Battery pack and powered device

Abstract

The application provides a battery pack and an electric device. The battery pack comprises a battery pack box body; and a first battery cell and a second battery cell accommodated in the battery pack box body, wherein the first battery cell is arranged at a position of the battery pack box body which is more easily subjected to heat exchange with the environment compared with the second battery cell, the capacity of the first battery cell is C1, the direct current impedance is R1, X1=C1*R1, the capacity of the second battery cell is C2, the direct current impedance is R2, X2=C2*R2, and X1 and X2 satisfy 1.1≤X1 / X2≤2.0. Thus, the low-temperature discharge capacity can be improved.

Description

Technical Field

[0001] This application relates to the field of batteries, and more particularly to a battery pack capable of improving low-temperature discharge capability and an electrical device including the battery pack. Background Technology

[0002] In recent years, with the continuous development of secondary battery technologies such as lithium-ion batteries, secondary batteries have been widely used in energy storage power systems such as hydropower, thermal power, wind power and solar power plants, as well as in many fields such as power tools, electric bicycles, electric motorcycles, electric cars, military equipment, and aerospace.

[0003] Lithium-ion batteries are greatly affected by temperature, especially at low temperatures, where individual battery cells become severely polarized, causing the discharge process to reach the termination voltage prematurely. This leads to problems such as low discharge energy and poor power performance at low temperatures, which urgently need to be addressed. As the battery pack capacity increases, the temperature difference between the internal and external areas of the battery pack further widens, resulting in increased power waste and affecting the user experience.

[0004] Existing battery packs can improve low-temperature performance by using external thermistors, but this is costly, takes up battery pack space, and reduces energy density. Other methods improve the overall low-temperature performance of the battery pack by placing low-temperature resistant batteries on the outside, but these usually use differentiated chemical systems, which leads to complex control by the battery management system (BMS). Moreover, low-temperature resistant batteries often have poor thermal stability, which deteriorates the overall collision safety of the battery pack. Summary of the Invention

[0005] This application is made in view of the above-mentioned technical problems, and its purpose is to provide a battery pack that can overcome the bottleneck effect of the battery pack and improve the low-temperature discharge capability, and an electrical device including the battery pack.

[0006] To achieve the above objectives, a first aspect of this application provides a battery pack, comprising: a battery pack housing; and a first battery cell and a second battery cell housed within the battery pack housing. Compared to the second battery cell, the first battery cell is disposed in a position within the battery pack housing where heat exchange with the environment is more likely to occur. Let the capacity of the first battery cell be C1, its DC resistance be R1, and X1 = C1 * R1. Let the capacity of the second battery cell be C2, its DC resistance be R2, and X2 = C2 * R2. X1 and X2 satisfy: 1.1 ≤ X1 / X2 ≤ 2.0.

[0007] Therefore, by placing the first battery cell with high impedance R1 and high capacity C1 in a position where it is easier to exchange heat with the environment, this application can overcome the battery pack bottleneck effect and improve the low-temperature discharge capability.

[0008] In any embodiment, the DC impedance R1 of the first battery cell and the DC impedance R2 of the second battery cell satisfy the condition: 1.0 < R1 / R2 ≤ 1.5. Therefore, by increasing the impedance, the heat generation of the first battery cell during discharge is increased, and the overall polarization of the battery cell is reduced, thereby improving the discharge capacity.

[0009] In any embodiment, the capacity C1 of the first battery cell and the capacity C2 of the second battery cell satisfy the following: when 1.0 < R1 / R2 ≤ 1.2, 1.00 < C1 / C2 ≤ 1.15; when 1.2 < R1 / R2 ≤ 1.5, 1.15 < C1 / C2 ≤ 1.30. Therefore, by ensuring that the capacity ratio and impedance ratio of the first and second battery cells are within the aforementioned ranges, the low-temperature discharge capability can be further improved.

[0010] In any embodiment, the specific heat capacity β1 of the first battery cell and the specific heat capacity β2 of the second battery cell satisfy: 0.10 ≤ β1 / β2 ≤ 0.99, optionally, 0.3 ≤ β1 / β2 ≤ 0.95. Therefore, the first battery cell has a low specific heat capacity, making it easier to achieve temperature increases under heat accumulation conditions, thus further improving low-temperature discharge capability.

[0011] In any embodiment, the first battery cell and the second battery cell are connected in series, parallel, or a combination thereof. This allows for the achievement of larger capacity or power.

[0012] In any embodiment, the first battery cell and the second battery cell are disposed within the battery pack housing; both the first battery cell and the second battery cell include electrode terminals, which face the top or bottom wall of the battery pack housing; when viewed from above, the first battery cell surrounds the second battery cell in a surrounding arrangement. This further improves the low-temperature discharge capability.

[0013] In any embodiment, the first battery cell is disposed close to the side wall of the battery pack housing. This further improves the low-temperature discharge capability.

[0014] In any embodiment, the first battery cell and the second battery cell are disposed within the battery pack housing; both the first battery cell and the second battery cell include electrode terminals facing the side wall of the battery pack housing; at least a portion of the first battery cell is disposed on the bottom wall of the battery pack housing. This further improves the low-temperature discharge capability.

[0015] In any embodiment, the first battery cell is disposed close to the side wall of the battery pack housing. This further improves the low-temperature discharge capability.

[0016] In any embodiment, the first and second battery cells are battery cells with the same chemical system. This allows for easy adjustment of the DC impedance and capacity of the battery cells.

[0017] A second aspect of this application provides an electrical device that includes the battery pack of the first aspect of this application.

[0018] Therefore, the electrical device of the second aspect of this application can improve the low-temperature discharge capability.

[0019] Invention Effects

[0020] By employing this invention, the first battery cell with high impedance R1 and high capacity C1 is positioned in a location where heat exchange with the environment is more likely to occur, thereby providing a battery pack that overcomes the battery pack bottleneck effect and improves low-temperature discharge capability, as well as an electrical device including the battery pack. Attached Figure Description

[0021] Figure 1 This is an exploded view of the overall structure of the battery pack according to one embodiment of this application.

[0022] Figure 2 yes Figure 1 The diagram shown is a top view of the battery pack according to one embodiment of this application after removing the casing.

[0023] Figure 3 This is an exploded view of a battery cell (secondary battery) according to one embodiment of this application.

[0024] Figure 4 This is an exploded view of the overall structure of the battery pack according to another embodiment of this application.

[0025] Figure 5 This is an exploded view showing the overall structure of the battery pack according to another embodiment of this application.

[0026] Figure 6 This is a schematic diagram of an electrical device that uses a battery pack according to an embodiment of this application as a power source.

[0027] Explanation of reference numerals in the attached figures

[0028] 1 Battery pack; 20 Battery box; 21 Upper box; 22 Lower box; 10 Unit structure; 11 First battery cell; 12 Second battery cell; 31 Housing; 32 End cap; 33 Electrode assembly; 34 Electrode terminal. Detailed Implementation

[0029] The following detailed description, with appropriate reference to the accompanying drawings, specifically discloses embodiments of the battery pack and power-consuming 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.

[0030] 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 ​​1 and 2 are listed, and maximum range values ​​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" means that all real numbers between "0-5" have been listed herein; "0-5" is merely a shortened representation of these numerical combinations. Furthermore, when a parameter is described as an integer greater than or equal to 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.

[0031] Unless otherwise specified, all embodiments and optional embodiments of this application can be combined to form new technical solutions.

[0032] Unless otherwise specified, all technical features and optional technical features of this application may be combined to form new technical solutions.

[0033] Unless otherwise specified, all steps of 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.

[0034] 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.

[0035] 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).

[0036] Currently, from a market development perspective, the application of power batteries is becoming increasingly widespread. Power batteries are not only used in energy storage power systems such as hydropower, thermal power, wind power, and solar power plants, but also widely used in electric vehicles such as electric bicycles, electric motorcycles, and electric cars, as well as in military equipment and aerospace, among other fields. With the continuous expansion of the application areas of power batteries, the market demand is also constantly increasing.

[0037] The inventors of this application have noticed that in a battery pack composed of secondary battery cells, because the same battery cells are arranged closely together, in a low-temperature environment, the battery cells in positions that are easily exposed to heat exchange with the outside world reach their termination voltage prematurely due to the low temperature, causing the entire battery pack to stop discharging (i.e., the battery pack bottleneck effect).

[0038] Therefore, the inventors of this application conceived of placing battery cells with high impedance R1 and high capacity C1 in a location where they are more likely to exchange heat with the environment, thereby overcoming the bottleneck effect of the battery pack and improving the low-temperature discharge capability.

[0039] Battery pack

[0040] Figure 1 This is an exploded view of the overall structure of the battery pack according to one embodiment of this application. Figure 2 yes Figure 1 The diagram shown is a top view of the battery pack according to one embodiment of this application after removing the casing. Figure 3 This is an exploded view of a battery cell (secondary battery) according to one embodiment of this application.

[0041] The battery pack 1 of this application, such as Figure 1 As shown, the battery pack 1 may include a battery pack housing 20 and a plurality of battery cells 11, 12 disposed in the battery pack housing 20. The battery pack housing 20 may include an upper housing 21 and a lower housing 22, the upper housing 21 being able to cover the lower housing 22 and forming a closed space for accommodating the battery cells 11, 12.

[0042] In one embodiment of this application, such as Figure 1 As shown, the battery pack 1 includes: a battery pack housing 20; and a first battery cell 11 and a second battery cell 12 housed within the battery pack housing 20. Compared to the second battery cell 12, the first battery cell 11 is positioned within the battery pack housing 20 at a location where heat exchange with the environment is more likely. Let the capacity of the first battery cell 11 be C1, its DC resistance be R1, and X1 = C1 * R1. Let the capacity of the second battery cell 12 be C2, its DC resistance be R2, and X2 = C2 * R2. X1 and X2 satisfy: 1.1 ≤ X1 / X2 ≤ 2.0. Here, the location where heat exchange with the environment is more likely can be, for example, the perimeter and top and bottom surfaces of the battery pack housing, or a location with a larger heat exchange area with the environment.

[0043] In this application, the energy density of a single battery cell is measured using the following method.

[0044] C: Single cell capacity

[0045] The initial discharge capacity of a battery cell is defined as the capacity of discharging from the upper cutoff voltage of each battery cell at 0.33C to the lower cutoff voltage of each battery cell at 25°C.

[0046] R: DC impedance

[0047] The battery cell was adjusted to 20% SOC using a 0.33C rate and placed in a constant temperature chamber at -20℃ for 2 hours. It was then discharged for 30 seconds using a constant current I. Based on the initial voltage V1, the final voltage V2, and the discharge current, the battery impedance R = (V1 - V2) / I was calculated.

[0048] Although the mechanism is not yet clear, the inventors of this application unexpectedly discovered that by placing the first battery cell 11 in a position within the battery pack housing 20 where heat exchange with the environment is more likely compared to the second battery cell 12, and satisfying the condition 1.1 ≤ (C1*R1) / (C2*R2) ≤ 2.0, the overall low-temperature discharge capability of the battery pack can be improved. The inventors speculate that the first battery cell 11, being of high impedance, experiences a temperature rise during discharge, which can compensate for the effects of low ambient temperature, reducing the polarization of the entire battery and thus improving the low-temperature discharge capability of the first battery cell 11. Placing the first battery cell in a position where heat exchange with the environment is easily achieved can solve the bottleneck effect problem of the battery pack, i.e., the premature arrival of the cutoff potential due to high polarization in the low-temperature region. Furthermore, high capacity can solve the problem of low capacity utilization caused by high impedance, improving the overall usable capacity of the battery pack.

[0049] like Figure 1As shown, the first battery cell 11 and the second battery cell 12 are vertically arranged inside the casing. That is, the first battery cell 11 and the second battery cell 12 are arranged along the X and Y directions, and can be stacked in the Z direction. This application does not impose any particular limitation on the shape of the secondary battery, which can be cylindrical, square, or other arbitrary shapes. Figure 3 This is an exploded view of a battery cell (secondary battery) according to one embodiment of this application. Figure 3 This is an example of a cylindrical secondary battery structure. Battery cells 11 and 12 may include a housing 31, an end cap 32, and one or more electrode assemblies 33 disposed within the housing 31. The housing 31 may be a hollow cylinder with an opening to allow one or more electrode assemblies 33 to be placed within it. The end face of the housing 31 may be an open face, meaning it lacks walls, allowing communication between the inside and outside of the housing 31. The end cap 32 covers the opening and connects to the housing 31 to form a closed cavity for housing the electrode assemblies 33. Positive electrode plates, negative electrode plates, and a separator may be formed into the electrode assemblies 33 using a winding or stacking process. The electrode assemblies 33 are encapsulated within the cavity. The housing 31 is filled with an electrolyte, such as a liquid electrolyte solution. Battery cells 11 and 12 may also include two electrode terminals 34, which may be disposed on the end cap 32 and protrude from the end cap 32 in a direction away from the interior of the battery cells 11 and 12.

[0050] Depending on different power demands, the number of battery cells 11 and 12 can be set to any value. Multiple battery cells 11 and 12 can be connected in series, parallel, or a combination of both to achieve larger capacity or power. For example, multiple battery cells 11 and 12 can be connected in series to form a group of battery cells. Multiple groups of battery cells can be connected together in parallel.

[0051] In some implementations, such as Figures 1-3 As shown, within the battery pack housing 20, a first battery cell 11 and a second battery cell 12 are disposed. Both the first battery cell 11 and the second battery cell 12 include electrode terminals 34, which face the top and / or bottom walls of the battery pack housing 20. In a top view, the first battery cell 11 surrounds the second battery cell 12. Optionally, the first battery cell 11 is disposed near the side wall of the battery pack housing 20. This allows for easier heat exchange between the first battery cell 11 and the environment, further improving low-temperature discharge capability.

[0052] In some embodiments, the DC impedance R1 of the first battery cell and the DC impedance R2 of the second battery cell satisfy the condition: 1.0 < R1 / R2 ≤ 1.5. Therefore, by increasing the impedance, the heat generated by the first battery cell during discharge is increased, which can compensate for the effects of low ambient temperature, reduce the overall polarization of the battery cell, and thus improve the discharge capacity.

[0053] In some embodiments, the capacity C1 of the first battery cell and the capacity C2 of the second battery cell satisfy the following conditions: when 1.0 < R1 / R2 ≤ 1.2, 1.00 < C1 / C2 ≤ 1.15; when 1.2 < R1 / R2 ≤ 1.5, 1.15 < C1 / C2 ≤ 1.30. The battery pack system operates based on the bottleneck effect, where the battery cell with the lowest energy output determines the discharge energy of all other battery cells. Therefore, the capacity of the first battery cell must be at least equal to the capacity of the second battery cell to improve the overall discharge energy of the battery pack. However, if the capacity of the first battery cell is too high, there is too much excess energy in the first battery cell, which cannot improve the overall discharge energy of the battery pack. The inventors of this application have discovered that by satisfying the above-mentioned relationship between the capacity ratio and impedance ratio of the first and second battery cells, the low-temperature discharge capability can be further improved. The reason is that the first battery cell has a high impedance, which reduces its capacity. To ensure that the battery pack maintains its original discharge capacity, the capacity of the first battery cell needs to be increased (for example, by increasing the coating weight (CW); increasing the proportion of active materials in the positive and negative electrode formulations; increasing the compaction density of the electrode sheets, etc.). The higher the impedance of the first battery cell, the more surplus capacity of the first battery cell is needed (the difference between the capacity of the first battery cell and the capacity of the second battery cell). Conversely, the surplus can be appropriately reduced. The impedance of the first battery cell should not be too high. Otherwise, even if the battery cell itself is too polarized, the heat accumulation rate will be lower than the voltage drop, which will worsen the low-temperature discharge capacity of the battery pack.

[0054] In some embodiments, the specific heat capacity β1 of the first battery cell and the specific heat capacity β2 of the second battery cell satisfy the following condition: 0.10 ≤ β1 / β2 ≤ 0.99, or optionally, 0.3 ≤ β1 / β2 ≤ 0.95. Therefore, the first battery cell has a low specific heat capacity, making it easier to achieve temperature increases under heat accumulation conditions, thus further improving low-temperature discharge capability.

[0055] In this application, the specific heat capacity β of the battery cell is measured using the following method.

[0056] 1) Specific heat capacity testing equipment: Netzsch STA449F3

[0057] 2) Specific heat capacity calculation method: The specific heat capacity of a single cell is equal to the sum of the specific heat capacities of each element, including active materials (positive electrode material / negative electrode material) and inactive materials (binder / conductive carbon / current collector / separator / mechanical parts, etc.).

[0058] 3) Specific heat capacity test method:

[0059] Under a certain heating rate and atmosphere, the sample chamber of the DSC is kept empty, and a DSC curve is measured, which serves as the baseline to obtain the DSC value S0. Then, a standard sapphire with a mass of m1 and a specific heat capacity of C1 is placed in the sample chamber, and the DSC curve is measured to obtain the DSC value S1. After that, the sapphire is removed and replaced with a test sample with a mass of m2 and an unknown specific heat capacity C2, and the DSC curve is measured to obtain the DSC value S2.

[0060] C2=[(S2-S0)*m1] / [(S1-S0)*m2]*C1

[0061] In some embodiments, the first and second battery cells are battery cells with the same chemical system. This allows for easy adjustment of the DC impedance and capacity of the battery cells.

[0062] In some embodiments, the first and second battery cells can be lithium-ion, sodium-ion, or potassium-ion batteries. This allows for the widespread application of various chemical systems in secondary batteries to meet diverse needs.

[0063] Figure 4 This is an exploded view of the overall structure of the battery pack 1A according to another embodiment of this application. Figure 4 As shown, the first battery cell 11 and the second battery cell 12 are disposed within the battery pack housing 20; both the first battery cell 11 and the second battery cell 12 include electrode terminals 34, which face the side wall of the battery pack housing 20; at least a portion of the first battery cell 11 is disposed on the bottom wall of the battery pack housing 20. Therefore, the first battery cell 11 disposed on the bottom wall of the battery pack housing can easily exchange heat with the environment, further improving its low-temperature discharge capability.

[0064] Figure 5 This is an exploded view of the overall structure of battery pack 1B according to another embodiment of this application. Figure 4 Compared to the battery pack 1A shown, optionally, the first battery cell 11 is disposed close to the side wall of the battery pack housing. This allows the first battery cell 11 to more easily exchange heat with the environment, further improving its low-temperature discharge capability.

[0065] In addition, the secondary battery, battery pack and power supply device of this application will be described below with appropriate reference to the accompanying drawings.

[0066] In one embodiment of this application, a secondary battery is provided.

[0067] 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.

[0068] [Positive electrode plate]

[0069] The positive electrode includes a positive current collector and a positive electrode film layer disposed on at least one surface of the positive current collector, the positive electrode film layer including the positive electrode active material of the first aspect of this application.

[0070] As an example, the positive current collector has two surfaces opposite each other in its own thickness direction, and the positive electrode film layer is disposed on either or both of the two opposite surfaces of the positive current collector.

[0071] 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.).

[0072] In some embodiments, the positive electrode active material may be a known battery positive electrode active material. As an example, the positive electrode active material may include at least one of the following: 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 may 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, lithium nickel cobalt manganese oxides (such as LiNi1 / 3Co1 / 3Mn1 / 3O2 (also abbreviated as NCM333), LiNi0.5Co0.2Mn0.3O2 (also abbreviated as NCM523), LiNi0.5Co0.25Mn0.25O2 (also abbreviated as NCM211), and LiNi0.6Co At least one of 0.2Mn0.2O2 (also abbreviated as NCM622), LiNi0.8Co0.1Mn0.1O2 (also abbreviated as NCM811), lithium nickel cobalt aluminum oxide (such as LiNi0.85Co0.15Al0.05O2) and their modified compounds. Examples of lithium-containing phosphates with an olivine structure may include, but are not limited to, at least one of lithium iron phosphate (such as LiFePO4 (also abbreviated 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.

[0073] In some embodiments, the positive electrode film 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.

[0074] In some embodiments, the positive electrode film 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.

[0075] 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.

[0076] [Negative electrode plate]

[0077] The negative electrode sheet includes a negative current collector and a negative electrode film layer disposed on at least one surface of the negative current collector, the negative electrode film layer including a negative electrode active material.

[0078] As an example, the negative electrode current collector has two surfaces opposite each other in its own thickness direction, and the negative electrode film layer is disposed on either or both of the two opposite surfaces of the negative electrode current collector.

[0079] 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.).

[0080] 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.

[0081] In some embodiments, the negative electrode film 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).

[0082] In some embodiments, the negative electrode film 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.

[0083] In some embodiments, the negative electrode film may optionally include other additives, such as thickeners (e.g., sodium carboxymethyl cellulose (CMC-Na)).

[0084] 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.

[0085] [Electrolytes]

[0086] 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.

[0087] In some embodiments, the electrolyte is an electrolyte solution. The electrolyte solution includes an electrolyte salt and a solvent.

[0088] 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.

[0089] 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.

[0090] 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.

[0091] [Isolation membrane]

[0092] 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.

[0093] 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.

[0094] In some implementations, the positive electrode, negative electrode, and separator can be fabricated into an electrode assembly using a winding or stacking process.

[0095] 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.

[0096] 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.

[0097] 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.

[0098] As the electrical device, a secondary battery, battery module, or battery pack can be selected according to its usage requirements.

[0099] Figure 6 This 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.

[0100] 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.

[0101] Example

[0102] 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.

[0103] (I) Preparation of battery cells

[0104] [Preparation Example 1]

[0105] 1) Preparation of positive electrode sheet

[0106] The first positive electrode active material, LiNi0.6Co0.2Mn0.2O2, the superconducting carbon black SP, the conductive agent, and the polyvinylidene fluoride (PVDF) as the binder are dispersed in N-methylpyrrolidone (NMP) as the solvent and mixed evenly to obtain a positive electrode slurry. The positive electrode slurry is uniformly coated on the positive electrode current collector aluminum foil, and after drying, cold pressing, slitting, and cutting, a positive electrode sheet is obtained.

[0107] The mass ratio of the positive electrode active material, conductive carbon black, and binder PVDF is 96:2:2.

[0108] 2) Preparation of negative electrode sheet

[0109] The negative electrode active material graphite, superconducting carbon black SP as a conductive agent, SBR as a binder, and CMC-Na as a thickener are dispersed in deionized water as a solvent at a mass ratio of 96:1:1:2 and mixed evenly to obtain a negative electrode slurry. The negative electrode slurry is then uniformly coated onto a negative electrode current collector copper foil. After drying, cold pressing, slitting, and cutting, a negative electrode sheet is obtained.

[0110] 3) Separating membrane

[0111] Polyethylene film was selected as the separator.

[0112] 4) Preparation of electrolyte

[0113] Ethyl carbonate (EC), dimethyl carbonate (DMC), and diethyl carbonate (DEC) were mixed uniformly in a volume ratio of 1:1:1 to obtain an organic solvent. Then, fully dried lithium salt LiPF6 was dissolved in the mixed organic solvent to prepare an electrolyte with a concentration of 1 mol / L.

[0114] 5) Preparation of battery cells

[0115] 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 cells are then wound to obtain a bare cell. The bare cell is placed in an outer packaging shell, dried, and then injected with electrolyte. After vacuum sealing, settling, formation, and shaping, a single battery cell A1 is obtained.

[0116] [Preparation Examples 2 to 10]

[0117] Except for adjusting the ratio of active material and conductive agent to make the parameters of the battery cell meet the requirements shown in Table 2 below, the same procedure as in Preparation Example 1 was followed to obtain battery cells A2 to A12.

[0118] (II) Assembly of the battery pack

[0119] [Example 1]

[0120] like Figure 2 As shown, battery cells A2 are arranged on the outer periphery of the battery pack housing as first battery cells 11, and second battery cells A1 are arranged on the inner side as second battery cells 12, and assembled into a battery pack. The ratio of the number of first battery cells 11 to the number of second battery cells 12 is 7:2.

[0121] [Examples 2 to 9, Comparative Examples 1 to 3]

[0122] Except for using different battery cells as the first battery cell 11 and the second battery cell as shown in Table 1, the battery pack was assembled in the same manner as in Example 1.

[0123] Table 1

[0124] Example 1 Battery cell A2 Battery cell A1 Example 2 Battery cell A3 Battery cell A1 Example 3 Battery cell A4 Battery cell A1 Example 4 Battery cell A5 Battery cell A1 Example 5 Battery cell A6 Battery cell A1 Example 6 Battery cell A5 Battery cell A7 Example 7 Battery cell A10 Battery cell A1 Example 8 Battery cell A11 Battery cell A1 Example 9 Battery cell A12 Battery cell A1 Comparative Example 1 Battery cell A7 Battery cell A7 Comparative Example 2 Battery cell A8 Battery cell A1 Comparative Example 3 Battery cell A9 Battery cell A1

[0125] (III) Performance test results of individual battery cells and battery packs

[0126] 1. Performance test results of individual battery cells

[0127] Using the above method, various performance parameters of battery cells A1 to A12 were measured, and the measurement and calculation results of each battery cell are shown in Table 1.

[0128] Table 2 Performance parameters of individual battery cells

[0129] Battery cell A1 20 60 950 Battery cell A2 21 63 800 Battery cell A3 24 68 800 Battery cell A4 23 65 800 Battery cell A5 28 72 800 Battery cell A6 28 72 700 Battery cell A7 20 60 800 Battery cell A8 35 72 800 Battery cell A9 56 72 800 Battery cell A10 33 72 800 Battery cell A11 28 63 800 Battery cell A12 21 72 800

[0130] 2. Battery pack performance test results

[0131] (1) Energy retention rate at 0℃

[0132] The energy retention rate at 0°C was evaluated for the battery packs of Examples 1-8 and Comparative Examples 1-4.

[0133] The evaluation steps are as follows:

[0134] 1) Rated energy of battery pack: With the battery pack fully charged and placed in a constant temperature chamber at 25°C for 2 hours, it is discharged at a rate of 0.33C to the lower limit cutoff voltage of the battery pack, and the energy value E3 is recorded.

[0135] 2) Battery pack energy retention rate at 0℃: The battery pack is fully charged and placed at 0℃ for 2 hours in a constant temperature chamber. It is then discharged at a rate of 0.33C to the lower limit cutoff voltage of the battery pack, and the energy value E4 is recorded. E4 / E3 is recorded as the battery pack energy retention rate at 0℃.

[0136] Table 3 Examples 1-6 and Comparative Examples 1-4

[0137]

[0138]

[0139] (iv) Comparison of test results of various embodiments and comparative examples

[0140] According to the results in Table 3 above, in Examples 1 to 9, X1 / X2 satisfies: 1.1≤X1 / X2≤2.0, and the energy retention rate of the battery pack at 0℃ all exceed 75%. However, in Comparative Examples 1 to 3, X1 / X2 is not within the above range, and the energy retention rate of the battery pack at 0℃ is lower.

[0141] In addition, according to the results in Table 3 above, in Examples 1 to 6 and 8 to 9, R1 / R2 all satisfy 1.0 < R1 / R2 ≤ 1.5, and the battery pack has a higher energy retention rate at 0°C.

[0142] Furthermore, according to the results in Table 3 above, in Examples 1 to 6, R1, R2, C1, and C2 satisfy the following conditions: when 1.0 < R1 / R2 ≤ 1.2, 1.00 < C1 / C2 ≤ 1.15; when 1.2 < R1 / R2 ≤ 1.5, 1.15 < C1 / C2 ≤ 1.30. This indicates a higher energy retention rate of the battery pack at 0°C. However, in Examples 8 and 9, R1, R2, C1, and C2 do not satisfy the above relationships, resulting in a lower energy retention rate at 0°C compared to Examples 1 to 6.

[0143] Furthermore, a comparison of Examples 4-5 and Example 6 in Table 3 shows that when X1 / X2 is the same, setting β1 / β2 to 0.10≤β1 / β2≤0.99 can improve the energy retention rate of the battery pack at 0°C.

[0144] 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 battery pack, comprising: Battery pack housing; and The first and second battery cells are housed within the battery pack housing. Compared to the second battery cell, the first battery cell is located in a position within the battery pack housing where heat exchange with the environment is more likely. Let the capacity of the first battery cell be C1, and its DC resistance be R1, then X1 = C1 * R1. Let the capacity of the second battery cell be C2, and its DC resistance be R2. Then, X2 = C2 * R2, and X1 and X2 satisfy: 1.1 ≤ X1 / X2 ≤ 2.

0. The capacity C1 of the first battery cell and the capacity C2 of the second battery cell satisfy the following: When 1.0 < R1 / R2 ≤ 1.2, 1.00 < C1 / C2 ≤ 1.

15. When 1.2 < R1 / R2 ≤ 1.5, 1.15 < C1 / C2 ≤ 1.

30.

2. The battery pack according to claim 1, wherein, The specific heat capacity β1 of the first battery cell and the specific heat capacity β2 of the second battery cell satisfy the following condition: 0.10≤β1 / β2≤0.

99.

3. The battery pack according to claim 2, wherein, The specific heat capacity β1 of the first battery cell and the specific heat capacity β2 of the second battery cell satisfy the following condition: 0.3≤β1 / β2≤0.

95.

4. The battery pack according to any one of claims 1 to 3, wherein, The first battery cell and the second battery cell are connected in series, parallel, or mixed connection.

5. The battery pack according to any one of claims 1 to 3, wherein, The first battery cell and the second battery cell are disposed inside the battery pack housing; both the first battery cell and the second battery cell include electrode terminals, which face the top wall and / or bottom wall of the battery pack housing. When viewed from above, the first battery cell surrounds the second battery cell in a circular arrangement.

6. The battery pack according to claim 5, wherein, The first battery cell is positioned close to the side wall of the battery pack housing.

7. The battery pack according to any one of claims 1 to 3, wherein, The first battery cell and the second battery cell are disposed inside the battery pack housing; both the first battery cell and the second battery cell include electrode terminals, which face the side wall of the battery pack housing. At least a portion of the first battery cell is disposed on the bottom wall of the battery pack housing.

8. The battery pack according to claim 7, wherein, The first battery cell is positioned close to the side wall of the battery pack housing.

9. The battery pack according to any one of claims 1 to 3, wherein, The first and second battery cells are battery cells with the same chemical system.

10. An electrical device comprising a battery pack according to any one of claims 1 to 9.

Images