Battery pack, battery package, power-consuming device, and manufacturing method and manufacturing equipment of battery pack

Abstract

The present application relates to a battery pack, comprising at least a first type of battery cell and a second type of battery cell electrically connected in series, the first type of battery cell and the second type of battery cell are battery cells of different chemical systems, the first type of battery cell comprises N first battery cells, the second type of battery cell comprises M second battery cells, N and M are positive integers; the positive electrode plate of the second battery cell contains two or more positive active substances, and when the dynamic SOC of the second battery cell is in the range of 90% to 98%, the change rate of OCV of the second battery cell relative to SOC ΔOCV / ΔSOC satisfies: 3≤ΔOCV / ΔSOC≤9, unit: mV / %SOC, wherein SOC represents the state of charge and OCV represents the open circuit voltage.

Description

Technical Field

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

[0002] Secondary batteries are a clean, renewable resource that can be used as a driving energy source or storage unit in the automotive, energy storage and other fields. With the increasing requirements for energy and environmental protection, the application of secondary batteries is becoming increasingly popular and extensive. In order to adapt to different environments and application scenarios, the industry has put forward new requirements for the performance of secondary batteries.

[0003] At present, in order to increase the total available energy of secondary batteries, multiple cells of the same chemical system are usually connected in series or parallel to form a battery pack (or battery pack). However, due to the limitations of the design of the battery cell chemical system, it is often difficult to achieve simultaneous improvement of multiple electrical properties of the battery pack by adjusting the chemical system inside a single cell. In the prior art, most battery packs (or battery packs) using single cells of the same chemical system are used, such as lithium iron phosphate cells, or lithium nickel cobalt manganese oxide ternary cells. However, the battery packs or battery packs composed of these are often prone to overcharging when they are close to full charge during the charging process, causing safety problems.

[0004] Therefore, on the basis of ensuring that secondary batteries (especially battery packs or battery packs) exert their good electrical performance, how to further improve their overcharge prevention capabilities and enhance the safety performance of battery packs has become one of the urgent issues to be solved in the field of secondary battery research. Summary of the invention

[0005] The present application is completed in view of the above-mentioned problems existing in the prior art, and its purpose is to provide 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. By matching the SOC-OCV curves of the first type of battery cell and the second type of battery cell, the second type of battery cell is used to accurately reflect the charging state of the battery pack when it is close to a fully charged state, thereby effectively preventing the overcharging of the battery cells in the battery pack and greatly improving the safety of the battery pack.

[0006] The first aspect of the present application provides a battery pack, comprising at least a first type of battery cell and a second type of battery cell electrically connected in series, the first type of battery cell and the second type of battery cell are battery cells of different chemical systems, the first type of battery cell includes N first battery cells, the second type of battery cell includes M second battery cells, N and M are positive integers; the positive electrode plate of the second battery cell contains two or more positive active substances, and when the dynamic SOC of the second battery cell is in the range of 90% to 98%, the change rate of OCV of the second battery cell relative to SOC ΔOCV / ΔSOC satisfies: 3≤ΔOCV / ΔSOC≤9, unit: mV / %SOC, wherein SOC represents the state of charge and OCV represents the open circuit voltage.

[0007] In any embodiment of the present application, when the dynamic SOC of the second battery cell is in the range of 90% to 98%, the rate of change of OCV of the second battery cell relative to SOC ΔOCV / ΔSOC satisfies: 3.5≤ΔOCV / ΔSOC≤7, unit: mV / %SOC.

[0008] In any embodiment of the present application, when the dynamic SOC of the second battery cell is in the range of 30% to 80%, the rate of change of OCV of the second battery cell relative to SOC ΔOCV / ΔSOC satisfies: ΔOCV / ΔSOC≤1, 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% to 80%, the rate of change of OCV of the second battery cell relative to SOC ΔOCV / ΔSOC satisfies: ΔOCV / ΔSOC≤0.25, unit: mV / %SOC.

[0010] 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.

[0011] In any embodiment of the present application, the positive electrode active material of the second battery cell at least includes a layered lithium transition metal oxide represented by formula (I) and a lithium-containing phosphate represented by formula (II).

[0012] Li 1+x1 Ni a1 C ob1 M1 c1 M2 1-a1-b1-c1 O 2-y1 A1 y1 Formula (I)

[0013] LiFe 1-x2-y2 Mn x2 M' y2 PO4 Formula (II)

[0014] 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, A1 is selected from S, N, F, Cl, Br, PO 4 3- and I; optionally, 0.5≤a1≤0.7, 0.01≤b1≤0.15;

[0015] In formula (II), 0≤x2≤1, optionally, 0≤x2≤0.5, 0≤y2≤0.1, and M′ is selected from one or more transition metal elements except Fe and Mn and non-transition metal elements.

[0016] In any embodiment of the present application, in the positive electrode active material of the second battery cell, the mass proportion of the layered lithium transition metal oxide represented by formula (I) is 0.5wt% to 30wt%, optionally 1wt% to 20wt%, and further optionally 3wt% to 15wt%.

[0017] In any embodiment of the present application, the first battery cell satisfies the following conditions 1 and 2:

[0018] 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;

[0019] Condition 2: When the dynamic SOC of the first battery cell is in the range of 30% to 80%, the rate of change of OCV of the first battery cell relative to SOC ΔOCV / ΔSOC satisfies ΔOCV / ΔSOC≤0.25, unit: mV / %SOC; Optionally, when the rate of change of the dynamic SOC of the first battery cell in the range of 30% to 80% ΔOCV / ΔSOC≤0.15.

[0020] 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.

[0021] 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),

[0022] LiFe 1-x3-y3Mn x3 M” y3 PO 4 Formula (III)

[0023] Wherein, 0≤x3≤1, 0≤y3≤0.1, and M″ is selected from one or more of transition metal elements and non-transition metal elements except Fe and Mn.

[0024] 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 the following, where x3 independently satisfies 0<x3<1.

[0025] In some other embodiments of the present application, the positive electrode active material of the first battery cell at least includes a layered lithium transition metal oxide represented by formula (IIII),

[0026] Li 1+x4 Ni a2 Co b2 M3 c2 M4 1-a2-b2-c2 O 2-y4 A2 y4 Formula (III)

[0027] 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 A1, 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.

[0028] A second aspect of the present application provides a battery pack, comprising the battery pack described in the first aspect.

[0029] A third aspect of the present application provides an electrical device, comprising the battery pack described in the first aspect or the battery pack described in the second aspect, wherein the battery pack or the battery pack serves as a power source or energy storage unit for the electrical device.

[0030] The fourth aspect of the present application provides a method for manufacturing a battery pack, comprising the following steps: obtaining 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, N and M are positive integers, the positive electrode plate 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 rate of change of OCV of the second battery cell relative to SOC ΔOCV / ΔSOC satisfies: 3≤ΔOCV / ΔSOC≤9, wherein 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 at least in series to form the battery pack described in the first aspect above.

[0031] The fifth aspect of the present application provides a battery pack manufacturing device, comprising: a clamping arm unit, the clamping arm unit is used to 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, N and M are positive integers, the positive electrode plate of the second battery cell contains two or more positive active substances, and when the dynamic SOC of the second battery cell is in the range of 90% to 98%, the change rate of OCV of the second battery cell relative to SOC ΔOCV / ΔSOC satisfies: 3≤ΔOCV / ΔSOC≤9, wherein SOC represents the state of charge and OCV represents the open circuit voltage; an assembly unit, the assembly unit is used to connect 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, the control unit is used to control the clamping arm unit and the assembly unit.

[0032] [Technical Effect]

[0033] 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 at least in series 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 a fully charged state, the second type of battery cell with higher recognition can be used to accurately reflect the overall charge state of the battery pack, effectively improving the problem of easy overcharging of the battery pack and greatly improving the safety of the battery pack. BRIEF DESCRIPTION OF THE DRAWINGS

[0034] Figure 1 is a schematic diagram showing an example of a battery cell of the present application.

[0035] Figure 2 It is shown Figure 1 An exploded view of an example of a battery cell of the present application is shown.

[0036] Figure 3 is a schematic diagram showing one example of the battery pack of the present application.

[0037] Figure 4 is a schematic diagram showing an example of a battery pack of the present application.

[0038] Figure 5 It is shown Figure 4 An exploded view of an example of a battery pack of the present application is shown.

[0039] Figure 6 1 is a schematic diagram showing an example of an electric device using the battery pack of the present application as a power source.

[0040] The reference numerals are described as follows:

[0041] 5, 5a, 5b cells

[0042] 51 Shell

[0043] 52 Electrode assembly

[0044] 53 Cover

[0045] 4 Battery Pack

[0046] 1 Battery Pack

[0047] 2 upper box

[0048] 3 lower box DETAILED DESCRIPTION

[0049] "Scope" disclosed herein is defined in the form of lower limit and upper limit, and a given range is defined by selecting a lower limit and an upper limit, and the selected lower limit and upper limit define the boundary of a particular range. The scope defined in this way can be including end values ​​or not including end values, and can be arbitrarily combined, that is, any lower limit can be combined with any upper limit to form a scope. For example, if the scope of 60-120 and 80-110 is listed for a particular parameter, it is understood that the scope of 60-110 and 80-120 is also expected. In addition, if the minimum range values ​​1 and 2 are listed, and if the maximum range values ​​3, 4 and 5 are listed, the following scope can all be expected: 1-3, 1-4, 1-5, 2-3, 2-4 and 2-5. In this application, unless otherwise specified, the numerical range "ab" represents the abbreviation of any real number combination between a and b, wherein a and b are real numbers. For example, the numerical range "0-5" means that all real numbers between "0-5" are listed in this document, and "0-5" is just an abbreviation of these numerical combinations. In addition, when a parameter is expressed as an integer ≥ 2, it is equivalent to disclosing that the parameter is, for example, an integer of 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, etc.

[0050] In this application, unless otherwise specified, all embodiments and preferred embodiments mentioned herein can be combined with each other to form a new technical solution.

[0051] In this application, unless otherwise specified, all technical features and preferred features mentioned herein can be combined with each other to form a new technical solution.

[0052] In the present application, unless otherwise specified, all steps mentioned herein may be performed sequentially or randomly, but are preferably performed sequentially. For example, the method includes steps (a) and (b), which means that the method may include steps (a) and (b) performed sequentially, or may include steps (b) and (a) performed sequentially. For example, the method may further include step (c), which means that step (c) may be added to the method in any order, for example, the method may include steps (a), (b) and (c), or may include steps (a), (c) and (b), or may include steps (c), (a) and (b), etc.

[0053] In this application, unless otherwise specified, the terms "include" and "comprising" mentioned herein may be open-ended or closed-ended. For example, the terms "include" and "comprising" may mean that other components not listed may also be included or only the listed components may be included or only the listed components may be included.

[0054] In the description of this article, it should be noted that, unless otherwise specified, "above" and "below" are inclusive of the number itself, and "several" in "one or several" means two or more.

[0055] In the description herein, unless otherwise specified, the term "or" is inclusive. For example, the phrase "A or B" means "A, B, or both A and B". More specifically, any of the following conditions satisfies the condition "A or B": A is true (or exists) and B is false (or does not exist); A is false (or does not exist) and B is true (or exists); or both A and B are true (or exist).

[0056] [Battery Cell]

[0057] In the present application, "battery cell" refers to a battery cell that can be charged and discharged independently. The battery cell includes a positive electrode sheet, a negative electrode sheet, a separator, an electrolyte, and an outer packaging for encapsulating the positive electrode sheet, the negative electrode sheet, the separator and the electrolyte. The present application has no special restrictions on the type and shape of the battery cell, which can be a soft-pack battery cell, a cylindrical battery cell, a square battery cell and other types of battery cells. The battery cell in the present application can be a lithium-ion battery cell, a potassium-ion battery cell, a sodium-ion battery cell, a lithium-sulfur battery cell, etc., and lithium-ion batteries are particularly preferred. During the charge and discharge process of the battery cell, the active ions are embedded and removed back and forth between the positive electrode sheet and the negative electrode sheet. The electrolyte plays the role of conducting ions between the positive electrode sheet and the negative electrode sheet.

[0058] In the present application, "battery cell" refers to a battery cell that can be charged and discharged independently. The components of the battery cell may include a positive electrode sheet, a negative electrode sheet, a separator, an electrolyte, and an outer packaging for encapsulating the positive electrode sheet, the negative electrode sheet, the separator and the electrolyte. The present application has no particular restrictions on the type and shape of the battery cell, which can be a soft-pack battery cell, a cylindrical battery cell, a square battery cell and other types of batteries. The battery cell in the present application can be a lithium-ion battery cell, a potassium-ion battery cell, a sodium-ion battery cell, a lithium-sulfur battery cell, etc., and lithium-ion batteries are particularly preferred. During the battery charging and discharging process, active ions are embedded and removed back and forth between the positive electrode sheet and the negative electrode sheet. The electrolyte plays the role of conducting ions between the positive electrode sheet and the negative electrode sheet.

[0059] In the present application, the "chemical system" of the battery cell is divided according to the components of the positive electrode active material used in the positive electrode plate of the battery cell, and there is no limitation on the doped or coated elements or substances of the positive electrode active material. For example, the battery cells whose positive electrode active material is lithium iron phosphate (including doped with Mn or V elements) can be defined as lithium iron phosphate chemical system battery cells. The battery cells whose positive electrode active material is lithium nickel cobalt manganese oxide (generally referred to as NCM) can be defined as NCM chemical system battery cells. Furthermore, the battery cell chemical system can be further limited according to the relative contents of nickel, cobalt, and manganese elements in the positive electrode active material. For example, the positive electrode active material is LiNi0.5 Co 0.2 Mn 0.3 O 2 The battery cell (generally referred to as NCM523) can be defined as the NCM523 chemical system battery cell, and the positive electrode active material is LiNi 0.6 Co 0.2 Mn 0.2 O 2 The battery cell (generally referred to as NCM622) can be defined as a NCM622 chemical system battery cell, with the positive electrode active material being LiNi 0.8 Co 0.1 Mn 0.1 O 2 A battery cell using a nickel cobalt aluminum oxide (NCA) system battery cell (generally referred to as NCM811) as the positive electrode material can be defined as an NCA chemical system battery cell. In addition, in the present application, a hybrid system battery cell can also be used, for example, a hybrid system battery cell including NCM and NCA.

[0060] Below, the basic structure of the negative electrode sheet, positive electrode sheet, electrolyte, and separator of the battery cell in the present application is first described.

[0061] <Positive electrode>

[0062] In the battery cell of the present application, the positive electrode plate includes a positive electrode current collector and a positive electrode film layer disposed on at least one surface of the positive electrode current collector and including a positive electrode active material. For example, the positive electrode current collector has two surfaces opposite to each other in the thickness direction thereof, and the positive electrode film layer is disposed on any one or both of the two opposite surfaces of the positive electrode current collector. In the battery cell of the present application, the positive electrode current collector may be a metal foil or a composite current collector, for example, the metal foil may be an aluminum foil, and the composite current collector may include a polymer material base layer and a metal layer formed on at least one surface of the polymer material base layer. The composite current collector may be formed by forming a metal material (aluminum, aluminum alloy, nickel, nickel alloy, titanium, titanium alloy, silver and silver alloy, etc.) on a polymer material substrate (such as a substrate of polypropylene PP, polyethylene terephthalate PET, polybutylene terephthalate PBT, polystyrene PS, polyethylene PE and its copolymers, etc.).

[0063] In the battery cell of the present application, the positive electrode active material may adopt the positive electrode active material for battery cells known in the art. For example, the positive electrode active material may 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 traditional materials that can be used as positive electrode active materials for battery cells may also be used. These positive electrode active materials may be used alone or in combination of two or more. Among them, examples of lithium transition metal oxides may include, but are not limited to, lithium cobalt oxides (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 its modified compounds, etc. Examples of lithium phosphates containing olivine structures may 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 ), one or more of a composite material of lithium manganese phosphate and carbon, a composite material of lithium iron manganese phosphate, and a composite material of lithium iron manganese phosphate and carbon.

[0064] In some embodiments, the positive electrode film layer may also optionally include a binder. Non-limiting examples of binders that can be used for the positive electrode film layer may include one or more of the following: polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), vinylidene fluoride-tetrafluoroethylene-propylene terpolymer, vinylidene fluoride-hexafluoropropylene-tetrafluoroethylene terpolymer, tetrafluoroethylene-hexafluoropropylene copolymer, and fluorine-containing acrylate resin.

[0065] In some embodiments, the positive electrode film layer may further optionally include a conductive agent. Examples of the conductive agent used in the positive electrode film layer may include one or more of superconducting carbon, acetylene black, carbon black, Ketjen black, carbon dots, carbon nanotubes, graphene, and carbon nanofibers.

[0066] In one embodiment of the present application, the positive electrode can be prepared in the following manner: the above-mentioned components for preparing the positive electrode, such as the positive electrode active material, the conductive agent, the binder and any other components are dispersed in a solvent (such as N-methylpyrrolidone) to form a uniform positive electrode slurry; the positive electrode slurry is coated on the positive electrode collector, and after drying, cold pressing and other processes, the positive electrode sheet can be obtained.

[0067] <Negative electrode>

[0068] The battery cell of the present application includes a negative electrode plate, wherein the negative electrode plate includes a negative electrode current collector and a negative electrode film layer disposed on at least one surface of the negative electrode current collector, wherein the negative electrode film layer contains a negative electrode active material.

[0069] In one embodiment of the present application, the negative electrode active material in the negative electrode film layer may be a commonly used negative electrode active material in the art, for example, one or more of natural graphite, artificial graphite, soft carbon, hard carbon, silicon-based materials, tin-based materials, and lithium titanate. The silicon-based material may be selected from one or more of elemental silicon, silicon oxide, and silicon-carbon composite. The tin-based material may be selected from one or more of elemental tin, tin oxide compounds, and tin alloys.

[0070] In the battery cell of the present application, the negative electrode membrane may further contain an optional binder, an optional conductive agent and other optional auxiliary agents in addition to the negative electrode active material. The negative electrode membrane of the present application is usually formed by coating and drying the negative electrode slurry. The negative electrode slurry is usually formed by dispersing the negative electrode active material and the optional conductive agent and binder in a solvent and stirring them evenly. The above-mentioned solvent can be N-methylpyrrolidone (NMP) or deionized water.

[0071] As an example, the conductive agent may include one or more of superconducting carbon, carbon black (eg, acetylene black, Ketjen black), carbon dots, carbon nanotubes, graphene, and carbon nanofibers.

[0072] As an example, the binder may include one or more of styrene-butadiene rubber (SBR), water-soluble unsaturated resin SR-1B, polyacrylic acid (PAA), sodium polyacrylate (PAAS), polyacrylamide (PAM), polyvinyl alcohol (PVA), sodium alginate (SA) and carboxymethyl chitosan (CMCS). As an example, the binder may include one or more of styrene-butadiene rubber (SBR), polyvinyl alcohol (PVA), sodium alginate (SA), polymethacrylic acid (PMAA) and carboxymethyl chitosan (CMCS). Other optional additives are, for example, thickeners (such as sodium carboxymethyl cellulose CMC-Na), PTC thermistor materials, etc.

[0073] In addition, in the battery cell of the present application, the negative electrode plate does not exclude other additional functional layers besides the negative electrode film layer. For example, in some embodiments, the negative electrode plate of the present application may also include a conductive primer layer (e.g., composed of a conductive agent and a binder) sandwiched between the negative electrode current collector and the first negative electrode film layer and disposed on the surface of the negative electrode current collector. In some other embodiments, the negative electrode plate of the present application may also include a covering protective layer covering the surface of the second negative electrode film layer.

[0074] 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 composed 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 (copper, copper alloy, nickel, nickel alloy, titanium, titanium alloy, silver and silver alloy, etc.) on a 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 copolymers thereof).

[0075] <Electrolyte>

[0076] The electrolyte plays a role in conducting ions between the positive electrode and the negative electrode. The electrolyte includes an electrolyte salt and a solvent. In some embodiments, the electrolyte salt can be selected from lithium hexafluorophosphate (LiPF 6 ), lithium tetrafluoroborate (LiBF 4 ), lithium perchlorate (LiClO 4 ) and lithium hexafluoroarsenate (LiA s F 6 ), lithium bis(fluorosulfonyl)imide (LiFSI), lithium bis(trifluoromethanesulfonyl)imide (LiTFSI), lithium trifluoromethanesulfonate (LiTFS), lithium difluorooxalatoborate (LiDFOB), lithium dioxalatoborate (LiBOB), lithium difluorophosphate (LiPO 2 F 2), one or more of lithium difluorooxalate phosphate (LiDFOP) and lithium tetrafluorooxalate phosphate (LiTFOP).

[0077] In one embodiment of the present application, the solvent can 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), methyl ethyl sulfone (EMS) and diethyl sulfone (ESE).

[0078] 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.

[0079] In one embodiment of the present application, the electrolyte may optionally 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 additives that can improve certain battery properties, such as additives that improve battery overcharge performance, additives that improve battery high temperature performance, additives that improve battery low temperature performance, etc.

[0080] <Isolation film>

[0081] In one embodiment of the present application, the battery cell also includes a separator, which separates the positive electrode plate from the negative electrode plate of the battery cell, and provides selective permeability or blocking for substances of different types, sizes and charges in the system. For example, the separator can insulate 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 allow ions in the battery to pass through the separator and move between the positive and negative electrodes.

[0082] In one embodiment of the present application, the material used to prepare the isolation membrane may include one or more of glass fiber, non-woven fabric, polyethylene, polypropylene and polyvinylidene fluoride. The isolation membrane may be a single-layer film or a multi-layer composite film. When the isolation membrane is a multi-layer composite film, the materials of each layer may be the same or different.

[0083] In one embodiment of the present application, the positive electrode sheet, the negative electrode sheet and the separator can be made into an electrode assembly / bare cell by a winding process or a lamination process.

[0084] In one embodiment of the present application, the battery cell further includes an outer packaging, which can be used to encapsulate the above-mentioned electrode assembly and electrolyte. In some embodiments, the outer packaging 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 packaging of the battery cell can be a soft package, such as a bag-type soft package. The material of the soft package can be plastic, such as one or more of polypropylene (PP), polybutylene terephthalate (PBT), polybutylene succinate (PBS), etc.

[0085] Figure 1 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 a battery cell 5 of the present application is shown.

[0086] The outer package may include a shell 51 and a cover plate 53. The shell 51 may include a bottom plate and a side plate connected to the bottom plate, and the bottom plate and the side plate enclose a receiving cavity. The shell 51 has an opening connected to the receiving cavity, and the cover plate 53 can be covered on the opening to close the receiving cavity. The positive electrode sheet, the negative electrode sheet and the isolation film can be formed into an electrode assembly 52 through a winding process or a lamination process. 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 contained in the battery cell 5 can be one or more.

[0087] [Battery Pack]

[0088] In the present application, a "battery pack" is formed by electrically connecting a certain number of cells together and placing them in a frame in order to protect the cells from external impact, heat, vibration, etc. The shape of the cells in the present application can be cylindrical, square or any other shape.

[0089] In the present application, several battery cells may be assembled together to form a battery pack, which includes 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.

[0090] Figure 3 is a schematic diagram showing an example of a battery pack of the present application. Figure 3In the battery pack 4, the multiple battery cells 5a and 5b can be arranged in sequence along the length direction of the battery pack 4 (wherein 5a can be the first battery cell and 5b can be the second battery cell). Of course, they can also be arranged in any other manner. The multiple battery cells 5a and 5b can be further fixed by fasteners. Optionally, the battery pack 4 can also include a shell having a storage space, and the multiple groups 5a and 5b are stored in the storage space.

[0091] <About the design of the first battery cell and the second battery cell>

[0092] 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, wherein the first type of battery cell and the second type of battery cell are battery cells of different chemical systems.

[0093] The first type of battery cells includes N first battery cells,

[0094] The second type of battery cells includes M second battery cells, where N and M are positive integers;

[0095] The positive electrode sheet of the second battery cell contains two or more positive active materials, and the change rate of OCV relative to SOC ΔOCV / ΔSOC of the second battery cell in the range of 90% to 98% during charging satisfies: 3≤ΔOCV / ΔSOC≤9, unit: mV / %SOC,

[0096] Among them, SOC stands for state of charge, and OCV stands for open circuit voltage.

[0097] In the field of batteries, the capacity of a battery is generally reflected by testing the state of charge (SOC) of the battery.

[0098] Generally, a battery pack is composed of multiple cells with the same chemical system connected in series or parallel to output electrical energy to the outside in a unified manner. The advantage of the same chemical system of multiple cells in a battery pack is that it is conducive to improving the charge and discharge consistency of multiple cells, avoiding the short board effect, and helping to improve the overall electrical performance and service life of the battery pack. Common positive electrode active materials include a class of olivine structure materials such as lithium iron phosphate, and a class of ternary layered materials such as lithium nickel cobalt manganese oxide. When the positive electrode active material of the battery cell in the battery pack is a material with a long charging platform such as lithium iron phosphate, when it is charged to a state close to full charge (i.e., 90% to 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 when it is close to full charge by OCV, and it is very easy to cause overcharge problems in the battery pack. At the same time, in order to improve the energy density of the battery pack, the amount of negative electrode active material is usually minimized, resulting in a sharp decrease in the active sites available for lithium ion embedding in the negative electrode sheet when the battery cell is charged close to full charge, which is very easy to cause overcharge 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.

[0099] 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 of different chemical systems, and the first type of battery cell and the second type of battery cell are at least connected in series, and the positive electrode 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 a high SOC state is within the range of 3 to 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 charging and discharging trends of the two types of batteries are consistent. As the charging state changes, the second type of battery cell can be easily and accurately identified by the change in open circuit voltage under a high SOC state. Therefore, the charge state change of the second type of battery cell can be used to accurately characterize the charge state change of the entire battery pack. 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 problem of easy overcharging of the battery pack under a high SOC state, thereby improving the safety of the battery pack.

[0100] In this application, the method for obtaining the dynamic OCV change curve of the battery cell in any range of 0%-100% SOC generally includes the following steps:

[0101] 1) Leave the battery at room temperature of 25°C for 120 minutes;

[0102] 2) Discharge the above battery cells 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 for 30 minutes;

[0103] 3) Charge the battery cell in step 2 at a constant current of 0.33C to the end-of-charge voltage, and then charge the battery cell at a constant current of ≤0.05C, and let it stand for 30 minutes;

[0104] 4) Discharge the battery cell in step 3 at a constant current of 0.33C to the discharge termination voltage, and record the discharged capacity as C 0 , let stand for 30 minutes;

[0105] 5) Heat the battery cell in step 4 at 0.33C 0 Constant current charging to charging termination voltage, constant voltage to current ≤ 0.05C 0 , let stand for 30 minutes;

[0106] 6) Heat the battery cell in step 5 above at ≤0.05C 0 Discharge at a constant current rate of 10000 to the discharge termination voltage (the stepping frequency is required to be fixed at 1s), and let it stand for 30 minutes;

[0107] 7) Heat the battery cell in step 6 at 0.05C 0 Charge at constant current to the charge termination voltage (the stepping frequency is required to be fixed at 1s), let it stand for 30 minutes, and obtain the dynamic OCV change curve of the battery cell in the 0%-100% SOC range.

[0108] In the above steps, the 0.33C discharge rate refers to the discharge rate parameter used when the time taken to charge or discharge a 1C capacity battery cell is 3 hours; 0 The discharge rate is 9.09min, and the capacity released is equal to 9.09min / 180min=0.05, which accounts for the total capacity C 0 5%. In the present application, the test rate in steps 1) to 5) of the battery dynamic SOC test method can also be any value between 0.01C and 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; for example, 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 formulated with reference to the provisions in the product technical specification or the GBT certification documents of the battery cell / battery pack.

[0109] According to the dynamic OCV change curve of the battery cell in the SOC range of 0%-100%, the OCV change difference corresponding to any SOC interval can be obtained, and the difference is the OCV change rate (ΔOCV / ΔSOC) of the battery cell in a certain SOC range.

[0110] In some embodiments of the present application, when the dynamic SOC of the second battery cell is in the range of 90% to 98%, the rate of change of the OCV of the second battery cell relative to the SOC ΔOCV / ΔSOC satisfies: 3.5≤ΔOCV / ΔSOC≤7, unit: mV / %SOC. That is to say, in the high SOC range, for every 1% increase or decrease in the state of charge of the second battery cell, 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, so that the change in the state of charge when the battery pack is about to be fully charged can be accurately obtained.

[0111] In some embodiments of the present application, when the dynamic SOC of the second battery cell is in the range of 30% to 80%, the rate of change of OCV of the second battery cell relative to SOC ΔOCV / ΔSOC satisfies: ΔOCV / ΔSOC≤1, unit: mV / %SOC.

[0112] Optionally, when the dynamic SOC of the second battery cell is in the range of 30% to 80%, the rate of change of the OCV of the second battery cell relative to the SOC ΔOCV / ΔSOC satisfies: ΔOCV / ΔSOC≤0.25, unit: mV / %SOC. In the present application, the OCV change rate of the second battery cell in the range of 30% to 80% SOC during the charging process is low, so that the second battery cell can maintain a longer and stable charging voltage platform during the charging and discharging process, which is conducive to ensuring that the positive electrode active material undergoes less structural and chemical changes during repeated charging and discharging, and the charge and discharge capacity decays less with long-term use, which is conducive to extending the overall cycle life of the battery pack.

[0113] 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 rate of the positive and negative active materials in the second battery cell can be further improved, which is beneficial to improve the single volume energy density of the second battery cell while ensuring that the risk of lithium plating in the second battery cell is low.

[0114] In this application, the discharge battery balance rate of the battery cell is a well-known meaning in the art and can be tested by conventional methods. As an example, the following test method can be used: test the discharge capacity per unit area of ​​the negative electrode sheet and the discharge capacity per unit area of ​​the positive electrode sheet in the battery cell respectively; then according to the formula: battery cell discharge battery balance rate = discharge capacity per unit area of ​​the negative electrode sheet / discharge capacity per unit area of ​​the positive electrode sheet, the discharge battery balance rate of the battery cell can be calculated.

[0115] The discharge capacity of the positive electrode sheet or the negative electrode sheet is well known in the art and can be tested by conventional methods. As an example, the following steps can be used for testing:

[0116] (1) The requirements for electrode sampling are as follows:

[0117] After fully discharging the battery cell, disassemble it, take out the positive and negative pole pieces, rinse them appropriately with dimethyl carbonate (DMC) solution, and dry them for later use. The sampling position of the positive pole piece is: select any position in the middle that is greater than 15mm from the edge. The sampling position of the negative pole piece is: select the negative pole piece that is opposite to the selected positive pole piece; and the sampling area of ​​the positive pole piece is the same as the sampling area of ​​the negative pole piece;

[0118] (2) Assembling a button cell using the above-cut positive electrode sheet, negative electrode sheet and lithium sheet as counter electrodes;

[0119] (3) Discharge capacity of negative electrode per unit area:

[0120] The test voltage is 0.05-2.0V, the test temperature is 25°C, the charge / discharge rate is 0.1C, and no less than 10 parallel samples are taken to test the discharge capacity of the button half-cell respectively. The lowest and highest values ​​are removed and the average value is taken to obtain the discharge capacity of the negative electrode sheet under the area; the discharge capacity of the negative electrode sheet obtained by the above test is divided by the area of ​​the negative electrode sheet to obtain the discharge capacity of the negative electrode sheet per unit area;

[0121] (4) Discharge capacity of positive electrode per unit area:

[0122] Within the operating voltage range specified in the GBT certification document for the sampled battery cell and at room temperature of 25°C, charge / discharge at 0.1C, take no less than 10 parallel samples, and test the discharge capacity of the button battery respectively. After removing the lowest and highest values, take the average value to obtain the discharge capacity of the positive electrode sheet under the area; divide the discharge capacity of the positive electrode sheet obtained by the above test by the area of ​​the positive electrode sheet to obtain the discharge capacity of the positive electrode sheet per unit area.

[0123] In some embodiments of the present application, the positive electrode active material of the second battery cell includes at least a layered lithium transition metal oxide represented by formula (I) and a lithium-containing phosphate represented by formula (II), Li 1+x1 Ni a1 Co b1 M 1-a1-b1 O 2-y1 A y1 Formula (I)

[0124] LiFe 1-x2-y2 Mn x2 M' y2 PO 4Formula (II)

[0125] 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, and A is selected from one or more of S, F, Cl and I;

[0126] In formula (II), 0≤x2≤1, 0≤y2≤0.1, and M' is selected from one or more transition metal elements and non-transition metal elements except Fe and Mn.

[0127] In the present application, when the positive electrode active material of the second battery cell includes the above two active materials, the change rate of OCV relative to SOC ΔOCV / ΔSOC of the second battery cell in the range of 30% to 80% of SOC during charging can satisfy: ΔOCV / ΔSOC≤1, and at the same time, the change rate of OCV relative to SOC ΔOCV / ΔSOC in the range of 90% to 98% of SOC satisfies: 3≤ΔOCV / ΔSOC≤9. In the present application, the positive electrode plate of the second battery cell contains two or more positive electrode active materials. When the second battery cell is about to be fully charged, the change rate of OCV and SOC of the second battery cell is still within an appropriate range, which is conducive to the BMS accurately obtaining the state of charge of the series-connected battery cells in the battery pack, thereby achieving a good overcharge prevention capability of the battery pack.

[0128] At the same time, the positive electrode active material in the second type of battery cell adopts a mixture of compounds of formula (I) and formula (II). Since the first coulombic efficiency of the compound of formula (I) is lower than that of the compound of formula (II), and the charge and discharge platform of the compound of formula (II) is longer, the active ions released from the compound of formula (I) with lower first coulombic efficiency can be stored in the negative electrode sheet and can continue to participate in the electrochemical reaction in the later stage of the battery cell use, thereby compensating for the capacity loss caused by the consumption of active ions, which helps to further improve the cycle life of the battery pack.

[0129] In some embodiments of the present application, in the positive electrode active material of the second battery cell, the mass proportion of the layered lithium transition metal oxide represented by formula (III) is 0.5wt% to 25wt%, optionally 1wt% to 20wt%, and further optionally 3wt% to 15wt%.

[0130] In some embodiments of the present application, the first battery cell satisfies condition 1 and condition 2.

[0131] 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 to the first battery cell is recorded as Q, and satisfies 2<Q≤40, optionally, 4≤Q≤32;

[0132] Condition 2: When the dynamic SOC of the first battery cell is in the range of 30% to 80%, the rate of change of OCV of the first battery cell relative to SOC ΔOCV / ΔSOC satisfies ΔOCV / ΔSOC≤0.25, unit: mV / %SOC; Optionally, when the rate of change of the dynamic SOC of the first battery cell in the range of 30% to 80% ΔOCV / ΔSOC≤0.15.

[0133] In the present 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 battery cells meet the above characteristics, on the one hand, the OCV change of the second type of battery cells in the high SOC state can be easily and accurately identified to accurately characterize the change in the overall state of charge of the battery pack, which is effectively beneficial to improve the problem of overcharging of the battery pack; at the same time, it can also ensure that the difference in charging and discharging performance between the first type of battery cells and the second type of battery cells is small, which is beneficial to improving the overall electrical performance output effect of the battery pack.

[0134] In some embodiments 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. In the present application, when the discharge battery balance rate of the first battery cell is small, such battery cell is prone to lithium precipitation when it is close to full charge due to the small amount of lithium vacancies that the negative electrode can accommodate. When it is connected in series with the second battery cell, the SOC of the first battery cell is accurately identified by identifying the real-time state of charge of the second battery cell, thereby improving the overcharge prevention capability of the battery pack. In addition, by matching the charge and discharge characteristics of different chemical system batteries in the battery pack in the above manner, 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. The active ions released from the positive active material in the second battery cell can also be stored in the negative electrode. The active ions are continuously consumed during the long-term charge and discharge process, and the active ions pre-stored in the negative electrode can make up for the consumed active ions, which is beneficial to extend the cycle life of the battery pack.

[0135] In some embodiments of the present application, the positive electrode active material of the first battery cell includes a lithium-containing phosphate represented by formula (III),

[0136] LiFe 1-x3-y 3Mn x3 M' y3 PO 4 Formula (III)

[0137] In formula (III), 0≤x3≤1, 0≤y3≤0.1, and M′ is selected from one or more transition metal elements except Fe and Mn and non-transition metal elements.

[0138] 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 them, x3 independently satisfies 0<x3<1. In the present application, the rate of change of OCV with SOC of lithium phosphate battery cells is relatively gentle in a relatively long SOC range, and overcharging is prone to occur in a high SOC range; however, the cycle stability of lithium phosphate battery cells is good, and they have a relatively 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, is conducive to extending the cycle life of the battery pack, can achieve good overcharge prevention capability of the battery pack, and can also effectively extend the cycle life of the battery pack.

[0139] In the present application, the positive electrode active material of the first type of battery cell can be pure lithium iron phosphate (LFP), while the positive electrode active material of the second type of battery cell can be a combination of a mixture of lithium nickel cobalt manganese oxide (NCM) and LFP. It is also possible to use a mixture of NCM and LFP as the positive electrode active material of the first type of battery cell, while the positive electrode active material of the second type of battery cell is also a combination of a mixture of NCM and LFP. The LFP and NCM here are just examples. As long as they are materials with similar properties, there is no special limitation. For example, LFP can also be made of LiMnPO 4 NCM can also be replaced by lithium nickel cobalt aluminum oxide (NCA) and the like.

[0140] As an example, the following describes a 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 mixture of NCM and LFP.

[0141] In the present application, when the positive active material of the first type of battery cell is LFP and charged to more than 90% SOC, the OCV increases sharply with the change of SOC. Due to the accuracy problem of BMS, it is difficult to accurately obtain the real-time SOC of the battery cell, and the safety problem of overcharging is prone to occur. In this regard, in the present application, a second type of battery cell using a mixture of NCM and LFP as the positive active material is connected in series in the battery pack, and the change rate of OCV relative to SOC ΔOCV / ΔSOC of the second type of battery cell in the range of 90% to 98% of SOC satisfies: 3≤ΔOCV / ΔSOC≤9. Since the first type of battery cell and the second type of battery cell are electrically connected in series at least, the charge state of the battery pack can be accurately reflected by identifying the SOC of the second battery cell, thereby realizing the charging control of the first type of battery cell, reducing the probability of overcharging, and greatly improving the safety performance of the battery pack.

[0142] In some other embodiments of the present application, the positive electrode active material of the first battery cell at least includes a layered lithium transition metal oxide represented by formula (IIII),

[0143] Li 1+x4 Ni a2 Co b2 M3 c2 M4 1-a2-b2-c2 O 2-y4 A2 y4 Formula (III)

[0144] 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.

[0145] In some other embodiments of the present application, the positive active material of the first type of battery cell is NCM, and the positive active material of the second type of battery cell is a combination of a mixed material 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 combination of battery packs, when its SOC is in the range of 90% to 98%, the rate of change of the OCV relative to the SOC of the second battery cell 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, thereby achieving excellent anti-overcharge performance of the battery pack; at the same time, due to the low initial coulomb efficiency of the NCM in the first battery cell, part of the lithium released from the positive electrode sheet cannot return to the positive electrode sheet, but can be pre-stored in the negative electrode sheet, so these pre-stored lithium will gradually play out during the use of the battery cell, so it can further improve the cycle life of the battery pack.

[0146] [Battery Pack]

[0147] In one embodiment of the present application, two or more of the above-mentioned battery packs can be assembled into a battery pack, and the number of battery packs contained in the battery pack depends on the application of the battery pack and the parameters of a single battery pack. The battery pack may include a battery box and a plurality of battery packs arranged in the battery box, and the battery box includes an upper box body and a lower box body, and the upper box body can cover the lower box body and match well with it to form a closed space for accommodating the battery pack. Two or more battery packs can be arranged in the battery box in a desired 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 packs (or a combination directly formed by multiple battery cells).

[0148] Figure 4 is a schematic diagram showing one example of the battery pack 1 of the present application. Figure 5 It is shown Figure 4 An exploded view of an example of the battery pack 1 of the present application is shown. Figure 4 and Figure 5 The battery pack 1 may include a battery box and a plurality of battery packs 4 disposed in the battery box. The battery box includes an upper box body 2 and a lower box body 3, wherein the upper box body 2 is used to cover the lower box body 3 and form a closed space for accommodating the battery packs 4. The plurality of battery packs 4 may be arranged in the battery box in any manner.

[0149] [Electrical devices]

[0150] In one embodiment of the present application, the electric device of the present application includes at least one of the battery pack or battery package of the present application, and the battery pack or battery package can be used as a power source of the electric device, and can also be used as an energy storage unit of the electric device. The electric device includes but is not limited to mobile digital devices (such as mobile phones, laptops, etc.), electric vehicles (such as pure electric vehicles, hybrid electric vehicles, plug-in hybrid electric vehicles, electric bicycles, electric scooters, electric golf carts, electric trucks, etc.), electric trains, ships and satellites, energy storage systems, etc.

[0151] Figure 6 The figure is a schematic diagram showing an example of an electric device using the battery pack of the present application as a power source. The electric device is a pure electric vehicle, a hybrid electric vehicle, or a plug-in hybrid electric vehicle. In order to meet the requirements of the electric device for high power and high energy density, a battery pack or a battery pack can be used.

[0152] [Battery Pack Manufacturing Method]

[0153] The present application proposes a method for manufacturing a battery pack, comprising the following steps:

[0154] Get the first type of battery cells and the second type of battery cells,

[0155] The first type of battery cells and the second type of battery cells are battery cells of different chemical systems.

[0156] The first type of battery cells includes N first battery cells,

[0157] The second type of battery cells includes M second battery cells, where N and M are positive integers.

[0158] The positive electrode sheet 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% to 98%, the change rate of OCV of the second battery cell relative to SOC ΔOCV / ΔSOC satisfies: 3≤ΔOCV / ΔSOC≤9, where SOC represents the state of charge and OCV represents the open circuit voltage; and

[0159] The first type of battery cell and the second type of battery cell are at least connected in series to form a battery pack as described in the first aspect of the present application.

[0160] [Battery Pack Manufacturing Equipment]

[0161] The present application proposes a battery pack manufacturing device, comprising:

[0162] A clamping arm unit, wherein the clamping arm unit is used to obtain the first type of battery cell and the second type of battery cell,

[0163] The first type of battery cells and the second type of battery cells are battery cells with different chemical systems.

[0164] The first type of battery cells includes N first battery cells,

[0165] The second type of battery cells includes M second battery cells, where N and M are positive integers.

[0166] The positive electrode sheet 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% to 98%, the change rate of OCV of the second battery cell relative to SOC ΔOCV / ΔSOC satisfies: 3≤ΔOCV / ΔSOC≤9, where SOC represents the state of charge and OCV represents the open circuit voltage;

[0167] an assembly unit, the assembly unit being used to connect the first type of battery cells and the second type of battery cells at least in series to form the battery pack as described in the first aspect of the present application; and

[0168] A control unit is used to control the clamping arm unit and the assembling unit.

[0169] Therefore, the battery pack manufactured using the manufacturing method and manufacturing equipment of the present application can significantly improve the control accuracy of the BMS, effectively prevent overcharging of the internal cells of the hybrid series battery pack, and greatly improve the safety of the battery pack.

[0170] Example

[0171] The technical solution and advantages of the present application are described in detail below through specific embodiments.

[0172] 《Battery Cell Preparation》

[0173] With reference 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 the embodiments and comparative examples are as follows.

[0174] 1. Preparation of positive electrode slurry

[0175] The positive electrode active material, conductive carbon Super P, and binder polyvinylidene fluoride (PVDF) are fully stirred and mixed in a proper amount of N-methylpyrrolidone (abbreviated as NMP) solvent at a weight ratio of 95:3:2 to form a uniform, stable slurry with a viscosity of 15000mPa·s. The slurry is left to stand for 38 hours without gelation, stratification or sedimentation.

[0176] 2. Preparation of positive electrode

[0177] The positive electrode material slurry is evenly coated on the positive electrode current collector Al foil. After drying, the electrode sheet is cold-pressed to the designed density and divided into strips for standby use to obtain the positive electrode sheet.

[0178] 3. Preparation of electrolyte

[0179] An equal volume of ethylene carbonate is dissolved in propylene carbonate, and then lithium hexafluorophosphate is uniformly dissolved in the mixed solvent for later use (the concentration of lithium hexafluorophosphate is 1.1 M / L), to obtain an electrolyte.

[0180] 4. Preparation of negative electrode sheet

[0181] The negative electrode active material such as graphite and conductive carbon, binder polystyrene butadiene copolymer (SBR), and thickener sodium carboxymethyl cellulose (CMC) are fully stirred and mixed in a suitable amount of water solvent at a weight ratio of 95:2:2:1 to form a uniform negative electrode stable slurry; the slurry is evenly coated on the negative electrode current collector Cu foil, and after drying, the electrode is cold pressed to the designed density and divided into strips for use.

[0182] 5. Isolation film

[0183] PP is selected as the isolation membrane.

[0184] 6. Preparation of battery cells

[0185] The conventional battery cell manufacturing process is adopted to wind the above-mentioned positive electrode plate, isolation film and negative electrode plate together into a bare battery cell, which is then placed in a battery casing, injected with the above-mentioned electrolyte, and then carried out the formation, sealing and other processes to finally obtain a rechargeable power battery cell.

[0186] Battery Pack Assembly

[0187] Obtain 10 first battery cells and 10 second battery cells, arrange the first battery cells and the second battery cells at intervals, and electrically connect them in series.

[0188] 《Test method for OCV change curve of battery cell in the range of 0%-100% SOC》

[0189] The method for testing the OCV change curve of the battery cell in the 0%-100% SOC range includes the following steps:

[0190] 1) Leave the battery at room temperature of 25°C for 120 minutes;

[0191] 2) Discharge the above battery cells 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 for 30 minutes;

[0192] 3) Charge the battery cell in step 2 at a constant current of 0.33C to the end-of-charge voltage, and then charge the battery cell at a constant current of ≤0.05C, and let it stand for 30 minutes;

[0193] 4) Discharge the battery cell in step 3 at a constant current of 0.33C to the discharge termination voltage, and record the discharged capacity as C 0 , let stand for 30 minutes;

[0194] 5) Heat the battery cell in step 4 at 0.33C 0 Constant current charging to charging termination voltage, constant voltage to current ≤ 0.05C 0 , let stand for 30 minutes;

[0195] 6) Heat the battery cell in step 5 above at ≤0.05C 0 Discharge at a constant current rate of 10000 to the discharge termination voltage (the stepping frequency is required to be fixed at 1s), and let it stand for 30 minutes;

[0196] 7) Heat the battery cell in step 6 at 0.05C 0 Charge at constant current to the charging termination voltage (the stepping frequency is required to be fixed at 1s), and let it stand for 30 minutes.

[0197] In the above steps, the 0.33C discharge rate refers to the discharge rate parameter used when the time taken to charge or discharge a 1C capacity battery cell is 3 hours; 0The discharge rate is 9.09min, and the capacity released is equal to 9.09min / 180min=0.05, which accounts for 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 50Ah, the nominal current can be 50A; for another example, when the capacity of the battery pack is 100Ah, the nominal current can be 100A. The charge termination voltage and discharge termination voltage can refer to the provisions in the product technical specification or the GBT certification documents of the battery cell / battery pack.

[0198] 《Test method for battery balance rate of battery cell discharge》

[0199] The discharge capacity of the negative electrode sheet per unit area and the discharge capacity of the positive electrode sheet per unit area are tested respectively; then, according to the formula: battery discharge battery balance rate = discharge capacity of the negative electrode sheet per unit area / discharge capacity of the positive electrode sheet per unit area, the discharge battery balance rate of the battery cell can be calculated.

[0200] Among them, the discharge capacity of the positive electrode sheet or the negative electrode sheet can be tested by the following steps:

[0201] (1) The requirements for electrode sampling are as follows:

[0202] After fully discharging the battery cell, disassemble it, take out the positive and negative electrodes, rinse them with DMC solution, and dry them for later use. The sampling position of the positive electrode is: select any position in the middle that is greater than 15mm from the edge. The sampling position of the negative electrode is: select the negative electrode that is opposite to the selected positive electrode; and the sampling area of ​​the positive electrode is the same as that of the negative electrode;

[0203] (2) Assembling a button cell using the above-cut positive electrode sheet, negative electrode sheet and lithium sheet as counter electrodes;

[0204] (3) Discharge capacity of negative electrode per unit area:

[0205] The test voltage is 0.05-2.0V, the test temperature is 25°C, the charge / discharge rate is 0.1C, and no less than 10 parallel samples are taken to test the discharge capacity of the button half-cell respectively. The lowest and highest values ​​are removed and the average value is taken to obtain the discharge capacity of the negative electrode sheet under the area; the discharge capacity of the negative electrode sheet obtained by the above test is divided by the area of ​​the negative electrode sheet to obtain the discharge capacity of the negative electrode sheet per unit area;

[0206] (4) Discharge capacity of positive electrode per unit area:

[0207] Within the operating voltage range specified in the GBT certification document for the sampled battery cell and at room temperature of 25°C, charge / discharge at 0.1C, take no less than 10 parallel samples, and test the discharge capacity of the button battery respectively. After removing the lowest and highest values, take the average value to obtain the discharge capacity of the positive electrode sheet under the area; divide the discharge capacity of the positive electrode sheet obtained by the above test by the area of ​​the positive electrode sheet to obtain the discharge capacity of the positive electrode sheet per unit area.

[0208] 《Test method for battery pack capacity retention rate》

[0209] Refer to GB / T 31484-2015 "Cycle life requirements and test methods for power batteries for electric vehicles".

[0210] 1500 cycles capacity retention rate (25°C) test method:

[0211] Initial capacity (calculated as: Cap0) test steps:

[0212] 1) Leave the new battery pack at 25°C for 30 minutes;

[0213] 2) Discharge at a constant current of 0.33C to the battery pack discharge termination voltage and leave it for 30 minutes;

[0214] 3) 0.33C constant current charge to the battery pack charging termination voltage, constant voltage charge until the current is less than 0.05C, and stand for 5 minutes;

[0215] 4) Discharge at a constant current of 0.33C to the battery pack discharge termination voltage, and then let it stand for 5 minutes.

[0216] The discharge capacity measured from step 3) to step 4) is counted as Cap0. Step 1) to step 4) are one charge and discharge cycle of the battery pack. Repeat the above steps 1) to step 4) 1500 times, and the discharge capacity measured at the 1500th time is counted as Capn. The capacity retention rate at the 1500th time is: Capn / Cap0×100%.

[0217] In the above test, C represents the rated capacity of the battery cell, the charge / discharge current is the rate multiplied by the rated capacity of the battery cell, and the rated capacity is based on the battery capacity recognized in the GBT certification document of the battery cell, the battery module to which the battery cell belongs, or the battery pack to which the battery cell belongs.

[0218] 《Battery Pack Overcharge Lithium Plating Detection Method》

[0219] At 25±2°C, charge the battery pack at a constant current of 1C to the upper cut-off voltage (the upper cut-off voltage of the battery pack can be determined by referring to the specification of the battery pack), then charge the battery pack at the upper cut-off voltage to a current of 0.05C, let it stand for 30 minutes, then fix the battery pack and place it on the overcharge safety test equipment, control the ambient temperature at 25±2°C, let it stand for 5 minutes, overcharge the fully charged battery pack at a rate of 1C, and record the real-time voltage and temperature changes of each battery until charging stops. Take 6 battery packs for each embodiment and comparative example for testing, disassemble the first type of battery cells in the battery pack, observe the lithium deposition on the surface of the negative electrode plate, and record the number of lithium depositions.

[0220] By the above-mentioned "battery cell preparation" method, the following battery packs of Examples 1 to 7 and the battery packs of Comparative Examples 1 and 2 can be obtained.

[0221] Example 1

[0222] In the first type of battery, the positive electrode active material is LiFePO 4 , the discharge battery balance rate CB1 is 1.04, the change rate of OCV relative to SOC ΔOCV / ΔSOC of the first type of battery cell in the range of 30% to 80% is 0.07, and the change rate of OCV relative to SOC in the range of 90% to 98% is 0.28;

[0223] In the second type of battery, the positive electrode active material is LiFePO 4 (LFP) and LiNi 0.55 Co 0.12 Mn 0.33 O 2 The mixture is composed of LFP and NCM, with a mixing ratio of LFP:NCM=0.99:0.01, a discharge battery balance rate CB2 of 1.11, a rate of change of OCV relative to SOC ΔOCV / ΔSOC of the second type of battery cell in the range of 30% to 80% SOC of 0.08, and a rate of change of OCV relative to SOC ΔOCV / ΔSOC of 8.89 in the range of 90% to 98% SOC.

[0224] Examples 2 to 7 and Comparative Examples 1 and 2

[0225] In Examples 2 to 7 and Comparative Examples 1 to 2, the battery pack also includes 10 first-type battery cells and 10 second-type battery cells, wherein the discharge battery balance rates CB1 and CB2 of the first-type battery cells and the second-type battery cells are the same as those in Example 1, and the differences are shown in Table 1.

[0226]

[0227] According to Table 1 above, the probability of lithium deposition in the first type of battery cell due to overcharging in Example 1 is 2 / 10, the probability of lithium deposition in the first type of battery cell due to overcharging in Example 2 is 1 / 10, and the probability of lithium deposition in the first type of battery cell due to overcharging in Examples 3 to 7 is 0 / 10.

[0228] On the other hand, in Comparative Example 1, both the first and second battery cells are LFP, and the rate of change of OCV relative to SOC ΔOCV / ΔSOC in the range of 90% to 98% of the SOC during charging of the battery pack is 0.71. That is, since the rate of change ΔOCV / ΔSOC of the first and second battery cells in the battery pack changes relatively slowly, the probability of lithium deposition in the first battery cells in the battery pack of Comparative Example 1 due to overcharging is very high (8 / 10).

[0229] In Comparative Example 2, although the rate of change of OCV relative to SOC ΔOCV / ΔSOC of the second type of battery cell in the range of 90% to 98% during charging is 1.53, because the positive electrode active material of the first type of battery cell adopts LFP and the positive electrode active material of the second type of battery cell adopts NCM, that is, there is no optimization design for the doping of the positive electrode active material of the first type of battery cell or the second type of battery cell, the probability of lithium deposition due to overcharging in the first type of battery cell in the battery pack of Comparative Example 2 is still relatively high (5 / 10).

[0230] It can be seen that in the present application, by connecting the first type of battery cells and the second type of battery cells of different chemical systems in series, and adjusting the rate of change of OCV relative to SOC ΔOCV / ΔSOC of the second type of battery cells when nearly fully charged within the range of 3 to 9 mV / % SOC, the probability of lithium plating in the first type of battery cells in the battery pack due to overcharging is greatly reduced in the optimized embodiments 1 to 7 compared to the unoptimized comparative examples 1 and 2, thereby significantly improving the safety of the battery pack.

[0231] In addition, according to the above Table 1, it can be seen that in the present application, by optimizing the doping design of the positive electrode active material of the first type of battery cell or the second type of battery cell, the capacity retention rate of the battery pack at the 1500th cycle of the optimized embodiments 1 to 7 is significantly improved compared with the non-optimized comparative examples 1 and 2, thereby improving the service life of the battery pack.

[0232] <About the design of the discharge battery balance rate of the second battery cell>

[0233] The technical solution and advantages of the present application are described in detail below through specific embodiments.

[0234] The preparation of the battery cell is similar to that of the "battery cell preparation" in the above-mentioned embodiments 1 to 7. The first battery cell in embodiments 8 to 12 is the same as the first battery cell in embodiment 3; the difference is that the specific parameters of the second battery cell in embodiments 8 to 12 are different.

[0235]

[0236] According to the above Table 2, in Examples 3, 8 to 10 where the CB2 of the second type of battery cell satisfies 1.00≤CB2≤1.16, the probability of lithium deposition in the first type of battery cell in the battery pack due to overcharging is extremely low, and the capacity retention rate of the battery pack at the 1500th cycle is maintained at a high level. On the contrary, in Example 11 where the CB2 of the second type of battery cell does not satisfy 1.00≤CB2≤1.16, the probability of lithium deposition in the first type of battery cell in the battery pack due to overcharging is not 0. In addition, in Example 12 where the CB2 of the second type of battery cell does not satisfy 1.00≤CB2≤1.16, although the probability of lithium deposition in the first type of battery cell in the battery pack due to overcharging is also low, the capacity retention rate of the battery pack at the 1500th cycle is relatively low.

[0237] It can be seen from this that the battery pack of the embodiment of the present application, while controlling the high SOC change characteristics of the second battery cell, further limits the discharge battery balance rate of the second battery cell to the range of 1 to 1.16, which can further effectively prevent the overcharging of the internal battery cells of the hybrid series battery pack, greatly improve the safety of the battery pack, and also improve the service life of the battery pack.

[0238] <About the design of the first cell discharge battery balance rate>

[0239] The technical solution and advantages of the present application are described in detail below through specific embodiments.

[0240] The preparation of the battery cell is similar to that of the "battery cell preparation" in the above-mentioned Examples 1 to 7. The second battery cell in Examples 13 to 21 is the same as the second battery cell in Example 3; the difference is that the specific parameters of the first battery cell in Examples 13 to 21 are different, see Table 3 for details.

[0241]

[0242] According to the above Table 3, in Examples 3 and 13 to 17 where the CB1 of the first type of battery cell satisfies 1.00≤CB1≤1.18, the probability of lithium deposition in the first type of battery cell due to overcharging is extremely low, and the capacity retention rate of the battery pack at the 1500th cycle is maintained at a 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 deposition in the first type of battery cell due to overcharging is also low, the capacity retention rate of the battery pack at the 1500th cycle is relatively low.

[0243] It can be seen that the battery pack of the embodiment of the present application further optimizes the discharge battery balance rate of the first type of battery cells on the basis of setting the curvature characteristics of the high SOC range of the second type of battery cells, and further improves the service life of the battery pack while effectively preventing the overcharging of the internal cells of the hybrid series battery pack and greatly improving the safety of the battery pack.

[0244] The various embodiments or implementation methods in this specification are described in a progressive manner. Each embodiment focuses on the differences from other embodiments, and the same or similar parts between the various embodiments can be referenced to each other.

[0245] In the description of this specification, the description with reference to the terms "one embodiment", "some embodiments", "illustrative embodiments", "examples", "specific examples", or "some examples" means that the specific features, structures, materials, or characteristics described in conjunction with the embodiments or examples are included in at least one embodiment or example of the present application. In this specification, the schematic representation of the above terms does not necessarily refer to the same embodiment or example. Moreover, the specific features, structures, materials, or characteristics described may be combined in any one or more embodiments or examples in a suitable manner.

[0246] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present application, rather than to limit it. Although the present application has been described in detail with reference to the aforementioned embodiments, those skilled in the art should understand that they can still modify the technical solutions described in the aforementioned embodiments, or replace some or all of the technical features therein with equivalents. However, 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: The invention comprises at least a first type of battery cell and a second type of battery cell electrically connected in series, wherein the first type of battery cell and the second type of battery cell are battery cells of different chemical systems, The first type of battery cells includes N first battery cells, The second type of battery cells includes M second battery cells, where N and M are positive integers; The positive electrode sheet 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% to 98%, the change rate of OCV of the second battery cell relative to SOC ΔOCV / ΔSOC satisfies: 3≤ΔOCV / ΔSOC≤9 unit: mV / %SOC, where SOC represents the state of charge and OCV represents the open circuit voltage; The positive electrode active material of the second battery cell at least comprises a layered lithium transition metal oxide represented by formula (I) and a lithium-containing phosphate represented by 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 PO4 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, A1 is selected from S, N, F, Cl, Br, PO4 3- and one or more of I; In formula (II), 0≤x2≤1, 0≤y2≤0.1, and M' is selected from one or more transition metal elements and non-transition metal elements except Fe and Mn.

2. The battery pack according to claim 1, wherein: When the dynamic SOC of the second battery cell is in the range of 90% to 98%, a change rate ΔOCV / ΔSOC of the OCV of the second battery cell relative to the SOC satisfies: 3.5≤ΔOCV / ΔSOC≤7, unit: mV / %SOC.

3. The battery pack according to claim 1, wherein: When the dynamic SOC of the second battery cell is in the range of 30% to 80%, a rate of change of OCV of the second battery cell relative to SOC ΔOCV / ΔSOC satisfies: ΔOCV / ΔSOC≤1, unit: mV / %SOC.

4. The battery pack according to claim 3, wherein: When the dynamic SOC of the second battery cell is in the range of 30% to 80%, a change rate of OCV of the second battery cell relative to SOC ΔOCV / ΔSOC satisfies: ΔOCV / ΔSOC≤0.25, unit: mV / %SOC.

5. The battery pack according to claim 1, wherein: The discharge battery balance rate of the second battery cell is CB2, 1.00≤CB2≤1.

16.

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

11.

7. The battery pack according to claim 1, wherein: The positive electrode active material of the second battery cell at least comprises a layered lithium transition metal oxide represented by formula (I) and a lithium-containing phosphate represented by 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 PO4 formula (II) In formula (I), -0.1≤x1≤0.2, 0.5≤a1≤0.7, 0.01≤b1≤0.15, 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, A1 is selected from S, N, F, Cl, Br, PO4 3- and one or more of I; In formula (II), 0≤x2≤0.5, 0≤y2≤0.1, and M' is one or more selected from transition metal elements other than Fe and Mn and non-transition metal elements.

8. The battery pack according to claim 1, wherein: In the positive electrode active material of the second battery cell, the mass percentage of the layered lithium transition metal oxide represented by formula (I) is 0.5wt% to 30wt%.

9. The battery pack according to claim 1, wherein: In the positive electrode active material of the second battery cell, the mass percentage of the layered lithium transition metal oxide represented by formula (I) is 1 wt % to 20 wt %.

10. The battery pack according to claim 1, wherein: In the positive electrode active material of the second battery cell, the mass percentage of the layered lithium transition metal oxide represented by formula (I) is 3wt% to 15wt%.

11. The battery pack according to claim 1, wherein: The first battery cell meets conditions 1 and 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 rate of change of OCV of the first battery cell relative to SOC ΔOCV / ΔSOC satisfies ΔOCV / ΔSOC≤0.25, unit: mV / %SOC.

12. The battery pack according to claim 1, wherein: The first battery cell meets conditions 1 and 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 change rate of the dynamic SOC of the first battery cell in the range of 30% to 80% is ΔOCV / ΔSOC≤0.

15.

13. 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.

14. The battery pack according to claim 1, wherein: The discharge battery balance rate of the first battery cell is CB1 and satisfies 1.04≤CB1≤1.

14.

15. 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 formula (III), LiFe 1-x3-y3 Mn x3 M’’ y3 PO4 formula (III) In formula (III), 0≤x3≤1, 0≤y3≤0.1, and M'' is selected from one or more transition metal elements other than Fe and Mn and non-transition metal elements.

16. The battery pack according to claim 1, wherein: The positive electrode active material of the first battery cell includes LiFePO4, LiMnPO4, LiMn 1-x3 Fe x3 PO4、LiV 1-x3 Fe x3 Any one of PO4, wherein x3 independently satisfies 0<x3<1.

17. The battery pack according to any one of claims 1 to 16, characterized in that: The positive electrode active material of the first battery cell includes a layered lithium transition metal oxide represented by formula (IIII), Li 1+x4 Ni a2 Co b2 M3 c2 M4 1-a2-b2-c2 O 2-y4 A2 y4 Formula (IIII) In formula (III), -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.

18. A battery pack, characterized in that: A battery pack comprising any one of claims 1-17.

19. An electrical device, characterized in that: It comprises the battery pack according to any one of claims 1 to 17 or the battery package according to claim 18, wherein the battery pack or the battery package serves as an energy storage unit of the electrical device.

20. A method for manufacturing a battery pack, characterized in that: The steps include: Get the first type of battery cells and the second type of battery cells, The first type of battery cells and the second type of battery cells are battery cells with different chemical systems. The first type of battery cells includes N first battery cells, The second type of battery cells includes M second battery cells, where N and M are positive integers. The positive electrode sheet 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% to 98%, the change rate of OCV of the second battery cell relative to SOC ΔOCV / ΔSOC 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 cells and the second type of battery cells are at least connected in series to form a battery pack as claimed in any one of claims 1 to 17.

21. A battery pack manufacturing device, characterized in that: include: A clamping arm unit, wherein the clamping arm unit is used to obtain the first type of battery cell and the second type of battery cell, The first type of battery cells and the second type of battery cells are battery cells with different chemical systems. The first type of battery cells includes N first battery cells, The second type of battery cells includes M second battery cells, where N and M are positive integers. The positive electrode sheet 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% to 98%, the change rate of OCV of the second battery cell relative to SOC ΔOCV / ΔSOC satisfies: 3≤ΔOCV / ΔSOC≤9, where SOC represents the state of charge and OCV represents the open circuit voltage; an assembly unit, the assembly unit being used to connect the first type of battery cells and the second type of battery cells at least in series to form a battery pack as claimed in any one of claims 1 to 17; and A control unit is used to control the clamping arm unit and the assembling unit.

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