Lithium ion secondary battery, method for manufacturing the same, and electric device

Abstract

The application provides a lithium ion secondary battery and a preparation method thereof, and an electric device, wherein the lithium ion secondary battery comprises a positive electrode sheet, the positive electrode sheet comprises a positive electrode active material layer, the positive electrode active material layer comprises a lithium-containing phosphate and an inorganic material modified polyacrylate binder; the inorganic material modified polyacrylate binder comprises a polyacrylate polymer and inorganic particles, at least part of the polyacrylate polymer is grafted on the surface of the inorganic particles; and the polyacrylate polymer comprises a structural unit derived from an acrylate monomer. By adding the inorganic material modified polyacrylate binder in the positive electrode active material layer with the lithium-containing phosphate as the positive electrode active material, the lithium ion secondary battery has a lower internal resistance and better kinetic performance.

Description

Technical Field

[0001] The present application relates to the technical field of secondary batteries, and in particular to a lithium-ion secondary battery, a preparation method thereof, and an electrical device. Background Art

[0002] In recent years, as the application scope of secondary batteries has become increasingly wider, secondary batteries have been widely used in energy storage power systems such as hydropower, thermal power, wind power and solar power stations, as well as in many fields such as power tools, electric bicycles, electric motorcycles and electric vehicles.

[0003] Lithium-ion secondary batteries using lithium-containing phosphates, such as lithium iron phosphate (LFP), as positive electrode active materials have the advantages of low cost and good safety, making them a hot area of ​​lithium-ion secondary battery development. PVDF (polyvinylidene fluoride) is commonly used as a binder in positive electrode plates using lithium-containing phosphates as positive electrode active materials. However, due to concerns about persistent pollution risks and bioaccumulative hazards, the use of fluorinated PVDF binders is restricted. Polyacrylate binders, which offer stronger adhesion and better stability, are often used in place of PVDF.

[0004] However, lithium-ion secondary batteries using lithium-containing phosphates as the positive electrode active material and polyacrylate binders typically have a relatively high internal resistance (DCR), resulting in poor kinetic performance. Therefore, reducing the internal resistance and improving the kinetic performance of these lithium-ion secondary batteries has become a key focus for those skilled in the art. Summary of the Invention

[0005] The present application is made in view of the above-mentioned problems, and one of its purposes is to provide a lithium-ion secondary battery with low internal resistance and good dynamic performance, and correspondingly provides a preparation method and an electrical device of the lithium-ion secondary battery.

[0006] To achieve the above-mentioned object, the first aspect of the present application provides a lithium-ion secondary battery, comprising a positive electrode plate, wherein the positive electrode plate comprises a positive electrode active material layer, wherein the positive electrode active material layer comprises a lithium-containing phosphate and an inorganic material-modified polyacrylate binder;

[0007] The inorganic material modified polyacrylate binder includes a polyacrylate polymer and inorganic particles, at least a portion of the polyacrylate polymer is grafted onto the surface of the inorganic particles; the polyacrylate polymer includes structural units derived from acrylic acid ester monomers.

[0008] By using the above-mentioned inorganic material to modify the polyacrylate binder, at least a portion of the polyacrylate polymer is grafted onto the surface of the inorganic particles, thereby avoiding the agglomeration of the inorganic particles, allowing the inorganic particles to be evenly dispersed in the binder, and enabling the inorganic particles to effectively inhibit the polyacrylate binder from forming a film on the surface of the lithium-phosphate material, reducing the density of the polyacrylate binder film on the surface of the lithium-phosphate material, accelerating the transmission of lithium ions, thereby reducing the internal resistance of the lithium-ion secondary battery and improving the dynamic performance of the battery.

[0009] In any embodiment, the acrylic acid ester monomer includes one or more of methyl methacrylate, butyl acrylate, or isooctyl acrylate.

[0010] In any embodiment, the structural units derived from acrylic acid ester monomers account for 60% to 80% by weight of the polyacrylate polymer.

[0011] In any embodiment, the polyacrylate polymer further comprises a structural unit derived from a first monomer, wherein the first monomer comprises one or more of styrene or acrylonitrile, thereby improving the cohesive force of the positive electrode.

[0012] In any embodiment, the mass proportion of the structural units derived from the non-polar monomer in the polyacrylate polymer is 20% to 40%.

[0013] In any embodiment, the inorganic particles include one or more of titanium dioxide (TiO2), silicon dioxide (SiO2), calcium stearate, or aluminum oxide (Al2O3). This effectively inhibits the formation of polyacrylate binders on the surface of the lithium-containing phosphate material, reduces the density of the film, accelerates lithium ion transport, and thereby reduces the battery's internal resistance and improves its dynamic performance. Furthermore, these inorganic particles are highly inert and will not negatively impact the positive electrode active material.

[0014] In any embodiment, the weight average molecular weight of the polyacrylate polymer is 150,000 to 400,000 Daltons, which is beneficial for improving the mechanical properties of the positive electrode sheet, such as adhesion and cohesion, and improving the processing performance of the positive electrode slurry.

[0015] In any embodiment, the mass fraction of the inorganic particles in the inorganic material-modified polyacrylate binder is 5% to 20%. This is beneficial for reducing the internal resistance of the battery and improving the battery dynamic performance while also taking into account the mechanical properties of the positive electrode sheet.

[0016] In any embodiment, the mass fraction of the inorganic particles in the inorganic material-modified polyacrylate binder is 10% to 15%. This helps to better balance the battery's kinetic performance and the mechanical properties of the positive electrode sheet. This allows the battery to have low internal resistance and good kinetic performance while also providing the positive electrode sheet with excellent mechanical properties.

[0017] In any embodiment, the mass fraction of the inorganic material-modified polyacrylate binder is 1% to 2% based on the total mass of the positive electrode active material layer as 100%. This helps to improve the dispersibility of the positive electrode slurry, enhance the mechanical properties of the positive electrode sheet, and minimize the adverse effect on the battery energy density.

[0018] In any embodiment, the positive electrode active material layer further includes a dispersant, which includes one or more of a phosphate dispersant and a styrene-ethylene / butylene-styrene block copolymer (SEBS) dispersant. This helps improve the dispersibility of the positive electrode slurry and the flexibility of the positive electrode sheet.

[0019] In any embodiment, based on the total mass of the positive electrode active material layer being 100%, the mass fraction of the dispersant is 0.1% to 0.5%, which is beneficial for effectively improving the dispersibility of the positive electrode slurry.

[0020] In any embodiment, based on the total mass of the positive electrode active material layer being 100%, the mass fraction of the dispersant is 0.3% to 0.5%, which is beneficial for further improving the dispersibility of the positive electrode slurry.

[0021] In any embodiment, based on the total mass of the positive electrode active material layer being 100%, the mass fraction of the lithium-containing phosphate is 95% to 99%.

[0022] In any embodiment, the lithium-containing phosphate includes one or more of lithium iron phosphate, lithium manganese phosphate, or lithium manganese iron phosphate.

[0023] A second aspect of the present application provides a method for preparing a lithium-ion secondary battery, comprising the following steps:

[0024] A lithium-containing phosphate, an inorganic material-modified polyacrylate binder, and a solvent are mixed to obtain a positive electrode slurry; the inorganic material-modified polyacrylate binder comprises a polyacrylate polymer and inorganic particles, at least a portion of the polyacrylate polymer is grafted onto the surface of the inorganic particles; the polyacrylate polymer comprises structural units derived from acrylic acid ester monomers;

[0025] Placing the positive electrode slurry on a positive electrode current collector and drying the positive electrode to obtain a positive electrode sheet; and

[0026] The positive electrode sheet, the separator and the negative electrode sheet are stacked so that the separator is disposed between the positive electrode sheet and the negative electrode sheet to obtain an electrode assembly, and the electrode assembly is made into a secondary battery.

[0027] By grafting polyacrylate polymers onto the surface of inorganic particles, agglomeration of the inorganic particles can be avoided, and the inorganic particles can be evenly dispersed in the binder. The inorganic particles can effectively inhibit the polyacrylate binder from forming a film on the surface of the lithium-phosphate material, reduce the density of the polyacrylate binder film on the surface of the lithium-phosphate material, accelerate the transmission of lithium ions, thereby reducing the internal resistance of the lithium-ion secondary battery and improving the dynamic performance of the battery.

[0028] In any embodiment, the preparation method of the inorganic material modified polyacrylate binder comprises the following steps:

[0029] Silane coupling agent is used to modify the surface of inorganic particles;

[0030] The surface-modified inorganic particles are mixed with acrylic acid ester monomers and an initiator, and the inorganic material-modified polyacrylate adhesive is obtained after reaction.

[0031] In this way, the inorganic particles and the polyacrylate polymer material can be connected through chemical bonds, thereby improving the compatibility between the inorganic particles and the polyacrylate polymer, enhancing the binding force between the inorganic particles and the polyacrylate polymer material, avoiding the agglomeration of the inorganic particles, and enabling the inorganic particles to be evenly dispersed in the binder, so that the inorganic particles can effectively inhibit the polyacrylate binder from forming a film on the surface of the lithium phosphate material.

[0032] In any embodiment, the silane coupling agent includes one or more of hexamethyldisilazane, γ-aminopropyltriethoxysilane, or γ-glycidoxypropyltrimethoxysilane.

[0033] In any embodiment, the initiator is a free radical polymerization initiator, and the initiator includes one or more of potassium persulfate, azobisisobutyronitrile or benzoyl peroxide.

[0034] In any embodiment, the acrylic acid ester monomer includes one or more of methyl methacrylate, butyl acrylate, or isooctyl acrylate.

[0035] In any embodiment, the inorganic particles include one or more of titanium dioxide, silicon dioxide, calcium stearate, or aluminum oxide.

[0036] In any embodiment, the Dv50 particle size of the inorganic particles is 1 μm to 5 μm. This is beneficial for fully dispersing the inorganic particles in the emulsion during the preparation of the inorganic material-modified polyacrylate binder.

[0037] The third aspect of the present application provides an electrical device comprising one or more of the lithium ion secondary battery of the first aspect of the present application or the lithium ion secondary battery prepared by the preparation method of the lithium ion secondary battery of the second aspect of the present application.

[0038] The details of one or more embodiments of the present application are set forth in the following drawings and description. Other features, objects, and advantages of the present application will become apparent from the description, drawings, and claims. BRIEF DESCRIPTION OF THE DRAWINGS

[0039] In order to better describe and illustrate the embodiments or examples provided in this application, reference may be made to one or more of the accompanying drawings. The additional details or examples used to describe the accompanying drawings should not be considered as limiting the scope of the disclosed application, the embodiments or examples currently described, and any of the best modes currently understood for these applications. Moreover, the same reference numerals are used throughout the drawings to represent the same components. In the accompanying drawings:

[0040] Figure 1 A schematic diagram of a battery cell according to an embodiment of the present application;

[0041] Figure 2 for Figure 1 An exploded view of a battery cell according to an embodiment of the present application is shown;

[0042] Figure 3 Schematic diagram of an electrical device using a lithium-ion secondary battery as a power source according to one embodiment of the present application.

[0043] Description of reference numerals:

[0044] 5. Battery cell; 51. Housing; 52. Electrode assembly; 53. Cover plate; 6. Electrical device. DETAILED DESCRIPTION

[0045] Below, the lithium-ion secondary battery of the present application, its preparation method, and the embodiment of the electric device thereof are described in detail with appropriate reference to the accompanying drawings. However, there may be cases where unnecessary detailed descriptions are omitted. For example, there are cases where detailed descriptions of well-known matters and repeated descriptions of actually the same structure are omitted. This is to avoid the following description from becoming unnecessarily lengthy and to facilitate the understanding of those skilled in the art. In addition, the drawings and the following description are provided for those skilled in the art to fully understand the present application and are not intended to limit the subject matter described in the claims.

[0046] The "range" disclosed in this application can be defined in the form of a lower limit and an upper limit. A given range is defined by selecting a lower limit and an upper limit, and the selected lower limit and upper limit define the boundaries of a particular range. The range defined in this way can be inclusive or exclusive of end values, and any end value can be independently included or excluded, and can be arbitrarily combined, i.e., any lower limit can be combined with any upper limit to form a range. For example, if a range of 60 to 120 and 80 to 110 is listed for a particular parameter, it is understood that a range of 60 to 110 and 80 to 120 is also contemplated. In addition, if the minimum range values ​​listed are 1 and 2, and if the maximum range values ​​3, 4, and 5 are also listed, the following ranges can all be contemplated: 1 to 3, 1 to 4, 1 to 5, 2 to 3, 2 to 4, and 2 to 5. In this application, unless otherwise specified, the numerical range "a to b" represents an abbreviation of any real number combination between a and b, wherein a and b are both real numbers. For example, the numerical range "0-5" indicates that all real numbers between "0-5" are listed herein, and "0-5" is simply an abbreviation for these numerical combinations. Furthermore, when a parameter is expressed as an integer ≥ 2, this is equivalent to listing the parameter as, for example, the integers 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, and so on. For example, when a parameter is expressed as an integer selected from "2-10", this is equivalent to listing the integers 2, 3, 4, 5, 6, 7, 8, 9, and 10.

[0047] In this application, "a plurality of" or "a plurality of" refers to a number greater than or equal to 2 unless otherwise specified. For example, "one or more" means one or more than or equal to two.

[0048] Unless otherwise specified, all embodiments and optional embodiments of the present application can be combined with each other to form a new technical solution.

[0049] References to "embodiments" herein mean that a particular feature, structure, or characteristic described in conjunction with the embodiments may be included in at least one embodiment or implementation of the present application. The appearance of such phrases in various locations in the specification does not necessarily refer to the same embodiment, nor does it necessarily refer to independent or alternative embodiments that are mutually exclusive with other embodiments. It is understood, both explicitly and implicitly, by those skilled in the art that the embodiments described herein may be combined with other embodiments. References to "implementations" herein have a similar understanding.

[0050] Those skilled in the art can understand that the order of writing each step in the method of each embodiment or example does not mean a strict execution order and does not constitute any limitation on the implementation process. The detailed execution order of each step should be determined by its function and possible internal logic. If not specifically stated, all steps of the present application can be performed in sequence or randomly, preferably in sequence. For example, the method comprises steps (a) and (b), which means that the method can comprise steps (a) and (b) in sequence, or steps (b) and (a) in sequence. For example, the method also comprises step (c), which means that step (c) can be added to the method in any order, for example, the method can comprise steps (a), (b) and (c), or steps (a), (c) and (b), or steps (c), (a) and (b), etc.

[0051] In the present application, the open technical features or technical solutions described by the words "containing", "including", "comprising" and the like do not exclude additional members other than the listed members, and can be regarded as providing both a closed feature or solution composed of the listed members and an open feature or solution including additional members in addition to the listed members. For example, A includes a1, a2 and a3, and unless otherwise specified, it can also include other members or can not include additional members, and can be regarded as providing both the feature or solution that "A is composed of a1, a2 and a3" and the feature or solution that "A includes a1, a2 and a3, and also includes other members". In the present application, unless otherwise specified, A (such as B) means that B is a non-limiting example of A, and it can be understood that A is not limited to B.

[0052] In the present application, "optionally", "optional" and "optional" mean that it can or can not be present, i.e. it can be selected from either of the two parallel solutions "yes" or "no". If there are multiple "optional" in a technical solution, unless otherwise specified, and there is no contradiction or mutual restriction, each "optional" is independent of each other.

[0053] Currently, PVDF is usually used as a binder in the positive electrode sheet of a battery with lithium-containing phosphate as a positive active material. However, due to the risk of persistent pollution and the hazard of biological accumulation, the use of fluorine-containing PVDF binder needs to be limited. A polyacrylate binder with stronger adhesion and better stability can be used to replace PVDF. However, the internal resistance of a lithium ion secondary battery with lithium-containing phosphate as a positive active material and using a polyacrylate binder is usually large, and the kinetic performance of the battery is poor.

[0054] Based on this, in an embodiment of the present application, a lithium ion secondary battery is provided, which includes a positive electrode sheet, the positive electrode sheet including a positive electrode active material layer, the positive electrode active material layer including a lithium-containing phosphate and an inorganic material modified polyacrylate binder; the inorganic material modified polyacrylate binder including a polyacrylate polymer and inorganic particles, at least part of the polyacrylate polymer being grafted on the surface of the inorganic particles; the polyacrylate polymer including structural units derived from an acrylate monomer.

[0055] A conventional positive electrode sheet using a lithium-containing phosphate as a positive electrode active material generally uses PVDF as a binder. In some batteries using PFAS (per / polyfluoroalkyl substances), the use of PVDF needs to be limited due to concerns about persistent pollution risk and biological accumulation hazards. For example, a polyacrylate binder with stronger adhesion and better stability can be used instead of PVDF. However, the lithium ion secondary battery using a lithium-containing phosphate and a polyacrylate binder has a large internal resistance (DCR) and poor kinetic performance. The main reason is that the polar groups in the polyacrylate binder can form hydrogen bonds and other interactions with the polar sites (such as phosphate groups) on the surface of the lithium-containing phosphate, thereby forming a relatively dense binder film on the surface of the lithium-containing phosphate. The poor ion conductivity of the polyacrylate binder itself and the dense binder film wrapped around the surface of the lithium-containing phosphate material result in a large internal resistance and poor kinetic performance of the lithium ion secondary battery.

[0056] The lithium ion secondary battery described above adds an inorganic material modified polyacrylate binder to the positive electrode active material layer of the positive electrode sheet. By grafting at least part of the polyacrylate polymer on the surface of the inorganic particles, the agglomeration of the inorganic particles can be avoided, the compatibility of the inorganic particles with the polyacrylate binder is good, the inorganic particles can be uniformly dispersed in the binder, and the inorganic particles can effectively inhibit the formation of a polyacrylate binder film on the surface of the lithium-containing phosphate material, reduce the density of the polyacrylate binder film on the surface of the lithium-containing phosphate material, and accelerate the transport of lithium ions, thereby reducing the internal resistance of the lithium ion secondary battery and improving the kinetic performance of the battery. The polyacrylate polymer is grafted on the surface of the inorganic particles, for example, the polyacrylate polymer can be connected to the surface of the inorganic particles by chemical bonding.

[0057] It should be noted that inorganic material-modified polyacrylate polymers refer to, but are not limited to, linking inorganic particles to polyacrylate polymers through physical or chemical methods. From a chemical perspective, this involves chemically reacting the active functional groups (such as carboxyl and hydroxyl groups) on the polyacrylate polymer molecular chains with active sites on the inorganic particle surfaces (such as hydroxyl groups on metal oxide particles), thereby firmly "grafting" the polymer chains onto the inorganic particles. Physically, in some cases, the polymer and inorganic particles can also form a tight bond through electrostatic interactions and adsorption, allowing the polymer to adhere to the inorganic particles, achieving a similar grafting effect. Fourier transform infrared spectroscopy (FT-IR) can be used to determine whether the inorganic particles and polyacrylate binder in inorganic material-modified polyacrylate binders are grafted. Specifically, if the inorganic particles and polyacrylate binder undergo a grafting reaction, new chemical bonds will form, resulting in the appearance of corresponding characteristic absorption peaks in the infrared spectrum, or changes in the position, intensity, or shape of some existing absorption peaks. For example, inorganic particles usually have hydroxyl groups on their surfaces. After being grafted with polyacrylates, the absorption peak of the hydroxyl groups may shift or broaden. By comparing the infrared spectrum with that of polyacrylate binders to which inorganic particles have not been grafted, it is possible to determine whether a grafting reaction has occurred between the inorganic particles and the polyacrylate binder.

[0058] A scanning electron microscope (SEM) combined with energy dispersive spectroscopy (EDS) can also be used for determination. Specifically, the surface morphology of the sample can be observed using a scanning electron microscope. If the inorganic particles are grafted onto a polyacrylate binder, the inorganic particles will be relatively evenly dispersed in the polyacrylate binder at a microscopic level, with a good bonding interface between the inorganic particles and the binder. Energy dispersive spectroscopy can then be used to qualitatively and quantitatively analyze the elements on the sample surface. By examining the distribution of the inorganic elements, it can be determined whether the inorganic particles have been grafted onto the polymer. If the inorganic elements are uniformly distributed within the binder, with no apparent separation at the interface, grafting can be determined to have occurred.

[0059] In some embodiments, the inorganic particles are grafted to the polyacrylate polymer via a silane coupling agent. In this way, the polyacrylate polymer can be grafted to the inorganic particles via the silane coupling agent, and the polyacrylate polymer and the inorganic particles can be connected via chemical bonding, such as covalent bonds. Specifically, the silane coupling agent is mixed with the inorganic particles in a solvent, and the silane coupling agent is grafted to the surface of the inorganic particles by stirring. Then, the inorganic particles with the modified surface are added to the acrylate monomer, and an initiator is added for copolymerization. During the reaction, the silane coupling agent on the surface of the inorganic particles reacts with the polyacrylate polymer, thereby grafting the polyacrylate polymer to the surface of the inorganic particles. In some embodiments, the acrylate monomer includes one or more of methyl methacrylate, butyl acrylate, or isooctyl acrylate. The use of the structural units of the acrylate monomers described above in the binder has good bonding performance, which is conducive to improving the mechanical properties of the pole piece.

[0060] In some embodiments, the mass fraction of the structural units derived from the acrylate monomer in the polyacrylate polymer is 60% to 80%. It can be understood that the mass fraction of the structural units derived from the acrylate monomer in the polyacrylate polymer can be 60%, 62%, 65%, 68%, 70%, 72%, 75%, 78%, 80%, and any value within the range formed by any two of the above values.

[0061] In some embodiments, the polyacrylate polymer further includes structural units derived from a first monomer, and the first monomer includes one or more of styrene or acrylonitrile. In this way, the use of the structural units derived from the first monomer described above in the polyacrylate polymer, the styrene contains a benzene ring structure, and the acrylonitrile contains a polar nitrile group. After polymerization with the acrylate monomer, the interaction sites between the polymer molecules can be increased, the intermolecular attraction can be enhanced, and the combination between the polymer molecules can be more closely, thereby facilitating the improvement of the cohesive force.

[0062] In some embodiments, the mass fraction of the structural units derived from the first monomer in the polyacrylate polymer is 20% to 40%. It can be understood that the mass fraction of the structural units derived from the first monomer in the polyacrylate polymer can be 20%, 22%, 25%, 28%, 30%, 32%, 35%, 38%, 40%, and any value within the range formed by any two of the above values.

[0063] In some embodiments, the inorganic particles include one or more of titanium dioxide, silicon dioxide, calcium stearate, or aluminum oxide. Modifying the polyacrylate binder with these inorganic particles effectively inhibits film formation on the surface of the lithium-containing phosphate material, accelerating lithium ion transport, thereby reducing battery internal resistance and improving battery dynamics. Furthermore, these inorganic particles exhibit excellent inertness in the positive electrode slurry and do not react with the positive electrode active material, negatively impacting its performance.

[0064] In some embodiments, the weight-average molecular weight of the polyacrylate polymer is between 150,000 and 400,000 Daltons. Controlling the weight-average molecular weight of the polyacrylate polymer within this range improves the mechanical properties of the positive electrode, provides better processing performance, and reduces the risk of gelation.

[0065] It is understood that the weight average molecular weight of the polyacrylate polymer can be 150,000 Daltons, 160,000 Daltons, 170,000 Daltons, 180,000 Daltons, 190,000 Daltons, 200,000 Daltons, 210,000 Daltons, 220,000 Daltons, 230,000 Daltons, 240,000 Daltons, 250,000 Daltons, 260,000 Daltons, 270,000 Daltons, 280,000 Daltons, 290,000 Daltons, 300,000 Daltons, 310,000 Daltons, 320,000 Daltons, 330,000 Daltons, 340,000 Daltons, 350,000 Daltons, 360,000 Daltons, 370,000 Daltons, 380,000 Daltons, 390,000 Daltons, 400,000 Daltons, and any value within the range formed by any two of the above values. It is understood that 10,000 Daltons is equal to 10 kDa.

[0066] In some embodiments, the mass fraction of inorganic particles in the inorganic material-modified polyacrylate binder is 5% to 20%. Controlling the mass fraction of inorganic particles in the inorganic material-modified polyacrylate binder within the above range is beneficial for reducing battery internal resistance and improving battery kinetic performance while also taking into account the mechanical properties of the positive electrode sheet.

[0067] It can be understood that the mass fraction of inorganic particles in the inorganic material modified polyacrylate adhesive can be 5%, 6%, 7%, 8%, 9%, 10%, 11%, 12%, 13%, 14%, 15%, 16%, 17%, 18%, 19%, 20% and any value within the range formed by any two of the above values.

[0068] In some embodiments, the mass fraction of inorganic particles in the inorganic material-modified polyacrylate binder is 10% to 15%. Controlling the mass fraction of inorganic particles in the inorganic material-modified polyacrylate binder within this range helps to better balance the battery's kinetic performance with the mechanical properties of the positive electrode sheet. This allows the battery to have low internal resistance and good kinetic performance while also providing the positive electrode sheet with excellent mechanical properties.

[0069] In some embodiments, the mass fraction of the inorganic material-modified polyacrylate binder is 1% to 2% based on the total mass of the positive electrode active material layer as 100%. Controlling the mass fraction of the inorganic material-modified polyacrylate binder in the positive electrode active material layer within the above range is beneficial for improving the dispersion of the positive electrode slurry and the mechanical properties of the positive electrode sheet without significantly affecting the energy density of the battery.

[0070] It can be understood that, based on the total mass of the positive electrode active material layer as 100%, the mass fraction of the inorganic material modified polyacrylate binder can be 1.0%, 1.1%, 1.2%, 1.3%, 1.4%, 1.5%, 1.6%, 1.7%, 1.8%, 1.9%, 2%, and any value within the range formed by any two of the above values.

[0071] In some embodiments, the mass fraction of the inorganic material-modified polyacrylate binder is 1% to 1.8% based on the total mass of the positive electrode active material layer as 100%. Further controlling the mass fraction of the inorganic material-modified polyacrylate binder in the positive electrode active material layer within the above range is beneficial for better balancing the dispersibility of the positive electrode slurry, the mechanical properties of the positive electrode sheet, and the energy density of the battery.

[0072] In some embodiments, the positive electrode active material layer further includes a dispersant, which includes a flexible dispersant. Adding a dispersant to the positive electrode active material layer can prevent gelation in a positive electrode slurry using an inorganic material-modified polyacrylate binder and facilitate processing. Using a flexible dispersant can also maintain good flexibility in a positive electrode sheet using an inorganic material-modified polyacrylate binder, further facilitating the prevention of gelation and ease of processing.

[0073] It can be understood that the flexible dispersant refers to a dispersant that can improve the flexibility of the positive electrode sheet and promote the formation of a good dispersion effect of the polyacrylate binder in the positive electrode slurry.

[0074] In some embodiments, the dispersant includes one or more of a phosphate dispersant or a styrene-ethylene / butylene-styrene block copolymer (SEBS) dispersant. Phosphate dispersants and SEBS dispersants are flexible and can effectively disperse inorganic material-modified polyacrylate binders, thereby improving the dispersibility of the positive electrode slurry and the flexibility of the positive electrode sheet.

[0075] Phosphate ester dispersants are organic compounds containing phosphate functional groups (-OPO(OR)2), where R represents an organic group. SEBS (Styrene Ethylene Butylene Styrene) dispersants are linear triblock copolymers with polystyrene as the terminal segments and an ethylene-butylene copolymer derived from hydrogenated polybutadiene as the central elastomeric block. Both the aforementioned phosphate ester and SEBS dispersants can be commercially available.

[0076] In some embodiments, the mass fraction of the dispersant is 0.1% to 0.5%, based on the total mass of the positive electrode active material layer as 100%. Controlling the mass fraction of the dispersant in the positive electrode active material layer within the above range is beneficial to improving the dispersibility of the positive electrode slurry. It is understood that the mass fraction of the dispersant in the positive electrode active material layer may be 0.1%, 0.12%, 0.15%, 0.18%, 0.2%, 0.22%, 0.25%, 0.28%, 0.3%, 0.32%, 0.35%, 0.38%, 0.4%, 0.42%, 0.45%, 0.48%, 0.5%, and any value within the range formed by any two of the above values.

[0077] In some embodiments, the mass fraction of the dispersant is 0.3% to 0.5% based on the total mass of the positive electrode active material layer as 100%. Further controlling the mass fraction of the flexible dispersant in the positive electrode active material layer within the above range is beneficial to further improve the dispersibility of the positive electrode slurry.

[0078] In some embodiments, the mass fraction of the lithium-containing phosphate is 95% to 99% based on the total mass of the positive electrode active material layer as 100%. The lithium-containing phosphate may include one or more of lithium iron phosphate, lithium manganese phosphate, or lithium manganese iron phosphate.

[0079] One embodiment of the present application provides a method for preparing the above-mentioned lithium-ion secondary battery, which comprises the following steps: mixing a lithium-containing phosphate, an inorganic material-modified polyacrylate binder, and a solvent to obtain a positive electrode slurry; the inorganic material-modified polyacrylate binder comprises a polyacrylate polymer and inorganic particles, at least a portion of the polyacrylate polymer is grafted onto the surface of the inorganic particles; the polyacrylate polymer comprises a structural unit derived from an acrylic acid ester monomer; the positive electrode slurry is placed on a positive electrode current collector and dried to obtain a positive electrode sheet; the positive electrode sheet, a separator, and a negative electrode sheet are stacked so that the separator is disposed between the positive electrode sheet and the negative electrode sheet to obtain an electrode assembly, and the electrode assembly is made into a lithium-ion secondary battery.

[0080] By grafting polyacrylate polymers onto the surface of inorganic particles, agglomeration of the inorganic particles can be avoided, and the inorganic particles can be evenly dispersed in the binder. The inorganic particles can effectively inhibit the polyacrylate binder from forming a film on the surface of the lithium-phosphate material, reduce the density of the polyacrylate binder film on the surface of the lithium-phosphate material, accelerate the transmission of lithium ions, thereby reducing the internal resistance of the lithium-ion secondary battery and improving the dynamic performance of the battery.

[0081] In some embodiments, the acrylic acid ester monomer includes one or more of methyl methacrylate, butyl acrylate, or isooctyl acrylate.

[0082] In some embodiments, the preparation method of the above-mentioned inorganic material modified polyacrylate adhesive includes the following steps: first, using a silane coupling agent to modify the surface of the inorganic particles; then, mixing the surface-modified inorganic particles with an acrylic ester monomer and an initiator, and obtaining the inorganic material modified polyacrylate adhesive after a polymerization reaction.

[0083] Surface modification of the inorganic particles using a silane coupling agent and subsequent polymerization to form a polyacrylate binder facilitates chemical bonding between the inorganic particles and the polyacrylate polymer material, improving compatibility and bonding between the inorganic particles and the polyacrylate polymer material. This prevents agglomeration of the inorganic particles, allows for uniform dispersion of the inorganic particles in the binder, and effectively inhibits film formation of the polyacrylate binder on the surface of the lithium phosphate-containing material. It is understood that the inorganic material-modified polyacrylate binder may also employ existing commercially available products.

[0084] In some embodiments, the silane coupling agent includes one or more of hexamethyldisilazane, γ-aminopropyltriethoxysilane, or γ-glycidoxypropyltrimethoxysilane. The initiator is a free radical polymerization initiator, and the initiator includes one or more of potassium persulfate, azobisisobutyronitrile, or benzoyl peroxide. The acrylate monomer includes one or more of methyl methacrylate, butyl acrylate, or isooctyl acrylate.

[0085] In some of the embodiments, the surface of the nano-SiO2 particles is first modified with hexamethyldisilazane (HMDS), and then mixed with methyl methacrylate (MMA) and butyl acrylate (BA) emulsions to form a Pickering emulsion, which is then reacted with the initiator potassium persulfate (KPS) to prepare a nano-SiO2 modified acrylate adhesive.

[0086] In some embodiments, the inorganic particles include one or more of titanium dioxide, silicon dioxide, calcium stearate, or aluminum oxide. Using these inorganic particles to modify the polyacrylate binder helps inhibit film formation on the surface of the lithium-containing phosphate material, accelerating lithium ion transport, thereby reducing battery internal resistance and improving battery dynamic performance. Furthermore, these inorganic particles exhibit excellent inertness in the positive electrode slurry and do not react with the positive electrode active material, negatively impacting its performance.

[0087] In some embodiments, the Dv50 particle size of the inorganic particles is 1 μm to 5 μm. Controlling the Dv50 particle size of the inorganic particles within the above range is beneficial to the preparation process of the inorganic material modified polyacrylate binder, so that the inorganic particles can be fully dispersed in the emulsion, and the filter element will not be blocked during subsequent filtration due to the excessive size of the inorganic particles. It is understandable that the Dv50 particle size of the inorganic particles can be 1 μm, 1.2 μm, 1.5 μm, 1.8 μm, 2 μm, 2.2 μm, 2.5 μm, 2.8 μm, 3 μm, 3.2 μm, 3.5 μm, 3.8 μm, 4 μm, 4.2 μm, 4.5 μm, 4.8 μm, 5 μm and any value within the range formed by any two of the above values.

[0088] It should be noted that the Dv50 particle size, also known as the median particle size, refers to the particle size corresponding to when the cumulative particle size distribution percentage reaches 50% in a particle size distribution.

[0089] In an embodiment of the present application, a positive electrode tab is provided, which includes a positive electrode active material layer, the positive electrode active material layer including a lithium-containing phosphate and an inorganic material modified polyacrylate binder; the inorganic material modified polyacrylate binder including a polyacrylate polymer and inorganic particles, at least part of the polyacrylate polymer being grafted on the surface of the inorganic particles.

[0090] By adding the inorganic material modified polyacrylate binder in the positive electrode active material layer of the positive electrode tab, and by grafting the polyacrylate polymer on the surface of the inorganic particles, the inorganic particles can be uniformly dispersed in the binder, and the polyacrylate binder can be effectively inhibited from forming a film on the surface of the lithium-containing phosphate material, thereby accelerating the transport of lithium ions, and reducing the internal resistance of the lithium ion secondary battery and improving the kinetic performance of the battery.

[0091] In some embodiments, the positive electrode tab further includes a positive electrode current collector, and the positive electrode active material layer is disposed on at least one side surface of the positive electrode current collector.

[0092] In an embodiment of the present application, a positive electrode slurry is provided, which includes a lithium-containing phosphate, an inorganic material modified polyacrylate binder, and an organic solvent; the inorganic material modified polyacrylate binder including a polyacrylate polymer and inorganic particles, at least part of the polyacrylate polymer being grafted on the surface of the inorganic particles.

[0093] In some embodiments, the mass fraction of the inorganic material modified polyacrylate binder is 0.5% to 2%, and the mass fraction of the dispersant is 0.1% to 0.5%, based on 100% of the dry weight of the positive electrode slurry.

[0094] In an embodiment of the present application, an electric device is provided, which includes one or more of the lithium ion secondary batteries described above or prepared by the method described above.

[0095] The lithium ion secondary battery and the electric device of the present application will be described below with reference to the accompanying drawings.

[0096] In an embodiment of the present application, a lithium ion secondary battery is provided.

[0097] Generally, a lithium ion secondary battery includes a positive electrode tab, a negative electrode tab, an electrolyte, and a separator. During the charging and discharging of the battery, active ions are inserted and extracted between the positive electrode tab and the negative electrode tab. The electrolyte plays a role in conducting ions between the positive electrode tab and the negative electrode tab. The separator is disposed between the positive electrode tab and the negative electrode tab, and mainly plays a role in preventing short circuiting between the positive and negative electrodes, while allowing ions to pass through.

[0098] The positive electrode sheet includes a positive electrode current collector and a positive electrode active material layer disposed on at least one surface of the positive electrode current collector.

[0099] As a non-limiting example, the positive electrode current collector has two surfaces facing each other in its thickness direction, and the positive electrode active material layer is disposed on either or both of the two facing surfaces of the positive electrode current collector.

[0100] 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 layer and a metal layer formed on at least one surface of the polymer material base layer. The composite current collector may be obtained by forming a metal material on a polymer material substrate. Non-limiting examples of the metal material in the positive electrode current collector may include one or more of aluminum, aluminum alloy, nickel, nickel alloy, titanium, titanium alloy, silver, and silver alloy. Non-limiting examples of the polymer material base material in the positive electrode current collector may include one or more of polypropylene (PP), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polystyrene (PS), polyethylene (PE), and the like.

[0101] In some embodiments, the positive electrode active material includes a lithium-containing phosphate and may further include other positive electrode active materials for batteries known in the art. Non-limiting examples of the lithium-containing phosphate may include, but are not limited to, one or more of lithium iron phosphate, a composite material of lithium iron phosphate and carbon, lithium manganese phosphate, a composite material of lithium manganese phosphate and carbon, lithium iron manganese phosphate, and a composite material of lithium iron manganese phosphate and carbon.

[0102] As non-limiting examples, other positive electrode active materials for batteries include lithium transition metal oxides and modified compounds thereof. Examples of lithium transition metal oxides may include, but are not limited to, one or more of lithium cobalt oxide, lithium nickel oxide, lithium manganese oxide, lithium nickel cobalt oxide, lithium manganese cobalt oxide, lithium nickel manganese oxide, lithium nickel cobalt manganese oxide and modified compounds thereof. Non-limiting examples of lithium cobalt oxide may include LiCoO2; non-limiting examples of lithium nickel oxide may include LiNiO2; non-limiting examples of lithium manganese oxide may include LiMnO2, LiMn2O4, etc.; non-limiting examples of lithium nickel cobalt manganese oxide may include LiNi 1 / 3 Co 1 / 3 Mn 1 / 3 O2 (also referred to as NCM 333 )、LiNi 0.5 Co 0.2 Mn 0.3 O2 (also referred to as NCM 523 )、LiNi 0.5 Co 0.25 Mn 0.25O2 (also referred to as NCM 211 )、LiNi 0.6 Co 0.2 Mn 0.2 O2 (also referred to as NCM 622 )、LiNi 0.8 Co 0.1 Mn 0.1 O2 (also referred to as NCM 811 ) etc.; Non-limiting examples of lithium nickel cobalt aluminum oxide may include LiNi 0.85 Co 0.1 Al 0.05 O2.

[0103] It is understandable that the battery will be accompanied by lithium (Li) deintercalation and consumption during the charge and discharge process, and the content of Li in the positive electrode plate is different when the battery is discharged to different states. In the list of positive electrode materials in this application, unless otherwise specified, the Li content is the initial state of the material. The positive electrode material is applied to the positive electrode plate in the battery system, and after the charge and discharge cycle, the Li content in the positive electrode material contained in the plate will usually change. Among them, the Li content can be measured by molar content, but is not limited to this. Regarding "the Li content is the initial state of the material", the initial state of the material refers to the state before the material is added to the positive electrode slurry. It is understandable that new materials obtained by appropriate modification on the basis of the listed positive electrode materials are also within the scope of positive electrode materials. The aforementioned appropriate modification refers to acceptable modification methods for positive electrode materials, and non-limiting examples include coating modification.

[0104] In the examples of positive electrode materials in this application, the oxygen (O) content is only a theoretical value. Lattice oxygen release will cause the molar content of oxygen to change, and the actual O content will fluctuate. The O content can be measured by molar content, but is not limited to this.

[0105] The weight ratio of the positive electrode active material in the positive electrode active material layer is 80 wt % to 100 wt % based on the total weight of the positive electrode active material layer.

[0106] In some embodiments, the positive electrode active material layer may further optionally include a conductive agent. As non-limiting examples, the conductive agent may include one or more of superconducting carbon, acetylene black, carbon black, Ketjen black, carbon dots, carbon nanotubes, graphene, and carbon nanofibers. The weight ratio of the conductive agent in the positive electrode active material layer is 0% to 20% by weight, based on the total weight of the positive electrode active material layer.

[0107] In some embodiments, the positive electrode sheet can be prepared by the following method: the components for preparing the positive electrode sheet, such as the positive electrode active 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, wherein the positive electrode slurry has a solid content of 40wt% to 80wt%, and the viscosity at room temperature is adjusted to 5000mPa·s to 25000mPa·s, the positive electrode slurry is coated on both sides of the positive electrode current collector, and after drying, it is cold-pressed by a cold rolling mill to form a positive electrode sheet.

[0108] The negative electrode sheet includes a negative electrode current collector and a negative electrode active material layer disposed on at least one surface of the negative electrode current collector, wherein the negative electrode active material layer includes a negative electrode active material.

[0109] As a non-limiting example, the negative electrode current collector has two surfaces facing each other in its thickness direction, and the negative electrode active material layer is disposed on either or both of the two facing surfaces of the negative electrode current collector.

[0110] In some embodiments, the negative electrode current collector may be a metal foil or a composite current collector. For example, copper foil may be used as the metal foil. The composite current collector may include a polymer base layer and a metal layer formed on at least one surface of the polymer base layer. The composite current collector may be obtained by forming a metal material on a polymer base layer. In the negative electrode current collector, non-limiting examples of the metal material may include one or more of copper, copper alloys, nickel, nickel alloys, titanium, titanium alloys, silver, and silver alloys. In the negative electrode current collector, non-limiting examples of the polymer base layer may include one or more of polypropylene (PP), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polystyrene (PS), polyethylene (PE), and the like.

[0111] In some embodiments, the negative electrode active material may be a negative electrode active material for batteries known in the art.

[0112] As a non-limiting example, the negative electrode active material of the lithium-ion secondary battery may include one or more of the following materials: artificial graphite, natural graphite, soft carbon, hard carbon, silicon-based materials, tin-based materials and lithium titanate. Silicon-based materials may include one or more of elemental silicon, silicon oxides, silicon-carbon composites, silicon-nitrogen composites and silicon alloys. Tin-based materials may include one or more of elemental tin, tin oxides and tin alloys. However, the present application is not limited to these materials, and other traditional materials that can be used as negative electrode active materials for batteries may also be used. These negative electrode active materials may be used alone or in combination of two or more.

[0113] In some embodiments, the negative electrode active material layer may further include a binder. The binder may include one or more of styrene-butadiene rubber (SBR), polyacrylic acid (PAA), sodium polyacrylate (PAAS), polyacrylamide (PAM), polyvinyl alcohol (PVA), sodium alginate (SA), polymethacrylic acid (PMAA), and carboxymethyl chitosan (CMCS).

[0114] In some embodiments, the negative electrode active material layer may further include a conductive agent, which may include one or more of superconducting carbon, acetylene black, carbon black, Ketjen black, carbon dots, carbon nanotubes, graphene, and carbon nanofibers.

[0115] In some embodiments, the negative electrode active material layer may further optionally include other additives, such as a thickener (eg, sodium carboxymethyl cellulose (CMC-Na)).

[0116] In some embodiments, a negative electrode sheet can be prepared by dispersing the aforementioned components for preparing a negative electrode sheet, such as a negative electrode active material, a conductive agent, a binder, and any other components, in a solvent (a non-limiting example of a solvent is deionized water) to form a negative electrode slurry; coating the negative electrode slurry on at least one surface of a negative electrode current collector, and performing processes such as drying and cold pressing to obtain a negative electrode sheet. The negative electrode slurry can be coated on a single surface of the negative electrode current collector or on both surfaces of the negative electrode current collector. The solid content of the negative electrode slurry can be 40 wt% to 60 wt%. The viscosity of the negative electrode slurry at room temperature can be adjusted to 2000 mPa·s to 10000 mPa·s.

[0117] The electrolyte conducts ions between the positive and negative electrodes. This application does not specifically limit the type of electrolyte, and the electrolyte can be selected based on the needs. For example, the electrolyte can be liquid, gel, or solid.

[0118] In some embodiments, the electrolyte is an electrolyte solution, which includes an electrolyte salt and a solvent.

[0119] In some embodiments, the electrolyte salt of the lithium ion secondary battery may include one or more of lithium hexafluorophosphate (LiPF6), lithium tetrafluoroborate (LiBF4), lithium perchlorate (LiClO4), lithium hexafluoroarsenate (LiAsF6), lithium bis(fluorosulfonyl)imide (LiFSI), lithium bis(trifluoromethanesulfonyl)imide (LiTFSI), lithium trifluoromethanesulfonate (LiTFS), lithium difluorooxalatoborate (LiDFOB), lithium bis(oxalatoborate) (LiBOB), lithium difluorophosphate (LiPO2F2), lithium difluorobis(oxalatophosphate) (LiDFOP), and lithium tetrafluorooxalatophosphate (LiTFOP).

[0120] In some embodiments, the solvent may include one or more of fluoroethylene carbonate (FEC), ethylene carbonate (EC), propylene carbonate (PC), ethyl methyl carbonate (EMC), diethyl carbonate (DEC), dimethyl carbonate (DMC), dipropyl carbonate (DPC), methyl propyl carbonate (MPC), ethyl propyl carbonate (EPC), butylene carbonate (BC), methyl formate (MF), methyl acetate (MA), ethyl acetate (EA), propyl acetate (PA), methyl propionate (MP), ethyl propionate (EP), propyl propionate (PP), methyl butyrate (MB), ethyl butyrate (EB), 1,4-butyrolactone (GBL), sulfolane (SF), dimethyl sulfone (MSM), ethyl methyl sulfone (EMS), and diethyl sulfone (ESE).

[0121] In some embodiments, the electrolyte may optionally include additives. For example, the additives may include negative electrode film-forming additives, positive electrode film-forming additives, and additives that can improve certain battery properties, such as additives that improve battery overcharge performance, and additives that improve battery high or low temperature performance.

[0122] In some embodiments, the additives in the electrolyte may include, but are not limited to, one or more of fluoroethylene carbonate (FEC), difluoroethylene carbonate (DFEC), trifluoromethylethylene carbonate (TFPC), and the like.

[0123] In some embodiments, the lithium-ion secondary battery further includes a separator. The present application has no particular limitation on the type of separator, and any known porous separator with good chemical and mechanical stability can be selected.

[0124] In some embodiments, the material of the separator can include one or more of glass fiber, non-woven fabric, polyethylene, polypropylene, and polyvinylidene fluoride. The separator can be a single-layer film or a multi-layer composite film, without particular limitation. When the separator is a multi-layer composite film, the materials of each layer can be the same or different, without particular limitation.

[0125] In some embodiments, the thickness of the isolation film is 6 μm to 40 μm, and may be 12 μm to 20 μm.

[0126] In some embodiments, the positive electrode sheet, the negative electrode sheet, and the separator can be formed into an electrode assembly through a winding process or a lamination process.

[0127] In some embodiments, the lithium-ion secondary battery may include an outer packaging that can be used to encapsulate the electrode assembly and the electrolyte.

[0128] In some embodiments, the outer packaging of the lithium-ion secondary battery can be a hard shell, such as a hard plastic shell, an aluminum shell, a steel shell, etc. The outer packaging of the secondary battery can also be a soft shell, such as a pouch-type soft shell. The material of the soft shell can be plastic. Further, non-limiting examples of plastic can include one or more of polypropylene, polybutylene terephthalate, and polybutylene succinate.

[0129] A lithium-ion secondary battery includes at least one battery cell. A lithium-ion secondary battery may include one or more battery cells.

[0130] In this application, unless otherwise specified, a "battery cell" refers to a basic unit that can achieve the mutual conversion of chemical energy and electrical energy. Further, generally speaking, it includes at least a positive electrode plate, a negative electrode plate, and an electrolyte. During the battery's charge and discharge process, active ions are embedded in and out of the positive and negative electrode plates. The electrolyte plays the role of conducting active ions between the positive and negative electrode plates.

[0131] The present application has no particular restrictions on the shape of the battery cell, which can be cylindrical, square or any other shape. For example, Figure 1 The battery cell 5 is a square structure as an example.

[0132] In some embodiments, reference Figure 2 , the outer packaging may include a shell 51 and a cover plate 53. The shell 51 may include a bottom plate and a side plate connected to the bottom plate, and the bottom plate and the side plate enclose a receiving cavity. The shell 51 has an opening connected to the receiving cavity, and the cover plate 53 can be covered on the opening to close the receiving cavity. The positive electrode sheet, the negative electrode sheet and the isolation membrane can form an electrode assembly 52 through a winding process or a lamination process. The electrode assembly 52 is encapsulated in the receiving cavity. The electrolyte is infiltrated in the electrode assembly 52. ​​The number of electrode assemblies 52 contained in the battery cell 5 can be one or more, and those skilled in the art can select according to specific actual needs.

[0133] In some embodiments, the battery cells 5 can be assembled into a battery module. The number of battery cells 5 contained in the battery module can be one or more. The specific number can be selected by those skilled in the art according to the application and capacity of the battery module.

[0134] In the battery module, the plurality of battery cells 5 can be arranged in sequence along the length of the battery module. Of course, they can also be arranged in any other manner. Furthermore, the plurality of battery cells 5 can be fixed by fasteners.

[0135] Optionally, the battery module may further include a housing having an accommodation space, and the plurality of battery cells 5 are accommodated in the accommodation space.

[0136] In some embodiments, the battery modules described above may also be assembled into a battery pack. The battery pack may contain one or more battery modules, and the specific number may be selected by those skilled in the art based on the application and capacity of the battery pack.

[0137] A battery pack may include a battery box and multiple battery modules disposed within the box. The battery box comprises an upper case and a lower case. The upper case can be placed over the lower case to form an enclosed space for accommodating the battery modules. The multiple battery modules can be arranged in any manner within the battery box.

[0138] In addition, the present application also provides an electrical device, which includes at least one of the lithium-ion secondary battery, battery module, or battery pack provided in the present application. The lithium-ion secondary battery, battery module, or battery pack can be used as a power source for the electrical device, and can also be used as an energy storage unit for the electrical device. The electrical device may include, but is not limited to, 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 and satellites, energy storage systems, etc.

[0139] As an electrical device, a lithium-ion secondary battery, a battery module or a battery pack can be selected according to its usage requirements.

[0140] Figure 3 The power consumption device 6 is used as an example. The power consumption device is a pure electric vehicle, a hybrid electric vehicle, or a plug-in hybrid electric vehicle. In order to meet the power consumption device's requirements for high power and high energy density of lithium-ion secondary batteries, a battery pack or battery module can be used.

[0141] Another example device may be a mobile phone, a tablet computer, a notebook computer, etc. Such a device is generally required to be lightweight and thin, and may use a secondary battery as a power source.

[0142] The following are some examples.

[0143] In order to make the technical problems, technical solutions and beneficial effects solved by this application clearer, the application will be further described in detail below with reference to the embodiments and drawings. Obviously, the described embodiments are only a part of the embodiments of this application, rather than all the embodiments. The following description of at least one exemplary embodiment is actually only illustrative and is in no way intended to limit the present application and its applications. Based on the embodiments in this application, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of this application.

[0144] If no specific techniques or conditions are specified in the examples, the experiments were carried out according to the techniques or conditions described in the literature in the field or according to the product instructions. All reagents or instruments used without specifying the manufacturer are commercially available conventional products.

[0145] Example 1:

[0146] (1) Preparation of positive electrode

[0147] (1.1) 0.19 g of hexamethyldisilazane (HMDS) and 0.95 g of SiO2 particles were stirred in anhydrous ethanol at 65°C for 2.5 h to modify the surface of the SiO2 particles and dried to obtain surface-modified SiO2. The mixture was then mixed with 9.5 g of styrene (ST), 9.5 g of methyl methacrylate (MMA), and 9.5 g of butyl acrylate (BA) to form a Pickering emulsion. The Pickering emulsion was reacted in the presence of 0.532 g of potassium persulfate (KPS) as an initiator at 80°C for 1 h to prepare a SiO2-modified polyacrylate adhesive.

[0148] The Dv50 particle size of the SiO2 particles is 1 μm; the weight average molecular weight of the polyacrylate in the SiO2-modified polyacrylate binder is 150,000 Daltons, and the mass fraction of SiO2 in the binder is 5%.

[0149] (1.2) The positive electrode active material LiFePO4, the conductive agent carbon black (Super P), the prepared SiO2-modified polyacrylate binder, and the dispersant SEBS were mixed uniformly in an appropriate amount of NMP at a mass ratio of 96.5:1:2:0.5 to obtain a positive electrode slurry. The positive electrode slurry was applied to both sides of the positive electrode current collector aluminum foil, and the positive electrode sheets were obtained through drying, cold pressing, slitting, and cutting. The solid content of the positive electrode slurry was 65%, and the single-sided coating density of the positive electrode slurry was 25 mg / cm. 2 .

[0150] (2) Preparation of negative electrode sheet

[0151] The negative electrode active material, artificial graphite, the thickener, sodium carboxymethyl cellulose, the binder, styrene-butadiene rubber, and the conductive agent, carbon black (Super P), were mixed in a mass ratio of 97:1:1:1, and deionized water was added. A negative electrode slurry was obtained using a vacuum mixer. The negative electrode slurry was evenly coated on both sides of the negative electrode current collector copper foil. The copper foil was dried at room temperature and then transferred to a 120°C oven for 1 hour. The negative electrode sheets were then cold pressed and slit. The solid content of the negative electrode slurry was 50%, and the single-sided coating density of the negative electrode slurry was 12 mg / cm. 2 .

[0152] (3) Isolation film

[0153] A 12 μm thick polypropylene film was selected as the isolation film.

[0154] (4) Electrolyte

[0155] Ethylene carbonate (EC) and ethyl methyl carbonate (EMC) are mixed in a mass ratio of 30:70 to obtain an organic solvent, and fully dried LiPF6 is dissolved in the above organic solvent to prepare an electrolyte with a LiPF6 concentration of 1 mol / L.

[0156] (5) Battery assembly

[0157] The positive electrode sheet, negative electrode sheet and separator are made into an electrode assembly through a winding process, and the electrode assembly is placed in the battery outer packaging. Then, after baking at 80°C to remove water, the electrolyte is injected and sealed. After standing, hot and cold pressing, formation, clamping, capacity division and other processes, a lithium-ion secondary battery is obtained.

[0158] Example 2:

[0159] This embodiment is substantially the same as embodiment 1, except that: in step (1.1), 0.19 g of hexamethyldisilazane (HMDS) and 0.95 g of TiO2 particles are stirred in anhydrous ethanol at 65°C for 2.5 h to modify the surface of the TiO2 particles, and then dried; the mixture is then mixed with an emulsion of 9.5 g of styrene (ST), 9.5 g of methyl methacrylate (MMA), and 9.5 g of butyl acrylate (BA) to form a Pickering emulsion; and the Pickering emulsion is reacted in the presence of 0.532 g of potassium persulfate (KPS) as an initiator at 80°C for 1 h to prepare a TiO2-modified polyacrylate binder.

[0160] The Dv50 particle size of the TiO2 particles is 1 μm; the weight average molecular weight of the polyacrylate in the TiO2-modified polyacrylate binder is 150,000 Daltons, and the mass fraction of TiO2 in the binder is 5%.

[0161] Example 3:

[0162] This example is basically the same as Example 1, except that: in step (1.1), the surface-modified SiO2 particles are mixed with 9.5 g of styrene (ST), 9.5 g of methyl methacrylate (MMA), and 9.5 g of butyl acrylate (BA) emulsion to form a Pickering emulsion; and the above Pickering emulsion is reacted at 80°C for 1 h in the presence of 0.3 g of potassium persulfate (KPS) as an initiator to prepare a SiO2-modified polyacrylate adhesive.

[0163] The weight average molecular weight of the polyacrylate in the SiO2 modified polyacrylate binder is 300,000 Daltons.

[0164] Example 4:

[0165] This example is basically the same as Example 1, except that: in step (1.1), the surface-modified SiO2 particles are mixed with 9.5 g of styrene (ST), 9.5 g of methyl methacrylate (MMA), and 9.5 g of butyl acrylate (BA) emulsion to form a Pickering emulsion; and the above Pickering emulsion is reacted at 80°C for 1 h in the presence of 0.18 g of potassium persulfate (KPS) as an initiator to prepare a SiO2-modified polyacrylate binder.

[0166] The weight average molecular weight of the polyacrylate in the SiO2 modified polyacrylate binder is 400,000 Daltons.

[0167] Example 5:

[0168] This embodiment is substantially the same as embodiment 1, except that: in step (1.1), 0.38 g of hexamethyldisilazane (HMDS) and 1.9 g of SiO2 particles are stirred in anhydrous ethanol at 65°C for 2.5 h to modify the surface of the SiO2 particles and then dried; the mixture is then mixed with 9.5 g of styrene (ST), 9.5 g of methyl methacrylate (MMA), and 9.5 g of butyl acrylate (BA) emulsion to form a Pickering emulsion; and the Pickering emulsion is reacted in the presence of 0.532 g of potassium persulfate (KPS) as an initiator at 80°C for 1 h to prepare a SiO2-modified polyacrylate binder.

[0169] The mass fraction of SiO2 in the SiO2 modified polyacrylate binder is 10%.

[0170] Example 6:

[0171] This embodiment is substantially the same as embodiment 1, except that: in step (1.1), 0.57 g of hexamethyldisilazane (HMDS) and 2.85 g of SiO2 particles are stirred in anhydrous ethanol at 65°C for 2.5 h to modify the surface of the SiO2 particles, and then dried; the mixture is then mixed with an emulsion of 9.5 g of styrene (ST), 9.5 g of methyl methacrylate (MMA), and 9.5 g of butyl acrylate (BA) to form a Pickering emulsion; and the Pickering emulsion is reacted in the presence of 0.532 g of potassium persulfate (KPS) as an initiator at 80°C for 1 h to prepare a SiO2-modified polyacrylate binder.

[0172] The mass fraction of SiO2 in the SiO2 modified polyacrylate binder is 15%.

[0173] Example 7:

[0174] This embodiment is substantially the same as embodiment 1, except that: in step (1.1), 0.76 g of hexamethyldisilazane (HMDS) and 3.8 g of SiO2 particles are stirred in anhydrous ethanol at 65°C for 2.5 h to modify the surface of the SiO2 particles, and then dried; the mixture is then mixed with an emulsion of 9.5 g of styrene (ST), 9.5 g of methyl methacrylate (MMA), and 9.5 g of butyl acrylate (BA) to form a Pickering emulsion; and the Pickering emulsion is reacted in the presence of 0.532 g of potassium persulfate (KPS) as an initiator at 80°C for 1 h to prepare a SiO2-modified polyacrylate binder.

[0175] The mass fraction of SiO2 in the SiO2 modified polyacrylate binder is 20%.

[0176] Example 8:

[0177] This embodiment is basically the same as embodiment 1, except that the Dv50 particle size of the SiO2 particles in step (1.1) is 5 μm.

[0178] Example 9:

[0179] This embodiment is basically the same as embodiment 1, except that in step (1.2), the mass ratio of the positive electrode active material LFP, the conductive agent carbon black (Super P), the SiO2 modified polyacrylate binder, and the dispersant SEBS is 96.5:1.2:1.8:0.5.

[0180] Example 10:

[0181] This embodiment is basically the same as embodiment 1, except that in step (1.2), the mass ratio of the positive electrode active material LFP, the conductive agent carbon black (Super P), the SiO2 modified polyacrylate binder, and the dispersant SEBS is 96.5:2:1:0.5.

[0182] Example 11:

[0183] This embodiment is basically the same as embodiment 1, except that in step (1.2), the mass ratio of the positive electrode active material LFP, the conductive agent carbon black (Super P), the SiO2 modified polyacrylate binder, and the dispersant SEBS is 96.5:1.2:2:0.3.

[0184] Example 12:

[0185] This embodiment is basically the same as embodiment 1, except that in step (1.2), the mass ratio of the positive electrode active material LFP, the conductive agent carbon black (Super P), the SiO2 modified polyacrylate binder, and the dispersant SEBS is 96.5:1.4:2:0.1.

[0186] Example 13:

[0187] This embodiment is basically the same as embodiment 1, except that the dispersant in step (1.2) is BYK-110 phosphate dispersant.

[0188] Example 14:

[0189] This embodiment is basically the same as embodiment 1, except that: in step (1.1), 2-ethylhexyl acrylate is used instead of butyl acrylate to prepare SiO2 modified polyacrylate binder; in step (1.2), lithium manganese iron phosphate LiMn is used. 0.6 Fe 0.4 PO4 replaces LiFePO4 as the positive electrode active material.

[0190] Comparative Example 1:

[0191] This comparative example is basically the same as Example 1, except that: the preparation method of the positive electrode sheet in step (1) is as follows: the positive electrode active material LiFePO4, the conductive agent carbon black (Super P), the polyacrylate binder and the dispersant SEBS are mixed uniformly in an appropriate amount of NMP in a mass ratio of 96.5:1:2:0.5 to obtain a positive electrode slurry, wherein the weight average molecular weight of the polyacrylate binder is 150,000; the above-mentioned positive electrode slurry is coated on both sides of the positive electrode current collector aluminum foil, and the positive electrode sheet is obtained by drying, cold pressing, slitting, cutting and other processes. The polyacrylate binder is prepared by mixing 9.5g of styrene (St), 9.5g of methyl methacrylate (MMA) and 9.5g of butyl acrylate (BA) to form an emulsion; and the above-mentioned emulsion is reacted at 80°C for 1h under the action of 0.532g of initiator potassium persulfate (KPS).

[0192] Comparative Example 2:

[0193] This comparative example is basically the same as Example 1, except that: step (1.1) is not provided; SiO2-modified polyacrylate binder is not used in the positive electrode slurry in step (1.2); the positive electrode active material LFP, conductive agent carbon black (Super P), SiO2, polyacrylate binder and dispersant SEBS are uniformly mixed in an appropriate amount of NMP in a mass ratio of 96.5:1:0.1:1.9:0.5 to obtain a positive electrode slurry.

[0194] The polyacrylate adhesive was prepared by the following method: 9.5 g of styrene (ST), 9.5 g of methyl methacrylate (MMA), and 9.5 g of butyl acrylate (BA) emulsion were mixed, and reacted at 80° C. for 1 h under the action of 0.532 g of initiator potassium persulfate (KPS) to prepare the polyacrylate adhesive.

[0195] Test method:

[0196] (1) Pole brittleness test

[0197] Take a 20mm x 100mm (vertical) sample of the prepared positive electrode sheet and sample it along the rolling direction of the sheet. Place the pre-folded experimental sheet on the test bench and roll it with a 2kg cylindrical roller. After each roll, observe whether the sheet is light-transmitting. When the sheet is light-transmitting, record the corresponding number of rolls. The number of rolls indicates the flexibility of the sheet. The greater the number of rolls, the better the flexibility.

[0198] (2) Electrode mechanical properties test

[0199] (2.1) Adhesion test

[0200] The prepared positive electrode sheet was cut into test specimens of 20mm×100mm size for later use; one side of the double-sided tape was adhered to the surface of the steel plate, and the other side was adhered to the positive electrode sheet to be tested, and compacted with a roller to make it completely fit with the sheet; one end of the current collector was bent in the opposite direction with a bending angle of 180°; a high-speed rail tensile testing machine was used for testing, one end of the steel plate was fixed to the lower fixture of the tensile testing machine, and the bent end of the current collector was fixed to the upper fixture, the angle of the current collector was adjusted to ensure that the upper and lower ends were in a vertical position, and the sample was stretched at a speed of 50mm / min until the active material layer was completely peeled off from the surface of the current collector, the displacement and force during the process were recorded, and the force when the force was balanced was used as the bonding force of the sheet.

[0201] (2.2) Cohesion test

[0202] The prepared positive electrode sheet was cut into test specimens of 20mm×100mm size for later use; one side of the double-sided tape was pasted on the surface of the steel plate, and the other side was adhered to the positive electrode sheet to be tested, and compacted with a roller to make it completely fit with the sheet; a special tape for cohesion testing was pasted on the other side of the sheet and compacted with a roller; one end of the special tape for cohesion testing was bent in reverse with a bending angle of 180°; a high-speed rail tensile testing machine was used for testing, one end of the steel plate was fixed to the lower fixture of the tensile testing machine, and the bent end of the current collector was fixed to the upper fixture, the angle of the current collector was adjusted to ensure that the upper and lower ends were in a vertical position, and then the sample was stretched at a speed of 50mm / min until the active material layer was completely peeled off from the surface of the current collector, the displacement and force during the process were recorded, and the force when the force was balanced was taken as the cohesion of the sheet.

[0203] (3) Battery DCR test

[0204] Let the battery cell stand for 10 minutes, charge to 3.65V at a constant current of 1 / 3C, then charge to 0.05C at a constant voltage and let it stand for 30 minutes; then discharge to 2.5V at 1C to obtain the capacity C1; let it stand for 30 minutes, then discharge to 0.5C1 at 1 / 3C, and measure the battery cell voltage V0 after standing for 30 minutes; then discharge at 3C for 30S and measure the battery cell V1 to calculate the DCR, DCR=(V0-V1) / 3C.

[0205] (4) Battery rate performance test

[0206] The battery cell was left to stand for 10 minutes, charged to 3.65V at a constant current of 1 / 3C, then reduced to 0.05C at a constant voltage, left to stand for 30 minutes, and discharged to 2.5V at 1 / 3C to obtain capacity C1; then charged to 3.65V at a constant current of 1 / 3C, reduced to 0.05C at a constant voltage, left to stand for 30 minutes, and discharged to 2.5V at 1C to obtain capacity C2; then charged to 3.65V at a constant current of 1 / 3C, reduced to 0.05C at a constant voltage, left to stand for 30 minutes, and discharged to 2.5V at 2C to obtain capacity C3. 1C capacity retention rate = C2 / C1×100%; 2C capacity retention rate = C3 / C1×100%.

[0207] (5) Test on the mass ratio of inorganic materials in inorganic material modified polyacrylate binder

[0208] X-ray photoelectron spectroscopy XPS and energy dispersive spectrometer EDS were used to detect the characteristic elements of inorganic fillers in the binder and quantitatively calculate the mass proportion of inorganic materials.

[0209] (6) Weight average molecular weight test

[0210] The weight average molecular weight of the polymer was measured using gel permeation chromatography.

[0211] (7) Dv50 particle size test of inorganic materials

[0212] The Dv50 particle size of inorganic materials was measured using a laser particle size analyzer.

[0213] The battery parameters for the above examples and comparative examples are shown in Table 1, and the performance data are shown in Table 2. In the table, the binder amount refers to the mass fraction of the binder in the positive electrode active material layer; the inorganic particle content refers to the mass fraction of the inorganic particles in the inorganic material-modified polyacrylate binder. The weight-average molecular weight, inorganic particle content, and inorganic particle Dv50 values ​​in Table 1 are rounded to the nearest integer.

[0214] Table 1

[0215]

[0216] Table 2

[0217]

[0218] As can be seen from Tables 1 and 2, the lithium-ion secondary batteries of the embodiments of the present application have low internal resistance and good dynamic performance. The lithium-ion secondary batteries of Comparative Examples 1 and 2, which do not use inorganic material-modified polyacrylate binders in their positive electrode slurries, have high internal resistance and poor dynamic performance.

[0219] The above description of the various embodiments tends to emphasize the differences between the various embodiments. The same or similar aspects can be referenced with each other and will not be repeated herein for the sake of brevity.

[0220] It should be noted that the present application is not limited to the above-mentioned embodiments. The above-mentioned embodiments are merely examples, and any embodiments having substantially the same structure and effect as the technical concept within the scope of the present application are all included in the technical scope of the present application. In addition, without departing from the scope of the present application, any other embodiments that can be conceived by those skilled in the art and that combine some of the constituent elements in the embodiments are also included in the scope of the present application.

Claims

1. A lithium-ion secondary battery, characterized in that: The positive electrode comprises a positive electrode plate, wherein the positive electrode plate comprises a positive electrode active material layer, and the positive electrode active material layer comprises a lithium-containing phosphate and an inorganic material-modified polyacrylate binder; The inorganic material modified polyacrylate binder comprises a polyacrylate polymer and inorganic particles, at least a portion of the polyacrylate polymer is grafted onto the surface of the inorganic particles; the polyacrylate polymer comprises structural units derived from acrylic acid ester monomers; The weight average molecular weight of the polyacrylate polymer is 150,000 to 400,000 Daltons; the positive electrode active material layer further includes a dispersant, which includes one or more of a phosphate dispersant or a styrene-ethylene / butylene-styrene block copolymer dispersant; based on the total mass of the positive electrode active material layer as 100%, the mass fraction of the dispersant is 0.1% to 0.5%; The polyacrylate polymer further includes a structural unit derived from a first monomer, wherein the first monomer includes styrene.

2. The lithium-ion secondary battery according to claim 1, wherein The acrylic acid ester monomer includes one or more of methyl methacrylate, butyl acrylate or isooctyl acrylate.

3. The lithium-ion secondary battery according to claim 1, wherein The mass proportion of the structural unit derived from the acrylic acid ester monomer in the acrylic acid ester polymer is 60% to 80%.

4. The lithium-ion secondary battery according to any one of claims 1 to 3, characterized in that The structural unit derived from the first monomer accounts for 20% to 40% by mass in the polyacrylate polymer.

5. The lithium ion secondary battery according to any one of claims 1 to 3, characterized in that The weight average molecular weight of the polyacrylate polymer is 300,000 Daltons to 400,000 Daltons.

6. The lithium-ion secondary battery according to any one of claims 1 to 3, characterized in that The inorganic particles include one or more of titanium dioxide, silicon dioxide, calcium stearate or aluminum oxide.

7. The lithium-ion secondary battery according to any one of claims 1 to 3, characterized in that The mass fraction of the inorganic particles in the inorganic material modified polyacrylate binder is 5% to 20%.

8. The lithium-ion secondary battery according to any one of claims 1 to 3, characterized in that The mass fraction of the inorganic particles in the inorganic material modified polyacrylate binder is 10% to 15%.

9. The lithium-ion secondary battery according to any one of claims 1 to 3, characterized in that Based on the total mass of the positive electrode active material layer being 100%, the mass fraction of the inorganic material modified polyacrylate binder is 1% to 2%.

10. The lithium ion secondary battery according to any one of claims 1 to 3, characterized in that Based on the total mass of the positive electrode active material layer being 100%, the mass fraction of the dispersant is 0.3% to 0.5%.

11. The lithium ion secondary battery according to any one of claims 1 to 3, characterized in that Based on the total mass of the positive electrode active material layer being 100%, the mass fraction of the lithium-containing phosphate is 95% to 99%.

12. The lithium-ion secondary battery according to any one of claims 1 to 3, characterized in that The lithium-containing phosphate includes one or more of lithium iron phosphate, lithium manganese phosphate or lithium manganese iron phosphate.

13. A method for preparing a lithium-ion secondary battery, characterized in that: The following steps are involved: A lithium-containing phosphate, an inorganic material-modified polyacrylate binder, a dispersant, and a solvent are mixed to obtain a positive electrode slurry; the inorganic material-modified polyacrylate binder comprises a polyacrylate polymer and inorganic particles, at least a portion of the polyacrylate polymer is grafted onto the surface of the inorganic particles; the polyacrylate polymer comprises structural units derived from acrylic acid ester monomers; The positive electrode slurry is placed on a positive electrode current collector and dried to obtain a positive electrode plate; the positive electrode plate comprises a positive electrode current collector and a positive electrode active material layer placed on the positive electrode current collector; and The positive electrode sheet, the separator and the negative electrode sheet are stacked so that the separator is disposed between the positive electrode sheet and the negative electrode sheet to obtain an electrode assembly, and the electrode assembly is made into a secondary battery; The weight average molecular weight of the polyacrylate polymer is 150,000 to 400,000 Daltons; the positive electrode active material layer includes a dispersant, and the dispersant includes one or more of a phosphate dispersant or a styrene-ethylene / butylene-styrene block copolymer dispersant; based on the total mass of the positive electrode active material layer as 100%, the mass fraction of the dispersant is 0.1% to 0.5%; The polyacrylate polymer further includes a structural unit derived from a first monomer, wherein the first monomer includes styrene.

14. The method for preparing a lithium-ion secondary battery according to claim 13, wherein: The preparation method of the inorganic material modified polyacrylate binder comprises the following steps: Silane coupling agent is used to modify the surface of inorganic particles; The surface-modified inorganic particles are mixed with an acrylic ester monomer, a first monomer, and an initiator, and the inorganic material-modified polyacrylate binder is obtained after reaction.

15. The method for preparing a lithium-ion secondary battery according to claim 14, wherein: The silane coupling agent includes one or more of hexamethyldisilazane, γ-aminopropyltriethoxysilane or γ-glycidoxypropyltrimethoxysilane.

16. The method for preparing a lithium-ion secondary battery according to claim 14, wherein: The initiator is a free radical polymerization initiator, and the initiator includes one or more of potassium persulfate, azobisisobutyronitrile or benzoyl peroxide.

17. The method for preparing a lithium-ion secondary battery according to claim 14, wherein: The acrylic acid ester monomer includes one or more of methyl methacrylate, butyl acrylate or isooctyl acrylate.

18. The method for preparing a lithium-ion secondary battery according to any one of claims 13 to 17, wherein: The inorganic particles include one or more of titanium dioxide, silicon dioxide, calcium stearate or aluminum oxide.

19. The method for preparing a lithium-ion secondary battery according to any one of claims 13 to 17, wherein: The Dv50 particle size of the inorganic particles is 1 μm to 5 μm.

20. An electrical device, characterized in that: The invention comprises one or more of the lithium ion secondary battery according to any one of claims 1 to 12 or the lithium ion secondary battery prepared by the method for preparing the lithium ion secondary battery according to any one of claims 13 to 19.

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