Battery cell of lithium ion battery, lithium ion battery and power utilization device

Abstract

The embodiment of the invention provides a single battery of a lithium ion battery, the lithium ion battery and an electric device. The time t for charging the single battery from 10% SOC to 80% SOC meets the following conditions: t is less than or equal to 20 minutes; the battery monomer comprises an electrolyte, and the ionic conductivity sigma of the electrolyte is greater than or equal to 9mS / cm and less than or equal to 25mS / cm; the battery monomer comprises an end cover, the end cover comprises an electrode terminal, and in the charging process of the battery monomer, the battery monomer is configured in a way that the temperature T1 of the electrode terminal when the electrode terminal is charged to 80% SOC meets the following conditions: T1 is smaller than or equal to 80 DEG C; the temperature T2 of the geometric center of the surface with the largest area of the battery monomer when the battery monomer is charged to 80% SOC meets the condition that T2 is greater than or equal to 30 DEG C. The battery monomer has excellent quick charge cycle performance.

Description

Technical Field

[0001] The present application relates to the field of batteries, and more specifically, to a battery cell of a lithium-ion battery, a lithium-ion battery, and an electrical device. Background Art

[0002] In recent years, secondary batteries, mainly lithium-ion batteries, have been widely used in energy storage power systems such as hydropower, thermal, wind and solar power stations, as well as power tools, electric bicycles, electric motorcycles, electric vehicles, military equipment, aerospace and other fields, and have thus achieved great development.

[0003] As people continue to pursue more efficient life, fast-charge lithium-ion batteries have become a development focus. Fast-charge lithium-ion batteries with carboxylic acid ester solvents in the electrolyte have poor cycle performance. Therefore, how to improve the cycle performance of fast-charge lithium-ion batteries is a technical problem that needs to be solved urgently. Summary of the invention

[0004] The present application is made in view of the above technical problems, and its purpose is to provide a lithium ion battery cell, a lithium ion battery and an electric device. The battery cell has good fast charge cycle performance.

[0005] In a first aspect, a battery cell of a lithium-ion battery is provided, wherein the time t for charging the battery cell from 10% SOC to 80% SOC satisfies: t≤20min; the battery cell comprises an electrolyte, and the ionic conductivity σ of the electrolyte satisfies: 9mS / cm≤σ≤25mS / cm; the battery cell comprises an end cap, and the end cap comprises an electrode terminal, and during the charging process of the battery cell, the battery cell is configured so that the temperature T1 of the electrode terminal when charged to 80% SOC satisfies: T1≤80°C; the temperature T2 of the geometric center of the surface with the largest area of ​​the battery cell when charged to 80% SOC satisfies: T2≥30°C.

[0006] In a fast-charging battery cell whose electrolyte is a high-conductivity electrolyte, the cycle performance of the fast-charging battery cell can be improved by controlling the temperature at the electrode terminal to not exceed 80°C and the temperature at the geometric center of the surface with the largest area to not be lower than 30°C.

[0007] In a possible implementation, 50°C ≤ T1 ≤ 80°C.

[0008] In a possible implementation, 45°C ≤ T2 ≤ 65°C.

[0009] In a possible implementation, the kinematic viscosity η of the electrolyte satisfies: 1.5 mm 2 / s≤η≤2.5mm 2 / s.

[0010] The electrode assembly expands and contracts during the cycle of the battery cell. As the electrode assembly expands and contracts, the electrolyte is sucked back and squeezed out. In the embodiment of the present application, by selecting a kinematic viscosity of 1.5 mm 2 / s-2.5mm 2 / s electrolyte can enable the electrolyte to be absorbed back by the electrode assembly during the circulation process of the battery cell, improving the problem of lithium precipitation inside the electrode assembly due to insufficient electrolyte infiltration, and improving the circulation performance of the fast-charging battery cell.

[0011] In a possible implementation, in a direction parallel to the end cap, the cross-sectional area S of the electrode terminal satisfies: 300 mm 2 ≤S≤500mm 2 .

[0012] In the embodiments of the present application, the cross-sectional area of ​​the electrode terminal is set within a larger range, which can increase the connection area between the electrode terminal and the pole ear of the pole piece, thereby increasing the flow area at the pole ear and reducing the heat generated by the pole ear during the charging process. Thus, the temperature of the battery cell is reduced, the problem of gas generation caused by side reactions of electrolytes including carboxylic acid ester solvents at high temperatures is improved, and the cycle performance of fast-charging battery cells is improved.

[0013] In a possible implementation, the battery cell includes an electrode assembly, the electrode assembly includes a main body and a tab, the width of the tab is d; in a direction parallel to the end cover, the width of the battery cell is D; d / D satisfies: 1 / 5≤d / D≤1 / 3.

[0014] In the embodiments of the present application, the width of the pole ear is set within a wider range, which can increase the flow area at the pole ear, reduce the heat generated by the pole ear during charging, thereby reducing the temperature of the battery cell and improving the cycle performance of the fast-charging battery cell.

[0015] In a possible implementation manner, a heat absorbing material is disposed on the electrode terminal and / or around the electrode terminal.

[0016] In the embodiments of the present application, by providing heat absorbing materials around the electrode terminals, the temperature of the battery cells during the fast charging process can be reduced, thereby improving the cycle performance of the fast charging battery cells.

[0017] In a possible implementation, the electrode terminal is connected to a busbar component, and a heat absorbing material is disposed on the busbar component.

[0018] In the embodiments of the present application, since the electrode terminals are connected to the busbar component, the heat at the electrode terminals can be transferred to the busbar component. By providing a heat-absorbing material at the busbar component, the temperature at the busbar component can be reduced, thereby accelerating the heat exchange between the electrode terminals and the busbar component. As a result, the temperature of the battery cells can be reduced and the cycle performance of the fast-charging battery cells can be improved.

[0019] In a possible implementation, the heat absorbing material includes at least one of thermally conductive silica gel and phase change graphite.

[0020] In a possible implementation, the electrode tab is directly connected to the electrode terminal.

[0021] In the embodiments of the present application, the pole tab is directly connected to the electrode terminal, eliminating the connecting component for connecting the electrode terminal and the pole tab, thereby improving the current flow capacity at the pole tab, thereby reducing the heat generated by the pole tab during fast charging. As a result, the temperature of the battery cell can be reduced and the cycle performance of the fast-charging battery cell can be improved.

[0022] In a possible implementation, a heat preservation component and / or a heating component is attached to the largest surface of the battery cell.

[0023] In the embodiments of the present application, heating components and heat preservation components can be provided on the surface with the largest area of ​​the battery cell to increase the temperature at the geometric center of the surface with the largest area, so that T2 is within the designed range, thereby helping to improve the fast charging cycle performance of the lithium-ion battery.

[0024] In a possible implementation, the electrolyte includes a carboxylate solvent, and the carboxylate solvent includes at least one of methyl formate, ethyl formate, methyl acetate, ethyl acetate, propyl acetate, methyl acrylate and ethyl acrylate.

[0025] In the embodiments of the present application, the selection of carboxylic acid ester solvents helps to improve the ionic conductivity of the electrolyte, thereby improving the fast charging performance of the battery cell.

[0026] In a possible implementation, based on the total mass of the electrolyte, the mass fraction W of the carboxylate solvent satisfies: 5wt%≤W≤80wt%.

[0027] In a possible implementation, 10wt%≤W≤40wt%.

[0028] In a second aspect, a lithium-ion battery is provided, wherein the lithium-ion battery comprises a battery cell according to any possible implementation of the first aspect.

[0029] In a third aspect, an electrical device is provided, wherein the electrical device comprises a battery cell in any possible implementation of the first aspect, and / or a lithium-ion battery in the second aspect. BRIEF DESCRIPTION OF THE DRAWINGS

[0030] In order to more clearly illustrate the technical solutions of the embodiments of the present application, the drawings required for use in the embodiments of the present application will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present application. For ordinary technicians in this field, other drawings can be obtained based on the drawings without paying creative work.

[0031] Figure 1 A schematic diagram of a battery cell.

[0032] Figure 2 An exploded diagram of a battery cell.

[0033] Figure 3 A schematic diagram of a lithium-ion battery. DETAILED DESCRIPTION

[0034] Hereinafter, the embodiments of the present application are specifically disclosed in detail with appropriate reference to the accompanying drawings. However, there may be cases where unnecessary detailed descriptions are omitted. For example, there may be cases where detailed descriptions of well-known matters and repeated descriptions of actually the same structures are omitted. This is to avoid the following description from becoming unnecessarily lengthy and to facilitate the understanding of those skilled in the art. In addition, the drawings and the following description are provided for those skilled in the art to fully understand the present application and are not intended to limit the subject matter described in the claims.

[0035] "Scope" disclosed in the present application is limited in the form of lower limit and upper limit, and a given range is limited by selecting a lower limit and an upper limit, and the selected lower limit and upper limit define the boundary of a special range. The scope limited in this way can be including end values ​​or not including end values, and can be arbitrarily combined, that is, any lower limit can be combined with any upper limit to form a scope. For example, if the scope of 60-120 and 80-110 is listed for a specific parameter, it is understood that the scope of 60-110 and 80-120 is also expected. In addition, if the minimum range values ​​1 and 2 are listed, and if the maximum range values ​​3, 4 and 5 are listed, the following scope can be all expected: 1-3, 1-4, 1-5, 2-3, 2-4 and 2-5. In the present application, unless otherwise specified, the numerical range "ab" represents the abbreviation of any real number combination between a and b, wherein a and b are real numbers. For example, the numerical range "0-5" means that all real numbers between "0-5" are listed in this document, and "0-5" is just an abbreviation of these numerical combinations. In addition, when a parameter is expressed as an integer ≥ 2, it is equivalent to disclosing that the parameter is, for example, an integer of 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, etc.

[0036] In the description of this application, it should be noted that, unless otherwise specified, "multiple" means more than two; the terms "upper", "lower", "left", "right", "inner", "outer", etc., indicating directions or positional relationships, are only for the convenience of describing this application and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific direction, be constructed and operated in a specific direction, and therefore cannot be understood as limiting this application. In addition, the terms "first", "second", "third", etc. are only used for descriptive purposes and cannot be understood as indicating or implying relative importance.

[0037] If not otherwise specified, in this application, the phrase "A and / or B" means "A, B, or both A and B". More specifically, any of the following conditions satisfies the condition "A and / or B": A is true (or exists) and B is false (or does not exist); A is false (or does not exist) and B is true (or exists); or both A and B are true (or exist).

[0038] If there is no special explanation, all steps of the present application can be performed sequentially or randomly, preferably sequentially. For example, the method includes steps (a) and (b), which means that the method may include steps (a) and (b) performed sequentially, or may include steps (b) and (a) performed sequentially. For example, the method may further include step (c), which means that step (c) may be added to the method in any order. For example, the method may include steps (a), (b) and (c), or may include steps (a), (c) and (b), or may include steps (c), (a) and (b), etc.

[0039] Unless otherwise specified, all embodiments and optional embodiments of the present application can be combined with each other to form a new technical solution.

[0040] If not specifically stated otherwise, any undefined terms have their art-recognized meanings.

[0041] Next, embodiments of the present application are introduced.

[0042] In recent years, secondary batteries have been widely used in power tools, electronic products, electric vehicles, aerospace and other fields due to their high energy density and long service life, and have achieved great development. Usually, a secondary battery includes a positive electrode sheet, a negative electrode sheet, an electrolyte and a separator. During the charge and discharge process of the battery, active ions are embedded and released back and forth between the positive electrode sheet and the negative electrode sheet. Among them, the electrolyte plays a role in conducting active ions between the positive electrode sheet and the negative electrode sheet. The separator is arranged between the positive electrode sheet and the negative electrode sheet, which allows active ions to pass through while preventing the positive and negative electrodes from short-circuiting, so that the electrochemical reaction of the secondary battery proceeds normally.

[0043] Take lithium-ion batteries as an example. Lithium-ion batteries are a typical secondary battery. Because they rely on the chemical reaction of lithium ions intercalating and disintercalating between the positive and negative electrodes for charging and discharging, lithium-ion batteries are also called rocking-chair batteries. During the charging process of lithium-ion batteries, lithium ions are released from the positive electrode active material, move to the negative electrode through the conduction of the electrolyte and embed into the negative electrode active material; and during the discharge process, lithium ions are released from the negative electrode active material, move to the positive electrode through the conduction of the electrolyte and embed into the positive electrode active material.

[0044] It should be understood that the "lithium insertion" and "embedding" processes described in this application refer to the process in which lithium ions are embedded in the positive electrode active material or the negative electrode active material due to an electrochemical reaction, and the "extraction", "delithium" and "extraction" processes described in this application refer to the process in which lithium ions are extracted from the positive electrode active material or the negative electrode active material due to an electrochemical reaction.

[0045] As the application scope of lithium-ion batteries becomes wider and wider, and the use scenarios become more and more diverse, new requirements are put forward for the charging capacity of lithium-ion batteries. For example, for power vehicles, mileage anxiety and long charging time have become the main problems hindering their development. Therefore, fast charging (FC) capability has become an important goal for the development of lithium-ion batteries. Fast charging, referred to as fast charging, refers to charging the battery to full or nearly full power through high-power direct current in a short period of time. The industry in different regions has different standards for the specific definition of fast charging. Generally speaking, if the battery can be charged to 80% of its full power within 30min to 60min, it is considered to be fast charging; further, charging time within 20min can be considered to be super fast charging; further, charging time less than 15min can be considered to be in the range of extreme fast charging (XFC). However, studies have shown that high-rate charging will cause rapid attenuation of battery capacity, output power and other performance. Therefore, in addition to meeting the requirements of fast charging, fast charging batteries also need to achieve a certain cycle life and meet relevant safety performance and electrochemical performance. In the embodiments of the present application, the fast-charging lithium-ion battery refers to a lithium-ion battery with fast-charging capability.

[0046] In order to achieve the fast charging requirements of lithium-ion batteries, a high-conductivity electrolyte that can quickly transport lithium ions is needed. However, the cycle performance of high-conductivity electrolytes is poor and cannot meet the fast charging cycle requirements.

[0047] The applicant has found that the fast charging process is usually accompanied by an increase in the temperature of the battery cell, and the high-conductivity electrolyte is sensitive to temperature. If the temperature of the battery cell is too high, the high-conductivity electrolyte is prone to decomposition and gasification due to side reactions at high temperatures, which deteriorates the cycle life of the battery cell. In addition, the temperature of the battery cell cannot be too low, because the viscosity of the high-conductivity electrolyte is also affected by temperature. The lower the temperature, the greater the viscosity of the high-conductivity electrolyte, and it is difficult to reabsorb the electrolyte squeezed out of the electrode assembly during the cycle, which is prone to local lithium precipitation, thereby deteriorating the cycle performance of the battery cell.

[0048] In view of this, the embodiments of the present application provide a battery cell, a secondary battery and an electrical device, wherein the battery cell can have good fast charging cycle performance.

[0049] Next, the battery cell provided in this application is introduced.

[0050] [Battery Cell]

[0051] First, a battery cell is provided, wherein the time t for charging the battery cell from 10% SOC to 80% SOC satisfies: t≤20min. The battery cell includes an electrolyte, and the ionic conductivity σ of the electrolyte satisfies: 9mS / cm≤σ≤25mS / cm. The battery cell includes an end cover, and the end cover includes an electrode terminal. During the charging process of the battery cell, the temperature T1 of the electrode terminal when charged to 80% SOC satisfies: T1≤80℃; optionally, 50℃≤T1≤80℃. The temperature T2 of the geometric center of the surface with the largest area of ​​the battery cell when charged to 80% SOC satisfies: 30℃≤T2; optionally, 45℃≤T2≤65℃.

[0052] Specifically, T1 can be 50℃, 51℃, 52℃, 53℃, 54℃, 55℃, 56℃, 57℃, 58℃, 59℃, 60℃, 61℃, 62℃, 63℃, 64℃, 65℃, 66℃, 67℃, 68℃, 69℃, 70℃, 71℃, 72℃, 73℃, 74℃, 75℃, 76℃, 77℃, 78℃, 79℃, 80℃, or its value is within the range obtained by combining any two of the above values; T2 can be 45℃, 46℃, 47℃, 48℃, 49℃, 50℃, 51℃, 52℃, 53℃, 54℃, 55℃, 56℃, 57℃, 58℃, 59℃, 60℃, or its value is within the range obtained by combining any two of the above values. The above charging process is a charging process at room temperature (25℃±2℃).

[0053] The above-mentioned battery cell has a fast charging capability of being charged from 10% SOC to 80% SOC in a time of less than or equal to 20 minutes. The fast charging process can be a constant current charging process or a step charging process. The constant current charging process is to charge the battery cell 10 at a fixed charging rate. The charging rate represents the ratio of the charging current to the capacity of the battery cell 10. For example, for a battery that supports 4C charging, the charging current can reach four times the battery capacity. The charging rate can be calculated by the ratio of the charging current and the capacity of the battery cell 10. During the fast charging process of the battery cell, the charging rate can also be variable. For example, when the battery cell is charged at a charging rate greater than or equal to 2.8C, the charging time from 10% SOC to 80% SOC is less than or equal to 20 minutes. In other words, in the process of charging from 10% SOC to 80% SOC, the charging rate may gradually decrease from greater than 2.8C to less than 2.8C. During this process, the battery cell 10 may undergo a transition from constant current charging to constant voltage charging, so the charging rate may not be constant. For example: the battery cell 10 starts charging at a room temperature of 25°C, charging from 10% SOC to 80% SOC, and the charging time is 10 minutes (equivalent charging rate ≥ 4C). The charging process can be: initially charging from 10% SOC to 45% SOC at 5C, then charging from 45% SOC to 50% SOC at 4.6C, charging from 50% SOC to 55% SOC at 4.3C, charging from 55% SOC to 60% SOC at 3.9C, charging from 60% SOC to 65% SOC at 3.6C, charging from 60% SOC to 65% SOC at 3.3C, charging from 65% SOC to 70% SOC at 3.1C, charging from 70% SOC to 75% SOC at 2.9C, and charging is completed. The charging time of the battery cell 10 from 0% SOC to 100% SOC at 1C is 60 minutes. Therefore, when the charging time of the battery cell 10 from 10% SOC to 80% SOC is measured to be 10 minutes, the equivalent charging rate of the process can be calculated as: [(80% SOC-10% SOC) / (100% SOC-0% SOC)]×[(1C×60min) / 10min]=4.2C.

[0054] If the battery cell 10 is charged on a charging pile with a power of 120W or above, the time it takes to charge from 10% SOC to 80% SOC can also be directly recorded. For example, if the time is around 15 minutes (the error does not exceed 1 minute), it is generally considered to be a 4C fast-charging battery. For another example, if the time is around 12 minutes (the error does not exceed 1 minute), it is generally considered to be a 5C fast-charging battery. For another example, if the time is around 10 minutes (the error does not exceed 1 minute), it is generally considered to be a 6C fast-charging battery.

[0055] σ can be 9mS / cm, 10mS / cm, 11mS / cm, 12mS / cm, 13mS / cm, 14mS / cm, 15mS / cm, 16mS / cm, 17mS / cm, 18mS / cm, 19mS / cm, 20mS / cm, 21mS / cm, 22mS / cm, 23mS / cm, 24mS / cm, 25mS / cm, or a value within the range obtained by combining any two of the above values.

[0056] It should be understood that, unless otherwise specified, the ionic conductivity referred to in this application refers to the ionic conductivity of the electrolyte at 20°C to 30°C.

[0057] During the fast charging process of the battery cell, the current enters and exits the battery cell through the electrode terminals to achieve the input or output of electrical energy. Therefore, compared with other positions of the battery cell, the electrode terminals are prone to heat during the fast charging process, and the temperature is higher than other positions. During the entire charging process of the battery cell, it is generally believed that the temperature of the battery cell is highest when it is charged to 80% SOC. Therefore, during the charging process of the battery cell, the temperature of the electrode terminals when charged to 80% SOC can represent the highest temperature of the battery cell during the entire charging process.

[0058] During the cycle of the battery cell, as lithium ions are extracted and embedded in the active material, the electrode assembly undergoes a corresponding expansion and contraction process. Specifically, during the charging process of the battery cell, the active lithium ions are extracted from the positive electrode active material, moved to the negative electrode and embedded in the negative electrode active material, the negative electrode active material expands, and the electrode assembly expands. During the discharge process of the battery cell, the active lithium ions are extracted from the negative electrode active material, moved and embedded in the positive electrode active material. Since the positive electrode active material itself has space for sodium active lithium ions, the positive electrode active material will not expand significantly during this process, while the negative electrode active material shrinks during this process, and the electrode assembly shrinks. For the electrode assembly, due to volume shrinkage, part of the electrolyte will be squeezed out. If this part of the electrolyte cannot be reabsorbed into the electrode assembly during the expansion process, the electrode assembly will be insufficiently wetted, resulting in local lithium precipitation. Especially in the middle position of the electrode assembly, the electrolyte infiltration path is long and the electrolyte reabsorption is the most difficult. The middle position of the electrode assembly usually corresponds to the geometric center of the surface with the largest area of ​​the battery cell shell. Therefore, by regulating the temperature at the geometric center of the surface with the largest area of ​​the battery cell, the temperature at the middle position of the electrode assembly can be affected.

[0059] Therefore, when charging to 80% SOC, by keeping the temperature T1 at the electrode terminal below 80°C in a fast-charging battery cell with an electrolyte ion conductivity of 9mS / cm-25mS / cm, the problem of carboxylic acid ester solvents producing gas due to high-temperature decomposition during fast charging can be improved; by controlling the temperature T2 at the geometric center of the largest surface area of ​​the battery cell to above 30°C, the middle position of the electrode assembly can be able to absorb the electrolyte in time, improving the problem of local lithium precipitation. Therefore, by controlling T1 and T2, the fast-charging cycle performance of battery cells including high-conductivity electrolytes can be improved.

[0060] In one embodiment, the kinematic viscosity η of the electrolyte satisfies: 1.5 mm 2 / s≤η≤2.5mm 2 / s.

[0061] Specifically, η can be 1.5 mm 2 / s、1.6mm 2 / s, 1.7mm 2 / s、1.8mm 2 / s, 1.9mm 2 / s, 2mm 2 / s, 2.1mm 2 / s, 2.2mm 2 / s, 2.3mm 2 / s, 2.4mm 2 / s, 2.5mm 2 / s, or its value is within the range obtained by combining any two of the above values.

[0062] The ease with which the electrode assembly can absorb electrolyte back is affected by the viscosity of the electrolyte, and the viscosity of the electrolyte is affected by the temperature. The higher the temperature, the lower the viscosity of the electrolyte, and the easier it is for the electrode assembly to absorb electrolyte back. At the same time, the higher the temperature, the lower the viscosity of the electrolyte, the easier it is for the carboxylic acid ester solvent in the electrolyte to decompose and produce gas, and the more side reactions there are inside the battery cell. Therefore, based on the control of the battery cell temperature in the aforementioned embodiment, by selecting a viscosity of 1.5 mm 2 / s-2.5mm 2 / s range can help further reduce the difficulty of electrolyte reabsorption and help improve the fast charging cycle performance of battery cells.

[0063] Next, a specific example of controlling the battery cell temperature will be described in detail.

[0064] Figure 1 This is a schematic structural diagram of a battery cell of the present application. Figure 2 The present application is a schematic exploded view of a battery cell.

[0065] like Figure 1 and Figure 2 As shown, the battery cell 10 generally includes a shell. The shell is used to encapsulate components such as electrode assemblies and electrolytes. The shell can be a steel shell, an aluminum shell, a plastic shell (such as polypropylene), a composite metal shell (such as a copper-aluminum composite shell) or an aluminum-plastic film. The shell of the battery cell 10 may include a plurality of walls, so that the battery cell 10 is a polyhedral structure. The shell includes a shell 11 and an end cover 12. Exemplarily, the shell can be a rectangular parallelepiped or a nearly rectangular parallelepiped, and the shell can include six walls, each of which is rectangular or approximately rectangular. Correspondingly, the shell 11 can also be a polyhedral structure with an opening.

[0066] The shell 11 can be in various shapes, such as a cylinder, a cuboid, etc. The shape of the shell 11 can be determined according to the specific shape of the electrode assembly 13. For example, if the electrode assembly 13 is a cylindrical structure, the shell 11 can be a cylindrical structure; if the electrode assembly 13 is a cuboid structure, the shell 11 can be a cuboid structure. Of course, the end cap 12 can also be in various structures, such as a plate-like structure or a hollow structure with one end open. For example, in Figure 1 In the embodiment, the shell 11 is a rectangular parallelepiped structure. It should be understood that the shell is not limited to the aforementioned structure, and the shell may also be other structures, for example, the shell includes the shell 11 and two end caps 12, the shell 11 is a hollow structure with two opposite openings, and one end cap 12 is correspondingly covered at one opening of the shell 11 and forms a sealed connection to form a sealed space for accommodating the electrode assembly 13 and the electrolyte.

[0067] The battery cell 10 includes an electrode assembly 13, which is usually formed by winding or laminating a positive electrode sheet, a separator and a negative electrode sheet. Structurally, the electrode assembly 13 usually includes a tab 131 and a body 132. The tab 131 is a component formed by stacking and connecting the areas on the positive electrode sheet that are not coated with the positive active material, or a component formed by stacking and connecting the areas on the negative electrode sheet that are not coated with the negative active material. The body 132 is a component formed by stacking or winding the areas on the positive electrode sheet or the negative electrode sheet that are coated with the active material. The tab 131 needs to be connected to the electrode terminal 121 to input or output current into or out of the electrode assembly 13.

[0068] The electrode terminal 121 is a component for outputting or inputting electric energy to the battery cell 10. For example, the material of the electrode terminal 121 can be various, for example, the material of the electrode terminal 121 can be copper, iron, aluminum, steel, aluminum alloy, etc. For the convenience of processing, the end of the electrode terminal 121 facing the electrode assembly 13 is usually connected to a transfer sheet, and the pole ear 131 is also connected to the transfer sheet, thereby realizing the connection between the pole ear 131 and the electrode terminal 121. The connection mentioned in this application can be welding, riveting, etc.

[0069] It can be seen that the electrode terminal 121 is connected to the pole ear 131 to realize the input or output of electric energy. Compared with the main body 132 of the pole piece, the pole ear 131 has a smaller flow area, and the heat is more serious during the fast charging process of the battery cell 10. Since the distance between the electrode terminal 121 and the pole ear 131 is very small, the temperature at the electrode terminal 121 will also increase with the temperature of the pole ear. Make the electrode terminal 121 the external structure with the highest temperature during the fast charging process of the battery cell.

[0070] Figure 1 A specific example of the geometric center of the largest surface of a battery cell is shown in FIG. Figure 1 As shown, the geometric center of the largest surface of the battery cell is position A. In other examples, the shell of the battery cell is a cylindrical structure, in which case the largest surface of the battery cell is the side wall of the cylinder, and the geometric center of the largest surface of the battery cell is the geometric center of the side wall.

[0071] In one embodiment, in a direction parallel to the end cap 12, the cross-sectional area S of the electrode terminal 121 satisfies: 300 mm 2 ≤S≤500mm 2 .

[0072] Specifically, S can be 300mm 2 、310mm 2 、320mm 2 、330mm 2 、340mm 2 、350mm 2 、360mm 2 、370mm 2 、380mm 2 、390mm 2 , 400mm 2 、410mm 2 、420mm 2 、430mm 2 、440mm 2 , 450mm 2 、460mm 2 、470mm 2 、480mm 2 、490mm 2 , 500mm 2, or its value is within the range obtained by combining any two of the above values. The cross-sectional area of ​​the electrode terminal 121 specifically refers to the area defined by the curve obtained by the intersection of any plane parallel to the end cap 12 and the electrode terminal 121, which can also be referred to as the cross-sectional area of ​​the electrode terminal 121. In some examples, the electrode terminal 121 has a main body portion and a step portion, so that the electrode terminal 121 has multiple cross-sectional areas. In the case where the electrode terminal has multiple cross-sectional areas, the cross-sectional area of ​​the electrode terminal referred to in this application is the minimum value of the multiple cross-sectional areas.

[0073] The larger the cross-sectional area of ​​the electrode terminal 121, the larger the area that can be used for electrical connection with the tab 131. The larger the current flow area of ​​the tab 131, the less heat generated by the tab 131 during fast charging, and the temperature of the tab 131 can be reduced. However, since the electrode terminal 121 usually needs to pass through the through hole on the end cap 12, considering the mechanical strength of the end cap 12, the cross-sectional area of ​​the electrode terminal 121 cannot be too large.

[0074] Therefore, this embodiment helps to reduce the temperature of the electrode terminal 121 during charging by setting the cross-sectional area of ​​the electrode terminal 121 within a larger range, so that T1 is within 80°C, improves the problem of gas generation due to decomposition of carboxylic acid ester solvents, and improves the fast charging cycle performance of the battery cell 10.

[0075] In one embodiment, the electrode assembly 13 includes a body 132 and a tab 131 , the width of the tab 131 is d; in a direction parallel to the end cover 12 , the width of the battery cell 10 is D; d / D satisfies: 1 / 5≤d / D≤1 / 3.

[0076] Specifically, the larger the width of the pole lug 131, the larger the flow area at the pole lug 131, and the less heat generated by the pole lug 131 during the fast charging process, which helps to reduce the temperature at the electrode terminal 121, reduce the temperature at the electrode terminal 121, make T1 within the designed range, improve the problem of gas production by decomposition of carboxylic acid ester solvents, and improve the fast charging cycle performance of the battery cell 10. However, the design of the pole lug 131 also needs to consider the coordination with other mechanical parts at the end cover. Based on this, within the range allowed by the mechanical parts, the width of the pole lug 131 can be made as wide as possible to increase the flow area.

[0077] In this embodiment, the width of the tab 131 is 1 / 5 to 1 / 3 of the width of the battery cell 10. For example, when the width D of the battery cell 10 is 200 mm, the width d of the tab 131 may be 50 mm to 60 mm. For another example, when the width D of the battery cell 10 is 300 mm, the width d of the tab 131 may be 70 mm to 80 mm.

[0078] In one embodiment, a heat absorbing material is disposed on the electrode terminal 121 ; and / or a heat absorbing material is disposed around the electrode terminal 121 .

[0079] Specifically, in order to reduce the temperature of the electrode terminal 121 during fast charging and to reduce the temperature of the battery cell, the temperature of the electrode terminal 121 can be reduced by providing an endothermic material on the electrode terminal 121. For example, an endothermic material can be provided on the side wall of the electrode terminal. Alternatively, an endothermic material can be provided around the electrode terminal 121 to reduce the temperature of the electrode terminal 121. For example, an endothermic material can be provided on the end cap around the electrode terminal. The endothermic material can be provided on the electrode terminal 121 and around the electrode terminal 121 by pasting, applying, etc. to absorb the heat of the electrode terminal 121.

[0080] Therefore, by setting heat-absorbing materials around the electrode terminal 121, the temperature of the electrode terminal 121 during the fast charging process is reduced, so that T1 is within the designed range, the problem of gas generation due to decomposition of carboxylic acid ester solvents is improved, and the fast charging cycle performance of the battery cell 10 is improved.

[0081] In one embodiment, the electrode terminal 121 is connected to a busbar component on which a heat absorbing material is disposed.

[0082] Specifically, the busbar is also called a busbar, and its material can be copper, iron, aluminum, steel, aluminum alloy, etc. When the battery cells 10 form a battery, the electrode terminals 121 of multiple battery cells 10 are connected in series, in parallel, or in mixed connection through the busbar, so that electric energy can be output or input into the battery. The electrode terminal 121 is generally directly connected to the busbar by welding or riveting, so the temperature at the electrode terminal 121 will be transferred to the busbar.

[0083] In this embodiment, by providing a heat absorbing material on the converging component, the temperature at the converging component can be reduced, and the heat exchange between the electrode terminal 121 and the converging component can be accelerated to reduce the temperature at the electrode terminal 121. In this way, T1 is within the designed range, the problem of gas generation due to decomposition of carboxylic acid ester solvents is improved, and the fast charging cycle performance of the battery cell 10 is improved.

[0084] In one embodiment, the heat absorbing material includes at least one of thermally conductive silica gel and phase change graphite.

[0085] Please continue to refer to Figure 2 In one embodiment, the tab 131 is directly connected to the electrode terminal 121 .

[0086] Specifically, for the convenience of processing, the end of the electrode terminal 121 facing the electrode assembly 13 is usually connected to a transfer plate, and the pole ear 131 is also connected to the transfer plate, thereby realizing the connection between the pole ear 131 and the electrode terminal 121. The current capacity at the pole ear 131 is also limited by the connection area between the pole ear 131 and the transfer plate.

[0087] In this embodiment, the tab 131 is directly connected to the electrode terminal 121, eliminating the adapter sheet, which can improve the current capacity at the tab 131, thereby reducing the heat generated by the tab 131 during fast charging and lowering the temperature at the electrode terminal 121. As a result, T1 can be within the designed range, improving the problem of gas generation by decomposition of carboxylic acid ester solvents, and improving the fast charging cycle performance of the battery cell 10.

[0088] In one embodiment, a heat preservation component and / or a heating component is attached to the largest surface of the battery cell 10 .

[0089] Specifically, the heating component may be a heating film, a heating wire, etc. The heating component may heat the surface with the largest area of ​​the battery cell 10 during the fast charging process of the battery cell 10. The heating component may continuously heat the surface with the largest area during the fast charging process of the battery cell 10, or may heat it according to the temperature of the surface with the largest area. For example, a temperature sensing element may be provided at the geometric center of the surface with the largest area to obtain the temperature of the position in real time during the fast charging process. When the temperature at the position is sensed to be lower than a preset threshold, the heating component heats the surface with the largest area of ​​the battery cell 10. Alternatively, when the temperature drop rate at the position is sensed to be higher than a preset threshold, the heating component heats the surface with the largest area of ​​the battery cell 10.

[0090] The heat preservation component can be heat preservation cotton, vacuum insulation board, foam board, glass fiber, etc. Placing the heat preservation component on the largest surface of the battery cell 10 can reduce the heat loss at the geometric center of the largest surface of the battery cell 10, so that T2 is within the set range.

[0091] This embodiment can make T2 within a set range by attaching a heating component and / or a heat-insulating component to the largest surface of the battery cell 10, thereby improving the problem of difficulty in reabsorbent of electrolyte due to low temperature and high viscosity of the electrolyte in the middle of the electrode assembly, and improving the fast charging cycle performance of the battery cell 10.

[0092] In one embodiment, the carboxylate solvent includes at least one of methyl formate, ethyl formate, methyl acetate, ethyl acetate, propyl acetate, methyl acrylate, and ethyl acrylate.

[0093] In one embodiment, based on the total mass of the electrolyte, the mass content W of the carboxylate solvent satisfies: 5wt%≤W≤80wt%; optionally, 10wt%≤W≤40wt%.

[0094] Specifically, W1 can be 5wt%, 10wt%, 15wt%, 20wt%, 25wt%, 30wt%, 35wt%, 40wt%, 45wt%, 50wt%, 55wt%, 60wt%, 65wt%, 70wt%, 75wt%, 80wt%, or its value is within the range obtained by combining any two of the above values. Carboxylic acid ester solvents are prone to side reactions and gas production at high temperatures. This embodiment can reduce the gas production of carboxylic acid ester solvents by controlling the mass content of carboxylic acid ester solvents within a suitable range, thereby helping to improve the fast charging cycle performance of the battery cell 10.

[0095] In one embodiment, the positive electrode sheet includes a positive electrode active material, and the positive electrode active material includes a lithium transition metal oxide.

[0096] Specifically, the positive electrode film layer of the positive electrode sheet contains positive electrode active materials. Lithium transition metal oxide refers to a class of oxides that include lithium and transition metal elements. Structurally, it includes ternary materials with layered structures, LiCoO 2 、LiNiO 2 etc., including LiMn with spinel structure 2 O 4 Etc. Ternary materials refer to lithium transition metal oxides including three different transition metal elements. It should be understood that trace amounts of other transition metal elements may also be doped in ternary materials, and ternary materials doped with other transition metal elements are generally considered to still belong to ternary materials. In this embodiment, lithium transition metal oxides generally have a higher gram capacity, and selecting lithium transition metal oxides as at least part of the positive electrode active material helps to improve the energy density of the battery cell 10.

[0097] In one embodiment, the lithium transition metal oxide includes a ternary material, and the ternary material satisfies the general formula: Li x Ni y Co z M k Me l O r E s; wherein, the M includes one or more elements of Mn and Al, the Me includes one or more elements of Zr, Zn, Cu, Cr, Mg, Fe, V, Ti, Sr, Sb, Y, W or Nb, and the E includes one or more elements of N, F, S and Cl; 0.8≤x≤1.15, 0<y<1, 0<z<1, 0<k<1, 0≤l≤0.1, 1≤r≤2, 0≤s≤1.

[0098] In the enumeration of positive electrode active materials in this application, the molar content of Li is the initial state of the material, that is, the state before feeding. The positive electrode active material is used in the battery system, and the molar content of Li will change after charge and discharge cycles. In the enumeration of positive electrode active materials in this application, the molar content of O is only an ideal state value. Lattice oxygen release will cause the molar content of O to change, and the actual molar content of O will fluctuate.

[0099] In one embodiment, when the positive electrode active material includes a lithium transition metal oxide, T1 satisfies: 60°C≤T1≤80°C; and / or T2 satisfies: 50°C≤T2≤65°C.

[0100] For the battery cell 10 whose positive electrode active material includes lithium transition metal oxide, its temperature rise during fast charging is higher. The possible reason is that the transition metal content in lithium transition metal oxide is high, which generates more heat during charging. However, lithium transition metal oxide has poor high-temperature stability and is prone to release oxygen at high temperatures, which aggravates the side reactions in the battery cell 10 and affects the cycle performance of the battery cell 10.

[0101] Therefore, for a battery cell 10 whose positive electrode active material includes lithium transition metal oxide, by controlling the temperature T1 of the electrode terminal 121 to be between 60°C and 80°C and the temperature T2 of the geometric center of the surface with the largest area of ​​the battery cell to be between 50°C and 65°C, the fast charging cycle performance of the battery cell 10 can be improved.

[0102] In one embodiment, the electrolyte includes a carbonate solvent, and the carbonate solvent includes at least one of ethylene carbonate, propylene carbonate, ethyl methyl carbonate, and dimethyl carbonate.

[0103] Specifically, carbonate solvents are more stable than carboxylate solvents, have better compatibility with negative electrode active materials, and can form a stable interface film. By introducing carbonate solvents into the solvent, it can help reduce the side reactions between carboxylate solvents and negative electrode active materials. Therefore, this embodiment, by using carbonate solvents as the solvent of the electrolyte on the basis of carboxylate solvents, can improve the decomposition and gas production problem of carboxylate solvents, thereby improving the fast charging cycle performance of the battery cell 10.

[0104] In one embodiment, the electrolyte includes an electrolyte salt including LiFSI.

[0105] Specifically, LiFSI, or lithium bis(fluorosulfonyl)imide, has a higher solubility and is more soluble than LiPF 6 It has a higher lithium ion transfer number and good stability at high temperatures. Therefore, by selecting LiFSI as the electrolyte salt, it will not decompose and produce gas at high temperatures, which helps to further improve the fast charging cycle performance of the lithium ion battery 20.

[0106] Next, the negative electrode sheet, the positive electrode sheet and the separator in the battery cell 10 are introduced in more detail.

[0107] [Negative electrode]

[0108] The negative electrode sheet generally includes a negative electrode current collector and a negative electrode film layer disposed on at least one surface of the negative electrode current collector. The negative electrode film layer includes a negative electrode active material.

[0109] As an example, the negative electrode current collector has two surfaces opposite to each other in its thickness direction, and the negative electrode film layer is disposed on any one or both of the two opposite surfaces of the negative electrode current collector.

[0110] In one embodiment, the negative electrode current collector may be a metal foil or a composite current collector. For example, as the metal foil, a copper foil may be used. The composite current collector may include a polymer material base layer and a metal layer formed on at least one surface of the polymer material substrate. The composite current collector may be formed by forming a metal material (copper, copper alloy, nickel, nickel alloy, titanium, titanium alloy, silver and silver alloy, etc.) on a polymer material substrate (such as a substrate of polypropylene (PP), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polystyrene (PS), polyethylene (PE), etc.).

[0111] In one embodiment, the negative electrode active material may adopt the negative electrode active material for batteries known in the art. As an example, the negative electrode active material may include at least one of the following materials: artificial graphite, natural graphite, soft carbon, hard carbon, silicon-based materials, tin-based materials, lithium titanate, etc. The silicon-based material may be selected from at least one of elemental silicon, silicon oxide compounds, silicon-carbon composites, silicon-nitrogen composites, and silicon alloys. The tin-based material may be selected from at least one of elemental tin, tin oxide compounds, and tin alloys. However, the present application is not limited to these materials, and other traditional materials that can be used as negative electrode active materials for batteries may also be used. These negative electrode active materials may be used alone or in combination of two or more.

[0112] In one embodiment, the negative electrode active material is a silicon-containing material. The silicon-containing material includes at least one of elemental silicon, silicon-oxygen compounds, silicon-carbon composites, silicon-nitrogen composites, silicon-containing alloys, or silicon-oxygen-carbon composite materials. By selecting a silicon-containing material as the negative electrode active material, it is beneficial to further improve the volume energy density of the battery cell 10. Combined with the structural design of the battery cell 10 in the aforementioned embodiment, the battery cell 10 can have both high energy density and excellent safety performance.

[0113] In one embodiment, the negative electrode film layer further includes a binder. The binder can be selected from at least one of styrene-butadiene rubber (SBR), polyacrylic acid (PAA), sodium polyacrylate (PAAS), polyacrylamide (PAM), polyvinyl alcohol (PVA), sodium alginate (SA), polymethacrylic acid (PMAA) and carboxymethyl chitosan (CMCS).

[0114] In one embodiment, the negative electrode film layer further includes a conductive agent, which can be selected from at least one of superconducting carbon, acetylene black, carbon black, Ketjen black, carbon dots, carbon nanotubes, graphene and carbon nanofibers.

[0115] In one embodiment, the negative electrode film layer further includes other additives, such as a thickener (eg sodium carboxymethyl cellulose (CMC-Na)).

[0116] In one embodiment, the negative electrode sheet can be prepared in the following manner: the components for preparing the negative electrode sheet are formed into a negative electrode slurry. For example, the negative electrode active material, the conductive agent, the binder and any other components are dispersed in a solvent (such as N-methylpyrrolidone) to form a negative electrode slurry. Then, the negative electrode slurry is coated on the negative electrode current collector, and after drying, cold pressing and other processes, the negative electrode sheet can be obtained.

[0117] [Positive electrode]

[0118] The positive electrode sheet includes a positive electrode current collector and a positive electrode film layer arranged on at least one surface of the positive electrode current collector, and the positive electrode film layer includes a positive electrode active material.

[0119] As an example, the positive electrode current collector has two surfaces opposite to each other in its thickness direction, and the positive electrode film layer is disposed on any one or both of the two opposite surfaces of the positive electrode current collector.

[0120] In one embodiment, the positive electrode current collector may be a metal foil or a composite current collector. For example, aluminum foil may be used as the metal foil. The composite current collector may include a polymer material base and a metal layer formed on at least one surface of the polymer material base. The composite current collector may be formed by forming a metal material (aluminum, aluminum alloy, nickel, nickel alloy, titanium, titanium alloy, silver and silver alloy, etc.) on a polymer material substrate (such as a substrate of polypropylene (PP), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polystyrene (PS), polyethylene (PE), etc.).

[0121] Examples of some positive electrode active materials have been mentioned above. In another embodiment, the positive electrode active material may also adopt positive electrode active materials for batteries that are well known in the art. As an example, the positive electrode active material may also include at least one of the following materials: lithium-containing phosphates with an olivine structure, lithium transition metal oxides, and their respective modified compounds. However, the present application is not limited to these materials, and other traditional materials that can be used as positive electrode active materials for batteries may also be used. Among them, examples of lithium transition metal oxides may include, but are not limited to, lithium cobalt oxides (such as LiCoO 2 ), lithium nickel oxide (such as LiNiO 2 ), lithium manganese oxide (such as LiMnO 2 、LiMn 2 O 4 ), lithium nickel cobalt oxide, lithium manganese cobalt oxide, lithium nickel manganese oxide, lithium nickel cobalt manganese oxide (such as LiNi 1 / 3 Co 1 / 3 Mn 1 / 3 O 2 (also referred to as NCM333), LiNi 0.5 Co 0.2 Mn 0.3 O 2 (also referred to as NCM523), LiNi 0.5 Co 0.25 Mn 0.25 O 2 (also referred to as NCM211), LiNi 0.6 Co 0.2 Mn 0.2 O 2 (also referred to as NCM622), LiNi 0.8 Co 0.1 Mn 0.1 O 2 (also referred to as NCM811), lithium nickel cobalt aluminum oxide (such as LiNi 0.85 Co 0.15 Al 0.05 O 2) and its modified compounds, etc. Examples of lithium phosphates containing olivine structures may include, but are not limited to, lithium iron phosphate (such as LiFePO 4 (also referred to as LFP), composite materials of lithium iron phosphate and carbon, lithium manganese phosphate (such as LiMnPO 4 ), at least one of a composite material of lithium manganese phosphate and carbon, lithium iron manganese phosphate, and a composite material of lithium iron manganese phosphate and carbon. The battery is accompanied by the deintercalation and consumption of Li during the charging and discharging process, and the molar content of Li in the positive electrode active material is different when the battery is discharged to different states.

[0122] In one embodiment, the positive electrode film layer further includes a binder. As an example, the binder may include at least one of polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), vinylidene fluoride-tetrafluoroethylene-propylene terpolymer, vinylidene fluoride-hexafluoropropylene-tetrafluoroethylene terpolymer, tetrafluoroethylene-hexafluoropropylene copolymer, and fluorine-containing acrylate resin.

[0123] In one embodiment, the positive electrode film layer further includes a conductive agent. As an example, the conductive agent may include at least one of superconducting carbon, acetylene black, carbon black, Ketjen black, carbon dots, carbon nanotubes, graphene, and carbon nanofibers.

[0124] In one embodiment, the positive electrode sheet can be prepared in the following manner: the components for preparing the positive electrode sheet are respectively formed into positive electrode slurries. For example, the first positive electrode active material and / or the second positive electrode active material, the conductive agent, the binder and any other components are dispersed in a solvent (such as N-methylpyrrolidone) to form a positive electrode slurry. Then, the positive electrode slurry is coated on the positive electrode current collector, and after drying, cold pressing and other processes, the positive electrode sheet can be obtained.

[0125] [Electrolyte]

[0126] The electrolyte conducts ions between the positive electrode and the negative electrode. Some examples of electrolytes have been mentioned above.

[0127] In another embodiment, the lithium salt further comprises at least one selected from lithium tetrafluoroborate, lithium perchlorate, lithium hexafluoroarsenate, lithium bis(trifluoromethanesulfonyl)imide, lithium trifluoromethanesulfonate, lithium difluorophosphate, lithium difluorooxalatoborate, lithium dioxalatoborate, lithium difluorobisoxalatophosphate and lithium tetrafluorooxalatophosphate.

[0128] In one embodiment, the solvent further comprises at least one of ethylene carbonate, propylene carbonate, diethyl carbonate, dimethyl carbonate, dipropyl carbonate, methylpropyl carbonate, ethylpropyl carbonate, butylene carbonate, fluoroethylene carbonate, propyl propionate, methyl butyrate, ethyl butyrate, 1,4-butyrolactone, cyclopentane sulfone, dimethyl sulfone, methyl ethyl sulfone and diethyl sulfone.

[0129] In one embodiment, the electrolyte includes additives. For example, the additives may include negative electrode film-forming additives, positive electrode film-forming additives, and may also include additives that can improve certain battery properties, such as additives that improve battery overcharge performance, additives that improve battery high or low temperature performance, etc.

[0130] [Isolation film]

[0131] The present application has no particular limitation on the type of isolation membrane. For example, any known porous isolation membrane with good chemical stability and mechanical stability may be selected.

[0132] In one embodiment, the material of the isolation membrane can be selected from at least one of glass fiber, non-woven fabric, polyethylene, polypropylene and polyvinylidene fluoride. The isolation membrane can be a single-layer film or a multi-layer composite film, without particular limitation. When the isolation membrane is a multi-layer composite film, the materials of each layer can be the same or different, without particular limitation. When the isolation membrane is a multi-layer composite film, the isolation membrane of the present application does not contain a PVDF coating.

[0133] [Lithium-ion battery]

[0134] The present application embodiment provides a lithium-ion battery, including the battery cell 10 in the above embodiment. The lithium-ion battery can be a single physical module including one or more battery cells 10 to provide higher voltage and capacity. When there are multiple battery cells 10, the multiple battery cells 10 are connected in series, in parallel or in hybrid through a busbar component.

[0135] In some embodiments, the lithium-ion battery may be a battery pack, and the battery includes a case and a battery cell 10 , wherein the battery cell 10 or a battery module is accommodated in the case.

[0136] In some embodiments, the box body can be used as a part of the chassis structure of the vehicle. For example, part of the box body can become at least a part of the floor of the vehicle, or part of the box body can become at least a part of the cross beam and longitudinal beam of the vehicle.

[0137] In some embodiments, the lithium-ion battery can be located in an energy storage device, which includes an energy storage container, an energy storage cabinet, and the like.

[0138] Figure 3 FIG. 1 is a schematic exploded view of a lithium-ion battery according to an embodiment of the present application. Figure 3 As shown, the lithium-ion battery 20 may include a plurality of battery cells 10 to meet different power requirements.

[0139] The lithium-ion battery 20 may also include a casing, the interior of which is a hollow structure, and a plurality of battery cells 10 are contained in the casing. The plurality of battery cells 10 are placed in the casing after being connected in parallel, in series, or in a mixed combination. The casing may include a first casing portion 31 and a second casing portion 32, which cover each other to form the casing. The shapes of the first casing portion 31 and the second casing portion 32 may be determined according to the shapes of the components contained therein, for example, they may be determined according to the shape of the combination of the plurality of battery cells 10 contained therein, and at least one of the first casing portion 31 and the second casing portion 32 may have an opening. Figure 3 As shown, the first box body 31 and the second box body 32 can both be hollow cuboids and each have an open face, the opening of the first box body 31 and the opening of the second box body 32 are arranged opposite to each other, and the first box body 31 and the second box body 32 are buckled together to form a box with a closed chamber, which can be used to accommodate multiple battery cells 10. Multiple battery cells 10 are connected in parallel, in series, or in mixed combination and placed in the box formed by the first box body 31 and the second box body 32 buckled together.

[0140] For example, Figure 3 Different from the example shown, only one of the first box body 31 and the second box body 32 may be a hollow rectangular parallelepiped with an opening, while the other may be a plate-shaped body to cover the opening. For example, if the second box body 32 is a hollow rectangular parallelepiped with an opening, and the first box body 31 is a plate-shaped body, the first box body 31 covers the opening of the second box body 32 to form a box with a closed chamber, which can be used to accommodate multiple battery cells 10.

[0141] In some embodiments, the lithium-ion battery 20 may further include other components. For example, the lithium-ion battery 20 may further include a busbar component, which may be used to achieve electrical connection between multiple battery cells 10, such as parallel connection, series connection, or mixed connection. Specifically, the busbar component may achieve electrical connection between the battery cells 10 by connecting the electrode terminals of the battery cells 10; or, the busbar component may also achieve electrical connection between the battery cells 10 by connecting other components of the battery cells 10. The busbar component may be fixed to the corresponding component of the battery cell 10 by welding, for example, it may be fixed to the electrode terminal, the sealing structure, or the housing by welding, etc., and the embodiments of the present application are not limited thereto.

[0142] The battery cells 10 can directly form a lithium-ion battery 20 , or can first form a battery module, and then multiple battery modules form a lithium-ion battery 20 .

[0143] [Electrical devices]

[0144] An embodiment of the present application provides an electrical device, comprising the lithium-ion battery described in the above embodiment.

[0145] The electrical device may be a vehicle, a mobile phone, a portable device, a laptop computer, a ship, a spacecraft, an electric toy, an electric tool, and the like. The vehicle may be a fuel vehicle, a gas vehicle, or a new energy vehicle, and the new energy vehicle may be a pure electric vehicle, a hybrid vehicle, or an extended-range vehicle, and the like; the spacecraft may include an airplane, a rocket, a space shuttle, and a spacecraft, and the like; the electric toy may include a fixed or mobile electric toy, such as a game console, an electric car toy, an electric ship toy, and an electric airplane toy, and the like; the electric tool may include a metal cutting electric tool, a grinding electric tool, an assembly electric tool, and an electric tool for railways, such as an electric drill, an electric grinder, an electric wrench, an electric screwdriver, an electric hammer, an impact drill, a concrete vibrator, and an electric planer, and the like. The embodiments of the present application do not impose any special restrictions on the above-mentioned electrical devices.

[0146] The present application provides an electrical device, which is a vehicle.

[0147] The vehicle can be a fuel vehicle, a gas vehicle or a new energy vehicle. The new energy vehicle can be a pure electric vehicle, a hybrid vehicle or an extended-range vehicle, etc. A motor, a controller and a lithium-ion battery 20 can be arranged inside the vehicle, and the controller is used to control the lithium-ion battery 20 to power the motor. For example, a lithium-ion battery 20 can be arranged at the bottom, front or rear of the vehicle. The lithium-ion battery 20 can be used to power the vehicle. For example, the lithium-ion battery 20 can be used as an operating power source for the vehicle, for the circuit system of the vehicle, for example, for the working power requirements during the start-up, navigation and operation of the vehicle. In another embodiment of the present application, the lithium-ion battery 20 can not only be used as an operating power source for the vehicle, but also as a driving power source for the vehicle, replacing or partially replacing fuel or natural gas to provide driving power for the vehicle.

[0148] Hereinafter, the embodiments of the present application will be described. The embodiments described below are exemplary and are only used to explain the present application, and should not be construed as limiting the present application. If no specific techniques or conditions are indicated in the embodiments, the techniques or conditions described in the literature in this area or the product specifications are used. If the manufacturer is not indicated in the reagents or instruments used, they are all conventional products that can be obtained commercially.

[0149] [Examples and Comparative Examples]

[0150] Example 1

[0151] Example 1

[0152] (1) Preparation of negative electrode sheet

[0153] The negative electrode active material artificial graphite, the conductive agent acetylene black, the binder styrene butadiene rubber (SBR), and the thickener sodium carboxymethyl cellulose (CMC-Na) are dissolved in deionized water at a mass ratio of 96:1.5:1.5:1.0, and the mixture is fully stirred and mixed to prepare a negative electrode slurry; the negative electrode slurry is coated on the surface of both sides of the negative electrode current collector copper foil, and then dried, cold pressed, and cut to obtain a negative electrode sheet.

[0154] (2) Preparation of positive electrode sheet

[0155] The positive electrode active material LiNi 0.65 Co 0.10 Mn 0.35 O 2 The binder polyvinylidene fluoride (PVDF) and the conductive agent (acetylene black) are mixed evenly in a mass ratio of 97.5:1.5:1, dissolved in a solvent N-methylpyrrolidone (NMP), and fully stirred and mixed to prepare a positive electrode slurry; the positive electrode slurry is evenly coated on the surface of both sides of the positive electrode current collector aluminum foil, and then dried, cold pressed and cut to obtain a positive electrode sheet.

[0156] (3) Preparation of battery cells

[0157] The positive electrode sheet, the separator, and the negative electrode sheet are stacked and wound in order to obtain an electrode assembly; the electrode assembly is placed in a shell, and an electrolyte is added. After packaging, standing, forming, aging and other processes, a battery cell 10 is obtained.

[0158] The lithium salt concentration in the electrolyte is 1.1M, and the lithium salt is LiPF 6 The carboxylic acid ester solvent used was methyl acetate, with a mass content of W = 18%; the ionic conductivity of the electrolyte was measured to be σ = 12.8 mS / cm; the dynamic viscosity η = 2.1 mm 2 The side wall of the pole of the battery cell 10 is provided with a heat absorbing material, and the surface with the largest area of ​​the battery cell is provided with a heat preservation component.

[0159] The battery cell 10 is cycle tested at room temperature (25°C-30°C). The test conditions are detailed in the test method section below. The real-time temperature T1 of the electrode terminal 121 and the real-time temperature T2 of the geometric center of the largest surface of the battery cell are monitored simultaneously during the cycle of charging the battery cell 10 to 80% SOC.

[0160] The difference between Examples 2-7 and Comparative Examples 1-3 and Example 1 is that the arrangement of the electrolyte and the battery cells is different from that of Example 1. The specific parameters are shown in Table 1.

[0161] The product parameters and performance parameters of Examples 1-7 and Comparative Examples 1-3.

[0162] Table 1: Product parameters and performance parameters of Examples 1-7 and Comparative Examples 1-3

[0163]

[0164] In Table 1, "σ" indicates the ionic conductivity of the electrolyte; "η" indicates the kinematic viscosity of the electrolyte; "√" in "Endothermic material" indicates that the side wall of the electrode terminal 121 of the battery cell 10 is affixed with endothermic material, and "×" indicates that no endothermic material is affixed; "√" in "Insulation component" indicates that the largest surface of the battery cell 10 is affixed with insulation cotton, and "×" indicates that no insulation cotton is affixed; "T1" indicates the temperature of the electrode terminal when charged to 80% SOC; "T2" indicates the temperature of the geometric center of the largest surface of the battery cell when charged to 80% SOC; "Number of cycles" indicates the number of cycles corresponding to the battery cell 10 cycling to 80% SOH in the cycle test; "Whether lithium deposition occurs" indicates whether lithium deposition occurs on the negative electrode sheet of the battery cell 10 after the cycle test when the battery cell 10 is disassembled.

[0165] According to the comparative analysis of the embodiments and the comparative examples, it can be seen that in embodiments 1-7, T1 and T2 are controlled within a limited range, and the cycle performance is better than that of comparative examples 1-3 during the fast charge cycle, and no lithium deposition occurs at the negative electrode. In the comparative example, T1 and T2 are not within the limited range, the fast charge cycle performance of the battery cell 10 deteriorates, and lithium deposition occurs at the negative electrode of some comparative examples. Therefore, through the embodiments and comparative examples of the present application, it is proved that by controlling the temperature of the electrode terminal 121 and the temperature at the geometric center of the surface with the largest area of ​​the fast charge battery cell 10 during charging within a suitable range, the fast charge cycle performance of the battery cell 10 can be effectively improved.

[0166] The following is a brief introduction to the test methods of the physical and chemical parameters and performance parameters involved in the embodiments of the present application. It should be understood that the following test methods are only examples, and other test methods known in the art may also be used for testing.

[0167] 1. Charging time test method

[0168] Place the battery cell 10 to be tested on the charging pile, adjust the state of charge of the battery cell 10 to 10% SOC (the charge is 10% of the rated charge), and then charge it on the charging pile, and record the time it takes for the lithium-ion battery to be charged to 80% SOC (80% of the rated charge), that is, the charging time of the battery cell 10.

[0169] 2. Test method for electrolyte conductivity

[0170] The test method is in accordance with HG / T 4067-2015. The conductivity of the electrolyte to be tested is tested with a conductivity meter: about 100 mL of the sample to be tested is taken from a dry, clean, corrosion-resistant sample bottle, and sealed in a constant temperature water bath at 25±0.5℃. When the temperature of the sample to be tested is constant, the sample bottle cap is replaced with a rubber stopper with an electrode inserted. When the temperature is within the range of 25±0.5℃, the data is read, which is the conductivity of the sample to be tested.

[0171] 3. Test method for temperature and temperature difference at each position of battery cell

[0172] It should be understood that any possible method may be used to measure the temperature of the battery cell 10. A resistance thermometer is used as an example below.

[0173] Place the probe of the resistance thermometer at any electrode terminal 121 and the geometric center of the largest surface of the battery cell 10. Then charge the battery cell 10. The charging process refers to the test method of cycle performance. The resistance thermometer can record the temperature change of the battery cell 10 during the charging process, and record the values ​​of T1 and T2 when the battery cell 10 is charged to 80% SOC.

[0174] 4. Test method for cross-sectional area of ​​electrode terminals

[0175] The battery cell 10 is CT scanned and the scanned image is tested. The shape and size of the electrode terminal 121 can be measured based on the scanned image. For a cylindrical electrode terminal 121, the formula S = π (d / 2) can be used. 2 , where d is the diameter of the cross section of the cylindrical electrode terminal 121. For an irregularly shaped electrode terminal 121, S can be calculated by fitting the irregularly shaped cross section into a regular shape on a computer and then using the area calculation formula for a regular shape.

[0176] 5. Test method for mass content of solvent (carboxylate)

[0177] The content of carboxylic acid ester in the electrolyte was quantitatively analyzed by organic gas chromatography analysis method with reference to standard GB / T 9722-2006.

[0178] 6. Cycle performance test method

[0179] At 25±5℃, a fully discharged battery cell was charged at a constant current of 0.33C to 10% SOC, then charged from 10% SOC to 45% SOC at 5C, then charged from 45% SOC to 50% SOC at 4.6C, charged from 50% SOC to 55% SOC at 4.3C, charged from 55% SOC to 60% SOC at 3.9C, charged from 60% SOC to 65% SOC at 3.6C, charged from 65% SOC to 70% SOC at 3.3C, charged from 70% SOC to 75% SOC at 3.1C, charged from 75% SOC to 80% SOC at 2.9C, charged from 80% SOC to 100% SOC at 0.33C, and after standing for 30min, discharged to 2.8V at 0.33C, and the discharge capacity C1 was recorded. This is one charge and discharge cycle. The battery cell is cycled for multiple cycles until the discharge capacity of the battery cell decays to 0.8C1 (ie, the battery health state reaches 80% SOH).

[0180] 7. Test method of kinematic viscosity

[0181] The viscosity of the electrolyte can be measured using instruments and methods known in the art. For example, non-Newtonian fluids can refer to the rotational viscometer method provided in the national standard GB / T22235-2008 "Determination of Liquid Viscosity". Specifically, a certain mass of electrolyte sample is placed in a sample container and tested using a rotational viscometer with the instrument model DV2TLV produced by Brookfield. At a certain temperature, the shear force exerted on the rotor when it rotates continuously at a constant speed in the sample causes the spring to generate torque, which is proportional to the viscosity, and the viscosity value is obtained. The test equipment meets the following test environmental conditions: 1. External environment of the equipment: temperature is 15-28°C, humidity is RH<80%; 2. Internal environment of the equipment: 2 / 3 of the sample container is immersed in a water bath, the medium is water, and water is used to keep the sample at a constant temperature.

[0182] Although the present application has been described with reference to preferred embodiments, various modifications may be made thereto and parts thereof may be replaced with equivalents without departing from the scope of the present application. In particular, the various technical features mentioned in the various embodiments may be combined in any manner as long as there are no structural conflicts. 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 of a lithium-ion battery, characterized in that: The time t for charging the battery cell from 10% SOC to 80% SOC satisfies: t≤20min; The battery cell includes an electrolyte, and the ion conductivity σ of the electrolyte satisfies: 9mS / cm≤σ≤25mS / cm; The battery cell includes an end cap, the end cap includes an electrode terminal, and during the charging process of the battery cell, the battery cell is configured such that a temperature T1 of the electrode terminal when charged to 80% SOC satisfies: T1≤80°C; The temperature T2 of the geometric center of the surface with the largest area of ​​the battery cell when charged to 80% SOC satisfies: T2 ≥ 30°C.

2. The battery cell according to claim 1, characterized in that: 50℃≤T1≤80℃; and / or 45℃≤T2≤65℃。 3. The battery cell according to claim 1 or 2, characterized in that: The kinematic viscosity η of the electrolyte satisfies: 1.5 mm 2 / s≤η≤2.5mm 2 / s.

4. The battery cell according to any one of claims 1 to 3, characterized in that: In the direction parallel to the end cap, the cross-sectional area S of the electrode terminal satisfies: 300 mm 2 ≤S≤500mm 2 .

5. The battery cell according to any one of claims 1 to 4, characterized in that: The battery cell comprises an electrode assembly, wherein the electrode assembly comprises a body portion and a tab, and the width of the tab is d; In a direction parallel to the end cover, the width of the battery cell is D; d / D satisfies: 1 / 5≤d / D≤1 / 3.

6. The battery cell according to any one of claims 1 to 5, characterized in that: A heat absorbing material is disposed on the electrode terminal; and / or a heat absorbing material is disposed around the electrode terminal.

7. The battery cell according to any one of claims 1 to 6, characterized in that: The electrode terminal is connected to a busbar component, and a heat absorbing material is disposed on the busbar component.

8. The battery cell according to claim 6 or 7, characterized in that: The heat absorbing material includes at least one of thermal conductive silica gel and phase change graphite.

9. The battery cell according to any one of claims 1 to 8, characterized in that: The largest surface of the battery cell is provided with a heat preservation component and / or a heating component.

10. The battery cell according to any one of claims 1 to 9, characterized in that: The electrolyte includes a carboxylate solvent, and the carboxylate solvent includes at least one of methyl formate, ethyl formate, methyl acetate, ethyl acetate, propyl acetate, methyl acrylate, and ethyl acrylate.

11. The battery cell according to any one of claims 1 to 10, characterized in that: Based on the total mass of the electrolyte, the mass fraction W1 of the carboxylic acid ester solvent satisfies: 5wt%≤W≤80wt%.

12. A lithium ion battery, characterized in that: The lithium-ion battery comprises the battery cell according to any one of claims 1 to 11.

13. An electrical device, characterized in that: The electrical device comprises the battery cell according to any one of claims 1 to 11, and / or the lithium-ion battery according to claim 12.

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