A positive electrode sheet, a secondary battery, a battery module, a battery pack, and an electric device

Abstract

The application provides a positive electrode tab, which comprises a positive electrode current collector, a positive electrode material layer, and a thermosensitive material layer between the positive electrode current collector and the positive electrode material layer, wherein the thermosensitive material layer comprises a negative temperature coefficient thermosensitive material, the room temperature resistance R 25 is 1KΩ-1000KΩ, preferably 1KΩ-100KΩ, and the thermosensitive constant B of the negative temperature coefficient thermosensitive material is 1000K-10000K, preferably 1000K-5000K. Thus, by arranging the thermosensitive material layer between the positive electrode current collector and the positive electrode material layer, the thermosensitive material layer comprises the negative temperature coefficient thermosensitive material, and the room temperature resistance R 25 and the thermosensitive constant B of the negative temperature coefficient thermosensitive material are within the above ranges, which is beneficial to improving the electrochemical performance of the secondary battery at low temperature and making the secondary battery have good normal temperature performance.

Description

Technical Field

[0001] This application relates to the field of lithium battery technology, and in particular to a positive electrode sheet, a secondary battery, a battery module, a battery pack, and an electrical device. Background Technology

[0002] Lithium-ion batteries possess advantages such as high energy density, high open-circuit voltage, low self-discharge rate, long cycle life, and good safety, and are widely used in various fields such as portable energy storage, electronic devices, and electric vehicles. However, this also places higher demands on the overall performance of lithium-ion batteries, such as maintaining good electrochemical performance at low temperatures (e.g., temperatures below or equal to 0°C).

[0003] However, at low temperatures, the diffusion ability of lithium ions between the positive and negative electrodes decreases, resulting in higher diffusion resistance and increased internal resistance of the lithium-ion battery. Simultaneously, the increased polarization of both the positive and negative electrode materials at low temperatures causes the lithium-ion battery to reach its discharge termination voltage prematurely, preventing some lithium ions embedded in the negative electrode from returning to the positive electrode. This repeated process further exacerbates the internal polarization of the lithium-ion battery, increasing internal losses and reducing its discharge capacity. Summary of the Invention

[0004] This application is made in view of the above-mentioned issues, and its purpose is to improve the electrochemical performance of secondary batteries at low temperatures.

[0005] To achieve the above objectives, this application provides a positive electrode sheet, a secondary battery, a battery module, a battery pack, and an electrical device.

[0006] A first aspect of this application provides a positive electrode, the positive electrode comprising a positive current collector, a positive electrode material layer, and a thermistor material layer located between the positive current collector and the positive electrode material layer, the thermistor material layer comprising a negative temperature coefficient thermistor material, the negative temperature coefficient thermistor material having a room temperature resistance R. 25 The resistance is 1KΩ-1000KΩ, preferably 1KΩ-100KΩ, and the thermistor constant B of the negative temperature coefficient thermistor material is 1000K-10000K, preferably 1000K-5000K. Therefore, this application achieves this by setting a thermistor material layer between the positive electrode current collector and the positive electrode material layer, the thermistor material layer comprising a negative temperature coefficient thermistor material, and adjusting the room temperature resistance R of the negative temperature coefficient thermistor material. 25 Having the thermistor constant B within the above range is beneficial for improving the electrochemical performance of secondary batteries at low temperatures and for giving secondary batteries good performance at room temperature.

[0007] In any embodiment, the negative temperature coefficient thermistor is selected from a composite metal oxide formed from a transition metal element of period IV. When the negative temperature coefficient thermistor includes the aforementioned composite metal oxide, the resulting secondary battery exhibits excellent low-temperature performance.

[0008] In any embodiment, the composite metal oxide is selected from Mn-Co-Ni-Cu composite metal oxides, and the composite metal oxide contains Fe. It has a low room temperature resistivity R. 25 The high thermistor constant B, along with good thermal stability and lower processing requirements, are beneficial for improving the performance of secondary batteries at low temperatures and enabling large-scale production.

[0009] In any embodiment, the volume average particle size Dv50 of the negative temperature coefficient thermistor is 0.1 μm-5 μm. By controlling the volume average particle size Dv50 of the negative temperature coefficient thermistor within the above range, it is beneficial to improve the low-temperature performance of the secondary battery and control the cost.

[0010] In any embodiment, based on the total mass of the thermistor material layer, the mass percentage of the negative temperature coefficient thermistor material is 80%-99%, preferably 90%-99%. By controlling the mass percentage of the negative temperature coefficient thermistor material within the above range, it is beneficial to improve the performance of the secondary battery at low temperatures.

[0011] In any embodiment, the thermosensitive material layer further includes a binder. Based on the mass of the thermosensitive material layer, the binder has a mass percentage content of 0.5%-10%, preferably 0.5%-2%. The binder includes at least one selected from polyacrylic acid, polyvinylidene fluoride, polyurethane, polycarbonate, epoxy resin, polyurethane, and acrylate. The aforementioned binder helps improve the stability of the thermosensitive material layer. Furthermore, by controlling the mass percentage content of the binder within the aforementioned range, it is beneficial to improve the performance of the secondary battery at low temperatures.

[0012] In any embodiment, the thermosensitive material layer further includes a conductive agent. Based on the mass of the thermosensitive material layer, the mass percentage of the conductive agent is 0.5%-10%, preferably 0.5%-5%. The conductive agent includes at least one of acetylene black, carbon fiber, carbon nanotubes, graphene, and conductive carbon black. The aforementioned conductive agent is beneficial for improving the conductivity of the thermosensitive material layer, resulting in good electrochemical performance of the secondary battery. Furthermore, by controlling the mass percentage of the conductive agent within the aforementioned range, it is beneficial for improving the performance of the secondary battery at low temperatures and ensuring good electrochemical performance.

[0013] In any embodiment, the thickness of the thermosensitive material layer is 1 μm-10 μm, preferably 3 μm-5 μm. Adjusting the thickness of the thermosensitive material layer within this range is beneficial for improving the performance of the secondary battery at low temperatures and for giving the secondary battery good electrochemical performance.

[0014] A second aspect of this application provides a secondary battery, including the positive electrode sheet of the first aspect of this application.

[0015] A third aspect of this application provides a battery module, including the secondary battery of the second aspect of this application.

[0016] A fourth aspect of this application provides a battery pack that includes the battery module of the third aspect of this application.

[0017] The fifth aspect of this application provides an electrical device including at least one selected from the second aspect of this application, the third aspect of this application, or the fourth aspect of this application.

[0018] The beneficial effects of this application are:

[0019] This application provides a positive electrode sheet, a secondary battery, a battery module, a battery pack, and an electrical device. The positive electrode sheet includes a positive electrode material layer, a positive electrode current collector, and a thermistor material layer located between the positive electrode current collector and the positive electrode material layer. The thermistor material layer includes a negative temperature coefficient thermistor material, and the room temperature resistance R of the negative temperature coefficient thermistor material is... 25 The resistance of the negative temperature coefficient (NTC) thermistor is 1KΩ-1000KΩ, preferably 1KΩ-100KΩ, and the thermistor constant B of the NTC thermistor is 1000K-10000K, preferably 1000K-5000K. The thermistor layer includes the aforementioned NTC thermistor. At low temperatures, the resistance of the NTC thermistor increases, causing the thermistor layer to heat up, thus enabling the secondary battery to self-heat at low temperatures. As the temperature of the secondary battery increases, the resistance of the NTC thermistor gradually decreases, achieving a balance between heat generation and heat loss through diffusion. This keeps the secondary battery temperature constant, improving its performance at low temperatures, such as rate capability and capacity. When the temperature rises to the normal operating temperature of the secondary battery, the resistance of the NTC thermistor can decrease to approximately 0KΩ, without affecting the normal operation of the secondary battery. This is achieved by adjusting the room temperature resistance R of the NTC thermistor. 25 Having the thermistor constant B within the above range is beneficial for improving the electrochemical performance of secondary batteries at low temperatures and for giving secondary batteries good performance at room temperature. Attached Figure Description

[0020] Figure 1 This is a cross-sectional structural diagram of the positive electrode sheet in one embodiment of this application.

[0021] Figure 2 This is a cross-sectional structural diagram of the positive electrode sheet in another embodiment of this application.

[0022] Figure 3 This is a graph showing the resistance of the negative temperature coefficient thermistor material in Embodiment 1-1 of this application as a function of temperature.

[0023] Figure 4 This is a schematic diagram of a secondary battery according to one embodiment of this application.

[0024] Figure 5 yes Figure 4 An exploded view of a secondary battery according to one embodiment of this application is shown.

[0025] Figure 6 This is a schematic diagram of a battery module according to one embodiment of this application.

[0026] Figure 7 This is a schematic diagram of a battery pack according to one embodiment of this application.

[0027] Figure 8 yes Figure 7 An exploded view of a battery pack according to one embodiment of this application is shown.

[0028] Figure 9 This is a schematic diagram of an electrical device that uses a secondary battery as a power source according to one embodiment of this application.

[0029] Explanation of reference numerals in the attached figures:

[0030] 1 Battery pack; 2 Upper casing; 3 Lower casing; 31 Positive current collector; 32 Thermistor material layer; 33 Positive electrode material layer; 4 Battery module; 5 Secondary battery; 51 Housing; 52 Electrode assembly; 53 Cover plate. Detailed Implementation

[0031] The following detailed description, with appropriate reference to the accompanying drawings, specifically discloses embodiments of the positive electrode, secondary battery, battery module, battery pack, and electrical device of this application. However, unnecessary detailed descriptions 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.

[0032] 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.

[0033] Unless otherwise specified, all embodiments and optional embodiments of this application can be combined to form new technical solutions.

[0034] Unless otherwise specified, all technical features and optional technical features of this application may be combined to form new technical solutions.

[0035] 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.

[0036] Unless otherwise specified, the terms "comprising" and "including" as used in this application can be open-ended or closed-ended. For example, "comprising" and "including" can mean that other components not listed may also be included, or that only the listed components may be included.

[0037] Unless otherwise specified, the term "or" is inclusive in this application. For example, the phrase "A or B" means "A, B, or both A and B". More specifically, the condition "A or B" is satisfied by any of the following conditions: A is true (or exists) and B is false (or does not exist); A is false (or does not exist) and B is true (or exists); or both A and B are true (or exist).

[0038] During its research on secondary batteries, the applicant discovered that the diffusion ability of lithium ions between the positive and negative electrodes decreases at low temperatures, resulting in higher diffusion resistance and increased internal resistance of the lithium-ion battery. Simultaneously, the increased polarization of both the positive and negative electrode materials at low temperatures causes the lithium-ion battery to reach its discharge termination voltage prematurely, preventing some lithium ions embedded in the negative electrode from returning to the positive electrode. This repeated process further exacerbates the internal polarization of the lithium-ion battery, increasing internal losses and reducing discharge capacity. To improve the electrochemical performance of secondary batteries at low temperatures, this application provides a positive electrode sheet. When applied to secondary batteries, this sheet exhibits excellent electrochemical performance at low temperatures, such as lower impedance and higher discharge capacity.

[0039] In one embodiment of this application, a positive electrode is provided, comprising a positive current collector, a positive electrode material layer, and a thermistor material layer located between the positive current collector and the positive electrode material layer. The thermistor material layer comprises a negative temperature coefficient thermistor material, and the room temperature resistance R of the negative temperature coefficient thermistor material is... 25 The resistance is 1KΩ-1000KΩ, preferably 1KΩ-100KΩ, and the thermistor constant B of the negative temperature coefficient thermistor material is 1000K-10000K, preferably 1000K-5000K.

[0040] Although the mechanism is not yet clear, the applicant unexpectedly discovered that by placing a thermistor layer between the positive electrode current collector and the positive electrode material layer, including the aforementioned negative temperature coefficient (NTC) thermistor, the resistance of the NTC thermistor increases at low temperatures, causing the thermistor layer to heat up, thus enabling the secondary battery to self-heat at low temperatures. As the temperature of the secondary battery increases, the resistance of the NTC thermistor gradually decreases, achieving a balance between the heat generated by heating and the heat lost through diffusion, keeping the temperature of the secondary battery constant and improving its performance at low temperatures, such as rate performance and capacity. When the temperature rises to the normal operating temperature of the secondary battery (e.g., 25°C), the resistance of the NTC thermistor is low and will not affect the normal operation of the secondary battery. Specifically, the room temperature resistance R of the NTC thermistor... 25 The thermistor constant B is an important parameter affecting the negative temperature coefficient thermistor material. When the room temperature resistance R 25When the resistance is too small (e.g., less than 1 kΩ), the fabrication of negative temperature coefficient thermistors becomes too difficult, increasing production costs; when the room temperature resistance R... 25 When the thermistor constant B is too large (e.g., greater than 1000 KΩ), it will affect the performance of the secondary battery at room temperature, such as its rate performance. When the thermistor constant B is too small (e.g., less than 1000 K), the negative temperature coefficient thermistor material is not sensitive to temperature changes significantly and cannot improve the low-temperature performance of the secondary battery in a timely manner; when the thermistor constant B is too large (e.g., greater than 10000 K), the preparation of the negative temperature coefficient thermistor material becomes too difficult, increasing production costs. This can be addressed by adjusting the room temperature resistance R of the negative temperature coefficient thermistor material. 25 Having the thermistor constant B within the above range is beneficial for improving the electrochemical performance of secondary batteries at low temperatures and for giving secondary batteries good performance at room temperature.

[0041] Among them, room temperature resistance R 25 This refers to the resistance value of a negative temperature coefficient thermistor material measured at room temperature (25℃). The thermistor constant B is a physical quantity that describes how quickly the resistance of a negative temperature coefficient thermistor material changes with temperature, measured in K, and can be calculated using the following formula:

[0042]

[0043] Where T1 and T2 are absolute temperatures, T1 is 298.15K (25℃) and T2 is 323.15K (50℃), R1 is the resistance at temperature T1 and R2 is the resistance at temperature T2.

[0044] For example, the positive current collector has two surfaces opposite each other in its own thickness direction, and a thermistor material layer and a positive electrode material layer are sequentially disposed on either or both of the two opposite surfaces of the positive current collector. Figure 1 As shown, a thermistor material layer 32 and a positive electrode material layer 33 are disposed on one surface of the positive electrode current collector 31, with the thermistor material layer 32 located between the positive electrode current collector 31 and the positive electrode material layer 33. Figure 2 As shown, a thermistor material layer 32 and a positive electrode material layer 33 are disposed on both surfaces of the positive electrode current collector 31.

[0045] In some embodiments, the negative temperature coefficient (NTC) thermistor material is selected from composite metal oxides formed from transition metal elements of period IV. A NTC thermistor material refers to a thermistor exhibiting a negative temperature coefficient phenomenon where its resistance decreases exponentially with increasing temperature. This material is a semiconductor ceramic produced by thoroughly mixing, molding, and sintering two or more metal oxides such as manganese, copper, silicon, cobalt, iron, nickel, and zinc. It can be used to fabricate thermistors with a negative temperature coefficient, the resistivity of which varies with the material composition ratio, sintering atmosphere, sintering temperature, and structural state. NTC thermistors also include non-oxide thermistor materials such as silicon carbide, tin selenide, and tantalum nitride. This application does not impose any particular limitation on the NTC thermistor material, as long as its room temperature resistance R... 25 The thermistor constant B only needs to meet the requirements of this application.

[0046] In some embodiments, the composite metal oxide is selected from Mn-Co-Ni-Cu composite metal oxides, and the composite metal oxide contains Fe. Based on the mass of the composite metal oxide, the mass percentage of Fe is typically 2.5%-7.0%. The aforementioned Fe-containing Mn-Co-Ni-Cu composite metal oxide has a low room temperature resistivity R0. 25 The high thermistor constant B, along with good thermal stability and lower processing requirements, are beneficial for improving the performance of secondary batteries at low temperatures and enabling large-scale production.

[0047] In some embodiments, the volume average particle size (Dv50) of the negative temperature coefficient (NTC) thermistor is 0.1 μm to 5 μm. When the NTC thermistor's volume average particle size (Dv50) is too small (e.g., less than 0.1 μm), the processing difficulty increases, and the cost rises. When the NTC thermistor's volume average particle size (Dv50) is too large (e.g., greater than 5 μm), it affects the uniformity of the thermistor layer thickness and poses a risk of NTC thermistor shedding during later use. By controlling the NTC thermistor's volume average particle size (Dv50) within the above-mentioned range, it is beneficial to improve the low-temperature performance of the secondary battery and control the cost.

[0048] In some embodiments, the mass percentage of the negative temperature coefficient (NTC) thermistor material is 80%-99%, preferably 90%-99%, based on the total mass of the thermistor material layer. When the mass percentage of the NTC thermistor material is too low (e.g., below 80%), the thermistor material layer cannot effectively improve the performance of the secondary battery at low temperatures. When the mass percentage of the NTC thermistor material is too high (e.g., above 99%), the structural stability of the thermistor material layer decreases, which also affects the performance of the secondary battery at low temperatures. By controlling the mass percentage of the NTC thermistor material within the above-mentioned range, it is beneficial to improve the performance of the secondary battery at low temperatures.

[0049] In some embodiments, the thermosensitive material layer further includes a binder. Based on the mass of the thermosensitive material layer, the binder's mass percentage is 0.5%-10%, preferably 0.5%-2%. The binder includes at least one of polyacrylic acid, polyvinylidene fluoride, polyurethane, polycarbonate, epoxy resin, polyurethane, and acrylate. When the binder's mass percentage is too low (e.g., below 0.5%), the adhesion between the particles of the negative temperature coefficient thermosensitive material in the thermosensitive material layer is low, leading to reduced structural stability of the thermosensitive material layer. Simultaneously, it also affects the adhesion between the thermosensitive material layer and the positive current collector and the positive electrode material layer, posing a risk of the thermosensitive material layer detaching during later use, both of which affect the performance of the secondary battery at low temperatures. When the binder's mass percentage is too high (e.g., above 10%), it affects the performance of the negative temperature coefficient thermosensitive material. The aforementioned binder is beneficial for improving the stability of the thermosensitive material layer. Furthermore, by controlling the binder's mass percentage within the aforementioned range, it is beneficial for improving the performance of the secondary battery at low temperatures.

[0050] In some embodiments, the thermistor layer further includes a conductive agent. Based on the mass of the thermistor layer, the mass percentage of the conductive agent is 0.5%-10%, preferably 0.5%-5%. The conductive agent includes at least one of acetylene black, carbon fiber, carbon nanotubes, graphene, and conductive carbon black. When the mass percentage of the conductive agent is too low (e.g., below 0.5%), the conductivity of the thermistor layer decreases, affecting the electrochemical performance of the secondary battery, such as rate performance. When the mass percentage of the conductive agent is too high (e.g., above 10%), it affects the performance of the negative temperature coefficient thermistor. The aforementioned conductive agent is beneficial for improving the conductivity of the thermistor layer, resulting in good electrochemical performance of the secondary battery. Furthermore, by controlling the mass percentage of the conductive agent within the aforementioned range, it is beneficial for improving the performance of the secondary battery at low temperatures and ensuring good electrochemical performance.

[0051] In some embodiments, the thickness of the thermistor layer is 1 μm-10 μm, preferably 3 μm-5 μm. When the thickness of the thermistor layer is too small (e.g., less than 1 μm), the improvement on the low-temperature performance of the secondary battery is not significant. When the thickness of the thermistor layer is too large (e.g., greater than 10 μm), it affects the transport of lithium ions and electrons, thereby affecting the electrochemical performance of the secondary battery. In addition, an excessively large thickness of the thermistor layer also affects the volumetric energy density of the secondary battery. By controlling the thickness of the thermistor layer within the above-mentioned range, it is beneficial to improve the performance of the secondary battery at low temperatures and to enable the secondary battery to have good electrochemical performance.

[0052] Dv50 in this application is a parameter well-known in the art and can be determined using a laser particle size analyzer (such as a Malvern Master Size 3000) with reference to the national standard GB / T 19077-2016 (Laser Diffraction Method for Particle Size Distribution). Dv50 refers to the particle size corresponding to a cumulative volume distribution percentage of 50% for the measured material.

[0053] In addition, the secondary battery, battery module, battery pack and power device of this application will be described below with appropriate reference to the accompanying drawings.

[0054] In one embodiment of this application, a secondary battery is provided, which includes the positive electrode sheet described in any of the above embodiments.

[0055] 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.

[0056] [Positive electrode plate]

[0057] 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.).

[0058] In some embodiments, the cathode material may be a cathode material known in the art for use in batteries. As an example, the cathode 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 cathode materials may also be used. These cathode 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 Co 1 / 3 Mn1 / 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.

[0059] In some embodiments, the positive electrode material layer may optionally include a positive electrode binder. As an example, the positive electrode binder may include at least one of polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), PVDF-tetrafluoroethylene-propylene terpolymer, PVDF-hexafluoropropylene-tetrafluoroethylene terpolymer, tetrafluoroethylene-hexafluoropropylene copolymer, and fluorinated acrylate resin.

[0060] In some embodiments, the positive electrode material layer may optionally include a positive electrode conductive agent. As an example, the positive electrode 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.

[0061] In some embodiments, the positive electrode sheet can be prepared by dispersing the components used to prepare the thermistor layer, such as negative temperature coefficient thermistors, binders, and conductive agents, in a solvent (e.g., N-methylpyrrolidone), forming a thermistor layer slurry. Then, the components used to prepare the positive electrode layer, such as positive electrode material, positive electrode conductive agent, positive electrode binder, and any other components, are dispersed in a solvent (e.g., N-methylpyrrolidone), forming a positive electrode slurry. The thermistor layer slurry is coated onto a positive electrode current collector, dried, and then coated with another positive electrode slurry. After drying, cold pressing, and other processes, the positive electrode sheet is obtained.

[0062] [Negative electrode plate]

[0063] The negative electrode sheet includes a negative current collector and a negative electrode material layer disposed on at least one surface of the negative current collector, the negative electrode material layer including a negative electrode material.

[0064] As an example, the negative electrode current collector has two surfaces opposite each other in its own thickness direction, and the negative electrode material layer is disposed on either or both of the two opposite surfaces of the negative electrode current collector.

[0065] 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.).

[0066] In some embodiments, the negative electrode material may be a negative electrode material known in the art for use in batteries. As an example, the negative electrode 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 battery negative electrode materials may also be used. These negative electrode materials may be used alone or in combination of two or more.

[0067] In some embodiments, the negative electrode material layer may optionally include a negative electrode binder. The negative electrode 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).

[0068] In some embodiments, the negative electrode material layer may optionally include a negative electrode conductive agent. The negative electrode 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.

[0069] In some embodiments, the negative electrode material layer may optionally include other additives, such as thickeners (e.g., sodium carboxymethyl cellulose (CMC-Na)).

[0070] In some embodiments, the negative electrode sheet can be prepared by dispersing the above-mentioned components for preparing the negative electrode sheet, such as negative electrode material, negative electrode conductive agent, negative electrode 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.

[0071] [Electrolytes]

[0072] The electrolyte acts as a conductor of ions between the positive and negative electrodes. This application does not impose specific limitations on the type of electrolyte; it can be selected according to requirements. For example, the electrolyte can be liquid.

[0073] In some embodiments, the electrolyte is an electrolyte solution. The electrolyte solution includes an electrolyte salt and a solvent.

[0074] 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 difluorooxalate borate, lithium dioxalate borate, lithium difluorodioxalate phosphate, and lithium tetrafluorooxalate phosphate.

[0075] 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.

[0076] 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.

[0077] [Isolation membrane]

[0078] 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.

[0079] 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.

[0080] In some implementations, the positive electrode, negative electrode, and separator can be fabricated into an electrode assembly using a winding or stacking process.

[0081] In some embodiments, the secondary battery may include an outer packaging. This outer packaging may be used to encapsulate the electrode assembly and electrolyte described above.

[0082] 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.

[0083] 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 4 This is an example of a square-structured secondary battery 5.

[0084] In some implementations, refer to Figure 5 The outer packaging may include a housing 51 and a cover 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 cover 53 can be placed over the opening to close the receiving cavity. A positive electrode, a negative electrode, and a separator can be formed into an electrode assembly 52 using a winding or 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.

[0085] 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.

[0086] Figure 6 This is battery module 4, used as an example. (See reference...) Figure 6 In battery module 4, multiple secondary batteries 5 can be arranged sequentially along the length of battery module 4. Of course, they can also be arranged in any other manner. Furthermore, these multiple secondary batteries 5 can be fixed in place using fasteners.

[0087] Optionally, the battery module 4 may also include a housing with a receiving space in which a plurality of secondary batteries 5 are received.

[0088] In some embodiments, the battery modules described above can also be assembled into a battery pack, and the number of battery modules contained in the battery pack 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 pack.

[0089] Figure 7 and Figure 8 This is battery pack 1 as an example. (See reference...) Figure 7 and Figure 8 The battery pack 1 may include a battery box and multiple battery modules 4 disposed within the battery box. The battery box includes an upper body 2 and a lower body 3, with the upper body 2 covering the lower body 3 to form a closed space for accommodating the battery modules 4. The multiple battery modules 4 can be arranged in any manner within the battery box.

[0090] In addition, this application also provides an electrical device, which includes at least one of the secondary battery, battery module, or battery pack provided in this application. The secondary battery, battery module, or battery pack 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.

[0091] As the electrical device, a secondary battery, battery module, or battery pack can be selected according to its usage requirements.

[0092] Figure 9This is an example of an electrical device. The device could be a pure electric vehicle, a hybrid electric vehicle, or a plug-in hybrid electric vehicle. To meet the high power and high energy density requirements of the secondary battery for this device, a battery pack or battery module can be used.

[0093] Another example device could be a mobile phone, tablet, or laptop. These devices typically require a slim and lightweight design and can use a rechargeable battery as their power source.

[0094] Example

[0095] 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.

[0096] Example 1-1

[0097] <Preparation of the positive electrode>

[0098] Lithium cobalt oxide, a positive electrode active material, carbon black, a positive electrode conductive agent, and polyvinylidene fluoride, a positive electrode binder, were mixed in a mass ratio of 95:2.5:2.5. Then, N-methylpyrrolidone was added as a solvent, and the mixture was stirred under vacuum until the system was homogeneous, resulting in a positive electrode slurry with a solid content of 70 wt%.

[0099] A negative temperature coefficient (NTC) thermistor, polyvinylidene fluoride (PVDF) binder, and conductive carbon black conductive agent were mixed in a mass ratio of 95:3:2. N-methylpyrrolidone was then added as a solvent, and the mixture was stirred under vacuum until homogeneous, yielding a thermistor slurry with a solid content of 60 wt%. The NTC thermistor was purchased from Aisheng Sensors Co., Ltd., and is a composite oxide ceramic of MnO, Fe2O3, NiO, CuO, and CoO, with a room temperature resistance R0. 25 The resistance is 10KΩ, the thermistor constant B is 3500K, and the Dv50 is 1μm, and its resistance changes with temperature as follows: Figure 3 As shown.

[0100] A thermistor material slurry was uniformly coated onto one surface of a 13 μm thick positive electrode current collector aluminum foil and dried at 90°C. The same process was repeated on the other surface of the positive electrode current collector. After cold pressing, a positive electrode sheet was obtained, which was then subjected to tab forming and slitting processes for later use. The thickness of the thermistor material layer coated on one side was 5 μm, and the thickness of the positive electrode material layer was 110 μm.

[0101] <Preparation of Negative Electrode Sheets>

[0102] Artificial graphite (anode material), conductive carbon black (anode conductive agent), styrene-butadiene rubber (anode binder), and sodium carboxymethyl cellulose (thickener) were mixed in a mass ratio of 96:0.9:1.6:1.5. Deionized water was added as a solvent, and the mixture was stirred under vacuum until homogeneous, yielding a negative electrode slurry with a solid content of 60 wt%. The negative electrode slurry was uniformly coated onto one surface of an 8 μm thick copper foil current collector and dried at 110 °C. The same operation was repeated on the other surface of the current collector. After cold pressing, a negative electrode sheet with a single-sided coated negative electrode material layer thickness of 110 μm was obtained. This sheet was then subjected to tab forming and slitting processes for later use.

[0103] <Preparation of Electrolyte>

[0104] In an environment with a water content of less than 10 ppm, ethylene carbonate, methyl ethyl carbonate, and diethyl carbonate were mixed in a volume ratio of 1:1:1 to obtain an electrolyte solvent. Then, lithium salt LiPF6 was dissolved in the mixed solvent to prepare an electrolyte with a lithium salt concentration of 1 mol / L.

[0105] <Preparation of the separating membrane>

[0106] A polyethylene film with a thickness of 14μm was selected as the separator. Before use, it was cut to the appropriate size according to the size of the positive and negative electrode plates.

[0107] <Preparation of Lithium-ion Batteries>

[0108] The positive electrode, separator, and negative electrode are stacked in sequence, with the separator acting as a separator between the positive and negative electrodes. The electrode assembly is then wound up. The electrode assembly is placed in an outer packaging shell, dried, and then injected with electrolyte. After vacuum sealing, settling, formation, and shaping, a lithium-ion battery is obtained.

[0109] Examples 1-2 to Examples 1-7

[0110] In addition to adjusting the room temperature resistance R of the negative temperature coefficient thermistor according to Table 4 25 Except for the thermistor constant B, the rest are the same as in Example 1-1.

[0111] Examples 2-1 to 2-3

[0112] Except for adjusting the volume average particle size Dv50 of the negative temperature coefficient thermistor and the thickness of the thermistor layer according to Table 5, the rest is the same as in Example 1-1.

[0113] Examples 3-1 to 3-4

[0114] Except for adjusting the mass percentage of the negative temperature coefficient thermosensitive material, the mass percentage of the binder, and the mass percentage of the conductive agent according to Table 6, the rest are the same as in Examples 1-1.

[0115] Examples 4-1 to 4-6

[0116] Except for adjusting the type of adhesive and conductive agent according to Table 7, the rest is the same as in Example 1-1.

[0117] Examples 5-1 to 5-3

[0118] Except for adjusting the thickness of the thermosensitive material layer according to Table 8, the rest is the same as in Example 1-1.

[0119] Comparative Example 1

[0120] Except for not providing a thermistor material layer in the positive electrode, it is the same as in Example 1-1.

[0121] Comparative Example 2 and Comparative Example 3

[0122] In addition to adjusting the room temperature resistance R of the negative temperature coefficient thermistor according to Table 4 25 Except for the thermistor constant B, the rest are the same as in Example 1-1.

[0123] The lithium-ion batteries obtained in the above embodiments and comparative examples were subjected to the following performance tests. The relevant preparation parameters and test results are shown in Tables 4 to 8.

[0124] (1) Discharge capacity test

[0125] The lithium-ion battery was fully charged to 3.65V, and then placed in a low-temperature chamber at -40℃ for 5 hours to allow the battery temperature to match the ambient temperature. Then, it was discharged at a constant current of 0.2C to 2.0V. The discharge capacity was recorded as the -40℃ discharge capacity.

[0126] (2) DC Impedance (DCR) Test

[0127] First, test the actual capacity Cn of the lithium-ion battery according to the steps shown in Table 1:

[0128] Table 1

[0129]

[0130] Then, test the DCR at 25°C according to the steps described in Table 2:

[0131] Table 2

[0132]

[0133]

[0134] Then test the DCR at -25℃ according to the steps described in Table 3:

[0135] Table 3

[0136]

[0137]

[0138] Table 4

[0139]

[0140] Note: " / " in Table 4 indicates that the corresponding parameter or substance does not exist.

[0141] As can be seen from Examples 1-1 to 1-7 and Comparative Example 1, when the positive electrode has a thermistor material layer, the lithium-ion battery has a higher discharge capacity and a smaller DCR at low temperatures, i.e., better low-temperature performance. Meanwhile, the DCR at room temperature (25°C) is not significantly different from that of Comparative Example 1, indicating that the thermistor material layer has virtually no impact on the performance of the lithium-ion battery at room temperature. As can be seen from Examples 1-1 to 1-7, Comparative Examples 2 and 3, when the negative temperature coefficient thermistor material has a room temperature resistance R... 25 With the thermistor constant B within the range of this application, the resulting lithium-ion battery exhibits better low-temperature performance.

[0142] Table 5

[0143]

[0144] The volume average particle size (Dv50) of negative temperature coefficient (NTC) thermistors typically affects the performance of lithium-ion batteries. As seen in Examples 1-1, 2-1, and 2-3, when the NTC thermistor's volume average particle size (Dv50) is too large, the thickness of the thermistor layer also increases, affecting the impedance of the lithium-ion battery at room temperature. When the NTC thermistor's volume average particle size (Dv50) is within the range specified in this application, it not only improves the performance of lithium-ion batteries at low temperatures but also exhibits good performance at room temperature.

[0145] Table 6

[0146]

[0147] The mass percentage of negative temperature coefficient thermistor, binder, and conductive agent in the thermistor layer usually affects the performance of lithium-ion batteries. As can be seen from Examples 1-1, 3-1 to 3-4, when the mass percentages of negative temperature coefficient thermistor, binder, and conductive agent are within the range of this application, the resulting lithium-ion battery has good low-temperature performance and room-temperature performance.

[0148] Table 7

[0149]

[0150] Note: The diameter of the carbon fiber in Table 7 is 7 μm; the aspect ratio of the carbon nanotube is 1250, the diameter of the tube is 20 nm, and the length is 25 μm.

[0151] The type of binder and conductive agent in the thermosensitive material layer usually affects the performance of lithium-ion batteries. As can be seen from Examples 1-1, 4-1 to 4-6, the lithium-ion batteries obtained by selecting binders and conductive agents within the scope of this application have good low-temperature performance and room-temperature performance.

[0152] Table 8

[0153]

[0154]

[0155] The thickness of the thermistor layer typically affects the performance of lithium-ion batteries. As can be seen from Examples 1-1, 5-1 to 5-3, an excessively thick thermistor layer can negatively impact the impedance of the lithium-ion battery at room temperature. When the thickness of the thermistor layer is within the range specified in this application, it can not only improve the performance of the lithium-ion battery at low temperatures but also maintain good performance at room temperature.

[0156] It should be noted that this application is not limited to the above-described embodiments. The above embodiments are merely examples, and any embodiments with the same structure and effect as the technical concept within the scope of this application are included in the technical scope of this application. Furthermore, various modifications that can be conceived by those skilled in the art to the embodiments, and other ways of constructing by combining some of the constituent elements of the embodiments, without departing from the spirit of this application, are also included in the scope of this application.

Claims

1. A positive electrode plate, characterized in that, The positive electrode includes a positive current collector, a positive electrode material layer, and a thermistor material layer located between the positive current collector and the positive electrode material layer. The thermistor material layer includes a negative temperature coefficient thermistor material, and the room temperature resistance R of the negative temperature coefficient thermistor material is... 25 The resistance is 1KΩ-1000KΩ, and the thermistor constant B of the negative temperature coefficient thermistor material is 1000K-10000K.

2. The positive electrode sheet according to claim 1, characterized in that, The room temperature resistance R of the negative temperature coefficient thermistor material 25 The resistance is 1KΩ-100KΩ, and the thermistor constant B of the negative temperature coefficient thermistor material is 1000K-5000K.

3. The positive electrode sheet according to any one of claims 1-2, characterized in that, The negative temperature coefficient thermistor is selected from a composite metal oxide formed by transition metal elements of period IV.

4. The positive electrode sheet according to claim 3, characterized in that, The composite metal oxide is selected from Mn-Co-Ni-Cu composite metal oxides, and the composite metal oxide contains Fe element.

5. The positive electrode sheet according to any one of claims 1-2, characterized in that, The volume average particle size Dv50 of the negative temperature coefficient thermistor is 0.1μm-5μm.

6. The positive electrode sheet according to any one of claims 1-2, characterized in that, Based on the total mass of the thermosensitive material layer, the mass percentage of the negative temperature coefficient thermosensitive material is 80%-99%.

7. The positive electrode sheet according to any one of claims 1-2, characterized in that, Based on the total mass of the thermosensitive material layer, the mass percentage of the negative temperature coefficient thermosensitive material is 90%-99%.

8. The positive electrode sheet according to any one of claims 1-2, characterized in that, The thermosensitive material layer further includes an adhesive, and the adhesive has a mass percentage content of 0.5%-10% based on the mass of the thermosensitive material layer. The adhesive includes at least one of polyacrylic acid, polyvinylidene fluoride, polyurethane, polycarbonate, and epoxy resin.

9. The positive electrode sheet according to claim 8, characterized in that, The adhesive has a mass percentage content of 0.5%-2%.

10. The positive electrode sheet according to any one of claims 1-2, characterized in that, The thermosensitive material layer further includes a conductive agent. Based on the mass of the thermosensitive material layer, the mass percentage of the conductive agent is 0.5%-10%, and the conductive agent includes at least one of carbon fiber, carbon nanotube, graphene, and conductive carbon black.

11. The positive electrode sheet according to claim 10, characterized in that, The conductive agent has a mass percentage content of 0.5%-5%.

12. The positive electrode sheet according to any one of claims 1-2, characterized in that, The thickness of the thermosensitive material layer is 1μm-10μm.

13. The positive electrode sheet according to any one of claims 1-2, characterized in that, The thickness of the thermosensitive material layer is 3μm-5μm.

14. A secondary battery, characterized in that, The secondary battery includes the positive electrode sheet according to any one of claims 1-13.

15. A battery module, characterized in that, The battery module includes the secondary battery as described in claim 14.

16. A battery pack, characterized in that, The battery pack includes the battery module of claim 15.

17. An electrical device, characterized in that, The electrical device includes any one selected from the secondary battery of claim 14, the battery module of claim 15, or the battery pack of claim 16.

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