides: (1) Due to the poor conductivity of inorganic metal oxides, the powder internal resistance of the coated material increases sharply, the conductivity decreases significantly, and the active ions (such as lithium ions) have greater resistance during the embedding and extraction process at the electrode / electrolyte interface, resulting in increased polarization of the secondary battery during the cycle process, affecting the battery's cycle performance; (2) The coating layer of the inorganic metal oxide is uneven, presenting an island-like and loose structure, and has low mechanical strength. During the electrode production rolling and cycle process, the coating layer is prone to cracking and dissolution, resulting in the formation of a new exposed interface, causing continuous structural degradation and performance attenuation at the electrode / electrolyte interface, resulting in a continuous decrease in the high-temperature storage performance of the secondary battery. In order to solve the above technical problems, the inventors proposed the following technical solution of this application.

[0052] A first aspect of the present application provides a method for preparing a positive electrode material, comprising the following steps:

[0053] S10, providing a ternary cathode material matrix;

[0054] S20, using a nitride nanoparticle coating agent and an organic combustion aid to wet-coat a ternary cathode material matrix to prepare a pre-coated material;

[0055] S30, sintering the pre-coated material to form a nitride coating layer on the surface of the ternary positive electrode material matrix to obtain a ternary positive electrode material.

[0056] In the preparation method of the positive electrode material provided in the present application, by wet-coating the ternary positive electrode material matrix with a nitride nanoparticle coating agent and an organic combustion aid and then performing a sintering treatment, a high-conductivity nitride coating layer can be uniformly coated on the surface of the ternary positive electrode material matrix. The coating layer can reduce the powder resistance of the ternary positive electrode material, reduce the resistance of active ions (such as lithium ions) in the positive electrode of the secondary battery during the embedding and release process at the electrode / electrolyte interface, reduce the polarization of the secondary battery during a long cycle, and thus improve the cycle performance of the secondary battery.

[0057] In addition, the addition of organic combustion aids during the sintering process is beneficial to lowering the sintering temperature, allowing the sintering process to be carried out at a lower temperature. This can to a certain extent avoid the titanium and nitrogen elements entering the material's crystal lattice due to traditional high-temperature sintering, which in turn leads to incomplete growth and uneven thickness of the formed coating layer, thereby enhancing the uniformity and mechanical strength of the nitride coating layer, thereby improving the stability of the electrode / electrolyte interface of the secondary battery's ternary positive electrode, which is beneficial to improving the high-temperature storage performance of the secondary battery.

[0058] Furthermore, the organic combustion aid can act as a cross-linking agent to consolidate the bonding force between the nitride nanoparticle coating agent and the surface of the ternary cathode material matrix at the initial stage of sintering treatment, which helps to form a dense nitride coating layer and improve the stability and mechanical strength of the coating layer structure. The dense and stable nitride coating layer can effectively stabilize the electrode / electrolyte interface of the secondary battery cathode, isolate the reaction path between the transition metal elements in the high oxidation state of the ternary cathode material and the electrolyte, thereby reducing the formation of hydrofluoric acid, reducing the dissolution of transition metal elements caused by hydrofluoric acid corrosion on the surface of the ternary cathode material, and reducing the distortion of the surface structure of the ternary cathode material caused by the dissolution of transition metal elements, thereby further improving the interface stability of the ternary cathode of the secondary battery and improving the cycle performance of the secondary battery.

[0059] In some embodiments, step S10 includes the following steps:

[0060] S100, contacting and mixing the ternary positive electrode precursor with a lithium source to obtain a mixture.

[0061] In some embodiments, the molecular formula of the ternary cathode precursor is Ni x Co y Mn 1-x-y (OH)2, where 0.33≤x≤0.95, 0.05≤y≤0.77.

[0062] In some embodiments, the type of lithium source is not particularly limited and can be selected according to actual needs. For example, the lithium source can include one or more of lithium carbonate, lithium hydroxide, lithium nitrate, and lithium acetate.

[0063] In some embodiments, the molar ratio of the lithium element in the lithium source to the sum of the metal elements in the ternary positive electrode precursor, that is, the molar ratio of Li in the lithium source to (Ni+Mn+Co) in the ternary positive electrode precursor is (1.0-1.1):1. For example, the molar ratio may be 1.02:1, 1.04:1, 1.06:1, 1.08:1 or within the range of any of the above values. By controlling the molar ratio of the lithium element to the alloying element within the above range, it is beneficial to obtain the desired ternary positive electrode material matrix.

[0064] S110, sintering the mixed material to provide a ternary positive electrode material matrix.

[0065] In some embodiments, the molecular formula of the ternary cathode material matrix is ​​LiNi x Co y Mn 1-x-y O2, where 0.33≤x≤0.95, 0.05≤y≤0.77.

[0066] In some embodiments, sintering the mixed material in step S110 includes:

[0067] S1100, subjecting the mixed material to a primary sintering treatment at 300°C to 1000°C, preferably at 350°C to 950°C, for 10h to 30h, preferably for 15h to 25h.

[0068] In some embodiments, the temperature of the primary sintering treatment in step S1100 is 300°C~1000°C, for example, it can be 350°C, 400°C, 450°C, 500°C, 550°C, 600°C, 650°C, 700°C, 750°C, 800°C, 850°C, 900°C, 950°C or within the range of any of the above values.

[0069] In some embodiments, the time for a sintering treatment in step S1100 is 10 h to 30 h, for example, 15 h, 20 h, 25 h, 30 h or any range thereof.

[0070] In the embodiment of the present application, by controlling the temperature and time of the primary sintering treatment within the above range, it is beneficial to obtain a ternary positive electrode material matrix with uniform component distribution.

[0071] In some embodiments, the sintering atmosphere of the primary sintering process is not particularly limited and can be selected according to actual needs. For example, the sintering atmosphere can be air, oxygen, or a mixed atmosphere of air and oxygen.

[0072] In some embodiments, after step S110, the obtained ternary positive electrode material matrix needs to be graded and crushed to break the ternary positive electrode material matrix into micron particles for subsequent coating. Preferably, when the ternary positive electrode material matrix is ​​graded and crushed, it can be firstly crushed by jaw crusher, and then finely crushed by air flow mill and double-stage roller.

[0073] In some embodiments, the average particle size of the micron particles after the ternary cathode material matrix is ​​crushed is 3 μm to 20 μm, for example, 5 μm, 7 μm, 9 μm, 11 μm, 13 μm, 15 μm, 17 μm, 19 μm or within the range of any of the above values. The average particle size of the micron particles of the ternary cathode material matrix is ​​within a suitable range, which is conducive to improving the uniformity of contact and mixing with the nitride nanoparticle coating agent, and improving the uniformity of the nitride nanoparticle coating agent coating it, thereby improving the uniformity and density of the nitride coating layer.

[0074] The average particle size of the micron particles of the ternary cathode material is well known in the art and can be measured by instruments and methods well known in the art. For example, it can be conveniently measured by a laser particle size analyzer, such as the Mastersizer 2000E laser particle size analyzer of Malvern Instruments Ltd., UK, with reference to GB / T 19077-2016 Particle Size Distribution Laser Diffraction Method.

[0075] In some embodiments, step S20 includes the following steps:

[0076] S200, contacting and mixing the ternary cathode material matrix, the nitride nanoparticle coating agent and the organic combustion aid in a dispersant to obtain a mixed slurry;

[0077] S210, ball milling and drying the mixed slurry to obtain a pre-coated material.

[0078] In some embodiments, the ternary cathode material matrix, the nitride nanoparticle coating agent and the organic combustion aid can be dispersed and mixed in a ball mill, and then a ball milling medium (such as zirconium oxide balls) is added to wet-mill the mixed slurry, and then dried after ball milling to finally obtain a pre-coated material. Preferably, the drying method is rotary evaporation drying.

[0079] In some embodiments, the type of organic combustion improver is not particularly limited and can be selected according to actual needs. For example, the organic combustion improver can include one or more of urea, glucose, melamine, phenolic resin and urea-ammonia resin.

[0080] In the embodiment of the present application, the addition of an organic combustion aid can reduce the temperature of the sintering process, so that the sintering process is carried out at a lower temperature, and it is lower than the temperature for achieving traditional oxide coating, which is beneficial to reducing energy consumption. When the sintering process is carried out at a lower temperature, the nitride nanoparticle coating agent is more likely to grow and coat along the surface of the ternary positive electrode material without forming its own crystal nucleus, so it is not easy to form island-shaped or point-shaped agglomerates, which can improve the uniformity of the coating layer; and sintering at a lower temperature can inhibit the occurrence of incomplete growth and uneven thickness of the coating layer formed due to the migration of nitrogen and titanium elements into the lattice to a certain extent, thereby enhancing the uniformity and mechanical strength of the nitride coating layer, thereby improving the stability of the electrode / electrolyte interface of the secondary battery ternary positive electrode, which is beneficial to improve the high temperature storage performance of the secondary battery.

[0081] In addition, the organic combustion aid can act as a cross-linking agent to consolidate the bonding force between the nitride nanoparticle coating agent and the surface of the ternary cathode material matrix at the initial stage of sintering treatment, which helps to form a dense nitride coating layer and improve the stability and mechanical strength of the coating layer structure; and then as the sintering temperature increases, the organic combustion aid can be completely decomposed at the end of sintering, so as not to affect the performance of the ternary cathode material. On the one hand, the dense and stable nitride coating layer can effectively stabilize the electrode / electrolyte interface of the secondary battery cathode, isolate the reaction path of the high oxidation state transition metal ions in the ternary cathode material and the electrolyte, thereby reducing the formation of hydrofluoric acid, reducing the dissolution of transition metal elements caused by hydrofluoric acid corrosion on the surface of the ternary cathode material, and alleviating the structural distortion of the material surface caused by the dissolution of transition metals, thereby further improving the interface stability of the secondary battery ternary cathode and improving the cycle performance of the secondary battery. On the other hand, it can also significantly reduce the powder resistance of the ternary cathode material, reduce the increase of the internal resistance of the material during high temperature storage and circulation, and improve the high temperature storage and cycle performance of the secondary battery.

[0082] In some embodiments, the type of dispersant is not particularly limited and can be selected according to actual needs. For example, the dispersant can include one or more of deionized water, ethanol, isopropanol and acetone.

[0083] In some embodiments, the mass ratio of the ternary cathode material matrix, the nitride nanoparticle coating agent, the organic combustion aid, and the dispersant is 1: (0.001-0.05): (0.01-1.0): (0.2-2.0). The mass ratio of the ternary cathode material matrix, the organic combustion aid, and the dispersant within the above range is conducive to improving the uniformity and density of the nitride coating layer.

[0084] In some embodiments, the nitride nanoparticle capping agent includes one or more of TiN, AlN, Si3N4, and BN.

[0085] In some embodiments, the average particle size of the nitride nanoparticle coating agent is 10 nm to 2000 nm, for example, 50 nm, 100 nm, 200 nm, 400 nm, 600 nm, 800 nm, 1000 nm, 1200 nm, 1400 nm, 1600 nm, 1800 nm or within the range of any of the above values. Preferably, the average particle size of the nitride nanoparticle coating agent is 10 nm to 500 nm.

[0086] By controlling the average particle size of the nitride nanoparticle coating agent within a suitable range, it is beneficial to improve the uniformity of the coating of the nitride nanoparticle coating agent on the ternary cathode material matrix, thereby improving the uniformity and density of the nitride coating layer. Controlling the average particle size of the nitride nanoparticle coating agent within this range can achieve effective and uniform coating. When the average particle size is too small, the difficulty and cost of the material processing technology increase sharply, which is not conducive to commercialization. If the average particle size is too large, it may result in the inability to form an effective coating layer or an uneven coating layer structure.

[0087] The average particle size of the nitride nanoparticle coating agent is well known in the art and can be measured using instruments and methods well known in the art. For example, it can be conveniently measured using a laser particle size analyzer, such as the Mastersizer 2000E laser particle size analyzer from Malvern Instruments Ltd., UK, with reference to GB / T 19077-2016 Particle Size Distribution Laser Diffraction Method.

[0088] In some implementations, step S30 includes the following steps:

[0089] S300, performing secondary sintering treatment on the pre-coated material at 200°C to 400°C, preferably at 250°C to 350°C, for 5h to 20h, preferably for 10h to 15h.

[0090] In some embodiments, the temperature of the secondary sintering in step S300 is 200° C. to 400° C., for example, 250° C., 200° C., 350° C. or any range thereof.

[0091] In some embodiments, the secondary sintering time in step S300 is 5 h to 20 h, for example, 10 h, 15 h, 20 h or any range thereof.

[0092] In the embodiment of the present application, by controlling the temperature and time of the secondary sintering treatment within the above range and combining the components of the pre-coating material, a ternary positive electrode material with a dense and uniform coating layer can be obtained.

[0093] In some embodiments, the secondary sintering process may be performed in a box-type furnace, and the sintering atmosphere is not particularly limited and may be selected according to actual needs. For example, the sintering atmosphere may be air, oxygen, or a mixed atmosphere of air and oxygen.

[0094] In some embodiments, the thickness of the nitride coating layer obtained after the secondary sintering process is 10-100 nm, for example, 20 nm, 30 nm, 40 nm, 50 nm, 60 nm, 70 nm, 80 nm, 90 nm or any range thereof.

[0095] A second aspect of the embodiments of the present application provides a positive electrode material, which is prepared by the preparation method provided according to the first aspect of the present application.

[0096] A third aspect of the embodiments of the present application provides a positive electrode plate, comprising a positive electrode material prepared by the preparation method provided by the first aspect of the present application or a positive electrode material provided by the second aspect of the present application.

[0097] In some embodiments, the positive electrode plate includes a positive electrode current collector and a positive electrode film layer disposed on at least one surface of the positive electrode current collector, and the positive electrode film layer includes the positive electrode material of the second aspect of the present application.

[0098] As an example, the positive electrode current collector has two surfaces opposite to each other in its thickness direction, and the positive electrode film layer is disposed on any one or both of the two opposite surfaces of the positive electrode current collector.

[0099] In some embodiments, the positive electrode current collector may be a metal foil or a composite current collector. For example, aluminum foil may be used as the metal foil. The composite current collector may include a polymer material base and a metal layer formed on at least one surface of the polymer material base. The composite current collector may be formed by forming a metal material (aluminum, aluminum alloy, nickel, nickel alloy, titanium, titanium alloy, silver and silver alloy, etc.) on a polymer material substrate (such as a substrate of polypropylene (PP), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polystyrene (PS), polyethylene (PE), etc.).

[0100] In some embodiments, the positive electrode film layer may further optionally include a binder. As an example, the binder may include at least one of polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), vinylidene fluoride-tetrafluoroethylene-propylene terpolymer, vinylidene fluoride-hexafluoropropylene-tetrafluoroethylene terpolymer, tetrafluoroethylene-hexafluoropropylene copolymer, and fluorine-containing acrylate resin.

[0101] In some embodiments, the positive electrode film layer may further include a conductive agent, for example, the conductive agent may include at least one of superconducting carbon, acetylene black, carbon black, Ketjen black, carbon dots, carbon nanotubes, graphene and carbon nanofibers.

[0102] In some embodiments, the positive electrode sheet can be prepared in the following manner: the components for preparing the positive electrode sheet, such as the ternary positive electrode material, the conductive agent, the binder and any other components are dispersed in a solvent (such as N-methylpyrrolidone) to form a positive electrode slurry; the positive electrode slurry is coated on the positive electrode collector, and after drying, cold pressing and other processes, the positive electrode sheet can be obtained.

[0103] A fourth aspect of the embodiments of the present application provides a secondary battery, comprising the positive electrode sheet provided in the third aspect of the present application.

[0104] In some embodiments, the type of secondary battery is not specifically limited, and may include any battery in which an electrochemical reaction occurs to convert chemical energy into electrical energy, for example, a lithium ion battery or a sodium ion battery.

[0105] In some embodiments, the secondary battery further includes a negative electrode sheet, an electrolyte, and a separator. During the battery charge and discharge process, active ions are embedded and removed back and forth between the positive electrode sheet and the negative electrode sheet. The electrolyte plays a role in conducting ions between the positive electrode sheet and the negative electrode sheet. The separator is arranged between the positive electrode sheet and the negative electrode sheet, mainly to prevent the positive and negative electrodes from short-circuiting, while allowing ions to pass through.

[0106] The fifth aspect of the embodiments of the present application provides an electronic device, comprising the secondary battery provided by the fourth aspect of the present application, wherein the secondary battery can be used as a power source in the electronic device.

[0107] In some embodiments, the type of electronic device is not particularly limited, and it can be any electronic device known in the prior art. For example, the electronic device can include, but is not limited to, a laptop computer, a pen-input computer, a mobile computer, an electronic book player, a portable phone, a portable fax machine, a portable copier, a portable printer, a head-mounted stereo headset, a video recorder, an LCD television, a portable cleaner, a portable CD player, a mini-disc, a transceiver, an electronic notepad, a calculator, a memory card, a portable recorder, a radio, a backup power supply, a motor, a car, a motorcycle, a power-assisted bicycle, a bicycle, a lighting fixture, a toy, a game console, a clock, an electric tool, a flashlight, a camera, a large household battery, and a lithium-ion capacitor. Example

[0108] The following are specific examples, which more specifically describe the contents disclosed in this application, and these examples are only for illustrative purposes, because it is obvious to those skilled in the art that various modifications and variations are made within the scope of the disclosure of this application. Unless otherwise stated, all parts, percentages, and ratios reported in the following examples are based on weight, and all reagents used in the examples are commercially available or synthesized according to conventional methods and can be used directly without further processing, and the instruments used in the examples are commercially available.

[0109] Example 1

[0110] (1) Ni with an average particle size of 3.5 μm 0.6 Co 0.1 Mn 0.3The (OH)2 precursor and lithium hydroxide were mixed evenly in a molar ratio of Li element / (Ni+Co+Mn) element of 1.05:1, and then sintered at 960°C for 10 h in an oxygen atmosphere in a box furnace, and crushed by jaw crusher and roller to obtain the ternary positive electrode material matrix LiNi 0.6 Co 0.1 Mn 0.3 O2;

[0111] (2) Take 50g of the ternary cathode material matrix LiNi obtained in step (1) 0.6 Co 0.1 Mn 0.3 O2, 0.5g titanium nitride with an average particle size of 30nm, 1.0g glucose and 0.5g phenolic resin are added to 50mL isopropanol solution, and 200g zirconium balls are added for ball milling for 2h to form a uniformly mixed slurry; the slurry is dried at 50°C by a rotary evaporator to obtain a pre-coated material;

[0112] (3) The pre-coated material obtained in step (2) is sintered in an air atmosphere at 350°C for 10 h to finally obtain a ternary positive electrode material LiNi coated with a titanium nitride layer. 0.6 Co 0.1 Mn 0.3 O2@TiN.

[0113] Example 2

[0114] (1) Ni with an average particle size of 3.5 μm 0.6 Co 0.1 Mn 0.3 The (OH)2 precursor and lithium hydroxide were mixed evenly in a molar ratio of Li element / (Ni+Co+Mn) element of 1.05:1, and then sintered at 960°C for 10 h in an oxygen atmosphere in a box furnace, and crushed by jaw crusher and roller to obtain the ternary positive electrode material matrix LiNi 0.6 Co 0.1 Mn 0.3 O2;

[0115] (2) Take 30g of the ternary cathode material matrix LiNi obtained in step (1) 0.6 Co 0.1 Mn 0.3 O2, 1.0g titanium nitride with an average particle size of 100nm, 1.0g glucose and 0.5g melamine are added to 50mL isopropanol solution, and 120g zirconium balls are added for ball milling for 2h to form a uniformly mixed slurry; the slurry is dried at 50°C by a rotary evaporator to obtain a pre-coated material;

[0116] (3) The pre-coated material obtained in step (2) is sintered in an air atmosphere at 350°C for 10 h to finally obtain a ternary positive electrode material LiNi coated with a titanium nitride layer. 0.6 Co 0.1 Mn 0.3 O2@TiN.

[0117] Example 3

[0118] (1) Ni with an average particle size of 4.0 μm 0.65 Co 0.07 Mn 0.28 The (OH)2 precursor and lithium hydroxide were mixed evenly in a molar ratio of Li element / (Ni+Co+Mn) element of 1.03:1, and then sintered at 900°C for 10 h in an oxygen atmosphere in a box furnace. The ternary cathode material matrix Li Ni 0.65 Co 0.07 Mn 0.28 O2;

[0119] (2) Take 100g of the ternary cathode material matrix Li Ni obtained in step (1) 0.65 Co 0.07 Mn 0.28 O2, 1.0 g of titanium nitride with an average particle size of 100 nm, and 0.5 g of melamine are added to 150 mL of isopropanol solution, and 400 g of zirconium balls are added and ball-milled for 2 hours to form a uniformly mixed slurry; the slurry is dried at 50° C. by a rotary evaporator to obtain a pre-coated material;

[0120] (3) The pre-coated material obtained in step (2) is sintered in an air atmosphere at 270°C for 10 h to finally obtain a ternary positive electrode material LiNi coated with a titanium nitride layer. 0.65 Co 0.07 Mn 0.28 O2@TiN.

[0121] Example 4

[0122] (1) Ni with an average particle size of 10 μm 0.8 Co 0.1 Mn 0.1 The (OH)2 precursor and lithium hydroxide were mixed evenly in a molar ratio of Li element / (Ni+Co+Mn) element of 1.06:1, and sintered at 750°C for 10 h in an oxygen atmosphere in a box furnace. The ternary positive electrode material matrix Li Ni was obtained by jaw crushing and roller crushing. 0.8 Co 0.1 Mn 0.1 O2;

[0123] (2) Take 60g of the ternary cathode material matrix LiNi obtained in step (1) 0.65 Co 0.07 Mn 0.28 O2, 1.5 g of titanium nitride with an average particle size of 50 nm, and 0.8 g of melamine are added to 120 mL of isopropanol solution, and 240 g of zirconium balls are added and ball-milled for 2 hours to form a uniformly mixed slurry; the slurry is dried at 50° C. by a rotary evaporator to obtain a pre-coated material;

[0124] (3) The pre-coated material obtained in step (2) is sintered in an air atmosphere at 200°C for 10 hours to finally obtain a ternary positive electrode material LiNi coated with a titanium nitride layer. 0.8 Co 0.1 Mn 0.1 O2@TiN.

[0125] Comparative Example 1

[0126] The preparation method of Comparative Example 1 is similar to that of Example 1, except that step (2) is omitted, i.e., the ternary positive electrode material matrix LiNi 0.6 Co 0.1 Mn 0.3 O2 is not coated to obtain the uncoated ternary positive electrode material LiNi 0.6 Co 0.1 Mn 0.3 O2.

[0127] Comparative Example 2

[0128] The preparation method of Comparative Example 2 is similar to that of Example 1, except that steps (2) and (3) are omitted, and the ternary positive electrode material matrix LiNi obtained in step (1) is 0.6 Co 0.1 Mn 0.3 O2 is coated with alumina using the traditional dry method, that is, 2.5 kg of the ternary cathode material matrix LiNi obtained in step (1) is taken. 0.6 Co 0.1 Mn 0.3 O2 was mixed evenly with 15g of nano-alumina and sintered at 400°C for 10h in an air atmosphere in a box furnace to obtain a ternary positive electrode material LiNi coated with a nano-alumina layer. 0.6 Co 0.1 Mn 0.3 O2@Al2O3.

[0129] Comparative Example 3

[0130] The preparation method of Comparative Example 3 is similar to that of Example 1, except that steps (2) and (3) are omitted, and the ternary positive electrode material matrix LiNi obtained in step (1) is0.6 Co 0.1 Mn 0.3 O2 is coated with titanium oxide using the traditional dry method, that is, 2.5 kg of the ternary cathode material matrix LiNi obtained in step (1) is taken. 0.6 Co 0.1 Mn 0.3 O2 was mixed evenly with 8g of nano-titanium oxide and sintered at 400°C for 10h in an air atmosphere in a box furnace to obtain a ternary positive electrode material LiNi coated with a nano-titanium oxide layer. 0.6 Co 0.1 Mn 0.3 O2@TiO2.

[0131] Comparative Example 4

[0132] The preparation method of Comparative Example 4 is similar to the preparation method of Example 1, except that no organic combustion aid is added in step (2).

[0133] Comparative Example 5

[0134] The preparation method of Comparative Example 5 is similar to that of Example 1, except that the sintering temperature in step (3) is 600°C.

[0135] The ternary positive electrode materials prepared in Examples 1 to 4 and Comparative Examples 1 to 5 or the lithium ion batteries further prepared therefrom were subjected to relevant performance tests, and the test results are shown in Table 1 below.

[0136] Among them, the test conditions or test standards for each performance test item are as follows:

[0137] (1) XRD test of ternary cathode materials

[0138] The ternary cathode material powder was placed on the sample stage of an XRD test instrument (model Bruker D8) with a scanning rate of 2° / min and a scanning angle range of 10° to 90°. Figure 1 XRD diffraction pattern shown.

[0139] (2) SEM test of ternary cathode materials

[0140] The ternary cathode material was tested using a ZEISS sigma 300 scanning electron microscope and the sample morphology was observed according to the standard JY / T010-1996. Figure 2 The morphology shown.

[0141] (3) Polarization test of lithium-ion batteries

[0142] The dQ / dV curve test was performed as follows: the prepared ternary cathode material was assembled into a button cell, wherein the electrode material: conductive carbon black = 90:10wt%, the solvent was NMP, and the battery electrode surface density was 1.2mg / cm 2 , at a voltage of 2.8-4.4V, at 25°C, charge and discharge for 3 cycles at a rate of 0.05C / 0.05C to obtain a cycle curve. The curve of the third cycle is taken to take the inverse of the capacity and voltage and plotted to obtain the dQ / dV curve, which represents the level of lithium insertion and extraction potential. The lower the lithium extraction potential or the higher the lithium extraction potential, the lower the polarization of the material, and vice versa. The results are as follows Figure 2 shown.

[0143] (4) Metal dissolution test of lithium-ion batteries after high-temperature storage

[0144] For the positive electrode materials prepared in Examples 1-2 and Comparative Examples 1-3, the metal dissolution of the three elements Ni, Co, and Mn was compared after being stored at 80°C for 30 days and 60 days respectively when the battery was fully charged. The test method is as follows: the prepared ternary positive electrode material was assembled into a button battery, and when the battery was fully charged (4.4V), the battery was disassembled after being stored at 80°C for 30 days and 60 days respectively, the positive electrode plate was cleaned with DMC, the active material layer of the positive electrode plate was scraped off, and then it was heated in aqua regia for 15min-30min to dissolve, and the solution was subjected to ICP test of Ni, Co, and Mn content to obtain the data in Table 1. The metal dissolution of the three elements Ni, Co, and Mn was tested, and the test results are shown in Table 1 below.

[0145] (5) High temperature cycle performance test of lithium-ion batteries

[0146] The lithium-ion battery is charged to 4.4V at 1C constant current at 55℃, then charged to 0.05C at constant voltage, left to stand for 5min, and then discharged to 2.5V at 1C constant current. This is one charge and discharge cycle, and the discharge capacity at this time is recorded as D01. According to the above charge and discharge process, the lithium-ion battery is cycled 3000 times, and the discharge capacity of the 50th cycle is recorded as D1. The charge and discharge cycle process is plotted into a comparison chart, as shown in the attached figure. Figure 4 A graph showing the capacity retention of a lithium-ion battery versus the number of cycles.

[0147] Table 1

[0148]

[0149] It can be seen from Table 1 above that after long-term high-temperature storage, the amount of metal elements dissolved in the ternary positive electrode materials obtained by the preparation method provided by the present application in Examples 1 to 4 is significantly lower than that in Comparative Examples 1 to 5, indicating that the ternary positive electrode material coated with the titanium nitride layer obtained by the preparation method provided by the present application can form an effective and stable interface in the lithium-ion battery, which can significantly reduce the interface reaction of the electrode / electrolyte and reduce the formation of hydrofluoric acid, thereby reducing the corrosion of hydrofluoric acid on the surface of the ternary positive electrode material and causing the dissolution of transition metal Ni / Co / Mn elements, which is beneficial to improving the high-temperature storage performance of the lithium-ion battery.

[0150] By comparing Examples 1 and 2 with Comparative Example 4, it can be seen that the amount of metal dissolved when the organic combustion aid is added during the sintering process is less than when the organic combustion aid is not added. This is because the organic combustion aid can reduce the temperature of the sintering treatment, making the titanium nitride coating layer denser and having higher mechanical strength, and can more effectively isolate the electrode / electrolyte interface.

[0151] By comparing Examples 1 and 2 with Comparative Example 5, it can be seen that when the preparation process using an organic combustion aid is sintered at a lower temperature, the amount of transition metal elements dissolved will be less. This is because the organic combustion aid can lower the sintering temperature and inhibit the entry of Ti and N elements into the lattice of the ternary positive electrode material; and the lower sintering temperature prevents the growth of titanium nitride coating agent particles, avoids the coating layer from presenting a point-like and island-like structure, makes the coating layer more uniform, has higher mechanical strength, and can more effectively isolate the electrode / electrolyte interface.

[0152] From the attached Figure 1 It can be seen that no impurity peaks appear in the samples of Example 1 and Comparative Examples 1 to 3, indicating that the coating layer does not change the crystal structure of the ternary positive electrode material, and the intensity ratio of the 003 / 104 peak of the sample exceeds 1.2, indicating that the material has a lower Li / Ni mixing value.

[0153] From the attached Figure 2 It can be seen that the first charging peak position of the dQ / dV charging curve of Example 2 is 3.72V, while the corresponding peak position of Comparative Example 2 is 3.76V, indicating that the material prepared by the method of Comparative Example 2 has a larger DCR and a larger polarization, resulting in a higher voltage required for delithiation. The gradient doping material prepared by the method of Example 2 can better inhibit the growth of DCR and reduce the polarization of the material.

[0154] From the attached Figure 4 It can be seen that the high-temperature cyclability of the ternary positive electrode material prepared by the preparation method provided in the present application is significantly higher than that of Comparative Examples 1 and 2, indicating that the preparation method provided in the present application can improve the cyclic performance of lithium-ion batteries, and the preparation method is significantly better than the traditional dry method of coating inorganic metal oxides.

[0155] The technical features of the above-described embodiments may be arbitrarily combined. To make the description concise, not all possible combinations of the technical features in the above-described embodiments are described. However, as long as there is no contradiction in the combination of these technical features, they should be considered to be within the scope of this specification.

[0156] The above-mentioned embodiments only express several implementation methods of the present application, and the descriptions thereof are relatively specific and detailed, but they cannot be understood as limiting the scope of the invention patent. It should be pointed out that, for a person of ordinary skill in the art, several variations and improvements can be made without departing from the concept of the present application, and these all belong to the protection scope of the present application. Therefore, the protection scope of the patent of the present application shall be subject to the attached claims.

Claims

1. A method for preparing a positive electrode material, characterized in that: include: Providing a ternary cathode material matrix; The ternary cathode material matrix is ​​wet coated by using a nitride nanoparticle coating agent and an organic combustion aid to prepare a pre-coated material, wherein the organic combustion aid includes one or more of urea, glucose, melamine, phenolic resin and urea-ammonia resin; The pre-coated material is sintered to form a nitride coating layer on the surface of the ternary positive electrode material matrix, and the sintering temperature is 200° C. to 400° C.

2. The preparation method according to claim 1, characterized in that: The wet coating treatment of the ternary cathode material matrix by using the nitride nanoparticle coating agent and the organic combustion aid comprises: The ternary cathode material matrix, the nitride nanoparticle coating agent and the organic combustion improver are contacted and mixed in a dispersant to obtain a mixed slurry; The mixed slurry is subjected to ball milling and drying treatment to obtain the pre-coated material.

3. The preparation method according to claim 2, characterized in that: The preparation method satisfies at least one of the following conditions: (1) The average particle size of the nitride nanoparticle coating agent is 10-2000 nm; (2) The nitride nanoparticle coating agent includes one or more of TiN, AlN, Si3N4, and BN; (3) The dispersant includes one or more of deionized water, ethanol, isopropanol and acetone.

4. The preparation method according to claim 3, characterized in that: The average particle size of the nitride nanoparticle coating agent is 10nm-500nm.

5. The preparation method according to any one of claims 2 to 4, characterized in that The mass ratio of the ternary positive electrode material matrix, the nitride nanoparticle coating agent, the organic combustion aid and the dispersant is 1: (0.001-0.05): (0.01-1.0): (0.2-2.0).

6. The preparation method according to claim 1, characterized in that: The preparation method satisfies at least one of the following conditions: (1) The sintering temperature is 250°C to 350°C; (2) The sintering time is 5h~20h; (3) The thickness of the nitride coating layer is 10 nm to 100 nm.

7. The preparation method according to claim 6, characterized in that: The sintering time is 10h~15h.

8. The preparation method according to claim 1, characterized in that: The providing of a ternary positive electrode material matrix comprises: The ternary cathode precursor is brought into contact with and mixed with a lithium source to obtain a mixed material; The mixed material is subjected to a sintering process.

9. The preparation method according to claim 8, characterized in that: The sintering treatment of the mixed material comprises: The mixture is sintered at 300° C. to 1000° C. for 10 h to 30 h.

10. The preparation method according to claim 9, characterized in that: The sintering process of the mixed material comprises: The mixture is sintered at 350° C. to 950° C. for 15 h to 25 h.

11. The preparation method according to any one of claims 8 to 10, characterized in that: The preparation process of the ternary positive electrode material matrix satisfies at least one of the following conditions: (1) The molecular formula of the ternary cathode precursor is Ni x Co y Mn 1-x-y (OH)2, where 0.33≤x≤0.95, 0.05≤y≤0.77; (2) The lithium source includes one or more of lithium carbonate, lithium hydroxide, lithium nitrate and lithium acetate; (3) The molar ratio of the lithium element in the lithium source to the sum of the metal elements in the ternary positive electrode precursor is (1.0-1.1):

1.

12. The preparation method according to claim 1 or 8, characterized in that: The preparation method satisfies at least one of the following conditions: (1) The molecular formula of the ternary cathode material matrix is ​​LiNi x Co y Mn 1-x-y O2, where 0.33≤x≤0.95, 0.05≤y≤0.77; (2) The matrix of the ternary positive electrode material is micron particles, and the average particle size of the micron particles is 3 μm to 20 μm.

13. The preparation method according to claim 12, characterized in that: The average particle size of the micron particles is 5 μm to 18 μm.

14. A positive electrode material, characterized in that: The method is prepared according to any one of claims 1 to 13.

15. A positive electrode sheet, characterized in that: It comprises a positive electrode material prepared by the preparation method according to any one of claims 1 to 13 or the positive electrode material according to claim 14.

16. A secondary battery, characterized in that: Including the positive electrode sheet as described in claim 15.

17. An electronic device, characterized in that: Includes the secondary battery as claimed in claim 16.

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