Battery cell, secondary battery, and electrical apparatus

Abstract

A battery cell (10), a secondary battery (2), and an electrical apparatus. The battery cell (10) comprises a housing (11) and an electrode assembly (12) disposed within the housing (11), and a group margin q of the battery cell (10) satisfies the expression: 85%≤q≤98%. The electrode assembly (12) comprises a negative electrode sheet (122). The negative electrode sheet (122) 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 comprises an electrolyte, and the kinematic viscosity η of the electrolyte satisfies the expression: 1 mm2 / s≤η≤3 mm2 / s. The battery cell (10) satisfying the above conditions has good cycling performance.

Description

Battery cells, secondary batteries and electrical devices

[0001] Cross-references to related applications

[0002] This patent document claims priority and benefit to Chinese Patent Application No. 202510227872.X, filed on February 27, 2025, entitled "Battery Cell, Secondary Battery and Electrical Device". The entire contents of the aforementioned patent application are incorporated herein by reference as a part of the disclosure of this patent document. Technical Field

[0003] This application relates to the field of batteries, and more specifically, to a battery cell, a secondary battery, and an electrical device. Background Technology

[0004] In recent years, secondary batteries, mainly lithium-ion batteries, have been widely used in energy storage power systems such as hydropower, thermal power, wind power and solar power plants, as well as in many fields such as power tools, electric bicycles, electric motorcycles, electric cars, military equipment, and aerospace, thus achieving great development.

[0005] With the development and application of secondary batteries, higher requirements are being placed on their capacity. Silicon-containing anodes represent an important development direction for high-capacity secondary batteries; however, the expansion and contraction of silicon-containing materials severely impacts the cycle performance of these batteries. Therefore, improving the cycle performance of silicon-containing secondary batteries is a pressing technical problem that needs to be solved. Summary of the Invention

[0006] This application is made in view of the above-mentioned technical problems, and its purpose is to provide a battery cell, a secondary battery and an electrical device, wherein the battery cell includes silicon-containing materials and has good cycle performance.

[0007] In a first aspect, a battery cell is provided, the battery cell comprising a housing and an electrode assembly disposed within the housing, the group margin q of the battery cell satisfying: 85% ≤ q ≤ 98%; the electrode assembly comprising a negative electrode sheet, the negative electrode sheet comprising a negative current collector and a negative electrode film layer disposed on at least one side of the surface of the negative current collector, the negative electrode film layer comprising a negative electrode active material, the negative electrode active material comprising a silicon-containing material; the battery cell comprising an electrolyte, the kinematic viscosity η of the electrolyte satisfying: 1 mm 2 / s≤η≤3mm 2 / s.

[0008] In the embodiments of this application, in battery cells where the negative electrode active material includes silicon-containing materials, by controlling the group margin of the battery cell to be 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 using an electrolyte with a viscosity within the above range, it is beneficial for the electrolyte to wet the electrode in the direction of gravity, improving the influence of group margin on electrode wetting, helping to reduce the polarization of the battery cell during the cycle, and improving the phenomenon of lithium plating on the negative electrode. Therefore, the embodiments of this application can effectively improve the cycle performance of battery cells.

[0009] In one possible implementation, the silicon-containing material includes at least one of elemental silicon, silicon carbide, and silicon oxide.

[0010] In one possible implementation, based on the total mass of the negative electrode sheet, the mass content m of silicon element satisfies: 0.5wt% ≤ m ≤ 15wt%; optionally, 3wt% ≤ m ≤ 15wt%.

[0011] In the embodiments of this application, the silicon content 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 cycle performance of the battery cell. Therefore, by controlling the silicon content to meet the above-mentioned range, the battery cell can have both high energy density and good cycle performance.

[0012] In one possible implementation, the electrode assembly is a stacked electrode assembly.

[0013] In the embodiments of this application, the design of stacked electrode assemblies can improve the space utilization rate within a single battery cell, thereby mitigating the impact of low group margin on the energy density of the battery cell.

[0014] In one possible implementation, the ionic conductivity σ of the electrolyte satisfies: 9 mS / cm ≤ σ ≤ 25 mS / cm.

[0015] In one possible implementation, the electrolyte comprises an electrolyte salt, which includes LiFSI.

[0016] In the embodiments of this application, LiFSI is selected as the electrolyte salt, which is less likely to undergo side reactions with silicon-containing materials and helps to improve the ionic conductivity of the electrolyte, further improving the lithium plating problem of the negative electrode sheet containing silicon materials, thereby improving the cycle performance of the battery cell.

[0017] In one possible implementation, the electrolyte comprises a carboxylic acid ester solvent, which includes at least one of methyl formate, ethyl formate, methyl acetate, ethyl acetate, propyl acetate, methyl acrylate, and ethyl acrylate.

[0018] In the embodiments of this application, selecting carboxylic acid ester solvents helps to improve the ionic conductivity of the electrolyte, improve the lithium plating problem of the negative electrode sheet containing silicon materials, and thus improve the cycle performance of the battery cell.

[0019] In one possible implementation, based on the total mass of the electrolyte, the mass content W1 of the carboxylic acid ester solvent satisfies: 30wt% ≤ W1 ≤ 80wt%.

[0020] In one possible implementation, the electrolyte comprises a carbonate solvent, which includes at least one of ethylene carbonate, propylene carbonate, ethyl methyl carbonate, and dimethyl carbonate.

[0021] In one possible implementation, the battery cell includes a positive electrode sheet, the positive electrode sheet includes a positive active material, and the positive active material includes a lithium transition metal oxide.

[0022] In one possible implementation, the electrolyte injection coefficient 'a' of the battery cell satisfies: 2.3 g / Ah ≤ a ≤ 2.5 g / Ah.

[0023] In the embodiments of this application, when the positive electrode active material includes a lithium transition metal oxide, by using an electrolyte with viscosity and ionic conductivity meeting the aforementioned ranges, the electrolyte can achieve a high ion transport rate. With a fixed amount of electrolyte, the problem of insufficient lithium-ion transport channels caused by a low electrolyte filler coefficient can be improved by increasing the lithium-ion transport rate, ensuring the normal progress of the electrochemical reaction. This reduces the electrolyte filler coefficient of the battery cell, 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.

[0024] In a second aspect, a secondary battery is provided, wherein the lithium-ion battery comprises a single cell as described in any possible implementation of the first aspect.

[0025] Thirdly, an electrical device is provided, the electrical device comprising a battery cell in any possible implementation of the first aspect, and / or a secondary battery in the second aspect. Attached Figure Description

[0026] To more clearly illustrate the technical solutions of the embodiments of this application, the drawings used in the embodiments of this application will be briefly introduced below. Obviously, the drawings described below are only some embodiments of this application. For those skilled in the art, other drawings can be obtained based on the drawings without creative effort.

[0027] Figure 1 is a schematic cross-sectional view of a single battery cell.

[0028] Figure 2 is a schematic structural diagram of a stacked electrode assembly.

[0029] Figure 3 is a schematic structural diagram of another type of stacked electrode assembly.

[0030] Figure 4 is a schematic structural diagram of a single battery cell.

[0031] Figure 5 is a schematic diagram of another type of secondary battery according to this application. Detailed Implementation

[0032] The following detailed description, with appropriate reference to the accompanying drawings, specifically discloses embodiments of the battery cell, secondary battery, and power-consuming device of this application. However, unnecessary detailed descriptions may be omitted. For example, detailed descriptions of well-known matters and repetitive descriptions of practically identical structures may be omitted. This is to avoid unnecessarily lengthy descriptions and to facilitate understanding by those skilled in the art. Furthermore, the accompanying drawings and the following description are provided to enable those skilled in the art to fully understand this application and are not intended to limit the subject matter of the claims.

[0033] The "range" disclosed in this application is defined by a lower limit and an upper limit. A given range is defined by selecting a lower limit and an upper limit, which define the boundaries of a particular range. Ranges defined in this way can include or exclude endpoints and can be arbitrarily combined; 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, it is expected that ranges of 60-110 and 80-120 are also included. Furthermore, if minimum range values ​​of 1 and 2 are listed, and if maximum range values ​​of 3, 4, and 5 are listed, then the following ranges are all expected: 1-3, 1-4, 1-5, 2-3, 2-4, and 2-5. In this application, unless otherwise stated, the numerical range "ab" represents a shortened representation of any combination of real numbers between a and b, where a and b are real numbers. For example, the numerical range "0-5" indicates that all real numbers between "0-5" have been listed in this article; "0-5" is simply a shortened representation of these numerical combinations. Furthermore, when a parameter is stated as an integer ≥2, it is equivalent to disclosing that the parameter is, for example, an integer such as 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, etc.

[0034] In the description of this application, it should be noted that, unless otherwise stated, "a plurality of" means two or more; the terms "upper," "lower," "left," "right," "inner," "outer," etc., indicating orientation 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 orientation, or be constructed and operated in a specific orientation, and therefore should not be construed as a limitation on this application. Furthermore, the terms "first," "second," "third," etc., are used for descriptive purposes only and should not be construed as indicating or implying relative importance.

[0035] Unless otherwise specified, in this application, the phrase "A and / or B" means "A, B, or both A and B". More specifically, the condition "A and / or B" is satisfied by any of the following conditions: 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).

[0036] Unless otherwise specified, all steps in this application may be performed sequentially or randomly, preferably sequentially. For example, the method includes steps (a) and (b), indicating that the method may include steps (a) and (b) performed sequentially, or it may include steps (b) and (a) performed sequentially. For example, the mention that the method may also include step (c) indicates that step (c) may be added to the method in any order. For example, the method may include steps (a), (b), and (c), or it may include steps (a), (c), and (b), or it may include steps (c), (a), and (b), etc.

[0037] Unless otherwise specified, all embodiments and optional embodiments of this application can be combined to form new technical solutions.

[0038] Unless otherwise specified, any undefined terms shall have their technically accepted meanings.

[0039] The embodiments of this application will be described next.

[0040] In recent years, rechargeable batteries have seen significant development due to their high energy density and long lifespan, finding widespread application in power tools, electronic products, electric vehicles, aerospace, and other fields. Typically, a rechargeable battery consists of a positive electrode, a negative electrode, an electrolyte, and a separator. During charging and discharging, active ions repeatedly insert and extract between the positive and negative electrodes. The electrolyte acts as a conductor of these active ions between the electrodes. The separator, positioned between the positive and negative electrodes, prevents short circuits while allowing active ions to pass through, ensuring the normal electrochemical reaction of the rechargeable battery.

[0041] Taking lithium-ion batteries as an example, lithium-ion batteries are a typical type of rechargeable battery. Because they rely on the chemical reaction of lithium ions intercalating and deintercalating between the positive and negative electrodes for charging and discharging, lithium-ion batteries are also known as rocking chair batteries. During the charging process of a lithium-ion battery, lithium ions are extracted from the positive electrode active material, move to the negative electrode through the conduction of the electrolyte, and intercalate into the negative electrode active material; while during the discharging process, lithium ions are extracted from the negative electrode active material, move to the positive electrode through the conduction of the electrolyte, and intercalate into the positive electrode active material.

[0042] It should be understood that the “lithium intercalation” or “intercalation” process described in this application refers to the process in which lithium ions are intercalated into the positive electrode active material or the negative electrode active material due to an electrochemical reaction, while the “de-lithium extraction”, “de-lithium extraction”, or “de-intercalation” process described in this application refers 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.

[0043] With the development of rechargeable batteries and the continuous expansion of their application scenarios, higher requirements are being placed on the energy density of individual battery cells. Active materials are one of the direct factors affecting the energy density of individual battery cells. Among them, silicon-containing materials have received widespread attention for negative electrode active materials due to their high specific capacity, which can significantly improve the energy density of individual battery cells. However, the volume expansion problem of silicon-containing materials is particularly serious; they expand during lithium insertion and contract during extraction. Similarly, positive electrode active materials also undergo corresponding expansion and contraction processes during cycling. These two factors combined result in the macroscopic expansion and contraction of the electrode assembly during battery cell cycling. During the contraction process, the electrode assembly squeezes out electrolyte. If this squeezed-out electrolyte cannot be absorbed back in time during the expansion process, it will cause insufficient wettability of the electrolyte on the electrode assembly, affecting lithium-ion transport during charging and discharging, leading to lithium plating on the negative electrode and a significant drop in battery cell cycle performance.

[0044] For battery cells with negative electrode active materials including silicon-containing materials, the expansion and contraction of the negative electrode sheet is greater than that of the negative electrode sheet using ordinary negative electrode materials, which has a greater impact on the cycle performance of the battery cell.

[0045] In view of this, embodiments of this application provide a battery cell, a secondary battery, and an electrical device, wherein the negative electrode active material of the battery cell, including silicon-containing materials, has good performance and cycle performance.

[0046] Next, the battery cell provided in this application will be introduced.

[0047] [Battery cell]

[0048] Firstly, a battery cell is provided, comprising a casing and an electrode assembly disposed within the casing. The group margin q of the battery cell satisfies: 85% ≤ q ≤ 98%; optionally, 85% ≤ q ≤ 90%. The electrode assembly includes a negative electrode sheet, which includes a negative current collector and a negative electrode film layer disposed on at least one side of the surface of the negative current collector. The negative electrode film layer includes a negative electrode active material, which includes a silicon-containing material. The battery cell includes an electrolyte, the kinematic viscosity η of which satisfies: 1 mm 2 / s≤η≤3mm 2 / s.

[0049] Specifically, the group margin q can be 85%, 86%, 87%, 88%, 89%, 90%, 91%, 92%, 93%, 94%, 95%, 96%, 97%, or 98%, or a value within the range obtained by any combination of the above two values. η can be 1 mm. 2 / s, 1.2mm 2 / s, 1.4mm 2 / s, 1.6mm 2 / s, 1.8mm 2 / s, 2mm 2 / s, 2.2mm 2 / s, 2.4mm 2 / s, 2.6mm 2 / s, 2.8mm 2 / s, 3mm 2 / s, or a value within the range obtained by combining any two of the above values. It should be understood that the ionic conductivity, viscosity, and other parameters of the electrolyte are all temperature-dependent. 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 normal errors in testing conditions, the above-mentioned ionic conductivity and viscosity range is not limited to 25°C, and can also be the ionic conductivity and viscosity measured at 20°C-30°C. Test results within this temperature range show relatively small differences and can be considered equivalent to test results at 25°C.

[0050] Battery cells containing silicon as the negative electrode active material are prone to severe expansion and contraction during cycling. Reducing the group margin of the battery cell can alleviate this problem, but if the group margin is too small, the spacing between the electrodes will continuously increase with the cycling of the battery cell, exacerbating the polarization inside the battery cell and also being detrimental to the cycle performance of the battery cell. This embodiment controls the group margin of the battery cell within a relatively small range of 85%-98%, which can provide sufficient expansion space for the silicon-containing material during the cycling process, reduce the risk of battery cell deformation caused by the expansion of the silicon-containing material, and improve the cycle performance of the battery cell.

[0051] When the group margin of a battery cell is controlled within 85%-98%, on the one hand, the electrolyte level inside the casing will decrease. This forces the electrode components located above the electrolyte level to rely on capillary action of the electrolyte to be wetted upwards in the direction of gravity. This makes "climbing" difficult, and the poor wetting can easily lead to polarization and lithium plating during battery cell cycling, affecting the cycle performance of the battery cell. On the other hand, electrolytes typically contain organic solvents, which results in a generally high viscosity. This makes it difficult for the electrolyte to be drawn back in time during the expansion of silicon-containing materials, leading to insufficient wetting of the electrode components and also negatively impacting the cycle performance of the battery cell. Therefore, in this embodiment, for high-capacity battery cells with silicon-containing negative electrode active materials, an electrolyte with a viscosity within the aforementioned range is used. The lower viscosity reduces the difficulty of electrolyte climbing in the direction of gravity and allows the electrolyte to be drawn back in time during the expansion of silicon-containing materials. This improves the wettability of the electrolyte to the electrode components during battery cell cycling, providing sufficient lithium-ion exchange pathways for the charge-discharge reaction and effectively improving the cycle performance of the battery cell. Therefore, the battery cell provided in this embodiment, when the negative electrode active material includes silicon-containing materials, can improve the cycle performance of the battery cell through a smaller group margin design and a low-viscosity electrolyte.

[0052] Figure 1 is a schematic cross-sectional view of a single battery cell. Figure 2 is a schematic structural diagram of a stacked electrode assembly. Figure 3 is a schematic structural diagram of another stacked electrode assembly. Figure 4 is a schematic structural diagram of a single battery cell.

[0053] Referring to Figures 1-4, specifically, the battery cell 10 includes a housing 11 and a stacked electrode assembly 12 disposed within the housing. The stacked electrode assembly 12 includes a positive electrode 121, a negative electrode 122, and a separator 123 disposed between the positive electrode 121 and the negative electrode 122. The housing 11 can have various shapes and sizes, such as cuboid, cylindrical, hexagonal prism, etc. Specifically, the shape of the housing 11 can be determined according to the specific shape and size of the electrode assembly 12. The material of the housing 11 can be various, such as copper, iron, aluminum, stainless steel, aluminum alloy, etc., and this embodiment does not impose any special limitations on this.

[0054] The term "group margin" in this article refers to the ratio of the thickness L1 of the electrode assembly 12 to the thickness L2 of the interior of the casing 11 in the cross-section of the battery cell 10. It can be expressed as the percentage of the thickness L1 of the electrode assembly 12 to the thickness L2 of the interior of the casing 11. The thickness L2 of the interior of the casing does not include the thickness of the casing itself. As shown in Figure 1, L1 is the thickness of the electrode assembly 12, L2 is the thickness of the interior of the casing 11, and the group margin q can be expressed as (L1 / L2) × 100%.

[0055] In one embodiment, the electrode assembly 12 is a stacked electrode assembly.

[0056] Generally speaking, since there are no corner areas, stacked electrode assemblies have higher space utilization and group margins compared to wound electrode assemblies, which helps to improve the energy density of individual cells.

[0057] When the group margin of the battery cell 10 is controlled at 85%-98%, the energy density of the battery cell 10 is affected. Therefore, this embodiment adopts a stacked electrode assembly 12 to improve the space utilization inside the casing 11 and mitigate the impact of the small group margin on the energy density of the battery cell 10.

[0058] In one embodiment, as shown in FIG2, the stacked electrode assembly 12 includes a plurality of positive electrode plates 121 and a plurality of negative electrode plates 122, and the plurality of positive electrode plates 121 and the plurality of negative electrode plates 122 are alternately stacked in the direction indicated by the arrows in the figure.

[0059] In another embodiment, as shown in FIG3, the stacked electrode assembly 12 includes a plurality of positive electrode sheets 121 and negative electrode sheets 122. The negative electrode sheet 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 sheets 121 and the plurality of stacked sections of the negative electrode sheet 122 are alternately stacked in the direction indicated by the arrows in the figure to form another form of the stacked electrode assembly 12. Alternatively, the stacked electrode assembly 12 includes a plurality of negative electrode sheets 122 and positive electrode sheets 121. The positive electrode sheet 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 sheets 122 and the plurality of stacked sections of the positive electrode sheet 121 are alternately stacked in the direction indicated by the arrows in the figure.

[0060] In one embodiment, the silicon-containing material includes at least one of elemental silicon, silicon carbide, and silicon oxide.

[0061] Specifically, elemental silicon can be silicon nanoparticles, silicon nanowires, or silicon nanotubes. Silicon-carbide compounds can be carbon-coated silicon materials with a core-shell structure, silicon-carbon nanotube composites, silicon-amorphous carbon composites, etc. Silicon-oxygen compounds can be silicon suboxide, etc.

[0062] In one embodiment, based on the total mass of the negative electrode film, the mass content m of silicon element satisfies: 0.5wt% ≤ m ≤ 15wt%; optionally, 3wt% ≤ m ≤ 15wt%.

[0063] Specifically, m can be 0.5wt%, 1wt%, 2wt%, 2.5wt%, 3wt%, 3.5wt%, 4wt%, 4.5wt%, 5wt%, 5.5wt%, 6wt%, 6.5wt%, 7wt%, 7.5wt%, 8wt%, 8.5wt%, 9wt%, 9.5wt%, 10wt%, 10.5wt%, 11wt%, 11.5wt%, 12wt%, 12.5wt%, 13wt%, 13.5wt%, 14wt%, 14.5wt%, 15wt%, or a value within the range obtained by any combination of the above two values.

[0064] The mass content of silicon in the negative electrode directly affects the expansion and contraction of the negative electrode active material during the cycling process of the battery cell 10. A higher silicon content results in a higher energy density for the battery cell 10 and a greater degree of expansion and contraction for the stacked electrode assembly 12. This embodiment controls the mass content of silicon in the negative electrode film within a suitable range, thereby enabling the battery cell 10 to possess both high energy density and good cycle performance.

[0065] In one embodiment, the electrolyte comprises an electrolyte salt, which includes LiFSI.

[0066] Specifically, LiFSI, or lithium bisfluorosulfonyl imide, has a higher lithium-ion transference number than LiPF6 and is less likely to react with silicon-containing materials to produce gas. Therefore, by selecting LiFSI as the lithium salt in this embodiment, the ionic conductivity of the electrolyte is improved, resulting in a faster diffusion rate of lithium ions in the electrolyte. This allows lithium ions to quickly move to active reaction sites during the expansion and contraction of the stacked electrode assembly 12, thereby improving lithium plating and enhancing the cycle performance of the battery cell 10. Furthermore, its low reactivity with silicon-containing materials helps reduce the expansion of the battery cell 10 during cycling, lowering the risk of damage to the battery cell casing 11 and leakage, thus improving the safety performance of the battery cell 10.

[0067] In one embodiment, the electrolyte comprises a carboxylic acid ester solvent, which includes at least one of methyl formate, ethyl formate, methyl acetate, ethyl acetate, propyl acetate, methyl acrylate, and ethyl acrylate.

[0068] Specifically, carboxylic acid ester solvents have lower density and viscosity, and higher ionic conductivity. In this embodiment, by selecting a carboxylic acid ester solvent as at least part of the electrolyte solvent, the problem of electrolyte backflow during electrode assembly expansion can be improved, the difficulty of electrolyte "crawling" can be reduced, and the migration rate of lithium ions in the electrolyte can be increased. Thus, the internal polarization of the battery cell 10 is reduced, and the cycle performance of the battery cell 10 is improved.

[0069] In one embodiment, based on the total mass of the electrolyte, the mass content W1 of the carboxylic acid ester solvent satisfies: 30wt% ≤ W1 ≤ 80wt%.

[0070] Specifically, W1 can be 30wt%, 35wt%, 40wt%, 45wt%, 50wt%, 55wt%, 60wt%, 65wt%, 70wt%, 75wt%, 80wt%, or a value within the range obtained by any combination of the above two values. The higher the mass content of the carboxylic acid ester solvent, the lower the viscosity of the electrolyte and the higher the ionic conductivity. Furthermore, considering some high-temperature application scenarios, carboxylic acid ester solvents are prone to side reactions and gas generation at high temperatures, which has a certain impact on the cycle performance of the battery cell 10. Therefore, this embodiment, by controlling the mass content of the carboxylic acid ester solvent within the above range, can reduce the electrolyte viscosity, increase the electrolyte conductivity, and improve the cycle performance of the battery cell 10 in high-temperature application scenarios.

[0071] In one embodiment, the electrolyte comprises a carbonate solvent, wherein the carbonate solvent comprises at least one of ethylene carbonate, propylene carbonate, ethyl methyl carbonate, and dimethyl carbonate.

[0072] Specifically, carbonate solvents possess low viscosity, high dielectric constant, and good electrochemical stability. Lower viscosity facilitates rapid lithium-ion migration in the electrolyte; a higher dielectric constant improves the solubility of lithium salts in the electrolyte, providing sufficient lithium-ion kinetics for the electrochemical reaction; and good electrochemical stability helps to increase the operating voltage range of the battery cell 10, thereby increasing its capacity. Therefore, this embodiment, by combining a carbonate solvent with a carboxylic acid ester solvent as a partial solvent in the electrolyte, helps to reduce electrolyte viscosity, improve lithium-ion kinetics, thereby reducing internal polarization of the battery cell 10, improving the cycle performance of the battery cell 10, and also contributing to increasing its capacity.

[0073] In one embodiment, the stacked electrode assembly 12 includes a positive electrode 121, which includes a positive current collector and a positive electrode film layer disposed on at least one side of the surface of the positive current collector. The positive electrode film layer includes a positive electrode active material, which includes a lithium transition metal oxide.

[0074] Specifically, lithium transition metal oxides refer to a class of oxides that include lithium and transition metal elements. Structurally, they include ternary materials with layered structures, such as LiCoO2 and LiNiO2, as well as spinel-structured materials such as LiMnO2 and LiMn2O4. Ternary materials refer to lithium transition metal oxides containing three different transition metal elements. It should be understood that ternary materials can also be doped with trace amounts of other transition metal elements; generally, ternary materials doped with other transition metal elements are still considered ternary materials. Lithium transition metal oxides typically have high specific capacity.

[0075] In this embodiment, when the group margin of the battery cell 10 is low, using 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 enable the high-energy-density battery cell 10 to have good cycle performance.

[0076] In one embodiment, the ionic conductivity σ of the electrolyte satisfies: 9 mS / cm ≤ σ ≤ 25 mS / cm.

[0077] 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, or 25 mS / cm, or a value within the range obtained by any combination of the above two values. Electrolytes with ionic conductivity within this range have good ion transport rates, enabling lithium ions to move rapidly in the electrolyte, and also helping to improve polarization during the electrochemical reaction process, thus helping to improve the cycle performance of the battery cell 10.

[0078] In one embodiment, the electrolyte injection coefficient 'a' of the battery cell 10 satisfies: 2.3 g / Ah ≤ a ≤ 2.5 g / Ah.

[0079] 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 a value within the range obtained by any combination of the above two values. The manufacturing process of the battery cell 10 typically involves first placing the stacked electrode assembly 12, which has been immersed in electrolyte, into a casing, injecting electrolyte into the casing, and then encapsulating it. In this process, the electrolyte injection coefficient is determined by the amount of electrolyte injected and is a key parameter in the lithium-ion battery manufacturing process.

[0080] For battery cells 10 with a group margin in the range of 85%-98%, theoretically, a larger electrolyte filling coefficient is needed to ensure sufficient height of the electrolyte within the casing 11 to fully wet the stacked electrode assembly 12, providing sufficient ion transport paths for the electrochemical reaction, reducing internal polarization of the battery cell 10, and improving its cycle performance. However, for battery cells 10 with silicon-containing materials as the negative electrode active material, more electrolyte will occupy the expansion space for the silicon-containing material to expand during cycling, increasing the risk of leakage in the battery cell 10 and negatively impacting its cycle performance. In this embodiment, by using the aforementioned electrolyte with low viscosity and high ionic conductivity, the electrolyte filling coefficient of the battery cell 10 can be reduced. The possible principle is that an electrolyte with an ionic conductivity in the range of 9mS / cm-25mS / cm helps to increase the lithium-ion transport rate in the electrolyte. Therefore, by increasing the ion transport rate, the problem of insufficient lithium-ion transport channels caused by a low electrolyte filling coefficient can be improved, ensuring the normal progress of the electrochemical reaction. The smaller injection coefficient can meet the wetting requirements of the stacked electrode assembly 12 while providing more space for the expansion and contraction of the stacked electrode assembly 12, thereby further improving the cycle performance of the battery cell 10.

[0081] Next, we will provide a more detailed description of the components in the battery cell 10 of this application.

[0082] [Negative electrode plate]

[0083] The negative electrode 122 typically includes a negative current collector and a negative electrode film layer disposed on at least one surface of the negative current collector. The negative electrode film layer includes a negative electrode active material.

[0084] As an example, the negative electrode current collector has two surfaces opposite each other in its own thickness direction, and the negative electrode film layer is disposed on either or both of the two opposite surfaces of the negative electrode current collector.

[0085] In one embodiment, the negative electrode current collector may be a metal foil or a composite current collector. For example, copper foil may be used as the metal foil. The composite current collector may include a polymeric material substrate and a metal layer formed on at least one surface of the polymeric 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 polymeric material substrate (such as a substrate of polypropylene (PP), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polystyrene (PS), polyethylene (PE), etc.).

[0086] In one embodiment, in addition to the silicon-containing material in the foregoing embodiments, the negative electrode active material may be a negative electrode active material known in the art for use in batteries. 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. Tin-based materials may be selected from at least one of elemental tin, tin oxides, and tin alloys. However, this application is not limited to these materials, and other conventional materials that can be used as battery negative electrode active materials may also be used. These negative electrode active materials may be used alone or in combination of two or more.

[0087] In one embodiment, the negative electrode film layer further includes an adhesive. The adhesive 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).

[0088] 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.

[0089] In one embodiment, the negative electrode film layer also includes other additives, such as thickeners (e.g., sodium carboxymethyl cellulose (CMC-Na)).

[0090] In one embodiment, the negative electrode 122 can be prepared by forming a negative electrode slurry using the components described above. For example, the negative electrode active material, conductive agent, binder, and any other components are dispersed in a solvent (e.g., N-methylpyrrolidone) to form the negative electrode slurry. The negative electrode slurry is then coated onto a negative electrode current collector, and after drying, cold pressing, and other processes, the negative electrode 122 is obtained.

[0091] [Positive electrode plate]

[0092] The positive electrode 121 includes a positive current collector and a positive electrode film layer disposed on at least one surface of the positive current collector, the positive electrode film layer including a positive electrode active material.

[0093] As an example, the positive current collector has two surfaces opposite each other in its own thickness direction, and the positive electrode film layer is disposed on either or both of the two opposite surfaces of the positive current collector.

[0094] In one embodiment, the positive 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 substrate and a metal layer formed on at least one surface of the polymer substrate. 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 substrate (such as a substrate of polypropylene (PP), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polystyrene (PS), polyethylene (PE), etc.).

[0095] In another embodiment, in addition to the lithium transition metal oxides and lithium phosphates mentioned in the foregoing embodiments, the positive electrode active material may also be a known positive electrode active material for batteries. As an example, the positive electrode active material may also include at least one of the following materials: modified compounds containing lithium phosphates, modified compounds of lithium transition metal oxides. However, this application is not limited to these materials, and other conventional materials that can be used as positive electrode active materials for batteries may also be used. Examples of lithium transition metal oxides may include, but are not limited to, lithium nickel cobalt oxide, lithium manganese cobalt oxide, lithium nickel manganese oxide, and lithium nickel cobalt manganese oxide (such as LiNi). 1 / 3 Co 1 / 3 Mn 1 / 3 O2 (also known as NCM333), LiNi 0.5 Co 0.2 Mn 0.3 O2 (also known as NCM523), LiNi 0.5 Co 0.25 Mn 0.25 O2 (also known as NCM211), LiNi 0.6 Co 0.2 Mn 0.2 O2 (also known as NCM622), LiNi 0.8 Co 0.1 Mn 0.1 O2 (also known 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. Examples of lithium phosphates include, but are not limited to, composites of lithium iron phosphate and carbon, lithium manganese phosphate (such as LiMnPO4), composites of lithium manganese phosphate and carbon, and composites of lithium iron manganese phosphate and carbon. During charging and discharging, Li undergoes insertion / extraction and consumption, resulting in different molar contents of Li in the positive electrode active material at different discharge states. In the examples of positive electrode active materials in this application, the molar content of Li refers to the initial state of the material, i.e., the state before feeding. After charge-discharge cycles, the molar content of Li changes when the positive electrode active material is applied to the battery system. In the examples of positive electrode active materials in this application, the molar content of O is only an ideal value; lattice oxygen release causes changes in the molar content of O, and the actual molar content of O will fluctuate.

[0096] 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), PVDF-tetrafluoroethylene-propylene terpolymer, PVDF-hexafluoropropylene-tetrafluoroethylene terpolymer, tetrafluoroethylene-hexafluoropropylene copolymer, and fluorinated acrylate resin.

[0097] In one embodiment, the positive electrode film layer further includes a conductive agent. As an example, the conductive agent may include at least one selected from superconducting carbon, acetylene black, carbon black, Ketjen black, carbon dots, carbon nanotubes, graphene, and carbon nanofibers.

[0098] In one embodiment, the positive electrode 121 can be prepared by forming a positive electrode slurry using the components described above. For example, the first positive electrode active material and / or the second positive electrode active material, a conductive agent, a binder, and any other components are dispersed in a solvent (e.g., N-methylpyrrolidone) to form a positive electrode slurry. The positive electrode slurry is then coated onto a positive electrode current collector, and after drying, cold pressing, and other processes, the positive electrode 121 is obtained.

[0099] Electrolyte

[0100] The electrolyte acts as a conductor of ions between the positive and negative electrodes. This application does not impose specific restrictions on the type of electrolyte; it can be selected according to requirements. The electrolyte includes an electrolyte salt and a solvent.

[0101] 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 dioxalate borate, lithium difluorodioxalate phosphate, and lithium tetrafluorooxalate phosphate.

[0102] In some embodiments, the solvent may be selected from at least one of ethylene carbonate, propylene carbonate, methyl ethyl carbonate, diethyl carbonate, dimethyl carbonate, dipropyl carbonate, methyl propyl carbonate, ethyl propyl carbonate, butyl carbonate, fluoroethylene carbonate, ethyl propionate, propyl propionate, methyl butyrate, ethyl butyrate, 1,4-butyrolactone, sulfolane, dimethyl sulfone, methyl ethyl sulfone, and diethyl sulfone.

[0103] In some embodiments, the electrolyte may optionally include additives. For example, 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 that improve battery overcharge performance, additives that improve battery high-temperature or low-temperature performance, etc.

[0104] [Isolation membrane]

[0105] This application does not impose any particular restrictions on the type of separator 123. For example, any known porous separator 123 with good chemical and mechanical stability can be selected.

[0106] In one embodiment, the material of the separator 123 may be selected from at least one of glass fiber, nonwoven fabric, polyethylene, polypropylene, and polyvinylidene fluoride. The separator 123 may be a single-layer film or a multi-layer composite film, without particular limitation. When the separator 123 is a multi-layer composite film, the materials of each layer may be the same or different, without particular limitation.

[0107] In one embodiment, the negative electrode 122, the positive electrode 121, and the separator 123 can be fabricated into a stacked electrode assembly 12 using a stacking process.

[0108] This application does not impose any particular restrictions on the shape of the battery cell 10, which can be cylindrical, square, or any other arbitrary shape.

[0109] [Rechargeable Battery]

[0110] This application provides a secondary battery 2, including the battery cell 10 described in the above embodiments. The secondary battery 2 can be a single physical module comprising 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, parallel, or mixed via a busbar.

[0111] In some embodiments, the housing 20 of the secondary battery 2 can be part of the vehicle's chassis structure. For example, a portion of the housing 20 can be at least a part of the vehicle's floor, or a portion of the housing can be at least a part of the vehicle's crossbeams and longitudinal beams.

[0112] 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.

[0113] Figure 5 is a schematic diagram of another type of secondary battery 2 according to this application. As shown in Figure 5, the secondary battery 2 may include multiple battery cells 10 to meet different power usage requirements.

[0114] The secondary battery 2 may further include a housing 20, which has a hollow interior structure, housing multiple battery cells 10. For example, multiple battery cells 10 may be connected in parallel, series, or a mixed configuration and then placed inside the housing 20. The housing 20 may include a first housing portion 201 and a second housing portion 202, which are fitted together to form the housing 20. The shapes of the first housing portion 201 and the second housing portion 202 may be determined by the shape of the components housed inside, for example, by the shape of the combination of multiple battery cells 10 housed inside. At least one of the first housing portion 201 and the second housing portion 202 may have an opening. For example, as shown in Figure 5, both the first housing portion 201 and the second housing portion 202 can be hollow cuboids with one open face. The openings of the first housing portion 201 and the second housing portion 202 are opposite to each other, and the first housing portion 201 and the second housing portion 202 are interlocked to form a housing 20 with a closed cavity, which can accommodate multiple battery cells 10. The multiple battery cells 10 are connected in parallel, series, or mixed and placed inside the housing 20 formed by the interlocking of the first housing portion 201 and the second housing portion 202.

[0115] For example, unlike what is shown in Figure 5, only one of the first housing portion 201 and the second housing portion 202 may be a hollow cuboid with an opening, while the other is plate-shaped to cover the opening. Taking the second housing portion 202 as a hollow cuboid with one opening, and the first housing portion 201 as a plate-shaped example, then the first housing portion 201 covers the opening of the second housing portion 202 to form a housing 20 with a closed chamber, which can be used to accommodate multiple battery cells 10.

[0116] In some embodiments, the secondary battery 2 may also include other components. For example, the secondary battery 2 may also include a busbar component, which can be used to realize electrical connections between multiple battery cells 10, such as in parallel, series, or mixed connections. Specifically, the busbar component can realize electrical connections between battery cells 10 by connecting to the electrode terminals of the battery cells 10; or, the busbar component can also realize electrical connections between battery cells 10 by connecting to other components of the battery cells 10. The busbar component can be fixed to corresponding components of the battery cells 10 by welding, for example, by welding to electrode terminals, sealing structures, or housings, etc., and the embodiments of this application are not limited thereto.

[0117] The battery cell 10 can be directly assembled into a secondary battery 2, or it can be first assembled into a battery module, and then multiple battery modules can be assembled into a secondary battery 2.

[0118] [Electrical appliances]

[0119] This application provides an electrical device, including the secondary battery 2 described in the above embodiments.

[0120] Electrical devices can include vehicles, mobile phones, portable devices, laptops, ships, spacecraft, electric toys, and power tools, etc. Vehicles can be gasoline-powered cars, natural gas-powered cars, or new energy vehicles; new energy vehicles can be pure electric vehicles, hybrid electric vehicles, or range-extended electric vehicles, etc. Spacecraft include airplanes, rockets, space shuttles, and spacecraft, etc. Electric toys include stationary or mobile electric toys, such as game consoles, electric car toys, electric ship toys, and electric airplane toys, etc. Power tools include metal cutting power tools, grinding power tools, assembly power tools, and railway power tools, such as electric drills, electric grinders, electric wrenches, electric screwdrivers, electric hammers, impact drills, concrete vibrators, and electric planers, etc. This application does not impose any special limitations on the above-mentioned electrical devices.

[0121] This application provides an electrical device, which is a vehicle.

[0122] The vehicle can be a gasoline-powered vehicle, a natural gas-powered vehicle, or a new energy vehicle. New energy vehicles can be pure electric vehicles, hybrid electric vehicles, or range-extended electric vehicles, etc. The vehicle's interior can house a motor, a controller, and a secondary battery 2. The controller is used to control the secondary battery 2 to supply power to the motor. For example, the secondary battery 2 can be located at the bottom, front, or rear of the vehicle. The secondary battery 2 can be used for vehicle power supply; for example, it can serve as the vehicle's operating power source for the vehicle's electrical system, such as meeting the power requirements for starting, navigation, and operation. In another embodiment of this application, the secondary battery 2 can not only serve as the vehicle's operating power source but also as the vehicle's driving power source, replacing or partially replacing gasoline or natural gas to provide driving power for the vehicle.

[0123] The following describes embodiments of this application. The embodiments described below are exemplary and are only used to explain this application, and should not be construed as limiting this application. Where specific techniques or conditions are not specified in the embodiments, they are performed according to the techniques or conditions described in the literature in this field or according to the product instructions. Reagents or instruments used, unless otherwise specified, are all conventional products that can be obtained commercially.

[0124] [Examples and Comparative Examples]

[0125] Example 1

[0126] (1) Preparation of negative electrode sheet

[0127] The negative electrode active material, consisting of 94% graphite, 3% SiO2, 1% SP, 1% PVDF, and 1% CMC thickener, was dissolved in water at a mass ratio of 1 / 3. After thorough mixing, a negative electrode slurry was prepared. The negative electrode slurry was then coated onto a copper foil used as a negative electrode current collector. After drying, cold pressing, and slitting, a negative electrode sheet was obtained.

[0128] (2) Preparation of positive electrode sheet

[0129] LiNi, the positive electrode active material 0.65 Co 0.10 Mn 0.25 O2, binder polyvinylidene fluoride (PVDF), and conductive agent acetylene black are mixed evenly in a mass ratio of 97.5:1.5:1 and dissolved in solvent N-methylpyrrolidone (NMP). After thorough mixing, a positive electrode slurry is prepared. The positive electrode slurry is evenly coated on the positive electrode current collector aluminum foil, and then dried, cold-pressed, and slit to obtain the positive electrode sheet.

[0130] (3) Preparation of battery cells

[0131] The separator, positive electrode, separator, and negative electrode are stacked sequentially to obtain an electrode assembly. The electrode assembly is placed in a housing, an electrolyte is added, and after encapsulation, settling, formation, and aging processes, a battery cell 10 is obtained. The electrolyte contains 30 wt% methyl acetate (a specific carboxylic acid ester) as solvent and 1.2 M LiFSI as lithium salt.

[0132] In the battery cell 10 of Example 1, the mass content of silicon in the negative electrode is m = 1.5%, the mass content of carboxylic acid ester in the electrolyte is W1 = 30%, the ionic conductivity of the electrolyte is σ = 13.3 mS / cm, and the kinematic viscosity is η = 1.9 mm. 2 / s, the group margin of battery cell 10 is q = 89%.

[0133] Examples 2-4

[0134] The difference between Example 1 and Example 2 is that the mass content of silicon in the negative electrode is different.

[0135] Examples 5-6

[0136] Compared with Example 2, the differences lie in the mass content of carboxylic acid ester solvent in the electrolyte, the ionic conductivity of the electrolyte, and the kinematic viscosity.

[0137] Examples 7-8

[0138] The difference between Example 2 and Example 3 is that the group margin of the battery cell 10 is different.

[0139] Comparative Examples 1-4

[0140] Compared with the examples, the kinematic viscosity of the electrolytes in Comparative Examples 1-2 is not within the defined range; the group margin of Comparative Examples 3-4 is not within the defined range.

[0141] Product parameters and performance parameters of Examples 1-8 and Comparative Examples 1-4.

[0142] Table 1: Product parameters and performance parameters of Examples 1-8 and Comparative Examples 1-4

[0143] In Table 1, "m" represents the mass content of silicon in the negative electrode 122; "W1" represents the mass content of carboxylic acid esters 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 the battery cell 10; "VED" represents the volumetric energy density of the battery cell 10; and "cycle count" represents the number of cycles that the battery cell 10 completes to 80% SOH during the cycle test. Detailed parameter testing procedures are described in the testing section below.

[0144] The comparative analysis of the embodiments and the comparative examples shows that the embodiments all exhibit better cycle performance than the comparative examples, proving that electrolytes with group margin and viscosity within the specified range effectively improve the cycle performance of battery cells 10, including those with silicon-containing materials, for negative electrode active materials.

[0145] Comparative analysis of Examples 1-4 shows that as the silicon content increases, the volumetric energy density of the battery cell 10 increases, and the cycle performance is somewhat affected, but it is still better than the comparative example. This indicates that for battery cells 10 with group margin and electrolyte viscosity within the specified range, increasing the silicon content can further improve the energy density of the battery cell 10, while also giving the battery cell 10 good cycle performance.

[0146] According to the comparative analysis of Examples 2 and 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 the battery cell 10 is further improved.

[0147] Comparative analysis of Examples 2 and 7-8 shows that, within the range of 85%-98%, as the group margin of the battery cells 10 decreases, the expansion and contraction space of the stacked electrode assembly 12 containing silicon materials increases, and the electrolyte level inside the casing 11 of the battery cells 10 decreases. However, the lower viscosity and higher ionic conductivity of the electrolyte result in a higher creepage height, thereby further improving the cycle performance of the battery cells 10.

[0148] The following is a brief description of the testing methods for the physicochemical and performance parameters involved in the embodiments of this application. It should be understood that the following testing methods are only examples, and other testing methods known in the art can also be used for testing.

[0149] 1. Test method for electrolyte ionic conductivity

[0150] The test method follows HG / T 4067-2015. The conductivity of the electrolyte to be tested is measured using a conductivity meter: Take about 100 ml of the sample to be tested in a dry, clean, corrosion-resistant sample bottle, seal it and place it in a constant temperature water bath at 25±0.5℃. When the temperature of the sample to be tested is constant, replace the cap of the sample bottle with a rubber stopper with an electrode inserted. When the temperature is within the range of 25±0.5℃, read the data, which is the conductivity of the sample to be tested.

[0151] 2. Test method for kinematic viscosity of electrolyte

[0152] The viscosity of electrolytes can be determined using instruments and methods known in the art. For example, for non-Newtonian fluids, the rotational viscometer method provided in the national standard GB / T22235-2008 "Determination of Viscosity of Liquids" can be used. Specifically, a certain mass of electrolyte sample is placed in a sample container and tested using a Brookfield DV2TLV rotational viscometer. At a certain temperature, the shear force experienced by the rotor rotating continuously at a constant speed in the sample causes the spring to generate torque. The torque is proportional to the viscosity, thus yielding the viscosity value. The testing equipment meets the following environmental conditions: 1. External environment: temperature 15–28℃, humidity RH < 80%; 2. Internal environment: 2 / 3 of the sample container is immersed in a water bath, the medium being water, which is used to maintain the temperature of the sample.

[0153] 3. Test method for silicon content in negative electrode film layer

[0154] The silicon content can be determined by inductively coupled plasma (ICP) spectroscopy, for example, by referring to standards YS / T1006.2-2014, GB / T23367.2-2009, or YS / T1028.5-2015. Specifically, according to the embodiments of this application, an inductively coupled plasma emission spectrometer (please fill in the specific equipment model and manufacturer) can be used, and the measurement can be performed according to the manufacturer's instructions.

[0155] 4. Test method for the mass content of carboxylic acid ester solvents in electrolyte

[0156] Weigh the battery and record the mass as M0. Disassemble the battery, pour out the free electrolyte, and take a sample of the free electrolyte to test its composition. Remove the internal electrode assembly and separate the positive electrode, negative electrode, separator, and mechanical parts. Soak the positive electrode, negative electrode, separator, and mechanical parts in DMC solvent for 24-48 hours, repeating the soaking process at least three times. Place the aforementioned positive electrode, negative electrode, separator, and mechanical parts in a 100°C oven for at least 24 hours until completely dried. Weigh the dried positive electrode, negative electrode, separator, and mechanical parts and record the mass as M1. Therefore, the electrolyte weight d3 in the lithium-ion battery is calculated as d3 = M0 - M1.

[0157] To test the inorganic content in the electrolyte using an IC ion chromatograph, weigh a quantitative amount of electrolyte (the concentration of the diluent should be in the middle of the standard curve), and dilute it to 100 mL with ultrapure water. Automated injection and detection by ion chromatography will be performed to obtain the inorganic ion chromatogram. The peak positions in the chromatogram will be compared to the corresponding inorganic species, and the corresponding inorganic ion concentration will be calculated based on the peak area. The mass of inorganic matter M2 in the electrolyte can be calculated from the electrolyte mass. The above-mentioned free electrolyte was diluted 3 to 10 times with acetonitrile to obtain the electrolyte dilution to be tested. Using a GC-MS 3100 organic component gas chromatograph, the above-mentioned electrolyte dilution was placed in the instrument for full-scan qualitative analysis. The injection port temperature was 250℃, and the scanning range was 35μm to 270μm. After the test was completed, the total ion chromatogram of each organic compound was obtained. According to the peak position of the chromatogram, the corresponding organic compound type was identified. The percentage content of each organic compound was calculated based on the peak area. The mass of each organic compound can be calculated based on the mass of organic compounds in the electrolyte d3-M2 and the percentage content of each organic compound. For example, the mass d1 of carboxylic acid ester solvents in the electrolyte can be calculated.

[0158] Finally, the mass content of the first solvent is calculated using d1 / d3.

[0159] 5. Test method for the group margin of individual battery cells

[0160] A cross-section of the battery cell 10 under test (or a battery cell 10 discharged to the lower cutoff voltage so that the battery's state of charge is approximately 0% SOC) is subjected to a CT scan, and the scanned images are tested. The thickness L1 of the electrode assembly and the thickness L2 of the inner casing can be measured from the scanned images. The group margin q of the battery cell 10 is (L1 / L2)×100%.

[0161] 6. Test method for volumetric energy density of a single battery cell

[0162] A commercially available, unused battery cell 10 was placed at 25°C and charged to 3.8V with a constant current of 0.33C, allowed to stand for 1 minute, then charged to 3.8V with a constant current of 0.1C, and allowed to stand for 30 minutes. It was then discharged to 2.0V with a constant current of 0.33C, and the discharge capacity A0 (Ah) was recorded. The length, width, and height of the outer surface of the battery cell 10 were measured using calipers, and the volume V0 (L) of the battery cell 10 was calculated. The volumetric energy density VED of the battery cell 10 was calculated as (A0 × discharge plateau voltage of the lithium-ion battery) / V0 (Wh / L). It should be understood that the discharge plateau voltage of battery cells 10 varies depending on the positive and negative electrode systems, and can be obtained by testing their charge-discharge curves or referring to existing literature.

[0163] 7. Test methods for the cycle performance of individual battery cells

[0164] At 25±5℃, a fully discharged battery cell 10 was charged at a constant current of 0.33C to 10% SOC, then charged at 3.7C from 10% SOC to 45% SOC, then charged at 3.4C from 45% SOC to 50% SOC, 3.2C from 50% SOC to 55% SOC, 2.9C from 55% SOC to 60% SOC, 2.6C from 60% SOC to 65% SOC, 2.4C from 65% SOC to 70% SOC, 2.1C from 70% SOC to 75% SOC, 1.9C from 75% SOC to 80% SOC, and 0.33C from 80% SOC to 100% SOC. After resting for 30 minutes, it was discharged at 1C to 2.0V, and the discharge capacity C1 was recorded. This constitutes one charge-discharge cycle. The battery cell 10 is subjected to multiple cycles until its discharge capacity decays to 0.8C1 (i.e., the battery's state of health reaches 80% SOH). The more cycles, the better the cycle performance of the battery cell 10.

[0165] Although this application has been described with reference to preferred embodiments, various modifications can be made thereto and components can be replaced with equivalents without departing from the scope of this application. In particular, the technical features mentioned in the various embodiments can be combined in any manner, provided there is no structural conflict. This 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 includes a housing and an electrode assembly disposed within the housing, and the group margin q of the battery cell satisfies: 85% ≤ q ≤ 98%; The electrode assembly includes a negative electrode sheet, the negative electrode sheet includes a negative current collector and a negative electrode film layer disposed on at least one side of the surface of the negative 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 the condition that 1 mm... 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 carbide, and silicon oxide.

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

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

5. The battery cell according to any one of claims 1-4, 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 1-5, characterized in that, The electrolyte includes an electrolyte salt, which includes LiFSI.

7. The battery cell according to any one of claims 1-6, characterized in that, The electrolyte includes a carboxylic acid ester solvent, which 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 1-8, characterized in that, The electrolyte includes carbonate solvents, which include at least one of ethylene carbonate, propylene carbonate, ethyl methyl carbonate, and dimethyl carbonate.

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

11. The battery cell according to claim 10, characterized in that, The electrolyte 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 1-11.

13. An electrical appliance, characterized in that, The electrical device includes a battery cell as described in any one of claims 1-11, and / or a secondary battery as described in claim 12.

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