Battery pack, battery pack, electric device and manufacturing method and manufacturing equipment of battery pack

Abstract

The invention relates to a battery pack which comprises at least a first type of battery cells and a second type of battery cells which are 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 comprises N first battery cells, the second type of battery cells comprises M second battery cells, and N and M are positive integers; a positive pole piece of the second battery cell contains two or more positive active materials, and when the dynamic SOC of the second battery cell is in the range of 90%-98%, the change rate delta OCV / delta SOC of the OCV of the second battery cell relative to the SOC meets the following conditions: 3 < = delta OCV / delta SOC < = 9, the unit is mV / % SOC, SOC represents the state of charge, and OCV represents the open-circuit voltage.

Description

[0001] This divisional application is based on the invention with the application number 202180004802.8, the application date of March 31, 2021, the applicant Contemporary Amperex Technology Co., Limited, and the invention title "Battery Pack, Battery Module, Electrical Device, and Manufacturing Method and Manufacturing Equipment for Battery Pack". Technical Field

[0002] The present application relates to the technical field of energy storage devices, and particularly to a battery pack, a battery module, an electrical device, a manufacturing method for a battery pack, and a manufacturing equipment for a battery pack. Background Art

[0003] Secondary batteries are a kind of clean and renewable resources, which can be used as driving energy or storage units in fields such as automobiles and energy storage. With the improvement of energy environmental protection requirements, 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.

[0004] At present, in order to improve the total energy that can be exerted by secondary batteries, usually multiple cells of the same chemical system are connected in series and parallel to form a battery pack (or battery module). However, due to the limitations of the chemical system design of the cells, it is often difficult to simultaneously improve multiple electrical performances of the battery pack only by adjusting the chemical system inside a single cell. In the prior art, most battery packs (or battery modules) use single cells of the same chemical system, such as lithium iron phosphate cells or lithium nickel cobalt manganese oxide ternary cells. However, when the battery pack or battery module composed of them is close to full charge during the charging process, overcharging is likely to occur, leading to safety problems.

[0005] Therefore, on the basis of ensuring that secondary batteries (especially battery packs or battery modules) exhibit their good electrical performances, how to further improve their overcharge prevention ability and enhance the safety performance of the battery pack has become one of the urgent problems to be solved in the research field of secondary batteries. Summary of the Invention

[0006] This 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. The first type of cell and the second type of cell are at least connected in series. By matching the SOC-OCV curves of the first type of cell and the second type of cell, the second type of cell is used to accurately reflect the charging state of the battery pack in a state close to full charge, thereby effectively preventing overcharging of the cells in the battery pack and greatly enhancing the safety of the battery pack.

[0007] The 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, 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 positive electrode tab of the second battery cell contains two or more positive electrode active materials, and when the dynamic SOC of the second battery cell is in the range of 90% - 98%, the change rate ΔOCV / ΔSOC of the OCV of the second battery cell with respect to SOC satisfies: 3 ≤ ΔOCV / ΔSOC ≤ 9, unit: mV / %SOC, where SOC represents the state of charge and OCV represents the open circuit voltage.

[0008] In any embodiment of the present application, when the dynamic SOC of the second battery cell is in the range of 90% - 98%, the change rate ΔOCV / ΔSOC of the OCV of the second battery cell with respect to SOC satisfies: 3.5 ≤ ΔOCV / ΔSOC ≤ 7, unit: mV / %SOC.

[0009] In any embodiment of the present application, when the dynamic SOC of the second battery cell is in the range of 30% - 80%, the change rate ΔOCV / ΔSOC of the OCV of the second battery cell with respect to SOC satisfies: ΔOCV / ΔSOC ≤ 1, unit: mV / %SOC.

[0010] In any embodiment of the present application, when the dynamic SOC of the second battery cell is in the range of 30% - 80%, the change rate ΔOCV / ΔSOC of the OCV of the second battery cell with respect to SOC satisfies: ΔOCV / ΔSOC ≤ 0.25, unit: mV / %SOC.

[0011] In any embodiment of the present application, the discharge battery balance rate of the second battery cell is CB2, 1.00 ≤ CB2 ≤ 1.16, optionally, 1.03 ≤ CB2 ≤ 1.11.

[0012] In any embodiment of the present application, the positive electrode active material of the second battery cell at least includes the layered lithium transition metal oxide shown in formula (I) and the lithium-containing phosphate shown in formula (II).

[0013] Li 1+x1 Ni a1 Co b1 M1 c1 M2 1-a1-b1-c1 O 2-y1 A1 y1 Formula (I)

[0014] LiFe 1-x2-y2 Mn x2 M’ y2 PO4 Formula (II)

[0015] In formula (I), -0.1 ≤ x1 ≤ 0.2, 0.3 ≤ a1 < 0.97, 0 < b1 ≤ 0.3, 0 < a1 + b1 + c1 < 1, 0 ≤ y1 < 0.2, M1 is selected from at least one of Mn and Al, M2 is selected from one or more of Fe, Cr, Ti, Zn, V, Al, W, Mg, B, Cu, Y, Si, Sr, Zr, and Ce, and A1 is selected from one or more of S, N, F, Cl, Br, PO 4 3- and I; optionally, 0.5 ≤ a1 ≤ 0.7, 0.01 ≤ b1 ≤ 0.15;

[0016] In formula (II), 0 ≤ x2 ≤ 1, optionally, 0 ≤ x2 ≤ 0.5, 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.

[0017] In any embodiment of the present application, in the positive electrode active material of the second battery cell, the mass ratio of the layered lithium transition metal oxide represented by formula (I) is 0.5 wt% to 30 wt%, optionally 1 wt% to 20 wt%, and further optionally 3 wt% to 15 wt%.

[0018] In any embodiment of the present application, the first battery cell satisfies the following condition 1 and condition 2,

[0019] Condition 1: When the dynamic SOC of the battery pack is in the range of 90% to 98%, the ratio Q of ΔOCV / ΔSOC of the second battery cell to ΔOCV / ΔSOC of the first battery cell is 2 ≤ Q ≤ 40, optionally, 4 ≤ Q ≤ 32;

[0020] Condition 2: When the dynamic SOC of the first battery cell is in the range of 30% to 80%, the change rate ΔOCV / ΔSOC of the OCV of the first battery cell with respect to the SOC satisfies ΔOCV / ΔSOC ≤ 0.25, unit: mV / %SOC; optionally, when the change rate ΔOCV / ΔSOC of the first battery cell is in the range of 30% to 80%, ΔOCV / ΔSOC ≤ 0.15.

[0021] In any embodiment of the present application, the discharge battery balance rate of the first battery cell is CB1 and satisfies 1.00 ≤ CB1 ≤ 1.18; optionally, 1.04 ≤ CB1 ≤ 1.14.

[0022] In any embodiment of the present application, the positive electrode active material of the first battery cell includes a lithium-containing phosphate represented by formula (III),

[0023] LiFe 1-x3-y3Mn x3 M” y3 PO 4 Formula (III)

[0024] Wherein, 0 ≤ x3 ≤ 1, 0 ≤ y3 ≤ 0.1, and M” is selected from one or more of transition metal elements other than Fe and Mn and non-transition metal elements.

[0025] In some embodiments of the present application, the positive electrode active material of the first battery cell includes LiFePO 4 , LiMnPO 4 , LiMn 1-x3 Fe x3 PO 4 , LiV 1-x3 Fe x3 PO 4 , etc., and among them, x3 independently satisfies 0 < x3 < 1.

[0026] In other embodiments of the present application, the positive electrode active material of the first battery cell at least includes the layered lithium transition metal oxide represented by Formula (IIII),

[0027] Li 1+x4 Ni a2 Co b2 M3 c2 M4 1-a2-b2-c2 O 2-y4 A2 y4 Formula (IIII)

[0028] In Formula (IIII), -0.1 ≤ x4 ≤ 0.2, 0.3 ≤ a2 < 0.95, 0 < b2 < 0.3, 0 < a2 + b2 + c2 < 1, 0 ≤ y4 < 0.2, M3 is selected from at least one of Mn and Al, M4 is selected from one or more of Fe, Cr, Ti, Zn, V, Al, Zr, and Ce, and A2 is selected from one or more of S, F, Cl, and I.

[0029] The second aspect of the present application provides a battery pack, including the battery pack described in the first aspect above.

[0030] 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.

[0031] 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, the second type of battery cell includes M second battery cells, N and M are positive integers, the positive electrode tab of the second battery cell contains two or more positive electrode active materials, and when the dynamic SOC of the second battery cell is in the range of 90% to 98%, the change rate ΔOCV / ΔSOC of the OCV of the second battery cell with respect to the SOC satisfies: 3 ≤ ΔOCV / ΔSOC ≤ 9, where SOC represents the state of charge and OCV represents the open circuit voltage; and connecting the first type of battery cell and the second type of battery cell in series at least to form the battery pack described in the first aspect above.

[0032] The fifth aspect of the present application provides a manufacturing device for a battery pack, including: 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, the second type of battery cell includes M second battery cells, N and M are positive integers, the positive electrode tab of the second battery cell contains two or more positive electrode active materials, and when the dynamic SOC of the second battery cell is in the range of 90% to 98%, the change rate ΔOCV / ΔSOC of the OCV of the second battery cell with respect to the SOC satisfies: 3 ≤ ΔOCV / ΔSOC ≤ 9, where SOC represents the state of charge and OCV represents the open circuit voltage; an assembly unit for connecting the first type of battery cell and the second type of battery cell in series at least to form the battery pack described in the first aspect above; and a control unit for controlling the clamping arm unit and the assembly unit.

[0033] [Technical effects]

[0034] The present application provides a battery pack, which includes a first type of battery cell and a second type of battery cell of different chemical systems. By electrically connecting the first type of battery cell and the second type of battery cell in series at least and matching the SOC-OCV curves of the first type of battery cell and the second type of battery cell, when the battery pack is close to the fully charged state, the second type of battery cell with higher recognition can accurately reflect the overall state of charge of the battery pack, effectively improving the overcharging problem of the battery pack and greatly enhancing the safety of the battery pack. Description of the drawings

[0035] In order to more clearly illustrate the technical solutions of the embodiments of the present application, the following will briefly introduce the drawings required to be used in the embodiments of the present application. Obviously, the following described drawings are only some embodiments of the present application. For those of ordinary skill in the art, other drawings can be obtained according to the drawings without creative efforts.

[0036] Figure 1 It is a schematic diagram showing an example of the battery cell of the present application.

[0037] Figure 2 It shows Figure 1 An exploded view of an example of the battery cell of the present application shown.

[0038] Figure 3 It is a schematic diagram showing an example of the battery pack of the present application.

[0039] Figure 4 It is a schematic diagram showing an example of the battery module of the present application.

[0040] Figure 5 It shows Figure 4 An exploded view of an example of the battery module of the present application shown.

[0041] Figure 6 It is a schematic diagram showing an example of an electrical device using the battery pack of the present application as a power source.

[0042] Among them, the reference numerals are explained as follows:

[0043] 5, 5a, 5b Battery cells

[0044] 51 Housing

[0045] 52 Electrode assembly

[0046] 53 Cover plate

[0047] 4 Battery pack

[0048] 1 Battery module

[0049] 2 Upper box body

[0050] 3 Lower box body Detailed implementation manners

[0051] The "ranges" disclosed herein are defined in terms 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 and upper limits define the boundaries of the particular range. The ranges defined in this way can include or exclude 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 particular parameter, ranges of 60 - 110 and 80 - 120 are also contemplated. In addition, if the minimum range values of 1 and 2 are listed, and if the maximum range values of 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 this application, unless otherwise stated, the numerical range "a - b" represents an abbreviated representation of any combination of real numbers 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" are fully listed herein, and "0 - 5" is just 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 integers 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, etc.

[0052] In this application, if there is no special instruction, all the embodiments and preferred embodiments mentioned herein can be combined with each other to form new technical solutions.

[0053] In this application, if there is no special instruction, all the technical features and preferred features mentioned herein can be combined with each other to form new technical solutions.

[0054] In this application, if there is no special instruction, all the steps mentioned herein can be carried out sequentially or randomly, but preferably sequentially. For example, the method includes steps (a) and (b), which means that the method can include steps (a) and (b) carried out sequentially, or can also include steps (b) and (a) carried out sequentially. 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.

[0055] In this application, if there is no special instruction, the "including" and "comprising" mentioned herein mean open-ended or can also be closed-ended. For example, the "including" and "comprising" can mean that other components not listed can also be included or comprised, or can also mean that only the listed components are included or comprised.

[0056] In the description of this application, it should be noted that unless otherwise specified, "above" and "below" include the number itself, and the meaning of "several" in "one or several" is two or more.

[0057] In the description of this application, 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) and B is true (or exists); or both A and B are true (or exist).

[0058] [Cell]

[0059] 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 special restrictions on the type and shape of the cell. It can be a soft-pack cell, a cylindrical cell, a square cell, or other various 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 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.

[0060] In this application, a "cell" refers to a battery single body that can be independently charged and discharged. The components of a cell can 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. This application has no special restrictions on the type and shape of the cell. It can be a soft-pack cell, a cylindrical cell, a square cell, or other various 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 charge and discharge 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.

[0061] In this application, the "chemical system" of a cell is divided 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 cell chemical system can be further defined according to the relative contents of nickel, cobalt, and manganese elements in the positive active material. For example, the positive active material is LiNi0.5 Co 0.2 Mn 0.3 O 2 (Generally abbreviated as NCM523) The battery cell can be defined as a battery cell with NCM523 chemical system, and the positive active material is LiNi 0.6 Co 0.2 Mn 0.2 O 2 (Generally abbreviated as NCM622) The battery cell can be defined as a battery cell with NCM622 chemical system, and the positive active material is LiNi 0.8 Co 0.1 Mn 0.1 O 2 (Generally abbreviated as NCM811) The battery cell can be defined as a battery cell with NCM811 chemical system. The battery cell with lithium nickel cobalt aluminate system (generally called NCA) as the positive electrode material can be defined as a battery cell with NCA chemical system. In addition, in this application, a hybrid system battery cell can also be used, such as a hybrid system battery cell including NCM and NCA.

[0062] Next, first, the basic structures of the negative electrode sheet, positive electrode sheet, electrolyte, and separator of the battery cell in this application will be described.

[0063] <Positive Electrode Sheet>

[0064] In the battery cell of this 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 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 this 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 substrates of polypropylene PP, polyethylene terephthalate PET, polybutylene terephthalate PBT, polystyrene PS, polyethylene PE, and their copolymers, etc.).

[0065] In the battery cell of the present application, the positive electrode active material can be the positive electrode active material for battery cells known in the art. For example, the positive electrode active material can include one or more of the following: lithium-containing phosphates 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 conventional materials that can be used as the positive electrode active material of the battery cell 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 LiCoO 2 ), lithium nickel oxide (such as LiNiO 2 ), lithium manganese oxide (such as LiMnO 2 , LiMn 2 O 4 ), 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 Mn 1 / 3 O 2 (NCM333), LiNi 0.5 Co 0.2 Mn 0.3 O 2 (NCM523), LiNi 0.5 Co 0.25 Mn 0.25 O 2 (NCM211), LiNi 0.6 Co 0.2 Mn 0.2 O 2 (NCM622), LiNi 0.8 Co 0.1 Mn 0.1 O 2 (NCM811)), lithium nickel cobalt aluminum oxide (such as LiNi 0.85 Co 0.15 Al 0.05 O 2 ) and their modified compounds, etc. One or several of them. Examples of lithium-containing phosphates with an olivine structure can include but are not limited to lithium iron phosphate (such as LiFePO 4 (LFP)), composite materials of lithium iron phosphate and carbon, lithium manganese phosphate (such as LiMnPO 4 ), composite materials of lithium manganese phosphate and carbon, lithium manganese iron phosphate, composite materials of lithium manganese iron phosphate and carbon.

[0066] In some embodiments, the positive electrode film layer may optionally further include a binder. Non-limiting examples of the binder that can be used in 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.

[0067] 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 several of superconducting carbon, acetylene black, carbon black, Ketjen black, carbon dots, carbon nanotubes, graphene, and carbon nanofibers.

[0068] In one embodiment 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 sheet can be obtained.

[0069] <Negative electrode sheet>

[0070] The battery cell of the present application includes a negative electrode sheet, the negative electrode sheet 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.

[0071] In one embodiment of the present application, the negative electrode active material in the negative electrode film layer can be a negative electrode active material commonly used in the art. For example, it can be one or several of natural graphite, artificial graphite, soft carbon, hard carbon, silicon-based materials, tin-based materials, and lithium titanate. The silicon-based material can be selected from one or several of elemental silicon, silicon oxide, and silicon-carbon composite. The tin-based material can be selected from one or several of elemental tin, tin oxide compound, and tin alloy.

[0072] In the battery cell of the present application, in addition to the negative electrode active material, the negative electrode film sheet may further optionally include a binder, an optional conductive agent, and other optional additives. The negative electrode film sheet 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 and optional conductive agent and binder in a solvent and stirring evenly. The above solvent can be N-methylpyrrolidone (NMP) or deionized water.

[0073] As an example, the conductive agent may include one or several of superconducting carbon, carbon black (such as acetylene black, Ketjen black), carbon dots, carbon nanotubes, graphene, and carbon nanofibers.

[0074] As an example, the binder may include one or several 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 several 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.

[0075] In addition, in the battery cell of the present application, the negative electrode sheet does not exclude other additional functional layers besides the negative electrode film layer. For example, in some embodiments, the negative electrode sheet of the present application may further include a conductive bottom coating (for example, 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 sheet of the present application may further include a covering protective layer covering the surface of the second negative electrode film layer.

[0076] In the battery cell of the present application, the negative electrode 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 base layer and a metal layer formed on at least one surface of the polymer material base layer, 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 base layer (such as a base layer made of materials such as polypropylene PP, polyethylene terephthalate PET, polybutylene terephthalate PBT, polystyrene PS, polyethylene PE, and their copolymers, etc.).

[0077] <Electrolyte>

[0078] The electrolyte plays a role in conducting ions between the positive electrode sheet and the negative electrode sheet. The electrolyte includes an electrolyte salt and a solvent. In some embodiments, the electrolyte salt may be selected from one or several of lithium hexafluorophosphate (LiPF 6 ), lithium tetrafluoroborate (LiBF 4 ), lithium perchlorate (LiClO 4 ), lithium hexafluoroarsenate (LiAsF 6 ), lithium bis(fluorosulfonyl)imide (LiFSI), lithium bis(trifluoromethanesulfonyl)imide (LiTFSI), lithium trifluoromethanesulfonate (LiTFS), lithium difluorooxalate borate (LiDFOB), lithium bis(oxalato)borate (LiBOB), lithium difluorophosphate (LiPO 2 F 2 ), lithium difluoro bis(oxalato)phosphate (LiDFOP), and lithium tetrafluoro bis(oxalato)phosphate (LiTFOP).

[0079] In one embodiment 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).

[0080] In one embodiment 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 one embodiment 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.

[0081] In one embodiment 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.

[0082] <Separator film>

[0083] In one embodiment of the present application, the battery cell further includes a separator film, which separates the positive electrode plate and the negative electrode plate of the battery cell, provides selective permeation or blocking to substances of different types, sizes, and charges in the system. For example, the separator film 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, and at the same time enable ions in the battery to pass through the separator film and move between the positive and negative electrodes.

[0084] In one embodiment of the present application, the materials used to prepare the separator film may include one or several of glass fiber, non-woven fabric, polyethylene, polypropylene, and polyvinylidene fluoride. The separator film can be a single-layer film or a multi-layer composite film. When the separator film is a multi-layer composite film, the materials of each layer can be the same or different.

[0085] In one embodiment 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.

[0086] In one embodiment 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 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.

[0087] Figure 1 It is a schematic diagram showing an example of the battery cell 5 of the present application. Figure 2 It is shown Figure 1 An exploded view of an example of the battery cell 5 of the present application shown.

[0088] 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 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 is infiltrated in the electrode assembly 52. The number of electrode assemblies 52 included in the battery cell 5 can be one or more.

[0089] [Battery pack]

[0090] In the present application, the "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 of the present application can be cylindrical, square, or any other shape.

[0091] In the present 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.

[0092] Figure 3 It is a schematic diagram showing an example of the battery pack of the present application. Refer to Figure 3, in the battery pack 4, a plurality of battery cells 5a, 5b may be arranged in sequence along the length direction of the battery pack 4 (where 5a may be the first battery cell and 5b may be the second battery cell). Of course, they may also be arranged in any other manner. Further, the plurality of battery cells 5a, 5b may be fixed by fasteners. Optionally, the battery pack 4 may further include a housing having an accommodation space, and the plurality of battery cells 5a, 5b are accommodated in the accommodation space.

[0093] <Design of the First Battery Cell and the Second Battery Cell>

[0094] In the present application, the battery pack includes at least a first type of battery cell and a second type of battery cell connected in series, and the first type of battery cell and the second type of battery cell are battery cells of different chemical systems.

[0095] The first type of battery cell includes N first battery cells.

[0096] The second type of battery cell includes M second battery cells, and N and M are positive integers.

[0097] The positive electrode tab of the second battery cell contains two or more positive electrode active materials, and the change rate ΔOCV / ΔSOC of the open circuit voltage (OCV) with respect to the state of charge (SOC) of the second battery cell in the range of 90% to 98% of the SOC during charging satisfies: 3 ≤ ΔOCV / ΔSOC ≤ 9, unit: mV / %SOC.

[0098] Wherein, SOC represents the state of charge and OCV represents the open circuit voltage.

[0099] In the field of batteries, generally, the capacity of the battery is reflected by testing the state of charge (abbreviated as SOC) of the battery.

[0100] Generally, a battery pack is composed of multiple battery cells with the same chemical system connected in series / parallel and outputting electrical energy externally in a unified manner. The advantage of having the same chemical system for multiple battery cells in the battery pack is that it is beneficial to improve the charge-discharge consistency of multiple battery cells, avoid the short-board effect, and help improve the overall electrical performance and service life of the battery pack. Common positive active materials include a type of olivine structure material such as lithium iron phosphate, and a type of ternary layered material such as lithium nickel cobalt manganese oxide. When the positive active material of the battery cells in the battery pack is a material with a relatively long charging platform like lithium iron phosphate, when it is charged to near the full charge state (i.e., in the 90% - 100% SOC range), the OCV of the battery cell increases sharply with the increase of SOC, making it impossible to accurately judge the SOC of the battery cell near full charge through OCV, and it is very easy to occur overcharging problems of the battery pack. At the same time, in order to improve the energy density of the battery pack, the amount of negative active material is usually minimized as much as possible, resulting in a sharp reduction in the active sites available for lithium ions to embed in the negative electrode plate when the battery cell is charged near full charge, and it is very easy to trigger overcharging problems. Therefore, on the basis of ensuring good electrical performance of the battery pack, how to further improve the overcharging problem of the battery pack and enhance the safety of the battery pack is a technical problem that urgently needs to be solved currently.

[0101] Based on the above technical problems, the present application provides a battery pack, which includes a first type of battery cell and a second type of battery cell with different chemical systems, and the first type of battery cell and the second type of battery cell are at least connected in series. The positive active material in the second type of battery cell uses a mixed material, so that the OCV change rate of the second type of battery cell in the high SOC state is within the range of 3 - 9 mV / %SOC. Since the first type of battery cell and the second type of battery cell in the battery pack are at least connected in series, the charge-discharge trends of the two types of battery cells are the same. With the change of the charging state, taking advantage of the characteristic that the change of the open circuit voltage in the high SOC state of the second type of battery cell is easy to accurately identify, therefore, the change amount of the state of charge of the battery pack as a whole can be accurately characterized by the change amount of the state of charge of the second type of battery cell. Therefore, based on the battery pack grouped in the above manner, on the premise of ensuring the stable output of the basic electrical performance of the battery pack, it can effectively improve the overcharging problem of the battery pack in the high SOC state and enhance the safety of the battery pack.

[0102] In the present application, the method for obtaining the dynamic OCV change curve of the battery cell in any interval of 0% - 100% SOC generally includes the following steps:

[0103] 1) At room temperature of 25°C, let the battery cell stand still for 120 minutes;

[0104] 2) Discharge the above battery cell at a constant current of 0.33C to the discharge termination voltage (C is the nominal or rated capacity in the product technical specification), and let it stand still for 30 minutes;

[0105] 3) Charge the battery cell in step 2 above at a constant current of 0.33C until the charge termination voltage, then charge at a constant voltage until the current ≤ 0.05C, and let it stand for 30 minutes;

[0106] 4) Discharge the battery cell in step 3 above at a constant current of 0.33C until the discharge termination voltage, record the discharged capacity as C0, and let it stand for 30 minutes;

[0107] 5) Charge the battery cell in step 4 above at a constant current of 0.33C0 until the charge termination voltage, then charge at a constant voltage until the current ≤ 0.05C0, and let it stand for 30 minutes;

[0108] 6) Discharge the battery cell in step 5 above at a constant current rate of ≤ 0.05C0 until the discharge termination voltage (requiring a fixed sampling frequency of 1s), and let it stand for 30 minutes;

[0109] 7) Charge the battery cell in step 6 above at a constant current of 0.05C0 until the charge termination voltage (requiring a fixed sampling frequency of 1s), let it stand for 30 minutes, and obtain the dynamic OCV change curve of the battery cell in the 0%-100% SOC range.

[0110] In the above steps, the 0.33C discharge rate refers to the discharge rate parameter used when the time required to fully charge or discharge a battery cell with a 1C capacity is 3h; using a discharge rate of 0.33C0, discharging for 9.09 minutes, the discharged capacity is equal to 9.09 min / 180 min = 0.05, that is, 5% of the total capacity C0. In this application, the test rate in steps 1) to 5) of the battery dynamic SOC test method can also be any value in the range of 0.01C to 0.5C. In addition, the nominal current can be freely selected according to the capacity of the battery pack. For example, when the capacity of the battery pack is 50Ah, the nominal current can be 50A; another example is that when the capacity of the battery pack is 100Ah, the nominal current can be 100A. The charge termination voltage and discharge termination voltage can be determined with reference to the regulations in the product technical specification or the GBT certification document of the battery cell / battery pack.

[0111] According to the dynamic OCV change curve of the battery cell in the 0%-100% SOC range, the OCV change difference corresponding to any SOC range can be obtained, and the quotient is the OCV change rate (ΔOCV / ΔSOC) of the battery cell in a certain SOC range.

[0112] In some embodiments of the present application, when the dynamic SOC of the second battery cell is within the range of 90% to 98%, the change rate ΔOCV / ΔSOC of the OCV of the second battery cell with respect to SOC satisfies: 3.5 ≤ ΔOCV / ΔSOC ≤ 7, unit: mV / %SOC. That is to say, in the high SOC range, when the state of charge of the second battery cell increases or decreases by 1%, the open-circuit voltage of the second battery cell will increase or decrease by at least 3.5 to 7 mV, and this value can meet the recognition accuracy of the BMS, enabling the change amount of the state of charge when the entire battery pack is about to be fully charged to be accurately obtained.

[0113] In some embodiments of the present application, when the dynamic SOC of the second battery cell is within the range of 30% to 80%, the change rate ΔOCV / ΔSOC of the OCV of the second battery cell with respect to SOC satisfies: ΔOCV / ΔSOC ≤ 1, unit: mV / %SOC.

[0114] Optionally, when the dynamic SOC of the second battery cell is within the range of 30% to 80%, the change rate ΔOCV / ΔSOC of the OCV of the second battery cell with respect to SOC satisfies: ΔOCV / ΔSOC ≤ 0.25, unit: mV / %SOC. In the present application, the OCV change rate of the second battery cell within the range of 30% to 80% during the charging process is relatively low, so that the second battery cell can maintain a relatively long and stable charging voltage platform during the charge and discharge process, which is beneficial to ensuring that the structural and chemical changes of the positive active material during repeated charge and discharge processes are small, the charge and discharge capacity decays less during long-term use, and it is beneficial to extend the overall cycle life of the battery pack.

[0115] In some embodiments of the present application, the discharge battery balance rate of the second battery cell is CB2, and CB2 satisfies: 1.00 ≤ CB2 ≤ 1.16. Optionally, 1.03 ≤ CB2 ≤ 1.10. In the present application, when the discharge battery balance rate of the second battery cell is within the above range, the utilization rates of the positive and negative active materials in the second battery cell can be further improved, which is beneficial to ensuring a relatively low risk of lithium plating while increasing the single-cell volumetric energy density of the second battery cell.

[0116] In the present application, the discharge battery balance rate of the battery cell has the meaning well-known in the art and can be tested by conventional methods. As an example, the following test method can be used: separately test the discharge capacity of the negative electrode plate per unit area and the discharge capacity of the positive electrode plate per unit area in the battery cell; then according to the formula: battery cell discharge battery balance rate = discharge capacity of negative electrode plate per unit area / discharge capacity of positive electrode plate per unit area, the discharge battery balance rate of the battery cell can be calculated.

[0117] Among them, the discharge capacity of the positive electrode sheet or the negative electrode sheet has the meaning well-known in the art and can be tested by conventional methods. As an example, the following steps can be used for testing:

[0118] (1) The requirements for sampling the electrode sheets are as follows:

[0119] After fully discharging the battery cell, disassemble it, take out the positive electrode sheet and the negative electrode sheet, rinse them appropriately with dimethyl carbonate (DMC) solution, and dry them for standby. The sampling position of the positive electrode sheet is: select any position in the middle more than 15 mm away from the edge. The sampling position of the negative electrode sheet is: select the negative electrode sheet at the position directly opposite to the selected positive electrode sheet; and the sampling area of the positive electrode sheet is the same as that of the negative electrode sheet;

[0120] (2) Use the above-cut positive electrode sheet and negative electrode sheet as the counter electrodes with lithium sheets respectively to assemble a coin-type half-cell;

[0121] (3) Discharge capacity of the negative electrode sheet per unit area:

[0122] The test voltage is 0.05 - 2.0 V, the test temperature is 25 °C, the charge / discharge rate is 0.1 C, take no less than 10 parallel samples, test the discharge capacity of the coin-type half-cell respectively, and take the average value after removing the lowest and the highest values to obtain the discharge capacity of the negative electrode sheet under this area; divide the discharge capacity of the negative electrode sheet obtained from the above test by the area of the negative electrode sheet, and the discharge capacity of the negative electrode sheet per unit area can be obtained;

[0123] (4) Discharge capacity of the positive electrode sheet per unit area:

[0124] Within the working voltage range specified in the GBT certification document of the sampled battery cell and at room temperature of 25 °C, charge / discharge at 0.1 C, take no less than 10 parallel samples, test the discharge capacity of the coin-type battery respectively, and take the average value after removing the lowest and the highest values to obtain the discharge capacity of the positive electrode sheet under this area; divide the discharge capacity of the positive electrode sheet obtained from the above test by the area of the positive electrode sheet, and the discharge capacity of the positive electrode sheet per unit area can be obtained.

[0125] In some embodiments of the present application, the positive electrode active material of the second battery cell at least includes the layered lithium transition metal oxide represented by formula (I) and the lithium-containing phosphate represented by formula (II),

[0126] Li 1+x1 Ni a1 Co b1 M 1-a1-b1 O 2-y1 A y1 Formula (I)

[0127] LiFe 1-x2-y2 Mn x2 M’y2 PO 4 Formula (II)

[0128] In Formula (I), -0.1 ≤ x1 ≤ 0.2, 0.3 ≤ a1 < 0.95, 0 < b1 < 0.2, 0 < a1 + b1 < 1, 0 ≤ y1 < 0.2, M is selected from one or more of Mn, Fe, Cr, Ti, Zn, V, Al, Zr, and Ce; A is selected from one or more of S, F, Cl, and I;

[0129] In Formula (II), 0 ≤ x2 ≤ 1, 0 ≤ y2 ≤ 0.1, M' is selected from one or more of transition metal elements other than Fe and Mn and non-transition metal elements.

[0130] In this application, when the positive electrode active material of the second battery cell includes the above two kinds of active materials, the change rate ΔOCV / ΔSOC of the OCV with respect to the SOC in the range of 30% to 80% of the SOC during the charging process of the second battery cell satisfies: ΔOCV / ΔSOC ≤ 1. At the same time, the change rate ΔOCV / ΔSOC of the OCV with respect to the SOC in the range of 90% to 98% of the SOC satisfies: 3 ≤ ΔOCV / ΔSOC ≤ 9. In this application, the positive electrode plate of the second battery cell contains two or more kinds of positive electrode active materials. When the second battery cell is about to reach full charge, the change rate of the OCV and the SOC of the second battery cell is still within an appropriate range, which is beneficial for the BMS to accurately obtain the state of charge of the series-connected battery cells in the battery pack, thereby realizing good overcharge prevention ability of the battery pack.

[0131] At the same time, since the first Coulomb efficiency of the compound of Formula (I) is lower than that of the compound of Formula (II), and the charge-discharge plateau of the compound of Formula (II) is longer, the active ions released from the compound of Formula (I) with a lower first Coulomb efficiency can be stored in the negative electrode plate and can continue to participate in the electrochemical reaction in the later stage of the use of the battery cell, thereby supplementing the capacity loss caused by the consumption of active ions and helping to further improve the cycle service life of the battery pack.

[0132] In some embodiments of this application, in the positive electrode active material of the second battery cell, the mass ratio of the layered lithium transition metal oxide shown in Formula (III) is 0.5 wt% to 25 wt%, optionally 1 wt% to 20 wt%, and further optionally 3 wt% to 15 wt%.

[0133] In some embodiments of this application, the first battery cell satisfies Condition 1 and Condition 2,

[0134] Condition 1: When the dynamic SOC of the battery pack is in the range of 90% to 98%, the ratio of ΔOCV / ΔSOC of the second battery cell and the first battery cell is denoted as Q, and 2 < Q ≤ 40 is satisfied. Optionally, 4 ≤ Q ≤ 32;

[0135] Condition 2: When the dynamic SOC of the first battery cell is in the range of 30% to 80%, the change rate ΔOCV / ΔSOC of the OCV of the first battery cell with respect to SOC satisfies ΔOCV / ΔSOC ≤ 0.25, unit: mV / %SOC. Optionally, when the change rate ΔOCV / ΔSOC of the dynamic SOC of the first battery cell in the range of 30% to 80% is ≤ 0.15.

[0136] In this application, when the battery pack contains battery cells with different OCV change rates in the high SOC range at the same time, and the SOC-OCV curves of the two types of battery cells meet the above characteristics, on the one hand, the characteristics that the OCV change of the second type of battery cell is easy to accurately identify in the high SOC state can be used to accurately characterize the change amount of the overall state of charge of the battery pack, which is effectively beneficial to improving the overcharge problem of the battery pack; at the same time, it can also ensure that the charge and discharge performance differences between the first type of battery cell and the second type of battery cell are small, which is beneficial to improving the overall electrical performance output effect of the battery pack.

[0137] In some embodiments of this application, the discharge battery balance rate of the first battery cell is CB1 and 1.00 ≤ CB1 ≤ 1.18 is satisfied. Optionally, 1.04 ≤ CB1 ≤ 1.14. In this application, when the discharge battery balance rate of the first battery cell is small, such battery cells are prone to lithium plating problems when approaching full charge due to the small amount of lithium vacancies that can be accommodated in the negative electrode. When it is connected in series with the second battery cell, by identifying the real-time state of charge of the second battery cell, the SOC of the first battery cell can be accurately identified, thereby improving the overcharge prevention ability of the battery pack. And by matching the charge and discharge characteristics of different chemical system battery cells in the battery pack in the above way, the utilization rate of the positive and negative active materials in the first battery cell and the second battery cell can be improved, which is beneficial to improving the volume and weight energy density of the battery pack. It is also possible to store the active ions released from the positive active material in the second battery cell in the negative electrode. During the long-term charge and discharge process, the active ions are continuously consumed, and the active ions pre-stored in the negative electrode can supplement the consumed active ions, which is beneficial to extending the cycle life of the battery pack.

[0138] In some embodiments of this application, the positive active material of the first battery cell includes a lithium-containing phosphate shown in formula (III),

[0139] LiFe 1-x3-y3 Mn x3 M’ y3 PO 4 Formula (III)

[0140] In formula (III), 0 ≤ x3 ≤ 1, 0 ≤ y3 ≤ 0.1, and M' is selected from one or more of transition metal elements other than Fe and Mn and non-transition metal elements.

[0141] In some embodiments of the present application, the positive electrode active material of the first battery cell includes LiFePO 4 , LiMnPO 4 , LiMn 1-x3 Fe x3 PO 4 , LiV 1-x3 Fe x3 PO 4 One or more of these, and x3 independently satisfies 0 < x3 < 1. In the present application, for lithium phosphate-based battery cells, the rate of change of their OCV with respect to SOC is relatively gentle within a relatively long SOC range, and overcharging is likely to occur in the high SOC range; however, the lithium phosphate-containing battery cells have good cycle stability and a long cycle life. Using such battery cells as the first battery cell and connecting the second battery cell in series, with the cooperation of the second battery cell, it is beneficial to extend the cycle life of the battery pack, can achieve good overcharge prevention ability of the battery pack, and can also effectively extend the cycle life of the battery pack.

[0142] In the present application, it is possible to use the positive electrode active material of the first type of battery cell as pure lithium iron phosphate (LFP), and the positive electrode active material of the second type of battery cell as a combination of a mixture of lithium nickel cobalt manganese oxide (NCM) and LFP. It is also possible to use the positive electrode active material of the first type of battery cell as a mixture of NCM and LFP, and the positive electrode active material of the second type of battery cell as a combination of a mixture of NCM and LFP. Here, LFP and NCM are just examples, and any substances with similar characteristics can be used, without special limitation. For example, LFP can also be replaced by LiMnPO 4 and so on, and NCM can also be replaced by lithium nickel cobalt aluminum oxide (NCA) and so on.

[0143] Hereinafter, as an example, an explanation will be given for the case where the positive electrode active material of the first type of battery cell is LFP, and the positive electrode active material of the second type of battery cell is a combination of a mixture of NCM and LFP.

[0144] In this application, when the positive electrode active material of the first type of battery cell is LFP and it is charged to more than 90% SOC, the OCV increases steeply with the change of SOC. Due to the accuracy problem of the BMS, it is difficult to accurately obtain the real-time SOC of this battery cell, and safety problems such as overcharging are likely to occur. In response to this, in this application, a second type of battery cell with a mixture of NCM and LFP as the positive electrode active material is connected in series in the battery pack, and the change rate of OCV with respect to SOC, ΔOCV / ΔSOC, of the second type of battery cell in the range of 90% to 98% SOC satisfies: 3 ≤ ΔOCV / ΔSOC ≤ 9. Since the first type of battery cell and the second type of battery cell are electrically connected at least in series, the state of charge of the battery pack can be accurately reflected by identifying the SOC of the second battery cell, so as to realize the charging control of the first type of battery cell, reduce the probability of overcharging, and greatly improve the safety performance of the battery pack.

[0145] In some other embodiments of this application, the positive electrode active material of the first battery cell at least includes the layered lithium transition metal oxide shown in formula (IIII).

[0146] Li 1+x4 Ni a2 Co b2 M3 c2 M4 1-a2-b2-c2 O 2-y4 A2 y4 Formula (IIII)

[0147] In formula (IIII), -0.1 ≤ x4 ≤ 0.2, 0.3 ≤ a2 < 0.95, 0 < b2 < 0.3, 0 < a2 + b2 + c2 < 1, 0 ≤ y4 < 0.2, M3 is selected from at least one of Mn and Al, M4 is selected from one or more of Fe, Cr, Ti, Zn, V, Al, Zr and Ce, and A2 is selected from one or more of S, F, Cl and I.

[0148] In some other embodiments of this application, it is also possible to adopt a combination in which the positive electrode active material of the first type of battery cell is NCM, and the positive electrode active material of the second type of battery cell is a mixture of NCM and LFP. Among them, the discharge battery balance rate CB1 of the first type of battery cell is in the range of 1.00 to 1.18. For this combined battery pack, when its SOC is in the range of 90% to 98%, the change rate of the OCV of the second battery cell with respect to SOC is lower than that of the first battery cell. The BMS can use the second battery cell to more accurately obtain the state of charge of the first battery cell, so as to realize excellent overcharge prevention performance of the battery pack; at the same time, since the initial Coulomb efficiency of NCM in the first battery cell is relatively low, some of the lithium that has escaped from the positive electrode plate cannot return to the positive electrode plate, but can be pre-stored in the negative electrode plate. Therefore, these pre-stored lithium will gradually be released during the use of the battery cell, so it can further improve the cycle service life of the battery pack.

[0149] [Battery Pack]

[0150] In one embodiment of the present application, two or more of the above-mentioned battery groups can be assembled into a battery pack. The number of battery groups included in the battery pack depends on the application of the battery pack and the parameters of a single battery group. The battery pack may include a battery box and a plurality of battery groups 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 groups. Two or more battery groups can be arranged in the battery box in a required manner. In the present application, a "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 groups (or a combination directly formed by a plurality of battery cells).

[0151] Figure 4 is a schematic diagram showing an example of the battery pack 1 of the present application. Figure 5 is showing Figure 4 an exploded view of an example of the battery pack 1 of the present application shown. Referring to Figure 4 and Figure 5 , the battery pack 1 may include a battery box and a plurality of battery groups 4 disposed in the battery box. The battery box includes an upper box body 2 and a lower box body 3. The upper box body 2 is used to cover the lower box body 3 and form a closed space for accommodating the battery groups 4. The plurality of battery groups 4 can be arranged in the battery box in any manner.

[0152] [Power-consuming Device]

[0153] In one embodiment of the present application, the power-consuming device of the present application includes at least one of the battery groups or battery packs of the present application. The battery groups or battery packs can be used as the power source of the power-consuming device or as the energy storage unit of the power-consuming device. The power-consuming 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.

[0154] Figure 6 is a schematic diagram showing an example of a power-consuming device using the battery group of the present application as a power source. The power-consuming 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 power-consuming device for high power and high energy density, a battery pack or a battery group can be used.

[0155] [Manufacturing Method of Battery Group]

[0156] The present application provides a manufacturing method of a battery group, including the following steps:

[0157] Obtain the first type of battery cells and the second type of battery cells,

[0158] The first type of battery cells and the second type of battery cells are battery cells of different chemical systems,

[0159] The first type of battery cells includes N first battery cells,

[0160] The second type of battery cells includes M second battery cells, where N and M are positive integers,

[0161] The positive electrode tab of the second battery cell contains two or more positive electrode active materials, and when the dynamic SOC of the second battery cell is in the range of 90% to 98%, the change rate ΔOCV / ΔSOC of the OCV of the second battery cell with respect to the SOC satisfies: 3 ≤ ΔOCV / ΔSOC ≤ 9, where SOC represents the state of charge and OCV represents the open circuit voltage; and

[0162] Connect the first type of battery cells and the second type of battery cells in series at least to form a battery pack as described in the first aspect of the present application.

[0163] [Manufacturing Equipment for Battery Pack]

[0164] The present application provides a manufacturing equipment for a battery pack, including:

[0165] A clamping arm unit for obtaining the first type of battery cells and the second type of battery cells,

[0166] The first type of battery cells and the second type of battery cells are battery cells of different chemical systems,

[0167] The first type of battery cells includes N first battery cells,

[0168] The second type of battery cells includes M second battery cells, where N and M are positive integers,

[0169] The positive electrode tab of the second battery cell contains two or more positive electrode active materials, and when the dynamic SOC of the second battery cell is in the range of 90% to 98%, the change rate ΔOCV / ΔSOC of the OCV of the second battery cell with respect to the SOC satisfies: 3 ≤ ΔOCV / ΔSOC ≤ 9, where SOC represents the state of charge and OCV represents the open circuit voltage;

[0170] An assembly unit for connecting the first type of battery cells and the second type of battery cells in series at least to form a battery pack as described in the first aspect of the present application; and

[0171] A control unit for controlling the clamping arm unit and the assembly unit.

[0172] Therefore, the battery pack manufactured by using the manufacturing method and manufacturing equipment of the present application can significantly improve the control accuracy of the BMS, effectively prevent the overcharging of the internal battery cells of the hybrid series battery pack, and greatly improve the safety of the battery pack.

[0173] Embodiment

[0174] Next, the technical solutions and their advantages of the present application will be described in detail through specific embodiments.

[0175] 《Preparation of Battery Cells》

[0176] 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.

[0177] 1. Preparation of positive electrode paste

[0178] Mix the positive electrode active material, conductive carbon Super P, and binder polyvinylidene fluoride (PVDF) in a weight ratio of 95:3:2 in an appropriate amount of N-methylpyrrolidone (abbreviated as NMP) solvent and stir well to form a uniform and stable paste with a viscosity of 15000 mPa·s. The paste does not gel, delaminate, or settle within 38 hours of standing.

[0179] 2. Preparation of positive electrode plate

[0180] Uniformly coat the positive electrode material paste on the positive electrode current collector Al foil. After drying, cold-press the electrode plate to the designed density and cut it into strips for standby to obtain the positive electrode plate.

[0181] 3. Preparation of electrolyte

[0182] Dissolve an equal volume of ethylene carbonate in propylene carbonate, and then uniformly dissolve lithium hexafluorophosphate salt in this mixed solvent for standby (the concentration of lithium hexafluorophosphate is 1.1 M / L) to obtain the electrolyte.

[0183] 4. Preparation of negative electrode plate

[0184] Mix the negative electrode active material such as graphite, 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 water solvent and stir well to form a uniform negative electrode stable paste; uniformly coat this paste on the negative electrode current collector Cu foil. After drying, cold-press the electrode plate to the designed density and cut it into strips for standby.

[0185] 5. Separator

[0186] Select PP as the separator.

[0187] 6. Preparation of battery cell

[0188] Using the conventional battery cell manufacturing process, the above-mentioned positive electrode sheet, separator film, and negative electrode sheet are wound together to form a bare battery cell, which is then placed into a battery housing, filled with the above-mentioned electrolyte, and then subjected to processes such as formation and sealing, finally obtaining a rechargeable power battery cell.

[0189] "Assembly of Battery Packs"

[0190] Obtain 10 first battery cells and 10 second battery cells, arrange the first battery cells and the second battery cells alternately, and electrically connect them in series.

[0191] "Test Method for OCV Variation Curve of Battery Cells in the 0%-100% SOC Range"

[0192] The method for testing the OCV variation curve of battery cells in the 0%-100% SOC range includes the following steps:

[0193] 1) At room temperature of 25°C, let the battery cell stand still for 120 minutes;

[0194] 2) Discharge the above-mentioned battery cell at a constant current of 0.33C until the discharge cut-off voltage (C is the nominal or rated capacity in the product technical specification), and let it stand still for 30 minutes;

[0195] 3) Charge the battery cell in step 2 above at a constant current of 0.33C until the charge cut-off voltage, and maintain a constant voltage until the current ≤ 0.05C, and let it stand still for 30 minutes;

[0196] 4) Discharge the battery cell in step 3 above at a constant current of 0.33C until the discharge cut-off voltage, record the discharged capacity as C0, and let it stand still for 30 minutes;

[0197] 5) Charge the battery cell in step 4 above at a constant current of 0.33C 0 until the charge cut-off voltage, and maintain a constant voltage until the current ≤ 0.05C0, and let it stand still for 30 minutes;

[0198] 6) Discharge the battery cell in step 5 above at a constant current of ≤ 0.05C 0 until the discharge cut-off voltage (requiring a fixed sampling frequency of 1 s), and let it stand still for 30 minutes;

[0199] 7) Charge the battery cell in step 6 above at a constant current of 0.05C 0 until the charge cut-off voltage (requiring a fixed sampling frequency of 1 s), and let it stand still for 30 minutes.

[0200] In the above steps, the 0.33C discharge rate refers to the discharge rate parameter used when the time required to charge or discharge a battery cell with a 1C capacity to completion is 3h; using 0.33C 0The discharge rate is such that when discharging for 9.09 minutes, the discharged capacity is equal to 9.09 min / 180 min = 0.05, that is, it accounts for 5% of the total capacity C 0 In addition, the nominal current can be freely selected according to the capacity of the battery pack. For example, when the capacity of the battery pack is 50 Ah, the nominal current can be 50 A; another example is that when the capacity of the battery pack is 100 Ah, the nominal current can be 100 A. The charging cut-off voltage and the discharging cut-off voltage can be determined with reference to the regulations in the product technical specification or the GBT certification document of the cell / battery pack

[0201] Test Method for the Discharge Battery Balance Rate of Cells

[0202] Respectively test the discharge capacity of the negative electrode sheet per unit area and the discharge capacity of the positive electrode sheet per unit area; then according to the formula: the discharge battery balance rate of the cell = the discharge capacity of the negative electrode sheet per unit area / the discharge capacity of the positive electrode sheet per unit area, the discharge battery balance rate of this cell can be calculated

[0203] Among them, the discharge capacity of the positive electrode sheet or the negative electrode sheet can be tested by the following steps

[0204] (1) The requirements for sampling the electrode sheet are as follows

[0205] After fully discharging the cell, disassemble it, take out the positive electrode sheet and the negative electrode sheet, rinse them appropriately with DMC solution, and dry them for standby. The sampling position of the positive electrode sheet is: select any position in the middle more than 15 mm away from the edge. The sampling position of the negative electrode sheet is: select the negative electrode sheet at the position directly opposite to the selected positive electrode sheet; and the sampling area of the positive electrode sheet is the same as that of the negative electrode sheet

[0206] (2) Assemble a coin-type half-cell with the above-cut positive electrode sheet and negative electrode sheet respectively using lithium sheets as counter electrodes

[0207] (3) Discharge capacity of the negative electrode sheet per unit area

[0208] The test voltage is 0.05 - 2.0 V, the test temperature is 25 °C, the charge / discharge rate is 0.1 C, take no less than 10 parallel samples, respectively test the discharge capacity of the coin-type half-cell, remove the lowest and the highest values and then take the average value to obtain the discharge capacity of the negative electrode sheet under this area; divide the discharge capacity of the negative electrode sheet obtained from the above test by the area of the negative electrode sheet, and the discharge capacity of the negative electrode sheet per unit area can be obtained

[0209] (4) Discharge capacity of the positive electrode sheet per unit area

[0210] Within the working voltage range specified in the GBT certification document of the sampled cell, at a room temperature of 25°C, charge and discharge at 0.1C. Take no less than 10 parallel samples and test the discharge capacity of the button cell respectively. After removing the lowest and highest values, take the average value to obtain the discharge capacity of the positive electrode sheet under this area; divide the discharge capacity of the positive electrode sheet obtained from the above test by the area of the positive electrode sheet, and the discharge capacity per unit area of the positive electrode sheet can be obtained.

[0211] "Test Method for Capacity Retention Rate of Battery Pack"

[0212] Refer to GB / T 31484-2015 "Requirements and Test Methods for Cycle Life of Power Batteries for Electric Vehicles".

[0213] Test method for capacity retention rate (25°C) at 1500 cycles:

[0214] Test steps for initial capacity (denoted as: Cap0):

[0215] 1) Let the newly manufactured battery pack stand still at 25°C for 30 minutes;

[0216] 2) Discharge at a constant current of 0.33C until the discharge end voltage of the battery pack is reached, and stand still for 30 minutes;

[0217] 3) Charge at a constant current of 0.33C until the charge end voltage of the battery pack is reached, and charge at a constant voltage until the current < 0.05C, then stand still for 5 minutes;

[0218] 4) Discharge at a constant current of 0.33C until the discharge end voltage of the battery pack is reached, and then stand still for 5 minutes.

[0219] The discharge capacity measured from step 3) to step 4) is denoted as Cap0. Steps 1) to 4) are one charge-discharge cycle of the battery pack. Repeat the above steps 1) to 4) 1500 times. The discharge capacity measured at the 1500th time is denoted as Capn, and the capacity retention rate at the 1500th time is: Capn / Cap0×100%.

[0220] In the above test, C represents the rated capacity of the cell. The charge / discharge current is the multiple multiplied by the rated capacity of the cell, and the rated capacity is based on the cell capacity recognized in the GBT certification document of this cell, or the battery module to which this cell belongs, or the battery pack to which this cell belongs.

[0221] "Detection Method for Lithium Deposition during Overcharge of Battery Pack"

[0222] At 25 ± 2°C, the battery pack is charged at a constant current of 1C to the upper cut-off voltage (the upper cut-off voltage of the battery pack can be determined with reference to the battery pack's specification sheet). Then, it is charged at a constant voltage of this upper cut-off voltage until the current reaches 0.05C, left to stand for 30 min. Then, the battery pack is fixed and placed on an overcharge safety test device. The ambient temperature is controlled at 25 ± 2°C. After standing for 5 min, the fully charged battery pack is overcharged at a rate of 1C, and the real-time voltage and temperature changes of each battery are recorded until the charging stops. For each example and comparative example, 6 battery packs are tested. The first type of battery cells in the battery pack are disassembled, and the lithium deposition condition on the surface of the negative electrode tab is observed, and the number of battery cells with lithium deposition is recorded.

[0223] Through the above-mentioned "Battery Cell Preparation" method, the battery packs of Examples 1 to 7 and the battery packs of Comparative Examples 1 and 2 can be obtained.

[0224] Example 1

[0225] In the first type of battery cells, the positive active material is LiFePO 4 , the discharge battery balance rate CB1 is 1.04, and the change rate ΔOCV / ΔSOC of the OCV with respect to the SOC in the range of 30% to 80% of the SOC of the first type of battery cells is 0.07, and the change rate ΔOCV / ΔSOC of the OCV with respect to the SOC in the range of 90% to 98% of the SOC is 0.28;

[0226] In the second type of battery cells, the positive active material is LiFePO 4 (LFP) and a mixture of LiNi 0.55 Co 0.12 Mn 0.33 O 2 (NCM), and the mixing ratio is LFP:NCM = 0.99:0.01. The discharge battery balance rate CB2 is 1.11, and the change rate ΔOCV / ΔSOC of the OCV with respect to the SOC in the range of 30% to 80% of the SOC of the second type of battery cells is 0.08, and the change rate ΔOCV / ΔSOC of the OCV with respect to the SOC in the range of 90% to 98% of the SOC is 8.89.

[0227] Examples 2 to 7 and Comparative Examples 1 and 2

[0228] In Examples 2 to 7 and Comparative Examples 1 to 2, the battery pack also includes 10 first type of battery cells and 10 second type of battery cells. Among them, the discharge battery balance rates CB1 and CB2 of the first type of battery cells and the second type of battery cells are the same as those in Example 1. The differences are shown in Table 1.

[0229] Table 1

[0230]

[0231] According to Table 1 above, in Example 1, the probability of lithium plating in the first type of battery cell due to overcharging is 2 / 10. In Example 2, the probability of lithium plating in the first type of battery cell due to overcharging is 1 / 10. In Examples 3 to 7, the probability of lithium plating in the first type of battery cell due to overcharging is 0 / 10.

[0232] On the other hand, in Comparative Example 1, both the first type of battery cell and the second type of battery cell are LFP. The change rate ΔOCV / ΔSOC of the OCV with respect to the SOC in the range of 90% - 98% of the SOC during the charging process of the battery pack is 0.71. That is, since the change rates ΔOCV / ΔSOC of the first type of battery cell and the second type of battery cell in the battery pack both change slowly, the probability of lithium plating in the first type of battery cell in the battery pack of Comparative Example 1 due to overcharging is very high (8 / 10).

[0233] In Comparative Example 2, although the change rate ΔOCV / ΔSOC of the OCV with respect to the SOC in the range of 90% - 98% of the SOC during the charging process of the second type of battery cell is 1.53, since the positive active material of the first type of battery cell is LFP and the positive active material of the second type of battery cell is NCM, that is, the doping of the positive active material of the first type of battery cell or the second type of battery cell is not optimized, the probability of lithium plating in the first type of battery cell in the battery pack of Comparative Example 2 due to overcharging is still relatively high (5 / 10).

[0234] It can be seen from this that in this application, by connecting the first type of battery cell and the second type of battery cell with different chemical systems in series, and adjusting the change rate ΔOCV / ΔSOC of the OCV with respect to the SOC of the second type of battery cell when approaching full charge within the range of 3 - 9 mV / %SOC, in Examples 1 - 7 after optimization design compared with Comparative Examples 1 and 2 without optimization design, the probability of lithium plating in the first type of battery cell in the battery pack due to overcharging is greatly reduced, thus significantly improving the safety of the battery pack.

[0235] In addition, according to Table 1 above, in this application, by optimizing the doping of the positive active material of the first type of battery cell or the second type of battery cell, in Examples 1 - 7 after optimization design compared with Comparative Examples 1 and 2 without optimization design, the capacity retention rate of the 1500th cycle of the battery pack is significantly improved, thus improving the service life of the battery pack.

[0236] <Design of the discharge battery balance rate of the second battery cell>

[0237] Next, the technical solutions and their advantages of this application will be described in detail through specific examples.

[0238] Regarding the preparation of the battery cells, a method similar to that of "Battery Cell Preparation" in the above Embodiments 1 to 7 is adopted. Among them, the first battery cells in Embodiments 8 to 12 are the same as those in Embodiment 3; the difference is that the specific parameters of the second battery cells in Embodiments 8 to 12 are different.

[0239] Table 2

[0240]

[0241] As can be seen from the above Table 2, in Embodiments 3, 8 to 10 where the CB2 of the second type of battery cell satisfies 1.00 ≤ CB2 ≤ 1.16, the probability of lithium plating occurring in the first type of battery cell in the battery pack due to overcharging is extremely low, and the capacity retention rate of the 1500th cycle of the battery pack remains at a relatively high level. On the contrary, in Embodiment 11 where the CB2 of the second type of battery cell does not satisfy 1.00 ≤ CB2 ≤ 1.16, the probability of lithium plating occurring in the first type of battery cell in the battery pack due to overcharging is not zero. In addition, in Embodiment 12 where the CB2 of the second type of battery cell does not satisfy 1.00 ≤ CB2 ≤ 1.16, although the probability of lithium plating occurring in the first type of battery cell in the battery pack due to overcharging is also relatively low, the capacity retention rate of the 1500th cycle of the battery pack is relatively low.

[0242] It can be seen therefrom that for the battery pack of the embodiments of the present application, while controlling the high SOC change characteristics of the second battery cell, when further limiting the discharge battery balance rate of the second battery cell within the range of 1 to 1.16, the overcharging phenomenon of the battery cells inside the hybrid series battery pack can be further effectively prevented, the safety of the battery pack is greatly improved, and the service life of the battery pack can also be improved.

[0243] <Design of the Discharge Battery Balance Rate of the First Battery Cell>

[0244] Next, the technical solutions and their advantages of the present application will be described in detail through specific embodiments.

[0245] Regarding the preparation of the battery cells, a method similar to that of "Battery Cell Preparation" in the above Embodiments 1 to 7 is adopted. Among them, the second battery cells in Embodiments 13 to 21 are the same as those in Embodiment 3; the difference is that the specific parameters of the first battery cells in Embodiments 13 to 21 are different, as shown in Table 3 for details.

[0247] Table 3

[0248]

[0249] As can be seen from Table 3 above, in Examples 3, 13 to 17 where the CB1 of the first type of battery cell satisfies 1.00 ≤ CB1 ≤ 1.18, the probability of lithium plating occurring in the first type of battery cells in the battery pack due to overcharging is extremely low, and the capacity retention rate of the battery pack at the 1500th cycle remains at a relatively high level. On the contrary, in Examples 18 to 21 where the CB1 of the first type of battery cell does not satisfy 1.00 ≤ CB1 ≤ 1.18, although the probability of lithium plating occurring in the first type of battery cells in the battery pack due to overcharging is also relatively low, the capacity retention rate of the battery pack at the 1500th cycle is relatively low.

[0250] From this, it can be seen that on the basis of setting the curvature characteristics of the high SOC range of the second type of battery cells in the embodiments of the present application, the discharge battery balance rate of the first type of battery cells is further optimized, which can effectively prevent overcharging of the battery cells inside the hybrid series battery pack, greatly improve the safety of the battery pack, and further improve the service life of the battery pack.

[0251] The various embodiments or implementation manners in this specification are described in a progressive manner. Each embodiment focuses on the differences from other embodiments. The same or similar parts among the various embodiments can be referred to each other.

[0252] In the description of this specification, the description with reference to terms such as "one implementation manner", "some implementation manners", "illustrative implementation manner", "example", "specific example", or "some examples" means that the specific features, structures, materials, or characteristics described in connection with the implementation manner or example are included in at least one implementation manner or example of the present application. In this specification, the schematic descriptions of the above terms do not necessarily refer to the same implementation manner or example. Moreover, the specific features, structures, materials, or characteristics described can be combined in a suitable manner in any one or more implementation manners or examples.

[0253] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present application, and are not intended to limit them; although the present 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 on 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 the present application.

Claims

1. A battery pack, characterized in that, it includes at least a first type of battery cell and a second type of battery cell 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, and N and M are positive integers; the first battery cell satisfies Condition 1 and Condition 2, Condition 1: When the dynamic SOC of the battery pack is in the range of 90% to 98%, the ratio Q of ΔOCV / ΔSOC of the second battery cell to ΔOCV / ΔSOC of the first battery cell is 2 < Q ≤ 40; Condition 2: When the dynamic SOC of the first battery cell is in the range of 30% to 80%, the change rate ΔOCV / ΔSOC of the OCV of the first battery cell with respect to SOC satisfies ΔOCV / ΔSOC ≤ 0.25, unit: mV / %SOC.

2. The battery pack according to claim 1, characterized in that, the positive electrode tab of the second battery cell contains two or more positive electrode active materials, and when the dynamic SOC of the second battery cell is in the range of 90% to 98%, the change rate ΔOCV / ΔSOC of the OCV of the second battery cell with respect to SOC satisfies: 3 ≤ ΔOCV / ΔSOC ≤ 9 unit: mV / %SOC, where SOC represents the state of charge and OCV represents the open circuit voltage.

3. The battery pack according to claim 1, characterized in that, when the dynamic SOC of the second battery cell is in the range of 90% to 98%, the change rate ΔOCV / ΔSOC of the OCV of the second battery cell with respect to SOC satisfies: 3.5 ≤ ΔOCV / ΔSOC ≤ 7, unit: mV / %SOC.

4. The battery pack according to claim 1, characterized in that, when the dynamic SOC of the second battery cell is in the range of 30% to 80%, the change rate ΔOCV / ΔSOC of the OCV of the second battery cell with respect to SOC satisfies: ΔOCV / ΔSOC ≤ 1, unit: mV / %SOC; Optionally, when the dynamic SOC of the second battery cell is in the range of 30% to 80%, the change rate ΔOCV / ΔSOC of the OCV of the second battery cell with respect to SOC satisfies: ΔOCV / ΔSOC ≤ 0.25, unit: mV / %SOC.

5. The battery pack according to claim 1, characterized in that, the discharge battery balance rate of the second battery cell is CB2, 1.00 ≤ CB2 ≤ 1.16, optionally, 1.03 ≤ CB2 ≤ 1.

11.

6. The battery pack according to claim 1, characterized in that, the positive electrode active material of the second battery cell at least includes the layered lithium transition metal oxide shown in formula (I) and the lithium-containing phosphate shown in formula (II), Li 1+x1 Ni a1 Co b1 M1 c1 M2 1-a1-b1-c1 O 2-y1 A1 y1 Formula (I) LiFe 1-x2-y2 Mn x2 M’ y2 PO 4 Formula (II) In formula (I), -0.1 ≤ x1 ≤ 0.2, 0.3 ≤ a1 < 0.97, 0 < b1 ≤ 0.3, 0 < a1 + b1 + c1 < 1, 0 ≤ y1 < 0.2, M1 is selected from at least one of Mn and Al, M2 is selected from one or more of Fe, Cr, Ti, Zn, V, Al, W, Mg, B, Cu, Y, Si, Sr, Zr, and Ce, and A1 is selected from one or more of S, N, F, Cl, Br, PO 4 3- and I; optionally, 0.5 ≤ a1 ≤ 0.7, 0.01 ≤ b1 ≤ 0.15; in formula (II), 0 ≤ x2 ≤ 1, optionally, 0 ≤ x2 ≤ 0.5, 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.

7. The battery pack according to claim 6, characterized in that, In the positive electrode active material of the second battery cell, the mass ratio of the layered lithium transition metal oxide represented by the formula (I) is 0.5 wt% to 30 wt%, optionally 1 wt% to 20 wt%, and further optionally 3 wt% to 15 wt%.

8. The battery pack according to claim 1, wherein, the first battery cell satisfies Condition 1 and Condition 2, Condition 1: When the dynamic SOC of the battery pack is in the range of 90% to 98%, the ratio Q of ΔOCV / ΔSOC of the second battery cell to ΔOCV / ΔSOC of the first battery cell is 4 ≤ Q ≤ 32; Condition 2: When the dynamic SOC of the first battery cell is in the range of 30% to 80%, the change rate ΔOCV / ΔSOC of the OCV of the first battery cell with respect to SOC satisfies ΔOCV / ΔSOC ≤ 0.15, unit: mV / %SOC.

9. The battery pack according to claim 1, wherein, the discharge battery balance rate of the first battery cell is CB1 and satisfies 1.00 ≤ CB1 ≤ 1.18; optionally, 1.04 ≤ CB1 ≤ 1.

14.

10. The battery pack according to claim 1, wherein, the positive electrode active material of the first battery cell includes a lithium-containing phosphate represented by the formula (III), LiFe 1-x3-y3 Mn x3 M” y3 PO 4 Formula (III) in the formula (III), 0 ≤ x3 ≤ 1, 0 ≤ y3 ≤ 0.1, and M'' is selected from one or more of transition metal elements other than Fe and Mn and non-transition metal elements; Optionally, the positive electrode active material of the first battery cell includes LiFePO 4 , LiMnPO 4 , LiMn 1-x3 Fe x3 PO 4 , LiV 1- x3 Fe x3 PO 4 wherein any one of them, and x3 independently satisfies 0 < x3 < 1.

11. The battery pack according to any one of claims 1-10, wherein, the positive electrode active material of the first battery cell includes a layered lithium transition metal oxide represented by the formula (IIII), Li 1+x4 Ni a2 Co b2 M3 c2 M4 1-a2-b2-c2 O 2-y4 A2 y4 Formula (IIII) in the formula (IIII), -0.1 ≤ x4 ≤ 0.2, 0.3 ≤ a2 < 0.95, 0 < b2 < 0.3, 0 < a2 + b2 + c2 < 1, 0 ≤ y4 < 0.2, M3 is selected from at least one of Mn and Al, M4 is selected from one or more of Fe, Cr, Ti, Zn, V, Al, Zr, and Ce, and A2 is selected from one of S, F, Cl, and I.

12. A battery pack, wherein, it includes the battery pack according to any one of claims 1-11.

13. An electrical device, wherein, it includes the battery pack according to any one of claims 1-11 or the battery pack according to claim 12, and the battery pack or the battery pack serves as the power source or energy storage unit of the electrical device.

14. A manufacturing method of a battery pack, wherein, it includes the following steps: obtain a first type of battery cell and a second type of battery cell, 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, and N and M are positive integers, The positive electrode tab of the second battery cell contains two or more positive electrode active materials, and when the dynamic SOC of the second battery cell is in the range of 90% to 98%, the change rate ΔOCV / ΔSOC of the OCV of the second battery cell with respect to the SOC satisfies: 3 ≤ ΔOCV / ΔSOC ≤ 9, where SOC represents the state of charge and OCV represents the open circuit voltage; and The first type of battery cell and the second type of battery cell are connected in series at least to form a battery pack according to any one of claims 1-11.

15. A manufacturing apparatus for a battery pack, Characterized in that, Comprising: A clamping arm unit for acquiring the first type of battery cell and the second type of battery cell, 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 positive electrode tab of the second battery cell contains two or more positive electrode active materials, and when the dynamic SOC of the second battery cell is in the range of 90% to 98%, the change rate ΔOCV / ΔSOC of the OCV of the second battery cell with respect to the SOC satisfies: 3 ≤ ΔOCV / ΔSOC ≤ 9, where SOC represents the state of charge and OCV represents the open circuit voltage; An assembly unit for connecting the first type of battery cell and the second type of battery cell in series at least to form a battery pack according to any one of claims 1-11; and A control unit for controlling the clamping arm unit and the assembly unit.

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