Battery and electric device

Abstract

The present application provides a battery and an electric device. The battery of the present application comprises a separator, a positive electrode and a negative electrode, wherein the separator comprises a polypropylene film; the heat-induced pore-closing temperature of the separator is T1, with the unit thereof being °C; the heat-induced pore-closing temperature of the polypropylene film is T2, with the unit thereof being °C; the intensity of the maximum exothermic peak in the differential scanning calorimetry curve of the positive electrode is P, with the unit thereof being mW / mg; when 0.15≤P≤0.6, T1=T2; and when 1.1≤P≤6, 0.7T2≤T1<T2. The battery of the present application has good safety without any influence on the normal use of the battery.

Description

Batteries and electrical devices

[0001] This application is based on and claims priority to the Chinese patent application with application number 202410263855.7 and application date March 7, 2024. All contents of the application are hereby introduced as a whole into this application. Technical Field

[0002] The present application relates to the technical field of secondary batteries, and in particular to a battery and an electrical device. Background Art

[0003] In recent years, the application of secondary batteries has become increasingly widespread. They are widely used in energy storage power systems such as hydropower, thermal power, wind power, and solar power plants, as well as in power tools, electric bicycles, electric motorcycles, electric vehicles, military equipment, aerospace, and other fields. As secondary batteries have achieved great development, higher requirements have been placed on their safety performance and cycle performance. Summary of the Invention

[0004] This application was developed in response to the aforementioned challenges and aims to provide a battery and electrical device. In the battery of this application, when the maximum exothermic peak intensity of the positive electrode DSC curve is low, a polypropylene film can be used directly as the separator. When the maximum exothermic peak intensity of the positive electrode DSC curve is high, the separator's thermal closure temperature is set to be lower than the polypropylene thermal closure temperature and not less than 0.7 times the polypropylene thermal closure temperature, thereby improving battery safety while not affecting normal battery operation.

[0005] To achieve the above-mentioned object, the first aspect of the present application provides a battery comprising a separator, a positive electrode and a negative electrode, wherein the separator comprises a polypropylene film; the thermal closure temperature of the separator is T1, in degrees Celsius; the thermal closure temperature of the polypropylene film is T2, in degrees Celsius; the maximum exothermic peak intensity of the differential scanning calorimetry curve of the positive electrode is P, in mW / mg;

[0006] When 0.15≤P≤0.6, T1=T2;

[0007] When 1.1≤P≤6, 0.7T2≤T1 <T2。

[0008] Therefore, when the intensity of the maximum exothermic peak of the differential scanning calorimetry curve of the positive electrode is low (e.g., 0.15-0.6 mW / mg), it indicates a low level of heat release from the positive electrode. At this low level, the heat released by the positive electrode is not likely to accumulate instantaneously, causing battery safety issues. Therefore, the battery has better stability, and the thermal closure temperature of the separator can be made equal to the thermal closure temperature of the polypropylene film. When the intensity of the maximum exothermic peak of the differential scanning calorimetry curve of the positive electrode is high (e.g., 1.1-6 mW / mg), it indicates a high level of heat release from the positive electrode. At this high level, the heat released by the positive electrode is likely to accumulate instantaneously, causing serious battery safety issues. Therefore, the thermal closure temperature of the separator is designed to be lower than the thermal closure temperature of the polypropylene film. When the thermal closure temperature is reached within the battery, the separator immediately closes its pores, blocking the positive and negative electrode pathways, thereby improving battery safety. Furthermore, the thermal closure temperature of the separator is designed to be greater than or equal to 0.7 times the thermal closure temperature of the polypropylene film, which helps prevent premature closure of the separator pores and does not affect normal battery operation.

[0009] In any embodiment, when 1.1≤P≤6, the isolation film further comprises a heat-sealing coating provided on one or both sides of the polypropylene film, the heat-sealing temperature of the heat-sealing coating is T3, and 0.7T2≤T3 <T2。

[0010] Therefore, when 1.1≤P≤6, on the one hand, a thermal closing temperature lower than that of the polypropylene film is used to form a thermal closing coating, which can obtain a lower thermal closing temperature T1 of the isolation membrane. When the battery temperature reaches T1, the pores of the isolation membrane are closed, blocking the path between the positive and negative electrodes and improving the safety of the battery. On the other hand, T3 is greater than or equal to 0.7 times the thermal closing temperature of the polypropylene membrane, which is beneficial to reduce the premature closure of the isolation membrane pores and does not affect the normal use of the battery.

[0011] In any embodiment, when 1.1≤P≤6, T3≤T1 <T2。

[0012] In any embodiment, the thermal sealing coating is disposed on a side of the polypropylene film close to the positive electrode.

[0013] In any embodiment, the thickness of the thermal closure coating accounts for 18% to 46% of the total thickness of the isolation film.

[0014] Therefore, when the heat release level of the positive electrode is high, it is beneficial to block the positive and negative electrode pathways in time, improve the safety of the battery, and at the same time reduce the premature closure of the isolation membrane pores without affecting the normal use of the battery.

[0015] In any embodiment, the heat-sealing coating comprises one or more materials selected from the group consisting of polypropylene, polyethylene, polyamide, and polyetheretherketone.

[0016] In any embodiment, the weight average molecular weight of the material of the thermal closure coating is 1 million to 2 million; and / or,

[0017] The molecular weight distribution coefficient of the material of the thermal sealing coating is 3-5.

[0018] Thus, the thermal closure coating described above can block the positive and negative electrode pathways when the battery reaches the thermal closure temperature of the separator (but not the thermal closure temperature of the polypropylene film), thereby improving battery safety. Specifically, polyethylene is used as the thermal closure coating. When the battery reaches the thermal closure temperature of the separator, the polyethylene melts and blocks the pores of the polypropylene film, thereby blocking the positive and negative electrode pathways and improving battery safety.

[0019] In any embodiment, the isolation film further comprises an adhesive layer disposed between the polypropylene film and the heat-sealing coating. Optionally, the adhesive layer comprises polyvinylidene fluoride.

[0020] This bonds the polypropylene film and the heat-sealing coating to each other, preventing them from peeling off.

[0021] In any embodiment, the separator further includes a functional coating layer disposed on a side of the polypropylene film close to the negative electrode.

[0022] In any embodiment, the thickness of the functional coating accounts for 3%-31% of the total thickness of the isolation film.

[0023] In any embodiment, the thermal sealing coating is disposed on a side of the polypropylene film close to the positive electrode, and the functional coating is disposed on a side of the polypropylene film close to the negative electrode.

[0024] In any embodiment, the thermal closure coating and the functional coating are disposed on a side of the polypropylene film close to the negative electrode, and the functional coating is closer to the negative electrode than the thermal closure coating.

[0025] In any embodiment, the functional coating comprises a ceramic and / or a binder.

[0026] Therefore, the functional coating can improve the fit between the separator and the negative electrode sheet, improve the fixing effect of the negative electrode sheet when the battery is fully charged, and reduce the wrinkling problem of the negative electrode sheet due to uneven force. On the other hand, the functional coating enhances the strength of the separator, making the separator less likely to be pierced by lithium dendrites during battery use, thereby improving the cycle performance of the battery. On the other hand, when the heat release level of the positive electrode is high, the functional coating helps to reduce the thermal closure temperature of the separator, which is conducive to timely blocking the positive and negative electrode pathways, thereby improving the safety of the battery.

[0027] In any embodiment, the ceramic includes one or more of aluminum oxide, titanium dioxide, silicon dioxide, zirconium dioxide, tin dioxide, magnesium oxide, zinc oxide, barium sulfate, boron nitride, aluminum nitride, and magnesium nitride; optionally, the binder is selected from one or more of polyvinylidene fluoride and styrene-butadiene rubber.

[0028] In any embodiment, the positive electrode comprises a positive electrode active material;

[0029] When 0.15≤P≤0.6, the positive electrode active material includes one or more of lithium iron phosphate with or without a coating layer, lithium manganese iron phosphate with or without a coating layer, and lithium manganese phosphate with or without a coating layer;

[0030] When 1.1≤P≤6, the positive electrode active material includes one or more of lithium nickel cobalt manganese oxide with or without a coating layer, lithium nickel cobalt aluminum oxide with or without a coating layer, and lithium-rich manganese-based oxide with or without a coating layer.

[0031] A second aspect of the present application provides an electrical device comprising the battery according to the first aspect of the present application. BRIEF DESCRIPTION OF THE DRAWINGS

[0032] FIG1 is a schematic diagram of a battery cell according to an embodiment of the present application.

[0033] FIG. 2 is an exploded view of the battery cell according to the embodiment of the present application shown in FIG. 1 .

[0034] FIG3 is a schematic diagram of a battery module according to an embodiment of the present application.

[0035] FIG4 is a schematic diagram of a battery pack according to an embodiment of the present application.

[0036] FIG. 5 is an exploded view of the battery pack shown in FIG. 4 according to an embodiment of the present application.

[0037] FIG6 is a schematic diagram of an electrical device using a battery cell as a power source according to an embodiment of the present application.

[0038] FIG7 is a differential scanning calorimetry curve of the positive electrode of Example 6 of the present application.

[0039] FIG8 is a curve showing the change in air permeability of the isolation membrane of Example 6 of the present application as a function of temperature.

[0040] Description of reference numerals:

[0041] 1 battery pack; 2 upper box; 3 lower box; 4 battery module; 5 battery cell; 51 shell; 52 electrode assembly; 53 top cover assembly. DETAILED DESCRIPTION

[0042] Below, the embodiments of the battery, battery module, battery pack and electrical device of the present application are described in detail with appropriate reference to the accompanying drawings. However, there may be cases where unnecessary detailed descriptions are omitted. For example, there may be cases where detailed descriptions of well-known matters and repeated descriptions of actually the same structures 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 description 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.

[0043] " range " disclosed in the present application is limited in the form of lower limit and upper limit, and 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 special range. The scope limited in this way can be to include end value or not include end value, and can be arbitrarily combined, that is, any lower limit can form a range with any upper limit combination. For example, if the scope of 60-120 and 80-110 is listed for specific parameters, it is understood that the scope of 60-110 and 80-120 is also expected. In addition, if the minimum range value 1 and 2 are listed, and if the maximum range value 3,4 and 5 are listed, then the following range can all be expected: 1-3, 1-4, 1-5, 2-3, 2-4 and 2-5. In this application, unless otherwise specified, the numerical range " ab " represents the abbreviation of any real number combination between a and b, wherein a and b are all real numbers. For example, a numerical range of "0-5" indicates that all real numbers between "0-5" are listed herein, and "0-5" is simply an abbreviation for these numerical combinations. Furthermore, when a parameter is expressed as an integer ≥ 2, this 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.

[0044] Unless otherwise specified, all embodiments and optional embodiments of the present application can be combined with each other to form a new technical solution.

[0045] 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.

[0046] Unless otherwise specified, all steps of the present application may be performed sequentially or randomly, preferably sequentially. For example, a method includes steps (a) and (b), which indicates that the method may include steps (a) and (b) performed sequentially, or may include steps (b) and (a) performed sequentially. For example, a method may further include step (c), which indicates 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.

[0047] [Battery]

[0048] Batteries, also known as rechargeable batteries or storage batteries, are batteries that can be recharged to activate the active materials after being discharged and continue to be used.

[0049] Typically, a battery cell consists of a positive electrode, a negative electrode, a separator, and an electrolyte. During the battery's charge and discharge process, active ions (such as lithium ions) are embedded and released back and forth between the positive and negative electrodes. The separator is placed between the positive and negative electrodes, primarily to prevent a short circuit between the positive and negative electrodes while allowing the active ions to pass through. The electrolyte, located between the positive and negative electrodes, primarily conducts the active ions.

[0050] One embodiment of the present application provides a battery, including a separator, a positive electrode, and a negative electrode, wherein the separator includes a polypropylene film; the thermal closure temperature of the separator is T1, in degrees Celsius; the thermal closure temperature of the polypropylene film is T2, in degrees Celsius; the maximum exothermic peak intensity of the differential scanning calorimetry curve of the positive electrode is P, in mW / mg;

[0051] When 0.15≤P≤0.6 (for example, P is 0.15, 0.2, 0.3, 0.5, 0.6 or within a range consisting of any of the above values), T1=T2;

[0052] When 1.1≤P≤6 (for example, P is 1.1, 2, 3, 4, 5, 6 or within the range of any of the above values), 0.7T2≤T1 <T2。

[0053] Although the mechanism remains unclear, the present applicants unexpectedly discovered that when the intensity of the maximum exothermic peak in the differential scanning calorimetry curve of the positive electrode is low (e.g., 0.15-0.6 mW / mg), this indicates a low level of heat release from the positive electrode. At this low level, the heat released by the positive electrode is less likely to accumulate instantaneously, potentially causing battery safety issues. Therefore, the battery exhibits better stability, enabling the thermal closure temperature of the separator to be equal to that of the polypropylene film. When the intensity of the maximum exothermic peak in the differential scanning calorimetry curve of the positive electrode is high (e.g., 1.1-6 mW / mg), this indicates a high level of heat release from the positive electrode. At this high level, the heat released by the positive electrode is more likely to accumulate instantaneously, potentially causing serious battery safety issues. Therefore, the thermal closure temperature of the separator is designed to be lower than that of the polypropylene film. When the thermal closure temperature is reached within the battery, the separator immediately closes its pores, blocking the path between the positive and negative electrodes and improving battery safety. Furthermore, the thermal closure temperature of the separator is designed to be greater than or equal to 0.7 times the thermal closure temperature of the polypropylene film, which helps prevent premature closure of the separator pores and does not affect normal battery operation.

[0054] In some embodiments, when 1.1≤P≤6, the isolation film further comprises a heat-sealing coating provided on one or both sides of the polypropylene film, the heat-sealing temperature of the heat-sealing coating is T3, and 0.7T2≤T3 <T2。

[0055] The differential scanning calorimetry curve of the positive electrode is tested according to conventional methods in the art; for example, a differential scanning calorimeter is used for testing; optionally, the sampling size is 5 cm×5 cm; optionally, the test conditions include: the instrument air pump pressure is 0.01-0.04 MPa, the purge gas flow rate is 50 ml / min, the protective gas flow rate is 100 ml / min, the temperature range is 25-250°C, and the heating rate is 2°C / min.

[0056] The thermal closure temperature is tested according to conventional methods in the art; for example, referring to the curve of the air permeability (i.e., the time required for 100 mL of air to pass through) of the test sample in GB / T458-2008 as in temperature, the starting temperature at which the air permeability shows a significant upward trend is the thermal closure temperature.

[0057] Therefore, when 1.1≤P≤6, on the one hand, a thermal closing temperature lower than that of the polypropylene film is used to form a thermal closing coating, which can obtain a lower thermal closing temperature T1 of the isolation membrane. When the battery temperature reaches T1, the pores of the isolation membrane are closed, blocking the path between the positive and negative electrodes and improving the safety of the battery. On the other hand, T3 is greater than or equal to 0.7 times the thermal closing temperature of the polypropylene membrane, which is beneficial to reduce the premature closure of the isolation membrane pores and does not affect the normal use of the battery.

[0058] In some embodiments, when 1.1≤P≤6, T3≤T1 <T2。

[0059] In some embodiments, the thermal sealing coating is disposed on a side of the polypropylene film close to the positive electrode.

[0060] In some embodiments, the thickness of the thermal closure coating accounts for 18%-46% of the total thickness of the isolation membrane, for example, 18%, 19%, 20%, 23%, 25%, 29%, 30%, 35%, 38%, 40%, 41%, 43%, 46% or a range consisting of any of the above values.

[0061] Therefore, when the heat release level of the positive electrode is high, it is beneficial to block the positive and negative electrode pathways in time, improve the safety of the battery, and at the same time reduce the premature closure of the isolation membrane pores without affecting the normal use of the battery.

[0062] In some embodiments, the thickness of the thermal closure coating accounts for 19% to 41% of the total thickness of the isolation film.

[0063] Therefore, on the one hand, it is beneficial to further improve battery safety, and on the other hand, it can reduce the polarization degree of the battery, thereby improving the power and cycle performance of the battery.

[0064] In some embodiments, the thermal closure coating comprises one or more materials selected from the group consisting of polypropylene, polyethylene, polyamide, and polyetheretherketone.

[0065] In some embodiments, the weight average molecular weight of the material of the thermal closure coating is 1 million to 2 million, for example, 1 million, 1.1 million, 1.2 million, 1.3 million, 1.4 million, 1.5 million, 1.6 million, 1.8 million, 1.9 million, 2 million, or any range thereof; and / or,

[0066] The molecular weight distribution coefficient of the material of the thermal sealing coating is 3-5, for example 4.

[0067] Thus, the thermal closure coating described above can block the positive and negative electrode pathways when the battery reaches the thermal closure temperature of the separator (but not the thermal closure temperature of the polypropylene film), thereby improving battery safety. Specifically, polyethylene is used as the thermal closure coating. When the battery reaches the thermal closure temperature of the separator, the polyethylene melts and blocks the pores of the polypropylene film, thereby blocking the positive and negative electrode pathways and improving battery safety.

[0068] In some embodiments, the isolation film further comprises an adhesive layer disposed between the polypropylene film and the thermal closure coating. Optionally, the adhesive layer comprises polyvinylidene fluoride.

[0069] This bonds the polypropylene film and the heat-sealing coating to each other, preventing them from peeling off.

[0070] In some embodiments, the separator further includes a functional coating disposed on a side of the polypropylene film close to the negative electrode.

[0071] In some embodiments, the thickness of the functional coating accounts for 3%-31% of the total thickness of the isolation membrane, for example, 3%, 4%, 5%, 6%, 8%, 10%, 12%, 15%, 17%, 20%, 23%, 25%, 27%, 29%, 30%, 31% or a range consisting of any of the above values.

[0072] In some embodiments, the thermal closure coating is disposed on a side of the polypropylene film close to the positive electrode, and the functional coating is disposed on a side of the polypropylene film close to the negative electrode.

[0073] In some embodiments, the thermal closure coating and the functional coating are disposed on a side of the polypropylene film close to the negative electrode, and the functional coating is closer to the negative electrode than the thermal closure coating.

[0074] In some embodiments, the functional coating includes a ceramic and / or a binder.

[0075] Therefore, the functional coating can improve the fit between the separator and the negative electrode sheet, improve the fixing effect of the negative electrode sheet when the battery is fully charged, and reduce the wrinkling problem of the negative electrode sheet due to uneven force. On the other hand, the functional coating enhances the strength of the separator, making the separator less likely to be pierced by lithium dendrites during battery use, thereby improving the cycle performance of the battery. On the other hand, when the heat release level of the positive electrode is high, the functional coating helps to reduce the thermal closure temperature of the separator, which is conducive to timely blocking the positive and negative electrode pathways, thereby improving the safety of the battery.

[0076] In some embodiments, the thickness of the functional coating accounts for 4%-30% of the total thickness of the isolation film.

[0077] Therefore, on the one hand, it is beneficial to enhance the strength of the isolation membrane, making the isolation membrane less likely to be pierced by lithium dendrites during battery use, thereby improving the battery's cycle performance; on the other hand, it is beneficial to reduce the degree of polarization of the battery, thereby improving the battery's power and cycle performance.

[0078] In some embodiments, the ceramic includes one or more of aluminum oxide, titanium dioxide, silicon dioxide, zirconium dioxide, tin dioxide, magnesium oxide, zinc oxide, barium sulfate, boron nitride, aluminum nitride, and magnesium nitride; optionally, the binder is selected from one or more of polyvinylidene fluoride and styrene-butadiene rubber.

[0079] In some embodiments, the positive electrode includes a positive electrode active material;

[0080] When 0.15≤P≤0.6 (for example, P is 0.15, 0.2, 0.3, 0.5, 0.6 or within a range consisting of any of the foregoing numerical values), the positive electrode active material includes one or more of lithium iron phosphate with or without a coating layer, lithium manganese iron phosphate with or without a coating layer, and lithium manganese phosphate with or without a coating layer;

[0081] When 1.1≤P≤6 (for example, P is 1.1, 2, 3, 4, 5, 6 or within the range of any of the above numerical values), the positive electrode active material includes one or more of lithium nickel cobalt manganese oxide with or without a coating layer, lithium nickel cobalt aluminum oxide with or without a coating layer, and lithium-rich manganese-based oxide with or without a coating layer.

[0082] In some embodiments, the coating layer is one or more layers.

[0083] In some embodiments, each coating layer is independently selected from one or more of carbon, pyrophosphate, and phosphate.

[0084] In some embodiments, the general formula compound Li x Mn y Fe z P m O4; when y is 0, x is greater than 0 and less than or equal to 1, and z and m are greater than 0 and less than 1, the general formula compound is lithium iron phosphate, such as LiFePO4 (which can also be abbreviated as LFP); when z is 0, x is greater than 0 and less than or equal to 1, and y and m are greater than 0 and less than 1, the general formula compound is lithium manganese phosphate, such as LiMnPO4.

[0085] In some embodiments, the chemical formula of lithium manganese iron phosphate is Li 1+x Mn 1-y A y P 1-z R z O4; x is any value within the range of -0.100 - 0.100, y is any value within the range of 0.001 - 0.800, z is any value within the range of 0.001 - 0.100; A includes Fe and optionally one or more elements selected from Zn, Al, Na, K, Mg, Mo, W, Ti, V, Zr, Ni, Co, Ga, Sn, Sb, Nb, and Ge, and can optionally include Fe and optionally one or more elements selected from Ti, V, Ni, Co, and Mg; the R includes one or more elements selected from B, Si, N, S, F, Cl, and Br, and can optionally include one element selected from B, Si, N, and S.

[0086] In some embodiments, the general formula compound Li a Ni b Co c M1 d M2 e O f R g ; where 0.75 ≤ a ≤ 1.2, 0 < b < 1, 0 < c < 1, 0 < d < 1, 0 ≤ e ≤ 0.2, 1 ≤ f ≤ 2.5, 0 ≤ g ≤ 1, f + g ≤ 3, M1 includes one or both elements of Mn and Al, M2 includes one or more elements selected from Zr, Zn, Cu, Cr, Mg, Fe, V, Ti, Sr, Sb, Y, W, Nb, and R includes one or more elements selected from N, F, S, Cl; when M1 is the Mn element, e is 0, and g is 0, the general formula compound is lithium nickel cobalt manganese oxide, such as LiNi 0.5 Co 0.2 Mn 0.3 O2; when M1 is the Al element, e is 0, and g is 0, the general formula compound is lithium nickel cobalt aluminate, such as LiNi 0.85 Co 0.15 Al 0.05 O2.

[0087] In some embodiments, the lithium-rich manganese-based oxide is a compound of the general formula xLi2MnO3·(1-x)LiMO2, where x is any value in the range of 0.2-0.55.

[0088] [positive electrode]

[0089] The positive electrode 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 the aforementioned positive electrode active material.

[0090] The battery's charge and discharge processes involve the intercalation and deintercalation of lithium, leading to different molar Li contents at different discharge states. The molar Li contents listed in this application for cathode materials refer to the initial state of the material, i.e., the state before addition of the materials. When the cathode material is used in a battery system, the molar Li content will change after charge and discharge cycles.

[0091] In the list of positive electrode materials in this application, the molar content of O is only a theoretical value. Lattice oxygen release will cause the molar content of oxygen to change, and the actual molar content of O will fluctuate.

[0092] 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 either or both of the two opposite surfaces of the positive electrode current collector.

[0093] 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.).

[0094] In some embodiments, the positive electrode film layer may further optionally include a binder. As an example, the binder may include at least one of polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), a vinylidene fluoride-tetrafluoroethylene-propylene terpolymer, a vinylidene fluoride-hexafluoropropylene-tetrafluoroethylene terpolymer, a tetrafluoroethylene-hexafluoropropylene copolymer, and a fluorine-containing acrylate resin.

[0095] 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.

[0096] In some embodiments, the positive electrode sheet can be prepared by the following method: 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 current collector, and after drying, cold pressing and other processes, the positive electrode sheet can be obtained.

[0097] [negative electrode]

[0098] The negative electrode includes a negative electrode current collector and a negative electrode film layer disposed on at least one surface of the negative electrode current collector, wherein the negative electrode film layer includes a negative electrode active material.

[0099] As an example, the negative electrode current collector has two surfaces opposite to each other in its thickness direction, and the negative electrode film layer is disposed on either or both of the two opposite surfaces of the negative electrode current collector.

[0100] In some embodiments, the negative electrode current collector may be a metal foil or a composite current collector. For example, copper foil may be used as the metal foil. The composite current collector may include a polymer base layer and a metal layer formed on at least one surface of the polymer base material. 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 base material (such as a base material of polypropylene (PP), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polystyrene (PS), polyethylene (PE), etc.).

[0101] In some embodiments, the negative electrode active material may be a negative electrode active material for a battery that is well 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, and lithium titanate. The silicon-based material may be selected from at least one of elemental silicon, silicon oxides, silicon-carbon composites, silicon-nitrogen composites, and silicon alloys. The tin-based material may be selected from at least one of elemental tin, tin oxides, 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.

[0102] In some embodiments, the negative electrode film layer may further include a binder. For 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).

[0103] In some embodiments, the negative electrode film layer may further include a conductive agent. For 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.

[0104] In some embodiments, the negative electrode film layer may optionally include other additives, such as a thickener (eg, sodium carboxymethyl cellulose (CMC-Na)).

[0105] In some embodiments, the negative electrode sheet can be prepared by the following method: 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 current collector, and after drying, cold pressing and other processes, the negative electrode sheet can be obtained.

[0106] [Electrolytes]

[0107] The electrolyte acts as a conductor of ions between the positive and negative electrodes. This application does not specifically limit the type of electrolyte, and the electrolyte can be selected based on the needs. For example, the electrolyte can be liquid, gel, or solid.

[0108] In some embodiments, the electrolyte is liquid and includes an electrolyte salt and a solvent.

[0109] In some embodiments, the electrolyte salt may 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.

[0110] 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, methylpropyl carbonate, ethylpropyl 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, dimethyl sulfone, methyl ethyl sulfone and diethyl sulfone.

[0111] In some embodiments, the electrolyte may optionally include additives. For example, 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, and additives that improve battery high or low temperature performance.

[0112] In some embodiments, the positive electrode sheet, the negative electrode sheet, and the separator can be formed into an electrode assembly through a winding process or a lamination process.

[0113] In some embodiments, the battery cell may include an outer packaging that can be used to encapsulate the electrode assembly and the electrolyte.

[0114] In some embodiments, the outer packaging of the battery cell may be a hard shell, such as a hard plastic shell, an aluminum shell, or a steel shell. Alternatively, the outer packaging of the battery cell may be a soft shell, such as a pouch-type soft shell. The soft shell may be made of plastic, such as polypropylene, polybutylene terephthalate, and polybutylene succinate.

[0115] The present application has no particular limitation on the shape of the battery cell, which can be cylindrical, square, or any other shape. For example, FIG1 shows a battery cell 5 with a square structure as an example.

[0116] In some embodiments, referring to Figure 2, the outer packaging may include a shell 51 and a cover plate 53. The shell 51 may include a bottom plate and a side plate connected to the bottom plate, and the bottom plate and the side plate enclose a receiving cavity. The shell 51 has an opening connected to the receiving cavity, and the cover plate 53 can be covered on the opening to close the receiving cavity. The positive electrode sheet, the negative electrode sheet and the isolation membrane can be formed into 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 battery cell 5 can be one or more, and those skilled in the art can select according to specific actual needs.

[0117] In some embodiments, battery cells may be assembled into a battery module. The battery module may contain one or more battery cells. The specific number may be selected by those skilled in the art based on the application and capacity of the battery module.

[0118] FIG3 shows an example battery module 4. Referring to FIG3 , within the battery module 4, multiple battery cells 5 may be arranged sequentially along the length of the battery module 4. Of course, they may also be arranged in any other manner. Furthermore, the multiple battery cells 5 may be secured together using fasteners.

[0119] Optionally, the battery module 4 may further include a housing having an accommodation space, and the plurality of battery cells 5 are accommodated in the accommodation space.

[0120] 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 based on the application and capacity of the battery pack.

[0121] Figures 4 and 5 illustrate an example battery pack 1. Referring to Figures 4 and 5 , the battery pack 1 may include a battery box and multiple battery modules 4 disposed within the battery box. The battery box comprises an upper case 2 and a lower case 3. The upper case 2 can be placed over the lower case 3 to form an enclosed space for accommodating the battery modules 4. The multiple battery modules 4 can be arranged in any manner within the battery box.

[0122] In addition, the present application also provides an electrical device, which includes at least one of the battery cells, battery modules, or battery packs provided in the present application. The battery cells, battery modules, or battery packs can be used as power sources for the electrical device, or as energy storage units 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 is not limited thereto.

[0123] As an electrical device, a battery cell, battery module or battery pack can be selected according to its usage requirements.

[0124] Figure 6 shows an example of an electric device. This device is a pure electric vehicle, hybrid electric vehicle, or plug-in hybrid electric vehicle. To meet the high power and high energy density requirements of the battery cells, a battery pack or battery module can be used.

[0125] [Example]

[0126] Below, the embodiment of the present application is described. The embodiment described below is exemplary and is only used to explain the present application, and is not to be construed as limiting the present application. Where specific techniques or conditions are not specified in the embodiments, the techniques or conditions described in the literature in this area or the product specifications are used. Reagents or instruments used that do not specify the manufacturer are conventional products that can be obtained commercially.

[0127] Example 1

[0128] (1) Isolation film: Polypropylene isolation film is used.

[0129] (2) Preparation of positive electrode sheet:

[0130] The positive electrode active material lithium iron phosphate, the binder polyvinylidene fluoride (PVDF), and the conductive agent conductive carbon are added to a certain amount of N-methylpyrrolidone (NMP). The mass ratio of the positive electrode active material, the binder, and the conductive agent is 90:5:5. The mixture is stirred in a drying room to form a uniform slurry with a viscosity controlled at 3000-10000 mPa·s. The slurry is then coated on aluminum foil and dried to form a positive electrode sheet.

[0131] (3) Preparation of negative electrode sheet:

[0132] Graphite, sodium carboxymethyl cellulose (CMC), styrene-butadiene rubber (SBR), and conductive carbon were added to a certain amount of deionized water in a mass ratio of 90:2:3:5. The mixture was stirred to form a uniform slurry with a viscosity controlled at 3000-10000 mPa·s. The slurry was then coated on copper foil and dried to form a negative electrode sheet.

[0133] (4) Preparation of electrolyte:

[0134] Ethylene carbonate (EC), dimethyl carbonate (DMC), and diethyl carbonate (DEC) were mixed in a volume ratio of 1:1:1, 5 wt.% fluoroethylene carbonate (FEC) was added, and LiPF6 was uniformly dissolved in the above solution to obtain an electrolyte. The concentration of LiPF6 in the electrolyte was 1 mol / L.

[0135] (5) Preparation of soft-pack laminated batteries:

[0136] The prepared positive electrode sheets, negative electrode sheets and separators are made into corresponding battery cells according to the Z-shaped stacking structure, and the battery cells are vacuum dried at 90°C for 12 hours, and then the positive and negative electrode tabs are ultrasonically welded. The positive electrode uses aluminum tabs and the negative electrode uses nickel tabs. The positive and negative electrode tabs are located on the same side of the battery cell. The battery cell after the tabs are welded is placed in an aluminum-plastic film of appropriate size for top-side sealing. The top-side sealing temperature is 145°C. Liquid is injected, allowed to stand, formed, aged, exhausted, sealed twice, and capacity tested to obtain the prepared soft-pack laminated battery.

[0137] The battery preparation methods of Examples 2-18 and Comparative Examples 1-2 are similar to those of Example 1, and the different parameters are detailed in Table 1.

[0138] Example 4

[0139] (1) Preparation of isolation membrane:

[0140] Polyethylene, dispersant polyacrylic acid, adhesive oxirane, surfactant polyoxyethylene sorbitan ester are mixed evenly with solvent N-methylrolidone in a mass ratio of 20:0.2:0.5:0.1 to obtain a heat-sealed coating slurry with a solid content of 60% by mass. The slurry is applied to the surface of the polypropylene base film by transfer coating using a diagonal groove roller at a coating speed of 110 m / min. The film is then placed in an oven for drying. The oven temperature can be set to 120°C, the wind speed is set to 20 m / min, and the oven is in a slightly negative pressure environment of ≤-30 Kpa. After drying, a base film with a heat-sealed coating is obtained, which can be rolled up.

[0141] (2)-(5) refer to (2)-(5) of Example 1; different parameters are shown in Table 1.

[0142] Example 11

[0143] (1) Preparation of isolation membrane:

[0144] According to item (1) of Example 4, a release film with a heat-sealing coating was prepared.

[0145] Alumina, dispersant polyether siloxane, adhesive oxirane, surfactant polyoxyethylene sorbitan ester are mixed evenly with solvent N-methylrolidone in a mass ratio of 10:0.3:0.4:0.7 to obtain a functional coating slurry with a solid content of 45% by mass. The slurry is transferred and coated on the surface of the polypropylene base film close to the negative electrode using a diagonal groove roller by transfer coating, and dried to obtain an isolation membrane.

[0146] (2)-(5) refer to (2)-(5) of Example 4; different parameters are shown in Table 1.

[0147] Comparative Example 1-2

[0148] Polypropylene was used as the isolation film; the rest was referred to Example 4 or 5.

[0149] Materials and battery testing

[0150] (1) Test of differential scanning calorimetry curve of positive electrode:

[0151] A differential scanning calorimeter (NETZSCH STA449F3-QMS403C instrument) was used for the test. After the instrument power was turned on and preheating was completed, a baseline calibration was performed first. Then, a 5 cm × 5 cm positive electrode piece was placed in a crucible, and the crucible was placed in the instrument for testing. Test conditions: the instrument air pump pressure was 0.01 to 0.04 MPa, the purge gas flow rate was 50 ml / min, the protective gas flow rate was 100 ml / min, the temperature range was 25 to 250 ° C, and the heating rate was 2 ° C / min.

[0152] The differential scanning calorimetry curve of the positive electrode of Example 6 is shown in FIG7 .

[0153] (2) Thermal closure temperature test of isolation membrane:

[0154] The separators were cut into 10 cm x 10 cm pieces and placed in ovens at 100-200°C (with ovens set at 5°C intervals). After 24 hours, the separators were removed and their air permeability measured (i.e., the time required for 100 mL of air to pass through). The temperature at which a clear upward trend in air permeability was observed was the thermal closure temperature. The air permeability versus temperature curve for the separator of Example 6 is shown in Figure 8.

[0155] Air permeability test: refer to GB / T458-2008;

[0156] Specific method: Use the American Gurley 4320N air permeability tester timer, turn on the device power, select Manual to enter the manual timing interface, select the test mode, lift and fix the upper cylinder of the air permeability tester, unscrew the bottom piston of the air permeability tester, place the isolation membrane on the bottom disc, then tighten the stopcock, gently lower the cylinder, and press the reset button of the digital timer. When the white area on the cylinder passes the sensor, the device automatically starts timing. When the white area completely passes the sensor, the device automatically stops timing. The result is the air permeability value.

[0157] (3) Battery thermal blocking test:

[0158] Place the battery in a high-temperature box, raise the temperature from room temperature to 100°C at a rate of 5°C / min, hold for 2 hours, then continue to raise the temperature at a rate of 5°C / min, hold for 30 minutes each time the temperature increases by 5°C, until the temperature reaches 200°C or the battery cell experiences thermal runaway (battery cell fire). End the test and record the temperature at the time of runaway as a basis for judgment.

[0159] (4) Battery cycle life test:

[0160] The battery was charged to 4.3V at 0.33C in a constant temperature environment of 25°C, then charged at a constant voltage to a current ≤ 0.05C, and allowed to stand for 10 minutes. Then, it was discharged to 2.5V at 0.33C and allowed to stand for 10 minutes. The above operation was repeated three times, and the capacity of the last charge was recorded as C0.

[0161] The battery was charged to 4.4V at 0.5C0 in a constant temperature environment of 25°C, then charged at 4.4V at a constant voltage until the current was ≤0.05C0, left to stand for 5 minutes, and then discharged to 2.5V at 1C0. The capacity was recorded as Cn (n=1, 2, 3...). The above operation was repeated. The cycle capacity retention rate was calculated according to the following formula. When the cycle capacity retention rate reached 80%, the corresponding number of cycles was used as the evaluation index of the cycle capacity.

[0162] Cycle capacity retention rate = 100% × Cn / C3.

[0163] The test results are shown in Table 2-3.

[0164] Table 2: Thermal blocking test results of Examples 1-18 and Comparative Examples 1-2

[0165] Table 3: Cycle life test results of Examples 1-18 and Comparative Examples 1-2

[0166] According to the above results, we can know that:

[0167] When the maximum exothermic peak intensity of the differential scanning calorimetry curve of the positive electrode is 1.1 mW / mg, compared with the comparative example 1 using polypropylene as the isolation membrane, the thermal runaway temperature of the battery made of the isolation membrane using polyethylene as the thermal closure coating in Example 4 of the present application is significantly higher and the safety is better.

[0168] When the maximum exothermic peak intensity of the differential scanning calorimetry curve of the positive electrode is 6 mW / mg, compared with the comparative example 2 using polypropylene as the isolation membrane, the thermal runaway temperature of the battery made of the isolation membrane using polyethylene as the thermal closure coating in Example 5 of the present application is significantly higher and the safety is better.

[0169] Compared with Example 15 in which the thickness ratio of the thermal closure coating in the isolation membrane is relatively low, the batteries made with the isolation membranes of Examples 6, 9-10 of the present application have higher thermal runaway temperatures and better safety.

[0170] Compared with Example 16 in which the thickness ratio of the thermal closure coating in the isolation membrane is higher, the battery made with the isolation membrane of Example 6 of the present application has a lower degree of polarization and a longer cycle life.

[0171] Compared with Example 17 in which the thickness ratio of the functional coating in the isolation membrane is relatively low, the batteries made with the isolation membranes of Examples 11 to 14 of the present application have a longer cycle life.

[0172] Compared with Example 18 in which the thickness ratio of the functional coating in the isolation membrane is relatively high, the batteries made with the isolation membranes of Examples 11-14 of the present application have lower polarization degrees and longer cycle life.

[0173] It should be noted that the present application is not limited to the above-mentioned embodiments. The above-mentioned embodiments are merely examples, and any embodiments having substantially the same structure and effect as the technical concept within the scope of the present application are all included in the technical scope of the present application. In addition, without departing from the scope of the present application, any other embodiments that can be conceived by those skilled in the art and that combine some of the constituent elements in the embodiments are also included in the scope of the present application.

Claims

1. A battery comprising a separator, a positive electrode, and a negative electrode, wherein the separator comprises a polypropylene film; the separator has a thermal closure temperature T1, in degrees Celsius; the polypropylene film has a thermal closure temperature T2, in degrees Celsius; and the positive electrode has a maximum exothermic peak intensity P, in mW / mg, of a differential scanning calorimetry curve. When 0.15≤P≤0.6, T1=T2; When 1.1≤P≤6, 0.7T2≤T1 <T2。 2. The battery according to claim 1, wherein When 1.1≤P≤6, the isolation film further comprises a heat-sealing coating provided on one or both sides of the polypropylene film, the heat-sealing temperature of the heat-sealing coating is T3, and 0.7T2≤T3 <T2。 3. The battery according to claim 2, wherein When 1.1≤P≤6, T3≤T1 <T2。 4. The battery according to claim 2 or 3, wherein The heat-sealing coating is disposed on a side of the polypropylene film close to the positive electrode.

5. The battery according to any one of claims 2 to 4, wherein The thickness of the thermal sealing coating accounts for 18%-46% of the total thickness of the isolation film.

6. The battery according to any one of claims 2 to 5, wherein The heat-sealing coating comprises one or more materials selected from the group consisting of polypropylene, polyethylene, polyamide, and polyetheretherketone.

7. The battery according to claim 6, wherein The weight average molecular weight of the material of the thermal closure coating is 1 million to 2 million; and / or, The molecular weight distribution coefficient of the material of the thermal sealing coating is 3-5.

8. The battery according to any one of claims 2 to 7, wherein The barrier film further includes an adhesive layer disposed between the polypropylene film and the heat-sealing coating.

9. The battery according to any one of claims 1 to 8, wherein The separator further includes a functional coating layer disposed on a side of the polypropylene film close to the negative electrode.

10. The battery according to claim 9, wherein The thickness of the functional coating accounts for 3%-31% of the total thickness of the isolation film.

11. The battery according to claim 9 or 10, wherein The thermal sealing coating is disposed on a side of the polypropylene film close to the positive electrode, and the functional coating is disposed on a side of the polypropylene film close to the negative electrode.

12. The battery according to claim 9 or 10, wherein The thermal sealing coating and the functional coating are disposed on a side of the polypropylene film close to the negative electrode, and the functional coating is closer to the negative electrode than the thermal sealing coating.

13. The battery according to any one of claims 9 to 12, wherein The functional coating includes ceramic and / or a binder.

14. The battery according to claim 13, wherein The ceramic includes one or more of aluminum oxide, titanium dioxide, silicon dioxide, zirconium dioxide, tin dioxide, magnesium oxide, zinc oxide, barium sulfate, boron nitride, aluminum nitride, and magnesium nitride.

15. The battery according to any one of claims 1 to 14, wherein The positive electrode includes a positive electrode active material; When 0.15≤P≤0.6, the positive electrode active material includes one or more of lithium iron phosphate with or without a coating layer, lithium manganese iron phosphate with or without a coating layer, and lithium manganese phosphate with or without a coating layer; When 1.1≤P≤6, the positive electrode active material includes one or more of lithium nickel cobalt manganese oxide with or without a coating layer, lithium nickel cobalt aluminum oxide with or without a coating layer, and lithium-rich manganese-based oxide with or without a coating layer.

16. An electrical device comprising the battery according to any one of claims 1 to 15.

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