Negative pole piece, secondary battery and electric device

Abstract

The invention relates to the technical field of batteries, in particular to a negative pole piece, a secondary battery and an electric device. The secondary battery comprises a positive pole piece, a negative pole piece and an isolating membrane arranged between the positive pole piece and the negative pole piece, the negative pole piece comprises a bottom coating, the bottom coating comprises a fire extinguishing material, and the fire extinguishing material can be used for reducing heat generated in a negative pole piece area; according to the technical scheme provided by the invention, the fire risk of the secondary battery can be reduced, and the safety performance of the secondary battery is improved.

Description

Negative electrode plate, secondary battery and electrical device Technical Field

[0001] This invention relates to the field of battery technology, and in particular to a negative electrode sheet, a secondary battery, and an electrical device. Background Technology

[0002] Existing secondary batteries typically include a positive electrode, a negative electrode, and a separator between them. In related technologies, secondary batteries are prone to thermal runaway, which can lead to battery fires and result in poor battery safety performance. Summary of the Invention

[0003] The main objective of this invention is to provide a negative electrode sheet, a secondary battery, and an electrical device, which aims to improve the safety performance of the battery.

[0004] To achieve the above objectives, the first aspect of the present invention provides a secondary battery, the secondary battery comprising a positive electrode, a negative electrode, and a separator disposed between the positive electrode and the negative electrode; the negative electrode comprises a base coating, the base coating comprising a fire extinguishing material, the fire extinguishing material being used to reduce the heat generated in the area of ​​the negative electrode.

[0005] In the secondary battery provided by this invention, the bottom coating of the negative electrode sheet includes a fire extinguishing material. Therefore, when the secondary battery is subjected to thermal abuse, the fire extinguishing material can be used to effectively reduce the heat generated in the negative electrode sheet area, thereby reducing the temperature rise rate of the negative electrode sheet area, reducing the risk of thermal runaway of the secondary battery, reducing the risk of fire of the secondary battery, and improving the safety performance of the secondary battery.

[0006] In one embodiment, the fire extinguishing material includes fire extinguishing microcapsules, the fire extinguishing microcapsules including a fire extinguishing medium and a shell covering at least a portion of the surface of the fire extinguishing medium.

[0007] In the fire extinguishing capsule of the fire extinguishing material of the present invention, when the outer shell covers part of the surface of the fire extinguishing medium, the exposed surface of the fire extinguishing medium (i.e., the uncovered surface) can react with oxygen during thermal abuse, effectively reducing the heat generated in the negative electrode area; or, during thermal abuse, the exposed surface of the fire extinguishing medium uses other mechanisms to effectively reduce the heat generated in the negative electrode area; furthermore, the outer shell can rupture at a certain temperature, thereby completely releasing the fire extinguishing medium inside, and thus more effectively reducing the heat generated in the negative electrode area; when the outer shell covers the entire surface of the fire extinguishing medium, the outer shell can rupture at a certain temperature, and after the outer shell ruptures, it releases the fire extinguishing medium inside to effectively reduce the heat generated in the negative electrode area.

[0008] In one embodiment, the rupture temperature of the outer casing is 120°C-150°C.

[0009] The present invention selects a shell with a suitable rupture temperature, which allows the shell to rupture more promptly during the thermal abuse of the secondary battery and release the fire extinguishing medium inside, effectively reducing the heat generated in the negative electrode area, thereby effectively reducing the risk of thermal runaway and improving the safety performance of the battery.

[0010] In one embodiment, the outer shell is made of a thermoplastic polymer. The thermoplastic polymer outer shell used in this invention will crack upon reaching its bursting temperature, thereby releasing the fire extinguishing medium therein to reduce the heat generated in the negative electrode area.

[0011] In one embodiment, the extinguishing medium includes at least one of fluorinated ketone polymers and fluorinated alkane polymers. Both fluorinated ketone polymers and fluorinated alkane polymers have good fire extinguishing performance. After the outer casing is broken, both fluorinated ketone polymers and fluorinated alkane polymers can effectively extinguish the fire, thereby effectively reducing the temperature rise rate in the negative electrode area, and thus effectively reducing the risk of thermal runaway and fire of the secondary battery, and effectively improving the safety performance of the secondary battery.

[0012] In one embodiment, the particle size of the fire extinguishing microcapsules is 6μm-11μm. The particle size of the fire extinguishing microcapsules of the present invention is about half that of the negative electrode active material DV50, which can ensure that the fire extinguishing microcapsules are uniformly distributed among the negative electrode active materials, and also ensure that the fire extinguishing microcapsules have a certain core material load-bearing capacity.

[0013] In one embodiment, the mass of the extinguishing medium is 20%-50% of the mass of the extinguishing microcapsule. This invention selects an appropriate proportion of extinguishing medium, which can effectively improve the safety performance of the secondary battery while also facilitating the production of the extinguishing microcapsule.

[0014] In one embodiment, the negative electrode sheet includes a negative electrode active material layer, and the negative electrode active material layer includes a fire extinguishing material. By adding fire extinguishing microcapsules to the negative electrode active material layer, the present invention brings the fire extinguishing microcapsules closer to the heat-generating material in the thermal runaway negative electrode region. The fire extinguishing microcapsules can then take effect more quickly and effectively, reducing the risk of thermal runaway in the secondary battery, lowering the risk of fire, and thus more effectively improving the safety performance of the secondary battery.

[0015] In one embodiment, the negative electrode active material layer further includes a negative electrode active material, a binder, and a conductive agent, wherein the mass ratio of the fire extinguishing material, the negative electrode active material, the binder, and the conductive agent is (1-3):(94-97.5):(1-2):(0.5-1). The appropriate proportions of each component in the negative electrode active material layer of this invention can effectively improve the safety performance of the secondary battery.

[0016] A second aspect of the present invention also provides a negative electrode sheet, the negative electrode sheet comprising a base coating, the base coating comprising a fire extinguishing material.

[0017] In one embodiment, the fire extinguishing material includes fire extinguishing microcapsules, the fire extinguishing microcapsules including a fire extinguishing medium and a shell covering at least a portion of the surface of the fire extinguishing medium.

[0018] In one embodiment, the particle size of the fire extinguishing microcapsules is 6μm-11μm.

[0019] In one embodiment, the rupture temperature of the outer casing is 120°C-150°C.

[0020] In one embodiment, the material of the housing includes a thermoplastic polymer.

[0021] In one embodiment, the extinguishing medium includes at least one of fluorinated ketone polymers and fluorinated alkane polymers.

[0022] In one embodiment, the base coating layer includes a negative electrode active material layer, which includes a negative electrode active material, a binder, a conductive agent, and a fire extinguishing material. The mass ratio of the fire extinguishing material, the negative electrode active material, the binder, and the conductive agent is (1-3):(94-97.5):(1-2):(0.5-1).

[0023] In one embodiment, the bonding force of the negative electrode sheet is 5 N / m-100 N / m. The use of a suitable bonding force in the negative electrode sheet of the present invention ensures the stability and reliability of the negative electrode active material layer, while also facilitating the processing of the negative electrode sheet.

[0024] A third aspect of the present invention also provides an electrical device, the electrical device comprising the secondary battery provided in the first aspect.

[0025] In the secondary battery provided by this invention, the bottom coating of the negative electrode sheet includes a fire extinguishing material. Therefore, when the secondary battery is subjected to thermal abuse, the fire extinguishing material can be used to effectively reduce the heat generated in the negative electrode sheet area, thereby reducing the temperature rise rate of the negative electrode sheet area, reducing the risk of thermal runaway of the secondary battery, reducing the risk of fire of the secondary battery, and improving the safety performance of the secondary battery. Attached Figure Description

[0026] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on the structures shown in these drawings without creative effort.

[0027] Figure 1 is a schematic diagram of a secondary battery according to an embodiment of the present invention;

[0028] Figure 2 is an exploded view of the secondary battery according to an embodiment of the present invention shown in Figure 1.

[0029] Explanation of icon numbers:

[0030] 5. Secondary battery; 51. Housing; 52. Electrode assembly; 53. End cap assembly.

[0031] The realization of the objective, functional features and advantages of the present invention will be further explained in conjunction with the embodiments and with reference to the accompanying drawings. Detailed Implementation

[0032] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only a part of the embodiments of the present invention, and not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative effort are within the scope of protection of the present invention.

[0033] The negative electrode, secondary battery, and power supply device of this application are hereby disclosed in detail with appropriate reference to the accompanying drawings. However, unnecessary details may be omitted. For example, detailed descriptions of well-known matters and repetitive descriptions of practically identical structures may be omitted. This is to avoid unnecessarily lengthy descriptions and to facilitate understanding by those skilled in the art. Furthermore, the accompanying drawings and the following description are provided for the purpose of enabling those skilled in the art to fully understand this application and are not intended to limit the subject matter of the claims.

[0034] The "range" disclosed in this application is defined by a lower limit and an upper limit. A given range is defined by selecting a lower limit and an upper limit, which define the boundaries of a particular range. Ranges defined in this way can include or exclude endpoints and can be arbitrarily combined; that is, any lower limit can be combined with any upper limit to form a range. For example, if ranges of 60-120 and 80-110 are listed for a specific parameter, it is expected that ranges of 60-110 and 80-120 are also included. Furthermore, if minimum range values ​​of 1 and 2 are listed, and if maximum range values ​​of 3, 4, and 5 are listed, then the following ranges are all expected: 1-3, 1-4, 1-5, 2-3, 2-4, and 2-5. In this application, unless otherwise stated, the numerical range "ab" represents a shortened representation of any combination of real numbers between a and b, where a and b are real numbers. For example, the numerical range "0-5" indicates that all real numbers between "0-5" have been listed in this article; "0-5" is simply a shortened representation of these numerical combinations. Furthermore, when a parameter is stated as an integer ≥2, it is equivalent to disclosing that the parameter is, for example, an integer such as 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, etc.

[0035] Unless otherwise specified, all embodiments and optional embodiments of this application can be combined to form new technical solutions.

[0036] Unless otherwise specified, all technical features and optional technical features of this application may be combined to form new technical solutions.

[0037] Unless otherwise specified, all steps in this application may be performed sequentially or randomly, preferably sequentially. For example, the method includes steps (a) and (b), indicating that the method may include steps (a) and (b) performed sequentially, or it may include steps (b) and (a) performed sequentially. For example, the mention that the method may also include step (c) 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 it may include steps (a), (c), and (b), or it may include steps (c), (a), and (b), etc.

[0038] Battery thermal runaway refers to the uncontrolled chemical reactions within a battery during use, caused by internal or external factors. This generates a large amount of heat, leading to a rapid rise in battery temperature and a sharp decline in battery performance (such as capacity loss, increased internal resistance, and shortened cycle life). It can even trigger a series of dangerous situations, such as overheating, fire, or explosion. Internal factors mainly include internal short circuits, overcharging and discharging, and electrolyte decomposition; external factors mainly include excessively high ambient temperatures, poor heat dissipation, and external short circuits.

[0039] Under normal circumstances, thermal abuse can lead to secondary thermal runaway. Therefore, this invention provides a secondary battery designed to reduce the risk of thermal runaway and improve the safety performance of secondary batteries.

[0040] In one embodiment of the present invention, the secondary battery includes a positive electrode, a negative electrode, and a separator disposed between the positive electrode and the negative electrode; the negative electrode includes a current collector and a base coating disposed on at least one surface of the current collector, the base coating including a fire extinguishing material.

[0041] Typically, a secondary battery consists of a positive electrode, a negative electrode, an electrolyte, and a separator. During charging and discharging, active ions move back and forth between the positive and negative electrodes, inserting and releasing. The electrolyte acts as a conductor between the positive and negative electrodes. The separator, positioned between the positive and negative electrodes, primarily prevents short circuits while allowing ions to pass through.

[0042] [Negative electrode plate]

[0043] The negative electrode sheet includes a negative current collector and a negative active material layer disposed on at least one surface of the negative current collector, wherein the negative active material layer includes a negative active material.

[0044] As an example, the negative electrode current collector has two surfaces opposite each other in its own thickness direction, and the negative electrode active material layer is disposed on either or both of the two opposite surfaces of the negative electrode current collector.

[0045] 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 substrate and a metal layer formed on at least one surface of the polymer 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 substrate (such as a substrate of polypropylene (PP), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polystyrene (PS), polyethylene (PE), etc.).

[0046] In some embodiments, the negative electrode active material may be a negative electrode active material known in the art for use in batteries. 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, etc. The silicon-based material may be selected from at least one of elemental silicon, silicon oxide compounds, silicon-carbon composites, silicon-nitrogen composites, and silicon alloys. The tin-based material may be selected from at least one of elemental tin, tin oxide compounds, and tin alloys. However, this application is not limited to these materials, and other conventional 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.

[0047] In some embodiments, the negative electrode active material layer may optionally include a binder. 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).

[0048] In some embodiments, the negative electrode active material layer may optionally include a conductive agent. 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.

[0049] In some embodiments, the negative electrode active material layer may also optionally include other additives, such as thickeners (e.g., sodium carboxymethyl cellulose (CMC-Na)).

[0050] In some embodiments, the negative electrode sheet can be prepared by dispersing the components used to prepare the negative electrode sheet, such as the negative electrode active material, conductive agent, binder and any other components, in a solvent (e.g., deionized water) to form a negative electrode slurry; coating the negative electrode slurry onto the negative electrode current collector, and then obtaining the negative electrode sheet after drying, cold pressing and other processes.

[0051] The negative electrode includes a base coating, which can be a layer of negative active material, in which case the fire extinguishing material is disposed within the negative active material layer. Alternatively, the base coating is located between the current collector and the negative active material layer, in which case the fire extinguishing material is disposed within the base coating between the current collector and the negative active material layer. Alternatively, when the current collector is a composite current collector, the composite current collector includes a polymer material base layer and a metal layer formed on at least one surface of the polymer material base layer; in this case, the base coating can be a polymer material layer, and the fire extinguishing material is disposed within the polymer material base layer. Of course, the fire extinguishing material can also be disposed simultaneously within the negative active material layer, the base coating located between the current collector and the negative active material layer, and the polymer material layer of the composite current collector.

[0052] Fire extinguishing materials can be used to reduce the heat generated in the negative electrode area. Specifically, the fire extinguishing material can absorb the heat generated in the negative electrode area or reduce the heat generated in the negative electrode area through other means. The specific structure and form of the fire extinguishing material are limited here, as long as it can reduce the heat.

[0053] In the secondary battery provided by the present invention, the bottom coating of the negative electrode sheet includes a fire extinguishing material. Therefore, when the secondary battery is subjected to thermal abuse, the fire extinguishing material can be used to effectively reduce the heat generated in the negative electrode sheet area, thereby reducing the temperature rise rate of the negative electrode sheet area, thus reducing the risk of thermal runaway of the secondary battery, reducing the risk of fire of the secondary battery, and improving the safety performance of the secondary battery.

[0054] In some embodiments, the fire extinguishing material includes fire extinguishing microcapsules, which include a fire extinguishing medium and a shell covering at least a portion of the surface of the fire extinguishing medium.

[0055] The fire extinguishing microcapsule can be spherical or ellipsoidal. The outer shell can cover part or all of the surface of the fire extinguishing medium; this is not limited. When the outer shell covers part of the surface of the fire extinguishing medium, in the event of thermal abuse, the exposed surface of the fire extinguishing medium (i.e., the uncovered surface) can react with oxygen, effectively reducing the heat generated in the negative electrode area. Alternatively, in the event of thermal abuse, the exposed surface of the fire extinguishing medium can effectively reduce the heat generated in the negative electrode area through other mechanisms. Furthermore, the outer shell can rupture at a certain temperature, thereby completely releasing the fire extinguishing medium and further reducing the heat generated in the negative electrode area. When the outer shell covers the entire surface of the fire extinguishing medium, the outer shell can rupture at a certain temperature (i.e., its rupture temperature), releasing the fire extinguishing medium to effectively reduce the heat generated in the negative electrode area. The fire extinguishing medium can be solid, liquid, or gaseous; this is not limited, as long as it effectively reduces heat.

[0056] It should be noted that the rupture temperature refers to the critical temperature at which a material cracks due to thermal stress during heating or cooling. In this invention, the rupture temperature of the outer shell refers to the critical temperature at which the outer shell cracks due to thermal stress during heating. During the thermal abuse of a secondary battery, as the temperature gradually increases, when the temperature reaches the glass transition temperature of the outer shell material, the outer shell begins to soften. Subsequently, as the temperature continues to rise, the strength of the outer shell material gradually decreases. When the critical temperature is reached, the outer shell will crack.

[0057] In some embodiments, the burst temperature of the casing is 120°C-150°C (e.g., 120°C, 125°C, 130°C, 135°C, 140°C, 145°C, 150°C, and any range between two endpoints). Selecting a casing with a suitable burst temperature allows the casing to burst more promptly during thermal abuse of the secondary battery, releasing the fire extinguishing medium within, effectively reducing the heat generated in the negative electrode area, thereby effectively reducing the risk of thermal runaway and improving battery safety performance. If the burst temperature of the casing is below 120°C, it will burst during the normal manufacturing process of the secondary battery (e.g., during the baking process), affecting its electrical performance; if the burst temperature of the casing is above 150°C, the casing cannot burst promptly and effectively during thermal abuse of the secondary battery, thus failing to effectively reduce the heat generated in the negative electrode area.

[0058] In some embodiments, the housing material includes a thermoplastic polymer.

[0059] This invention uses a thermoplastic polymer shell. During the thermal abuse of a secondary battery, as the temperature gradually increases, the forces between the molecular chains inside the thermoplastic polymer weaken. When a certain temperature is reached, the molecular chains begin to gain enough energy to move relatively freely, and the material softens. Subsequently, as the temperature continues to rise, the molecular chains inside the thermoplastic polymer become further disordered, and the strength of the material continuously decreases. When the critical temperature is reached, the thermoplastic polymer shell will crack, thereby releasing the fire extinguishing medium inside to effectively reduce the heat generated in the negative electrode area.

[0060] Thermoplastic polymers include, but are not limited to, at least one of polyacrylate, polyethylene, polypropylene, and polyurethane.

[0061] In some embodiments, the present invention selects a shell material with adhesive properties (such as polyacrylate or polyurethane) to replace part of the binder in the negative electrode active material layer, thereby ensuring that the proportion of negative electrode active material is not reduced and that the secondary battery has good cycle performance.

[0062] In some embodiments, the extinguishing medium includes at least one of fluorinated ketone polymers and fluorinated alkane polymers. Both fluorinated ketone polymers and fluorinated alkane polymers have good fire extinguishing properties. After the outer casing is broken, both fluorinated ketone polymers and fluorinated alkane polymers can effectively extinguish the fire, thereby effectively reducing the temperature rise rate in the negative electrode area, and thus effectively reducing the risk of thermal runaway and fire of the secondary battery, and effectively improving the safety performance of the secondary battery.

[0063] Fluorinated ketone polymers include, but are not limited to, perfluorohexanone; fluorinated alkane polymers include, but are not limited to, at least one of heptafluoropropane, hexafluoropropane, monobromochlorodifluoromethane, monobromotrifluoromethane, and dibromotetrafluoroethane.

[0064] As an example, the extinguishing medium is perfluorohexanone, which is a colorless, odorless, and transparent liquid at room temperature. It is easily vaporized and has good fire extinguishing performance. Its boiling point is 49.2℃, which is lower than the bursting temperature of the casing. Therefore, perfluorohexanone can vaporize before the casing bursts. The vaporization process absorbs the heat generated in the negative electrode area, reducing the temperature rise rate in the negative electrode area. At the same time, after the casing bursts, perfluorohexanone is released and plays a fire extinguishing role, further reducing the temperature of the negative electrode area, thereby reducing the risk of thermal runaway of the secondary battery, reducing the risk of secondary battery fire, and improving the safety performance of the secondary battery.

[0065] As an example, the extinguishing medium is at least one of heptafluoropropane, hexafluoropropane, bromochlorodifluoromethane, bromotrifluoromethane, and dibromotetrafluoroethane. Among these, heptafluoropropane, hexafluoropropane, bromochlorodifluoromethane, and bromotrifluoromethane are all gases at room temperature and possess good fire extinguishing properties. After the outer casing ruptures, the release of these substances effectively reduces the temperature of the negative electrode area, thereby reducing the risk of thermal runaway of the secondary battery, lowering the risk of secondary battery fire, and improving the safety performance of the secondary battery. Dibromotetrafluoroethane is a liquid at room temperature with a boiling point of 47°C. This boiling point is lower than the rupture temperature of the casing, allowing dibromotetrafluoroethane to vaporize before the casing ruptures. During vaporization, it absorbs heat generated in the negative electrode area, reducing the rate of temperature rise in the negative electrode region. Simultaneously, after the casing ruptures, the dibromotetrafluoroethane is released and effectively reduces the heat generated in the negative electrode region, thereby reducing the risk of thermal runaway and fire in the secondary battery, and improving its safety performance.

[0066] In some embodiments, the particle size of the fire extinguishing microcapsules is 6μm-11μm (e.g., 6μm, 7μm, 8μm, 9μm, 10μm, 11μm, and any range between the two endpoints). This particle size is approximately half that of the negative electrode active material DV50, ensuring both uniform distribution of the fire extinguishing microcapsules among the negative electrode active material and a certain core material load-bearing capacity. If the particle size is less than 6μm, the load-bearing capacity will be low; if the particle size is greater than 11μm, uniform distribution of the fire extinguishing microcapsules among the negative electrode active material cannot be guaranteed.

[0067] DV50 refers to the particle size corresponding to 50% of the material's volume distribution.

[0068] In some embodiments, the mass of the extinguishing medium is 20%-50% of the mass of the extinguishing microcapsule (e.g., 20%, 30%, 40%, 50%, and any range between the two endpoints). Using the aforementioned suitable proportion of extinguishing medium can effectively improve the safety performance of the secondary battery while also facilitating the fabrication of the extinguishing microcapsule. If the mass proportion of the extinguishing medium is less than 20%, the performance improvement effect is limited; if the mass proportion of the extinguishing medium is greater than 50%, it is difficult to fabricate extinguishing microcapsules.

[0069] In some embodiments, the base coating layer includes a negative electrode active material layer, which includes a fire extinguishing material.

[0070] In this invention, adding fire-extinguishing microcapsules to the negative electrode active material layer brings the heat-generating material closer to the negative electrode region where thermal runaway occurs. The fire-extinguishing microcapsules can take effect more quickly and effectively, reducing the risk of thermal runaway of the secondary battery and the risk of fire, thereby improving the safety performance of the secondary battery more effectively.

[0071] In some embodiments, the negative electrode active material layer further includes a negative electrode active material, a binder, and a conductive agent, with the mass ratio of fire extinguishing material, negative electrode active material, binder, and conductive agent being (1-3):(94-97.5):(1-2):(0.5-1). As an example, the mass ratio of fire extinguishing material, negative electrode active material, binder, and conductive agent is 1:96:2:1, 2:95.5:2:0.5, 3:94.5:2:0.5, 3:94:2:1, and any range between the two endpoints. Using the above-mentioned suitable ratio can effectively improve the safety performance of the secondary battery. If the mass of the fire extinguishing material is too small, the performance improvement effect will be limited; if the mass of the fire extinguishing material is too large, the energy density of the secondary battery will be reduced.

[0072] It should be noted that the method for manufacturing fire extinguishing microcapsules is a conventional method. As long as the composition and particle size of the prepared fire extinguishing microcapsules meet the requirements of the above embodiments, they are acceptable. Fire extinguishing microcapsules are commercially available.

[0073] In some embodiments, the solvent used in the fabrication of the negative electrode active material layer is water; the viscosity of the negative electrode active material layer slurry is 2000 mPa·s-10000 Pa·s (e.g., 2000 mPa·s, 4000 mPa·s, 6000 mPa·s, 8000 mPa·s, 10000 mPa·s, and any range between two endpoints); and the solid content of the negative electrode active material layer slurry is 40 wt%-60 wt% (e.g., 40 wt%, 45 wt%, 50 wt%, 55 wt%, 60 wt%, and any range between two endpoints).

[0074] In some embodiments, the bonding force of the negative electrode sheet is 5 N / m-100 N / m (e.g., 5 N / m, 10 N / m, 30 N / m, 50 N / m, 80 N / m, 100 N / m, and any range between the two endpoints). Using the aforementioned suitable bonding force for the negative electrode sheet ensures the stability and reliability of the negative electrode active material layer, while also facilitating the processing of the negative electrode sheet. If the bonding force is lower than 5 N / m, the negative electrode active material layer will detach during the preparation process or when subjected to external impact or vibration, thus affecting the performance and lifespan of the secondary battery. If the bonding force is higher than 100 N / m, the flexibility of the negative electrode sheet is relatively low, which may lead to cracks or breakage.

[0075] [Positive electrode plate]

[0076] The positive electrode includes a positive current collector and a positive active material layer disposed on at least one surface of the positive current collector, wherein the positive active material layer includes a positive electrode material.

[0077] As an example, the positive current collector has two surfaces opposite each other in its own thickness direction, and the positive active material layer is disposed on either or both of the two opposite surfaces of the positive current collector.

[0078] In some embodiments, the positive 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 substrate and a metal layer formed on at least one surface of the polymer substrate. 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 substrate (such as a substrate of polypropylene (PP), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polystyrene (PS), polyethylene (PE), etc.).

[0079] In some embodiments, the secondary battery is a lithium-ion battery, and the positive electrode active material can be a positive electrode active material known in the art for lithium-ion batteries. As an example, the positive electrode active material may include at least one of the following materials: lithium phosphates with an olivine structure, lithium transition metal oxides, and their respective modified compounds. However, this application is not limited to these materials, and other conventional materials that can be used as battery positive electrode active materials may also be used. These positive electrode active materials may be used alone or in combination of two or more. Examples of lithium transition metal oxides include, but are not limited to, lithium cobalt oxides (such as LiCoO2), lithium nickel oxides (such as LiNiO2), lithium manganese oxides (such as LiMnO2, LiMn2O4), lithium nickel cobalt oxides, lithium manganese cobalt oxides, lithium nickel manganese oxides, and lithium nickel cobalt manganese oxides (such as LiNi). 1 / 3 Co1 / 3 Mn 1 / 3 O2 (also known as NCM) 333 LiNi 0.5 Co 0.2 Mn 0.3 O2 (also known as NCM) 523 LiNi 0.5 Co 0.25 Mn 0.25 O2 (also known as NCM) 211 LiNi 0.6 Co 0.2 Mn 0.2 O2 (also known as NCM) 622 LiNi 0.8 Co 0.1 Mn 0.1 O2 (also known as NCM) 811 ), lithium nickel cobalt aluminum oxide (such as LiNi) 0.85 Co 0.15 Al 0.05 At least one of O2 and its modified compounds. Examples of lithium phosphates with an olivine structure include, but are not limited to, lithium iron phosphate (such as LiFePO4 (also referred to as LFP)), lithium iron phosphate and carbon composites, lithium manganese phosphate (such as LiMnPO4), lithium manganese phosphate and carbon composites, lithium manganese iron phosphate, and lithium manganese iron phosphate and carbon composites.

[0080] In some embodiments, the secondary battery is a sodium-ion battery, and the positive electrode active material in the positive electrode slurry can be a positive electrode active material known in the art for sodium-ion batteries.

[0081] In an optional embodiment of the present invention, the transition metal in the sodium transition metal oxide can be at least one selected from Mn, Fe, Ni, Co, Cr, Cu, Ti, Zn, V, Zr, and Ce, and the sodium transition metal oxide is, for example, Na. x MO2, where M is one or more of Ti, V, Mn, Co, Ni, Fe, Cr and Cu, and 0 < x ≤ 1.

[0082] In an optional embodiment of the present invention, the polyanionic compound may be a compound containing sodium ions, transition metal ions, or a tetrahedral (YO4) structure. n- A class of compounds with anionic units. The transition metal can be at least one of Mn, Fe, Ni, Co, Cr, Cu, Ti, Zn, V, Zr, and Ce; Y can be at least one of P, S, and Si; n represents (YO4). n- The price state.

[0083] Polyanionic compounds can also contain sodium ions, transition metal ions, or tetrahedral (YO4) ions. n- A class of compounds containing anionic units and halide anions. The transition metal can be at least one of Mn, Fe, Ni, Co, Cr, Cu, Ti, Zn, V, Zr, and Ce; Y can be at least one of P, S, and Si; n represents (YO4). n- The valence state; the halogen can be at least one of F, Cl and Br.

[0084] Polyanionic compounds can also be sodium-containing tetrahedral (YO4) compounds. n- Anionic unit, tetrahedral unit (ZO) y ) m+ And a class of compounds with optional halide anions, where Y can be at least one of P, S, and Si; n represents (YO4). n- The valence state; Z represents a transition metal, which can be at least one of Mn, Fe, Ni, Co, Cr, Cu, Ti, Zn, V, Zr, and Ce; m represents (ZO) y ) m+ The valence state; the halogen can be at least one of F, Cl and Br.

[0085] Prussian blue compounds can be compounds containing sodium ions, transition metal ions, and cyanide ions (CN). - A class of compounds. The transition metal can be at least one of Mn, Fe, Ni, Co, Cr, Cu, Ti, Zn, V, Zr, and Ce. Prussian blue compounds include, for example, Na. a Me b Me' c (CN)6, wherein Me and Me' are each independently at least one of Ni, Cu, Fe, Mn, Co and Zn, 0 < a ≤ 2, 0 < b < 1, 0 < c < 1.

[0086] In some embodiments, the positive electrode active material layer may optionally include a binder. As an example, the binder may include at least one selected from polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), PVDF-tetrafluoroethylene-propylene terpolymer, PVDF-hexafluoropropylene-tetrafluoroethylene terpolymer, tetrafluoroethylene-hexafluoropropylene copolymer, and fluorinated acrylate resin.

[0087] In some embodiments, the positive electrode active material layer may optionally include a conductive agent. As an example, the conductive agent may include at least one selected from superconducting carbon, acetylene black, carbon black, Ketjen black, carbon dots, carbon nanotubes, graphene, and carbon nanofibers.

[0088] In some embodiments, the positive electrode sheet can be prepared by dispersing the above-mentioned components for preparing the positive electrode sheet, such as positive active material, conductive agent, binder and any other components, in a solvent (e.g., N-methylpyrrolidone) to form a positive electrode slurry; coating the positive electrode slurry onto the positive electrode current collector, and then obtaining the positive electrode sheet after drying, cold pressing and other processes.

[0089] [Electrolytes]

[0090] The electrolyte acts as a conductor of ions between the positive and negative electrodes. This application does not impose specific restrictions on the type of electrolyte; it can be selected according to requirements. For example, the electrolyte can be liquid, gel, or entirely solid.

[0091] In some embodiments, the electrolyte may be an electrolyte solution, which includes an electrolyte salt and a solvent.

[0092] In some embodiments, the electrolyte comprises lithium hexafluorophosphate or a mixture of lithium hexafluorophosphate and one other lithium salt, the other lithium salt being 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 difluorooxalate borate, lithium dioxalate borate, lithium difluorodioxalate phosphate, and lithium tetrafluorooxalate phosphate.

[0093] In some embodiments, the solvent may be selected from at least one of ethylene carbonate, propylene carbonate, methyl ethyl carbonate, diethyl carbonate, dimethyl carbonate, dipropyl carbonate, methyl propyl carbonate, ethyl propyl carbonate, butyl carbonate, fluoroethylene carbonate, methyl formate, methyl acetate, ethyl acetate, propyl acetate, methyl propionate, ethyl propionate, propyl propionate, methyl butyrate, ethyl butyrate, 1,4-butyrolactone, sulfolane, dimethyl sulfone, methyl ethyl sulfone, and diethyl sulfone.

[0094] In some embodiments, the electrolyte may optionally include additives. For example, additives may include negative electrode film-forming additives, positive electrode film-forming additives, and may also include additives that can improve certain battery performance, such as additives that improve battery overcharge performance, additives that improve battery high-temperature or low-temperature performance, etc.

[0095] [Isolation membrane]

[0096] In some embodiments, the secondary battery also includes a separator. This application does not impose any particular limitation on the type of separator; any known porous separator with good chemical and mechanical stability can be selected.

[0097] In some embodiments, the material of the separator can be selected from at least one of glass fiber, nonwoven fabric, polyethylene, polypropylene, and polyvinylidene fluoride. The separator can be a single-layer film or a multi-layer composite film, without particular limitation. When the separator is a multi-layer composite film, the materials of each layer can be the same or different, without particular limitation.

[0098] In some implementations, the positive electrode, negative electrode, and separator can be fabricated into an electrode assembly using a winding or stacking process.

[0099] In some embodiments, the secondary battery may include an outer packaging. This outer packaging may be used to encapsulate the aforementioned electrode assembly and electrolyte.

[0100] In some embodiments, the outer packaging of the secondary battery can be a hard shell, such as a hard plastic shell, an aluminum shell, or a steel shell. The outer packaging of the secondary battery can also be a soft pack, such as a pouch. The material of the soft pack can be plastic; examples of plastics include polypropylene, polybutylene terephthalate, and polybutylene succinate.

[0101] This application does not impose any particular limitation on the shape of the secondary battery; it can be cylindrical, square, or any other arbitrary shape. For example, Figure 1 shows a square-structured secondary battery 5 as an example.

[0102] In some embodiments, referring to FIG2, the outer packaging may include a housing 51 and an end cap assembly 53. The housing 51 may include a base plate and side plates connected to the base plate, the base plate and side plates forming a receiving cavity. The housing 51 has an opening communicating with the receiving cavity, and the end cap assembly 53 can be closed by covering the opening. A positive electrode, a negative electrode, and a separator can be formed into an electrode assembly 52 by a winding process or a stacking process. The electrode assembly 52 is encapsulated within the receiving cavity. Electrolyte is immersed in the electrode assembly 52. ​​The secondary battery 5 may contain one or more electrode assemblies 52, which can be selected by those skilled in the art according to specific practical needs.

[0103] In some implementations, the secondary batteries can be assembled into a battery module, and the number of secondary batteries contained in the battery module can be one or more, the specific number of which can be selected by those skilled in the art according to the application and capacity of the battery module.

[0104] The second aspect of this application also provides a negative electrode sheet, which is the negative electrode sheet in the secondary battery provided in the first aspect of this invention. Its specific materials, structure and preparation method can be referred to the above embodiments, and will not be repeated here.

[0105] A third aspect of this application also provides an electrical device comprising the secondary battery described above. The electrical device of this application possesses at least all the beneficial effects of the aforementioned secondary battery, which will not be elaborated further here. The secondary battery can be used as a power source for the electrical device or as an energy storage unit for the electrical device. The electrical device may include, but is not limited to, mobile devices (e.g., mobile phones, laptops, etc.), electric vehicles (e.g., 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.

[0106] As an example, the electrical device is a pure electric vehicle, a hybrid electric vehicle, or a plug-in hybrid electric vehicle, a mobile phone, a tablet computer, a laptop computer, etc.

[0107] Example

[0108] The following describes embodiments of this application. The embodiments described below are exemplary and are only used to explain this application, and should not be construed as limiting this application. Where specific techniques or conditions are not specified in the embodiments, they are performed according to the techniques or conditions described in the literature in this field or according to the product instructions. Reagents or instruments used, unless otherwise specified, are all conventional products that can be obtained commercially.

[0109] Examples 1-13

[0110] 1. Preparation of negative electrode active material layer slurry:

[0111] The negative electrode active material layer solid slurry was prepared according to Table 1. The composition and particle size of the fire extinguishing microcapsules were as specified in Table 1. The negative electrode active material was graphite, the binder was acrylate, and the conductive agent was amorphous carbon. Then, water was added to the negative electrode active material layer solid slurry, and the mixture was stirred until homogeneous, yielding a negative electrode active material layer slurry with a viscosity of 2500 mPa·s and a solid content of 45 wt%.

[0112] 2. Making the negative electrode plate:

[0113] The prepared negative electrode active material slurry was coated onto both surfaces of the copper foil by extrusion coating, with a coating thickness of 80 μm. After drying in an oven at 100°C, the foil was rolled and punched to obtain the negative electrode sheet.

[0114] 3. Making the positive electrode sheet:

[0115] 1.5 wt% polyvinylidene fluoride binder was fully dissolved in N-methylpyrrolidone, and 1.5 wt% carbon black conductive agent and 97 wt% recycled positive electrode material were added to make a uniformly dispersed slurry. The slurry was uniformly coated on the surface of aluminum foil and then transferred to a vacuum drying oven for complete drying. The dried electrode was then rolled and punched to obtain the positive electrode.

[0116] 4. Separating membrane: Polypropylene film is used as the separating membrane.

[0117] 5. Electrolyte: In an argon-atmospheric glove box (H2O < 0.1 ppm, O2 < 0.1 ppm), dissolve 1 mol / L lithium hexafluorophosphate in an organic solvent, which includes a mixture of ethylene carbonate, dimethyl carbonate, and ethyl methyl carbonate in a volume ratio of 1:1:1. Add 10% fluoroethylene carbonate and 2% vinylene carbonate by volume to the mixed solvent, and stir until homogeneous to obtain the electrolyte.

[0118] 6. Assemble the battery: Wind the positive electrode, separator, and negative electrode in sequence, with the separator positioned between the positive and negative electrodes. Add electrolyte and assemble into a pouch battery, which is a lithium-ion battery.

[0119] 7. Performance Testing:

[0120] The negative electrode sheet was subjected to DSC test according to the national standard GB / T13464-2008 "Test Method for Thermal Stability of Substances". The heat generation data of DSC test are shown in Table 1.

[0121] The assembled battery cells were subjected to overcharge tests in accordance with the national standard GB38031-2020 "Safety Requirements for Power Batteries for Electric Vehicles". The results of whether the overcharge test passed are shown in Table 1.

[0122] Meanwhile, the assembled battery cells were subjected to thermal diffusion tests in accordance with the national standard GB38031-2020 "Safety Requirements for Power Batteries for Electric Vehicles". The results of the thermal diffusion test to determine whether the cells caught fire are shown in Table 1.

[0123] Comparative Example 1

[0124] The difference between this comparative example and Example 1 is that the negative electrode active material layer slurry does not contain fire extinguishing microcapsules, while all other operations are the same as in Example 1.

[0125] Table 1. Parameter results for Examples 1-13 and Comparative Example 1

[0126]

[0127]

[0128] As can be seen from the data in Table 1, compared with Comparative Example 1, the DSC heat generation of the negative electrode sheets prepared in Examples 1 to 13 of the present invention is reduced by reasonably adjusting the particle size of the fire extinguishing microcapsules, the type of fire extinguishing medium, the proportion of the fire extinguishing medium, the shell material, and the amount of each component in the negative electrode active material layer slurry. Furthermore, the overcharge test of the battery cells assembled from the negative electrode sheets is passed, and the thermal diffusion test of the battery cells assembled from the negative electrode sheets does not result in any fire. This indicates that the secondary battery provided by the embodiments of the present invention has a low risk of thermal runaway and a low risk of fire, thus exhibiting high safety performance.

[0129] The above description is merely an exemplary embodiment of the present invention and does not limit the patent scope of the present invention. Any equivalent structural transformations made using the contents of the present invention specification and drawings under the technical concept of the present invention, or direct / indirect applications in other related technical fields, are included within the patent protection scope of the present invention.

Claims

1. A secondary battery, characterized in that, The secondary battery includes a positive electrode, a negative electrode, and a separator disposed between the positive electrode and the negative electrode; the negative electrode includes a base coating, which includes a fire extinguishing material, and the fire extinguishing material can be used to reduce the heat generated in the area of ​​the negative electrode.

2. The secondary battery as described in claim 1, characterized in that, The fire extinguishing material includes fire extinguishing microcapsules, each comprising a fire extinguishing medium and a shell covering at least a portion of the surface of the fire extinguishing medium.

3. The secondary battery as described in claim 2, characterized in that, The shell has a cracking temperature of 120℃-150℃.

4. The secondary battery as described in claim 2, characterized in that, The outer casing is made of thermoplastic polymers.

5. The secondary battery as described in claim 2, characterized in that, The extinguishing medium includes at least one of fluorinated ketone polymers and fluorinated alkane polymers.

6. The secondary battery as described in claim 2, characterized in that, The fire extinguishing microcapsules have a particle size of 6μm-11μm.

7. The secondary battery as described in claim 2, characterized in that, The mass of the extinguishing medium is 20%-50% of the mass of the extinguishing microcapsules.

8. The secondary battery as described in any one of claims 1 to 7, characterized in that, The base coating includes a negative electrode active material layer, which includes fire extinguishing material.

9. The secondary battery as described in claim 8, characterized in that, The negative electrode active material layer also includes a negative electrode active material, a binder and a conductive agent, and the mass ratio of the fire extinguishing material, the negative electrode active material, the binder and the conductive agent is (1-3):(94-97.5):(1-2):(0.5-1).

10. A negative electrode sheet, characterized in that, The negative electrode sheet includes a base coating, which includes a fire extinguishing material.

11. The negative electrode sheet as described in claim 10, characterized in that, The fire extinguishing material includes fire extinguishing microcapsules, which include a fire extinguishing medium and a shell covering at least a portion of the surface of the fire extinguishing medium.

12. The negative electrode sheet as described in claim 11, characterized in that, The fire extinguishing microcapsules have a particle size of 6μm-11μm.

13. The negative electrode sheet as described in claim 11, characterized in that, The shell has a cracking temperature of 120℃-150℃.

14. The negative electrode sheet as described in claim 11, characterized in that, The outer casing is made of thermoplastic polymers.

15. The negative electrode sheet as described in claim 11, characterized in that, The extinguishing medium includes at least one of fluorinated ketone polymers and fluorinated alkane polymers.

16. The negative electrode sheet according to any one of claims 10 to 15, characterized in that, The base coating includes a negative electrode active material layer, which includes a negative electrode active material, a binder, a conductive agent, and a fire extinguishing material. The mass ratio of the fire extinguishing material, the negative electrode active material, the binder, and the conductive agent is (1-3):(94-97.5):(1-2):(0.5-1).

17. The negative electrode sheet as described in any one of claims 10 to 15, characterized in that, The bonding strength of the negative electrode sheet is 5N / m-100N / m.

18. An electrical appliance, characterized in that, The electrical device includes a secondary battery as described in any one of claims 1 to 9.

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