Battery monomer, battery device and electric equipment

Abstract

The invention discloses a battery monomer, a battery device and electric equipment, the battery monomer comprises a positive pole piece, and the positive pole piece comprises a positive current collector and a negative current collector; the first positive electrode active material layer is arranged on at least one side of the positive electrode current collector, and the first positive electrode active material layer comprises first lithium-containing phosphate; the second positive electrode active material layer is arranged on one side, far away from the positive electrode current collector, of the first positive electrode active material layer, and the second positive electrode active material layer comprises second lithium-containing phosphate; wherein the average particle size of the first lithium-containing phosphate is larger than that of the second lithium-containing phosphate, and the second positive electrode active material layer comprises a conductive polymer. Therefore, the diffusion rate of lithium ions on the positive pole piece is improved, the rate capability of the battery is improved, meanwhile, the structural stability of a positive active material is improved, the influence of transition metal dissolution on a negative electrolyte interface film (SEI film) is reduced, and the cycle performance of a battery monomer is improved.

Description

Technical Field

[0001] The present application relates to the field of batteries, and in particular, to battery cells, battery devices and electrical equipment. Background Art

[0002] Batteries are not only used in energy storage power systems such as hydropower, thermal power, wind power and solar power stations, but are also widely used in electric vehicles such as electric bicycles, electric motorcycles, electric cars, as well as military equipment and aerospace. The diffusion rate of lithium ions in the positive electrode of the battery in the related technology is low, and the rate performance of the battery cannot meet the demand. Summary of the invention

[0003] In a first aspect, the present application provides a battery cell, the battery cell includes a positive electrode plate, the positive electrode plate includes: a positive electrode collector; a first positive electrode active material layer, the first positive electrode active material layer is arranged on at least one side of the positive electrode collector, the first positive electrode active material layer includes a first lithium-containing phosphate; a second positive electrode active material layer, the second positive electrode active material layer is arranged on a side of the first positive electrode active material layer away from the positive electrode collector, the second positive electrode active material layer includes a second lithium-containing phosphate; wherein the average particle size of the first lithium-containing phosphate is greater than the average particle size of the second lithium-containing phosphate, the second positive electrode active material layer includes a conductive polymer, and the conductive polymer includes one or more of polyacetylene, polypyrrole, polythiophene, polyphenylene vinylene, and polyaniline. Therefore, the present application can form positive electrode active material layers with different porosities by setting two layers of positive electrode active material layers containing lithium phosphate with different average particle sizes. The first positive electrode active material layer close to the positive electrode current collector has a larger porosity, and the second positive electrode active material layer close to the electrolyte has a relatively smaller porosity, which can improve the infiltration effect of the electrolyte on the first positive electrode active material layer, increase the diffusion rate of lithium ions on the positive electrode sheet, and improve the rate performance of the battery. At the same time, by setting a conductive polymer in the second positive electrode active material layer, the structural stability of the positive electrode active material is improved, the effect of transition metal dissolution on the negative electrode electrolyte interface film (SEI film) is reduced, and the cycle performance of the battery cell is improved.

[0004] According to some embodiments of the present application, the difference between the average particle size of the first lithium-containing phosphate and the average particle size of the second lithium-containing phosphate is 0.1 μm-0.9 μm. Thus, the porosity of the first positive electrode active material layer is increased, and the wetting effect of the electrolyte on the first positive electrode active material layer is improved.

[0005] According to some embodiments of the present application, the average particle size of the first lithium-containing phosphate is 1.2 μm-1.6 μm; and / or the average particle size of the second lithium-containing phosphate is 0.7 μm-1.1 μm. Thus, the porosity of the first positive electrode active material layer is increased, and the infiltration effect of the electrolyte on the first positive electrode active material layer is improved.

[0006] According to some embodiments of the present application, based on the total mass of the second positive electrode active material layer, the mass proportion of the conductive polymer is 0.1%-0.4%, thereby improving the coating effect on the second positive electrode active material and reducing the dissolution of transition metals.

[0007] According to some embodiments of the present application, the first positive electrode active material layer includes a conductive agent, and the conductive agent includes one or more of carbon nanotubes and conductive carbon, thereby improving the electronic conductivity of the first positive electrode active material layer.

[0008] According to some embodiments of the present application, the first positive electrode active material layer includes a conductive agent, and the conductive agent includes single-walled carbon nanotubes, thereby improving the electron transfer rate of the first positive electrode active material layer.

[0009] According to some embodiments of the present application, based on the total mass of the first positive electrode active material layer, the mass proportion of the single-walled carbon nanotubes is 0.05%-0.8%. Thus, while improving the electronic conductivity of the first positive electrode active material layer, the bonding effect between the first positive electrode active material and the positive electrode current collector can also be improved.

[0010] According to some embodiments of the present application, the thickness of the first positive electrode active material layer is greater than or equal to the thickness of the second positive electrode active material layer, thereby increasing the migration rate of lithium ions in the positive electrode sheet.

[0011] According to some embodiments of the present application, the difference between the thickness of the first positive electrode active material layer and the thickness of the second positive electrode active material layer is 0-50 μm, thereby increasing the migration rate of lithium ions in the positive electrode sheet.

[0012] According to some embodiments of the present application, the thickness of the first positive electrode active material layer is 50 μm-90 μm; and / or the thickness of the second positive electrode material layer is 40 μm-70 μm. Thus, rapid migration of lithium ions on the positive electrode sheet is achieved.

[0013] According to some embodiments of the present application, both the first positive electrode active material layer and the second positive electrode active material layer include pores, and the porosity of the first positive electrode active material layer is greater than or equal to the porosity of the second positive electrode active material layer, thereby improving the wetting effect of the electrolyte on the first positive electrode active material layer.

[0014] According to some embodiments of the present application, the difference between the porosity of the first positive electrode active material layer and the porosity of the second positive electrode active material layer is 1%-10%. Thus, while improving the wetting effect of the electrolyte on the first positive electrode active material layer, the compaction density of the positive electrode sheet is increased.

[0015] According to some embodiments of the present application, the porosity of the first positive electrode active material layer is 24%-30%; and / or the porosity of the second positive electrode active material layer is 20%-26%. Thus, a battery with both excellent rate performance and high energy density is obtained.

[0016] According to some embodiments of the present application, the first lithium-containing phosphate and the second lithium-containing phosphate each independently include a compound represented by Formula I: LiFe x Mn 1-x PO4 formula 1, wherein 0≤x≤1.

[0017] According to some embodiments of the present application, the first lithium-containing phosphate and the second lithium-containing phosphate independently include LiFePO4, LiMnPO4, LiFe 0.8 Mn 0.2 One or more of PO4. Thus, the safety and cycle performance of the battery are improved.

[0018] According to some embodiments of the present application, at least part of the surface of the first lithium-containing phosphate has a first carbon material, and at least part of the surface of the second lithium-containing phosphate has a second carbon material, and based on the total mass of the first lithium-containing phosphate, the mass proportion of the first carbon material is 0.05%-0.8%; and / or based on the total mass of the second lithium-containing phosphate, the mass proportion of the second carbon material is 0.1%-0.4%. Thus, the electronic conductivity of the positive electrode sheet is improved.

[0019] A second aspect of the present application provides a battery device, comprising the battery cell provided in the first aspect of the present application.

[0020] The third aspect of the present application provides an electrical device, comprising the battery cell provided by the first aspect of the present application or the battery device provided by the second aspect of the present application.

[0021] Additional aspects and advantages of the present application will be given in part in the description below, and in part will become apparent from the description below, or will be learned through the practice of the present application. BRIEF DESCRIPTION OF THE DRAWINGS

[0022] Various other advantages and benefits will become apparent to those of ordinary skill in the art by reading the detailed description of the preferred embodiments below. The accompanying drawings are only for the purpose of illustrating the preferred embodiments and are not to be considered as limiting the present application. Moreover, the same reference numerals are used throughout the drawings to represent the same components. In the drawings:

[0023] Figure 1 It is a schematic diagram of the structure of the positive electrode plate of one embodiment of the present application.

[0024] Figure 2 It is a schematic structural diagram of a positive electrode plate according to another embodiment of the present application.

[0025] Figure 3 It is a schematic diagram of a battery cell according to an embodiment of the present application.

[0026] Figure 4 yes Figure 3 An exploded view of a battery cell according to an embodiment of the present application is shown.

[0027] Figure 5 is a schematic diagram of a battery module according to an embodiment of the present application.

[0028] Figure 6 It is a schematic diagram of a battery pack according to one embodiment of the present application.

[0029] Figure 7 yes Figure 6 An exploded view of a battery pack according to an embodiment of the present application is shown.

[0030] Figure 8 It is a schematic diagram of an electrical device using a battery cell according to an embodiment of the present application as a power source.

[0031] Description of reference numerals:

[0032] 1 battery pack; 2 upper box; 3 lower box; 4 battery module; 5 battery cell; 51 shell; 52 electrode assembly; 53 cover plate; 51 positive electrode plate; 510 positive electrode current collector; 511 first positive electrode active material layer; 512 second positive electrode active material layer. DETAILED DESCRIPTION

[0033] The following is a detailed description of the embodiments of the technical solution of the present application. The following embodiments are only used to more clearly illustrate the technical solution of the present application, and are therefore only used as examples, and cannot be used to limit the scope of protection of the present application.

[0034] Reference to "embodiments" herein means that a particular feature, structure, or characteristic described in conjunction with the embodiments may be included in at least one embodiment of the present application. The appearance of the phrase in various locations in the specification does not necessarily refer to the same embodiment, nor is it an independent or alternative embodiment that is mutually exclusive with other embodiments. It is explicitly and implicitly understood by those skilled in the art that the embodiments described herein may be combined with other embodiments.

[0035] Unless otherwise specified, all embodiments and optional embodiments of the present application can be combined with each other to form a new technical solution.

[0036] Unless otherwise specified, all technical features and optional technical features of this application can be combined with each other to form a new technical solution.

[0037] If there is no special explanation, all steps of the present application can be performed sequentially or randomly, preferably sequentially. For example, the method includes steps (a) and (b), which means that the method may include steps (a) and (b) performed sequentially, or may include steps (b) and (a) performed sequentially. For example, the method may further include step (c), which means that step (c) may be added to the method in any order. For example, the method may include steps (a), (b) and (c), or may include steps (a), (c) and (b), or may include steps (c), (a) and (b), etc.

[0038] At present, from the perspective of market development, the application of batteries is becoming more and more extensive. Batteries are not only used in energy storage power systems such as hydropower, thermal power, wind power and solar power stations, but also widely used in electric vehicles such as electric bicycles, electric motorcycles, electric cars, as well as military equipment and aerospace and other fields. With the continuous expansion of battery application areas, its market demand is also constantly expanding.

[0039] In order to improve the rate performance of the battery, the ion transmission capacity between lithium iron phosphate particles can be enhanced by carbon coating or carbon doping on the surface of the lithium iron phosphate material, but it still cannot meet the demand for battery rate performance.

[0040] The battery cell proposed in the present application can improve the porosity of the first positive electrode active material layer by using a first lithium-containing phosphate with a larger average particle size in the first positive electrode active material layer close to the positive electrode current collector and using a second lithium-containing phosphate with a smaller average particle size in the second positive electrode active material layer far from the positive electrode current collector, so that the electrolyte can quickly infiltrate the first positive electrode active material layer even if it infiltrates the second positive electrode active material layer, thereby improving the overall diffusion rate of lithium ions on the positive electrode sheet. After the lithium ion diffusion rate is accelerated, the positive electrode active material in the second positive electrode active material layer is prone to collapse. By arranging a conductive polymer in the second positive electrode active material layer, the conductive polymer can be coated on the surface of the second positive electrode active material, reducing the risk of rapid collapse of the structure of the positive electrode active material due to the accelerated lithium ion diffusion rate, reducing the dissolution of transition metal ions, reducing the damage of transition metal ions to the SEI film, reducing the attenuation of the battery cell capacity, and improving the cycle performance of the battery cell.

[0041] The battery cell proposed in this application can be used in electrical equipment that uses the battery cell as a power source or various energy storage systems that use the battery cell as an energy storage element. Electrical equipment may include, but is not limited to, mobile phones, tablets, laptops, electric toys, electric tools, battery cars, electric cars, ships, spacecraft, etc. Among them, electric toys may include fixed or mobile electric toys, such as game consoles, electric car toys, electric ship toys, and electric airplane toys, etc., and spacecraft may include airplanes, rockets, space shuttles, and spacecraft, etc.

[0042] The present application provides a battery cell according to a first aspect, wherein the battery cell comprises a positive electrode plate, Figure 1 and Figure 2 The positive electrode sheet 51 includes: a positive electrode current collector 510; a first positive electrode active material layer 511, the first positive electrode active material layer 511 is arranged on at least one side of the positive electrode current collector 510, and the first positive electrode active material layer 511 includes a first lithium-containing phosphate; a second positive electrode active material layer 512, the second positive electrode active material layer 512 is arranged on the side of the first positive electrode active material layer 511 away from the positive electrode current collector 510, and the second positive electrode active material layer 512 includes a second lithium-containing phosphate; wherein the average particle size of the first lithium-containing phosphate is greater than the average particle size of the second lithium-containing phosphate, and the second positive electrode active material layer includes a conductive polymer, and the conductive polymer includes one or more of polyacetylene, polypyrrole, polythiophene, polyphenylene vinylene, and polyaniline. Thus, the diffusion rate of lithium ions on the positive electrode sheet is increased, the rate performance of the battery is improved, and at the same time, the structural stability of the positive electrode active material is improved, the influence of transition metal dissolution on the SEI film is reduced, and the cycle performance of the battery cell is improved.

[0043] According to some embodiments of the present application, the difference between the average particle size of the first lithium-containing phosphate and the average particle size of the second lithium-containing phosphate is 0.1 μm-0.9 μm. For example, it can be 0.1 μm, 0.3 μm, 0.5 μm, 0.7 μm, 0.9 μm, etc., or can be a range composed of any of the above values. Thus, the porosity of the first positive electrode active material layer is increased, and the wetting effect of the electrolyte on the first positive electrode active material layer is improved.

[0044] In the present application, the battery is disassembled to obtain the positive electrode sheet, the positive electrode sheet is cut along its thickness direction to obtain a cross section of the positive electrode sheet, and the cross section is observed by a scanning electron microscope (SEM). The first positive electrode active material layer and the second positive electrode active material layer have an obvious dividing line, the first positive electrode active material layer is close to the positive electrode current collector, and the side of the first positive electrode active material layer away from the positive electrode current collector is the second positive electrode active material layer.

[0045] In the present application, when testing the average particle size of the first lithium-containing phosphate and the second lithium-containing phosphate, the positive electrode sheet is cut along its thickness direction by plasma to obtain a cross-section of the positive electrode sheet, the cross-section is observed by SEM, and 10 primary particles are randomly selected. The average particle size of a single primary particle = (the longest diameter of a single particle + the shortest diameter of a single particle) / 2, and the average value of the 10 particles is the average particle size of the lithium-containing phosphate particles.

[0046] In the present application, when testing whether the second positive electrode active material layer contains a conductive polymer and the type of the conductive polymer, an infrared spectrum test can be performed. Specifically, the battery is disassembled to obtain a positive electrode sheet, the positive electrode sheet is cut by plasma along its thickness direction to obtain a cross section of the positive electrode sheet, the cross section of the positive electrode sheet is observed by SEM, the thickness of the second positive electrode active material layer is tested, and the powder of the second active material layer on the positive electrode sheet is scraped off according to the thickness of the second positive electrode active material layer for infrared spectrum testing.

[0047] When the infrared spectrum is at 1600cm -1 When the C=C characteristic peak appears and there is no benzene ring or heteroatom peak, it can be determined that the second positive electrode active material layer includes a conductive polymer, and the conductive polymer is polyacetylene.

[0048] When the infrared spectrum is at 1200cm -1 -1300cm -1 The CN characteristic peak appears and the ring vibration is at 1450cm -1 When the second positive electrode active material layer contains a conductive polymer, the conductive polymer is polypyrrole.

[0049] When the infrared spectrum is at 690cm -1 -790cm -1The CS characteristic peak appears, and the ring vibration is at 1500cm -1 -1600cm -1 When the second positive electrode active material layer includes a conductive polymer, the conductive polymer is polythiophene.

[0050] When the infrared spectrum is at 750cm -1 The characteristic peak of benzene ring appears at 1600cm -1 When the C=C characteristic peak appears, it can be determined that the second positive electrode active material layer includes a conductive polymer, and the conductive polymer is polyphenylene vinylene.

[0051] When the infrared spectrum is at 3200cm -1 -3400cm -1 The NH characteristic peak appears at 1140cm -1 When the doping peak appears, it can be determined that the second positive electrode active material layer includes a conductive polymer, and the conductive polymer is polyaniline.

[0052] According to some embodiments of the present application, the average particle size of the first lithium-containing phosphate may be 1.2 μm-1.6 μm, for example, 1.2 μm, 1.3 μm, 1.4 μm, 1.5 μm, 1.6 μm, etc., or may be within a range consisting of any of the above values.

[0053] According to some embodiments of the present application, the average particle size of the second lithium-containing phosphate may be 0.7 μm-1.1 μm, for example, 0.7 μm, 0.8 μm, 0.9 μm, 1 μm, 1.1 μm, etc., or may be within a range consisting of any of the above values.

[0054] By making the average particle sizes of the first lithium-containing phosphate and the second lithium-containing phosphate within the above range, the transmission rate of lithium ions is increased while the compaction density of the positive electrode plate is increased, so that the battery has excellent rate performance and high energy density.

[0055] According to some embodiments of the present application, at least part of the surface of the first lithium-containing phosphate has a first carbon material, and based on the total mass of the first lithium-containing phosphate, the mass proportion of the first carbon material can be 0.05%-0.8%. For example, it can be 0.05%, 0.1%, 0.2%, 0.3%, 0.4%, 0.5%, 0.6%, 0.7%, 0.8%, etc., or can be a range composed of any of the above values. Thereby, the conductivity of the first lithium-containing phosphate is improved.

[0056] According to some embodiments of the present application, at least part of the surface of the second lithium-containing phosphate has a second carbon material, and based on the total mass of the second lithium-containing phosphate, the mass proportion of the second carbon material can be 0.1%-0.4%. For example, it can be 0.1%, 0.2%, 0.3%, 0.4%, etc., or it can be a range composed of any of the above values. Thereby, the electronic conductivity of the positive electrode sheet is improved. Thereby, the conductivity of the second lithium-containing phosphate is improved.

[0057] According to some embodiments of the present application, based on the total mass of the second positive electrode active material layer, the mass proportion of the conductive polymer is 0.1%-0.4%. For example, it can be 0.1%, 0.2%, 0.3%, 0.4%, etc., or it can be a range composed of any of the above numerical values. Thus, when the diffusion rate of lithium ions in the positive electrode sheet is relatively fast, by making the content of the conductive polymer within the above range, the coating effect on the second positive electrode active material is improved, the probability of collapse of the positive electrode active material structure due to rapid lithium ion deintercalation is reduced, and the dissolution of transition metals is reduced. At the same time, the coating of the conductive polymer can also reduce the side reactions between the electrolyte and the positive electrode surface, and improve the cycle performance of the battery.

[0058] According to some embodiments of the present application, the first positive electrode active material layer includes a conductive agent, and the conductive agent includes one or more of carbon nanotubes and conductive carbon, thereby improving the electronic conductivity of the first positive electrode active material layer.

[0059] According to some embodiments of the present application, the first positive electrode active material layer includes a conductive agent, and the conductive agent includes carbon nanotubes. Thereby, the electronic conductivity of the first positive electrode active material layer is improved. Specifically, the average particle size of the first lithium-containing phosphate is greater than the average particle size of the second lithium-containing phosphate, the first positive electrode active material layer contains carbon nanotubes, and the second positive electrode active material layer contains a conductive polymer. That is, along the direction from the positive electrode current collector to the surface of the positive electrode sheet, the average particle size of the first lithium-containing phosphate gradually decreases, and the porosity gradually decreases. In other words, the porosity of the first positive electrode active material layer close to the positive electrode current collector is larger, and the electrolyte is easier to infiltrate. At the same time, carbon nanotubes can also increase the diffusion rate of lithium ions in the first lithium-containing phosphate particles with large particle size, thereby improving the rate performance of the battery. Lithium ions are rapidly deintercalated, the structural collapse rate of lithium-containing phosphates is accelerated, and the conductive polymer of the second positive electrode active material layer can be coated on the surface of the second positive electrode active material, thereby improving the structural stability of the second positive electrode active material, improving the stability of the positive electrode surface, reducing the dissolution of transition metals, reducing the side reactions between the electrolyte and the positive electrode surface, and improving the cycle performance of the battery. In general, a battery with both good rate performance and cycle performance can be obtained.

[0060] According to some embodiments of the present application, the first positive electrode active material layer includes a conductive agent, and the conductive agent includes single-walled carbon nanotubes. Thus, the electron transfer rate of the first positive electrode active material layer is improved. The single-walled carbon nanotubes have better conductivity and can further improve the rate performance of the battery.

[0061] According to some embodiments of the present application, based on the total mass of the first positive electrode active material layer, the mass proportion of the single-walled carbon nanotubes can be 0.05%-0.8%. For example, it can be 0.05%, 0.1%, 0.3%, 0.5%, 0.7%, 0.8%, etc., or it can be a range composed of any of the above values. Thus, while improving the electronic conductivity of the first positive electrode active material layer, it can also improve the bonding effect between the first positive electrode active material and the positive electrode current collector, and reduce the risk of the first positive electrode active material layer being loosely bonded to the positive electrode current collector due to particle expansion and delamination.

[0062] According to some embodiments of the present application, the thickness of the first positive electrode active material layer is greater than or equal to the thickness of the second positive electrode active material layer. Thus, under the condition that the thickness of the positive electrode active material layer is constant, increasing the thickness of the first positive electrode active material layer can increase the migration rate of lithium ions in the positive electrode sheet.

[0063] According to some embodiments of the present application, the difference between the thickness of the first positive electrode active material layer and the thickness of the second positive electrode active material layer is 0-50 μm. For example, it can be 0, 10 μm, 20 μm, 30 μm, 40 μm, 50 μm, etc., or can be a range composed of any of the above values. Thus, rapid migration of lithium ions on the positive electrode sheet is achieved, and fast charging of more than 4C is achieved.

[0064] According to some embodiments of the present application, the thickness of the first positive electrode active material layer is 50 μm-90 μm, for example, 50 μm, 60 μm, 70 μm, 80 μm, 90 μm, etc., or a range consisting of any of the above values.

[0065] According to some embodiments of the present application, the thickness of the second positive polarity material layer is 40 μm-70 μm. For example, it can be 40 μm, 50 μm, 60 μm, 70 μm, etc., or can be a range of any of the above values. In this way, both the energy density and fast charging performance of the battery can be taken into account.

[0066] According to some embodiments of the present application, both the first positive electrode active material layer and the second positive electrode active material layer include pores, and the porosity of the first positive electrode active material layer is greater than or equal to the porosity of the second positive electrode active material layer, thereby improving the wetting effect of the electrolyte on the first positive electrode active material layer.

[0067] In the present application, the battery is disassembled to obtain the positive electrode sheet, the positive electrode sheet is cut along its thickness direction by plasma to obtain the cross section of the positive electrode sheet, and the porosity of the first positive electrode active material layer and the second positive electrode active material layer is observed by SEM.

[0068] According to some embodiments of the present application, the difference between the porosity of the first positive electrode active material layer and the porosity of the second positive electrode active material layer is 1%-10%. For example, it can be 1%, 3%, 5%, 7%, 9%, 10%, etc., or it can be a range composed of any of the above values. Thus, while improving the wetting effect of the electrolyte on the first positive electrode active material layer, the compaction density of the positive electrode sheet is improved.

[0069] According to some embodiments of the present application, the porosity of the first positive electrode active material layer may be 24%-30%, for example, 24%, 25%, 26%, 27%, 28%, 29%, 30%, etc., or may be a range consisting of any of the above values.

[0070] According to some embodiments of the present application, the porosity of the second positive electrode active material layer may be 20%-26%. For example, it may be 20%, 22%, 24%, 26%, etc., or may be a range of any of the above values. Thus, a battery having both excellent rate performance and high energy density is obtained.

[0071] In the present application, the porosity can be tested by forming the first positive electrode active material layer and the second positive electrode active material layer on two positive electrode current collectors respectively. When the coating weight, coating thickness, and average particle size of the positive electrode active material are the same, the porosity measured on the two positive electrode current collectors can represent the porosity of the two individual layers when the first positive electrode active material layer and the second positive electrode active material layer are formed on the same positive electrode current collector.

[0072] Specifically, when the first positive electrode active material layer and the second positive electrode active material layer are respectively formed on two positive electrode current collectors, the porosity can be tested by the following method: by cutting a certain area of ​​the electrode sheet, weighing and measuring the thickness, calculating the volume v of the electrode sheet, immersing it in liquid to absorb it and placing it until no liquid drips, and weighing it. The weight difference before and after absorbing the liquid is the weight m of the pore liquid. The liquid density is p, and the porosity of the electrode sheet can be obtained as m / p / v×100%.

[0073] According to some embodiments of the present application, the first lithium-containing phosphate and the second lithium-containing phosphate each independently include a compound represented by Formula I: LiFe x Mn 1-x PO4 formula 1, wherein 0≤x≤1.

[0074] According to some embodiments of the present application, the first lithium-containing phosphate and the second lithium-containing phosphate independently include LiFePO4, LiMnPO4, LiFe 0.8 Mn 0.2 One or more of PO4. Thus, the safety and cycle performance of the battery are improved.

[0075] In some embodiments, the first positive electrode active material layer and the second positive electrode active material layer may further optionally include a binder. As an example, the binder may include at least one of polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), vinylidene fluoride-tetrafluoroethylene-propylene terpolymer, vinylidene fluoride-hexafluoropropylene-tetrafluoroethylene terpolymer, tetrafluoroethylene-hexafluoropropylene copolymer, and fluorine-containing acrylate resin.

[0076] As an example, the positive electrode current collector may be a metal foil or a composite current collector. For example, as the metal foil, aluminum foil may be used. The composite current collector may include a polymer material base and a metal layer formed on at least one surface of the polymer material base. The composite current collector may be formed by forming a metal material (aluminum, aluminum alloy, nickel, nickel alloy, titanium, titanium alloy, silver and silver alloy, etc.) on a polymer material substrate (such as a substrate of polypropylene (PP), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polystyrene (PS), polyethylene (PE), etc.).

[0077] In some embodiments, the positive electrode sheet can be prepared in the following manner: the components for preparing the positive electrode sheet, such as the 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; the positive electrode slurry is coated on the positive electrode collector, and after drying, cold pressing and other processes, the positive electrode sheet can be obtained.

[0078] The battery further includes a negative electrode sheet, which includes a negative electrode collector and a negative electrode active material layer disposed on at least one surface of the negative electrode collector, wherein the negative electrode active material layer includes a negative electrode active material.

[0079] As an 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 any one or both of the two facing surfaces of the negative electrode current collector.

[0080] In some embodiments, the negative electrode current collector may be a metal foil or a composite current collector. For example, as the metal foil, a copper foil may be used. 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 substrate. The composite current collector may be formed by forming a metal material (copper, copper alloy, nickel, nickel alloy, titanium, titanium alloy, silver and silver alloy, etc.) on a polymer material substrate (such as a substrate of polypropylene (PP), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polystyrene (PS), polyethylene (PE), etc.).

[0081] In some embodiments, the negative electrode active material may adopt the negative electrode active material for the battery known in the art. 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 titanates, etc. The silicon-based material may be selected from at least one of elemental silicon, silicon oxide compounds, silicon-carbon composites, silicon-nitrogen composites and silicon alloys. The tin-based material may be selected from at least one of elemental tin, tin oxide compounds and tin alloys. When the battery is a lithium-ion battery, the titanate adopts lithium titanate; 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 can also be used. These negative electrode active materials can be used alone or in combination of two or more.

[0082] In some embodiments, the negative electrode active material layer may further include a binder. The binder may be selected from at least one 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).

[0083] In some embodiments, the negative electrode active material layer may further include a conductive agent, which may be selected from at least one of superconducting carbon, acetylene black, carbon black, Ketjen black, carbon dots, carbon nanotubes, graphene, and carbon nanofibers.

[0084] 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)).

[0085] In some embodiments, the negative electrode sheet can be prepared in the following manner: the components for preparing the negative electrode sheet, such as the negative electrode active material, the conductive agent, the binder and any other components are dispersed in a solvent (such as deionized water) to form a negative electrode slurry; the negative electrode slurry is coated on the negative electrode collector, and after drying, cold pressing and other processes, the negative electrode sheet can be obtained.

[0086] The battery also includes an electrolyte, which plays a role in conducting ions between the positive electrode and the negative electrode. The present application has no specific restrictions on the type of electrolyte, which can be selected according to needs.

[0087] In some embodiments, the electrolyte is an electrolyte solution, which includes an electrolyte salt and a solvent.

[0088] In some embodiments, the electrolyte salt may include at least one of lithium hexafluorophosphate, lithium tetrafluoroborate, lithium perchlorate, lithium hexafluoroarsenate, lithium bisfluorosulfonyl imide, lithium bistrifluoromethanesulfonyl imide, lithium trifluoromethanesulfonate, lithium difluorophosphate, lithium difluorooxalatoborate, lithium dioxalatoborate, lithium difluorodioxalatophosphate, and lithium tetrafluorooxalatophosphate.

[0089] In some embodiments, the solvent can be selected from at least one of ethylene carbonate, propylene carbonate, ethyl methyl carbonate, diethyl carbonate, dimethyl carbonate, dipropyl carbonate, methyl propyl carbonate, ethyl propyl carbonate, butylene carbonate, fluoroethylene carbonate, methyl formate, methyl acetate, ethyl acetate, propyl acetate, methyl propionate, ethyl propionate, propyl propionate, methyl butyrate, ethyl butyrate, 1,4-butyrolactone, cyclopentane sulfone, dimethyl sulfone, methyl ethyl sulfone and diethyl sulfone.

[0090] In some embodiments, the electrolyte may further include additives, such as 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, additives that improve battery high or low temperature performance, etc.

[0091] In some embodiments, the 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 stability and mechanical stability can be selected.

[0092] In some embodiments, the material of the isolation membrane can be selected from at least one of glass fiber, non-woven fabric, polyethylene, polypropylene and polyvinylidene fluoride. The isolation membrane can be a single-layer film or a multi-layer composite film, without particular limitation. When the isolation membrane is a multi-layer composite film, the materials of each layer can be the same or different, without particular limitation.

[0093] In some embodiments, the positive electrode sheet, the negative electrode sheet, and the separator may be formed into an electrode assembly by a winding process or a lamination process.

[0094] In some embodiments, the battery may include an outer packaging, which may be used to encapsulate the electrode assembly and the electrolyte.

[0095] In some embodiments, the outer packaging of the battery may be a hard shell, such as a hard plastic shell, an aluminum shell, a steel shell, etc. The outer packaging of the battery may also be a soft package, such as a bag-type soft package. The material of the soft package may be plastic, and examples of the plastic include polypropylene, polybutylene terephthalate, and polybutylene succinate.

[0096] The present application has no particular limitation on the shape of the battery cell, which may be cylindrical, square or any other shape. Figure 3 The battery cell 5 is a square structure as an example.

[0097] In some embodiments, reference Figure 4 , the outer packaging may include a shell 51 and a cover plate 53. Among them, 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 5 can be one or more, and those skilled in the art can select according to specific actual needs.

[0098] A second aspect of the present application provides a battery device, comprising the battery cell provided in the first aspect of the present application.

[0099] In some embodiments, the battery device may be a battery module, which includes battery cells. The number of battery cells contained in the battery module may be one or more, and the specific number may be selected by those skilled in the art according to the application and capacity of the battery module.

[0100] Figure 5 4 is an example of a battery module. Figure 5 In the battery module 4, the plurality of battery cells 5 may be arranged in sequence along the length direction of the battery module 4. Of course, they may also be arranged in any other manner. Further, the plurality of battery cells 5 may be fixed by fasteners.

[0101] Optionally, the battery module 4 may further include a housing having a receiving space, and the plurality of battery cells 5 are received in the receiving space.

[0102] In some embodiments, the battery device may further include a battery pack, which includes multiple battery modules. The number of battery modules contained in the battery pack may be one or more, and the specific number may be selected by those skilled in the art according to the application and capacity of the battery pack.

[0103] Figure 6 and Figure 71 is a battery pack 1 as an example. Figure 6 and Figure 7 The battery pack 1 may include a battery box and a plurality of battery modules 4 disposed in the battery box. The battery box includes an upper box body 2 and a lower box body 3. The upper box body 2 can cover the lower box body 3 and form a closed space for accommodating the battery modules 4. The plurality of battery modules 4 can be arranged in the battery box in any manner.

[0104] The second aspect of the present application provides an electric device, including the battery cell provided in the first aspect of the present application or the battery device provided in the second aspect of the present application. The battery cell and the battery device can be used as a power source for the electric device, and can also be used as an energy storage unit for the electric device. The electric device may include mobile devices (such as mobile phones, laptops, etc.), electric vehicles (such as pure electric vehicles, hybrid electric vehicles, plug-in hybrid electric vehicles, electric bicycles, electric scooters, electric golf carts, electric trucks, etc.), electric trains, ships and satellites, energy storage systems, etc., but are not limited thereto.

[0105] As the electrical equipment, a battery cell or a battery device can be selected according to its usage requirements.

[0106] Figure 8 The power consumption device is taken as an example. The power consumption device is a pure electric vehicle, a hybrid electric vehicle, or a plug-in hybrid electric vehicle, etc. In order to meet the power consumption device's requirements for high power and high energy density of the battery, a battery pack or a battery module can be used.

[0107] As another example, the device may be a mobile phone, a tablet computer, a notebook computer, etc. The device is usually required to be light and thin, and a battery may be used as a power source.

[0108] In order to make the technical problems, technical solutions and beneficial effects solved by the embodiments of the present application clearer, the following will be further described in detail with reference to the embodiments and the accompanying drawings. Obviously, the described embodiments are only a part of the embodiments of the present application, rather than all of the embodiments. The following description of at least one exemplary embodiment is actually only illustrative and is by no means intended to limit the present application and its applications. Based on the embodiments in the present application, all other embodiments obtained by ordinary technicians in the field without creative work are within the scope of protection of the present application.

[0109] Example 1

[0110] 1. Preparation of positive electrode sheet

[0111] Adding a first lithium-containing phosphate lithium iron phosphate (LFP), conductive carbon, a binder polyvinylidene fluoride (PVDF), and a surfactant polyvinyl pyrrolidone into a solvent N-methylpyrrolidone (NMP) in a ratio of 97.5:0.4:1.8:0.3, and stirring to form a first slurry, wherein the average particle size of the LFP is 1.15 μm;

[0112] Add LFP, PVDF, conductive polymer polypyrrole, and surfactant polyvinyl pyrrolidone into NMP in a ratio of 97.7:1.8:0.2:0.3, and stir to form a second slurry, wherein the average particle size of LFP is 1.1 μm;

[0113] The first slurry and the second slurry are coated by a coating machine, dried, and rolled to form a first positive electrode active material layer and a second positive electrode active material layer. The total coating weight of the first positive electrode active material layer and the second positive electrode active material layer is 290 mg / 1540.25 m 2 , the thickness of the first positive electrode active material layer is 75 μm, and the thickness of the second positive electrode active material layer is 50 μm.

[0114] 2. Preparation of negative electrode sheet

[0115] Active material artificial graphite, conductive carbon, binder styrene-butadiene rubber (SBR), thickener sodium carboxymethyl cellulose (CMC-Na), single-walled carbon nanotubes are added to solvent deionized water in a weight ratio of 97.7:0.7:0.5:0.6:0.5, mixed evenly to prepare negative electrode slurry, coated the negative electrode slurry on the negative electrode collector copper foil, and dried, cold pressed, and cut to obtain negative electrode sheets.

[0116] 3. Isolation film

[0117] Polypropylene film.

[0118] 4. Preparation of Electrolyte

[0119] In an argon atmosphere glove box (H2O<0.1ppm, O2<0.1ppm), organic solvents ethylene carbonate (EC) and ethyl methyl carbonate (EMC) were evenly mixed in a volume ratio of 3:7, and LiPF6 was added to dissolve in the organic solvent, with the mass proportion of LiPF6 being 12.5%.

[0120] 5. Preparation of batteries

[0121] The positive electrode sheet, the separator, and the negative electrode sheet are stacked in order, so that the separator is between the positive and negative electrodes to play an isolating role. A copper wire is inserted between the two layers of separators as the third electrode to obtain a bare cell. The bare cell is placed in an aluminum-plastic bag and baked at 60°C to remove water. Then, the electrolyte is injected and sealed to obtain an uncharged battery. The uncharged battery then goes through the processes of static, hot and cold pressing, formation, shaping, and capacity testing to obtain a lithium-ion stacked three-electrode battery product.

[0122] The preparation methods of the batteries in Examples 2 to 22 and Comparative Examples 1 to 3 are the same as those in Example 1, and the differences are detailed in Table 1.

[0123]

[0124]

[0125] Performance Testing

[0126] 1. Three-electrode charging window test:

[0127] Use 0.00002A to charge for 2h to plate lithium on the copper wire as a reference electrode to monitor the anode potential, set the charging rates to 15C, 9C, 7C, 5.5C, 4C, 3C, 2.2C, 1.6C, 0.8C, and 0.5C, discharge the battery cell at 0.33C to 2.0V, and charge it in sequence using the set rates. When the anode potential drops to 0mV, jump to the next rate for charging until all rates are charged. Fit the charging window of the battery cell based on the test data and the binomial exponential function to obtain the equivalent charging rate of the battery cell (for example, if it is equivalent to 2C, it means that the battery cell 30% SOC-80% SOC meets the 2C charging rate, that is, the charging time for 30% SOC-80% SOC is 1h).

[0128] 2-cycle capacity test:

[0129] At 25°C, charge the battery at a constant current of 1 / 3C to 3.8V, then charge at a constant voltage of 3.8V to a current of 0.05C, leave for 5 minutes, and then discharge at 1 / 3C to 2.0V. The resulting capacity is recorded as the initial capacity C0. Repeat the above steps and record the discharge capacity C of the battery after the nth cycle. n , then the battery capacity retention rate P after each cycle n =C n / C0×100%. During the test, the first cycle corresponds to n=1, the second cycle corresponds to n=2, and ... the 1000th cycle corresponds to n=1000.

[0130] 3.DCR test:

[0131] The battery is charged to 3.8V at a constant current of 1 / 3C, then charged to a full charge state at a constant voltage of 3.8V with a current of 0.05C, then discharged at a constant capacity of 1 / 3C to 0.5C0 to 50% SOC, and discharged at 2C for 30s to obtain DCR1. After 1000 cycles, DCR2 is measured according to the test method of DCR1. The DCR growth rate of 1000 cycles = (DCR2 / DCR1-1)×100%.

[0132] 4. Porosity of the first positive electrode active material layer and the second positive electrode active material layer

[0133] The first slurry and the second slurry are coated on two positive electrode sheets respectively to form the first positive electrode sheet and the second positive electrode sheet, and the coating weight and coating thickness are the same. The volume v of the electrode sheet is calculated by cutting a certain area of ​​the electrode sheet, weighing it and measuring the thickness, immersing it in liquid and placing it until no liquid drips, and weighing it. The weight difference before and after absorbing the liquid is the pore liquid weight m, and the liquid density is p, then the porosity of the electrode sheet can be obtained = m / p / v×100%, which can represent the porosity of the first positive electrode active material layer and the second positive electrode active material layer on the same positive electrode current collector.

[0134] The performance test results of the batteries in Examples 1 to 22 and Comparative Examples 1 to 3 are shown in Table 2.

[0135] Table 2

[0136]

[0137]

[0138] It can be seen from the comparison between Examples 1 to 22 and Comparative Examples 1 to 3 that the battery proposed in the present application has a higher equivalent charge rate, which means that by making the average particle size of the first lithium-containing phosphate larger than the average particle size of the second lithium-containing phosphate and adding a conductive polymer to the second positive electrode active material layer, the wetting effect of the electrolyte on the first positive electrode active material layer can be improved, and the risk of rapid collapse of the structure of the positive electrode active material due to the accelerated diffusion rate of lithium ions can be reduced, the dissolution of transition metal ions can be reduced, the damage of transition metal ions to the SEI film can be reduced, the attenuation of the battery cell capacity can be reduced, and the cycle performance of the battery cell can be improved.

[0139] It can be seen from Examples 1 to 7 that by adjusting the particle size of the first lithium-containing phosphate or the second lithium-containing phosphate, the difference in the average particle size of the first lithium-containing phosphate and the second lithium-containing phosphate can be adjusted, and then the difference in the porosity of the first positive electrode active material layer and the second positive electrode active material layer can be adjusted, thereby improving the wetting effect of the electrolyte on the first positive electrode active material layer, thereby improving the equivalent charge rate and cycle capacity retention rate of the battery, and reducing the DCR growth rate after the battery cycle.

[0140] It can be seen from Examples 8 to 10 that by adjusting the content of the conductive polymer in the second active material layer, the equivalent charge rate and cycle performance of the battery can be adjusted to obtain a battery with both a higher equivalent charge rate and better cycle performance.

[0141] It can be seen from Examples 11 to 14 that different types of conductive polymers can all play the role of coating the second lithium-containing phosphate and improving the structural stability of the second lithium-containing phosphate.

[0142] It can be seen from Examples 15 to 19 that by replacing the conductive agent in the first positive electrode active material layer with carbon nanotubes, the conductivity of the carbon nanotubes is better, which can further improve the rate performance and cycle performance of the battery.

[0143] It can be seen from Examples 20 to 22 that by adjusting the thickness of the first positive electrode active material layer and the second positive electrode active material layer, the equivalent charge rate and cycle performance of the battery can also be adjusted to obtain a battery with both a higher equivalent charge rate and better cycle performance.

[0144] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present application, rather than to limit them; although the present application has been described in detail with reference to the aforementioned embodiments, those skilled in the art should understand that they can still modify the technical solutions described in the aforementioned embodiments, or replace some or all of the technical features therein by equivalents; and these modifications or replacements do not make the essence of the corresponding technical solutions deviate from the scope of the technical solutions of the embodiments of the present application, and they should all be included in the scope of the claims and specification of the present application. In particular, as long as there is no structural conflict, the various technical features mentioned in the various embodiments can be combined in any way. The present application is not limited to the specific embodiments disclosed herein, but includes all technical solutions that fall within the scope of the claims.

Claims

1. A battery cell, characterized in that: The invention comprises a positive electrode sheet, wherein the positive electrode sheet comprises: Positive electrode current collector; a first positive electrode active material layer, the first positive electrode active material layer being disposed on at least one side of the positive electrode current collector, the first positive electrode active material layer comprising a first lithium-containing phosphate; A second positive electrode active material layer, wherein the second positive electrode active material layer is disposed on a side of the first positive electrode active material layer away from the positive electrode current collector, and the second positive electrode active material layer comprises a second lithium-containing phosphate; wherein, The average particle size of the first lithium-containing phosphate is greater than that of the second lithium-containing phosphate. The second positive electrode active material layer includes a conductive polymer, and the conductive polymer includes one or more of polyacetylene, polypyrrole, polythiophene, polyphenylene vinylene, and polyaniline.

2. The battery cell according to claim 1, characterized in that: The difference between the average particle size of the first lithium-containing phosphate and the average particle size of the second lithium-containing phosphate is 0.1 μm-0.9 μm.

3. The battery cell according to claim 1 or 2, characterized in that: The average particle size of the first lithium-containing phosphate is 1.2 μm-1.6 μm; and / or The average particle size of the second lithium-containing phosphate is 0.7 μm-1.1 μm.

4. The battery cell according to any one of claims 1 to 3, characterized in that: Based on the total mass of the second positive electrode active material layer, the mass proportion of the conductive polymer is 0.1%-0.4%.

5. The battery cell according to any one of claims 1 to 4, characterized in that: The first positive electrode active material layer includes a conductive agent, and the conductive agent includes one or more of carbon nanotubes and conductive carbon.

6. The battery cell according to any one of claims 1 to 5, characterized in that: The first positive active material layer includes a conductive agent, and the conductive agent includes single-walled carbon nanotubes.

7. The battery cell according to claim 6, characterized in that: Based on the total mass of the first positive electrode active material layer, the mass proportion of the single-walled carbon nanotubes is 0.05%-0.8%.

8. The battery cell according to any one of claims 1 to 7, characterized in that: The thickness of the first positive electrode active material layer is greater than or equal to the thickness of the second positive electrode active material layer.

9. The battery cell according to any one of claims 1 to 8, characterized in that: The difference between the thickness of the first positive electrode active material layer and the thickness of the second positive electrode active material layer is 0-50 μm.

10. The battery cell according to any one of claims 1 to 9, characterized in that: The thickness of the first positive electrode active material layer is 50 μm-90 μm; and / or The thickness of the second positive polarity material layer is 40 μm-70 μm.

11. The battery cell according to any one of claims 1 to 10, characterized in that: The first positive electrode active material layer and the second positive electrode active material layer both include pores, and the porosity of the first positive electrode active material layer is greater than or equal to the porosity of the second positive electrode active material layer.

12. The battery cell according to claim 11, characterized in that: The difference between the porosity of the first positive electrode active material layer and the porosity of the second positive electrode active material layer is 1%-10%.

13. The battery cell according to claim 12, characterized in that: The porosity of the first positive electrode active material layer is 24%-30%; and / or the porosity of the second positive electrode active material layer is 20%-26%.

14. The battery cell according to any one of claims 1 to 13, characterized in that: The first lithium-containing phosphate and the second lithium-containing phosphate each independently comprise a compound represented by Formula I: Life x Mn 1-x PO4 formula I Among them, 0≤x≤1.

15. The battery cell according to any one of claims 1 to 14, characterized in that: The first lithium-containing phosphate and the second lithium-containing phosphate independently include LiFePO4, LiMnPO4, LiFe 0.8 Mn 0.2 One or more of PO4.

16. The battery cell according to any one of claims 1 to 15, characterized in that: At least a portion of the surface of the first lithium-containing phosphate has a first carbon material, and at least a portion of the surface of the second lithium-containing phosphate has a second carbon material, and based on the total mass of the first lithium-containing phosphate, the mass proportion of the first carbon material is 0.05%-0.8%; and / or Based on the total mass of the second lithium-containing phosphate, the mass proportion of the second carbon material is 0.1%-0.4%.

17. A battery device, characterized in that: A battery cell comprising the battery cell according to any one of claims 1 to 16.

18. An electrical equipment, characterized in that: The invention comprises the battery cell according to any one of claims 1 to 16 or the battery device according to claim 17.

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