Battery pack and electrical device

Abstract

A battery pack and an electrical device. The battery pack has a columnar structure. The battery pack comprises: a housing, the length L range of the housing: 510 mm ≤ L ≤ 650 mm, and the range of the radial cross sectional area S0 of the housing: 2100 mm 2 ≤ S0 ≤ 3200 mm 2. A battery cell assembly comprises a plurality of battery cells arranged in an accommodating space, the plurality of battery cells successively being arranged in the axial direction of the housing. At the ambient temperature of 25℃ and at a discharge rate which is less than or equal to 1C, the volume energy density VED0 of the battery pack satisfies: VED0 ≥ 410 Wh / L.

Description

Battery pack and electrical equipment

[0001] This application claims priority to the Chinese patent application filed with the China Patent Office on February 18, 2024, with application number 202410180238.0 and invention name “A battery pack and electrical equipment”, the entire contents of which are incorporated by reference into this application. Technical Field

[0002] The present application relates to the field of energy storage technology, and in particular to a battery pack and electrical equipment. Background Art

[0003] An electric-assisted bicycle, also known as an electric-assisted bicycle or e-bike, is a vehicle that combines traditional bicycles with electric technology. Its working principle is to convert the electrical energy stored in the battery into mechanical energy, driving the electric motor to assist riding, making riding easier and more convenient.

[0004] In electric scooters, the battery's volumetric energy density is a key performance indicator. This reflects the amount of energy a battery can store within a given volume and determines the scooter's range. Due to the low volumetric energy density of current electric scooter batteries, a larger battery installation space is required. This not only takes up significant space, reducing the scooter's space efficiency, but also affects its aesthetics and the user experience. Summary of the Invention

[0005] The purpose of the embodiments of the present application is to provide a battery pack and electrical equipment with high volume energy density to achieve a long driving range for electric power-assisted vehicles. The specific technical solutions are as follows:

[0006] A battery pack having a columnar structure, comprising: a housing having a storage space, a length L of the housing ranging from 510 mm to 650 mm, and a radial cross-sectional area S0 of the housing ranging from 2100 mm to 3100 mm. 2 ≤S0≤3200mm 2 The battery cell assembly comprises: a plurality of battery cells arranged in the accommodating space, and the plurality of battery cells are arranged in sequence in the axial direction of the shell; when the ambient temperature is 25°C and the discharge rate is less than or equal to 1C, the volume energy density VED0 of the battery pack satisfies: VED0 ≥ 410Wh / L. Compared with the battery pack of the existing electric power-assisted bicycle, the battery pack of this solution has a higher volume energy density at 25°C and a discharge rate less than or equal to 1C. Under the condition of the same mileage, the battery installation space of the electric power-assisted bicycle can be reduced and the space utilization rate can be improved. And under the condition of the same battery installation space, the mileage of the electric power-assisted bicycle can be increased.

[0007] In one or more embodiments, at an ambient temperature of 25°C and a discharge rate of 0.2C, the volumetric energy density (VED0) of the battery pack satisfies the requirement of VED0 ≥ 450Wh / L. Compared to existing electric power-assisted bicycle battery packs, the battery pack of this solution has a higher volumetric energy density at 25°C and a 0.2C discharge rate. For the same mileage, the battery installation space of the electric power-assisted bicycle can be reduced, improving space utilization. Furthermore, for the same battery installation space, the mileage of the electric power-assisted bicycle can be increased.

[0008] In one or more embodiments, when the ambient temperature is 25°C and the discharge rate is equal to 1C, the volume energy density VED0 of the battery pack satisfies: VED0≤560Wh / L; and / or, when the ambient temperature is 25°C and the discharge rate is equal to 0.2C, the volume energy density VED0 of the battery pack satisfies: VED0≤620Wh / L.

[0009] In one or more embodiments, when the ambient temperature is 25°C and the discharge rate is equal to 1C, the volume energy density VED0 of the battery pack satisfies: VED0 ≥ 450Wh / L; and / or, when the ambient temperature is 25°C and the discharge rate is equal to 0.2C, the volume energy density VED0 of the battery pack satisfies: VED0 ≥ 500Wh / L.

[0010] In one or more embodiments, when the ambient temperature is 25°C and the discharge rate is equal to 1C, the volume energy density VED1 of the battery cell satisfies: 950Wh / L≥VED1≥670Wh / L; and / or, when the ambient temperature is 25°C and the discharge rate is equal to 0.2C, the volume energy density VED1 of the battery cell satisfies: 1050Wh / L≥VED1≥740Wh / L.

[0011] In one or more embodiments, the capacity-to-output ratio of the battery pack = the actual output capacity of the battery pack / the rated capacity of the battery pack; wherein the actual output capacity of the battery pack is the capacity output when the battery pack is in a fully charged state and continuously discharged at a constant current until the battery pack is in a fully discharged state, and the capacity-to-output ratio satisfies at least one of the following ratios: at an ambient temperature of 25°C and a discharge rate of 1C, the capacity-to-output ratio is greater than or equal to 95%; at an ambient temperature of 25°C and a discharge rate of 2C, the capacity-to-output ratio is greater than or equal to 94%. Compared with existing battery packs for electric power-assisted vehicles, the battery pack of this solution has a higher capacity-to-output ratio at 25°C and discharge rates of 1C and 2C.

[0012] In one or more embodiments, 510 mm ≤ L ≤ 550 mm; and / or 2400 mm 2 ≤S0≤2800mm2 Compared with the battery pack of the existing electric power-assisted bicycle, the battery pack of this solution occupies a smaller space when the battery pack energy is the same.

[0013] In one or more embodiments, the length l of the battery core is in the range of 45 mm ≤ l ≤ 83 mm, and the radial cross-sectional area S1 of the battery core is in the range of 1450 mm 2 ≤S1≤2300mm 2 By adopting a battery cell of this size, multiple battery cells are arranged in sequence in the axial direction of the housing, which can achieve high space utilization of the battery cells in the housing.

[0014] In one or more embodiments, the battery cell has a cylindrical structure; wherein the diameter of the battery cell is 49±0.5 mm and the length of the battery cell is 48±0.5 mm; or the diameter of the battery cell is 46±0.5 mm and the length of the battery cell is 80±0.5 mm. Using battery cells of this size helps to balance the size and energy of the battery pack.

[0015] In one or more embodiments, in the outer contour of the radial cross-section of the battery pack, the two points with the longest distance form a first connecting line, and the size of the first connecting line is DL1. The perpendicular bisector of the first connecting line and the two intersection points of the outer contour form a second connecting line, and the size of the second connecting line is DL2. DL1 and DL2 satisfy: 0mm≤DL1-DL2≤8mm.

[0016] In practice, using a battery pack within the above-mentioned size range is beneficial to improving the space utilization of the battery cells.

[0017] In one or more embodiments, the nominal voltage range of the battery cell is 3.5V to 3.7V.

[0018] In one or more embodiments, the number of the battery cells is between 6 and 12.

[0019] In one or more embodiments, the gap between the housing and the battery cell is filled with thermally conductive adhesive, and the thermal conductivity of the thermally conductive adhesive is 0.02W / (m·K) to 0.5W / (m·K), which can quickly conduct the heat of the battery cell to the housing.

[0020] In one or more embodiments, the battery pack further includes a battery management system for managing the status of the battery cell components to improve the operating stability of the battery pack.

[0021] In one or more embodiments, the plurality of battery cells are connected in series.

[0022] In one or more embodiments, the rated capacity of the battery pack is C, 17Ah≤C≤43Ah.

[0023] In one or more embodiments, the rated capacity of the battery cell is c, 17Ah≤c≤43Ah.

[0024] In one or more embodiments, the nominal voltage range of the battery pack is 21V to 44.4V.

[0025] In one or more embodiments, the radial cross-section of the housing is substantially elliptical.

[0026] In one or more embodiments, the battery cell has a cylindrical structure, and the battery cell includes an electrode assembly with a wound structure, and the electrode assembly includes: a first pole piece, a second pole piece, and a diaphragm; wherein, the first pole piece and the second pole piece have opposite polarity, and at least one of the first pole piece and the second pole piece includes: a current collector and an active material arranged on the current collector, and the current collector includes a main body area and a hollow foil area, and the active material is arranged in the main body area, and the hollow foil area includes a flattened area, and the flattened area is away from the main body area. The flattened area adopts a flattening process to form a full-pole ear structure, which is beneficial to reducing the internal resistance of the battery cell. The battery cell with a full-pole ear structure has good heat dissipation performance, and when used with a high-nickel system battery, it is beneficial to improve the energy density of the battery pack.

[0027] In one or more embodiments, notches are provided at the corners of the hollow foil area at the outer end of the electrode assembly. The winding direction of the electrode assembly is the length direction of the current collector, and the direction of the hollow foil area away from the main area is the width direction of the current collector. When the current collector is flattened, the size of the notch in the length direction of the current collector is l1, and the size of the hollow foil area in the width direction of the current collector is W1, and the sizes of l1 and W1 satisfy the following: 0.2W1≤l1≤4W1. Providing notches at the corners of the hollow foil area at the outer end of the electrode assembly can reduce the risk of excessive protrusion at the end of the flattened area after the electrode assembly is wound, which is beneficial to improving the safety of the battery pack.

[0028] In one or more embodiments, in the width direction of the current collector, the size of the cutout is w1, and the sizes of w1 and W1 satisfy: 0.2W1≤w1≤W1.

[0029] In one or more embodiments, the battery cell further includes: a shell, a cover, a current collecting disk and insulating tape, the electrode assembly is arranged in the shell, and the current collecting disk connects the cover and the flattened area of ​​the first pole piece. The cutout is provided at the corner of the empty foil area of ​​the first pole piece. The flattened area of ​​the first pole piece is surrounded by insulating tape, and an overlapping area is provided at the surrounding interface of the insulating tape, and the length of the overlapping area along the winding direction is 0.5mm to 2mm. Compared with the battery cell with multiple turns of insulating tape, in the embodiment of this scheme, the number of winding turns of the insulating tape can be reduced, which is conducive to reducing the use of insulating tape around the electrode assembly.

[0030] In one or more embodiments, the cutout is a rectangular cutout, a triangular cutout, or a curved cutout. Rectangular cutouts and triangular cutouts are more convenient to process and are beneficial to improving the production efficiency of the battery pack.

[0031] In one or more embodiments, the empty foil area includes a plurality of sub-tabs, and the plurality of sub-tabs are separately arranged along the winding direction of the electrode assembly. The separate arrangement of the plurality of sub-tabs is conducive to reducing the resistance during the tab flattening process.

[0032] In one or more embodiments, the plurality of sub-tabs include: a first tab region near the inner end of the electrode assembly winding, a second tab region located in the middle of the electrode assembly winding, and a third tab region near the outer end of the electrode assembly winding; wherein the minimum spacing between adjacent sub-tabs in the first tab region is d1, the minimum spacing between adjacent sub-tabs in the second tab region is d2, and the minimum spacing between adjacent sub-tabs in the third tab region is d3, and the distances d1, d2, and d3 satisfy: d2 < d1, and d2 < d3; the battery cell further includes: a current collecting disk, and the second tab region is connected to the current collecting disk. The spacing between adjacent sub-tabs in the first and third tab regions is larger, and is convenient for liquid injection after being flattened. The spacing between adjacent sub-tabs in the second tab region is smaller, and is convenient for meeting welding thickness requirements after being flattened.

[0033] In one or more embodiments, the plurality of tabs include: a plurality of tabs located near the inner ends of the electrode assembly winding, a continuous tab located in the middle of the electrode assembly winding, and a plurality of tabs located near the outer ends of the electrode assembly winding; wherein the battery cell further includes a current collector plate, to which the continuous tab is connected. After being flattened, the continuous tab facilitates meeting the required weld strength between the tab and the current collector plate, reducing the risk of cold welds, thereby improving the current carrying capacity of the battery cell and reducing the internal resistance of the battery cell, thereby improving the current carrying capacity of the battery pack and reducing the internal resistance of the battery pack.

[0034] In one or more embodiments, when the current collector is flattened, the length of the hollow foil area is L1, and the length of the main area is L2, where L1 and L2 satisfy the relationship: 0.8 ≤ L1 / L2 ≤ 1. A longer hollow foil area helps improve the current carrying capacity of the battery cell and reduce the internal resistance of the battery cell, thereby improving the current carrying capacity of the battery pack and reducing the internal resistance of the battery pack.

[0035] In one or more embodiments, the first electrode sheet is a positive electrode sheet, the second electrode sheet is a negative electrode sheet, the active material of the positive electrode sheet includes a positive electrode active material, the active material of the negative electrode sheet includes a negative electrode active material; the positive electrode active material includes a positive electrode active material, a binder and a conductive agent, and the positive electrode active material includes Li 1+a Ni x1 Co y1 Mn z1 O2 or Li 1+a Ni x2 Co y2 Al z2 O2; wherein x1 and x2 are both greater than or equal to 0.9, y1 and y2 are both greater than 0, z1 and z2 are both greater than 0, x1+y1+z1=1, x2+y2+z2=1; -0.05≤a≤0.2. In this solution, the battery cell can adopt a high-nickel system, thereby achieving a higher energy density.

[0036] In one or more embodiments, the negative electrode active material includes: a negative electrode active material, a negative electrode binder and a negative electrode conductor, the negative electrode active material includes graphite and silicon, and based on the mass of the graphite and the silicon, the mass percentage of the graphite is 85% to 99%.

[0037] An electrical device includes the above-mentioned battery pack.

[0038] In one or more embodiments, the electrical device is an electric power-assisted vehicle, which includes a frame, two wheels, and a motor;

[0039] The two wheels include: a front wheel and a rear wheel;

[0040] The frame comprises: a front fork, a front tube, a diagonal tube, a seat frame and a rear fork;

[0041] The front wheel is rotatably mounted on the front fork, the rear wheel is rotatably mounted on the rear fork, the top end of the front fork is rotatably mounted on the front tube, the top end of the inclined tube is connected to the front tube, and the bottom end of the inclined tube is connected to the rear fork;

[0042] The battery pack is arranged on the oblique tube.

[0043] The battery pack has a high volumetric energy density. Therefore, while maintaining the same range, the frame tube size (e.g., diameter) can be reduced in the electric bicycle, improving the appearance of the electric bicycle. While maintaining the same battery pack volume, the range of the electric bicycle can be increased.

[0044] Beneficial effects of the embodiments of the present application:

[0045] The battery pack provided in the embodiment of the present application has a columnar structure, the length L of the shell ranges from 510 mm to 650 mm, and the radial cross-sectional area S0 of the shell ranges from 2100 mm to 3100 mm. 2 ≤S0≤3200mm 2 . A plurality of battery cells of the battery cell assembly are arranged in the accommodating space, and the plurality of battery cells are arranged in sequence in the axial direction of the outer shell. When the ambient temperature is 25°C and the discharge rate is less than or equal to 1C, the volume energy density of the battery pack is greater than or equal to 410Wh / L. Compared with the battery pack of the existing electric power-assisted bicycle, the battery pack of this solution has a higher volume energy density. Under the condition of the same mileage, the battery installation space of the electric power-assisted bicycle can be reduced and the space utilization rate can be improved. And under the condition of the same battery installation space, the mileage of the electric power-assisted bicycle can be increased.

[0046] Of course, it is not necessary to achieve all the advantages described above at the same time when implementing any product or method of the present application. BRIEF DESCRIPTION OF THE DRAWINGS

[0047] In order to more clearly illustrate the embodiments of the present application or the technical solutions in the prior art, the following briefly introduces the drawings required for use in the embodiments or the description of the prior art. The drawings described below are only some embodiments of the present application. For ordinary technicians in this field, other embodiments can also be obtained based on these drawings.

[0048] FIG1 is a schematic diagram of a radial cross-sectional structure of an 18650 cell assembled battery pack in the related art;

[0049] FIG2 is a schematic diagram of a radial cross-sectional structure of a 21700 cell assembled battery pack in the related art;

[0050] FIG3 is a schematic diagram of an axial longitudinal cross-sectional structure of a battery pack according to one embodiment of the present application;

[0051] FIG4 is a schematic cross-sectional view of the structure taken along line AA of FIG3 ;

[0052] FIG5 is a schematic diagram of a radial cross-sectional structure of a battery pack housing according to one embodiment of the present application;

[0053] FIG6 is a schematic diagram of a radial cross-sectional structure of a battery cell of a battery pack according to one embodiment of the present application;

[0054] FIG7 is a schematic diagram of a radial cross-sectional structure of a battery pack according to a second embodiment of the present application;

[0055] FIG8 is a schematic diagram of a radial cross-sectional structure of a battery pack according to a third embodiment of the present application;

[0056] FIG9 is a schematic diagram of the internal structure of a battery pack according to a fourth embodiment of the present application;

[0057] FIG10 is a schematic diagram of the structure of a battery cell in a battery pack according to an embodiment of the present application;

[0058] FIG11 is a schematic diagram of an exploded structure of a battery cell in a battery pack according to one embodiment of the present application;

[0059] FIG12 is a schematic diagram of the front view of the structure of a cell electrode assembly in a battery pack according to one embodiment of the present application;

[0060] FIG13 is a schematic cross-sectional view of the structure of BB in FIG12;

[0061] FIG14 is a schematic diagram of the expanded structure of one electrode piece of the first type of battery cell electrode assembly in a battery pack according to an embodiment of the present application;

[0062] FIG15 is a schematic side view of the structure of the pole piece shown in FIG14;

[0063] FIG16 is a schematic side view of the structure of a second electrode in a battery pack according to one embodiment of the present application;

[0064] FIG17 is a schematic cross-sectional view of the flattened area at the end of the hollow foil area of ​​the electrode assembly shown in FIG12;

[0065] FIG18 is a schematic diagram of the expanded structure of one electrode piece of the second type of cell electrode assembly in the battery pack according to an embodiment of the present application;

[0066] FIG19 is a schematic diagram of the expanded structure of one electrode piece of the third type of battery cell electrode assembly in a battery pack according to an embodiment of the present application;

[0067] FIG20 is a schematic diagram of the expanded structure of one electrode piece of the fourth type of battery cell electrode assembly in a battery pack according to an embodiment of the present application;

[0068] FIG21 is a schematic diagram of the expanded structure of one electrode piece of the fifth type of battery cell electrode assembly in a battery pack according to an embodiment of the present application;

[0069] FIG22 is a schematic diagram of the expanded structure of one electrode piece of the sixth type of battery cell electrode assembly in a battery pack according to an embodiment of the present application;

[0070] FIG23 is a schematic diagram of the expanded structure of one electrode piece of the seventh type of battery cell electrode assembly in a battery pack according to an embodiment of the present application;

[0071] FIG24 is a schematic diagram of the expanded structure of one electrode piece of the eighth type of battery cell electrode assembly in the battery pack according to an embodiment of the present application;

[0072] FIG25 is a schematic diagram of the expanded structure of one electrode piece of the ninth type of battery cell electrode assembly in a battery pack according to an embodiment of the present application;

[0073] FIG26 is a schematic diagram of the expanded structure of one electrode piece of the tenth type of battery cell electrode assembly in the battery pack according to an embodiment of the present application;

[0074] FIG27 is a schematic diagram of the structure of the outer periphery of the flattened area surrounded by insulating tape inside the battery cell in a battery pack according to an embodiment of the present application;

[0075] FIG28 is a schematic diagram of the structure of an insulating tape ring in a battery cell of a battery pack according to an embodiment of the present application;

[0076] Figure 29 is a structural diagram of an electrical device according to an embodiment of the present application.

[0077] The accompanying drawings are numbered as follows: 18650 battery cell 1A, 21700 battery cell 1B. Battery pack 100, casing 10, battery cell 20, circuit board 30, conductive member 40, shell 21, electrode assembly 22, cover 23, current collecting plate 24, first pole piece 22a, second pole piece 22b, separator 22c, current collector 221, active material 222, main body area 223, hollow foil area 224, flattened area 225, sub-electrode tab 226, incision 227, insulating tape 228, overlapping area 229, frame 101, front wheel 102, rear wheel 103, front fork 104, front tube 105, oblique tube 106, seat frame 107, rear fork 108, first pole tab area Q1, second pole tab area Q2, third pole tab area Q3, winding direction V. DETAILED DESCRIPTION

[0078] The following will be combined with the drawings in the embodiments of this application to clearly and completely describe the technical solutions in the embodiments of this application. The described embodiments are only part of the embodiments of this application, not all of the embodiments. Based on the embodiments in this application, all other embodiments obtained by ordinary technicians in this field based on this application are within the scope of protection of this application.

[0079] Electric assisted bicycles (Pedelec), which combine the convenience of traditional pedal bicycles with the dynamic driving characteristics of electric vehicles, can provide riders with a unique riding experience. They are becoming popular among users, and the growth rate of cycling users has begun to far exceed the growth rate of electric vehicle users.

[0080] In the design of electric scooters, on the one hand, to create a visually appealing electric scooter, the battery pack is typically designed as a tube-shaped, concealed structure. The battery pack can be concealed within a slanted tube on the lower front side of the scooter frame, thereby enhancing the scooter's overall appearance and aesthetics. On the other hand, to design an electric scooter with excellent performance, the battery pack, which serves as the power battery for the scooter's drive motor, must have excellent performance parameters, playing a decisive role in all aspects of the scooter's performance.

[0081] At present, the battery pack of electric power-assisted bicycles uses a combination of multiple 18650 battery cells or a combination of multiple 21700 battery cells as the battery components of the battery pack. Figure 1 is a schematic diagram of the radial cross-sectional structure of the 18650 battery cell combination battery pack in the related art. As shown in Figure 1, the 18650 combination battery pack is a hexagonal column as a whole. The 18650 combination battery pack is composed of 50 18650 battery cells 1A. In the axial direction of the 18650 combination battery pack, a total of 5 layers are designed. In the radial direction of the 18650 combination battery pack, each layer has a total of 10 18650 battery cells 1A arranged, wherein in its radial cross section, the 10 18650 battery cells 1A are arranged in three rows, and the three rows of 18650 battery cells 1A are arranged in the numbers 3, 4, and 3. In a radial cross-section, the three 18650 battery cells 1A in the upper and lower rows are placed on opposite straight sides of the hexagonal column, while the four 18650 battery cells 1A in the middle row are placed between the opposite straight sides of the hexagonal column. The outer contours of the ten 18650 battery cells 1A in each layer form a hexagon. The five 18650 battery cells 1A in each layer are connected in parallel to form a 18650 parallel cell. Each 18650 parallel cell is then connected in series to form the battery assembly of the 18650 modular battery pack.

[0082] FIG2 is a schematic diagram of a radial cross-sectional structure of a 21700 battery cell combination battery pack in the related art. Referring to FIG2 , the 21700 battery pack is a rectangular cylinder. The 21700 battery pack is composed of 30 21700 battery cells 1B. In the axial direction of the 21700 battery pack, there are 5 layers. In the radial direction of the 21700 battery pack, each layer has 6 21700 battery cells 1B arranged. In the radial cross-section, the 6 21700 battery cells 1B are arranged in two rows, with the two rows of 21700 battery cells 1B arranged in a number of 3, 3. In the radial cross-section, the three 21700 battery cells 1B in the upper and lower rows are respectively arranged on the two opposite long sides of the rectangular cylinder. The outer contours of the 6 21700 battery cells 1B in each layer form a rectangle. Among them, the three 21700 battery cells 1B in each layer are connected in parallel to form a 21700 parallel battery cell, and then each 21700 parallel battery cell is connected in series to form a battery assembly of the 21700 combined battery pack.

[0083] Among them, volume energy density is an important parameter of battery pack performance, which is used to measure the differences between different battery packs. The volume energy density of the above-mentioned 18650 combined battery pack and 21700 combined battery pack is relatively low. In order to meet the demand for longer driving range of electric power-assisted bicycles, the volume of the battery pack can only be increased. However, in order to provide sufficient installation space, the diameter of the lower front oblique tube of the electric power-assisted bicycle frame needs to be designed to be larger. Although this design can meet the driving range requirements, it will cause the frame oblique tube to be too large, affecting the appearance of the entire vehicle, increasing the wind resistance during riding, and giving users a poor experience.

[0084] In order to improve the above problems, an embodiment of the present application proposes a battery pack. A battery pack according to an embodiment of the present application is described below with reference to the accompanying drawings.

[0085] Figure 3 is a schematic diagram of the axial longitudinal cross-sectional structure of a battery pack according to an embodiment of the present application, and Figure 4 is a schematic diagram of the AA cross-sectional structure of Figure 3. The battery pack of the embodiment of the present application can be applied to electrical equipment as a power battery for the electrical equipment. For example, when used in an electric power-assisted vehicle, the battery pack can supply power to a drive motor to drive at least one wheel of the electric power-assisted vehicle to rotate, thereby serving as a power battery for the electric power-assisted vehicle. The battery pack can be installed in the oblique tube on the lower front side of the frame of a tube-hidden electric power-assisted vehicle. The specific implementation and application of the battery pack of the embodiment of this scheme is not limited to application in tube-hidden electric power-assisted vehicles. The battery pack of the embodiment of this scheme can also be used in electric power-assisted vehicles with other types of installation methods such as external and detachable installation. That is, the embodiment of the present application does not limit how the battery pack of this scheme is installed on an electric power-assisted vehicle.

[0086] As shown in Figures 3 and 4, a battery pack 100 has a columnar structure and includes a housing 10 and a cell assembly. The housing 10 has a storage space, and the length L of the housing 10 ranges from 510 mm to 650 mm. The radial cross-sectional area S0 of the housing 10 ranges from 2100 mm to 3100 mm. 2 ≤S0≤3200mm 2 The battery cell assembly includes: a plurality of battery cells 20, which are arranged in the accommodating space, and the plurality of battery cells 20 are arranged in sequence in the axial direction of the housing 10, that is, in the axial direction of the housing 10, the plurality of battery cells 20 are arranged in a row in the axial direction of the housing 10, and a separate battery cell 20 is provided in the radial direction of the housing 10. At an ambient temperature of 25°C and a discharge rate of less than or equal to 1C, the volume energy density VED0 of the battery pack satisfies: VED0 ≥ 410Wh / L.

[0087] The battery pack provided in the embodiment of the present application has a columnar structure, the length L of the shell ranges from 510 mm to 650 mm, and the radial cross-sectional area S0 of the shell ranges from 2100 mm to 3100 mm. 2 ≤S0≤3200mm 2 The multiple cells of the battery assembly are arranged in the accommodation space, and the multiple cells are arranged in sequence in the axial direction of the shell. At an ambient temperature of 25°C and a discharge rate of less than or equal to 1C, the volume energy density of the battery pack can be greater than or equal to 410Wh / L.

[0088] In the related art, as mentioned above, the 18650 combined battery pack has 10 18650 cells arranged in each layer. In its radial cross section, three rows of 18650 cells are arranged in numbers of 3, 4, and 3. Since the 18650 cells are cylindrical in shape, there will be more gaps between the 10 adjacent 18650 cells. Similarly, the 21700 combined battery pack has 6 21700 cells arranged in each layer. In its radial cross section, two rows of 21700 cells are arranged in numbers of 3 and 3. Similarly, since the 21700 cells are cylindrical in shape, there will be more gaps between the 6 adjacent 21700 cells. Their volume energy density is low at an ambient temperature of 25°C and a discharge rate of less than or equal to 1C.

[0089] Compared to existing battery packs for electric power-assisted vehicles, the battery pack of this solution has multiple battery cells arranged within the accommodation space, and the multiple battery cells are arranged sequentially in the axial direction of the housing. Therefore, each layer of the battery pack has one battery cell, and there is no gap between two adjacent battery cells in each layer of the 18650 or 21700 modular battery packs. Therefore, the battery pack as a whole has a higher space utilization rate for the battery cells and can have a higher volume energy density. With the same mileage, the battery installation space of the electric power-assisted vehicle can be reduced, improving space utilization. And with the same battery installation space, the mileage of the electric power-assisted vehicle can be increased.

[0090] definition

[0091] Definition of charge rate and discharge rate:

[0092] Charge rate = charge current / rated capacity; discharge rate = discharge current / rated capacity.

[0093] Charge and discharge rates are important parameters for battery packs and are crucial for high-power applications. High charge and discharge rates can provide faster charging speeds and higher discharge power, but exceeding the specified charge and discharge rates can affect the lifespan and safety of the battery pack. Therefore, battery packs must be configured with appropriate charge and discharge rates according to their instructions to ensure proper operation and safety.

[0094] The charge rate and discharge rate of a battery pack refer to the ratio of the charging or discharging rate of the battery pack per unit time to its rated capacity.

[0095] The charge rate and discharge rate are usually expressed as C, where C represents the rated capacity of the battery pack. For example, a battery pack with a rated capacity of 1000mAh has a charge rate of 1C, which means it can be charged at a rate of 1000mA (1A). A battery pack with a rated capacity of 1000mAh has a discharge rate of 1C, which means it can be discharged at a rate of 1000mA (1A). A battery pack with a rated capacity of 1000mAh, if the charge rate and discharge rate are set to 2C, means it can be charged and discharged at a rate of 2000mA (2A). Similarly, a battery with a rated capacity of 1000mAh, if the charge rate and discharge rate are 0.5C, means it can be charged and discharged at a rate of 500mA (0.5A).

[0096] Definition of nominal voltage

[0097] The nominal voltage of a battery cell is the voltage corresponding to when the capacity of the battery cell is half of the rated capacity during the rated capacity test phase of the battery cell.

[0098] When multiple battery cells are connected in series, the nominal voltage of the battery pack is the nominal voltage of a single battery cell multiplied by the number of battery cells connected in series.

[0099] When multiple battery cells are connected in parallel, the nominal voltage of the battery pack is the nominal voltage of a single battery cell.

[0100] When multiple battery cells are mixed in series (in the form of a combination of series and parallel connection), the nominal voltage of the battery pack is the nominal voltage of a single battery cell multiplied by the number of battery cells connected in series.

[0101] The nominal voltage of a battery pack can be obtained from the battery pack manufacturer or battery pack seller on the battery pack product label, packaging, user manual, instruction manual, advertisement, marketing, or other supporting documents for user reference. The nominal voltage of the battery pack mentioned in the advertisement may include at least one of a numeric voltage value, a word, a phrase, an alphanumeric character combination, an icon, or a logo related to the nominal voltage. The logo can be used to indicate to the user how the battery pack works.

[0102] The nominal voltage of a battery cell can be obtained from the battery cell manufacturer or battery cell seller on the battery cell product's label, packaging, user manual, instruction manual, advertisement, marketing, or other supporting documents for user reference. The nominal voltage of a battery cell mentioned in an advertisement may include at least one of a numerical voltage value, a word, a phrase, an alphanumeric character combination, an icon, or a logo related to the nominal voltage, which can be used to indicate to the user how the battery cell works.

[0103] Rated capacity definition

[0104] The rated capacity of a battery pack can be obtained from the battery pack manufacturer or battery pack seller on the battery pack product's label, packaging, user manual, instruction manual, advertising, marketing, or other supporting documentation for user convenience. The rated capacity of the battery pack mentioned in the advertisement may include at least one of a numeric voltage value, a word, a phrase, an alphanumeric character combination, an icon, or a logo related to the rated capacity. The logo can be used to indicate to the user how the battery pack works.

[0105] The rated capacity of a battery cell can be obtained from the battery cell manufacturer or battery cell seller on the battery cell product's label, packaging, user manual, instruction manual, advertisement, marketing, or other supporting documents for user reference. The rated capacity of a battery cell mentioned in an advertisement may include at least one of a numerical voltage value, a word, a phrase, an alphanumeric character combination, an icon, or a logo related to the rated capacity, which can be used to indicate to the user how the battery cell works.

[0106] Definition of charge cut-off voltage and discharge cut-off voltage

[0107] The battery pack's discharge cut-off voltage and charge cut-off voltage can be obtained from the battery pack manufacturer or seller on the battery pack product's label, packaging, user manual, instructions, advertising, marketing, or other supporting documentation for user convenience. The battery pack's discharge cut-off voltage and charge cut-off voltage mentioned in advertisements may include at least one of a numerical voltage value, a word, a phrase, an alphanumeric character combination, an icon, or a logo related to the discharge cut-off voltage and the charge cut-off voltage. The logo can be used to indicate to users how the battery pack operates.

[0108] The battery pack's discharge cutoff voltage and charge cutoff voltage are related to the cells used in the battery pack and the series and parallel connection between the cells. In some embodiments, the battery pack's discharge cutoff voltage may be 25V, and the battery pack's charge cutoff voltage may be 42.5V.

[0109] The discharge cut-off voltage and charge cut-off voltage of a battery cell can be obtained from the battery cell manufacturer or battery cell seller on the battery cell product's label, packaging, user manual, instruction manual, advertising, marketing, or other supporting documents for user convenience. The discharge cut-off voltage and charge cut-off voltage of a battery cell mentioned in advertisements may include at least one of a numerical voltage value, a word, a phrase, an alphanumeric character combination, an icon, or a logo related to the discharge cut-off voltage and the charge cut-off voltage. Such a logo can be used to indicate to users how the battery cell operates.

[0110] Outer contour

[0111] In a specific embodiment, the battery pack has a columnar structure. When the battery pack is used in a tube-mounted electric power-assisted vehicle, the specific shape and size of the columnar structure can be determined based on the shape and size of the battery storage space in the oblique tube of the tube-mounted electric power-assisted vehicle. The columnar structure can be an elliptical column, a circular column, or a polygonal column, that is, the radial cross-section of the columnar structure can be elliptical, circular, or polygonal. The polygonal column can be a regular polygonal column, such as a triangular column, a rectangular column, a pentagonal column, or a hexagonal column, or it can be an irregular polygonal column.

[0112] In some embodiments, the elliptical cylindrical battery pack is not limited to a strict elliptical shape, but can be roughly elliptical, and its outer edge is not limited to a strict elliptical arc edge. Correspondingly, the radial cross section of the housing 10 is roughly elliptical.

[0113] In implementation, in the outer contour of the radial cross-section of the battery pack, the two points with the longest distance form a first connecting line, the size of the first connecting line is DL1, and the perpendicular bisector of the first connecting line and the two intersection points of the outer contour form a second connecting line, the size of the second connecting line is DL2.

[0114] For example, the columnar structure can be an elliptical column or a circular column. Figure 5 is a schematic diagram of a radial cross-sectional structure of a battery pack housing according to one embodiment of the present application, and Figure 6 is a schematic diagram of a radial cross-sectional structure of a battery pack cell according to one embodiment of the present application. As shown in Figures 4, 5, and 6, the columnar structure can be an elliptical column, and the radial cross-section of the battery pack is elliptical, and the radial cross-section of the battery pack is perpendicular to the axis of the battery pack.

[0115] The major axis of the battery pack's radial cross section is the first line connecting the two longest points in the outer contour of the battery pack's radial cross section. The dimension of the major axis is the dimension DL1 of the first line. The minor axis of the battery pack's radial cross section is the second line connecting the perpendicular bisector of the first line and the two intersection points of the battery pack's outer contour. The dimension of the minor axis is the dimension DL2 of the second line. The major axis of the battery pack's radial cross section is perpendicular to the minor axis of the battery pack's radial cross section and intersects at the center of the battery pack's elliptical radial cross section. The major radius of the battery pack's radial cross section is RL1, where RL1 = DL1 / 2. That is, the major radius RL1 is half the major axis DL1. The minor radius of the battery pack's radial cross section is RL2, where RL2 = DL2 / 2. That is, the minor radius RL2 is half the intersection point of the line connecting the perpendicular bisector of the major axis and the outer perimeter of the elliptical radial cross section.

[0116] In some embodiments, RL1>RL2, and the columnar structure is an elliptical column. FIG5 is a schematic diagram of a radial cross-sectional structure of a battery pack housing according to one embodiment of the present application. As shown in FIG5 , the area of ​​the radial cross-section of housing 10 is S0. FIG6 is a schematic diagram of a radial cross-sectional structure of a battery cell according to one embodiment of the present application. As shown in FIG6 , the area of ​​the radial cross-section of cell 20 is S1.

[0117] In practice, the battery cell can be a circular cylinder, and accordingly, the radial cross-section of the battery cell is a circular cross-section. When the difference between RL1 and RL2 is large, a large gap will exist between the outer wall of the battery cell and the inner wall of the housing, making it impossible for the battery cell to effectively utilize the space in the gap, resulting in low space utilization of the battery cell in the housing.

[0118] DL1 Example Data:

[0119] The value of DL1 can be: 57mm≤DL1≤68mm. For example, DL1 can be: 57mm, 58mm, 59mm, 60mm, 61mm, 62mm, 63mm, 64mm, 65mm, 66mm, 67mm, 68mm or a range consisting of any two values ​​therebetween.

[0120] DL2 Example Data:

[0121] The value of DL2 can be: 49mm≤DL2≤60mm. For example, DL2 can be: 49mm, 50mm, 51mm, 52mm, 53mm, 54mm, 55mm, 56mm, 57mm, 58mm, 59mm, 60mm or a range consisting of any two values ​​therebetween.

[0122] DL1-DL2 Example Data:

[0123] The difference between DL1 and DL2 can satisfy the following condition: 0mm ≤ DL1-DL2 ≤ 8mm, minimizing the gap between the outer cell wall and the inner wall of the housing. For example, the difference between DL1 and DL2 can be 0mm, 1mm, 2mm, 3mm, 4mm, 5mm, 6mm, 7mm, 8mm, or any range consisting of two values ​​in between. This smaller gap further improves the cell's utilization of the housing's internal space, thereby increasing the battery pack's volumetric energy density.

[0124] The gap between the outer wall of the battery cell and the inner wall of the shell can be between 0mm and 14mm, such as: 0mm, 1mm, 2mm, 3mm, 4mm, 5mm, 6mm, 7mm, 8mm, 9mm, 10mm, 11mm, 12mm, 13mm, 14mm or a range consisting of any two values ​​therebetween.

[0125] When 0mm<DL1-DL2≤8mm, the battery pack can make full use of the gap between the outer wall of the battery cell and the inner wall of the shell, for example, a circuit board or copper busbar can be placed in the gap. The battery pack can be suitable for installation in the elliptical cylindrical inclined tube of the electric power-assisted bicycle.

[0126] In some embodiments, DL1-DL2 = 0, i.e., RL1 = RL2, and the columnar structure is a circular cylinder. Figure 7 is a schematic diagram of a radial cross-sectional structure of a battery pack according to another embodiment of the present application. As shown in Figure 7, the columnar structure is a circular cylinder, DL1 = DL2, and RL1 = RL2. The gap between the outer wall of the battery cell 20 and the inner wall of the housing 10 is small, facilitating the battery pack's high volumetric energy density. This battery pack is suitable for installation in the cylindrical oblique tube of an electric power-assisted bicycle.

[0127] In implementation, the columnar structure may be a polygonal column, for example, a regular or irregular polygonal column. In actual application scenarios of battery packs, shells of different shapes will be customized according to actual needs. Figure 8 is a schematic diagram of the radial cross-sectional structure of a battery pack according to another embodiment of the present application. As shown in Figure 8, the columnar structure is an irregular polygonal column. The radial cross-section of the battery pack is polygonal. Similarly, in order to achieve a smaller gap between the outer wall of the battery cell 20 and the inner wall of the outer shell 10, the outer contour of the radial cross-section of the battery pack has a first connecting line with the longest distance between the two points. The size of the second connecting line between the perpendicular bisector of the first connecting line and the two intersection points of the outer contour is DL2. DL1 and DL2 satisfy: 0mm≤DL1-DL2≤8mm. In some embodiments, the columnar structure may be a regular polygonal column. Similarly, to minimize the gap between the outer wall of the battery cell and the inner wall of the outer shell, the dimension of the first line connecting the two longest points in the outer contour of the radial cross-section of the battery pack is DL1, and the dimension of the second line connecting the perpendicular bisector of this first line and the two intersection points of the outer contour is DL2. DL1 and DL2 satisfy the following: 0mm≤DL1-DL2≤8mm. This battery pack is suitable for installation in the polygonal cylindrical oblique tube of an electric power-assisted bicycle.

[0128] Cross-sectional area measurement

[0129] Measurement of the radial cross-sectional area S0 of the battery pack:

[0130] Referring to Figures 3 and 4 , in the embodiment of this solution, a cross-sectional area perpendicular to the axis of the battery pack housing 10 is cut and measured. The cross-sectional area S0 of the housing 10 can be: the cross-sectional area S0 at the location where the battery cell 20 is located in the housing 10. Typically, in the axial direction of some battery packs 100, the radial cross-sectional areas S0 at different locations are equal. For other battery packs 100, where the radial cross-sectional areas S0 at different locations are unequal in the axial direction, the radial cross-sectional area S0 in this embodiment can be: the cross-sectional area at the location where the battery cell 20 is located in the housing 10.

[0131] Alternatively, a radial cross-sectional profile of the battery pack is drawn using a Keyence IM 8000, and S0 is calculated by fitting. For the area calculation of a regular circle, π is taken as 3.14.

[0132] S0 embodiment data:

[0133] As shown in FIG3, FIG4 and FIG5, the radial cross-sectional area S0 of the housing 10 is in the range of: 2100mm 2 ≤S0≤3200mm 2 The radial cross-sectional area S0 of the housing 10 may be: 2100 mm 2, 2200mm 2 , 2300mm 2 , 2400mm 2 , 2500mm 2 , 2600mm 2 , 2700mm 2 , 2800mm 2 , 2900mm 2 , 3000mm 2 、3100mm 2 , 3200mm 2 Or a range consisting of any two values. Optional, 2400mm 2 ≤S0≤2800mm 2 .

[0134] Measurement of the radial cross-sectional area S1 of the battery cell:

[0135] The cross-sectional area perpendicular to the axis of the battery cell 20 is intercepted and the size of the cross-sectional area is measured. The cross-sectional area S1 of the battery cell 20 can be: the cross-sectional area at the position where the electrode assembly 22 is set in the battery cell 20 is S1. Generally, in the axial direction of some battery cells 20, the radial cross-sectional areas S1 at different positions are equal. For other battery cells 20, the radial cross-sectional areas S1 at different positions in the axial direction are unequal. In this embodiment, the radial cross-sectional area S1 can be: the largest radial cross-sectional area in the axial direction of the battery cell 20 is S1.

[0136] Alternatively, a radial cross-sectional profile of the cell is drawn using a KEYENCE IM 8000, and S1 is calculated by fitting. For the area calculation of a regular circle, π is taken as 3.14.

[0137] d Example data:

[0138] In an embodiment of this solution, the battery cell has a cylindrical structure, and the diameter d of the battery cell is in the range of 43mm≤d≤54mm. For example, the diameter d of the battery cell can be 43mm, 44mm, 45mm, 46mm, 47mm, 48mm, 49mm, 50mm, 51mm, 52mm, 53mm, 54mm, or a range consisting of any two values ​​therebetween. For example, a 4948 cylindrical structure can be used, with a diameter of 49mm and a height of 48mm. In practice, due to manufacturing tolerances, the diameter of the battery cell can be 49±0.5mm, and the length of the battery cell can be 48±0.5mm. Using a cylindrical structure of this size helps balance the size and energy of the battery pack. For another example, a 4680 cylindrical structure can be used, with a diameter of 46mm and a height of 80mm. In practice, due to manufacturing tolerances, the diameter of the battery cell is 46±0.5mm, and the length of the battery cell is 80±0.5mm.

[0139] Alternatively, a KEYENCE IM 8000 is used to draw a circular outline of the battery cell, and after determining the center of the circle, different diameters are measured 10 times and the average value is taken.

[0140] S1 Example Data:

[0141] As shown in Figures 3, 4 and 6, the radial cross-sectional area S1 of the battery cell is in the range of 1450 mm 2 ≤S1≤2300mm 2 For example, the radial cross-sectional area S1 of the battery cell can be: 1450mm 2 , 1500mm 2 , 1600mm 2 , 1700mm 2 、1800mm 2 , 1900mm 2 , 2000mm 2 , 2100mm 2 , 2200mm 2 , 2300mm 2 Or a range consisting of any two values ​​in between.

[0142] S1 / S0 Example Data:

[0143] The radial cross-sectional area S0 of the battery pack may satisfy: 66% ≤ S1 / S0 ≤ 72%, for example, S1 / S0 = 66%, S1 / S0 = 66.5%, S1 / S0 = 67%, S1 / S0 = 67.5%, S1 / S0 = 68%, S1 / S0 = 68.5%, S1 / S0 = 69%, S1 / S0 = 69.5%, S1 / S0 = 70%, S1 / S0 = 70.5%, S1 / S0 = 71%, S1 / S0 = 71.5%, S1 / S0 = 72%, or a range consisting of any two values ​​therebetween. Optionally, 68% ≤ S1 / S0 ≤ 72%, the S1 / S0 ratio is relatively favorable, the outer diameter of the battery pack can be thinner, which facilitates reducing the diameter of the inclined tube for installing the battery pack on the electric power-assisted bicycle and reducing the wind resistance of the electric power-assisted bicycle. With the outer diameter being the same, the battery pack can have greater energy and increase the range of the electric assisted vehicle.

[0144] L Example data:

[0145] The length L of the housing 10 refers to the longest dimension of the housing 10 in the axial direction.

[0146] As shown in FIG3 , the length L of the housing 10 ranges from 510 mm to 650 mm. For example, the length L of the housing 10 can be 510 mm, 520 mm, 530 mm, 540 mm, 550 mm, 560 mm, 570 mm, 580 mm, 590 mm, 600 mm, 610 mm, 620 mm, 630 mm, 640 mm, or 650 mm, or a range consisting of any two values ​​therebetween. Alternatively, 510 mm to 550 mm is acceptable.

[0147] 1 Example data:

[0148] The length l of the battery cell 20 refers to the longest length of the battery cell 20 in the axial length direction.

[0149] As shown in FIG10 , the range of the length l of the battery cell is: 45 mm ≤ l ≤ 83 mm. For example, the length l of the battery cell can be: 45 mm, 50 mm, 55 mm, 60 mm, 65 mm, 70 mm, 75 mm, 80 mm, 83 mm or a range consisting of any two values ​​therebetween.

[0150] volume

[0151] The volume (V0) of a battery pack refers to the three-dimensional space occupied by the entire pack. This volume can be measured in various ways, including displacement. For example, the battery pack is sealed with a blister film, which is vacuum-sealed inside and held tightly against the pack surface. When the sealed pack is immersed in water, the volume of water displaced is V11. When the blister film is removed and immersed in water, the volume of water displaced is V12. Thus, the battery pack volume (V0) is calculated as V11 - V12. Other measurement methods, such as 3D scanning, can also be used.

[0152] V0 embodiment data:

[0153] The range of the volume V0 of the battery pack is: 1.1L≤V0≤1.8L. For example, the volume V0 of the battery pack can be: 1.1L, 1.2L, 1.3L, 1.4L, 1.5L, 1.6L, 1.7L, 1.8L or a range consisting of any two values ​​therebetween.

[0154] V1 Example Data:

[0155] The range of the volume V1 of the battery cell is: 0.07L≤V1≤0.19L. For example, the volume V1 of the battery cell can be: 0.07L, 0.08L, 0.09L, 0.10L, 0.11L, 0.12L, 0.13L, 0.14L, 0.15L, 0.16L, 0.17L, 0.18L, 0.19L or a range consisting of any two values ​​therebetween.

[0156] The volume V1 of a battery cell refers to the three-dimensional space occupied by the cell. This volume can be measured in various ways, including displacement. For example, the cell is sealed with a blister pack, which is vacuum-sealed inside and held tightly against the cell surface. When the sealed cell is immersed in water, the volume of water displaced is V13. When the blister pack is removed and immersed in water, the volume of water displaced is V14. Thus, the cell volume V1 = V13 - V14. Other measurement methods, such as 3D scanning, can also be used.

[0157] weight

[0158] The battery pack weight G0 refers to the total weight of the entire battery pack, including the weight of all components such as multiple battery cells, connecting lines, casing, circuit components, etc.

[0159] G0 embodiment data:

[0160] The range of the weight G0 of the battery pack is: 2.7kg≤G0≤3.7kg. For example, the weight G0 of the battery pack can be: 2.7kg, 2.8kg, 2.9kg, 3.0kg, 3.1kg, 3.2kg, 3.3kg, 3.4kg, 3.5kg, 3.6kg, 3.7kg or a range consisting of any two values ​​therebetween.

[0161] The cell weight G1 refers to the weight of a single cell.

[0162] G1 Example Data:

[0163] The range of the weight G1 of the battery cell is: 0.2kg≤G1≤0.5kg. For example, the weight G1 of the battery cell can be: 0.2kg, 0.25kg, 0.3kg, 0.35kg, 0.4kg, 0.45kg, 0.5kg or a range consisting of any two values ​​therebetween.

[0164] Voltage

[0165] Multiple battery cells 20 are arranged in sequence in the axial direction of the shell 10. In implementation, the multiple battery cells 20 can be connected in series, in parallel, or in a combination of series and parallel. After the multiple battery cells 20 are electrically connected, the voltage of the battery pack will be different depending on the different electrical connection methods.

[0166] Battery pack nominal voltage example data:

[0167] Taking multiple battery cells 20 connected in series as an example: the range of the nominal voltage of the battery pack is: 21V≤Vb≤44.4V. For example, the nominal voltage Vb of the battery pack can be: 21V, 21.6V, 23V, 25V, 27V, 29V, 31V, 33V, 35V, 37V, 39V, 41V, 43V, 44.4V or a range consisting of any two values ​​therebetween.

[0168] Taking a plurality of battery cells 20 connected in parallel as an example: the nominal voltage range of the battery pack is: 3.5V≤Vb≤3.7V, and illustratively it may be 3.62V.

[0169] Example data of battery cell operating voltage range:

[0170] The discharge cut-off voltage of the battery cell corresponds to the minimum value of the battery cell's operating voltage range, and the charge cut-off voltage corresponds to the maximum value of the battery cell's operating voltage range.

[0171] In some embodiments, the charge cut-off voltage of the battery cell may be 4.25V, and the discharge cut-off voltage of the battery cell may be 2.5V.

[0172] Battery cell nominal voltage example data:

[0173] The nominal voltage of the battery cell corresponds to the voltage of the voltage platform when the battery cell is at 25°C and a 0.2C discharge rate.

[0174] In some embodiments, the nominal voltage of the battery cell ranges from 3.5V to 3.7V, and exemplarily may be 3.62V.

[0175] In a battery pack with the same shell length L and radial cross-sectional area S0, using cells of different sizes will have different effects. For example, L = 520mm. When using 4680 cells, due to the size limitation of the shell length L, six 4680 cells can be arranged in sequence in the axial direction of the shell, that is, the total length of the six 4680 cells is 6×80mm=480mm. Taking the nominal voltage of the cell as 3.6V as an example, after six 4680 cells are connected in series, the nominal voltage of the cell assembly is equal to 6×3.6V=21.6V.

[0176] When using 4948 battery cells, due to the limited length L of the outer shell, 10 4948 battery cells can be arranged in sequence in the axial direction of the outer shell. That is, the total length of 10 4948 battery cells is 10 × 48 mm = 480 mm. Taking the nominal voltage of the battery cell as an example, the nominal voltage of the battery cell assembly is 3.6V. After 10 4948 battery cells are connected in series, the nominal voltage of the battery cell assembly is equal to 10 × 3.6V = 36V.

[0177] When the shell length L and radial cross-sectional area S0 are the same, if a battery pack with 4948 cells is selected, more cells can be accommodated inside the shell. When multiple cells are connected in series, the voltage platform of the battery pack can be significantly increased, which can provide greater output power for the electric motor.

[0178] In a specific implementation, the nominal voltage of the battery cell will vary depending on the adjustment of the battery cell material and the battery cell structure. The nominal voltage range of the battery cell can be 3.5V to 3.7V. For example, the nominal voltage of the battery cell can be: 3.5V, 3.52V, 3.54V, 3.56V, 3.58V, 3.6V, 3.62V, 3.64V, 3.66V, 3.68V, 3.7V or a range consisting of any two values ​​therebetween. In a specific implementation, the number of battery cells will vary, depending on the length L of the shell and the length l of the battery cell. The number of battery cells can be 6 to 12. For example, the number of battery cells can be: 6, 7, 8, 9, 10, 11 or 12. The voltage range of a battery pack composed of different voltages and different numbers of battery cells can be 21V to 44.4V. For example, the battery pack voltage may be: 21V, 23V, 25V, 27V, 29V, 31V, 33V, 35V, 37V, 39V, 41V, 43V, 44.4V, or a range consisting of any two values ​​therebetween.

[0179] For example, the nominal voltage range of an 18650 battery cell may be 3.58 V to 3.65 V. For example, the nominal voltage range of an 18650 battery cell may be 3.6 V. For example, the nominal voltage range of a 21700 battery cell may be 3.58 V to 3.65 V. For example, the nominal voltage range of a 21700 battery cell may be 3.6 V.

[0180] Capacity test

[0181] Test steps for rated capacity C of battery pack

[0182] Constant current charging stage: at 25° C., using a 0.5C charging rate, the battery pack is charged with a constant current to the charging cut-off voltage of the battery pack.

[0183] Constant voltage charging stage: at 25° C., using a charging cut-off voltage, the battery pack charged to the charging cut-off voltage is charged at a constant voltage and charged to a cut-off charging rate, which is 0.02C.

[0184] Rated capacity measurement stage: At 25°C, use a discharge rate of 0.2C to discharge the battery pack that has completed constant voltage charging to the discharge cut-off voltage of the battery pack. Integrate the discharge time and discharge current to obtain the rated capacity C of the battery pack.

[0185] C Example data:

[0186] In an embodiment of the present scheme, the rated capacity of the battery pack is C, and the rated capacity C of the battery pack satisfies: 17Ah≤C≤43Ah, for example, C=17Ah, 18Ah, 19Ah, 20Ah, 21Ah, 22Ah, 23Ah, 24Ah, 25Ah, 26Ah, 27Ah, 28Ah, 29Ah, 30Ah, 31Ah, 32Ah, 33Ah, 34Ah, 35Ah, 36Ah, 37Ah, 38Ah, 39Ah, 40Ah, 41Ah, 42Ah, 43Ah or a range consisting of any two values ​​therebetween.

[0187] Test steps for the rated capacity c of the battery cell

[0188] Constant current charging stage: at 25° C., using a 0.5C charging rate, the battery cell is charged at a constant current to the charging cut-off voltage of the battery cell.

[0189] Constant voltage charging stage: at 25°C, using a charging cut-off voltage, the battery cell charged to the charging cut-off voltage is charged at a constant voltage and charged to a cut-off charging rate, which is 0.02C.

[0190] Rated capacity measurement stage: At 25°C, use a discharge rate of 0.2C to discharge the battery cell that has completed constant voltage charging to the discharge cut-off voltage of the battery cell. Integrate the discharge time and discharge current to obtain the rated capacity c of the battery cell.

[0191] c Example data:

[0192] In an embodiment of the present scheme, the rated capacity of the battery cell is c, and the rated capacity c of the battery cell satisfies: 17Ah≤c≤43Ah, for example, c=17Ah, 18Ah, 19Ah, 20Ah, 21Ah, 22Ah, 23Ah, 24Ah, 25Ah, 26Ah, 27Ah, 28Ah, 29Ah, 30Ah, 31Ah, 32Ah, 33Ah, 34Ah, 35Ah, 36Ah, 37Ah, 38Ah, 39Ah, 40Ah, 41Ah, 42Ah, 43Ah or a range consisting of any two values ​​therebetween.

[0193] Capacity output ratio test

[0194] Steps for measuring the actual output capacity of the battery pack:

[0195] The battery pack can reach a full charge state by executing a constant current charging stage and a constant voltage charging stage.

[0196] Constant current charging stage: at 25° C., using a 0.5C charging rate, the battery pack is charged with a constant current to the charging cut-off voltage of the battery pack.

[0197] Constant voltage charging stage: at 25° C., using a charging cut-off voltage, the battery pack charged to the charging cut-off voltage is charged at a constant voltage and charged to a cut-off charging rate, which is 0.02C.

[0198] The battery pack can be discharged by performing continuous current discharge and performing discharge operation at a fixed discharge rate until the voltage of the battery pack reaches the discharge cut-off voltage, reaching the full discharge state of the battery pack.

[0199] Actual output capacity measurement stage: At 25°C, use the test discharge rate to discharge the battery pack that has completed constant voltage charging to the discharge cut-off voltage of the battery pack. Integrate the discharge time and discharge current to obtain the actual output capacity of the battery.

[0200] At the same temperature, the actual output capacity of the battery pack will vary at different discharge rates. For example, if the discharge rate is 1C, then during the energy measurement phase, at 25°C, using a 1C discharge rate, the battery pack, after constant voltage charging, is DC-discharged to the discharge cutoff voltage. The discharge time and discharge current are integrated to obtain the actual output capacity of the battery pack at 25°C and a 1C discharge rate. For example, if the discharge rate is 2C, then during the energy measurement phase, at 25°C, using a 2C discharge rate, the battery pack, after constant voltage charging, is DC-discharged to the discharge cutoff voltage. The discharge time and discharge current are integrated to obtain the actual output capacity of the battery pack at 25°C and a 2C discharge rate.

[0201] Among them, the capacity output ratio of the battery pack = the actual output capacity of the battery pack / the rated capacity of the battery pack, and the actual output capacity of the battery pack 100 is the capacity output when the battery pack 100 is in a fully charged state and continuously discharged at a constant current until the battery pack 100 is in a fully discharged state.

[0202] Capacity output ratio data:

[0203] When the ambient temperature is 25°C and the discharge rate is equal to 1C, the capacity output ratio is greater than or equal to 95%. Optionally, the capacity output ratio of the battery pack is between 95% and 96%, for example, 95%, 95.1%, 95.2%, 95.3%, 95.4%, 95.5%, 95.6%, 95.7%, 95.8%, 95.9%, 96% or a range consisting of any two values ​​therebetween.

[0204] When the ambient temperature is 25°C and the discharge rate is equal to 2C, the capacity output ratio is greater than or equal to 94%. Optionally, the capacity output ratio of the battery pack is between 94% and 95%, for example, 94%, 94.1%, 94.2%, 94.3%, 94.4%, 94.5%, 94.6%, 94.7%, 94.8%, 94.9%, 95% or a range consisting of any two values ​​therebetween.

[0205] Energy test

[0206] The test steps of the battery pack energy E0 are as follows:

[0207] Constant current charging stage: at 25° C., using a 0.5C charging rate, the battery pack is charged with a constant current to the charging cut-off voltage of the battery pack.

[0208] Constant voltage charging stage: At 25°C, the battery pack is charged to the charging cut-off voltage and charged to the cut-off charging rate, which is 0.02C. At this time, the state of charge of the battery pack is 100%.

[0209] Energy measurement phase: At 25°C, the battery pack, which has completed constant voltage charging, is DC-discharged at the test discharge rate. The output energy of the battery pack is measured until the battery pack's discharge cutoff voltage is reached. This is referred to as the battery pack's energy, E0. When the battery pack is discharged to the battery pack's discharge cutoff voltage, its state of charge (SOC) is 0%.

[0210] For example, if the ambient temperature is 25°C and the discharge rate of the test is 1C, then in the energy measurement stage, the battery pack that has completed constant voltage charging is DC discharged at 25°C using a 1C discharge rate, and the discharge is measured to the discharge cut-off voltage. The output energy of the battery pack is used as the energy E0 of the battery pack at 25°C and a 1C discharge rate.

[0211] For example, if the ambient temperature is 25°C and the discharge rate of the test is 0.2C, then in the energy measurement stage, the battery pack that has completed constant voltage charging is DC discharged at 25°C using a 0.2C discharge rate, and the discharge is measured to the discharge cut-off voltage. The output energy of the battery pack is used as the energy E0 of the battery pack at 25°C and a 0.2C discharge rate.

[0212] E0 embodiment data:

[0213] When the ambient temperature is 25°C and the discharge rate is equal to 0.2C, the energy E0 of the battery pack ranges from 620Wh≤E0≤920Wh, for example, E0=620Wh, E0=640Wh, E0=626Wh, E0=680Wh, E0=700Wh, E0=720Wh, E0=740Wh, E0=760Wh, E0=780Wh, E0=800Wh, E0=820Wh, E0=840Wh, E0=860Wh, E0=880Wh, E0=900Wh, E0=920Wh or a range consisting of any two values ​​therebetween.

[0214] When the ambient temperature is 25°C and the discharge rate is equal to 1C, the energy E0 of the battery pack ranges from 560Wh≤E0≤830Wh, for example, E0=560Wh, E0=600Wh, E0=650Wh, E0=700Wh, E0=750Wh, E0=800Wh, E0=830Wh or a range consisting of any two values ​​therebetween.

[0215] E0 / S0 embodiment data:

[0216] When the ambient temperature is 25°C and the discharge rate is 0.2C, the ratio E0 / S0 of the energy E0 of the battery pack and the radial cross-sectional area S0 of the housing 10 satisfies: 0.25Wh / mm 2 ≤E0 / S0≤0.34Wh / mm2 For example, E0 / S0 = 0.25Wh / mm 2 、E0 / S0=0.26Wh / mm 2 、E0 / S0=0.27Wh / mm 2 、E0 / S0=0.28Wh / mm 2 、E0 / S0=0.29Wh / mm 2 、E0 / S0=0.30Wh / mm 2 、E0 / S0=0.31Wh / mm 2 、E0 / S0=0.32Wh / mm 2 、E0 / S0=0.33Wh / mm 2 、E0 / S0=0.34Wh / mm 2 Or a range consisting of any two values. Optional, 0.28Wh / mm 2 ≤E0 / S0≤0.34Wh / mm 2 .

[0217] When the ambient temperature is 25°C and the discharge rate is 1C, the ratio of the energy E0 of the battery pack to the radial cross-sectional area S0 of the shell satisfies the following conditions: 0.23Wh / mm 2 ≤E0 / S0≤0.30Wh / mm 2 For example, E0 / S0=0.23Wh / mm 2 、E0 / S0=0.24Wh / mm 2 、E0 / S0=0.25Wh / mm 2 、E0 / S0=0.26Wh / mm 2 、E0 / S0=0.27Wh / mm 2 、E0 / S0=0.28Wh / mm 2 、E0 / S0=0.29Wh / mm 2 、E0 / S0=0.30Wh / mm 2 Or a range consisting of any two values. Optional, 0.25Wh / mm 2 ≤E0 / S0≤0.30Wh / mm 2 .

[0218] The test steps of the battery cell energy E1 are:

[0219] Constant current charging stage: at 25° C., using a 0.5C charging rate, the battery cell is charged at a constant current to the charging cut-off voltage of the battery cell.

[0220] Constant voltage charging stage: At 25°C, using the charging cut-off voltage, the battery cell charged to the charging cut-off voltage is charged at constant voltage and charged to the cut-off charge rate, which is 0.02C. At this time, the state of charge of the battery cell is 100%.

[0221] Energy measurement phase: At 25°C, the constant voltage charged cell is DC discharged using the test discharge rate. The output energy of the cell is measured until the cell's discharge cutoff voltage is reached. This energy is used as the cell's energy E1. When the cell is discharged to the cell's discharge cutoff voltage, the cell's state of charge is 0%.

[0222] For example, if the ambient temperature is 25°C and the discharge rate of the test is 1C, then in the energy measurement stage, at 25°C, a 1C discharge rate is used to discharge the battery cell that has completed constant voltage charging with DC, and the discharge to the discharge cut-off voltage is measured. The output energy of the battery cell is used as the energy E1 of the battery cell at 25°C and a 1C discharge rate.

[0223] For example, if the ambient temperature is 25°C and the discharge rate of the test is 0.2C, then in the energy measurement stage, at 25°C, a discharge rate of 0.2C is used to DC discharge the battery cell that has completed constant voltage charging, and the discharge is measured to the discharge cut-off voltage. The output energy of the battery cell is used as the energy E1 of the battery cell at 25°C and a discharge rate of 0.2C.

[0224] E1 Example Data:

[0225] When the ambient temperature is 25°C and the discharge rate is equal to 0.2C, the energy E1 of the battery cell ranges from 60Wh≤E1≤160Wh, for example, E1=60Wh, E1=70Wh, E1=80Wh, E1=90Wh, E1=100Wh, E1=110Wh, E1=120Wh, E1=130Wh, E1=140Wh, E1=150Wh, E1=160Wh or a range consisting of any two values ​​therebetween.

[0226] When the ambient temperature is 25°C and the discharge rate is equal to 1C, the range of the energy E1 of the battery cell is: 50Wh≤E1≤140Wh, for example, E1=50Wh, E1=60Wh, E1=70Wh, E1=80Wh, E1=90Wh, E1=100Wh, E1=110Wh, E1=120Wh, E1=130Wh, E1=140Wh or a range consisting of any two values ​​therebetween.

[0227] VED test

[0228] Battery pack volume energy density VED0 test:

[0229] The volume energy density VED0 of the battery pack is calculated as follows: the energy E0 of the battery pack / the volume V0 of the battery pack.

[0230] At an ambient temperature of 25°C, the value of VED0 will vary at different discharge rates.

[0231] VED0 Example Data:

[0232] When the ambient temperature is 25°C and the discharge rate is equal to 0.2C, the volume energy density VED0 of the battery pack can meet the following requirements: 450Wh / L≤VED0≤620Wh / L. For another example, VED0=450Wh / L, VED0=455Wh / L, VED0=460Wh / L, VED0=470Wh / L, VED0=480Wh / L, VED0=490Wh / L, VED0=500Wh / L, VED0=510Wh / L, VED0=520Wh / L, VED0=530Wh / L, VED0=540Wh / L, VED0=550Wh / L, VED0=560Wh / L, VED0=570Wh / L, VED0=580Wh / L, VED0=590Wh / L, VED0=600Wh / L, VED0=610Wh / L, VED0=615Wh / L, VED0=620Wh / L or a range consisting of any two values ​​therebetween. Optional, VED0 ≥ 500Wh / L.

[0233] When the ambient temperature is 25° C. and the discharge rate is 1C, the volume energy density VED0 of the battery pack can meet the following requirements: 410Wh / L≤VED0≤560Wh / L. For another example, VED0=410Wh / L, VED0=415Wh / L, VED0=420Wh / L, VED0=430Wh / L, VED0=440Wh / L, VED0=450Wh / L, VED0=460Wh / L, VED0=470Wh / L, VED0=480Wh / L, VED0=490Wh / L, VED0=500Wh / L, VED0=510Wh / L, VED0=520Wh / L, VED0=530Wh / L, VED0=540Wh / L, VED0=550Wh / L, VED0=555Wh / L, VED0=560Wh / L, or a range consisting of any two values ​​therebetween. Optionally, VED0≥450Wh / L.

[0234] Test of volume energy density VED1 of battery cell:

[0235] The volume energy density VED1 of the battery cell is calculated as follows: the energy E1 of the battery cell / the volume V1 of the battery cell.

[0236] At an ambient temperature of 25°C, the value of VED1 will be different at different discharge rates.

[0237] VED1 Example Data:

[0238] When the ambient temperature is 25°C and the discharge rate is 1C, the volume energy density VED1 of the battery cell satisfies: 670Wh / L≤VED1≤950Wh / L. For example, VED1=670Wh / L, VED1=675Wh / L, VED1=680Wh / L, VED1=700Wh / L, VED1=720Wh / L, VED1=740Wh / L, VED1=760Wh / L, VED1=780Wh / L, VED1=800Wh / L, VED1=810Wh / L, VED1=820Wh / L, VED1=830Wh / L, VED1=840Wh / L, VED1=860Wh / L, VED1=880Wh / L, VED1=900Wh / L, VED1=920Wh / L, VED1=940Wh / L, VED1=945Wh / L, VED1=950Wh / L or a range consisting of any two values ​​therebetween.

[0239] When the ambient temperature is 25°C and the discharge rate is equal to 0.2C, the volume energy density VED1 of the battery cell satisfies: 740Wh / L≤VED1≤1050Wh / L, for example, VED1=740Wh / L, VED1=745Wh / L, VED1=750Wh / L, VED1=770Wh / L, VED1=790Wh / L, VED1=810Wh / L, VED1=830Wh / L, VED1=850Wh / L, VED1 =870Wh / L, VED1=890Wh / L, VED1=910Wh / L, VED1=930Wh / L, VED1=950Wh / L, VED1=970Wh / L, VED1=990Wh / L, VED1=1010Wh / L, VED1=1030Wh / L, VED1=1040Wh / L, VED1=1045Wh / L, VED1=1050Wh / L or a range consisting of any two values ​​therebetween.

[0240] GED Test

[0241] Battery pack mass energy density GED0 test:

[0242] The mass energy density GED0 of the battery pack is calculated as follows: the energy E0 of the battery pack / the mass G0 of the battery pack.

[0243] At an ambient temperature of 25°C, the value of GED0 will vary at different discharge rates.

[0244] GED0 Example Data:

[0245] At an ambient temperature of 25°C and a discharge rate of 0.2C, the mass energy density GED0 of the battery pack may satisfy the following conditions: 220Wh / kg ≤ GED0 ≤ 280Wh / kg. For example, GED0 = 220Wh / kg, GED0 = 225Wh / kg, GED0 = 230Wh / kg, GED0 = 240Wh / kg, GED0 = 250Wh / kg, GED0 = 260Wh / kg, GED0 = 270Wh / kg, GED0 = 275Wh / kg, GED0 = 280Wh / kg, or a range consisting of any two values ​​therebetween. Optionally, GED0 ≥ 250Wh / kg.

[0246] At an ambient temperature of 25°C and a discharge rate of 1C, the mass energy density GED0 of the battery pack may satisfy the following conditions: 200Wh / kg ≤ GED0 ≤ 250Wh / kg. For example, GED0 = 200Wh / kg, GED0 = 205Wh / kg, GED0 = 210Wh / kg, GED0 = 220Wh / kg, GED0 = 230Wh / kg, GED0 = 240Wh / kg, GED0 = 245Wh / kg, GED0 = 250Wh / kg, or a range consisting of any two values ​​therebetween. Optionally, GED0 ≥ 225Wh / kg.

[0247] Test of mass energy density GED1 of battery cells:

[0248] The mass energy density GED1 of the battery cell=the energy E1 of the battery cell / the mass G1 of the battery cell.

[0249] At an ambient temperature of 25°C, the value of GED1 will vary at different discharge rates.

[0250] GED1 Example Data:

[0251] When the ambient temperature is 25°C and the discharge rate is 0.2C, the mass energy density GED1 of the battery cell may satisfy: 260Wh / kg≤GED1≤330Wh / kg. For example, GED1=260Wh / kg, GED1=265Wh / kg, GED1=270Wh / kg, GED1=280Wh / kg, GED1=290Wh / kg, GED1=300Wh / kg, GED1=310Wh / kg, GED1=320Wh / kg, GED1=325Wh / kg, GED1=330Wh / kg, or a range consisting of any two values ​​therebetween.

[0252] At an ambient temperature of 25°C and a discharge rate of 1C, the mass energy density GED1 of the battery cell may satisfy the following: 240Wh / kg≤GED1≤290Wh / kg. For example, GED1=240Wh / kg, GED1=245Wh / kg, GED1=250Wh / kg, GED1=260Wh / kg, GED1=270Wh / kg, GED1=280Wh / kg, GED1=285Wh / kg, GED1=290Wh / kg, or a range consisting of any two values ​​therebetween.

[0253] Resistance test

[0254] Test steps for the battery pack's AC resistance R0:

[0255] Constant current charging stage: at 25° C., using a 0.5C charging rate, the battery pack is charged with a constant current to the charging cut-off voltage of the battery pack.

[0256] Constant voltage charging stage: At 25°C, the battery pack is charged to the charging cut-off voltage and charged to the cut-off charging rate, which is 0.02C. At this time, the corresponding capacity of the battery pack is C.

[0257] AC resistance measurement stage: At 25°C, the battery pack, which has completed constant voltage charging, is discharged at a DC discharge rate of 0.2C until the battery pack capacity reaches 30%C. The internal resistance tester (HIOKI BT3563) is set to a frequency of 1 kHz, and the battery pack with a capacity of 30%C is tested to obtain the AC resistance value R0 of the battery pack.

[0258] R0 embodiment data:

[0259] The battery pack AC resistance R0 has a range of 17 mΩ ≥ R0 ≥ 11 mΩ, for example, R0 = 11 mΩ, R0 = 12 mΩ, R0 = 13 mΩ, R0 = 14 mΩ, R0 = 15 mΩ, R0 = 16 mΩ, R0 = 17 mΩ, or a range consisting of any two values ​​therebetween.

[0260] Testing steps for the AC resistance r0 of the battery cell:

[0261] Constant current charging stage: at 25° C., using a 0.5C charging rate, the battery cell is charged at a constant current to the charging cut-off voltage of the battery cell.

[0262] Constant voltage charging stage: At 25°C, using the charging cut-off voltage, the battery cell charged to the charging cut-off voltage is charged at constant voltage and charged to the cut-off charge rate, which is 0.02C. At this time, the corresponding capacity of the battery cell is c.

[0263] AC resistance measurement stage: At 25°C, the battery cell that has completed constant voltage charging is discharged at a discharge rate of 0.2C until the capacity of the battery cell is 30%C. The internal resistance tester (HIOKI BT3563) is set to a frequency of 1 kHz, and the battery cell with a capacity of 30%C is tested to obtain the AC resistance value r0 of the battery cell.

[0264] r0 Example data:

[0265] In the embodiment of this solution, the battery cell has a relatively low AC resistance. The battery cell satisfies the following conditions: 0.9mΩ≤r0≤1.5mΩ. For example, r0=0.9mΩ, r0=1mΩ, r0=1.1mΩ, r0=1.2mΩ, r0=1.3mΩ, r0=1.4mΩ, r0=1.5mΩ, or a range consisting of any two values ​​therebetween.

[0266] R0 / V0 ratio example data:

[0267] In the embodiment of the present solution, 6mΩ / L≤R0 / V0≤11mΩ / L. For example, R0 / V0=6mΩ / L, 7mΩ / L, 7.5mΩ / L, 8mΩ / L, 8.5mΩ / L, 9mΩ / L, 9.5mΩ / L, 10mΩ / L, 10.5mΩ / L, 11mΩ / L, or a range consisting of any two values ​​therebetween.

[0268] R0 / C ratio example data:

[0269] In the embodiment of the present solution, 0.2mΩ / Ah≤R0 / C≤0.9mΩ / Ah. For example, R0 / C=0.2mΩ / Ah, R0 / C=0.25mΩ / Ah, R0 / C=0.3mΩ / Ah, R0 / C=0.4mΩ / Ah, R0 / C=0.5mΩ / Ah, R0 / C=0.6mΩ / Ah, R0 / C=0.7mΩ / Ah, R0 / C=0.8mΩ / Ah, R0 / C=0.85mΩ / Ah, R0 / C=0.9mΩ / Ah, or a range consisting of any two values ​​therebetween.

[0270] Battery pack management

[0271] In a specific implementation, the above-mentioned battery pack also includes: a battery management system (BMS) that manages the status of the battery cell components. The BMS can monitor and collect various working status parameters of the battery pack in real time, such as battery cell voltage, battery cell temperature, battery cell current, battery pack voltage, battery pack temperature, battery pack current, battery pack resistance, etc. By monitoring and collecting these parameters, the BMS can evaluate the working status of the battery pack and ensure its safe operation. In addition, the BMS can also control the working status of the battery pack, including charging and discharging, heating, cooling, and overcurrent cut-off protection of each battery cell.

[0272] Figure 9 is a schematic diagram of the internal structure of a battery pack according to another embodiment of the present application. The outer shell 10 has an elliptical radial cross-section. The battery cells 20 have circular radial cross-sections. A large gap exists between the sidewalls of the outer shell 10 on either side of the long axis and the outer walls of the battery cells 20. The battery management system includes a circuit board 30. The circuit board 30 can be positioned within the gap on one side of the long axis of the elliptical outer shell 10. The circuit board 30 extends axially of the outer shell 10 and can collect and manage the voltage, temperature, and current of each battery cell 20. The conductive member 40 for the battery cell 20 can be positioned within the gap on the other side of the long axis of the elliptical outer shell. The conductive member 40 extends axially of the outer shell and can be electrically connected to the negative electrode of each battery cell 20. This structural arrangement allows the circuit board 30 and conductive member 40 to effectively utilize the internal space on both sides of the long axis of the elliptical outer shell. Compared to placement in other locations, this effectively increases the available space in the battery pack 100, thereby increasing the volume utilization and volumetric energy density of the battery pack 100. In addition, in this solution, a battery cell is separately arranged in the radial direction of the shell. Compared with the existing technology, the battery cell is larger in volume and smaller in number, and the number of circuit boards 30 and conductive parts 40 is smaller, which is beneficial to reduce the weight of the battery pack and improve the volume energy density of the battery pack.

[0273] The battery pack 100 generates heat during the charging and discharging process. In the related art, in the 18650 combined battery pack and the 21700 combined battery pack, in the radial cross section, the battery cells close to the center area are farther away from the outer shell and have a slower heat dissipation rate. The outer battery cells are closer to the outer shell, so they dissipate heat faster, and the heat dissipation effect of the inner and outer battery cells is quite different. Therefore, on the one hand, the heat dissipation rate of the internal battery cells is slower, and on the other hand, for the battery management system, since the temperature difference between the internal battery cells and the external battery cells is large during operation, the battery management system needs to perform complex temperature control management on the battery cells with a large temperature difference, which will lead to a higher complexity of the battery management system.

[0274] In this solution, the perimeter of each cell is closer to the outer casing, which facilitates heat dissipation within each cell and improves overall heat dissipation within the battery pack. Furthermore, because the perimeter of each cell is closer to the outer casing, the temperature difference between each cell during operation is smaller, facilitating temperature control by the battery management system.

[0275] In order to further improve the heat dissipation performance of the battery pack, in this solution, the gap between the outer shell and the battery core is filled with thermally conductive adhesive, which can quickly transfer the heat generated by the battery core to the outer shell. The thermal conductivity of the thermally conductive adhesive can be 0.02W / (m·K) to 0.5W / (m·K). For example, the thermal conductivity of the thermally conductive adhesive can be: 0.02W / (m·K), 0.05W / (m·K), 0.1W / (m·K), 0.2W / (m·K), 0.3W / (m·K), 0.4W / (m·K), 0.5W / (m·K) or a range consisting of any two values ​​therebetween. Exemplarily, the thermally conductive adhesive may include but is not limited to at least one of polyurethane, epoxy resin, polybutadiene rubber, and silicone.

[0276] Battery cell electrode assembly

[0277] Figure 10 is a schematic diagram of the structure of a battery cell in a battery pack according to one embodiment of the present application, and Figure 11 is a schematic diagram of the exploded structure of a battery cell in a battery pack according to one embodiment of the present application. As shown in Figures 10 and 11, the battery cell 20 may include: a housing 21, an electrode assembly 22, a cover 23, and a current collecting plate 24. The length l of the battery cell 20 is the maximum length of the battery cell 20 in the axial direction.

[0278] In the related art 18650 and 21700 modular battery packs, the positive tab is located at the end of one end of the positive electrode sheet, and the negative tab is located at the end of the other end of the negative electrode sheet. During operation, the cross-sectional area of ​​the positive and negative tabs is small, resulting in a small flow area and weak current carrying capacity. This increases the resistance of the battery cell, resulting in a high resistance of the battery pack, high heat generation, and significant heat loss.

[0279] In this solution, the battery cell can adopt a full-tab structure. During operation, the full-tab structure has a larger cross-sectional area, a larger flow area, and a stronger current-carrying capacity. Therefore, the current path can be greatly shortened, the internal resistance of the battery pack can be reduced, and the battery cell heat generation and heat loss can be reduced.

[0280] Figure 12 is a schematic diagram of the front view of a cell electrode assembly in a battery pack according to one embodiment of the present application. Figure 13 is a schematic diagram of the cross-sectional view of the battery cell 20 in Figure 12. Figure 14 is a schematic diagram of the expanded structure of at least one electrode sheet of the first type of cell electrode assembly in the battery pack according to an embodiment of the present application. Figure 15 is a schematic diagram of the side view of the electrode sheet shown in Figure 14. Figure 17 is a schematic diagram of the cross-sectional view of the flattened end portion of the hollow foil region of the electrode assembly shown in Figure 12. Referring to Figures 12, 13, 14, 15, and 17, in practice, the cell 20 has a cylindrical structure and includes a wound electrode assembly 22. The electrode assembly 22 includes a first electrode sheet 22a, a second electrode sheet 22b, and a separator 22c. Among them, the first pole piece 22a and the second pole piece 22b have opposite polarities, and at least one of the first pole piece 22a and the second pole piece 22b includes: a current collector 221 and an active material 222 arranged on the current collector 221, the current collector 221 includes a main body area 223 and a hollow foil area 224, the active material 222 is arranged in the main body area 223, and the hollow foil area 224 includes a flattened area 225, and the flattened area 225 is away from the main body area 223. The full-tab battery cell has good heat dissipation performance, and is beneficial to improving the energy density of the battery pack when used with a high-nickel system battery. The flattened area adopts a flattening process to form a full-tab structure, which is beneficial to reducing the internal resistance of the battery cell. In the embodiment of this solution, the battery cell adopts a full-tab structure. Compared with the battery cell with a bipolar tab structure, the heat conduction path of the battery cell with a full-tab structure is transformed from two tabs to the full-tab structure with a hollow foil area 224, which constitutes "countless" heat conduction paths, which can greatly improve the heat dissipation performance. The combination of full-tab battery cells and high-nickel system is conducive to improving the energy density of the battery pack.

[0281] FIG16 is a schematic side view of the structure of the second electrode in a battery pack according to an embodiment of the present application. As shown in FIG15 , FIG16 and FIG17 , in implementation, the electrode shown in FIG15 is the first electrode 22a, and the electrode shown in FIG16 is the second electrode 22b. The first electrode 22a and the second electrode 22b can both adopt a full-tab structure. In implementation, the first electrode 22a and the second electrode 22b can both include: a current collector 221 and an active material 222 disposed on the current collector 221. The current collector 221 includes a main body area 223 and a hollow foil area 224. The active material 222 is disposed in the main body area 223. The hollow foil area 224 includes a flattened area 225, and the flattened area 225 is away from the main body area 223. The hollow foil area 224 of the first electrode 22a and the hollow foil area 224 of the second electrode 22b are disposed oppositely at the two ends of the electrode assembly 22. The first electrode piece 22a can be a positive electrode, and the second electrode piece 22b can be a negative electrode. The empty foil area 224 of the positive electrode is flattened to form a flattened area 225 at the end away from the main area 223, and the flattened area 225 of the positive electrode is welded to the positive electrode collector plate. The empty foil area 224 of the negative electrode is flattened to form a flattened area 225 at the end away from the main area, and the flattened area 225 of the negative electrode is welded to the negative electrode collector plate, or the flattened area 225 of the negative electrode is electrically connected to the shell of the battery cell 20.

[0282] In some embodiments, housing 21 can be a metal housing, with the negative electrode current collector electrically connected to the metal housing, which serves as the negative electrode of the battery cell. The positive electrode current collector is electrically connected to cover 23, with an insulating layer between cover 23 and metal housing 21, which serves as the positive electrode of battery cell 20.

[0283] As shown in Figures 13 and 14, the winding direction V of the electrode assembly is the length direction of the current collector 221, and the direction in which the hollow foil area 224 is away from the main area 223 is the width direction of the current collector 221. In the winding direction of the electrode assembly, that is, the length direction of the current collector 221, when the current collector 221 is in a flat state, the length of the hollow foil area 224 is L1, and the length of the main area 223 is L2. In the width direction of the current collector 221, when the current collector 221 is flat, the size of the hollow foil area 224 is W1, and the total size of the current collector 221 is W2. In Figure 13, the number of winding turns of the electrode assembly is only exemplary and does not limit the specific number of winding turns.

[0284] Optionally, when the current collector 221 is in a flattened state, L1 is the maximum dimension of the empty foil area 224 in the length direction of the current collector 221 .

[0285] Among them, L1=L2. In this electrode assembly, the length of the empty foil area 224 is equal to the length of the current collector 221. The battery cell of this structure has a shorter current path, a larger flow area, a smaller internal resistance of the battery cell, a smaller heat generation of the battery cell, and a lower heat loss.

[0286] Optionally, W1 and W2 can satisfy the following: 0.05 ≤ W1 / W2 ≤ 0.1, which can meet the dimensional requirements for flattening the end of the empty foil area 224. For example, W1 / W2 can be 0.05, 0.06, 0.07, 0.08, 0.09, 0.1, or a range consisting of any two values ​​therebetween. In this embodiment, the value of W1 can be 3 mm ≤ W1 ≤ 6 mm. For example, W1 can be 3 mm, 3.5 mm, 4 mm, 4.5 mm, 5 mm, 5.5 mm, 6 mm, or a range consisting of any two values ​​therebetween. The value of W2 can be: 36mm≤W2≤81mm. For example, W2 can be: 36mm, 38mm, 40mm, 42mm, 44mm, 46mm, 48mm, 50mm, 52mm, 54mm, 56mm, 58mm, 60mm, 62mm, 64mm, 66mm, 68mm, 70mm, 72mm, 74mm, 76mm, 78mm, 80mm, 81mm or a range consisting of any two values ​​therebetween.

[0287] When L1=L2, the ends of the empty foil area 224 are flattened and welded to the current collecting plate, which is beneficial to improving the current carrying capacity of the battery cell. As shown in Figure 17, there is a liquid injection port in the center area of ​​the battery cell to realize liquid injection into the battery cell.

[0288] Optionally, 0.8≤L1 / L2<1. For example, L1 / L2 can be: 0.8, 0.82, 0.84, 0.85, 0.86, 0.9, 0.92, 0.94, 0.96, 0.98, or a range consisting of any two values ​​therebetween. That is, in practice, compared to the above-mentioned embodiment where L1=L2, the empty foil area 224 can be omitted from some areas of the current collector. Thus, in areas where the empty foil area 224 is omitted, there is no flattened area, resulting in a larger gap, which is beneficial for the injection and infiltration of the electrolyte.

[0289] Furthermore, in order to balance the injection efficiency and the current path of the positive and negative electrodes of the battery cell, 0.9≤L1 / L2≤0.95, which has a better balancing effect. For example, L1 / L2 can be: 0.9, 0.91, 0.92, 0.93, 0.94, 0.95, or a range consisting of any two values ​​therebetween. When the injection efficiency is high, the internal resistance can also be small. At the same time, since the area of ​​the empty foil area 224 is reduced, the mass of the battery cell will be reduced. This can improve the mass energy density of the battery pack.

[0290] In a specific implementation, along the length direction of the current collector, the empty foil area 224 can be continuous or multiple at intervals. When the empty foil area 224 is continuous, the dimension L1 is the length of the continuous empty foil area 224. When the empty foil area 224 is at intervals, the dimension L1 is the sum of the lengths of the multiple at intervals.

[0291] When the empty foil area 224 is continuous, the empty foil area 224 is continuously arranged and wound into multiple turns along the winding direction V of the electrode assembly. The flattened area 225 at the end of the multiple turns of the empty foil area 224 can be used for welding to the current collecting plate to serve as the tab of the battery cell.

[0292] Optionally, the empty foil area 224 may not be provided at the inner end of the winding of the electrode assembly. Figure 18 is a schematic diagram of the unfolded structure of at least one electrode sheet of the second type of battery cell electrode assembly in the battery pack according to an embodiment of the present application. In the winding direction of the electrode assembly, the inner end of the winding of the empty foil area 224 and the inner end of the winding of the main body area 223 are separated by a first distance D1, and the size of the first main body area 223 is L2. 0<D1 / L2≤0.2. Optionally, 0.05≤D1 / L2≤0.1. For example, D1 / L2 can be: 0.01, 0.02, 0.03, 0.04, 0.05, 0.06, 0.07, 0.08, 0.09, 0.10, 0.11, 0.12, 0.13, 0.14, 0.15, 0.16, 0.17, 0.18, 0.19, 0.2 or a range consisting of any two values ​​therebetween. Among them, since the empty foil area 224 is not provided at the inner end of the winding at the collector end of the electrode assembly, there are more electrolyte injection gaps at the inner end of the winding, which facilitates the injection of the electrolyte.

[0293] Optionally, the empty foil area 224 may not be provided at the wound outer end of the electrode assembly. Figure 19 is a schematic diagram of the unfolded structure of at least one electrode sheet of the third type of battery cell electrode assembly in the battery pack according to an embodiment of the present application. In the winding direction of the electrode assembly, the wound outer end of the empty foil area 224 and the wound outer end of the main body area 223 are separated by a second distance D2, and the size of the main body area 223 is L2. 0<D2 / L2≤0.2. Optionally, 0.05≤D2 / L2≤0.1. For example, D2 / L2 can be: 0.01, 0.02, 0.03, 0.04, 0.05, 0.06, 0.07, 0.08, 0.09, 0.10, 0.11, 0.12, 0.13, 0.14, 0.15, 0.16, 0.17, 0.18, 0.19, 0.2 or a range consisting of any two values ​​therebetween. Among them, since the empty foil area 224 is not provided at the outer end of the winding at the collector end of the electrode assembly, there are more electrolyte injection gaps at the outer end of the winding, which facilitates the injection of the electrolyte.

[0294] Optionally, no empty foil area 224 may be provided at both the inner and outer ends of the electrode assembly. Figure 20 is a schematic diagram of the unfolded structure of at least one electrode sheet of the fourth type of cell electrode assembly in the battery pack according to an embodiment of the present application. In the winding direction of the electrode assembly, the inner end of the empty foil area 224 and the inner end of the main body area 223 are separated by a first distance D1, and the outer end of the empty foil area 224 and the outer end of the main body area 223 are separated by a second distance D2. The size of the first main body area 223 is L2. 0<(D1+D2) / L2≤0.2. Optionally, 0.05≤(D1+D2) / L2≤0.1. For example, (D1+D2) / L2 can be 0.01, 0.03, 0.05, 0.07, 0.09, 0.1, 0.11, 0.13, 0.15, 0.17, 0.18, 0.2, or a range consisting of any two values ​​therebetween. Since no empty foil region 224 is provided at either the inner or outer ends of the winding at the current collector end of the electrode assembly, there are more gaps for electrolyte injection at the inner and outer ends of the winding, facilitating electrolyte injection.

[0295] In the length direction of the current collector, the empty foil area 224 can be a plurality of spaced apart arrangements. Figure 21 is a schematic diagram of the unfolded structure of at least one pole piece of the fifth type of battery cell electrode assembly in the battery pack according to an embodiment of the present application. The empty foil area 224 includes a plurality of sub-pole ears 226, and the plurality of sub-pole ears 226 are separated and arranged along the winding direction of the electrode assembly. The separate arrangement of the plurality of sub-pole ears is beneficial to reducing the resistance during the flattening of the pole ears. In the length direction of the current collector, the length of each sub-pole ear 226 is M. In some embodiments, the length M of each sub-pole ear 226 may be equal or unequal. Rapid injection of electrolyte can be achieved through the gaps between the sub-pole ears 226.

[0296] Optionally, the number of the sub-electrode tabs 226 is greater than or equal to 4. Optionally, the minimum spacing D between adjacent sub-electrode tabs 226 satisfies: 0 mm < D ≤ 300 mm, which is conducive to rapid infiltration of the electrolyte. The larger the value of the minimum spacing D between the sub-electrode tabs 226, the faster the electrolyte injection speed. Optionally, the minimum spacing D between the sub-pole ears 226 can be: 0.1mm, 10mm, 20mm, 30mm, 40mm, 50mm, 60mm, 70mm, 80mm, 90mm, 100mm, 110mm, 120mm, 130mm, 140mm, 150mm, 160mm, 170mm, 180mm, 190mm, 200mm, 210mm, 220mm, 230mm, 240mm, 250mm, 260mm, 270mm, 280mm, 290mm, 300mm or a range consisting of any two values ​​therebetween.

[0297] In the winding direction of the electrode assembly, the sum of the sizes of the multiple sub-electrode ears 226 is L1, and the size of the main area 223 is L2. L1 and L2 satisfy: 0.8≤L1 / L2≤1. Optionally, 0.9≤L1 / L2≤0.95. Optionally, L1 / L2 can be: 0.8, 0.85, 0.9, 0.95, 1 or a range consisting of any two values ​​therebetween. Among them, when the ratio of L1 / L2 is larger, its heat dissipation performance is better, and when combined with a battery with a higher proportion of high nickel system, it is beneficial to further improve the energy density of the battery pack.

[0298] In some embodiments, the flattened area is welded to the current collector, which is then connected to the electrode terminal. Therefore, the thickness of the current collector has certain dimensional requirements, ensuring that the thickness of the flattened area meets the welding requirements. In this embodiment, Figure 22 is a schematic diagram of the unfolded structure of at least one electrode sheet of the sixth type of cell electrode assembly in a battery pack according to an embodiment of the present application. The multiple sub-tabs 226 include: a first tab region Q1 near the inner end of the electrode assembly winding, a second tab region Q2 located in the middle of the electrode assembly winding, and a third tab region Q3 near the outer end of the electrode assembly winding. The minimum spacing between adjacent sub-tabs 226 in the first tab region Q1 is d1, the minimum spacing between adjacent sub-tabs 226 in the second tab region Q2 is d2, and the minimum spacing between adjacent sub-tabs 226 in the third tab region Q3 is d3. The distances d1, d2, and d3 satisfy the following conditions: d2 < d1, and d2 < d3. The battery cell also includes a current collector 24, to which the second tab region Q2 is welded. The first and third tab regions Q1 and Q3 are non-welding areas of the current collector. The spacing between adjacent sub-tabs 226 in the first and third tab regions Q1 and Q3 is large, making it easier to inject liquid after flattening, thereby improving the efficiency of liquid injection in the battery cell. The spacing between adjacent sub-tabs 226 in the second tab region Q2 is smaller. The thickness of the flattened area of ​​the second tab region Q2 after flattening is greater than the thickness of the flattened areas of the first and third tab regions Q1 and Q3, making it easier to meet welding thickness requirements.

[0299] Optionally, d2 < 0.3 × d1, and d2 < 0.3 × d3. For example, d2 < 0.25 × d1, and d2 < 0.25 × d3. Or, d2 < 0.2 × d1, and d2 < 0.2 × d3. Or, d2 < 0.15 × d1, and d2 < 0.15 × d3. Or, d2 < 0.1 × d1, and d2 < 0.1 × d3. Or, d2 < 0.05 × d1, and d2 < 0.05 × d3.

[0300] Optionally, when the current collector 221 is in the expanded state, the size of the sub-tab 226 in the first tab region Q1 is M1, the size of the sub-tab 226 in the second tab region Q2 is M2, and the size of the sub-tab 226 in the third tab region Q3 is M3, and M1, M2, and M3 satisfy the following: 0.8≤M2 / M1≤1.2, 0.8≤M2 / M3≤1.2. For example, M2 / M1 can be: 0.8, 0.9, 1, 1.1, 1.2, or a range consisting of any two values ​​therebetween. For example, M2 / M3 can be: 0.8, 0.9, 1, 1.1, 1.2, or a range consisting of any two values ​​therebetween.

[0301] In the above embodiment, the multiple sub-pole tabs 226 in the middle region serve as the welding area of ​​the current collecting disk 24 and are welded to the current collecting disk 24, while the multiple sub-pole tabs 226 on both sides do not serve as the welding area of ​​the current collecting disk 24 and are not welded to the current collecting disk 24. In this embodiment, the difference is that the sub-pole tab 226 in the middle region that is welded to the current collecting disk can be a continuous sub-pole tab 226. Figure 23 is a schematic diagram of the unfolded structure of at least one electrode sheet of the seventh type of battery cell electrode assembly in the battery pack according to the embodiment of the present application. The multiple sub-pole tabs 226 include: multiple sub-pole tabs 226 near the inner end of the electrode assembly winding, a continuous sub-pole tab 226 located in the middle of the electrode assembly winding, and multiple sub-pole tabs 226 near the outer end of the electrode assembly winding. The length M0 of the continuous sub-pole tab 226 in the winding direction of the electrode assembly is between 1m and 4m, and the continuous sub-pole tab 226 serves as the welding area of ​​the current collecting disk. For example, the length M0 of the continuous sub-tab 226 in the winding direction of the electrode assembly can be: 1m, 1.5m, 2m, 2.5m, 3m, 3.5m, 4m or a range consisting of any two values ​​therebetween. After the tab is flattened, it is easy to meet the welding strength requirements between the tab and the current collecting plate, reduce the risk of cold welding, and is beneficial to improving the current carrying capacity of the battery cell and reducing the internal resistance of the battery cell, thereby helping to improve the current carrying capacity of the battery pack and reduce the internal resistance of the battery pack. Compared with multiple sub-tabs arranged at intervals, the use of continuous sub-tabs makes the battery pack have the advantages of strong current carrying capacity, good rate performance, low internal resistance, and high output power.

[0302] Typically, the empty foil area 224 will extend to the outer end of the current collector. After the electrode assembly is wound and flattened, the empty foil area 224 located at the outer end of the current collector tends to form a bulge at the end of the electrode assembly winding structure. In the preparation process of the battery pack, the end of the electrode assembly winding structure needs to be wrapped with insulating tape. A large bulge can easily damage the insulating tape. Therefore, in the existing solution, the number of wrapped insulating tape turns is large, and the amount of insulating tape consumed is large. Moreover, the insulating tape with a large number of turns occupies a larger space, which reduces the energy of the battery cell under the same volume. In this solution, Figure 24 is a schematic diagram of the unfolded structure of at least one electrode sheet of the eighth type of battery cell electrode assembly in the battery pack according to an embodiment of the present application. At the outer end of the electrode assembly winding, the corners of the empty foil area 224 are provided with cutouts 227. The winding direction of the electrode assembly is the length direction of the current collector, and the direction of the empty foil area 224 away from the main area 223 is the width direction of the current collector. When the current collector is in a flattened state, the size of the cutout 227 in the length direction of the current collector is l1, and the size of the empty foil area in the width direction of the current collector is W1, and the sizes of l1 and W1 satisfy: 0.2W1≤l1≤4W1. For example, l1 can be: 0.2W1, 0.5W1, W1, 1.5W1, 2W1, 2.5W1, 3W1, 3.5W1, 4W1, or a range consisting of any two values ​​therebetween. Optionally, in the width direction of the current collector, the size of the cutout 227 is w1, and the sizes of w1 and W1 satisfy: 0.2W1≤w1≤W1. For example, w1 can be: 0.2W1, 0.3W1, 0.4W1, 0.5W1, 0.6W1, 0.7W1, 0.8W1, 0.9W1, W1, or a range consisting of any two values ​​therebetween. At the outer end of the electrode assembly, a cutout 227 is provided at the corner of the empty foil area 224 to reduce the risk of excessive bulge at the end of the empty foil area 224 after the electrode assembly is wound, which is beneficial to improving the safety of the battery pack.

[0303] As shown in Figure 24, the incision 227 can be a curved incision. With the curved incision, the empty foil area 224 at the outer end of the current collector winding can be well fitted with the peripheral wall of the electrode assembly winding structure after being flattened. By providing the incision 227, after the empty foil area 224 is flattened to form the flattened area 225, when the insulating tape is attached to the outer periphery of the flattened area 225, the risk of puncturing the insulating tape due to the excessive protrusion at the end of the empty foil area 224 is reduced, which is conducive to reducing the use of insulating tape and improving the safety of the battery pack.

[0304] In some embodiments, the cutout 227 can be of other shapes. Figure 25 shows the expanded structure of at least one electrode sheet of the ninth type of cell electrode assembly in a battery pack according to an embodiment of the present application. The cutout 227 can be a triangular cutout. Compared to a curved cutout, a triangular cutout can reduce processing difficulty and improve production efficiency.

[0305] Alternatively, Figure 26 is a schematic diagram of the expanded structure of at least one electrode sheet of the tenth type of cell electrode assembly in a battery pack according to an embodiment of the present application, where the cutout 227 can be a rectangular cutout. Compared to a triangular cutout, a rectangular cutout can further reduce processing difficulty and improve production efficiency.

[0306] Generally, in the related art, after the electrode assembly is wound, due to the phenomenon of bulges on the outer edge of the flattened area 225, multiple turns of insulating tape need to be wound around the outer periphery of the flattened area 225. By winding multiple turns of insulating tape, the risk of the bulges on the outer edge of the flattened area 225 puncturing the insulating tape can be reduced. Figure 27 is a schematic diagram of the structure of the insulating tape surrounding the outer periphery of the flattened area in the battery cell of the battery pack according to an embodiment of the present application, and Figure 28 is a schematic diagram of the structure of the insulating tape ring in the battery cell of the battery pack according to an embodiment of the present application. Referring to Figures 27 and 28, in this solution, at the outer end of the winding of the electrode assembly, the cutout 227 is provided at the corner of the empty foil area of ​​the first pole piece. Since the cutout 227 is provided at the corner of the empty foil area 224, the phenomenon of bulges on the outer edge of the flattened area 225 after the electrode assembly is wound can be reduced, or the height of the bulge can be reduced. In the embodiment of this solution, the insulating tape can be wound, for example, one circle of insulating tape. Optionally, the battery cell further comprises: a shell 21, a cover 23, a current collecting disc 24 and insulating tape 228. The electrode assembly 22 is arranged in the shell 21, and the current collecting disc 24 is electrically connected to the cover 23 and the flattened area 225 of the first pole piece 22a. The cutout 227 is provided at the corners of the hollow foil area 224 of the first pole piece 22a. The flattened area 225 of the first pole piece 22a is surrounded by insulating tape 228. The surrounding interface of the insulating tape 228 is provided with an overlapping area 229. The length Ld of the overlapping area 229 along the winding direction is 0.5mm to 2mm. Ld is the length of the overlapping area 229 after it is unfolded. The cutout 227 is a rectangular cutout, a triangular cutout or a curved cutout. That is, after the insulating tape 228 is wound, its two ends are stacked to form a closed insulating tape 228 ring. The length of the stacked ends can be between 0.5mm and 2mm, which is conducive to reducing aluminum leakage. For example, the length of the stacked ends is: 0.5mm, 0.6mm, 0.7mm, 0.8mm, 0.9mm, 1.0mm, 1.1mm, 1.2mm, 1.3mm, 1.4mm, 1.5mm, 1.6mm, 1.7mm, 1.8mm, 1.9mm, 2.0mm or a range consisting of any two values ​​therebetween.

[0307] In some embodiments, the housing 21 may be a metal housing, and the flattened region 225 of the second electrode piece 22b and the metal housing may be electrically connected via another current collecting plate. When the metal housing is an aluminum housing, the aluminum housing serves as the positive electrode, and the cover serves as the negative electrode. When the metal housing is a steel housing, the steel housing serves as the negative electrode, and the cover serves as the positive electrode.

[0308] The first electrode sheet may be a positive electrode sheet, and the second electrode sheet may be a negative electrode sheet. The active material of the positive electrode sheet includes a positive electrode active material, and the active material of the negative electrode sheet includes a negative electrode active material. The positive electrode sheet includes: a positive electrode current collector and a positive electrode active material disposed on the positive electrode current collector. The positive electrode current collector includes a positive electrode main body region and a positive electrode hollow foil region. The positive electrode active material is disposed on the positive electrode main body region. The positive electrode hollow foil region includes a positive electrode flattening region, and the positive electrode flattening region is away from the positive electrode main body region. The negative electrode sheet includes: a negative electrode current collector and a negative electrode active material disposed on the negative electrode current collector. The negative electrode current collector includes a negative electrode main body region and a negative electrode hollow foil region. The negative electrode active material is disposed on the negative electrode main body region. The negative electrode hollow foil region includes a negative electrode flattening region, and the negative electrode flattening region is away from the negative electrode main body region. The positive electrode hollow foil region of the positive electrode sheet and the negative electrode hollow foil region of the negative electrode sheet are disposed oppositely at the two ends of the electrode assembly. The positive electrode flattening area of ​​the positive electrode sheet and the positive electrode current collecting plate are welded, and the negative electrode flattening area of ​​the negative electrode sheet and the negative electrode current collecting plate are welded.

[0309] The positive electrode active material includes a positive electrode active material, a positive electrode binder and a positive electrode conductive agent, and the positive electrode active material includes Li 1+a Ni x1 Co y1 Mn z1 O2 or Li 1+a Ni x2 Co y2 Al z2 At least one of O2. Wherein, x1 and x2 are both greater than or equal to 0.9, y1 and y2 are both greater than 0, z1 and z2 are both greater than 0, x1+y1+z1=1, x2+y2+z2=1; -0.05≤a≤0.2.

[0310] Among them, in the specific implementation, Li 1+a Ni x1 Co y1 Mn z1 O2 can be made of Ni91 (LiNi 0.91 Co 0.04 Mn 0.05 O2), Ni92(LiNi 0.92 Co 0.03 Mn 0.05 O2), Ni93(LiNi 0.93 Co 0.02 Mn 0.05 O2), Ni94(LiNi 0.94 Co 0.01 Mn 0.05 O2), Ni95(LiNi 0.95 Co 0.01 Mn 0.04O2) at least one.

[0311] The positive electrode binder includes at least one of polyacrylic acid, polyacrylonitrile, polyvinylidene fluoride, polytetrafluoroethylene or polyamide.

[0312] The positive electrode conductive agent includes at least one of acetylene black, conductive carbon black, carbon nanotubes, carbon fibers, flake graphite, Ketjen black or graphene.

[0313] In the positive electrode active material, the mass percentage of the positive electrode active material is 90% to 98%, the mass percentage of the positive electrode binder is 1.25% to 5%, and the mass percentage of the positive electrode conductor is 0.75% to 5%.

[0314] The negative electrode active material includes a negative electrode active material, a negative electrode binder, and a negative electrode conductive agent, and the negative electrode active material includes at least one of artificial graphite, natural graphite, or silicon material. Optionally, the negative electrode active material includes graphite and silicon, and the mass percentage of the graphite is 85% to 99% based on the mass of the graphite and the silicon. For example, the mass percentage of the graphite is 85%, 86%, 87%, 88%, 89%, 90%, 91%, 92%, 93%, 94%, 95%, 96%, 97%, 98%, 99%, or a range consisting of any two values ​​therebetween.

[0315] The negative electrode conductive agent may include but is not limited to at least one of conductive carbon black (Super P), carbon nanotubes (CNTs), carbon fibers, flake graphite, graphene, metal materials or conductive polymers. The above-mentioned carbon nanotubes may include but are not limited to single-walled carbon nanotubes and / or multi-walled carbon nanotubes. The above-mentioned carbon fibers may include but are not limited to vapor-grown carbon fibers (VGCF) and / or nano-carbon fibers. The above-mentioned metal materials may include but are not limited to metal powder and / or metal fibers, and optionally, the metal may include but is not limited to at least one of copper, nickel, aluminum or silver. The above-mentioned conductive polymers may include but are not limited to at least one of polyphenylene derivatives, polyaniline, polythiophene, polyacetylene or polypyrrole.

[0316] The negative electrode binder may include, but is not limited to, at least one of polyacrylic acid, sodium polyacrylate, potassium polyacrylate, lithium polyacrylate, polyimide, polyvinyl alcohol, carboxymethyl cellulose, sodium carboxymethyl cellulose, lithium carboxymethyl cellulose, polyimide, polyamide-imide, styrene-butadiene rubber, or polyvinylidene fluoride (PVDF).

[0317] In the negative electrode active material, the mass percentage of the negative electrode active material is 90% to 97%, the mass percentage of the negative electrode binder is 1.5% to 5%, and the mass percentage of the negative electrode conductive agent is 0.5% to 5%.

[0318] The present application does not particularly limit the separator, as long as it can achieve the purpose of the present application. For example, the material of the separator may include, but is not limited to, at least one of polyethylene (PE), polypropylene (PP)-based polyolefins (PO), polyesters (e.g., polyethylene terephthalate (PET) film), cellulose, polyimide (PI), polyamide (PA), spandex, or aramid. The type of separator may include at least one of a woven membrane, a non-woven membrane, a microporous membrane, a composite membrane, a rolled membrane, or a spun membrane.

[0319] In some embodiments of the present application, the diaphragm may include a substrate layer and a surface treatment layer. The substrate layer may be a non-woven fabric, a film or a composite film having a porous structure, and the material of the substrate layer may include at least one of polyethylene, polypropylene, polyethylene terephthalate or polyimide. Optionally, a polypropylene porous film, a polyethylene porous film, a polypropylene non-woven fabric, a polyethylene non-woven fabric or a polypropylene-polyethylene-polypropylene porous composite film may be used. Optionally, a surface treatment layer is provided on at least one surface of the substrate layer, and the surface treatment layer may be a polymer layer or an inorganic layer, or a layer formed by a mixed polymer and an inorganic substance.

[0320] For example, the inorganic layer includes inorganic particles and a binder, and the inorganic particles are not particularly limited, and for example, can include at least one of aluminum oxide, silicon oxide, magnesium oxide, titanium oxide, hafnium dioxide, tin oxide, cerium dioxide, nickel oxide, zinc oxide, calcium oxide, zirconium oxide, yttrium oxide, silicon carbide, boehmite, aluminum hydroxide, magnesium hydroxide, calcium hydroxide or barium sulfate. The binder is not particularly limited, and for example, can be at least one of the above-mentioned binders. Polymer is included in the polymer layer, and the material of the polymer includes at least one of polyamide, polyacrylonitrile, acrylate polymer, polyacrylic acid, polyacrylate, polyvinyl pyrrolidone, polyvinyl ether or polyvinylidene fluoride or poly (vinylidene fluoride-hexafluoropropylene).

[0321] In the present application, the battery pack further includes an electrolyte contained in the housing, and the electrolyte includes lithium salt and other non-aqueous solvents.

[0322] The present application does not specifically limit the lithium salt, as long as the objectives of the present application can be achieved. For example, the lithium salt may include, but is not limited to, at least one of LiPF6, LiBF4, LiAsF6, LiClO4, LiB(C6H5)4, LiCH3SO3, LiCF3SO3, LiN(SO2CF3)2, LiC(SO2CF3)3, Li2SiF6, lithium bis(oxalatoborate) (LiBOB), or lithium difluoroborate. The present application does not specifically limit the concentration of the lithium salt in the electrolyte, as long as the objectives of the present application can be achieved.

[0323] The present application has no particular limitation on other non-aqueous solvents, as long as the purpose of the present application can be achieved. For example, it may include but is not limited to at least one of carbonate compounds, carboxylate compounds, ether compounds or other organic solvents.

[0324] Above-mentioned carbonate compound can include but not limited to at least one in linear carbonate compound, cyclic carbonate compound or fluorinated carbonate compound.Above-mentioned linear carbonate compound can include but not limited to at least one in dimethyl carbonate (DMC), diethyl carbonate (DEC), dipropyl carbonate (DPC), methylpropyl carbonate (MPC), ethylpropyl carbonate (EPC) or methyl ethyl carbonate (MEC).Above-mentioned cyclic carbonate can include but not limited to at least one in ethylene carbonate (EC), propylene carbonate (PC), butylene carbonate (BC) or vinyl ethylene carbonate (VEC). The fluorinated carbonate compound may include, but is not limited to, at least one of fluoroethylene carbonate (FEC), 1,2-difluoroethylene carbonate, 1,1-difluoroethylene carbonate, 1,1,2-trifluoroethylene carbonate, 1,1,2,2-tetrafluoroethylene carbonate, 1-fluoro-2-methylethylene carbonate, 1-fluoro-1-methylethylene carbonate, 1,2-difluoro-1-methylethylene carbonate, 1,1,2-trifluoro-2-methylethylene carbonate, or trifluoromethylethylene carbonate.

[0325] The carboxylate compound may include, but is not limited to, at least one of methyl formate, methyl acetate, ethyl acetate, n-propyl acetate, tert-butyl acetate, methyl propionate, ethyl propionate, propyl propionate, γ-butyrolactone, decanoic acid, valerolactone, or caprolactone. The ether compound may include, but is not limited to, at least one of dibutyl ether, tetraglyme, diglyme, 1,2-dimethoxyethane, 1,2-diethoxyethane, 1-ethoxy-1-methoxyethane, 2-methyltetrahydrofuran, or tetrahydrofuran.

[0326] The above-mentioned other organic solvents may include but are not limited to at least one of dimethyl sulfoxide, 1,2-dioxolane, sulfolane, methyl sulfolane, 1,3-dimethyl-2-imidazolidinone, N-methyl-2-pyrrolidone, dimethylformamide, acetonitrile, trimethyl phosphate, triethyl phosphate or trioctyl phosphate.

[0327] In some embodiments, the electrolyte includes lithium hexafluorophosphate (LiPF6) and fluoroethylene carbonate (FEC).

[0328] An embodiment of the present application further provides an electrical device, including: the battery pack of the above embodiment.

[0329] The electrical equipment provided in the embodiments of the present application is not particularly limited and can be any electrical equipment known in the prior art. For example, the electrical equipment can include, but is not limited to, electric bicycles, electric motorcycles, electric toy cars, household appliances, and power tools.

[0330] Figure 29 is a schematic diagram of the structure of an electrical device according to an embodiment of the present application. As shown in Figure 29, the electrical device is optionally an electric power-assisted bicycle, which includes a frame 101, two wheels, and a motor. The two wheels include a front wheel 102 and a rear wheel 103. The frame includes a front fork 104, a front tube 105, an oblique tube 106, a seat 107, and a rear fork 108. The front wheel 102 is rotatably mounted in a socket at the bottom of the front fork 104, and the rear wheel 103 is rotatably mounted in a socket at the end of the rear fork 108. The top end of the front fork 104 is rotatably mounted in the front tube 105, the top end of the oblique tube 106 is connected to the front tube 105, and the bottom end of the oblique tube 106 is connected to the rear fork 108. The battery pack is mounted in the oblique tube 106. The motor can be a drive motor that drives at least one wheel, and the battery pack can serve as a power battery for the drive motor.

[0331] The battery pack supplies power to the drive motor to drive at least one wheel of the electric power-assisted vehicle to rotate, thereby serving as a power battery for the electric power-assisted vehicle. The battery pack can be installed in the oblique tube on the lower front side of the frame of the tube-hidden electric power-assisted vehicle. The specific implementation and application of the battery pack in the embodiment of this solution is not limited to application in tube-hidden electric power-assisted vehicles. The battery pack in the embodiment of this solution can also be connected to the frame of the electric power-assisted vehicle using other types of installation methods such as external and detachable installation. That is, the embodiment of this application does not limit how the battery pack of this solution is installed on the electric power-assisted vehicle.

[0332] Test method description:

[0333] 1. In the embodiment of this solution, the charge and discharge test of the battery pack or battery cell can be tested by a battery tester (battery tester model: Neware CT-4016-5V-100A).

[0334] 2. In the embodiment of this solution, the resistance of the battery pack can be tested by an internal resistance tester (internal resistance tester model: HIOKI BT3563).

[0335] 3. In the embodiment of this solution, for the charge and discharge test of the battery pack or battery cell, the battery pack or battery cell can be placed in a constant temperature box (constant temperature box model: Keming EH-1000), and after standing for 2 hours, the charge and discharge test is performed.

[0336] Example 1 (5048×10)

[0337] <Preparation of Separator>

[0338] An aluminum oxide coating was formed on one surface of a base film to prepare a diaphragm. The base film was a polyethylene base film with a thickness of 9 μm (provided by Celgard Company), and the aluminum oxide coating had a thickness of 2 μm.

[0339] <Preparation of positive electrode sheet>

[0340] The positive electrode active material Ni92 (LiNi 0.92 Co 0.03 Mn 0.05 O2), binder PVDF, conductive agent conductive carbon black and carbon nanotubes are mixed in a mass ratio of 96:2:1:1, N-methylpyrrolidone (NMP) is added as a solvent, and stirred under the action of a vacuum mixer until the solid content is 75wt% and the system is uniform. The positive electrode slurry is evenly coated on one surface of a positive electrode current collector aluminum foil with a thickness of 13μm, and dried at 90°C to obtain a positive electrode sheet with a single-sided coating of a positive electrode active material layer (thickness 100μm) (the unit area coating weight of the positive electrode active material layer on one side of the positive electrode sheet is 380mg / 1540.25mm 2 ). Then, repeat the above steps on the other surface of the aluminum foil to obtain a positive electrode sheet coated with a positive electrode active material layer on both sides. Then, cold press and cut the sheet to obtain a positive electrode sheet for use.

[0341] The specifications of the positive electrode sheet are as follows: the empty foil area of ​​the current collector is continuous, with a length of L1 = 5.1m, the main area of ​​the current collector is L2 = 5.1m, and the total width of the current collector is W2 = 41mm. Among them, the width of the empty foil area is W1 = 4mm, and the width of the main area of ​​the current collector is W2-W1 = 37mm.

[0342] <Preparation of negative electrode sheet>

[0343] The negative electrode active materials graphite and silicon (mass ratio 90:10), styrene-butadiene rubber, and negative electrode conductive agent Super P were mixed in a mass ratio of 97.4:1.2:1.4, and then deionized water was added as a solvent. The mixture was stirred under the action of a vacuum mixer until the solid content was 50wt% and the system was uniform. The negative electrode slurry was evenly coated on one surface of a negative electrode current collector copper foil with a thickness of 8μm and dried at 85°C to obtain a negative electrode sheet with a single-sided negative electrode active material layer (thickness 60μm) (the unit area coating weight of the negative electrode active material layer on one side of the negative electrode sheet is 170mg / 1540.25mm 2 ). Then, repeat the above steps on the other surface of the copper foil to obtain a negative electrode sheet coated with a negative electrode active material layer on both sides. Then, cold pressing and cutting are performed to obtain a negative electrode sheet for use.

[0344] The negative electrode sheet specifications are as follows: the empty foil area of ​​the current collector is continuous, with a length of L1 = 5.2m, the main area of ​​the current collector is L2 = 5.2m, and the total width of the current collector is W2 = 42.1mm. Among them, the width of the empty foil area is W1 = 4mm, and the width of the main area of ​​the current collector is W2-W1 = 38.1mm.

[0345] <Preparation of Electrolyte>

[0346] In an environment with a water content of less than 10 ppm, the non-aqueous organic solvents ethylene carbonate (EC) and ethyl methyl carbonate (EMC) are uniformly mixed in a mass ratio of 1:1 to form a base solvent. Additives vinylene carbonate and 1,3-propane sultone are then added to the base solvent. Lithium salt LiPF6 and fluoroethylene carbonate (FEC) are then added, dissolved, and mixed uniformly to form an electrolyte. Based on the mass of the electrolyte, the mass percentage of vinylene carbonate is 1%, the mass percentage of 1,3-propane sultone is 3%, the mass percentage of LiPF6 is 12.5%, the mass percentage of fluoroethylene carbonate is 1%, and the balance is the non-aqueous organic solvent.

[0347] <Preparation of Electrode Assembly>

[0348] The negative electrode sheet, separator and positive electrode sheet prepared above are stacked and wound in sequence to obtain an electrode assembly, with the empty foil area of ​​the positive electrode sheet and the empty foil area of ​​the negative electrode sheet being located at opposite ends of the electrode assembly;

[0349] The ends of the empty foil areas of the positive electrode sheet and the negative electrode sheet of the electrode assembly are flattened to form flattened areas as tabs.

[0350] The insulating adhesive paper is wound around the outer circle of the flattened area of ​​the empty foil area of ​​the positive electrode sheet for two weeks.

[0351] <Preparation of Battery Pack>

[0352] The electrode assembly is placed in a steel shell. The positive electrode current collector is welded to the cover and the flattened area of ​​the positive electrode sheet. The negative electrode current collector is welded to the steel shell and the flattened area of ​​the negative electrode sheet. After drying, the electrolyte is injected. After vacuum packaging, standing, formation, capacity measurement, and degassing, a lithium-ion battery cell is obtained. The diameter of the battery cell is 50 mm and the length l is 48 mm. Ten battery cells prepared in this example are connected in series to form a battery cell assembly, which is assembled into the housing space and then packaged to obtain a battery pack.

[0353] Example 2 (5048×10)

[0354] The same as in Example 1 except that a triangular cut is provided at the outer end of the wound empty foil area of ​​the positive electrode sheet, the dimensions of the triangular cut are: l1 = 0.2W1, w1 = 0.2W1, and the insulating tape is wound around the outer circle of the flattened area of ​​the empty foil area of ​​the positive electrode sheet.

[0355] Example 3 (5048×10)

[0356] The process is the same as in Example 1 except that a triangular cut is provided at the outer end of the wound empty foil area of ​​the positive electrode sheet, the dimensions of the triangular cut are: l1=4W1, w1=W1, and the insulating tape is wound around the outer circle of the flattened area of ​​the empty foil area of ​​the positive electrode sheet.

[0357] Example 4 (5048×10)

[0358] In addition to setting the positive electrode sheet specifications to: when the positive electrode sheet is flattened, control L1 / L2 = 0.8, the main area length of the current collector L2 = 5.1m, the empty foil area of ​​the current collector includes 10 sub-electrode tabs of uniform size, and the sum of the lengths M of the 10 sub-electrode tabs L1 = 4.08m. The distance D between two adjacent sub-electrode tabs is 0.113m.

[0359] The negative electrode sheet specifications were set as follows: when the negative electrode sheet is flattened, L1 / L2 = 0.8, the main current collector area length L2 = 5.2m, the empty foil area of ​​the current collector includes 10 sub-electrode tabs of uniform size, and the sum of the lengths M of the 10 sub-electrode tabs L1 = 4.16m. The distance D between two adjacent sub-electrode tabs is 0.116m.

[0360] Other than that, the rest is the same as Example 1.

[0361] Example 5 (5048×10)

[0362] In addition to setting the specifications of the positive electrode sheet to: when the positive electrode sheet is flattened, controlling L1 / L2=0.8, the main area length of the current collector L2=5.1m, the empty foil area of ​​the current collector includes 10 sub-pole ears of the same size, the first pole ear area includes 3 sub-pole ears, and the spacing between adjacent sub-pole ears in the first pole ear area is 230mm, the second pole ear area includes 4 sub-pole ears, and the spacing between adjacent sub-pole ears in the second pole ear area is 20mm, the third pole ear area includes 3 sub-pole ears, and the spacing between adjacent sub-pole ears in the third pole ear area is 230mm, and the sum of the lengths M of the 10 sub-pole ears L1=4.08m.

[0363] The specifications of the negative electrode sheet are set to: when the negative electrode sheet is flattened, L1 / L2 is controlled to be 0.8, the length of the main area of ​​the current collector is L2 = 5.2m, the empty foil area of ​​the current collector includes 10 sub-pole ears of the same size, the first pole ear area includes 3 sub-pole ears, and the spacing between adjacent sub-pole ears in the first pole ear area is 235mm, the second pole ear area includes 4 sub-pole ears, and the spacing between adjacent sub-pole ears in the second pole ear area is 20mm, the third pole ear area includes 3 sub-pole ears, and the spacing between adjacent sub-pole ears in the third pole ear area is 235mm, and the sum of the lengths M of the 10 sub-pole ears is L1 = 4.16m.

[0364] Other than that, the rest is the same as Example 1.

[0365] Example 6 (5048×10)

[0366] In addition to setting the specifications of the positive electrode sheet to: when the positive electrode sheet is flattened, controlling L1 / L2=0.8, the main area length of the current collector L2=5.1m, the empty foil area of ​​the current collector includes 7 sub-pole ears, the first pole ear area includes 3 sub-pole ears, and the spacing between adjacent sub-pole ears in the first pole ear area is 170mm, the second pole ear area includes 1 continuous sub-pole ear, and the continuous sub-pole ear is 1.632m long, the third pole ear area includes 3 sub-pole ears, and the spacing between adjacent sub-pole ears in the third pole ear area is 170mm, the sum of the lengths M of the 7 sub-pole ears L1=4.08m, and the sizes of the sub-pole ears in the first pole ear area and the third pole ear area are the same.

[0367] The specifications of the negative electrode sheet are set to: when the negative electrode sheet is flattened, L1 / L2 is controlled to be 0.8, the length of the main area of ​​the current collector is L2 = 5.2m, the empty foil area of ​​the current collector includes 7 sub-pole ears, the first pole ear area includes 3 sub-pole ears, and the spacing between adjacent sub-pole ears in the first pole ear area is 173mm, the second pole ear area includes 1 continuous sub-pole ear, and the continuous sub-pole ear is 1.664m long. The third pole ear area includes 3 sub-pole ears, and the spacing between adjacent sub-pole ears in the third pole ear area is 173mm. The sum of the lengths M of the 7 sub-pole ears is L1 = 4.16m, and the sub-pole ears in the first pole ear area and the third pole ear area have the same size.

[0368] Other than that, the rest is the same as Example 1.

[0369] Example 7 (4648×10)

[0370] In addition to setting the positive electrode active material to: Ni91(LiNi 0.91 Co 0.04 Mn 0.05 O2).

[0371] The specifications of the positive electrode sheet are set as follows: the empty foil area of ​​the current collector is continuous, the length of the empty foil area is L1 = 5m, and the length of the main area of ​​the current collector is L2 = 5m.

[0372] The negative electrode sheet specifications are set as follows: the empty foil area of ​​the current collector is continuous, the length of the empty foil area is L1 = 5.1m, and the length of the main area of ​​the current collector is L2 = 5.1m.

[0373] The diameter of the battery cell is 46mm.

[0374] Other than that, the rest is the same as Example 1.

[0375] Example 8 (4645×10)

[0376] In addition to setting the positive electrode active material to: Ni91(LiNi 0.91 Co 0.04 Mn 0.05 O2).

[0377] The specifications of the positive electrode sheet are set as follows: the empty foil area of ​​the current collector is continuous, the length of the empty foil area is L1 = 5m, the length of the main area of ​​the current collector is L2 = 5m, and the total width of the current collector is W2 = 38mm. Among them, the width of the empty foil area is W1 = 4mm, and the width of the main area of ​​the current collector is W2-W1 = 34mm.

[0378] The negative electrode sheet specifications are set as follows: the empty foil area of ​​the current collector is continuous, with a length of L1 = 5.1m, a length of L2 = 5.1m for the main area of ​​the current collector, and a total width of W2 = 39.1mm. Among them, the width of the empty foil area is W1 = 4mm, and the width of the main area of ​​the current collector is W2-W1 = 35.1mm.

[0379] The diameter of the battery cell is 46mm and the length l is 45mm.

[0380] Other than that, the rest is the same as Example 1.

[0381] Example 9 (4948×12)

[0382] In addition to setting the positive electrode active material to: Ni92(LiNi 0.92 Co 0.03 Mn 0.05 O2).

[0383] The specifications of the positive electrode sheet are set as follows: the empty foil area of ​​the current collector is continuous, the length of the empty foil area is L1 = 5.05m, and the length of the main area of ​​the current collector is L2 = 5.05m.

[0384] The negative electrode sheet specifications are set as follows: the empty foil area of ​​the current collector is continuous, the length of the empty foil area is L1 = 5.15m, and the length of the main area of ​​the current collector is L2 = 5.15m.

[0385] The diameter of the battery cell is 49 mm, and 12 battery cells prepared in this embodiment are connected in series to form a battery cell assembly.

[0386] Other than that, the rest is the same as Example 1.

[0387] Example 10 (5448×10)

[0388] In addition to setting the positive electrode active material to: Ni93(LiNi 0.93 Co 0.02 Mn 0.05 O2).

[0389] The specifications of the positive electrode sheet are set as follows: the empty foil area of ​​the current collector is continuous, the length of the empty foil area is L1 = 5.5m, and the length of the main area of ​​the current collector is L2 = 5.5m.

[0390] The negative electrode sheet specifications are set as follows: the empty foil area of ​​the current collector is continuous, the length of the empty foil area is L1 = 5.6m, and the length of the main area of ​​the current collector is L2 = 5.6m.

[0391] The diameter of the battery cell is 54mm.

[0392] Other than that, the rest is the same as Example 1.

[0393] Example 11 (4958×10)

[0394] In addition to setting the positive electrode active material to: Ni93(LiNi 0.93 Co 0.02 Mn 0.05 O2).

[0395] The specifications of the positive electrode sheet are set as follows: the empty foil area of ​​the current collector is continuous, with a length of L1 = 5.05m, a length of L2 = 5.05m for the main area of ​​the current collector, and a total width of W2 = 51mm. Among them, the width of the empty foil area is W1 = 4mm, and the width of the main area of ​​the current collector is W2-W1 = 47mm.

[0396] The negative electrode sheet specifications are set as follows: the empty foil area of ​​the current collector is continuous, with a length of L1 = 5.15m, a length of L2 = 5.15m for the main area of ​​the current collector, and a total width of W2 = 52.1mm. Among them, the width of the empty foil area is W1 = 4mm, and the width of the main area of ​​the current collector is W2-W1 = 48.1mm.

[0397] Example 12 (4680×6)

[0398] In addition to setting the positive electrode active material to: Ni94(LiNi 0.94 Co 0.01 Mn 0.05 O2).

[0399] The specifications of the positive electrode sheet are set as follows: the empty foil area of ​​the current collector is continuous, the length of the empty foil area is L1 = 5m, the length of the main area of ​​the current collector is L2 = 5m, and the total width of the current collector is W2 = 74mm. Among them, the width of the empty foil area is W1 = 4mm, and the width of the main area of ​​the current collector is W2-W1 = 70mm.

[0400] The negative electrode sheet specifications are set as follows: the empty foil area of ​​the current collector is continuous, with a length of L1 = 5.1m, a length of L2 = 5.1m for the main current collector area, and a total current collector width of W2 = 75mm. Of these, the width of the empty foil area is W1 = 4mm, and the width of the main current collector area is W2 - W1 = 71mm.

[0401] The diameter of the battery cell is adjusted to 46mm, the length l is adjusted to 80mm, and the number of battery cells is adjusted to 6.

[0402] Other than that, the rest is the same as Example 1.

[0403] Example 13 (4380×6)

[0404] In addition to setting the positive electrode active material to: Ni94(LiNi 0.94 Co 0.01 Mn 0.05 O2).

[0405] The specifications of the positive electrode sheet are set as follows: the empty foil area of ​​the current collector is continuous, with a length of L1 = 4.7m, a length of L2 = 4.7m for the main area of ​​the current collector, and a total width of W2 = 74mm. Among them, the width of the empty foil area is W1 = 4mm, and the width of the main area of ​​the current collector is W2-W1 = 70mm.

[0406] The negative electrode sheet specifications are set as follows: the empty foil area of ​​the current collector is continuous, with a length of L1 = 4.8m, the main area of ​​the current collector is L2 = 4.8m, and the total width of the current collector is W2 = 75mm. Among them, the width of the empty foil area is W1 = 4mm, and the width of the main area of ​​the current collector is W2-W1 = 71mm.

[0407] The diameter of the battery cell is adjusted to 43mm, the length l is adjusted to 80mm, and the number of battery cells is adjusted to 6.

[0408] Other than that, the rest is the same as Example 1.

[0409] Example 14 (4683×6)

[0410] In addition to setting the positive electrode active material to: Ni95(LiNi 0.95 Co 0.01 Mn 0.04 O2).

[0411] The specifications of the positive electrode sheet are set as follows: the empty foil area of ​​the current collector is continuous, with a length of L1 = 5m, a length of L2 = 5m for the main area of ​​the current collector, and a total width of W2 = 77mm. Among them, the width of the empty foil area is W1 = 4mm, and the width of the main area of ​​the current collector is W2-W1 = 73mm.

[0412] The negative electrode sheet specifications are set as follows: the empty foil area of ​​the current collector is continuous, with a length of L1 = 5.6m, a length of L2 = 5.1m for the main area of ​​the current collector, and a total width of W2 = 78mm. Among them, the width of the empty foil area is W1 = 4mm, and the width of the main area of ​​the current collector is W2-W1 = 74mm.

[0413] The diameter of the battery cell is adjusted to 46mm, the length l is adjusted to 83mm, and the number of battery cells is adjusted to 6.

[0414] Other than that, the rest is the same as Example 1.

[0415] Example 15 (5480×6)

[0416] In addition to setting the positive electrode active material to: Ni95(LiNi 0.95 Co 0.01 Mn 0.04 O2).

[0417] The specifications of the positive electrode sheet are set as follows: the empty foil area of ​​the current collector is continuous, with a length of L1 = 5.5m, a length of L2 = 5.5m for the main area of ​​the current collector, and a total width of W2 = 74mm. Among them, the width of the empty foil area is W1 = 4mm, and the width of the main area of ​​the current collector is W2-W1 = 70mm.

[0418] The negative electrode sheet specifications are set as follows: the empty foil area of ​​the current collector is continuous, with a length of L1 = 5.6m, a length of L2 = 5.6m for the main current collector area, and a total current collector width of W2 = 75mm. Of these, the width of the empty foil area is W1 = 4mm, and the width of the main current collector area is W2 - W1 = 71mm.

[0419] The diameter of the battery cell is adjusted to 54mm, the length l is adjusted to 80mm, and the number of battery cells is adjusted to 6.

[0420] Other than that, the rest is the same as Example 1.

[0421] Comparative Example 1

[0422] The purchased battery pack 1 has a radial cross-sectional structure schematic diagram as shown in FIG1 .

[0423] Comparative Example 2

[0424] The purchased battery pack 2 has a radial cross-sectional structure schematic diagram as shown in FIG2 .

[0425] In Examples 1 to 15, a schematic diagram of the radial cross-sectional structure of the battery pack is shown in FIG4 .

[0426] The parameters and performances of each embodiment and comparative example are shown in the comparative example and embodiment comparison table.

[0427] Comparative Examples and Examples Comparative Examples Notes:

[0428] L is the length of the housing.

[0429] S0 is the radial cross-sectional area of ​​the battery pack.

[0430] V0 is the volume of the battery pack.

[0431] G0 is the weight of the battery pack.

[0432] DL1 is the first connecting line dimension of the radial cross section of the battery pack.

[0433] DL2 is the second connecting line dimension of the radial cross section of the battery pack.

[0434] The meaning of mSnP can be understood as: a total of m×n battery cells, where every n battery cells are connected in parallel to form a parallel body, totaling m parallel bodies, and m parallel bodies are connected in series to form a battery cell assembly.

[0435] l is the length of the battery cell.

[0436] S1 is the radial cross-sectional area of ​​the cell.

[0437] V1 is the volume of the battery cell.

[0438] c is the rated capacity of the battery cell.

[0439] E1 is the energy of the battery cell.

[0440] VED1 is the volume energy density of the battery cell.

[0441] r0 is the AC resistance r0 of the battery cell in the above embodiment. In the test step of r0, a battery cell with a capacity of 30% c is tested to obtain the AC resistance r0.

[0442] E0 is the energy of the battery pack.

[0443] VED0 is the volume energy density of the battery pack.

[0444] GED0 is the mass energy density of the battery pack.

[0445] R0 is the AC resistance of the battery pack in the above embodiment. In the test step of R0, the battery pack with a capacity of 30% C is tested to obtain the resistance value R0.

[0446] G1 is the weight of the battery cell.

[0447] GED1 is the mass energy density of the battery cell.

[0448] C is the rated capacity of the battery pack.

[0449] Comparative Analysis

[0450] By comparing and analyzing the above-mentioned embodiments 1 to 15 with comparative examples 1 and 2, it can be seen that: in the embodiments of this solution, the battery pack has a VED0 of 450Wh / L≤620Wh / L at a discharge rate of 0.2C at 25°C, and a VED0 of 410Wh / L≤560Wh / L at a discharge rate of 1C at 25°C. The battery pack has a high volume energy density at a discharge rate of 0.2C or 1C at 25°C. When the battery pack volume is the same, the cruising range of the electric power-assisted vehicle can be increased. When the battery pack energy is the same, in the embodiments of this solution, the volume of the battery pack is smaller, so the diameter of the battery pack can be smaller, and the battery pack can be set in the electric power-assisted vehicle's smaller diameter inclined tube, which is beneficial to reducing the wind resistance during the riding process of the electric power-assisted vehicle. In the existing solution, the diameter of the electric power-assisted vehicle's inclined tube is relatively thick. In this solution, the electric power-assisted vehicle can use an inclined tube with a smaller diameter, which improves the aesthetics of the electric power-assisted vehicle. On the other hand, since the diameter of the electric power-assisted bicycle's oblique tube is thinner, the wind resistance of the electric power-assisted bicycle during riding can be reduced (the faster the riding speed, the greater the difference), which is conducive to further improving the cruising range of the electric power-assisted bicycle.

[0451] By comparing and analyzing Examples 1 to 15 above with Comparative Examples 1 and 2, it can be seen that in the embodiments of this solution, the battery pack has a mass energy density of 220Wh / kg ≤ GED0 ≤ 280Wh / kg at a discharge rate of 0.2C at 25°C, and a mass energy density of 200Wh / kg ≤ GED0 ≤ 250Wh / kg at a discharge rate of 1C at 25°C. The battery pack has a high mass energy density at either a 0.2C discharge rate or a 1C discharge rate at 25°C. With the same mileage, the battery pack weighs less, thereby reducing the weight of the electric power-assisted vehicle and facilitating lightweighting of the electric power-assisted vehicle. Furthermore, with the same mass, the battery pack can increase the mileage of the electric power-assisted vehicle.

[0452] By comparing and analyzing the above-mentioned embodiments 1 to 15 with comparative examples 1 and 2, it can be seen that: when the energy of the battery pack is similar, the number of battery cells required in the embodiment of the present scheme is smaller, and the number of battery cells per layer in the scheme is only one, compared with the comparative example, in which multiple battery cells are set per layer. The assembly process of the battery pack in the embodiment of the present scheme is simpler, which is conducive to improving the assembly efficiency of the battery pack.

[0453] In Examples 2 to 3, a triangular cut is provided at the outer end of the wound empty foil area of ​​the positive electrode plate, which is beneficial to reducing the protrusion at the tail end of the empty foil area, and is beneficial to reducing the amount of insulating tape used in the outer circle of the flattened area of ​​the empty foil area of ​​the first electrode plate in the electrode assembly, thereby improving safety.

[0454] In Example 4, Example 5, and Example 6, the battery cells with multiple sub-electrode tab structures are used, which is beneficial for the injection and infiltration of the electrolyte, reduces the resistance during flattening, and is beneficial for improving the mass energy density of the battery pack.

[0455] In Example 5, the spacing between adjacent sub-pole tabs in the second tab region is smaller than the spacing between adjacent sub-pole tabs in the first and third tab regions. In Example 6, the second tab region adopts continuous sub-pole tabs, and the first and third tab regions adopt multiple adjacent sub-pole tabs. In Examples 5 and 6, after the first, second, and third tab regions are flattened, the thickness of the flattened area formed in the second tab region is greater than the thickness of the flattened area formed in the first and third tab regions. The current collector and the flattened area formed in the thicker second tab region are welded to meet the welding thickness requirements. When the thickness of the current collector is the same, the welding yield of the battery cell can be improved. In addition, when the thickness of the welded flattened area is the same, this solution can adopt a thinner current collector, which is beneficial to reduce the space and weight of the battery cell occupied by the current collector, and is beneficial to improve the volume energy density and mass energy density of the battery pack.

[0456] By comparing the above examples 1 to 15 with comparative examples 1 and 2, it can be seen that in the embodiment of this solution, the ratio S1 / S0 of the radial cross-sectional area S1 of the battery cell to the radial cross-sectional area S0 of the housing can meet the following conditions: 66%≤S1 / S0≤72%. Compared with comparative examples 1 and 2, the ratio S1 / S0 is higher. At 25°C and 0.2C discharge rate, the battery pack meets the following conditions: 0.25Wh / mm 2 ≤E0 / S0≤0.34Wh / mm 2 At 25℃ and 1C discharge rate, the battery pack meets the following requirements: 0.23Wh / mm 2 ≤E0 / S0≤0.30Wh / mm 2Compared to Comparative Examples 1 and 2, the E0 / S0 ratio is higher. Given the same energy content, the battery pack's outer diameter can be thinner due to the higher proportion of the cell's cross-sectional area to the battery casing's cross-sectional area. This reduces the diameter of the oblique tube that mounts the battery pack to the e-bike, thereby reducing wind resistance. Given the same outer diameter, the battery pack can hold more energy, extending the e-bike's range.

[0457] By comparing and analyzing the above embodiments 1 to 15 with comparative examples 1 and 2, it can be seen that in the embodiment of this scheme, the ratio of the radial cross-sectional area S1 of the battery pack cell to the radial cross-sectional area S0 of the battery pack: S1 / S0 is relatively high, which is conducive to achieving high space utilization of the battery cell inside the battery pack.

[0458] A comparison of Examples 1 to 15 with Comparative Examples 1 and 2 reveals that in the embodiments of this solution, the battery pack has a lower AC resistance R0. On the one hand, given the same battery pack energy, the lower AC resistance of the battery pack in this embodiment allows the battery pack energy to be converted into more power output, thereby increasing the range of the electric power-assisted vehicle. On the other hand, due to the lower heat generation during battery power supply, the battery pack can operate at a lower temperature, achieving stable power supply and improving the riding stability of the electric power-assisted vehicle.

[0459] By comparing Examples 1 to 15 with Comparative Examples 1 and 2, it can be seen that in the embodiments of this solution, the ratio of battery pack resistance to battery pack volume is small, which is conducive to achieving low resistance characteristics when the battery pack volume is the same. When the battery pack volume of the electric power-assisted bicycle is the same, even lower resistance is achieved.

[0460] By comparing Examples 1 to 15 with Comparative Examples 1 and 2, it can be seen that in the embodiments of this solution, the ratio of the resistance R of the battery pack to the rated capacity C of the battery pack is relatively small, which is conducive to achieving low resistance characteristics when the battery pack has the same capacity. When the battery pack capacity of the electric power-assisted bicycle is the same, lower resistance is achieved.

[0461] In this document, relational terms such as first and second, etc., are used only to distinguish one entity or operation from another entity or operation, and do not necessarily require or imply any such actual relationship or order between these entities or operations. Moreover, the terms "comprises," "comprising," or any other variations thereof are intended to cover non-exclusive inclusion, such that a process, method, article, or apparatus comprising a series of elements includes not only those elements, but also other elements not explicitly listed, or elements inherent to such process, method, article, or apparatus. In the absence of further limitations, an element defined by the phrase "comprising a ..." does not exclude the presence of additional identical elements in the process, method, article, or apparatus comprising the element.

[0462] Each embodiment in this specification is described in a related manner. The same or similar parts between the embodiments can be referred to each other. Each embodiment focuses on the differences from other embodiments.

[0463] The above description is only a preferred embodiment of the present application and is not intended to limit the scope of protection of the present application. Any modifications, equivalent replacements, improvements, etc. made within the spirit and principles of the present application are included in the scope of protection of the present application.

Claims

1. A battery pack, characterized in that: The battery pack has a columnar structure and includes: The housing has a receiving space, the length L of the housing is in the range of 510 mm ≤ L ≤ 650 mm, and the radial cross-sectional area S0 of the housing is in the range of 2100 mm 2 ≤S0≤3200mm 2 ; The battery cell assembly comprises: a plurality of battery cells disposed in the accommodation space, the plurality of battery cells being arranged in sequence in the axial direction of the housing; When the ambient temperature is 25°C and the discharge rate is less than or equal to 1C, the volume energy density VED0 of the battery pack satisfies: VED0 ≥ 410Wh / L.

2. The battery pack according to claim 1, wherein: When the ambient temperature is 25°C and the discharge rate is equal to 0.2C, the volume energy density VED0 of the battery pack satisfies: VED0 ≥ 450Wh / L.

3. The battery pack according to claim 1 or 2, characterized in that: At an ambient temperature of 25°C and a discharge rate of 1C, the volume energy density VED0 of the battery pack satisfies: VED0≤560Wh / L; and / or, When the ambient temperature is 25°C and the discharge rate is equal to 0.2C, the volume energy density VED0 of the battery pack satisfies: VED0≤620Wh / L.

4. The battery pack according to claim 3, wherein: At an ambient temperature of 25°C and a discharge rate of 1C, the volume energy density VED0 of the battery pack satisfies: VED0 ≥ 450Wh / L; and / or, When the ambient temperature is 25°C and the discharge rate is equal to 0.2C, the volume energy density VED0 of the battery pack satisfies: VED0 ≥ 500Wh / L.

5. The battery pack according to any one of claims 1 to 4, characterized in that: At an ambient temperature of 25°C and a discharge rate of 1C, the volume energy density VED1 of the battery cell satisfies the following conditions: 950Wh / L ≥ VED1 ≥ 670Wh / L; and / or, When the ambient temperature is 25°C and the discharge rate is equal to 0.2C, the volume energy density VED1 of the battery cell satisfies: 1050Wh / L≥VED1≥740Wh / L.

6. The battery pack according to any one of claims 1 to 5, characterized in that: The capacity output ratio of the battery pack = the actual output capacity of the battery pack / the rated capacity of the battery pack; The actual output capacity of the battery pack is the capacity output when the battery pack is in a fully charged state and continuously discharged at a constant current until the battery pack is in a fully discharged state. The capacity output ratio satisfies at least one of the following ratios: When the ambient temperature is 25°C and the discharge rate is 1C, the capacity output ratio is greater than or equal to 95%; When the ambient temperature is 25° C. and the discharge rate is 2C, the capacity output ratio is greater than or equal to 94%.

7. The battery pack according to claim 1, wherein: 510mm≤L≤550mm; and / or, 2400mm 2 ≤S0≤2800mm 2 。 8. The battery pack according to any one of claims 1 to 7, characterized in that: The range of the length l of the battery core is: 45mm≤l≤83mm, and the range of the radial cross-sectional area S1 of the battery core is: 1450mm 2 ≤S1≤2300mm 2 .

9. The battery pack according to claim 8, characterized in that: The battery cell has a cylindrical structure; wherein, The diameter of the battery core is 49±0.5 mm, and the length of the battery core is 48±0.5 mm; or The diameter of the battery core is 46±0.5 mm, and the length of the battery core is 80±0.5 mm.

10. The battery pack according to any one of claims 1 to 9, characterized in that: In the outer contour of the radial cross-section of the battery pack, the two points with the longest distance form a first connecting line, and the size of the first connecting line is DL1. The perpendicular bisector of the first connecting line and the two intersection points of the outer contour form a second connecting line, and the size of the second connecting line is DL2. DL1 and DL2 satisfy: 0mm≤DL1-DL2≤8mm.

11. The battery pack according to any one of claims 1 to 10, characterized in that: The nominal voltage range of the battery cell is 3.5V to 3.7V.

12. The battery pack according to any one of claims 1 to 11, characterized in that: The number of the battery cells is between 6 and 12.

13. The battery pack according to any one of claims 1 to 12, characterized in that: The multiple battery cells are connected in series.

14. The battery pack according to claim 13, wherein: The nominal voltage range of the battery pack is 21V to 44.4V.

15. The battery pack according to claim 13, wherein: The rated capacity of the battery pack is C, 17Ah≤C≤43Ah.

16. The battery pack according to claim 13, characterized in that: The rated capacity of the battery cell is c, 17Ah≤c≤43Ah.

17. The battery pack according to any one of claims 1 to 16, characterized in that: The radial cross-section of the housing is substantially elliptical.

18. The battery pack according to any one of claims 1 to 17, characterized in that: The battery cell has a cylindrical structure, and the battery cell includes an electrode assembly with a wound structure, and the electrode assembly includes: a first electrode sheet, a second electrode sheet and a diaphragm; wherein, The first pole piece and the second pole piece have opposite polarities. At least one of the first pole piece and the second pole piece includes: a current collector and an active material arranged on the current collector. The current collector includes a main body area and a hollow foil area. The active material is arranged in the main body area. The hollow foil area includes a flattened area, and the flattened area is far away from the main body area.

19. The battery pack according to claim 18, wherein: At the outer end of the electrode assembly, a notch is provided at the corner of the empty foil area; When the current collector is in a flattened state, the size of the cutout in the length direction of the current collector is l1, and the size of the empty foil area in the width direction of the current collector is W1, and the sizes of l1 and W1 satisfy: 0.2W1≤l1≤4W1.

20. The battery pack according to claim 19, wherein: In the width direction of the current collector, the size of the cutout is w1, and the sizes of w1 and W1 satisfy: 0.2W1≤w1≤W1.

21. The battery pack according to claim 19, wherein: The battery cell further includes: a shell, a cover, a current collecting plate and insulating tape, the electrode assembly is arranged in the shell, and the current collecting plate is connected to the cover and the flattened area of ​​the first electrode; wherein, The cutouts are provided at the corners of the empty foil area of ​​the first pole piece; The outer periphery of the flattened area of ​​the first pole piece is surrounded by insulating tape, and an overlapping area is provided at the surrounding interface of the insulating tape. The length of the overlapping area along the winding direction is 0.5 mm to 2 mm.

22. The battery pack according to any one of claims 18 to 21, characterized in that: When the current collector is in a flattened state, the length of the empty foil area is L1, the length of the main area is L2, and L1 and L2 satisfy: 0.8≤L1 / L2≤1.

23. The battery pack according to any one of claims 18 to 22, characterized in that: The first electrode sheet is a positive electrode sheet, the second electrode sheet is a negative electrode sheet, the active material of the positive electrode sheet includes a positive electrode active material, and the active material of the negative electrode sheet includes a negative electrode active material; The positive electrode active material includes a positive electrode active material, a positive electrode binder and a positive electrode conductor. The positive electrode active material includes Li 1+a Ni x1 Co y1 Mn z1 O2 or Li 1+a Ni x2 Co y2 Al z2 At least one of O2; Among them, x1 and x2 are both greater than or equal to 0.9, y1 and y2 are both greater than 0, z1 and z2 are both greater than 0, x1+y1+z1=1, x2+y2+z2=1; -0.05≤a≤0.

2.

24. The battery pack according to claim 23, wherein: The negative electrode active material includes: a negative electrode active material, a negative electrode binder and a negative electrode conductor. The negative electrode active material includes graphite and silicon. Based on the mass of the graphite and the silicon, the mass percentage of the graphite is 85% to 99%.

25. An electrical device, characterized in that: include: The battery pack according to any one of claims 1 to 24.

26. The electrical equipment according to claim 25, characterized in that: The electrical equipment is an electric power-assisted bicycle, which includes a frame, two wheels and a motor; The two wheels include: a front wheel and a rear wheel; The frame comprises: a front fork, a front tube, a diagonal tube, a seat frame and a rear fork; The front wheel is rotatably mounted on the front fork, the rear wheel is rotatably mounted on the rear fork, the top end of the front fork is rotatably mounted on the front tube, the top end of the inclined tube is connected to the front tube, and the bottom end of the inclined tube is connected to the rear fork; The battery pack is arranged on the oblique tube.

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