A secondary battery, a battery module containing the same, a battery pack and an electric device

Abstract

The present application provides a secondary battery, including a wound battery cell, the wound battery cell including: a negative electrode plate, the negative electrode plate including a negative electrode collector, the negative electrode collector including a first surface and a second surface opposite to the first surface, the first surface is located on a side of the wound battery cell away from the center, and the second surface is located on a side of the wound battery cell close to the center; a first negative electrode film layer, arranged on the first surface of the negative electrode collector; a second negative electrode film layer, arranged on the second surface of the negative electrode collector; the first negative electrode film layer and the second negative electrode film layer both include negative electrode active materials, the negative electrode active materials both include carbon materials, the OI value of the first negative electrode film layer is recorded as OI1, and the OI value of the second negative electrode film layer is recorded as OI2; the secondary battery satisfies: OI1<OI2.

Description

Technical Field

[0001] The present application relates to the technical field of secondary batteries, and in particular to a negative electrode plate, a secondary battery, a battery module, a battery pack and an electrical device. Background Art

[0002] In recent years, as the application scope of secondary batteries has become more and more extensive, secondary batteries are widely used in energy storage power systems such as hydropower, thermal power, wind power and solar power stations, as well as power tools, electric bicycles, electric motorcycles, electric vehicles, military equipment, aerospace and other fields. As the requirements for the range of secondary batteries are getting higher and higher, wound cells have more and more usage scenarios. If the internal stress of the wound cell is too large during its cycle, it will cause the bends at both ends of the wound cell to break, and even cause safety problems.

[0003] How to make the battery have both good electrical performance and safety performance is still a problem that needs to be solved urgently. Summary of the invention

[0004] In order to achieve the above-mentioned object, the first aspect of the present application provides a secondary battery, including a wound-type battery cell, the wound-type battery cell includes: a negative electrode plate, the negative electrode plate includes a negative electrode current collector, the negative electrode current collector includes a first surface and a second surface opposite to the first surface, the first surface is located on a side of the wound-type battery cell away from the center, and the second surface is located on a side of the wound-type battery cell close to the center; a first negative electrode film layer, arranged on the first surface of the negative electrode current collector; a second negative electrode film layer, arranged on the second surface of the negative electrode current collector; the first negative electrode film layer and the second negative electrode film layer both include negative electrode active materials, the negative electrode active materials both include carbon materials, and the O I The value is recorded as OI1, and the OI value of the second negative electrode film layer is recorded as OI2; the secondary battery satisfies: OI1<OI2.

[0005] A secondary battery provided in the present application has a differentiated design for the negative electrode plate, thereby reducing stress accumulation on the outside of the plate and avoiding the phenomenon of the plate breaking at the corners, so that the secondary battery has both good cycle performance and safety performance.

[0006] In any implementation, OI1 and OI2 satisfy the relationship: 1.05≤OI2 / OI1≤1.4; optionally, 1.15≤OI2 / OI1≤1.3.

[0007] In any embodiment, OI1 and OI2 satisfy the relationship: 5<OI2-OI1<20.

[0008] In any embodiment, 15≤OI1≤80, optionally 20≤OI1≤60; and / or 25≤OI2≤90, optionally 30≤OI2≤70.

[0009] In any embodiment, the first negative electrode film layer and the second negative electrode film layer further include silicon material, and the mass proportion of the silicon material in the first negative electrode film layer in the negative electrode active material is recorded as C A The mass proportion of silicon material in the second negative electrode film layer in the negative electrode active material is recorded as C B , then the secondary battery satisfies: C A <C B .

[0010] In any embodiment, 0.1%≤C B -C A ≤1.0%, optionally, 0.2%≤C B -C A ≤0.5%. In any embodiment, 8%≤C A ≤32%, optionally, 10%≤C A ≤15%; and / or 9%≤C B ≤33%, optionally, 11%≤C B ≤16%.

[0011] In any embodiment, the number of core layers of the wound battery cell is greater than 20, and can be selected from 21 to 120.

[0012] In any embodiment, the expansion coefficient of the first negative electrode film layer is α1, and the expansion coefficient of the second negative electrode film layer is α2, then the secondary battery satisfies: α2 / α1≤1.022; optionally, 1.005≤α2 / α1≤1.02.

[0013] A second aspect of the present application provides a battery module, comprising the secondary battery of the first aspect of the present application.

[0014] A third aspect of the present application provides a battery pack, comprising the battery module of the second aspect of the present application.

[0015] A fourth aspect of the present application provides an electrical device comprising at least one selected from the secondary battery of the first aspect of the present application, the battery module of the second aspect of the present application, or the battery pack of the third aspect of the present application. BRIEF DESCRIPTION OF THE DRAWINGS

[0016] Figure 1 It is a schematic diagram of the negative electrode sheet of the wound battery cell of the present application.

[0017] Figure 2 This is an enlarged view of the structure of the bending part of the negative electrode plate of the wound battery cell of the present application.

[0018] Figure 3 is a schematic diagram of a secondary battery according to one embodiment of the present application.

[0019] Figure 4 yes Figure 3 An exploded view of a secondary battery according to an embodiment of the present application is shown.

[0020] Figure 5 is a schematic diagram of a battery module according to an embodiment of the present application.

[0021] Figure 6 It is a schematic diagram of a battery pack according to one embodiment of the present application.

[0022] Figure 7 yes Figure 6 An exploded view of a battery pack according to an embodiment of the present application is shown.

[0023] Figure 8 FIG. 1 is a schematic diagram of an electric device using a secondary battery according to an embodiment of the present application as a power source.

[0024] Description of reference numerals:

[0025] 1 battery pack; 2 upper box; 3 lower box; 4 battery module; 5 secondary battery; 51 shell; 52 electrode assembly; 53 top cover assembly. DETAILED DESCRIPTION

[0026] Below, the secondary battery and its manufacturing method, positive electrode sheet, negative electrode sheet, electrolyte, separator, battery module, battery pack and electric device of the present application are described in detail with appropriate reference to the accompanying drawings. However, there are cases where unnecessary detailed descriptions are omitted. For example, there are cases where detailed descriptions of well-known matters and repeated descriptions of actually the same structure are omitted. This is to avoid the following description from becoming unnecessarily lengthy and to facilitate the understanding of those skilled in the art. In addition, the drawings and the following descriptions are provided for those skilled in the art to fully understand the present application and are not intended to limit the subject matter described in the claims.

[0027] "Scope" disclosed in the present application is limited in the form of lower limit and upper limit, and a given range is limited by selecting a lower limit and an upper limit, and the selected lower limit and upper limit define the boundary of a special range. The scope limited 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 specific 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 be all expected: 1-3, 1-4, 1-5, 2-3, 2-4 and 2-5. In the present 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.

[0028] If not otherwise specified, all embodiments and optional embodiments of the present application can be combined with each other to form a new technical solution.

[0029] Unless otherwise specified, all technical features and optional technical features of this application can be combined with each other to form a new technical solution.

[0030] If there is no special explanation, all steps of the present application can be performed sequentially or randomly, preferably sequentially. For example, the method includes steps (a) and (b), which means that the method may include steps (a) and (b) performed sequentially, or may include steps (b) and (a) performed sequentially. For example, the method may further include step (c), which means that step (c) may be added to the method in any order. For example, the method may include steps (a), (b) and (c), or may include steps (a), (c) and (b), or may include steps (c), (a) and (b), etc.

[0031] If there is no special explanation, the "include" and "comprising" mentioned in this application are open-ended or closed-ended. For example, the "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.

[0032] If not specifically stated, in this application, 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).

[0033] [Secondary battery]

[0034] Secondary batteries, also known as rechargeable batteries or storage batteries, refer to batteries that can continue to be used by recharging the active materials after the battery is discharged.

[0035] Secondary batteries usually include a positive electrode sheet, a negative electrode sheet, a separator and an electrolyte. During the battery charging and discharging process, active ions (such as lithium ions) are embedded and removed back and forth between the positive electrode sheet and the negative electrode sheet. The separator is set between the positive electrode sheet and the negative electrode sheet, mainly to prevent the positive and negative electrodes from short-circuiting, and at the same time allow active ions to pass through. The electrolyte is between the positive electrode sheet and the negative electrode sheet, mainly to conduct active ions.

[0036] In the secondary battery of the present application, the positive electrode sheet, the negative electrode sheet and the separator are formed into a wound battery cell through a winding process.

[0037] [Negative electrode]

[0038] The negative electrode plate of the present application includes a negative electrode collector, the negative electrode collector includes a first surface and a second surface opposite to the first surface, the first surface is located on a side of the wound battery cell away from the center, and the second surface is located on a side of the wound battery cell close to the center; a first negative electrode film layer is arranged on the first surface of the negative electrode collector; a second negative electrode film layer is arranged on the second surface of the negative electrode collector; the first negative electrode film layer and the second negative electrode film layer both include negative electrode active materials, the negative electrode active materials both include carbon materials, the OI value of the first negative electrode film layer is recorded as OI1, and the OI value of the second negative electrode film layer is recorded as OI2; the secondary battery satisfies: OI1<OI2.

[0039] After extensive research, the inventors found that the first negative electrode film layer is the outer convex layer, which is subjected to greater tension than the inner circle. During the service of the battery cell, local stress imbalance will occur at the bend of the wound battery cell, reducing the battery life. This application reduces the expansion of the battery cell in the thickness direction of the current collector by setting different OI values ​​on both sides of the battery cell, thereby enhancing the cycle performance of the battery.

[0040] In some embodiments, OI1 and OI2 satisfy the relationship: 1.05≤OI2 / OI1≤1.4; optionally, 1.15≤OI2 / OI1≤1.3.

[0041] In some embodiments, OI1 and OI2 satisfy the relationship: 5<OI2-OI1<20.

[0042] In some embodiments, 15≤OI1≤80, optionally 20≤OI1≤60; and / or 25≤OI2≤90, optionally 30≤OI2≤70.

[0043] It should be noted that the OI value of the negative electrode film layer is a well-known parameter in the art and can be adjusted by known methods. For example, during the preparation of the negative electrode sheet, the desired OI value can be obtained by adjusting the compaction density of the negative electrode film layer.

[0044] In some embodiments, the first negative electrode film layer and the second negative electrode film layer further include silicon material, and the mass proportion of the silicon material in the first negative electrode film layer in the negative electrode active material is denoted as C A The mass proportion of silicon material in the second negative electrode film layer in the negative electrode active material is recorded as C B , then the secondary battery satisfies: C A <C B .

[0045] In some embodiments, 0.1%≤C B -C A ≤1.0%, optionally, 0.2%≤C B -C A ≤0.5%.

[0046] In some embodiments, 8%≤C A ≤32%, optionally, 10%≤C A ≤15%.

[0047] In some embodiments, 9%≤C B ≤33%, optionally, 11%≤C B ≤16%.

[0048] The inventors found that the tension on the first negative electrode film layer is greater than that on the inner ring. A Less than the inner ring silicon content C B , especially when a specific relationship is met, the absolute expansion of the outer ring along the direction perpendicular to the current collector plane can be made smaller than the absolute expansion of the inner ring along the direction perpendicular to the current collector plane, which can effectively balance the tension between the inner and outer rings, thereby improving the cycle performance of the battery.

[0049] In some embodiments, the number of core layers of the wound battery cell is greater than 20, and can be selected as 21-120. When the number of core layers of the wound battery cell is within the given range, the tension difference between the inner and outer bends of the battery cell is also large, and the beneficial effects brought by the present application are also more obvious.

[0050] In some embodiments, the expansion coefficient of the first negative electrode film layer is α1, and the expansion coefficient of the second negative electrode film layer is α2, then the secondary battery satisfies: α2 / α1≤1.022; optionally, 1.005≤α2 / α1≤1.02.

[0051] In some embodiments, the negative electrode current collector may be a metal foil or a composite current collector. For example, as the metal foil, a copper foil may be used. The composite current collector may include a polymer material base layer and a metal layer formed on at least one surface of the polymer material substrate. The composite current collector may be formed by forming a metal material (copper, copper alloy, nickel, nickel alloy, titanium, titanium alloy, silver and silver alloy, etc.) on a polymer material substrate (such as a substrate of polypropylene (PP), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polystyrene (PS), polyethylene (PE), etc.).

[0052] In some embodiments, the negative electrode active material may adopt the negative electrode active material for the battery known in the art. As an example, the negative electrode active material may include at least one of the following materials: artificial graphite, natural graphite, soft carbon, hard carbon, silicon-based materials, tin-based materials, lithium titanate, etc. The silicon-based material may be selected from at least one of elemental silicon, silicon oxide compounds, silicon-carbon composites, silicon-nitrogen composites, and silicon alloys. The tin-based material may be selected from at least one of elemental tin, tin oxide compounds, and tin alloys. However, the present application is not limited to these materials, and other traditional materials that can be used as negative electrode active materials for batteries may also be used. These negative electrode active materials may be used alone or in combination of two or more.

[0053] In some embodiments, the negative electrode film layer may further include a binder. As an example, the binder may be selected from at least one of styrene-butadiene rubber (SBR), polyacrylic acid (PAA), sodium polyacrylate (PAAS), polyacrylamide (PAM), polyvinyl alcohol (PVA), sodium alginate (SA), polymethacrylic acid (PMAA) and carboxymethyl chitosan (CMCS).

[0054] In some embodiments, the negative electrode film layer may further include a conductive agent. As an example, the conductive agent may be selected from at least one of superconducting carbon, acetylene black, carbon black, Ketjen black, carbon dots, carbon nanotubes, graphene, and carbon nanofibers.

[0055] In some embodiments, the negative electrode film layer may optionally include other additives, such as a thickener (eg, sodium carboxymethyl cellulose (CMC-Na)).

[0056] In some embodiments, the negative electrode sheet can be prepared in the following manner: the components for preparing the negative electrode sheet, such as the negative electrode active material, the conductive agent, the binder and any other components are dispersed in a solvent (such as deionized water) to form a negative electrode slurry; the negative electrode slurry is coated on the negative electrode collector, and after drying, cold pressing and other processes, the negative electrode sheet can be obtained.

[0057] [Positive electrode]

[0058] The positive electrode sheet generally includes a positive electrode current collector and a positive electrode film layer disposed on at least one surface of the positive electrode current collector, wherein the positive electrode film layer includes a positive electrode active material.

[0059] As an example, the positive electrode current collector has two surfaces opposite to each other in its thickness direction, and the positive electrode film layer is disposed on any one or both of the two opposite surfaces of the positive electrode current collector.

[0060] In some embodiments, the positive electrode current collector may be a metal foil or a composite current collector. For example, aluminum foil may be used as the metal foil. The composite current collector may include a polymer material base and a metal layer formed on at least one surface of the polymer material base. The composite current collector may be formed by forming a metal material (aluminum, aluminum alloy, nickel, nickel alloy, titanium, titanium alloy, silver and silver alloy, etc.) on a polymer material substrate (such as a substrate of polypropylene (PP), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polystyrene (PS), polyethylene (PE), etc.).

[0061] In some embodiments, the positive electrode active material may adopt a positive electrode active material for a battery that is well known in the art. As an example, the positive electrode active material may include at least one of the following materials: a lithium-containing phosphate with an olivine structure, a lithium transition metal oxide, 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 batteries 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 oxide (such as LiCoO2), lithium nickel oxide (such as LiNiO2), lithium manganese oxide (such as LiMnO2, LiMn2O4), lithium nickel cobalt oxide, lithium manganese cobalt oxide, lithium nickel manganese oxide, lithium nickel cobalt manganese oxide (such as LiNi 1 / 3 Co 1 / 3 Mn 1 / 3 O2 (also referred to as NCM 333 )、LiNi 0.5 Co 0.2 Mn 0.3 O2 (also referred to as NCM 523 )、LiNi 0.5 Co0.25 Mn 0.25 O2 (also referred to as NCM 211 )、LiNi 0.6 Co 0.2 Mn 0.2 O2 (also referred to as NCM 622 )、LiNi 0.8 Co 0.1 Mn 0.1 O2 (also referred to as NCM 811 ), lithium nickel cobalt aluminum oxide (such as LiNi 0.85 Co 0.15 Al 0.05 O2) and its modified compounds, etc. Examples of lithium-containing phosphates with an olivine structure may include, but are not limited to, at least one of lithium iron phosphate (such as LiFePO4 (also referred to as LFP)), a composite material of lithium iron phosphate and carbon, lithium manganese phosphate (such as LiMnPO4), a composite material of lithium manganese phosphate and carbon, lithium iron manganese phosphate, and a composite material of lithium iron manganese phosphate and carbon.

[0062] In some embodiments, the positive electrode film layer may also optionally include a binder. As an example, the binder may include at least one of polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), vinylidene fluoride-tetrafluoroethylene-propylene terpolymer, vinylidene fluoride-hexafluoropropylene-tetrafluoroethylene terpolymer, tetrafluoroethylene-hexafluoropropylene copolymer, and fluorine-containing acrylate resin.

[0063] In some embodiments, the positive electrode film layer may further include a conductive agent, for example, the conductive agent may include at least one of superconducting carbon, acetylene black, carbon black, Ketjen black, carbon dots, carbon nanotubes, graphene and carbon nanofibers.

[0064] In some embodiments, the positive electrode sheet can be prepared in the following manner: the components for preparing the positive electrode sheet, such as the positive electrode active material, the conductive agent, the binder and any other components are dispersed in a solvent (such as N-methylpyrrolidone) to form a positive electrode slurry; the positive electrode slurry is coated on the positive electrode collector, and after drying, cold pressing and other processes, the positive electrode sheet can be obtained.

[0065] [Electrolytes]

[0066] The electrolyte plays the role of conducting ions between the positive electrode and the negative electrode. The present application has no specific restrictions on the type of electrolyte, which can be selected according to needs. For example, the electrolyte can be liquid, gel or all-solid.

[0067] In some embodiments, the electrolyte is liquid and includes an electrolyte salt and a solvent.

[0068] In some embodiments, the electrolyte salt can be selected from at least one of lithium hexafluorophosphate, lithium tetrafluoroborate, lithium perchlorate, lithium hexafluoroarsenate, lithium bis(fluorosulfonyl)imide, lithium bis(trifluoromethanesulfonyl)imide, lithium trifluoromethanesulfonate, lithium difluorophosphate, lithium difluorooxalatoborate, lithium dioxalatoborate, lithium difluorodioxalatophosphate, and lithium tetrafluorooxalatophosphate.

[0069] In some embodiments, the solvent can be selected from at least one of ethylene carbonate, propylene carbonate, ethyl methyl carbonate, diethyl carbonate, dimethyl carbonate, dipropyl carbonate, methyl propyl carbonate, ethyl propyl carbonate, butylene carbonate, fluoroethylene carbonate, methyl formate, methyl acetate, ethyl acetate, propyl acetate, methyl propionate, ethyl propionate, propyl propionate, methyl butyrate, ethyl butyrate, 1,4-butyrolactone, cyclopentane sulfone, dimethyl sulfone, methyl ethyl sulfone and diethyl sulfone.

[0070] In some embodiments, the electrolyte may further include additives. As examples, the additives may include negative electrode film-forming additives, positive electrode film-forming additives, and additives that can improve certain battery properties, such as additives that improve battery overcharge performance, additives that improve battery high or low temperature performance, etc.

[0071] [Isolation film]

[0072] In some embodiments, the secondary battery further includes a separator. The present application has no particular limitation on the type of separator, and any known porous separator with good chemical stability and mechanical stability can be selected.

[0073] In some embodiments, the material of the isolation membrane can be selected from at least one of glass fiber, non-woven fabric, polyethylene, polypropylene and polyvinylidene fluoride. The isolation membrane can be a single-layer film or a multi-layer composite film, without particular limitation. When the isolation membrane is a multi-layer composite film, the materials of each layer can be the same or different, without particular limitation.

[0074] In some embodiments, the secondary battery may include an outer package, which may be used to encapsulate the electrode assembly and the electrolyte.

[0075] In some embodiments, the outer packaging of the secondary battery may be a hard shell, such as a hard plastic shell, an aluminum shell, a steel shell, etc. The outer packaging of the secondary battery may also be a soft package, such as a bag-type soft package. The material of the soft package may be plastic, and examples of the plastic include polypropylene, polybutylene terephthalate, and polybutylene succinate.

[0076] The present application has no particular limitation on the shape of the secondary battery, which may be cylindrical, square or any other shape. Figure 3 The secondary battery 5 is a square structure as an example.

[0077] In some embodiments, reference Figure 4 , the outer packaging may include a shell 51 and a cover plate 53. Among them, the shell 51 may include a bottom plate and a side plate connected to the bottom plate, and the bottom plate and the side plate are enclosed to form a accommodating cavity. The shell 51 has an opening connected to the accommodating cavity, and the cover plate 53 can be covered on the opening to close the accommodating cavity. The positive electrode sheet, the negative electrode sheet and the isolation membrane are wound to form a wound battery cell 52. The wound battery cell 52 is encapsulated in the accommodating cavity. The electrolyte is infiltrated in the wound battery cell 52. The number of wound battery cells 52 contained in the secondary battery 5 can be one or more, and those skilled in the art can choose according to specific actual needs.

[0078] In some embodiments, secondary batteries may be assembled into a battery module. The number of secondary batteries contained in the battery module may be one or more, and the specific number may be selected by those skilled in the art according to the application and capacity of the battery module.

[0079] Figure 5 4 is an example of a battery module. Figure 5 In the battery module 4, the plurality of secondary batteries 5 may be arranged in sequence along the length direction of the battery module 4. Of course, they may also be arranged in any other manner. Further, the plurality of secondary batteries 5 may be fixed by fasteners.

[0080] Optionally, the battery module 4 may further include a housing having a receiving space, and the plurality of secondary batteries 5 are received in the receiving space.

[0081] In some embodiments, the battery modules described above may also be assembled into a battery pack. The battery pack may contain one or more battery modules, and the specific number may be selected by those skilled in the art according to the application and capacity of the battery pack.

[0082] Figure 6 and Figure 7 1 is a battery pack 1 as an example. Figure 6 and Figure 7 The battery pack 1 may include a battery box and a plurality of battery modules 4 disposed in the battery box. The battery box includes an upper box body 2 and a lower box body 3. The upper box body 2 can cover the lower box body 3 and form a closed space for accommodating the battery modules 4. The plurality of battery modules 4 can be arranged in the battery box in any manner.

[0083] In addition, the present application also provides an electrical device, which includes at least one of the secondary battery, battery module, or battery pack provided in the present application. The secondary battery, battery module, or battery pack can be used as a power source for the electrical device, and can also be used as an energy storage unit for the electrical device. The electrical device may include mobile devices (such as mobile phones, laptops, etc.), electric vehicles (such as pure electric vehicles, hybrid electric vehicles, plug-in hybrid electric vehicles, electric bicycles, electric scooters, electric golf carts, electric trucks, etc.), electric trains, ships and satellites, energy storage systems, etc., but are not limited thereto.

[0084] As the electrical device, a secondary battery, a battery module or a battery pack may be selected according to its usage requirements.

[0085] Figure 8 The power consumption device is taken as an example. The power consumption device is a pure electric vehicle, a hybrid electric vehicle, or a plug-in hybrid electric vehicle. In order to meet the high power and high energy density requirements of the power consumption device for the secondary battery, a battery pack or a battery module can be used.

[0086] [Example]

[0087] Hereinafter, the embodiments of the present application will be described. The embodiments described below are exemplary and are only used to explain the present application, and should not be construed as limiting the present application. If no specific techniques or conditions are indicated in the embodiments, the techniques or conditions described in the literature in this area or the product specifications are used. If the manufacturer is not indicated in the reagents or instruments used, they are all conventional products that can be obtained commercially.

[0088] Example 1

[0089] 1. Preparation of positive electrode sheets: The positive electrode active material NCM523, the conductive agent acetylene black, and the binder polyvinylidene fluoride (PVDF) are dissolved in a solvent N-methylpyrrolidone (NMP) at a weight ratio of 96.5:1.5:2, and the positive electrode slurry is obtained after being fully stirred and mixed; the positive electrode slurry is then evenly coated on the positive electrode collector, and then dried, cold pressed, and cut to obtain the positive electrode sheet.

[0090] 2. Preparation of negative electrode sheet:

[0091] Preparation of negative electrode slurry: artificial graphite, conductive agent acetylene black, thickener CMC, and binder SBR are mixed in a mass ratio of 96.4:1:1.2:1.4, deionized water is added as a solvent, and the negative electrode slurry is obtained after mixing;

[0092] Preparation of negative electrode sheet: The negative electrode slurry is coated on the two surfaces of the negative electrode current collector respectively, and the compaction density of the negative electrode film layers on both sides is adjusted so that the OI value of the first negative electrode film layer is 50 and the OI value of the second negative electrode film layer is 55.1.

[0093] 3. Isolation film: polypropylene film.

[0094] 4. Preparation of electrolyte: Ethylene carbonate (EC), ethyl methyl carbonate (EMC), and diethyl carbonate (DEC) were mixed in a volume ratio of 1:1:1, and then LiPF6 was uniformly dissolved in the above solution to obtain an electrolyte. The concentration of LiPF6 in the electrolyte was 1 mol / L.

[0095] 5. Preparation of secondary batteries: stack and wind the above-mentioned positive electrode sheets, separators, and negative electrode sheets in order to obtain a wound battery cell; put the wound battery cell into an outer package, add the above-prepared electrolyte, and obtain a secondary battery after packaging, standing, formation, aging and other processes.

[0096] The secondary battery preparation methods of Examples 2-5 and Comparative Examples 1-2 are similar to those of Example 1, but the OI values ​​of the first negative electrode film layer and the second negative electrode film layer are adjusted respectively. The different product parameters are detailed in Table 1.

[0097] Table 1: Parameter results of Examples 1-5 and Comparative Examples 1-2

[0098] Serial number <![CDATA[OI1]]> <![CDATA[OI2]]> <![CDATA[OI2 / OI1]]> Example 1 50.0 55.1 1.10 Example 2 50.0 58.0 1.16 Example 3 50.0 60.0 1.20 Example 4 50.0 65.0 1.30 Example 5 50.0 69.9 1.40 Comparative Example 1 50.0 50.0 1.00 Comparative Example 2 50.0 45.0 0.90

[0099] Battery Test

[0100] (1) OI value test of negative electrode film layer

[0101] The OI value of the negative electrode film layer has a well-known meaning in the art and can be tested by methods known in the art. For example, it can be obtained by using an X-ray diffractometer (such as Bruker D8 Discover), and according to the general rules of X-ray diffraction analysis and the method for determining the lattice parameters of graphite JIS K 0131-1996 and JB / T4220-2011, an X-ray diffraction spectrum is obtained, and the OI value of the negative electrode film layer = C004 / C110, wherein C004 is the peak area of ​​the 004 crystal plane diffraction peak, and C110 is the peak area of ​​the 110 crystal plane diffraction peak. Specifically, the OI value test method of the negative electrode film layer can be: directly placing the prepared negative electrode pole piece in an X-ray powder diffractometer, and obtaining the peak area of ​​the 004 crystal plane diffraction peak and the peak area of ​​the 110 crystal plane diffraction peak by X-ray diffraction analysis, and then obtaining the OI value of the negative electrode film layer. The 2θ angle corresponding to the 004 crystal plane of graphite is 53.5°-55.5° (eg, 54.5°); the 2θ angle corresponding to the 110 crystal plane of graphite is 76.5°-78.5° (eg, 77.4°).

[0102] (2) Battery thickness and expansion rate test

[0103] The secondary batteries prepared in Examples 1-5 and Comparative Examples 1-2 were cycled at 45°C 1C / 1C, with a voltage of 2.8-4.2V. The thickness of the fully charged battery was measured before the cycle. The battery was clamped and a clamp force of 5000N was applied to simulate the force applied by the end plate to the battery during the module assembly process. Then, the battery was cycled with the clamp for 1500 times, the clamp was removed, the battery was fully charged and left to stand for 12 hours, and the thickness change of the battery was measured. The difference in the thickness of the battery before and after the cycle was divided by the thickness of the battery before the cycle and multiplied by 100%, and the expansion rate of the battery was obtained.

[0104] (3) Cyclic performance test

[0105] At 25° C., the secondary battery was subjected to a full charge and discharge cycle test at a 1C rate until the capacity of the secondary battery decayed to 80% of the initial capacity, and the number of cycles was recorded.

[0106] Table 2: Performance test results of Examples 1-5 and Comparative Examples 1-2

[0107] Serial number Number of cycles Battery thickness before cycle / mm Battery thickness after cycle / mm Expansion rate Example 1 2400 26.63 28.56 7.3％ Example 2 2450 26.6 28.44 6.9％ Example 3 2500 26.55 28.22 6.3％ Example 4 2460 26.61 28.47 7.0％ Example 5 2440 26.66 28.55 7.1％ Comparative Example 1 2000 26.49 29.67 12.0％ Comparative Example 2 1900 26.53 29.85 12.5％

[0108] According to the above results, compared with comparative examples 1-2, embodiments 1-5 effectively reduce the expansion rate of the battery, avoid the breakage of accessories due to external stress accumulation at the corners during battery use, and improve the safety performance and cycle life of the secondary battery.

[0109] It should be noted that the present application is not limited to the above-mentioned embodiments. The above-mentioned embodiments are only examples, and the embodiments having the same structure as the technical idea and exerting the same effect within the scope of the technical solution of the present application are all included in the technical scope of the present application. In addition, without departing from the scope of the main purpose of the present application, various modifications that can be thought of by those skilled in the art to the embodiments and other methods of combining some of the constituent elements in the embodiments are also included in the scope of the present application.

Claims

1. A secondary battery, comprising a wound-type battery cell, the wound-type battery cell comprising: A negative electrode sheet, the negative electrode sheet comprising a negative electrode current collector, the negative electrode current collector comprising a first surface and a second surface opposite to the first surface, the first surface being located on a side of the wound-type battery core away from the center, and the second surface being located on a side of the wound-type battery core close to the center; A first negative electrode film layer is disposed on a first surface of the negative electrode current collector; A second negative electrode film layer is disposed on the second surface of the negative electrode current collector; The first negative electrode film layer and the second negative electrode film layer both include negative electrode active materials, and the negative electrode active materials both include carbon materials. The OI value of the first negative electrode film layer is recorded as OI1, and the OI value of the second negative electrode film layer is recorded as OI2; the OI value=C004 / C110, wherein C004 is the peak area of ​​the diffraction peak of the 004 crystal plane, and C110 is the peak area of ​​the diffraction peak of the 110 crystal plane; The secondary battery satisfies: OI1<OI2; 15≤OI1≤80;25≤OI2≤90.

2. The secondary battery according to claim 1, characterized in that: The OI1 and the OI2 satisfy the relationship: 1.05≤OI2 / OI1≤1.

4.

3. The secondary battery according to claim 2, characterized in that: 1.15≤OI2 / OI1≤1.

3.

4. The secondary battery according to claim 1, characterized in that: The OI1 and the OI2 satisfy the relationship: 5<OI2-OI1<20.

5. The secondary battery according to claim 1, characterized in that: 20≤OI1≤60.

6. The secondary battery according to claim 1, characterized in that: 30≤OI2≤70.

7. The secondary battery according to any one of claims 1 to 4, characterized in that: The first negative electrode film layer and the second negative electrode film layer further include silicon material, and the mass proportion of the silicon material in the first negative electrode film layer in the negative electrode active material is denoted as C A The mass proportion of the silicon material in the second negative electrode film layer in the negative electrode active material is recorded as C B , then the secondary battery satisfies: C A <C B .

8. The secondary battery according to claim 7, characterized in that: 0.1%≤C B -C A ≤1.0%。 9. The secondary battery according to claim 8, characterized in that: 0.2%≤C B -C A ≤0.5%。 10. The secondary battery according to claim 7, characterized in that: 8%≤C A ≤32%; and / or 9%≤C B ≤33%。 11. The secondary battery according to claim 8, characterized in that 8%≤C A ≤32%; and / or 9%≤C B ≤33%。 12. The secondary battery according to claim 10, characterized in that: 10%≤C A ≤15%。 13. The secondary battery according to claim 10, characterized in that: 11%≤C B ≤16%。 14. The secondary battery according to any one of claims 1 to 4, characterized in that: The number of core layers of the wound battery core is greater than 20.

15. The secondary battery according to claim 14, characterized in that: The number of core layers of the wound battery core is 21-120.

16. The secondary battery according to any one of claims 1 to 4, characterized in that: The expansion coefficient of the first negative electrode film layer is α1, and the expansion coefficient of the second negative electrode film layer is α2, then the secondary battery satisfies: α2 / α1≤1.

022.

17. The secondary battery according to claim 16, characterized in that: 1.005≤α2 / α1≤1.02。 18. A battery module, characterized in that: A secondary battery comprising any one of claims 1 to 17.

19. A battery pack, characterized in that: Comprising the battery module as claimed in claim 18.

20. An electrical device, characterized in that: The invention comprises at least one of the secondary battery according to any one of claims 1 to 17, the battery module according to claim 18 or the battery pack according to claim 19.

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