Battery cell, battery device, electric device

Abstract

The application discloses a battery monomer, a battery device and a power utilization device. The battery monomer comprises: a positive electrode active material comprising titanium-doped lithium iron phosphate, the content of titanium in the lithium iron phosphate being 400 ppm-2000 ppm; an electrolyte comprising a solvent and a lithium salt, the solvent comprising linear carboxylic acid ester and cyclic carbonate, the mass fraction of the linear carboxylic acid ester in the electrolyte being 1%-10%, the mass fraction of the cyclic carbonate in the electrolyte being 15%-30%, and the lithium salt comprising lithium bisfluorosulfonylimide, the mass fraction of the lithium bisfluorosulfonylimide in the electrolyte being 2%-5%.

Description

Cross-references to related applications

[0001] This patent document claims priority and benefit to PCT patent application No. PCT / CN2025 / 135170, filed on November 14, 2025, entitled "Battery Cell, Battery Device, Electrical Device". The entire contents of the aforementioned patent application are incorporated herein by reference as a part of the disclosure of this patent document. Technical Field

[0002] This disclosure relates to the field of lithium-ion batteries, specifically to battery cells, battery devices, and electrical devices. Background Technology

[0003] Lithium-ion batteries possess characteristics such as high capacity and long lifespan, making them widely used in electronic devices, electric vehicles, electric airplanes, electric ships, and power tools. With the development of lithium-ion battery applications, the performance requirements for lithium-ion batteries are increasing daily. However, the performance of individual battery cells in fast-charging scenarios still needs further improvement.

[0004] It should be noted that the above statements are only used to provide background information related to this application and do not necessarily constitute prior art. Summary of the Invention

[0005] In a first aspect, this application proposes a battery cell comprising: an electrode assembly including a positive electrode, a negative electrode, and a separator; the positive electrode including a positive current collector and a positive electrode film layer located on at least one side of the positive current collector; the positive electrode film layer including a positive active material including titanium-doped lithium iron phosphate, wherein the titanium content in the lithium iron phosphate is 400ppm-2000ppm; and an electrolyte including a solvent and a lithium salt; the solvent including a linear carboxylic acid ester and a cyclic carbonate, wherein the mass fraction of the linear carboxylic acid ester in the electrolyte is 1%-10%, the mass fraction of the cyclic carbonate in the electrolyte is 15%-30%, and the lithium salt including lithium bis(fluorosulfonyl)imide, wherein the mass fraction of the lithium bis(fluorosulfonyl)imide in the electrolyte is 2%-5%. Therefore, by adding an appropriate amount of linear carboxylic acid ester to the electrolyte solvent, and combining it with the use of LiFSI and titanium-doped lithium iron phosphate, the kinetic performance of the battery cell can be improved by enhancing the desolvation effect of lithium ions. Furthermore, the superior stability of the positive electrode active material can be utilized to suppress the occurrence of side reactions between the electrolyte and the active material, thereby improving the stability of the electrolyte and resulting in superior fast-charging and cycle performance of the battery cell.

[0006] Cyclic carbonates in the solvent facilitate efficient dissociation of lithium salts and synergistically improve the desolvation of lithium ions with lithium bis(fluorosulfonyl)imide, forming free Li...+ By combining with anions, an ion conduction network is constructed, which enhances the migration rate of lithium ions in the electrolyte and improves the dynamic performance of the battery cell.

[0007] In some embodiments, the titanium-doped lithium iron phosphate has an average primary particle size of 100 nm to 500 nm. This suppresses side reactions between the positive electrode active material and the electrolyte, improving the cycle performance of the battery cell.

[0008] In some embodiments, the titanium-doped lithium iron phosphate comprises primary particles and secondary particles formed by the agglomeration of primary particles. This results in more solid-phase contact sites between the positive electrode active materials, a shorter migration path for lithium ions within the positive electrode active materials, and superior kinetic performance of the positive electrode active materials.

[0009] In some embodiments, the titanium-doped lithium iron phosphate satisfies the chemical formula: Li a Fe b Ti c M d PO4, a is 0.5-1.0, b is 0.9-1.5, c is 0-0.5, d is 0-0.5, and M includes one or more of Nb, V, Al, and Mn. Therefore, the positive electrode active material has high specific capacity and excellent stability, and can maintain its original crystal structure even under conditions such as overcharging and high temperature of the battery cell, making it suitable for high-power charging and discharging scenarios such as fast charging.

[0010] In some embodiments, the linear carboxylic acid ester includes one or more of ethyl acetate, ethyl acrylate, propyl acetate, and ethyl propionate. This effectively reduces the viscosity of the electrolyte and increases its ionic conductivity.

[0011] In some embodiments, the electrolyte further includes additives, including vinylene carbonate. Thus, vinylene carbonate not only forms an elastic polymer on the surface of the negative electrode active material, which is superior to electrolyte solvents and alleviates SEI film rupture and recombination caused by the expansion and contraction of the negative electrode active material, but also inhibits side reactions between active components such as linear carboxylic esters and the positive electrode active material, thereby improving the cycle performance of the battery cell in multiple ways.

[0012] In some embodiments, the mass fraction of vinylene carbonate in the electrolyte is 0.2%-1.5%. Therefore, adding an appropriate amount of vinylene carbonate helps to form an SEI film of moderate thickness and good elasticity, with minimal impact on the internal resistance of the battery cell.

[0013] In some embodiments, the additive further includes lithium difluorophosphate, wherein the mass fraction of lithium difluorophosphate in the electrolyte is 0.1%-2%. This optimizes the film-forming composition of the SEI film, improves the rigidity of the SEI film, and enhances the lithium-ion transport rate and structural stability of the SEI film.

[0014] In some embodiments, the solvent further includes a linear carbonate, and the mass fraction of the linear carbonate in the electrolyte is 25%-60%. This results in a high ionic conductivity of the electrolyte, fewer side reactions between the electrolyte and the active material, and a significant improvement in the chemical stability of the electrolyte.

[0015] In some embodiments, the linear carbonate includes one or more of dimethyl carbonate and ethyl methyl carbonate.

[0016] In some embodiments, the solvent further includes a cyclic carbonate, and the cyclic carbonate in the electrolyte comprises 15%-30% by mass. This allows for efficient dissociation of the lithium salt, further improving the desolvation of lithium ions and forming free Li⁻. + It combines with anions to construct an ion conduction network, thereby improving the migration rate of lithium ions in the electrolyte.

[0017] In some embodiments, the cyclic carbonate includes one or more of ethylene carbonate and propylene carbonate.

[0018] In some embodiments, the lithium salt further includes lithium hexafluorophosphate, and the mass fraction of lithium hexafluorophosphate in the electrolyte is 5%-20%. Therefore, lithium hexafluorophosphate has advantages such as mature production technology, low cost, and good overall electrochemical performance, and can significantly increase the number of active lithium ions in the electrolyte and improve the ionic conductivity of the electrolyte.

[0019] In some embodiments, the electrolyte has an ionic conductivity of 10 mS / cm to 12.5 mS / cm at 25°C. Therefore, lithium ions migrate rapidly in the electrolyte, making it suitable for high-power charge and discharge scenarios.

[0020] In some embodiments, the negative electrode sheet includes a negative current collector and a negative electrode film layer located on at least one side of the negative current collector. The negative electrode film layer includes a negative electrode active material, which includes graphite, and the graphite includes secondary particles. Therefore, compared to primary particles, secondary particles exhibit isotropic behavior during lithium intercalation, facilitating rapid lithium-ion insertion and improving the fast-charging performance of the battery cell.

[0021] In some embodiments, the graphite has a graphitization degree of 90%-94%. This results in superior conductivity of the negative electrode active material, reducing heat generation in the negative electrode sheet, thereby reducing heat generation in the battery cell and improving the fast-charging performance of the battery cell.

[0022] In some embodiments, the Dv50 particle size of the graphite is 7μm-12μm. This shortens the solid-phase transport path of lithium ions, improving fast-charging performance, and also reduces the agglomeration of the negative electrode active material, enhancing its stability and compaction density.

[0023] In some embodiments, at least a portion of the surface of the graphite has an amorphous carbon coating layer with a thickness of 100 nm to 500 nm. Therefore, by forming an amorphous carbon coating layer on the graphite surface, the interlayer spacing of the graphite particles can be increased, reducing the resistance to lithium-ion insertion, accelerating lithium-ion insertion, and effectively suppressing lithium plating caused by the inability of lithium ions to quickly insert into the negative electrode active material under fast charging conditions.

[0024] In some embodiments, the porosity of the negative electrode sheet is 25%-30%. This results in better wettability of the electrolyte on the negative electrode sheet, a shorter solid-phase transport distance for lithium ions within the negative electrode sheet, and facilitates rapid migration of lithium ions.

[0025] In some embodiments, when the battery cell has a state of 0% SOC, the compaction density of the negative electrode film is 1.3 g / cm³. 3 -1.52g / cm 3 Therefore, the negative electrode active material in the negative electrode film layer is packed more tightly, the contact resistance between particles is smaller, and the solid-phase transport distance of lithium ions in the negative electrode sheet is shorter, which is conducive to the rapid migration of lithium ions. This can further reduce the resistance of the negative electrode sheet, thereby reducing heat generation, and the energy density of the negative electrode sheet is higher.

[0026] In some embodiments, the single-sided coating weight of the negative electrode film is 0.12 g / 1540.25 mm. 2 -0.15g / 1540.25mm 2 Therefore, the negative electrode sheet has suitable porosity and high energy density.

[0027] In some embodiments, the porosity of the positive electrode is 18%-27%. Therefore, there is ample space within the positive electrode for wetting the electrolyte, ensuring thorough wetting of the positive electrode by the electrolyte.

[0028] In some embodiments, when the battery cell has a state of 0% SOC, the compaction density of the positive electrode film is 2.4 g / cm³. 3 -2.63g / cm 3Therefore, the positive electrode film has many contact points between the positive electrode active materials, the particles are tightly bonded, the electron transport path is stable, there are many lithium ion transport channels, and the positive electrode film has high structural stability, which helps to improve the energy density of the positive electrode and reduce the internal resistance of the positive electrode.

[0029] In some embodiments, the single-sided coating weight of the positive electrode film is 0.27 g / 1540.25 mm. 2 -0.33g / 1540.25mm 2 Therefore, the positive electrode sheet has suitable porosity and high energy density.

[0030] In some embodiments, the electrode assembly has a wound structure. The positive electrode includes a connected positive electrode coating portion and a positive electrode sheet portion, with the positive electrode film layer located within the positive electrode coating portion. The negative electrode includes a connected negative electrode coating portion and a negative electrode sheet portion, with the negative electrode film layer located within the negative electrode coating portion. The positive electrode coating portion includes a positive electrode straight section, and the negative electrode coating portion includes a negative electrode straight section. The positive electrode straight section and the negative electrode straight section are stacked along the thickness direction of the electrode assembly. The ratio of the number of positive electrode tabs to the number of positive electrode straight sections is greater than 0.5 and not greater than 1, and / or the ratio of the number of negative electrode tabs to the number of negative electrode straight sections is greater than 0.5 and not greater than 1. Therefore, the increased number of tabs enhances the current shunting capacity of the tabs and further improves the fast-charging performance of the battery cell.

[0031] In some embodiments, multiple positive electrode tabs are located on the same side of the positive electrode coating, and / or multiple negative electrode tabs are located on the same side of the negative electrode coating. This facilitates the connection of the stacked tabs to other components, such as adapters.

[0032] In some embodiments, the positive electrode sheet is wound to form multiple ring-shaped structures, each ring-shaped structure including two straight positive electrode segments. The ring-shaped structures include a first ring-shaped structure and a second ring-shaped structure. Either of the two straight positive electrode segments of the first ring-shaped structure is connected to the positive electrode tab, and both straight positive electrode segments of the second ring-shaped structure are connected to the positive electrode tab. The second ring-shaped structure is located outside the first ring-shaped structure. Therefore, given the same total number of positive electrode tabs, the sum of the distances between the aforementioned multiple positive electrode tabs and the welding sheet is the shortest, reducing welding difficulty. The positive electrode tabs have a smaller impact on the energy density of the battery cell, and the foil reserved on the positive current collector as the positive electrode tab is of moderate length, making it less prone to bending during the winding of the electrode assembly and effectively preventing the phenomenon of the tab being inserted backwards into the electrode assembly.

[0033] In some embodiments, the negative electrode sheet is wound to form multiple ring-shaped structures, each ring-shaped structure including two straight negative electrode segments. The ring-shaped structures include a first ring-shaped structure and a second ring-shaped structure. Either of the two straight negative electrode segments of the first ring-shaped structure is connected to the negative electrode tab, and both straight negative electrode segments of the second ring-shaped structure are connected to the negative electrode tab. The second ring-shaped structure is located outside the first ring-shaped structure. Therefore, given the same total number of negative electrode tabs, the sum of the distances between the aforementioned multiple negative electrode tabs and the welding sheet is minimized, reducing welding difficulty. The negative electrode tabs have a smaller impact on the energy density of the battery cell, and the foil reserved on the negative electrode current collector as the negative electrode tab is of moderate length, making it less prone to bending during the winding of the electrode assembly and effectively preventing the phenomenon of the tab being inserted backwards into the electrode assembly.

[0034] In a second aspect, this application proposes a battery device comprising the aforementioned battery cell, wherein the battery device includes one or more of a battery module, a battery pack, and an energy storage device. Thus, the battery device possesses all the features and advantages of the aforementioned battery cell, which will not be elaborated further here.

[0035] In a third aspect, this application proposes an electrical device comprising the aforementioned battery cell. Therefore, the electrical device possesses all the features and advantages of the aforementioned battery cell, which will not be repeated here. Attached Figure Description

[0036] The above and / or additional aspects and advantages of this application will become apparent and readily understood from the description of the embodiments taken in conjunction with the following drawings, in which: Figure 1 This is a schematic diagram of a battery cell according to some embodiments of this application; Figure 2 This is an exploded view of a battery cell according to some embodiments of this application; Figure 3 This is a schematic diagram of the electrode assembly of a battery cell according to some embodiments of this application; Figure 4 This is a schematic diagram of the electrode assembly of a battery cell according to other embodiments of this application; Figure 5 This is a schematic diagram of a battery module according to some embodiments of this application; Figure 6 This is a schematic diagram of a battery pack according to some embodiments of this application; Figure 7 yes Figure 6 An exploded view of the battery pack shown; Figure 8 This is a schematic diagram of a power supply device for a battery cell power source according to some embodiments of this application.

[0037] Explanation of reference numerals in the attached figures: Y, thickness direction; 1 Battery pack; 2 Upper housing; 3 Lower housing; 4 Battery module; 5 Battery cell; 51 Housing; 52 Electrode assembly; 53 Cover plate; 13 Positive electrode plate; 131 Straight section of positive electrode; 132 Bent section of positive electrode; 111 Positive electrode tab; 14 Negative electrode plate; 141 Straight section of negative electrode; 142 Bent section of negative electrode; 112 Negative electrode ear; 15. Separating membrane. Detailed Implementation

[0038] The embodiments of this application are described in detail below, with examples of these embodiments shown in the accompanying drawings. However, unnecessary detailed descriptions may be omitted. For example, detailed descriptions of well-known matters and repetitive descriptions of practically identical structures may be omitted. This is to avoid unnecessarily lengthy descriptions and to facilitate understanding by those skilled in the art. Furthermore, the accompanying drawings and the following description are provided to enable those skilled in the art to fully understand this application and are not intended to limit the subject matter of the claims.

[0039] Unless otherwise defined, all technical and scientific terms used in this application have the same meaning as commonly understood by one of ordinary skill in the art to which this application pertains; the terminology used in this application is for the purpose of describing particular embodiments only and is not intended to limit this application; unless otherwise stated, the values ​​of the parameters mentioned in this application can be measured using various measurement methods commonly used in the art (e.g., they can be tested according to the methods given in the embodiments of this application).

[0040] The terms “comprising” and “having”, and any variations thereof, in the specification and claims of this application are open-ended expressions, meaning they include what is specified in this application but do not exclude other aspects.

[0041] In the description of this application, all figures disclosed herein, whether or not the words "approximately" or "about" are used, are approximate values. Each figure may vary by less than 10% or by a difference that is considered reasonable by one of the art, such as 1%, 2%, 3%, 4%, or 5%.

[0042] The "range" disclosed in this application is defined by a lower limit and an upper limit. A given range is defined by selecting a lower limit and an upper limit, which define the boundaries of a particular range. Ranges defined in this way can include or exclude endpoints and can be arbitrarily combined; that is, any lower limit can be combined with any upper limit to form a range. For example, if ranges of 60-120 and 80-110 are listed for a specific parameter, it is expected that ranges of 60-110 and 80-120 are also included. Furthermore, if minimum range values ​​of 1 and 2 are listed, and if maximum range values ​​of 3, 4, and 5 are listed, then the following ranges are all expected: 1-3, 1-4, 1-5, 2-3, 2-4, and 2-5. In this application, unless otherwise stated, the numerical range "ab" represents a shortened representation of any combination of real numbers between a and b, where a and b are real numbers. For example, the numerical range "0-5" indicates that all real numbers between "0-5" have been listed in this article; "0-5" is simply a shortened representation of these numerical combinations. Furthermore, when a parameter is stated as an integer ≥2, it is equivalent to disclosing that the parameter is, for example, an integer such as 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, etc.

[0043] In the description of this application, it should be understood that the terms "length", "width", "thickness", "upper", "lower", "front", "rear", "left", "right", etc., indicate the orientation or positional relationship based on the orientation or positional relationship shown in the accompanying drawings, and are only for the convenience of describing this application and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation, and therefore should not be construed as a limitation of this application.

[0044] In the description of this application, the first feature being "above" or "below" the second feature may include the first and second features being in direct contact, or the first and second features being in contact through another feature between them.

[0045] In the description of this application, the terms "above," "over," and "on top" for the first feature and the second feature include the first feature being directly above or diagonally above the second feature, or simply indicate that the first feature is at a higher horizontal level than the second feature.

[0046] In the description of this application, the terms "first" and "second" are used for descriptive purposes only and should not be construed as indicating or implying relative importance or implicitly specifying the number of technical features indicated. "First feature" and "second feature" may include one or more of the indicated feature.

[0047] In the description of this application, "multiple" means two or more.

[0048] In the description of this application, "A and / or B" can include any of the cases of A alone, B alone, or A and B, where A and B are merely examples and can be any technical feature connected by "and / or" in this application.

[0049] Unless otherwise specified, all embodiments and optional embodiments of this application can be combined to form new technical solutions.

[0050] Unless otherwise specified, all technical features and optional technical features of this application may be combined to form new technical solutions.

[0051] The battery mentioned in the embodiments of this application can be a single physical module comprising one or more battery cells to provide higher voltage and capacity. For example, the battery mentioned in this application can include battery cells, battery modules, or battery packs.

[0052] A battery cell is the smallest unit that makes up a battery, and it can independently perform the functions of charging and discharging. A battery cell can be cylindrical, cuboid, or other shapes, and the embodiments of this application are not limited in this respect. Figure 1 The example shown is a rectangular battery cell 5.

[0053] A single battery cell includes electrode components and an electrolyte.

[0054] The battery cell may also include an outer packaging, which can be used to encapsulate the electrode components and electrolyte. The outer packaging can be a rigid shell, such as a hard plastic shell, aluminum shell, or steel shell. The outer packaging can also be a flexible package, such as a pouch-type flexible package. The material of the flexible package can be plastic, such as one or more of polypropylene (PP), polybutylene terephthalate (PBT), and polybutylene succinate (PBS).

[0055] In some embodiments, such as Figure 2 As shown, the outer packaging may include a housing 51 and a cover 53. The housing 51 may include a base plate and side plates connected to the base plate, the base plate and side plates enclosing a receiving cavity. The housing 51 has an opening communicating with the receiving cavity, and the cover 53 is used to cover the opening to close the receiving cavity. Electrode assemblies 52 are encapsulated in the receiving cavity. The number of electrode assemblies 52 contained in the battery cell 5 may be one or more, and can be adjusted according to requirements.

[0056] Electrode assemblies typically include a positive electrode and a negative electrode. The negative electrode is responsible for the reaction that occurs during charging, where lithium ions are absorbed or lithiated, and during discharging, lithium ions are released or delithiated. The positive electrode is responsible for the reaction that occurs during charging, where lithium ions are released or delithiated, and during discharging, lithium ions are absorbed or lithiated. During the charging and discharging process of a single battery cell, active lithium ions repeatedly insert and extract between the positive and negative electrodes. The electrolyte acts as a conductor for these active ions between the positive and negative electrodes.

[0057] The electrode assembly can be at least one, and optionally at least two, such as two, three, four, etc., with two being optional. At least two electrode assemblies can be stacked along the thickness direction of the electrode assembly. Figure 2 The two electrode assemblies are shown in a stacked configuration.

[0058] When there are multiple battery cells, they are connected in series, parallel, or mixed via a busbar. In some embodiments, the battery can be a battery module; when there are multiple battery cells, they are arranged and fixed to form a battery module. In some embodiments, the battery can be a battery pack, which includes a housing and battery cells, with the battery cells or battery modules housed within the housing. In some embodiments, the housing can be part of the vehicle's chassis structure. For example, a portion of the housing can be at least part of the vehicle's floor, or a portion of the housing can be at least part of the vehicle's crossbeams and longitudinal beams.

[0059] In some embodiments, the battery can be an energy storage device. Energy storage devices include energy storage containers, energy storage cabinets, etc.

[0060] In some embodiments, individual battery cells can be assembled into a battery module, and the number of individual battery cells contained in the battery module can be multiple, the specific number of which can be adjusted according to the application and capacity of the battery module. Figure 5 This is a schematic diagram of battery module 4 as an example. Figure 5 As shown, in battery module 4, multiple battery cells 5 can be arranged sequentially along the length of battery module 4. Of course, they can also be arranged in any other manner. Furthermore, these multiple battery cells 5 can be fixed in place using fasteners.

[0061] Optionally, the battery module 4 may also include a housing with a receiving space in which multiple battery cells 5 are received.

[0062] In some embodiments, the battery modules described above can also be assembled into a battery pack, and the number of battery modules contained in the battery pack can be adjusted according to the application and capacity of the battery pack.

[0063] Figure 6 and Figure 7This is a schematic diagram of battery pack 1 as an example. Figure 6 and Figure 7 As shown, the battery pack 1 may include a housing and multiple battery modules 4 disposed within the housing. The housing includes an upper housing 2 and a lower housing 3. The upper housing 2 covers the lower housing 3, forming a closed space for accommodating the battery modules 4. The multiple battery modules 4 can be arranged in any manner within the housing.

[0064] Adding low-viscosity linear carboxylic acid esters to the electrolyte can effectively improve its ionic conductivity and enhance the kinetic performance of the battery cells. However, linear carboxylic acid esters are prone to side reactions with the active materials, and the degree of side reactions intensifies significantly with increasing dosage. Reducing the dosage of linear carboxylic acid esters can effectively suppress side reactions, but it cannot fully meet the requirements for improving the ionic conductivity of the electrolyte, resulting in poor fast-charging performance of the battery cells. Furthermore, side reactions between linear carboxylic acid esters and the positive electrode active materials still occur. For example, the small particle size of lithium iron phosphate materials makes them susceptible to side reactions with linear carboxylic acid esters, leading to the dissolution of transition metals in the lithium iron phosphate material, thus requiring further improvement in the cycle performance of the battery cells.

[0065] In this application, by adding a small amount of lithium bisfluorosulfonylimide (LiFSI) to the electrolyte, the desolvation of lithium ions in the electrolyte and the synergistic effect with linear carboxylic acid esters to improve the ionic conductivity of the electrolyte can be achieved. Simultaneously, the risk of thermal runaway that may result from excessive LiFSI addition can be suppressed, thus achieving a balance between the fast-charging performance and safety performance of the battery cell. Meanwhile, by using lithium iron phosphate doped with an appropriate amount of Ti as the positive electrode active material, the enhancing effect of Ti on the stability of lithium iron phosphate can be fully utilized, the side reactions between the positive electrode active material and linear carboxylic acid esters can be greatly reduced, and the dissolution of transition metals in lithium iron phosphate can be effectively suppressed. Furthermore, the negative impact on the specific capacity and structural integrity of lithium iron phosphate is minimal. The feasibility of lithium iron phosphate preparation, its superior capacity performance, and its excellent structural stability are fully preserved, resulting in superior cycle performance and capacity performance of the battery cell.

[0066] In a first aspect of this application, a battery cell is provided, comprising: an electrode assembly including a positive electrode, a negative electrode, and a separator; the positive electrode including a positive current collector and a positive electrode film layer located on at least one side of the positive current collector; the positive electrode film layer including a positive active material including titanium-doped lithium iron phosphate, wherein the titanium content in the lithium iron phosphate is 400ppm-2000ppm; and an electrolyte including a solvent and a lithium salt; the solvent including a linear carboxylic acid ester, wherein the mass fraction of the linear carboxylic acid ester in the electrolyte is 1%-10%; and the lithium salt including lithium bis(fluorosulfonyl)imide, wherein the mass fraction of the lithium bis(fluorosulfonyl)imide in the electrolyte is 2%-5%. Therefore, by adding an appropriate amount of linear carboxylic acid ester to the electrolyte solvent, and combining it with the use of LiFSI and titanium-doped lithium iron phosphate, the kinetic performance of the battery cell can be improved by enhancing the desolvation effect of lithium ions. Furthermore, the superior stability of the positive electrode active material can be utilized to suppress the occurrence of side reactions between the electrolyte and the active material, thereby improving the stability of the electrolyte and resulting in superior fast-charging and cycle performance of the battery cell.

[0067] As an example, the titanium content in lithium iron phosphate can be 400ppm, 600ppm, 800ppm, 1000ppm, 1200ppm, 1400ppm, 1600ppm, 1800ppm, 2000ppm, or any value between two of these.

[0068] When the titanium content in lithium iron phosphate is within the aforementioned range, it can reduce the occurrence of side reactions between the electrolyte and the positive electrode active material, suppress the dissolution of transition metal ions, such as iron ions, in lithium iron phosphate, thereby avoiding the destruction of the SEI film due to the migration of transition metals to the negative electrode after dissolution, and improving the cycle life of the battery cell. It can also simultaneously reduce the amount of film-forming additives used in the electrolyte to form the SEI film on the negative electrode, thereby reducing the thickness of the SEI film, and further reducing the negative electrode interface impedance, thus improving the fast charging performance of the battery cell.

[0069] The elemental content in the positive electrode active material has a well-known meaning in the art and can be detected using well-known equipment and methods. For example, referring to EPA 6010D-2014, it can be tested by inductively coupled plasma atomic emission spectrometry (ICP-OES, instrument model: Thermo ICAP7400). After discharging the battery cell to 0% SOC, the positive electrode sheet is disassembled, cleaned and dried with DMC, and then calcined at high temperature to remove impurities. 0.4g of the positive electrode active material is weighed and 10ml (50% concentration) of aqua regia is added. It is then placed on a plate at 180℃ for 30min. After digestion on the plate, the volume is adjusted to 100mL, and quantitative testing is performed using the standard curve method.

[0070] As an example, the mass fraction of linear carboxylic acid esters in the electrolyte can be 1%, 1.5%, 2%, 2.5%, 3%, 3.5%, 4%, 4.5%, 5%, 5.5%, 6%, 6.5%, 7%, 7.5%, 8%, 8.5%, 9%, 9.5%, 10%, or any value between the two.

[0071] As an example, the mass fraction of lithium bis(fluorosulfonyl)imide in the electrolyte can be 2%, 2.5%, 3%, 3.5%, 4%, 4.5%, 5%, or any value between the two.

[0072] As an example, the types and concentrations of inorganic components (which may include electrolyte salts and inorganic additives) in the electrolyte can be tested with reference to relevant standards such as GB / T 34672-2017 General Rules for Determination of Chemical Reagents by Ion Chromatography, JY / T020-1996 General Rules for Ion Chromatography Analysis, and GB / T 6040-2019 General Rules for Infrared Spectroscopy Analysis, and the latest version of the standard method can be preferred.

[0073] As an example, the types and contents of organic components (including non-aqueous solvents and organic additives) in the electrolyte can be tested with reference to relevant standards such as GB / T 9722-2023 General Rules for Gas Chromatography of Chemical Reagents.

[0074] As an example, those skilled in the art can also identify the components of the electrolyte in a lithium-ion battery using one or more of the following detection methods, including but not limited to: 1H NMR, high-performance liquid chromatography (HPLC), matrix-assisted laser desorption / ionization mass spectrometry (MADI-TOF), Fourier transform infrared spectroscopy (FT-IR), ultraviolet spectroscopy, and gas chromatography (GC). The sample preparation and testing methods for these methods are known to those skilled in the art, and the test parameters can be appropriately adjusted according to the structure of the material or substance and the characteristics of the sample. As a non-limiting example, one or more of the following methods can be used to detect the types and contents of electrolyte components, but are not limited to these: FT-IR, ultraviolet spectroscopy, 1H NMR, mass spectrometry, MADI-TOF, and GC.

[0075] In the embodiments of this application, freshly prepared electrolyte can be used as the sample to be tested, or the free electrolyte of a fresh battery can be used as the sample. Alternatively, a battery that has been completely discharged (discharged to the lower limit cutoff voltage so that the battery's state of charge is about 0% SOC) can be disassembled in reverse, and the free electrolyte obtained from the battery can be used as the sample for detection by ion chromatography analysis.

[0076] In some embodiments, the titanium-doped lithium iron phosphate has an average primary particle size of 100 nm to 500 nm. This can suppress side reactions between the positive electrode active material and the electrolyte, thereby improving the cycle performance of the battery cell.

[0077] As an example, the average primary particle size of titanium-doped lithium iron phosphate can be 100 nm, 150 nm, 200 nm, 250 nm, 300 nm, 350 nm, 400 nm, 450 nm, 500 nm, or any value between the two.

[0078] When the average primary particle size of titanium-doped lithium iron phosphate is within the aforementioned range, the particle size of the cathode active material is relatively small, the lithium ion insertion / extraction path in the cathode active material is shorter, the heat generation is less, and the kinetic performance is better. Furthermore, the cathode active material does not agglomerate during processing, resulting in superior processing performance.

[0079] As an example, the battery cell is disassembled to obtain the positive electrode sheet, and the positive electrode sheet is subjected to ion polishing to obtain a cross-sectional sample. Fifty primary particles of positive electrode active material are randomly selected under a scanning electron microscope at 10,000x magnification. The longest distance between any two points on the boundary of the primary particle is taken as the particle size, and the average particle size of the 50 particles is taken as the average particle size of the primary particles.

[0080] In some embodiments, titanium-doped lithium iron phosphate comprises primary particles and secondary particles formed by the agglomeration of primary particles. This results in more solid-phase contact sites between the positive electrode active materials, a shorter migration path for lithium ions within the positive electrode active materials, and superior kinetic performance of the positive electrode active materials.

[0081] Secondary particles refer to aggregated particles formed by the aggregation of two or more primary particles. Primary and secondary particles can be distinguished experimentally (such as by taking SEM images using a scanning electron microscope).

[0082] In some embodiments, titanium-doped lithium iron phosphate satisfies the chemical formula: Li a Fe b Ti c M d PO4, a is 0.5-1.0, b is 0.9-1.5, c is 0-0.5, d is 0-0.5, and M includes one or more of Nb, V, Al, and Mn. Therefore, the positive electrode active material has high specific capacity and excellent stability, and can maintain its original crystal structure even under conditions such as overcharging and high temperature of the battery cell, making it suitable for high-power charging and discharging scenarios such as fast charging.

[0083] In fast-charging scenarios, the current density at the tabs is typically high, leading to increased heat generation and higher temperatures within the battery cells. This can cause degradation of active materials and decomposition of organic solvents in the electrolyte, resulting in poor cycle performance. Titanium-doped lithium iron phosphate exhibits structural stability during charge and discharge, is less prone to capacity decay, and thus improves the cycle performance of individual battery cells.

[0084] During the charging and discharging process, the active Li ions in a single battery cell undergo intercalation and deintercalation, resulting in varying molar Li content at different discharge states. The molar Li content listed for positive electrode active materials refers to the initial state of the material, i.e., before feeding. After charge-discharge cycles, the molar Li content may change when the positive electrode active material is applied to the battery system. The molar oxygen content of the positive electrode active material described in this application is only a theoretical value. Lattice oxygen release can cause changes in the molar oxygen content; in reality, the molar oxygen content may fluctuate. All of these situations fall within the scope of protection of this application.

[0085] In some embodiments, at least a portion of the surface of the titanium-doped lithium iron phosphate may be provided with a carbon coating layer. The carbon coating layer provides a suitable channel for electron transport, which can significantly improve the electron conduction rate during multiple lithium delithiation and lithium insertion processes. It can also improve the structural stability of the positive electrode active material and effectively alleviate the iron dissolution phenomenon of the positive electrode active material during long-term storage and cyclic use of the battery cell, thereby improving the cycle life of the battery cell.

[0086] In some embodiments, the linear carboxylic acid ester includes one or more of ethyl acetate, ethyl acrylate, propyl acetate, and ethyl propionate. This effectively reduces the viscosity of the electrolyte and increases its ionic conductivity.

[0087] In some embodiments, the electrolyte further includes additives, including vinylene carbonate. Thus, vinylene carbonate not only forms an elastic polymer on the surface of the negative electrode active material, which is superior to electrolyte solvents and mitigates SEI film rupture and recombination caused by the expansion and contraction of the negative electrode active material, but also inhibits side reactions between active components such as linear carboxylic esters and the positive electrode active material, thereby improving the cycle performance of the battery cell in multiple ways.

[0088] In some embodiments, the mass fraction of vinylene carbonate in the electrolyte is 0.2%-1.5%. Thus, adding an appropriate amount of vinylene carbonate helps to form an SEI film of moderate thickness and good elasticity, with minimal impact on the internal resistance of the battery cell.

[0089] As an example, the mass fraction of vinylene carbonate in the electrolyte can be 0.2%, 0.4%, 0.6%, 0.8%, 1.0%, 1.2%, 1.4%, 1.5%, or any value between the two.

[0090] Vinylene carbonate can suppress side reactions between linear carboxylic acid esters and positive electrode active materials. When the mass fraction of vinylene carbonate in the electrolyte is within the aforementioned range, it can effectively suppress side reactions between the aforementioned amount of linear carboxylic acid esters and positive electrode active materials, reduce the thickness of the SEI film, reduce the negative electrode film resistance, and improve the fast-charging performance of the battery cell.

[0091] In some embodiments, the additive also includes lithium difluorophosphate, with a mass fraction of 0.1%-2% in the electrolyte. This optimizes the film-forming composition of the SEI film, improves its rigidity, and enhances its lithium-ion transport rate and structural stability.

[0092] As an example, the mass fraction of lithium difluorophosphate in the electrolyte can be 0.1%, 0.3%, 0.5%, 0.7%, 0.9%, 1.1%, 1.3%, 1.5%, 1.7%, 1.9%, 2.0%, or any value range between the two.

[0093] In some embodiments, the solvent also includes linear carbonate, with the mass fraction of linear carbonate in the electrolyte being 25%-60%. This results in a higher ionic conductivity of the electrolyte, fewer side reactions between the electrolyte and the active material, and a significant improvement in the chemical stability of the electrolyte.

[0094] As an example, the mass fraction of linear carbonate in the electrolyte can be 25%, 30%, 35%, 40%, 45%, 50%, 55%, 60%, or any value between the two.

[0095] Linear carbonates and linear carboxylic esters can be mixed uniformly, resulting in a high degree of electrolyte homogeneity. However, linear carbonates have a slightly higher viscosity than linear carboxylic esters, and their effect on improving the ionic conductivity of the electrolyte is slightly less significant. Linear carbonates exhibit superior chemical stability compared to linear carboxylic esters, significantly reducing side reactions between the electrolyte and the positive electrode active material, while also providing a relatively better improvement in the ionic conductivity of the electrolyte.

[0096] In some embodiments, the linear carbonate includes one or more of dimethyl carbonate and ethyl methyl carbonate.

[0097] In some embodiments, the solvent also includes cyclic carbonates, with the mass fraction of cyclic carbonates in the electrolyte being 15%-30%. This allows for efficient dissociation of the lithium salt, further improving the desolvation of lithium ions and forming free Li₂. + It combines with anions to construct an ion conduction network, thereby improving the migration rate of lithium ions in the electrolyte.

[0098] As an example, the mass fraction of cyclic carbonates in the electrolyte can be 15%, 20%, 25%, 30%, or any value between the two.

[0099] In some embodiments, the cyclic carbonate includes one or more of ethylene carbonate and propylene carbonate.

[0100] In some embodiments, the lithium salt also includes lithium hexafluorophosphate, with the mass fraction of lithium hexafluorophosphate in the electrolyte being 5%-20%. Therefore, lithium hexafluorophosphate has advantages such as mature production technology, low cost, and good overall electrochemical performance, and can significantly increase the number of active lithium ions in the electrolyte, thereby improving the ionic conductivity of the electrolyte.

[0101] As an example, the mass fraction of lithium hexafluorophosphate in the electrolyte can be 5%, 8%, 11%, 14%, 17%, 20%, or any value between two of these.

[0102] In some embodiments, the additives in the electrolyte may include negative electrode film-forming additives, positive electrode film-forming additives, and additives that can improve certain battery performance, such as additives that improve battery overcharge performance, additives that improve battery high-temperature performance, and additives that improve battery low-temperature power performance.

[0103] In some embodiments, the electrolyte has an ionic conductivity of 10 mS / cm to 12.5 mS / cm at 25°C. This results in a relatively fast migration rate of lithium ions in the electrolyte, making it suitable for high-power charge and discharge scenarios.

[0104] As an example, the ionic conductivity of the electrolyte at 25°C can be 10.0 mS / cm, 10.5 mS / cm, 11.0 mS / cm, 11.5 mS / cm, 12.0 mS / cm, 12.5 mS / cm, or any value between the two.

[0105] When the conductivity of the electrolyte at room temperature is within the above range, the migration rate of lithium ions in the electrolyte is relatively high, which can further reduce the internal resistance of the battery cell, thereby reducing heat generation and improving the fast charging performance of the battery cell.

[0106] The ionic conductivity of an electrolyte has a well-known meaning in the art and can be tested and analyzed using existing methods. For example, ionic conductivity can be obtained using a conductivity meter, such as the DDSJ-318 conductivity meter. The testing temperature can be 25±0.1℃. The method described in HG / T 4067-2015 can be followed. Unless otherwise specified, the unit of ionic conductivity of the electrolyte is millisiemens per centimeter (mS / cm).

[0107] In some embodiments, the negative electrode sheet includes a negative current collector and a negative electrode film layer located on at least one side of the negative current collector. The negative electrode film layer includes a negative electrode active material, which includes graphite, and the graphite includes secondary particles. Thus, compared to primary particles, secondary particles exhibit isotropic behavior during lithium intercalation, which facilitates rapid lithium-ion intercalation and improves the fast-charging performance of the battery cell.

[0108] In some embodiments, the graphitization degree of graphite is 90%-94%. As a result, the conductivity of the negative electrode active material is relatively excellent, which can reduce the heat generation of the negative electrode sheet, thereby reducing the heat generation of the battery cell and improving the fast charging performance of the battery cell.

[0109] As an example, the degree of graphitization of graphite can be 90%, 90.5%, 91%, 91.5%, 92%, 92.5%, 93%, 93.5%, 94%, or any value between two of these.

[0110] When the degree of graphitization of graphite is within the above range, the graphite particles have excellent electrical conductivity, which can reduce the heat generation of the negative electrode sheet, reduce the heat generation of the battery cell, and improve the fast charging performance of the battery cell.

[0111] As an example, the negative electrode sheet obtained from disassembly can be scraped to obtain negative electrode active material powder, which can then be subjected to XRD testing and the degree of graphitization calculated. The higher the degree of graphitization of the material, the lower the degree of disorder. For example, it can be tested according to the general rules of X-ray diffraction analysis in JIS / K 0131-1996.

[0112] In some embodiments, the Dv50 particle size of graphite is 7μm-12μm. This shortens the solid-phase transport path of lithium ions, improving fast-charging performance, and also reduces the agglomeration of the negative electrode active material, thereby improving its stability and compaction density.

[0113] As an example, the Dv50 particle size of graphite can be 7 μm, 7.5 μm, 8 μm, 8.5 μm, 9 μm, 9.5 μm, 10 μm, 10.5 μm, 11 μm, 11.5 μm, 12 μm or any value between the two.

[0114] When the Dv50 of the negative electrode active material is within the above range, it can shorten the solid-phase transport path of lithium ions and improve fast charging performance. On the other hand, the material is not prone to agglomeration during the preparation process, and the material has better processing performance.

[0115] The aforementioned Dv50 particle size refers to the particle size corresponding to a cumulative volume distribution percentage of 50%.

[0116] As an example, graphite material can be obtained by scraping the disassembled negative electrode sheet. The volume average particle size Dv50 of the graphite material can be determined by laser diffraction particle size analysis. Specifically, the particle size of the negative electrode active material can be determined using a laser particle size analyzer (e.g., Malvern Master Size 3000) in accordance with standard GB / T 19077-2016.

[0117] When the negative electrode active material includes other materials besides graphite, the volume distribution particle size of the negative electrode active material refers to the volume distribution particle size of all negative electrode active materials.

[0118] In some embodiments, at least a portion of the graphite surface has an amorphous carbon coating layer with a thickness of 100 nm to 500 nm. Therefore, by forming an amorphous carbon coating layer on the graphite surface, the interlayer spacing of the graphite particles can be increased, reducing the resistance to lithium-ion insertion, accelerating lithium-ion insertion, and effectively suppressing lithium plating caused by the inability of lithium ions to quickly insert into the negative electrode active material under fast charging conditions.

[0119] Amorphous carbon refers to transitional carbon materials with very low levels of graphitization and crystallization, exhibiting an approximately amorphous morphology (or lacking a fixed shape and periodic structural regularity).

[0120] As an example, the thickness of the amorphous carbon coating can be 100 nm, 150 nm, 200 nm, 250 nm, 300 nm, 350 nm, 400 nm, 450 nm, 500 nm or any value between the two.

[0121] As an example, graphite material can be obtained by scraping the disassembled negative electrode sheet, and the thickness of the coating layer can be observed and measured by transmission electron microscopy after sample preparation.

[0122] The negative electrode sheet includes a negative current collector and a negative electrode film layer disposed on at least one surface of the negative current collector and comprising a negative electrode active material. For example, the negative current collector has two surfaces opposite each other in its thickness direction, and the negative electrode film layer is disposed on either or both of the two opposite surfaces of the negative current collector.

[0123] In some embodiments, the porosity of the negative electrode is 25%-30%. This results in better wettability of the electrolyte on the negative electrode, a shorter solid-phase transport distance for lithium ions within the negative electrode, and facilitates rapid lithium ion migration.

[0124] As an example, the porosity of the negative electrode sheet can be 25%, 26%, 27%, 28%, 29%, 30%, or any value between two of these.

[0125] As an example, the porosity of the negative electrode sheet can be determined by the gas displacement method. Specifically, refer to GB / T24586-2009, and determine it through the following steps: Immerse the electrode sheet in ethyl methyl carbonate (EMC) for cleaning. Measure using the gas displacement method. The porosity is the percentage of pore volume to the total volume of the electrode sheet, calculated using the formula: Porosity = (V - V0) / V × 100%, where V0 is the true volume and V is the apparent volume.

[0126] In some implementations, when the battery cell is at 0% SOC, the compaction density of the negative electrode film is 1.3 g / cm³. 3 -1.52g / cm 3 Therefore, the negative electrode active material in the negative electrode film layer is packed more tightly, the contact resistance between particles is smaller, and the solid-phase transport distance of lithium ions in the negative electrode sheet is shorter, which is conducive to the rapid migration of lithium ions. This can further reduce the resistance of the negative electrode sheet, thereby reducing heat generation, and the energy density of the negative electrode sheet is higher.

[0127] As an example, when the battery cell is at 0% SOC, the compaction density of the negative electrode film can be 1.30 g / cm³, 1.32 g / cm³, 1.34 g / cm³, 1.36 g / cm³, 1.38 g / cm³, 1.40 g / cm³, 1.42 g / cm³, 1.44 g / cm³, 1.46 g / cm³, 1.48 g / cm³, 1.50 g / cm³, 1.52 g / cm³, or any value between the two.

[0128] When the compaction density of the negative electrode film is within the above range, it is beneficial to improve the energy density of the battery cell; and because the negative electrode active material in the negative electrode film is packed more tightly, the contact resistance between particles is smaller, which can further reduce the resistance of the electrode sheet, thereby reducing heat generation.

[0129] The state of charge (SOC) of a battery cell is defined as follows: charging the battery cell at a constant current charging rate of 0.33C to the upper limit voltage of the battery, and then charging it at a constant voltage to 0.05C, corresponds to the state of 100% SOC of the battery cell; discharging the battery cell at a constant current discharging rate of 0.33C to the cutoff voltage corresponds to the state of 0% SOC of the battery cell.

[0130] In this embodiment, the compaction density of the negative electrode film layer of a battery cell at 0% State of Charge (SOC) is determined by disassembling the battery cell at 0% SOC and measuring the compaction density of the negative electrode film layer. For example, the disassembled negative electrode sheet is soaked in dimethyl carbonate, cleaned, and dried. A single-sided coated negative electrode sheet (if it is a double-sided coated electrode sheet, the negative electrode film layer on one side can be wiped off first) is taken, cut into small circular pieces with an area of ​​S1, weighed, and recorded as M1, and its thickness H1 is measured. Then, the negative electrode film layer of the weighed negative electrode sheet is wiped off, the weight of the negative current collector is weighed and recorded as M0, and its thickness H0 is measured. The single-sided coating weight of the negative electrode film = (weight of the negative electrode sheet M1 - weight of the negative electrode current collector M0) / S1, the thickness of the negative electrode film = the thickness of the negative electrode sheet H1 - the thickness of the negative electrode current collector H0, and the compaction density of the negative electrode film = the single-sided coating weight of the negative electrode film / the thickness of the negative electrode film.

[0131] In some embodiments, the single-sided coating weight of the negative electrode film is 0.12 g / 1540.25 mm. 2 -0.15g / 1540.25mm 2 Therefore, the negative electrode sheet has suitable porosity and high energy density.

[0132] As an example, the coating weight on one side of the negative electrode film can be 0.120g / 1540.25mm², 0.125g / 1540.25mm², 0.130g / 1540.25mm², 0.135g / 1540.25mm², 0.140g / 1540.25mm², 0.145g / 1540.25mm², 0.150g / 1540.25mm², or any value range between the two.

[0133] When the single-sided coating weight of the negative electrode film is within the above range, the porosity of the negative electrode sheet is moderate, and it can also improve the energy density of the battery cell.

[0134] As an example, the single-sided coating weight of the negative electrode film can be tested using the following method: Take a single-sided coated negative electrode sheet (if it is a double-sided coated negative electrode sheet, the negative electrode film layer on one side can be wiped off first), and cut it into a piece with an area of ​​1540.25 mm². 2 Small circular plates. Weigh them and record the weight as M1. Then wipe off the negative electrode film on the weighed negative electrode plate and weigh the negative electrode current collector, recording the weight as M0. Based on an area of ​​1540.25 mm². 2 The weight of the single-sided coating of the negative electrode film on the small disc is equal to the weight of the negative electrode sheet M1 minus the weight of the negative electrode current collector M0.

[0135] The positive electrode includes a positive current collector and a positive electrode film layer disposed on at least one surface of the positive current collector and comprising a positive electrode active material. For example, the positive current collector has two surfaces opposite each other in its thickness direction, and the positive electrode film layer is disposed on either or both of the two opposite surfaces of the positive current collector.

[0136] In some embodiments, the porosity of the positive electrode is 18%-27%. As a result, there is more space in the positive electrode that can be used for wetting the electrolyte, and the electrolyte can fully wet the positive electrode.

[0137] As an example, the porosity of the positive electrode sheet can be 18%, 19%, 20%, 21%, 22%, 23%, 24%, 25%, 26%, 27%, or any value between the two.

[0138] The porosity of the positive electrode sheet can be obtained by referring to the corresponding test method for the negative electrode film, and will not be repeated here.

[0139] In some implementations, when the battery cell is at 0% SOC, the compaction density of the positive electrode film is 2.4 g / cm³. 3 -2.63g / cm 3 Therefore, the positive electrode film has many contact points between the positive electrode active materials, the particles are tightly bonded, the electron transport path is stable, there are many lithium ion transport channels, and the positive electrode film has high structural stability, which helps to improve the energy density of the positive electrode and reduce the internal resistance of the positive electrode.

[0140] As an example, when the battery cell is at 0% SOC, the compaction density of the positive electrode film can be 2.40 g / cm³, 2.43 g / cm³, 2.46 g / cm³, 2.49 g / cm³, 2.52 g / cm³, 2.55 g / cm³, 2.58 g / cm³, 2.61 g / cm³, 2.63 g / cm³, or any value between the two.

[0141] When the battery cell is at 0% SOC, the compaction density of the positive electrode film can be obtained by referring to the corresponding test method for the negative electrode film, and will not be repeated here.

[0142] In some embodiments, the single-sided coating weight of the positive electrode film is 0.27 g / 1540.25 mm. 2 -0.33g / 1540.25mm 2 Therefore, the positive electrode sheet has suitable porosity and high energy density.

[0143] As an example, the coating weight on one side of the positive electrode film can be 0.27g / 1540.25mm², 0.28g / 1540.25mm², 0.29g / 1540.25mm², 0.30g / 1540.25mm², 0.31g / 1540.25mm², 0.32g / 1540.25mm², 0.33g / 1540.25mm², or any value between the two.

[0144] The coating weight of the positive electrode film on one side can be obtained by referring to the corresponding test method for the negative electrode film, and will not be repeated here.

[0145] In some implementations, reference Figure 2 and Figure 3 The electrode assembly includes a negative electrode straight section 141, and the negative electrode straight section 141 and the positive electrode straight section 131 are alternately stacked along the thickness direction Y of the electrode assembly. A negative electrode tab 112 is used to electrically connect the negative electrode straight section 141 and the negative electrode terminal, and a positive electrode tab 111 is used to electrically connect the positive electrode straight section 131 and the positive electrode terminal. Optionally, the battery cell also includes a separator 15, and the positive electrode straight section 131, the separator 15, and the negative electrode straight section 141 are alternately stacked.

[0146] In the case of a wound structure of electrode assembly, from a structural point of view, the electrode assembly includes a positive electrode 13, a negative electrode 14 and a separator 15. The positive electrode 13, the negative electrode 14 and the separator 15 are all integral structures. The separator 15 is disposed between the positive electrode 13 and the negative electrode 14. The positive electrode 13, the separator 15 and the negative electrode 14 are wound in one direction to form the electrode assembly.

[0147] After the electrode assembly is formed by winding, the positive electrode coating portion of the positive electrode sheet 13 may include multiple positive electrode straight sections 131 and multiple positive electrode bent sections 132. The positive electrode bent sections 132 and the positive electrode straight sections 131 are arranged along the winding direction of the electrode assembly, and the positive electrode bent sections 132 and the positive electrode straight sections 131 are connected. The positive electrode tab 111 is connected to the positive electrode straight section 131. During the winding process of the electrode assembly, the positive electrode sheet 13 can form a positive electrode straight section 131 by winding half a turn. The negative electrode coating portion of the negative electrode sheet 14 may include multiple negative electrode straight sections 141 and multiple negative electrode bent sections 142. The negative electrode bent sections 142 and negative electrode straight sections 141 are arranged along the winding direction of the electrode assembly, and the negative electrode bent sections 142 are connected to the negative electrode straight sections 141. The negative electrode tab 112 is connected to the negative electrode straight section 141. During the winding process of the electrode assembly, the negative electrode sheet 14 can form a negative electrode straight section 141 by winding half a turn.

[0148] The positive electrode straight section 131 and the negative electrode straight section 141 are alternately stacked, and the positive electrode bent section 132 and the negative electrode bent section 142 are alternately stacked. From an external perspective, the electrode assembly includes straight regions, bent regions, and tabs. The straight regions include the positive electrode straight section 131 and the negative electrode straight section 141. The bent regions include the positive electrode bent section 132 and the negative electrode bent section 142.

[0149] In some embodiments, the electrode assembly has a wound structure. The positive electrode includes a positive electrode coating portion and a positive electrode sheet portion connected together. The positive electrode film layer is located within the positive electrode coating portion. The positive electrode coating portion includes a positive electrode straight section 131, and the negative electrode coating portion includes a negative electrode straight section 141. The positive electrode straight sections 131 and 141 are stacked along the thickness direction of the electrode assembly. The ratio of the number of positive electrode tabs 111 to the number of positive electrode straight sections 131 is greater than 0.5 and not greater than 1. Therefore, the number of tabs is relatively large, and the total current-carrying area of ​​the tabs is large, which can increase the current-shunting capacity of a single tab and further improve the fast-charging performance of the battery cell.

[0150] The portion of the positive electrode sheet coated with a positive electrode film is the positive electrode coating portion, and the corresponding tab is the positive electrode tab portion 111. The positive electrode film contains a positive electrode active material. The positive electrode coating portion includes a positive electrode current collector and a positive electrode film disposed on at least one side of the positive electrode current collector. When the positive electrode coating portion includes a positive electrode straight section 131, the positive electrode straight section 131 includes a positive electrode current collector and a positive electrode film disposed on at least one side of the positive electrode current collector.

[0151] As an example, the ratio of the number of positive electrode tabs 111 to the number of positive electrode straight segments 131 can be 0.55, 0.6, 0.65, 0.7, 0.75, 0.8, 0.85, 0.9, 0.95, or 1.0.

[0152] In some embodiments, the electrode assembly has a wound structure, and the negative electrode sheet includes a connected negative electrode coating portion and a negative electrode sheet portion. The negative electrode film layer is located within the negative electrode coating portion, and the ratio of the number of negative electrode tabs 112 to the number of negative electrode straight sections 141 is greater than 0.5 and not greater than 1. Therefore, the number of tabs is relatively large, and the total current-carrying area of ​​the tabs is large, which can increase the current-shunting capacity of a single tab and further improve the fast-charging performance of the battery cell.

[0153] The portion of the negative electrode sheet coated with a negative electrode film is the negative electrode coating portion, and the corresponding tab is the negative electrode tab portion 112. The negative electrode film contains a negative electrode active material. The negative electrode coating portion includes a negative electrode current collector and a negative electrode film disposed on at least one side of the negative electrode current collector. When the negative electrode coating portion includes a negative electrode straight section 141, the negative electrode straight section 141 includes a negative electrode current collector and a negative electrode film disposed on at least one side of the negative electrode current collector.

[0154] As an example, the ratio of the number of negative electrode tabs 112 to the number of negative electrode straight sections 141 can be 0.55, 0.6, 0.65, 0.7, 0.75, 0.8, 0.85, 0.9, 0.95, or 1.0.

[0155] In some embodiments, reference is made to Figure 3 , Figure 3 The diagram shows a case where the ratio of the number of positive electrode tabs 111 to the number of positive electrode straight sections 131 of the positive electrode 13 is 0.75. The positive electrode 13 is wound multiple times, with each turn forming two positive electrode straight sections 131. At least one turn of the multiple turns can have one positive electrode tab 111 on each of the two positive electrode straight sections 131, i.e., one positive electrode tab 111 per turn. At least another turn of the multiple turns can have two positive electrode tabs 111 on each of the two positive electrode straight sections 131, i.e., two positive electrode tabs 111 per turn. In the electrode assembly, this can be converted to 0.75 positive electrode tabs 111 on each positive electrode straight section 131. Figure 3 The ratio of the number of negative electrode tabs 112 in the negative electrode plate to the number of negative electrode straight sections 141 in the negative electrode plate 14 is 0.75, which will not be elaborated here.

[0156] In some embodiments, reference is made to Figure 4 , Figure 4 The diagram shows a case where the ratio of the number of positive electrode tabs 111 to the number of positive electrode straight sections 131 of the positive electrode 13 is 1. The positive electrode 13 can form two positive electrode straight sections 131 by winding it once. Each positive electrode straight section 131 is connected to a positive electrode tab 111, that is, each positive electrode straight section 131 is provided with a positive electrode tab 111. Figure 4 The ratio of the number of negative electrode tabs 112 in the negative electrode plate to the number of negative electrode straight sections 141 in the negative electrode plate 14 is 1, which will not be elaborated here.

[0157] In some implementations, when the number of positive electrode tabs 111 and negative electrode tabs 112 is the same, the overcurrent density of a single tab is the same, the performance matching is better, which is conducive to improving the uniformity of the battery cell reaction, improving the current shunting effect, and improving the charging and discharging capability of the battery cell.

[0158] In some embodiments, multiple positive electrode tabs are located on the same side of the positive electrode coating, and / or multiple negative electrode tabs are located on the same side of the negative electrode coating. This facilitates the connection of the stacked tabs to other components, such as adapters, and subsequently to electrode terminals for electrical connection.

[0159] In some embodiments, the positive electrode sheet is wound to form multiple ring-shaped structures. Each ring-shaped structure includes two straight positive electrode segments 131. The ring-shaped structure includes a first ring-shaped structure and a second ring-shaped structure. Either of the two straight positive electrode segments 131 of the first ring-shaped structure is connected to the positive electrode tab 111. Both straight positive electrode segments 131 of the second ring-shaped structure are connected to the positive electrode tab 111. The second ring-shaped structure is located outside the first ring-shaped structure. Therefore, under the premise that the total number of positive electrode tabs 111 is the same, the sum of the distances between the aforementioned multiple positive electrode tabs 111 and the welding sheet is the shortest, the welding difficulty is lower, the positive electrode tabs 111 have a smaller impact on the energy density of the battery cell, and the foil reserved on the positive current collector as the positive electrode tab 111 is of moderate length, which is not easy to bend during the winding of the electrode assembly, effectively preventing the phenomenon of the tab being inserted into the electrode assembly backwards.

[0160] refer to Figure 2 and Figure 3 Starting from the winding start point of the positive electrode sheet, the first ring structure formed by the positive electrode sheet may only include two straight positive electrode sections 131 and one bent positive electrode section 132. The subsequent nth (n>1) ring structure may include two straight positive electrode sections 131 and two bent positive electrode sections 132, and the position of the nth ring structure is closer to the casing of the battery cell than the first ring structure.

[0161] As an example, when n equals 2, the first ring structure formed by the positive electrode sheet can have only one positive electrode straight segment 131 with a positive electrode tab 111; the two positive electrode straight segments 131 of the second ring structure formed by the positive electrode sheet can have positive electrode tabs 111. At this time, the first and second ring structures have a total of four positive electrode straight segments 131 and three positive electrode tabs 111. The ratio of the number of positive electrode tabs 111 to the number of positive electrode straight segments 131 is 0.75, and the second ring structure is located outside the first ring structure, that is, on the side closer to the casing of the battery cell.

[0162] In some embodiments, the negative electrode sheet is wound to form multiple ring-shaped structures. Each ring-shaped structure includes two straight negative electrode segments 141. The ring-shaped structure includes a first ring-shaped structure and a second ring-shaped structure. Either of the two straight negative electrode segments 141 of the first ring-shaped structure is connected to the negative electrode tab 112. Both straight negative electrode segments 141 of the second ring-shaped structure are connected to the negative electrode tab 112. The second ring-shaped structure is located outside the first ring-shaped structure. Therefore, under the premise that the total number of negative electrode tabs 112 is the same, the sum of the distances between the aforementioned multiple negative electrode tabs 112 and the welding sheet is the shortest, the welding difficulty is lower, the negative electrode tabs 112 have a smaller impact on the energy density of the battery cell, and the foil reserved on the negative electrode current collector as the negative electrode tab 112 is of moderate length, which is not easy to bend during the winding of the electrode assembly, effectively preventing the phenomenon of the tab being inserted into the electrode assembly backwards.

[0163] refer to Figure 2 and Figure 3 Starting from the winding start point of the negative electrode sheet, the first ring structure formed by the negative electrode sheet may only include two straight negative electrode sections 141 and one bent negative electrode section 142. The subsequent nth (n>1) ring structure may include two straight negative electrode sections 141 and two bent negative electrode sections 142, and the position of the nth ring structure is closer to the casing of the battery cell than the first ring structure.

[0164] As an example, when n equals 2, the first ring structure formed by the negative electrode sheet can have only one negative electrode straight segment 141 with a negative electrode tab 112; the two negative electrode straight segments 141 of the second ring structure formed by the negative electrode sheet can have negative electrode tabs 112. At this time, the first and second ring structures have a total of four negative electrode straight segments 141 and three negative electrode tabs 112. The ratio of the number of negative electrode tabs 112 to the number of negative electrode straight segments 141 is 0.75, and the second ring structure is located outside the first ring structure, that is, on the side closer to the casing of the battery cell.

[0165] In some embodiments, the positive electrode film layer may optionally include a positive electrode conductive agent. This application does not impose particular limitations on the type of positive electrode conductive agent. As an example, the positive electrode conductive agent includes at least one selected from superconducting carbon, conductive graphite, acetylene black, carbon black, Ketjen black, carbon dots, carbon nanotubes, graphene, and carbon nanofibers. In some embodiments, the mass content of the positive electrode conductive agent is ≤5% based on the mass of the positive electrode film layer.

[0166] In some embodiments, the positive electrode film layer may optionally include a positive electrode binder. This application does not impose particular limitations on the type of positive electrode binder. As an example, the positive electrode binder may include at least one selected from polyvinylidene fluoride, polytetrafluoroethylene, a terpolymer of vinylidene fluoride-tetrafluoroethylene-propylene, a terpolymer of vinylidene fluoride-hexafluoropropylene-tetrafluoroethylene, a tetrafluoroethylene-hexafluoropropylene copolymer, polyacrylic acid, and fluorinated acrylate resins. In some embodiments, the mass content of the positive electrode binder is ≤5% based on the mass of the positive electrode film layer.

[0167] In some embodiments, the positive current collector may be a metal foil or a composite current collector. Examples of metal foils include at least one foil selected from aluminum, aluminum alloys, nickel, nickel alloys, titanium, titanium alloys, silver, and silver alloys. The composite current collector may include a polymeric material substrate and a metal material layer formed on at least one surface of the polymeric material substrate. As an example, the metal material layer may include at least one selected from aluminum, aluminum alloys, nickel, nickel alloys, titanium, titanium alloys, silver, and silver alloys. As an example, the polymeric material substrate may include at least one selected from polypropylene (PP), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polystyrene (PS), and polyethylene (PE).

[0168] The positive electrode film is typically formed by coating a positive electrode slurry onto a positive electrode current collector, followed by drying and cold pressing. The positive electrode slurry is usually formed by dispersing the positive electrode active material, optional conductive agent, optional binder, and any other components in a solvent and stirring until homogeneous. The solvent can be N-methylpyrrolidone (NMP), but is not limited to this.

[0169] In some embodiments, the negative electrode film layer may optionally include a negative electrode conductive agent. This application does not impose particular limitations on the type of negative electrode conductive agent. As an example, the negative electrode conductive agent may include at least one selected from superconducting carbon, conductive graphite, acetylene black, carbon black, Ketjen black, carbon dots, carbon nanotubes, graphene, and carbon nanofibers. In some embodiments, the mass content of the negative electrode conductive agent is ≤5% based on the total weight of the negative electrode film layer.

[0170] In some embodiments, the negative electrode film layer may optionally include a negative electrode binder. In some embodiments, the mass content of the negative electrode binder is ≤5% based on the total weight of the negative electrode film layer.

[0171] In some embodiments, the negative electrode film may optionally include other additives. As examples, other additives may include thickeners, dispersants, etc., such as sodium carboxymethyl cellulose (CMC-Na), PTC thermistor materials, etc. In some embodiments, the mass content of other additives is ≤2% based on the total weight of the negative electrode film.

[0172] In some embodiments, the negative electrode current collector may be a metal foil or a composite current collector. Examples of metal foils include at least one foil selected from copper, copper alloys, nickel, nickel alloys, titanium, titanium alloys, silver, and silver alloys. The composite current collector may include a polymeric material substrate and a metal material layer formed on at least one surface of the polymeric material substrate. As an example, the metal material layer may include at least one selected from copper, copper alloys, nickel, nickel alloys, titanium, titanium alloys, silver, and silver alloys. As an example, the polymeric material substrate may include at least one selected from polypropylene (PP), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polystyrene (PS), and polyethylene (PE).

[0173] The negative electrode film is typically formed by coating a negative electrode slurry onto a negative electrode current collector, followed by drying and cold pressing. The negative electrode slurry is usually formed by dispersing the negative electrode active material, optional conductive agent, optional binder, and other optional additives in a solvent and stirring until homogeneous. The solvent can be N-methylpyrrolidone (NMP) or deionized water, but is not limited to these.

[0174] In a second aspect, this application proposes a battery device comprising the aforementioned battery cell, wherein the battery device includes one or more of a battery module, a battery pack, and an energy storage device. Thus, the battery device possesses all the features and advantages of the aforementioned battery cell, which will not be elaborated further here.

[0175] In a third aspect, this application proposes an electrical device comprising the aforementioned battery cell. Therefore, the electrical device possesses all the features and advantages of the aforementioned battery cell, which will not be repeated here.

[0176] Battery cells, battery modules, or battery packs can be used as power sources for electrical devices or as energy storage units for electrical devices. Electrical devices can be vehicles, mobile phones, portable devices, laptops, ships, spacecraft, electric toys, and power tools, etc. Vehicles can be gasoline-powered cars, natural gas-powered cars, or new energy vehicles; new energy vehicles can be pure electric vehicles, hybrid electric vehicles, or range-extended electric vehicles, etc. Spacecraft include airplanes, rockets, space shuttles, and spacecraft, etc. Electric toys include stationary or mobile electric toys, such as game consoles, electric car toys, electric ship toys, and electric airplane toys, etc. Power tools include metal cutting power tools, grinding power tools, assembly power tools, and railway power tools, such as electric drills, electric grinders, electric wrenches, electric screwdrivers, electric hammers, impact drills, concrete vibrators, and electric planers, etc. This application does not impose special limitations on the above-mentioned electrical devices.

[0177] As an electrical device, you can choose individual battery cells, battery modules, or battery packs according to your usage requirements.

[0178] Figure 8 This is an example of an electrical device. The device could be a pure electric vehicle, a hybrid electric vehicle, or a plug-in hybrid electric vehicle. To meet the device's requirements for high power and high energy density, a battery pack or battery module can be used.

[0179] Another example device could be a mobile phone, tablet, or laptop. These devices typically require a slim and lightweight design and can use a single battery cell as their power source.

[0180] The following specific embodiments illustrate the solution of this application. It should be noted that these embodiments are for illustrative purposes only and should not be considered as limiting the scope of 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 whose manufacturers are not specified are all conventional products that can be obtained commercially.

[0181] Example 1 1) Preparation of the positive electrode sheet: The positive electrode sheet includes a positive current collector aluminum foil and a positive electrode film layer coated on both sides of the positive current collector. The positive electrode film layer is formed by uniformly coating the surface of the positive current collector aluminum foil with a positive electrode slurry (solvent is N-methylpyrrolidone), and then drying and cold pressing it.

[0182] The positive electrode film layer includes positive electrode active material, conductive agent (SP), and binder (polyvinylidene fluoride) in a weight ratio of 97:1:2.

[0183] Among them, the positive electrode active material is titanium-doped lithium iron phosphate. The positive electrode active material includes primary particles and secondary particles. The titanium content in lithium iron phosphate is 1000ppm, and the average particle size of the primary particles of the positive electrode active material is 100nm. The porosity of the positive electrode sheet is 21.3%, the single-sided thickness of the positive electrode film is 73 μm, and the single-sided coating weight of the positive electrode film is 0.293 g / 1540.25 mm. 2 The compaction density of the positive electrode film is 2.6 g / cm³. 3 .

[0184] 2) Preparation of the negative electrode sheet: The negative electrode sheet includes a negative current collector copper foil and a negative electrode film layer coated on both sides of the negative current collector. The negative electrode film layer is formed by uniformly coating the surface of the negative current collector copper foil with negative electrode slurry (solvent is deionized water), and then drying and cold pressing it.

[0185] The negative electrode film layer comprises negative electrode active material in a weight ratio of 97.2:1.2:0.8:0.8, styrene-butadiene rubber (SBR) binder, sodium carboxymethyl cellulose (CMC-Na) thickener, and carbon black (Super P) conductive agent.

[0186] The negative electrode active material is graphite, at least part of the surface of the graphite has an amorphous carbon coating layer with a thickness of 200 nm, the graphitization degree of the graphite is 92.8%, and the Dv50 particle size is 10.3 μm.

[0187] The porosity of the negative electrode sheet is 26.7%; the single-sided coating weight of the negative electrode film is 0.132 g / 1540.25 mm. 2 The compaction density of the negative electrode film is 1.46 g / cm³. 3 .

[0188] 3) Separating membrane: The base film is made of polyethylene with a thickness of 5 μm. A ceramic coating is provided on one side of the base film. A polyvinylidene fluoride adhesive layer is provided between the ceramic coating and the base film. The total thickness of the separator is 9 μm.

[0189] 4) Preparation of electrolyte: Solvent: Linear carboxylic acid ester: Ethyl acetate, the mass fraction of linear carboxylic acid ester in the electrolyte is 8%.

[0190] Linear carbonate: dimethyl carbonate, with a mass fraction of 55% in the electrolyte.

[0191] Cyclic carbonate: Ethylene carbonate, the mass fraction of cyclic carbonate in the electrolyte is 21%.

[0192] Lithium salts: Lithium difluorosulfonylimide, with a mass fraction of 2% in the electrolyte.

[0193] Lithium hexafluorophosphate, the mass fraction of lithium hexafluorophosphate in the electrolyte is 12%.

[0194] additive: Ethylene carbonate, the mass percentage of ethylene carbonate in the electrolyte is 1.2%.

[0195] Lithium difluorophosphate, with a mass fraction of 0.8% in the electrolyte.

[0196] 5) Preparation of individual battery cells: A battery cell includes a casing, electrode assembly, and electrolyte. The electrode assembly and electrolyte are disposed within the casing. The electrode assembly is a wound electrode assembly, wherein the ratio of the number of positive electrode tabs to the number of straight positive electrode sections is 0.75, and the ratio of the number of negative electrode tabs to the number of straight negative electrode sections is 0.75. A separator is disposed between the positive and negative electrode plates. The battery cell is obtained by inserting the electrode assembly into the casing, injecting electrolyte, allowing it to stand, forming, and shaping.

[0197] The differences between the remaining embodiments and comparative examples and Embodiment 1 are shown in the table below.

[0198] The following tests were performed on the individual battery cells in the examples and comparative examples: Dynamic performance (DCR): At 25℃, the battery cell was charged to 3.65V with a constant current of 0.33C, then charged to 0.05C with a constant voltage of 3.65V, and then discharged to 50% capacity with a constant current of 0.33C. After resting for 30 minutes, it was discharged at 4C for 10 seconds. The voltages V1 and V2 before and after discharge were recorded. The DCR was calculated as (V1-V2) / I, where I is the discharge current in A.

[0199] Cycle life: At 25℃, charge the battery cell to 3.65V at a charging rate of 0.5C (the nominal capacity of the individual cells), then charge it to 0.05C at a constant voltage of 3.65V. After charging is complete, disconnect the charging circuit of the battery device and let it stand for 10 minutes. Then, discharge the battery cell to 2.5V at a discharge rate of 1C (the nominal capacity of the individual cells in the battery device), and let it stand for 10 minutes. One charge-discharge cycle is one cycle. The test is stopped when the capacity decays to 80% of the nominal capacity. This number of cycles is recorded as the number of cycles corresponding to the 80% capacity decay.

[0200] Safety Performance: At 25℃, charge the battery cell to 3.65V at a 0.5C charging rate (the nominal capacity of each cell), then charge it to 0.05C at a constant voltage of 3.65V. After charging, pierce the large surface of the cell with a 5mm steel needle at a speed of 1m / s and observe whether the cell opens normally. If it does, the test is qualified; if the casing cracks, the test is unqualified. The test results are represented by a / b, where a represents the number of unqualified battery cells and b represents the total number of successfully tested battery cells.

[0201] Table 1

[0202] As shown in Table 1, when the titanium content in lithium iron phosphate is within the aforementioned range, it can reduce the occurrence of side reactions between the electrolyte and the positive electrode active material, suppress the dissolution of transition metal ions, such as iron ions, in lithium iron phosphate, thereby avoiding the destruction of the SEI film due to the migration of transition metals to the negative electrode after dissolution, and improving the cycle life of the battery cell. It can also simultaneously reduce the amount of film-forming additives used in the electrolyte to form the SEI film on the negative electrode, thereby reducing the thickness of the SEI film, and further reducing the negative electrode interface impedance, improving the fast-charging performance of the battery cell. When the titanium content in lithium iron phosphate is too high or too low, it is difficult to achieve a balance between the cycle performance and fast-charging performance of the battery cell. When the titanium doping amount is too low, the stability of the positive electrode active material is poor, there are more side reactions between the positive electrode active material and the electrolyte, and the cycle life is significantly reduced. When the titanium doping amount is too high, the structural integrity of lithium iron phosphate is destroyed, lithium ion migration is hindered, and the kinetic performance of the battery cell decreases.

[0203] Table 2

[0204] Table 2 shows that when the amount of linear carboxylic acid ester is within the aforementioned range, adding low-viscosity linear carboxylic acid ester to the electrolyte can effectively improve the ionic conductivity of the electrolyte and improve the kinetic performance of the battery cell. When the amount of linear carboxylic acid ester is too small, the improvement effect on the ionic conductivity of the electrolyte is poor, and the fast-charging performance of the battery cell is poor; when the amount of linear carboxylic acid ester is too large, the side reactions between the electrolyte and the positive electrode active material are aggravated, and the cycle performance of the battery cell is poor.

[0205] Table 3

[0206] Table 3 shows that adding a small amount of LiFSI to the electrolyte can promote the desolvation of lithium ions in the electrolyte, synergistically improve the ionic conductivity of the electrolyte with linear carboxylic acid esters, and suppress the risk of thermal runaway that may be caused by excessive LiFSI addition, thus achieving a balance between the fast-charging performance and safety performance of the battery cell. When the amount of LiFSI is too small, the effect on improving the ionic conductivity of the electrolyte is poor, and the fast-charging performance of the battery cell is poor; when the amount of LiFSI is too large, the safety performance of the battery cell decreases.

[0207] Table 4

[0208] As shown in Table 4, when the average particle size of the primary particles of titanium-doped lithium iron phosphate is within the aforementioned range, the particle size of the cathode active material is relatively small, the lithium ion insertion / extraction path in the cathode active material is shorter, the heat generation is less, and the kinetic performance is better. Furthermore, the cathode active material does not agglomerate during processing, resulting in better processing performance. When the cathode active material includes both primary and secondary particles, there are more solid-phase contact sites between the cathode active materials, the lithium ion migration path in the cathode active material is shorter, and the kinetic performance of the cathode active material is better.

[0209] It should be noted that this application is not limited to the above-described embodiments. The above embodiments are merely examples, and any embodiments with the same structure and effect as the technical concept within the scope of this application are included in the technical scope of this application. Furthermore, various modifications that can be conceived by those skilled in the art to the embodiments, and other ways of constructing by combining some of the constituent elements of the embodiments, without departing from the spirit of this application, are also included in the scope of this application.

Claims

1. A battery cell, characterized in that, include: An electrode assembly, comprising a positive electrode, a negative electrode, and a separator, wherein the positive electrode comprises a positive current collector and a positive electrode film layer located on at least one side of the positive current collector, the positive electrode film layer comprises a positive electrode active material, the positive electrode active material comprising titanium-doped lithium iron phosphate, wherein the titanium content in the lithium iron phosphate is 400ppm-2000ppm; An electrolyte comprising a solvent and a lithium salt, wherein the solvent comprises a linear carboxylic acid ester and a cyclic carbonate, wherein the mass fraction of the linear carboxylic acid ester in the electrolyte is 1%-10%, the mass fraction of the cyclic carbonate in the electrolyte is 15%-30%, and the lithium salt comprises lithium bis(fluorosulfonyl)imide, wherein the mass fraction of the lithium bis(fluorosulfonyl)imide in the electrolyte is 2%-5%.

2. The battery cell according to claim 1, characterized in that, The titanium-doped lithium iron phosphate has an average primary particle size of 100nm-500nm.

3. The battery cell according to claim 1, characterized in that, The titanium-doped lithium iron phosphate comprises primary particles and secondary particles formed by the agglomeration of primary particles.

4. The battery cell according to claim 1, characterized in that, The titanium-doped lithium iron phosphate satisfies the chemical formula: Li a Fe b Ti c M d PO4, a is 0.5-1.0, b is 0.9-1.5, c is 0-0.5, d is 0-0.5, and M includes one or more of Nb, V, Al, and Mn.

5. The battery cell according to claim 1, characterized in that, The linear carboxylic acid ester includes one or more of ethyl acetate, ethyl acrylate, propyl acetate, and ethyl propionate.

6. The battery cell according to claim 1, characterized in that, The electrolyte also includes additives, including vinylene carbonate.

7. The battery cell according to claim 6, characterized in that, The mass fraction of vinylene carbonate in the electrolyte is 0.2%-1.5%.

8. The battery cell according to claim 6, characterized in that, The additive also includes lithium difluorophosphate, and the mass fraction of lithium difluorophosphate in the electrolyte is 0.1%-2%.

9. The battery cell according to claim 1, characterized in that, The solvent also includes linear carbonate, and the mass fraction of the linear carbonate in the electrolyte is 25%-60%.

10. The battery cell according to claim 9, characterized in that, The linear carbonate includes one or more of dimethyl carbonate and ethyl methyl carbonate.

11. The battery cell according to claim 1, characterized in that, The cyclic carbonates include one or more of ethylene carbonate and propylene carbonate.

12. The battery cell according to claim 1, characterized in that, The lithium salt also includes lithium hexafluorophosphate, and the mass fraction of lithium hexafluorophosphate in the electrolyte is 5%-20%.

13. The battery cell according to claim 1, characterized in that, The electrolyte has an ionic conductivity of 10 mS / cm to 12.5 mS / cm at 25°C.

14. The battery cell according to claim 1, characterized in that, The negative electrode sheet includes a negative current collector and a negative electrode film layer located on at least one side of the negative current collector. The negative electrode film layer includes a negative electrode active material, which includes graphite and secondary particles.

15. The battery cell according to claim 14, characterized in that, The graphite has a graphitization degree of 90%-94%.

16. The battery cell according to claim 14, characterized in that, The Dv50 particle size of the graphite is 7μm-12μm.

17. The battery cell according to claim 14, characterized in that, At least a portion of the surface of the graphite has an amorphous carbon coating layer with a thickness of 100 nm to 500 nm.

18. The battery cell according to claim 1, characterized in that, The porosity of the negative electrode sheet is 25%-30%.

19. The battery cell according to claim 14, characterized in that, When the battery cell is at 0% SOC, the compaction density of the negative electrode film is 1.3 g / cm³. 3 -1.52g / cm 3 .

20. The battery cell according to claim 14, characterized in that, The single-sided coating weight of the negative electrode film is 0.12g / 1540.25mm. 2 -0.15g / 1540.25mm 2 .

21. The battery cell according to claim 1, characterized in that, The porosity of the positive electrode sheet is 18%-27%.

22. The battery cell according to claim 1, characterized in that, When the battery cell is at 0% SOC, the compaction density of the positive electrode film is 2.4 g / cm³. 3 -2.63g / cm 3 .

23. The battery cell according to claim 1, characterized in that, The single-sided coating weight of the positive electrode film is 0.27g / 1540.25mm. 2 -0.33g / 1540.25mm 2 .

24. The battery cell according to claim 1, characterized in that, The electrode assembly has a wound structure. The positive electrode includes a positive electrode coating portion and a positive electrode sheet portion connected together, and the positive electrode film layer is located within the positive electrode coating portion. The negative electrode includes a negative electrode coating portion and a negative electrode sheet portion connected together, and the negative electrode film layer is located within the negative electrode coating portion. The positive electrode coating portion includes a positive electrode straight section, and the negative electrode coating portion includes a negative electrode straight section. The positive electrode straight section and the negative electrode straight section are stacked along the thickness direction of the electrode assembly. The ratio of the number of positive electrode tabs to the number of positive electrode straight sections is greater than 0.5 and not greater than 1, and / or the ratio of the number of negative electrode tabs to the number of negative electrode straight sections is greater than 0.5 and not greater than 1.

25. The battery cell according to claim 24, characterized in that, The plurality of positive electrode tabs are located on the same side of the positive electrode coating portion, and / or the plurality of negative electrode tabs are located on the same side of the negative electrode coating portion.

26. The battery cell according to claim 24, characterized in that, The positive electrode sheet is wound to form multiple ring-shaped structures, each ring-shaped structure including two positive electrode straight sections. The ring-shaped structure includes a first ring-shaped structure and a second ring-shaped structure. Either of the two positive electrode straight sections of the first ring-shaped structure is connected to the positive electrode tab. Both positive electrode straight sections of the second ring-shaped structure are connected to the positive electrode tab. The second ring-shaped structure is located outside the first ring-shaped structure.

27. The battery cell according to claim 24, characterized in that, The negative electrode sheet is wound to form multiple ring-shaped structures, each ring-shaped structure including two negative electrode straight sections. The ring-shaped structure includes a first ring-shaped structure and a second ring-shaped structure. Either of the two negative electrode straight sections of the first ring-shaped structure is connected to the negative electrode tab. Both negative electrode straight sections of the second ring-shaped structure are connected to the negative electrode tab. The second ring-shaped structure is located outside the first ring-shaped structure.

28. A battery device, characterized in that, The battery device includes the battery cell according to any one of claims 1-27, and the battery device includes one or more of the following: battery module, battery pack, and energy storage device.

29. An electrical appliance, characterized in that, Includes the battery cell described in any one of claims 1-27.

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