Battery cell, secondary battery, and electric device

Abstract

The embodiment of the invention provides a battery monomer, a secondary battery and a power utilization device, the battery monomer comprises a shell and an electrode assembly arranged in the shell, and the group margin q of the battery monomer is greater than or equal to 85% and less than or equal to 98%; the electrode assembly comprises a negative electrode plate, the negative electrode plate comprises a negative electrode current collector and a negative electrode film layer arranged on the surface of at least one side of the negative electrode current collector, the negative electrode film layer comprises a negative electrode active material, and the negative electrode active material comprises a silicon-containing material; the battery monomer comprises an electrolyte, and the kinematic viscosity eta of the electrolyte is greater than or equal to 1 mm < 2 > / s and less than or equal to 3 mm < 2 > / s. The battery monomer of which the negative active material comprises the silicon-containing material has good cycle performance.

Description

Technical Field

[0001] The present application relates to the field of batteries, and more specifically, to a battery cell, a secondary 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] With the development and application of secondary batteries, higher requirements are placed on the capacity of secondary batteries. Silicon-containing negative electrodes are an important development direction for high-capacity secondary batteries, but the expansion and contraction problems of silicon-containing materials seriously affect the cycle performance of secondary batteries. Therefore, how to improve the cycle performance of silicon-containing secondary 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 battery cell, a secondary battery and an electrical device, wherein the battery cell includes a silicon-containing material and has good cycle performance.

[0005] In a first aspect, a battery cell is provided, the battery cell comprising a housing and an electrode assembly disposed in the housing, the group margin q of the battery cell satisfies: 85%≤q≤98%; the electrode assembly comprises a negative electrode plate, the negative electrode plate comprises a negative electrode current collector and a negative electrode film layer disposed on a surface of at least one side of the negative electrode current collector, the negative electrode film layer comprises a negative electrode active material, the negative electrode active material comprises a silicon-containing material; the battery cell comprises an electrolyte, the kinematic viscosity η of the electrolyte satisfies, 1mm 2 / s≤η≤3mm 2 / s.

[0006] In the embodiments of the present application, in a battery cell in which the negative electrode active material includes a silicon-containing material, by controlling the group margin of the battery cell to 85%-98%, sufficient expansion space can be provided for the silicon-containing material during the cycle of the battery cell, which helps to improve the cycle performance of the battery cell; by matching an electrolyte whose viscosity meets the above range, it helps the electrolyte to infiltrate the pole piece in the direction of gravity, improves the effect of the group margin on the infiltration of the pole piece, helps to reduce the polarization of the battery cell during the cycle, and improves the phenomenon of lithium precipitation of the negative electrode pole piece. Therefore, the embodiments of the present application can effectively improve the cycle performance of the battery cell.

[0007] In a possible implementation, the silicon-containing material includes at least one of elemental silicon, silicon-carbon compounds, and silicon-oxygen compounds.

[0008] In a possible implementation, based on the total mass of the negative electrode sheet, the mass content m of silicon element satisfies: 0.5 wt% ≤ m ≤ 15 wt%; optionally, 3 wt% ≤ m ≤ 15 wt%.

[0009] In the embodiments of the present application, the content of silicon element directly affects the degree of expansion and contraction of the negative electrode active material during the cycling process of the battery cell, thereby affecting the cycling performance of the battery cell. Thus, by controlling the content of silicon element to meet the above range, the battery cell can have a high energy density and good cycling performance at the same time.

[0010] In a possible implementation, the electrode assembly is a stacked electrode assembly.

[0011] In the embodiments of the present application, through the design of the stacked electrode assembly, the space utilization rate inside the battery cell can be improved, thereby improving the influence of low group margin on the energy density of the battery cell.

[0012] In a possible implementation, the ionic conductivity σ of the electrolyte satisfies: 9 mS / cm ≤ σ ≤ 25 mS / cm.

[0013] In a possible implementation, the electrolyte includes an electrolyte salt, and the electrolyte salt includes LiFSI.

[0014] In the embodiments of the present application, by selecting LiFSI as the electrolyte salt, it is not easy to have side reactions with silicon-containing materials, and it helps to improve the ionic conductivity of the electrolyte, further improving the lithium deposition problem of the negative electrode sheet including silicon-containing materials, thereby improving the cycling performance of the battery cell.

[0015] In a possible implementation, the electrolyte includes a carboxylic ester solvent, and the carboxylic ester solvent includes at least one of methyl formate, ethyl formate, methyl acetate, ethyl acetate, propyl acetate, methyl acrylate, and ethyl acrylate.

[0016] In the embodiments of the present application, by selecting a carboxylic ester solvent, it helps to improve the ionic conductivity of the electrolyte, improve the lithium deposition problem of the negative electrode sheet including silicon-containing materials, thereby improving the cycling performance of the battery cell.

[0017] In a possible implementation, based on the total mass of the electrolyte, the mass content W1 of the carboxylic ester solvent satisfies: 30 wt% ≤ W1 ≤ 80 wt%.

[0018] In a possible implementation, 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.

[0019] In a possible implementation, the battery cell includes a positive electrode plate, the positive electrode plate includes a positive electrode active material, and the positive electrode active material includes a lithium transition metal oxide.

[0020] In a possible implementation, the liquid injection coefficient a of the battery cell satisfies: 2.3 g / Ah ≤ a ≤ 2.5 g / Ah.

[0021] In the embodiments of the present application, when the positive electrode active material includes a lithium transition metal oxide, by matching an electrolyte with a viscosity and ionic conductivity within the above ranges, the electrolyte can have a high ionic transport rate. When the amount of the electrolyte is fixed, the problem of insufficient lithium ion transport channels caused by a low liquid injection coefficient can be improved by increasing the lithium ion transport rate, ensuring the normal progress of the electrochemical reaction. Thus, the liquid injection coefficient of the battery cell can be reduced, providing more space for the expansion and contraction of the negative electrode active material and helping to improve the cycle performance of the battery cell.

[0022] In a second aspect, a secondary battery is provided, and the lithium ion battery includes the battery cell in any possible implementation of the first aspect.

[0023] In a third aspect, an electrical device is provided, and the electrical device includes the battery cell in any possible implementation of the first aspect, and / or the secondary battery in the second aspect. BRIEF DESCRIPTION OF THE DRAWINGS

[0024] To more clearly illustrate the technical solutions in 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 those of ordinary skill in the art, other drawings can be obtained based on the drawings without creative efforts.

[0025] Figure 1 It is a schematic cross-sectional view of a battery cell.

[0026] Figure 2 It is a schematic structural diagram of a stacked electrode assembly.

[0027] Figure 3 It is a schematic structural diagram of another stacked electrode assembly.

[0028] Figure 4 It is a schematic structural diagram of a battery cell.

[0029] Figure 5 It is a schematic diagram of another secondary battery of the present application. DETAILED DESCRIPTION OF THE EMBODIMENTS

[0030] Hereinafter, embodiments of the battery cell, secondary battery, and electrical device of the present application will be specifically disclosed with appropriate reference to the accompanying drawings. However, there may be cases where unnecessary details are omitted. For example, there are cases where details of well-known matters are omitted and repeated descriptions of actually identical structures are omitted. This is to prevent the following description from becoming unnecessarily lengthy and to facilitate understanding by those skilled in the art. In addition, the accompanying drawings and the following description are provided to enable those skilled in the art to fully understand the present application and are not intended to limit the subject matter recited in the claims.

[0031] The "range" disclosed in the present application is defined in the form of a lower limit and an upper limit. A given range is defined by selecting a lower limit and an upper limit, and the selected lower limit and upper limit define the boundary of a particular range. The ranges defined in this way can include the end values or not include the end values, and can be combined arbitrarily, that is, any lower limit can be combined with any upper limit to form a range. For example, if ranges of 60-120 and 80-110 are listed for a specific parameter, ranges of 60-110 and 80-120 are also contemplated. In addition, if the minimum range values 1 and 2 are listed, and if the maximum range values 3, 4, and 5 are listed, then the following ranges are all contemplated: 1-3, 1-4, 1-5, 2-3, 2-4, and 2-5. In the present application, unless otherwise specified, the numerical range "a-b" represents an abbreviated representation of any real number combination between a and b, where a and b are both real numbers. For example, the numerical range "0-5" means that all real numbers between "0-5" have been fully listed herein, and "0-5" is only an abbreviated representation of these numerical combinations. Additionally, when stating that a certain parameter is an integer ≥2, it is equivalent to disclosing that the parameter is, for example, the integers 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, etc.

[0032] In the description of the present application, it should be noted that unless otherwise specified, the meaning of "a plurality of" is two or more; the orientation or positional relationship indicated by terms such as "upper", "lower", "left", "right", "inner", "outer", etc. is only for the convenience of describing the present application and simplifying the description, and does not indicate or imply that the device or element referred to must have a specific orientation, be constructed and operated in a specific orientation, and therefore cannot be construed as a limitation of the present application. In addition, terms such as "first", "second", "third", etc. are only used for descriptive purposes and cannot be construed as indicating or implying relative importance.

[0033] If there is no special specification, in the present 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) while B is true (or exists); or both A and B are true (or exist).

[0034] Unless otherwise specified, all steps of this application can be carried out 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) carried out sequentially, or may also include steps (b) and (a) carried out sequentially. For example, when it is mentioned that the method may further include step (c), it means that step (c) can be added to the method in any order. For example, the method may include steps (a), (b), and (c), or may also include steps (a), (c), and (b), or may include steps (c), (a), and (b), etc.

[0035] Unless otherwise specified, all embodiments and optional embodiments of this application can be combined with each other to form new technical solutions.

[0036] Unless otherwise specified, any undefined terms have their generally recognized meanings in the art.

[0037] Next, embodiments of this application will be introduced.

[0038] In recent years, secondary batteries have been widely used in many fields such as power tools, electronic products, electric vehicles, aerospace, etc. due to their high energy density and long service life, and thus have achieved great development. Generally, a secondary battery includes a positive electrode plate, a negative electrode plate, an electrolyte, and a separator. During the charge and discharge process of the battery, active ions are embedded and extracted back and forth between the positive electrode plate and the negative electrode plate. Among them, the electrolyte plays a role in conducting active ions between the positive electrode plate and the negative electrode plate. The separator is disposed between the positive electrode plate and the negative electrode plate, preventing short circuit between the positive and negative electrodes while allowing active ions to pass through, enabling the normal progress of the electrochemical reaction of the secondary battery.

[0039] Taking a lithium-ion battery as an example, a lithium-ion battery is a typical secondary battery. Since it relies on the chemical reaction of lithium ions deintercalating and intercalating between the positive and negative electrodes, a lithium-ion battery is also called a rocking-chair battery. During the charging process of a lithium-ion battery, lithium ions are extracted from the positive electrode active material, move through the conduction of the electrolyte to the negative electrode, and are embedded in the negative electrode active material; during the discharging process, lithium ions are extracted from the negative electrode active material, move through the conduction of the electrolyte to the positive electrode, and are embedded in the positive electrode active material.

[0040] It should be understood that the "lithium intercalation" and "intercalation" processes described in this application refer to the process of lithium ions being intercalated into the positive electrode active material or the negative electrode active material due to an electrochemical reaction, and the "extraction", "lithium extraction", and "deintercalation" processes described in this application refer to the process of lithium ions being extracted from the positive electrode active material or the negative electrode active material due to an electrochemical reaction.

[0041] With the development of secondary batteries and the continuous expansion of application scenarios, higher requirements are put forward for the energy density of battery cells. Active materials are one of the direct factors affecting the energy density of battery cells. Among them, for negative electrode active materials, silicon-containing materials have received extensive attention because of their high specific capacity, which can greatly improve the energy density of battery cells. However, at the same time, the volume expansion problem of silicon-containing materials is particularly serious. The silicon-containing materials expand in volume during the lithium insertion process and contract in volume during the lithium deinsertion process. Similarly, the positive electrode active materials also have corresponding expansion and contraction processes during the cycling process. The combined effect of the two leads to the macroscopic expansion and contraction of the electrode assembly during the cycling of the battery cell. During the contraction process of the electrode assembly, the electrolyte will be extruded. If this part of the extruded electrolyte cannot be sucked back in time during the expansion process, it will cause insufficient wettability of the electrolyte to the electrode assembly, affect the transport of lithium ions during charge and discharge, and then lead to lithium deposition on the negative electrode plate and a sharp decline in the cycling performance of the battery cell.

[0042] For a battery cell with a negative electrode active material including a silicon-containing material, since the degree of expansion and contraction of the negative electrode plate is larger than that of the negative electrode plate using ordinary negative electrode materials, it has a greater impact on the cycling performance of the battery cell.

[0043] In view of this, the embodiments of the present application provide a battery cell, a secondary battery, and an electrical device. The battery cell with a negative electrode active material including a silicon-containing material has good cycling performance.

[0044] Next, the battery cell provided by the present application will be introduced.

[0045] [Battery cell]

[0046] First, a battery cell is provided. The battery cell includes a housing and an electrode assembly disposed within the housing. The group margin q of the battery cell satisfies: 85% ≤ q ≤ 98%; optionally, 85% ≤ q ≤ 90%; the electrode assembly includes a negative electrode plate, and the negative electrode plate includes a negative electrode current collector and a negative electrode film layer disposed on at least one side surface of the negative electrode current collector. The negative electrode film layer includes a negative electrode active material, and the negative electrode active material includes a silicon-containing material; the battery cell includes an electrolyte, and the kinematic viscosity η of the electrolyte satisfies 1 mm 2 / s ≤ η ≤ 3 mm 2 / s.

[0047] Specifically, the group margin q can be 85%, 86%, 87%, 88%, 89%, 90%, 91%, 92%, 93%, 94%, 95%, 96%, 97%, 98%, or its value is within the range obtained by combining any two of the above values. η can be 1 mm 2 / s, 1.2 mm 2 / s, 1.4 mm 2 / s, 1.6 mm2 / s, 1.8 mm 2 / s, 2 mm 2 / s, 2.2 mm 2 / s, 2.4 mm 2 / s, 2.6 mm 2 / s, 2.8 mm 2 / s, 3 mm 2 / s, or its value is within the range obtained by any combination of the above two values. It should be understood that parameters such as the ionic conductivity and viscosity of the electrolyte are related to temperature. Unless otherwise specified, the ionic conductivity and viscosity mentioned in this application refer to the ionic conductivity and viscosity of the electrolyte measured at 25°C. However, considering the normal errors in the test conditions, the above ranges of ionic conductivity and viscosity are not limited to 25°C, and can also be the ionic conductivity and viscosity measured at 20°C - 30°C. The test results within this temperature range have relatively small differences and can be equivalent to the test results at 25°C.

[0048] During the cycling process of a battery cell with a negative electrode active material including a silicon-containing material, serious expansion and contraction are likely to occur. Reducing the group margin of the battery cell can improve this problem. However, if the group margin is too small, the distance between the electrode sheets will continuously increase with the cycling of the battery cell, exacerbating the polarization inside the battery cell and also being unfavorable to the cycling performance of the battery cell. In this embodiment, by controlling the group margin of the battery cell within a relatively small range of 85% - 98%, sufficient expansion space can be provided for the silicon-containing material during the cycling process of the battery cell, reducing the risk of deformation of the battery cell caused by the expansion of the silicon-containing material, and improving the cycling performance of the battery cell.

[0049] When the group margin of the battery cell is controlled between 85% and 98%, on the one hand, the liquid level of the electrolyte inside the outer shell will decrease, resulting in the electrode assembly located above the liquid level of the electrolyte needing to rely on the capillary action of the electrolyte to infiltrate upward in the direction of gravity. The "liquid climbing" is difficult, the infiltration is difficult, and it is easy to polarize and deposit lithium during the cycling process of the battery cell, affecting the cycling performance of the battery cell. On the other hand, the electrolyte usually includes organic solvents, which makes the viscosity of the electrolyte generally large and cannot be sucked back in time during the expansion process of the silicon-containing material, resulting in insufficient infiltration of the electrode assembly and being unfavorable to the cycling performance of the battery cell. Therefore, in this embodiment, for a high-capacity battery cell with a silicon-containing material as the negative electrode active material, by matching an electrolyte with a viscosity within the above range, the lower viscosity can reduce the liquid climbing difficulty of the electrolyte in the direction of gravity and enable the electrolyte to be sucked back in time during the expansion process of the silicon-containing material, improving the wettability of the electrolyte to the electrode assembly during the cycling process of the battery cell, providing sufficient lithium-ion exchange paths for the charge and discharge reactions, and effectively improving the cycling performance of the battery cell. Therefore, the battery cell provided in this embodiment can improve the cycling performance of the battery cell through a smaller group margin design and a low-viscosity electrolyte when the negative electrode active material includes a silicon-containing material.

[0050] Figure 1 It is a schematic cross-sectional view of a battery cell. Figure 2 It is a schematic structural diagram of a stacked electrode assembly. Figure 3 It is a schematic structural diagram of another stacked electrode assembly. Figure 4 It is a schematic structural diagram of a battery cell.

[0051] Reference Figures 1-4 , specifically, the battery cell 10 includes an outer shell 11 and a stacked electrode assembly 12 disposed in the outer shell. The stacked electrode assembly 12 includes a positive electrode tab 121, a negative electrode tab 122, and a separator 123 disposed between the positive electrode tab 121 and the negative electrode tab 122. The outer shell 11 can be of various shapes and sizes, such as cuboid, cylindrical, hexagonal prism, etc. Specifically, the shape of the outer shell 11 can be determined according to the specific shape and size of the electrode assembly 12. The material of the outer shell 11 can be various, such as copper, iron, aluminum, stainless steel, aluminum alloy, etc., and the embodiments of the present application do not make special restrictions on this.

[0052] The "group margin" mentioned in this article refers to the ratio of the thickness L1 of the electrode assembly 12 to the thickness L2 inside the outer shell 11 in the cross-section of the battery cell 10, and can be expressed as the percentage of the thickness L1 of the electrode assembly 12 occupying the thickness L2 inside the outer shell 11. Among them, the thickness L2 inside the outer shell does not include the thickness of the outer shell itself. As Figure 1As shown, L1 is the thickness of the electrode assembly 12, and L2 is the thickness inside the housing 11. The value of the group margin q can be expressed as (L1 / L2)×100%.

[0053] In one embodiment, the electrode assembly 12 is a laminated electrode assembly.

[0054] Generally speaking, since there is no corner area, the laminated electrode assembly has higher space utilization and group margin compared to the wound electrode assembly, which helps to improve the energy density of the battery cell 10.

[0055] When the group margin of the battery cell 10 is controlled between 85% and 98%, the energy density of the battery cell 10 is affected. Therefore, in this embodiment, a laminated electrode assembly 12 is adopted to improve the space utilization inside the housing 11 and improve the influence of the smaller group margin on the energy density of the battery cell 10.

[0056] In one embodiment, as Figure 2 shown, the laminated electrode assembly 12 includes a plurality of positive electrode plates 121 and a plurality of negative electrode plates 122. The plurality of positive electrode plates 121 and the plurality of negative electrode plates 122 are alternately stacked in the direction indicated by the arrow in the figure.

[0057] In another embodiment, as Figure 3 shown, the laminated electrode assembly 12 includes a plurality of positive electrode plates 121 and a negative electrode plate 122. The negative electrode plate 122 may include at least one bent section and a plurality of stacked sections. Each bent section is used to connect two stacked sections. The plurality of positive electrode plates 121 and the plurality of stacked sections of the negative electrode plate 122 are alternately stacked in the direction indicated by the arrow in the figure to form another form of the laminated electrode assembly 12. Alternatively, the laminated electrode assembly 12 includes a plurality of negative electrode plates 122 and a positive electrode plate 121. The positive electrode plate 121 includes at least one bent section and a plurality of stacked sections. Each bent section is used to connect two stacked sections. The plurality of negative electrode plates 122 and the plurality of stacked sections of the positive electrode plate 121 are alternately stacked in the direction indicated by the arrow in the figure.

[0058] In one embodiment, the silicon-containing material includes at least one of elemental silicon, silicon carbide compound, and silicon oxide compound.

[0059] Specifically, the elemental silicon can be silicon nanoparticles, silicon nanowires, or silicon nanotubes. The silicon carbide compound can be a carbon-coated silicon material with a core-shell structure, a silicon-carbon tube composite material, a silicon-amorphous carbon composite material, etc. The silicon oxide compound can be silicon monoxide, etc.

[0060] In one embodiment, based on the total mass of the negative electrode film layer, the mass content m of silicon element satisfies: 0.5wt% ≤ m ≤ 15wt%; optionally, 3wt% ≤ m ≤ 15wt%.

[0061] Specifically, m can be 0.5 wt%, 1 wt%, 2 wt%, 2.5 wt%, 3 wt%, 3.5 wt%, 4 wt%, 4.5 wt%, 5 wt%, 5.5 wt%, 6 wt%, 6.5 wt%, 7 wt%, 7.5 wt%, 8 wt%, 8.5 wt%, 9 wt%, 9.5 wt%, 10 wt%, 10.5 wt%, 11 wt%, 11.5 wt%, 12 wt%, 12.5 wt%, 13 wt%, 13.5 wt%, 14 wt%, 14.5 wt%, 15 wt%, or a value within the range obtained by combining any two of the above values.

[0062] The mass content of silicon element in the negative electrode sheet directly affects the degree of expansion and contraction of the negative electrode active material during the cycling process of the battery cell 10. The higher the content of silicon element, the higher the energy density of the battery cell 10, and the greater the degree of expansion and contraction of the stacked electrode assembly 12. In this embodiment, by controlling the mass content of silicon element in the negative electrode film layer within a suitable range, on the one hand, the battery cell 10 has a high energy density, and on the other hand, the degree of expansion and contraction of the stacked electrode assembly 12 is within a suitable range. Thus, the battery cell 10 can have both a high energy density and good cycling performance.

[0063] In one embodiment, the electrolyte includes an electrolyte salt, and the electrolyte salt includes LiFSI.

[0064] Specifically, LiFSI is lithium bis(fluorosulfonyl)imide, which has a higher lithium ion transference number than LiPF6 and is not easily reactive with silicon-containing materials to generate gas. Thus, by selecting LiFSI as the lithium salt in this embodiment, it helps to improve the ionic conductivity of the electrolyte, making the diffusion rate of lithium ions in the electrolyte faster, and enabling them to quickly move to the active reaction sites during the expansion and contraction process of the stacked electrode assembly 12, thereby improving the problem of lithium deposition and enhancing the cycling performance of the battery cell 10. In addition, its non-reactivity with silicon-containing materials to generate gas also helps to reduce the expansion of the battery cell 10 during the cycling process, lower the risk of damage to the outer shell 11 of the battery cell 10 and leakage of liquid, and contribute to improving the safety performance of the battery cell 10.

[0065] In one embodiment, the electrolyte includes a carboxylic ester solvent, and the carboxylic ester solvent includes at least one of methyl formate, ethyl formate, methyl acetate, ethyl acetate, propyl acetate, methyl acrylate, and ethyl acrylate.

[0066] Specifically, carboxylic ester solvents have relatively low density and viscosity, and relatively high ionic conductivity. In this embodiment, by selecting carboxylic ester solvents as at least part of the electrolyte solvent, the problem of difficult reabsorption of the electrolyte during the expansion process of the electrode assembly can be improved, the difficulty of "creeping" of the electrolyte can be reduced, and the migration rate of lithium ions in the electrolyte can be increased. Thereby, the internal polarization within the battery cell 10 is reduced, and the cycle performance of the battery cell 10 is improved.

[0067] In one embodiment, based on the total mass of the electrolyte, the mass content W1 of the carboxylic ester solvent satisfies: 30 wt% ≤ W1 ≤ 80 wt%.

[0068] Specifically, W1 can be 30 wt%, 35 wt%, 40 wt%, 45 wt%, 50 wt%, 55 wt%, 60 wt%, 65 wt%, 70 wt%, 75 wt%, 80 wt%, or a value within the range obtained by combining any two of the above values. The higher the mass content of the carboxylic ester solvent, the lower the viscosity of the electrolyte and the higher the ionic conductivity. In addition, considering some usage scenarios with relatively high temperatures, the carboxylic ester solvent is prone to side reactions to generate gas at relatively high temperatures, which has a certain impact on the cycle performance of the battery cell 10. Thereby, in this embodiment, by controlling the mass content of the carboxylic ester solvent within the above range, while reducing the viscosity of the electrolyte and increasing the conductivity of the electrolyte, the cycle performance of the battery cell 10 in application scenarios with relatively high temperatures can be improved.

[0069] In one embodiment, the electrolyte includes carbonate solvents, and the carbonate solvents include at least one of ethylene carbonate, propylene carbonate, ethyl methyl carbonate, and dimethyl carbonate.

[0070] Specifically, carbonate solvents have relatively low viscosity, relatively high dielectric constant, and good electrochemical stability. The relatively low viscosity is conducive to the rapid migration of lithium ions in the electrolyte; the relatively high dielectric constant is conducive to increasing the solubility of lithium salts in the electrolyte, providing sufficient lithium ion kinetics for the electrochemical reaction; good electrochemical stability helps to increase the working voltage range of the battery cell 10, thereby increasing the capacity of the battery cell 10. Thereby, in this embodiment, on the basis of selecting carboxylic ester solvents as part of the electrolyte solvent, by combining carbonate solvents as part of the electrolyte solvent, it helps to reduce the viscosity of the electrolyte, increase lithium ion kinetics, thereby reducing the internal polarization within the battery cell 10, improving the cycle performance of the battery cell 10, and also helping to increase the capacity of the battery cell 10.

[0071] In one embodiment, the laminated electrode assembly 12 includes a positive electrode tab 121, the positive electrode tab 121 includes a positive electrode current collector and a positive electrode film layer disposed on at least one side surface of the positive electrode current collector, the positive electrode film layer includes a positive electrode active material, and the positive electrode active material includes a lithium transition metal oxide.

[0072] Specifically, the lithium transition metal oxide refers to a class of oxides including lithium elements and transition metal elements. Structurally, it includes ternary materials with a layered structure, LiCoO2, LiNiO2, etc., and also includes LiMnO2, LiMn2O4, etc. with a spinel structure. The ternary material refers to a lithium transition metal oxide including three different transition metal elements. It should be understood that trace amounts of other transition metal elements can also be doped in the ternary material, and the ternary material doped with other transition metal elements is generally considered to still belong to the ternary material. The lithium transition metal oxide usually has a relatively high specific capacity.

[0073] In this embodiment, when the group margin of the battery cell 10 is relatively low, using a lithium transition metal oxide as at least part of the positive electrode active material helps to further improve the energy density of the battery cell 10 and enables the battery cell 10 with high energy density to have good cycling performance.

[0074] In one embodiment, the ionic conductivity σ of the electrolyte satisfies: 9 mS / cm ≤ σ ≤ 25 mS / cm.

[0075] σ can be 9 mS / cm, 10 mS / cm, 11 mS / cm, 12 mS / cm, 13 mS / cm, 14 mS / cm, 15 mS / cm, 16 mS / cm, 17 mS / cm, 18 mS / cm, 19 mS / cm, 20 mS / cm, 21 mS / cm, 22 mS / cm, 23 mS / cm, 24 mS / cm, 25 mS / cm, or its value is within the range obtained by combining any two of the above values. The electrolyte with ionic conductivity within this range has good ion transport rate, enabling lithium ions to move quickly in the electrolyte, which also helps to improve the polarization in the electrochemical reaction process and helps to enhance the cycling performance of the battery cell 10.

[0076] In one embodiment, the liquid injection coefficient a of the battery cell 10 satisfies: 2.3 g / Ah ≤ a ≤ 2.5 g / Ah.

[0077] Specifically, a can be 2.3 g / Ah, 2.35 g / Ah, 2.4 g / Ah, 2.45 g / Ah, 2.5 g / Ah, or its value is within the range obtained by combining any two of the above values. The preparation process flow of the battery cell 10 is usually to first place the laminated electrode assembly 12 impregnated in the electrolyte into the housing, inject the electrolyte into the housing, and then perform encapsulation. In this process, the injection coefficient is determined by the amount of electrolyte injected and is a key parameter in the lithium-ion battery manufacturing process.

[0078] For the battery cell 10 with a group margin in the range of 85%-98%, theoretically, a larger injection coefficient is required to make the electrolyte have sufficient height in the outer shell 11 to fully impregnate the laminated electrode assembly 12, provide sufficient ion transport paths for the electrochemical reaction, reduce the polarization inside the battery cell 10, and improve its cycling performance. However, for the battery cell 10 with a negative electrode active material including a silicon-containing material, more electrolyte will occupy the expansion space for the silicon-containing material to expand during cycling, increasing the leakage risk of the battery cell 10 and being unfavorable to the cycling performance of the battery cell 10. In this embodiment, by matching the aforementioned electrolyte with low viscosity and high ionic conductivity, the injection coefficient of the battery cell 10 can be reduced. The possible principle is that the electrolyte with an ionic conductivity in the range of 9 mS / cm - 25 mS / cm helps to improve the transport rate of lithium ions in the electrolyte. Thus, the problem of insufficient lithium ion transport channels caused by a low injection coefficient can be improved by increasing the ion transport rate, ensuring the normal progress of the electrochemical reaction. This smaller injection coefficient can provide more space for the expansion and contraction of the laminated electrode assembly 12 while meeting the impregnation requirements of the laminated electrode assembly 12. Thus, the cycling performance of the battery cell 10 is further improved.

[0079] Next, a more specific introduction to the components in the battery cell 10 of the present application will be given.

[0080] [Negative electrode plate]

[0081] The negative electrode plate 122 generally includes a negative electrode current collector and a negative electrode film layer provided on at least one surface of the negative electrode current collector. The negative electrode film layer includes a negative electrode active material.

[0082] As an example, the negative electrode current collector has two surfaces opposite to each other in its own thickness direction, and the negative electrode film layer is provided on either or both of the two opposite surfaces of the negative electrode current collector.

[0083] In one embodiment, the negative electrode current collector may be a metal foil or a composite current collector. For example, as the metal foil, 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 (such as 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.).

[0084] In one embodiment, in addition to the silicon-containing material in the foregoing embodiment, the negative electrode active material may be a negative electrode active material for a battery well-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, tin-based materials, and lithium titanate, etc. The tin-based material may be selected from at least one of elemental tin, tin oxides, and tin alloys. However, the present application is not limited to these materials, and other conventional materials that can be used as the negative electrode active material of the battery may also be used. These negative electrode active materials may be used alone or in combination of two or more.

[0085] In one embodiment, the negative electrode film layer further includes a binder. The binder may 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).

[0086] In one embodiment, the negative electrode film layer further includes a conductive agent. The conductive agent may be selected from at least one of superconducting carbon, acetylene black, carbon black, Ketjen black, carbon dots, carbon nanotubes, graphene, and carbon nanofibers.

[0087] In one embodiment, the negative electrode film layer further includes other additives, such as thickeners (such as sodium carboxymethyl cellulose (CMC-Na)), etc.

[0088] In one embodiment, the negative electrode plate 122 may be prepared in the following manner: forming a negative electrode slurry from the components for preparing the negative electrode plate 122. For example, dispersing the negative electrode active material, the conductive agent, the binder, and any other components in a solvent (such as N-methylpyrrolidone) to form a negative electrode slurry. Then, coating the negative electrode slurry on the negative electrode current collector, and after processes such as drying and cold pressing, the negative electrode plate 122 can be obtained.

[0089] [Positive electrode plate]

[0090] The positive electrode plate 121 includes a positive electrode current collector and a positive electrode film layer provided on at least one surface of the positive electrode current collector, and the positive electrode film layer includes a positive electrode active material.

[0091] As an example, the positive electrode current collector has two surfaces opposite to each other in its own thickness direction, and the positive electrode film layer is provided on any one or both of the two opposite surfaces of the positive electrode current collector.

[0092] In one embodiment, the positive electrode current collector can be a metal foil or a composite current collector. For example, as the metal foil, aluminum foil can be used. The composite current collector can include a polymer material base layer and a metal layer formed on at least one surface of the polymer material base layer. The composite current collector can be formed by forming a metal material (such as 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.).

[0093] In another embodiment, in addition to the lithium transition metal oxides and lithium-containing phosphates already mentioned in the foregoing embodiments, the positive electrode active material can also adopt positive electrode active materials for batteries well known in the art. As an example, the positive electrode active material can also include at least one of the following materials: modified compounds of lithium-containing phosphates, modified compounds of lithium transition metal oxides. However, the present application is not limited to these materials, and other conventional materials that can be used as battery positive electrode active materials can also be used. Among them, examples of lithium transition metal oxides can include, but are not limited to, lithium nickel cobalt oxides, lithium manganese cobalt oxides, lithium nickel manganese oxides, lithium nickel cobalt manganese oxides (such as LiNi 1 / 3 Co 1 / 3 Mn 1 / 3 O2 (which can also be abbreviated as NCM333), LiNi 0.5 Co 0.2 Mn 0.3 O2 (which can also be abbreviated as NCM523), LiNi 0.5 Co 0.25 Mn 0.25 O2 (which can also be abbreviated as NCM211), LiNi 0.6 Co 0.2 Mn 0.2 O2 (which can also be abbreviated as NCM622), LiNi 0.8 Co 0.1 Mn 0.1 O2 (which can also be abbreviated as NCM811), lithium nickel cobalt aluminum oxide (such as LiNi 0.85 Co 0.15 Al 0.05At least one of O2) and its modified compounds, etc. Examples of the lithium-containing phosphate may include, but are not limited to, at least one of a composite material of lithium iron phosphate and carbon, lithium manganese phosphate (such as LiMnPO4), a composite material of lithium manganese phosphate and carbon, and a composite material of lithium manganese iron phosphate and carbon. During the charge and discharge process of the battery, the insertion and extraction and consumption of Li will occur, and the molar content of Li in the positive electrode active material is different when the battery is discharged to different states. In the enumeration of the positive electrode active material in this application, the molar content of Li is the initial state of the material, that is, the state before feeding. When the positive electrode active material is applied to the battery system, after charge and discharge cycles, the molar content of Li will change. In the enumeration of the positive electrode active material in this application, the molar content of O is only the ideal state value, and the release of oxygen from the lattice will cause the molar content of O to change, and the actual molar content of O will fluctuate.

[0094] 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 fluorinated acrylate resin.

[0095] 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.

[0096] In one embodiment, the positive electrode plate 121 can be prepared in the following manner: The components used to prepare the positive electrode plate 121 are respectively formed into a positive electrode slurry. 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 processes such as drying and cold pressing, the positive electrode plate 121 can be obtained.

[0097] [Electrolyte]

[0098] The electrolyte plays a role in conducting ions between the positive electrode plate and the negative electrode plate. This application does not specifically limit the type of electrolyte, and it can be selected according to requirements. The electrolyte includes an electrolyte salt and a solvent.

[0099] In some embodiments, the electrolyte salt may also be selected from at least one of lithium hexafluorophosphate, lithium tetrafluoroborate, lithium perchlorate, lithium hexafluoroarsenate, lithium bis(trifluoromethanesulfonyl)imide, lithium trifluoromethanesulfonate, lithium difluorophosphate, lithium difluorooxalate borate, lithium bis(oxalate) borate, lithium difluorobis(oxalate) phosphate, and lithium tetrafluorooxalate phosphate.

[0100] In some embodiments, the solvent may be selected from at least one of ethylene carbonate, propylene carbonate, ethyl methyl carbonate, diethyl carbonate, dimethyl carbonate, dipropyl carbonate, methyl propyl carbonate, ethyl propyl carbonate, butylene carbonate, fluoroethylene carbonate, ethyl propionate, propyl propionate, methyl butyrate, ethyl butyrate, 1,4-butyrolactone, sulfolane, dimethyl sulfone, methyl ethyl sulfone and diethyl sulfone.

[0101] In some embodiments, the electrolyte may also optionally include 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 performance, such as additives for improving the overcharge performance of the battery, additives for improving the high-temperature or low-temperature performance of the battery, and the like.

[0102] [Separator membrane]

[0103] This application does not particularly limit the type of the separator membrane 123. For example, any well-known porous structure separator membrane 123 with good chemical stability and mechanical stability can be selected.

[0104] In one embodiment, the material of the separator membrane 123 may be selected from at least one of glass fiber, non-woven fabric, polyethylene, polypropylene and polyvinylidene fluoride. The separator membrane 123 may be a single-layer film or a multi-layer composite film, without particular limitation. When the separator membrane 123 is a multi-layer composite film, the materials of each layer may be the same or different, without particular limitation.

[0105] In one embodiment, the negative electrode plate 122, the positive electrode plate 121 and the separator 123 may be made into a stacked electrode assembly 12 by a stacking process.

[0106] This application does not particularly limit the shape of the battery cell 10, which may be cylindrical, square or any other shape.

[0107] [Secondary battery]

[0108] The embodiment of this application provides a secondary battery 2, including the battery cell 10 in the above embodiment. The secondary battery 2 may be a single physical module including one or more battery cells 10 to provide a higher voltage and capacity. When there are multiple battery cells 10, the multiple battery cells 10 are connected in series, parallel or in a hybrid connection through a bus bar component.

[0109] In some embodiments, the housing 20 of the secondary battery 2 may be a part of the chassis structure of a vehicle. For example, a part of the housing 20 may become at least a part of the vehicle floor, or a part of the housing may become at least a part of the cross beam and longitudinal beam of the vehicle.

[0110] In some embodiments, the secondary battery 2 may be located in an energy storage device. The energy storage device includes an energy storage container, an energy storage cabinet, etc.

[0111] Figure 5 This is a schematic diagram of another secondary battery 2 of the present application. As Figure 5 shown, the secondary battery 2 may include a plurality of battery cells 10 to meet different power usage requirements.

[0112] The secondary battery 2 may further include a box body 20. The interior of the box body 20 is a hollow structure, and a plurality of battery cells 10 are accommodated in the box body 20. For example, a plurality of battery cells 10 are connected in parallel or in series or in a mixed connection combination and then placed in the box body 20. The box body 20 may include a first box body part 201 and a second box body part 202. The first box body part 201 and the second box body part 202 are covered with each other to form the box body 20. The shapes of the first box body part 201 and the second box body part 202 may be determined according to the shapes of the components accommodated inside. For example, they may be determined according to the shape of the combination of a plurality of battery cells 10 accommodated inside. At least one of the first box body part 201 and the second box body part 202 has an opening. For example, as Figure 5 shown, the first box body part 201 and the second box body part 202 may both be hollow cuboids and each has an opening surface. The opening of the first box body part 201 and the opening of the second box body part 202 are arranged opposite to each other, and the first box body part 201 and the second box body part 202 are buckled with each other to form a box body 20 with a closed chamber, and this chamber can be used to accommodate a plurality of battery cells 10. A plurality of battery cells 10 are connected in parallel or in series or in a mixed connection combination and then placed in the box body 20 formed after the first box body part 201 and the second box body part 202 are buckled.

[0113] For another example, different from Figure 5 shown, only one of the first box body part 201 and the second box body part 202 may be a hollow cuboid with an opening, and the other may be a plate-shaped one to cover the opening. Taking the second box body part 202 as a hollow cuboid with an opening and the first box body part 201 as a plate-shaped one as an example, then the first box body part 201 covers the opening of the second box body part 202 to form a box body 20 with a closed chamber, and this chamber can be used to accommodate a plurality of battery cells 10.

[0114] In some embodiments, the secondary battery 2 may further include other components. For example, the secondary battery 2 may further include a current collecting component, and the current collecting component can be used to achieve electrical connection between a plurality of battery cells 10, such as parallel connection or series connection or mixed connection. Specifically, the current collecting component can achieve electrical connection between battery cells 10 by connecting the electrode terminals of the battery cells 10; or, the current collecting component can also achieve electrical connection between battery cells 10 by connecting other components of the battery cells 10. The current collecting component can be fixed to the corresponding components of the battery cells 10 by welding. For example, it can be fixed to the electrode terminals, the sealing structure or the housing, etc. by welding. The embodiments of the present application are not limited thereto.

[0115] The battery cell 10 can directly form the secondary battery 2, or can first form a battery module, and then multiple battery modules form the secondary battery 2.

[0116] [Power-consuming device]

[0117] An embodiment of the present application provides a power-consuming device, including the secondary battery 2 described in the above embodiment.

[0118] The power-consuming device can be a vehicle, a mobile phone, a portable device, a laptop computer, a ship, a spacecraft, an electric toy, an electric tool, etc. 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.; the spacecraft includes an airplane, a rocket, a space shuttle, a spaceship, etc.; the electric toy includes a fixed or mobile electric toy, for example, a game console, an electric vehicle toy, an electric ship toy, an electric airplane toy, etc.; the electric tool includes a metal cutting electric tool, a grinding electric tool, an assembly electric tool and a railway electric tool, for example, an electric drill, an electric grinding wheel, an electric wrench, an electric screwdriver, a hammer drill, an impact electric drill, a concrete vibrator, a power planer, etc. The embodiment of the present application does not make special restrictions on the above power-consuming devices.

[0119] The present application provides a power-consuming device, and the power-consuming device is a vehicle.

[0120] 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 the secondary battery 2 can be arranged inside the vehicle. The controller is used to control the secondary battery 2 to supply power to the motor. For example, the secondary battery 2 can be arranged at the bottom, the front end or the rear end of the vehicle. The secondary battery 2 can be used for power supply of the vehicle. For example, the secondary battery 2 can be used as the operating power supply of the vehicle for the vehicle's circuit system, 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 secondary battery 2 can not only be used as the operating power supply of the vehicle, but also be used as the driving power supply of the vehicle, replacing or partially replacing fuel or natural gas to provide driving power for the vehicle.

[0121] Hereinafter, 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 a limitation to the present application. For those techniques or conditions not specified in the embodiments, they shall be carried out according to the techniques or conditions described in the literature in the art or according to the product instructions. For the reagents or instruments not specified in the manufacturer, they are all conventional products that can be obtained through commercial purchase.

[0122] [Embodiments and comparative examples]

[0123] Example 1

[0124] (1) Preparation of negative electrode sheet

[0125] Graphite accounting for 94% of the negative electrode active material, 3% of SiO2, 1% of SP, 1% of PVDF, and 1% of thickener CMC are dissolved in water. After fully stirring and mixing evenly, a negative electrode slurry is prepared; the negative electrode slurry is coated on a negative electrode current collector copper foil, and then dried, cold-pressed, and slit to obtain a negative electrode sheet.

[0126] (2) Preparation of positive electrode sheet

[0127] The positive electrode active material LiNi 0.65 Co 0.10 Mn 0.25 O2, binder polyvinylidene fluoride (PVDF), and conductive agent acetylene black are mixed evenly according to a mass ratio of 97.5:1.5:1, dissolved in solvent N-methylpyrrolidone (NMP), and fully stirred and mixed evenly to prepare a positive electrode slurry; the positive electrode slurry is evenly coated on a positive electrode current collector aluminum foil, and then dried, cold-pressed, and slit to obtain a positive electrode sheet.

[0128] (3) Preparation of battery cell

[0129] The separator, positive electrode sheet, separator, and negative electrode sheet are stacked in sequence to obtain an electrode assembly; the electrode assembly is placed in a housing, electrolyte is added, and after processes such as encapsulation, standing, formation, and aging, a battery cell 10 is obtained. In the electrolyte, the solvent includes 30 wt% of methyl acetate (specific carboxylic ester substance), and the lithium salt concentration is 1.2 M of LiFSI.

[0130] In the battery cell 10 of Example 1, the mass content m of silicon element in the negative electrode sheet is 1.5%, the mass content W1 of carboxylic ester in the electrolyte is 30%, the ionic conductivity σ of the electrolyte is 13.3 mS / cm, the kinematic viscosity η is 1.9 mm 2 / s, and the group margin q of the battery cell 10 is 89%.

[0131] Examples 2 - 4

[0132] Compared with Example 1, the difference lies in that the mass content of silicon element in the negative electrode sheet is different from that in Example 1.

[0133] Examples 5 - 6

[0134] Compared with Example 2, the difference lies in that the mass content of carboxylic ester solvent in the electrolyte, the ionic conductivity of the electrolyte, and the kinematic viscosity are different from those in Example 2.

[0135] Examples 7 - 8

[0136] Compared with Example 2, the difference lies in that the group margin of battery cell 10 is different from that of Example 2.

[0137] Comparative Examples 1-4

[0138] Compared with the examples, the kinematic viscosity of the electrolytes in Comparative Examples 1-2 is not within the defined range; the group margins of Comparative Examples 3-4 are not within the defined range.

[0139] Product parameters and performance parameters of Examples 1-8 and Comparative Examples 1-4.

[0140] Table 1: Product parameters and performance parameters of Examples 1-8 and Comparative Examples 1-4

[0141]

[0142] In Table 1, "m" represents the mass content of silicon element in the negative electrode sheet 122; "W1" represents the mass content of carboxylic acid ester in the electrolyte; "σ" represents the ionic conductivity of the electrolyte, "η" represents the kinematic viscosity of the electrolyte; "q" represents the group margin of battery cell 10; "VED" represents the volume energy density of battery cell 10; "Number of cycles" represents the number of cycles corresponding to 80% SOH of battery cell 10 in the cycle test. The specific parameter test process is described in detail in the test section below.

[0143] According to the comparative analysis of the examples and comparative examples, the examples all show better cycle performance than the comparative examples, proving that the group margin and viscosity of battery cell 10 of the electrolyte within the defined range can effectively improve the cycle performance of battery cell 10 with negative active materials including silicon-containing materials.

[0144] According to the comparative analysis of Examples 1-4, as the mass content of silicon element increases, the volume energy density of battery cell 10 increases, and the cycle performance is affected to a certain extent, but it is still better than the comparative examples. It shows that in battery cell 10 with the group margin of battery cell 10 and the viscosity of the electrolyte within the defined range, by increasing the silicon element content, the energy density of battery cell 10 can be further improved, and at the same time, battery cell 10 has good cycle performance.

[0145] According to the comparative analysis of Examples 2, 5-6, as the mass content of carboxylic acid ester solvent increases, the ionic conductivity of the electrolyte increases, the kinematic viscosity decreases, and the cycle performance of battery cell 10 is further improved.

[0146] According to the comparative analysis of Embodiments 2 and 7-8, in the range of 85%-98%, as the margin of the 10 groups of battery cells decreases, the expansion and contraction space of the laminated electrode assembly 12 including the silicon-containing material increases, and the liquid level of the electrolyte inside the outer shell 11 of the battery cell 10 drops. However, at the same time, the lower viscosity and higher ionic conductivity of the electrolyte result in a higher liquid climbing height. Based on this, the cycle performance of the battery cell 10 is further improved.

[0147] The following briefly introduces the test methods for 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 well-known test methods in the art can also be used for testing.

[0148] 1. Test method for ionic conductivity of electrolyte

[0149] The test method follows HG / T 4067-2015. Use a conductivity meter to test the conductivity of the electrolyte to be tested: Take about 100 ml of the sample to be tested with a dry, clean and corrosion-resistant sample bottle, seal it and place it in a constant temperature water bath at 25±0.5°C. When the temperature of the sample to be tested is constant, replace the sample bottle cap with a rubber stopper with electrodes inserted. When the temperature is within the range of 25±0.5°C, read the data, which is the conductivity of the sample to be tested.

[0150] 2. Test method for kinematic viscosity of electrolyte

[0151] The viscosity of the electrolyte can be measured by instruments and methods well-known in the art. For example, for non-Newtonian fluids, the rotational viscometer method provided in the national standard GB / T22235-2008 "Determination of Liquid Viscosity" can be referred to. Specifically, take a certain mass of the electrolyte sample and place it in a sample loading container, and use a rotational viscometer with the model DV2TLV produced by Brookfield Company for testing. At a certain temperature, the shear force exerted on the spring when the rotor rotates continuously at a constant speed in the sample generates torque, and the torque is proportional to the viscosity, thus obtaining the viscosity value. 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 loading container is immersed in the water bath pot, and the medium is water, and the water is used to keep the sample at a constant temperature.

[0152] 3. Test method for mass content of silicon element in the negative electrode film layer

[0153] The content of silicon element is determined by inductively coupled plasma (ICP) spectrometry. For example, reference can be made to the standards YS / T 1006.2-2014, GB / T 23367.2-2009 or YS / T 1028.5-2015. Specifically, according to the embodiments of the present application, an inductively coupled plasma emission spectrometer (fill in the specific equipment model and manufacturer) can be used to perform measurements in accordance with the manufacturer's instructions.

[0154] 4. Test method for the mass content of carboxylic ester solvents in the electrolyte

[0155] Weigh the battery, and record the mass as M0. Disassemble the battery, pour out the free electrolyte, and take the free electrolyte to test the electrolyte composition. Take out the internal electrode assembly and separate the positive electrode plate, negative electrode plate, separator and mechanical parts. Immerse and clean the positive electrode plate, negative electrode plate, separator and mechanical parts with DMC solvent for 24 h to 48 h, and soak repeatedly for more than 3 times. Place the aforementioned positive electrode plate, negative electrode plate, separator and mechanical parts in an oven at 100 °C for more than 24 h until completely dried. Weigh the dried positive electrode plate, negative electrode plate, separator and mechanical parts, and record the mass as M1. Thus, the weight d3 of the electrolyte in the lithium-ion battery is obtained as d3 = M0 - M1.

[0156] Use an IC ion chromatograph to test the content of inorganic substances in the electrolyte. Weigh a quantitative electrolyte (the dilution concentration is in the middle of the standard curve), make up the volume to 100 mL with ultrapure water, and perform automatic injection detection by ion chromatography to test the ion chromatogram of inorganic substances. According to the peak position of the chromatogram, compare the corresponding types of inorganic substances, and calculate the concentration of the corresponding inorganic ions according to the peak area. The mass M2 of the inorganic substances in the electrolyte can be calculated through the mass of the electrolyte. Dilute the above-mentioned free electrolyte with acetonitrile by 3 to 10 times to obtain the diluted electrolyte solution to be tested. Use a GC-MS 3100 organic component gas chromatograph to perform full-scan qualitative analysis on the above-mentioned diluted electrolyte solution. The inlet temperature is 250 °C, and the scanning range is 35 μm to 270 μm. After the test is completed, the total ion current chromatogram of each organic substance is obtained. According to the peak position of the chromatogram, compare the corresponding types of organic substances, calculate the percentage content of each organic substance according to the peak area, and calculate the mass of each organic substance according to the mass of the organic substances d3 - M2 in the electrolyte and the percentage content of each organic substance. For example, the mass d1 of the carboxylic ester solvent in the electrolyte can be calculated.

[0157] Finally, calculate the mass content of the first solvent by d1 / d3.

[0158] 5. Test method for the group margin of battery cells

[0159] Perform a CT scan on the cross-section of the battery cell 10 to be tested (or the battery cell 10 that has been discharged to the lower cut-off voltage so that the state of charge of the battery is approximately 0% SOC), and test the scanned image. The thickness L1 of the electrode assembly and the thickness L2 inside the outer shell can be measured from the scanned image. The group margin q of the battery cell 10 = (L1 / L2) × 100%.

[0160] 6. Test method for the volumetric energy density of a battery cell

[0161] Place the commercially available and unused battery cell 10 at 25°C, charge it at a constant current of 0.33C to 3.8V, let it stand for 1 min, then charge it at a constant current of 0.1C to 3.8V, and let it stand for 30 min; discharge it at a constant current of 0.33C to 2.0V, and record the discharge capacity A0 at this time, unit: Ah; use a caliper to measure the length, width, and height of the outer surface of the battery cell 10, and calculate the volume V0 of the battery cell 10, unit: L; the volumetric energy density VED of the battery cell 10 = (A0 × discharge platform voltage of the lithium-ion battery) / V0, unit: Wh / L. It should be understood that the discharge platform voltages of battery cells 10 with different positive and negative electrode systems are different, and can be obtained by testing their charge-discharge curves or referring to existing literature.

[0162] 7. Test method for the cycling performance of a battery cell

[0163] At 25 ± 5°C, charge a fully discharged battery cell 10 at a constant current of 0.33C to 10% SOC, then charge it from 10% SOC to 45% SOC at 3.7C, then charge it from 45% SOC to 50% SOC at 3.4C, from 50% SOC to 55% SOC at 3.2C, from 55% SOC to 60% SOC at 2.9C, from 60% SOC to 65% SOC at 2.6C, from 65% SOC to 70% SOC at 2.4C, from 70% SOC to 75% SOC at 2.1C, from 75% SOC to 80% SOC at 1.9C, and from 80% SOC to 100% SOC at 0.33C. After standing for 30 min, discharge it to 2.0V at 1C, and record the discharge capacity C1. This is one charge-discharge cycle. Perform multiple cycles on the battery cell 10 until the discharge capacity of the battery cell 10 decays to 0.8C1 (i.e., the state of health of the battery reaches 80% SOH). The more cycles, the better the cycling performance of the battery cell 10.

[0164] Although the present application has been described with reference to the preferred embodiments, various modifications can be made thereto and components thereof can be replaced with equivalents without departing from the scope of the present application. In particular, as long as there is no structural conflict, the technical features mentioned in each embodiment can be combined in any manner. 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 in that: The battery cell comprises a housing and an electrode assembly disposed in the housing, and a group margin q of the battery cell satisfies: 85%≤q≤98%; The electrode assembly comprises a negative electrode sheet, the negative electrode sheet comprises a negative electrode current collector and a negative electrode film layer disposed on a surface of at least one side of the negative electrode current collector, the negative electrode film layer comprises a negative electrode active material, and the negative electrode active material comprises a silicon-containing material; The battery cell includes an electrolyte, and the kinematic viscosity η of the electrolyte satisfies, 1mm 2 / s≤η≤3mm 2 / s.

2. The battery cell according to claim 1, characterized in that: The silicon-containing material includes at least one of elemental silicon, silicon-carbon compounds, and silicon-oxygen compounds.

3. The battery cell according to claim 1 or 2, characterized in that: Based on the total mass of the negative electrode film layer, the mass content m of the silicon element satisfies: 0.5wt%≤m≤15wt%.

4. The battery cell according to any one of claims 1 to 3, characterized in that: The electrode assembly is a laminated electrode assembly.

5. The battery cell according to any one of claims 1 to 4, characterized in that: The ionic conductivity σ of the electrolyte satisfies: 9mS / cm≤σ≤25mS / cm.

6. The battery cell according to any one of claims 1 to 5, characterized in that: The electrolyte solution includes an electrolyte salt, and the electrolyte salt includes LiFSI.

7. The battery cell according to any one of claims 1 to 6, 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.

8. The battery cell according to claim 7, characterized in that: Based on the total mass of the electrolyte, the mass content W1 of the carboxylic acid ester solvent satisfies: 30wt%≤W1≤80wt%.

9. The battery cell according to any one of claims 1 to 8, characterized in that: 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.

10. The battery cell according to any one of claims 1 to 9, characterized in that: The electrode assembly includes a positive electrode plate, the positive electrode plate includes a positive electrode current collector and a positive electrode film layer disposed on a surface of at least one side of the positive electrode current collector, the positive electrode film layer includes a positive electrode active material, and the positive electrode active material includes a lithium transition metal oxide.

11. The battery cell according to claim 10, characterized in that: The liquid injection coefficient a of the battery cell satisfies: 2.3g / Ah≤a≤2.5g / Ah.

12. A secondary battery, characterized in that: The secondary 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 secondary battery according to claim 12.

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