Battery pack, battery module, electrical device, manufacturing method and manufacturing equipment for battery pack

Abstract

The present application relates to a battery pack, which includes at least a first type of battery cells and a second type of battery cells electrically connected in series. The first type of battery cells and the second type of battery cells are battery cells of different chemical systems. The first type of battery cells includes N first battery cells, and the second type of battery cells includes M second battery cells, where N and M are positive integers. The first battery cell includes a first separator and a first electrolyte, and the second battery cell includes a second separator and a second electrolyte. The kinetic characteristic factor x1 of the first battery cell is: x1 = 1000×(ε1×r1) / (τ1×t1×θ1), and the kinetic characteristic factor x2 of the second battery cell is: x2 = 1000×(ε2×r2) / (τ2×t2×θ2), and x1 and x2 satisfy: 0.01 ≤ x1 / x2 ≤ 160.

Description

Technical Field

[0001] The present application relates to the technical field of energy storage devices, and in particular, to a battery pack, a battery module, an electrical device, a manufacturing method of the battery pack, and a manufacturing apparatus of the battery pack. Background Art

[0002] The secondary battery is a clean and renewable resource, which can be used as a driving energy source or a storage unit in fields such as automobiles and energy storage. With the improvement of the requirements for energy environmental protection, the application of secondary batteries is becoming increasingly popular and widespread. In order to adapt to different environments and application scenarios, the industry has put forward new requirements for the performance of secondary batteries.

[0003] In order to improve the safety of secondary batteries after grouping, a technical solution has been proposed to connect a plurality of single cells with different chemical systems in series and / or in parallel to form a battery pack. However, for single cells with different chemical systems, their kinetic characteristics are significantly different. After connecting single cells with different electrochemical characteristics in series to form a battery pack, due to the short-board effect, the rate performance and power performance of the battery pack are often limited by the single cell with poor kinetic characteristics, resulting in it being difficult for some single cells in the battery pack to fully exert their electrical performance advantages.

[0004] Therefore, how to match the single cells with different chemical systems in the battery pack to ensure that the battery pack has high rate performance and power performance is an urgent technical problem to be solved in the field of secondary batteries. Summary of the Invention

[0005] Regarding the key technology of hybrid series-connected cells, the prior art only stays at the conceptual level, and there is no specific implementation plan for how to match the kinetic characteristics of cells with different chemical systems. In particular, in the prior art, there is no specific implementation plan for the kinetic characteristics of cells and battery packs, the design and matching of the separator film that plays a key role in the kinetic characteristics, etc. Therefore, it is impossible to truly ensure the performance of cells, battery packs, battery modules, and even the entire vehicle level.

[0006] The present application is completed in view of the above problems existing in the prior art, and its purpose is to provide a battery pack, which includes a first type of cell and a second type of cell with different chemical systems, and the first type of cell and the second type of cell are electrically connected at least in series. By adjusting multiple parameters of the separator films of the first type of cell and the second type of cell respectively: comprehensive optimization from the substrate to the coating, from the bulk phase to the surface, from the pore structure to the interfacial contact, etc., to achieve the matching of the kinetic characteristics of the first cell and the second cell, thereby improving the rate performance and power performance of the battery pack.

[0007] A first aspect of the present application provides a battery pack, including at least a first type of battery cell and a second type of battery cell electrically connected in series. The first type of battery cell and the second type of battery cell are battery cells of different chemical systems. The first type of battery cell includes N first battery cells, and the second type of battery cell includes M second battery cells. N and M are positive integers. The first battery cell includes a first separator and a first electrolyte, and the second battery cell includes a second separator and a second electrolyte. The kinetic characteristic factor x1 of the first battery cell is: x1 = 1000×(ε1×r1) / (τ1×t1×θ1), and the kinetic characteristic factor x2 of the second battery cell is: x2 = 1000×(ε2×r2) / (τ2×t2×θ2), and x1 and x2 satisfy: 0.01 ≤ x1 / x2 ≤ 160, where ε1 and ε2 are the porosities of the first separator and the second separator respectively, with the unit of %; r1 and r2 are the average pore diameters of the first separator and the second separator respectively, with the unit of μm; τ1 and τ2 are the tortuosities of the first separator and the second separator respectively; t1 and t2 are the average thicknesses of the first separator and the second separator respectively, with the unit of μm; θ1 is the contact angle between the first separator and the first electrolyte, with the unit of radian; θ2 is the contact angle between the second separator and the second electrolyte, with the unit of radian.

[0008] In any embodiment of the present application, the first battery cell and the second battery cell satisfy: 0.1 ≤ x1 / x2 ≤ 100. Optionally, 0.3 ≤ x1 / x2 ≤ 60. Further optionally, 0.5 ≤ x1 / x2 ≤ 15.

[0009] In any embodiment of the present application, the first battery cell and the second battery cell satisfy: 0.3 ≤ x1 ≤ 95, and / or, 0.2 ≤ x2 ≤ 55. Optionally, 0.5 ≤ x1 ≤ 40, and / or, 0.5 ≤ x2 ≤ 35. Further optionally, 1 ≤ x1 ≤ 20, and / or, 1 ≤ x2 ≤ 20.

[0010] In any embodiment of the present application, the average thickness t1 of the first separator and the average thickness t2 of the second separator satisfy: 4μm ≤ t1 ≤ 20μm, and / or, 8μm ≤ t2 ≤ 16μm. Optionally, 7μm ≤ t1 ≤ 10μm, and / or, 11μm ≤ t2 ≤ 14μm.

[0011] In any embodiment of the present application, the average pore diameter r1 of the first separator and the average pore diameter r2 of the second separator satisfy: 0.01μm ≤ r1 ≤ 3μm, and / or, 0.01μm ≤ r2 ≤ 2μm. Optionally, 0.03μm ≤ r1 ≤ 1.2μm, and / or, 0.03μm ≤ r2 ≤ 1μm.

[0012] In any embodiment of the present application, the porosity ε1 of the first separator and the porosity ε2 of the second separator satisfy: 25% ≤ ε1 ≤ 60%, and / or, 25% ≤ ε2 ≤ 60%. Optionally, 30% ≤ ε1 ≤ 50%, and / or, 30% ≤ ε2 ≤ 50%.

[0013] In any embodiment of the present application, the tortuosity τ1 of the first separator and the tortuosity τ2 of the second separator satisfy: 1.1 ≤ τ1 ≤ 3.9, and / or, 1.1 ≤ τ2 ≤ 3.9. Optionally, 1.3 ≤ τ1 ≤ 3, and / or, 1.3 ≤ τ2 ≤ 3.

[0014] In any embodiment of the present application, the contact angle θ1 between the first separator and the first electrolyte and the contact angle θ2 between the second separator and the second electrolyte satisfy: 0.35 ≤ θ1 ≤ 1.35, and / or, 0.35 ≤ θ2 ≤ 1.35, unit: radian.

[0015] In any embodiment of the present application, in the first battery cell, the first separator includes a first substrate and a first coating provided on at least one surface of the first substrate; in the second battery cell, the second separator includes a second substrate and a second coating provided on at least one surface of the second substrate, and at least one of the following conditions is satisfied:

[0016] (1) The thickness of the first substrate is 3 μm to 19.5 μm; and / or, the thickness of the second substrate is 4 μm to 15 μm;

[0017] (2) The thickness of the first coating on one side is 0.05 μm to 2 μm; and / or, the thickness of the second coating on one side is 0.25 μm to 3.5 μm;

[0018] (3) The first coating contains inorganic particles, and the inorganic particles are selected from one or more of boehmite (γ-AlOOH), alumina (Al2O3), barium sulfate (BaSO4), magnesia (MgO), magnesium hydroxide (Mg(OH)2), silica (SiO2), tin dioxide (SnO2), titanium dioxide (TiO2), calcium oxide (CaO), zinc oxide (ZnO), zirconium oxide (ZrO2), yttrium oxide (Y2O3), nickel oxide (NiO), cerium oxide (CeO2), strontium titanate (SrTiO3), barium titanate (BaTiO3), magnesium fluoride (MgF2); optionally, based on the weight of the first coating, the weight percentage of the inorganic particles is 50% to 99%, optionally 70% to 90%;

[0019] (4) The second coating contains at least organic particles, and the organic particles are selected from one or more of polytetrafluoroethylene, polyvinylidene fluoride, polychlorotrifluoroethylene, polyvinylidene difluoride, modified polyvinylidene fluoride, vinylidene fluoride hexafluoropropylene copolymer, polyethylene, polypropylene, polyacrylonitrile, polyethylene oxide, acrylate, polymethyl methacrylate, polyacrylonitrile, ethyl cellulose, copolymers of different fluoroalkenyl monomer units, copolymers of fluoroalkenyl monomer units and olefinic monomer units, copolymers of fluoroalkenyl monomer units and acrylic monomer units, copolymers of fluoroalkenyl monomer units and acrylate monomer units, and modified compounds of the above homopolymers or copolymers; optionally, based on the weight of the second coating, the weight percentage of the organic particles is 30% to 99%, optionally 50% to 90%.

[0020] In any embodiment of the present application, in the first battery cell, first coatings are provided on both the upper and lower surfaces of the first substrate.

[0021] In any embodiment of the present application, in the second battery cell, second coatings are provided on both the upper and lower surfaces of the second substrate.

[0022] In any embodiment of the present application, the positive electrode active material of the first battery cell includes at least one of the lithium phosphate shown by formula (I) or the lithium manganese-based oxide shown by formula (II).

[0023] LiFe 1-x2-y2 Mn x2 M’ y2 PO4 Formula (I)

[0024] Li 1+x3 Mn e N 2-e O 4-d B d Formula (II)

[0025] Among them, in formula (I), 0 ≤ x2 ≤ 1, 0 ≤ y2 ≤ 0.1, and M’ is selected from one or several of transition metal elements other than Fe and Mn and non-transition metal elements; in formula (II), -0.1 ≤ x3 ≤ 0.2, 0 < e ≤ 2, 0 ≤ d < 1, N is one or more of Ni, Fe, Cr, Ti, Zn, V, Al, Mg, Zr, and Ce, and B is one or more of S, N, F, Cl, Br, and I.

[0026] In any embodiment of the present application, the positive electrode active material of the first battery cell includes LiFePO4, LiMnPO4, LiMn 1-x3 Fe x3 PO4, LiV 1-x3 Fe x3PO4, LiMn2O4, LiMn 1.9 Al 0.1 One or more of O4, where x3 independently satisfies 0 < x3 < 1.

[0027] In any embodiment of the present application, based on the weight of the positive electrode active material of the first battery cell being 100%, the weight percentage of at least one of the lithium-containing phosphate shown in formula (I) or the lithium manganese-based oxide shown in formula (II) is not less than 70%.

[0028] In any embodiment of the present application, the positive electrode active material of the second battery cell includes a lithium transition metal oxide shown in formula (III),

[0029] Li 1+x1 Ni a Co b M 1-a-b O 2-y1 A y1 Formula (III)

[0030] Wherein, -0.1 ≤ x1 ≤ 0.2, 0.3 ≤ a < 0.95, 0 < b < 0.2, 0 < a + b < 1, 0 ≤ y1 < 0.2, M is selected from one or more of Mn, Fe, Cr, Ti, Zn, V, Al, Zr, and Ce, and A is selected from one or more of S, F, Cl, and I; optionally, 0.5 ≤ a < 0.95, 0 < b < 0.15.

[0031] In any embodiment of the present application, based on the weight of the positive electrode active material of the second battery cell being 100%, the weight percentage of the lithium transition metal oxide shown in formula (III) is not less than 70%.

[0032] The second aspect of the present application provides a battery pack, including the battery pack described in the first aspect above.

[0033] The third aspect of the present application provides an electrical device, including the battery pack described in the first aspect above or the battery pack described in the second aspect above, and the battery pack or the battery pack serves as the power source or energy storage unit of the electrical device.

[0034] The fourth aspect of the present application provides a method for manufacturing a battery pack, including the following steps: obtaining a first type of battery cell and a second type of battery cell, where the first type of battery cell and the second type of battery cell are battery cells of different chemical systems. The first type of battery cell includes N first battery cells, and the second type of battery cell includes M second battery cells, where N and M are positive integers. The first battery cell includes a first separator and a first electrolyte, and the second battery cell includes a second separator and a second electrolyte. The kinetic characteristic factor x1 of the first battery cell is: x1 = 1000×(ε1×r1) / (τ1×t1×θ1), and the kinetic characteristic factor x2 of the second battery cell is: x2 = 1000×(ε2×r2) / (τ2×t2×θ2), and x1 and x2 satisfy: 0.01 ≤ x1 / x2 ≤ 160, where ε1 and ε2 are the porosities of the first separator and the second separator respectively, in units of %; r1 and r2 are the average pore diameters of the first separator and the second separator respectively, in units of μm; τ1 and τ2 are the tortuosities of the first separator and the second separator respectively; t1 and t2 are the average thicknesses of the first separator and the second separator respectively, in units of μm; θ1 is the contact angle between the first separator and the first electrolyte, in units of radians; θ2 is the contact angle between the second separator and the second electrolyte, in units of radians; and electrically connecting the first type of battery cell and the second type of battery cell in a series connection to form the battery pack described in the first aspect of the present application.

[0035] The fifth aspect of the present application provides a manufacturing device for a battery pack, including:

[0036] A clamping arm unit for obtaining a first type of battery cell and a second type of battery cell, where the first type of battery cell and the second type of battery cell are battery cells of different chemical systems. The first type of battery cell includes N first battery cells, and the second type of battery cell includes M second battery cells, where N and M are positive integers,

[0037] The first battery cell includes a first separator and a first electrolyte,

[0038] The second battery cell includes a second separator and a second electrolyte,

[0039] The kinetic characteristic factor x1 of the first battery cell is: x1 = 1000×(ε1×r1) / (τ1×t1×θ1),

[0040] The kinetic characteristic factor x2 of the second battery cell is: x2 = 1000×(ε2×r2) / (τ2×t2×θ2),

[0041] and x1 and x2 satisfy: 0.01 ≤ x1 / x2 ≤ 160, where,

[0042] ε1 and ε2 are the porosities of the first separator and the second separator respectively, unit: %;

[0043] r1 and r2 are the average pore diameters of the first separator and the second separator respectively, unit: μm;

[0044] τ1 and τ2 are the tortuosities of the first separator and the second separator respectively;

[0045] t1 and t2 are the average thicknesses of the first separator and the second separator respectively, unit: μm;

[0046] θ1 is the contact angle between the first separator and the first electrolyte, unit: radian;

[0047] θ2 is the contact angle between the second separator and the second electrolyte, unit: radian;

[0048] An assembly unit, which is used to connect at least the first type of battery cell and the second type of battery cell in series to form the battery pack described in the first aspect above;

[0049] And a control unit, which is used to control the clamping arm unit and the assembly unit.

[0050] [Technical effects]

[0051] In this application, the battery pack contains battery cells with different chemical systems. By matching the kinetic factors of the first battery cell and the second battery cell, starting from multiple key technical indicators of the separator, including the substrate, coating, from the bulk phase to the surface, and from the pore structure to the interfacial contact, etc., comprehensive optimization is carried out in many aspects to ensure the matching of the kinetic characteristics of the first battery cell and the second battery cell, thereby improving the rate performance and power performance of the battery pack.

[0052] Since the battery pack and the electrical device in this application include the battery pack, they thus have at least the same technical advantages as the battery pack. Description of the drawings

[0053] Figure 1 It is a schematic diagram showing an example of the battery cell of this application.

[0054] Figure 2 It is shown Figure 1 An exploded view of an example of the battery cell of this application shown in.

[0055] Figure 3 It is a schematic diagram showing an example of the battery pack of this application.

[0056] Figure 4 It is a schematic diagram showing an example of the battery pack of this application.

[0057] Figure 5 is a exploded view showing Figure 4 an example of the battery pack of the present application shown.

[0058] Figure 6 is a schematic diagram showing an example of an electrical device using the battery pack of the present application as a power source.

[0059] Among them, the reference numerals are explained as follows:

[0060] 5, 5a, 5b battery cells

[0061] 51 housing

[0062] 52 electrode assembly

[0063] 53 cover plate

[0064] 4 battery pack

[0065] 1 battery module

[0066] 2 upper box

[0067] 3 lower box Detailed implementation manners

[0068] The "range" disclosed herein is defined in the form of a lower limit and an upper limit. A given range is defined by selecting a lower limit and an upper limit, and the selected lower limit and upper limit define the boundary of a particular range. The range defined in this way can include the end values or not include the end values, and can be combined arbitrarily, 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, ranges of 60 - 110 and 80 - 120 are also contemplated. In addition, if the minimum range values 1 and 2 are listed, and if the maximum range values 3, 4, and 5 are listed, then the following ranges are all contemplated: 1 - 3, 1 - 4, 1 - 5, 2 - 3, 2 - 4, and 2 - 5. In the present application, unless otherwise specified, the numerical range "a - b" represents an abbreviated representation of any real number combination between a and b, where a and b are both real numbers. For example, the numerical range "0 - 5" means that all real numbers between "0 - 5" have been fully listed herein, and "0 - 5" is only an abbreviated representation of these numerical combinations. Additionally, when stating that a certain parameter is an integer ≥2, it is equivalent to disclosing that the parameter is, for example, the integer 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, etc.

[0069] In the present application, if there is no special instruction, all the embodiments and preferred embodiments mentioned herein can be combined with each other to form a new technical solution.

[0070] In this application, unless otherwise specified, all technical features and preferred features mentioned herein can be combined with each other to form a new technical solution.

[0071] In this application, unless otherwise specified, all steps mentioned herein can be carried out in sequence or randomly, but preferably in sequence. For example, the method includes steps (a) and (b), which means that the method can include steps (a) and (b) carried out in sequence, or can also include steps (b) and (a) carried out in sequence. For example, it is mentioned that the method may further include step (c), which means that step (c) can be added to the method in any order. For example, the method can include steps (a), (b) and (c), or can also include steps (a), (c) and (b), or can also include steps (c), (a) and (b), etc.

[0072] In this application, unless otherwise specified, the terms "comprising" and "including" mean open-ended or can also be closed-ended. For example, the terms "comprising" and "including" can mean that other components not listed can also be included or comprised, or can also mean only the components listed are included or comprised.

[0073] In the description herein, it should be noted that unless otherwise stated, "above" and "below" include the corresponding numbers, and in "one or several", the meaning of "several" is two or more.

[0074] In the description herein, unless otherwise specified, the term "or" is inclusive. For example, the phrase "A or B" means "A, B, or both A and B". More specifically, any of the following conditions satisfies the condition "A or B": A is true (or exists) and B is false (or does not exist); A is false (or does not exist) while B is true (or exists); or both A and B are true (or exist).

[0075] [Cell]

[0076] In this application, a "cell" refers to a battery single body that can be independently charged and discharged. A cell includes a positive electrode plate, a negative electrode plate, a separator, an electrolyte, and an outer package for encapsulating the positive electrode plate, negative electrode plate, separator, and electrolyte, etc. This application has no particular restrictions on the type and shape of the cell. It can be a soft-pack cell, or a cylindrical cell, or a square cell, etc. The cells in this application can be lithium-ion cells, potassium-ion cells, sodium-ion cells, lithium-sulfur cells, etc., and lithium-ion cells are particularly preferred. During the charge and discharge process of the battery single body, active ions are embedded and extracted back and forth between the positive electrode plate and the negative electrode plate. The electrolyte plays a role in conducting ions between the positive electrode plate and the negative electrode plate.

[0077] In this application, a "cell" refers to a single battery that can be charged and discharged independently. The components of a cell may include a positive electrode plate, a negative electrode plate, a separator, an electrolyte, and an outer package for encapsulating the positive electrode plate, negative electrode plate, separator, and electrolyte, etc. There are no specific restrictions on the type and shape of the cell in this application. It can be a soft-pack cell, a cylindrical cell, a square cell, or various other types of cells. The cells in this application can be lithium-ion cells, potassium-ion cells, sodium-ion cells, lithium-sulfur cells, etc., and lithium-ion cells are particularly preferred. During the charging and discharging process of the battery, active ions are embedded and extracted back and forth between the positive electrode plate and the negative electrode plate. The electrolyte plays a role in conducting ions between the positive electrode plate and the negative electrode plate.

[0078] In this application, the "chemical system" of a cell is classified according to the components of the positive active material used in the positive electrode plate of the cell, and the elements or substances doped or coated on the positive active material are not limited. For example, cells with lithium iron phosphate (including doped with Mn or V elements) as the positive active material can be defined as lithium iron phosphate chemical system cells. Cells with lithium nickel cobalt manganese oxide (generally abbreviated as NCM) as the positive active material can be defined as NCM chemical system cells. Further, the chemical system of the cell can be further defined based on the relative contents of nickel, cobalt, and manganese elements in the positive active material. For example, cells with LiNi 0.5 Co 0.2 Mn 0.3 O2 (generally abbreviated as NCM523) as the positive active material can be defined as NCM523 chemical system cells, and cells with LiNi 0.6 Co 0.2 Mn 0.2 O2 (generally abbreviated as NCM622) as the positive active material can be defined as NCM622 chemical system cells, and cells with LiNi 0.8 Co 0.1 Mn 0.1 O2 (generally abbreviated as NCM811) as the positive active material can be defined as NCM811 chemical system cells. Cells with lithium nickel cobalt aluminate system (generally called NCA) as the positive electrode material can be defined as NCA chemical system cells. In addition, in this application, hybrid system cells can also be used, such as hybrid system cells including NCM and NCA.

[0079] Next, first, the basic structures of the separator, positive electrode plate, negative electrode plate, and electrolyte of the cells in this application will be described.

[0080] <Separator>

[0081] In some embodiments of the present application, the battery cell includes a separator, which separates the positive electrode sheet and the negative electrode sheet of the battery cell, provides selective permeation or blockage to substances of different types, sizes, and charges in the system. For example, the separator can be electrically insulating to electrons, physically isolate the positive and negative active materials of the battery cell, prevent internal short circuits, and form an electric field in a certain direction. At the same time, ions in the battery can pass through the separator and move between the positive and negative electrodes.

[0082] In some embodiments of the present application, the separator can be prepared by the following method: (1) providing a substrate; (2) providing a coating slurry: the coating slurry includes component materials, a binder, and a solvent, and the component materials include inorganic particles and / or organic particles; (3) coating the coating slurry described in step (2) on at least one side of the substrate described in step (1), forming a coating and drying to obtain the separator.

[0083] <Positive electrode sheet>

[0084] In the battery cell of the present application, the positive electrode sheet includes a positive electrode current collector and a positive electrode film layer provided on at least one surface of the positive electrode current collector and including a positive electrode active material. For example, the positive electrode current collector has two surfaces opposite to each other in its own thickness direction, and the positive electrode film layer is provided on any one or both of the two opposite surfaces of the positive electrode current collector. In the battery cell of the present application, the positive electrode current collector can be a metal foil or a composite current collector. For example, the metal foil can be aluminum foil, and the composite current collector can include a polymer material base layer and a metal layer formed on at least one surface of the polymer material base layer. The composite current collector can be formed by forming a metal material (such as 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, and their copolymers, etc.).

[0085] In the battery cell of the present application, the positive electrode active material can be a positive electrode active material for battery cells well-known in the art. For example, the positive electrode active material can include one or more of the following: lithium phosphate with an olivine structure, lithium transition metal oxides, and their respective modified compounds. However, the present application is not limited to these materials, and other traditional materials that can be used as positive electrode active materials for battery cells can also be used. These positive electrode active materials can be used alone or in combination of two or more. Among them, examples of lithium transition metal oxides can include but are not limited to lithium cobalt oxide (such as LiCoO2), lithium nickel oxide (such as LiNiO2), lithium manganese oxide (such as LiMnO2, LiMn2O4), lithium nickel cobalt oxide, lithium manganese cobalt oxide, lithium nickel manganese oxide, lithium nickel cobalt manganese oxide (such as LiNi 1 / 3 Co 1 / 3 Mn1 / 3 O2 (NCM333), LiNi 0.5 Co 0.2 Mn 0.3 O2 (NCM523), LiNi 0.5 Co 0.25 Mn 0.25 O2 (NCM211), LiNi 0.6 Co 0.2 Mn 0.2 O2 (NCM622), LiNi 0.8 Co 0.1 Mn 0.1 O2 (NCM811)), lithium nickel cobalt aluminum oxide (such as LiNi 0.85 Co 0.15 Al 0.05 O2) and one or more of its modified compounds, etc. Examples of the lithium-containing phosphate with olivine structure may include, but are not limited to, lithium iron phosphate (such as LiFePO4 (LFP)), composite material of lithium iron phosphate and carbon, lithium manganese phosphate (such as LiMnPO4), composite material of lithium manganese phosphate and carbon, lithium manganese iron phosphate, and composite material of lithium manganese iron phosphate and carbon.

[0086] In some embodiments, the positive electrode film layer may optionally further include a binder. Non-limiting examples of the binder that can be used for the positive electrode film layer may include one or more of the following: polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), vinylidene fluoride-tetrafluoroethylene-propylene terpolymer, vinylidene fluoride-hexafluoropropylene-tetrafluoroethylene terpolymer, tetrafluoroethylene-hexafluoropropylene copolymer, and fluorinated acrylate resin.

[0087] In some embodiments, the positive electrode film layer may optionally further contain a conductive agent. Examples of the conductive agent for the positive electrode film layer may include one or more of superconducting carbon, acetylene black, carbon black, Ketjen black, carbon dots, carbon nanotubes, graphene, and carbon nanofibers.

[0088] In some embodiments of the present application, the positive electrode can be prepared by the following method: dispersing the above-mentioned components for preparing the positive electrode, such as the positive electrode active material, conductive agent, binder, and any other components, in a solvent (such as N-methylpyrrolidone) to form a uniform positive electrode slurry; coating the positive electrode slurry on the positive electrode current collector, and after processes such as drying and cold pressing, the positive electrode plate can be obtained.

[0089] <Negative electrode plate>

[0090] The battery cell of the present application includes a negative electrode plate, the negative electrode plate includes a negative electrode current collector and a negative electrode film layer provided on at least one surface of the negative electrode current collector, and the negative electrode film layer contains a negative electrode active material.

[0091] In some embodiments of the present application, the negative electrode active material in the negative electrode film layer may be a negative electrode active material commonly used in the art. For example, it may be one or more of natural graphite, artificial graphite, soft carbon, hard carbon, silicon-based materials, tin-based materials, and lithium titanate. The silicon-based materials may be selected from one or more of elemental silicon, silicon oxides, and silicon-carbon composites. The tin-based materials may be selected from one or more of elemental tin, tin oxides, and tin alloys.

[0092] In the battery cell of the present application, in addition to the negative electrode active material, the negative electrode film may further include an optional binder, an optional conductive agent, and other optional additives. The negative electrode film of the present application is usually formed by coating and drying a negative electrode slurry. The negative electrode slurry is usually formed by dispersing the negative electrode active material, the optional conductive agent, the binder, etc. in a solvent and stirring evenly. The above solvent may be N-methylpyrrolidone (NMP) or deionized water.

[0093] As an example, the conductive agent may include one or more of superconducting carbon, carbon black (such as acetylene black, Ketjen black), carbon dots, carbon nanotubes, graphene, and carbon nanofibers.

[0094] As an example, the binder may include one or more of styrene-butadiene rubber (SBR), water-soluble unsaturated resin SR-1B, polyacrylic acid (PAA), sodium polyacrylate (PAAS), polyacrylamide (PAM), polyvinyl alcohol (PVA), sodium alginate (SA), and carboxymethyl chitosan (CMCS). As an example, the binder may include one or more of styrene-butadiene rubber (SBR), polyvinyl alcohol (PVA), sodium alginate (SA), polymethacrylic acid (PMAA), and carboxymethyl chitosan (CMCS). Other optional additives are, for example, thickeners (such as sodium carboxymethyl cellulose CMC-Na), PTC thermistor materials, etc.

[0095] In addition, in the battery cell of the present application, the negative electrode plate does not exclude other additional functional layers in addition to the negative electrode film layer. For example, in some embodiments, the negative electrode plate of the present application may further include a conductive bottom coating (such as composed of a conductive agent and a binder) disposed on the surface of the negative electrode current collector and sandwiched between the negative electrode current collector and the first negative electrode film layer. In some other embodiments, the negative electrode plate of the present application may further include a covering protective layer covering the surface of the second negative electrode film layer.

[0096] In the battery cell of the present application, the negative current collector may be a metal foil or a composite current collector. For example, the metal foil may be a copper foil, a silver foil, an iron foil, or a foil made of an alloy of the above metals. The composite current collector may include a polymer material substrate and a metal layer formed on at least one surface of the polymer material substrate, and may be formed by forming a metal material (such as copper, copper alloy, nickel, nickel alloy, titanium, titanium alloy, silver, and silver alloy, etc.) on the polymer material substrate (such as a substrate made of materials such as polypropylene (PP), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polystyrene (PS), polyethylene (PE), and their copolymers, etc.).

[0097] <Electrolyte>

[0098] The electrolyte plays a role in conducting ions between the positive electrode plate and the negative electrode plate. The electrolyte includes an electrolyte salt and a solvent. In some embodiments, the electrolyte salt may be selected from one or more of lithium hexafluorophosphate (LiPF6), lithium tetrafluoroborate (LiBF4), lithium perchlorate (LiClO4), lithium hexafluoroarsenate (LiAsF6), lithium bis(fluorosulfonyl)imide (LiFSI), lithium bis(trifluoromethanesulfonyl)imide (LiTFSI), lithium trifluoromethanesulfonate (LiTFS), lithium difluoro(oxalato)borate (LiDFOB), lithium bis(oxalato)borate (LiBOB), lithium difluorophosphate (LiPO2F2), lithium difluoro(dioxalato)phosphate (LiDFOP), and lithium tetrafluoro(oxalato)phosphate (LiTFOP).

[0099] In some embodiments of the present application, the solvent may be selected from one or more of the following: ethylene carbonate (EC), propylene carbonate (PC), ethyl methyl carbonate (EMC), diethyl carbonate (DEC), dimethyl carbonate (DMC), dipropyl carbonate (DPC), methyl propyl carbonate (MPC), ethyl propyl carbonate (EPC), butylene carbonate (BC), fluoroethylene carbonate (FEC), methyl formate (MF), methyl acetate (MA), ethyl acetate (EA), propyl acetate (PA), methyl propionate (MP), ethyl propionate (EP), propyl propionate (PP), methyl butyrate (MB), ethyl butyrate (EB), 1,4-butyrolactone (GBL), sulfolane (SF), dimethyl sulfone (MSM), ethyl methyl sulfone (EMS), and diethyl sulfone (ESE).

[0100] In some embodiments of the present application, based on the total weight of the electrolyte, the content of the solvent is 60-99% by weight, such as 65-95% by weight, or 70-90% by weight, or 75-89% by weight, or 80-85% by weight. In some embodiments of the present application, based on the total weight of the electrolyte, the content of the electrolyte is 1-40% by weight, such as 5-35% by weight, or 10-30% by weight, or 11-25% by weight, or 15-20% by weight.

[0101] In some embodiments of the present application, the electrolyte may optionally further contain additives. For example, the additives may include one or more of the following: negative electrode film-forming additives, positive electrode film-forming additives, and may also include additives that can improve certain battery performances, such as additives for improving the overcharge performance of the battery, additives for improving the high-temperature performance of the battery, additives for improving the low-temperature performance of the battery, etc.

[0102] In some embodiments of the present application, the above-mentioned positive electrode sheet, negative electrode sheet, and separator can be made into an electrode assembly / naked battery cell through a winding process or a stacking process.

[0103] In some embodiments of the present application, the battery cell further includes an outer package, which can be used to encapsulate the above-mentioned electrode assembly and electrolyte. In some embodiments, the outer package of the battery cell can be a hard shell, such as a hard plastic shell, an aluminum shell, a steel shell, etc. In some other embodiments, the outer package of the battery cell can be a soft package, such as a pouch soft package. The material of the soft package can be plastic, such as one or several of polypropylene (PP), polybutylene terephthalate (PBT), polybutylene succinate (PBS), etc.

[0104] Figure 1 It is a schematic diagram showing an example of the battery cell 5 of the present application. Figure 2 It shows Figure 1 An exploded view of an example of the battery cell 5 of the present application shown.

[0105] The outer package may include a housing 51 and a cover plate 53. The housing 51 may include a bottom plate and side plates connected to the bottom plate. The bottom plate and the side plates enclose to form a receiving cavity. The housing 51 has an opening communicating with the receiving cavity, and the cover plate 53 can be covered on the opening to close the receiving cavity. The positive electrode sheet, negative electrode sheet, and separator can form an electrode assembly 52 through a winding process or a stacking process, and the electrode assembly is encapsulated in the receiving cavity, and the electrolyte infiltrates into the electrode assembly 52. The number of the electrode assemblies 52 contained in the battery cell 5 can be one or more.

[0106] [Battery pack]

[0107] In this application, a "battery pack" is formed by electrically connecting a certain number of battery cells together and placing them in a frame to protect the battery cells from external impacts, heat, vibrations, etc. The shape of the battery cells in this application can be cylindrical, square, or any other shape.

[0108] In this application, several battery cells can be assembled together to form a battery pack. The battery pack contains two or more battery cells, and the specific number depends on the application of the battery pack and the parameters of a single battery pack.

[0109] Figure 3 is a schematic diagram showing an example of the battery pack of this application. Refer to Figure 3 , in the battery pack 4, multiple battery cells 5a, 5b can be arranged in sequence along the length direction of the battery pack 4 (where 5a can be the first battery cell and 5b can be the second battery cell). Of course, they can also be arranged in any other way. Further, the multiple battery cells 5a, 5b can be fixed by fasteners. Optionally, the battery pack 4 can further include a housing with an accommodation space, and the multiple groups 5a, 5b are accommodated in this accommodation space.

[0110] <Design of the kinetic characteristic factors of the first battery cell and the second battery cell>

[0111] In some embodiments of this application, the battery pack includes at least a first type of battery cell and a second type of battery cell electrically connected in series. The first type of battery cell and the second type of battery cell are battery cells of different chemical systems. The first type of battery cell includes N first battery cells, and the second type of battery cell includes M second battery cells. N and M are positive integers. The first battery cell includes a first separator and a first electrolyte, and the second battery cell includes a second separator and a second electrolyte. The kinetic characteristic factor x1 of the first battery cell is: x1 = 1000×(ε1×r1) / (τ1×t1×θ1), and the kinetic characteristic factor x2 of the second battery cell is: x2 = 1000×(ε2×r2) / (τ2×t2×θ2), and x1 and x2 satisfy: 0.01 ≤ x1 / x2 ≤ 160, where ε1 and ε2 are the porosities of the first separator and the second separator respectively, unit: %; r1 and r2 are the average pore diameters of the first separator and the second separator respectively, unit: μm; τ1 and τ2 are the tortuosities of the first separator and the second separator respectively; t1 and t2 are the average thicknesses of the first separator and the second separator respectively, unit: μm; θ1 is the contact angle between the first separator and the first electrolyte, unit: radian; θ2 is the contact angle between the second separator and the second electrolyte, unit: radian.

[0112] In order to more accurately assemble battery cells of different chemical systems to form a battery pack with large capacity and high kinetic characteristics, the inventors of the present application use the kinetic characteristic factor of the battery cell to characterize the migration ability of active ions in the battery cell during the charge and discharge process. By matching the kinetic factors of battery cells of different chemical systems, the short-board effect after grouping different types of battery cells is overcome, and the overall rate performance and power performance of the battery pack are improved. In the present application, the kinetic factor of the battery cell is obtained by comprehensively considering five key parameters: the thickness, pore size, porosity, tortuosity of the separator, and the wettability of the electrolyte in the separator. The inventors of the present application have discovered through painstaking research that the kinetic performance of battery cells of different chemical systems varies greatly. If their kinetic performance is not adaptively adjusted, the rate performance and power performance of the series-connected battery pack of hybrid battery cells will be greatly affected. Therefore, it is necessary to make the ratio of the kinetic characteristic factors of the separators of the two types of battery cells fall within a certain range.

[0113] In some embodiments of the present application, the first battery cell and the second battery cell further satisfy: 0.1 ≤ x1 / x2 ≤ 100. Optionally, 0.3 ≤ x1 / x2 ≤ 60. Further optionally, 0.5 ≤ x1 / x2 ≤ 15. Specifically, x1 / x2 can be 0.01, 0.05, 0.1, 0.15, 0.2, 0.25, 0.3, 0.35, 0.4, 0.5, 0.6, 0.7, 0.8, 0.9, 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20, 21, 22, 23, 24, 25, 26, 27, 28, 29, 30, 31, 32, 33, 34, 35, 36, 37, 38, 39, 40, 41, 42, 43, 44, 45, 46, 47, 48, 49, 50, 51, 52, 53, 54, 55, 56, 57, 58, 59, 60, 61, 62, 63, 64, 65, 66, 67, 68, 69, 70, 71, 72, 73, 74, 75, 76, 77, 78, 79, 80, 81, 82, 83, 84, 85, 86, 87, 88, 89, 90, 91, 92, 93, 94, 95, 96, 97, 98, 99, 100, 101, 102, 103, 104, 105, 106, 107, 108, 109, 110, 111, 112, 113, 114, 115, 116, 117, 118, 119, 120, 121, 122, 123, 124, 125, 126, 127, 128, 129, 130, 131, 132, 133, 134, 135, 136, 137, 138, 139, 140, 141, 142, 143, 144, 145, 146, 147, 148, 149, 150, 151, 152, 153, 154, 155, 156, 157, 158, 159, 160, or its value is within the range obtained by combining any two of the above values. In the present application, when the ratio of the kinetic factors of the first battery cell and the second battery cell is within the above range, the DC impedance of the battery pack can be further reduced, which helps to overcome the short-board effect of the cell assembly of different chemical systems, improve the consistency of the kinetic characteristics of multiple types of cells in the battery pack, and improve the rate performance and power performance of the battery pack.

[0114] In some embodiments of the present application, the kinetic factor x1 of the first battery cell satisfies: 0.3 ≤ x1 ≤ 95. Optionally, 0.5 ≤ x1 ≤ 40. Further optionally, 1 ≤ x1 ≤ 20. Specifically, x1 can be 0.3, 0.35, 0.4, 0.5, 0.6, 0.7, 0.8, 0.9, 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20, 21, 22, 23, 24, 25, 26, 27, 28, 29, 30, 31, 32, 33, 34, 35, 36, 37, 38, 39, 40, 41, 42, 43, 44, 45, 46, 47, 48, 49, 50, 51, 52, 53, 54, 55, 56, 57, 58, 59, 60, 61, 62, 63, 64, 65, 66, 67, 68, 69, 70, 71, 72, 73, 74, 75, 76, 77, 78, 79, 80, 81, 82, 83, 84, 85, 86, 87, 88, 89, 90, 91, 92, 93, 94, 95, or its value is within the range obtained by combining any two of the above values.

[0115] In some embodiments of the present application, the kinetic factor x2 of the second battery cell satisfies: 0.2 ≤ x2 ≤ 55. Optionally, 0.5 ≤ x2 ≤ 35. Further optionally, 1 ≤ x2 ≤ 20. Specifically, x2 can be 0.2, 0.25, 0.3, 0.35, 0.4, 0.5, 0.6, 0.7, 0.8, 0.9, 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20, 21, 22, 23, 24, 25, 26, 27, 28, 29, 30, 31, 32, 33, 34, 35, 36, 37, 38, 39, 40, 41, 42, 43, 44, 45, 46, 47, 48, 49, 50, 51, 52, 53, 54, 55, or its value is within the range obtained by combining any two of the above values.

[0116] In some embodiments of the present application, the average thickness t1 of the first separator and the average thickness t2 of the second separator satisfy: 4μm ≤ t1 ≤ 20μm, and / or, 8μm ≤ t2 ≤ 16μm. Optionally, 7μm ≤ t1 ≤ 10μm, and / or, 11μm ≤ t2 ≤ 14μm. Specifically, the average thickness t1 of the first separator can be 4μm, 5μm, 6μm, 7μm, 8μm, 9μm, 10μm, 11μm, 12μm, 13μm, 14μm, 15μm, 16μm, 17μm, 18μm, 19μm, 20μm, or its value is within the range obtained by combining any two of the above values. The average thickness t2 of the second separator can be 8μm, 8.5μm, 9μm, 9.5μm, 10μm, 10.5μm, 11μm, 11.5μm, 12μm, 12.5μm, 13μm, 13.5μm, 14μm, 14.5μm, 15μm, 15.5μm, 16μm, or its value is within the range obtained by combining any two of the above values. In the present application, when the thicknesses of the separators of the first battery cell and the second battery cell are within the above ranges, while ensuring a relatively high volumetric energy density of the battery pack, due to the relatively high mechanical strength of the separators in their respective battery cells, they are not easily affected by foreign objects, the unevenness of the electrode surface, or the interfacial side reaction products, thereby further improving the safety performance of the battery pack.

[0117] In the present application, the thicknesses of the first separator and the second separator can be measured by methods well-known in the art. As an example, a X-ray surface density measuring instrument of the model Dacheng DC PRECISION can be used for measurement, and the non-contact measurement of the material thickness is realized by using the absorption and backscattering effects of X-rays penetrating the substance. Optionally, referring to the national standard GB / T36363-2018, the thickness of the separator can be measured by the contact probe method.

[0118] As a separator material for lithium-ion batteries, it has a microporous structure by itself, allowing the absorption of electrolyte for the transmission of free lithium ions between the positive and negative electrodes. Among them, when the micropores are evenly distributed on the large surface of the entire separator material, the consistent electrode / electrolyte interface properties and uniform current density in the battery can be ensured. The size and uniformity of the pore size have a direct impact on the battery performance: when the pore size is within an appropriate range, on the one hand, the battery impedance can be reduced, and on the other hand, it can ensure that the positive and negative electrodes cannot be in direct contact or are easily pierced by lithium dendrites to cause a short circuit.

[0119] In some embodiments of the present application, the average pore size r1 of the first separator membrane and the average pore size r2 of the second separator membrane satisfy: 0.01 μm ≤ r1 ≤ 3 μm, and / or, 0.01 μm ≤ r2 ≤ 2 μm. Optionally, 0.03 μm ≤ r1 ≤ 1.2 μm, and / or, 0.03 μm ≤ r2 ≤ 1 μm. Specifically, the average pore size r1 of the first separator membrane may be 0.01 μm, 0.10 μm, 0.20 μm, 0.30 μm, 0.40 μm, 0.50 μm, 0.6 μm, 0.7 μm, 0.8 μm, 0.9 μm, 1.0 μm, 1.1 μm, 1.2 μm, 1.3 μm, 1.4 μm, 1.5 μm, 1.6 μm, 1.7 μm, 1.8 μm, 1.9 μm, 2.0 μm, 2.1 μm, 2.2 μm, 2.3 μm, 2.4 μm, 2.5 μm, 2.6 μm, 2.7 μm, 2.8 μm, 2.9 μm, 3.0 μm, or a value within the range obtained by combining any two of the above values. The average pore size r2 of the second separator membrane may be 0.01 μm, 0.10 μm, 0.20 μm, 0.30 μm, 0.40 μm, 0.50 μm, 0.6 μm, 0.7 μm, 0.8 μm, 0.9 μm, 1.0 μm, 1.1 μm, 1.2 μm, 1.3 μm, 1.4 μm, 1.5 μm, 1.6 μm, 1.7 μm, 1.8 μm, 1.9 μm, 2.0 μm, or a value within the range obtained by combining any two of the above values.

[0120] In the present application, the pore size of the separator membrane can be measured by methods well known in the art. As an example, it can be measured using a TriStar II 3020 type automatic sorptometer. The specific test method can refer to the standards: GB / T 19587-2017 "Determination of Specific Surface Area of Solid Materials by Gas Adsorption BET Method" and GB / T 21650.2-2008 "Determination of Pore Size Distribution and Porosity of Solid Materials by Mercury Intrusion Method and Gas Adsorption Method".

[0121] In some embodiments of the present application, the porosity ε1 of the first separator and the porosity ε2 of the second separator satisfy: 25% ≤ ε1 ≤ 60%, and / or, 25% ≤ ε2 ≤ 60%. Optionally, 30% ≤ ε1 ≤ 50%, and / or, 30% ≤ ε2 ≤ 50%. Specifically, the porosity ε1 of the first separator and the porosity ε2 of the second separator can independently be 25%, 25.5%, 26%, 26.5%, 27%, 27.5%, 28%, 28.5%, 29%, 29.5%, 30%, 30.5%, 31%, 31.5%, 32%, 32.5%, 33%, 33.5%, 34%, 34.5%, 35%, 35.5%, 36%, 36.5%, 37%, 37.5%, 38%, 38.5%, 39%, 39.5%, 40%, 40.5%, 41%, 41.5%, 42%, 42.5%, 43%, 43.5%, 44%, 44.5%, 45%, 45.5%, 46%, 46.5%, 47%, 47.5%, 48%, 48.5%, 49%, 49.5%, 50%, 50.5%, 51%, 51.5%, 52%, 52.5%, 53%, 53.5%, 54%, 54.5%, 55%, 55.5%, 56%, 56.6%, 57%, 57.5%, 58%, 58.5%, 59%, 59.5%, 60%, or a value within the range obtained by combining any two of the above values. The porosity of the separator is very important for its permeability and the electrolyte accommodation capacity. It can be defined as: the ratio of the volume of pores to the volume occupied by the separator, that is, the volume percentage of pores in the volume of the unit membrane.

[0122] In the present application, the porosity of the separator can be measured by methods well-known in the art. As an example, it can be measured using a AccuPyc II 1340 type true density tester. The specific test method is to respectively test the total volume V1 and the true volume V2 of the separator, and according to the formula: porosity = (V1 - V2) / V1 × 100%, the porosity of the separator can be obtained.

[0123] In some embodiments of the present application, the tortuosity τ1 of the first separator membrane and the tortuosity τ2 of the second separator membrane satisfy: 1.1 ≤ τ1 ≤ 3.9, and / or, 1.1 ≤ τ2 ≤ 3.9. Optionally, 1.3 ≤ τ1 ≤ 3, and / or, 1.3 ≤ τ2 ≤ 3. Specifically, the tortuosity τ1 of the first separator membrane and the tortuosity τ2 of the second separator membrane can each independently be 1.1, 1.2, 1.3, 1.4, 1.5, 1.6, 1.7, 1.8, 1.9, 2.0, 2.1, 2.2, 2.3, 2.4, 2.5, 2.6, 2.7, 2.8, 2.9, 3.0, 3.1, 3.2, 3.3, 3.4, 3.5, 3.6, 3.7, 3.8, 3.9, or a value within the range obtained by combining any two of the above values. The tortuosity of the separator membrane is an important parameter describing the tortuous degree of the internal pore channels of the separator membrane. The tortuosity is defined as the ratio of the actual length of the pore channel to the apparent length (macroscopic distance) passing through the percolation medium, that is, when the percolating fluid particles cross a unit distance of the medium, the true length of the movement trajectory of the particles in the pore channels.

[0124] In the present application, the tortuosity of the separator membrane can be measured by a test method well-known in the art. As an example, the tortuosity can be calculated by the following formula: tortuosity where N m represents the McMullin number, and ε is the porosity of the separator membrane. Among them, the McMullin number N m is the ratio of the resistivity of the separator membrane when immersed in the electrolyte to the resistivity of the electrolyte. The resistivity of the separator membrane immersed in the electrolyte and the resistivity of the electrolyte can be obtained by the following methods.

[0125] Measurement of separator membrane resistivity: An electrochemical workstation can be used, such as Shanghai Chenhua CHI600E, Solartron or Princeton. According to the resistance law formula Rs = ρ × l0 / (S × n), the Rs of different separator membrane layers (n) is measured using the EIS method of a confined symmetric cell. A graph of Rs and n is plotted to obtain the slope k = (ρ × l0) / S, and the resistivity ρ = (k × S) / l0 is obtained under the conditions of known effective area S and separator membrane thickness l0.

[0126] Measurement of electrolyte resistivity: An electrical conductivity meter (such as Leici DDSJ-318) is used to measure the resistance R of the electrolyte at 25 °C and an AC impedance of 1 kHz, and the resistivity of the electrolyte is calculated using the formula ρ = R × S / l based on the length 1 and cross-sectional area S of the measured electrolyte.

[0127] The inventors of the present application have found through painstaking research that the pore size, porosity, and tortuosity of the separator affect the dynamic performance, self-discharge rate, and lifespan of the battery cell. The larger the pore size, the higher the porosity, and the smaller the tortuosity, the more conducive it is to the transmission of the electrolyte, the higher the conductivity, the higher the dynamic performance of the battery cell, and thus the better the charge-discharge rate, low-temperature performance, and power performance. However, if the pore size is too large, the porosity is too high, and the tortuosity is too small, it will easily lead to a large self-discharge rate of the battery cell, and in severe cases, it will directly cause a short circuit. In addition, the smaller the pore size, the lower the porosity, and the larger the tortuosity of the separator, the lower the self-discharge rate, but the dynamic performance of the battery cell will deteriorate. At the same time, the small-pore-size separator is prone to being blocked by the accumulation of interfacial side reaction products during long-term use, which will increase the impedance of the battery cell and thus reduce the service life.

[0128] Therefore, in the present application, by designing the pore size, porosity, and tortuosity of the separators of the first type of battery cell and the second type of battery cell as described above, it is possible to improve the charge-discharge rate, low-temperature performance, and power performance of the battery cell and the battery pack while reducing the self-discharge rate of the battery cell and the battery pack, and improving the safety performance and service life.

[0129] In some embodiments of the present application, the contact angle θ1 between the first separator and the first electrolyte and the contact angle θ2 between the second separator and the second electrolyte satisfy: 0.35 ≤ θ1 ≤ 1.35, and / or, 0.35 ≤ θ2 ≤ 1.35, unit: radian. The inventors of the present application have found through painstaking research that the contact angle between the separator and the electrolyte reflects the wettability of the electrolyte in the separator and the diffusion rate of the electrolyte in the separator; the smaller the contact angle, the faster the rate of the electrolyte from the surface of the contact separator to the inside of the separator, the better the dynamic performance of the battery cell, and the better the charge-discharge rate, power performance, and low-temperature performance; the larger the contact angle, the slower the rate of the electrolyte from the surface of the contact separator to the inside of the separator, the worse the dynamic performance of the battery cell, and the worse the charge-discharge rate, power performance, and low-temperature performance.

[0130] Therefore, in the present application, by designing the contact angles between the separators of the first type of battery cell and the second type of battery cell and the electrolyte as described above, it is possible to improve the charge-discharge rate, low-temperature performance, and power performance of the battery cell and the battery pack.

[0131] In this application, the contact angle between the separator and the electrolyte reflects the wettability of the electrolyte in the separator and the diffusion rate of the electrolyte within the separator. The contact angle between the separator and the electrolyte can be measured using testing methods well-known in the art. By way of example, contact angle testing can be performed using methods known in the art. An exemplary testing method is as follows: Place the test sample on a water contact angle tester (model SL200KB from Konor Industries, USA), and drop 10 μL of the electrolyte at a position 1 cm above the positive electrode film layer. Take pictures of the water droplet landing on the surface of the sample using an optical microscope and a high-speed camera. The testing conditions are 25°C and normal pressure (0.1 MPa). Through software analysis, measure the angle between the tangent to the surface of the contact point of the water droplet with the sample and the horizontal plane, which is the contact angle, with the unit of radian.

[0132] In some embodiments of this application, in the first battery cell, the first separator includes a first substrate and a first coating provided on at least one surface of the first substrate; in the second battery cell, the second separator includes a second substrate and a second coating provided on at least one surface of the second substrate. Among them, the first substrate and the second substrate are porous structures. The first substrate and the second substrate can each independently be a polymer film formed from one or more polymers selected from the following: polyolefins (such as polyethylene and polypropylene), polyesters (such as polyethylene terephthalate and polybutylene terephthalate), polyacetals, polyamides, polyimides, polycarbonates, polyether ether ketones, polyaryl ether ketones, polyetherimides, polyamideimides, polybenzimidazoles, polyether sulfones, polyphenylene ethers, cycloolefin copolymers, polyphenylene sulfides, polyethylene naphthalate, glass fibers, Teflon, and polytetrafluoroethylene, or copolymers or mixtures of two or more of them, but not limited thereto.

[0133] In some embodiments of this application, optionally, the first substrate and the second substrate can be polyolefin-based substrates of polyolefins. Since polyolefin-based substrates have improved shut-off functions, it helps to improve battery safety. Further optionally, the polyolefin-based substrates can be selected from at least one of a polyethylene single-layer film, a polypropylene single-layer film, a polyethylene / polypropylene bilayer film, a polypropylene / polyethylene / polypropylene trilayer film, and a polyethylene / polypropylene / polyethylene trilayer film. In addition, in addition to including olefin resins, the first substrate and the second substrate can also include non-olefin resins, or can include copolymers of olefins and non-olefin monomers.

[0134] In some embodiments of the present application, the thickness of the first substrate is 3 μm to 15 μm; and / or, the thickness of the second substrate is 4 μm to 13 μm. In the present application, when the thicknesses of the first substrate and the second substrate are within the above ranges, on the one hand, short circuit between the positive and negative electrode plates can be effectively avoided, and at the same time, the volume energy density of the first battery cell and the second battery cell can be ensured to be relatively high, thereby improving the safety performance and volume energy density of the battery pack.

[0135] In some embodiments of the present application, the first coating contains inorganic particles, and the inorganic particles are selected from one or more of boehmite (γ-AlOOH), alumina (Al2O3), barium sulfate (BaSO4), magnesium oxide (MgO), magnesium hydroxide (Mg(OH)2), silicon dioxide (SiO2), tin dioxide (SnO2), titanium dioxide (TiO2), calcium oxide (CaO), zinc oxide (ZnO), zirconium oxide (ZrO2), yttrium oxide (Y2O3), nickel oxide (NiO), cerium oxide (CeO2), strontium titanate (SrTiO3), barium titanate (BaTiO3), and magnesium fluoride (MgF2). In the present application, when the first coating on the surface of the separator of the first battery cell contains the above inorganic particles, the thermal stability of the separator of the first battery cell can be improved, the thermal shrinkage rate of the separator can be reduced at a relatively high temperature, and internal short circuit caused by the shrinkage of the separator can be effectively improved, greatly enhancing the use safety of the first battery cell. At the same time, since the coated separator has good electrolyte wettability and good oxidation resistance, the kinetics and service life of the battery cell can be improved. Moreover, when the first coating contains the above inorganic particles, the resistivity of the coating is relatively high, and the self-discharge of the first battery cell can also be improved.

[0136] In some embodiments of the present application, based on the weight of the first coating, the weight percentage of the inorganic particles is 50% to 99%, optionally 70% to 90%. In the present application, when the content of the inorganic particles in the first coating on the surface of the separator of the first battery cell is within the above range, the uniformity and denseness of the coating can be ensured on the premise of ensuring the thermal stability and high resistivity of the separator of the first battery cell, and the characteristics of better pore size, porosity and tortuosity can be satisfied.

[0137] In some embodiments of the present application, the second coating contains organic particles selected from one or more of polytetrafluoroethylene, polyvinylidene fluoride, polytrifluorochloroethylene, polyvinylidene difluoride, modified polyvinylidene fluoride, vinylidene fluoride - hexafluoropropylene copolymer, polyethylene, polypropylene, polyacrylonitrile, polyethylene oxide, acrylate, polymethyl methacrylate, polyacrylonitrile, ethyl cellulose, copolymers of different fluoroalkenyl monomer units, copolymers of fluoroalkenyl monomer units and olefinic monomer units, copolymers of fluoroalkenyl monomer units and acrylic monomer units, copolymers of fluoroalkenyl monomer units and acrylate monomer units, and modified compounds of the above homopolymers or copolymers. In the present application, the surface of the separator of the second battery cell is a coating containing organic particles, which can increase the adhesion between the electrode sheets. Strong adhesion can improve the hardness of the bare battery cell, prevent dislocation or deformation, and at the same time, it is also beneficial to improve the flatness and consistency of the interface during the manufacturing and use of the second battery cell, and prevent phenomena such as electrode sheet wrinkling or lithium plating.

[0138] In some embodiments of the present application, the second coating may further contain inorganic particles selected from one or more of boehmite (γ - AlOOH), alumina (Al2O3), barium sulfate (BaSO4), magnesium oxide (MgO), magnesium hydroxide (Mg(OH)2), silicon dioxide (SiO2), tin dioxide (SnO2), titanium dioxide (TiO2), calcium oxide (CaO), zinc oxide (ZnO), zirconium oxide (ZrO2), yttrium oxide (Y2O3), nickel oxide (NiO), cerium oxide (CeO2), strontium titanate (SrTiO3), barium titanate (BaTiO3), magnesium fluoride (MgF2).

[0139] In some embodiments of the present application, based on the weight of the second coating, the weight percentage of the organic particles is 30% - 99%, optionally 50% - 90%. In the present application, when the content of the organic particles in the second coating on the surface of the separator of the second battery cell is within the above range, it can not only ensure an effective adhesion effect, but also will not excessively increase the weight and / or volume, and does not affect the energy density of the battery cell.

[0140] In some embodiments of the present application, the thickness of the single - side first coating is 0.05μm - 2μm; and / or, the thickness of the single - side second coating is 0.25μm - 3.5μm. In the present application, when the thickness of the single - side coating on the surface of the separator in the first battery cell and the second battery cell is within the above range, it can improve the volume energy density of the first battery cell with higher chemical stability, and at the same time improve the safety performance of the second battery cell with higher volume energy density, thereby enhancing the comprehensive volume energy density and safety of the module.

[0141] In some embodiments of the present application, in the first battery cell, first coatings are provided on both the upper and lower surfaces of the first substrate.

[0142] In some embodiments of the present application, in the second battery cell, second coatings are provided on both the upper and lower surfaces of the second substrate.

[0143] In some embodiments of the present application, the positive electrode active material of the first battery cell includes at least one of a lithium-containing phosphate represented by formula (I) or a lithium manganese-based oxide represented by formula (II),

[0144] LiFe 1-x2-y2 Mn x2 M’ y2 PO4 Formula (I)

[0145] Li 1+x3 Mn e N 2-e O 4-d B d Formula (II)

[0146] Wherein, in formula (I), 0 ≤ x2 ≤ 1, 0 ≤ y2 ≤ 0.1, and M’ is selected from one or more of transition metal elements other than Fe and Mn and non-transition metal elements; in formula (II), -0.1 ≤ x3 ≤ 0.2, 0 < e ≤ 2, 0 ≤ d < 1, N is one or more of Ni, Fe, Cr, Ti, Zn, V, Al, Mg, Zr, and Ce, and B is one or more of S, N, F, Cl, Br, and I.

[0147] In some embodiments of the present application, the positive electrode active material of the first battery cell includes LiFePO4, LiMnPO4, LiMn 1-x3 Fe x3 PO4, LiV 1-x3 Fe x3 PO4, LiMn2O4, LiMn 1.9 Al 0.1 O4, wherein x3 independently satisfies 0 < x3 < 1. In the present application, the lithium-containing phosphate has good cycle stability and a long cycle life. The first battery cell using such a positive electrode active material has a long cycle life, which is beneficial to extending the cycle life of the battery pack. In the middle and late stages of the cycle life of the battery pack, the technical advantage of slow power decay of such a first battery cell can be used to further improve the power output characteristics of the battery pack. The crystal structure of the spinel-type lithium manganate material has good stability. The first battery cell using such a positive electrode active material has good rate performance, which is beneficial to further improving the rate performance of the battery pack.

[0148] In some embodiments of the present application, the positive electrode active material of the second battery cell includes a lithium transition metal oxide represented by formula (III).

[0149] Li 1+x1 Ni a Co b M 1-a-b O 2-y1 A y1 Formula (III)

[0150] Wherein, -0.1 ≤ x1 ≤ 0.2, 0.5 ≤ a < 0.95, 0 < b < 0.2, 0 < a + b < 1, 0 ≤ y1 < 0.2, M is selected from one or more of Mn, Fe, Cr, Ti, Zn, V, Al, Zr, and Ce, and A is selected from one or more of S, F, Cl, and I. In the present application, when the above positive electrode active material is used in the second battery cell, due to the relatively high specific capacity of the above material, the volume energy density of the second battery cell can be further increased, thereby significantly improving the volume energy density of the battery pack.

[0151] [Battery pack]

[0152] In some embodiments of the present application, two or more of the above battery packs can be assembled into a battery pack, and the number of battery packs included in the battery pack depends on the application of the battery pack and the parameters of a single battery pack. The battery pack may include a battery box and a plurality of battery packs disposed in the battery box. The battery box includes an upper box body and a lower box body. The upper box body can cover the lower box body and match well with it to form a closed space for accommodating the battery packs. Two or more battery packs can be arranged in the battery box in a required manner. In the present application, the "battery pack" is made by further assembling various control and protection systems such as a battery management system and a thermal management system for one or more battery packs (or a combination directly formed by a plurality of battery cells).

[0153] Figure 4 is a schematic diagram showing an example of the battery pack 1 of the present application. Figure 5 is shown Figure 4 An exploded view of an example of the battery pack 1 of the present application shown. Refer to Figure 4 and Figure 5 , in the battery pack 1, a battery box and a plurality of battery packs 4 disposed in the battery box can be included. The battery box includes an upper box body 2 and a lower box body 3. The upper box body 2 is used to cover the lower box body 3 and form a closed space for accommodating the battery packs 4. The plurality of battery packs 4 can be arranged in the battery box in any manner.

[0154] [Power-consuming device]

[0155] In some embodiments of the present application, the electrical device of the present application includes at least one of the battery pack or battery module of the present application. The battery pack or battery module can be used as the power source of the electrical device or as the energy storage unit of the electrical device. The electrical device includes, but is not limited to, mobile digital devices (such as mobile phones, laptop computers, etc.), electric vehicles (such as pure electric vehicles, hybrid electric vehicles, plug-in hybrid electric vehicles, electric bicycles, electric scooters, electric golf carts, electric trucks, etc.), electric trains, ships, satellites, energy storage systems, etc.

[0156] Figure 6 FIG. is a schematic diagram showing an example of an electrical device using the battery pack of the present application as a power source. The electrical device is a pure electric vehicle, a hybrid electric vehicle, or a plug-in hybrid electric vehicle, etc. In order to meet the requirements of the electrical device for high power and high energy density, a battery module or a battery pack can be used.

[0157] [Manufacturing Method of Battery Pack]

[0158] The present application provides a manufacturing method of a battery pack, including the following steps:

[0159] Obtain a first type of battery cell and a second type of battery cell,

[0160] The first type of battery cell and the second type of battery cell are battery cells of different chemical systems,

[0161] The first type of battery cell includes N first battery cells,

[0162] The second type of battery cell includes M second battery cells, where N and M are positive integers,

[0163] The first battery cell includes a first separator and a first electrolyte,

[0164] The second battery cell includes a second separator and a second electrolyte,

[0165] The kinetic characteristic factor x1 of the first battery cell is: x1 = 1000×(ε1×r1) / (τ1×t1×θ1),

[0166] The kinetic characteristic factor x2 of the second battery cell is: x2 = 1000×(ε2×r2) / (τ2×t2×θ2),

[0167] And x1 and x2 satisfy: 0.01 ≤ x1 / x2 ≤ 160, where,

[0168] ε1 and ε2 are the porosities of the first separator and the second separator respectively, unit: %,

[0169] r1 and r2 are the average pore sizes of the first separator and the second separator respectively, unit: μm,

[0170] τ1 and τ2 are the tortuosities of the first separator and the second separator respectively,

[0171] t1 and t2 are the average thicknesses of the first separator and the second separator respectively, unit: μm,

[0172] θ1 is the contact angle between the first separator and the first electrolyte, unit: radian,

[0173] θ2 is the contact angle between the second separator and the second electrolyte, unit: radian; and

[0174] The first type of battery cells and the second type of battery cells are connected in series at least to form a battery pack as described in the first aspect of the present application.

[0175] [Manufacturing Equipment for Battery Pack]

[0176] The present application provides a manufacturing equipment for a battery pack, including:

[0177] A clamping arm unit, which is used to obtain the first type of battery cells and the second type of battery cells,

[0178] The first type of battery cells and the second type of battery cells are battery cells of different chemical systems,

[0179] The first type of battery cells includes N first battery cells,

[0180] The second type of battery cells includes M second battery cells, where N and M are positive integers,

[0181] The first battery cell includes a first separator and a first electrolyte,

[0182] The second battery cell includes a second separator and a second electrolyte,

[0183] The kinetic characteristic factor x1 of the first battery cell is: x1 = 1000×(ε1×r1) / (τ1×t1×θ1),

[0184] The kinetic characteristic factor x2 of the second battery cell is: x2 = 1000×(ε2×r2) / (τ2×t2×θ2),

[0185] And x1 and x2 satisfy: 0.01 ≤ x1 / x2 ≤ 160, where

[0186] ε1 and ε2 are the porosities of the first separator and the second separator respectively, unit: %,

[0187] r1 and r2 are the average pore diameters of the first separator and the second separator respectively, unit: μm,

[0188] τ1 and τ2 are the tortuosities of the first separator and the second separator respectively,

[0189] t1 and t2 are the average thicknesses of the first separator and the second separator respectively, unit: μm,

[0190] θ1 is the contact angle between the first separator and the first electrolyte, unit: radian,

[0191] θ2 is the contact angle between the second separator and the second electrolyte, unit: radian;

[0192] An assembly unit, which is used to connect at least the first type of battery cells and the second type of battery cells in series to form the battery pack as described in the first aspect of the present application; and

[0193] A control unit, which is used to control the clamping arm unit and the assembly unit.

[0194] Embodiment

[0195] Next, the technical solutions and their advantages of the present application will be described in detail through specific embodiments.

[0196] "Battery Cell Preparation"

[0197] Referring to GB / T 31484-2015 "Requirements and Test Methods for Cycle Life of Power Batteries for Electric Vehicles", the preparation methods of the battery cells in each embodiment and comparative example are as follows.

[0198] 1. Preparation of the positive electrode paste

[0199] The positive electrode active material, conductive carbon Super P, and binder polyvinylidene fluoride (PVDF) are fully stirred and mixed in a weight ratio of 95:3:2 in an appropriate amount of N-methylpyrrolidone (abbreviated as NMP) solvent to form a uniform and stable paste with a viscosity of 10,000 mPa·s. The paste does not gel, delaminate, or settle within 24 hours of standing (wherein, the positive electrode active materials of the first battery cell and the second battery cell are shown in Table 1 and Table 2 respectively).

[0200] 2. Preparation of the positive electrode plate

[0201] The positive electrode material paste is uniformly coated on the positive electrode current collector Al foil. After drying, the electrode plate is cold-pressed to the designed density and cut into strips for standby to obtain the positive electrode plate.

[0202] 3. Preparation of the electrolyte

[0203] Dissolve an equal volume of ethylene carbonate in propylene carbonate, and then uniformly dissolve lithium hexafluorophosphate in this mixed solvent for standby (the concentration of lithium hexafluorophosphate is 1.1 M / L) to obtain an electrolyte solution.

[0204] 4. Preparation of the negative electrode sheet

[0205] Mix the negative electrode active material, such as graphite, with conductive carbon, binder styrene-butadiene copolymer (SBR), and thickener sodium carboxymethyl cellulose (CMC) in a weight ratio of 95:2:2:1 in an appropriate amount of aqueous solvent and stir well to form a uniform negative electrode stable slurry; uniformly coat this slurry on the negative electrode current collector Cu foil, and after drying, cold press the electrode sheet to the designed density and cut it into strips for standby.

[0206] 5. Separator

[0207] In Example 1, the separator of the first battery cell includes a PE substrate with a thickness of 7 μm and a first coating with a thickness of 1 μm on one side and containing 70 wt% of AlOOH inorganic particles by mass. The specific preparation method is as follows: Disperse inorganic particles γ-AlOOH, binder acrylate emulsion, and sodium carboxymethyl cellulose in deionized water of equal mass in a mass ratio of 70 wt%:25%:5%, and mix them evenly to prepare a first coating slurry; uniformly coat the first coating slurry on the surfaces of both sides of the substrate and dry it. The thickness of the first coating is 1 μm to obtain the separator of the first battery cell.

[0208] In Example 1, the separator of the second type of battery cell includes a PE substrate with a thickness of 4 μm and an inorganic-organic composite coating with a thickness of 0.25 μm on one side (wherein, on the surface of the substrate, there are successively arranged: a sub-coating of AlOOH inorganic particles with a thickness of 0.15 μm and a mass ratio of 80 wt%; and a sub-coating of PVDF organic particles with a thickness of 0.10 μm and a mass ratio of 30 wt%). The specific preparation method is as follows:

[0209] 1) Disperse inorganic particles γ-AlOOH, binder acrylate emulsion, and sodium carboxymethyl cellulose in deionized water of equal mass in a mass ratio of 80 wt%:15%:5%, and mix them evenly to prepare a γ-AlOOH inorganic particle sub-coating slurry;

[0210] 2) Disperse PVDF organic particles and binder styrene-butadiene rubber in deionized water with twice the mass in a mass ratio of 30 wt%:70 wt%, and mix them evenly to prepare a PVDF organic particle sub-coating slurry;

[0211] 3) Uniformly coat the γ-AlOOH inorganic particle sub-coating slurry on the surfaces of both sides of the substrate and dry it;

[0212] 4) The PVDF organic particle coating is partially applied to the surface of the AlOOH inorganic particle coating by spraying, and then dried to finally obtain the separator membrane of the second battery cell.

[0213] Among them, for various parameters of the separator membrane of the first battery cell and the second battery cell, refer to Table 1 and Table 2.

[0214] The various parameters of the separator membranes in other embodiments are shown in Table 1 below.

[0215] 6. Preparation of battery cells

[0216] Using the conventional battery cell manufacturing process, the above-mentioned positive electrode sheet, separator membrane and negative electrode sheet are wound together into a bare battery cell, then placed in a battery case, the above-mentioned electrolyte is injected, and then processes such as formation and sealing are carried out to finally obtain a rechargeable power battery cell.

[0217] Below, the test methods for the separator membrane and the battery cell will be described.

[0218] "Test method for the thickness of the separator membrane"

[0219] As a measurement method for the thickness of the separator membrane, an X-ray surface density measuring instrument of the model Dacheng DC PRECISION can be used. That is, the non-contact measurement of the thickness and surface density of the material is realized by using the absorption and backscattering effects of X-rays penetrating the material.

[0220] "Test method for the pore size of the separator membrane"

[0221] It is measured by using an automatic adsorption instrument of the model TriStar II 3020. The specific test method can refer to the standards: GB / T19587-2017 "Determination of specific surface area of solid materials by gas adsorption BET method" and GB / T 21650.2-2008 Mercury intrusion method and gas adsorption method for determination of pore size distribution and porosity of solid materials.

[0222] "Test method for the porosity of the separator membrane"

[0223] It is measured by using a true density tester of the model AccuPyc II 1340. The specific test method is to respectively test the total volume V1 and the true volume V2 of the separator membrane. According to the formula: porosity = (V1 - V2) / V1 × 100%, the porosity of the separator membrane can be obtained.

[0224] "Test method for the tortuosity of the separator membrane"

[0225] The tortuosity can be calculated by the following formula: tortuosity where, N m represents the Makmalin number, and ε is the porosity of the separator membrane. Among them, the Makmalin number N mIt is the ratio of the resistivity of the separator when immersed in the electrolyte to the resistivity of the electrolyte. The resistivity of the separator immersed in the electrolyte and the resistivity of the electrolyte can be measured by the following methods.

[0226] Measurement of separator resistivity: An electrochemical workstation can be used, such as Shanghai Chenhua CHI600E, Solartron or Princeton. According to the resistance law formula Rs = ρ×l0 / (S×n), the Rs of different separator layers (n) can be measured by the EIS method of a confined symmetric cell. Plotting Rs against n gives a slope k = (ρ×l0) / S, and the resistivity ρ = (k×S) / l0 can be obtained under the conditions of known effective area S and separator thickness l0.

[0227] Measurement of electrolyte resistivity: An electrical conductivity meter (such as Leici DDSJ-318) is used to measure the resistance R of the electrolyte at 25°C and an AC impedance of 1 kHz, and the resistivity of the electrolyte is calculated using the formula ρ = R×S / l based on the length l and cross-sectional area S of the measured electrolyte.

[0228] "Test Method for the Contact Angle between the Separator and the Electrolyte"

[0229] The test sample is placed on a water contact angle tester (model SL200KB from Konos Industry, USA). 10 μL of the electrolyte is dropped at a position 1 cm above the positive electrode film layer, and the water droplet falling on the sample surface is photographed using an optical microscope and a high-speed camera. The test conditions are 25°C and normal pressure (0.1 MPa). The angle between the tangent of the contact point surface of the water droplet and the sample and the horizontal plane is measured by software analysis, which is the contact angle, with the unit of radian.

[0230] Through the above "Cell Preparation" method, the battery packs of Examples 1 to 14 below can be obtained.

[0231] In addition, through the above test methods, Table 1 (Batteries 1-1 to 1-14) showing the thickness, pore size, porosity, tortuosity, contact angle, kinetic characteristic factor, and self-discharge rate of the separators of the first type of cells, and Table 2 (Batteries 2-1 to 2-14) showing the thickness, pore size, porosity, tortuosity, contact angle, kinetic characteristic factor, and self-discharge rate of the separators of the second type of cells can be obtained.

[0232]

[0233]

[0234] "Assembly of the Battery Pack"

[0235] Six first battery cells (denoted as A) and three second battery cells (denoted as B) are obtained. Battery cells with better consistency in electrical properties such as formation capacity, charge-discharge capacity, initial Coulomb efficiency, impedance, self-discharge, state of charge, etc. are selected. The first battery cells and the second battery cells are arranged in the order of BAAABAAAB and electrically connected in series.

[0236] Test Method for Low-Temperature Discharge Energy Retention Rate of Battery Pack

[0237] The discharge energy retention rate of the battery pack is tested using a charge and discharge machine in a high and low temperature chamber. The minimum nominal capacity of the first battery cells and the second battery cells as single battery cells is C0. The battery pack is discharged at a rate of 0.33C0 to the discharge cut-off voltage of each single battery cell, left standing for 1 hour, then charged at a rate of 0.33C0 until any single battery cell reaches the charge cut-off voltage, left standing for 5 minutes, and charged at a rate of 0.05C0 until any single battery cell reaches the charge cut-off voltage, left standing for 1 hour. The battery pack is discharged at a rate of 0.33C0 until any single battery cell reaches the discharge cut-off voltage, and the actual discharge capacity of the battery pack is recorded as C1. The battery pack is discharged at a rate of 0.33C1 to the discharge cut-off voltage of each single battery cell, left standing for 1 hour, then charged at a rate of 0.33C1 until any single battery cell reaches the charge cut-off voltage, left standing for 5 minutes, and charged at a rate of 0.05C1 until any single battery cell reaches the charge cut-off voltage, left standing for 1 hour. After the battery pack is left standing at the target temperature, such as 0 °C, for 24 hours, it is discharged at a rate of 0.33C1 until the voltage of any single battery cell reaches the recommended discharge cut-off voltage of the product, and this voltage value shall not be lower than 80% of the discharge cut-off voltage at room temperature (25 °C). Calculate the discharge energy. The ratio of the discharge energy of the battery pack at low temperature to the discharge energy at room temperature is the low-temperature discharge energy retention rate.

[0238] Test Method for Rate Performance of Battery Pack

[0239] The discharge energy retention rate of the battery pack is tested using a charge and discharge machine. First, the actual discharge capacity C1 of the battery pack is tested according to the above steps. The battery pack is discharged at a rate of 0.33C1 to the discharge cut-off voltage of each single battery cell, left standing for 1 hour, then charged at a rate of 0.33C1 until any single battery cell reaches the charge cut-off voltage, left standing for 5 minutes, and charged at a rate of 0.05C1 until any single battery cell reaches the charge cut-off voltage, left standing for 1 hour. The battery pack is discharged at a rate of 2C1 until any single battery cell reaches the discharge cut-off voltage. Measure the discharge capacity. The ratio of the discharge capacity of the battery pack at 2C1 to the discharge capacity at 0.33C1 is the rate capacity retention rate.

[0240] Test Method for Degree of Wrinkle of Negative Electrode Plate of Battery Pack at 100% SOC

[0241] Fully charge the battery pack according to the above steps, leave it for 10 hours in the fully charged state, and then disassemble the single cells in the battery pack. Take the disassembled negative electrode plate and observe the degree of through and non-through wrinkles of the electrode plate per unit length and unit area.

[0242] Through the above battery pack preparation method, the first type of cells and the second type of cells with different kinetic characteristics are assembled to obtain the battery packs of Examples 1-10 and Comparative Examples 1-2. Perform discharge energy retention rate tests and rate performance tests on the battery packs of each example and comparative example. For the design parameters and performance test results of each battery pack, see Table 3.

[0243] Table 3

[0244]

[0245] According to Table 3 above, in Examples 1-10 of the present application, by optimizing the matching design of the thickness, pore size, porosity, tortuosity, and contact angle with the electrolyte of the first separator of the first type of cells and the second separator of the second type of cells, the kinetic characteristics of the first type of cells and the second type of cells can be made to have good consistency, and further the discharge energy retention rate of the battery pack at room temperature and low temperature can be increased, and the rate performance can be good.

[0246] Table 4

[0247]

[0248]

[0249] According to Table 4 above, in Examples 6, 11-14 of the present application, on the basis of Example 6, the coating structure and components of the first separator of the first type of cells are further optimized. The coating structure is an inorganic-organic composite coating with a single-sided thickness of 1 μm (including: a γ-AlOOH inorganic particle sub-coating with a thickness of 0.6 μm and a sub-composite coating of PVDF organic particles with a thickness of 0.4 μm. For the specific mass ratio, see Table 4). Thereby, the degree of wrinkles of the negative electrode plate in the fully charged state can be effectively improved, and the rate performance of the battery pack can be further enhanced.

[0250] In this specification, each example or embodiment is described in a progressive manner. The key point of each example is to illustrate the differences from other examples. The same or similar parts among the various examples can be referred to each other.

[0251] In the description of this specification, the descriptions with reference to terms such as "some embodiments", "some embodiments", "schematic embodiments", "examples", "specific examples", or "some examples", etc. mean that the specific features, structures, materials, or characteristics described in connection with the embodiments or examples are included in at least some embodiments or examples of this application. In this specification, the schematic expressions of the above terms do not necessarily refer to the same embodiments or examples. Moreover, the specific features, structures, materials, or characteristics described can be combined in a suitable manner in any one or more embodiments or examples.

[0252] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of this application and are not intended to limit them; although this application has been described in detail with reference to the foregoing embodiments, those of ordinary skill in the art should understand that they can still modify the technical solutions described in the foregoing embodiments, or perform equivalent replacements for some or all of the technical features; and these modifications or replacements 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.

Claims

1. A battery pack, which includes at least a first type of battery cell and a second type of battery cell that are electrically connected in series, and the first type of battery cell and the second type of battery cell are battery cells of different chemical systems. The first type of battery cell includes N first battery cells. The second type of battery cell includes M second battery cells, where N and M are positive integers. The first battery cell includes a first separator and a first electrolyte. The second battery cell includes a second separator and a second electrolyte. The kinetic characteristic factor x1 of the first battery cell is: x1 = 1000×(ε1×r1) / (τ1×t1×θ1). The kinetic characteristic factor x2 of the second battery cell is: x2 = 1000×(ε2×r2) / (τ2×t2×θ2). And x1 and x2 satisfy: 3 ≤ x1 / x2 ≤ 160, 0.3 ≤ x1 ≤ 95, 0.2 ≤ x2 ≤ 55; 4μm ≤ t1 ≤ 20μm, 8μm ≤ t2 ≤ 16μm; 0.01μm ≤ r1 ≤ 3μm, 0.01μm ≤ r2 ≤ 2μm; 25% ≤ ε1 ≤ 60%, 25% ≤ ε2 ≤ 60%. 1.1 ≤ τ1 ≤ 3.9, 1.1 ≤ τ2 ≤ 3.9; 0.35 ≤ θ1 ≤ 1.35, 0.35 ≤ θ2 ≤ 1.35; Among them, ε1 and ε2 are the porosities of the first separator and the second separator respectively, unit: % r1 and r2 are the average pore diameters of the first separator and the second separator respectively, unit: μm τ1 and τ2 are the tortuosities of the first separator and the second separator respectively t1 and t2 are the average thicknesses of the first separator and the second separator respectively, unit: μm θ1 is the contact angle between the first separator and the first electrolyte, unit: radian θ2 is the contact angle between the second separator and the second electrolyte, unit: radian 2. The battery pack according to claim 1, wherein, The first battery cell and the second battery cell satisfy: 3 ≤ x1 / x2 ≤ 100.

3. The battery pack according to claim 1, wherein, The first battery cell and the second battery cell satisfy: 3 ≤ x1 / x2 ≤ 60.

4. The battery pack according to claim 1, wherein, The first battery cell and the second battery cell satisfy: 3 ≤ x1 / x2 ≤ 15.

5. The battery pack according to claim 1, wherein The first battery cell and the second battery cell satisfy: 0.5 ≤ x1 ≤ 40, and / or, 0.5 ≤ x2 ≤ 35.

6. The battery pack according to claim 1, wherein The first battery cell and the second battery cell satisfy: 1 ≤ x1 ≤ 20, and / or, 1 ≤ x2 ≤ 20.

7. The battery pack according to claim 1, wherein, The average thickness t1 of the first separator and the average thickness t2 of the second separator satisfy: 7μm ≤ t1 ≤ 10μm, and / or, 11μm ≤ t2 ≤ 14μm.

8. The battery pack according to claim 1, wherein, The average pore diameter r1 of the first separator and the average pore diameter r2 of the second separator satisfy: 0.03μm ≤ r1 ≤ 1.2μm, and / or, 0.03μm ≤ r2 ≤ 1μm.

9. The battery pack according to claim 1, wherein, The porosity ε1 of the first separator and the porosity ε2 of the second separator satisfy: 30% ≤ ε1 ≤ 50%, and / or, 30% ≤ ε2 ≤ 50%.

10. The battery pack according to claim 1, wherein, The tortuosity τ1 of the first separator and the tortuosity τ2 of the second separator satisfy: 1.3 ≤ τ1 ≤ 3, and / or, 1.3 ≤ τ2 ≤ 3.

11. The battery pack according to claim 1, wherein In the first battery cell, the first separator includes a first substrate and a first coating provided on at least one surface of the first substrate; in the second battery cell, the second separator includes a second substrate and a second coating provided on at least one surface of the second substrate, and at least one of the following conditions is satisfied: (1) The thickness of the first substrate is 3μm - 19.5μm; and / or, the thickness of the second substrate is 4μm - 15μm; (2) The thickness of the first coating on one side is 0.05μm - 2μm; and / or, the thickness of the second coating on one side is 0.25μm - 3.5μm; (3) The first coating contains inorganic particles, and the inorganic particles are selected from one or more of boehmite, alumina, barium sulfate, magnesium oxide, magnesium hydroxide, silicon dioxide, tin dioxide, titanium oxide, calcium oxide, zinc oxide, zirconium oxide, yttrium oxide, nickel oxide, cerium oxide, zirconium titanate, barium titanate, magnesium fluoride. (4) The second coating contains organic particles selected from one or more of polytetrafluoroethylene, polyvinylidene fluoride, polytrifluorochloroethylene, modified polyvinylidene fluoride, polyethylene, polypropylene, polyacrylonitrile, polyethylene oxide, acrylate, polymethyl methacrylate, ethyl cellulose, copolymers of different fluoroalkenyl monomer units, copolymers of fluoroalkenyl monomer units and olefinic monomer units, copolymers of fluoroalkenyl monomer units and acrylic monomer units, copolymers of fluoroalkenyl monomer units and acrylate monomer units, and modified compounds of the above copolymers.

12. The battery pack according to claim 11, wherein, Based on the weight of the first coating, the weight percentage of the inorganic particles is 50% to 99%.

13. The battery pack according to claim 11, wherein, Based on the weight of the first coating, the weight percentage of the inorganic particles is 70% to 90%.

14. The battery pack according to claim 11, wherein, Based on the weight of the second coating, the weight percentage of the organic particles is 30% to 99%.

15. The battery pack according to claim 11, wherein, Based on the weight of the second coating, the weight percentage of the organic particles is 50% to 90%.

16. The battery pack according to claim 1, wherein the positive electrode active material of the first battery cell includes at least one of the lithium phosphate represented by formula (I) or the lithium manganese-based oxide represented by formula (II), LiFe 1-x2-y2 Mn x2 M’ y2 Formula (I) of M’PO4 Li 1+x3 Mn e N 2-e O 4-d B d Formula (II) wherein, in formula (I), 0 ≤ x2 ≤ 1, 0 ≤ y2 ≤ 0.1, and M' is selected from one or several of transition metal elements other than Fe and Mn and non-transition metal elements; in formula (II), -0.1 ≤ x3 ≤ 0.2, 0 < e ≤ 2, 0 ≤ d < 1, N is one or more of Ni, Fe, Cr, Ti, Zn, V, Al, Mg, Zr, and Ce, and B is one or more of S, N, F, Cl, Br, and I.

17. The battery pack according to claim 16, wherein, The positive electrode active material of the first battery cell includes one or more of LiFePO4, LiMnPO4, LiMn 1-x3 Fe x3 PO4, LiV 1-x3 Fe x3 PO4, LiMn2O4, LiMn 1.9 Al 0.1 O4.

18. The battery pack according to claim 16, wherein, Based on 100% by weight of the positive electrode active material of the first battery cell, the weight percentage of at least one of the lithium phosphate represented by formula (I) or the lithium manganese-based oxide represented by formula (II) is not less than 70%.

19. The battery pack according to claim 1, wherein the positive electrode active material of the second battery cell includes the lithium transition metal oxide represented by formula (III), Li 1+x1 Ni a Co b M 1-a-b O 2-y1 A y1 Formula (III) wherein, -0.1 ≤ x1 ≤ 0.2, 0.3 ≤ a < 0.95, 0 < b < 0.2, 0 < a + b < 1, 0 ≤ y1 < 0.2, M is selected from one or several of Mn, Fe, Cr, Ti, Zn, V, Al, Zr, and Ce, and A is selected from one or several of S, F, Cl, and I.

20. The battery pack according to claim 19, wherein, 0.5 ≤ a < 0.95, 0 < b < 0.

15.

21. The battery pack according to claim 19, wherein, Based on 100% by weight of the positive electrode active material of the second battery cell, the weight percentage of the lithium transition metal oxide represented by formula (III) is not less than 70%.

22. A battery pack, wherein, Comprising the battery pack according to any one of claims 1 to 21.

23. An electrical device, wherein, Comprising the battery pack according to any one of claims 1 to 21 or the battery pack according to claim 22, and the battery pack or the battery pack is used as the power source or energy storage unit of the electrical device.

24. A manufacturing method of a battery pack, wherein, Comprising the following steps: Obtain a first type of battery cell and a second type of battery cell, and the first type of battery cell and the second type of battery cell are battery cells of different chemical systems. The first type of battery cells includes N first battery cells, the second type of battery cells includes M second battery cells, where N and M are positive integers, the first battery cell includes a first separator and a first electrolyte, the second battery cell includes a second separator and a second electrolyte, the kinetic characteristic factor x1 of the first battery cell is: x1 = 1000×(ε1×r1) / (τ1×t1×θ1), the kinetic characteristic factor x2 of the second battery cell is: x2 = 1000×(ε2×r2) / (τ2×t2×θ2), and x1 and x2 satisfy: 3 ≤ x1 / x2 ≤ 160, 0.3 ≤ x1 ≤ 95, 0.2 ≤ x2 ≤ 55; 4μm ≤ t1 ≤ 20μm, 8μm ≤ t2 ≤ 16μm; 0.01μm ≤ r1 ≤ 3μm, 0.01μm ≤ r2 ≤ 2μm; 25% ≤ ε1 ≤ 60%, 25% ≤ ε2 ≤ 60%; 1.1 ≤ τ1 ≤ 3.9, 1.1 ≤ τ2 ≤ 3.9; 0.35 ≤ θ1 ≤ 1.35, 0.35 ≤ θ2 ≤ 1.35; where, ε1 and ε2 are the porosities of the first separator and the second separator respectively, unit: %, r1 and r2 are the average pore diameters of the first separator and the second separator respectively, unit: μm, τ1 and τ2 are the tortuosities of the first separator and the second separator respectively, t1 and t2 are the average thicknesses of the first separator and the second separator respectively, unit: μm, θ1 is the contact angle between the first separator and the first electrolyte, unit: radian, θ2 is the contact angle between the second separator and the second electrolyte, unit: radian; and electrically connect the first type of battery cells and the second type of battery cells in a manner including series connection to form the battery pack according to any one of claims 1 to 21.

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