Battery pack and powered device

Abstract

This application provides a battery pack and an electrical device. The battery pack includes a battery pack housing and individual battery cells housed within the housing. In a top view, the internal space of the battery pack housing is rectangular, consisting of a first region, a second region, a third region, and a fourth region. In the top view, the first region is located at the center of the rectangular shape of the internal space, the fourth region is located at the four corners of the rectangular shape, the third region is located on the sides of the rectangular shape excluding the corners, and the second region is located between the first and third regions. A first battery cell is disposed in the first region, a second battery cell is disposed in the second region, a third battery cell is disposed in the third region, and a fourth battery cell is disposed in the fourth region. In the top view, the second battery cell does not contact the inner surface of the battery pack housing, and the third battery cell only contacts one side of the battery pack housing. The first, second, third, and fourth battery cells each have a first discharge voltage plateau and a second discharge voltage plateau. The average discharge voltage of the first discharge voltage plateau is higher than the average discharge voltage of the second discharge voltage plateau. Among the first, second, third, and fourth battery cells, when the sum of the discharge capacity corresponding to the first discharge voltage plateau and the discharge capacity corresponding to the second discharge voltage plateau is 100%, the percentage of discharge capacity corresponding to the second discharge voltage plateau of the fourth battery cell is greater than that of the third battery cell, which is greater than that of the second battery cell, which is greater than that of the first battery cell.

Description

Technical Field

[0001] This application relates to the field of lithium-ion batteries, and more particularly to a battery pack with high energy retention at low temperatures and an electrical device including the battery pack. Background Technology

[0002] In recent years, with the continuous development of lithium-ion battery technology, lithium-ion 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] In the aforementioned fields, the capacity of individual lithium-ion rechargeable battery cells sometimes cannot meet the usage requirements. In such cases, it is necessary to connect multiple lithium-ion rechargeable battery cells in series or parallel to form a battery pack. The lithium-ion rechargeable battery cells used in the battery pack mainly include ternary batteries such as lithium nickel cobalt manganese oxide batteries or lithium nickel cobalt aluminum oxide batteries, lithium iron phosphate batteries, lithium manganese oxide batteries, lithium cobalt oxide batteries, lithium titanate batteries, and manganese dioxide batteries.

[0004] However, battery packs composed of lithium-ion rechargeable battery cells experience a significant decrease in energy retention when used in low-temperature environments such as winter, resulting in a severe reduction in driving range at low temperatures. Therefore, improving the overall driving range of the battery pack at low temperatures has become a critical issue that urgently needs to be addressed. Consequently, the energy retention rate of existing battery packs composed of lithium-ion rechargeable battery cells at low temperatures still needs improvement. 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 composed of lithium-ion secondary batteries with excellent energy retention at low temperatures and improved battery life at low temperatures, 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 battery cells housed within the battery pack housing. The battery pack is characterized in that, in a top view, the internal space of the battery pack housing is rectangular, and the internal space is composed of a first region, a second region, a third region, and a fourth region. In the top view, the first region is located at the center of the rectangular shape of the internal space, the fourth region is located at the four corners of the rectangular shape of the internal space, the third region is located on the sides of the rectangular shape of the internal space excluding the corners, the second region is located between the first region and the third region, a first battery cell is disposed in the first region, a second battery cell is disposed in the second region, a third battery cell is disposed in the third region, and a fourth battery cell is disposed in the fourth region. In the top view, the second battery cell does not contact the inner surface of the battery pack housing, and the third battery cell... Each battery cell contacts only one inner surface of the battery pack housing, while the fourth battery cell contacts both inner surfaces of the battery pack housing. Each of the first, second, third, and fourth battery cells has a first discharge voltage plateau and a second discharge voltage plateau. The average discharge voltage of the first discharge voltage plateau is higher than the average discharge voltage of the second discharge voltage plateau. In each of the first, second, third, and fourth battery cells, when the sum of the discharge capacity corresponding to the first discharge voltage plateau and the discharge capacity corresponding to the second discharge voltage plateau is 100%, the percentage of discharge capacity corresponding to the second discharge voltage plateau of the fourth battery cell is greater than the percentage of discharge capacity corresponding to the second discharge voltage plateau of the third battery cell, which in turn is greater than the percentage of discharge capacity corresponding to the second discharge voltage plateau of the second battery cell.

[0007] Therefore, this application improves the overall energy retention rate of the battery pack at low temperatures by configuring battery cells with different discharge capacities at low temperatures according to the temperature distribution within the battery pack. Specifically, battery cells with different low-temperature energy retention rates, each having a dual discharge voltage platform (a first discharge voltage platform with a higher discharge voltage and a second discharge voltage platform with a lower discharge voltage), are configured in different temperature zones within the battery pack housing. Furthermore, battery cells with higher low-temperature energy retention rates are configured in lower temperature zones. By configuring battery cells with relatively lower low-temperature performance (relatively lower low-temperature energy retention rate) in relatively higher temperature zones within the battery pack housing, and configuring battery cells with relatively higher low-temperature performance (relatively higher low-temperature energy retention rate) in relatively lower temperature zones, the cycle consistency of battery cells in different temperature zones of the battery pack is improved, thereby enhancing the overall low-temperature energy retention rate of the battery pack and improving the overall low-temperature driving range of the battery pack.

[0008] The term "rectangular shape" as used in this application is not limited to a strictly rectangular shape; any approximate rectangular shape is acceptable. "Contact with the inner surface of the battery pack housing" includes "contact with structural components disposed on the inner surface of the battery pack housing."

[0009] In any embodiment, in the first, second, third, and fourth battery cells, the difference between the lowest discharge voltage of the first discharge voltage platform and the highest discharge voltage of the second discharge voltage platform is 0.25-0.6V.

[0010] Therefore, by utilizing the first discharge voltage platform with a higher discharge voltage for discharge, and then continuing to discharge using the second discharge voltage platform with a lower discharge voltage, the energy that each battery cell can release at low temperatures can be increased, thereby improving the overall energy retention rate of the battery pack at low temperatures.

[0011] In a preferred embodiment, in the first battery cell, when the sum of the discharge capacity corresponding to the first discharge voltage platform and the discharge capacity corresponding to the second discharge voltage platform is 100%, the discharge capacity corresponding to the first discharge voltage platform accounts for 91.8% to 99%, and the discharge capacity corresponding to the second discharge voltage platform accounts for 1% to 8.2%.

[0012] Therefore, by ensuring that the proportions of the discharge capacity corresponding to the first discharge voltage plateau and the discharge capacity corresponding to the second discharge voltage plateau in the first battery cell are within the aforementioned range, the energy that the first battery cell can release at low temperatures can be increased, thereby improving the overall low-temperature energy retention rate of the battery pack.

[0013] In a preferred embodiment, in the second battery cell, when the sum of the discharge capacity corresponding to the first discharge voltage platform and the discharge capacity corresponding to the second discharge voltage platform is 100%, the discharge capacity corresponding to the first discharge voltage platform accounts for 75.7% to 96.8%, and the discharge capacity corresponding to the second discharge voltage platform accounts for 3.2% to 24.3%.

[0014] Therefore, by ensuring that the proportions of the discharge capacity corresponding to the first discharge voltage plateau and the discharge capacity corresponding to the second discharge voltage plateau in the second battery cell are within the aforementioned range, the energy that the second battery cell can release at low temperatures can be increased, thereby further improving the overall low-temperature energy retention rate of the battery pack.

[0015] In a preferred embodiment, in the third battery cell, when the sum of the discharge capacity corresponding to the first discharge voltage platform and the discharge capacity corresponding to the second discharge voltage platform is 100%, the discharge capacity corresponding to the first discharge voltage platform accounts for 60.2% to 89.4%, and the discharge capacity corresponding to the second discharge voltage platform accounts for 10.6% to 39.8%.

[0016] Therefore, by ensuring that the proportions of the discharge capacity corresponding to the first discharge voltage plateau and the discharge capacity corresponding to the second discharge voltage plateau in the third battery cell are within the aforementioned range, the energy that the third battery cell can release at low temperatures can be increased, thereby further improving the overall low-temperature energy retention rate of the battery pack.

[0017] In a preferred embodiment, in the fourth battery cell, when the sum of the discharge capacity corresponding to the first discharge voltage platform and the discharge capacity corresponding to the second discharge voltage platform is 100%, the discharge capacity corresponding to the first discharge voltage platform accounts for 52.5% to 80.3%, and the discharge capacity corresponding to the second discharge voltage platform accounts for 19.7% to 47.5%.

[0018] Therefore, by ensuring that the proportions of the discharge capacity corresponding to the first discharge voltage plateau and the discharge capacity corresponding to the second discharge voltage plateau in the fourth battery cell are within the aforementioned range, the energy that the fourth battery cell can release at low temperatures can be increased, thereby further improving the overall low-temperature energy retention rate of the battery pack.

[0019] In a preferred embodiment, the positive electrode active material of each of the first battery cell, the second battery cell, the third battery cell, and the fourth battery cell is a mixture of a first positive electrode active material having the first discharge voltage platform and a second positive electrode active material having the second discharge voltage platform.

[0020] Therefore, the first, second, third, and fourth battery cells each have a first discharge voltage platform and a second discharge voltage platform with different discharge voltages. After discharging using the first discharge voltage platform with a higher discharge voltage, they can continue to discharge using the second discharge voltage platform with a lower discharge voltage, thereby improving the low-temperature performance of the first, second, third, and fourth battery cells.

[0021] In a preferred embodiment, the first positive electrode active material and the second positive electrode active material are each independently selected from at least one of lithium nickel oxide, lithium cobalt oxide, lithium nickel cobalt manganese oxide, lithium nickel cobalt aluminum oxide, lithium iron phosphate, lithium manganese oxide, lithium titanate, and manganese dioxide.

[0022] Therefore, as long as the ratio of the discharge voltage and discharge capacity of the first discharge voltage plateau generated by the first positive electrode active material and the second discharge voltage plateau generated by the second positive electrode active material satisfies the above relationship, the first positive electrode active material and the second positive electrode active material can be selected from various existing positive electrode active materials, thereby enabling the battery pack of this application to be easily realized using existing positive electrode active materials.

[0023] In a preferred embodiment, the first positive electrode active material is lithium nickel cobalt manganese oxide and the second positive electrode active material is lithium iron phosphate; or, the first positive electrode active material is lithium nickel cobalt manganese oxide and the second positive electrode active material is lithium manganese oxide or lithium titanate; or, the first positive electrode active material is lithium iron phosphate and the second positive electrode active material is lithium manganese oxide or lithium titanate.

[0024] The voltage platform and specific energy are generally in the following order: lithium nickel cobalt manganese oxide (LCO) > lithium iron phosphate (LFP) > lithium manganese oxide (LMO) or lithium titanate. Therefore, relatively speaking, the energy density order is: LCO + LFP > LCO + LMO or LMO > LFP + LMO or LMO. Correspondingly, in modules or battery packs of the same volume, the driving range order of the above three systems is: LCO + LFP > LCO + LMO or LMO > LFP + LMO or LMO. Therefore, the LCO + LFP system is more suitable for scenarios with higher driving range or higher output power requirements; LCO + LMO or LMO is suitable for scenarios with moderate driving range or moderate output power; and LFP + LMO or LMO is more suitable for scenarios with low-speed commuter vehicles and other scenarios with low output power requirements.

[0025] In a preferred embodiment, when the first positive electrode active material and the second positive electrode active material are of the same type in the first battery cell, the second battery cell, the third battery cell, and the fourth battery cell, the mass percentage of the first positive electrode active material in the positive electrode active material decreases in the order of the first battery cell, the second battery cell, the third battery cell, and the fourth battery cell, and the mass percentage of the second positive electrode active material in the positive electrode active material increases in the order of the first battery cell, the second battery cell, the third battery cell, and the fourth battery cell.

[0026] The greater the mass proportion of the second positive electrode active material used to generate the second discharge voltage platform with a lower discharge voltage, the greater the discharge capacity proportion corresponding to the second discharge voltage platform, and the higher the low-temperature energy retention rate of the battery cell. By ensuring that the mass proportion of the second positive electrode active material of the fourth battery cell configured in the fourth region is greater than the mass proportion of the second positive electrode active material of the third battery cell configured in the third region, which in turn is greater than the mass proportion of the second positive electrode active material of the second battery cell configured in the second region, which is greater than the mass proportion of the second positive electrode active material of the first battery cell configured in the first region, the low-temperature energy retention rate of the fourth battery cell is greater than that of the third battery cell, which in turn is greater than that of the second battery cell, which is greater than that of the first battery cell. This allows the energy released by the first, second, third, and fourth battery cells at low temperatures to be approximately the same, thereby further improving the overall energy retention rate of the battery pack at low temperatures.

[0027] In a preferred embodiment, in the first battery cell, when the total mass of the first positive electrode active material and the second positive electrode active material is 100%, the mass of the first positive electrode active material accounts for 92.5% to 97.5%, and the mass of the second positive electrode active material accounts for 2.5% to 7.5%.

[0028] Therefore, by ensuring that the mass ratio of the first positive electrode active material and the second positive electrode active material in the first battery cell is within the above-mentioned range, the proportions of the discharge capacity corresponding to the first discharge voltage plateau and the discharge capacity corresponding to the second discharge voltage plateau in the first battery cell can be within the above-mentioned range, thereby increasing the energy that the first battery cell can release at low temperatures and thus improving the overall low-temperature energy retention rate of the battery pack.

[0029] In a preferred embodiment, in the second battery cell, when the total mass of the first positive electrode active material and the second positive electrode active material is 100%, the mass of the first positive electrode active material accounts for 77.5% to 92.5%, and the mass of the second positive electrode active material accounts for 7.5% to 22.5%.

[0030] Therefore, by ensuring that the mass ratio of the first positive electrode active material and the second positive electrode active material in the second battery cell is within the above-mentioned range, the proportions of the discharge capacity corresponding to the first discharge voltage plateau and the discharge capacity corresponding to the second discharge voltage plateau in the second battery cell can be within the above-mentioned range, thereby increasing the energy that the second battery cell can release at low temperatures, and further improving the overall low-temperature energy retention rate of the battery pack.

[0031] In a preferred embodiment, in the third battery cell, when the total mass of the first positive electrode active material and the second positive electrode active material is 100%, the mass of the first positive electrode active material accounts for 62.5% to 77.5%, and the mass of the second positive electrode active material accounts for 22.5% to 37.5%.

[0032] Therefore, by ensuring that the mass ratio of the first positive electrode active material and the second positive electrode active material in the third battery cell is within the above-mentioned range, the proportions of the discharge capacity corresponding to the first discharge voltage plateau and the discharge capacity corresponding to the second discharge voltage plateau in the third battery cell can be within the above-mentioned range, thereby increasing the energy that the third battery cell can release at low temperatures, and further improving the overall low-temperature energy retention rate of the battery pack.

[0033] In a preferred embodiment, in the fourth battery cell, when the total mass of the first positive electrode active material and the second positive electrode active material is 100%, the mass of the first positive electrode active material accounts for 50% to 62.5%, and the mass of the second positive electrode active material accounts for 37.5% to 50%.

[0034] Therefore, by ensuring that the mass ratio of the first positive electrode active material and the second positive electrode active material in the fourth battery cell is within the above-mentioned range, the proportions of the discharge capacity corresponding to the first discharge voltage plateau and the discharge capacity corresponding to the second discharge voltage plateau in the fourth battery cell can be within the above-mentioned range, thereby increasing the energy that the fourth battery cell can release at low temperatures, and further improving the overall low-temperature energy retention rate of the battery pack.

[0035] In a preferred embodiment, when the first positive electrode active material is lithium nickel cobalt manganese oxide and the second positive electrode active material is lithium iron phosphate, the mass ratio of the second positive electrode active material in the first battery cell, the second battery cell, the third battery cell, and the fourth battery cell is 1:(1-3):(3-5):(5-9); when the first positive electrode active material is lithium nickel cobalt manganese oxide and the second positive electrode active material is lithium titanate or lithium manganese oxide, the mass ratio of the second positive electrode active material in the first battery cell, the second battery cell, the third battery cell, and the fourth battery cell is 1:(1-2):(3-4):(5-7); when the first positive electrode active material is lithium iron phosphate and the second positive electrode active material is lithium titanate or lithium manganese oxide, the mass ratio of the second positive electrode active material in the first battery cell, the second battery cell, the third battery cell, and the fourth battery cell is 1:(1-3):(3-5):(5-9).

[0036] Therefore, by using specific first positive electrode active materials and specific second positive electrode active materials in specific mass ratios in the first, second, third, and fourth battery cells, the battery pack of this application can be easily adapted to different scenarios.

[0037] In a preferred embodiment, at temperatures below 0°C, the discharge cutoff voltage of the first battery cell is 0-0.3V higher than that of the second battery cell, the discharge cutoff voltage of the second battery cell is 0-0.3V higher than that of the third battery cell, the discharge cutoff voltage of the third battery cell is 0-0.3V higher than that of the fourth battery cell, and the discharge cutoff voltage of the fourth battery cell is 1.6V or higher.

[0038] Therefore, by setting the discharge cutoff voltages of the first, second, third, and fourth battery cells as described above, the energy released by the first, second, third, and fourth battery cells at low temperatures can be made approximately the same, thereby improving the overall energy retention rate of the battery pack at low temperatures.

[0039] In a preferred embodiment, the ratio of the number of the first battery cell to the number of the second battery cell to the number of the third battery cell to the number of the fourth battery cell is (3-8):(8-13):(9-14):1. In other words, when the sum of the number of the first, second, third, and fourth battery cells is 100%, the proportion of the first battery cells is 10-30%, the proportion of the second battery cells is 25-50%, the proportion of the third battery cells is 30-55%, and the proportion of the fourth battery cells is 2-5%.

[0040] Therefore, the battery pack of this application can be easily realized by setting the number of the first, second, third, and fourth battery cells according to the temperature distribution range of common battery packs.

[0041] In a preferred embodiment, capacitors are disposed in the gaps between different battery cells.

[0042] This allows for full utilization of the gaps between individual battery cells, thereby increasing the overall volumetric energy density of the battery pack.

[0043] A second aspect of this application provides an electrical device that includes the battery pack of the first aspect of this application.

[0044] Therefore, the electrical device of the second aspect of this application has a strong endurance at low temperatures and can be used normally for a long time even at low temperatures.

[0045] Invention Effects

[0046] By employing this invention, by configuring battery cells with different low-temperature energy retention rates and dual discharge voltage platforms in different temperature regions inside the battery pack housing, it is possible to provide a battery pack and an electrical device including the battery pack that can make the energy released by the battery cells in different temperature regions approximately the same at low temperatures and improve the overall energy retention rate at low temperatures. Attached Figure Description

[0047] Figure 1 This is a schematic diagram of the structure of a battery pack according to one embodiment of this application.

[0048] Figure 2 yes Figure 1 The image shown is a top view of the structural components of a battery pack according to one embodiment of this application after removing the casing.

[0049] Figure 3 This is a constant current discharge curve diagram showing the battery cells with a first discharge voltage plateau and a second discharge voltage plateau in the battery pack according to an embodiment of this application.

[0050] Figure 4This is a schematic diagram of an electrical device that uses a battery pack according to an embodiment of this application as a power source.

[0051] Explanation of reference numerals in the attached figures

[0052] 1 Battery pack; 2 Upper housing; 3 Lower housing; g1 and g2 gaps; C11 and C12 capacitors; BL1 first boundary line; BL2 second boundary line; BL3 third boundary line; BL4 fourth boundary line; R1 first region; R2 second region; R3 third region; R4 fourth region; 61 first battery cell; 62 second battery cell; 63 third battery cell; 64 fourth battery cell. Detailed Implementation

[0053] 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.

[0054] 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.

[0055] Unless otherwise specified, all embodiments and optional embodiments of this application can be combined to form new technical solutions.

[0056] Unless otherwise specified, all technical features and optional technical features of this application may be combined to form new technical solutions.

[0057] 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.

[0058] 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.

[0059] 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).

[0060] The inventors observed that when a battery pack composed of lithium-ion rechargeable battery cells is used in low-temperature environments during winter, the varying heat dissipation and insulation capabilities of the cells in different locations within the pack lead to inconsistent charge and discharge performance. Specifically, in low-temperature environments, the cells located on the inner side of the battery pack have relatively higher temperatures and better discharge performance at low temperatures, while the cells on the outer side have relatively lower temperatures and poorer discharge performance at low temperatures. This difference in discharge capacity among the cells in different parts of the battery pack at low temperatures significantly reduces the overall energy retention rate of the battery pack at low temperatures.

[0061] Therefore, the inventors realized that by arranging battery cells with better low-temperature discharge performance in the lower temperature areas of the battery pack, the energy released by battery cells in different locations in the battery pack can be roughly the same in a low-temperature environment, thereby improving the overall energy performance of the battery pack in a low-temperature environment, and thus increasing the driving range of electrical devices using the battery pack as a power source in a low-temperature environment.

[0062] To achieve the above objectives, the inventors conducted repeated research and discovered that by giving the battery cells located in the low-temperature region two discharge voltage platforms, and continuing to discharge using the lower discharge voltage platform after the higher discharge voltage platform has finished discharging, the discharge capacity of these battery cells can be increased, thereby making the discharge performance of these battery cells better at low temperatures.

[0063] Furthermore, when the mass of the positive electrode active material at the lower discharge voltage platform accounts for no more than 50% of the total mass of the positive electrode active material at both the higher and lower discharge voltage platforms, the higher the proportion of the discharge capacity corresponding to the lower discharge voltage platform to the total discharge capacity corresponding to both higher and lower discharge voltage platforms, the better the low-temperature performance of the battery cell. Thus, by using battery cells with a higher proportion of discharge capacity corresponding to the lower discharge voltage platform in lower temperature regions, the energy output of battery cells configured in different temperature regions can be made approximately consistent at low temperatures. This improves the overall energy retention rate of the battery pack at low temperatures, thereby increasing the driving range of electric vehicles and other electrical devices using this battery pack as a power source at low temperatures.

[0064] Battery pack

[0065] The battery pack 1 of this application will now be described in detail.

[0066] Figure 1 This is a schematic diagram of the structure of a battery pack 1 according to one embodiment of this application. Figure 2 yes Figure 1 The battery pack 1 shown is a top view of its structural components after the casing has been removed.

[0067] like Figure 1 and Figure 2 As shown, the battery pack 1 of this application includes a battery box and a plurality of battery cells (61, 62, 63, 64) disposed in the battery box. The battery box includes an upper box 2 and a lower box 3. The upper box 2 can cover the lower box 3 and form a closed space (battery pack cavity) for accommodating the plurality of battery cells.

[0068] like Figure 2 As shown, the outermost battery cell among multiple battery cells can be in contact with the inner surface of the battery pack housing (upper housing 2, lower housing 3), or it can be in contact with a structural component located on the inner surface of the battery pack housing. Figure 2 In the top view shown, gaps g1 and g2 are optionally formed between the outermost battery cells and the inner surface of the battery pack housing. Various structural components of the battery pack can be installed in these gaps g1 and g2. Capacitors C11, C12, etc., can optionally be installed in the gaps between different battery cells to improve the overall energy density of the battery pack.

[0069] The specific location and number of individual battery cells contained in battery pack 1 can be selected according to the actual application of the battery pack.

[0070] like Figure 2 As shown, the battery pack 1 includes a battery pack housing and individual battery cells 61, 62, 63, and 64 housed within the battery pack housing. Figure 2 In the top view of the battery pack 1 shown, the internal space of the battery pack housing is rectangular in shape. The internal space of the battery pack housing is composed of a first region R1, a second region R2, a third region R3, and a fourth region R4. In the top view, the first region R1 is located at the center of the rectangular shape of the internal space, the fourth region R4 is located at the four corners of the rectangular shape of the internal space, the third region R3 is located on the four sides of the rectangular shape of the internal space excluding the corners, and the second region R2 is located between the first region R1 and the third region R3. The first region R1 is a roughly rectangular region surrounded by the first boundary line BL1, located at the center of the rectangular shape of the internal space of the battery pack housing (for example, the length and width of the rectangular shape of the first region R1 can be approximately half the length and width of the rectangular shape of the internal space of the battery pack housing, respectively). The fourth region R4 is a region surrounded by the fourth boundary line BL4, located at the four corners of the rectangular shape of the internal space of the battery pack housing. The third region R3 is located on the four sides of the rectangular shape of the internal space of the battery pack housing, excluding the corners. The second region R2 is a roughly annular region located between the first boundary line BL1 and the third boundary line BL3 (i.e., between the first region R1 and the third region R3). The first boundary line BL1, the second boundary line BL2, the third boundary line BL3, and the fourth boundary line BL4 are virtual lines drawn to clearly represent the first region R1, the second region R2, the third region R3, and the fourth region R4.

[0071] Further, a first battery cell 61 is disposed in the first region R1, a second battery cell 62 is disposed in the second region R2, a third battery cell 63 is disposed in the third region R3, and a fourth battery cell 64 is disposed in the fourth region R4. In the top view, the second battery cell 62 does not contact the inner surface of the battery pack housing, the third battery cell 63 only contacts one inner surface of the battery pack housing, and the fourth battery cell 64 contacts both inner surfaces of the battery pack housing. The first battery cell 61, the second battery cell 62, the third battery cell 63, and the fourth battery cell 64 each have a first discharge voltage plateau and a second discharge voltage plateau. The average discharge voltage of the discharge voltage platform is higher than the average discharge voltage of the second discharge voltage platform. In each of the first battery cell 61, the second battery cell 62, the third battery cell 63, and the fourth battery cell 64, when the sum of the discharge capacity corresponding to the first discharge voltage platform and the discharge capacity corresponding to the second discharge voltage platform is 100%, the percentage of discharge capacity corresponding to the second discharge voltage platform of the fourth battery cell 64 is greater than the percentage of discharge capacity corresponding to the second discharge voltage platform of the third battery cell 63, which is greater than the percentage of discharge capacity corresponding to the second discharge voltage platform of the second battery cell 62, which is greater than the percentage of discharge capacity corresponding to the second discharge voltage platform of the first battery cell 61. When placed in an external environment at the same temperature, within the battery pack 1, the temperature of the fourth region R4 is lower than the temperature of the third region R3, the temperature of the third region R3 is lower than the temperature of the second region R2, and the temperature of the second region R2 is lower than the temperature of the first region R1. The term "rectangular shape" is not limited to a strictly rectangular shape; any approximate rectangular shape is acceptable. "Contact with the inner surface of the battery pack housing" includes "contact with structural components disposed on the inner surface of the battery pack housing."

[0072] It should be noted that the "discharge voltage plateau" is the relatively stable portion of the discharge curve; during discharge at the discharge voltage plateau, the discharge amount per unit time is relatively high. For example... Figure 3 The constant current discharge curves of the two types of battery cells are shown: The discharge curve represented by the solid line has only one discharge voltage plateau. After passing point A', the discharge voltage drops sharply (corresponding to a single-plateau battery cell); The discharge curve represented by the dashed line has two discharge voltage plateaus. After passing point A, the discharge voltage drops sharply, and after dropping to point B, it tends to stabilize and continues to discharge using the discharge voltage plateau (corresponding to a dual-plateau battery cell).

[0073] like Figure 3As shown by the dashed line, the first discharge voltage plateau (i.e., the high-voltage discharge plateau, also known as the first discharge voltage plateau of this application) is before point B, where the first voltage drop ends. Its data value is equal to the ratio of all energy released by the high-voltage positive electrode active material to the current (a balanced value, which can also be roughly regarded as the average voltage before point B). The second discharge voltage plateau (i.e., the low-voltage discharge plateau, also known as the second discharge voltage plateau of this application) is after point B, which is reflected as the ratio of all energy released by the low-voltage positive electrode active material to the current (a balanced value, which can also be roughly regarded as the average voltage after point B).

[0074] In this application, battery cells 61, 62, 63, and 64 with different low-temperature energy retention rates and dual discharge voltage platforms (a first discharge voltage platform with a higher discharge voltage and a second discharge voltage platform with a lower discharge voltage) are respectively arranged in different temperature regions inside the battery pack housing. Furthermore, battery cells with higher low-temperature energy retention rates are arranged in regions with lower temperatures. Specifically, according to the typical temperature distribution inside a battery pack, the temperature of the first region R1 > the temperature of the second region R2 > the temperature of the third region R3 > the temperature of the fourth region R4. In this application, the discharge capacity percentage corresponding to the second discharge voltage platform of the fourth battery cell 64 > the discharge capacity percentage corresponding to the second discharge voltage platform of the third battery cell 63 > the discharge capacity percentage corresponding to the second discharge voltage platform of the second battery cell 62 > the discharge capacity percentage corresponding to the second discharge voltage platform of the first battery cell 61.

[0075] It should be noted that the specific definition and test method of the discharge capacity percentage corresponding to the second discharge voltage plateau of the first / second / third / fourth battery cell in this application are provided in the "Related Tests" section of this specification.

[0076] Battery cells located in different parts of a battery pack have varying heat dissipation capabilities. Generally, the outermost cells dissipate heat more efficiently, meaning they cool down faster. As you move from the outside of the battery pack towards the inside, the heat dissipation rate decreases. Conversely, as you move from the inside of the battery pack towards the outside, the heat retention capacity of the cells decreases. This temperature difference between cells in different areas of the battery pack leads to inconsistent charge and discharge performance. For example, in low-temperature environments, inner cells dissipate heat more slowly and have higher temperatures, resulting in better performance in low temperatures (but poorer performance at high temperatures). Conversely, outer cells dissipate heat more quickly and have lower temperatures, resulting in poorer performance in low temperatures (but better performance at high temperatures). Therefore, this significant difference in electrical performance between cells in different areas of the battery pack at low temperatures reduces the overall energy retention rate of the battery pack in low-temperature environments.

[0077] To address the aforementioned issues, the inventors of this application have installed a first battery cell 61, a second battery cell 62, a third battery cell 63, and a fourth battery cell 64, each with a dual discharge voltage platform (i.e., a first discharge voltage platform with a relatively high discharge voltage and a second discharge voltage platform with a relatively low discharge voltage) in a first region R1, a second region R2, a third region R3, and a fourth region R4, each with a different temperature. After the discharge of the first discharge voltage platform is completed, the second discharge voltage platform can be used to continue discharging (i.e., to achieve tiered discharge of the same battery cell), thereby increasing the energy released by each battery cell in a low-temperature environment and thus improving the overall low-temperature energy retention rate of the battery pack.

[0078] Furthermore, it was found that by further adjusting the discharge capacity ratios corresponding to the second discharge voltage platforms of the first battery cell 61, the second battery cell 62, the third battery cell 63, and the fourth battery cell 64, a battery pack 1 with a higher overall low-temperature energy retention rate can be obtained, and this setting significantly improves the low-temperature energy retention rate of the battery pack under low-temperature conditions in winter. Specifically, by ensuring that the discharge capacity ratio corresponding to the second discharge voltage platform of the fourth battery cell 64 > the discharge capacity ratio corresponding to the second discharge voltage platform of the third battery cell 63 > the discharge capacity ratio corresponding to the second discharge voltage platform of the second battery cell 62 > the discharge capacity ratio corresponding to the second discharge voltage platform of the first battery cell 61, the second battery cell 62, the third battery cell 63, and the fourth battery cell 64 can continue to discharge in low-temperature environments where the first battery cell 61 can no longer discharge; the third battery cell 63 and the fourth battery cell 64 can continue to discharge in low-temperature environments where the first battery cell 61, the second battery cell 62, and the third battery cell 63 can no longer discharge; and the fourth battery cell 64 can continue to discharge in low-temperature environments where the first battery cell 61, the second battery cell 62, and the third battery cell 63 can no longer discharge, thus ensuring that the overall discharge capacity of the battery pack remains at a high level.

[0079] The inventors further conducted an in-depth study on the relationship between the discharge capacity ratio corresponding to the second discharge voltage platform of each battery cell 61, 61, 63, 64 with dual discharge voltage platforms in different temperature regions R1, R2, R3, R4 and the total energy retention rate of the battery pack at -20℃. The results showed that, in each of the first battery cell 61, the second battery cell 62, the third battery cell 63, and the fourth battery cell 64, when the sum of the discharge capacity corresponding to the first discharge voltage platform and the discharge capacity corresponding to the second discharge voltage platform is 100%, by ensuring that the proportion of the discharge capacity corresponding to the second discharge voltage platform of the fourth battery cell 64 > the proportion of the discharge capacity corresponding to the second discharge voltage platform of the third battery cell 63 > the proportion of the discharge capacity corresponding to the second discharge voltage platform of the second battery cell 62 > the proportion of the discharge capacity corresponding to the second discharge voltage platform of the first battery cell 61, the low-temperature energy retention rate of the fourth battery cell 64 > the low-temperature energy retention rate of the third battery cell 63 > the low-temperature energy retention rate of the second battery cell 62 > the low-temperature energy retention rate of the first battery cell 61 can be made greater than that of the third battery cell 63 > the low-temperature energy retention rate of the second battery cell 62 > the low-temperature energy retention rate of the first battery cell 61. This ensures that the energy released by each battery cell 61, 62, 63, and 64 in the different temperature regions R1, R2, R3, and R4 of the battery pack (discharge capacity at low temperatures) is approximately the same, thereby improving the overall low-temperature energy retention rate of the battery pack 1 (total energy retention rate of the battery pack at -20℃) and improving the overall range of the battery pack at low temperatures.

[0080] In some embodiments, in the first, second, third, and fourth battery cells 61, 62, 63, and 64, the difference between the lowest discharge voltage of the first discharge voltage platform and the highest discharge voltage of the second discharge voltage platform is 0.25-0.6V.

[0081] Reference Figure 3 In this application, the "lowest discharge voltage of the first discharge voltage platform" refers to the discharge voltage corresponding to point A, and the "highest discharge voltage of the second discharge voltage platform" refers to the discharge voltage corresponding to point B.

[0082] Therefore, for a battery cell with two discharge voltage platforms, if the difference between the lowest discharge voltage of the first discharge voltage platform and the highest discharge voltage of the second discharge voltage platform is less than 0.25V, it is equivalent to an excessive amount of positive electrode active material contributing to the second discharge voltage platform. However, the energy output by the positive electrode active material contributing to the second discharge voltage platform is less than the energy output by the positive electrode active material contributing to the first discharge voltage platform. This results in low overall energy output of the battery cell, and consequently, low overall energy output of the battery pack. Conversely, if the difference between the lowest discharge voltage of the first discharge voltage platform and the highest discharge voltage of the second discharge voltage platform is greater than 0.6V, it is equivalent to an excessive amount of positive electrode active material contributing to the first discharge voltage platform (but insufficient amount contributing to the second discharge voltage platform). In low ambient temperature environments, the first discharge voltage platform will be unable to output energy prematurely, while the energy output of the second discharge voltage platform will be limited, leading to poor overall low-temperature energy retention of the battery pack.

[0083] In some embodiments, in the first battery cell 61, when the sum of the discharge capacity corresponding to the first discharge voltage platform and the discharge capacity corresponding to the second discharge voltage platform is 100%, the discharge capacity corresponding to the first discharge voltage platform accounts for 91.8% to 99%, and the discharge capacity corresponding to the second discharge voltage platform accounts for 1% to 8.2%.

[0084] Therefore, by ensuring that the proportions of the discharge capacity corresponding to the first discharge voltage plateau and the discharge capacity corresponding to the second discharge voltage plateau in the first battery cell 61 are within the aforementioned range, the energy that the first battery cell 61 can release at low temperatures can be increased, thereby improving the overall low-temperature energy retention rate of the battery pack 1.

[0085] In some embodiments, in the second battery cell 62, when the sum of the discharge capacity corresponding to the first discharge voltage platform and the discharge capacity corresponding to the second discharge voltage platform is 100%, the discharge capacity corresponding to the first discharge voltage platform accounts for 75.7% to 96.8%, and the discharge capacity corresponding to the second discharge voltage platform accounts for 3.2% to 24.3%.

[0086] Therefore, by ensuring that the proportions of the discharge capacity corresponding to the first discharge voltage plateau and the discharge capacity corresponding to the second discharge voltage plateau in the second battery cell 62 are within the aforementioned range, the energy that the second battery cell 62 can release at low temperatures can be increased, thereby further improving the overall low-temperature energy retention rate of the battery pack 1.

[0087] In some embodiments, in the third battery cell 63, when the sum of the discharge capacity corresponding to the first discharge voltage platform and the discharge capacity corresponding to the second discharge voltage platform is 100%, the discharge capacity corresponding to the first discharge voltage platform accounts for 60.2% to 89.4%, and the discharge capacity corresponding to the second discharge voltage platform accounts for 10.6% to 39.8%.

[0088] Therefore, by ensuring that the proportions of the discharge capacity corresponding to the first discharge voltage plateau and the discharge capacity corresponding to the second discharge voltage plateau in the third battery cell 63 are within the aforementioned range, the energy that the third battery cell 63 can release at low temperatures can be increased, thereby further improving the overall low-temperature energy retention rate of the battery pack 1.

[0089] In some embodiments, in the fourth battery cell 64, when the sum of the discharge capacity corresponding to the first discharge voltage platform and the discharge capacity corresponding to the second discharge voltage platform is 100%, the discharge capacity corresponding to the first discharge voltage platform accounts for 52.5% to 80.3%, and the discharge capacity corresponding to the second discharge voltage platform accounts for 19.7% to 47.5%.

[0090] Therefore, by ensuring that the proportions of the discharge capacity corresponding to the first discharge voltage plateau and the discharge capacity corresponding to the second discharge voltage plateau in the fourth battery cell 64 are within the aforementioned range, the energy that the fourth battery cell 64 can release at low temperatures can be increased, thereby further improving the overall low-temperature energy retention rate of the battery pack 1.

[0091] In some embodiments, the positive electrode active material of each of the first battery cell 61, the second battery cell 62, the third battery cell 63 and the fourth battery cell 64 is a mixture of a first positive electrode active material having the first discharge voltage platform and a second positive electrode active material having the second discharge voltage platform.

[0092] Therefore, the first battery cell 61, the second battery cell 62, the third battery cell 63, and the fourth battery cell 64 each have a first discharge voltage platform and a second discharge voltage platform with different discharge voltages. After discharging using the first discharge voltage platform with a higher discharge voltage, they can continue to discharge using the second discharge voltage platform with a lower discharge voltage, thereby improving the low-temperature energy retention rate of the first battery cell 61, the second battery cell 62, the third battery cell 63, and the fourth battery cell 64.

[0093] In some embodiments, the first positive electrode active material and the second positive electrode active material are each independently selected from at least one of lithium nickel oxide, lithium cobalt oxide, lithium nickel cobalt manganese oxide, lithium nickel cobalt aluminum oxide, lithium iron phosphate, lithium manganese oxide, lithium titanate, and manganese dioxide.

[0094] Therefore, as long as the ratio of the discharge voltage and discharge capacity of the first discharge voltage plateau generated by the first positive electrode active material and the second discharge voltage plateau generated by the second positive electrode active material satisfies the above relationship, the first positive electrode active material and the second positive electrode active material can be selected from various existing positive electrode active materials, thereby enabling the battery pack of this application to be easily realized using existing positive electrode active materials.

[0095] In some embodiments, the first positive electrode active material is lithium nickel cobalt manganese oxide and the second positive electrode active material is lithium iron phosphate; or, the first positive electrode active material is lithium nickel cobalt manganese oxide and the second positive electrode active material is lithium manganese oxide or lithium titanate; or, the first positive electrode active material is lithium iron phosphate and the second positive electrode active material is lithium manganese oxide or lithium titanate.

[0096] The voltage platform and specific energy are generally in the following order: lithium nickel cobalt manganese oxide (LCO) > lithium iron phosphate (LFP) > lithium manganese oxide (LMO) or lithium titanate. Therefore, relatively speaking, the energy density order is: LCO + LFP > LCO + LMO or LMO > LFP + LMO or LMO. Correspondingly, in modules or battery packs of the same volume, the driving range order of the above three systems is: LCO + LFP > LCO + LMO or LMO > LFP + LMO or LMO. Therefore, the LCO + LFP system is more suitable for scenarios with higher driving range or higher output power requirements; LCO + LMO or LMO is suitable for scenarios with moderate driving range or moderate output power; and LFP + LMO or LMO is more suitable for scenarios with low-speed commuter vehicles and other scenarios with low output power requirements.

[0097] In some embodiments, when the first positive electrode active material and the second positive electrode active material are the same in the first battery cell 61, the second battery cell 62, the third battery cell 63, and the fourth battery cell 64, the mass percentage of the first positive electrode active material in the positive electrode active material decreases in the order of the first battery cell 61, the second battery cell 62, the third battery cell 63, and the fourth battery cell 64, and the mass percentage of the second positive electrode active material in the positive electrode active material increases in the order of the first battery cell 61, the second battery cell 62, the third battery cell 63, and the fourth battery cell 64.

[0098] The greater the mass ratio of the second positive electrode active material used to generate the second discharge voltage platform with a lower discharge voltage, the greater the discharge capacity ratio corresponding to the second discharge voltage platform, and the higher the low-temperature energy retention rate of the battery cell. By ensuring that the mass ratio of the second positive electrode active material of the fourth battery cell 64 configured in the fourth region R4 is greater than the mass ratio of the second positive electrode active material of the third battery cell 63 configured in the third region R3, which in turn is greater than the mass ratio of the second positive electrode active material of the second battery cell 62 configured in the second region R2, which in turn is greater than the mass ratio of the second positive electrode active material of the first battery cell 61 configured in the first region R1, the low-temperature energy retention rate of the fourth battery cell 64 is greater than that of the third battery cell 63, which in turn is greater than that of the second battery cell 62, which in turn is greater than that of the first battery cell 61. This ensures that the energy released by the first battery cell 61, the second battery cell 62, the third battery cell 63, and the fourth battery cell 64 at low temperatures is approximately the same, thereby improving the overall energy retention rate of the battery pack 1 at low temperatures.

[0099] In some embodiments, in the first battery cell 61, when the total mass of the first positive electrode active material and the second positive electrode active material is 100%, the mass of the first positive electrode active material accounts for 92.5% to 97.5%, and the mass of the second positive electrode active material accounts for 2.5% to 7.5%.

[0100] Therefore, by ensuring that the mass ratio of the first positive electrode active material and the second positive electrode active material in the first battery cell 61 is within the above-mentioned range, the proportions of the discharge capacity corresponding to the first discharge voltage plateau and the discharge capacity corresponding to the second discharge voltage plateau in the first battery cell 61 are respectively within the above-mentioned range, thereby increasing the energy that the first battery cell 61 can release at low temperatures, and thus improving the overall low-temperature energy retention rate of the battery pack 1.

[0101] In some embodiments, in the second battery cell 62, when the total mass of the first positive electrode active material and the second positive electrode active material is 100%, the mass of the first positive electrode active material accounts for 77.5% to 92.5%, and the mass of the second positive electrode active material accounts for 7.5% to 22.5%.

[0102] Therefore, by ensuring that the mass ratio of the first positive electrode active material and the second positive electrode active material in the second battery cell 62 is within the above-mentioned range, the proportions of the discharge capacity corresponding to the first discharge voltage plateau and the discharge capacity corresponding to the second discharge voltage plateau in the second battery cell 62 are respectively within the above-mentioned range, thereby increasing the energy that the second battery cell 62 can release at low temperatures, and further improving the overall low-temperature energy retention rate of the battery pack 1.

[0103] In some embodiments, in the third battery cell 63, when the total mass of the first positive electrode active material and the second positive electrode active material is 100%, the mass of the first positive electrode active material accounts for 62.5% to 77.5%, and the mass of the second positive electrode active material accounts for 22.5% to 37.5%.

[0104] Therefore, by ensuring that the mass ratio of the first positive electrode active material and the second positive electrode active material in the third battery cell 63 is within the above-mentioned range, the proportions of the discharge capacity corresponding to the first discharge voltage platform and the discharge capacity corresponding to the second discharge voltage platform in the third battery cell 63 can be within the above-mentioned range, thereby increasing the energy that the third battery cell 63 can release at low temperatures, and further improving the overall low-temperature energy retention rate of the battery pack 1.

[0105] In some embodiments, in the fourth battery cell 64, when the total mass of the first positive electrode active material and the second positive electrode active material is 100%, the mass of the first positive electrode active material accounts for 50% to 62.5%, and the mass of the second positive electrode active material accounts for 37.5% to 50%.

[0106] Therefore, by ensuring that the mass ratio of the first positive electrode active material and the second positive electrode active material in the fourth battery cell 64 is within the above-mentioned range, the proportions of the discharge capacity corresponding to the first discharge voltage plateau and the discharge capacity corresponding to the second discharge voltage plateau in the fourth battery cell 64 can be within the above-mentioned range, thereby increasing the energy that the fourth battery cell 64 can release at low temperatures, and further improving the overall low-temperature energy retention rate of the battery pack 1.

[0107] In some embodiments, when the first positive electrode active material is lithium nickel cobalt manganese oxide and the second positive electrode active material is lithium iron phosphate, the mass ratio of the second positive electrode active material in the first battery cell 61, the second battery cell 62, the third battery cell 63, and the fourth battery cell 64 is 1:(1-3):(3-5):(5-9); when the first positive electrode active material is lithium nickel cobalt manganese oxide and the second positive electrode active material is lithium titanate or lithium manganese oxide, the mass ratio of the second positive electrode active material in the first battery cell 61, the second battery cell 62, the third battery cell 63, and the fourth battery cell 64 is 1:(1-2):(3-4):(5-7); when the first positive electrode active material is lithium iron phosphate and the second positive electrode active material is lithium titanate or lithium manganese oxide, the mass ratio of the second positive electrode active material in the first battery cell 61, the second battery cell 62, the third battery cell 63, and the fourth battery cell 64 is 1:(1-3):(3-5):(5-9).

[0108] Therefore, by using specific first positive electrode active materials and specific second positive electrode active materials in specific mass ratios in the first battery cell 61, the second battery cell 62, the third battery cell 63 and the fourth battery cell 64, the battery pack of this application suitable for different scenarios can be easily realized.

[0109] In some embodiments, at temperatures below 0°C, the discharge cutoff voltage of the first battery cell 61 is 0 to 0.3V higher than that of the second battery cell 62, the discharge cutoff voltage of the second battery cell 62 is 0 to 0.3V higher than that of the third battery cell 63, the discharge cutoff voltage of the third battery cell 63 is 0 to 0.3V higher than that of the fourth battery cell 64, and the discharge cutoff voltage of the fourth battery cell 64 is 1.6V or higher.

[0110] Therefore, by setting the discharge cutoff voltages of the first battery cell 61, the second battery cell 62, the third battery cell 63, and the fourth battery cell 64 as described above, the energy released by the first battery cell 61, the second battery cell 62, the third battery cell 63, and the fourth battery cell 64 at low temperatures can be made to be approximately the same, thereby improving the overall energy retention rate of the battery pack at low temperatures.

[0111] Excessively high charging cut-off voltage or excessively low discharging cut-off voltage can damage the cycle performance of individual battery cells. With an excessively high charging cut-off voltage, the battery cell will overcharge. Continuing to charge a fully charged cell will cause structural changes in the positive electrode material, resulting in capacity loss. Furthermore, the oxygen released from the decomposition of the positive electrode material will react violently with the electrolyte, potentially leading to an explosion. With an excessively low discharging cut-off voltage, the battery cell will over-discharge. Over-discharging increases the internal pressure of the battery cell, disrupting the reversibility of the positive and negative electrode active materials. Even with charging, only partial recovery is possible, and capacity will significantly decrease. Deep charging and discharging of battery cells increases cell wear. The ideal operating state for a battery cell is shallow charging and shallow discharging, which extends its lifespan.

[0112] In some embodiments, the ratio of the number of the first battery cell 61 to the number of the second battery cell 62 to the number of the third battery cell 63 to the number of the fourth battery cell 64 is (3-8):(8-13):(9-14):1. In other words, when the sum of the numbers of the first battery cell 61, the second battery cell 62, the third battery cell 63, and the fourth battery cell 64 is 100%, the proportion of the first battery cell 61 is 10-30%, the proportion of the second battery cell 62 is 25-50%, the proportion of the third battery cell 63 is 30-55%, and the proportion of the fourth battery cell 64 is 2-5%.

[0113] In some implementations, the number of first battery cells can be 1.

[0114] Therefore, the battery pack of this application can be easily realized by setting the number of the first battery cell 61, the second battery cell 62, the third battery cell 63 and the fourth battery cell 64 according to the temperature distribution range of common battery packs.

[0115] In some embodiments, capacitors are disposed in the gaps between different battery cells (e.g., see reference). Figure 2 (Capacitors C11 and C12 in the capacitor).

[0116] This allows for full utilization of the gaps between individual battery cells, thereby increasing the overall volumetric energy density of the battery pack.

[0117] Electrical appliances

[0118] In addition, this application also provides an electrical device, which includes the battery pack of this application. The 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.

[0119] As the electrical device, a single battery cell or a battery pack can be selected according to its usage requirements.

[0120] Figure 4 This is an example of an electrical device. The device can be a pure electric vehicle, a hybrid electric vehicle, or a plug-in hybrid electric vehicle, etc. To meet the device's requirement for range at low temperatures, the battery pack described in this application can be used.

[0121] Example

[0122] 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.

[0123] (I) Preparation of battery cells

[0124] I. Preparation of the first battery cell

[0125] [Preparation Example I-1]

[0126] 1) Preparation of positive electrode sheet

[0127] LiNi will be used as the first positive electrode active material. 0.6 Co 0.2 Mn 0.2 O2 (NCM), lithium iron phosphate (LFP) as the second positive electrode active material, superconducting carbon black (SP) as a conductive agent, and polyvinylidene fluoride (PVDF) as a binder are dispersed in N-methylpyrrolidone (NMP) as a 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.

[0128] The mass ratio of the positive electrode active material, conductive carbon black, and binder PVDF is 96:2:2, and the mass ratio of the second positive electrode active material LFP to the first positive electrode active material NCM is 5:95.

[0129] 2) Preparation of negative electrode sheet

[0130] 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.

[0131] 3) Separating membrane

[0132] Polyethylene film was selected as the separator.

[0133] 4) Preparation of electrolyte

[0134] 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.

[0135] 5) Preparation of battery cells

[0136] 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, the first battery cell I-1 is obtained.

[0137] [Preparation Example I-2]

[0138] In addition to using LiNi as the primary positive electrode active material 0.6 Co 0.2 Mn 0.2 Except for O2 (NCM) and the second positive electrode active material lithium manganese oxide (LMO), the same procedure as in Preparation Example I-1 was followed to obtain the first battery cell I-2.

[0139] [Preparation Example I-3]

[0140] In addition to using LiNi as the primary positive electrode active material 0.6 Co 0.2 Mn 0.2 Except for O2 (NCM) and the second positive electrode active material lithium titanate (LTO), the same procedure as in Preparation Example I-1 was followed to obtain the first battery cell I-3.

[0141] [Preparation Example I-4]

[0142] Except that the first positive electrode active material used is lithium iron phosphate (LFP) and the second positive electrode active material is lithium manganese oxide (LMO), the same procedure as in preparation example I-1 was followed to obtain the first battery cell I-4.

[0143] [Preparation Example I-5]

[0144] Except that the first positive electrode active material used is lithium iron phosphate (LFP) and the second positive electrode active material is lithium titanate (LTO), the same procedure as in preparation example I-1 was followed to obtain the first battery cell I-5.

[0145] [Preparation Examples I-6]

[0146] Except that the mass ratio of the second positive electrode active material LFP to the first positive electrode active material NCM is 2.5:97.5, the same procedure as in preparation example I-1 was followed to obtain the first battery cell I-6.

[0147] [Preparation Example I-7]

[0148] Except that the mass ratio of the second positive electrode active material LMO to the first positive electrode active material NCM is 2.5:97.5, the same procedure as in preparation example I-2 was followed to obtain the first battery cell I-7.

[0149] [Preparation Example I-8]

[0150] Except that the mass ratio of the second positive electrode active material LTO to the first positive electrode active material NCM is 2.5:97.5, the same procedure as in preparation example I-3 was followed to obtain the first battery cell I-8.

[0151] [Preparation Example I-9]

[0152] Except that the mass ratio of the second positive electrode active material LMO to the first positive electrode active material LFP is 2.5:97.5, the same procedure as in preparation example I-4 was followed to obtain the first battery cell I-9.

[0153] [Preparation Example I-10]

[0154] Except that the mass ratio of the second positive electrode active material LTO to the first positive electrode active material LFP is 2.5:97.5, the same procedure as in preparation example I-5 was followed to obtain the first battery cell I-10.

[0155] [Preparation Example I-11]

[0156] Except that the mass ratio of the second positive electrode active material LTO to the first positive electrode active material LFP is 7.5:92.5, the same procedure as in preparation example I-5 was followed to obtain the first battery cell I-11.

[0157] [Preparation Example I-12]

[0158] Except that only NCM is used as the positive electrode active material, the same procedure as in Preparation Example I-1 was followed to obtain the first battery cell I-12.

[0159] [Preparation Example I-13]

[0160] Except that the mass ratio of the second positive electrode active material LFP to the first positive electrode active material NCM is 37.5:62.5, the same procedure as in preparation example I-1 was followed to obtain the first battery cell I-13.

[0161] [Preparation Example I-14]

[0162] Except that the mass ratio of the second positive electrode active material LTO to the first positive electrode active material NCM is 55:45, the same procedure as in preparation example I-3 was followed to obtain the first battery cell I-14.

[0163] [Preparation Example I-15]

[0164] Except that the mass ratio of the second positive electrode active material LTO to the first positive electrode active material NCM is 0.5:99.5, the same procedure as in preparation example I-3 was followed to obtain the first battery cell I-15.

[0165] [Preparation Example I-16]

[0166] Except that the mass ratio of the second positive electrode active material LTO to the first positive electrode active material LFP is 22.5:77.5, the same procedure as in preparation example I-5 was followed to obtain the first battery cell I-16.

[0167] II. Preparation of the second battery cell

[0168] [Preparation Example II-1]

[0169] Except that the mass ratio of the second positive electrode active material LFP to the first positive electrode active material NCM is 12.5:87.5, the same procedure as in Preparation Example I-1 was followed to obtain the second battery cell II-1.

[0170] [Preparation Example II-2]

[0171] Except that the mass ratio of the second positive electrode active material LMO to the first positive electrode active material NCM is 12.5:87.5, the same procedure as in preparation example I-2 was followed to obtain the second battery cell II-2.

[0172] [Preparation Example II-3]

[0173] Except that the mass ratio of the second positive electrode active material LTO to the first positive electrode active material NCM is 12.5:87.5, the same procedure as in preparation example I-3 was followed to obtain the second battery cell II-3.

[0174] [Preparation Example II-4]

[0175] Except that the mass ratio of the second positive electrode active material LMO to the first positive electrode active material LFP is 12.5:87.5, the same procedure as in Preparation Example I-4 was followed to obtain the second battery cell II-4.

[0176] [Preparation Example II-5]

[0177] Except that the mass ratio of the second positive electrode active material LTO to the first positive electrode active material LFP is 12.5:87.5, the same procedure as in preparation example I-5 was followed to obtain the second battery cell II-5.

[0178] [Preparation Example II-6]

[0179] Except that the mass ratio of the second positive electrode active material LMO to the first positive electrode active material NCM is 7.5:92.5, the same procedure as in preparation example I-2 was followed to obtain the second battery cell II-6.

[0180] [Preparation Example II-7]

[0181] Except that the mass ratio of the second positive electrode active material LTO to the first positive electrode active material LFP is 22.5:77.5, the same procedure as in Preparation Example I-5 was followed to obtain the second battery cell II-7.

[0182] [Preparation Example II-8]

[0183] Except that only LFP is used as the positive electrode active material, the same procedure as in Preparation Example I-1 was followed to obtain the second battery cell II-8.

[0184] [Preparation Example II-9]

[0185] Except that only NCM is used as the positive electrode active material, the same procedure as in Preparation Example I-1 was followed to obtain the second battery cell II-9.

[0186] [Preparation Example II-10]

[0187] Except that the mass ratio of the second positive electrode active material LFP to the first positive electrode active material NCM is 22.5:77.5, the same procedure as in Preparation Example I-1 was followed to obtain the second battery cell II-10.

[0188] [Preparation Example II-11]

[0189] Except that the mass ratio of the second positive electrode active material LTO to the first positive electrode active material NCM is 65:35, the same procedure as in Preparation Example I-3 was followed to obtain the second battery cell II-11.

[0190] [Preparation Example II-12]

[0191] Except that the mass ratio of the second positive electrode active material LTO to the first positive electrode active material NCM is 1:99, the same procedure as in Preparation Example I-3 was followed to obtain the second battery cell II-12.

[0192] [Preparation Example II-13]

[0193] Except that the mass ratio of the second positive electrode active material LTO to the first positive electrode active material LFP is 60:40, the same procedure as in Preparation Example I-5 was followed to obtain the second battery cell II-13.

[0194] III. Preparation of the third battery cell

[0195] [Preparation Example III-1]

[0196] Except that the mass ratio of the second positive electrode active material LFP to the first positive electrode active material NCM is 22.5:77.5, the same procedure as in Preparation Example I-1 was followed to obtain the third battery cell III-1.

[0197] [Preparation Example III-2]

[0198] Except that the mass ratio of the second positive electrode active material LMO to the first positive electrode active material NCM is 22.5:77.5, the same procedure as in Preparation Example I-2 was followed to obtain the third battery cell III-2.

[0199] [Preparation Example III-3]

[0200] Except that the mass ratio of the second positive electrode active material LTO to the first positive electrode active material NCM is 22.5:77.5, the same procedure as in Preparation Example I-3 was followed to obtain the third battery cell III-3.

[0201] [Preparation Example III-4]

[0202] Except that the mass ratio of the second positive electrode active material LMO to the first positive electrode active material LFP is 22.5:77.5, the same procedure as in Preparation Example I-4 was followed to obtain the third battery cell III-4.

[0203] [Preparation Example III-5]

[0204] Except that the mass ratio of the second positive electrode active material LTO to the first positive electrode active material LFP is 22.5:77.5, the same procedure as in Preparation Example I-5 was followed to obtain the third battery cell III-5.

[0205] [Preparation Example III-6]

[0206] Except that the mass ratio of the second positive electrode active material LTO to the first positive electrode active material LFP is 37.5:62.5, the same procedure as in Preparation Example I-5 was followed to obtain the third battery cell III-6.

[0207] [Preparation Example III-7]

[0208] Except that LMO was used as the positive electrode active material, the same procedure as in Preparation Example I-1 was followed to obtain the third cell III-7.

[0209] [Preparation Example III-8]

[0210] Except that only NCM was used as the positive electrode active material, the same procedure as in Preparation Example I-1 was followed to obtain the third battery cell III-8.

[0211] [Preparation Example III-9]

[0212] Except that the mass ratio of the second positive electrode active material LFP to the first positive electrode active material NCM is 12.5:87.5, the same procedure as in Preparation Example I-1 was followed to obtain the third battery cell III-9.

[0213] [Preparation Example III-10]

[0214] Except that the mass ratio of the second positive electrode active material LTO to the first positive electrode active material NCM is 65:35, the same procedure as in Preparation Example I-3 was followed to obtain the third battery cell III-10.

[0215] [Preparation Example III-11]

[0216] Except that the mass ratio of the second positive electrode active material LTO to the first positive electrode active material NCM is 1.5:98.5, the same procedure as in Preparation Example I-3 was followed to obtain the third battery cell III-11.

[0217] [Preparation Example III-12]

[0218] Except that the mass ratio of the second positive electrode active material LTO to the first positive electrode active material LFP is 50:50, the same procedure as in Preparation Example I-5 was followed to obtain the third battery cell III-12.

[0219] IV. Preparation of the fourth battery cell

[0220] [Preparation Example IV-1]

[0221] Except that the mass ratio of the second positive electrode active material LFP to the first positive electrode active material NCM is 37.5:62.5, the same procedure as in Preparation Example I-1 was followed to obtain the fourth battery cell IV-1.

[0222] [Preparation Example IV-2]

[0223] Except that the mass ratio of the second positive electrode active material LMO to the first positive electrode active material NCM is 37.5:62.5, the same procedure as in Preparation Example I-2 was followed to obtain the fourth battery cell IV-2.

[0224] [Preparation Example IV-3]

[0225] Except that the mass ratio of the second positive electrode active material LTO to the first positive electrode active material NCM is 37.5:62.5, the same procedure as in preparation example I-3 was followed to obtain the fourth battery cell IV-3.

[0226] [Preparation Example IV-4]

[0227] Except that the mass ratio of the second positive electrode active material LMO to the first positive electrode active material LFP is 37.5:62.5, the same procedure as in Preparation Example I-4 was followed to obtain the fourth battery cell IV-4.

[0228] [Preparation Example IV-5]

[0229] Except that the mass ratio of the second positive electrode active material LTO to the first positive electrode active material LFP is 37.5:62.5, the same procedure as in Preparation Example I-5 was followed to obtain the fourth battery cell IV-5.

[0230] [Preparation Example IV-6]

[0231] Except that the mass ratio of the second positive electrode active material LFP to the first positive electrode active material NCM is 50:50, the same procedure as in Preparation Example I-1 was followed to obtain the fourth battery cell IV-6.

[0232] [Preparation Example IV-7]

[0233] Except that the mass ratio of the second positive electrode active material LMO to the first positive electrode active material NCM is 50:50, the same procedure as in Preparation Example I-2 was followed to obtain the fourth battery cell IV-7.

[0234] [Preparation Example IV-8]

[0235] Except that the mass ratio of the second positive electrode active material LTO to the first positive electrode active material NCM is 50:50, the same procedure as in Preparation Example I-3 was followed to obtain the fourth battery cell IV-8.

[0236] [Preparation Example IV-9]

[0237] Except that the mass ratio of the second positive electrode active material LMO to the first positive electrode active material LFP is 50:50, the same procedure as in Preparation Example I-4 was followed to obtain the fourth battery cell IV-9.

[0238] [Preparation Example IV-10]

[0239] Except that the mass ratio of the second positive electrode active material LTO to the first positive electrode active material LFP is 50:50, the same procedure as in Preparation Example I-5 was followed to obtain the fourth battery cell IV-10.

[0240] [Preparation Example IV-11]

[0241] Except that the mass ratio of the second positive electrode active material LFP to the first positive electrode active material NCM is 22.5:77.5, the same procedure as in Preparation Example I-1 was followed to obtain the fourth battery cell IV-11.

[0242] [Preparation Example IV-12]

[0243] Except that LTO was used as the positive electrode active material, the same procedure as in Preparation Example I-1 was followed to obtain the fourth battery cell IV-12.

[0244] [Preparation Example IV-13]

[0245] Except that only NCM was used as the positive electrode active material, the same procedure as in Preparation Example I-1 was followed to obtain the fourth battery cell IV-13.

[0246] [Preparation Example IV-14]

[0247] Except that the mass ratio of the second positive electrode active material LFP to the first positive electrode active material NCM is 5:95, the same procedure as in Preparation Example I-1 was followed to obtain the fourth battery cell IV-14.

[0248] [Preparation Example IV-15]

[0249] Except that the mass ratio of the second positive electrode active material LTO to the first positive electrode active material NCM is 65:35, the same procedure as in Preparation Example I-3 was followed to obtain the fourth battery cell IV-15.

[0250] [Preparation Example IV-16]

[0251] Except that the mass ratio of the second positive electrode active material LTO to the first positive electrode active material NCM is 2:98, the same procedure as in Preparation Example I-3 was followed to obtain the fourth battery cell IV-16.

[0252] (II) Assembly of the battery pack

[0253] [Example 1]

[0254] like Figure 2 As shown, the internal space of the battery pack housing is divided into a first region R1, a second region R2, a third region R3, and a fourth region R4. In the first region R1, a first battery cell I-1 is configured as the first battery cell 61; in the second region R2, a second battery cell II-1 is configured as the second battery cell 62; in the third region R3, a third battery cell III-1 is configured as the third battery cell 63; and in the fourth region R4, a fourth battery cell IV-1 is configured as the fourth battery cell 64, assembled into a battery pack. The ratio of the number of first battery cells 61 to the number of second battery cells 62 to the number of third battery cells 63 to the number of fourth battery cells 64 is 12:32:36:4.

[0255] [Example 2]

[0256] Except for replacing the first battery cell I-1 with the first battery cell I-2, replacing the second battery cell II-1 with the second battery cell II-2, replacing the third battery cell III-1 with the third battery cell III-2, and replacing the fourth battery cell IV-1 with the fourth battery cell IV-2, the battery pack is assembled in the same manner as in Example 1.

[0257] [Example 3]

[0258] Except for replacing the first battery cell I-1 with the first battery cell I-3, replacing the second battery cell II-1 with the second battery cell II-3, replacing the third battery cell III-1 with the third battery cell III-3, and replacing the fourth battery cell IV-1 with the fourth battery cell IV-3, the battery pack is assembled in the same manner as in Example 1.

[0259] [Example 4]

[0260] Except for replacing the first battery cell I-1 with the first battery cell I-4, replacing the second battery cell II-1 with the second battery cell II-4, replacing the third battery cell III-1 with the third battery cell III-4, and replacing the fourth battery cell IV-1 with the fourth battery cell IV-4, the battery pack is assembled in the same manner as in Example 1.

[0261] [Example 5]

[0262] Except for replacing the first battery cell I-1 with the first battery cell I-5, replacing the second battery cell II-1 with the second battery cell II-5, replacing the third battery cell III-1 with the third battery cell III-5, and replacing the fourth battery cell IV-1 with the fourth battery cell IV-5, the battery pack is assembled in the same manner as in Example 1.

[0263] [Example 6]

[0264] Except for replacing the first battery cell I-1 with the first battery cell I-6 and replacing the fourth battery cell IV-1 with the fourth battery cell IV-6, the battery pack is assembled in the same manner as in Example 1.

[0265] [Example 7]

[0266] Except for replacing the first battery cell I-1 with the first battery cell I-7, replacing the second battery cell II-1 with the second battery cell II-2, replacing the third battery cell III-1 with the third battery cell III-2, and replacing the fourth battery cell IV-1 with the fourth battery cell IV-7, the battery pack is assembled in the same manner as in Example 1.

[0267] [Example 8]

[0268] Except for replacing the first battery cell I-1 with the first battery cell I-8, replacing the second battery cell II-1 with the second battery cell II-3, replacing the third battery cell III-1 with the third battery cell III-3, and replacing the fourth battery cell IV-1 with the fourth battery cell IV-8, the battery pack is assembled in the same manner as in Example 1.

[0269] [Example 9]

[0270] Except for replacing the first battery cell I-1 with the first battery cell I-9, replacing the second battery cell II-1 with the second battery cell II-4, replacing the third battery cell III-1 with the third battery cell III-4, and replacing the fourth battery cell IV-1 with the fourth battery cell IV-9, the battery pack is assembled in the same manner as in Example 1.

[0271] [Example 10]

[0272] Except for replacing the first battery cell I-1 with the first battery cell I-10, replacing the second battery cell II-1 with the second battery cell II-5, replacing the third battery cell III-1 with the third battery cell III-5, and replacing the fourth battery cell IV-1 with the fourth battery cell IV-10, the battery pack is assembled in the same manner as in Example 1.

[0273] [Example 11]

[0274] Except for replacing the first battery cell I-1 with the first battery cell I-14, replacing the second battery cell II-1 with the second battery cell II-11, replacing the third battery cell III-1 with the third battery cell III-10, and replacing the fourth battery cell IV-1 with the fourth battery cell IV-15, the battery pack is assembled in the same manner as in Example 1.

[0275] [Example 12]

[0276] Except for replacing the first battery cell I-1 with the first battery cell I-15, replacing the second battery cell II-1 with the second battery cell II-12, replacing the third battery cell III-1 with the third battery cell III-11, and replacing the fourth battery cell IV-1 with the fourth battery cell IV-16, the battery pack is assembled in the same manner as in Example 1.

[0277] [Example 13]

[0278] Except for replacing the first battery cell I-1 with the first battery cell I-7, replacing the second battery cell II-1 with the second battery cell II-6, replacing the third battery cell III-1 with the third battery cell III-2, and replacing the fourth battery cell IV-1 with the fourth battery cell IV-2, the battery pack is assembled in the same manner as in Example 1.

[0279] [Example 14]

[0280] Except for replacing the first battery cell I-1 with the first battery cell I-7, replacing the second battery cell II-1 with the second battery cell II-6, replacing the third battery cell III-1 with the third battery cell III-6, and replacing the fourth battery cell IV-1 with the fourth battery cell IV-10, the battery pack is assembled in the same manner as in Example 1.

[0281] [Example 15]

[0282] Except that the first battery cell I-1 is replaced by the first battery cell I-11, the second battery cell II-1 is replaced by the second battery cell II-7, the third battery cell III-1 is replaced by the third battery cell III-6, and the fourth battery cell IV-10 is replaced by the fourth battery cell IV-1, the battery pack is assembled in the same manner as in Example 1.

[0283] [Example 16]

[0284] Except for replacing the first battery cell I-1 with the first battery cell I-16, replacing the second battery cell II-3 with the second battery cell II-13, replacing the third battery cell III-1 with the third battery cell III-12, and replacing the fourth battery cell IV-1 with the fourth battery cell IV-10, the battery pack is assembled in the same manner as in Example 1.

[0285] [Example 17]

[0286] The same procedure as in Example 1 was followed to assemble the battery pack.

[0287] [Example 18]

[0288] The same procedure as in Example 1 was followed to assemble the battery pack.

[0289] [Example 19]

[0290] The same procedure as in Example 1 was followed to assemble the battery pack.

[0291] [Example 20]

[0292] The same procedure as in Example 1 was followed to assemble the battery pack.

[0293] [Example 21]

[0294] The same procedure as in Example 1 was followed to assemble the battery pack.

[0295] [Example 22]

[0296] The same procedure as in Example 1 was followed to assemble the battery pack.

[0297] [Example 23]

[0298] The same procedure as in Example 1 was followed to assemble the battery pack.

[0299] [Comparative Example 1]

[0300] Except that the first battery cell I-1 is replaced by the first battery cell I-12, the second battery cell II-1 is replaced by the second battery cell II-8, the third battery cell III-1 is replaced by the third battery cell III-7, and the fourth battery cell IV-12 is replaced by the fourth battery cell IV-1, the battery pack is assembled in the same manner as in Example 1.

[0301] [Comparative Example 2]

[0302] Except that the first battery cell I-1 is replaced by the first battery cell I-12, the second battery cell II-1 is replaced by the second battery cell II-9, the third battery cell III-1 is replaced by the third battery cell III-8, and the fourth battery cell IV-13 is replaced by the fourth battery cell IV-1, the battery pack is assembled in the same manner as in Example 1.

[0303] [Comparative Example 3]

[0304] Except that the first battery cell I-1 is replaced by the first battery cell I-13, the second battery cell II-1 is replaced by the second battery cell II-10, the third battery cell III-1 is replaced by the third battery cell III-9, and the fourth battery cell IV-14 is replaced by the fourth battery cell IV-1, the battery pack is assembled in the same manner as in Example 1.

[0305] (III) Related Tests

[0306] 1. Determination of discharge capacity corresponding to the first discharge voltage plateau and the second discharge voltage plateau of a single battery cell.

[0307] For the first, second, third, and fourth battery cells in each battery pack of Examples 1-23 and Comparative Examples 1-3, the discharge capacity corresponding to the first discharge voltage plateau and the discharge capacity corresponding to the second discharge voltage plateau of each of the first, second, third, and fourth battery cells at 25°C were measured using a Xinwei Power Battery Tester (model BTS-5V300A-4CH). Then, the percentage of discharge capacity corresponding to the second discharge voltage plateau of each of the first, second, third, and fourth battery cells was calculated.

[0308] The method for measuring the discharge capacity of a single battery cell is as follows:

[0309] (1) Let the battery cell stand at 25°C for 2 hours to ensure that the temperature of the battery cell is 25°C;

[0310] (2) Charge the battery cell at 0.33C at 25°C to the charging cutoff voltage shown in Table 1 below, and continue constant voltage charging at the charging cutoff voltage until the current is 0.05C and the charging is cut off (where C represents the rated capacity of the battery cell).

[0311] (3) Let the battery cells stand at 25°C for 1 hour;

[0312] (4) Discharge the battery cell at 0.33C at 25℃ to the discharge cutoff voltage shown in Table 1 below, and record the total discharge capacity C0 of the battery cell.

[0313] (5) Obtain the discharge curve from step (4), for example, as in this application. Figure 3 The discharge curve represented by the dashed line in the middle, Figure 3 In the discharge curve represented by the dashed line, the total discharge capacity before point B is the discharge capacity C1 corresponding to the first discharge voltage plateau, and the discharge capacity from point B to the discharge cutoff voltage is the discharge capacity C2 corresponding to the second discharge voltage plateau.

[0314] Therefore, the discharge capacity percentage corresponding to the first discharge voltage plateau of a battery cell is C1 / C0, and the discharge capacity percentage corresponding to the second discharge voltage plateau of a battery cell is C2 / C0.

[0315] [Table 1]

[0316] NCM+LFP 4.2 2.5 NCM+LMO 4.2 2 NCM+LTO 4.2 2 LFP+LMO 3.6 2 LFP+LTO 3.6 2

[0317] 2. Determination of total energy retention rate of battery pack at -20℃

[0318] In addition, for each battery pack of Examples 1 to 23 and Comparative Examples 1 to 3, the total full discharge energy at 25°C and the total full discharge energy at -20°C of the battery pack were measured using a Xinwei Power Battery Tester (model BTS-5V300A-4CH). The total energy retention rate (%) of the battery pack at -20°C was calculated by dividing the total full discharge energy at -20°C by the total full discharge energy at 25°C.

[0319] The total fully discharged energy of the battery pack at 25℃ was measured in accordance with "7.1.2 Capacity and energy test at room temperature" in "GBT 31467.2-2015 Battery Pack and System High Energy Application Test Procedure".

[0320] The total fully discharged energy of the battery pack at -20℃ was measured according to "7.1.4 Capacity and energy test at low temperature" in GB / T 31467.2-2015 Battery Pack and System High Energy Application Test Procedure. The composition and test results of each battery pack of Examples 1-23 and Comparative Examples 1-3 are shown in Tables 2-5 below.

[0321]

[0322] According to the results in Table 2 above, in Examples 1 to 5, the first battery cell, the second battery cell, the third battery cell, and the fourth battery cell all have a first discharge voltage plateau and a second discharge voltage plateau. Furthermore, the discharge capacity percentage corresponding to the second discharge voltage plateau of the fourth battery cell is greater than that corresponding to the second discharge voltage plateau of the third battery cell, which in turn is greater than that corresponding to the second discharge voltage plateau of the second battery cell, which is greater than that corresponding to the second discharge voltage plateau of the first battery cell. The total energy retention rate of the battery pack at -20°C reaches 89% to 95%.

[0323] In Comparative Examples 1 and 2, the first, second, third, and fourth battery cells each have only one discharge voltage plateau, and the total energy retention rate of the battery pack at -20°C is only 73% and 71%, respectively.

[0324] In Comparative Example 3, although the first, second, third, and fourth battery cells all have a first discharge voltage plateau and a second discharge voltage plateau, the discharge capacity percentage corresponding to the second discharge voltage plateau of the fourth battery cell is less than that of the third battery cell, which is less than that of the second battery cell, which is less than that of the first battery cell. As a result, the total energy retention rate of the battery pack at -20°C is only 64%.

[0325]

[0326] According to the results in Table 3 above, in Examples 1, 6-10, the first battery cell, the second battery cell, the third battery cell, and the fourth battery cell all have a first discharge voltage platform and a second discharge voltage platform. The discharge capacity percentage corresponding to the second discharge voltage platform of the fourth battery cell is greater than that corresponding to the second discharge voltage platform of the third battery cell, which in turn is greater than that corresponding to the second discharge voltage platform of the second battery cell, which is greater than that corresponding to the second discharge voltage platform of the first battery cell. Furthermore, the difference between the lowest discharge voltage of the first discharge voltage platform and the highest discharge voltage of the second discharge voltage platform of each of the first, second, third, and fourth battery cells is in the range of 0.25-0.6V. The total energy retention rate of the battery pack at -20℃ reaches 83%-95%.

[0327] In Example 11, the difference between the lowest discharge voltage of the first discharge voltage platform and the highest discharge voltage of the second discharge voltage platform of each of the first, second, third, and fourth battery cells is less than 0.25V, and the total energy retention rate of the battery pack at -20℃ is 63%.

[0328] In Example 12, the difference between the lowest discharge voltage of the first discharge voltage plateau and the highest discharge voltage of the second discharge voltage plateau of each of the first, second, third, and fourth battery cells is greater than 0.6V, and the total energy retention rate of the battery pack at -20°C is 71%.

[0329]

[0330] According to the results in Table 4 above, in Examples 1, 13-15, the first battery cell, the second battery cell, the third battery cell, and the fourth battery cell all have a first discharge voltage plateau and a second discharge voltage plateau. The discharge capacity percentage corresponding to the second discharge voltage plateau of the fourth battery cell is greater than that corresponding to the second discharge voltage plateau of the third battery cell, which is greater than that corresponding to the second discharge voltage plateau of the second battery cell, which is greater than that corresponding to the second discharge voltage plateau of the first battery cell. Furthermore, the mass percentage of the second positive electrode active material and the discharge capacity percentage corresponding to the second discharge voltage plateau in each of the first, second, third, and fourth battery cells are within the preferred range described in this application, and the total energy retention rate of the battery pack at -20°C reaches 84% ​​to 95%.

[0331] In Example 16, the mass percentage of the second positive electrode active material in each of the first, second, and third battery cells and the discharge capacity percentage corresponding to the second discharge voltage platform are outside the preferred range described in this application, and the total energy retention rate of the battery pack at -20°C is 60%.

[0332]

[0333] According to the results in Table 5 above, in Examples 1 and 17-18, the first battery cell, the second battery cell, the third battery cell, and the fourth battery cell all have a first discharge voltage plateau and a second discharge voltage plateau. The discharge capacity percentage corresponding to the second discharge voltage plateau of the fourth battery cell is greater than that corresponding to the second discharge voltage plateau of the third battery cell, which in turn is greater than that corresponding to the second discharge voltage plateau of the second battery cell, which is greater than that corresponding to the second discharge voltage plateau of the first battery cell. Furthermore, at -20°C, the difference between the discharge cutoff voltage of the first battery cell and the discharge cutoff voltage of the second battery cell, the difference between the discharge cutoff voltage of the second battery cell and the discharge cutoff voltage of the third battery cell and the discharge cutoff voltage of the fourth battery cell, and the discharge cutoff voltage of the fourth battery cell are all within the preferred ranges described in this application. The total energy retention rate of the battery pack at -20°C reaches 87% to 96%.

[0334] In Example 19, the discharge cutoff voltage of the second battery cell at -20°C is greater than that of the first battery cell, and the total energy retention rate of the battery pack at -20°C is 75%.

[0335] In Example 20, at -20°C, the discharge cutoff voltage of the third battery cell is greater than that of the second battery cell, which is greater than that of the first battery cell, and the total energy retention rate of the battery pack at -20°C is 73%.

[0336] In Example 21, at -20°C, the discharge cutoff voltage of the fourth battery cell is greater than that of the third battery cell, which is greater than that of the second battery cell, which is greater than that of the first battery cell. The total energy retention rate of the battery pack at -20°C is 73%.

[0337] In Example 22, the discharge cutoff voltages of the first, second, third, and fourth battery cells at -20°C are too low. Although the total energy retention rate of the battery pack reaches 88% at -20°C, as mentioned above, this will impair the cycle performance of the battery cells.

[0338] In Example 23, although the differences between the discharge cutoff voltage of the first battery cell and the discharge cutoff voltage of the second battery cell, the differences between the discharge cutoff voltage of the second battery cell and the discharge cutoff voltage of the third battery cell, and the differences between the discharge cutoff voltage of the third battery cell and the discharge cutoff voltage of the fourth battery cell at -20°C are within the preferred ranges described in this application, the discharge cutoff voltages of the first battery cell, the second battery cell, the third battery cell, and the fourth battery cell at -20°C are too high, and the total energy retention rate of the battery pack at -20°C is 65%.

[0339] 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, characterized in that, Includes a battery pack housing and individual battery cells housed within the battery pack housing; In the top view, the internal space of the battery pack housing is rectangular in shape; The internal space of the battery pack housing is composed of a first region, a second region, a third region, and a fourth region. In a top view, the first region is located at the center of the rectangular shape of the internal space, the fourth region is located at the four corners of the rectangular shape of the internal space, the third region is located on the four sides of the rectangular shape of the internal space excluding the corners, and the second region is located between the first region and the third region. A first battery cell is disposed in the first region, a second battery cell is disposed in the second region, a third battery cell is disposed in the third region, and a fourth battery cell is disposed in the fourth region. In the top view, the second battery cell does not contact the inner surface of the battery pack housing, the third battery cell only contacts one inner surface of the battery pack housing, and the fourth battery cell contacts both inner surfaces of the battery pack housing. Each of the first battery cell, the second battery cell, the third battery cell, and the fourth battery cell has a first discharge voltage platform and a second discharge voltage platform, and the average discharge voltage of the first discharge voltage platform is higher than the average discharge voltage of the second discharge voltage platform. In each of the first, second, third, and fourth battery cells, when the sum of the discharge capacity corresponding to the first discharge voltage platform and the discharge capacity corresponding to the second discharge voltage platform is 100%, the percentage of discharge capacity corresponding to the second discharge voltage platform of the fourth battery cell is greater than the percentage of discharge capacity corresponding to the second discharge voltage platform of the third battery cell, which in turn is greater than the percentage of discharge capacity corresponding to the second discharge voltage platform of the second battery cell, which is greater than the percentage of discharge capacity corresponding to the second discharge voltage platform of the first battery cell. In the first, second, third, and fourth battery cells, the difference between the lowest discharge voltage of the first discharge voltage platform and the highest discharge voltage of the second discharge voltage platform is 0.25-0.6V. The positive electrode active material of each of the first, second, third, and fourth battery cells is a mixture of a first positive electrode active material having the first discharge voltage platform and a second positive electrode active material having the second discharge voltage platform.

2. The battery pack according to claim 1, characterized in that, In the first battery cell, when the sum of the discharge capacity corresponding to the first discharge voltage platform and the discharge capacity corresponding to the second discharge voltage platform is 100%, the discharge capacity corresponding to the first discharge voltage platform accounts for 91.8%-99%, and the discharge capacity corresponding to the second discharge voltage platform accounts for 1%-8.2%.

3. The battery pack according to claim 1, characterized in that, In the second battery cell, when the sum of the discharge capacity corresponding to the first discharge voltage platform and the discharge capacity corresponding to the second discharge voltage platform is 100%, the discharge capacity corresponding to the first discharge voltage platform accounts for 75.7%-96.8%, and the discharge capacity corresponding to the second discharge voltage platform accounts for 3.2%-24.3%.

4. The battery pack according to claim 1, characterized in that, In the third battery cell, when the sum of the discharge capacity corresponding to the first discharge voltage platform and the discharge capacity corresponding to the second discharge voltage platform is 100%, the discharge capacity corresponding to the first discharge voltage platform accounts for 60.2%-89.4%, and the discharge capacity corresponding to the second discharge voltage platform accounts for 10.6%-39.8%.

5. The battery pack according to claim 1, characterized in that, In the fourth battery cell, when the sum of the discharge capacity corresponding to the first discharge voltage platform and the discharge capacity corresponding to the second discharge voltage platform is 100%, the discharge capacity corresponding to the first discharge voltage platform accounts for 52.5%-80.3%, and the discharge capacity corresponding to the second discharge voltage platform accounts for 19.7%-47.5%.

6. The battery pack according to claim 1, characterized in that, The first positive electrode active material and the second positive electrode active material are each independently selected from at least one of lithium nickel oxide, lithium cobalt oxide, lithium nickel cobalt manganese oxide, lithium nickel cobalt aluminum oxide, lithium iron phosphate, lithium manganese oxide, lithium titanate and manganese dioxide.

7. The battery pack according to claim 1, characterized in that, The first positive electrode active material is lithium nickel cobalt manganese oxide, and the second positive electrode active material is lithium iron phosphate; Alternatively, the first positive electrode active material is lithium nickel cobalt manganese oxide, and the second positive electrode active material is lithium manganese oxide or lithium titanate; Alternatively, the first positive electrode active material is lithium iron phosphate, and the second positive electrode active material is lithium manganese oxide or lithium titanate.

8. The battery pack according to claim 1, characterized in that, When the first positive electrode active material and the second positive electrode active material are of the same type in the first battery cell, the second battery cell, the third battery cell, and the fourth battery cell, the mass percentage of the first positive electrode active material in the positive electrode active material decreases in the order of the first battery cell, the second battery cell, the third battery cell, and the fourth battery cell, and the mass percentage of the second positive electrode active material in the positive electrode active material increases in the order of the first battery cell, the second battery cell, the third battery cell, and the fourth battery cell.

9. The battery pack according to claim 1, characterized in that, In the first battery cell, when the total mass of the first positive electrode active material and the second positive electrode active material is 100%, the mass of the first positive electrode active material accounts for 92.5% to 97.5%, and the mass of the second positive electrode active material accounts for 2.5% to 7.5%.

10. The battery pack according to claim 1, characterized in that, In the second battery cell, when the total mass of the first positive electrode active material and the second positive electrode active material is 100%, the mass of the first positive electrode active material accounts for 77.5% to 92.5%, and the mass of the second positive electrode active material accounts for 7.5% to 22.5%.

11. The battery pack according to claim 1, characterized in that, In the third battery cell, when the total mass of the first positive electrode active material and the second positive electrode active material is 100%, the mass of the first positive electrode active material accounts for 62.5% to 77.5%, and the mass of the second positive electrode active material accounts for 22.5% to 37.5%.

12. The battery pack according to claim 1, characterized in that, In the fourth battery cell, when the total mass of the first positive electrode active material and the second positive electrode active material is 100%, the mass of the first positive electrode active material accounts for 50% to 62.5%, and the mass of the second positive electrode active material accounts for 37.5% to 50%.

13. The battery pack according to claim 1, characterized in that, When the first positive electrode active material is lithium nickel cobalt manganese oxide and the second positive electrode active material is lithium iron phosphate, the mass ratio of the second positive electrode active material in the first battery cell, the second battery cell, the third battery cell and the fourth battery cell is 1:(1-3):(3-5):(5-9). When the first positive electrode active material is lithium nickel cobalt manganese oxide and the second positive electrode active material is lithium titanate or lithium manganese oxide, the mass ratio of the second positive electrode active material in the first battery cell, the second battery cell, the third battery cell and the fourth battery cell is 1:(1-2):(3-4):(5-7). When the first positive electrode active material is lithium iron phosphate and the second positive electrode active material is lithium titanate or lithium manganese oxide, the mass ratio of the second positive electrode active material in the first battery cell, the second battery cell, the third battery cell and the fourth battery cell is 1:(1-3):(3-5):(5-9).

14. The battery pack according to claim 1, characterized in that, At temperatures below 0°C, the discharge cutoff voltage of the first battery cell is 0~0.3V higher than that of the second battery cell, the discharge cutoff voltage of the second battery cell is 0~0.3V higher than that of the third battery cell, the discharge cutoff voltage of the third battery cell is 0~0.3V higher than that of the fourth battery cell, and the discharge cutoff voltage of the fourth battery cell is above 1.6V.

15. The battery pack according to claim 1, characterized in that, The number of the first battery cell: the number of the second battery cell: the number of the third battery cell: the number of the fourth battery cell = (3~8): (8~13): (9~14):

1.

16. The battery pack according to any one of claims 1-15, characterized in that, Capacitors are placed in the gaps between different battery cells.

17. An electrical device, characterized in that, The battery pack includes any one of claims 1-16.

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