Battery monomer, battery device and power utilization device

Abstract

The invention relates to the technical field of batteries, and provides a battery monomer, a battery device and a power utilization device.The battery monomer comprises an electrolyte and an electrode assembly, the electrode assembly comprises a positive pole piece and a negative pole piece, and the negative pole piece comprises a negative current collector and a negative active material layer arranged on at least one side of the negative current collector; the negative electrode active material layer comprises carbon-coated graphite, and amorphous carbon is arranged on the surface of the carbon-coated graphite; the electrolyte comprises a solvent, and the solvent comprises linear carboxylic ester; in the first direction, the size of the negative electrode active material layer is larger than 130 mm, and the first direction is parallel to the gravity direction. According to the present invention, the carbon-coated graphite is adopted as the negative electrode active material, and is matched with the electrolyte containing the linear carboxylic ester, such that the problems of electrolyte local aggregation and low heat dissipation efficiency in the high battery cell can be effectively improved so as to prolong the cycle life of the battery monomer.

Description

Technical Field

[0001] This application belongs to the field of battery technology, and in particular relates to a battery cell, a battery device, and an electrical device. Background Technology

[0002] Lithium-ion batteries are widely used in energy storage systems such as hydropower, thermal power, wind power, and solar power plants due to their high energy density, long cycle life, and environmental friendliness. They also have extensive applications in power tools, electric bicycles, electric motorcycles, electric vehicles, aerospace, and many other fields. As the market's demand for higher energy replenishment efficiency in electrical devices continues to increase, higher requirements are being placed on the cycle performance of individual battery cells.

[0003] The above statements are for the purpose of providing background information in relation to this application only and do not necessarily constitute prior art. Summary of the Invention

[0004] The purpose of this application is to provide a battery cell, a battery device, and an electrical device, which aim to improve the cycle performance of the battery cell.

[0005] To achieve the above-mentioned objectives, the technical solution adopted in this application is as follows: Firstly, this application provides a battery cell. Specifically, the battery cell of this application includes: an electrolyte and an electrode assembly, wherein the negative electrode sheet includes a negative current collector and a negative active material layer disposed on at least one side of the negative current collector, the negative active material layer including carbon-coated graphite, and the surface of the carbon-coated graphite having amorphous carbon; The electrolyte includes a solvent, which includes linear carboxylic acid esters; Along the first direction, the size of the negative electrode active material layer is greater than 130 mm, and the first direction is parallel to the direction of gravity.

[0006] In this application's technical solution, using high-density cells can improve energy density. Employing carbon-coated graphite as the negative electrode active material, combined with an electrolyte containing linear carboxylic acid esters, effectively addresses the issues of localized electrolyte aggregation and low heat dissipation efficiency in high-density cells, thereby improving the cycle life of individual battery cells. Specifically, the amorphous carbon in the carbon-coated graphite has excellent adsorption capacity for the electrolyte, effectively "locking in" the electrolyte, strengthening its retention effect, and mitigating the tendency for the electrolyte to aggregate towards the lower part of the high-density cell under gravity. This improves the electrolyte wetting state of the upper electrode, reduces reaction differences caused by insufficient local wetting, and makes the current distribution more balanced. The amorphous carbon on the surface of the carbon-coated graphite can significantly improve its electronic conductivity, which can optimize the diffusion path of lithium ions inside the negative electrode, greatly reducing ion diffusion resistance and making lithium ions more readily absorbed. To ensure uniform distribution within the battery system and effectively mitigate the lithium-ion concentration gradient problem caused by the long transport path in high-performance cells, linear carboxylic acid esters are used as the solvent in the electrolyte. This helps reduce the viscosity of the electrolyte, significantly improving its wettability and reflux capacity within the high-performance cells. This enhances the electrolyte's ability to creep within the cells, improves its uniform distribution, further optimizes the ion transport environment inside the cells, and effectively reduces the risk of electrolyte accumulation at the bottom of the cells. Ultimately, this significantly improves the cycle life of the high-performance cells.

[0007] In some embodiments, the negative electrode active material layer includes a first negative electrode active material layer and a second negative electrode active material layer disposed along the thickness direction of the negative electrode current collector, and the first negative electrode active material layer is disposed between the negative electrode current collector and the second negative electrode active material layer; the first negative electrode active material layer includes a first graphite, the second negative electrode active material layer includes a second graphite, and the second graphite includes carbon-coated graphite; the graphitization degree of the first graphite is 94%-98%.

[0008] The negative electrode sheet of this application adopts a double-layer coating design. By differentiating the negative electrode active material layer, the side reaction between carbon-coated graphite and linear carboxylic acid ester can be effectively mitigated, and the battery cell can have both good fast charging capability and high energy density.

[0009] In some embodiments, the Dv50 particle size of the first graphite is larger than the Dv50 particle size of the second graphite.

[0010] By selecting a second graphite with a smaller median particle size in the second negative electrode active material layer near the electrolyte, the lithium ion transport path is shortened, thereby improving the lithium ion transport rate and significantly improving the battery's fast charging capability.

[0011] In some embodiments, the specific capacity of the first graphite is greater than or equal to the specific capacity of the second graphite.

[0012] In the first negative electrode active material layer near the negative electrode current collector, graphite with a high specific capacity is selected as the active material, so that the layer can have good stability and high capacity, thereby helping to improve the energy density of the high-energy cell.

[0013] In some embodiments, the first graphite satisfies at least one of the following features (1)-(3): (1) the Dv50 particle size of the first graphite is 14.0μm-18.5μm; (2) the specific capacity of the first graphite is 358mAh / g-368mAh / g; (3) the first graphite includes one or more of primary particles and secondary particles.

[0014] By screening and optimizing the first graphite, the first negative electrode active material layer can achieve a high capacity level, thereby giving the battery cell a high energy density. At the same time, it can effectively reduce irreversible lithium loss during cycling and significantly extend the cycle life of the battery.

[0015] In some embodiments, the second graphite satisfies at least one of the following features (1)-(4): (1) the Dv50 particle size of the second graphite is 9.8μm-13.8μm; (2) the graphitization degree of the first graphite is 90%-93%; (3) the specific capacity of the second graphite is 350mAh / g-358mAh / g; (4) the OI value of the second graphite is 3.6-4.1, the OI value of the second graphite is C004 / C110, C004 is the peak area of ​​the diffraction peak of the 004 crystal plane of the second graphite, and C110 is the peak area of ​​the diffraction peak of the 110 crystal plane of the second graphite.

[0016] By screening and optimizing the second graphite, lithium ions can be inserted and extracted at a faster rate, giving the second anode active material layer better kinetic performance.

[0017] In some embodiments, the thickness ratio of the second negative electrode active material layer to the first negative electrode active material layer is (7:3) to (5:5).

[0018] Within the aforementioned range, the battery cells not only possess good dynamic performance and exhibit excellent charge and discharge capabilities, but also have high capacity, meeting the needs of long-range electric devices.

[0019] In some embodiments, the negative electrode sheet satisfies at least one of the following features (1)-(3): (1) The single-sided coating weight of the negative electrode active material layer is 130 mg / 1540 mm. 2 ~160mg / 1540mm 2 (2) The thickness of the negative electrode sheet is 0.115mm-0.125mm; (3) The compaction density of the negative electrode sheet is 1.6 g / cm³. 3 -1.78g / cm 3 .

[0020] By controlling the single-sided coating weight, thickness, and compaction density of the negative electrode sheet within the above-mentioned range, the battery cell can have good kinetic performance while possessing high energy density.

[0021] In some embodiments, the positive electrode sheet includes a positive current collector and a positive active material layer disposed on at least one side of the positive current collector, wherein the positive electrode sheet satisfies at least one of the following features (1)-(3): (1) the single-sided coating weight of the positive active material layer is 310 mg / 1540 mm. 2 ~350mg / 1540mm 2 (2) The thickness of the positive electrode sheet is 0.17mm-0.18mm; (3) The compaction density of the positive electrode sheet is 2.6 g / cm³. 3 -2.8 g / cm 3 .

[0022] By controlling the compaction density and thickness of the positive electrode sheet within the above-mentioned range, the battery cell can have a high energy density, meeting the requirements of long-range electric devices.

[0023] In some embodiments, the solvent further includes cyclic carbonates, wherein the mass ratio of linear carboxylic acid ester to cyclic carbonate is (6-7):(3-4).

[0024] The combination of these two components results in an electrolyte with high conductivity and low viscosity, thereby improving the electrolyte's climbing ability and wetting effect in high-performance cells, reducing the risk of electrolyte accumulation in certain areas, enhancing the wetting effect of the upper electrode on the electrolyte, reducing concentration polarization, mitigating the risk of lithium plating on the electrode, and improving the cycle life of the battery.

[0025] In some embodiments, the solvent further includes linear carbonates and cyclic carbonates, wherein the mass ratio of linear carboxylic acid ester, linear carbonate to cyclic carbonate is (2-4):(3-4):(3-4).

[0026] The combination of these three components can reduce the flow resistance of the electrolyte, improve its reflux efficiency in the battery, thereby reducing the concentration difference in high-energy cells and improving the battery's fast charging capability and cycle performance.

[0027] In some embodiments, the conductivity of the electrolyte is 9 mS / cm-18.5 mS / cm.

[0028] In some embodiments, the conductivity of the electrolyte is 14 mS / cm-18.5 mS / cm.

[0029] By controlling the conductivity of the electrolyte within the above range, the active ions can have a high transport capacity. This allows them to maintain a high migration capacity even in a thicker positive electrode active material layer formed by a higher single-sided coating weight, significantly improving the migration efficiency of active ions and enabling the battery cell to exhibit better kinetic performance.

[0030] In some embodiments, the viscosity of the electrolyte is 0.5 mm at 25°C. 2 / s-4mm 2 / s.

[0031] Controlling the electrolyte viscosity within the aforementioned range signifies that the electrolyte possesses high conductivity and low viscosity characteristics. High conductivity and low viscosity electrolytes can significantly enhance the diffusion rate of active ions and reduce their migration resistance, thereby increasing the transport rate of active ions in thicker electrodes formed with high coating weight, and consequently significantly improving the kinetic performance of high VED systems.

[0032] In some embodiments, the electrolyte comprises a lithium salt, which includes at least one of lithium hexafluorophosphate, lithium tetrafluoroborate, lithium bis(trifluoromethanesulfonyl)imide, lithium perchlorate, and lithium hexafluoroarsenate.

[0033] By selecting the aforementioned lithium salt, this application helps to improve the ionic conductivity of the electrolyte, thereby increasing the diffusion rate of lithium ions in the electrolyte and improving the kinetic performance of the battery.

[0034] In some embodiments, the electrolyte injection coefficient of a single battery cell is 2.7 g / Ah to 3.2 g / Ah.

[0035] Within the aforementioned range, not only is the wetting of the electrode components satisfied, but more electrolyte is also formed into a gel-like structure fixed inside and around the electrode pores, meeting the electrolyte consumption requirements of long-life cells. Furthermore, lithium ions have a high transport rate and sufficient transport channels in the electrolyte, enabling the battery to have a high electrochemical reaction rate. Thus, the battery cell can have both good cycle stability and high energy density.

[0036] In some embodiments, the electrolyte further includes additives, including vinylene carbonate; and / or, the mass concentration of the additives in the electrolyte is 1%-2%.

[0037] Selecting the above-mentioned additives and controlling their content within the above-mentioned range helps to improve the conductivity of the electrolyte and reduce its viscosity, thereby obtaining a high-conductivity, low-viscosity electrolyte.

[0038] In some embodiments, the negative electrode active material layer includes a first conductive agent, which includes a zero-dimensional conductive agent and a multi-dimensional conductive agent, and the multi-dimensional conductive agent includes at least one of a one-dimensional conductive agent and a two-dimensional conductive agent.

[0039] This application utilizes a combination of zero-dimensional conductive agents and multi-dimensional conductive agents. The zero-dimensional conductive agent forms point contact with the negative electrode active material to construct a local conductive network, while the multi-dimensional conductive agent can construct a continuous electron transport network. Thus, the two work synergistically to enable electrons to not only have the ability to transport over long distances but also to enhance the uniformity of electron conduction. This alleviates the local polarization and lithium plating problems of the negative electrode sheet, thereby improving the cycle performance of the high-performance battery cell.

[0040] In some embodiments, the zero-dimensional conductive agent includes at least one of conductive carbon black, Ketjen black, and acetylene black.

[0041] These conductive agents are mainly dispersed between the negative electrode active materials through point contact, which can effectively reduce the contact resistance between the particles of the negative electrode active materials and improve the overall conductivity uniformity of the electrode.

[0042] In some embodiments, the one-dimensional conductive agent includes at least one of carbon nanotubes and carbon nanofibers, and the carbon nanotubes include at least one of multi-walled carbon nanotubes, single-walled carbon nanotubes, and few-walled nanotubes. Such conductive agents can construct long-range continuous conductive pathways through line contact methods. In some embodiments, the two-dimensional conductive agent includes at least one of layered conductive graphite and graphene.

[0043] These conductive agents can contact the negative electrode active material particles through surface contact, forming a large-area conductive connection, thereby effectively improving local conductivity and increasing the transport rate of active ions.

[0044] In some embodiments, the mass ratio of zero-dimensional conductive agent to multi-dimensional conductive agent is 4:1 to 1:4.

[0045] Within the aforementioned range, it helps to form an electron transport channel that combines long-range continuous conductive network with local conductivity, improves the transport efficiency of active ions, reduces the risk of local lithium plating on the electrode, and thus improves the cycle performance of the battery.

[0046] In some embodiments, the negative electrode active material layer further includes a first dispersant, which includes an amino-containing dispersant and a cellulose ether dispersant. The amino-containing dispersant includes at least one of polyethyleneimine, a polyetheramine-polydopamine complex, and an amino-containing zwitterionic polymer. The cellulose ether dispersant includes sodium carboxymethyl cellulose.

[0047] The combination of amino-containing dispersants and cellulose ether dispersants effectively improves the dispersibility of multidimensional conductive agents, thereby forming a more efficient conductive network.

[0048] In some embodiments, the mass ratio of amino dispersant to cellulose ether dispersant is 2:1 to 1:4.

[0049] In some embodiments, the negative electrode active material layer further includes a first binder, which includes a dot binder and a linear binder; wherein the linear binder includes at least one of the following groups: carboxyl group, lithium-ionized carboxyl group.

[0050] The polar functional groups contained in the linear binder can react with the amino-containing dispersant to form a high-mechanical-strength elastic network in the active material layer, which can fully exert the binding effect on the negative electrode active material and not only suppress the volume expansion of the negative electrode sheet.

[0051] In some embodiments, the linear binder includes at least one of polyacrylic acid, polymethacrylic acid, lithium polyepoxysuccinate, lithium-ionized polyacrylic acid, and lithium polymethacrylate.

[0052] In some embodiments, the dotted adhesive includes at least one of styrene-butadiene rubber and fluorinated rubber.

[0053] In some embodiments, the mass ratio of dotted adhesive to linear adhesive is 4:1 to 1:1.

[0054] Within the aforementioned range, the battery system not only has sufficient linear binders to form a highly adhesive elastic network, but also utilizes dotted binders to compensate for the rigidity of the linear binders, further enhancing the adhesion ability of the negative electrode active material.

[0055] In some embodiments, the first negative electrode active material layer further includes a first binder, a first conductive agent, and a first dispersant. Based on the total mass of the first negative electrode active material layer, the content of the first graphite is 95%-97.5%, the content of the first binder in the first negative electrode active material layer is 1.2%-2.5%, the content of the first conductive agent in the first negative electrode active material layer is 0.8%-1.3%, and the content of the first dispersant in the first negative electrode active material layer is 0.5%-1.2%; and / or, The second negative electrode active material layer also includes a first binder, a first conductive agent, and a first dispersant. Based on the total mass of the second negative electrode active material layer, the content of the second graphite is 96%-98%, the content of the first binder in the second negative electrode active material layer is 0.8%-2%, the content of the first conductive agent in the second negative electrode active material layer is 0.7%-1%, and the content of the first dispersant in the second negative electrode active material layer is 0.5%-1%.

[0056] In some embodiments, the negative electrode sheet further includes a coating disposed between the negative electrode current collector and the negative electrode active material layer; wherein the coating includes a second conductive agent, a second binder, and a second dispersant.

[0057] By setting a coating between the negative electrode current collector and the negative electrode active material layer, the contact resistance between the negative electrode active material layer and the negative electrode current collector can be effectively reduced, allowing electrons to be conducted from the negative electrode active material layer to the negative electrode current collector at a faster speed, thereby improving the electron conduction rate and the dynamic performance of the battery.

[0058] In some embodiments, based on the mass of the coating, the content of the second conductive agent is 63%-65%, the content of the second binder is 30%-32%, and the content of the second dispersant is 3%-5%.

[0059] In some embodiments, the coating thickness is 1 μm-3 μm.

[0060] By controlling the coating thickness within the aforementioned range, the coating exhibits low contact resistance and strong adhesion, thereby contributing to improved battery kinetic performance and cycle life.

[0061] In some embodiments, the size of the negative electrode active material layer is greater than or equal to 150 mm along a first direction, and the first direction is parallel to the direction of gravity.

[0062] Secondly, this application provides a battery device including the battery cell described in the above embodiments.

[0063] Thirdly, this application provides an electrical device, including the battery cell or the battery device described in the above embodiments. Attached Figure Description

[0064] Various other advantages and benefits will become apparent to those skilled in the art upon reading the detailed description of the preferred embodiments below. The accompanying drawings are for illustrative purposes only and are not intended to limit the scope of this application. Furthermore, the same reference numerals denote the same parts throughout the drawings. In the drawings: Figure 1 This application provides structural schematic diagrams of vehicles for some embodiments; Figure 2 Schematic diagram of a battery device provided for some embodiments of this application; Figure 3 This is a schematic diagram of the structure of a battery cell provided in some embodiments of this application; Figure 4 for Figure 3 The diagram shows an exploded view of a single battery cell. Figure 5 A cross-sectional schematic diagram of an electrode assembly provided in some embodiments of this application; Figure 6 A schematic diagram of the negative electrode sheet in its unfolded state, provided in some embodiments of this application; Figure 7 For along Figure 6 Schematic diagram of the cross section of the middle BB line; The following are the labeling elements in the figure: 1. Vehicle; 2. Battery unit; 3. Controller; 4. Motor; 5. Housing; 51. First housing; 52. Second housing; 6. Battery cell; 10. Electrode assembly; 11. Positive electrode; 12. Negative electrode; 121. Negative current collector; 122. Negative active material layer; 13. Separator; 20. Outer shell; 21. Housing; 22. End cap; 221. Pressure relief mechanism; 30. Electrode terminal. Detailed Implementation

[0065] The embodiments of the technical solution of this application will now be described in detail with reference to the accompanying drawings. These embodiments are only used to more clearly illustrate the technical solution of this application and are therefore merely examples, and should not be used to limit the scope of protection of this application.

[0066] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this application pertains; the terminology used herein is for the purpose of describing particular embodiments only and is not intended to limit the application; the terms “comprising” and “having”, and any variations thereof, in the specification, claims, and foregoing description of the drawings are intended to cover non-exclusive inclusion.

[0067] In the description of the embodiments of this application, technical terms such as "first" and "second" are used only to distinguish different objects and should not be construed as indicating or implying relative importance or implicitly specifying the number, specific order, or primary and secondary relationship of the indicated technical features. In the description of the embodiments of this application, "multiple" means two or more, unless otherwise explicitly defined.

[0068] In this document, the term "embodiment" means that a particular feature, structure, or characteristic described in connection with an embodiment may be included in at least one embodiment of this application. The appearance of this phrase in various places throughout the specification does not necessarily refer to the same embodiment, nor is it a separate or alternative embodiment mutually exclusive with other embodiments. It will be explicitly and implicitly understood by those skilled in the art that the embodiments described herein can be combined with other embodiments.

[0069] In the description of the embodiments in this application, the term "and / or" is merely a description of the relationship between related objects, indicating that three relationships can exist. For example, A and / or B can represent: A existing alone, A and B existing simultaneously, and B existing alone. Additionally, the character " / " in this document generally indicates that the preceding and following related objects have an "or" relationship.

[0070] In the description of the embodiments of this application, the term "multiple" refers to two or more (including two), similarly, "multiple sets" refers to two or more (including two sets), and "multiple pieces" refers to two or more (including two pieces).

[0071] In the description of the embodiments of this application, the technical terms "center," "longitudinal," "lateral," "length," "width," "thickness," "upper," "lower," "front," "rear," "left," "right," "vertical," "horizontal," "top," "bottom," "inner," "outer," "clockwise," "counterclockwise," "axial," "radial," and "circumferential" indicate the orientation or positional relationship based on the orientation or positional relationship shown in the accompanying drawings. They are only for the convenience of describing the embodiments of this application and simplifying the description, and are not intended to indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation. Therefore, they should not be construed as limitations on the embodiments of this application.

[0072] In the description of the embodiments of this application, unless otherwise expressly specified and limited, technical terms such as "installation," "connection," "joining," and "fixing" should be interpreted broadly. For example, they can refer to a fixed connection, a detachable connection, or an integral part; they can refer to a mechanical connection or an electrical connection; they can refer to a direct connection or an indirect connection through an intermediate medium; they can refer to the internal communication of two components or the interaction between two components. For those skilled in the art, the specific meaning of the above terms in the embodiments of this application can be understood according to the specific circumstances.

[0073] In this application, "at least one" means one or more, and "more than one" means two or more. "At least one of the following" or similar expressions refer to any combination of these items, including any combination of single or multiple items. For example, "at least one of a, b, or c", or "at least one of a, b, and c", can both mean: a, b, c, ab (i.e., a and b), ac, bc, or abc, where a, b, and c can be single or multiple.

[0074] Unless otherwise specified, all embodiments and optional embodiments of this application can be combined to form new technical solutions.

[0075] Unless otherwise specified, all technical features and optional technical features of this application may be combined to form new technical solutions.

[0076] Unless otherwise specified, all steps of 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.

[0077] The weights of the relevant components mentioned in the embodiments of this application can refer not only to the specific content of each component, but also to the proportional relationship between the weights of the components. Therefore, any scaling up or down of the content of the relevant components according to the embodiments of this application is within the scope disclosed in the embodiments of this application. Specifically, the mass described in the embodiments of this application can be a well-known unit of mass in the chemical industry, such as µg, mg, g, or kg.

[0078] In this embodiment of the application, the battery cell can be a secondary battery. A secondary battery refers to a battery cell that can be recharged to activate the active materials and continue to be used after the battery cell has been discharged.

[0079] In the embodiments of this application, SEI film is short for "solid electrolyte interface", which refers to a solid electrolyte interface film with the characteristics of a solid electrolyte. That is, during the first charge and discharge process of a liquid lithium-ion battery, a passivation layer formed by the reaction between the electrode material and the electrolyte at the solid-liquid interface is formed and covers the surface of the negative electrode material.

[0080] With the continuous expansion of the application fields of power batteries, people have placed higher demands on the driving range of new energy vehicles. Battery cells with a height greater than 130mm are called high-capacity cells. Due to their superior height, they can accommodate more positive electrode active materials and possess higher energy density, making them widely used in electric vehicles such as commercial vehicles and trucks where extremely long driving ranges are required. To improve the ease of use of long-range electric vehicles, enhancing the fast-charging capabilities of high-capacity cells and giving them excellent charging performance has become an urgent need.

[0081] To address the aforementioned issues, low-viscosity electrolytes are typically used. This improves the reflux efficiency of the electrolyte within the high-performance battery cell and accelerates the lithium-ion transport rate within the battery system, ultimately optimizing the fast-charging performance of the high-performance battery cell. For example, using linear carboxylic acid esters containing ethyl acetate as a solvent can effectively reduce electrolyte viscosity, providing conditions for improved fast-charging performance. However, it should be noted that using ethyl acetate as a solvent to improve the fast-charging performance of high-performance batteries can negatively impact the cycle life of the high-performance battery cell, as detailed below: Firstly, as the height of the battery cell increases, the influence of gravity on electrolyte distribution becomes significantly stronger. Under this effect, the electrolyte tends to accumulate in the lower part of the cell, resulting in insufficient electrolyte content in the upper region, which in turn leads to inadequate wetting of the upper electrode. This phenomenon directly affects the effective transport of ions within the cell, resulting in uneven current distribution during charging and discharging. Specifically, the current density of the upper electrode is lower, while the current density of the lower electrode is relatively higher, ultimately affecting the stability and consistency of the overall cell performance and worsening the cycle life of the high-strength battery cell. Secondly, the long heat dissipation path of the high-temperature battery cell will significantly weaken the heat transfer efficiency inside the cell, and the poor thermal stability of ethyl acetate will further amplify this risk, threatening the safety performance and service life of the battery.

[0082] Based on this, the first aspect of the present application provides a battery cell. Specifically, the battery cell of the present application includes an electrolyte and an electrode assembly, wherein the negative electrode sheet includes a negative current collector and a negative active material layer disposed on at least one side of the negative current collector, the negative active material layer includes carbon-coated graphite, and the surface of the carbon-coated graphite has amorphous carbon; The electrolyte includes a solvent, which includes linear carboxylic acid esters; Along the first direction, the size of the negative electrode active material layer is greater than 130 mm, and the first direction is parallel to the direction of gravity.

[0083] Battery cells are used in electrical devices. They are installed inside electrical devices and serve as energy storage or discharge units for storing or releasing electrical energy.

[0084] The first direction is parallel to the direction of gravity. The "direction of gravity" can be the direction of gravity of the battery cell when the electrical device is in use or when the battery cell is mounted on the electrical device. For example, when the vehicle is parked on a level surface, the direction of gravity of the battery cell is its height, and the first direction is parallel to the height of the battery cell.

[0085] In some examples, when the negative electrode is in the unfolded state, the first direction may be parallel to the width direction of the negative electrode.

[0086] Along the first direction, the size of the negative electrode active material layer is L, where L > 130 mm.

[0087] Along the first direction, the size of the negative electrode active material layer can refer to the distance between two end faces of the negative electrode active material layer that are relatively distributed along the first direction.

[0088] In some examples, the value of L can be any value greater than 130 mm; for example, the value of L can be, but is not limited to, 135 mm, 140 mm, 150 mm, 160 mm, 200 mm, 300 mm, 400 mm, 500 mm, 600 mm, 700 mm, etc.; along the first direction, the size L of the negative electrode active material layer can be the width or height of the negative electrode active material layer. A battery cell with L > 130 mm can be called a high-strength battery cell.

[0089] In some examples, linear carboxylic acid esters may include, but are not limited to, at least one of methyl formate, methyl acetate, ethyl acetate, methyl propionate, ethyl propionate, methyl butyrate, and ethyl butyrate.

[0090] In this application's technical solution, carbon-coated graphite is used as the negative electrode active material, which can effectively improve the problems of local electrolyte accumulation and low heat dissipation efficiency in high-efficiency battery cells, thereby improving the cycle life of individual battery cells. Specifically: On the one hand, the amorphous carbon contained in carbon-coated graphite has excellent adsorption capacity for electrolyte, which can effectively "lock" in the electrolyte, enhance the retention effect of the electrolyte, alleviate the tendency of electrolyte to gather towards the lower part of the cell under the action of gravity, and thus improve the electrolyte wetting state of the upper electrode. At the same time, the rich pore structure of amorphous carbon can enhance capillary action, making the electrolyte more evenly distributed in the electrode. The more even distribution of electrolyte can directly optimize the internal reaction environment of the battery, reduce the reaction differences caused by insufficient local wetting, make the current distribution more balanced, reduce the risk of local current overload, and thus improve the cycle life of the battery cell.

[0091] On the other hand, the amorphous carbon on the surface of carbon-coated graphite can significantly improve its electronic conductivity. On this basis, the abundant pore structure contained in its amorphous carbon can serve as a fast migration channel for lithium ions. Thus, by optimizing the diffusion path of lithium ions inside the negative electrode, the ion diffusion resistance can be greatly reduced, making lithium ions more evenly distributed in the battery system. This effectively alleviates the lithium ion concentration gradient problem caused by the long transport path in high-density cells, reduces concentration polarization, and thus greatly improves the cycle life of the battery.

[0092] On the other hand, carbon-coated graphite possesses both excellent thermal conductivity and structural stability. Its superior thermal conductivity accelerates the rapid conduction and dispersion of heat within the cell, preventing heat accumulation and the formation of hot spots in localized areas. The reduction of localized hot spots directly lowers the risk of ethyl acetate in the electrolyte decomposing due to high temperatures, thereby reducing side reactions caused by solvent decomposition. Simultaneously, in fast-charging scenarios, the amorphous carbon on the surface of carbon-coated graphite effectively disperses current, reducing localized overheating and significantly improving the overall thermal uniformity of the cell. Ultimately, this slows down battery performance degradation and greatly extends its cycle life.

[0093] Furthermore, in this embodiment, a linear carboxylic acid ester is used as the solvent for the electrolyte. This helps to reduce the viscosity of the electrolyte, significantly improving its wettability and reflux capability in the high-performance battery cell. This enhances the electrolyte's creeping ability within the high-performance battery cell, improves its uniform distribution, further optimizes the ion transport environment inside the high-performance battery cell, effectively reduces the risk of electrolyte accumulation at the bottom of the cell, and ensures good electrolyte wetting of the upper electrode. This reduces local reaction differences caused by uneven electrolyte distribution, makes the current density distribution more balanced, reduces the risk of polarization aggravation and overheating caused by local current overload, and further improves the cycle life of the high-performance battery cell.

[0094] However, in practical applications of battery cells, although ethyl acetate, as a linear carboxylic acid ester, possesses low viscosity characteristics and can improve the reflux capacity of the electrolyte by reducing the overall viscosity of the electrolyte, thus playing a positive role in improving fast charging capability, it also has the following problems, both in itself and in combination with carbon-coated graphite: First, ethyl acetate has poor reduction stability and easily loses electrons and decomposes on the surface of carbon-coated graphite. This not only continuously consumes the active sites on the surface of the electrolyte and carbon-coated graphite but may also damage the stability of the negative electrode SEI film, adversely affecting the cycle life of the battery; Second, although carbon-coated graphite achieves excellent conductivity due to the amorphous carbon on its surface, its theoretical specific capacity is low, making it difficult to meet the higher requirements of high-energy-density batteries for negative electrode capacity; and ethyl acetate also has insufficient oxidation stability and poor compatibility with high-voltage positive electrode materials, making it difficult to achieve stable cycling under high-voltage conditions. The combination of these two factors limits the improvement of the energy density of battery cells.

[0095] Based on this, in this embodiment, the negative electrode active material layer has a double-layer structure, wherein the layer closer to the negative electrode current collector is the first negative electrode active material layer, and the layer farther away from the negative electrode current collector is the second negative electrode active material layer. The first negative electrode active material layer includes first graphite, and the second negative electrode active material layer includes second graphite.

[0096] Specifically, the negative electrode active material layer includes a first negative electrode active material layer and a second negative electrode active material layer disposed along the thickness direction of the negative electrode current collector, and the first negative electrode active material layer is disposed between the negative electrode current collector and the second negative electrode active material layer; the first negative electrode active material layer includes a first graphite, the second negative electrode active material layer includes a second graphite, and the second graphite includes carbon-coated graphite; the graphitization degree of the first graphite is 94%-98%.

[0097] The negative electrode sheet in this application adopts a double-layer coating design. By differentiating the negative electrode active material layer, the side reaction between carbon-coated graphite and linear carboxylic acid ester can be effectively mitigated, and the battery cell can achieve both good fast charging capability and high energy density, as detailed below: The second active material layer, located near the electrolyte, is made of carbon-coated graphite. The amorphous carbon on the surface of this type of graphite not only significantly improves its conductivity and further reduces ion diffusion resistance to accelerate lithium-ion transport, but also promotes the uniform distribution of lithium ions within the battery system. Simultaneously, the presence of amorphous carbon in the second active material layer, due to its proximity to the electrolyte, enhances the electrode's ability to retain the electrolyte. Combined with the low-viscosity electrolyte containing linear carboxylic acid esters used in this application, the electrolyte's creepage and reflux efficiency can be further optimized, constructing a rapid lithium-ion transport channel, increasing the electrochemical reaction rate of lithium ions, and endowing the battery cell with excellent fast-charging capabilities.

[0098] The first active material layer, located near the negative electrode current collector, uses highly graphitized graphite as the active material. Specific values ​​are shown above. High graphitization means a complete crystal structure and regular interlayer spacing. Although the ion diffusion rate is relatively slow, it provides a higher specific capacity. Placing it near the negative electrode current collector avoids the direct impact of the intense ion flow during fast charging, improving structural stability, while also fully leveraging its high specific capacity to support stable energy storage and increase overall energy density.

[0099] As an example, the graphitization degree of the first graphite can be typical but not limiting values ​​such as 94%, 95%, 95%, 97%, 98%.

[0100] In some embodiments, the Dv50 particle size of the first graphite is larger than the Dv50 particle size of the second graphite.

[0101] The second active material layer, located near the electrolyte, uses graphite with a small median particle size as the negative electrode active material. The small particle size significantly increases its specific surface area, providing more active sites for lithium ion insertion and extraction. This results in a faster lithium ion insertion / extraction rate and a significant improvement in solid-phase transport capability, thereby enhancing the battery's fast-charging capability.

[0102] In this application, "Dv50" refers to the particle size that, in the particle size distribution, the cumulative volume percentage reaches 50% when measured from the smallest particle size side. The method for determining the Dv50 particle size can refer to GB / T19077-2016 Particle Size Distribution Laser Diffraction Method, such as using a Malvern 2000 (Malvern Master Size 3000) laser particle size analyzer.

[0103] In some embodiments, the specific capacity of the first graphite is greater than or equal to the specific capacity of the second graphite.

[0104] In the first negative electrode active material layer near the negative electrode current collector, graphite with a high specific capacity is selected as the active material, so that the layer can have good stability and high capacity, thereby helping to improve the energy density of the high-energy cell.

[0105] In some embodiments, the first graphite satisfies at least one of the following features (1)-(3): (1) the Dv50 particle size of the first graphite is 14.0μm-18.5μm; (2) the specific capacity of the first graphite is 358mAh / g-368mAh / g; (3) the first graphite includes one or more of primary particles and secondary particles.

[0106] For example, the Dv50 particle size of the first graphite can be typical but not limiting values ​​such as 14.0 μm, 14.5 μm, 15.5 μm, 16.5 μm, 17.5 μm, and 18.5 μm; the specific capacity of the first graphite can be typical but not limiting values ​​such as 358 mAh / g, 360 mAh / g, 362 mAh / g, 364 mAh / g, and 368 mAh / g.

[0107] By screening and optimizing the first graphite layer, the first negative electrode active material layer achieves a high capacity level, thereby giving the battery cell a high energy density. Simultaneously, it effectively reduces irreversible lithium loss during cycling, significantly extending the battery's cycle life. Specifically: Choosing graphite with a larger Dv50 particle size, as shown in the above figures, results in a more regular layered structure and a smoother lithium-ion insertion path. This reduces the disordered accumulation of lithium ions on the surface, thereby lowering the risk of lithium dendrite formation. Furthermore, a larger particle size means a smaller specific surface area, resulting in a lower degree of side reactions and a more uniform and dense SEI film. This effectively reduces lithium consumption during cycling and improves cycle life.

[0108] Choosing the first graphite with a higher specific capacity, as shown above, means that the first graphite has a higher lithium storage capacity, resulting in a higher overall energy density for the battery cell.

[0109] In some embodiments, the second graphite satisfies at least one of the following features (1)-(4): (1) the Dv50 particle size of the second graphite is 9.8μm-13.8μm; (2) the graphitization degree of the second graphite is 90%-93%; (3) the specific capacity of the second graphite is 350mAh / g-358mAh / g; (4) the OI value of the second graphite is 3.6-4.1, the OI value of the second graphite is C004 / C110, C004 is the peak area of ​​the diffraction peak of the 004 crystal plane of the second graphite, and C110 is the peak area of ​​the diffraction peak of the 110 crystal plane of the second graphite.

[0110] For example, the Dv50 particle size of the second graphite can be a typical but not limiting value such as 9.8 μm-13.8 μm; the degree of graphitization of the second graphite can be a typical but not limiting value such as 90%, 91%, 92%, 93%; the specific capacity of the second graphite can be a typical but not limiting value such as 350 mAh / g, 352 mAh / g, 354 mAh / g, 358 mAh / g; and the OI value of the second graphite can be a typical but not limiting value such as 3.6, 3.7, 3.9, 4, 4.1.

[0111] By screening and optimizing the second graphite, lithium ions can be inserted and extracted at a faster rate, giving the second anode active material layer better kinetic performance. Specifically: Choosing graphite with a smaller Dv50 particle size, as shown in the above figures, allows for a shorter diffusion path of lithium ions from the particle surface to the interior, enabling insertion / deintercalation in a shorter time and improving the transport rate.

[0112] Choosing graphitization degree and OI value within the above range is more conducive to building continuous electron conduction channels, providing more lithium-ion diffusion channels, thereby significantly improving the lithium-ion migration rate, reducing concentration polarization caused by the long lithium-ion diffusion path, and extending the battery's cycle life while improving the battery's charge and discharge capabilities.

[0113] In this application, "Dv50" refers to the particle size that, in the particle size distribution, the cumulative volume percentage reaches 50% when measured from the smallest particle size side. The method for determining the Dv50 particle size can refer to GB / T19077-2016 Particle Size Distribution Laser Diffraction Method, such as using a Malvern 2000 (Malvern Master Size 3000) laser particle size analyzer.

[0114] In some embodiments, the thickness ratio of the second negative electrode active material layer to the first negative electrode active material layer is (7:3) to (5:5).

[0115] For example, the thickness ratio of the second negative electrode active material layer to the first negative electrode active material layer can be a typical but non-limiting value such as 7:3, 6:4, or 5:5.

[0116] By controlling the mass ratio of the second negative electrode active material layer to the first negative electrode active material layer within the above range, the battery cell not only has good dynamic performance and excellent charge and discharge capability, but also has high capacity, meeting the needs of long-range electric devices. In some embodiments, the negative electrode sheet satisfies at least one of the following features (1)-(3): (1) The single-sided coating weight of the negative electrode active material layer is 130 mg / 1540 mm. 2 ~160mg / 1540mm 2 (2) The thickness of the negative electrode sheet is 0.115mm-0.125mm; (3) The compaction density of the negative electrode sheet is 1.6 g / cm³. 3 -1.78g / cm 3 .

[0117] By controlling the single-sided coating weight of the negative electrode active material layer within the aforementioned range, the negative electrode capacity is matched with the positive electrode capacity. Furthermore, because the single-sided coating weight of the positive electrode active material layer is relatively high, this means the battery cell possesses a high energy density and discharge level. For example, the single-sided coating weight of the negative electrode active material layer can be 130 mg / 1540 mm². 2 140mg / 1540mm 2 150mg / 1540mm 2 160mg / 1540mm 2 Typical but not restrictive values.

[0118] Controlling the thickness of the negative electrode sheet within the aforementioned range can effectively reduce the rebound of the negative electrode sheet, reduce the expansion force of the battery, and thus reduce the risk of electrolyte drying due to excessive expansion force in the later stages of cycling, thereby improving the cycle life of the battery. For example, the thickness of the negative electrode sheet can be typical but not limiting values ​​such as 0.115mm, 0.117mm, 0.120mm, 0.123mm, and 0.125mm.

[0119] By controlling the compaction density of the negative electrode sheet within the aforementioned range, the battery cell can achieve both high energy density and good kinetic performance. For example, the compaction density of the negative electrode sheet can be 1.6 g / cm³. 3 1.65 g / cm 3 1.7 g / cm 3 1.72 g / cm 3 1.75 g / cm 3 1.78g / cm3 Typical but not restrictive values.

[0120] In some embodiments, the negative electrode sheet is cold-pressed twice or multiple times to obtain a negative electrode sheet with a specific thickness or compaction density.

[0121] After repeated cold pressing, the negative electrode sheet is reduced in terms of rebound, which reduces the expansion force of the cell. This reduces the risk of electrolyte leakage and subsequent battery drain in the later stages of cycling due to excessive expansion force, thus improving battery life.

[0122] In some embodiments, the negative electrode sheet is heated and baked and then subjected to secondary or multiple cold pressing to obtain a negative electrode sheet with a specific thickness or compaction density.

[0123] The baking process helps release residual stress in the negative electrode sheet, and the subsequent cold pressing can fix the electrode sheet well, thereby reducing electrode rebound, reducing cell expansion force, reducing the risk of electrolyte squeezing out due to excessive expansion force in the later stages of cycling, and thus improving battery life.

[0124] In some embodiments, the positive electrode sheet includes a positive current collector and a positive active material layer disposed on at least one side of the positive current collector, wherein the positive electrode sheet satisfies at least one of the following features (1)-(3): (1) the single-sided coating weight of the positive active material layer is 310 mg / 1540 mm. 2 ~350mg / 1540mm 2 (2) The thickness of the positive electrode sheet is 0.17mm-0.18mm; (3) The compaction density of the positive electrode sheet is 2.6 g / cm³. 3 -2.8 g / cm 3 .

[0125] Controlling the single-sided coating weight of the positive electrode active material layer within the aforementioned range is more beneficial for improving the energy density of the battery. For example, the single-sided coating weight of the positive electrode active material layer can be 310 mg / 1540 mm². 2 320mg / 1540mm 2 330mg / 1540mm 2 340mg / 1540mm 2 350mg / 1540mm 2 Typical but not restrictive values.

[0126] Controlling the thickness of the positive electrode within the above range allows lithium ions to have an appropriate transport path, which helps to improve the lithium ion transport rate. For example, the thickness of the positive electrode can be a typical but not limiting value such as 0.17mm, 0.172mm, 0.175mm, 0.177mm, or 0.18mm.

[0127] By controlling the compaction density of the positive electrode sheet within the aforementioned range, the battery cell achieves a high energy density, meeting the requirements of long-range electric devices. For example, the compaction density of the positive electrode sheet can be 2.6 g / cm³. 3 2.65 g / cm 3 2.7g / cm 3 2.75 g / cm 3 2.8 g / cm 3 Typical but not restrictive values.

[0128] In some embodiments, the solvent further includes cyclic carbonates, wherein the mass ratio of linear carboxylic acid ester to cyclic carbonate is (6-7):(3-4).

[0129] For example, cyclic carbonates include, but are not limited to, one or more of ethylene carbonate (EC), propylene carbonate (PC), and butene carbonate (BC).

[0130] For example, the mass ratio of linear carboxylic acid ester to cyclic carbonate ester can be typical but not limiting values ​​such as 6:4, 7:3, 6.5:3.5.

[0131] Carbonate solvents can better dissociate lithium salts, which helps to improve the conductivity of the electrolyte, while linear carboxylic esters are more conducive to reducing the viscosity of the electrolyte. The combination of the two results in an electrolyte with high conductivity and low viscosity, thereby improving the electrolyte's climbing ability and wetting effect in high-performance cells, reducing the risk of electrolyte accumulation in local areas, improving the wetting effect of the upper electrode on the electrolyte, reducing concentration polarization, improving the risk of lithium plating on the electrode, and improving the cycle life of the battery.

[0132] In some embodiments, the solvent further includes linear carbonates and cyclic carbonates, wherein the mass ratio of linear carboxylic acid ester, linear carbonate to cyclic carbonate is (2-4):(3-4):(3-4).

[0133] For example, the mass ratio of linear carboxylic esters, linear carbonates to cyclic carbonates can be typical but not limiting values ​​such as 3:3:4, 3:4:3, 3:4:3, 2:4:3, 2:4:4, etc.

[0134] As an example, linear carbonates include, but are not limited to, at least one of dimethyl carbonate (DMC), diethyl carbonate (DEC), and ethyl methyl carbonate (EMC).

[0135] Linear carbonates and linear carboxylic acids help reduce the viscosity of the electrolyte, while cyclic carbonates can better dissociate lithium salts. The combination of these three can reduce the flow resistance of the electrolyte, improve its reflux efficiency in the battery, thereby reducing the concentration difference in high-capacity cells and improving the battery's fast charging capability and cycle performance.

[0136] In some embodiments, the conductivity of the electrolyte is 9 mS / cm-18 mS / cm.

[0137] For example, the conductivity of the electrolyte can be any one of 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, 18.5 S / cm, or fall within any range of two of these values. Within the aforementioned range, active ions exhibit a high migration rate, thereby significantly improving the battery's kinetic performance.

[0138] In some embodiments, the conductivity of the electrolyte is 14 mS / cm-18.5 mS / cm.

[0139] For example, the conductivity of the electrolyte can be any one of 14 mS / cm, 15 mS / cm, 16 mS / cm, 17 mS / cm, 18 mS / cm, 18.5 S / cm, or within any range of two.

[0140] By controlling the electrolyte conductivity within the aforementioned range, active ions can exhibit high transport capabilities. This allows for high migration efficiency even along the long transport paths of high-performance cells, significantly improving the migration efficiency of active ions and resulting in better kinetic performance of the battery cell. Simultaneously, stable and efficient ion transport can also mitigate concentration polarization caused by concentration gradients within the electrode, ensuring timely and sufficient ion supply at the electrode interface. This, in turn, enables the battery cell to possess both high volumetric energy density and good kinetic performance.

[0141] In this application, conductivity is a physical quantity that measures the ability of ions in an electrolyte to conduct current. It is the reciprocal of the electrolyte's resistivity, and its unit is Siemens per meter (S / m). Conductivity is typically measured using a conductivity meter. The specific testing procedure is as follows: Take about 10 mL of sample in a dry, clean, corrosion-resistant sample bottle, seal it, and place it in a constant temperature water bath at 25°C ± 0.5°C. Shake it occasionally. When the sample temperature is constant, replace the bottle cap with a rubber stopper with an electrode inserted. When the temperature is within the range of 25°C ± 0.5°C, read the data, which is the conductivity of the tested sample.

[0142] In some embodiments, the viscosity of the electrolyte is 0.5 mm at 25°C. 2 / s-4mm 2 / s.

[0143] The viscosity of an electrolyte can be determined using instruments and methods known in the art. For example, for non-Newtonian fluids, the capillary viscometer method provided in the national standard GB / T22235-2008 "Determination of Viscosity of Liquids" can be referenced. A capillary viscometer calculates viscosity by measuring the time required for a given volume of electrolyte to flow through a capillary of known diameter at a constant temperature.

[0144] For example, the viscosity of the electrolyte can be 0.5 mm. 2 / s, 1mm 2 / s, 1.5mm 2 / s, 2mm 2 / s, 2.5mm 2 / s, 3mm 2 / s, 3.5mm 2 / s, 4mm 2 / s, etc., or within the range of any two of them.

[0145] Controlling the electrolyte viscosity within the aforementioned range signifies that the electrolyte possesses high conductivity and low viscosity characteristics. On one hand, a high-conductivity, low-viscosity electrolyte significantly enhances the diffusion rate of active ions and reduces their migration resistance. This results in significantly improved wettability and reflux capacity of the electrolyte within the battery cell, thereby increasing the transport rate of active ions and significantly improving the battery's kinetic performance. On the other hand, a low-viscosity electrolyte exhibits high fluidity. During charge-discharge cycles, it can not only more rapidly transport ions from high-concentration regions to low-concentration regions, reducing the concentration difference between the interface and the bulk, improving concentration polarization, and increasing the electrochemical reaction rate, but also effectively enhance the electrolyte's wetting effect and penetration capacity onto the electrodes. This allows the electrolyte to more easily penetrate the micropores within the electrodes, expanding the effective channels for ion transport, increasing the contact area between the electrolyte and the electrodes, further optimizing charge transfer efficiency, and ultimately improving the battery's kinetic performance. Thus, a high-conductivity, low-viscosity electrolyte enables battery cells to achieve both high energy density and good fast-charging performance.

[0146] In some embodiments, the electrolyte comprises a lithium salt, which includes at least one of lithium hexafluorophosphate, lithium tetrafluoroborate, lithium bis(oxalatoborate) (LiBOB), lithium bis(trifluoromethanesulfonyl)imide, lithium perchlorate, and lithium hexafluoroarsenate.

[0147] These lithium salts have high lithium-ion transference numbers. Therefore, by selecting the above-mentioned lithium salts in the embodiments of this application, it is helpful to improve the ionic conductivity of the electrolyte, so that the diffusion rate of lithium ions in the electrolyte is faster, thereby improving the kinetic performance of the battery.

[0148] In some embodiments, the concentration of lithium salt in the electrolyte can be 1 mol / L to 1.4 mol / L.

[0149] In some embodiments, the electrolyte injection coefficient of a single battery cell is 2.7 g / Ah to 3.2 g / Ah.

[0150] The electrolyte filling factor of a battery cell refers to the ratio of the mass of electrolyte inside the battery cell to the battery capacity. The electrolyte filling factor of a battery cell can be obtained by any method known in the art. For example, the mass of electrolyte in a battery cell can be obtained by the following method: Weigh the battery and record the mass as M0. Disassemble the battery cell and pour out the free electrolyte. 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 dimethyl carbonate (DMC) solvent for 24-48 hours, repeating the soaking 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 dry. Weigh the dried positive electrode, negative electrode, separator, and mechanical parts and record the mass as M1. The electrolyte mass in the battery cell is thus (M0-M1). The electrolyte filling coefficient is calculated by dividing (M0-M1) by the rated capacity of the battery cell. The rated capacity is the nominal capacity of the battery.

[0151] In this embodiment, by using the aforementioned electrolyte with low viscosity and high ionic conductivity, and limiting the injection coefficient to the above range, not only is the wetting of the electrode assembly satisfied, but more electrolyte is also formed into a gel and fixed inside and around the electrode pores, satisfying the electrolyte consumption of the long-life cell. It also allows lithium ions to have a high transport rate and sufficient transport channels in the electrolyte, so that the battery has a high electrochemical reaction rate. Thus, the battery cell can have both good cycle stability and high energy density.

[0152] For example, the electrolyte injection coefficient of a single battery cell can be a typical but non-limiting value such as 2.7 g / Ah, 2.8 g / Ah, 2.9 g / Ah, 3.0 g / Ah, 3.1 g / Ah, or 3.2 g / Ah.

[0153] In some embodiments, the electrolyte also includes additives, including vinylene carbonate, and the mass concentration of the additives in the electrolyte is 1%-2%.

[0154] Selecting the above-mentioned additives and controlling their content within the above-mentioned range helps to improve the conductivity of the electrolyte and reduce its viscosity, thereby obtaining a high-conductivity, low-viscosity electrolyte.

[0155] In some embodiments, the negative electrode active material layer includes a first conductive agent, which includes a zero-dimensional conductive agent and a multi-dimensional conductive agent, and the multi-dimensional conductive agent includes at least one of a one-dimensional conductive agent and a two-dimensional conductive agent.

[0156] This application utilizes a combination of zero-dimensional and multi-dimensional conductive agents. The zero-dimensional conductive agent forms point contacts with the negative electrode active material to construct a local conductive network, while the multi-dimensional conductive agent can construct a continuous electron transport network. For example, a one-dimensional conductive agent can construct a long-range conductive network, and a two-dimensional conductive agent can construct a large-area conductive connection. In this way, the two work synergistically to form a stable and efficient conductive network, enabling electrons to not only have the ability to transport over long distances but also enhancing the uniformity of electron conduction. This alleviates the local polarization and lithium plating problems of the negative electrode sheet, thereby improving the cycle performance of the high-performance battery cell.

[0157] In this application, zero-dimensional conductive agents refer to conductive materials whose length, width, and height dimensions are all at the nanoscale (typically 1-100 nm) in three-dimensional space. Their particle morphology is spherical or near-spherical and lacks obvious directionality. As an example, zero-dimensional conductive agents may include, but are not limited to, at least one of conductive carbon black, Ketjen black, and acetylene black. These conductive agents are mainly dispersed between the negative electrode active materials through point contact, filling gaps and constructing local conductive connections. This effectively reduces the contact resistance between the negative electrode active material particles and improves the overall conductivity uniformity of the electrode.

[0158] In this application, a one-dimensional conductive agent refers to a conductive material in three-dimensional space where one dimension (length) is much larger than the other two dimensions (diameter), exhibiting a fibrous, rod-like, or tubular structure and possessing obvious directionality. As an example, a one-dimensional conductive agent may include, but is not limited to, at least one of carbon nanotubes and carbon nanofibers, wherein the aspect ratio of the one-dimensional conductive agent is 5000-15000. As an example, carbon nanotubes include at least one of multi-walled carbon nanotubes, single-walled carbon nanotubes, and few-walled nanotubes. These conductive agents can construct long-range continuous conductive pathways through line contact methods, and multiple one-dimensional conductive agents can form a three-dimensional conductive network by interleaving and overlapping each other, thereby reducing the resistance of the electrode, increasing the lithium-ion transport rate, and reducing local polarization. Simultaneously, the network structure formed by the overlapping of one-dimensional conductive agents has a certain degree of elasticity and toughness, which can constrain the negative electrode active material, reduce the expansion of the negative electrode active material during battery charging and discharging, and ultimately improve the battery's cycle performance and kinetic performance.

[0159] In this application, the length and diameter of the one-dimensional conductive agent can be measured using any method commonly used in the art, such as taking pictures of the one-dimensional conductive agent using a scanning electron microscope or a scanning transmission electron microscope.

[0160] This application discloses, in some embodiments, a method for determining the average tube length of the one-dimensional conductive agent in the negative electrode active material layer. Taking carbon nanotubes as an example, the specific process is as follows: In this application, the battery cell is first placed in a 1.0 mol / L sodium hydroxide aqueous solution at room temperature for discharge treatment. After the discharge is completed, the negative electrode sheet is manually disassembled and finely sliced ​​layer by layer at different thickness positions using cryo-focused ion beam (FIB) (the smallest scale can be nanoscale thin film), and different layer samples along different thickness positions are separated. The samples from different layers at different locations were placed in a scanning electron microscope. The magnification of the instrument was adjusted to 30K / 40K. 20 to 50 carbon nanotubes were selected in the field of view, and their lengths were counted. The average length was taken as the average length (μm) of the carbon nanotubes.

[0161] In this application, a two-dimensional conductive agent refers to a conductive material in three-dimensional space where two dimensions (length and width) are much larger than the third dimension (thickness), exhibiting a sheet-like or layered structure. It possesses planar ductility, with a thickness typically in the nanometer range and a planar size reaching the micrometer range. As an example, a two-dimensional conductive agent may include, but is not limited to, at least one of layered conductive graphite and graphene. This type of conductive agent can contact the negative electrode active material particles through surface contact, forming a large-area conductive connection. Simultaneously, it can cover a greater portion of the negative electrode active material surface, thereby effectively improving local conductivity and increasing the transport rate of active ions.

[0162] In some embodiments, the mass ratio of zero-dimensional conductive agent to multi-dimensional conductive agent is 4:1 to 1:4.

[0163] For example, the mass ratio of zero-dimensional conductive agent to multi-dimensional conductive agent can be typical but not limiting values ​​such as 4:1, 3:1, 2:1, 1:1, 1:2, 1:3, 1:4, etc.

[0164] Controlling the mass ratio of zero-dimensional conductive agent to multi-dimensional conductive agent within the above-mentioned range allows for easier and more uniform dispersion of multi-dimensional conductive agent in the negative electrode active material layer, reducing the risk of agglomeration and stacking. On the other hand, it promotes the insertion and filling of zero-dimensional conductive agent between multi-dimensional conductive agents, thereby forming an electron transport channel that combines long-range continuous conductive network and local conductivity, improving the transport efficiency of active ions, reducing the risk of local lithium plating on the electrode, and thus improving the cycle performance of the battery.

[0165] In some embodiments, the mass ratio of zero-dimensional conductive agent to one-dimensional conductive agent is 4:1 to 1:1. As an example, the mass ratio of zero-dimensional conductive agent to one-dimensional conductive agent can be typical but not limiting values ​​such as 4:1, 3:1, 2:1, 1:1, etc.

[0166] To further improve the dispersibility of the multidimensional conductive agent in the negative electrode active material layer, this application embodiment employs a compound of an amino-containing dispersant and a cellulose ether dispersant, effectively improving the dispersibility of the multidimensional conductive agent and thus forming a more efficient conductive network. Specifically, the negative electrode active material layer further includes a first dispersant, which comprises an amino-containing dispersant and a cellulose ether dispersant. The amino-containing dispersant includes at least one of polyethyleneimine, a polyetheramine-polydopamine complex, and an amino-containing zwitterionic polymer, and the cellulose ether dispersant includes sodium carboxymethyl cellulose.

[0167] Because amino-containing dispersants contain amino groups on their surface, they can, on the one hand, be tightly adsorbed onto the surface of multidimensional conductive agents through hydrogen bonds, electrostatic attraction, and other forces. By utilizing their own steric hindrance, they can inhibit the aggregation of multidimensional conductive agents and improve the dispersion uniformity of multidimensional conductive agents. On the other hand, they can form surface adsorption with negative electrode active materials through hydrogen bonds and dipole interactions. In this way, amino-containing dispersants bridge the negative electrode active materials and multidimensional conductive agents, improve the contact effect between active materials and conductive agents, and help to build continuous and efficient conductive pathways.

[0168] For example, the structure of zwitterionic polymers is shown in Formula I. This type of dispersant can simultaneously adsorb charged particles, enhance the electrostatic shielding effect, and thus further improve the dispersibility of multidimensional conductive agents.

[0169] Formula I.

[0170] Cellulose ether dispersants act as thickeners, significantly increasing the viscosity of the negative electrode slurry. This increases the cohesive force of the system, inhibiting the sedimentation of individual components and ensuring uniform suspension of the conductive agent and negative electrode active material within the slurry. This reduces the risk of stratification due to gravity. Simultaneously, cellulose ether dispersants can form hydrogen bonds with the hydroxyl groups on the surface of the negative electrode active material. This interaction effectively inhibits the aggregation of negative electrode active material particles, improving the dispersibility of the negative electrode active material. For multidimensional conductive agents, the molecular chains of the cellulose ether dispersant can wrap around the surface of the multidimensional conductive agent through steric hindrance, inhibiting secondary aggregation and further enhancing the dispersion effect of the multidimensional conductive agent.

[0171] Therefore, this application uses two dispersants in combination. The amino-containing dispersant helps to improve the dispersibility of the multidimensional conductive agent, thereby constructing a continuous and stable conductive path. The cellulose ether dispersant improves the dispersion stability of the entire system through thickening, so that the negative electrode sheet still has a good continuous conductive network during cycling, thus ensuring the long cycle life of the battery.

[0172] Furthermore, since binders are prone to swelling and can easily fill the interlayer of the negative electrode active material, thus blocking the lithium-ion transport channels, the use of amino-containing dispersants to bridge the multidimensional conductive agent and the negative electrode active material allows the rigid multidimensional conductive agent to act as a scaffold and fill the interlayer of the negative electrode active material. The multidimensional conductive agent itself can act as an electron transport channel or form an ion transport channel, which helps to maintain the stability of the ion diffusion channel and improve ion transport efficiency.

[0173] In some embodiments, the mass ratio of amino dispersant to cellulose ether dispersant is 2:1 to 1:4.

[0174] For example, the mass ratio of amino-containing dispersant to cellulose ether dispersant can be typical but not limiting values ​​such as 2:1, 1:1, 1:2, 1:3, 1:4, etc.

[0175] By controlling the mass ratio of amino-containing dispersant and cellulose ether dispersant within the above range, an appropriate amount of amino-containing dispersant is contained in the negative electrode system to improve the dispersibility of multidimensional conductive agent and negative electrode active material. This allows for the construction of a stable and continuous penetrating conductive network in the high VED system, improving electron transport efficiency. It also enables the negative electrode slurry to have better uniformity, making it less prone to particle sedimentation and improving the slurry processing performance, thereby enhancing the uniformity of the negative electrode active material layer.

[0176] In some embodiments, the negative electrode active material layer further includes a first binder, which includes a dot binder and a linear binder; wherein the linear binder contains at least one of the following groups: carboxyl group, lithium carboxyl group.

[0177] Linear binders contain numerous polar functional groups, such as carboxyl groups and lithium-ionized carboxyl groups. These groups can react with amino-containing dispersants; for example, carboxyl groups and amine groups (-NH2) undergo a condensation reaction to form amide bonds (-CO-NH-), thereby creating a high-mechanical-strength elastic network within the active material layer. Amino-containing dispersants can bridge the multidimensional conductive agent and the negative electrode active material. Furthermore, they can undergo condensation reactions with linear binders. Thanks to the excellent conductivity of amide bonds, multidimensional conductive agents can form a continuous and efficient three-dimensional conductive network through amino-containing dispersants and linear binders. Therefore, during cycling, the presence of this high-mechanical-strength elastic network effectively restrains the negative electrode active material, not only suppressing the volume expansion of the negative electrode sheet but also helping to maintain the circuit integrity of the three-dimensional conductive network, thereby improving the electron transport rate and ultimately endowing the battery with better cycle performance and excellent kinetic performance.

[0178] Meanwhile, multiple linear binders and multiple amino-containing dispersants cross-link with each other through condensation reaction to form hydrophilic nanochannels, which increase the adsorption capacity of electrolyte and thus form a rapid lithium-ion transport chain, further improving the reaction kinetics performance of the battery.

[0179] Therefore, dotted binders provide adhesion between negative electrode active materials through point contact, while linear binders provide a continuous and high-strength elastic network, effectively connecting the components tightly. The combination of the two significantly enhances the cohesion of the negative electrode sheet, thereby effectively improving the adhesion and conductivity of the negative electrode active material layer, suppressing the volume expansion of the negative electrode sheet, and improving the cycle performance and dynamic performance of the battery.

[0180] In some embodiments, the linear binder includes at least one of polyacrylic acid, polymethacrylic acid, lithium polyepoxysuccinate, lithium-ionized polyacrylic acid, and lithium polymethacrylate.

[0181] The carboxyl groups and lithium carboxyl groups in these linear binders enable them to react with the amino groups in the amino-containing dispersants, thus obtaining an elastic network with high mechanical strength and high adhesion, which fully exerts its binding effect on the negative electrode active material and reduces the degree of electrode expansion.

[0182] In some embodiments, the dotted adhesive includes at least one of styrene-butadiene rubber and fluorinated rubber.

[0183] These dot-shaped adhesives have good adhesion and can improve the uniformity of the bonding effect through point contact.

[0184] In some embodiments, the mass ratio of dotted adhesive to linear adhesive is 4:1 to 1:1.

[0185] For example, the mass ratio of dotted adhesive to linear adhesive can be typical but not limiting values ​​such as 4:1, 3:1, 2:1, 1:1, etc.

[0186] Within the aforementioned range, the battery system not only has sufficient linear binders to form a highly adhesive elastic network, but also utilizes dotted binders to compensate for the rigidity of the linear binders, further enhancing the adhesion ability of the negative electrode active material.

[0187] In some embodiments, the negative electrode active material layer includes a first conductive agent, a first binder, and a first dispersant. The first conductive agent includes a zero-dimensional conductive agent and a multi-dimensional conductive agent, and the multi-dimensional conductive agent includes at least one of a one-dimensional conductive agent and a two-dimensional conductive agent. The first binder includes a dot-like binder and a linear binder. The linear binder includes at least one of the following groups: carboxyl group and lithium-ionized carboxyl group. The first dispersant includes an amino-containing dispersant and a cellulose ether dispersant. The amino-containing dispersant includes at least one of polyethyleneimine, polyetheramine-polydopamine complex, and amino-containing zwitterionic polymer. The cellulose ether dispersant includes sodium carboxymethyl cellulose.

[0188] This application embodiment screens conductive agents, dispersants, and binders in the negative electrode sheet, utilizes multidimensional conductive agents to construct a long-range and continuous conductive network, improves the dispersion effect of multidimensional conductive agents through the bridging effect of amino-containing dispersants, and forms a high-mechanical-strength elastic network through the condensation reaction of amino-containing dispersants and linear binders. Ultimately, this endows the negative electrode sheet with excellent electron transport capability and high structural stability, thereby improving the dynamic performance and cycle life of the battery.

[0189] Meanwhile, by combining a high-conductivity, low-viscosity electrolyte, the transport rate and diffusion coefficient of lithium ions in the electrolyte are improved, which is more conducive to the electrolyte penetrating into the pores in the negative electrode active material layer, increasing the contact area between the electrolyte and the electrode, thereby improving the ion transport efficiency and giving the battery better dynamic performance.

[0190] In some embodiments, the first negative electrode active material layer further includes a first binder, a first conductive agent, and a first dispersant. Based on the total mass of the first negative electrode active material layer, the content of the first graphite is 95%-97.5%, the content of the first binder in the first negative electrode active material layer is 1.2%-2.5%, the content of the first conductive agent in the first negative electrode active material layer is 0.8%-1.3%, and the content of the first dispersant in the first negative electrode active material layer is 0.5%-1.2%.

[0191] In some embodiments, in the first negative electrode active material layer, the mass ratio of zero-dimensional conductive agent to multi-dimensional conductive agent in the first conductive agent can be 4:1 to 2:1. The mass ratio of dot-shaped binder to linear binder in the first binder can be 4:1 to 2:1. The mass ratio of amino-containing dispersant to cellulose ether dispersant in the first dispersant can be 1:2 to 1:4.

[0192] In some embodiments, the second negative electrode active material layer further includes a first binder, a first conductive agent, and a first dispersant. Based on the total mass of the second negative electrode active material layer, the content of the second graphite is 96%-98%, the content of the first binder in the second negative electrode active material layer is 0.8%-2%, the content of the first conductive agent in the second negative electrode active material layer is 0.7%-1%, and the content of the first dispersant in the second negative electrode active material layer is 0.5%-1%.

[0193] In some embodiments, in the second negative electrode active material layer, the mass ratio of zero-dimensional conductive agent to multi-dimensional conductive agent in the first conductive agent can be 2:1 to 1:1. The mass ratio of dot-like binder to linear binder in the first binder can be 2:1 to 1:1. The mass ratio of amino-containing dispersant to cellulose ether dispersant in the first dispersant can be 2:1 to 1:2.

[0194] In some embodiments, the negative electrode sheet further includes a coating disposed between the negative electrode current collector and the negative electrode active material layer; wherein the coating includes a second conductive agent, a second binder, and a second dispersant.

[0195] By setting a coating between the negative electrode current collector and the negative electrode active material layer, the contact resistance between the two can be effectively reduced, allowing electrons to be conducted from the negative electrode active material layer to the negative electrode current collector at a faster speed, reducing charge accumulation, increasing electron conduction rate, and improving the battery's dynamic performance. At the same time, the coating also has good adhesion properties, allowing the negative electrode active material layer to be better fixed on the surface of the negative electrode current collector, significantly improving the peel strength of the negative electrode active material layer, reducing the risk of detachment, and thus optimizing the battery's cycle life.

[0196] For example, the second adhesive may include one or more 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).

[0197] For example, the second dispersant includes sodium carboxymethyl cellulose (CMC-Na).

[0198] For example, the second conductive agent may include one or more of carbon black, carbon dots, carbon nanotubes, graphene, and carbon nanofibers. The carbon black may include one or more of superconducting carbon, acetylene black, and Ketjen black.

[0199] To further enhance the electronic conductivity of the coating and optimize its kinetic properties, the second conductive agent includes graphene and carbon black, for example, the mass ratio of graphene to carbon black is (1-3):1. This allows for the combination of planar conductive networks with synergistic point contacts to construct an efficient and continuous conductive network, thereby enhancing electronic conductivity and improving the kinetic properties of the coating.

[0200] In some embodiments, based on the mass of the coating, the content of the second conductive agent is 63%-65%, the content of the second binder is 30%-32%, and the content of the second dispersant is 3%-5%.

[0201] By controlling the content of each component in the coating within the above range, the synergistic effect of each component is promoted, forming a stable and uniform coating, and giving it better conductivity and adhesion properties.

[0202] In some embodiments, the coating thickness is 1 μm-3 μm.

[0203] For example, the thickness of the coating can be a typical but non-limiting value such as 1 μm, 1.5 μm, 2 μm, 2.5 μm, 3 μm.

[0204] By controlling the coating thickness within the aforementioned range, the coating exhibits low contact resistance and strong adhesion, thereby contributing to improved battery kinetic performance and cycle life.

[0205] In some embodiments, the size of the negative electrode active material layer is greater than or equal to 150 mm along a first direction, and the first direction is parallel to the direction of gravity.

[0206] Along the first direction, the size of the negative electrode active material layer is L, where L≥150mm.

[0207] Along the first direction, the size of the negative electrode active material layer can refer to the distance between two end faces of the negative electrode active material layer that are relatively distributed along the first direction.

[0208] In some examples, the value of L can be any value of 150 mm or more; for example, the value of L can be, but is not limited to, 150 mm, 160 mm, 200 mm, 300 mm, 400 mm, 500 mm, 600 mm, 700 mm, etc.; along the first direction, the size L of the negative electrode active material layer can be the width or height of the negative electrode active material layer.

[0209] Generally, a battery cell includes a positive electrode, a negative electrode, an electrolyte, and a separator. During charging and discharging, active ions move back and forth between the positive and negative electrodes, inserting and releasing. The electrolyte acts as a conductor of active ions between the positive and negative electrodes. The separator, located between the positive and negative electrodes, primarily prevents short circuits while allowing ions to pass through. The composition of the electrolyte has been described above; the other components of the battery cell will be discussed below.

[0210] Positive electrode sheet In some embodiments, the positive electrode sheet includes a positive current collector and a positive active material layer disposed on at least one surface of the positive current collector, wherein the positive active material layer includes a positive active material.

[0211] As a non-limiting example, the positive current collector has two surfaces opposite each other in its own thickness direction, and the positive active material layer is disposed on either or both of the two opposite surfaces of the positive current collector.

[0212] In some embodiments, the positive electrode current collector may be a metal foil or a composite current collector. For example, aluminum foil may be used as the metal foil. The composite current collector may include a polymer material substrate and a metal layer formed on at least one surface of the polymer material substrate. The composite current collector can be obtained by forming a metal material on a polymer material substrate. Non-limiting examples of the metal material in the above-described positive electrode current collector may include one or more of aluminum, aluminum alloys, nickel, nickel alloys, titanium, titanium alloys, silver, and silver alloys. Non-limiting examples of the polymer material substrate in the above-described positive electrode current collector may include one or more of polypropylene (PP), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polystyrene (PS), and polyethylene (PE).

[0213] In some embodiments, the positive electrode active material may comprise positive electrode active materials known in the art for use in batteries. As an example, the positive electrode active material of a battery cell may include at least one of the following materials: lithium-containing phosphates with an olivine structure, lithium transition non-aluminum metal oxides, and their respective modified compounds. 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. These positive electrode active materials may be used alone or in combination of two or more. Examples of lithium transition non-aluminum metal oxides include, but are not limited to, at least one of lithium cobalt oxide, nickel-cobalt-manganese ternary materials, nickel-cobalt-aluminum ternary materials, nickel-cobalt-manganese-aluminum quaternary materials, lithium iron phosphate, lithium manganese phosphate, lithium vanadium phosphate, lithium manganese oxide, and their modified compounds. Examples of lithium-containing phosphates with an olivine structure include, but are not limited to, one or more of lithium iron phosphate, lithium iron phosphate and carbon composites, lithium manganese phosphate, lithium manganese phosphate and carbon composites, lithium iron manganese phosphate, and lithium iron manganese phosphate and carbon composites.

[0214] In some embodiments, the positive electrode active material layer may optionally include a binder. As a non-limiting example, the binder may include at least one of carboxymethyl cellulose, polypropylene, polyethylene, polyethylene oxide, polyvinylidene fluoride, polyvinylidene fluoride, polytetrafluoroethylene, polyhexafluoropropylene, polyvinylidene fluoride-hexafluoropropylene copolymer, polyamide, polyacrylonitrile, polyacrylate, polyacrylic acid, polyvinylpyrrolidone, polyvinyl ether, polymethyl methacrylate, and styrene-butadiene rubber.

[0215] In some embodiments, the positive electrode active material layer may optionally include a conductive agent. As a non-limiting example, the conductive agent may include one or more of carbon black, carbon dots, carbon nanotubes, graphene, and carbon nanofibers. The carbon black includes one or more of superconducting carbon, acetylene black, and Ketjen black.

[0216] In some embodiments, the positive electrode sheet can be prepared by dispersing the components used to prepare the positive electrode sheet, such as the positive active material, conductive agent, binder, and any other components, in a solvent to form a positive electrode slurry; coating the positive electrode slurry onto at least one surface of the positive electrode current collector, and then obtaining the positive electrode sheet after drying, cold pressing, and other processes. The solvent can be selected from, but is not limited to, any of the solvents in the foregoing embodiments, such as N-methylpyrrolidone (NMP). The surface of the positive electrode current collector coated with the positive electrode slurry can be a single surface of the positive electrode current collector or both surfaces of the positive electrode current collector.

[0217] Negative electrode sheet The negative electrode sheet includes a negative current collector and a negative active material layer disposed on at least one surface of the negative current collector, wherein the negative active material layer includes a negative active material.

[0218] As a non-limiting example, the negative electrode current collector has two surfaces opposite each other in its own thickness direction, and the negative electrode active material layer is disposed on either or both of the two opposite surfaces of the negative electrode current collector.

[0219] In some embodiments, 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 polymer material substrate and a metal layer formed on at least one surface of the polymer material substrate. The composite current collector can be obtained by forming a metal material on the polymer material substrate. Non-limiting examples of the metal material in the above-described negative electrode current collector may include one or more of copper, copper alloys, nickel, nickel alloys, titanium, titanium alloys, silver, and silver alloys. Non-limiting examples of the polymer material substrate in the above-described negative electrode current collector may include one or more of polypropylene (PP), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polystyrene (PS), and polyethylene (PE).

[0220] In some embodiments, the negative electrode sheet can be prepared by dispersing the components used to prepare the negative electrode sheet, such as the negative electrode active material, conductive agent, binder, and any other components, in a solvent (a non-limiting example of a solvent is deionized water) to form a negative electrode slurry; coating the negative electrode slurry onto at least one surface of the negative electrode current collector, and then obtaining the negative electrode sheet after processes such as drying and cold pressing. The surface of the negative electrode current collector coated with the negative electrode slurry can be a single surface of the negative electrode current collector or both surfaces of the negative electrode current collector.

[0221] Separating membrane In some embodiments, the battery cell also includes a separator. This application does not impose any particular limitation on the type of separator; any known porous separator with good chemical and mechanical stability can be selected.

[0222] In some embodiments, the material of the separator may include one or more of glass fiber, nonwoven fabric, polyethylene, polypropylene, and polyvinylidene fluoride. The separator may be a single-layer film or a multi-layer composite film, without particular limitation. When the separator is a multi-layer composite film, the materials of each layer may be the same or different, without particular limitation.

[0223] In some embodiments, the thickness of the isolation membrane is 6μm-40μm, optionally 12μm-20μm.

[0224] In some embodiments, the positive electrode, negative electrode, and separator can be fabricated into an electrode assembly using a winding process or a stacking process.

[0225] In some embodiments, the battery cell may include an outer packaging. This outer packaging can be used to encapsulate the electrode assembly and electrolyte described above.

[0226] In some embodiments, the outer packaging of the battery cell can be a rigid shell, such as a hard plastic shell, an aluminum shell, a steel shell, etc. The outer packaging of the battery cell can also be a flexible package, such as a pouch-type flexible package. The material of the flexible package can be plastic; further, non-limiting examples of plastic may include one or more of polypropylene, polybutylene terephthalate, and polybutylene succinate.

[0227] A second aspect of this application provides a battery device including a plurality of battery cells as described in the above embodiments.

[0228] The battery device mentioned in the embodiments of this application may include one or more battery cell assemblies for providing voltage and capacity. A battery cell assembly may include multiple battery cells, which are connected in series, parallel, or mixed connections via a busbar.

[0229] In some embodiments, a battery cell assembly is typically formed by arranging multiple battery cells.

[0230] As an example, a battery cell assembly can be a battery module, which is formed by arranging and fixing multiple battery cells together to form an independent module. As another example, a battery module can be formed by bundling multiple battery cells together with cable ties.

[0231] In some embodiments, the battery device may be a battery pack, which includes a housing and one or more individual battery cell assemblies housed within the housing.

[0232] As an example, the battery cell assembly can be a battery module, which can be housed in a housing by fixing the battery module in the housing.

[0233] As an example, battery cell assemblies can also be housed in a housing by directly fixing multiple battery cells to the housing.

[0234] As an example, the enclosure may include a first enclosure and a second enclosure. The first enclosure and the second enclosure are fastened together to form a closed space inside the enclosure to house the individual battery cells. Here, "closed" refers to covering or closing, and can be either sealed or unsealed. The first enclosure may be a top cover or a bottom plate.

[0235] As an example, the enclosure may include a top cover, a frame, and a bottom plate. The top cover and bottom plate are connected to the frame, creating an enclosed space inside the enclosure to house the individual battery cells.

[0236] In some embodiments, the housing may be part of the vehicle's chassis structure. For example, a portion of the housing may be at least a part of the vehicle's floor, or a portion of the housing may be at least a part of the vehicle's crossbeams and longitudinal beams.

[0237] A third aspect of the embodiment provides an electrical device, including a battery cell or a battery device as described in the above embodiments, wherein the battery cell and the battery device are used to store or provide electrical energy.

[0238] The technical solutions described in the embodiments of this application are applicable to various electrical devices that use individual battery cells, such as mobile phones, portable devices, laptops, electric vehicles, electric toys, power tools, vehicles, ships, and spacecraft. For example, spacecraft include airplanes, rockets, space shuttles, and spacecraft.

[0239] The following description, with appropriate reference to the accompanying drawings, describes the battery cell, battery device, and power-consuming device provided in the embodiments of this application.

[0240] like Figure 1 As shown, a battery device 2 is installed inside the vehicle 1. The battery device 2 can be located at the bottom, front, or rear of the vehicle 1. The battery device 2 can be used to power the vehicle 1; for example, the battery device 2 can serve as the operating power source for the vehicle 1.

[0241] The vehicle 1 may also include a controller 3 and a motor 4. The controller 3 is used to control the battery device 2 to supply power to the motor 4, for example, for the power needs of the vehicle 1 during starting, navigation and driving.

[0242] In some embodiments of this application, the battery device 2 can not only serve as the operating power source for the vehicle 1, but also as the driving power source for the vehicle 1, replacing or partially replacing fuel or natural gas to provide driving power for the vehicle 1.

[0243] See Figure 2 As shown, in some embodiments, the battery device 2 may include one or more battery cell assemblies for providing voltage and capacity.

[0244] A battery cell assembly may include multiple battery cells 6, which are connected in series, parallel, or mixed connection via a busbar. Mixed connection means that multiple battery cells 6 are connected in both series and parallel.

[0245] Battery cell 6 can be a secondary battery cell. A secondary battery cell refers to a battery cell that can be recharged after being discharged, allowing the active materials to be activated and continue to be used.

[0246] As an example, the battery cell 6 can be a lithium-ion battery cell, a sodium-ion battery cell, a sodium-lithium-ion battery cell, a lithium metal battery cell, a sodium metal battery cell, a lithium-sulfur battery cell, a magnesium-ion battery cell, a nickel-metal hydride battery cell, a nickel-cadmium battery cell, a lead-acid battery cell, etc.

[0247] In some embodiments, a battery cell assembly is typically formed by arranging multiple battery cells 6; as an example, a battery cell assembly can be a battery module, which is formed by arranging and fixing multiple battery cells 6 into a single module. As an example, a battery module can be formed by bundling multiple battery cells 6 together with cable ties.

[0248] In some embodiments, the battery device 2 may be a battery pack, which includes a housing 5 and one or more battery cell assemblies housed within the housing 5. As an example, the battery cell assembly may be a battery module, which can be housed within the housing 5 by securing the battery module to the housing 5. Alternatively, as an example, the battery cell assembly may be housed within the housing 5 by directly securing multiple battery cells 6 to the housing 5.

[0249] In some embodiments, the housing 5 is used to house the battery cell 6, and the housing 5 can have various structures.

[0250] In some embodiments, the housing 5 may include a first housing 51 and a second housing 52. The first housing 51 and the second housing 52 are fastened together to form a closed space inside the housing 5 to house the battery cell assembly. Here, "closed" refers to covering or closing, and can be either sealed or unsealed. The first housing 51 may be a top cover or a bottom plate.

[0251] In some embodiments, the housing 5 may include a top cover, a frame, and a bottom plate. The top cover and the bottom plate are respectively connected to the frame, so that the interior of the housing 5 forms an enclosed space to accommodate the battery cell assembly. As an example, the frame may include multiple side beams.

[0252] In some embodiments, the housing 5 may be part of the chassis structure of the vehicle 1. For example, a portion of the housing 5 may be at least a portion of the floor of the vehicle 1, or a portion of the housing 5 may be at least a portion of the crossbeams and longitudinal beams of the vehicle 1.

[0253] In some embodiments, the battery device 2 may be an energy storage device.

[0254] Energy storage devices can be used in energy storage power stations, wind power generation systems, solar power generation systems, mobile power systems, or temporary power supply systems. Energy storage devices can store electrical energy as needed and output it when appropriate. For example, energy storage devices can store electrical energy during off-peak hours and provide power to relevant users or electrical equipment during peak hours.

[0255] In some embodiments, the energy storage device includes an energy storage container, an energy storage cabinet, etc.

[0256] The following, in conjunction with the appendix Figures 3 to 7 The battery cell 6 of this application will be described in detail with reference to specific embodiments. In the embodiments of this application, see [reference needed]. Figure 3 and Figure 4 As shown, the height direction of the battery cell 6 and the height direction of the casing 21 can be referenced to the Z' direction; the length direction of the battery cell 6 and the length direction of the casing 21 can be referenced to the Y' direction; the thickness direction of the battery cell 6 and the thickness direction of the casing 21 can be referenced to the X' direction; and the thickness direction of the electrode assembly can be referenced to the X' direction. (See also...) Figure 5 As shown, the winding direction of the electrode assembly can be referenced to the direction indicated by arrow V; see also... Figure 6 and Figure 7 As shown, the negative electrode 12 is in an unfolded state. The thickness direction of the negative electrode 12 can be referred to in the Y direction, the length direction of the negative electrode 12 can be referred to in the X direction, and the width direction of the negative electrode 12 can be referred to in the Z direction.

[0257] This application provides a battery cell 6, which includes a housing 20 and an electrode assembly 10, with at least a portion of the electrode assembly 10 housed within the housing 20.

[0258] The outer shell 20 may be a hollow structure, with an internal space for accommodating the electrode assembly 10 and the electrolyte.

[0259] In some embodiments, the housing 20 may be a metal housing, such as a steel housing, an aluminum housing, a composite metal housing (e.g., a copper-aluminum composite housing), or other metal housings. Alternatively, the housing 20 may also be a non-metallic housing, such as a plastic housing (e.g., polypropylene).

[0260] In some embodiments, the housing 20 can be a sealed structure or a non-sealed structure. As an example, when the housing 20 is a non-sealed structure, it serves to protect the electrode assembly, and a sealing bag is included between the housing 20 and the electrode assembly 10 to encapsulate the electrode assembly 10 and the electrolyte. Specifically, the sealing bag can be a bag-shaped insulating component or an aluminum-plastic film. When the housing is a sealed structure, it is used to encapsulate the electrode assembly 10 and components such as the electrolyte.

[0261] As an example, the battery cell 6 can be a square battery cell, a blade-shaped battery cell, a cylindrical battery cell, etc.

[0262] In some embodiments, the housing 20 includes a housing 21 and an end cap 22, the housing 21 having an opening, and the end cap 22 being connected to the housing 21 and covering the opening.

[0263] The housing 21 is a component used to fit the end cap 22 to form the internal cavity of the battery cell 6. The formed internal cavity can be used to accommodate the electrode assembly 10, electrolyte, and other components.

[0264] The housing 21 and the end cap 22 can be separate components. For example, an opening can be provided on the housing 21, and the end cap 22 can be used to close the opening to form an internal cavity for the battery cell.

[0265] The shell 21 can be made of various materials, such as copper, iron, aluminum, stainless steel, aluminum alloy, etc.

[0266] The shape of the end cap 22 can be adapted to the shape of the housing 21 to fit the housing 21. The material of the end cap 22 can be the same as or different from the material of the housing 21. Optionally, the end cap 22 can be made of a material with a certain hardness and strength (such as copper, iron, aluminum, stainless steel, aluminum alloy, plastic, etc.), so that the end cap 22 is not easily deformed when subjected to compression and impact, so that the battery cell can have higher structural strength and improve reliability.

[0267] The end cap 22 is connected to the housing 21 by welding, bonding, snap-fitting or other means.

[0268] The housing 21 may be open at one end or open at both ends. In some examples, the housing 21 may be a structure with an opening on one side, and one end cap 22 is provided to cover the housing 21. In other examples, the housing 21 may also be a structure with openings on both sides, and two end caps 22 are provided, with the two end caps 22 respectively covering the two openings of the housing 21.

[0269] In some embodiments, the end cap 22 may be provided with functional components such as electrode terminals 30. The electrode terminals 30 can be used to electrically connect with the electrode assembly 10 for outputting or inputting electrical energy from the battery cell 6.

[0270] In some embodiments, the end cap 22 may also be provided with a pressure relief mechanism 221 for releasing internal pressure when the internal pressure or temperature of the battery cell 6 reaches a threshold.

[0271] In some embodiments, an insulating element may be provided on the inner side of the end cap 22. The insulating element can be used to isolate the electrical connection components within the housing 21 from the end cap 22 to reduce the risk of short circuits. For example, the insulating element may be made of plastic, rubber, etc.

[0272] Electrode assembly 10 is the component in the battery cell 6 where the electrochemical reaction takes place. Electrode assembly 10 can be entirely housed within housing 20 or partially housed within housing 20. For example, a portion of the tabs of electrode assembly 10 can extend outside housing 20.

[0273] Optionally, the electrode assembly 10 is entirely housed within the housing 20.

[0274] In some embodiments, the electrode assembly 10 includes a positive electrode 11 and a negative electrode 12. During the charging and discharging process of the battery cell 6, active ions (e.g., lithium ions) are inserted and extracted back and forth between the positive electrode 11 and the negative electrode 12.

[0275] In some embodiments, the negative electrode sheet 12 may include a negative electrode current collector 121 and a negative electrode active material layer 122 disposed on at least one surface of the negative electrode current collector 121.

[0276] In some embodiments, the electrode assembly 10 further includes a separator 13 disposed between the positive electrode 11 and the negative electrode 12. The separator 13 serves to prevent short circuits between the positive and negative electrodes while allowing active ions to pass through.

[0277] The separator 13 may be partially located between the positive electrode 11 and the negative electrode 12. For example, the separator 13 protrudes from both ends of the positive electrode 11 and the negative electrode 12 along the height direction of the battery cell 6; or the entire separator 13 may be located between the positive electrode 11 and the negative electrode 12.

[0278] The electrode assembly 10 can be a wound structure, a stacked structure, or a hybrid structure of wound and stacked.

[0279] In some embodiments, the positive electrode 11, the negative electrode 12, and the separator 13 are wound together.

[0280] The electrode assembly 10 has a wound structure. For example, the positive electrode 11, the separator 13, and the negative electrode 12 are wound into a flat wound structure.

[0281] In some embodiments, the electrode assembly 10 has a stacked structure.

[0282] As an example, multiple positive electrode plates 11 and multiple negative electrode plates 12 can be set, and multiple positive electrode plates 11 and multiple negative electrode plates 12 can be stacked alternately.

[0283] As an example, multiple positive electrode plates 11 can be provided, and negative electrode plates 12 can be folded to form multiple stacked folded segments, with a positive electrode plate 11 sandwiched between adjacent folded segments.

[0284] As an example, both the positive electrode 11 and the negative electrode 12 are folded to form multiple stacked folded segments.

[0285] As an example, multiple separators 13 can be provided, respectively disposed between any adjacent positive electrode 11 or negative electrode 12.

[0286] As an example, the separator 13 can be continuously arranged and disposed between any adjacent positive electrode 11 or negative electrode 12 by means of folding or rolling.

[0287] In some embodiments, the electrode assembly 10 may be flat.

[0288] Example 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.

[0289] Example 1 This embodiment provides a single battery cell.

[0290] Preparation of positive electrode sheet The positive electrode active material (lithium iron phosphate), conductive agent carbon black, and binder (polyvinylidene fluoride PVDF) were uniformly mixed at a mass ratio of 8:1:1. N-methylpyrrolidone was then added for dispersion, and the solid content of the slurry was controlled at 55%. The mixture was coated on both sides of an aluminum foil, pre-dried, and then rolled to obtain the positive electrode active material layer. The single-sided coating weight of the positive electrode active material layer was 350 mg / 1540 mm². 2 The compacted density is 2.7 g / cm³. 3 The positive electrode sheet is obtained by heating the material to 110°C in a 40m long oven at a baking speed of 5-20m / min, controlling the water content of the positive electrode active material layer to be below 250ppm.

[0291] Preparation of negative electrode sheet A negative electrode active material (carbon-coated graphite, Dv50 of 12 μm, specific capacity of 355 mAh / g, graphitization degree of 92%), binder (styrene-butadiene rubber SBR), conductive agent (carbon black), and dispersant (sodium carboxymethyl cellulose CMC-Na) were mixed in a weight ratio of 97.8:1:0.7:0.5. Deionized water was added as a solvent, and the mixture was stirred thoroughly to prepare a negative electrode slurry. The negative electrode slurry was uniformly coated on both sides of a copper foil, pre-dried, and then rolled to obtain a negative electrode active material layer. The single-sided coating weight of the negative electrode active material layer was 160 mg / 1540 mm². 2 The compacted density is 1.68 g / cm³. 3 The material is dried in a 40m long oven at a baking speed of 5m / min and a drying temperature of 110℃. The water content of the negative electrode active material layer is controlled to be below 300ppm to obtain the negative electrode sheet.

[0292] electrolyte Ethyl acetate (EA), dimethyl carbonate (DMC), and ethylene carbonate (EC) were mixed in a mass ratio of 4:3:3. Lithium bis(trifluoromethanesulfonyl)imide (LiTFSI) and ethylene carbonate were then added. The molar concentration of LiTFSI was 1.0 mol / L, and the mass content of ethylene carbonate was 1.5%.

[0293] The electrolyte has a conductivity of 15.6 mS / cm and a viscosity of 2.7 mm at 25℃. 2 / s.

[0294] Separating membrane A polyethylene diaphragm with a thickness of 12 μm is used as the separation membrane.

[0295] Preparation of battery cells The separator is placed in the order of "separator-negative electrode sheet-separator-positive electrode sheet". Note that the part of the separator coated with the first slurry should be aligned with the tab side. One end of the negative electrode sheet, positive electrode sheet and separator is fixed to the discharge roller, and the other end is stacked together and fixed to the winding shaft for winding to obtain the battery cell. After winding, the hard-shell battery cell is prepared by cold pressing, casing, drying, liquid injection, wetting, high-temperature standing, formation, liquid replenishment and aging to obtain the battery cell. Among them, the size of the negative electrode active material layer is 150mm along the first direction, and the first direction is parallel to the direction of gravity.

[0296] Example 2 This embodiment provides a battery cell that differs from Embodiment 1 in that it uses a different negative electrode sheet. Specifically, the negative electrode sheet includes a negative current collector and negative active material layers disposed on two opposite surfaces of the negative current collector. The negative active material layers include a first negative active material layer and a second negative active material layer, with the first negative active material layer disposed between the negative current collector and the second negative active material layer. The thickness ratio of the first negative active material layer to the second negative active material layer is 1:1.

[0297] The aforementioned second negative electrode active material layer comprises a second graphite (carbon-coated graphite, Dv50 of 12μm, specific capacity of 355mAh / g, and graphitization degree of 92%) in a mass ratio of 97.8:1:0.7:0.5, a binder (styrene-butadiene rubber SBR), a conductive agent (carbon black), and a dispersant (sodium carboxymethyl cellulose CMC-Na).

[0298] The aforementioned first negative electrode active material layer comprises a first graphite (artificial graphite, Dv50 particle size of 16μm, specific capacity of 362 mAh / g, graphitization degree of 98%), a binder (styrene-butadiene rubber SBR), a conductive agent (carbon black), and a dispersant (sodium carboxymethyl cellulose CMC-Na) in a mass ratio of 97.3:1.5:0.4:0.8.

[0299] Example 3 This embodiment provides a battery cell that differs from Embodiment 2 in that the first graphite in the negative electrode is different. Specifically, the parameters of the first graphite are: artificial graphite, Dv50 particle size of 16μm, specific capacity of 362 mAh / g, and graphitization degree of 96%.

[0300] Example 4 This embodiment provides a battery cell that differs from Embodiment 2 in that the first graphite in the negative electrode is different. Specifically, the parameters of the first graphite are: artificial graphite, Dv50 particle size of 16μm, specific capacity of 362 mAh / g, and graphitization degree of 94%.

[0301] Example 5 This embodiment provides a battery cell that differs from Embodiment 2 in that the first graphite in the negative electrode is different. Specifically, the parameters of the first graphite are: artificial graphite, Dv50 particle size of 16μm, specific capacity of 358 mAh / g, and graphitization degree of 98%.

[0302] Example 6 This embodiment provides a battery cell that differs from Embodiment 2 in that the first graphite in the negative electrode is different. Specifically, the parameters of the first graphite are: artificial graphite, Dv50 particle size of 16μm, specific capacity of 368 mAh / g, and graphitization degree of 98%.

[0303] Example 7 This embodiment provides a battery cell that differs from Embodiment 2 in that the first graphite in the negative electrode is different. Specifically, the parameters of the first graphite are: artificial graphite, Dv50 particle size of 14μm, specific capacity of 362 mAh / g, and graphitization degree of 98%.

[0304] Example 8 This embodiment provides a battery cell that differs from Embodiment 2 in that the first graphite in the negative electrode is different. Specifically, the parameters of the first graphite are: artificial graphite, Dv50 particle size of 18.2 μm, specific capacity of 362 mAh / g, and graphitization degree of 98%.

[0305] Example 9 This embodiment provides a battery cell that differs from Embodiment 2 in that the conductive agent in the negative electrode is different. Specifically, the conductive agent in the first negative electrode active material layer is a 1:1 mass ratio of single-arm carbon nanotubes and carbon black, with the aspect ratio of the single-arm carbon nanotubes being 10000; the conductive agent in the second negative electrode active material layer is a 1:1 mass ratio of single-arm carbon nanotubes and carbon black, with the aspect ratio of the carbon nanotubes being 10000.

[0306] Example 10 This embodiment provides a battery cell that differs from Embodiment 2 in that the conductive agent and dispersant in the negative electrode are different. Specifically, in the first and second negative electrode active material layers: the conductive agent is a 1:1 mass ratio of single-arm carbon nanotubes and carbon black, with the aspect ratio of the single-arm carbon nanotubes being 10000; the dispersant is a 2:1 mass ratio of sodium carboxymethyl cellulose (CMC-Na) and polyethyleneimine (PEI).

[0307] Example 11 This embodiment provides a battery cell that differs from Embodiment 2 in that the binder and dispersant in the negative electrode sheet are different. Specifically, in the first and second negative electrode active material layers: the binder is styrene-butadiene rubber (SBR) and polyacrylic acid (PAA) in a mass ratio of 1:1; the dispersant is sodium carboxymethyl cellulose (CMC-Na) and polyethyleneimine (PEI) in a mass ratio of 2:1.

[0308] Example 12 This embodiment provides a battery cell that differs from Embodiment 2 in that the conductive agent, binder, and dispersant in the negative electrode sheet are all different. Specifically, in the first and second negative electrode active material layers: the conductive agent is a 1:1 mass ratio of single-arm carbon nanotubes and carbon black, with the aspect ratio of the single-arm carbon nanotubes being 10000; the binder is a 1:1 mass ratio of styrene-butadiene rubber (SBR) and polyacrylic acid (PAA); and the dispersant is a 2:1 mass ratio of sodium carboxymethyl cellulose (CMC-Na) and polyethyleneimine (PEI).

[0309] Example 13 This embodiment provides a battery cell that differs from Embodiment 2 in that the negative electrode sheet is different. Specifically, the negative electrode sheet further includes a coating, which is disposed between the negative electrode current collector and the negative electrode active material layer, and the coating thickness is 2 μm.

[0310] The coating materials include binder (styrene-butadiene rubber SBR), conductive agent (carbon black), and dispersant (sodium carboxymethyl cellulose CMC-Na) in a weight ratio of 30:65:5.

[0311] Example 14 This embodiment provides a battery cell, which differs from Embodiment 1 in that the conductive agent, binder, and dispersant in the negative electrode are different. Specifically: The conductive agent is a 1:1 mass ratio of single-arm carbon nanotubes and carbon black, with the aspect ratio of the single carbon nanotubes being 10000; the binder is a 1:1 mass ratio of styrene-butadiene rubber (SBR) and polyacrylic acid (PAA); the dispersant is a 2:1 mass ratio of sodium carboxymethyl cellulose (CMC-Na) and polyethyleneimine (PEI).

[0312] The preparation process of the negative electrode sheet is as follows: The following materials are provided in a weight ratio of 97.8:1:0.7:0.5: graphite (carbon-coated graphite, Dv50 of 10μm, specific capacity of 350mAh / g, degree of graphitization of 92%), binder (styrene-butadiene rubber SBR: polyacrylic acid PAA = 1:1), conductive agent (carbon nanotubes: carbon black = 1:1) and dispersant (sodium carboxymethyl cellulose CMC-Na: polyethyleneimine PEI = 2:1). First, CMC-Na was dispersed in deionized water and stirred for 30 min. Then, PEI was added and stirred for 20 min. Next, carbon nanotubes were slowly added and stirred for 30 min. Then, SBR and PAA were added and stirred for 40 min. Carbon black was added and stirred for 20 min. Finally, artificial graphite, the negative electrode active material, was added and stirred for 30 min to obtain a uniform negative electrode slurry. The negative electrode slurry was uniformly coated on both sides of a copper foil, pre-dried, and then rolled to obtain the negative electrode active material layer. The single-sided coating weight of the negative electrode active material layer was 160 mg / 1540 mm². 2 The compacted density is 1.68 g / cm³. 3 The material is dried in a 40m long oven at a baking speed of 5m / min and a drying temperature of 110℃. The water content of the negative electrode active material layer is controlled to be below 300ppm to obtain the negative electrode sheet.

[0313] Example 15 This embodiment provides a battery cell, which differs from Embodiment 1 in that the negative electrode sheet further includes a coating. The coating is disposed between the negative electrode current collector and the negative electrode active material layer, and the thickness of the coating is 2μm.

[0314] The preparation process of the negative electrode sheet is as follows: The binder (styrene-butadiene rubber SBR), conductive agent (carbon black) and dispersant (sodium carboxymethyl cellulose CMC-Na) are mixed in a weight ratio of 30:65:5. Deionized water is added as a solvent and the mixture is stirred thoroughly to prepare a coating slurry. The coating slurry is then evenly applied to both sides of the copper foil and pre-dried to form a coating. The following materials are provided in a weight ratio of 97.8:1:0.7:0.5: graphite (carbon-coated graphite, Dv50 of 12μm, specific capacity of 355mAh / g, degree of graphitization of 92%), binder (styrene-butadiene rubber SBR: polyacrylic acid PAA = 1:1), conductive agent (carbon nanotubes: carbon black = 1:1) and dispersant (sodium carboxymethyl cellulose CMC-Na: polyethyleneimine PEI = 2:1). First, CMC-Na was dispersed in deionized water and stirred for 30 min. Then, PEI was added and stirred for 20 min. Next, carbon nanotubes were slowly added and stirred for 30 min. Then, SBR and PAA were added and stirred for 40 min. Carbon black was added and stirred for 20 min. Finally, artificial graphite, the negative electrode active material, was added and stirred for 30 min to obtain a uniform negative electrode slurry. The negative electrode slurry was uniformly coated onto both sides of a copper foil. After pre-drying, it was rolled to obtain the negative electrode active material layer. The single-sided coating weight of the negative electrode active material layer was 160 mg / 1540 mm². 2 The compacted density is 1.68 g / cm³. 3 The material is dried in a 40m long oven at a baking speed of 5m / min and a drying temperature of 110℃. The water content of the negative electrode active material layer is controlled to be below 300ppm to obtain the negative electrode sheet.

[0315] Comparative Example 1 This comparative example provides a single battery cell, which differs from Example 1 in that the negative electrode active material is different. Specifically, the negative electrode active material is non-carbon-coated graphite: Dv50 is 12μm, specific capacity is 355mAh / g, and graphitization degree is 92%.

[0316] Comparative Example 2 This comparative example provides a single battery cell, which differs from Example 1 in that the negative electrode active material is different. Specifically, the negative electrode active material is non-carbon-coated graphite: Dv50 particle size is 16μm, specific capacity is 362 mAh / g, and graphitization degree is 98%.

[0317] Comparative Example 3 This comparative example provides a single battery cell, which differs from Example 1 in that the electrolyte is different.

[0318] Specifically, propylene carbonate (PC), dimethyl carbonate (DMC), and ethylene carbonate (EC) are mixed in a mass ratio of 4:3:3, and lithium bis(trifluoromethanesulfonyl)imide (LiTFSI) and ethylene carbonate are added. The molar concentration of LiTFSI is 1.0 mol / L, and the mass content of ethylene carbonate is 1.5%.

[0319] The electrolyte has a conductivity of 15.0 mS / cm and a viscosity of 2.8 mm at 25℃. 2 / s.

[0320] Performance testing (1) Volumetric energy density (VED) The volumetric energy density test procedure is as follows: 1) Let stand for 30 min; 2) Discharge with DC current at 1 / 3C to 2.0 V; 3) Let stand for 30 min; 4) Charge with constant current at 1 / 3C to 3.8 V, then charge with constant voltage to 0.05C; 5) Let stand for 30 min; 6) Discharge with DC current at 1 / 3C to 2.0 V; 7) Repeat steps 3-6 3 times (the last cycle is recorded as the actual capacity C0); 8) Let stand for 5 min; the energy is obtained by 3 constant volume tests.

[0321] VED = Energy / Battery Volume.

[0322] (2) Cyclic performance test The constant-capacity process is as follows: 1) Let stand for 30 minutes; 2) Discharge with a DC current of 1 / 3C to 2.0V; 3) Let stand for 30 minutes; 4) Charge with a constant current of 1 / 3C to 3.8V, then charge with a constant voltage to 0.05C; 5) Let stand for 30 minutes; 6) Discharge with a DC current of 1 / 3C to 2.0V; 7) Repeat steps 3-8 twice; 8) Discharge with a DC current of 0.1C to 2.0V; 9) Let stand for 30 minutes.

[0323] Cyclic procedure: 1) Pause operation at 25℃; 2) Let stand for 30 min; 3) Discharge to 2.0V with a DC current of 1 / 3Cn; 4) Let stand for 30 min; 5) Charge to 3.8V with a constant current of 1Cn, then charge to 0.05C with a constant voltage; 6) Let stand for 30 min; 7) Discharge to 2.0V with a DC current of 1Cn; 8) Let stand for 30 s; 9) Discharge to 2.0V with a DC current of 1 / 3Cn; 10) Repeat steps 4-9 until the capacity decays to ≤80%; 11) Let stand for 5 min.

[0324] (3) DC Impedance (DCR) Test Procedure The DCR test method is as follows: The volume was determined at an ambient temperature of 25°C. The specific process was as follows: 1) Let it stand for 30 minutes; 2) Discharge it with a DC current of 1 / 3C to 2.0V; 3) Let it stand for 30 minutes; 4) Charge it with a constant current of 1 / 3C to 3.8V, and then charge it with a constant voltage to 0.05C; 5) Let it stand for 30 minutes; 6) Discharge it with a DC current of 1 / 3C to 2.0V; 7) Repeat steps 3-6 three times (the last cycle is recorded as the actual capacity C0); 8) Let it stand for 5 minutes.

[0325] The DCR (180s DCR) test procedure is as follows: 1) Stage 1: Ambient temperature 25℃, stand for 30 min; 2) Charge with 1 / 3 C0 current at constant current to 3.8V, then charge at constant voltage to 0.05C; 3) Stand for 30 min; 4) Discharge with 1 / 3 C0 current at DC for 0.5C0Ah; 5) Stand for 60 min; 6) Discharge with 1 C0 current at DC for 180s; 7) Stand for 5 min; 8) Charge with 1 C0 current at constant current for 180s; 9) Stand for 30 min; 10) Charge with 1 / 3 C0 current at constant current to 3.8V, then charge at constant voltage to 0.05C; 11) Stand for 30 min; 12) Stage 2: Ambient temperature -20℃, stand for 2 h; 13) Charge with 1 / 3 C0 current at constant current for 2 hours; 14) Discharge with 1 / 3 C0 current at constant current for 2 hours; 15) Discharge with 1 / 3 C0 current at constant current for 2 hours; 16) Discharge with 1 / 3 C0 current at constant current for 2 hours; 17) Discharge with 1 / 3 C0 current at constant current for 2 hours; 18) Discharge with 1 / 3 C0 current at constant current for 2 hours; 18) Discharge with 1 / 3 C0 current at constant current for 2 hours; 19) Discharge with 1 / 3 C0 current at constant current for 2 hours; 10) Discharge with 1 / 3 C0 current at constant current for 2 hours; 10) Discharge with 1 / 3 C0 current at constant current for 2 hours; 11) Discharge with 1 / 3 C0 current at constant current for 2 hours; 12) Discharge with 1 / 3 C0 current at constant current for 2 hours 14) Discharge at 0.5C0Ah DC current; 15) Let stand for 0 min; 16) Discharge at 1C0 DC current for 180 s; 17) Let stand for 5 min; 18) Charge at 1C0 constant current for 180 s; 19) Let stand for 30 min.

[0326] The test results of the battery cells provided in the above embodiments and comparative examples are shown in Table 1.

[0327] Table 1

[0328] According to Table 1, and in conjunction with Example 1 and Comparative Example 1, it can be seen that adding carbon-coated graphite as the negative electrode active material to the negative electrode sheet helps to improve the cycle performance of the battery and reduce DC resistance.

[0329] According to Table 1 and in conjunction with Examples 1-4, by differentiating the design of the negative electrode active material layer, the overall content of carbon-coated graphite in the negative electrode sheet is reduced. This slightly increases the DC impedance of the battery, but effectively alleviates the side reaction between carbon-coated graphite and linear carboxylic acid ester, thereby significantly improving the cycle performance of the battery.

[0330] According to Table 1, and in conjunction with Examples 2, 5, and 6, using graphite with a higher specific capacity results in a corresponding increase in the energy density of the battery. In conjunction with Examples 2, 7, and 8, it is evident that as the Dv50 particle size increases, the DC resistance of the battery gradually increases, but the cycle performance gradually improves. This is because smaller particle size facilitates lithium-ion transport, thereby helping to reduce DC resistance, while larger particle size results in fewer side reactions, leading to better cycle performance.

[0331] According to Table 1 and in conjunction with Examples 9-12, the addition of carbon nanotubes to the conductive agent helps reduce the DC impedance of the battery, while the addition of polyethyleneimine to the dispersant and polyacrylic acid to the binder helps improve the cycle performance of the battery. Therefore, Example 11 shows a significant improvement in cycle performance and a substantial decrease in DC impedance compared to Example 2. Similarly, Example 14 shows significant improvements in both cycle performance and DC impedance compared to Example 1.

[0332] According to Table 1, compared with Examples 1 and 15, and Examples 2 and 13, it can be found that the coating helps to significantly reduce the DC impedance of the battery and improve cycle performance.

[0333] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of this application, and not to limit them. Although this application has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some or all of the technical features therein. These modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments of this application, and they should all be covered within the scope of the claims and specification of this application. In particular, as long as there is no structural conflict, the various technical features mentioned in the embodiments can be combined in any way. 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, include: Electrode assembly and electrolyte; The electrode assembly includes a positive electrode and a negative electrode. The negative electrode includes a negative current collector and a negative active material layer disposed on at least one side of the negative current collector. The negative active material layer includes carbon-coated graphite, and the surface of the carbon-coated graphite has amorphous carbon. The electrolyte includes a solvent, and the solvent includes a linear carboxylic acid ester; Along the first direction, the size of the negative electrode active material layer is greater than 130 mm, and the first direction is parallel to the direction of gravity.

2. The battery cell as described in claim 1, characterized in that, The negative electrode active material layer includes a first negative electrode active material layer and a second negative electrode active material layer disposed along the thickness direction of the negative electrode current collector, and the first negative electrode active material layer is disposed between the negative electrode current collector and the second negative electrode active material layer; the first negative electrode active material layer includes a first graphite, the second negative electrode active material layer includes a second graphite, and the second graphite includes the carbon-coated graphite; the graphitization degree of the first graphite is 94%-98%.

3. The battery cell as described in claim 2, characterized in that, The Dv50 particle size of the first graphite is larger than that of the second graphite.

4. The battery cell as described in claim 2 or 3, characterized in that, The specific gravity of the first graphite is greater than or equal to that of the second graphite.

5. The battery cell according to any one of claims 2 to 4, characterized in that, The first graphite satisfies at least one of the following features (1)-(3): (1) The Dv50 particle size of the first graphite is 14.0 μm-18.5 μm; (2) The specific capacity of the first graphite is 358mAh / g-368mAh / g; (3) The first graphite includes one or more of primary particles and secondary particles.

6. The battery cell according to any one of claims 2 to 5, characterized in that, The second graphite satisfies at least one of the following features (1)-(4): (1) The Dv50 particle size of the second graphite is 9.8 μm-13.8 μm; (2) The graphitization degree of the second graphite is 90%-93%; (3) The specific capacity of the second graphite is 350mAh / g-358mAh / g; (4) The OI value of the second graphite is 3.6-4.

1. The OI value of the second graphite is C004 / C110, where C004 is the peak area of ​​the diffraction peak of the 004 crystal plane of the second graphite, and C110 is the peak area of ​​the diffraction peak of the 110 crystal plane of the second graphite.

7. The battery cell according to any one of claims 2 to 6, characterized in that, The thickness ratio of the second negative electrode active material layer to the first negative electrode active material layer is (7:3) to (5:5).

8. The battery cell according to any one of claims 1 to 7, characterized in that, The negative electrode sheet satisfies at least one of the following characteristics (1)-(3): (1) The single-sided coating weight of the negative electrode active material layer is 130 mg / 1540 mm. 2 ~160mg / 1540mm 2 ; (2) The thickness of the negative electrode sheet is 0.115mm-0.125mm; (3) The compaction density of the negative electrode sheet is 1.6 g / cm³. 3 -1.78g / cm 3 .

9. The battery cell according to any one of claims 1 to 8, characterized in that, The positive electrode includes a positive current collector and a positive active material layer disposed on at least one side of the positive current collector, and the positive electrode satisfies at least one of the following features (1)-(3): (1) The single-sided coating weight of the positive electrode active material layer is 310 mg / 1540 mm. 2 ~350mg / 1540mm 2 ; (2) The thickness of the positive electrode sheet is 0.17mm-0.18mm; (3) The compaction density of the positive electrode sheet is 2.6 g / cm³. 3 -2.8 g / cm 3 .

10. The battery cell according to any one of claims 1 to 9, characterized in that, The solvent also includes cyclic carbonates, wherein the mass ratio of the linear carboxylic acid ester to the cyclic carbonate is (6-7):(3-4).

11. The battery cell according to any one of claims 1 to 9, characterized in that, The solvent also includes linear carbonates and cyclic carbonates, wherein the mass ratio of the linear carboxylic acid ester, the linear carbonate, and the cyclic carbonate is (2-4):(3-4):(3-4).

12. The battery cell according to any one of claims 1 to 11, characterized in that, The conductivity of the electrolyte is 9 mS / cm - 18.5 mS / cm.

13. The battery cell as described in claim 12, characterized in that, The conductivity of the electrolyte is 14 mS / cm - 18.5 mS / cm.

14. The battery cell according to any one of claims 1 to 13, characterized in that, The viscosity of the electrolyte at 25°C is 0.5 mm. 2 / s-4mm 2 / s.

15. The battery cell according to any one of claims 1 to 14, characterized in that, The electrolyte also includes lithium salts, which include at least one of lithium hexafluorophosphate, lithium tetrafluoroborate, lithium bis(oxalatoborate), lithium bis(trifluoromethanesulfonyl)imide, lithium perchlorate, and lithium hexafluoroarsenate.

16. The battery cell according to any one of claims 1 to 15, characterized in that, The electrolyte injection coefficient of the battery cell is 2.7 g / Ah to 3.2 g / Ah.

17. The battery cell according to any one of claims 1 to 16, characterized in that, The electrolyte also includes additives; wherein the additives include vinylene carbonate, and / or the mass concentration of the additives in the electrolyte is 1%-2%.

18. The battery cell according to any one of claims 1 to 17, characterized in that, The negative electrode active material layer includes a first conductive agent, which includes a zero-dimensional conductive agent and a multi-dimensional conductive agent. The multi-dimensional conductive agent includes at least one of a one-dimensional conductive agent and a two-dimensional conductive agent.

19. The battery cell as described in claim 18, characterized in that, The zero-dimensional conductive agent includes at least one of conductive carbon black, Ketjen black, and acetylene black; and / or, The one-dimensional conductive agent includes at least one of carbon nanotubes and carbon nanofibers, and the carbon nanotubes include at least one of multi-walled carbon nanotubes, single-walled carbon nanotubes, and few-walled nanotubes; and / or, The two-dimensional conductive agent includes at least one of layered conductive graphite and graphene.

20. The battery cell as described in claim 18 or 19, characterized in that, The mass ratio of the zero-dimensional conductive agent to the multi-dimensional conductive agent is 4:1 to 1:

4.

21. The battery cell according to any one of claims 1 to 20, characterized in that, The negative electrode active material layer further includes a first dispersant, which includes an amino-containing dispersant and a cellulose ether dispersant. The amino-containing dispersant includes at least one of polyethyleneimine, polyetheramine-polydopamine complex, and amino-containing zwitterionic polymer. The cellulose ether dispersant includes sodium carboxymethyl cellulose.

22. The battery cell as described in claim 21, characterized in that, The mass ratio of the amino-containing dispersant to the cellulose ether dispersant is 2:1 to 1:

4.

23. The battery cell as described in claims 1 to 22, characterized in that, The negative electrode active material layer further includes a first binder, which comprises a dotted binder and a linear binder; wherein... The linear adhesive contains at least one of the following groups: carboxyl group, lithium carboxyl group.

24. The battery cell as described in claim 23, characterized in that, The linear adhesive comprises at least one of polyacrylic acid, polymethacrylic acid, lithium epoxy succinate, lithium-ionized polyacrylic acid, and lithium polymethacrylate; and / or The dotted adhesive includes at least one of styrene-butadiene rubber and fluorinated rubber.

25. The battery cell as described in claim 23 or 24, characterized in that, The mass ratio of the dotted adhesive to the linear adhesive is 4:1 to 1:

1.

26. The battery cell according to any one of claims 18 to 25, characterized in that, The first negative electrode active material layer further includes the first binder, the first conductive agent, and the first dispersant. Based on the total mass of the first negative electrode active material layer, the content of the first graphite is 95%-97.5%, the content of the first binder in the first negative electrode active material layer is 1.2%-2.5%, the content of the first conductive agent in the first negative electrode active material layer is 0.8%-1.3%, and the content of the first dispersant in the first negative electrode active material layer is 0.5%-1.2%; and / or, The second negative electrode active material layer further includes the first binder, the first conductive agent, and the first dispersant. Based on the total mass of the second negative electrode active material layer, the content of the second graphite is 96%-98%, the content of the first binder in the second negative electrode active material layer is 0.8%-2%, the content of the first conductive agent in the second negative electrode active material layer is 0.7%-1%, and the content of the first dispersant in the second negative electrode active material layer is 0.5%-1%.

27. The battery cell according to any one of claims 1 to 26, characterized in that, The negative electrode sheet further includes a coating, which is disposed between the negative electrode current collector and the negative electrode active material layer; The coating comprises a second conductive agent, a second binder, and a second dispersant.

28. The battery cell as described in claim 27, characterized in that, Based on the mass of the coating as 100%, the content of the second conductive agent is 63%-65%, the content of the second binder is 30%-32%, and the content of the second dispersant is 3%-5%.

29. The battery cell as described in claim 27 or 28, characterized in that, The thickness of the coating is 1μm-3μm.

30. The battery cell according to any one of claims 1 to 29, characterized in that, Along the first direction, the size of the negative electrode active material layer is greater than or equal to 150 mm, and the first direction is parallel to the direction of gravity.

31. A battery device, characterized in that, Includes the battery cell as described in any one of claims 1-30.

32. An electrical appliance, characterized in that, Includes the battery cell as described in any one of claims 1-30 or the battery device as described in claim 31.

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