Lithium-ion battery, lithium-ion cell, and electric device

Abstract

A lithium-ion battery, a lithium-ion cell, and an electric device. The battery comprises a positive electrode sheet, a negative electrode sheet, and an electrolyte. The negative electrode sheet comprises a negative electrode current collector and a negative electrode active layer located on at least one surface of the negative electrode current collector. A negative electrode active material of the negative electrode active layer includes graphite, and the Id / Ig value of graphite is 0.05-0.4. The electrolyte comprises a film-forming additive, and the film-forming additive comprises methylene methane disulfonate of which the mass fraction in the electrolyte is less than or equal to 2%.

Description

Lithium-ion batteries, lithium-ion cells, and electrical devices

[0001] Related applications

[0002] This application claims priority to Chinese patent application filed on February 28, 2025, with application number 2025102382901 and entitled "Lithium-ion Battery, Lithium-ion Cell and Electrical Device", the entire contents of which are incorporated herein by reference. Technical Field

[0003] This application relates to the field of battery technology, and in particular to lithium-ion batteries, lithium-ion cells, and electrical devices. Background Technology

[0004] In recent years, lithium-ion batteries have been widely used in energy storage systems for hydropower, thermal power, wind power, and solar power plants, as well as in power tools, electric bicycles, electric motorcycles, electric cars, military equipment, aerospace, and many other fields. With the continuous expansion of the application range of lithium-ion batteries, correspondingly higher requirements are being placed on their performance. For example, the storage performance of lithium-ion batteries needs further improvement. Summary of the Invention

[0005] The first aspect of this application provides a lithium-ion battery. The lithium-ion battery includes a positive electrode, a negative electrode, and an electrolyte; the negative electrode includes a negative current collector and a negative active layer located on at least one surface of the negative current collector, the negative active material of the negative active layer comprising graphite, wherein the graphite has an I... d / I g The value is 0.05 to 0.4, where I d This indicates that the Raman spectrum is at 1350±50 cm⁻¹ -1 peak intensity at d, I g This indicates that the Raman spectrum is at 1580±50 cm⁻¹. -1 The intensity of the g peak at the specified location. The electrolyte includes a film-forming additive, which comprises methylene methane disulfonate (MMDS) at a mass percentage of less than or equal to 2% of the electrolyte.

[0006] In the aforementioned lithium-ion batteries, the solid electrolyte interphase (SEI) film formed with the participation of MMDS exhibits good thermal stability, which can limit the increase in internal resistance of the battery during high-temperature storage; simultaneously, selecting a suitable I... d / I g High-quality graphite can promote the consumption of MMDS during SEI film formation, reduce the residual amount of MMDS in the battery, reduce the impact of residual MMDS decomposition on battery cycle performance, and thus enable the battery to achieve both good high-temperature storage performance and cycle performance.

[0007] In some embodiments, the methylene methane disulfonate accounts for less than or equal to 0.01% of the mass of the electrolyte; alternatively, the methylene methane disulfonate accounts for 0% of the mass of the electrolyte.

[0008] In some embodiments, the graphite I d / I g The value is 0.1 to 0.3.

[0009] In some embodiments, the film-forming additive further includes one or more of cyclic carbonates and cyclic sulfates. Adding one or more of cyclic carbonates and cyclic sulfates to the electrolyte can improve the toughness of the SEI film, reduce the risk of damage to the SEI film under high-temperature cycling, and thus improve the high-temperature cycling performance of lithium-ion batteries.

[0010] In some embodiments, the cyclic carbonate accounts for 0.1% to 10% of the electrolyte by mass. A cyclic carbonate mass percentage greater than or equal to 0.1% allows for more effective utilization of its role in improving SEI toughness and promoting improved high-temperature cycle performance of the battery. The cyclic carbonate has a high viscosity; a mass percentage less than or equal to 10% allows the electrolyte to maintain a low viscosity, which is beneficial for promoting lithium-ion transport and improving the battery's charge-discharge efficiency.

[0011] In some embodiments, the cyclic carbonate accounts for 2% to 5% of the mass percentage of the electrolyte;

[0012] In some embodiments, the cyclic carbonate includes one or more of vinylene carbonate and fluoroethylene carbonate.

[0013] In some embodiments, the cyclic sulfate accounts for 0.01% to 5% of the electrolyte by mass. A cyclic sulfate mass percentage greater than or equal to 0.01% allows for more sufficient utilization of its effect on improving SEI toughness and promoting improved high-temperature cycle performance of the battery. The cyclic sulfate has a high viscosity; a mass percentage less than or equal to 5% of the electrolyte helps maintain a low viscosity, which is beneficial for promoting lithium-ion transport and improving the battery's charge-discharge efficiency.

[0014] In some embodiments, the cyclic sulfate ester accounts for 0.5% to 1% of the electrolyte by mass;

[0015] In some embodiments, the cyclic sulfate ester includes vinyl sulfate.

[0016] In some embodiments, the lithium-ion conductivity of the electrolyte at 25°C is 8 mS / cm to 18 mS / cm. A lithium-ion conductivity greater than or equal to 8 mS / cm at 25°C allows the battery to have lower internal resistance, further improving its room-temperature cycle performance. Simultaneously, a lithium-ion conductivity greater than or equal to 8 mS / cm at 25°C provides the electrolyte with better kinetic properties, reducing battery polarization and helping the battery maintain higher power. Furthermore, a lithium-ion conductivity less than or equal to 18 mS / cm at 25°C allows for a more suitable rate of lithium-ion insertion and extraction in the electrode active material, reducing stress impact on the electrode active material during charging and discharging, and enabling the electrode active material to maintain a more stable crystal structure. This further promotes improvement in the battery's room-temperature cycle performance. Simultaneously, a lithium-ion conductivity less than or equal to 18 mS / cm at 25°C maintains good thermal stability in the electrolyte, further improving the battery's high-temperature cycle performance.

[0017] In some embodiments, the electrolyte has a lithium-ion conductivity of 9 mS / cm to 13 mS / cm at 25°C.

[0018] In some embodiments, the total molar concentration of the lithium salt in the electrolyte is 0.8 mol / L to 1.2 mol / L. By selecting a suitable molar concentration of lithium salt, the electrolyte can have a suitable lithium-ion conductivity, thereby promoting improved battery cycle performance.

[0019] In some embodiments, the lithium salt includes one or more of lithium hexafluorophosphate, lithium bisfluorosulfonylimide, and lithium bistrifluoromethylsulfonylimide.

[0020] In some embodiments, the electrolyte further includes a solvent; the solvent comprises, by mass percentage, 15%–50% ethylene carbonate, 10%–70% dimethyl carbonate, and 5%–50% methyl ethyl carbonate. By selecting a suitable solvent ratio, the electrolyte can have a suitable lithium-ion conductivity, thereby promoting improved battery cycle performance.

[0021] In some embodiments, the graphite has a Dv50 of 7 μm to 13 μm. A Dv50 greater than or equal to 7 μm can further reduce side reactions between graphite and electrolyte, improving the cycle performance of the battery. A Dv50 less than or equal to 13 μm allows the graphite to maintain good kinetic properties, further improving the cycle performance of the battery.

[0022] In some embodiments, the graphite constitutes 95% to 100% of the negative electrode active material by mass. This range of graphite percentage within the negative electrode active material allows for full utilization of graphite's role in consuming MMDS, further improving the battery's high-temperature storage performance and cycle performance.

[0023] In some embodiments, the graphite includes synthetic graphite. Synthetic graphite has a higher cycle life, which is beneficial for improving battery cycle life.

[0024] In some embodiments, the compaction density of the negative electrode active layer is 1.3 g / cm³. 3 ~1.7g / cm 3 The compaction density of the negative electrode active layer is greater than or equal to 1.3 g / cm³. 3 This can enable the battery to have a higher energy density, while also maintaining better contact between the negative electrode active materials, which is beneficial to improving the battery's dynamic performance and further promoting the improvement of battery cycle performance.

[0025] In some embodiments, the positive electrode includes a positive current collector and a positive active layer located on at least one surface of the positive current collector; the positive active material of the positive active layer includes a lithium phosphate. Lithium phosphates have a higher cycle life and can further improve the cycle performance of the battery.

[0026] In some embodiments, the lithium phosphate comprises 90% to 100% of the positive electrode active material by mass.

[0027] A second aspect of this application provides a lithium-ion battery cell, comprising a positive electrode, a negative electrode, and an electrolyte; the negative electrode includes a negative current collector and a negative active layer located on at least one surface of the negative current collector, the negative active material of the negative active layer comprising graphite, wherein the graphite has an I d / I g The value is 0.05 to 0.4, where I d This indicates that the Raman spectrum is at 1350±50 cm⁻¹ -1 peak intensity at d, I g This indicates that the Raman spectrum is at 1580±50 cm⁻¹. -1 The intensity of the g peak at the specified location; the electrolyte includes a film-forming additive, which includes methylene methane disulfonate, and the methylene methane disulfonate accounts for 0.5% to 3% of the mass of the electrolyte.

[0028] In some embodiments, the film-forming additive further includes one or more of cyclic carbonates and cyclic sulfates.

[0029] In some embodiments, the cyclic carbonate accounts for 1% to 15% of the mass percentage of the electrolyte.

[0030] In some embodiments, the cyclic carbonate includes one or more of vinylene carbonate and fluoroethylene carbonate.

[0031] In some embodiments, the cyclic sulfate ester accounts for 1% to 8% of the mass percentage of the electrolyte.

[0032] In some embodiments, the cyclic sulfate ester includes vinyl sulfate.

[0033] In some embodiments, the electrolyte has a lithium-ion conductivity of 10 mS / cm to 20 mS / cm at 25°C.

[0034] A third aspect of this application provides an electrical device including the lithium-ion battery described in the first aspect. Attached Figure Description

[0035] To better describe and illustrate the embodiments or examples provided in this application, reference may be made to one or more accompanying drawings. Additional details or examples used to describe the drawings should not be considered as limiting the scope of any of the disclosed applications, the currently described embodiments or examples, or the best mode of conduct of these applications as currently understood. Furthermore, the same reference numerals denote the same parts throughout the drawings. In the drawings:

[0036] Figure 1 is a schematic diagram of a lithium-ion battery according to an embodiment of this application.

[0037] Figure 2 is an exploded view of a lithium-ion battery according to an embodiment of this application, as shown in Figure 1.

[0038] Figure 3 is a schematic diagram of an electrical device using a lithium-ion battery as a power source according to an embodiment of this application.

[0039] Explanation of reference numerals in the attached figures:

[0040] 1. Lithium-ion battery; 11. Casing; 12. Electrode assembly; 13. Cover plate; 2. Electrical device. Detailed Implementation

[0041] To facilitate understanding of this application, a more comprehensive description will be provided below with reference to the accompanying drawings; however, some unnecessary details may be omitted. For example, detailed descriptions of well-known matters and repetitive descriptions of essentially the same structures may be omitted. This is to avoid unnecessarily lengthy descriptions and to facilitate understanding by those skilled in the art. Furthermore, the drawings and the following description are provided for the purpose of enabling those skilled in the art to fully understand this application and are not intended to limit the scope of protection of this application.

[0042] The "range" disclosed in this application can be defined in the form of a lower limit and an upper limit. A given range is defined by selecting a lower limit and an upper limit, which define the boundaries of the specific range. Ranges defined in this way can include or exclude endpoints; any endpoint can be independently included or excluded, and they can be arbitrarily combined, meaning 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 ​​1 and 2 are listed, and maximum range values ​​3, 4, and 5 are also 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 "a–b" 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" and "5" have been listed in this article; "0-5" is simply a shortened representation of these numerical combinations. Furthermore, when a parameter is described as an integer ≥ 2, it is equivalent to listing integers such as 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, etc. For instance, when a parameter is described as an integer selected from "2-10", it is equivalent to listing the integers 2, 3, 4, 5, 6, 7, 8, 9, and 10.

[0043] In this application, unless otherwise specified, "about" means within a reasonable range above and below the stated number, and the range of fluctuation may vary depending on the type and value of the stated number. For example, a range of ±10%, ±5%, ±2%, ±1%, etc., may be allowed. For example, taking "about 20°C" and its approximation as ±1°C, approximate values ​​such as 19°C, 19.5°C, etc., within the approximation range indicated by "about 20°C" should also be included in the range indicated by "about 20°C".

[0044] In this application, the terms "multiple," "various," "multiple items," "several," etc., unless otherwise specified, refer to a quantity greater than or equal to 2. For example, "one or more" means one or more (greater than or equal to) two. It can be understood that when "any number of" items are involved, it refers to any suitable combination of multiple items, that is, a combination of "any number of" items in a manner that does not conflict and enables the implementation of this application.

[0045] Unless otherwise specified, all embodiments and optional embodiments of this application can be combined to form new technical solutions.

[0046] In this application, the reference to "embodiment" means that a specific feature, structure, or characteristic described in connection with an embodiment may be included in at least one embodiment or implementation of this application. The appearance of this phrase in various places throughout the specification does not necessarily refer to the same embodiment, nor is it a separate or alternative embodiment mutually exclusive with other embodiments. It will be explicitly and implicitly understood by those skilled in the art that the embodiments described herein can be combined with other embodiments. The term "implementation" as used herein has a similar understanding.

[0047] Those skilled in the art will understand that the order in which the steps are written in the methods of various embodiments or examples does not imply a strict execution order and does not constitute any limitation on the implementation process. The detailed execution order of each step should be determined by its function and possible internal logic. Unless otherwise specified, all steps of this application may be performed sequentially or randomly, but are preferably performed sequentially. For example, if method M includes steps (a) and (b), it means that the method may include steps (a) and (b) performed sequentially, or it may include steps (b) and (a) performed sequentially. For example, method M may also include step (c), meaning that step (c) can be added to method M in any order. For example, method M may include steps (a), (b), and (c), or it may include steps (a), (c), and (b), or it may include steps (c), (a), and (b), etc.

[0048] In this application, unless otherwise specified, M (e.g., m1) means that m1 is a non-limiting example of M, and it is understood that M is not limited to m1.

[0049] In this application, "optionally," "optionally," and "optional" mean that something is optional, that is, it is selected from either "with" or "without." If multiple "options" appear in a technical solution, unless otherwise specified and there are no contradictions or mutual constraints, each "option" is independent. Unless otherwise specified, the descriptions such as "optionally include" and "optionally contain" in this application, taking "optionally include" as an example, mean "may include or not include."

[0050] In this application, unless otherwise specified, the features or solutions corresponding to "and / or" include any one of two or more of the related listed items, as well as any and all combinations of the related listed items. Any and all combinations include any two related listed items, any more related listed items, or a combination of all related listed items. For example, "M and / or N" represents the group consisting of M, N, and "a combination of M and N". "Containing M and / or N" can mean "containing M, containing N, and containing both M and N", or "containing M, containing N, or containing both M and N", and can be appropriately understood according to the context.

[0051] The terms “combinations thereof,” “any combination thereof,” and “any combination thereof” as used in this application include all suitable combinations of any two or more of the listed items.

[0052] In this application, the term "suitable" in "suitable combination", "suitable method", "any suitable method", etc., refers to the technical solution that can implement this application.

[0053] In this application, terms such as "further," "even more," "especially," "for example," "as," "example," and "exemplary" are used for descriptive purposes to indicate differences in content, but should not be construed as limiting the scope of protection of this application.

[0054] In this application, the terms "first aspect," "second aspect," etc., are used for descriptive purposes only and should not be construed as indicating or implying relative importance or quantity, nor should they be construed as implicitly indicating the importance or quantity of the indicated technical features. Moreover, "first aspect," "second aspect," etc., serve only as a non-exhaustive enumeration and should be understood not to constitute a closed limitation on quantity.

[0055] In this application, unless otherwise expressly specified and limited, the phrase "above" or "below" the second feature can mean that the first and second features are in direct contact, or that the first and second features are in indirect contact through an intermediate medium. In this application, unless otherwise expressly specified and limited, the phrase "above" or "below" the second feature can indicate a horizontal positional relationship, or it can simply indicate the existence of an attachment relationship without specifying a horizontal positional relationship.

[0056] In this application, the terms "room temperature" and "normal temperature" generally refer to 4℃ to 35℃, and may refer to 20℃ ± 5℃. In some embodiments or examples of this application, room temperature and normal temperature may refer to 20℃ to 30℃.

[0057] In this application, when a unit is specified for a data range, if the unit is only followed by the right endpoint, it indicates that the units for the left and right endpoints are the same. For example, 3~5h or 3~5h both mean that the unit for the left endpoint "3" and the right endpoint "5" is h (hours), and both have the same meaning as 3h~5h. Furthermore, similar descriptions of other parameters such as temperature and size are interpreted in the same way.

[0058] In this application, the exemplary descriptions such as "in some implementations (or embodiments)" and "in one implementation (or embodiment)" may cover, but are not limited to, the following meanings: these solutions can be combined with other solutions in a suitable manner to form new technical solutions.

[0059] In this application, unless otherwise specified, "lithium-ion battery" refers to a basic unit capable of converting chemical energy into electrical energy, and more generally includes a positive electrode, a negative electrode, and an electrolyte. During the charging and discharging process, active ions repeatedly insert and extract between the positive and negative electrode. The electrolyte acts as a conductor for the active ions between the positive and negative electrode.

[0060] In some implementations, lithium-ion batteries can be either power batteries or energy storage batteries.

[0061] When lithium-ion batteries are stored at high temperatures, such as above 45°C, changes in the battery's internal materials, SEI film, and electrolyte can increase the battery's internal resistance, affecting its storage performance. For example, during high-temperature storage, the SEI film on the negative electrode surface may remodel and thicken, increasing the battery's internal resistance, leading to a decrease in energy conversion efficiency, and thus affecting its storage performance.

[0062] Based on this, one embodiment of this application provides a lithium-ion battery. The lithium-ion battery includes a positive electrode, a negative electrode, and an electrolyte. The negative electrode includes a negative current collector and a negative active layer located on at least one surface of the negative current collector. The negative active material of the negative active layer includes graphite, and the graphite has an I... d / I g The value is 0.05 to 0.4, where I d This indicates that the Raman spectrum is at 1350±50 cm⁻¹ -1 peak intensity at d, I g This indicates that the Raman spectrum is at 1580±50 cm⁻¹. -1 The intensity of the g peak at that location. The electrolyte includes film-forming additives, which include methylene methane disulfonate at a mass percentage of less than or equal to 2% of the electrolyte.

[0063] In lithium-ion batteries, the SEI film formed with the participation of MMDS exhibits good thermal stability. Introducing MMDS into the electrolyte can limit the increase in internal resistance during high-temperature storage, improving the battery's high-temperature storage performance. However, MMDS easily decomposes to produce acidic substances, such as sulfonic acid. When the residual amount of MMDS in the electrolyte is high, the acidic substances produced by decomposition can damage the SEI film, leading to a reduction in the battery's cycle life. In this embodiment, I is selected... d / I g Graphite with an Ig value greater than or equal to 0.05 can promote the consumption of MMDS during SEI film formation, reduce the residual amount of MMDS in the battery, and reduce the impact of residual MMDS decomposition on battery cycle performance. Simultaneously, graphite's Ig value... d / I gA value less than or equal to 0.4 can reduce excessive electrolyte consumption on the negative electrode surface, thus mitigating the adverse effects of excessive electrolyte consumption on battery cycle life. Therefore, the lithium-ion battery of this embodiment can achieve a good balance between high-temperature storage performance and cycle performance.

[0064] It is understood that the above principle analysis should not be taken as a limitation on the technical solution and technical effect of this application. The graphite I in this application... d / I g The synergistic effect between the value and the quality percentage of MMDS can be verified through examples.

[0065] It should be noted that MMDS may no longer be present in lithium-ion batteries (corresponding to 0% MMDS by mass in the electrolyte). This is because during the formation or cycling process of the finished lithium-ion battery, MMDS participates in the formation of a thermally stable SEI film on the negative electrode surface, during which MMDS is consumed. When the amount added is small, the MMDS by mass in the electrolyte of the finished lithium-ion battery may be 0% after formation or cycling.

[0066] Optionally, in the electrolyte of the lithium-ion battery, methylene methane disulfonate accounts for 0 to 2% of the electrolyte by mass.

[0067] The mass percentage of MMDS in the electrolyte of this application can be determined by liquid chromatography, mass spectrometry or nuclear magnetic resonance spectroscopy.

[0068] In some embodiments, the mass percentage of methylene methane disulfonate in the electrolyte can be ≤2%, ≤1.8%, ≤1.5%, ≤1.2%, ≤1%, ≤0.9%, ≤0.8%, ≤0.7%, ≤0.6%, ≤0.5%, ≤0.4%, ≤0.3%, ≤0.2%, ≤0.1%, ≤0.09%, ≤0.08%, ≤0.07%, ≤0.06%, ≤0.05%, ≤0.04%, ≤0.03%, ≤0.02%, ≤0.01%, 0, or any value within the range of any two of the above values. Optionally, the mass percentage of methylene methane disulfonate in the electrolyte is less than or equal to 0.01%. More preferably, the mass percentage of methylene methane disulfonate in the electrolyte is 0%.

[0069] It is understandable that the material I d / I g The value can represent the degree of defect in a material. In this application, the I value for graphite... d / I g The value can represent the degree of defect in graphite.

[0070] In this application, graphite I d / I gThe values ​​can be measured using a Raman spectrometer. The test conditions are as follows: excitation wavelength 532 nm, grating 600 lines, objective lens 50x, integration time 10 s, cumulative scan 3 times, area scan, obtaining the d-peak and g-peak intensities at 100 points, and calculating the I values ​​at 100 points. d / I g Remove the largest and smallest 25 I's. d / I g The average of the remaining 50 points is the I of graphite. d / I g The testing instrument can be a Horiba LabRAM HR800 Raman spectrometer.

[0071] In some implementations, graphite I d / I g The value can be 0.05, 0.08, 0.1, 0.12, 0.15, 0.18, 0.2, 0.22, 0.25, 0.28, 0.3, 0.32, 0.35, 0.38, 0.4, or any value within the range of any two of the above values. Optionally, the I of graphite d / I g The value is 0.1 to 0.3.

[0072] In some embodiments, the film-forming additives also include one or more of cyclic carbonates and cyclic sulfates. Further investigation of the battery revealed that the combination of MMDS and graphite can improve the high-temperature storage performance of the battery; however, the SEI film formed with MMDS has poor toughness and may be damaged during high-temperature cycling, such as at temperatures above 45°C. In these embodiments, adding one or more of cyclic carbonates and cyclic sulfates to the electrolyte can improve the toughness of the SEI film, reduce the risk of damage to the SEI film under high-temperature cycling, and thus improve the high-temperature cycling performance of lithium-ion batteries.

[0073] In some embodiments, the cyclic carbonate accounts for 0.1% to 10% of the electrolyte by mass. A cyclic carbonate mass percentage greater than or equal to 0.1% allows for more effective utilization of its role in improving SEI toughness and promoting improved high-temperature cycle performance of the battery. Cyclic carbonates have high viscosity; a mass percentage less than or equal to 10% allows the electrolyte to maintain a low viscosity, which is beneficial for promoting lithium-ion transport and improving battery charge-discharge efficiency. Optionally, the mass percentage of cyclic carbonate in the electrolyte can be 0.1%, 0.2%, 0.3%, 0.4%, 0.5%, 0.6%, 0.7%, 0.8%, 0.9%, 1%, 2%, 3%, 4%, 5%, 6%, 7%, 8%, 9%, 10%, or any value within the range of any two of the above values. Further optionally, the mass percentage of cyclic carbonate in the electrolyte is 2% to 5%.

[0074] In some embodiments, the cyclic carbonate includes one or more of vinylene carbonate and fluoroethylene carbonate.

[0075] In some embodiments, the cyclic sulfate ester accounts for 0.01% to 5% of the electrolyte by mass. A cyclic sulfate ester mass percentage greater than or equal to 0.01% allows for more sufficient utilization of its effect on improving SEI toughness and promoting improved high-temperature cycle performance of the battery. Cyclic sulfate esters have high viscosity; a mass percentage less than or equal to 5% in the electrolyte helps maintain a low viscosity, which is beneficial for promoting lithium-ion transport and improving the battery's charge-discharge efficiency. Optionally, the mass percentage of the cyclic sulfate ester in the electrolyte can be 0.01%, 0.05%, 0.08%, 0.1%, 0.2%, 0.3%, 0.4%, 0.5%, 0.6%, 0.7%, 0.8%, 0.9%, 1%, 2%, 3%, 4%, 5%, or any value within the range of any two of the above values. Further optionally, the cyclic sulfate ester accounts for 0.5% to 1% of the electrolyte by mass.

[0076] In some embodiments, cyclic sulfates include vinyl sulfate (abbreviated as DTD).

[0077] It is understandable that the electrolyte may also include other functional additives, such as additives that improve the overcharge performance of lithium-ion batteries and additives that improve the low-temperature performance of batteries.

[0078] Further research into batteries revealed that adding one or more cyclic carbonates and cyclic sulfates to the electrolyte can improve the high-temperature cycle performance of lithium-ion batteries. However, the addition of one or more cyclic carbonates and cyclic sulfates results in a large impedance of the SEI film generated on the negative electrode surface during formation, which increases battery polarization and restricts the room-temperature cycle performance of the battery. Therefore, the room-temperature cycle performance of the battery can be improved by making the electrolyte have a suitable lithium-ion conductivity.

[0079] In some embodiments, the lithium-ion conductivity of the electrolyte at 25°C is 8 millisiemens / cm (mS / cm) to 18 mS / cm. An electrolyte conductivity greater than or equal to 8 mS / cm at 25°C results in lower internal resistance in the battery, further improving its room-temperature cycle performance. Simultaneously, an electrolyte conductivity greater than or equal to 8 mS / cm at 25°C provides better kinetic properties, reduces battery polarization, and helps maintain higher battery power. Furthermore, an electrolyte conductivity less than or equal to 18 mS / cm at 25°C allows for a more suitable rate of lithium-ion insertion and extraction in the electrode active material, reducing stress impacts on the electrode active material during charging and discharging, and enabling the electrode active material to maintain a more stable crystal structure. This further promotes improved room-temperature cycle performance. Meanwhile, the lithium-ion conductivity of the electrolyte at 25°C is less than or equal to 18 mS / cm, which can maintain good thermal stability of the electrolyte and is beneficial to further improve the high-temperature cycle performance of the battery.

[0080] As examples, the lithium-ion conductivity of the electrolyte at 25°C can be 8 mS / cm, 9 mS / cm, 10 mS / cm, 11 mS / cm, 12 mS / cm, 13 mS / cm, 14 mS / cm, 15 mS / cm, 16 mS / cm, 17 mS / cm, 18 mS / cm, or any value within the range of any two of the above values. Further optionally, the lithium-ion conductivity of the electrolyte at 25°C is 9 mS / cm to 13 mS / cm.

[0081] In this application, the lithium-ion conductivity of the electrolyte describes the ability of dissociated ions in the electrolyte solution to conduct electricity through the directional movement of these ions in an electric field, and can be tested using any method known in the art. As an example, the lithium-ion conductivity of the electrolyte can be tested as follows: Disassemble the battery, take approximately 100 ml (mL) of electrolyte sample in a dry, clean, corrosion-resistant sample bottle, seal it, and place it in a constant-temperature water bath. Shake the sample and maintain the temperature at 25 degrees Celsius (°C), with a temperature deviation of ±0.5°C. After the sample temperature stabilizes, use a commercially available conductivity meter to test its conductivity. Clean and dry the conductivity meter with calibration solution, then vertically place it into the liquid to be tested. Click to start the test, and record the test result after the data stabilizes for at least 10 seconds.

[0082] In some embodiments, the electrolyte further includes a lithium salt. The total molar concentration of the lithium salt in the electrolyte is from 0.8 mol / L to 1.2 mol / L. By selecting a suitable molar concentration of lithium salt, the electrolyte can have a suitable lithium-ion conductivity, promoting improved battery cycle performance. Optionally, the total molar concentration of lithium salt in the electrolyte can be 0.8 mol / L, 0.85 mol / L, 0.9 mol / L, 0.95 mol / L, 1 mol / L, 1.05 mol / L, 1.1 mol / L, 1.15 mol / L, 1.2 mol / L, or any value within the range of any two of the above values.

[0083] In some embodiments, the lithium salt includes one or more of lithium hexafluorophosphate (LiPF6), lithium bisfluorosulfonylimide (LiFSI), and lithium bistrifluoromethanesulfonylimide (LiTFSI).

[0084] In some embodiments, the electrolyte further includes a solvent. The solvent includes one or more of chain solvents and cyclic solvents. Optionally, the solvent includes one or more of cyclic carbonates, chain carbonates, and chain carboxylic acid esters. Cyclic carbonates include ethylene carbonate (EC, EC chemical formula: ), fluoroethylene carbonate (FEC), propylene carbonate (PC, chemical formula: ) and butylene carbonate (butylene carbonate chemical formula: One or more of the following: Chain carbonates include ethyl methyl carbonate (EMC), diethyl carbonate (DEC), dimethyl carbonate (DMC), dipropyl carbonate (DPC), methyl propyl carbonate (MPC), and ethyl propyl carbonate (EPC). Chain carboxylic acid esters include one or more of methyl formate, methyl acetate, ethyl acetate, isopropyl acetate, butyl acetate, isoamyl acetate, methyl propionate, ethyl propionate, methyl butyrate, ethyl butyrate, propyl butyrate, and butyl butyrate.

[0085] In some embodiments, the solvent comprises, by mass percentage, the following components: ethylene carbonate (EC) 15%–50%, dimethyl carbonate (DMC) 10%–70%, and ethyl methyl carbonate (EMC) 5%–50%. By selecting appropriate solvent ratios, the electrolyte can have suitable lithium-ion conductivity, thereby promoting improved battery cycle performance.

[0086] Optionally, the mass percentage of EC as a percentage of the solvent can be 15%, 20%, 25%, 30%, 35%, 40%, 45%, 50%, or any value within the range of any two of the above values.

[0087] Optionally, the mass percentage of DMC as a percentage of the solvent can be 10%, 15%, 20%, 25%, 30%, 35%, 40%, 45%, 50%, 55%, 60%, 65%, 70%, or any value within the range of any two of the above values.

[0088] Optionally, the mass percentage of EMC, as a percentage of the solvent, can be 5%, 10%, 15%, 20%, 25%, 30%, 35%, 40%, 45%, 50%, or any value within the range of any two of the above values.

[0089] In some embodiments, the Dv50 of graphite is 7 micrometers (μm) to 13 μm. In lithium-ion batteries, the combination of MMDS and graphite can give the battery better high-temperature storage performance and better cycle performance. A Dv50 of graphite greater than or equal to 7 μm can further reduce side reactions between graphite and electrolyte, improving the cycle performance of the battery. A Dv50 of graphite less than or equal to 13 μm can maintain good kinetic properties of graphite, further improving the cycle performance of the battery. Optionally, the Dv50 of graphite can be 7 μm, 8 μm, 9 μm, 10 μm, 11 μm, 12 μm, 13 μm, or any value within the range of any two of the above values.

[0090] In this application, Dv50 represents the particle size corresponding to a cumulative volumetric distribution percentage of 50%. It can be determined using a laser particle size analyzer, referring to standard GB / T 19077-2016. For example, a Malvern Master Size 3000 laser particle size analyzer could be used.

[0091] It is understandable that Dv50 of graphite represents the particle size corresponding to a cumulative volumetric distribution percentage of 50%. This can be determined using a laser particle size analyzer, as per standard GB / T 19077-2016. For example, a Malvern Master Size 3000 laser particle size analyzer could be used.

[0092] In some embodiments, the graphite includes synthetic graphite. Synthetic graphite has a higher cycle life, which is beneficial for improving battery cycle life. However, synthetic graphite has fewer active sites, resulting in lower MMDS consumption during SEI film formation. When MMDS is introduced into the electrolyte to participate in film formation, the limited number of active sites in synthetic graphite can easily lead to a large amount of MMDS residue after SEI film formation. In this case, the I... d / I g When the value is in the range of 0.05 to 0.4, it can promote the consumption of MMDS, keep the residual amount of MMDS in the electrolyte at a low level, and thus enable the battery to achieve both high energy conversion efficiency and long cycle life.

[0093] In some embodiments, the compaction density of the negative electrode active layer is 1.3 g / cm³ (abbreviated as g / cm). 3 ~1.7g / cm 3 The compaction density of the negative electrode active layer is greater than or equal to 1.3 g / cm³. 3 This allows the battery to achieve a higher energy density while maintaining good contact between the negative electrode active materials, which is beneficial for improving the battery's kinetic performance and further promoting improved battery cycle performance. Additionally, the compaction density of the negative electrode active layer is less than or equal to 1.7 g / cm³. 3 The electrolyte can more fully wet the negative electrode active layer, enabling lithium ions to be transported more efficiently within it. This promotes improved battery cycle performance and reduces the risk of lithium plating on the negative electrode. Optionally, the compaction density of the negative electrode active layer can be 1.3 g / cm³. 3 1.35g / cm 3 1.4g / cm 3 1.45g / cm 3 1.5g / cm 3 1.55g / cm 3 1.6g / cm 31.65g / cm 3 1.7g / cm 3 1.75g / cm 3 And any value within the range consisting of any two of the above values.

[0094] In some embodiments, graphite constitutes 95% to 100% of the negative electrode active material by mass. This mass percentage range allows graphite to fully utilize its ability to consume MMDS (Multi-Melt Filter Demand), further improving the battery's high-temperature storage performance and cycle performance. Optionally, the mass percentage of graphite in the negative electrode active material can be 95%, 96%, 97%, 98%, 99%, 100%, or any value within the range of any two of the above values.

[0095] In some embodiments, the negative electrode active material of the negative electrode active layer may also include negative electrode active materials known in the art for use in batteries. As a non-limiting example, the negative electrode active material may also include one or more of the following materials: soft carbon, hard carbon, tin-based materials, and lithium titanate, etc. Tin-based materials may include one or more of elemental tin, tin oxides, and tin alloys. However, this application is not limited to these materials, and other conventional materials that can be used as negative electrode active materials for batteries may also be used. These negative electrode active materials may be used alone or in combination of two or more.

[0096] Optionally, the negative electrode active material accounts for 95% to 98% of the mass of the negative electrode active layer. Optionally, the positive electrode active material accounts for 95%, 96%, 97%, 98% of the mass of the positive electrode active layer, or any value within the range of any two of the above values.

[0097] In some embodiments, the negative electrode active layer may optionally include a binder. The binder may include one or more of styrene-butadiene rubber (SBR), polyacrylic acid (PAA), sodium polyacrylate (PAAS), polyacrylamide (PAM), polyvinyl alcohol (PVA), sodium alginate (SA), polymethacrylic acid (PMAA), and carboxymethyl chitosan (CMCS). Optionally, the binder constitutes 0.5% to 5% of the negative electrode active layer by mass. Optionally, the mass percentage of the binder in the negative electrode active layer may be 0.5%, 1%, 1.5%, 2%, 2.5%, 3%, 3.5%, 4%, 4.5%, 5%, or any value within the range of any two of the above values.

[0098] In some embodiments, the negative electrode active layer may optionally include a conductive agent. The conductive agent may include one or more of superconducting carbon, acetylene black, carbon black, Ketjen black, carbon dots, carbon nanotubes, graphene, and carbon nanofibers. Optionally, the conductive agent accounts for 0.1% to 5% of the mass percentage of the negative electrode active layer. Optionally, the mass percentage of the conductive agent in the negative electrode active layer may be 0.1%, 0.3%, 0.5%, 1%, 1.5%, 2%, 2.5%, 3%, 3.5%, 4%, 4.5%, 5%, or any value within the range of any two of the above values.

[0099] In some embodiments, the negative electrode active layer may optionally include other additives, such as thickeners. Thickeners include sodium carboxymethyl cellulose (CMC-Na). Optionally, the thickener constitutes 0.5% to 5% of the negative electrode active layer by mass. Optionally, the mass percentage of the thickener in the negative electrode active layer can be 0.5%, 1%, 1.5%, 2%, 2.5%, 3%, 3.5%, 4%, 4.5%, 5%, or any value within the range of any two of the above values.

[0100] In some embodiments, the negative electrode current collector may be a metal foil or a composite current collector. For example, copper foil may be used as the metal foil. The composite current collector may include a polymeric material substrate and a metal layer formed on at least one surface of the polymeric material substrate. The composite current collector can be obtained by forming a metal material on the polymeric material substrate. Non-limiting examples of the metal material in the negative electrode current collector may include one or more of copper, copper alloys, nickel, nickel alloys, titanium, titanium alloys, silver, and silver alloys. Non-limiting examples of the polymeric material substrate in the negative electrode current collector may include one or more of polypropylene (PP), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polystyrene (PS), and polyethylene (PE).

[0101] In some embodiments, the negative electrode sheet can be prepared by dispersing the components used to prepare the negative electrode sheet, such as the negative electrode active material, conductive agent, binder, and any other components, in a solvent to form a negative electrode slurry. A non-limiting example of the solvent is deionized water. The negative electrode slurry is coated onto at least one surface of the negative electrode current collector, and after drying, cold pressing, or other processes, the negative electrode sheet is obtained. The surface of the negative electrode current collector coated with the negative electrode slurry can be a single surface of the negative electrode current collector or both surfaces of the negative electrode current collector.

[0102] In some embodiments, the positive electrode includes a positive current collector and a positive active layer located on at least one surface of the positive current collector; the positive active material of the positive active layer includes a lithium phosphate. Lithium phosphates have a higher cycle life and can further improve the cycle performance of the battery.

[0103] Alternatively, if the positive electrode active material includes lithium phosphate, the lithium-ion battery can be an energy storage battery.

[0104] Optionally, the mass percentage of lithium phosphate in the positive electrode active material is 90% to 100%. Optionally, the mass percentage of lithium phosphate in the positive electrode active material can be 90%, 91%, 92%, 93%, 94%, 95%, 96%, 97%, 98%, 99%, 100%, or any value within the range of any two of the above values.

[0105] Optionally, the positive electrode active material accounts for 95% to 98% of the mass of the positive electrode active layer. Optionally, the mass percentage of the positive electrode active material in the positive electrode active layer can be 95%, 96%, 97%, 98%, or any value within the range of any two of the above values.

[0106] Optionally, lithium-containing phosphates may include at least one of lithium iron phosphate, lithium iron phosphate and carbon composites, lithium manganese iron phosphate, and lithium manganese iron phosphate and carbon composites. Lithium-containing phosphates may also include one or more of lithium manganese phosphate and lithium manganese phosphate and carbon composites.

[0107] In some embodiments, the positive electrode active material includes Li x (Ni a Co b Mn c ) 1-d M d O 2-y A y A lithium-containing transition metal oxide, wherein 0.2≤x≤1.2, 0.2≤a≤1, 0≤b≤0.1, 0≤c≤0.1, a+b+c=1, 0≤d<1, 0≤y<2, M includes one or more of Zr, Sr, B, Sn, Al, Mg, Fe, Cu, V, Ti, W, Sb, Dy, and Te, and A includes one or more of N, P, S, and halogen elements. The chemical formula is Li. x (Ni a Co b Mn c ) 1-d M d O 2-y A y Lithium-containing transition metal oxides have high specific capacity, which can further improve the energy density of batteries.

[0108] Understandably, 'a' is typically used to represent the nickel content in lithium-containing transition metal oxides. A larger 'a' indicates a higher nickel content, while a smaller 'a' indicates a lower nickel content. As some possible examples of 'a', it can be 0.2, 0.3, 0.4, 0.5, 0.6, 0.7, 0.8, 0.9, 1, or any value within the range of any two of these values. For example, 'a' can be 0.2–0.5, 0.55–0.75, 0.65–0.85, 0.75–0.95, etc.

[0109] Understandably, 'b' is typically used to represent the cobalt content in lithium-containing transition metal oxides. A larger 'b' indicates a higher cobalt content, while a smaller 'b' indicates a lower cobalt content. As some possible examples of 'b', it can be 0, 0.01, 0.02, 0.03, 0.04, 0.05, 0.06, 0.07, 0.08, 0.09, 0.1, or any value within the range of any two of these values. For example, 'b' can be 0.005–0.015, 0.025–0.055, 0.045–0.075, 0.055–0.095, etc.

[0110] Understandably, 'c' is typically used to represent the manganese content in lithium-containing transition metal oxides. A larger 'c' indicates a higher manganese content, while a smaller 'c' indicates a lower manganese content. As some possible examples of 'c', it can be 0, 0.01, 0.02, 0.03, 0.04, 0.05, 0.06, 0.07, 0.08, 0.09, 0.1, or any value within the range of any two of these values. For example, 'c' can be 0.005–0.015, 0.025–0.055, 0.045–0.075, 0.055–0.095, etc.

[0111] Understandably, 'd' is typically used to represent the content of element M in lithium-containing transition metal oxides. A larger 'd' indicates a higher content of element M, while a smaller 'd' indicates a lower content of element M. As some possible examples of 'd', it can be 0, 0.01, 0.02, 0.03, 0.04, 0.05, 0.06, 0.07, 0.08, 0.09, 0.1, 0.2, 0.3, 0.4, 0.5, 0.6, 0.7, 0.8, 0.9, or any value within the range of any two of these values. For example, 'd' can be 0.005–0.015, 0.025–0.055, 0.045–0.075, 0.055–0.095, 0.15–0.55, 0.35–0.85, 0.55–0.95, etc. Optionally, 0 ≤ d ≤ 0.05.

[0112] Understandably, x is typically used to represent the lithium content in lithium-containing transition metal oxides. A larger x indicates a higher lithium content, while a smaller x indicates a lower lithium content. As some possible examples of x, x can be 0.2, 0.3, 0.4, 0.5, 0.6, 0.7, 0.8, 0.9, 1, 1.1, 1.2, and any value within the range of any two of the above values. Optionally, x can be 0.25–0.45, 0.35–0.75, 0.55–0.95, 1.05–1.15, etc.

[0113] Understandably, y is typically used to represent the content of element A in lithium-containing transition metal oxides. A larger y indicates a higher content of element A, while a smaller y indicates a lower content of element A. As some possible examples of y, y can be 0, 0.01, 0.02, 0.03, 0.04, 0.05, 0.06, 0.07, 0.08, 0.09, 0.1, 0.2, 0.3, 0.4, 0.5, 0.6, 0.7, 0.8, 0.9, 1, 1.1, 1.2, 1.3, 1.4, 1.5, 1.6, 1.7, 1.8, 1.9, 1.91, 1.92, 1.93, 1.94, 1.95, 1.96, 1.97, 1.98, 1.99, and any value within the range of any two of the above values. For example, y can be 0.005–0.015, 0.025–0.055, 0.045–0.075, 0.055–0.095, 0.15–0.55, 0.35–0.85, 0.55–0.95, 1.05–1.15, 1.25–1.55, 1.45–1.95, etc. Optionally, 0 ≤ y ≤ 0.05.

[0114] It is understandable that A includes one or more of N, P, S and halogen elements, where halogen elements can be F, Cl, Br, etc.

[0115] Optionally, the lithium-containing transition metal oxide includes LiNi 1 / 3 Co 1 / 3 Mn 1 / 3 O2, LiNi 0.5 Co 0.2 Mn 0.3 O2, LiNi 0.5 Co 0.25 Mn 0.25 O2, LiNi 0.6 Co 0.2 Mn 0.2 O2, LiNi 0.8 Co 0.1 Mn 0.1 O2, LiNi 0.9 Co 0.09 Mn 0.01 O2, LiNi 0.92 Co 0.05 Mn 0.03 O2, LiNi 0.96 Co 0.02 Mn 0.02 O2, LiNi 0.8 Co 0.15 Al 0.05 O2, etc.

[0116] Optionally, the chemical formula is Li x (Ni a Co b Mn c ) 1-d M d O 2-y A y The lithium-containing transition metal oxide accounts for 90% to 100% of the mass of the positive electrode active material. Optionally, the mass percentage of the lithium-containing transition metal oxide in the positive electrode active material can be 90%, 91%, 92%, 93%, 94%, 95%, 96%, 97%, 98%, 99%, 100%, or any value within the range of any two of the above values.

[0117] In some embodiments, the positive electrode active material may further include one or more of the following materials: lithium cobalt oxide, lithium manganese oxide, lithium manganese cobalt oxide, and modified compounds thereof. Non-limiting examples of lithium cobalt oxide may include LiCoO2. Non-limiting examples of lithium manganese oxide may include LiMnO2, LiMn2O4, etc.

[0118] In some embodiments, the positive electrode active layer may optionally include a binder. As a non-limiting example, the binder may include one or more of polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), PVDF-tetrafluoroethylene-propylene terpolymer, PVDF-hexafluoropropylene-tetrafluoroethylene terpolymer, tetrafluoroethylene-hexafluoropropylene copolymer, and fluorinated acrylate resins. Optionally, the binder constitutes 0.5% to 5% of the positive electrode active layer by mass. Optionally, the binder's mass percentage of the positive electrode active layer may be 0.5%, 1%, 1.5%, 2%, 2.5%, 3%, 3.5%, 4%, 4.5%, 5%, or any value within the range of any two of the above values.

[0119] In some embodiments, the positive electrode active layer may optionally include a conductive agent. As a non-limiting example, the conductive agent may include one or more of superconducting carbon, acetylene black, carbon black, Ketjen black, carbon dots, carbon nanotubes, graphene, and carbon nanofibers. Optionally, the conductive agent accounts for 0.1% to 5% of the mass percentage of the positive electrode active layer. Optionally, the mass percentage of the conductive agent in the positive electrode active layer may be 0.1%, 0.3%, 0.5%, 1%, 1.5%, 2%, 2.5%, 3%, 3.5%, 4%, 4.5%, 5%, or any value within the range of any two of the above values.

[0120] In some embodiments, the positive electrode current collector may be a metal foil or a composite current collector. For example, aluminum foil may be used as the metal foil. The composite current collector may include a polymer material substrate and a metal layer formed on at least one surface of the polymer material substrate. The composite current collector can be obtained by forming a metal material on the polymer material substrate. Non-limiting examples of the metal material in the positive electrode current collector may include one or more of aluminum, aluminum alloys, nickel, nickel alloys, titanium, titanium alloys, silver, and silver alloys. Non-limiting examples of the polymer material substrate in the positive electrode current collector may include one or more of polypropylene (PP), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polystyrene (PS), and polyethylene (PE).

[0121] In some embodiments, the positive electrode sheet can be prepared by dispersing the components used to prepare the positive electrode sheet, such as the positive electrode active material, conductive agent, binder, and any other components, in a solvent to form a positive electrode slurry; coating the positive electrode slurry onto at least one surface of the positive electrode current collector, and then obtaining the positive electrode sheet after drying, cold pressing, and other processes. The solvent can be selected from, but is not limited to, any of the solvents described in the foregoing embodiments, such as N-methylpyrrolidone (NMP). The surface of the positive electrode current collector coated with the positive electrode slurry can be a single surface of the positive electrode current collector or both surfaces of the positive electrode current collector.

[0122] It is understood that lithium-ion batteries may also include a separator. The separator is located between the positive electrode and the negative electrode. This application does not impose any particular restriction on the type of separator; any well-known porous separator with good chemical and mechanical stability can be selected.

[0123] In some embodiments, the material of the separator may include one or more of glass fiber, nonwoven fabric, polyethylene, polypropylene, and polyvinylidene fluoride. The separator may be a single-layer film or a multi-layer composite film, without particular limitation. When the separator is a multi-layer composite film, the materials of each layer may be the same or different, without particular limitation.

[0124] In some implementations, the positive electrode, negative electrode, and separator can be fabricated into an electrode assembly using a winding or stacking process.

[0125] In some embodiments, the lithium-ion battery may include an outer packaging. This outer packaging can be used to encapsulate the electrode assembly and electrolyte described above.

[0126] In some embodiments, the outer packaging of the lithium-ion battery can be a rigid shell, such as a hard plastic shell, an aluminum shell, or a steel shell. The outer packaging of the lithium-ion battery can also be a soft pack, such as a pouch. The material of the soft pack can be plastic; further, non-limiting examples of plastic may include one or more of polypropylene, polybutylene terephthalate, and polybutylene succinate.

[0127] Another embodiment of this application provides a lithium-ion battery cell. The lithium-ion battery cell includes a positive electrode, a negative electrode, and an electrolyte. The negative electrode includes a negative current collector and a negative active layer located on at least one surface of the negative current collector. The negative active material of the negative active layer includes graphite, and the graphite has an I... d / I g The value is 0.05 to 0.4, where I d This indicates that the Raman spectrum is at 1350±50 cm⁻¹ -1peak intensity at d, I g This indicates that the Raman spectrum is at 1580±50 cm⁻¹. -1 The intensity of the g peak at that location. The electrolyte includes film-forming additives, including methylene methane disulfonate, which accounts for 0.5% to 3% of the electrolyte by mass.

[0128] For ease of understanding, this application refers to batteries after formation or recycling as "lithium-ion batteries," and batteries before formation and recycling as "lithium-ion cells." The content of substances in a lithium-ion cell can represent the amount of substances added during the preparation of the lithium-ion battery. The following descriptions of the mass percentage or concentration of components will be based on these two aspects.

[0129] The aforementioned lithium-ion battery can be obtained by forming the aforementioned lithium-ion cell. Optionally, the formation method includes charging the lithium-ion cell at 0.02C for 600 minutes at 5°C.

[0130] As an example, corresponding to the above-mentioned lithium-ion battery where "methylene methane disulfonate accounts for less than or equal to 2% of the electrolyte by mass", the lithium-ion cell contains "methylene methane disulfonate accounting for 0.5% to 3% of the electrolyte by mass".

[0131] Optionally, the mass percentage of methylene disulfonate in the electrolyte of the lithium-ion battery cell is 0.5% to 3%, which can be interpreted as the amount of MMDS added to the electrolyte during the preparation of the lithium-ion battery being 0.5% to 3% of the electrolyte mass. It is understood that since MMDS is consumed to some extent during battery formation or cycling, the mass percentage of MMDS in the electrolyte of the finished lithium-ion battery is less than the mass percentage of MMDS in the electrolyte of the lithium-ion battery cell. That is, corresponding to the above statement that "the mass percentage of methylene disulfonate in the electrolyte of the lithium-ion battery is less than or equal to 2%", the mass percentage of methylene disulfonate in the electrolyte of the lithium-ion battery cell is "0.5% to 3%".

[0132] Optionally, the mass percentage of MMDS in the electrolyte of the lithium-ion battery cell can be 0.5%, 0.8%, 1%, 1.2%, 1.5%, 1.8%, 2%, 2.2%, 2.5%, 2.8%, 3%, or any value within the range of any two of the above values.

[0133] In some embodiments, the film-forming additive in the lithium-ion battery cell further includes one or more of cyclic carbonates and cyclic sulfates. Optionally, the cyclic carbonate includes one or more of vinylene carbonate and fluoroethylene carbonate. The cyclic sulfate includes vinyl sulfate.

[0134] It is understandable that film-forming additives are consumed to some extent during the formation or recycling of batteries. Therefore, the mass percentage of film-forming additives in the finished lithium-ion battery electrolyte is less than the mass percentage of negative electrode film-forming additives in the lithium-ion cell electrolyte.

[0135] For example, corresponding to the statement in the above-mentioned lithium-ion battery that "cyclic carbonates account for 0.1% to 10% of the electrolyte by mass," the statement in the lithium-ion cell that "cyclic carbonates account for 1% to 15% of the electrolyte by mass" can represent the amount of cyclic carbonates added during the preparation of the lithium-ion battery. Optionally, the percentage of cyclic carbonates in the electrolyte of the lithium-ion cell can be 1%, 2%, 3%, 4%, 5%, 6%, 7%, 8%, 9%, 10%, 11%, 12%, 13%, 14%, 15%, or any value within the range of any two of the above values.

[0136] For example, corresponding to the statement in the above-mentioned lithium-ion battery that "cyclic sulfate accounts for 0.01% to 5% of the electrolyte by mass," the statement in the lithium-ion cell that "cyclic sulfate accounts for 1% to 8% of the electrolyte by mass" indicates the amount of cyclic sulfate added during the preparation of the lithium-ion battery. Optionally, the percentage of cyclic sulfate in the electrolyte of the lithium-ion cell can be 1%, 2%, 3%, 4%, 5%, 6%, 7%, 8%, or any value within the range of any two of the above values.

[0137] It is understandable that film-forming additives are consumed to some extent during battery formation or cycling, thus reducing the lithium-ion conductivity of the electrolyte in the finished lithium-ion battery. Optionally, corresponding to the "lithium-ion conductivity of the electrolyte at 25°C is 8 mS / cm to 18 mS / cm" in the aforementioned lithium-ion battery, the "lithium-ion conductivity of the electrolyte at 25°C is 10 mS / cm to 20 mS / cm" in the lithium-ion cell. Optionally, in the lithium-ion cell, the lithium-ion conductivity of the electrolyte at 25°C can be 10 mS / cm, 11 mS / cm, 12 mS / cm, 13 mS / cm, 14 mS / cm, 15 mS / cm, 16 mS / cm, 17 mS / cm, 18 mS / cm, 19 mS / cm, 20 mS / cm, or any value within the range of any two of the above values.

[0138] It is understandable that the total molar concentration of lithium salt in the electrolyte remains essentially unchanged during formation or cycling. Therefore, correspondingly, the "total molar concentration of lithium salt in the electrolyte in a lithium-ion cell is 0.8 mol / L to 1.2 mol / L".

[0139] It is understandable that the solvent in the electrolyte remains essentially unchanged during formation or cycling. Therefore, correspondingly, in lithium-ion cells, the electrolyte includes a solvent. By mass percentage, the solvent includes the following components: ethylene carbonate (EC) 15%–50%, dimethyl carbonate (DMC) 10%–70%, and ethyl methyl carbonate (EMC) 5%–50%.

[0140] This application does not impose any particular limitation on the shape of the lithium-ion battery; it can be cylindrical, square, or any other arbitrary shape. For example, Figure 1 shows a square-structured lithium-ion battery 1 as an example.

[0141] In some embodiments, referring to FIG2, the outer packaging may include a housing 11 and a cover plate 13. The housing 11 may include a bottom plate and side plates connected to the bottom plate, the bottom plate and side plates forming a receiving cavity. The housing 11 has an opening communicating with the receiving cavity, and the cover plate 13 can be placed over the opening to close the receiving cavity. A positive electrode sheet, a negative electrode sheet, and a separator can be formed into an electrode assembly 12 by a winding process or a stacking process. The electrode assembly 12 is encapsulated within the receiving cavity. Electrolyte is immersed in the electrode assembly 12. The lithium-ion battery 1 may contain one or more electrode assemblies 12, which can be selected by those skilled in the art according to actual needs.

[0142] In some implementations, the lithium-ion battery can be a single cell, a battery module, or a battery pack.

[0143] The battery module includes at least one lithium-ion battery. The battery module may contain one or more lithium-ion batteries, and those skilled in the art can select an appropriate number based on the application and capacity of the battery module.

[0144] In a battery module, multiple lithium-ion batteries can be arranged sequentially along the length of the module. Of course, they can also be arranged in any other manner. Furthermore, these multiple lithium-ion batteries can be secured using fasteners.

[0145] Optionally, the battery module may also include a housing with a receiving space in which multiple lithium-ion batteries are housed.

[0146] In some embodiments, the battery modules can also be assembled into a battery pack, and the number of battery modules contained in the battery pack can be one or more. Those skilled in the art can select an appropriate number according to the application and capacity of the battery pack.

[0147] The battery pack may include a battery box and multiple battery modules disposed within the battery box. The battery box includes an upper body and a lower body, with the upper body covering the lower body to form a closed space for accommodating the battery modules. The multiple battery modules can be arranged in any manner within the battery box.

[0148] In addition, this application also provides an electrical device, which includes the lithium-ion battery provided in this application. The battery can be used as a power source for the electrical device or as an energy storage unit of the electrical device. The electrical device may include, but is not limited to, mobile devices, electric vehicles, electric trains, ships and satellites, energy storage systems, etc. Among them, mobile devices may be, for example, mobile phones, laptops, etc.; electric vehicles may be, for example, pure electric vehicles, hybrid electric vehicles, plug-in hybrid electric vehicles, electric bicycles, electric scooters, electric golf carts, electric trucks, etc., but are not limited to.

[0149] As an electrical device, lithium-ion batteries can be selected based on its usage requirements.

[0150] Figure 3 shows an example of an electrical device 2. This electrical device is a pure electric vehicle, a hybrid electric vehicle, or a plug-in hybrid electric vehicle, etc. To meet the high power and high energy density requirements of this electrical device, a battery pack or battery module can be used.

[0151] Another example device could be a mobile phone, tablet, laptop, etc. These devices typically require a slim and lightweight design and can use a battery as their power source.

[0152] To make the technical problems, technical solutions, and beneficial effects solved by this application clearer, the application will be further described in detail below with reference to embodiments and accompanying drawings. Obviously, the described embodiments are only some embodiments of this application, and not all embodiments. The following description of at least one exemplary embodiment is merely illustrative and is in no way intended to limit this application or its applications. Based on the embodiments in this application, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of this application.

[0153] Where specific techniques or conditions are not specified in the examples, they shall be performed in accordance with the techniques or conditions described in the literature in this field or in accordance with the product instructions. Reagents or instruments whose manufacturers are not specified are all commercially available conventional products.

[0154] Example 1

[0155] (1) Positive electrode plate

[0156] Lithium iron phosphate (LiFePO4), polyvinylidene fluoride (PVDF), and super P (SPF) were mixed with NMP solvent in a mass ratio of 96:2:2. The mixture was stirred to obtain a uniformly dispersed positive electrode slurry. This slurry was then evenly coated onto the surface of aluminum foil. After drying, the foil was cold-pressed, slited, and cut into sheets to form the positive electrode sheet. The compacted density of the positive electrode active layer of the positive electrode sheet was 2.4 g / cm³.3 .

[0157] (2) Negative electrode plate

[0158] Artificial graphite (negative electrode active material), carbon black (conductive agent), sodium carboxymethyl cellulose (thickener), and styrene-butadiene rubber (binder) were mixed in a weight ratio of 97:0.5:1:1.5, and then added to deionized water as a solvent. The mixture was stirred to prepare a negative electrode slurry. This slurry was then coated onto the surface of copper foil, dried, and subsequently cold-pressed, slit, and cut into sheets to produce the negative electrode sheet. (Graphite's I...) d / I g The value is 0.11. The Dv50 of graphite is 8.2 μm. The compaction density of the negative electrode active layer of the negative electrode sheet is 1.6 g / cm³. 3 .

[0159] (3) Separating membrane

[0160] Polyethylene film is used as the separation membrane.

[0161] (4) Electrolyte

[0162] In an argon-atmospheric glove box with a water content <1 ppm and an oxygen content <1 ppm, ethylene carbonate (EC), dimethyl carbonate (DMC), and ethyl methyl carbonate (EMC) were mixed in a mass ratio of 30:50:20 to obtain a mixed solvent. To the mixed solvent, 1% MMDS (by mass of the electrolyte), 3.5% ethylene carbonate (VC) (by mass of the electrolyte), 2% fluoroethylene carbonate (FEC) (by mass of the electrolyte), 0.5% ethylene sulfate (DTD) (by mass of the electrolyte), and 1 mol / L lithium hexafluorophosphate were added.

[0163] (5) Lithium-ion batteries

[0164] The positive electrode, separator, and negative electrode are prepared in sequence, with the separator positioned between the positive and negative electrodes to provide isolation. They are then wound to obtain a bare cell, and tabs are welded on. The bare cell is placed in an outer packaging shell, dried, and then injected with electrolyte. After vacuum sealing, settling, formation, and shaping processes, a lithium-ion battery is obtained. Formation includes charging the settling product at 0.02C for 600 minutes at 45°C.

[0165] Examples 2 to 11, Comparative Examples 1 to 2

[0166] The differences between Examples 2 to 11 and Comparative Examples 1 to 2 compared to Example 1 are shown in Table 1.

[0167] Test case

[0168] (1) The internal resistance growth rate of lithium-ion batteries at high temperatures was tested. The test method was as follows:

[0169] At 25℃, the DC resistance at 50% SOC was measured and recorded as the initial DC internal resistance. The lithium-ion battery was charged at a constant current of 0.33C to 3.65V, and then charged at a constant voltage of 3.65V until the current was less than 0.05C. It was then stored at 60℃. The actual capacity at 25℃ was tested every month under the following conditions: constant current discharge at 0.33C to 2.5V until the battery's state of health reached 90% SOH. The battery was then adjusted to 50% SOC, and its DC internal resistance was measured; this is the 90% SOH DC internal resistance. The internal resistance growth rate is calculated as (90% SOH DC internal resistance - initial DC internal resistance) / initial DC internal resistance × 100%. A smaller internal resistance growth rate indicates better high-temperature storage performance. The test results are shown in Table 1.

[0170] (2) High-temperature cycling test of lithium-ion battery, the test method is as follows:

[0171] At 60°C, the lithium-ion battery is charged at a constant current of 0.33C to 3.65V, then charged at a constant voltage of 3.65V until the current is less than 0.05C. Finally, the lithium-ion battery is discharged at a constant current of 0.33C to 2.5V. This constitutes one charge-discharge cycle. This charging and discharging process is repeated, and the capacity retention rate of the lithium-ion battery after 1000 cycles is calculated.

[0172] The capacity retention rate (%) of a lithium-ion battery after 1000 cycles at 60℃ is calculated as (discharge capacity of the 1000th cycle / discharge capacity of the first cycle) × 100%. The test results are shown in Table 1.

[0173] (3) Conduct a room temperature cycle test on the lithium-ion battery. The test method is as follows:

[0174] At 25°C, the lithium-ion battery was charged at a constant current of 0.33C to 3.65V, then charged at a constant voltage of 3.65V until the current was less than 0.05C. Finally, the lithium-ion battery was discharged at a constant current of 0.33C to 2.5V. This constitutes one charge-discharge cycle. This charging and discharging process was repeated, and the capacity retention rate of the lithium-ion battery after 1000 cycles was calculated.

[0175] The capacity retention rate (%) of a lithium-ion battery after 1000 cycles at 25°C is calculated as (discharge capacity of the 1000th cycle / discharge capacity of the first cycle) × 100%. The test results are shown in Table 1.

[0176] Table 1

[0177] In Table 1, “I” d / I g "I" represents artificial graphite d / Ig Values. "MMDS" indicates the mass percentage of MMDS added to the electrolyte. "VC" indicates the mass percentage of VC added to the electrolyte. "FEC" indicates the mass percentage of FEC added to the electrolyte. "DTD" indicates the mass percentage of DTD added to the electrolyte. "LiPF6" indicates the molar concentration of LiPF6 in the electrolyte, in mol / L. "Conductivity" indicates the lithium-ion conductivity of the electrolyte at 25℃, in mS / cm. " / " indicates that the corresponding substance is not added to the electrolyte.

[0178] As can be seen from Table 1, the I of graphite d / I g The combination of MMDS and MMDS can enable the battery to achieve a low internal resistance growth rate, good high-temperature cycle performance, and good room-temperature cycle performance.

[0179] As can be seen from Examples 5, 10 and 11, setting an electrolyte with appropriate conductivity in the battery can further improve the high-temperature cycle performance and low-temperature cycle performance of the battery.

[0180] The technical features of the above embodiments can be combined in any way. For the sake of brevity, not all possible combinations of the technical features in the above embodiments are described. However, as long as there is no contradiction in the combination of these technical features, they should be considered to be within the scope of this specification.

[0181] The embodiments described above are merely illustrative of several implementation methods of this application, and while the descriptions are relatively specific and detailed, they should not be construed as limiting the scope of the invention patent. It should be noted that those skilled in the art can make various modifications and improvements without departing from the concept of this application, and these all fall within the protection scope of this application. Therefore, the protection scope of this patent application should be determined by the appended claims.

Claims

1. A lithium-ion battery, comprising a positive electrode, a negative electrode, and an electrolyte; the negative electrode comprising a negative current collector and a negative active layer located on at least one surface of the negative current collector, the negative active material of the negative active layer comprising graphite, wherein the graphite has an I d / I g The value ranges from 0.05 to 0.4, where, I d This indicates that the Raman spectrum is at 1350±50 cm⁻¹ -1 peak intensity at d, I g This indicates that the Raman spectrum is at 1580±50 cm⁻¹. -1 The intensity of the g peak at the specified location; the electrolyte includes a film-forming additive, which includes methylene methane disulfonate at a mass percentage of less than or equal to 2% of the electrolyte.

2. The lithium-ion battery according to claim 1, wherein, The methylene disulfonate accounts for less than or equal to 0.01% of the mass of the electrolyte; optionally, the methylene disulfonate accounts for 0% of the mass of the electrolyte.

3. The lithium-ion battery according to any one of claims 1 to 2, wherein, The graphite I d / I g The value is 0.1 to 0.

3.

4. The lithium-ion battery according to any one of claims 1 to 3, wherein, The film-forming additives also include one or more of cyclic carbonates and cyclic sulfates.

5. The lithium-ion battery according to claim 4, wherein, The cyclic carbonates satisfy one or more of the following characteristics: (1) The cyclic carbonate accounts for 0.1% to 10% of the mass of the electrolyte; optionally, the cyclic carbonate accounts for 2% to 5% of the mass of the electrolyte. (2) The cyclic carbonates include one or more of vinylene carbonate and fluoroethylene carbonate.

6. The lithium-ion battery according to any one of claims 4 to 5, wherein, The cyclic sulfate ester satisfies one or more of the following characteristics: (1) The cyclic sulfate ester accounts for 0.01% to 5% of the mass of the electrolyte; optionally, the cyclic sulfate ester accounts for 0.5% to 1% of the mass of the electrolyte. (2) The cyclic sulfates include vinyl sulfate.

7. The lithium-ion battery according to any one of claims 1 to 6, wherein, The electrolyte has a lithium-ion conductivity of 8 mS / cm to 18 mS / cm at 25°C, and optionally, the electrolyte has a lithium-ion conductivity of 9 mS / cm to 13 mS / cm at 25°C.

8. The lithium-ion battery according to any one of claims 1 to 7, wherein, The electrolyte further includes a lithium salt; the lithium salt satisfies one or more of the following characteristics: (1) The total molar concentration of the lithium salt in the electrolyte is 0.8 mol / L to 1.2 mol / L; (2) The lithium salt includes one or more of lithium hexafluorophosphate, lithium bisfluorosulfonylimide and lithium bistrifluoromethylsulfonylimide.

9. The lithium-ion battery according to any one of claims 1 to 8, wherein, The electrolyte further includes a solvent; the solvent comprises the following components by mass percentage: 15%–50% ethylene carbonate, 10%–70% dimethyl carbonate, and 5%–50% methyl ethyl carbonate.

10. The lithium-ion battery according to any one of claims 1 to 9, wherein, The graphite satisfies one or more of the following characteristics: (1) The Dv50 of the graphite is 7μm to 13μm; (2) The graphite accounts for 95% to 100% of the mass of the negative electrode active material; (3) The graphite includes artificial graphite.

11. The lithium-ion battery according to any one of claims 1 to 10, wherein, The compaction density of the negative electrode active layer is 1.3 g / cm³. 3 ~1.7g / cm 3 .

12. The lithium-ion battery according to any one of claims 1 to 11, wherein, The positive electrode sheet includes a positive current collector and a positive active layer located on at least one surface of the positive current collector; the positive active material of the positive active layer includes lithium phosphate; optionally, the lithium phosphate accounts for 90% to 100% of the mass percentage of the positive active material.

13. A lithium-ion battery cell, comprising a positive electrode, a negative electrode, and an electrolyte; the negative electrode comprises a negative current collector and a negative active layer located on at least one surface of the negative current collector, the negative active material of the negative active layer comprising graphite, wherein the graphite has an I d / I g The value ranges from 0.05 to 0.4, where, I d This indicates that the Raman spectrum is at 1350±50 cm⁻¹ -1 peak intensity at d, I g This indicates that the Raman spectrum is at 1580±50 cm⁻¹. -1 The intensity of the g peak at the specified location; the electrolyte includes a film-forming additive, which includes methylene methane disulfonate, and the methylene methane disulfonate accounts for 0.5% to 3% of the mass of the electrolyte.

14. The lithium-ion battery cell according to claim 13, wherein, The film-forming additives also include one or more of cyclic carbonates and cyclic sulfates.

15. The lithium-ion battery cell according to claim 14, wherein, The film-forming additive satisfies one or more of the following characteristics: (1) The cyclic carbonate accounts for 1% to 15% of the mass of the electrolyte; (2) The cyclic carbonates include one or more of vinylene carbonate and fluoroethylene carbonate; (3) The cyclic sulfate ester accounts for 1% to 8% of the mass of the electrolyte; (4) The cyclic sulfates include vinyl sulfate.

16. The lithium-ion cell according to any one of claims 13 to 15, wherein, The electrolyte has a lithium-ion conductivity of 10 mS / cm to 20 mS / cm at 25°C.

17. An electrical device comprising a lithium-ion battery as claimed in any one of claims 1 to 12.

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