Battery pack and electric device

Abstract

This application relates to the field of batteries, and provides a battery pack and an electrical device. The battery pack includes a battery assembly, which includes at least two battery cells arranged along a first direction. The extension length of the battery cells in the first direction is less than the extension length in a second direction. Each battery cell includes a cover plate and a housing. The cover plate is fixedly connected to a set end of the housing by welding. A weld line is formed between the cover plate and the housing, and the weld line extending along the first direction between the cover plate and the housing is a first weld line. In a longitudinal section of the battery pack perpendicular to the first direction, the depth of the molten pool of the first weld line is D mm, the width at 2 / 3 depth of the molten pool along the depth direction is N mm, the maximum width of the first weld line is L mm, L-N satisfies 0.4 mm ≤ L-N ≤ 1.5 mm, and D / N satisfies 0.3 ≤ D / N ≤ 10.

Description

Technical Field

[0001] This application relates to the field of batteries, specifically to a battery pack and an electrical device. Background Technology

[0002] In high-energy-density battery packs used in large electric commercial vehicles or trucks, individual battery cells are typically fixed to the battery pack, usually using a method of stacking them adjacent to each other on their large surfaces. By stacking the battery cells adjacent to each other on their large surfaces, the mutual constraint between adjacent batteries effectively suppresses the overall vibration amplitude of the battery.

[0003] For the aforementioned existing battery packs, the long side weld lines of the cover plate located at the edge of the battery surface are subject to strong constraints due to their proximity to other battery cells. However, the short side weld lines of the cover plate, lacking direct contact and constraints from adjacent batteries, are prone to being subjected to more concentrated and severe vibration stress over a long period of time. This can lead to the short side weld lines of the cover plate being easily broken and damaged, causing safety issues such as battery leakage. Summary of the Invention

[0004] In view of this, the present application aims to provide a battery pack and electrical equipment to solve the technical problem that the short side weld lines of the cover plates of existing battery packs are prone to breakage and damage due to the lack of direct contact and constraint between adjacent batteries, which makes them susceptible to long-term exposure to more concentrated and severe vibration stress.

[0005] The first aspect of this application provides a battery pack, including a battery assembly, the battery assembly including at least two battery cells, the at least two battery cells being arranged along a first direction, the extension length of the battery cells in the first direction being less than the extension length in a second direction, and the first direction, the second direction and the height direction of the battery cells being mutually perpendicular to each other. The battery cell includes a cover plate and a housing. The cover plate is fixedly connected to a set end of the housing by welding. A weld line is formed between the cover plate and the housing, and the weld line extending along the first direction between the cover plate and the housing is the first weld line. In the longitudinal section of the battery pack perpendicular to the first direction, the depth of the molten pool of the first bonding wire is D mm, the width of the molten pool at 2 / 3 depth along the depth direction of the molten pool is N mm, the maximum width of the first bonding wire is L mm, LN satisfies 0.4 mm ≤ LN ≤ 1.5 mm, and D / N satisfies 0.3 ≤ D / N ≤ 10.

[0006] Another aspect of this application provides an electrical device including the battery pack.

[0007] In the battery pack of this application embodiment, when LN satisfies 0.4 mm ≤ LN ≤ 1.5 mm and 0.3 ≤ D / N ≤ 10, the cover plate and the shell can achieve a good metallurgical bond, reduce bubble defects, thereby improving the welding yield of the first weld line. It can also effectively avoid the heat-affected zone formed at the edge of the molten pool of the first weld line being too large, effectively avoid the coarse grains in the internal region of the molten pool caused by excessive heat input, effectively improve the structural strength of the first weld line, thereby reducing the probability of the first weld line cracking and being damaged due to long-term vibration stress, causing safety problems such as leakage of battery cells, improving the working safety of battery cells, and thus improving the overall reliability and service life of the battery pack. Attached Figure Description

[0008] It should be understood that the following figures only illustrate certain embodiments of this application and should not be construed as limiting the scope.

[0009] It should be understood that the same or similar reference numerals are used in the accompanying drawings to denote the same or similar elements.

[0010] It should be understood that the accompanying drawings are only schematic, and the dimensions and scales of the elements in the drawings are not necessarily precise.

[0011] Figure 1 This is a three-dimensional schematic diagram of a battery cell according to an embodiment of this application.

[0012] Figure 2 This is a partial cross-sectional schematic diagram of a battery cell according to an embodiment of this application.

[0013] Figure 3 This is a partial cross-sectional schematic diagram of a battery cell according to an embodiment of this application.

[0014] Figure 4 This is a partial cross-sectional schematic diagram of a battery cell according to an embodiment of this application.

[0015] Figure 5 This is a partial cross-sectional schematic diagram of another battery cell according to an embodiment of this application.

[0016] Figure 6 This is a partial cross-sectional schematic diagram of another battery cell according to an embodiment of this application.

[0017] Figure 7 This is a partial cross-sectional schematic diagram of another battery cell according to an embodiment of this application.

[0018] Figure 8 This is a partial cross-sectional schematic diagram of a battery cell according to an embodiment of this application.

[0019] Figure 9 This is a partial cross-sectional schematic diagram of a battery cell according to an embodiment of this application.

[0020] Attached image labels: 10. Battery cell; 1. Casing; 11. First inclined surface; 2. Cover plate; 21. Second inclined surface; 3. First weld line; 31. First welding area; 32. Second welding area; 4. Second weld line; 5. Molten pool.

[0021] X - First direction; Y - Second direction; Z - Height direction. Detailed Implementation

[0022] Numerous specific details are set forth below to provide an understanding of the structure, function, and use of the embodiments described and illustrated in the specification and figures. It is to be understood that the embodiments described and illustrated herein are non-limiting examples, and thus it will be appreciated that the particular structural and functional details disclosed herein are representative and exemplary. Variations and changes may be made to these embodiments without departing from the scope of the claims.

[0023] The technical solutions of the embodiments of this application will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of this application, and not all embodiments. Based on the embodiments of this application, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of this application.

[0024] Research has found that for battery packs assembled using the above-mentioned method of stacking large adjacent surfaces, the long side weld lines of the cover plate located at the edge of the large surface of the battery are subject to strong constraints due to their proximity to other battery cells. However, the short side weld lines of the cover plate, lacking direct contact and constraints with adjacent batteries, are prone to long-term exposure to more concentrated and severe vibration stresses, which can easily lead to cracking and damage of the short side weld lines of the cover plate, causing safety issues such as battery leakage.

[0025] In the battery pack of this application embodiment, when LN satisfies 0.4 mm ≤ LN ≤ 1.5 mm and 0.3 ≤ D / N ≤ 10, the cover plate 2 and the shell 1 can achieve a good metallurgical bond, reduce bubble defects, thereby improving the welding yield of the first welding line 3. It can also effectively avoid the heat-affected zone formed at the edge of the molten pool 5 of the first welding line 3 being too large, effectively avoid the coarse grains in the internal region of the molten pool 5 caused by excessive heat input, effectively improve the structural strength of the first welding line 3, thereby reducing the probability of the first welding line 3 cracking and being damaged due to long-term vibration stress, causing safety problems such as leakage of the battery cell 10, improving the working safety of the battery cell 10, and thus improving the overall reliability and service life of the battery pack.

[0026] Therefore, this application provides a battery pack. The battery pack of this application can be a complete functional unit that can directly output electrical energy, which is formed by combining multiple battery cells in series and / or parallel to form a battery pack, a battery management system (BMS), a thermal management system, an electrical connection system (high voltage / low voltage connectors, wiring harnesses, etc.), structural components (shell, brackets, etc.), and protective components, and placing the above components into a box and sealing it with a cover plate.

[0027] Specifically, the battery pack in this application embodiment includes at least a battery pack, which includes at least two battery cells 10 arranged along a first direction. Multiple battery cells 10 with comparable capacity and internal resistance can be connected in series or parallel to form a battery pack. Each battery cell 10 can store chemical energy and controllably convert it into electrical energy. In recyclable batteries, the active materials can be activated by charging after discharge for continued use. The battery cell 10 can be a lithium-ion battery, sodium-ion battery, sodium-lithium-ion battery, lithium metal battery, sodium metal battery, lithium-sulfur battery, magnesium-ion battery, nickel-metal hydride battery, nickel-cadmium battery, lead-acid battery, etc., and this application embodiment is not limited to these types. The battery cell 10 typically includes a casing 1, a cell, an adapter plate, and an electrolyte. The casing 1 is used to house the cell and electrolyte, and generally includes a casing body and a cover plate.

[0028] The housing 1 of the battery cell 10 is a component that provides a receiving space to house the electrode assembly and other components and isolate them from the outside environment. The housing 1 generally includes a body with an opening at at least one end and a receiving cavity. The opening of the housing 1 can be closed by a cover plate 2 to seal and isolate the internal environment of the battery cell 10 from the external environment. The materials of the housing 1 include, but are not limited to, copper, iron, aluminum, stainless steel, aluminum alloy, and plastic.

[0029] The cover plate 2 of the battery cell 10 is a component used to close the opening of the housing 1 to isolate the internal environment of the battery cell 10 from the external environment. The material of the cover plate 2 includes, but is not limited to, copper, iron, aluminum, stainless steel, aluminum alloy, plastic, etc.

[0030] At least one positive electrode post and at least one negative electrode post are disposed on the housing 1 and / or cover plate 2. The battery cell includes one or more electrode assemblies, which are formed by stacking or winding positive electrode plates, negative electrode plates and separators. The separator is located between adjacent positive and negative electrode plates to insulate the positive and negative electrode plates, and at least one end of the electrode assembly has a tab. One end of the adapter is electrically connected to the tab, and the other end is electrically connected to the electrode post.

[0031] like Figure 1As shown, in the battery pack of this application embodiment, the extension length of the battery cell 10 in the first direction is less than the extension length in the second direction, and the first direction, the second direction and the height direction of the battery cell 10 are all perpendicular to each other. That is, the first direction is the short side direction of the battery cell 10, the second direction is the long side direction of the battery cell 10, and the short side direction, the long side direction and the height direction of the battery cell 10 are all perpendicular to each other.

[0032] like Figure 1 and Figure 9 As shown, the battery cell 10 of this application embodiment includes a cover plate 2 and a housing 1. The cover plate 2 is fixedly connected to the set end of the housing 1 by welding methods such as laser welding, thereby forming a weld line between the cover plate 2 and the housing 1. The weld line extending along the first direction between the cover plate 2 and the housing 1 is the first weld line 3, that is, the first weld line 3 is the short side weld line between the housing 1 and the cover plate 2 of the battery cell 10. Similarly, the weld line extending along the second direction between the cover plate 2 and the housing 1 is the second weld line 4; that is, the second weld line 4 is the long side weld line between the housing 1 and the cover plate 2 of the battery cell 10.

[0033] like Figure 2 As shown, in the longitudinal section of the battery pack perpendicular to the first direction, the depth of the molten pool 5 of the first bonding line 3 is D mm, the width of the molten pool 5 at 2 / 3 depth along the depth direction of the molten pool 5 is N mm, the maximum width of the first bonding line 3 is L mm, LN satisfies 0.4 mm≤LN≤1.5 mm, and D / N satisfies 0.3≤D / N≤10.

[0034] Among them, the molten pool 5 is the metal area that is locally melted by the heat source and then re-solidified during the welding process. The depth D mm of the molten pool 5 is the distance from the surface of the heated surface of the molten pool 5 along the extension direction of the molten pool 5 to the deepest point of the molten pool 5. The depth direction of the molten pool 5 is parallel to the welding direction. Along the depth direction of the molten pool 5, the depth of the molten pool 5 usually decreases continuously. The width of the molten pool 5 is its maximum width. The 2 / 3 depth of the molten pool 5 is from the surface of the molten pool 5 downwards to the 2 / 3 depth of the molten pool 5.

[0035] Understandably, by cutting the first weld line 3 of the battery pack and observing the longitudinal section under a microscope, the cross-sectional morphology of the weld pool 5 formed by welding can be clearly seen. This allows for the acquisition of the depth D mm of the weld pool 5, the width N mm at 2 / 3 depth of the weld pool 5, and the maximum width L mm of the first weld line 3, thus obtaining the specific values ​​of LN and D / N. Furthermore, by optimizing the laser welding process parameters, LN and D / N can be effectively adjusted to the preset range.

[0036] Specifically, in the embodiments of this application, measuring instruments such as micrometers or calipers can be used to measure parameters such as length, width, depth, diameter, radius, distance, and thickness, and to obtain parameters such as area through calculation.

[0037] In the embodiments of this application, the preparation steps of the battery cell are as follows: (1) Preparation of the positive electrode: The positive electrode active material, conductive agent acetylene black, and binder PVDF are mixed, and solvent NMP is added. The mixture is stirred under vacuum until the system is homogeneous to obtain a positive electrode slurry. The positive electrode slurry is uniformly coated on both surfaces of the positive electrode current collector aluminum foil, air-dried at room temperature, and then transferred to an oven for further drying. Finally, it is cold-pressed and slit to obtain the positive electrode sheet. Specifically, the mass ratio of positive electrode active material: conductive agent: binder satisfies (92~98):(4~1):(4~1).

[0038] (2) Preparation of negative electrode: The negative electrode active material, conductive agent acetylene black, thickener CMC, and binder SBR are mixed, and deionized water is added as a solvent. The mixture is stirred under vacuum until the system is homogeneous to obtain a negative electrode slurry. The negative electrode slurry is uniformly coated on both surfaces of the negative electrode current collector copper foil, air-dried at room temperature, and then transferred to an oven for further drying. After cold pressing and slitting, the negative electrode sheet is obtained. The ratio of negative electrode active material: conductive agent: thickener: binder satisfies (90~96): (4~2): (2~1): (4~1).

[0039] (3) Preparation of electrolyte: Ethylene carbonate (EC), ethyl methyl carbonate (EMC), and diethyl carbonate (DEC) were mixed in a volume ratio of 1:1:1 to obtain an organic solvent. Then, fully dried lithium salt LiPF6 was dissolved in the mixed organic solvent to prepare an electrolyte with a concentration of 1 mol / L.

[0040] (4) Preparation of the diaphragm: Polyethylene film is selected as the diaphragm.

[0041] (5) Battery fabrication: The positive electrode, separator, and negative electrode are stacked in sequence and wound to form a bare battery cell, which is then placed in a prismatic battery casing. The battery is dried, injected with electrolyte, sealed with a sealing device, and then subjected to settling, formation, and volume adjustment to obtain the battery.

[0042] The positive electrode active material can be selected from one or more lithium-containing positive electrode active materials, including lithium iron phosphate, ternary materials containing nickel, cobalt, and manganese, and lithium manganese iron phosphate; the negative electrode active material can be selected from one or more negative electrode active main materials, such as artificial graphite, natural graphite, silicon carbide, silicon oxide, and lithium titanate.

[0043] The adhesive includes, but is not limited to, one or more combinations of polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), PVDF-tetrafluoroethylene-propylene terpolymer, PVDF-hexafluoropropylene-tetrafluoroethylene terpolymer, tetrafluoroethylene-hexafluoropropylene copolymer, fluorinated acrylate resin, styrene-butadiene rubber, polyacrylic acid, sodium polyacrylate, polyacrylamide, polyvinyl alcohol, sodium alginate, polymethacrylic acid, carboxymethyl chitosan, etc.

[0044] The solvent can be deionized water, NMP (N-methylpyrrolidone), alcohol, ether, ketone or other types of pyrrolidone, etc.

[0045] The positive electrode current collector foil can be a metal foil or a composite current collector. For example, as a metal foil, it can be made of stainless steel, copper, aluminum, nickel, carbon electrode, carbon, nickel, or titanium with a silver-plated surface. The composite current collector may include a polymer material base layer and a metal layer. The composite current collector can be formed by forming a metal material (aluminum, aluminum alloy, nickel, nickel alloy, titanium, titanium alloy, silver and silver alloy, etc.) on a polymer material substrate (such as a substrate of polypropylene, polyethylene terephthalate, polybutylene terephthalate, polystyrene, polyethylene, etc.).

[0046] The negative electrode current collector foil can be made of stainless steel, copper, aluminum, nickel, carbon electrodes, or titanium, and can be surface-plated with silver. Composite current collectors may include a polymer base layer and a metal layer. Composite current collectors can be formed by forming metal materials (aluminum, aluminum alloys, copper, nickel, nickel alloys, titanium, titanium alloys, silver and silver alloys, etc.) on a polymer base material (such as polypropylene, polyethylene terephthalate, polybutylene terephthalate, polystyrene, polyethylene, etc.).

[0047] This application embodiment includes two tests: Test Method 1 is used to test the battery leakage rate under vibration conditions, and Test Method 2 is used to test the battery leakage rate after 1000 cycles.

[0048] Test Method 1: The steps for determining the battery leakage rate under vibration conditions are as follows: According to the above battery preparation method, for each embodiment and comparative example, corresponding batteries were prepared. 500 batteries were prepared, and four batteries were grouped together. Two of the batteries were arranged along the width direction of the battery to form a battery column. The two battery columns were arranged along the length direction of the battery to form a battery pack, for a total of 125 battery packs. The values ​​of D and N for each embodiment and comparative example are shown in Table 2 below. All other test conditions were kept consistent.

[0049] The battery was mounted on a vibration table according to GB / T2423.43. The testing procedure was carried out according to GB / T2423.56. Random and fixed-frequency vibration loads were applied in each direction, and the loading sequence should preferably be random z-axis, fixed-frequency z-axis, random y-axis, fixed-frequency y-axis, random x-axis, fixed-frequency x-axis (the direction of the line connecting the front and rear of the battery is the x-axis direction, and the other horizontal direction perpendicular to the x-axis direction is the y-axis direction). The vibration frequency, power spectral density (PSD), vibration time, etc., are shown in Table 1 below.

[0050] Table 1 is shown above.

[0051] After the vibration is complete, observe the junction between the short side of the battery cover and the battery casing to check for leakage. The leakage rate is calculated as (number of batteries leaking / 500). 100%.

[0052] If the battery leakage rate is less than or equal to 1%, the test result is considered good; if the battery leakage rate is less than or equal to 3% but greater than 1%, the test result is considered qualified; if the battery leakage rate is greater than 3%, it is considered unqualified.

[0053] Test Method 2: The steps for determining the battery leakage rate after 1000 cycles are as follows: Following the battery preparation method described above, corresponding batteries were prepared for each embodiment and comparative example. The values ​​of D and N for the 500 prepared batteries are shown in Table 2 below, and other test conditions remained consistent.

[0054] The battery was charged at room temperature (25℃) with a constant current of 0.33C to the upper limit voltage of 4.25V, then discharged at a constant voltage until the current dropped to 0.05C. After resting for 5 minutes, the battery was discharged at a constant current of 0.33C to the lower limit voltage of 2.5V. This constitutes one cycle. After performing 1000 cycles on the lithium-ion battery, the junction of the short side of the battery cover and the battery casing was observed for leakage. The leakage rate was calculated as (number of leaking batteries / 500). 100%.

[0055] If the battery leakage rate is less than or equal to 1%, the test result is considered good; if the battery leakage rate is less than or equal to 3% but greater than 1%, the test result is considered qualified; if the battery leakage rate is greater than 3%, it is considered unqualified.

[0056] Different systems require corresponding adjustments to their upper and lower voltage limits: Lithium iron phosphate (LFP) - upper limit 3.65V, lower limit 2.5V; Nickel-cobalt-manganese ternary NCM - upper limit 4.25V, lower limit 2.5V; Lithium manganese iron phosphate (LFMP) - upper limit 4.25V, lower limit 2.5V; Lithium nickel manganese oxide - upper limit 4.8V, lower limit 3.5V.

[0057] In this test, the active material for the positive electrode of the battery was selected from a nickel-cobalt-manganese ternary LiNi alloy. 0.6 Co 0.2 Mn 0.2 Taking O2 as an example, all other positive electrode materials meet the above test requirements, and the mass ratio of positive electrode active material: conductive agent: binder meets 96:2:2; the negative electrode active material is selected from artificial graphite, and the ratio of negative electrode active material: conductive agent: thickener: binder meets 95:2:1:2.

[0058] The relevant parameters and performance test results of the embodiments and comparative examples of this application are as follows: Table 2 is shown above.

[0059] As can be seen from Table 2 above, the D / N ratios of each embodiment satisfy 0.3≤D / N≤10, and the results of Performance 1: under vibration conditions, battery leakage ratio and Performance 2: after cycle, are both qualified or good. The D / N value of Comparative Example 1 is less than 0.3, and the result of Performance 1: under vibration conditions, battery leakage ratio is unqualified. The D / N value of Comparative Example 2 is greater than 10, and the result of Performance 2: after cycle, battery leakage ratio is unqualified.

[0060] Specifically, according to analysis, in the battery pack of this application embodiment, the depth D mm of the molten pool 5 of the first bonding wire 3, the width N mm at 2 / 3 depth of the molten pool 5, and the maximum width L mm of the first bonding wire 3; when D / N is less than 0.3, the heat-affected zone formed at the edge of the molten pool 5 of the first bonding wire 3 is too large, which easily leads to structural failure of the heat-affected zone around the first bonding wire 3; when D / N is greater than 10, too many pores are formed in the first bonding wire 3, which easily affects the airtightness of the first bonding wire 3, and thus affects the service life of the battery cell 10. In the battery pack of this application embodiment, when LN satisfies 0.4 mm ≤ LN ≤ 1.5 mm and 0.3 ≤ D / N ≤ 10, the cover plate 2 and the shell 1 can achieve a good metallurgical bond, reduce bubble defects, thereby improving the welding yield of the first welding line 3. It can also effectively avoid the heat-affected zone formed at the edge of the molten pool 5 of the first welding line 3 being too large, effectively avoid the coarse grains in the internal region of the molten pool 5 caused by excessive heat input, effectively improve the structural strength of the first welding line 3, thereby reducing the probability of the first welding line 3 cracking and being damaged due to long-term vibration stress, causing safety problems such as leakage of the battery cell 10, improving the working safety of the battery cell 10, and thus improving the overall reliability and service life of the battery pack.

[0061] In specific embodiments, D / N can be selected from specific values ​​such as 0.3, 0.8, 1.5, 2.3, 3.2, 4.2, 5.3, 6.5, 7.9, and 10, or other reasonable specific values ​​within the range of 0.3 to 10. D (mm) ranges from 0.36mm to 1.4mm, and can be selected from specific values ​​such as 0.36mm, 0.45mm, 0.55mm, 0.65mm, 0.75mm, 0.85mm, 0.95mm, 1.05mm, 1.2mm, and 1.4mm, or other reasonable specific values ​​within the range of 0.36mm to 1.4mm. N (mm) ranges from 0.1mm to 1.2mm, and can be selected from 0.1mm, 0.2mm, 0.3mm, 0.4mm, 0.5mm, 0.6mm, 0.7mm, 0.8mm, 1.0mm, and 1.2mm. Other reasonable specific values ​​can be selected within the range of 0.1mm to 1.2mm, and no restrictions are imposed here.

[0062] Specifically, the battery cells 10 can be arranged in a linear fashion to form a battery pack, or they can be arranged in an array to form a battery pack, without limitation. For example, in one embodiment of this application, the battery pack includes at least two battery cells 10, which are configured to be stacked along a first direction, that is, each battery cell 10 is stacked with its large surface adjacent to each other. By utilizing the mutual constraint between adjacent batteries, the overall vibration amplitude of the battery is effectively suppressed. It is understood that end plates, side plates, and other structural components can also be used to fix and constrain a row of battery cells 10.

[0063] like Figure 2 As shown, in one embodiment of this application, the molten pool 5 is formed on the top surface of the cover plate 2; D / N satisfies 1.2≤D / N≤10.

[0064] Since the molten pool 5 is formed on the top surface of the cover plate 2, the battery cell 10 in this embodiment adopts a top-side welding process to weld the side of the cover plate 2 and the shell 1 together. In this process, the main direction of the welding heat source comes from the top of the cover plate 2. When the molten pool 5 is formed on the top surface of the cover plate 2, the weld strength of the top-side welding is higher than that of the side-side welding, and the hardness of the heat-affected zone is higher. In order to reduce the number and area of ​​pores in the first weld line 3, when D / N satisfies 1.2≤D / N≤10, it can further ensure that the cover plate 2 and the shell 1 are effectively welded, effectively reduce the risk of welding defects, and also ensure the structural strength of the first weld line 3, thereby ensuring the structural strength of the side of the cover plate 2 and the shell 1 after welding. In a specific embodiment, D / N in the above structure can be selected from specific values ​​such as 1.2, 2.1, 3.0, 3.9, 4.8, 5.7, 6.6, 7.5, 8.4, 10, etc., or other reasonable specific values ​​can be selected within the range of 1.2 to 10, without any restrictions.

[0065] Furthermore, such as Figure 3 As shown, in one embodiment of this application, in a longitudinal section of the battery pack perpendicular to the first direction, the contact point between the boundary of the molten pool 5 and the outer surface of the casing 1 is the first contact point; the straight line passing through the first contact point and extending along the second direction is the first dividing line, the area of ​​the region of the molten pool 5 on the side adjacent to the opening of the molten pool 5 on the first dividing line is S(1) mm²; the area of ​​the region of the molten pool 5 on the side away from the opening of the molten pool 5 on the first dividing line is S(2) mm²; S(1) / S(2) satisfies 0.5≤S(1) / S(2)≤3.

[0066] When the molten pool 5 is formed on the top surface of the cover plate 2, the contact point between the boundary of the molten pool 5 and the outer surface of the shell 1 is the first contact point. The first dividing line is a straight line that passes through the first contact point and extends along the second direction. If the ratio S(1) / S(2) of the area of ​​the molten pool 5 on the side adjacent to the opening of the molten pool 5 on the first dividing line and the area of ​​the molten pool 5 on the side away from the opening of the molten pool 5 on the first dividing line is less than 0.5, it indicates that the areas of the molten pool 5 on the side adjacent to the opening of the molten pool 5 and the area away from the opening of the molten pool 5 are relatively close. There are usually more bubbles inside the molten pool 5, which can easily affect the welding yield of the first welding line 3.

[0067] When S(1) / S(2) is greater than 3, it indicates that there is a relatively large area on the side of the opening of the molten pool 5, the welding energy is relatively large, and the grains in the internal area of ​​the molten pool 5 will be relatively coarse, which will reduce the strength of the first weld line 3. Therefore, when S(1) / S(2) satisfies 0.5≤S(1) / S(2)≤3, it can ensure a good welding connection between the shell 1 and the cover plate 2, and can also avoid the strength reduction caused by excessive melting during the welding process, effectively realizing a weld structure that can uniformly bear stress, thereby further improving the structural stability of the short side weld line of the battery cell 10.

[0068] In a specific embodiment, S(1) / S(2) can be selected from specific values ​​such as 0.5, 0.8, 1.2, 1.6, 2.0, 2.5, 3, etc., or other reasonable specific values ​​can be selected within the range of 0.5 to 3; the range of S(1) mm² is 0.4mm² to 0.9mm², and specific values ​​such as 0.4mm², 0.5mm², 0.6mm², 0.7mm², 0.8mm², 0.9mm², etc., or other reasonable specific values ​​can be selected within the range of 0.4mm² to 0.9mm²; the range of S(2) mm² is 0.3mm² to 0.85mm², and specific values ​​such as 0.3mm², 0.4mm², 0.5mm², 0.6mm², 0.7mm², 0.8mm², 0.85mm², etc., or other reasonable specific values ​​can be selected within the range of 0.3mm² to 0.85mm². Other reasonable specific values ​​can be selected within the range, without any restrictions.

[0069] like Figure 2 As shown, in one embodiment of this application, the ratio D / H of the depth D mm of the molten pool 5 of the first bonding wire 3 to the thickness H mm of the cover plate 2 satisfies 0.2≤D / H≤0.9.

[0070] When the molten pool 5 is formed on the top surface of the cover plate 2, and the ratio of the depth D mm of the molten pool 5 of the first weld line 3 to the thickness H mm of the cover plate 2 is less than 0.2, the molten pool 5 formed by welding is too shallow, making it difficult to ensure a tight bond between the cover plate 2 and the shell 1; when D / H is greater than 0.9, the molten pool 5 formed by welding is too deep, which can easily lead to a relatively large heat-affected zone formed by welding, thereby reducing the connection strength of the first weld line 3.

[0071] Therefore, when the ratio D / H of the depth D mm of the molten pool 5 of the first weld line 3 to the thickness H mm of the cover plate 2 satisfies 0.2≤D / H≤0.9, it can be ensured that the ratio between the molten pool 5 of the first weld line 3 and the thickness of the cover plate 2 is appropriate, ensuring a high-strength connection between the cover plate 2 and the shell 1, reducing the risk of incomplete welding due to insufficient molten depth, and effectively reducing the heat-affected zone formed by welding, thereby improving the connection strength of the first weld line 3. In a specific embodiment, D / H can be selected from specific values ​​such as 0.2, 0.3, 0.4, 0.5, 0.6, 0.7, 0.8, 0.9, etc., or other reasonable specific values ​​can be selected within the range of 0.2 to 0.9. H mm ranges from 1.5 to 3 mm, and H mm can be selected from specific values ​​such as 1.5 mm, 1.8 mm, 2.1 mm, 2.4 mm, 2.7 mm, 3 mm, etc., or other reasonable specific values ​​can be selected within the range of 1.5 mm to 3 mm. No restrictions are imposed here.

[0072] like Figure 4 As shown, in one embodiment of this application, in the longitudinal section of the battery pack perpendicular to the first direction, along the height direction of the battery cell 10, the deepest point of the molten pool 5 is the effective melting point, and the contact point between the boundary of the molten pool 5 and the outer surface of the shell 1 is the first contact point; the effective melting point is constructed to be lower than the first contact point, and the smaller angle between the line connecting the first contact point and the effective melting point and the straight line extending along the second direction is E(1)°, satisfying 5°≤E(1)°≤70°.

[0073] It is understandable that by controlling the location of the heat source introduction, the deepest point of the molten pool 5, i.e., the effective melting point, can be effectively controlled to be lower than the aforementioned first contact point. When the small angle between the line connecting the first contact point and the effective melting point and the straight line extending along the second direction satisfies 5°≤E(1)°≤70°, a better molten pool 5 can be formed, the welding heat input is more appropriate, which helps the gas in the molten pool 5 to escape, effectively reducing the bubble defects in the molten pool 5, thereby significantly improving the welding yield of the first weld line 3. In a specific embodiment, E(1)° can be selected from specific values ​​such as 5°, 10°, 20°, 30°, 40°, 50°, 60°, and 70°, or other reasonable specific values ​​can be selected within the range of 5° to 70°, which are not limited here.

[0074] It is understood that in another embodiment of this application, the effective melting point and the first contact point are the same point, that is, the deepest point of the molten pool 5 is the contact point between the boundary of the molten pool 5 and the outer surface of the shell 1.

[0075] Similarly, such as Figure 4As shown, in one embodiment of this application, in the longitudinal section of the battery pack perpendicular to the first direction, along the height direction of the battery cell 10, the deepest point of the molten pool 5 is the effective melting point, and the contact point between the boundary of the molten pool 5 and the upper surface of the cover plate 2 is the second contact point; the smaller angle between the line connecting the second contact point and the effective melting point and the straight line extending along the second direction is E(2)°, and E(2)° satisfies 20°≤E(2)°≤70°.

[0076] When the smaller angle E(2)° between the line connecting the boundary of the molten pool 5 and the contact point on the upper surface of the cover plate 2 (i.e., the second contact point and the effective penetration point) and the straight line extending along the second direction satisfies 20°≤E(2)°≤70°, a better molten pool 5 can be formed, the welding heat input is more appropriate, which helps the gas in the molten pool 5 to escape, effectively reducing the bubble defects in the molten pool 5, thereby significantly improving the welding yield of the first weld line 3. In a specific embodiment, E(2)° can be selected from specific values ​​such as 20°, 30°, 40°, 50°, 60°, 70°, etc., or other reasonable specific values ​​can be selected within the range of 20° to 70°, without limitation.

[0077] like Figure 2 As shown, in one embodiment of this application, the inner side of the top of the housing 1 has a first inclined surface 11 facing the middle of the cover plate 2, and the lower side of the edge of the cover plate 2 has a second inclined surface 21 facing the housing 1; in the longitudinal section of the battery pack perpendicular to the first direction, the angle between the first inclined surface 11 and the second inclined surface 21 is K°, and K° satisfies 0°≤K°≤20°.

[0078] Specifically, a first inclined surface 11 facing the middle of the cover plate 2 can be formed on the inner side of the top of the shell 1 through manufacturing processes such as stamping, and a second inclined surface 21 facing the shell 1 can be formed on the lower side of the edge of the cover plate 2, and a notch area with an included angle can be formed between the first inclined surface 11 and the second inclined surface 21.

[0079] When K° is greater than 20°, a small amount of spatter formed during the welding process between the casing 1 and the cover plate 2 can easily enter the battery cell 10 and cause a short circuit in the battery cell 10.

[0080] Therefore, when the included angle between the first inclined plane 11 and the second inclined plane 21 is K°, satisfying 0°≤K°≤20°, interference between the housing 1 and the cover plate 2 can be prevented, welding misalignment between the housing 1 and the cover plate 2 can be minimized, and the first inclined plane 11 and the second inclined plane 21 can also absorb a small amount of spatter generated during the welding process, preventing spatter from entering the battery cell 10 and improving the working safety of the battery cell 10. In specific embodiments, K° can be selected from specific values ​​such as 0°, 2°, 4°, 6°, 8°, 10°, 12°, 14°, 16°, 18°, 20°, etc., or other reasonable specific values ​​can be selected within the range of 0° to 20°, without limitation.

[0081] like Figure 5 As shown, in another embodiment of this application, the molten pool 5 is formed on the side of the cover plate 2, and the D / N ratio satisfies 0.3≤D / N≤8.5.

[0082] The molten pool 5 is formed on the side of the cover plate 2. In this embodiment, the battery cell 10 adopts a side welding process to weld the lower surface of the top edge of the cover plate 2 to the shell 1 as a whole. In this process, the main direction of the welding heat source comes from the side of the cover plate 2 and the shell 1. When the molten pool 5 is formed on the side of the cover plate 2, and D / N satisfies 0.2≤D / N≤2, it can further ensure that the cover plate 2 and the shell 1 are effectively welded, effectively reduce the risk of welding defects, and also ensure the structural strength of the first weld line 3, thereby ensuring the structural strength of the side of the cover plate 2 and the shell 1 after welding.

[0083] In specific embodiments, D / N can be selected from specific values ​​such as 0.3, 1.0, 1.8, 2.6, 3.4, 4.2, 5.0, 5.8, 6.8, and 8.5, or other reasonable specific values ​​within the range of 0.3 to 8.5. D mm can be selected from specific values ​​such as 0.35mm, 0.5mm, 0.7mm, 0.9mm, 1.1mm, 1.3mm, 1.5mm, 1.6mm, 1.8mm, and 2.0mm, or other reasonable specific values ​​within the range of 0.35mm to 2.0mm. L mm can be selected from specific values ​​such as 0.5mm, 0.7mm, 0.9mm, 1.1mm, 1.3mm, 1.5mm, 1.7mm, 1.9mm, 2.1mm, 2.3mm, and 2.5mm, or other reasonable specific values ​​within the range of 0.5mm to 2.5mm. No restrictions are imposed here.

[0084] like Figure 6As shown, in one embodiment of this application, in a longitudinal section of the battery pack perpendicular to the first direction, the contact point between the boundary of the molten pool 5 and the upper surface of the cover plate 2 is the third contact point; the straight line passing through the third contact point and extending along the height direction is the second dividing line, the area of ​​the region of the molten pool 5 on the second dividing line adjacent to the opening of the molten pool 5 is T(1) mm²; the area of ​​the region of the molten pool 5 on the second dividing line away from the opening of the molten pool 5 is T(2) mm²; T(1) / T(2) satisfies 0.25≤T(1) / T(2)≤9.

[0085] When the molten pool 5 is formed on the side of the cover plate 2, the contact point between the boundary of the molten pool 5 and the upper surface of the cover plate 2 is the third contact point. The straight line that passes through the third contact point and extends along the height direction is the second boundary line. The area T(1) mm² of the region of the molten pool 5 on the side adjacent to the opening of the molten pool 5 on the second boundary line and the area T(2) mm² of the region of the molten pool 5 on the side away from the opening of the molten pool 5 on the second boundary line are less than 0.25. This indicates that the areas of the region of the molten pool 5 adjacent to the opening of the molten pool 5 and the region away from the opening of the molten pool 5 are relatively close. There are usually more bubbles inside the molten pool 5, which can easily affect the welding yield of the first welding line 3.

[0086] When T(1) / T(2) is greater than 9, it indicates that there is a relatively large area on the side of the opening of the molten pool 5, the welding energy is relatively large, and the grains in the internal area of ​​the molten pool 5 will be relatively coarse, which will reduce the strength of the first weld line 3. Therefore, when T(1) / T(2) satisfies 0.25≤T(1) / T(2)≤9, it can ensure a good welding connection between the shell 1 and the cover plate 2, and can also avoid the strength reduction caused by excessive melting during the welding process, effectively realizing a weld structure that can uniformly bear stress, thereby further improving the structural stability of the short side weld line of the battery cell 10.

[0087] In a specific embodiment, T(1) / T(2) can be selected from specific values ​​such as 0.25, 0.8, 1.5, 2.3, 3.2, 4.2, 5.3, 6.5, 7.9, and 9, or other reasonable specific values ​​can be selected within the range of 0.25 to 9. The range of T(1) mm² is 0.2 mm² to 0.9 mm², and specific values ​​such as 0.2 mm², 0.3 mm², 0.4 mm², 0.5 mm², 0.6 mm², 0.7 mm², 0.8 mm², and 0.9 mm² can be selected, or other reasonable specific values ​​can be selected within the range of 0.2 mm² to 0.9 mm². The range of T(2) mm² is 0.1 mm². The value can be up to 0.85 mm², and specific values ​​such as 0.1 mm², 0.2 mm², 0.3 mm², 0.4 mm², 0.5 mm², 0.6 mm², 0.7 mm², 0.75 mm², 0.8 mm², and 0.85 mm² can be selected. Other reasonable specific values ​​can also be selected within the range of 0.1 mm² to 0.85 mm², and there are no restrictions here.

[0088] like Figure 5 As shown, in one embodiment of this application, the ratio D / J of the depth D mm of the molten pool 5 of the first bonding wire 3 to the thickness J mm of the shell 1 satisfies 0.2≤D / J≤4.

[0089] When the molten pool 5 is formed on the side of the cover plate 2, and the ratio of the depth D mm of the molten pool 5 of the first weld line 3 to the thickness J mm of the shell 1 is less than 0.2, the molten pool 5 formed by welding is too shallow, making it difficult to ensure a tight bond between the cover plate 2 and the shell 1; when D / J is greater than 4, the molten pool 5 formed by welding is too deep, which can easily lead to a relatively large heat-affected zone formed by welding, thereby reducing the connection strength of the first weld line 3.

[0090] Therefore, when the ratio D / J of the depth D mm of the molten pool 5 of the first weld line 3 to the thickness J mm of the shell 1 satisfies 0.2≤D / J≤4, it can be ensured that the ratio between the molten pool 5 of the first weld line 3 and the thickness of the cover plate 2 is appropriate, ensuring a high-strength connection between the cover plate 2 and the shell 1, reducing the risk of incomplete welding due to insufficient molten depth, and effectively reducing the heat-affected zone formed by welding, thereby improving the connection strength of the first weld line 3. In a specific embodiment, D / J can be selected from specific values ​​such as 0.2, 0.5, 0.8, 1.2, 1.6, 2.0, 2.5, 3.0, 3.5, and 4, or other reasonable specific values ​​can be selected within the range of 0.2 to 4. J mm ranges from 0.5 mm to 3 mm, and can be selected from specific values ​​such as 0.5 mm, 0.8 mm, 1.0 mm, 1.2 mm, 1.5 mm, 1.8 mm, 2.0 mm, 2.2 mm, 2.5 mm, and 3 mm, or other reasonable specific values ​​can be selected within the range of 0.5 mm to 3 mm. No restrictions are imposed here.

[0091] like Figure 7 As shown, in one embodiment of this application, in the longitudinal section of the battery pack perpendicular to the first direction, along the first direction, the deepest point of the molten pool 5 is the effective melting point, and the contact point between the boundary of the molten pool 5 and the upper surface of the cover plate 2 is the third contact point; the effective melting point is constructed to be located inside the third contact point, and the smaller angle between the line connecting the third contact point and the effective melting point and the straight line extending along the height direction is F(1)°, F(1)°≤80°.

[0092] It is understandable that by controlling the location of the heat source, the deepest point of the molten pool 5, i.e. the effective penetration point, can be effectively controlled to be located inside the third contact point. When the angle F(1)° between the line connecting the third contact point and the effective penetration point and the straight line extending along the height direction is small (≤80°), a better molten pool 5 can be formed, the welding heat input is more appropriate, which helps the gas in the molten pool 5 to escape, effectively reduces the bubble defects in the molten pool 5, and thus significantly improves the welding yield of the first weld line 3.

[0093] Similarly, such as Figure 7 As shown, in one embodiment of this application, in the longitudinal section of the battery pack perpendicular to the first direction, along the first direction, the deepest point of the molten pool 5 is the effective melting point, and the contact point between the boundary of the molten pool 5 and the outer surface of the shell 1 is the fourth contact point; the smaller angle between the line connecting the fourth contact point and the effective melting point and the straight line extending along the height direction is F(2)°, and F(2)°≤80°.

[0094] When the angle between the line connecting the boundary of the molten pool 5 and the contact point on the outer surface of the shell 1 (i.e., the fourth contact point and the effective molten depth point) and the straight line extending along the height direction is F(2)°≤80°, a better molten pool 5 can be formed, the welding heat input is more appropriate, which helps the gas in the molten pool 5 to escape, effectively reduces the bubble defects in the molten pool 5, and thus significantly improves the welding yield of the first weld line 3.

[0095] like Figure 8 As shown, in a longitudinal section of the battery pack perpendicular to the first direction, the portion between the surface of the molten pool 5 and 1 / 3 of its depth is the first welding area 31, and the portion below 1 / 3 of the depth of the molten pool 5 is the second welding area 32. Along the depth direction of the molten pool 5, the width-reducing slope of the first welding area 31 is less than that of the second welding area 32. When the width-reducing slope of the first welding area 31 is less than that of the second welding area 32 along the depth direction of the molten pool 5, the coverage area of ​​the heat-affected zone around the first weld line 3 can be effectively reduced, effectively improving the connection strength between the first weld and the housing 1 and the cover plate 2.

[0096] like Figure 8 As shown, further, in one embodiment of this application, in the longitudinal section of the battery pack perpendicular to the first direction, the bottom width of the first welding area 31 is U mm, where U mm satisfies 0.1 mm ≤ U mm ≤ 4 mm. When U mm is greater than 4 mm, the heat-affected zone around the first welding wire 3 has an excessively large coverage area, making it prone to breakage; when U mm is less than 0.1 mm, the proportion of pores within the first welding wire 3 is too large, easily affecting the service life and airtightness of the first welding wire 3. In specific embodiments, the range of U mm is from 0.1 mm to 4 mm, and specific values ​​such as 0.1 mm, 0.5 mm, 1.0 mm, 1.5 mm, 2.0 mm, 2.5 mm, 3.0 mm, 3.2 mm, 3.6 mm, and 4 mm can be selected, or other reasonable specific values ​​can be selected within the range of 0.1 mm to 4 mm, which are not limited here.

[0097] Specifically, such as Figure 8 As shown, in one embodiment of this application, the depth of the first welding area 31 is G(1) mm, where G(1) mm satisfies 0.1 mm ≤ G(1) mm ≤ 0.5 mm. When the depth G(1) mm of the first welding area 31 satisfies 0.1 mm ≤ G(1) mm ≤ 0.5 mm, the coverage depth of the first welding area 31 can be effectively guaranteed, thereby ensuring that the coverage area of ​​the first welding line 3 can meet the requirements and thus guaranteeing the structural strength of the first welding line 3.

[0098] Similarly, such as Figure 8As shown, in one embodiment of this application, the depth of the second welding area 32 is G(2) mm, where G(2) mm satisfies 0.5 mm ≤ G(2) mm ≤ 1.4 mm. When the depth G(2) mm of the second welding area 32 satisfies 0.5 mm ≤ G(2) mm ≤ 1.4 mm, the coverage depth of the second welding area 32 can be effectively guaranteed, thereby ensuring that the coverage area of ​​the first weld line 3 meets the requirements and thus guaranteeing the structural strength of the first weld line 3.

[0099] In one embodiment of this application, the extension length of the cover plate 2 along the first direction is V mm, where V mm satisfies 10 mm ≤ V mm ≤ 100 mm; and / or, the extension length of the cover plate 2 along the second direction is W mm, where W mm satisfies 100 mm ≤ W mm ≤ 1200 mm. That is, the battery pack of this embodiment can be effectively applied to battery cells 10 where the extension length V mm of the cover plate 2 along the first direction satisfies 10 mm ≤ V mm ≤ 100 mm and / or the extension length W mm of the cover plate 2 along the second direction satisfies 100 mm ≤ W mm ≤ 1200 mm, effectively improving the space utilization of the battery pack while avoiding deformation of the first bonding line 3.

[0100] Specifically, in one embodiment of this application, the extension length V mm of the cover plate 2 along the first direction is ≥60 mm, and 0.4 ≤ D / N ≤ 1. That is, when the extension length V mm of the cover plate 2 along the first direction is ≥60 mm and D / N satisfies 0.8 ≤ D / N ≤ 9.6, the structural strength of the first welding wire 3 can be further improved, thereby reducing the probability of the first welding wire 3 cracking and being damaged due to long-term vibration stress, causing safety problems such as leakage of the battery cell 10, improving the working safety of the battery cell 10, and thus improving the overall reliability and service life of the battery pack. In a specific embodiment, the range of D / N is 0.8 to 9.6, and specific values ​​such as 0.8, 1.6, 2.4, 3.2, 4.0, 4.8, 5.6, 6.4, 7.2, and 9.6 can be selected, or other reasonable specific values ​​can be selected within the range of 0.8 to 9.6, which are not limited here. This application embodiment also provides an electrical device, which includes the aforementioned battery pack. It is understood that the electrical equipment can be various electrical devices such as energy storage devices, electric ships, aircraft, laptops, power tools, electric bicycles, electric motorcycles, and electric vehicles. The aforementioned battery pack can be used as the operating power source for the electrical equipment or as the driving power source for the electrical equipment, replacing or partially replacing fuel or natural gas to provide driving power for vehicles. It can be applied in many fields such as civilian, military equipment, and aerospace, without any restrictions.

[0101] It should be noted that the elements described in the above specific embodiments can be combined in any suitable manner without contradiction. To avoid unnecessary repetition, this application will not describe the various possible combinations separately.

[0102] It should be understood that multiple components and / or parts can be provided by a single integrated component or part. Alternatively, a single integrated component or part can be divided into multiple separate components and / or parts. The use of the public designation "a" or "an" to describe a component or part does not exclude other components or parts.

[0103] It should be understood that while terms such as "first" or "second" may be used in this application to describe various elements, these elements are not limited by these terms; these terms are merely used to distinguish one element from another. The terminology used in one or more embodiments of this application is for the purpose of describing particular embodiments only and is not intended to limit the scope of one or more embodiments of this application. The singular forms "a," "the," and "the" as used in one or more embodiments of this application and the appended claims are also intended to include the plural forms unless the context clearly indicates otherwise. It should also be understood that the term "and / or" as used in one or more embodiments of this application refers to and includes any or all possible combinations of one or more associated listed items.

[0104] In this document, terms such as "upper," "lower," "front," "back," "left," and "right" are used only to indicate the relative positional relationship between related parts, and not to limit the absolute position of these related parts. In this document, terms such as "equal" and "same" are not strict mathematical and / or geometric limitations, but also include errors that are understandable to those skilled in the art and permissible in manufacturing or use. Unless otherwise stated, the numerical ranges in this document include not only the entire range within its two endpoints, but also several sub-ranges contained therein. The basic principles of this application have been described above in conjunction with specific embodiments. However, it should be noted that the advantages, benefits, and effects mentioned in this application are merely examples and not limitations, and should not be considered as essential features of the various embodiments of this application. Furthermore, the specific details disclosed above are only for illustrative and facilitative purposes, and are not limitations. The above details do not limit the application to the necessity of adopting the above specific details for implementation.

[0105] The above are merely specific embodiments of this application, but the scope of protection of this application is not limited thereto. Any variations or substitutions that can be easily conceived by those skilled in the art within the scope of the technology disclosed in this application should be included within the scope of protection of this application. Therefore, the scope of protection of this application should be determined by the scope of the claims.

Claims

1. A battery pack, characterized in that, The battery pack includes at least two battery cells (10), which are arranged along a first direction. The extension length of the battery cell (10) in the first direction is less than the extension length in the second direction, and the first direction, the second direction, and the height direction of the battery cell (10) are all perpendicular to each other. The battery cell (10) includes a cover plate (2) and a housing (1). The cover plate (2) is fixedly connected to the set end of the housing (1) by welding. A welding line is formed between the cover plate (2) and the housing (1), and the welding line extending along the first direction between the cover plate (2) and the housing (1) is the first welding line (3). In the longitudinal section of the battery pack perpendicular to the first direction, the depth of the molten pool (5) of the first bonding line (3) is D mm, the width of the molten pool (5) at 2 / 3 depth along the depth direction of the molten pool (5) is N mm, the maximum width of the first bonding line (3) is L mm, LN satisfies 0.4 mm≤LN≤1.5 mm, and D / N satisfies 0.3≤D / N≤10.

2. The battery pack according to claim 1, characterized in that, The molten pool (5) is formed on the side of the cover plate (2) and parallel to the side of the cover plate (2); D / N satisfies 1.2≤D / N≤10.

3. The battery pack according to claim 2, characterized in that, In the longitudinal section of the battery pack perpendicular to the first direction, the contact point between the boundary of the molten pool (5) and the outer surface of the shell (1) is the first contact point; Taking a straight line passing through the first contact point and extending along the second direction as the first dividing line, the area of ​​the region of the molten pool (5) located on the side adjacent to the opening of the molten pool (5) on the first dividing line is S(1) mm. 2 The area of ​​the molten pool (5) located on the side of the opening away from the first boundary line is S(2) mm. 2 S(1) / S(2) satisfies 0.5≤S(1) / S(2)≤3.

4. The battery pack according to claim 2, characterized in that, The ratio D / H of the depth D mm of the molten pool (5) of the first weld line (3) to the thickness H mm of the cover plate (2) satisfies 0.2≤D / H≤0.

9.

5. The battery pack according to claim 2, characterized in that, In the longitudinal section perpendicular to the first direction of the battery pack, along the height direction of the battery cell (10), the deepest point of the molten pool (5) is the effective melting depth point, and the contact point between the boundary of the molten pool (5) and the outer surface of the shell (1) is the first contact point. The effective melting point is configured to be lower than the first contact point, and the smaller angle between the line connecting the first contact point and the effective melting point and the straight line extending along the second direction is E(1)°, where E(1)° satisfies 5°≤E(1)°≤70°.

6. The battery pack according to claim 2, characterized in that, In the longitudinal section perpendicular to the first direction of the battery pack, along the height direction of the battery cell (10), the deepest point of the molten pool (5) is the effective melting depth point, and the contact point between the boundary of the molten pool (5) and the upper surface of the cover plate (2) is the second contact point. The smaller angle between the line connecting the second contact point and the effective melting point and the straight line extending along the second direction is E(2)°, and E(2)° satisfies 20°≤E(2)°≤70°.

7. The battery pack according to claim 2, characterized in that, The top inner side of the housing (1) has a first inclined surface (11) facing the middle side of the cover plate (2), and the lower side of the edge of the cover plate (2) has a second inclined surface (21) facing the housing (1). In the longitudinal section perpendicular to the first direction of the battery pack, the angle between the first inclined plane (11) and the second inclined plane (21) is K°, and K° satisfies 0°≤K°≤20°.

8. The battery pack according to claim 1, characterized in that, The molten pool (5) is formed on the top surface of the cover plate (2), and the D / N ratio satisfies 0.3≤D / N≤8.

5.

9. The battery pack according to claim 8, characterized in that, In the longitudinal section of the battery pack perpendicular to the first direction, the contact point between the boundary of the molten pool (5) and the upper surface of the cover plate (2) is the third contact point; Using a straight line extending along the height direction through the third contact point as the second boundary line, the area of ​​the region of the molten pool (5) located on the side adjacent to the opening of the molten pool (5) on the second boundary line is T(1) mm. 2 The area of ​​the molten pool (5) located on the second boundary line away from the opening of the molten pool (5) is T(2) mm. 2 T(1) / T(2) satisfies 0.25≤T(1) / T(2)≤9.

10. The battery pack according to claim 8, characterized in that, The ratio D / J of the depth Dmm of the molten pool (5) of the first weld line (3) to the thickness J mm of the shell (1) satisfies 0.2≤D / J≤4.

11. The battery pack according to claim 8, characterized in that, In the longitudinal section perpendicular to the first direction of the battery pack, along the first direction, the deepest point of the molten pool (5) is the effective melting depth point, and the contact point between the boundary of the molten pool (5) and the upper surface of the cover plate (2) is the third contact point. The effective melting point is configured to be located inside the third contact point, and the smaller angle between the line connecting the third contact point and the effective melting point and the straight line extending along the height direction is F(1)°, where F(1)°≤80°.

12. The battery pack according to claim 8, characterized in that, In the longitudinal section perpendicular to the first direction of the battery pack, along the first direction, the deepest point of the molten pool (5) is the effective melting depth point, and the contact point between the boundary of the molten pool (5) and the outer surface of the shell (1) is the fourth contact point. The smaller angle between the line connecting the fourth contact point and the effective melting point and the straight line extending along the height direction is F(2)°, where F(2)°≤80°.

13. The battery pack according to any one of claims 1 to 12, characterized in that, The battery pack includes at least two battery cells (10) configured to be stacked along the first direction.

14. The battery pack according to any one of claims 1 to 12, characterized in that, In the longitudinal section of the battery pack perpendicular to the first direction, the portion between the surface of the molten pool (5) and 1 / 3 of its depth is the first welding area (31), and the portion below 1 / 3 of the depth of the molten pool (5) is the second welding area (32). Along the depth direction of the molten pool (5), the width narrowing slope of the first welding area (31) is less than the width narrowing slope of the second welding area (32).

15. The battery pack according to claim 14, characterized in that, In the longitudinal section of the battery pack perpendicular to the first direction, the bottom width of the first welding area (31) is U mm, where U mm satisfies 0.1 mm ≤ U mm ≤ 4 mm.

16. The battery pack according to claim 14, characterized in that, The depth of the first welding area (31) is G(1) mm, where G(1) mm satisfies 0.1 mm ≤ G(1) mm ≤ 0.5 mm; and / or, the depth of the second welding area (32) is G(2) mm, where G(2) mm satisfies 0.5 mm ≤ G(2) mm ≤ 1.4 mm.

17. The battery pack according to any one of claims 1 to 12, characterized in that, The extension length of the cover plate (2) along the first direction is V mm, where V mm satisfies 10 mm ≤ V mm ≤ 100 mm; And / or, the extension length of the cover plate (2) along the second direction is W mm, where W mm satisfies 100 mm ≤ W mm ≤ 1200 mm.

18. The battery pack according to any one of claims 1 to 12, characterized in that, The extension length V mm of the cover plate (2) along the first direction is ≥60 mm, and 0.8 ≤ D / N ≤ 9.

6.

19. An electrical appliance, characterized in that, Includes the battery pack according to any one of claims 1 to 18.

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