Battery cell, battery device and electric device

Abstract

The invention relates to the technical field of batteries, in particular to a battery monomer, a battery device and a power utilization device. The battery monomer comprises a positive pole piece, a negative pole piece and a separator, the positive pole piece comprises a positive current collector and a positive film layer arranged on at least one surface of the positive current collector; the positive electrode film layer comprises a positive electrode active material, and the positive electrode active material comprises an inner core layer and a shell layer arranged on the surface of the inner core layer; the inner core layer comprises first lithium manganese iron phosphate, and the shell layer comprises second lithium manganese iron phosphate; the average particle size of primary particles of the first lithium manganese iron phosphate is smaller than the average particle size of primary particles of the second lithium manganese iron phosphate. In the positive electrode active material provided by the invention, the dissolution of transition metal is less, and the cycle performance of the further formed battery monomer is better.

Description

TECHNICAL FIELD

[0001] The present application relates to the field of batteries, in particular to a battery monomer, a battery device and a power utilization device. BACKGROUND

[0002] Battery monomers are widely used in many fields, such as energy storage power systems of hydropower, thermal power, wind power and solar power plants, and electric tools, electric bicycles, electric motorcycles, electric vehicles, military equipment, aerospace, etc.

[0003] Among them, lithium iron phosphate batteries also attract widespread attention, but lithium iron phosphate can cause poor cycle performance of battery monomers due to transition metal leaching.

[0004] Therefore, it is essential to develop a battery monomer that can overcome the above-mentioned defects. SUMMARY

[0005] In view of the above problems, the present application provides a battery monomer, a battery device and a power utilization device, wherein the transition metal leaching of the positive electrode active material is less, and the further formed battery monomer has good cycle performance.

[0006] In a first aspect, the present application provides a battery monomer, which comprises a positive electrode sheet, a negative electrode sheet and a separator;

[0007] The positive electrode sheet comprises a positive electrode current collector and a positive electrode film layer arranged on at least one surface of the positive electrode current collector;

[0008] The positive electrode film layer comprises a positive electrode active material, and the positive electrode active material comprises an inner core layer and an outer shell layer arranged on the surface of the inner core layer;

[0009] The inner core layer comprises first lithium manganese iron phosphate, and the outer shell layer comprises second lithium manganese iron phosphate;

[0010] The average particle size of the primary particles of the first lithium manganese iron phosphate is smaller than the average particle size of the primary particles of the second lithium manganese iron phosphate.

[0011] In the technical solution of the present application, the first lithium manganese iron phosphate with small particles is used as the inner core layer, and the second lithium manganese iron phosphate with large particles is used as the outer shell layer, which can reduce the leaching of transition metals in the first lithium manganese iron phosphate in the inner core layer under the protection of the outer shell layer. Moreover, the outer shell layer uses the second lithium manganese iron phosphate with large particles, which has relatively less contact with the external environment and a lower probability of transition metal leaching, compared with the use of small particles of lithium manganese iron phosphate. Therefore, the battery monomer described in the present application has good cycle performance.

[0012] In some embodiments, the average particle size of the secondary particles of the positive electrode active material is ≤100 μm.

[0013] In the technical solution of this application, the average particle size of the secondary particles of the positive electrode active material is within the specified range. When forming the positive electrode sheet or battery cell, it is not easy to break, and the positive electrode active material can play its full role, which can reduce the adverse effects on the performance of the battery cell.

[0014] In some embodiments, the specific surface area of ​​the positive electrode active material is 5-50 cm². 2 / g.

[0015] In the technical solution of this application, the specific surface area of ​​the positive electrode active material is within the specified range. On the one hand, the outer shell layer can effectively protect the core layer; on the other hand, the contact area between the large particles of lithium manganese iron phosphate in the outer shell layer and the external environment such as electrolyte is small. Therefore, less transition metal is dissolved in the positive electrode active material, which reduces the occurrence of side reactions and gas production and improves the cycle performance of the battery cell.

[0016] In some embodiments, the porosity of the positive electrode active material is ≤10%.

[0017] In the technical solution of this application, the porosity of the positive electrode active material is within the above-mentioned range, which can not only satisfy the free insertion and extraction of active ions in the core layer and the outer shell layer, but also reduce the dissolution of transition metals in the positive electrode active material, thereby improving the cycle performance and storage performance of the battery cell.

[0018] In some embodiments, the average particle size of the first primary particles of lithium manganese iron phosphate is 0.05-5 μm.

[0019] In the technical solution of this application, the average particle size of the primary particles of the first lithium manganese iron phosphate is within the above-mentioned range, which allows them to be tightly packed without breaking, thereby improving the energy density of the battery cell and thus improving the cycle performance and storage performance of the battery cell.

[0020] In some embodiments, the average particle size of the primary particles of the second lithium manganese iron phosphate is 2-50 μm.

[0021] In the technical solution of this application, the average particle size of the primary particles of the second lithium manganese iron phosphate is within the above range, which can form a positive electrode active material with a small specific surface area and can also provide better protection for the core layer. Therefore, it reduces the dissolution of transition metals, side reactions and gas generation, thereby improving the cycle performance and storage performance of the battery cell.

[0022] In some embodiments, the average particle size ratio of the primary particles of the second lithium manganese iron phosphate and the first lithium manganese iron phosphate is (2-10):1.

[0023] In the technical solution of this application, the average particle size ratio of the primary particles of the second lithium manganese iron phosphate and the first lithium manganese iron phosphate is within the above range, which can effectively reduce the dissolution of transition metals in the positive electrode active material and improve the cycle performance and storage performance of the battery cell.

[0024] In some embodiments, the mass ratio of the second lithium manganese iron phosphate to the first lithium manganese iron phosphate is (0.1-10):1.

[0025] In the technical solution of this application, the mass ratio of the second lithium manganese iron phosphate and the first lithium manganese iron phosphate is within the above range, which can effectively control the radius of the core layer and the thickness of the outer shell layer, minimize the dissolution of transition metals, and improve the cycle performance and storage performance of the battery cell.

[0026] In some implementations, the ratio of the radius of the core layer to the thickness of the outer shell layer is (1-10):1.

[0027] In the technical solution of this application, the ratio of the radius of the core layer to the thickness of the outer shell layer is within the above-mentioned range. The outer shell layer is thinner than the core layer, which is more conducive to the dense stacking of small lithium manganese iron phosphate particles in the core layer. It is also conducive to the control of the specific surface area of ​​the overall positive electrode active material by the outer shell layer, thereby reducing the dissolution of transition metals, side reactions and gas generation in the positive electrode active material, and improving the cycle performance and storage performance of the battery cell.

[0028] In a second aspect, this application provides a battery device comprising a plurality of battery cells according to the first aspect.

[0029] Thirdly, this application provides an electrical device, which includes the battery cell described in the first aspect, or the battery device described in the second aspect.

[0030] The above description is only an overview of the technical solution of this application. In order to better understand the technical means of this application and to implement it in accordance with the contents of the specification, and to make the above and other objects, features and advantages of this application more obvious and understandable, the following are specific embodiments of this application. Attached Figure Description

[0031] Various other advantages and benefits will become apparent to those skilled in the art upon reading the following detailed description of preferred embodiments. The accompanying drawings are for illustrative purposes only and are not intended to limit the scope of this application. Furthermore, the same reference numerals denote the same parts throughout the drawings. In the drawings:

[0032] Figure 1 This is a schematic diagram of the structure of the positive electrode active material in some embodiments of this application;

[0033] The reference numerals in the detailed embodiments are as follows:

[0034] 1-Lithium manganese iron phosphate (MFP); 2-Lithium manganese iron phosphate (MFP). Detailed Implementation

[0035] The embodiments of the technical solution of this application will now be described in detail with reference to the accompanying drawings. These embodiments are only used to more clearly illustrate the technical solution of this application and are therefore merely examples, and should not be used to limit the scope of protection of this application.

[0036] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this application pertains; the terminology used herein is for the purpose of describing particular embodiments only and is not intended to limit the application; the terms “comprising” and “having”, and any variations thereof, in the specification, claims, and foregoing description of the drawings are intended to cover non-exclusive inclusion.

[0037] In the description of the embodiments of this application, technical terms such as "first" and "second" are used only to distinguish different objects and should not be construed as indicating or implying relative importance or implicitly specifying the number, specific order, or primary and secondary relationship of the indicated technical features. In the description of the embodiments of this application, "multiple" means two or more, unless otherwise explicitly defined.

[0038] In this document, the term "embodiment" means that a particular feature, structure, or characteristic described in connection with an embodiment may be included in at least one embodiment of this application. The appearance of this phrase in various places throughout the specification does not necessarily refer to the same embodiment, nor is it a separate or alternative embodiment mutually exclusive with other embodiments. It will be explicitly and implicitly understood by those skilled in the art that the embodiments described herein can be combined with other embodiments.

[0039] The "range" disclosed in this application is defined by a lower limit and an upper limit. A given range is defined by selecting a lower limit and an upper limit, which define the boundaries of a particular range. Ranges defined in this way can include or exclude endpoints and can be arbitrarily combined; that is, any lower limit can be combined with any upper limit to form a range. For example, if ranges of 60–120 and 80–110 are listed for a specific parameter, it is also expected that ranges of 60–110 and 80–120 are also included. Furthermore, if minimum range values ​​of 1 and 2 are listed, and if maximum range values ​​of 3, 4, and 5 are listed, then the following ranges are all expected: 1–3, 1–4, 1–5, 2–3, 2–4, and 2–5. In this application, unless otherwise stated, the numerical range "ab" represents a shortened representation of any combination of real numbers between a and b, where a and b are real numbers. For example, the numerical range "2-10" indicates that all real numbers between "2-10" have been listed in this article; "2-10" is simply a shortened representation of these numerical combinations. Furthermore, when a parameter is stated as an integer ≥2, it is equivalent to disclosing that the parameter is, for example, an integer such as 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, etc.

[0040] In the description of the embodiments in this application, the term "and / or" is merely a description of the relationship between related objects, indicating that three relationships can exist. For example, A and / or B can represent three cases: A exists, A and B exist simultaneously, and B exists. In addition, the character " / " in this document generally indicates that the related objects before and after it have an "or" relationship.

[0041] Lithium iron phosphate batteries are a very important type of battery cell, but lithium iron phosphate batteries suffer from poor cycle performance due to the dissolution of transition metals.

[0042] This application uses small-particle lithium manganese iron phosphate as the core layer and large-particle lithium manganese iron phosphate as the outer shell layer, which can reduce the dissolution of transition metals in lithium manganese iron phosphate and improve the cycle performance of the battery cell. This application studies and develops a battery cell, a battery device, and an electrical device.

[0043] [Battery cell]

[0044] In this embodiment of the application, the battery cell can be a secondary battery, which refers to a battery cell that can be recharged to activate the active materials and continue to be used after the battery cell has been discharged.

[0045] [Electrode Assembly]

[0046] A single battery cell typically includes an electrode assembly. The electrode assembly includes a positive electrode, a negative electrode, and a separator, with the separator positioned between the positive and negative electrodes. During the charging and discharging process of a single battery cell, active ions (such as lithium ions) repeatedly insert and extract between the positive and negative electrodes. The separator, positioned between the positive and negative electrodes, prevents short circuits while allowing active ions to pass through.

[0047] [Positive electrode plate]

[0048] In some embodiments, the positive electrode may be a positive electrode sheet, which includes a positive current collector and a positive electrode film layer disposed on at least one surface (e.g., one or two) of the positive current collector;

[0049] The positive electrode film layer includes a positive electrode active material, the structural schematic of which is shown below. Figure 1 As shown, the positive electrode active material includes a core layer and a shell layer disposed on the surface of the core layer;

[0050] The core layer includes a first lithium manganese iron phosphate 1, and the outer shell layer includes a second lithium manganese iron phosphate 2;

[0051] The average particle size of the primary particles of the first lithium manganese iron phosphate is less than the average particle size of the primary particles of the second lithium manganese iron phosphate.

[0052] In this application, lithium manganese iron phosphate, hereinafter referred to as LMFP.

[0053] In the technical solution of this application embodiment, the positive electrode active material uses small-particle first lithium manganese iron phosphate as the core layer and large-particle second lithium manganese iron phosphate as the outer shell layer. Under the protection of the outer shell layer, the dissolution of transition metals in the first lithium manganese iron phosphate in the core layer can be reduced. Moreover, the outer shell layer uses large-particle second lithium manganese iron phosphate, which has relatively less contact with the external environment compared to using small-particle lithium manganese iron phosphate, and the probability of transition metal dissolution is lower. Therefore, the battery cell described in this application has better cycle performance.

[0054] In some embodiments, the average particle size of the secondary particles of the positive electrode active material is ≤100μm, such as 90μm, 80μm, 70μm, 60μm, 50μm, 40μm, 30μm, 20μm, 10μm, etc.

[0055] In this application, the average particle size refers to the sum of the particle sizes of all particles divided by the total number of particles. The average particle size is measured using a laser particle size analyzer; the laser particle size analyzer measures particle size distribution based on the physical phenomenon that particles can scatter laser light. When a beam of light encounters a particle, some of the light will be scattered. The propagation direction of the scattered light forms an angle with the propagation direction of the main beam, i.e., the scattering angle, and its magnitude is inversely proportional to the particle size. The larger the particle, the smaller the scattering angle of the scattered light; the smaller the particle, the larger the scattering angle of the scattered light.

[0056] In this application, when testing the average particle size of each material in a battery cell, the positive electrode sheet can be peeled off, and the average particle size of the positive electrode active material can be tested using a laser particle size analyzer; for the average particle size of the first LMFP and the second LMFP, the positive electrode active material can be crushed from secondary particles into primary particles before measurement; before the above tests, a preliminary judgment can be made by observing the local condition using a scanning electron microscope.

[0057] In this application, the average particle size of the positive electrode active material refers to the particle size of secondary particles, while the average particle size of the first LMFP and the second LMFP mentioned below refers to the particle size of primary particles. The particle size of primary particles refers to the grain size; the particle size of secondary particles refers to the particle size of the aggregated particles. We usually refer to the particle size of a single fine grain as the primary particle size, also called the original particle size. In some cases, even with amorphous particles, when there are similar original and aggregated particles, the concepts of primary and secondary particle sizes are introduced. When the crystals are very small, due to the large surface energy of the grains, the small grains are easily bonded together by weak interaction forces, leading to agglomeration, that is, many small grains clump together to form larger secondary particles. All of these involve the issue of agglomeration. The particles before agglomeration are primary particles, and the particles after agglomeration are secondary particles.

[0058] In this application, the average particle size of the secondary particles of the positive electrode active material is mainly achieved by adjusting parameters such as sintering temperature and sintering time in the granulation and sintering processes. The granulation process mainly adjusts the radius of the core layer, while the sintering process mainly controls the growth or cessation of the secondary particles and regulates the thickness of the outer shell layer. By using the above methods, the average particle size of the positive electrode active material is adjusted to the required level as a whole.

[0059] In the technical solution of this application embodiment, the average particle size of the secondary particles of the positive electrode active material is within the specified range. When forming the positive electrode sheet or battery cell, it is not easy to break, and the positive electrode active material can play its full role, which can reduce the adverse effects on the performance of the battery cell.

[0060] In some embodiments, the specific surface area of ​​the positive electrode active material is 5-50 cm². 2 / g, for example, 10cm 2 / g, 15cm 2 / g、20cm 2 / g、25cm 2 / g, 30cm 2 / g, 35cm 2 / g、40cm 2 / g、45cm 2 / g etc.

[0061] In this application, the specific surface area refers to the total area per unit mass of material, and the testing method is the gas adsorption method; specifically, the BET method.

[0062] (1) The sample to be tested is degassed at ultra-low temperature to remove the gas in the pores of the sample;

[0063] (2) At liquid nitrogen temperature, a certain amount of adsorbate gas (usually nitrogen) is introduced into the sample to be tested, so that the gas molecules are adsorbed on the surface of the sample to be tested.

[0064] (3) The amount of adsorption is obtained by measuring the pressure or volume at adsorption equilibrium;

[0065] (4) The adsorption data were fitted using the BET equation to calculate the adsorption amount and specific surface area of ​​the monolayer.

[0066] In this application, the specific surface area of ​​the positive electrode active material is related to the average particle size of the positive electrode active material. By adjusting the average particle size of the positive electrode active material, a positive electrode active material that meets the specific surface area requirements can be obtained.

[0067] In the technical solution of this application embodiment, the specific surface area of ​​the positive electrode active material is within the specified range. On the one hand, the outer shell layer can effectively protect the core layer; on the other hand, the contact area between the large particles of lithium manganese iron phosphate in the outer shell layer and the external environment such as electrolyte is small. Therefore, less transition metal is dissolved in the positive electrode active material, which reduces the occurrence of side reactions and gas production, and improves the cycle performance of the battery cell.

[0068] In some embodiments, the porosity of the positive electrode active material is ≤10%, for example, 2%, 4%, 6%, 8%, etc.

[0069] In this application, the porosity refers to the ratio of the volume occupied by pores in the positive electrode active material to the total volume of the positive electrode active material; the testing method is the weighing method, specifically determining the pore volume of the positive electrode active material based on the weight change before and after being wetted by a suitable liquid (such as water). The skeletal volume of the positive electrode active material can be obtained from the density and dry weight of the raw materials, and the porosity can be calculated using the following formula:

[0070] ρ = v1 / v1 + v2;

[0071] In the formula, v1 is the pore volume of the material, and v2 is the skeleton volume of the material.

[0072] In this application, the porosity is mainly adjusted by adjusting the tight packing degree of the first lithium manganese iron phosphate in the core layer during the granulation process, and by adjusting the density of the outer shell layer during the sintering process.

[0073] In the technical solution of this application embodiment, the porosity of the positive electrode active material is within the above-mentioned range, which can not only satisfy the free insertion and extraction of active ions in the core layer and the outer shell layer, but also reduce the dissolution of transition metals in the positive electrode active material, thereby improving the cycle performance and storage performance of the battery cell.

[0074] In some embodiments, the average particle size of the primary particles of the first lithium manganese iron phosphate is 0.05-5 μm, such as 0.1 μm, 0.5 μm, 1 μm, 2 μm, 3 μm, 4 μm, etc.

[0075] In the technical solution of this application embodiment, the average particle size of the first lithium manganese iron phosphate primary particles is within the above range, which allows them to be tightly packed without breaking, thereby improving the energy density of the battery cell and thus improving the cycle performance and storage performance of the battery cell.

[0076] In some embodiments, the average particle size of the primary particles of the second lithium manganese iron phosphate is 2-50 μm, such as 5 μm, 10 μm, 15 μm, 20 μm, 25 μm, 30 μm, 35 μm, 40 μm, 45 μm, etc.

[0077] In the technical solution of this application embodiment, the average particle size of the primary particles of the second lithium manganese iron phosphate is within the above range, which can form a positive electrode active material with a small specific surface area and can also provide better protection for the core layer. Therefore, it reduces the dissolution of transition metals, side reactions and gas generation, thereby improving the cycle performance and storage performance of the battery cell.

[0078] In some embodiments, the average particle size ratio of the primary particles of the second lithium manganese iron phosphate and the first lithium manganese iron phosphate is (2-10):1, wherein 2-10 can be 3, 4, 5, 6, 7, 8, 9, etc.

[0079] In the technical solution of this application embodiment, the average particle size ratio of the primary particles of the second lithium manganese iron phosphate and the first lithium manganese iron phosphate is within the above range, which can effectively reduce the dissolution of transition metals in the positive electrode active material and improve the cycle performance and storage performance of the battery cell.

[0080] In some embodiments, the mass ratio of the second lithium manganese iron phosphate to the first lithium manganese iron phosphate is (0.1-10):1, wherein 0.1-10 can be 1, 2, 3, 4, 5, 6, 7, 8, 9, etc.

[0081] In the technical solution of this application embodiment, the mass ratio of the second lithium manganese iron phosphate and the first lithium manganese iron phosphate is within the above range, which can effectively control the radius of the core layer and the thickness of the outer shell layer, minimize the dissolution of transition metals, and improve the cycle performance and storage performance of the battery cell.

[0082] In some embodiments, the ratio of the radius of the kernel layer to the thickness of the outer shell layer is (1-10):1, where 1-10 can be 2, 3, 4, 5, 6, 7, 8, 9, etc.

[0083] In this application, the radius refers to the radius of the smallest circumscribed sphere. For a three-dimensional shape, the radius of the smallest sphere that can completely enclose the shape can be found, which is called the radius of the smallest circumscribed sphere. That is, when the kernel layer is a regular sphere, the radius is the radius of the kernel layer sphere; when the kernel layer is an irregular shape, the radius is the radius of the smallest circumscribed sphere corresponding to the irregular shape.

[0084] In the technical solution of this application embodiment, the ratio between the radius of the core layer and the thickness of the outer shell layer is within the above range. The outer shell layer is thinner than the core layer, which is more conducive to the dense stacking of small particles of lithium manganese iron phosphate in the core layer. It is also conducive to the control of the specific surface area of ​​the overall positive electrode active material by the outer shell layer, thereby reducing the dissolution of transition metals, side reactions and gas generation in the positive electrode active material, and improving the cycle performance and storage performance of the battery cell.

[0085] In some embodiments, the chemical formula of the LMFP is LiMn. x Fe 1-x PO4, where x represents the molar ratio of Mn to Fe, 0 ≤ x ≤ 1, and optionally, 0.1 ≤ x ≤ 0.4. The first and second lithium manganese iron phosphates of this application can each independently use any known material.

[0086] In some embodiments, the core layer further includes an adhesive, such as polytetrafluoroethylene (PTFE), polyvinylidene fluoride (PVDF), etc. The adhesive can be any known material.

[0087] Positive electrode active material production method

[0088] In some embodiments, the preparation method of the positive electrode active material described in this application includes the following steps:

[0089] (1) The LMFP is crushed and screened to obtain powder that meets the particle size requirements, namely the first LMFP powder and the second LMFP powder;

[0090] (2) The first LMFP powder obtained in step (1), optionally including a binder (e.g., polytetrafluoroethylene, polyvinylidene fluoride, etc.) and / or other arbitrary additives, is mixed, granulated, and sintered to form a core layer; the second LMFP powder obtained in step (1) is sprayed during the sintering process, cooled, and secondary particles are prepared to form a shell layer; the positive electrode active material is obtained.

[0091] In some embodiments, the mixing and granulation can be carried out using a spray dryer or a pellet mill.

[0092] In some embodiments, the mixing and granulation pressure is 100-1000 bar, such as 200 bar, 400 bar, 600 bar, 800 bar, etc.

[0093] In some embodiments, the mixing and granulation speed is 10-100 rpm, such as 20 rpm, 40 rpm, 60 rpm, 80 rpm, etc.

[0094] In some embodiments, the mixing and granulation time is ≤10 min, such as 1 min, 4 min, 6 min, 8 min, etc.

[0095] In some embodiments, the relative humidity of the mixed granulation is 5%-50%, such as 10%, 15%, 20%, 25%, 30%, 35%, 40%, 45%, etc.

[0096] In some embodiments, the sintering temperature is ≥2000℃, such as 2100℃, 2200℃, 2300℃, etc.

[0097] In some embodiments, the sintering time is 4-24h, such as 6h, 8h, 10h, 12h, 14h, 16h, 18h, 20h, 22h, etc.

[0098] In some embodiments, the preparation method of the positive electrode active material described in this application includes the following steps:

[0099] (1) The LMFP is crushed and screened to obtain powder that meets the particle size requirements, namely the first LMFP powder and the second LMFP powder;

[0100] (2) The first LMFP powder obtained in step (1), optionally including a binder (e.g., polytetrafluoroethylene, polyvinylidene fluoride, etc.) and other arbitrary additives are mixed and granulated under a pressure of 100-1000 bar, a rotation speed of 10-100 rpm and a relative humidity of 5%-50%, and sintered at ≥2000℃ for 4-24 h to form a core layer; and the second LMFP powder obtained in step (1) is sprayed during the sintering process to form a shell layer, cooled, and secondary particles are prepared to obtain the positive electrode active material.

[0101] As an example, the positive current collector has two surfaces opposite each other in its own thickness direction, and the positive electrode film layer is disposed on either or both of the two opposite surfaces of the positive current collector.

[0102] As an example, the positive electrode current collector can be a metal foil, a conductive polymer material, a carbon material, or a composite current collector. For example, as a metal foil, pure metals, alloys, or surface-treated metals can be used, including but not limited to stainless steel, copper, aluminum, nickel, titanium, or silver. The composite current collector may include a polymer material substrate and a metal layer. The composite current collector can be formed by forming a metal material (aluminum, aluminum alloys, nickel, nickel alloys, titanium, titanium alloys, silver, and silver alloys, etc.) on a polymer material substrate (such as a substrate of polypropylene, polyethylene terephthalate, polybutylene terephthalate, polystyrene, polyethylene, etc.). In some embodiments, the positive electrode film layer further includes an adhesive and / or a conductive agent.

[0103] In some embodiments, the adhesive comprises any one or a combination of at least two of polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), polyacrylic acid, PVDF-tetrafluoroethylene-propylene terpolymer, PVDF-hexafluoropropylene-tetrafluoroethylene terpolymer, tetrafluoroethylene-hexafluoropropylene copolymer, or fluorinated acrylate resin.

[0104] In some embodiments, the conductive agent includes any one or a combination of at least two of acetylene black, Ketjen black, carbon dots, carbon nanotubes, graphene, or carbon nanofibers.

[0105] In some embodiments, the method for preparing the positive electrode sheet includes: dissolving a positive electrode material, such as a positive electrode active material, a conductive agent, a binder, and other arbitrary components in a solvent (e.g., N-methylpyrrolidone) to form a positive electrode slurry; coating the positive electrode slurry onto a positive electrode current collector; and then drying, cold pressing, and slitting the slurry to obtain the positive electrode sheet.

[0106] [Negative electrode plate]

[0107] In some embodiments, the negative electrode can be a negative electrode sheet, and the negative electrode sheet can include a negative current collector.

[0108] As an example, the negative electrode current collector can be a metal foil, a conductive polymer material, a carbon material, or a composite current collector. For example, as a metal foil, pure metals, alloys, or surface-treated metals can be used, including but not limited to stainless steel, copper, aluminum, nickel, titanium, or silver. The composite current collector may include a polymer material substrate and a metal layer. The composite current collector can be formed by forming a metal material (copper, copper alloys, nickel, nickel alloys, titanium, titanium alloys, silver, and silver alloys, etc.) on a polymer material substrate (such as a substrate of polypropylene, polyethylene terephthalate, polybutylene terephthalate, polystyrene, polyethylene, etc.).

[0109] As an example, the negative electrode sheet may include a negative current collector and a negative electrode film layer disposed on at least one surface of the negative current collector.

[0110] As an example, the negative electrode current collector has two surfaces opposite each other in its own thickness direction, and the negative electrode film layer is disposed on either or both of the two opposite surfaces of the negative electrode current collector.

[0111] As an example, the negative electrode active material in the negative electrode film layer can be a negative electrode active material known in the art for use in battery cells. As an example, the negative electrode active material may include at least one of the following materials: artificial graphite, natural graphite, soft carbon, hard carbon, silicon-based materials, tin-based materials, and lithium titanate, etc. Silicon-based materials may be selected from at least one of elemental silicon, silicon oxide compounds, silicon-carbon composites, silicon-nitrogen composites, and silicon alloys. Tin-based materials may be selected from at least one of elemental tin, tin oxide compounds, and tin alloys. However, this application is not limited to these materials, and other conventional materials that can be used as negative electrode active materials for battery cells may also be used. These negative electrode active materials may be used alone or in combination of two or more.

[0112] In some embodiments, the negative electrode can be made of foamed metal. The foamed metal can be foamed nickel, foamed copper, foamed aluminum, foamed alloy, or foamed carbon, etc. When foamed metal is used as the negative electrode, the surface of the foamed metal may or may not contain a negative electrode active material.

[0113] As an example, negative electrode active materials can be filled or / and deposited within the negative electrode current collector.

[0114] In some embodiments, the positive current collector can be made of aluminum, and the negative current collector can be made of copper. In some embodiments, the method for preparing the negative electrode sheet includes: dissolving a negative electrode material, such as a negative electrode active material, a conductive agent, a binder, and other arbitrary components in a solvent (e.g., water) to form a negative electrode slurry; coating the negative electrode slurry onto the negative current collector; and then drying, cold pressing, and slitting to obtain the negative electrode sheet.

[0115] [Isolation Component]

[0116] In some embodiments, the electrode assembly further includes an isolator disposed between the positive and negative electrodes.

[0117] In some embodiments, the separator is a separator membrane. This application does not impose any particular limitation on the type of separator membrane; any known porous separator membrane with good chemical and mechanical stability can be selected.

[0118] As an example, the main material of the separator can be selected from at least one of glass fiber, non-woven fabric, polyethylene, polypropylene, polyvinylidene fluoride, and ceramic. 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. The separator can be a single component located between the positive and negative electrodes, or it can be attached to the surfaces of the positive and negative electrodes. An inorganic particle coating, an organic particle coating, or an organic / inorganic composite coating can also be applied to the surface of the separator.

[0119] In some embodiments, the separator is a solid electrolyte. The solid electrolyte is disposed between the positive and negative electrodes, serving both to transport ions and to isolate the positive and negative electrodes.

[0120] [Electrolytes]

[0121] In some embodiments, the battery cell also includes an electrolyte, which acts as a conductor of ions between the positive and negative electrodes. This application does not impose specific limitations on the type of electrolyte; it can be selected according to requirements. The electrolyte can be liquid, gel, or solid.

[0122] Liquid electrolytes include electrolyte salts and solvents.

[0123] In some embodiments, the electrolyte salt may be selected from at least one of lithium hexafluorophosphate, lithium tetrafluoroborate, lithium perchlorate, lithium hexafluoroarsenate, lithium bis(fluorosulfonyl)imide, lithium bis(trifluoromethanesulfonyl)imide, lithium trifluoromethanesulfonate, lithium difluorophosphate, lithium difluorooxalate borate, lithium dioxalate borate, lithium difluorodioxalate phosphate, and lithium tetrafluorooxalate phosphate.

[0124] In some embodiments, the solvent may be selected from at least one of ethylene carbonate, propylene carbonate, methyl ethyl carbonate, diethyl carbonate, dimethyl carbonate, dipropyl carbonate, methyl propyl carbonate, ethyl propyl carbonate, butyl carbonate, fluoroethylene carbonate, methyl formate, methyl acetate, ethyl acetate, propyl acetate, methyl propionate, ethyl propionate, propyl propionate, methyl butyrate, ethyl butyrate, 1,4-butyrolactone, sulfolane, dimethyl sulfone, methyl ethyl sulfone, and diethyl sulfone. The solvent may also be an ether solvent. Ether solvents may include one or more of ethylene glycol dimethyl ether, ethylene glycol diethyl ether, diethylene glycol dimethyl ether, triethylene glycol dimethyl ether, tetraethylene glycol dimethyl ether, 1,3-dioxolane, tetrahydrofuran, methyl tetrahydrofuran, diphenyl ether, and crown ethers.

[0125] In some embodiments, the electrolyte may optionally include additives. For example, additives may include negative electrode film-forming additives, positive electrode film-forming additives, and additives that can improve certain properties of the battery cell, such as additives that improve the overcharge / fast charge performance of the battery cell, additives that improve the high-temperature performance of the battery cell, and additives that improve the low-temperature performance of the battery cell.

[0126] The gel electrolyte includes a polymer as a backbone network and can be used in conjunction with an ionic liquid-lithium salt.

[0127] Solid electrolytes include polymer solid electrolytes, inorganic solid electrolytes, and composite solid electrolytes.

[0128] As an example, the polymers of polymeric solid electrolytes may include polyethers (polyoxyethylene), polysiloxanes, polycarbonates, polyacrylonitrile, polyvinylidene fluoride, polymethyl methacrylate, monoionic polymers, polyionic liquids, cellulose, etc.

[0129] As an example, inorganic solid electrolytes can be one or more of the following: oxide solid electrolytes (crystalline perovskite, sodium superconducting ion conductor, garnet, amorphous LiPON thin film), sulfide solid electrolytes (crystalline lithium superconducting ion conductor (lithium germanium phosphorus sulfide, silver sulfide germanium ore), amorphous sulfides), halide solid electrolytes, nitride solid electrolytes, and hydride solid electrolytes.

[0130] As an example, composite solid electrolytes are formed by adding inorganic solid electrolyte fillers to polymer solid electrolytes.

[0131] [Structure of the electrode assembly]

[0132] The electrode assembly can be a wound structure, a stacked structure, or a hybrid structure of wound and stacked.

[0133] In some embodiments, the electrode assembly is a wound structure. The positive electrode and the negative electrode are wound into a wound structure.

[0134] In some implementations, the electrode assembly is a stacked structure.

[0135] As an example, multiple positive and negative electrode plates can be set, and multiple positive and multiple negative electrode plates can be stacked alternately.

[0136] As an example, multiple positive electrode sheets can be set, and negative electrode sheets are folded to form multiple stacked folded segments, with a positive electrode sheet sandwiched between adjacent folded segments.

[0137] As an example, both the positive and negative electrode sheets are folded to form multiple stacked folded segments.

[0138] As an example, multiple separators can be provided, each positioned between any adjacent positive or negative electrode plates.

[0139] As an example, the separator can be continuously arranged between any adjacent positive or negative electrode plates by folding or rolling.

[0140] In some embodiments, the electrode assembly can be cylindrical, flat, or polygonal, etc.

[0141] In some embodiments, the electrode assembly is provided with tabs that allow current to be drawn from the electrode assembly. The tabs include a positive tab and a negative tab.

[0142] [shell]

[0143] In some embodiments, the battery cell may include a casing. The casing may be a steel casing, an aluminum casing, a plastic casing (such as a polypropylene casing), a composite metal casing (such as a copper-aluminum composite casing), or an aluminum-plastic film, etc. In some embodiments, the casing may be a sealed structure or a non-sealed structure. As an example, when the casing is a non-sealed structure, the casing serves to protect the electrode assembly, and a sealing bag is included between the casing and the electrode assembly to encapsulate the electrode assembly and electrolyte. Specifically, the sealing bag may be a bag-shaped insulating component or an aluminum-plastic film. When the casing is a sealed structure, it is used to encapsulate components such as the electrode assembly and electrolyte.

[0144] As an example, the battery cell can be a cylindrical battery cell, a prismatic battery cell, a pouch battery cell, or a battery cell of other shapes. Prismatic battery cells include prismatic battery cells, blade-shaped battery cells, and multi-prismatic batteries, such as hexagonal prismatic batteries. This application does not have any particular limitations.

[0145] In some embodiments, the housing includes an end cap and a housing, the housing having an opening, and the end cap covering the opening. The housing may have one or more openings. The end cap may also have one or more.

[0146] [Electrode terminals]

[0147] In some embodiments, at least one electrode terminal is provided on the housing, and the electrode terminal is electrically connected to the tab. The electrode terminal can be directly connected to the tab, or it can be indirectly connected to the tab through a current collector. The electrode terminal can be provided on the end cap or on the housing.

[0148] [Pressure relief mechanism]

[0149] In some embodiments, a pressure relief mechanism is provided on the casing. The pressure relief mechanism is used to release the internal gas of the battery cell.

[0150] As an example, the internal pressure or temperature of a battery cell is actuated to release the internal pressure or temperature when it reaches a predetermined threshold. When the internal pressure or temperature of the battery cell reaches the predetermined threshold, the pressure relief mechanism is activated or a weak structure in the pressure relief mechanism is broken, thereby creating an opening or channel for the internal pressure or temperature to be released. The threshold design varies depending on the design requirements. The threshold may depend on the materials of one or more of the positive electrode, negative electrode, electrolyte, and separator in the battery cell.

[0151] As an example, the pressure relief mechanism can be integrally molded with the housing.

[0152] As an example, the pressure relief mechanism can also be separately installed and connected to the housing.

[0153] The term "actuation" as used in this application refers to the activation or actuation of the pressure relief mechanism to a certain state, thereby releasing the internal pressure and temperature of the battery cell. The actions of the pressure relief mechanism may include, but are not limited to: movement of components within the mechanism to form an exhaust channel, rupture, breakage, tearing, or opening of at least a portion of the mechanism, etc. When the pressure relief mechanism is activated, the high-temperature, high-pressure substances inside the battery cell are discharged as waste from the activated portion. This method allows for pressure and temperature relief of the battery cell under controllable pressure or temperature, thereby preventing potentially more serious accidents.

[0154] In some embodiments, when the housing is a non-sealed structure, the pressure relief mechanism can be configured as a through hole for venting gas inside the battery cell.

[0155] The emissions from battery cells mentioned in this application include, but are not limited to: electrolyte, dissolved or split positive and negative electrode plates, fragments of separators, high-temperature and high-pressure gases generated by the reaction, flames, etc.

[0156] [Battery Device]

[0157] The battery apparatus mentioned in the embodiments of this application may include one or more battery cell assemblies for providing voltage and capacity. A battery cell assembly may include multiple battery cells connected in series, parallel, or mixed connections via a busbar.

[0158] In some embodiments, a battery cell assembly is typically formed by arranging multiple battery cells.

[0159] As an example, a battery cell assembly can be a battery module, which is formed by arranging and fixing multiple battery cells together to form an independent module. As another example, a battery module can be formed by bundling multiple battery cells together with cable ties.

[0160] In some embodiments, the battery device may be a battery pack, which includes a housing and one or more individual battery cells housed within the housing.

[0161] As an example, the battery cell assembly can be a battery module, which can be housed in a housing by fixing the battery module in the housing.

[0162] As an example, battery cell assemblies can also be housed in a housing by directly fixing multiple battery cells to the housing.

[0163] As an example, the enclosure may include a first enclosure and a second enclosure. The first enclosure and the second enclosure are fastened together to form a closed space inside the enclosure to house the individual battery cells. Here, "closed" refers to covering or closing, and can be either sealed or unsealed. The first enclosure may be a top cover or a bottom plate.

[0164] As an example, the enclosure may include a top cover, a frame, and a bottom plate. The top cover and bottom plate are connected to the frame, creating an enclosed space inside the enclosure to house the individual battery cells.

[0165] In some embodiments, the housing may be part of the vehicle's chassis structure. For example, a portion of the housing may be at least a part of the vehicle's floor, or a portion of the housing may be at least a part of the vehicle's crossbeams and longitudinal beams.

[0166] [ Electrical appliances ]

[0167] The technical solutions described in the embodiments of this application are applicable to various electrical devices that use individual battery cells, such as mobile phones, portable devices, laptops, electric vehicles, electric toys, power tools, vehicles, ships, and spacecraft. For example, spacecraft include airplanes, rockets, space shuttles, and spacecraft.

[0168] [Example]

[0169] Example 1

[0170] Positive electrode active material:

[0171] (1) LMFP (chemical formula LiMnFePO4) was crushed and sieved to obtain first LMFP powder with an average particle size of 2.5 μm and second LMFP powder with an average particle size of 13 μm.

[0172] (2) The first LMFP powder obtained in step (1) and polytetrafluoroethylene are mixed and granulated at a mass ratio of 100:1 under conditions of 500 bar pressure, 50 rpm rotation speed and 25% relative humidity. The mixture is then sintered at 2300℃ for 6 hours to form a core layer. During the sintering process, the second LMFP powder obtained in step (1) is sprayed to form an outer shell layer. After cooling, an average particle size of 55 μm and a specific surface area of ​​33 cm² are obtained. 2 / g and a positive electrode active material with a porosity of 9.5%, wherein the ratio of the radius of the core layer to the thickness of the outer shell layer is 5:1.

[0173] Positive electrode sheet:

[0174] The positive electrode active material, acetylene black, and polyvinylidene fluoride are dissolved in a solvent (N-methylpyrrolidone) at a mass ratio of 0.975:0.005:0.02 to form a positive electrode slurry. The positive electrode slurry is coated onto a positive electrode current collector (aluminum foil), and after drying, cold pressing, and slitting, the positive electrode sheet is obtained.

[0175] Negative electrode plate:

[0176] (1) Natural graphite, styrene-butadiene rubber, carboxymethyl cellulose and conductive carbon black are dissolved in a solvent (water) in a mass ratio of 0.965:0.02:0.011:0.004 to form the first negative electrode slurry;

[0177] Natural graphite, styrene-butadiene rubber, carboxymethyl cellulose, and conductive carbon black are dissolved in a solvent (water) at a mass ratio of 0.977:0.01:0.006:0.007 to form a second negative electrode slurry.

[0178] (2) The first negative electrode slurry is coated on the negative electrode current collector (copper foil) to form the first negative electrode film layer. After drying, the second negative electrode slurry is coated on the first negative electrode film layer to form the second negative electrode film layer. After drying, cold pressing and slitting, the negative electrode sheet is obtained, wherein the thickness ratio of the first negative electrode film layer and the second negative electrode film layer is 4:6.

[0179] Separating membrane: A 7μm polyethylene film is used as the substrate layer, and a 1μm adhesive coating (made of polyvinylidene fluoride) and a 2μm ceramic coating (made of boehmite) are sequentially disposed on the surface of the substrate layer.

[0180] Electrolyte: LiFSI is used as the lithium salt and ethylene carbonate is used as the solvent. The two are mixed to form the electrolyte, wherein the concentration of LiFSI is 1 mol / L.

[0181] Battery cell: The positive electrode, separator, and negative electrode are stacked and wound in sequence to obtain the cell; the cell is placed in the outer packaging, electrolyte is added, and after vacuum sealing, standing, formation, shaping, capacity measurement and other processes, the battery cell is obtained.

[0182] Example 2

[0183] The difference between this embodiment and Embodiment 1 lies in the different positive electrode active materials, as detailed below:

[0184] (1) LMFP is crushed and sieved to obtain first LMFP powder with an average particle size of 1 μm and second LMFP powder with an average particle size of 10 μm.

[0185] (2) The first LMFP powder obtained in step (1) and polytetrafluoroethylene are mixed and granulated at a mass ratio of 100:1 under conditions of 100 bar pressure, 100 rpm rotation speed and 5% relative humidity. The mixture is then sintered at 2200℃ for 4 hours to form a core layer. During the sintering process, the second LMFP powder obtained in step (1) is sprayed to form an outer shell layer. After cooling, an average particle size of 20 μm and a specific surface area of ​​42 cm² are obtained. 2 / g and a positive electrode active material with a porosity of 5%, wherein the ratio of the radius of the core layer to the thickness of the outer shell layer is 2:1.

[0186] Example 3

[0187] The difference between this embodiment and Embodiment 1 lies in the different positive electrode active materials, as detailed below:

[0188] (1) LMFP is crushed and sieved to obtain first LMFP powder with an average particle size of 5 μm and second LMFP powder with an average particle size of 10 μm.

[0189] (2) The first LMFP powder obtained in step (1) and polytetrafluoroethylene are mixed and granulated at a mass ratio of 100:1 under conditions of 1000 bar pressure, 10 rpm rotation speed and 50% relative humidity. The mixture is then sintered at 2250℃ for 8 hours to form a core layer. During the sintering process, the second LMFP powder obtained in step (1) is sprayed to form an outer shell layer. After cooling, an average particle size of 95 μm and a specific surface area of ​​18 cm² are obtained. 2 / g and a positive electrode active material with a porosity of 8%, wherein the ratio of the radius of the core layer to the thickness of the outer shell layer is 10:1.

[0190] Example 4

[0191] The core difference between this embodiment and Embodiment 1 is that by controlling the granulation process (increasing the core layer radius) and extending the sintering time (increasing the outer shell layer thickness), the average particle size of the positive electrode active material is adjusted to 110 μm. The rest is basically the same as Embodiment 1.

[0192] Example 5

[0193] The core difference between this embodiment and embodiment 2 is that by controlling the granulation process and the mass ratio of the second lithium manganese iron phosphate to the first lithium manganese iron phosphate, the radius of the core layer and the thickness of the outer shell layer are adjusted, with a ratio of 11:1. The rest is basically the same as in embodiment 2.

[0194] Comparative Example 1

[0195] The difference between this comparative example and Example 1 is that it does not include the outer shell layer; otherwise, they are the same as Example 1.

[0196] Comparative Example 2

[0197] The difference between this comparative example and Example 1 is that the first lithium manganese iron phosphate forms the outer shell layer and the second lithium manganese iron phosphate forms the core layer; otherwise, they are the same as in Example 1.

[0198] [Performance Testing]

[0199] (1) Cyclic performance: The specific process is to use stepped charging (equivalent to 1C) to charge the battery cell to 100% SOC with constant current, and then discharge the battery to 3% SOC with constant current at 0.5C. This is one charge and discharge process. After 50 cycles, the final capacity retention rate is detected.

[0200] Here, 100% SOC refers to the battery.

[0201] (2) Storage performance: Test storage performance; the specific process is as follows: take the first day of storage at 60℃ as the baseline, store at 60℃ for 30 days, calculate the capacity retention rate, and record it as storage performance 60℃@30d.

[0202] The test results are summarized in Table 1.

[0203] Table 1

[0204]

[0205] Analysis of the data in Table 1 shows that the battery cell described in this application retains more than 96.8% of its capacity after 50 cycles at 25°C and more than 96.2% of its capacity after 30 days of storage at 60°C; the battery cell described in this application has excellent cycle performance and storage performance.

[0206] Analysis of Comparative Examples 1-2 and Example 1 shows that the performance of Comparative Examples 1-2 is not as good as that of Example 1, proving that the battery cell formed by the positive electrode active material described in this application has better performance.

[0207] Analysis of Example 4 and Example 1 shows that the performance of Example 4 is not as good as that of Example 1, proving that the battery cells formed by the average particle size of the positive electrode active material within the specified range have better performance.

[0208] Analysis of Example 5 and Example 2 shows that the performance of Example 5 is not as good as that of Example 2, proving that in the positive electrode active material, the ratio of the radius of the core layer and the thickness of the outer shell layer is within the specified range, resulting in a better positive electrode monomer performance.

[0209] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of this application, and not to limit them. Although this application has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some or all of the technical features therein. These modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments of this application, and they should all be covered within the scope of the claims and specification of this application. In particular, as long as there is no structural conflict, the various technical features mentioned in the embodiments can be combined in any way. This application is not limited to the specific embodiments disclosed herein, but includes all technical solutions falling within the scope of the claims.

Claims

1. A battery cell, characterized by, The battery cell comprises a positive electrode sheet, a negative electrode sheet and a separator; The positive electrode sheet comprises a positive electrode current collector and a positive electrode film layer arranged on at least one surface of the positive electrode current collector; The positive electrode film layer comprises a positive electrode active material, the positive electrode active material comprises an inner core layer and an outer shell layer arranged on a surface of the inner core layer; The inner core layer comprises a first lithium iron manganese phosphate, and the outer shell layer comprises a second lithium iron manganese phosphate; The average particle size of the primary particles of the first lithium iron manganese phosphate is smaller than the average particle size of the primary particles of the second lithium iron manganese phosphate.

2. The battery cell of claim 1, wherein, The average particle size of the secondary particles of the positive electrode active material is ≤100 μm.

3. The battery cell according to claim 1 or 2, characterized in that, The specific surface area of the positive electrode active material is 5 to 50 cm 2 / g.

4. The battery cell according to any one of claims 1 to 3, characterized in that, The porosity of the positive electrode active material is ≤10%.

5. The battery cell of any one of claims 1-4, wherein, The average particle size of the primary particles of the first lithium iron manganese phosphate is 0.05-5 μm.

6. The battery cell of any one of claims 1-5, wherein, The average particle size of the primary particles of the second lithium iron manganese phosphate is 2-50 μm.

7. The battery cell of any one of claims 1-6, wherein, The ratio of the average particle size of the primary particles of the second lithium iron manganese phosphate to the first lithium iron manganese phosphate is (2-10):

1.

8. The battery cell of any one of claims 1-7, wherein, The mass ratio of the second lithium iron manganese phosphate to the first lithium iron manganese phosphate is (0.1-10):

1.

9. The battery cell of any one of claims 1-8, wherein, The ratio of the radius of the inner core layer to the thickness of the outer shell layer is (1-10):

1.

10. A battery device characterized by comprising: The battery device comprises a plurality of battery cells according to any one of claims 1-9.

11. An electrical device, characterized by The electric device comprises the battery cell according to any one of claims 1-9, or the battery device according to claim 10.

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