Battery cells and devices, electric devices, energy storage devices and systems, charging networks

Abstract

The application provides a battery monomer and device, an electric device, an energy storage device and system, and a charging network, and belongs to the technical field of batteries. The battery monomer comprises a shell assembly and an electrode assembly. The shell assembly comprises a shell and an end cover, the shell comprises a containing cavity with an opening, and the end cover covers the opening. The electrode assembly is arranged in the containing cavity, and the electrode assembly comprises a negative plate containing graphite. The end cover comprises a central part and a lap part surrounding the outer periphery of the central part, the lap part is fixedly connected with the end face of the shell forming the opening, a part of the central part extends into the containing cavity through the opening, the BET specific surface area of the graphite is greater than 2.25 m² / g, and the change rate M of the interlayer spacing of the graphite before and after charging of the battery monomer satisfies 8.3%≤M≤9.1%. The application can reduce the risk of shell cracking caused by expansion of the battery monomer and improve the comprehensive performance of the battery monomer.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of batteries, in particular to a battery monomer and device, an electric device, an energy storage device and system, and a charging network. BACKGROUND

[0002] Energy saving and emission reduction is the key to the sustainable development of society. The rechargeable battery has the characteristics of storing energy or releasing energy according to the needs, and is widely used in various electric devices or energy storage systems, and is an important part of promoting energy transformation and sustainable development. For the new energy industry, battery technology is an important factor for its development.

[0003] With the development of battery technology, the performance requirements of various electric devices for battery monomers are also continuously improved. For example, in the field of energy storage, it is desired that the battery has large capacity and long cycle life, and the reliability of the battery operation is high, so as to improve the economy and product competitiveness of the energy storage system. Therefore, how to balance the performance requirements of multiple aspects and improve the comprehensive performance of the battery monomer is an important aspect of battery design. SUMMARY

[0004] The present application aims to at least solve one of the technical problems existing in the prior art. To this end, one object of the present application is to provide a battery monomer and device, an electric device, an energy storage device and system, and a charging network, so as to reduce the risk of shell cracking caused by battery monomer swelling and improve the comprehensive performance of the battery monomer.

[0005] An embodiment of the first aspect of the present application provides a battery monomer, comprising a shell assembly and an electrode assembly. The shell assembly comprises a shell and an end cover, the shell comprises a receiving cavity with an opening, and the end cover covers the opening. The electrode assembly is arranged in the receiving cavity, and the electrode assembly comprises a negative electrode sheet containing graphite. The end cover comprises a center part and a lap part surrounding the outer periphery of the center part, the lap part is fixedly connected with the end face of the shell forming the opening, a part of the center part extends into the receiving cavity through the opening, and the BET specific surface area of the graphite is greater than 2.25 m² / g, and the interlayer spacing change rate M of the graphite before and after charging of the battery monomer satisfies: 8.3%≤M≤9.1%.

[0006] In the technical solution of the embodiment of the present application, the BET specific surface area of the graphite is set to be greater than 2.25 m² / g, so as to improve the capacity, fast charging performance and cycle life of the battery monomer at room temperature by increasing the active point of the graphite. At the same time, the end cover is provided to comprise a center part and a lap part surrounding the outer periphery of the center part, which can simplify the positioning before welding and reduce the probability of laser damage to the electrode assembly, thereby improving the yield of the battery monomer. Such a structure in combination with the power type graphite with large BET specific surface area and small interlayer spacing change rate can balance the capacity, cycle life and structural reliability of the battery monomer, and improve the comprehensive performance of the battery monomer.

[0007] In some embodiments, the BET specific surface area of the graphite is less than or equal to 4.85 m2 / g. By reasonably selecting the BET specific surface area of the graphite, a balance between the capacity requirement, cycle life and structural reliability of the battery cell can be achieved, so that the performance and economy of the battery can be optimized, and the product competitiveness of the final power utilization device or energy storage system can be improved.

[0008] In some embodiments, the volume average particle size Dv50 of the graphite satisfies: 4.5 μm≤Dv50<8.5 μm. By setting the volume average particle size Dv50 of the graphite, the risk of uneven coating caused by uneven particle size of the graphite can be reduced, and the BET specific surface area of the graphite particles can be better controlled, thereby facilitating the improvement of the overall performance of the battery cell.

[0009] In some embodiments, the shell includes four side walls connected in sequence and a bottom wall connected with the side walls; the four side walls include two first side walls oppositely arranged along a second direction, and two second side walls oppositely arranged along a first direction, the area of the first side wall being larger than that of the second side wall; wherein the first direction and the second direction intersect and are perpendicular to the thickness direction of the end cover. The thickness of at least one of the four side walls at the first end connected with the end cover is greater than the thickness of the second end connected with the bottom wall. The thickened side wall has a larger contact area with the welding position of the end cover, which can achieve a more reliable welding effect, and the thickened side wall has better rigidity when coping with the expansion force generated by multiple cycles, thereby reducing the risk of deformation failure of the connection structure of the shell and the end cover.

[0010] In some embodiments, the first side wall includes a first portion connected with the end cover, and a second portion located between the first portion and the bottom wall, the thickness of at least a partial area of the first portion being greater than the thickness of the second portion. Since the area of the first side wall is larger than that of the second side wall, the connection length between the first side wall and the end cover is also larger, and the range of elastic deformation of the first side wall is also slightly larger than that of the second side wall. Therefore, the connection welding seam between the first side wall and the end cover is more likely to fail due to fatigue failure under the action of the expansion force during the charging and discharging cycle of the battery. By increasing the thickness of the end of the first side wall close to the opening, the welding quality and connection strength of the first side wall and the end cover can be further improved, so that they can better withstand repeated expansion deformation under long cycle life, improve the reliability of their connection and the service life of the battery cell structure, and better meet the requirements of long cycle life on the structure.

[0011] In some embodiments, the first portion includes a first region and a second region arranged along the first direction, and the first region is located between the second side wall and the second region. The thickness of at least a part of the second region is greater than the thickness of the first region. By thickening the second region in the middle, the anti-deformation ability of the first portion of the first side wall can be improved, the deformation amount of the swelling deformation can be reduced, the reliability of the connection between the shell and the end cover can be improved, and the service life and overall performance of the battery cell can be improved.

[0012] In some embodiments, the second region is connected to the first region through a first transition region, and the thickness of the first transition region decreases along a direction from the second region to the first region. The connection of the first transition region between the first region and the second region allows a smooth transition therebetween, so that the stress distribution of the first side wall is relatively uniform when the battery cell swells after multiple cycles, and stress concentration is less likely to occur.

[0013] In some embodiments, the second region is connected to the second portion through a second transition region, and the thickness of the second transition region decreases along a direction from the first portion to the second portion. The connection of the second transition region between the second region and the second portion allows a smooth transition therebetween, so that the stress distribution of the first side wall is relatively uniform when the battery cell swells after multiple cycles, and stress concentration is less likely to occur.

[0014] In some embodiments, the surface of the first portion facing away from the accommodation cavity is flush with the surface of the second portion facing away from the accommodation cavity. The thickened side wall extends towards the inside of the accommodation cavity, so that the battery cell can be arranged as closely as possible in the direction of the large thickness, and the large surface is less likely to deform under the action of the swelling force.

[0015] In some embodiments, the size of the second region along the first direction is L1, and the size of the first side wall along the first direction is L, and the following conditions are satisfied: 0.2≤L1 / L≤0.6. By reasonably setting the size of the second region in the first direction X, the influence of the thickened side wall on the weight of the battery and the risk of structural failure can be considered, and the overall performance of the battery cell can be improved.

[0016] In some embodiments, the second region has opposite first and second ends along the first direction, and the first side wall has opposite third and fourth ends along the first direction, the first end is close to the third end, and the second end is close to the fourth end. The size of the first side wall along the first direction is L, the minimum distance between the first end and the third end along the first direction is L2, and the minimum distance between the second end and the fourth end along the first direction is L3. The following conditions are satisfied: L2 / L≤0.3; and / or, L3 / L≤0.3. In this way, the second region is arranged in a relatively central position on the first side wall, so that the swelling deformation can be more targetedly inhibited, and the reliability of the connection between the shell and the end cover can be improved.

[0017] In some embodiments, the second region has a dimension L4 in the thickness direction of the end cover, and satisfies 0.05mm≤L4≤0.75mm. Reasonably setting the dimension of the second region in the thickness direction of the end cover can reduce the risk of cracking at the connection between the end cover and the shell, and limiting the size of the second region is more conducive to the arrangement of the internal components of the shell.

[0018] In some embodiments, L4 satisfies 0.1mm≤L4≤0.6mm. Reasonably setting the dimension of the second region in the thickness direction of the end cover can reduce the risk of cracking at the connection between the end cover and the shell, and limit the size of the second region is more conducive to the arrangement of the internal components of the shell.

[0019] In some embodiments, the second side wall includes a third portion connected with the end cover, and a fourth portion between the third portion and the bottom wall, and the thickness of at least a partial region of the third portion is greater than the thickness of the fourth portion. The area of the second side wall is smaller than the area of the first side wall, and the elastic deformation margin of the connection between the second side wall and the end cover is smaller, and the rigidity is greater. When the internal pressure of the battery monomer rapidly increases, the connection between the second side wall and the end cover may crack due to excessive pressure. By thickening the third portion of the second side wall, the reliability of the connection between the second side wall and the end cover can be improved, and the risk of cracking failure of the connection due to excessive internal pressure of the battery monomer can be reduced.

[0020] In some embodiments, the surface of the third portion facing the accommodation cavity is flush with the surface of the fourth portion facing the accommodation cavity. The thickened side wall extends outward from the accommodation cavity, so that the thickened side wall does not occupy the space of the accommodation cavity, which is conducive to the internal arrangement of the battery monomer.

[0021] In some embodiments, the maximum thickness of the third portion is D1, the maximum thickness of the fourth portion is D2, and the ratio of D2 to D1 satisfies 0.5≤D2 / D1≤0.8. By selecting a suitable ratio of D2 to D1, the processing and forming of the shell can be facilitated, and the effect of resisting swelling deformation can be improved.

[0022] In some embodiments, the maximum depth D3 of the central portion extending into the opening is less than the length D4 of the third portion in the thickness direction of the end cover. Designing the length of the third portion in the thickness direction of the end cover to be greater than the maximum depth of the central portion extending into the opening can provide sufficient structural strength for the connection between the side wall and the end cover, and the second side wall is not prone to deformation when the battery monomer swells after multiple cycles.

[0023] In some embodiments, the length D4 of the third portion in the thickness direction of the end cover satisfies 0.05mm≤D4≤0.75mm. In this embodiment, the third portion is thickened to a certain extent in the thickness direction of the end cover, which can prevent cracking of the end cover and the shell, and can also inhibit deformation of the third portion due to stress concentration of the battery assembly.

[0024] In some embodiments, the center portion includes a bottom surface facing the electrode assembly and side surfaces connecting the bottom surface; and a distance a between an outer edge of the lap portion and the side surface in a first direction or a second direction satisfies: 0.5mm≤a≤1.5mm. The first direction and the second direction are perpendicular to a thickness direction of the end cover.

[0025] In the embodiment, the lap portion can stably connect the end cover, and the end cover is not easy to fall off when the shell is deformed.

[0026] In some embodiments, a thickness b of the lap portion in the thickness direction of the end cover satisfies: 0.3mm≤b≤1mm.

[0027] In the embodiment, the lap portion can stably connect the end cover, and the end cover is not easy to fall off when the shell is deformed.

[0028] In some embodiments, the capacity of the battery monomer is greater than or equal to 360Ah.

[0029] In the embodiment, by combining the capacity of the battery monomer with the parameters of the graphite and the shell structure, the capacity, cycle life and structural deformation resistance of the battery monomer can be considered, and the overall performance of the battery monomer is improved.

[0030] In some embodiments, the electrode assembly includes an active material of a lithium phosphate salt.

[0031] In the embodiment, the lithium phosphate salt has good low-temperature performance, and cooperates with the graphite to further improve the room-temperature cycle life of the battery monomer, inhibit the transition expansion of the graphite during the cycle process, reduce the fluctuation of the interlayer spacing change rate, and more favorably improve the comprehensive performance of the battery monomer.

[0032] Embodiments of the second aspect of the application provide a battery device including the battery monomer described above.

[0033] Embodiments of the third aspect of the application provide a power utilization device, which includes the battery device described above, and the battery device is used to provide electric energy.

[0034] Embodiments of the fourth aspect of the application provide an energy storage device, which includes a plurality of battery monomers or a plurality of battery devices described above, and the battery monomers or the battery devices are used to store or provide electric energy.

[0035] Embodiments of the fifth aspect of the application provide an energy storage system, which includes a power conversion device and the energy storage device described above, and the power conversion device is used to electrically connect a power generation device and the energy storage device.

[0036] Embodiments of the sixth aspect of the application provide a charging network, which includes a charging pile and the energy storage device or the energy storage system described above, and the energy storage device or the energy storage system is used to provide electric energy for the charging pile.

[0037] The above description is only a summary of the technical solutions of the present application. In order to make the technical means of the present application more clearly understood and implemented according to the content of the specification, and in order to make the above and other purposes, features and advantages of the present application more obvious and easy to understand, the following specific embodiments of the present application are described. BRIEF DESCRIPTION OF DRAWINGS

[0038] In the drawings, like reference numerals refer to same or similar components throughout the several views. The drawings are not necessarily to scale. It should be understood that the drawings only depict some embodiments in accordance with the present disclosure and should not be considered as limiting the scope of the present application.

[0039] Figure 1 Exploded structural schematic diagram of a battery device provided for some embodiments of the present application;

[0040] Figure 2 Structural schematic diagram of an energy storage system provided for some embodiments of the present application;

[0041] Figure 3 Structural schematic diagram of a charging network provided for some embodiments of the present application;

[0042] Figure 4 Exploded structural schematic diagram of a battery cell provided for some embodiments of the present application;

[0043] Figure 5 Structural schematic diagram of a housing assembly provided for some embodiments of the present application;

[0044] Figure 6 Structural schematic diagram of an end cap provided for some embodiments of the present application;

[0045] Figure 7 Top view of a housing provided for some embodiments of the present application;

[0046] Figure 8 Structural schematic diagram of a first side wall provided for some embodiments of the present application;

[0047] Figure 9 Cross-sectional view of a first side wall provided for some embodiments of the present application;

[0048] Figure 10 Top view of another housing structure provided for some embodiments of the present application;

[0049] Figure 11 Structural schematic diagram of a second side wall provided for some embodiments of the present application;

[0050] Figure 12A cross-sectional view of a second sidewall provided for some embodiments of the present application.

[0051] Figure 13 A schematic view of another housing structure provided for some embodiments of the present application.

[0052] Legend of reference signs:

[0053] 100, battery device; 200, energy storage device; 300, power conversion device; 400, power generation device; 500, charging pile; 600, connector; 10, box body; 11, first part; 12, second part; 20, battery cell; 210, shell assembly; 21, end cover, 21a, electrode terminal, 211, center part, 212, lap joint part, 211a, protruding part; 22, housing, 221, accommodating cavity, 222, opening; 223, first sidewall, 2231, first part, 2232, second part, 2231a, first area, 2231b, second area; 2231c, first transition area, 2231d, second transition area; 223a, first end, 223b, second end, 223c, third end, 223d, fourth end; 224, second sidewall, 2241, third part, 2242, fourth part; 225, bottom wall; 23, electrode assembly; 23a, tab; 24, insulating film; 25, support; X, first direction; Y, second direction; Z, thickness direction of the end cover. DETAILED DESCRIPTION

[0054] The embodiments of the technical solutions of the present application will be described in detail below with reference to the drawings. The following embodiments are only used to more clearly illustrate the technical solutions of the present application, and therefore only serve as examples, and cannot limit the protection scope of the present application.

[0055] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which the present application belongs; the terms used herein are only for the purpose of describing specific embodiments and are not intended to limit the present application; the terms "include" and "have" and any variations thereof in the specification and claims of the present application and the above description of drawings are intended to cover non-exclusive inclusion.

[0056] In the description of the embodiments of the present application, the technical terms "first", "second", etc. are only used to distinguish different objects, and cannot be understood as indicating or implying relative importance or implicitly indicating the number, specific order or primary and secondary relationship of the indicated technical features. In the description of the embodiments of the present application, the meaning of "multiple" is two or more, unless otherwise explicitly and specifically limited.

[0057] Reference to“an embodiment” herein means that a particular feature, structure, or characteristic described in connection with the embodiment can be included in at least one embodiment of the application. The appearances of the phrase“in an embodiment” in various places in the specification are not necessarily referring to the same embodiment, nor are separate or alternative embodiments mutually exclusive of other embodiments. As will be apparent to those of ordinary skill in the art, embodiments described herein can be combined with other embodiments in accordance with the application.

[0058] In the description of the embodiments of the application, the term“and / or” only means an association relationship of the associated objects, which means that there can be three relationships, for example, A and / or B, which can mean that A exists alone, A and B exist together, and B exists alone. In addition, the character“ / ” herein generally means that the front and rear associated objects have an“or” relationship.

[0059] In the description of the embodiments of the application, the term“a plurality of” means two or more (including two), and similarly, “a plurality of groups” means two or more groups (including two groups), and “a plurality of pieces” means two or more pieces (including two pieces).

[0060] In the description of the embodiments of the application, the technical terms“center”,“longitudinal”,“transverse”,“length”,“width”,“thickness”,“upper”,“lower”,“front”,“rear”,“left”,“right”,“vertical”,“horizontal”,“top”,“bottom”,“inner”,“outer”,“clockwise”,“counterclockwise”,“axial”,“radial”,“circumferential” and the like indicate the orientation or positional relationship based on the orientation or positional relationship shown in the drawings, and are only for the convenience of describing the embodiments of the application and simplifying the description, and do not indicate or imply that the devices or elements referred to must have a particular orientation, be constructed and operated in a particular orientation, and therefore cannot be understood as a limitation on the embodiments of the application.

[0061] In the description of the embodiments of the application, unless otherwise explicitly specified and limited, the technical terms“mounting”,“connection”,“connection”,“fixing” and the like should be understood broadly, for example, can be fixedly connected, or can be detachably connected, or can be integrated; can be mechanically connected, or can be electrically connected; can be directly connected, or can be indirectly connected through an intermediate medium; can be the internal communication of two elements or the interaction relationship between two elements. For those of ordinary skill in the art, the specific meaning of the above terms in the embodiments of the application can be understood according to the specific circumstances.

[0062] At present, from the development of market situation, the application of rechargeable battery is more and more widely. Rechargeable battery is not only applied to energy storage power supply system of hydropower, thermal power, wind power and solar power station, but also widely used in various electronic equipment, such as electric bicycle, electric motorcycle, electric vehicle and other electric vehicles, military equipment and aerospace and other fields. With the continuous expansion of the application field of rechargeable battery, the market demand is also increasing.

[0063] With the development of energy storage system technology and the continuous expansion of market demand, the capacity and cycle life of battery cells in energy storage system are continuously improved, but the improvement of the capacity and cycle life of battery cells often means that the structure of battery cells faces more severe challenges. For example, more gas will be generated when the battery cell is in thermal runaway state, which may cause serious consequences if not discharged in time, seriously affecting the reliability of the battery cell. Especially in the scenario of large-scale application such as energy storage system, the number of battery cells is much more than other electric devices, and the out-of-control of a single battery cell may cause significant loss of the whole system. Therefore, how to balance the large capacity, long cycle life and high reliability of battery cells in the application scenario similar to energy storage system has become a difficult problem of battery design.

[0064] The increase of specific surface area of graphite means that the surface of unit mass of material can contact more electrolyte, providing more active sites for adsorption and desorption of lithium ions, and also can improve the capacity of battery cell through surface lithium storage and other ways. The applicant has also found that appropriately increasing the specific surface area of graphite can improve the cycle life of lithium ion battery cell at room temperature. However, the increase of specific surface area will also lead to more violent gas production when the battery cell is in thermal runaway, and the pressure in the battery cell will increase rapidly, which will pose greater challenges to the structure of the battery cell, and may cause the cracking of the connection between the shell and the end cover, and even may affect the whole energy storage system.

[0065] In order to solve the above problems, the application embodiment provides a battery cell, which comprises an outer shell assembly and an electrode assembly. The outer shell assembly comprises a shell and an end cover, the shell comprises a containing cavity with an opening, and the end cover covers the opening. The electrode assembly is arranged in the containing cavity, and the electrode assembly comprises a negative electrode sheet containing graphite. The end cover comprises a center part and a lap joint part surrounding the outer periphery of the center part, the lap joint part is fixedly connected with the end face of the shell forming the opening, and a part of the center part extends into the containing cavity through the opening. The BET specific surface area of the graphite is greater than 2.25 m² / g, and the change rate M of the interlayer spacing of the graphite before and after charging of the battery cell satisfies: 8.3%≤M≤9.1%.

[0066] The capacity, fast charging performance and cycle life of the battery monomer in a normal temperature environment are improved by increasing the active point of the graphite, the reliability of the connection between the shell and the end cover is improved by setting the end cover to include a center part and a lap part surrounding the center part, thereby reducing the risk of structural failure, and the expansion force in the cycle process is effectively controlled by further limiting the interlayer spacing change rate of the graphite, so that the capacity, cycle life and structural reliability of the battery monomer are considered, and the comprehensive performance of the battery monomer is improved.

[0067] The battery monomer disclosed in the embodiments of the present application can be used in, but is not limited to, an electric device or an energy storage device for a vehicle, a ship or an aircraft. The power supply system of the electric device or the energy storage device can be composed of the battery monomer and the battery disclosed in the present application, so that the comprehensive performance of the battery monomer, the electric device, the battery device and the energy storage system is improved.

[0068] The embodiments of the present application provide an electric device using a battery as a power supply. The electric device can be, but is not limited to, a mobile phone, a tablet computer, a notebook computer, an electric toy, an electric tool, an electric car, an electric vehicle, a ship, a spacecraft and the like. The electric toy can include a fixed or mobile electric toy, such as a game console, an electric car toy, an electric ship toy and an electric aircraft toy, and the spacecraft can include an airplane, a rocket, a space shuttle and a spacecraft.

[0069] The following embodiments are described by taking a battery device of an embodiment of the present application as an example for convenience of description.

[0070] Please refer to Figure 1 , Figure 1 The exploded structural schematic diagram of the battery device provided in some embodiments of the present application is shown. The battery device 100 includes a box body 10 and a battery monomer 20, and the battery monomer 20 is accommodated in the box body 10. The box body 10 is used to provide an accommodation space for the battery monomer 20, and the box body 10 can adopt various structures. In some embodiments, the box body 10 can include a first part 11 and a second part 12, the first part 11 and the second part 12 are overlapped with each other, and the first part 11 and the second part 12 jointly define an accommodation space for accommodating the battery monomer 20. The second part 12 can be a hollow structure with one end open, and the first part 11 can be a plate-shaped structure, which is overlapped with the open side of the second part 12 to jointly define the accommodation space with the second part 12. The first part 11 and the second part 12 can also be hollow structures with one side open, and the open side of the first part 11 is overlapped with the open side of the second part 12. Of course, the box body 10 formed by the first part 11 and the second part 12 can have various shapes, such as a cylinder, a cuboid and the like.

[0071] In the battery device 100, the battery cells 20 can be multiple, and the multiple battery cells 20 can be connected in series or in parallel or in a mixed manner. The mixed manner means that the multiple battery cells 20 are connected in series and in parallel. The multiple battery cells 20 can be directly connected in series or in parallel or in a mixed manner, and the whole of the multiple battery cells 20 is accommodated in the cabinet 10. Of course, the battery device 100 can also be that the multiple battery cells 20 are connected in series or in parallel or in a mixed manner to form a battery module, and the multiple battery modules are connected in series or in parallel or in a mixed manner to form a whole, and the whole is accommodated in the cabinet 10. The battery device 100 can also include other structures, for example, the battery device 100 can also include a current collection component for realizing the electrical connection between the multiple battery cells 20.

[0072] Each battery cell 20 can be a secondary battery or a primary battery, and can also be a lithium-sulfur battery, a sodium-ion battery, or a magnesium-ion battery, but is not limited thereto. The battery cell 20 can be in the shape of a cylinder, a flat body, a cuboid, or other shapes.

[0073] Please refer to Figure 2 , Figure 2 A structural diagram of an energy storage system provided by some embodiments of the present application is shown. An energy storage device 200 provided by an embodiment of the present application includes one or more battery clusters to improve the voltage and capacity of the energy storage device 200. The battery cluster can include multiple battery devices 100, and the multiple battery devices 100 are connected in series by a current collection component to improve the voltage of the energy storage device 200. When the energy storage device 200 includes multiple battery clusters, the multiple battery clusters are connected in parallel to improve the capacity of the energy storage device 200. The energy storage device 200 can be used in an energy storage power station, a wind power system, a solar power system, a mobile power system, or a temporary power supply system, etc. The energy storage device 200 can store electrical energy as needed and output electrical energy at an appropriate time. For example, the energy storage device 200 can store electrical energy during the off-peak period of electricity consumption, and provide electrical energy for related users or electrical equipment during the peak period of electricity consumption. The energy storage system provided by an embodiment of the present application can be any power system that needs to use the energy storage device 200. In some embodiments, the energy storage device 200 is an energy storage container or an energy storage cabinet.

[0074] In some embodiments, the energy storage device 200 can include a cabinet body and one or more battery clusters, and the battery clusters are accommodated in the cabinet body.

[0075] In some embodiments, the energy storage device 200 can include a thermal management module, a master control module, a general control module, a power distribution module, and a fire-fighting module, etc.

[0076] As an example, the thermal management module can include a liquid cooling unit, and the liquid cooling unit provides a cooling liquid for adjusting the temperature of the battery cells 20 to each battery device 100 through a pipeline.

[0077] As an example, the master module can be used as a battery management unit of the battery cluster for monitoring and managing the battery cluster. The master module can monitor information such as current, voltage, power or temperature of the battery cluster. For example, the charging and discharging current, voltage, etc. of the battery cluster can be controlled. The master module includes a slave battery management unit (SBMU), a fuse module, etc.

[0078] As an example, the master module can be used as a battery management unit of the battery cluster for monitoring and managing the battery cluster. The master module can monitor information such as current, voltage, power or temperature of the battery cluster. For example, the charging and discharging current, voltage, etc. of the battery cluster can be controlled. The master module includes a slave battery management unit (SBMU), a fuse module, etc.

[0079] As an example, the fire control system includes a control panel, a detector, an alarm device, etc. for detecting, alarming or extinguishing the energy storage system.

[0080] As an example, the power distribution device can be used to distribute power to the power utilization module of the energy storage device 200.

[0081] In some embodiments, the energy storage system can include one or more energy storage devices 200 and a power conversion device 300 (PCS) connected between the power generation device 400 and the energy storage device 200. The power generation device 400 is used to generate electric energy, and the electric energy generated by the power generation device 400 can be stored in the energy storage device 200 through the power conversion device 300, and the electric energy stored in the energy storage device 200 can be released to the power generation device 400 through the power conversion device 300. As an example, the power generation device 400 can be a power grid, a solar panel, a hydroelectric power generation device 400, a thermal power generation device 400, a wind power generation device 400, etc. The specific type of the power generation device 400 is not limited in the present application.

[0082] Please refer to Figure 3 , Figure 3A schematic diagram of a charging network is provided for some embodiments of the present application. The embodiments of the present application provide a charging network, which includes a charging pile 500 and an energy storage device 200. The charging pile 500 is electrically connected to the energy storage device 200, and the energy storage device 200 is configured to provide electric energy for the charging pile 500. The charging pile 500 is electrically connected to a battery device 100 in the energy storage device 200 through a cable. The battery device 100 can provide the electric energy stored therein to the charging pile 500. The charging pile 500 has one or more connectors 600, which are configured to be connected to an electric device (e.g., a vehicle), so that the electric device can be charged.

[0083] The energy storage device 200 can be located inside the charging pile 500 (e.g., a charging and storage integrated machine) or outside the charging pile 500.

[0084] Please refer to Figure 4 , Figure 4 A schematic diagram of a battery cell is provided for some embodiments of the present application. The battery cell 20 refers to the smallest unit of a battery. As shown in Figure 4 , the battery cell 20 includes an end cover 21, a shell 22, an electrode assembly 23, and other functional components.

[0085] The end cover 21 refers to a component that covers the opening of the shell 22 to isolate the internal environment of the battery cell 20 from the external environment. Without limitation, the shape of the end cover 21 can be adapted to the shape of the shell 22 to fit the shell 22. Optionally, the end cover 21 can be made of a material (e.g., an aluminum alloy) having a certain hardness and strength, so that the end cover 21 is not easily deformed when subjected to extrusion and collision, and the battery cell 20 can have higher structural strength and improved safety performance. The end cover 21 can be provided with functional components such as an electrode terminal 21a. The electrode terminal 21a can be used to electrically connect to the electrode assembly 23 for outputting or inputting the electric energy of the battery cell 20. In some embodiments, the end cover 21 can also be provided with a pressure relief mechanism for relieving the internal pressure of the battery cell 20 when the internal pressure or temperature reaches a threshold value. The material of the end cover 21 can also be various, such as copper, iron, aluminum, stainless steel, aluminum alloy, plastic, etc., which are not specially limited in the embodiments of the present application. In some embodiments, an insulating member can also be provided on the inner side of the end cover 21. The insulating member can be used to isolate the electrical connection components in the shell 22 from the end cover 21 to reduce the risk of short circuit. Exemplarily, the insulating member can be plastic, rubber, etc.

[0086] The shell 22 is a component for cooperating with the end cover 21 to form an internal environment of the battery cell 20, and the formed internal environment can be used to accommodate the electrode assembly 23, electrolyte and other components. The shell 22 and the end cover 21 can be independent components, and an opening can be provided on the shell 22, and the end cover 21 is used to cover the opening to form the internal environment of the battery cell 20. Without limitation, the end cover 21 and the shell 22 can also be integrated, specifically, the end cover 21 and the shell 22 can form a common connecting surface before other components enter the shell, and when it is necessary to seal the internal environment of the shell 22, the end cover 21 is used to cover the shell 22. The shell 22 can be various shapes and various sizes, such as a cuboid, a cylinder, a hexagonal prism, etc. Specifically, the shape of the shell 22 can be determined according to the specific shape and size of the electrode assembly 23. The material of the shell 22 can be various, such as copper, iron, aluminum, stainless steel, aluminum alloy, plastic, etc., and the embodiments of the present application do not make special limitations.

[0087] The electrode assembly 23 is a component in which electrochemical reactions occur in the battery cell 20. One or more electrode assemblies 23 can be contained in the shell 22. The electrode assembly 23 is mainly formed by winding or stacking the positive electrode sheet and the negative electrode sheet, and a separator is usually arranged between the positive electrode sheet and the negative electrode sheet. The positive electrode sheet and the negative electrode sheet have a part of active material constituting the main body of the electrode assembly, and a part of the positive electrode sheet and the negative electrode sheet without active material each constitutes a tab 23a. The positive electrode tab and the negative electrode tab can be located at one end of the main body together or at two ends of the main body respectively. In the charging and discharging process of the battery, the positive active material and the negative active material react with the electrolyte, and the tab 23a connects the electrode terminal to form a current loop.

[0088] The embodiments of the present application provide a battery cell 20, which comprises a shell assembly 210 and an electrode assembly 23. The shell assembly 210 comprises a shell 22 and an end cover 21, the shell 22 comprises a containing cavity 221 with an opening 222, and the end cover 21 covers the opening 222. The electrode assembly 23 is arranged in the containing cavity 221, and the electrode assembly 23 comprises a negative electrode sheet containing graphite. The end cover 21 comprises a center part 211 and a lap part 212 surrounding the outer periphery of the center part 211, the lap part 212 is fixedly connected with the end face of the shell 22 forming the opening 222, and a part of the center part 211 extends into the containing cavity 221 through the opening 222. The BET specific surface area of the graphite is greater than 2.25 m² / g, and the change rate M of the interlayer spacing of the graphite before and after charging of the battery cell 20 satisfies: 8.3%≤M≤9.1%.

[0089] The negative electrode sheet in the electrode assembly 23 comprises graphite; the graphite can be artificial graphite, can also be natural graphite, and can also be a composite system formed by using natural graphite and artificial graphite together.

[0090] The specific surface area of graphite is an important physical parameter for measuring the surface activity thereof, specifically refers to the total surface area per unit mass of graphite material, and specifically can be obtained by dividing the total surface area of graphite by the mass of graphite, with the unit of square meters per gram (m2 / g). The specific surface area can reflect the roughness of the surface of graphite and the degree of development of pores. The larger the specific surface area, the larger the contact area between graphite and electrolyte, and the more surface active sites, which directly affect the adsorption, diffusion and interface reaction of lithium ions. The specific surface area of graphite can be detected by gas adsorption method, solution adsorption method or dynamic light scattering method, and can also be determined by scanning electron microscopy or transmission electron microscopy.

[0091] In this embodiment, the BET specific surface area determination technology is specifically adopted, which is a classical method for measuring the specific surface area of solid materials by gas adsorption method, and is widely used in the fields of porous materials, catalysts, nanomaterials, adsorbents and the like. The BET theory is based on a multi-layer gas molecule adsorption model, and the total surface area per unit mass (or volume) of material is calculated by measuring the adsorption amount of inert gas at low temperature (usually liquid nitrogen temperature, 77K).

[0092] Compared with power batteries or consumer batteries, the battery monomer 20 in the energy storage system has higher requirements for cycle life and reliability, and the battery monomer 20 in the energy storage system has more shallow charging and discharging working conditions, and the SEI film of the low specific surface area graphite is thinner and more stable under this working condition.

[0093] Therefore, in some embodiments, when designing the graphite parameters of the battery negative electrode, the BET specific surface area thereof is controlled in a relatively small range, for example, the value range of the BET specific surface area of the graphite applied in the negative electrode sheet in the battery monomer 20 in the energy storage system is set to be greater than or equal to 1.25 m2 / g and less than or equal to 2.25 m2 / g. However, too low BET specific surface area will also significantly limit the fast charging performance and capacity of the battery, and will also limit the pursuit of the energy storage system for the ultimate cost performance and reliability.

[0094] The BET specific surface area of the graphite in the embodiment of the present application is set to be greater than 2.25 m2 / g, which can relatively balance the capacity, cycle life and fast charging performance of the battery and the like. The value of the BET specific surface area of the graphite can be 2.3 m2 / g, 2.4 m2 / g, 2.5 m2 / g, 2.85 m2 / g, 3 m2 / g, 3.5 m2 / g, 3.85 m2 / g, 4 m2 / g, 4.5 m2 / g and 4.85 m2 / g and the like.

[0095] Please refer to Figure 5In the embodiment, the battery monomer 20 is composed of a shell assembly 210 and an electrode assembly 23. The shell assembly 210 is surrounded by a casing 22 and an end cover 21 to form a containing cavity 221. The end cover 21 is fixedly connected with the end surface of the casing 22 through a lap joint 212 to realize the packaging of the battery monomer 20. The fixed connection can be welding, riveting, bonding or other structures such as a sealing element. The size of the end cover 21 can be equal to, slightly smaller than or slightly larger than the external size of the casing 22. The overall shape of the end cover 21 is protruding and surrounding, that is, the edge of the end cover 21 in contact with the casing 22 is stepped, the lap joint 212 protrudes from the outer side of the center part 211, and the top surface of the lap joint 212 away from the electrode assembly 23 is flush with the top surface of the center part 211 away from the electrode assembly 23. The side of the center part 211 facing the electrode assembly 23 protrudes relative to the lap joint 212 to form a protruding part 211a. When the lap joint 212 is connected with the end surface of the casing 22, the protruding part 211a extends into the containing cavity 221 inside the casing 22. The protruding part 211a can be in interference fit, transition fit or clearance fit with the casing 22.

[0096] In the embodiment, when graphite is used as the negative electrode material of the lithium ion battery, the interlayer spacing of the graphite refers to the vertical distance d between the adjacent two layers of carbon atoms in the graphite crystal parallel to the (002) crystal face 002 .

[0097] The interlayer spacing d of the (002) crystal face in the graphite crystal structure 002 The structure expands or shrinks when lithium ions are inserted or extracted. The interlayer spacing (i.e., the distance between graphene layers) changes dynamically during the charging and discharging process due to the insertion or extraction of lithium ions. The dynamic change can be calculated to obtain the graphite interlayer spacing change rate. This parameter can be obtained by XRD (X-ray diffraction) testing. XRD scanning is performed at different stages of battery charging, and the change curve is obtained after analysis. The charging interlayer spacing change rate of graphite is an index for measuring the structural stability of the electrode material. The interlayer spacing change rate of graphite before and after charging of the battery monomer 20 can be specifically expressed as the ratio of the difference between the interlayer spacing of graphite before charging and the interlayer spacing of graphite after charging to the interlayer spacing of graphite before charging.

[0098] In some embodiments, the initial graphite interlayer spacing before charging of the battery cell 20 can be the graphite interlayer spacing corresponding to SOC≤5% (e.g. SOC=0%, i.e. the battery cell is fully discharged to the cut-off voltage), at which almost no lithium ions are intercalated into the graphite, and the interlayer spacing is at the initial minimum value. The graphite interlayer spacing after charging of the battery cell 20 can be the graphite interlayer spacing corresponding to SOC≥95% (e.g. 100%, i.e. fully charged), at which lithium ions are fully intercalated into the graphite interlayer, forming a stable graphite interlayer compound (e.g. LiC6), and the interlayer spacing reaches the maximum value.

[0099] For example, Table 1 below shows the comparison of the interlayer spacing data of three different BET specific surface area graphites. The 0% SOC graphite interlayer spacing d002 is the interlayer spacing n1 of the graphite before charging, which can be achieved by discharging the battery cell prepared from the graphite at 0.1C to the cut-off voltage. The specific detection method is as follows: the graphite powder is obtained by drying the active material scraped from the negative electrode sheet or the negative electrode sheet disassembled from the battery cell prepared from the corresponding graphite at 0% SOC in an inert atmosphere after solvent cleaning (e.g. NMP, alcohol) or high-temperature calcination (in an inert atmosphere to avoid oxidation) to remove organic matter for 2 hours in a vacuum drying box, the diffraction angle 2theta of the (002) crystal plane is measured by X-ray diffraction method, and the corresponding interlayer spacing d002 is calculated by Bragg's formula to obtain the interlayer spacing n1 of the graphite before charging.

[0100] Similarly, the 100% SOC graphite interlayer spacing d002 is the interlayer spacing n2 of the graphite after full charging, which can be achieved by charging the battery cell prepared from the graphite at 0.1C to the cut-off voltage, and then to constant voltage charging until the current decreases to below 0.01C. The specific detection method is as follows: the graphite powder is obtained by drying the active material scraped from the negative electrode sheet or the negative electrode sheet disassembled from the battery cell prepared from the corresponding graphite at 100% SOC in an inert atmosphere after solvent cleaning (e.g. NMP, alcohol) or high-temperature calcination (in an inert atmosphere to avoid oxidation) to remove organic matter for 2 hours in a vacuum drying box, the diffraction angle 2theta of the (002) crystal plane is measured by X-ray diffraction method, and the corresponding interlayer spacing d002 is calculated by Bragg's formula to obtain the interlayer spacing n2 of the graphite after full charging.

[0101] The graphite interlayer spacing change rate η can be calculated by the following formula: η=(n2-n1) / n1x100%.

[0102] Table 1

[0103]

[0104] As shown in Table 1, the BET specific surface area of the graphite one is 2.45 m² / g, and the corresponding graphite interlayer spacing change rate is 8.96%. The BET specific surface area of the graphite two is 1.65 m² / g, and the corresponding graphite interlayer spacing change rate is 9.43%. The BET specific surface area of the graphite three is 6.5 m² / g, and the corresponding graphite interlayer spacing change rate is 7.74%. It can be seen that the graphite interlayer spacing of the graphite one is moderate, which is more conducive to balancing the capacity and cycle life, thereby improving the comprehensive performance of the battery cell.

[0105] In the embodiment, the graphite interlayer spacing change rate M of the battery cell 20 before and after charging can be 8.40%, 8.45%, 8.55%, 8.6%, 8.75%, 8.85%, 8.90%, 9%, 9.05%, 9.1%, etc. In some embodiments, the value range of the graphite interlayer spacing change rate M can also be 8.45%≤M≤9.05%, or 8.55%≤M≤9.0%.

[0106] In the embodiment of the application, the BET specific surface area of the graphite is greater than 2.25 m² / g, and the graphite interlayer spacing change rate is controlled between 8.3% and 9.1%. The capacity, fast charging performance and cycle life of the battery cell 20 under normal temperature environment can be improved by increasing the active point of the graphite, while the expansion force during the cycle is reduced, the impact on the shell structure is reduced, and the probability of laser damage to the electrode assembly is further reduced. The positioning before welding can be simplified, the reliability of the connection is improved, the risk of cracking of the shell 22 caused by the expansion force during the cycle of the battery cell 20 is reduced, the capacity, cycle life and structural reliability of the battery cell are balanced, the comprehensive performance of the battery cell is improved, and the economic performance and market competitiveness of the power utilization device, energy storage device or energy storage system with the battery cell are improved.

[0107] According to some embodiments of the application, the BET specific surface area of the graphite is less than or equal to 4.85 m² / g.

[0108] If the BET specific surface area is too large, the side reaction will be more intense, causing lithium ion consumption and active material loss, and the battery capacity will rapidly decay. Moreover, the larger the specific surface area, the more the cost of the battery material will increase, and the risk of thermal runaway will also increase significantly. The structural stability and reliability may face deficiencies, and the benefits brought by the large specific surface area are not enough to offset the adverse effects.

[0109] In some embodiments, the BET specific surface area of the graphite can be 2.26 m2 / g, 2.28 m2 / g, 2.30 m2 / g, 2.35 m2 / g, 2.40 m2 / g, 2.45 m2 / g, 2.50 m2 / g, 2.80 m2 / g, 3.00 m2 / g, 3.20 m2 / g, 3.50 m2 / g, 3.80 m2 / g, 4.00 m2 / g, 4.20 m2 / g, 4.50 m2 / g, 4.80 m2 / g, 4.85 m2 / g, or any value between any two adjacent values described above.

[0110] The applicant has also found that the high-temperature cycle performance of graphite with a BET specific surface area of less than 2.25 m2 / g is relatively better, while the cycle performance at room temperature of graphite with a BET specific surface area of more than 2.25 m2 / g is more excellent, i.e., the cycle life is longer at room temperature. For an energy storage system with stronger temperature control capability, the battery cell 20 made of graphite with a BET specific surface area of more than 2.25 m2 / g can bring more benefits to the energy storage system.

[0111] The following will be described in combination with the cycle life test results of the battery cell 20 of three kinds of graphite with different specific surface areas at different temperatures. The battery cell one, the battery cell two and the battery cell three are completely the same in other material components, preparation process and structure except for the different BET specific surface areas of the graphite, for example, the positive active material is lithium iron phosphate, the BET specific surface area of the graphite in the battery cell one is 2.85 m2 / g, the BET specific surface area of the graphite in the battery cell two is 1.65 m2 / g, and the BET specific surface area of the graphite in the battery cell three is 6.5 m2 / g.

[0112] The cycle life test is repeated at the corresponding environmental temperature according to the set charge and discharge system. The set charge and discharge system is a constant current and constant voltage mode, specifically, first charging at 0.5P constant power to the upper limit voltage value 3.65V of the battery cell 20, and discharging at 0.5P constant power to the lower limit voltage value 2.5V of the battery cell 20. The capacity is calibrated once every 100 cycles to evaluate the capacity attenuation of the battery, and the cycle life is considered to be terminated when the capacity attenuation of the battery is 70% of the initial capacity. The specific test results are shown in Table 2.

[0113] Table 2

[0114]

[0115] As can be seen from Table 2, the cycle life of the battery cell one at 25°C is the best, the cycle life of the battery cell two with the smallest BET specific surface area of the graphite is the best at 60°C, and the cycle life of the battery cell three with the largest BET specific surface area of the graphite is the worst at the three environmental temperatures.

[0116] In this embodiment, the BET specific surface area of the graphite is less than or equal to 4.85 m2 / g. By reasonably selecting the BET specific surface area of the graphite, a balance between the capacity requirement, cycle life, processability and safety of the battery cell 20 can be achieved, so that the performance and economy of the battery can be optimized, and the product competitiveness of the final power utilization device or energy storage system can be improved.

[0117] According to some embodiments of the present application, the volume average particle size Dv50 of the graphite satisfies: 4.5 pm≤Dv50<8.5 pm.

[0118] Dv50 refers to the particle size value corresponding to the cumulative volume ratio of 50% in the volume distribution of particles, also known as "median particle size" or "median particle size". The Dv50 of the graphite can be measured by a laser particle size analyzer.

[0119] For the graphite, if the Dv50 is too small, the BET specific surface area of the graphite will increase, which will cause the side reactions to be intensified and other adverse effects. If the Dv50 is too large, the lithium ion diffusion path will become longer, the polarization will be serious during high-rate charging and discharging, and the capacity will not be fully developed.

[0120] In some embodiments, the volume average particle size Dv50 of the graphite can be 4.5 pm, 5.0 pm, 5.5 pm, 6.0 pm, 6.5 pm, 7.0 pm, 7.5 pm, 8.0 pm, 8.4 pm, or any value between any two adjacent values in the above.

[0121] The following will be described in combination with the cycle life test results of the battery cells 20 of seven kinds of graphite with different BET specific surface areas and Dv50 at different temperatures. Among them, the battery cell four to the battery cell ten are completely the same in other material components, preparation process and structure except for the different BET specific surface area Dv50 of the graphite. The cycle life test method is the same as the test method adopted in Table 1 above, which will not be described here. The specific results are shown in Table 3.

[0122] Table 3

[0123]

[0124] As can be seen from Table 3, the cycle life of the battery monomer four to the battery monomer seven at 25°C can reach more than 8700 cycles, while the battery monomer eight to the battery monomer ten is not more than 8000 cycles, it can be seen that the cycle life of the battery monomer four to the battery monomer seven at room temperature is obviously longer, and the cycle life of the battery monomer eight to the battery monomer ten at high temperature of 45°C and 60°C is better. Under the condition that Dv50 is the same, for example, it is equal to 6.5 μm, the cycle life of the graphite BET specific surface area of the battery monomer seven is the smallest at room temperature, and the cycle life at high temperature is better than that of the battery monomer four to the battery monomer six; when Dv50 is equal to 10.5 μm, the performance of the battery monomer nine with the smallest graphite BET specific surface area is similar to that of the battery monomer seven, which will not be described here.

[0125] In the embodiment, the volume average particle size Dv50 of the graphite is set to be between 4.5 μm≤Dv50<8.5 μm, which can prevent uneven coating caused by uneven graphite particle size, better control the specific surface area of the graphite particles, and thus be conducive to improving the comprehensive performance of the battery monomer 20.

[0126] According to some embodiments of the present application, the shell 22 includes four side walls connected in sequence and a bottom wall 225 connected with the side walls; the four side walls include two first side walls 223 oppositely arranged along a second direction, and two second side walls 224 oppositely arranged along a first direction, the area of the first side wall 223 is greater than the area of the second side wall 224; wherein the first direction and the second direction intersect and are perpendicular to the thickness direction of the end cover 21. The thickness of at least one of the four side walls at the first end 223a connected with the end cover 21 is greater than the thickness of the second end 223b connected with the bottom wall 225.

[0127] In the embodiment, please refer to Figure 5 and Figure 7 , the accommodating cavity 221 of the shell 22 is surrounded by four continuous side walls and a bottom wall 225, two first side walls 223 are oppositely arranged along a second direction Y, and two second side walls 224 are oppositely arranged along a first direction X, wherein the first direction X and the second direction Y can be perpendicular to each other, or can not be perpendicular to each other. But the first direction X and the second direction Y are both perpendicular to the thickness direction Z of the end cover 21, that is, the first side wall 223 and the second side wall 224 can be perpendicular to each other, or can not be perpendicular to each other, but both are perpendicular to the bottom wall 225. Since the first side wall 223 is configured as a large surface, the entire battery monomer 20 can be configured as a cuboid, a rhombic body, a trapezoidal body, etc. The shape of the battery monomer 20 can be adaptively adjusted according to the shape and size of the battery device 100, and a plurality of battery monomers 20 can be arranged along the thickness direction of the first side wall 223 in a manner that the first side wall 223 directly faces.

[0128] In the embodiment, the two ends of the side wall along the thickness direction Z of the end cover 21 are defined as the first end 223a connected with the end cover 21 and the second end 223b connected with the bottom wall 225, and the overall structure is that the side wall is thicker at the end close to the end cover 21 than at the end close to the bottom wall 225. In this way, during the welding of the end cover 21 and the shell 22, the welding area of the thickened side wall and the end cover 21 is larger, which is beneficial to the welding process and improves the welding quality and connection reliability of the shell 22 and the end cover 21.

[0129] It can be understood that one of the four side walls is thickened, or two, three or all of the side walls are thickened.

[0130] In the embodiment, the welding position of the thickened side wall and the end cover 21 has a larger contact area, which can achieve more reliable welding effect, and the thickened side wall has better rigidity when coping with the expansion force generated by multiple cycles, thereby reducing the risk of deformation failure of the connection structure of the shell 22 and the end cover 21.

[0131] According to some embodiments of the present application, please refer to Figure 9 The first side wall 223 includes a first part 2231 connected with the end cover 21 and a second part 2232 located between the first part 2231 and the bottom wall 225. The thickness of at least part of the first part 2231 is greater than the thickness of the second part 2232.

[0132] In the embodiment, the first side wall 223 is divided into two parts along the thickness direction of the end cover 21, wherein the part close to the end cover 21 is the first part 2231, and the first part 2231 is fixedly connected with the end cover 21 through the opening 222 of the shell 22; the part close to the bottom wall 225 is the second part 2232, and the second part 2232 is connected with the bottom wall 225.

[0133] The thickness of the first part 2231 can be equal everywhere, or the thickness of some regions is greater than that of other parts of the first part 2231; the thickness of the second part 2232 can be equal everywhere; but overall, the thickness of at least part of the first part 2231 connected with the end cover 21 is greater than the thickness of the second part 2232, so that the contact area of the end cover 21 and the shell 22 is as large as possible when they are connected.

[0134] In the embodiment, the area of the first side wall 223 is larger than the area of the second side wall 224, the connection length between the first side wall 223 and the end cover 21 is also large, and the elastic deformation range of the first side wall 223 is slightly larger than that of the second side wall 224. Therefore, the connection weld between the first side wall 223 and the end cover 21 is more likely to fail due to fatigue failure under the expansion force during the battery charging and discharging cycle. Increasing the thickness of the end of the first side wall 223 close to the opening 222 can further improve the welding quality and connection strength of the first side wall 223 and the end cover 21, so as to better withstand repeated expansion deformation under long cycle life, improve the reliability of the connection between the two and the service life of the battery monomer structure, and better meet the requirements of long cycle life on the structure.

[0135] According to some embodiments of the present application, please refer to Figure 8 The first part 2231 includes a first region 2231a and a second region 2231b arranged along the first direction X, and the first region 2231a is located between the second side wall 224 and the second region 2231b. The thickness of at least part of the second region 2231b is greater than the thickness of the first region 2231a.

[0136] It can be understood that, please refer to Figure 6 The two second side walls 224 are oppositely arranged along the first direction X, and the first part 2231 of the first side wall 223 divides two first regions 2231a connected with the second side wall 224 and a second region 2231b located between the two first regions 2231a along the first direction X, that is, both ends of the second region 2231b along the first direction X are the first region 2231a.

[0137] The thickness of the first region 2231a can be equal everywhere, or the thickness can be uneven, for example, the thickness of the part connected with the end cover 21 is greater than the thickness of other regions of the first region 2231a; the thickness of the second region 2231b can be equal everywhere. Overall, the thickness of at least part of the second region 2231b connected with the end cover is greater than the thickness of the first region 2231a, so that the area of the connection part of the end cover 21 and the shell 22 is as large as possible.

[0138] In the embodiment, by thickening the second region 2231b in the middle, the anti-deformation ability of the first part of the first side wall 223 can be improved, and the deformation amount of the expansion deformation can be reduced, thereby improving the reliability of the connection between the shell 22 and the end cover 21, and further improving the service life and comprehensive performance of the battery monomer.

[0139] According to some embodiments of the present application, please refer to Figure 8 and Figure 9The second area 2231b is connected with the first area 2231a through a first transition area 2231c, and the thickness of the first transition area 2231c gradually decreases along a direction from the second area 2231b to the first area 2231a.

[0140] It can be understood that the first area 2231a and the second area 2231b of the first side wall 223 can be connected through a first transition area 2231c formed by a chamfer, a circular arc or the like, or can be connected through a first transition area 2231c formed by a step structure. Since the thickness of the second area 2231b is greater than that of the first area 2231a, the thickness of the first transition area 2231c close to the second area 2231b is greater than that of the first transition area 2231c close to the first area 2231a, and overall, the thickness of the first transition area 2231c gradually decreases along a direction from the second area 2231b to the first area 2231a.

[0141] In this embodiment, the first transition area 2231c connects the first area 2231a and the second area 2231b to make a smooth transition, which can make the stress distribution of the first side wall 223 relatively uniform when the battery cell 20 expands after multiple cycles, and is not prone to stress concentration.

[0142] According to some embodiments of the present application, please refer to Figure 8 and Figure 9 The second area 2231b is connected with the second part 2232 through a second transition area 2231d, and the thickness of the second transition area 2231d gradually decreases along a direction from the first part 2231 to the second part 2232.

[0143] It can be understood that the second area 2231b and the second part 2232 can be connected through a second transition area 2231d formed by a chamfer, a circular arc or the like, or can be connected through a second transition area 2231d formed by a step structure. Since the thickness of the second area 2231b is greater than that of the second part 2232, the thickness of the second transition area 2231d close to the second area 2231b is greater than that of the second transition area 2231d close to the second part 2232, and overall, the thickness of the second transition area 2231d gradually decreases along a direction from the first part 2231 to the second part 2232.

[0144] In this embodiment, the second transition area 2231d connects the second area 2231b and the second part 2232 to make a smooth transition, which can make the stress distribution of the first side wall 223 relatively uniform when the battery cell 20 expands after multiple cycles, and is not prone to stress concentration.

[0145] According to some embodiments of the present application, please refer to Figure 5 and Figure 13The surface of the first portion 2231 facing away from the accommodation cavity 221 is flush with the surface of the second portion 2232 facing away from the accommodation cavity 221.

[0146] It can be understood that the first portion 2231 and the second portion 2232 each have an outer surface facing away from the accommodation cavity 221 and an inner surface facing the accommodation cavity 221. Since the thickness of the first portion 2231 is greater than that of the second portion 2232, when the outer surfaces of the first portion 2231 and the second portion 2232 are flush, the inner surface of the first portion 2231 will be relatively protruding from the inner surface of the second portion 2232.

[0147] The surface of the first portion 2231 facing away from the accommodation cavity 221 is flush with the surface of the second portion 2232 facing away from the accommodation cavity 221, which can keep the outer size of the battery cell 20 unchanged, so as not to affect the arrangement of the battery cell 20 in the battery device or the electrical device.

[0148] In the embodiment, the thickened side wall extends to the inside of the accommodation cavity 221, which can enable the battery cell 20 to be arranged as closely as possible in the thickness direction of the large face, and the large face is not easy to deform under the action of the swelling force.

[0149] According to some embodiments of the present application, the size of the second region 2231b in the first direction is L1, the size of the first side wall 223 in the first direction is L, and the following is satisfied: 0.2≤L1 / L≤0.6.

[0150] It can be understood that the value of L1 / L represents the length ratio of the second region 2231b on the first side wall 223, and the value of L1 / L can be 0.2, 0.25, 0.3, 0.35, 0.4, 0.45, 0.5, 0.55, 0.6, etc. In some embodiments, there can also be other ranges, such as 0.2≤L1 / L≤0.5, for example, 0.3≤L1 / L≤0.5, or 0.2≤L1 / L≤0.4.

[0151] In the embodiment, by reasonably setting the size of the second region in the first direction X, the influence of the thickened side wall on the weight of the battery and the risk of structural failure can be considered, and the overall performance of the battery cell can be improved.

[0152] According to some embodiments of the present application, please refer to Figure 7The second area 2231b has opposite first and second ends 223a and 223b along the first direction, the first side wall 223 has opposite third and fourth ends 223c and 223d along the first direction, the first end 223a is close to the third end 223c, the second end 223b is close to the fourth end 223d, the size of the first side wall 223 along the first direction is L, the minimum distance between the first end 223a and the third end 223c along the first direction is L2, and the minimum distance between the second end 223b and the fourth end 223d along the first direction is L3; and L2 / L≤0.3 and / or L3 / L≤0.3 are satisfied.

[0153] It can be understood that the second area 2231b and the first side wall 223 extend along the first direction X, the third and fourth ends 223c and 223d of the first side wall 223 are connected with the second side wall 224 respectively, one end of the second area 2231b close to the third end 223c is the first end 223a, and one end of the second area 2231b away from the third end 223c and close to the fourth end 223d is the second end 223b. That is, L2 and L3 represent the proximity of the second area 2231b on the first side wall 223 to the two second side walls 224, and the length of the second area 2231b plus L2 and L3 is equal to the length of the first side wall 223.

[0154] In some embodiments, the first side wall 223 and the second side wall 224 are connected by a circular arc segment, and the size L of the first side wall 223 along the first direction X in the embodiment does not include the size of the circular arc segment at both ends.

[0155] In the embodiment, such arrangement can make the second area 2231b be in a relatively central position on the first side wall 223, so as to more specifically inhibit the expansion deformation and improve the reliability of the connection between the shell 22 and the end cover 21.

[0156] According to some embodiments of the present application, referring to Figure 9 The size of the second area 2231b along the thickness direction of the end cover 21 is L4, and 0.05mm≤L4≤0.75mm is satisfied.

[0157] It can be understood that the size L4 of the second area 2231b along the thickness direction Z of the end cover 21 is the thickening length of the first side wall 223 in this direction, which can be measured by a vernier caliper or a micrometer. As an example, the size L4 can be any one of 0.05mm, 0.1mm, 0.15mm, 0.2mm, 0.25mm, 0.3mm, 0.4mm, 0.5mm, 0.6mm, 0.7mm, 0.75mm, etc., or a range value between any two of them.

[0158] In the embodiment, the size of the second area 2231b along the thickness direction Z of the end cover 21 can reduce the risk of cracking at the connection between the end cover 21 and the shell 22, and limiting the size of the second area 2231b is conducive to the arrangement of the internal components of the shell 22.

[0159] According to some embodiments of the present application, L4 satisfies 0.1mm≤L4≤0.6mm.

[0160] It can be understood further that the size L4 can be any one of 0.1mm, 0.15mm, 0.2mm, 0.25mm, 0.3mm, 0.35mm, 0.4mm, 0.45mm, 0.5mm, 0.55mm, 0.6mm, or a range value between any two of them.

[0161] In the embodiment, the size of the second area 2231b along the thickness direction Z of the end cover 21 can reduce the risk of cracking at the connection between the end cover 21 and the shell 22, and limiting the size of the second area 2231b is conducive to the arrangement of the internal components of the shell 22.

[0162] According to some embodiments of the present application, please refer to Figure 9 , the second side wall 224 includes a third part 2241 connected with the end cover 21, and a fourth part 2242 located between the third part 2241 and the bottom wall 225. The thickness of at least a partial region of the third part 2241 is greater than the thickness of the fourth part 2242.

[0163] In the embodiment, the second side wall 224 is divided into two regions along the thickness direction of the end cover 21, one of which is the third part 2241 close to the end cover 21, and the third part 2241 is fixedly connected with the end cover 21 through the opening 222 of the shell 22; the other is the fourth part 2242 close to the bottom wall 225, and the fourth part 2242 is connected with the bottom wall 225. The thickness of the third part 2241 can be equal everywhere, or the thickness of a local region can be greater than that of other parts; the thickness of the fourth part 2242 can be equal everywhere. Overall, the thickness of at least a partial region of the third part 2241 connected with the end cover 21 is greater than the thickness of the fourth part 2242, so that the connection area of the end cover 21 and the shell 22 is as large as possible.

[0164] In the embodiment, the area of the second side wall 224 is smaller than the area of the first side wall 223, the elastic deformation margin at the connection position of the second side wall 224 and the end cover 21 is smaller, and the rigidity is greater. When the internal pressure of the battery monomer 20 increases rapidly, cracking may occur due to excessive pressure. By thickening the third part 2241 of the second side wall 224, the reliability of the connection between the second side wall 224 and the end cover 21 can be improved, and the risk of cracking failure of the connection due to excessive internal pressure of the battery monomer 20 can be reduced.

[0165] According to some embodiments of the present application, referring to Figure 10 The surface of the third portion 2241 facing the accommodating cavity 221 is flush with the surface of the fourth portion 2242 facing the accommodating cavity 221.

[0166] It can be understood that the third portion 2241 and the fourth portion 2242 each have an outer surface facing away from the accommodating cavity 221 and an inner surface facing the accommodating cavity 221. Since the thickness of the third portion 2241 is greater than that of the fourth portion 2242, when the inner surfaces of the third portion 2241 and the fourth portion 2242 are flush, the outer surface of the third portion 2241 is relatively protruding from the outer surface of the fourth portion 2242. That is, the inner surface of the second side wall 224 of the shell 22 is a smooth surface, while the outer surface of the second side wall 224 is a non-smooth surface.

[0167] In the present embodiment, the thickened side wall extends outwardly from the accommodating cavity 221, so that the thickened side wall does not occupy the space of the accommodating cavity 221, which is conducive to the internal arrangement of the battery monomer 20.

[0168] According to some embodiments of the present application, referring to Figure 12 The maximum thickness of the third portion 2241 is D1, the maximum thickness of the fourth portion 2242 is D2, and the ratio of D2 to D1 satisfies 0.5≤D2 / D1≤0.8.

[0169] For example, the ratio of D2 to D1 can be 0.5, 0.55, 0.6, 0.65, 0.7, 0.75, 0.8, etc.; in some embodiments, the maximum thickness D1 of the third portion 2241 can be a value between 1.0 mm and 1.5 mm, and the maximum thickness D2 of the fourth portion 2242 can be a value between 0.5 mm and 1.2 mm.

[0170] In the present embodiment, by selecting a suitable ratio of D2 to D1, the processing and forming of the shell 22 are facilitated, and the effect of resisting swelling deformation is improved.

[0171] According to some embodiments of the present application, referring to Figure 6 The maximum depth D3 of the center portion 211 extending into the opening 222 is less than the length D4 of the third portion 2241 in the thickness direction Z of the end cover 21.

[0172] It can be understood that in the thickness direction Z of the end cover 21, the length of the thickened portion of the second side wall 224 is greater than the maximum depth of the center portion 211 extending into the accommodating cavity 221, that is, the lower end of the third portion 2241 is lower than the position of the center portion 211.

[0173] In the present embodiment, the length of the third portion 2241 in the thickness direction Z of the end cover 21 can be greater than the maximum depth of the third portion 2241 extending into the opening 222 of the center portion 211, which can provide sufficient structural strength to the connection between the side wall and the end cover 21, and the second side wall 224 is less likely to deform when the battery cell 20 expands after multiple cycles.

[0174] According to some embodiments of the present application, referring to Figure 12 , the length D4 of the third portion 2241 in the thickness direction Z of the end cover 21 satisfies 0.05mm≤D4≤0.75mm.

[0175] It can be understood that the size of the third portion 2241 in the thickness direction Z of the end cover 21 is the thickened length of the second side wall 224 in this direction, which can be measured by a vernier caliper or a micrometer. As an example, the size L4 can be any one of 0.05mm, 0.1mm, 0.15mm, 0.2mm, 0.25mm, 0.3mm, 0.4mm, 0.5mm, 0.6mm, 0.7mm, 0.75mm, etc., or a range value between any two of them.

[0176] In the present embodiment, thickening the size of the third portion 2241 in the thickness direction Z of the end cover 21 to a certain extent can prevent cracking of the end cover 21 and the shell 22, and can also inhibit deformation of the third portion 2241 due to stress concentration caused by the expansion force of the battery assembly.

[0177] According to some embodiments of the present application, referring to Figure 6 , the center portion includes a bottom surface facing the electrode assembly and a side surface connecting the bottom surface; along the first direction X or the second direction Y, the distance a between the outer edge of the lap portion 212 and the side surface satisfies: 0.5mm≤a≤1.5mm, wherein the first direction X and the second direction Y intersect and are perpendicular to the thickness direction of the end cover 21.

[0178] It can be understood that the protruding portion 211a is arranged on the center portion 211 and has a greater thickness in the thickness direction Z of the end cover 21, and thus protrudes relative to the lap portion 212 surrounding the outer periphery of the center portion 211. When the end cover 21 is covered on the shell 22, the protruding portion 211a extends into the accommodation cavity 221, and the surface between the outer edge of the lap portion 212 and the side surface of the protruding portion 211a is connected with the opening 222 of the shell 22. The distance a can be 0.5mm, 0.55mm, 0.6mm, 0.65mm, 0.7mm, 0.75mm, 0.8mm, 0.85mm, 0.9mm, 0.95mm, 1mm, 1.1mm, 1.2mm, 1.3mm, 1.4mm, 1.5mm, etc.

[0179] In this embodiment, the overlapping portion 212 is connected to the shell 22 through the bottom surface and the side surface, and the increased connection area can enable the end cover 21 to be stably connected and not easily fall off when the shell deforms.

[0180] According to some embodiments of the present application, the thickness b of the overlapping portion 212 in the thickness direction of the end cover 21 satisfies 0.3mm≤b≤1mm.

[0181] It can be understood that when the end cover 21 is covered on the shell 22, the protruding portion 211a extends into the accommodating cavity 221, and the side edge of the overlapping portion 212 has a certain thickness. The thickness b can be 0.3mm, 0.4mm, 0.5mm, 0.6mm, 0.7mm, 0.8mm, 0.9mm, 1.0m, etc.

[0182] In some embodiments, there can also be other ranges, such as 0.3mm≤b≤0.5mm, for example, 0.5mm≤b≤1mm, or 0.5mm≤b≤0.8mm.

[0183] In this embodiment, the overlapping portion 212 can enable the end cover 21 to be stably connected and not easily fall off when the shell deforms.

[0184] According to some embodiments of the present application, the capacity of the battery monomer 20 is greater than or equal to 360Ah.

[0185] The capacity of the battery monomer 20 refers to the total charge amount that the battery monomer 20 can release under certain discharge conditions, which is usually expressed in ampere hours (Ah) or milliampere hours (mAh).

[0186] It can be understood that the capacity claimed in the embodiments of the present application refers to the rated capacity of the battery monomer 20. For example, for a lithium battery, the rated capacity can be determined according to the provisions of Chinese standard GB / T18287-2000, or the minimum capacity detected under the test conditions of IEC61960 standard can be determined.

[0187] In some embodiments, the capacity of the battery monomer 20 can be 360Ah, 380Ah, 400Ah.

[0188] By combining the capacity of the battery monomer 20 with the parameters of graphite and the structure of the shell, the capacity, cycle life and structural deformation resistance of the battery monomer 20 can be considered, and the overall performance of the battery monomer 20 can be improved.

[0189] According to some embodiments of the present application, the electrode assembly 23 includes an active material of lithium phosphate salt.

[0190] The electrode assembly 23 includes a positive electrode active material and a negative electrode active material, wherein the positive electrode active material can include a lithium phosphate salt, which can be one or more of lithium iron phosphate, lithium manganese phosphate, lithium manganese iron phosphate, lithium cobalt phosphate, lithium vanadium phosphate, etc.

[0191] The lithium phosphate salt has good low-temperature performance, and in combination with the graphite in the embodiments of the present application, can further improve the room-temperature cycle life of the battery monomer, inhibit the transition expansion of the graphite during the cycle process, reduce the fluctuation of the interlayer spacing change rate, and is more conducive to improving the comprehensive performance of the battery monomer.

[0192] The embodiments of the present application provide a battery device 100, which includes the battery monomer 20 in the above embodiments.

[0193] The battery device 100 of the embodiments has the same technical effects as the battery monomer 20 in the above embodiments, and thus will not be described here.

[0194] The embodiments of the present application provide a power-using device, which includes the battery device 100 in the above embodiments, and the battery device 100 is used to provide electric energy.

[0195] The power-using device of the embodiments has the same technical effects as the battery device 100 in the above embodiments, and thus will not be described here.

[0196] The embodiments of the present application provide a power storage device 200, which includes a plurality of battery monomers 20 or battery devices 100 in the above embodiments, and the battery monomers 20 or battery devices 100 are used to store or provide electric energy.

[0197] The power storage device 200 of the embodiments has the same technical effects as the battery monomer 20 or battery device 100 in the above embodiments, and thus will not be described here.

[0198] The embodiments of the present application provide a power storage system, which includes a power conversion device and the power storage device 200 in the above embodiments, and the power conversion device is used to electrically connect a power generation device and the power storage device 200.

[0199] The power storage system of the embodiments has the same technical effects as the power storage device 200 in the above embodiments, and thus will not be described here.

[0200] The embodiments of the present application provide a charging network, which includes a charging pile 500 and the power storage device 200 in the above embodiments or the power storage system in the above embodiments, and the power storage device 200 is used to provide electric energy for the charging pile 500.

[0201] The charging network of the embodiment has the same technical effects as the energy storage device 200 or the energy storage system in the above embodiment, and thus will not be described again.

[0202] The application will be further described in combination with a specific embodiment.

[0203] The battery cell 20 includes an end cover 21, a housing 22, an electrode assembly 23, an insulating film 24, and a support 25.

[0204] The housing assembly 210 includes the housing 22 and the end cover 21, the housing 22 includes a receiving cavity 221 with an opening 222, and the end cover 21 covers the opening 222; the electrode assembly 23 is arranged in the receiving cavity 221, and the electrode assembly 23 includes a negative electrode sheet containing graphite.

[0205] The end cover 21 includes a central portion 211 and a lap portion 212 surrounding the outer periphery of the central portion 211, the lap portion 212 is fixedly connected with the end face of the housing 22 forming the opening 222, and the central portion 211 has a protruding portion 211a protruding to the side of the electrode assembly 23 relative to the lap portion 212, the protruding portion 211a extends into the receiving cavity 221 through the opening 222.

[0206] The BET specific surface area of the graphite is greater than 2.25 m² / g and less than or equal to 4.85 m² / g, and the volume average particle size Dv50 of the graphite satisfies: 4.5 μm≤Dv50<8.5 μm. The positive electrode sheet of the electrode assembly 23 includes an active material of a lithium phosphate salt. The electrode assembly 23 is arranged in the receiving cavity 221 of the housing 22. The interlayer spacing change rate M of the graphite before and after charging of the battery cell 20 satisfies: 8.3%≤M≤9.1%.

[0207] The housing 22 includes four side walls connected in sequence and a bottom wall 225 connected with the side walls; the four side walls include two first side walls 223 arranged opposite to each other along the second direction, and two second side walls 224 arranged opposite to each other along the first direction, and the area of the first side wall 223 is greater than the area of the second side wall 224.

[0208] The thickness of at least one of the four side walls at the first end 223a connected with the end cover 21 is greater than the thickness of the second end 223b connected with the bottom wall 225, the first side wall 223 includes a first portion 2231 connected with the end cover 21 and a second portion 2232 between the first portion 2231 and the bottom wall 225; the thickness of at least a part of the first portion 2231 is greater than the thickness of the second portion 2232. The first portion 2231 includes a first region 2231a and a second region 2231b arranged in the first direction, the first region 2231a is between the second side wall 224 and the second region 2231b; the thickness of at least a part of the second region 2231b is greater than the thickness of the first region 2231a. The second region 2231b is connected with the first region 2231a through a first transition region 2231c, the thickness of the first transition region 2231c decreases in the direction from the second region 2231b to the first region 2231a.

[0209] Embodiment section

[0210] Some comparative examples and embodiments of the present application are provided below. The embodiments described below are exemplary and are intended to explain the present application only, and should not be understood as a limitation of the present application. If a specific technique or condition is not specified in the embodiments, the technique or condition described in the literature in the art or according to the product specification is used. If the manufacturer of the reagent or instrument is not specified, it is a conventional product that can be obtained on the market.

[0211] Comparative Example 1

[0212] A battery cell includes a casing, an end cover, an electrode assembly, and an electrode terminal. The electrode assembly includes a positive electrode sheet, a negative electrode sheet, and a separator, wherein the positive electrode sheet includes a lithium phosphate salt, and the negative electrode sheet includes graphite. The BET specific surface area of the graphite is 3.8 m² / g, the volume average particle size Dv50 of the graphite is 4.0 μm, and the graphite interlayer spacing variation rate is 7.8%.

[0213] The end cover is a conventional end cover, i.e., a flat plate-shaped end cover, and is used to be fixedly connected with the casing, and the electrode terminal is arranged through the end cover and connected with the tab of the electrode assembly. The large face of the casing is a flat surface with a thickness of 0.6 mm.

[0214] The preparation method of the battery monomer mainly comprises the following steps: stacking the positive electrode sheet, the isolation film and the negative electrode sheet in sequence, so that the isolation film is between the positive electrode sheet and the negative electrode sheet to play a role of isolation, then winding to obtain an electrode assembly, assembling the electrode assembly into a shell, welding the tab of the electrode assembly and the electrode terminal, extending the end cover into the accommodating cavity of the shell through the opening of the shell, so that the top surface of the end cover is flush with the end surface of the shell, and then fixing by laser welding. The battery monomer after being assembled into the shell is dried to remove water, then electrolyte is injected and sealed to obtain a non-charged battery. The non-charged battery sequentially undergoes the processes of standing, hot and cold pressing, formation, shaping, capacity testing and the like to obtain a secondary battery product.

[0215] Comparative Example 2

[0216] A battery monomer, which is different from Comparative Example 1 in that the BET specific surface area of the graphite in the negative electrode sheet is 1.65 m² / g, the volume average particle size Dv50 of the graphite is 10.5 μm, and the graphite interlayer spacing change rate is 9.42%. The other conditions are the same as those in Comparative Example 1.

[0217] Comparative Example 3

[0218] A battery monomer, which is different from Comparative Example 1 in that the BET specific surface area of the graphite in the negative electrode sheet is 2.85 m² / g, the volume average particle size Dv50 of the graphite is 6.3 μm, and the graphite interlayer spacing change rate is 8.9%. The other conditions are the same as those in Comparative Example 1.

[0219] Example 1

[0220] A battery monomer, which is different from Comparative Example 1 in that the BET specific surface area of the graphite in the negative electrode sheet is 2.85 m² / g, the volume average particle size Dv50 of the graphite is 6.3 μm, and the graphite interlayer spacing change rate is 8.9%; the end cover is a T-shaped end cover, that is, the end cover comprises a center part and a lap part surrounding the outer periphery of the center part, when installed, the lap part is in contact with the end surface of the shell and is fixed by laser welding, and a part of the center part extends into the accommodating cavity of the shell through the opening of the shell. The other conditions are the same as those in Comparative Example 1.

[0221] Example 2

[0222] A battery monomer, which is different from Example 1 in that the thickened area is arranged on the end part of the large surface close to the opening of the shell, the thickness of the thickened area is 0.8 mm, the thickness of the non-thickened area is 0.6 mm, and the thickened area and the non-thickened area are transitionally connected; the ratio of the length of the thickened area along the length direction (horizontal direction) of the large surface to the length of the large surface is 0.6, and the height of the thickened area along the height direction (vertical direction) of the large surface is 0.6 mm. The other conditions are the same as those in Example 1.

[0223] Example 3

[0224] A battery cell, which is different from Example 2 in that the thickness of the thickened region provided at the end of the large face of the shell near the opening is 1 mm. The rest is the same as Example 2.

[0225] The battery cells prepared in Comparative Examples 1-3 and Example 1-3 were tested, and the test contents included the capacity of the graphite and the corresponding cycle number when the shell structure failed.

[0226] The test method for the capacity of the graphite was a half-cell test method, and the specific provisions can be referred to in the standard GB / T 24533-2019. The detection method was as follows:

[0227] Electrode preparation: The graphite powder was mixed with a binder (such as PVDF) and a conductive agent (such as acetylene black) in a certain proportion, a solvent (such as NMP) was added to make a slurry, which was coated on a copper foil, dried, and then cut into a working electrode.

[0228] Battery assembly: In an argon glove box, the battery shell, lithium sheet, separator, electrolyte, and working electrode were sequentially assembled to seal a CR2032 type button half-cell.

[0229] Charge-discharge test: The half-cell was connected to a battery test system, and the test parameters (such as voltage range 0.01~2.0 V vs Li⁺ / Li, current density 0.1C~1C, usually activated first with small current) were set.

[0230] Capacity calculation: The discharge curve during the discharge (lithium intercalation) process was recorded, and the stable discharge capacity after multiple cycles was divided by the mass of the graphite active material to obtain the reversible capacity of the graphite, which was taken as the capacity detection result of the graphite.

[0231] The test method for the corresponding cycle number when the shell structure failed was as follows: repeated cycling was carried out in a thermostat at 25℃ according to the set charge-discharge system, and the set charge-discharge system was a constant current and constant voltage mode, specifically first charged at 0.5P constant power to the upper limit voltage value 3.65V of the battery cell, and discharged at 0.5P constant power to the lower limit voltage value 2.5V of the battery cell. Shell structure detection was carried out once every 100 cycles, and X-ray detection or ultrasonic detection could be used to detect whether the shell had cracks, and if so, the current cycle number was taken as the cycle number when the shell structure failed.

[0232] The specific detection results are shown in Table 4.

[0233] Table 4

[0234]

[0235] According to the above test results, the graphite interlayer spacing change rate of Example 1 is greater than that of Comparative Example 1. Although the cycle number at which the shell structure of Comparative Example 1 fails is close to 15200 cycles of Example 1 and 16300 cycles of Example 1, the graphite capacity of Comparative Example 1 is significantly lower than that of Example 1.

[0236] Example 1 has a larger graphite specific surface area than Comparative Example 2, but the graphite Dv50 and graphite interlayer spacing change rate of Example 1 are smaller than those of Comparative Example 2. At this time, the cycle number at which the shell structure of Example 1 fails is 16300 cycles, which is significantly greater than 10500 cycles of Comparative Example 2.

[0237] Example 1 and Comparative Example 3 have the same graphite parameters, and the only difference is the type of end cap. The capacity of the two is the same, but the cycle number at which the shell structure of Example 1 fails is 16300 cycles, which is significantly greater than 12100 cycles of Comparative Example 3.

[0238] Example 2, Example 3 and Example 1 only differ in the maximum thickness of the shell opening. The capacity of the three is equal, but the cycle number at which the shell structure fails increases with the increase of the maximum thickness of the shell opening.

[0239] As can be seen from the above, in Example 1, the T-shaped end cap is combined with the graphite having corresponding parameter characteristics, which can significantly improve the fatigue resistance of the structure of the battery monomer, reduce the risk of shell cracking caused by battery monomer expansion, and balance the capacity, cycle life and structural reliability of the battery. Compared with Comparative Examples 1-3, it has better comprehensive performance. In addition, through the comparison of Examples 1-3, it can be concluded that the increase of the thickness of the shell opening is also beneficial to improve the cycle number at which the structure fails, thereby improving the structural reliability of the battery monomer.

[0240] Finally, it should be noted that: the above embodiments are only used to illustrate the technical solutions of the present application, but not to limit them; although the present application has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that: it can still modify the technical solutions recorded in the foregoing embodiments, or make equivalent replacement to part or all of the technical features; and these modifications or replacements do not make the essence of the corresponding technical solutions deviate from the scope of the technical solutions of the embodiments of the present application, and they should be covered in the scope of the claims and the description of the present application. Especially, as long as there is no structural conflict, each technical feature mentioned in each embodiment can be combined in any way. The present application is not limited to the specific embodiments disclosed herein, but includes all technical solutions falling within the scope of the claims.

Claims

1. A battery cell, characterized by, The application relates to a battery, comprising: a housing assembly comprising a shell and an end cover, the shell comprising a receiving cavity with an opening, and the end cover covering the opening; an electrode assembly arranged in the receiving cavity, the electrode assembly comprising a negative electrode sheet containing graphite; the end cover comprises a central part and a lap part arranged around the periphery of the central part, the lap part protruding from the outer side of the central part, and the top surface of the lap part away from the electrode assembly is flush with the top surface of the central part away from the electrode assembly, and the side of the central part facing the electrode assembly protrudes to form a protruding part relative to the lap part; the lap part is fixedly connected with the end surface of the shell forming the opening, and the protruding part of the central part extends into the receiving cavity through the opening; and The BET specific surface area of the graphite is greater than 2.25 m 2 / g and less than or equal to 4.85 m 2 / g, the volume average particle diameter Dv50 of the graphite satisfies 4.5 pm ≤ Dv50 < 8.5 pm, and the interlayer distance change rate M of the graphite before and after charging of the battery cell satisfies 8.3% ≤ M ≤ 9.1%.

2. The battery cell of claim 1, wherein, the shell comprises four side walls connected in sequence and a bottom wall connected with the side walls; the four side walls comprise two first side walls oppositely arranged along a second direction and two second side walls oppositely arranged along a first direction, and the area of the first side wall is larger than that of the second side wall; wherein the first direction and the second direction intersect and are perpendicular to the thickness direction of the end cover; the thickness of at least one of the four side walls at a first end connected with the end cover is greater than the thickness at a second end connected with the bottom wall.

3. The battery cell of claim 2, wherein, the first side wall comprises a first part connected with the end cover and a second part between the first part and the bottom wall; the thickness of at least a part of the first part is greater than the thickness of the second part.

4. The battery cell of claim 3, wherein, the first part comprises a first region and a second region arranged along the first direction, and the first region is located between the second side wall and the second region; the thickness of at least a part of the second region is greater than the thickness of the first region.

5. The battery cell of claim 4, wherein, the second region is connected with the first region through a first transition region, and the thickness of the first transition region decreases along the direction from the second region to the first region.

6. The battery cell of claim 4, wherein, the second region is connected with the second part through a second transition region, and the thickness of the second transition region decreases along the direction from the first part to the second part.

7. The battery cell of claim 3, wherein, the surface of the first part away from the receiving cavity is flush with the surface of the second part away from the receiving cavity.

8. The battery cell of claim 4, wherein, the size of the second region along the first direction is L1, the size of the first side wall along the first direction is L, and 0.2<=L1 / L<=0.6 is satisfied.

9. The battery cell of claim 4, wherein, the second region has opposite first and second ends along the first direction, and the first side wall has opposite third and fourth ends along the first direction, the first end is close to the third end, the second end is close to the fourth end, the size of the first side wall along the first direction is L, the minimum distance between the first end and the third end along the first direction is L2, and the minimum distance between the second end and the fourth end along the first direction is L3; and L2 / L<=0.3 and / or L3 / L<=0.3 are satisfied.

10. The battery cell of claim 4, wherein, the size of the second region along the thickness direction of the end cover is L4, and 0.05mm<=L4<=0.75mm is satisfied.

11. The battery cell of claim 10, wherein, L4 satisfies 0.1mm<=L4<=0.6mm.

12. The battery cell of claim 2, wherein, The second side wall comprises a third portion connected with the end cover, and a fourth portion between the third portion and the bottom wall; The third portion has a thickness greater than that of the fourth portion.

13. The battery cell of claim 12, wherein, The surface of the third portion facing the accommodating cavity is flush with the surface of the fourth portion facing the accommodating cavity.

14. The battery cell of claim 12, wherein, The maximum thickness of the third portion is D1, and the maximum thickness of the fourth portion is D2, and the ratio of D2 and D1 satisfies 0.5≤D2 / D1≤0.

8.

15. The battery cell of claim 12, wherein, The maximum depth D3 of the center portion into the opening is less than the length D4 of the third portion along the thickness direction of the end cover.

16. The battery cell of claim 12, wherein, The length D4 of the third portion along the thickness direction of the end cover satisfies 0.05mm≤D4≤0.75mm.

17. The battery cell of claim 1, wherein, The center portion comprises a bottom surface facing the electrode assembly and a side surface connecting the bottom surface; along a first direction or a second direction, the distance a between the outer edge of the lap portion and the side surface satisfies 0.5mm≤a≤1.5mm; The first direction and the second direction are perpendicular to the thickness direction of the end cover.

18. The battery cell of claim 1, wherein, The thickness b of the lap portion along the thickness direction of the end cover satisfies 0.3mm≤b≤1mm.

19. The battery cell of claim 1, wherein, The capacity of the battery monomer is greater than or equal to 360Ah.

20. The battery cell of claim 19, wherein, The electrode assembly comprises an active material of lithium phosphate salt.

21. A battery device, characterized by The battery monomer comprises the battery monomer according to any one of claims 1-20.

22. An electrical device, comprising: The battery device comprises the battery device according to claim 21, and the battery device is used to provide electric energy.

23. An energy storage device, comprising: The energy storage device comprises a plurality of battery monomers according to any one of claims 1-20 or a plurality of battery devices according to claim 21, and the battery monomers or the battery devices are used to store or provide electric energy.

24. An energy storage system characterized by, The energy storage device comprises the power conversion device and the energy storage device according to claim 23, and the power conversion device is used to electrically connect a power generation device and the energy storage device.

25. A charging network characterized by, The energy storage device comprises the energy storage device or the energy storage system according to claim 23 or 24, and the energy storage device or the energy storage system is used to provide electric energy for the charging pile. The energy storage device comprises the energy storage device or the energy storage system according to claim 23 or 24, and the energy storage device or the energy storage system is used to provide electric energy for the charging pile.

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