Secondary battery, preparation method thereof and electric device

Abstract

The invention relates to a secondary battery, a preparation method thereof and a power utilization device, the secondary battery comprises a positive pole piece, the positive pole piece comprises a positive current collector, and a bottom coating and a positive material layer which are sequentially arranged on at least one surface of the positive current collector; and the bottom coating layer comprises a polyolefin elastomer and a conductive agent. By applying the undercoat layer containing the polyolefin elastomer, the secondary battery has good puncture resistance, and the safety of the battery can be improved.

Description

Technical Field

[0001] The present application relates to the technical field of secondary batteries, and in particular to a secondary battery, a preparation method thereof, and an electrical device. Background Art

[0002] Secondary batteries have been widely used. However, when the inside or outside of the battery is squeezed, collided or punctured, it is easy to cause a short circuit between the positive and negative electrodes, which in turn causes thermal runaway of the battery cell. Summary of the invention

[0003] The purpose of the present application is to provide a secondary battery, a preparation method thereof and an electrical device. The secondary battery has good puncture resistance by applying a primer layer containing a polyolefin elastomer, which helps to improve the safety of the battery.

[0004] To this end, in a first aspect of the present application, a secondary battery is provided, which includes a positive electrode sheet,

[0005] The positive electrode sheet comprises a positive electrode current collector, and a primer layer and a positive electrode material layer sequentially arranged on at least one surface of the positive electrode current collector; the positive electrode material layer comprises a positive electrode active material;

[0006] The primer layer comprises a polyolefin elastomer and a conductive agent.

[0007] Polyolefin elastomers have good compatibility with battery systems and excellent physical and mechanical properties. By applying polyolefin elastomers in the base coat, the base coat can have good elasticity and toughness, thereby significantly improving the battery's puncture resistance, helping to reduce the risk of internal short circuits and thermal runaway in the battery and improving the battery's safety performance.

[0008] In some embodiments, in the primer layer, the mass percentage of the polyolefin elastomer is 40% to 60%.

[0009] When the mass ratio of the polyolefin elastomer is within the above range, on the one hand, the polyolefin elastomer can effectively increase the elasticity and toughness of the base coating; on the other hand, the conductive agent can still occupy a relatively reasonable mass ratio, thereby ensuring the basic conductivity of the base coating. Therefore, by adopting the above mass ratio, the puncture resistance and the conductivity of the base coating can be better balanced, thereby improving the puncture resistance and short circuit prevention performance of the positive electrode while maintaining good electrochemical performance.

[0010] In some embodiments, the degree of polymerization of the polyolefin elastomer is 2500-3000.

[0011] The polyolefin elastomer with a degree of polymerization of 2500 to 3000 has a narrow molecular weight distribution and has the advantages of good fluidity, good compatibility and easy processing.

[0012] In some embodiments, the polyolefin elastomer is a copolymer of ethylene and α-olefin; wherein the α-olefin is selected from linear, branched or cyclic α-olefins having 5 to 15 carbon atoms.

[0013] The polyolefin elastomer is copolymerized with ethylene and the above-mentioned high-carbon alpha olefins. The soft chain curling structure of the high-carbon olefins and the crystalline ethylene chains serve as physical crosslinking points, so that it has excellent toughness and good processing performance.

[0014] In some embodiments, the polyolefin elastomer comprises ethylene / α-octene copolymer.

[0015] Octene has a very suitable chain length and curled structure, so that the polyolefin elastomer obtained by copolymerizing it with ethylene can bring better mechanical properties such as toughness and elongation to the positive electrode when used in the base coating of the positive electrode.

[0016] In some embodiments, the polyolefin elastomer has a tensile strength of 20 to 45 MPa.

[0017] When the tensile strength of the polyolefin elastomer is within the above range, it is beneficial for the primer layer containing the polyolefin elastomer to have better elasticity and toughness, and further improve the battery's anti-puncture and anti-short circuit performance.

[0018] In some embodiments, the primer layer has a thickness of 1 to 10 μm.

[0019] When the thickness of the primer layer is as described above, the anti-puncture performance can be significantly improved without affecting the electrochemical performance of the positive electrode sheet.

[0020] In some embodiments, the conductive agent in the primer layer includes at least one selected from the group consisting of carbon nanotubes, carbon fibers, carbon black, and acetylene black.

[0021] When carbon nanotubes or carbon fibers are used, they have better mechanical properties than other conductive agents, thereby helping to further improve the mechanical strength of the primer layer. In addition, carbon black and acetylene black can also be used, which have advantages in terms of cost and ease of processing.

[0022] In some embodiments, the primer layer further includes a hydroxide.

[0023] In some embodiments, the hydroxide of the base coating comprises lithium hydroxide.

[0024] By applying hydroxide in the undercoat layer, the pH value of the undercoat layer can be adjusted, which helps to improve its stability. For example, sodium oxide, aluminum hydroxide, calcium hydroxide, lithium hydroxide, etc. can be used. When lithium hydroxide is used, it is beneficial to further improve the energy density of the positive electrode.

[0025] In some embodiments, the base coating further includes a binder.

[0026] In some embodiments, the binder includes at least one of polyacrylic acid, sodium polyacrylate, polyurethane, polyacrylamide, and polyvinyl alcohol.

[0027] The polyolefin elastomer has a certain bonding effect, which can reduce or completely replace the use of other binders in the primer layer. When the primer layer also contains a binder, it helps to further improve the bonding force between the primer layer and the positive electrode collector, thereby improving the stability of the positive electrode sheet.

[0028] The second aspect of the present application provides a method for preparing the secondary battery described in the first aspect of the present application, comprising: providing a primer slurry comprising a polyolefin elastomer and a conductive agent; applying the primer slurry on at least one surface of a positive electrode current collector, and after the primer is formed, providing a positive electrode material layer on the surface of the primer, so as to prepare the positive electrode sheet;

[0029] The positive electrode sheet, the separator and the negative electrode sheet are assembled to obtain a secondary battery.

[0030] In some embodiments, the viscosity of the base coating slurry is 100-1000 CPS.

[0031] By using the base coating slurry having a viscosity within the above range, processing properties can be improved.

[0032] In some embodiments, the polyolefin elastomer has a tensile strength of 20 to 45 MPa.

[0033] When the tensile strength of the polyolefin elastomer is within the above range, it is beneficial for the primer layer containing the polyolefin elastomer to have better elasticity and toughness, and further improve the battery's anti-puncture and anti-short circuit performance.

[0034] The third aspect of the present application provides an electric device, which includes the secondary battery described in the first aspect of the present application, or the secondary battery prepared according to the preparation method described in the second aspect of the present application. The electric device has all the characteristics and advantages of the secondary battery or positive electrode sheet described above, which will not be repeated here.

[0035] The above description is only an overview of the technical solution of the present application. In order to more clearly understand the technical means of the present application, it can be implemented in accordance with the contents of the specification. In order to make the above and other purposes, features and advantages of the present application more obvious and easy to understand, the specific implementation methods of the present application are listed below. BRIEF DESCRIPTION OF THE DRAWINGS

[0036] Various other advantages and benefits will become apparent to those skilled in the art by reading the detailed description of the preferred embodiments below. The accompanying drawings are only used to illustrate the preferred embodiments and are not to be considered as limiting the present application. In the accompanying drawings:

[0037] Figure 1 is a schematic diagram of a secondary battery according to an embodiment of the present application;

[0038] Figure 2 yes Figure 1 An exploded view of a secondary battery according to an embodiment of the present application is shown;

[0039] Figure 3 is a schematic diagram of a battery module according to an embodiment of the present application;

[0040] Figure 4 is a schematic diagram of a battery pack according to an embodiment of the present application;

[0041] Figure 5 yes Figure 4 An exploded view of a battery pack according to an embodiment of the present application is shown;

[0042] Figure 6 is a schematic diagram of an electrical device using a secondary battery according to an embodiment of the present application as a power source;

[0043] Figure 7 It is a temperature change diagram of the battery puncture safety test of Examples 1 to 5 and Comparative Example 1.

[0044] Description of reference numerals:

[0045] 1 battery pack; 2 upper box; 3 lower box; 4 battery module; 5 secondary battery; 51 shell; 52 electrode assembly; 53 cover plate. DETAILED DESCRIPTION

[0046] The exemplary embodiments of the present disclosure will be described in more detail below. It should be understood that the present disclosure can be implemented in various forms and should not be limited by the embodiments set forth herein. On the contrary, these embodiments are provided to enable a more thorough understanding of the present disclosure and to fully convey the scope of the present disclosure to those skilled in the art.

[0047] The "range" disclosed in the present application is defined in the form of a lower limit and an 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 boundaries of the particular range. The range defined in this way can be inclusive or exclusive of the end values, and can be arbitrarily combined, that is, any lower limit can be combined with any upper limit to form a range. For example, if a range of 60 to 120 and 80 to 110 is listed for a particular parameter, it is understood that a range of 60 to 110 and 80 to 120 is also expected. In addition, if the minimum range values ​​1 and 2 are listed, and the maximum range values ​​3, 4 and 5 are listed, the following ranges can all be expected: 1 to 3, 1 to 4, 1 to 5, 2 to 3, 2 to 4 and 2 to 5. In the present application, unless otherwise specified, the numerical range "a to b" represents an abbreviation of any real number combination between a and b, where a and b are both real numbers. For example, the numerical range "0-5" means that all real numbers between "0-5" 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.

[0048] Unless otherwise specified, all embodiments and optional embodiments of the present application can be combined with each other to form a new technical solution.

[0049] 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.

[0050] 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, it is mentioned that the method may also include step (c), which means that step (c) can 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.

[0051] 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.

[0052] Secondary batteries have been widely used. However, when the inside or outside of the battery is squeezed, collided or punctured, it is easy to cause a short circuit between the positive and negative electrodes, which in turn causes thermal runaway of the battery cell. In the prior art, there are technical solutions reported to set a safety coating on the surface of the active material layer of the electrode, which has the defects of limited improvement in anti-puncture effect and poor stability.

[0053] The present application mainly improves the mechanical properties of the positive electrode sheet by applying a polyolefin elastomer in the bottom coating of the positive electrode sheet, thereby improving its puncture resistance and improving the safety of the battery.

[0054] The solutions described in the embodiments of the present application are applicable to secondary batteries, battery modules using the secondary batteries, battery packs using the secondary batteries or battery modules, and electrical devices using at least one of the secondary batteries, battery modules and battery packs.

[0055] Secondary battery

[0056] [Positive electrode]

[0057] In some embodiments, a secondary battery is provided, comprising a positive electrode sheet,

[0058] The positive electrode sheet comprises a positive electrode current collector, and a primer layer and a positive electrode material layer sequentially arranged on at least one surface of the positive electrode current collector; the positive electrode material layer comprises a positive electrode active material;

[0059] The primer layer comprises a polyolefin elastomer and a conductive agent.

[0060] Polyolefin elastomers have good compatibility with battery systems and excellent physical and mechanical properties. By applying polyolefin elastomers in the base coat, the base coat can have good elasticity and toughness, thereby significantly improving the battery's puncture resistance, helping to reduce the risk of internal short circuits and explosions in the battery and improving safety.

[0061] Polyolefin elastomer (POE) is a type of polyolefin material polymerized by ethylene and propylene or other α-olefins under the action of a homogeneous metal catalyst (e.g., a metallocene catalyst). Polyolefin elastomers have the advantages of both plastics and rubbers, and have excellent weather resistance, chemical resistance, transparency, and flexibility. In addition, they have no unsaturated double bonds and have excellent aging resistance. As an example, copolymers of ethylene and at least one of propylene, 1-butene, 1-hexene, 1-pentene, 1-octene, or other α-olefins can be cited.

[0062] In some embodiments, the primer layer is disposed on one surface of the positive electrode current collector, and a positive electrode material layer is disposed on the surface of the primer layer.

[0063] In some embodiments, the primer layer is disposed on both surfaces of the positive electrode current collector, and a positive electrode material layer is disposed on the surface of the primer layer.

[0064] In some embodiments, in the primer layer, the mass proportion of the polyolefin elastomer is 40% to 60%, for example, selected from about 40%, 41%, 42%, 43%, 44%, 45%, 46%, 47%, 48%, 49%, 50%, 51%, 52%, 53%, 54%, 55%, 56%, 57%, 58%, 59%, 60%, etc.

[0065] When the mass ratio of the polyolefin elastomer is within the above range, on the one hand, the polyolefin elastomer can effectively increase the elasticity and toughness of the base coating; on the other hand, the conductive agent can still occupy a relatively reasonable mass ratio, thereby ensuring the basic conductivity of the base coating. Therefore, by adopting the above mass ratio, the puncture resistance and the conductivity of the base coating can be better balanced, thereby improving the puncture resistance and short circuit prevention performance of the positive electrode while maintaining good electrochemical performance.

[0066] In some embodiments, the degree of polymerization of the polyolefin elastomer is 2500 to 3000; for example, it may be about 2500, 2600, 2700, 2800, 2900, 3000, etc.

[0067] The polyolefin elastomer with the above polymerization degree has a narrow molecular weight distribution and has the advantages of good fluidity, good compatibility and easy processing.

[0068] In some embodiments, the polyolefin elastomer is a copolymer of ethylene and α-olefin; wherein the α-olefin is selected from linear, branched or cyclic α-olefins having 3 to 15 carbon atoms.

[0069] Compared with olefins with lower (e.g., less than 5) or higher (e.g., greater than 15) carbon atoms, olefins with 5 to 15 carbon atoms have a moderate carbon chain length, and the polyolefin elastomer synthesized therefrom has better toughness. By copolymerizing ethylene with the above-mentioned high-carbon α-olefins, the soft chain curling structure of the high-carbon olefins and the crystallized ethylene chains are used as physical crosslinking points, so that the polyolefin elastomer has excellent toughness and good processing properties.

[0070] In some embodiments, the polyolefin elastomer comprises ethylene / α-octene copolymer.

[0071] Octene has a very suitable chain length and curled structure, so that the polyolefin elastomer obtained by copolymerizing it with ethylene can bring better mechanical properties such as toughness and elongation to the positive electrode when used in the base coating of the positive electrode.

[0072] In some embodiments, the tensile strength of the polyolefin elastomer is 20 to 45 MPa; for example, it may be about 20 MPa, 22 MPa, 25 MPa, 27 MPa, 30 MPa, 33 MPa, 35 MPa, 38 MPa, 40 MPa, 42 MPa, 45 MPa, etc.

[0073] When the tensile strength of the polyolefin elastomer is within the above range, it is beneficial for the primer layer containing the polyolefin elastomer to have better elasticity and toughness, and further improve the battery's anti-puncture and anti-short circuit performance.

[0074] The tensile strength of the polyolefin elastomer can be detected by methods known in the art. For example, the tensile strength of the polyolefin elastomer can be detected by the following method: the test refers to GB / T 1040.2-2018 "Determination of tensile properties of plastics", the test instrument is RGM-4100 universal material testing machine (Shenzhen Rigel Instrument Manufacturing Co., Ltd.), and an I-shaped spline is used, with the following specifications: total length 150mm, initial distance between clamps 115mm, gauge length 50mm, narrow parallel part length 80mm, distance between wide parallel parts 108mm, end width 20mm, narrow part width 10mm, thickness 4mm; 5 samples are tested in each group, and the results are averaged.

[0075] In some embodiments, the thickness of the primer layer is 1 to 10 μm; for example, it can be selected from about 1 μm, 2 μm, 3 μm, 4 μm, 5 μm, 6 μm, 7 μm, 8 μm, 9 μm, 10 μm, etc.

[0076] When the thickness of the primer layer is as described above, the anti-puncture performance can be significantly improved without affecting the electrochemical performance of the positive electrode sheet.

[0077] In some embodiments, the conductive agent in the base coating layer includes at least one selected from the group consisting of carbon nanotubes (eg, single-walled carbon nanotubes, multi-walled carbon nanotubes), carbon fibers, carbon black, and acetylene black.

[0078] When carbon nanotubes or carbon fibers are used, they have better mechanical properties than other conductive agents, thereby helping to further improve the mechanical strength of the primer layer. In addition, carbon black and acetylene black can also be used, which have advantages in terms of cost and ease of processing.

[0079] In some embodiments, the base coating further comprises a hydroxide, such as sodium hydroxide, aluminum hydroxide, calcium hydroxide, lithium hydroxide, etc. In some embodiments, the hydroxide of the base coating comprises lithium hydroxide.

[0080] By using hydroxide in the undercoat layer, the pH value of the undercoat layer can be adjusted, which helps to improve its stability. When lithium hydroxide is used, it is beneficial to further increase the energy density of the positive electrode.

[0081] In some embodiments, the primer layer does not contain a binder other than polyolefin elastomer. Polyolefin elastomer has a certain bonding effect, and no additional binder may be added to the primer layer, so that the positive electrode plate is more likely to maintain a good energy density.

[0082] In some embodiments, the base coating further includes a binder.

[0083] In some embodiments, the binder includes at least one of polyacrylic acid, sodium polyacrylate, polyurethane, polyacrylamide, and polyvinyl alcohol.

[0084] The polyolefin elastomer has a certain bonding effect, which can reduce or completely replace the use of other binders in the primer layer. When the primer layer also contains a binder, it helps to further improve the bonding force between the primer layer and the positive electrode collector, thereby improving the stability of the positive electrode sheet.

[0085] 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.).

[0086] In some embodiments, the positive electrode material layer includes a positive electrode active material, and the positive electrode active material may be a positive electrode active material for lithium-ion batteries that is well known in the art. As an example, the positive electrode active material may include at least one of the following materials: 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 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 / 3Mn 1 / 3 O2 (also referred to as NCM333 )、LiNi 0.5 Co 0.2 Mn 0.3 O2 (also referred to as NCM 523 )、LiNi 0.5 Co 0.25 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.

[0087] In some embodiments, the positive electrode material layer may also optionally include a binder. For example, the binder may include one or more combinations selected from the group consisting of polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), vinylidene fluoride-tetrafluoroethylene-propylene terpolymer, vinylidene fluoride-hexafluoropropylene-tetrafluoroethylene terpolymer, tetrafluoroethylene-hexafluoropropylene copolymer, and fluorine-containing acrylate resin.

[0088] In some embodiments, the positive electrode material layer may further include a conductive agent. For example, the conductive agent may include one or a combination of two or more selected from the group consisting of Super P, acetylene black, carbon black, Ketjen black, carbon dots, carbon nanotubes, graphene, and carbon nanofibers.

[0089] [Preparation of positive electrode sheet]

[0090] In some embodiments, a method for preparing a positive electrode plate is provided, comprising providing a primer slurry comprising a polyolefin elastomer and a conductive agent; applying the primer slurry on at least one surface of a positive electrode current collector, and after the primer is formed, disposing a positive electrode material layer on the surface of the primer, thereby preparing the positive electrode plate.

[0091] In some embodiments, the viscosity of the base coating slurry is 100 to 1000 CPS; for example, it can be selected from about 100 CPS, 200 CPS, 300 CPS, 400 CPS, 500 CPS, 600 CPS, 700 CPS, 800 CPS, 900 CPS, 1000 CPS, etc.

[0092] By using the base coating slurry having a viscosity within the above range, processing properties can be improved.

[0093] CPS (Centipoise) is a unit of viscosity, which indicates the resistance of a liquid to flow. The viscosity of the slurry can be detected by methods known in the art. For example, the viscosity measurement method in GB / T 10247-2008 can be used for detection. The relevant test conditions include: test temperature 25°C, test instrument: accuracy: ±1% FS, Brookfield DV2T viscometer.

[0094] In some embodiments, the tensile strength of the polyolefin elastomer is 20 to 45 MPa; for example, it may be about 20 MPa, 22 MPa, 25 MPa, 27 MPa, 30 MPa, 33 MPa, 35 MPa, 38 MPa, 40 MPa, 42 MPa, 45 MPa, etc.

[0095] When the tensile strength of the polyolefin elastomer is within the above range, it is beneficial for the primer layer containing the polyolefin elastomer to have better elasticity and toughness, and further improve the battery's anti-puncture and anti-short circuit performance.

[0096] In some embodiments, the positive electrode sheet can be prepared in the following manner: the components of the above-mentioned positive electrode material layer, such as the positive electrode active material, the positive electrode lithium supplement, the additives, the optional 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 base coating layer, and after drying, cold pressing and other processes, the positive electrode sheet can be obtained.

[0097] [Negative electrode]

[0098] In some embodiments, the secondary battery includes a negative electrode sheet; the negative electrode sheet includes a negative electrode collector and a negative electrode material disposed on at least one surface of the negative electrode collector, and the negative electrode material includes a negative electrode active material.

[0099] 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.).

[0100] In some embodiments, the negative electrode active material may be a negative electrode active material for lithium ion batteries known in the art. For example, the negative electrode active material includes one or a combination of two or more selected from the following groups: natural graphite, artificial graphite, mesophase microcarbon beads (MCMB), hard carbon, soft carbon, silicon, silicon-carbon composite, Li-Sn alloy, Li-Sn-O alloy, Sn, SnO, SnO2, TiO2-Li4Ti5O 12 ,Li-Al alloy.

[0101] In some embodiments, the negative electrode material may further include a binder. For example, the binder may include one or a combination of two or more selected from the group consisting 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).

[0102] In some embodiments, the negative electrode material may further include a conductive agent. For example, the conductive agent may include one or a combination of two or more selected from the group consisting of Super P, acetylene black, carbon black, Ketjen black, carbon dots, carbon nanotubes, graphene, and carbon nanofibers.

[0103] In some embodiments, the negative electrode material may further include other auxiliary agents. For example, the other auxiliary agent may be a thickener (such as sodium carboxymethyl cellulose (CMC-Na)).

[0104] In some embodiments, the negative electrode sheet can be prepared by the following method: the above-mentioned negative electrode materials, such as negative electrode active materials, conductive agents, binders 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.

[0105] [Isolation film]

[0106] In some embodiments, the secondary battery includes an isolation membrane. The present application has no particular restrictions on the type of isolation membrane, and any known porous structure isolation membrane with good chemical stability and mechanical stability can be selected. For example, the material of the isolation membrane can be selected from one or a combination of two or more of the following groups: glass fiber, non-woven fabric, polyethylene, polypropylene, polyvinylidene fluoride. The isolation membrane can be a single-layer film or a multi-layer composite film without particular restrictions. When the isolation membrane is a multi-layer composite film, the materials of each layer can be the same or different without particular restrictions.

[0107] In some embodiments, the secondary battery is a solid-state battery and does not include a separator; the solid-state battery includes a solid electrolyte. The solid electrolyte is disposed between the positive electrode plate and the negative electrode plate, and plays the role of transmitting ions and isolating the positive and negative electrodes.

[0108] [Electrolytes]

[0109] In some embodiments, the secondary battery further comprises an electrolyte, which acts as a conductor of ions between the positive electrode and the negative electrode. The present application does not specifically limit the type of electrolyte, and it can be selected according to needs. The electrolyte can be liquid, gel or solid. In some embodiments, the electrolyte is an electrolyte, and the electrolyte comprises an electrolyte salt and a solvent.

[0110] In some embodiments, the electrolyte salt may be selected from LiN(C x2 F 2x2+1 SO2)(C y2 F 2y2+1 SO2), LiPF6, LiBF4, LiBOB, LiAsF6, Li(FSO2)2N, LiCF3SO3 and LiClO4, wherein x2 and y2 are natural numbers. In the electrolyte, the concentration range of the lithium salt can be 0.5M to 2.5M, specifically 0.8M to 2M, such as 0.5M, 0.6M, 0.7M, 0.8M, 0.9M, 1.0M, 1.2M, 1.5M, 1.8M, 2.0M, 2.2M, 2.5M, etc.

[0111] In some embodiments, the solvent may be selected from one or more of linear carbonates, cyclic carbonates, and carboxylates. Wherein, the types of linear carbonates, cyclic carbonates, and carboxylates are not specifically limited and can be selected according to actual needs. As an example, the organic solvent may include one or more of diethyl carbonate, dipropyl carbonate, ethyl methyl carbonate, methyl propyl carbonate, ethyl propyl carbonate, ethylene carbonate, propylene carbonate, butylene carbonate, γ-butyrolactone, methyl formate, ethyl formate, methyl acetate, ethyl acetate, propyl acetate, methyl propionate, ethyl propionate, methyl propionate, and tetrahydrofuran.

[0112] In some embodiments, the electrolyte may also optionally include electrolyte additives. For example, the electrolyte additives may include negative electrode film-forming additives, positive electrode film-forming additives, and may also include electrolyte additives that can improve certain battery properties, such as electrolyte additives that improve battery overcharge performance, electrolyte additives that improve battery high temperature or low temperature performance, etc. As an example, the electrolyte additive may be selected from at least one of monofluoro lithium phosphate, difluoro lithium phosphate, fluorosulfonate, cyclic carbonate compounds containing unsaturated bonds, halogen-substituted cyclic carbonate compounds, sulfate compounds, sulfite compounds, sultone compounds, disulfonic acid compounds, nitrile compounds, aromatic compounds, isocyanate compounds, phosphazene compounds, cyclic anhydride compounds, phosphite compounds, phosphate compounds, borate compounds, and carboxylate compounds.

[0113] In some embodiments, the gel electrolyte includes a polymer as a skeleton network and can be used in combination with an ionic liquid-lithium salt.

[0114] In some embodiments, the solid electrolyte includes a polymer solid electrolyte, an inorganic solid electrolyte, or a composite solid electrolyte.

[0115] As examples, the polymer of the polymer solid electrolyte may include polyether (polyethylene oxide), polysiloxane, polycarbonate, polyacrylonitrile, polyvinylidene fluoride, polymethyl methacrylate, a single ion polymer, a polyionic liquid, cellulose, and the like.

[0116] As an example, the inorganic solid electrolyte can be an oxide solid electrolyte (crystalline perovskite, sodium superconducting ion conductor, garnet, amorphous LiPON film), a sulfide solid electrolyte (crystalline lithium superion conductor (lithium germanium phosphide, germanium argentum sulfide), amorphous sulfide) and one or more of a halide solid electrolyte, a nitride solid electrolyte and a hydride solid electrolyte.

[0117] As an example, the composite solid electrolyte is formed by adding an inorganic solid electrolyte filler to a polymer solid electrolyte.

[0118] [Preparation of Secondary Battery]

[0119] In some embodiments, a method for preparing a secondary battery in any embodiment of the present application is provided, comprising: providing a primer slurry comprising a polyolefin elastomer and a conductive agent; applying the primer slurry on at least one surface of a positive electrode current collector, and after forming a primer, providing a positive electrode material layer on the surface of the primer, so as to prepare the positive electrode sheet;

[0120] The positive electrode sheet, the separator and the negative electrode sheet are assembled to obtain a secondary battery.

[0121] In some embodiments, the viscosity of the base coating slurry is 100 to 1000 CPS; for example, it can be selected from about 100 CPS, 200 CPS, 300 CPS, 400 CPS, 500 CPS, 600 CPS, 700 CPS, 800 CPS, 900 CPS, 1000 CPS, etc.

[0122] By using the base coating slurry having a viscosity within the above range, processing properties can be improved.

[0123] The positive electrode sheet, the negative electrode sheet and the isolation membrane can be made into an electrode assembly through a winding process or a lamination process, and then the electrolyte is injected after being packaged in an outer package to prepare a secondary battery.

[0124] The outer packaging may be a hard shell, such as a hard plastic shell, an aluminum shell, a steel shell, etc. The outer packaging 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.

[0125] The present application has no particular limitation on the shape of the secondary battery, which may be cylindrical, square or any other shape. Figure 1 The secondary battery 5 is a square structure as an example.

[0126] In some embodiments, reference Figure 2 , the outer packaging may include a shell 51 and a cover plate 53. Among them, the shell 51 may include a bottom plate and a side plate connected to the bottom plate, and the bottom plate and the side plate enclose a receiving cavity. The shell 51 has an opening connected to the receiving cavity, and the cover plate 53 can be covered on the opening to close the receiving cavity. The positive electrode sheet, the negative electrode sheet and the isolation membrane can form an electrode assembly 52 through a winding process or a lamination process. The electrode assembly 52 is encapsulated in the receiving cavity. The electrolyte is infiltrated in the electrode assembly 52. ​​The number of electrode assemblies 52 contained in the secondary battery 5 can be one or more, and those skilled in the art can select according to specific actual needs.

[0127] Battery modules, battery packs

[0128] 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.

[0129] Figure 3 4 is an example of a battery module. Figure 3In 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.

[0130] 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.

[0131] In some embodiments, the secondary batteries may also be assembled into a battery pack.

[0132] In some embodiments, the battery modules 4 may also be assembled into a battery pack. The number of battery modules contained in the battery pack may be one or more, and the specific number may be selected by those skilled in the art according to the application and capacity of the battery pack.

[0133] Figure 4 and Figure 5 1 is a battery pack 1 as an example. Figure 4 and Figure 5 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.

[0134] Electrical devices

[0135] In addition, the present application also provides an electric device, which includes a secondary battery provided in the present application. In some embodiments, the electric device includes at least one of the battery modules or battery packs provided in the present application. The secondary battery, battery module, or battery pack can be used as a power source for the electric device, and can also be used as an energy storage unit for the electric device. The electric device may include mobile devices (such as mobile phones, laptops, etc.), electric vehicles (such as pure electric vehicles, hybrid electric vehicles, plug-in hybrid electric vehicles, electric bicycles, electric scooters, electric golf carts, electric trucks, etc.), electric trains, ships and satellites, energy storage systems, etc., but are not limited to these.

[0136] As the electrical device, a secondary battery, a battery module or a battery pack may be selected according to its usage requirements.

[0137] Figure 6 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.

[0138] Another example of a device may be a mobile phone, a tablet computer, a notebook computer, etc. Such a device is usually required to be light and thin, and a secondary battery may be used as a power source.

[0139] Example 1

[0140] This embodiment provides a lithium ion secondary battery, and the preparation method thereof is as follows:

[0141] (1) Positive electrode

[0142] Setting the primer layer: Add polyolefin elastomer ethylene-α-octene copolymer (degree of polymerization of 2500, tensile strength of 43MPa) and lithium hydroxide to the solvent N-methylpyrrolidone (NMP), stir and dissolve, add acetylene black as a conductive agent, and continue stirring until the viscosity of the slurry is 150CPS, so as to prepare the primer slurry; wherein the mass ratio of polyolefin elastomer, conductive agent and lithium hydroxide is 49:49:2. The primer slurry is applied to both surfaces of the positive electrode current collector, and then dried to prepare the current collector with the primer layer, and the thickness of the primer layer is 2μm.

[0143] A positive electrode material layer is provided: lithium iron phosphate as a positive electrode active material, polyvinylidene fluoride (PVDF) as a binder, and acetylene black as a conductive agent are dissolved in a solvent N-methylpyrrolidone (NMP) at a mass ratio of 97:2:1, and the positive electrode slurry is obtained after being fully stirred and mixed; the positive electrode slurry is then evenly coated on the base coating layer, and then dried, cold pressed, and cut to obtain a positive electrode sheet.

[0144] (2) Negative electrode

[0145] Artificial graphite as a negative electrode active material, acetylene black as a conductive agent, styrene butadiene rubber (SBR) as a binder, and sodium carboxymethyl cellulose (CMC) as a thickener are dissolved in deionized water as a solvent in a mass ratio of 95:2:2:1 and uniformly mixed with the deionized water as a solvent to prepare a negative electrode slurry; then the negative electrode slurry is uniformly coated on the negative electrode current collector copper foil, and a negative electrode film is obtained after drying, and then a negative electrode sheet is obtained by cold pressing and slitting.

[0146] (3) Electrolyte

[0147] In an argon atmosphere glove box (H2O<0.1ppm, O2<0.1ppm), 1 mol / L LiPF6 was dissolved in an organic solvent (EC / DMC / EMC=1 / 1 / 1) and stirred evenly to obtain the corresponding electrolyte.

[0148] (4) Isolation film

[0149] Conventional polypropylene film was used as the isolation film.

[0150] (5) Preparation of lithium-ion batteries

[0151] The positive electrode sheet, the separator, and the negative electrode sheet are stacked in order, so that the separator is placed between the positive and negative electrode sheets to play an isolating role, and then they are wound to obtain an electrode assembly; the electrode assembly is placed in a battery casing, and after drying, the electrolyte is injected, and then a lithium-ion battery is obtained through processes such as formation and standing.

[0152] Perform the following test:

[0153] 1. Acupuncture safety test

[0154] According to the test method in GB / T31485-2015, the prepared lithium-ion battery is subjected to a needle puncture safety test, and the temperature of the lithium-ion battery after the needle puncture is recorded. Specifically including:

[0155] At room temperature, discharge the lithium-ion battery at 1C to 2.5V and leave it for 1h; then charge it at 1C to 4.2V, switch to constant voltage charging, and stop charging when the current drops to 0.05C, and leave it for 1h. Then perform a needle puncture test: use a 5mm diameter high-temperature resistant steel needle to penetrate the battery plate at a speed of (25±5)mm / s from a direction perpendicular to the battery plate. The penetration position is close to the geometric center of the punctured surface, and the steel needle stays in the battery. Record the relevant parameters, and the test results are as follows: Figure 7 If there is no fire, it is evaluated as passing the needle puncture safety test; otherwise, it is evaluated as failing the needle puncture safety test.

[0156] 2. 25℃ DCR ​​test

[0157] At 25°C, the secondary battery was charged to 4.25V at a constant current of 1 / 3C, and then charged to a current of 0.05C at a constant voltage of 4.25V. After standing for 30 minutes, the voltage U1 was recorded; then it was discharged at 1 / 3C for 30 seconds, and the voltage U2 was recorded; then the internal resistance DCR of the secondary battery before storage was calculated based on the formula (U2-U1) / 1 / 3C. The test results are shown in Table 1.

[0158] 3. 1C cycle capacity retention test

[0159] At 25°C, first charge the lithium-ion battery to 4.25V at a constant current of 1C; further charge at a constant voltage of 4.25V to a current of 0.05C and leave for 30 minutes; then discharge the lithium-ion battery to 2.8V at a constant current of 1C. This is a charge and discharge cycle; the discharge capacity this time is the discharge capacity of the first cycle, recorded as Cap6. The lithium-ion battery is subjected to a cyclic charge and discharge test in the above manner, and the discharge capacity of the 100th cycle is taken and recorded as Cap7. The capacity retention rate (%) of the lithium-ion battery after 100 cycles is M4 = [Cap7 / Cap6] × 100%. The larger the M4 value, the smaller the capacity loss of the battery and the better the cycle performance. The test results are shown in Table 1.

[0160] Embodiments 2 to 5

[0161] Except that the mass ratios of the polyolefin elastomer, the conductive agent and the lithium hydroxide in the positive electrode bottom coating are shown in Table 1, the lithium ion battery was prepared and tested according to the steps of Example 1. The results of the needle puncture test are shown in Table 1. Figure 7 The test results of DCR and cycle retention rate are shown in Table 1.

[0162] Comparative Example 1

[0163] The lithium ion battery was prepared and tested according to the steps of Example 1 except that polyacrylic acid (PAA) was used instead of polyolefin elastomer. The results of the needle puncture test are as follows: Figure 7 The test results of DCR and cycle retention rate are shown in Table 1.

[0164] Table 1

[0165]

[0166] Embodiments 6 to 8

[0167] Except that the polymerization degree of the polyolefin elastomer is shown in Table 2, the lithium ion battery was prepared and tested according to the steps of Example 1. The test results are shown in Table 2.

[0168] Table 2

[0169]

[0170] Examples 9 to 12

[0171] Except that the specific components of the polyolefin elastomer are as follows, lithium ion batteries were prepared and tested according to the steps of Example 1. The lithium ion batteries prepared in Examples 9 to 12 all passed the needle puncture safety test.

[0172] Example 9: Ethylene-α-butene copolymer;

[0173] Example 10: Ethylene-α-heptene copolymer;

[0174] Example 11: Ethylene-α-pentene copolymer;

[0175] Example 12: Ethylene-α-hexene copolymer.

[0176] Embodiments 13 to 16

[0177] Except that the thickness of the positive electrode bottom coating layer is shown in Table 3, the lithium ion battery was prepared and tested according to the steps of Example 1. The results are shown in Table 3.

[0178] Table 3

[0179]

[0180] The above is only a preferred specific implementation of the present application, but the protection scope of the present application is not limited thereto. Any changes or substitutions that can be easily thought of by a person skilled in the art within the technical scope disclosed in the present application should be included in the protection scope of the present application. Therefore, the protection scope of the present application shall be based on the protection scope of the claims.

Claims

1. A secondary battery, characterized in that: Including positive electrode, The positive electrode sheet comprises a positive electrode current collector, and a primer layer and a positive electrode material layer sequentially arranged on at least one surface of the positive electrode current collector; the positive electrode material layer comprises a positive electrode active material; The primer layer comprises a polyolefin elastomer and a conductive agent.

2. The secondary battery according to claim 1, wherein: In the primer layer, the mass proportion of the polyolefin elastomer is 40% to 60%.

3. The secondary battery according to claim 1 or 2, characterized in that: The polymerization degree of the polyolefin elastomer is 2500-3000.

4. The secondary battery according to any one of claims 1 to 3, characterized in that The polyolefin elastomer is a copolymer of ethylene and α-olefin; wherein the α-olefin is selected from linear, branched or cyclic α-olefins having 5 to 15 carbon atoms.

5. The secondary battery according to claim 4, characterized in that: The polyolefin elastomer includes ethylene / α-octene copolymer.

6. The secondary battery according to any one of claims 1 to 5, characterized in that The thickness of the primer layer is 1 to 10 μm.

7. The secondary battery according to any one of claims 1 to 6, wherein The conductive agent includes at least one of carbon nanotubes, carbon fibers, carbon black, and acetylene black.

8. The secondary battery according to any one of claims 1 to 7, wherein The primer layer also includes a hydroxide.

9. The secondary battery according to any one of claims 1 to 8, wherein The base coating further includes a binder; and / or, The binder includes at least one of polyacrylic acid, sodium polyacrylate, polyurethane, polyacrylamide and polyvinyl alcohol.

10. A method for preparing a secondary battery, characterized in that: include: Providing a primer slurry including a polyolefin elastomer and a conductive agent; Applying the primer slurry on at least one surface of the positive electrode current collector to form a primer layer; Disposing a positive electrode material layer on the surface of the primer layer; Prepare the positive electrode plate; The positive electrode sheet, the separator and the negative electrode sheet are assembled to obtain a secondary battery.

11. The preparation method according to claim 10, characterized in that: The viscosity of the base coating slurry is 100-1000 CPS.

12. The preparation method according to claim 10 or 11, characterized in that: The tensile strength of the polyolefin elastomer is 20-45 MPa.

13. An electrical device, characterized in that: A secondary battery comprising the secondary battery according to any one of claims 1 to 9, or a secondary battery prepared by the preparation method according to any one of claims 10 to 12.

Images