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

Abstract

A lithium-ion battery, a lithium-ion battery cell, and an electric device. The lithium-ion battery comprises a positive electrode sheet and an electrolyte. The positive electrode sheet comprises a positive electrode current collector and a positive electrode active layer located on at least one surface of the positive electrode current collector. The specific surface area of a positive electrode active material of the positive electrode active layer ranges from 5 m2 / g to 30 m2 / g, and the coating weight of the positive electrode active layer ranges from 12 mg / cm2 to 32 mg / cm2. The electrolyte comprises a film-forming additive, and the film-forming additive comprises methylene methanedisulfonate.

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 2025102376845, 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 a lithium-ion battery, a lithium-ion cell, and an electrical device. 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 vehicles, 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 battery performance. For example, the balance between storage performance and cycle 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 and an electrolyte; 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 specific surface area of ​​the positive active material of the positive active layer being 5 m² / s. 2 / g~30m 2 / g, the coating weight of the positive electrode active layer is 12mg / cm³. 2 ~32mg / cm 2 The electrolyte includes a film-forming additive, which includes methylene methane disulfonate (MMDS).

[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 during high-temperature storage and improve the battery's high-temperature storage performance. However, the positive electrode active material has a certain degree of water absorption, and MMDS will react with water, deteriorating the battery's cycle performance. By selecting a positive electrode active material with an appropriate specific surface area and keeping the coating weight of the positive electrode active layer within a suitable range, the positive electrode active layer can maintain a low water content, reducing the reaction between MMDS and water, and minimizing the impact of the reaction products on the battery's cycle performance. This allows the lithium-ion battery to achieve both good high-temperature storage performance and good high-temperature cycle performance.

[0007] In some embodiments, the electrolyte further includes a dehydration additive. The dehydration additive can reduce the water content in the electrolyte, lower the risk of MMDS reacting with water, and help further improve the high-temperature cycle life of the battery.

[0008] In some embodiments, the dehydrating additive accounts for 0.05% to 1% of the electrolyte by mass. When the mass percentage of the dehydrating additive in the lithium-ion battery electrolyte is greater than or equal to 0.05%, its dehydration effect can be fully utilized, promoting improved battery cycle life. When the mass percentage of the dehydrating additive is less than or equal to 1%, the additional adverse effects that the introduction of the dehydrating additive might have on the electrolyte's viscosity, conductivity, chemical balance, etc., can be reduced, allowing the electrolyte to maintain better stability, thereby maintaining better battery performance. Furthermore, when the mass percentage of the dehydrating additive is less than or equal to 1%, the potential reaction between the introduced dehydrating additive and active lithium can be reduced, decreasing the consumption of active lithium and maintaining high energy conversion efficiency of the battery.

[0009] In some embodiments, the dehydration additive includes one or more of cyanide additives, isocyanate additives, and silicon oxide additives.

[0010] In some embodiments, the film-forming additive further includes cyclic carbonates. Adding cyclic carbonates 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 further improve the high-temperature cycling performance of the lithium-ion battery.

[0011] In some embodiments, the cyclic carbonate accounts for 0.1% to 5% 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 5% allows the electrolyte to maintain a low viscosity, which is beneficial for promoting lithium-ion transport and improving the battery's charge-discharge efficiency.

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

[0013] In some embodiments, the electrolyte has a lithium-ion conductivity of 8 mS / cm to 20 mS / cm at 25°C. A lithium-ion conductivity greater than or equal to 8 mS / cm allows the battery to have lower internal resistance, improving its room-temperature cycling performance. Simultaneously, a lithium-ion conductivity greater than or equal to 8 mS / cm provides better kinetic performance, reduces battery polarization, and helps maintain higher battery power. Furthermore, a lithium-ion conductivity less than or equal to 20 mS / cm 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 cycling performance. Simultaneously, a lithium-ion conductivity less than or equal to 20 mS / cm helps the electrolyte maintain better thermal stability, further improving the battery's high-temperature cycling performance.

[0014] In some embodiments, the electrolyte includes a solvent; the solvent comprises, by mass percentage, the following components: 15%–50% ethylene carbonate, 10%–70% dimethyl carbonate, and 0%–70% methyl ethyl carbonate. By selecting a suitable solvent ratio, the electrolyte can have a suitable lithium-ion conductivity, promoting improved battery cycle performance at room temperature.

[0015] In some embodiments, the mass percentage of methylene methane disulfonate in the electrolyte is less than or equal to 2%; alternatively, the mass percentage of methylene methane disulfonate in the electrolyte is less than or equal to 0.01%.

[0016] In some embodiments, the lithium-ion battery further includes a negative electrode sheet, the negative electrode sheet 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 a carbon-based material, wherein the carbon-based material I d / I g The value is 0.03 to 0.4, where I d This indicates that the Raman displacement is within 1350 ± 50 cm. -1 The d-peak intensity within the range, I g This indicates that the Raman displacement is within 1580±50cm. -1 The intensity of peak g within the range. Select I. d / I g Carbon-based materials with an Ig value greater than or equal to 0.03 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, the Ig value of carbon-based materials... d / I gA value less than or equal to 0.4 can reduce excessive consumption of electrolyte on the negative electrode surface and reduce the adverse effects of excessive electrolyte consumption on battery cycle life.

[0017] In some embodiments, the carbon-based material includes graphite.

[0018] In some embodiments, the specific surface area of ​​the carbon-based material is 0.9 m². 2 / g~1.7m 2 / g. Select a specific surface area greater than or equal to 0.9m². 2 A carbon-based material of / g 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, the specific surface area is less than or equal to 1.7m². 2 The carbon-based material has fewer side reactions with the electrolyte, which can reduce the impact of side reactions on the battery cycle performance, thus enabling the battery to better balance high-temperature storage performance and cycle performance.

[0019] In some embodiments, the Dv50 of the carbon-based material is 7 μm to 13 μm. A Dv50 greater than or equal to 7 μm can further reduce side reactions between the carbon-based material and the electrolyte, improving the battery's cycle performance. A Dv50 less than or equal to 13 μm allows graphite to maintain good kinetic properties, further improving the battery's cycle performance.

[0020] In some embodiments, the carbon-based material accounts for 60% to 100% of the mass percentage of the negative electrode active material. This range of carbon-based material percentage allows graphite to fully utilize its role in consuming MMDS, further improving the battery's high-temperature storage performance and cycle performance.

[0021] In some embodiments, the compaction density of the positive electrode active layer is 2.3 g / cm³. 3 ~2.8g / cm 3 At this point, lithium-ion batteries can exhibit high energy density. Simultaneously, the compaction density of the positive electrode active layer within this range can promote electrolyte wetting of the positive electrode sheet, further improving the battery's cycle performance.

[0022] In some embodiments, the thickness of the positive electrode active layer is 0.03 mm to 0.1 mm. A thickness within this range allows the lithium-ion battery to have a higher energy density, while also enabling lithium ions to travel a shorter distance within the positive electrode active layer, thus improving the lithium ion transport rate and ultimately enhancing the battery's rate performance.

[0023] In some embodiments, the positive electrode active material accounts for 90% to 99% of the mass percentage of the positive electrode active layer.

[0024] In some embodiments, the positive electrode active material includes a lithium phosphate. Lithium phosphates have a high cycle life, which can further improve the cycle performance of the battery.

[0025] In some embodiments, the lithium phosphate comprises 80% to 100% of the positive electrode active material by mass.

[0026] A second aspect of this application provides a lithium-ion battery cell, comprising a positive electrode and an electrolyte; the positive electrode includes a positive current collector and a positive active layer located on at least one surface of the positive current collector, wherein the specific surface area of ​​the positive active material of the positive active layer is 5 m² / s. 2 / g~30m 2 / g, the coating weight of the positive electrode active layer is 12mg / cm³. 2 ~32mg / cm 2 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.

[0027] In some embodiments, the electrolyte further includes a dehydration additive.

[0028] In some embodiments, the dehydration additive accounts for 0.1% to 2% of the mass percentage of the electrolyte;

[0029] In some embodiments, the dehydration additive includes one or more of cyanide additives, isocyanate additives, and silicon oxide additives.

[0030] In some embodiments, the film-forming additive further includes cyclic carbonates.

[0031] In some embodiments, the cyclic carbonate accounts for 2% to 10% of the mass percentage of the electrolyte.

[0032] In some embodiments, the cyclic carbonate includes one or more of vinylene carbonate, vinyl sulfate, and fluoroethylene carbonate.

[0033] A third aspect of this application provides an electrical device including the lithium-ion battery described in the first aspect. Attached Figure Description

[0034] 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:

[0035] Figure 1 is a schematic diagram of a lithium-ion battery according to an embodiment of this application.

[0036] Figure 2 is an exploded view of a lithium-ion battery according to an embodiment of this application, as shown in Figure 1.

[0037] 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.

[0038] Explanation of reference numerals in the attached drawings: 1. Lithium-ion battery; 11. Casing; 12. Electrode assembly; 13. Cover plate; 2. Electrical device. Detailed Implementation

[0039] 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.

[0040] 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.

[0041] 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 degrees Celsius (abbreviated as: °C)" and its approximation as ±1 °C, the approximate values ​​of 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".

[0042] In this application, the terms "multiple," "various," "several," etc., unless otherwise specified, refer to a quantity greater than or equal to 2. For example, "one or more" means one or more or more. It is 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.

[0043] Unless otherwise specified, all embodiments and optional embodiments of this application can be combined to form new technical solutions.

[0044] 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.

[0045] 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.

[0046] 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."

[0047] 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.

[0048] 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.

[0049] 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.

[0050] 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.

[0051] 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.

[0052] 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.

[0053] 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℃.

[0054] 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, 3–5 hours (abbreviated as h) or 3–5h both mean that the units for the left endpoint "3" and the right endpoint "5" are both h, 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.

[0055] 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.

[0056] 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.

[0057] In some implementations, the lithium-ion battery can be a power battery or an energy storage battery.

[0058] 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.

[0059] Based on this, one embodiment of this application provides a lithium-ion battery. The lithium-ion battery includes a positive electrode and an electrolyte. 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 specific surface area of ​​the positive active material in the positive active layer is 5 m² / g (abbreviated as: m²). 2 / g)~30m 2 / g. The coating weight of the positive electrode active layer is 12 mg / cm² (abbreviated as: mg / cm²). 2 )~32mg / cm 2 The electrolyte includes film-forming additives, including methylene methane disulfonate (MMDS).

[0060] In the lithium-ion battery of this embodiment, the solid electrolyte interphase (SEI) film formed with the participation of MMDS exhibits good thermal stability, which can limit the increase of internal resistance during high-temperature storage and improve the high-temperature storage performance of the battery. Therefore, introducing MMDS into the electrolyte of a lithium-ion battery can improve its high-temperature storage performance. However, in our research on lithium-ion batteries, we found that positive electrode active materials often have a certain degree of water absorption. When using positive electrode active materials in batteries, it is unavoidable to introduce a certain amount of water. MMDS is quite sensitive to water and can react with water to generate acidic substances, such as sulfonic acid. The generation of acidic substances will damage the SEI film, leading to a reduction in the cycle life of the battery. Therefore, although introducing MMDS into a lithium-ion battery can improve its high-temperature storage performance, the reaction of MMDS with water will lead to a decrease in battery performance.

[0061] In this embodiment, a specific surface area of ​​less than or equal to 30m² is selected. 2 / g of positive electrode active material and ensure that the coating weight of the positive electrode active layer is less than or equal to 32mg / cm³. 2 This reduces the adsorption capacity of the positive electrode active material for moisture and maintains a low water content in the positive electrode active layer, thereby reducing the reaction between MMDS and water and minimizing the impact of the reaction products on battery cycle performance. Simultaneously, the specific surface area of ​​the positive electrode active material is greater than or equal to 5 m² / g. 2 / g and the coating weight of the positive electrode active layer is greater than or equal to 12mg / cm³. 2 This provides more reactive sites, promoting lithium-ion intercalation and improving battery cycle performance. Additionally, the coating weight of the positive electrode active layer is greater than or equal to 12 mg / cm³. 2 This allows the battery to have a high energy density. Therefore, through the configuration in this embodiment, the lithium-ion battery can achieve both good high-temperature storage performance and good high-temperature cycle performance.

[0062] It is understood that the above principle analysis should not be regarded as a limitation on the technical solution and technical effect of this application. The synergistic effect between the specific surface area of ​​the positive electrode active material and the coating weight of the positive electrode active layer in this application can be verified through examples.

[0063] In this application, the specific surface area of ​​the material can be tested using methods known in the art. For example, it can be tested using the nitrogen adsorption specific surface area analysis method according to GB / T 19587-2017, and calculated using the Brunauer Emmett Telle method (BET method). The nitrogen adsorption specific surface area analysis can be performed using a Tri-Star 3020 specific surface area and pore size analyzer from Micromeritics, USA.

[0064] It is understood that the specific surface area of ​​the positive electrode active material can be tested using methods known in the art. For example, it can be tested using the nitrogen adsorption specific surface area analysis method according to GB / T 19587-2017, and calculated using the Brunauer Emmett Telle method (BET method). The nitrogen adsorption specific surface area analysis can be performed using the Tri-Star 3020 specific surface area and pore size analyzer from Micromeritics, Inc.

[0065] Optionally, the specific surface area of ​​the positive electrode active material can be 5m². 2 / g、6m 2 / g、7m 2 / g、8m 2 / g、9m 2 / g, 10m 2 / g、11m 2 / g、12m 2 / g、13m 2 / g、14m 2 / g, 15m 2 / g, 16m 2 / g、17m 2 / g、18m 2 / g、19m 2 / g、20m 2 / g、21m 2 / g、22m 2 / g、23m 2 / g、24m 2 / g、25m 2 / g、26m 2 / g、27m 2 / g、28m 2 / g、29m 2 / g、30m 2 / g and any value within the range consisting of any two of the above values.

[0066] In this application, the coating weight of the positive electrode active layer can be tested using methods known in the art. For example, take a positive electrode sheet, cut it into a small circular piece with an area of ​​S1, weigh it, and record its weight as M1. Then wipe off the positive electrode active layer of the weighed positive electrode sheet, weigh the positive current collector, and record it as M0. The coating weight of the positive electrode active layer = (weight of the positive electrode sheet M1 - weight of the positive current collector M0) / S1.

[0067] Optionally, the coating weight of the positive electrode active layer can be 12 mg / cm³. 2 13mg / cm 2 14mg / cm 2 15mg / cm 2 16mg / cm 2 17mg / cm 2 18mg / cm 2 19mg / cm 2 20mg / cm 2 21mg / cm 2 22mg / cm 2 23mg / cm 2 24mg / cm 2 25mg / cm 2 26mg / cm 2 27mg / cm 2 28mg / cm 2 29mg / cm 2 30mg / cm 2 31mg / cm2 32mg / cm 2 And any value within the range consisting of any two of the above values.

[0068] In some embodiments, the electrolyte also includes a dehydration additive. This additive reduces the water content in the electrolyte, lowers the risk of MMDS reacting with water, and helps to further improve the battery's high-temperature cycle life.

[0069] Optionally, in lithium-ion batteries, the dehydration additive accounts for 0.05% to 1% of the electrolyte by mass. When the mass percentage of the dehydration additive in the electrolyte of a lithium-ion battery is greater than or equal to 0.05%, the dehydration effect of the additive can be fully utilized, promoting the improvement of battery cycle life. When the mass percentage of the dehydration additive is less than or equal to 1%, the additional adverse effects that the introduction of the dehydration additive may have on the viscosity, conductivity, chemical balance, etc. of the electrolyte can be reduced, thus maintaining better electrolyte stability and consequently, better battery performance. Furthermore, when the mass percentage of the dehydration additive is less than or equal to 1%, the potential reaction between the dehydration additive and active lithium can be reduced, decreasing the consumption of active lithium and maintaining high energy conversion efficiency of the battery.

[0070] As examples, the percentage of dehydration additive in the electrolyte of a lithium-ion battery can be 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%, or any value within the range of any two of the above values.

[0071] Further optionally, the dehydration additive includes one or more of cyanide additives, isocyanate additives, and silicon oxide additives.

[0072] Optionally, the dehydration additive includes 1,6-hexamethylene diisocyanate (HDI), toluene diisocyanate, tris(trimethylsilane) phosphate, and one or more of the following materials:

[0073] In some embodiments, the film-forming additive also includes cyclic carbonates. Further investigation of the battery revealed that the SEI film formed with the participation of MMDS has poor toughness and may be damaged under high-temperature cycling conditions, such as cycling temperatures above 45°C. Adding cyclic carbonates to the electrolyte can improve the toughness of the SEI film, reduce the risk of damage under high-temperature cycling, and further improve the high-temperature cycling performance of the lithium-ion battery.

[0074] Optionally, the cyclic carbonate accounts for 0.1% to 5% 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 5% helps maintain a low electrolyte 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%, 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 4%.

[0075] Optionally, the cyclic carbonate includes one or more of vinylene carbonate, vinyl sulfate, and fluoroethylene carbonate.

[0076] 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.

[0077] In further research on batteries, this application found that adding cyclic carbonates to the electrolyte can improve the high-temperature cycle performance of lithium-ion batteries. However, the addition of cyclic carbonates may affect the initial DCR and charging capacity of the battery, which may lead to insufficient charging capacity at room temperature, resulting in lithium plating at the interface and restricting the room temperature cycle performance of the battery. In this case, the room temperature cycle performance of the battery can be improved by making the electrolyte have a suitable lithium-ion conductivity.

[0078] In some embodiments, the lithium-ion conductivity of the electrolyte at 25°C is 8 millisiemens / cm (mS / cm) to 20 mS / cm. A lithium-ion conductivity greater than or equal to 8 mS / cm allows the battery to have lower internal resistance, improving its room-temperature cycle performance. Simultaneously, a lithium-ion conductivity greater than or equal to 8 mS / cm provides better kinetic properties, reduces battery polarization, and helps maintain higher power output. Furthermore, a lithium-ion conductivity less than or equal to 20 mS / cm allows for a more suitable rate of lithium-ion insertion and extraction in the electrode active material, reducing stress 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 20 mS / cm helps the electrolyte maintain better thermal stability, further improving the battery's high-temperature cycle performance.

[0079] As examples, the lithium-ion conductivity of the electrolyte 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, 19 mS / cm, 20 mS / cm, or any value within the range of any two of the above values. Further optionally, the lithium-ion conductivity of the electrolyte is between 9 mS / cm and 13 mS / cm.

[0080] 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°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 immerse it in the liquid to be tested. Click "Start Test," and record the test result after the data stabilizes for at least 10 seconds.

[0081] In some embodiments, the electrolyte 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 the 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.

[0082] In some embodiments, the lithium salt includes one or more of lithium hexafluorophosphate (LiPF6), lithium bisfluorosulfonylimide (LiFSI), and lithium bistrifluoromethanesulfonylimide (LiTFSI).

[0083] In some embodiments, the electrolyte 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, with the chemical formula: [insert chemical formula here]). ), fluoroethylene carbonate (FEC), propylene carbonate (PC, chemical formula of PC is: ) and butylene carbonate (butylene carbonate has the 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.

[0084] 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) 0%–70%. By selecting a suitable solvent ratio, the electrolyte can have a suitable lithium-ion conductivity, thereby improving the battery's room-temperature cycling performance.

[0085] 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.

[0086] 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.

[0087] Optionally, the mass percentage of EMC, as a percentage of the solvent, can be 1%, 5%, 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] In some embodiments, the mass percentage of methylene methane disulfonate in the electrolyte is less than or equal to 2%. As described above, the SEI film formed with the participation of MMDS can improve the high-temperature storage performance of the battery. However, MMDS is prone to decomposition, producing acidic substances such as sulfonic acid. When the residual amount of MMDS in the electrolyte is high, the decomposition products can damage the SEI film, potentially hindering the improvement of cycle performance. A lower residual amount of MMDS in the electrolyte can reduce the risk of hindering cycle improvement caused by excessive MMDS residue, while still improving the high-temperature storage performance of the battery.

[0089] It should be noted that MMDS may no longer be present in lithium-ion batteries, corresponding to a 0% mass percentage of MMDS in the electrolyte. This is because during the formation or recycling 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 mass percentage of MMDS in the electrolyte of the finished lithium-ion battery may be 0% after formation or recycling.

[0090] The mass percentage of MMDS in the electrolyte of this application can be determined by liquid chromatography, mass spectrometry, and nuclear magnetic resonance spectroscopy.

[0091] 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%.

[0092] In some embodiments, the lithium-ion battery further includes a negative electrode sheet, which 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 a carbon-based material. d / I g The value is 0.03 to 0.4, where I d This indicates that the Raman displacement is within 1350 ± 50 cm. -1 The d-peak intensity within the range, I g This indicates that the Raman displacement is within 1580±50cm. -1 The peak intensity of g within the range. In these embodiments, I is selected. d / I g Carbon-based materials with an Ig value greater than or equal to 0.03 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, the Ig value of carbon-based materials... d / I g A value less than or equal to 0.4 can reduce excessive consumption of electrolyte on the negative electrode surface and reduce the adverse effects of excessive electrolyte consumption on battery cycle life.

[0093] It is understandable that the material I d / I gThe value can represent the degree of defect in a material. In this application, the I value for carbon-based materials... d / I g The value can represent the degree of defect in carbon-based materials.

[0094] In this application, carbon-based materials I d / I g The 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 the carbon-based material. d / I g The testing instrument can be a Horiba LabRAM HR800 Raman spectrometer.

[0095] In some embodiments, carbon-based materials I d / I g The value can be 0.03, 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.

[0096] In some embodiments, the specific surface area of ​​the carbon-based material is 0.9 m². 2 / g~1.7m 2 / g. In these embodiments, a specific surface area greater than or equal to 0.9m² is selected. 2 A carbon-based material of / g 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, the surface area is less than or equal to 1.7m². 2 The reduced number of side reactions between the carbon-based material ( / g) and the electrolyte can decrease the impact of these side reactions on battery cycle performance, thereby enabling the battery to achieve a better balance between high-temperature storage performance and cycle performance. Optionally, the carbon-based material has a specific surface area of ​​0.9 m². 2 / g、1m 2 / g, 1.1m 2 / g, 1.2m 2 / g, 1.3m 2 / g, 1.4m 2 / g, 1.5m 2 / g, 1.6m 2 / g, 1.7m2 / g and any value within the range consisting of any two of the above values.

[0097] Understandably, the specific surface area of ​​carbon-based materials can be tested using methods known in the art. For example, it can be tested using the nitrogen adsorption specific surface area analysis method according to GB / T 19587-2017, and calculated using the Brunauer Emmett Teller method (BET method). The nitrogen adsorption specific surface area analysis can be performed using the Tri-Star 3020 specific surface area and pore size analyzer from Micromeritics, Inc.

[0098] In some embodiments, the Dv50 of the carbon-based material is between 7 micrometers (μm) and 13 μm. A Dv50 greater than or equal to 7 μm can further reduce side reactions between the carbon-based material and the electrolyte, improving the battery's cycle performance. A Dv50 less than or equal to 13 μm allows graphite to maintain good kinetic properties, further improving the battery's cycle performance. Optionally, the Dv50 of the carbon-based material 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.

[0099] 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 according to standard GB / T 19077-2016; the laser particle size analyzer can be a Malvern Master Size 3000.

[0100] In some embodiments, the carbon-based material includes graphite. Optionally, the graphite includes one or more of synthetic graphite and natural graphite.

[0101] 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 0.03 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.

[0102] In some embodiments, the carbon-based material accounts for 60% to 100% of the mass percentage of the negative electrode active material. Within this range, the mass percentage of carbon-based material in the negative electrode active material can fully utilize the MMDS-consuming effect of graphite, further improving the battery's high-temperature storage performance and cycle performance. Optionally, the mass percentage of carbon-based material in the negative electrode active material can be 60%, 65%, 70%, 75%, 80%, 85%, 90%, 95%, 100%, or any value within the range of any two of the above values.

[0103] 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.

[0104] Optionally, the negative electrode active material accounts for 92% to 99% of the mass of the negative electrode active layer. Optionally, the mass percentage of the negative electrode active material in the negative electrode active layer can be 92%, 93%, 94%, 95%, 96%, 97%, 98%, 99%, or any value within the range of any two of the above values.

[0105] 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.

[0106] 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 0.5% 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 0.5%, 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.

[0107] 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.

[0108] 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).

[0109] 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.

[0110] In some embodiments, the compaction density of the negative electrode active layer is 1.3 g / cm³. 3 ~1.7g / cm 3Within this compaction density range, the battery can achieve a higher energy density. Simultaneously, within this compaction density range, the electrolyte can more fully wet the negative electrode active layer, allowing for more efficient lithium-ion transport within the active layer. This improves 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 3 1.65g / cm 3 1.7g / cm 3 And any value within the range consisting of any two of the above values.

[0111] The compaction density of the negative electrode active layer in this application can be tested by the following method: Disassemble the battery, take the negative electrode sheet, and punch it into a small circular piece with an area of ​​S. Measure the mass M and thickness L of the small circular piece. Take another negative electrode sheet, wipe off the active layer on the surface, and remove the remaining negative electrode current collector. Similarly, punch it into a small circular piece with an area of ​​S. Measure the mass M0 and thickness L0 of the negative electrode current collector. Then, the compaction density of the negative electrode active layer = (M-M0) / S / (L-L0).

[0112] In some embodiments, the water content of the negative electrode is less than or equal to 200 ppm. A water content of less than or equal to 200 ppm in the negative electrode can further reduce the risk of MMDS reacting with water and further improve the cycle performance of the battery. It is understood that the moisture in the negative electrode is difficult to completely remove; therefore, during the preparation of the negative electrode, the water content can be reduced as much as possible through drying.

[0113] Understandably, the moisture content of the negative electrode can be tested using the following method: Fully fill the battery, disassemble it, remove the negative electrode, and soak it thoroughly in DMC for at least 2 hours. Pour out the DMC and allow the electrode to air dry naturally. Test the moisture content of the positive electrode using a fully automated moisture content analyzer. Optionally, the fully automated moisture content analyzer can be a Metrohm 874+831.

[0114] In some embodiments, the positive electrode active material accounts for 90% to 99% of the mass percentage of the positive electrode active layer. A mass percentage greater than or equal to 90% allows for a higher concentration of positive electrode active material in the active layer, providing more reactive sites and further improving the cycle performance of the lithium-ion battery. Simultaneously, a higher concentration of positive electrode active material can also improve the energy density of the lithium-ion battery, resulting in a higher energy density. A mass percentage less than or equal to 99% allows for appropriate content of functional additives such as conductive agents and binders in the active layer, which is beneficial for improving the overall performance of the positive electrode sheet. Optionally, the mass percentage of the positive electrode active material in the active layer can be 90%, 91%, 92%, 93%, 94%, 95%, 96%, 97%, 98%, 99%, or any value within the range of any two of the above values.

[0115] In some embodiments, the Dv50 of the positive electrode active material is 0.7 μm to 1.8 μm. A Dv50 greater than or equal to 0.7 μm allows the positive electrode active material to have a smaller specific surface area, which helps reduce its water absorption capacity, further reducing the water content of the positive electrode sheet, lowering the risk of MMDS reacting with water in the battery, and thus improving the battery's cycle performance. Simultaneously, a Dv50 greater than or equal to 0.7 μm reduces side reactions between the positive electrode active material and the electrolyte, further improving the battery's cycle performance. A Dv50 less than or equal to 1.8 μm allows lithium ions to have a shorter transport distance within the positive electrode active material, increasing the lithium ion transport rate within the positive electrode active material, which is beneficial for improving the battery's rate performance. Optionally, the Dv50 of the positive electrode active material can be 0.7μm, 0.8μm, 0.9μm, 1μm, 1.1μm, 1.2μm, 1.3μm, 1.4μm, 1.5μm, 1.6μm, 1.7μm, 1.8μm, or any value within the range of any two of the above values.

[0116] In some embodiments, the compaction density of the positive electrode active layer is 2.3 g / cm³. 3 ~2.8g / cm 3 At this point, lithium-ion batteries exhibit high energy density. Simultaneously, the compaction density of the positive electrode active layer within this range promotes electrolyte wetting of the positive electrode sheet, further improving the battery's cycle performance. Optionally, the compaction density of the positive electrode active layer can be 2.3 g / cm³. 3 2.35g / cm 3 2.4g / cm 3 2.45g / cm 3 2.5g / cm 32.55g / cm 3 2.6g / cm 3 2.65g / cm 3 2.7g / cm 3 2.75g / cm 3 2.8g / cm 3 And any value within the range consisting of any two of the above values.

[0117] The compaction density of the positive electrode active layer in this application can be tested by the following method: Disassemble the battery, take the positive electrode sheet, and punch it into a small circular piece with an area of ​​S. Measure the mass M and thickness L of the small circular piece. Take another positive electrode sheet, wipe off the active layer on the surface, and remove the remaining positive electrode current collector. Similarly, punch it into a small circular piece with an area of ​​S. Measure the mass M0 and thickness L0 of the positive electrode current collector. Then, the compaction density of the positive electrode active layer = (M-M0) / S / (L-L0).

[0118] In some embodiments, the thickness of the positive electrode active layer is 0.03 mm to 0.1 mm. Within this range, the thickness of the positive electrode active layer allows the lithium-ion battery to have a higher energy density, while also enabling lithium ions to travel a shorter distance within the positive electrode active layer, thus improving the lithium ion transport rate and enhancing the battery's rate performance. Optionally, the thickness of the positive electrode active layer can be 0.03 mm, 0.04 mm, 0.05 mm, 0.06 mm, 0.07 mm, 0.08 mm, 0.09 mm, 0.1 mm, or any value within the range of any two of the above values.

[0119] In some embodiments, the positive electrode active material includes a lithium-containing phosphate. Lithium-containing phosphates have a high cycle life, which can further improve the cycle performance of the battery.

[0120] Alternatively, if the positive electrode active material includes lithium phosphate, the lithium-ion battery can be an energy storage battery.

[0121] Optionally, the lithium phosphate content in the positive electrode active material is 80% to 100% by mass. Optionally, the lithium phosphate content in the positive electrode active material can be 80%, 81%, 82%, 83%, 84%, 85%, 86%, 87%, 88%, 89%, 90%, 91%, 92%, 93%, 94%, 95%, 96%, 97%, 98%, 99%, 100%, or any value within the range of any two of the above values.

[0122] 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.

[0123] 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.

[0124] 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.

[0125] 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.

[0126] 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.

[0127] 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.

[0128] 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.

[0129] 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.

[0130] 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.

[0131] 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.

[0132] 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 20% to 100% of the mass of the positive electrode active material. Optionally, the chemical formula is Li x (Ni a Co b Mn c ) 1-d M d O 2-y A y The percentage of lithium-containing transition metal oxides in the positive electrode active material by mass can be 20%, 25%, 30%, 35%, 40%, 45%, 50%, 55%, 60%, 65%, 70%, 75%, 80%, 85%, 90%, 95%, 100%, or any value within the range of any two of the above values.

[0133] 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.

[0134] 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.

[0135] 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 0.5% 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 0.5%, 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.

[0136] 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).

[0137] 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.

[0138] In some implementations, the moisture content of the positive electrode is less than or equal to 300 ppm. A moisture content of less than or equal to 300 ppm in the positive electrode can further reduce the risk of MMDS reacting with water, thereby further improving the battery's cycle performance. It is understood that moisture in the positive electrode is difficult to completely remove; therefore, during the preparation of the positive electrode, the moisture content can be minimized by drying.

[0139] The moisture content of the positive electrode in this application can be tested using the following method: Fully fill the battery, disassemble the battery, remove the positive electrode, and soak it thoroughly in DMC for at least 2 hours. Pour out the DMC and allow the electrode to air dry naturally. Test the moisture content of the positive electrode using a fully automated moisture content analyzer. Optionally, the fully automated moisture content analyzer can be a Metrohm 874+831.

[0140] 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.

[0141] 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.

[0142] In some implementations, the positive electrode, negative electrode, and separator can be fabricated into an electrode assembly using a winding or stacking process.

[0143] 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.

[0144] 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.

[0145] Another embodiment of this application provides a lithium-ion battery cell. The lithium-ion battery cell includes a positive electrode and an electrolyte. 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 specific surface area of ​​the positive active material in the positive active layer being 5 m² / s. 2 / g~30m 2 / g, the coating weight of the positive electrode active layer is 12mg / cm³. 2 ~32mg / cm 2 The electrolyte includes film-forming additives, including methylene methane disulfonate, which accounts for 0.5% to 3% of the electrolyte by mass.

[0146] 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.

[0147] 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 0.1C to 5% SOC, then charging it at 0.2C to 10% SOC, and then charging it at 0.3C to 30% SOC.

[0148] 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".

[0149] 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%".

[0150] 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.

[0151] In some embodiments, the electrolyte of the lithium-ion battery cell further includes a dehydration additive. Optionally, the dehydration additive accounts for 0.1% to 2% of the electrolyte by mass. The dehydration additive includes one or more of cyanide additives, isocyanate additives, and silicon oxide additives.

[0152] It is understood that, corresponding to the statement in the lithium-ion battery that "the mass percentage of the dehydration additive in the electrolyte is 0.05% to 1%", the statement in the lithium-ion cell that "the mass percentage of the dehydration additive in the electrolyte is 0.1% to 2%" is correct. The mass percentage of the dehydration additive in the electrolyte of a lithium-ion cell can represent the amount of dehydration additive added during the manufacture of the lithium-ion battery. Optionally, the mass percentage of the dehydration additive in the electrolyte of a lithium-ion cell can be 0.1%, 0.3%, 0.5%, 0.8%, 1%, 1.2%, 1.5%, 1.8%, 2%, or any value within the range of any two of the above values.

[0153] In some embodiments, the film-forming additives in the electrolyte of the lithium-ion battery cell further include cyclic carbonates. Optionally, the cyclic carbonates account for 2% to 10% of the electrolyte by mass. Cyclic carbonates include one or more of vinylene carbonate, vinyl sulfate, and fluoroethylene carbonate.

[0154] For example, corresponding to the statement in the above-mentioned lithium-ion battery that "cyclic carbonates account for 0.1% to 5% of the electrolyte by mass," the statement in the lithium-ion cell that "cyclic carbonates account for 2% to 10% of the electrolyte by mass" indicates 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 2%, 3%, 4%, 5%, 6%, 7%, 8%, 9%, 10%, or any value within the range of any two of the above values.

[0155] 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 is 8 mS / cm to 20 mS / cm" in the aforementioned lithium-ion battery, the "lithium-ion conductivity of the electrolyte is 10 mS / cm to 22 mS / cm" in the lithium-ion cell. Optionally, in the lithium-ion cell, the lithium-ion conductivity of the electrolyte 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, 21 mS / cm, 22 mS / cm, or any value within the range of any two of the above values.

[0156] 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".

[0157] 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 comprises the following components: ethylene carbonate (EC) 15%–50%, dimethyl carbonate (DMC) 10%–70%, and ethyl methyl carbonate (EMC) 0%–70%.

[0158] 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.

[0159] 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.

[0160] In some implementations, the lithium-ion battery can be a single cell, a battery module, or a battery pack.

[0161] 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.

[0162] 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.

[0163] Optionally, the battery module may also include a housing with a receiving space in which multiple lithium-ion batteries are housed.

[0164] 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.

[0165] 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.

[0166] 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.

[0167] As an electrical device, lithium-ion batteries can be selected based on its usage requirements.

[0168] 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.

[0169] 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.

[0170] 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.

[0171] 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.

[0172] Example 1

[0173] (1) Positive electrode plate

[0174] 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 specific surface area of ​​the positive electrode active material was 10 m² / g. 2 / g. The coating weight of the positive electrode active layer is 20 mg / cm³. 2 The compaction density of the positive electrode active layer of the positive electrode sheet is 2.4 g / cm³. 3 .

[0175] (2) Negative electrode plate

[0176] 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 form the negative electrode plate. The negative electrode active material I... d / I g The value is 0.11. The specific surface area of ​​the negative electrode active material is 1.3 m². 2 / g. The compacted density of the negative electrode active layer of the negative electrode sheet is 1.6 g / cm³. 3 .

[0177] (3) Separating membrane

[0178] Polyethylene film is used as the separation membrane.

[0179] (4) Electrolyte

[0180] In an argon-atmosphere 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. MMDS (1% by mass of the electrolyte), ethylene carbonate (VC) (3.5% by mass of the electrolyte), and lithium hexafluorophosphate (1 mol / L) were added to the mixed solvent.

[0181] (5) Lithium-ion batteries

[0182] 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. The formation method includes charging at 0.1C to 5% SOC, then at 0.2C to 10% SOC, and finally at 0.3C to 30% SOC.

[0183] Examples 2 to 13, Comparative Examples 1 to 3

[0184] The differences between Examples 2 to 13 and Comparative Examples 1 to 3 compared to Example 1 are shown in Table 1.

[0185] Test case

[0186] (1) The internal resistance growth rate of lithium-ion batteries at high temperatures was tested. The test method was as follows:

[0187] 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℃. Every month, the actual capacity at 25℃ was tested (discharged at a constant current of 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 higher energy conversion efficiency. The test results are shown in Table 1.

[0188] (2) High-temperature cycling test of lithium-ion battery, the test method is as follows:

[0189] 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.

[0190] 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.

[0191] Table 1

[0192] In Table 1, BET represents the specific surface area of ​​the positive electrode active material, in m². 2 / g. Coating weight indicates the weight of the positive electrode active layer coated, in mg / cm³. 2 I d / I g I represents graphite d / I g Value. The BET of graphite represents the specific surface area of ​​graphite, in m². 2 / g. MMDS indicates the mass percentage of MMDS added to the electrolyte. Dehydration additive indicates the type and mass percentage of dehydration additive 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. " / " indicates that the corresponding substance is not added to the electrolyte.

[0193] As can be seen from Table 1, the specific surface area of ​​the positive electrode active material, the coating weight of the positive electrode active layer, and the MMDS can enable the battery to achieve both a low internal resistance growth rate and good high-temperature cycling performance.

[0194] 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.

[0195] 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 and an electrolyte; the positive electrode comprising a positive current collector and a positive active layer located on at least one surface of the positive current collector, wherein the specific surface area of ​​the positive active material of the positive active layer is 5 m² / s. 2 / g~30m 2 / g, the coating weight of the positive electrode active layer is 12mg / cm³. 2 ~32mg / cm 2 The electrolyte includes a film-forming additive, which includes methylene methane disulfonate.

2. The lithium-ion battery according to claim 1, wherein, The electrolyte also includes a water-removing additive.

3. The lithium-ion battery according to claim 2, wherein, The dehydrating additive satisfies one or more of the following characteristics: (1) The water-removing additive accounts for 0.05% to 1% of the mass of the electrolyte; (2) The dehydration additives include one or more of cyanide additives, isocyanate additives and silicon oxide additives.

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

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 5% of the mass of the electrolyte; (2) The cyclic carbonates include one or more of vinylene carbonate, vinyl sulfate and fluoroethylene carbonate.

6. The lithium-ion battery according to any one of claims 1 to 5, wherein, The electrolyte has a lithium-ion conductivity of 8 mS / cm to 20 mS / cm at 25°C.

7. The lithium-ion battery according to any one of claims 1 to 6, wherein, The electrolyte includes a solvent; the solvent comprises the following components by mass percentage: 15%–50% ethylene carbonate, 10%–70% dimethyl carbonate, and 0%–70% methyl ethyl carbonate.

8. The lithium-ion battery according to any one of claims 1 to 7, wherein, The mass percentage of methylene disulfonate in the electrolyte is less than or equal to 2%; optionally, the mass percentage of methylene disulfonate in the electrolyte is less than or equal to 0.01%.

9. The lithium-ion battery according to any one of claims 1 to 8, wherein, The lithium-ion battery further includes a negative electrode sheet, which 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 comprises a carbon-based material. d / I g The value is 0.03 to 0.4, where I d This indicates that the Raman displacement is within 1350 ± 50 cm. -1 The d-peak intensity within the range, I g This indicates that the Raman displacement is within 1580±50cm. -1 The intensity of the g peak within the range.

10. The lithium-ion battery according to claim 9, wherein, The carbon-based material satisfies one or more of the following characteristics: (1) The carbon-based material includes graphite; (2) The specific surface area of ​​the carbon-based material is 0.9 m². 2 / g~1.7m 2 / g; (3) The Dv50 of the carbon-based material is 7μm to 13μm; (4) The carbon-based material accounts for 60% to 100% of the mass of the negative electrode active material.

11. The lithium-ion battery according to any one of claims 1 to 10, wherein, The positive electrode active layer satisfies one or more of the following characteristics: (1) The compaction density of the positive electrode active layer is 2.3 g / cm³. 3 ~2.8g / cm 3 ; (2) The thickness of the positive electrode active layer is 0.03 mm to 0.1 mm.

12. The lithium-ion battery according to any one of claims 1 to 11, wherein, The positive electrode active material satisfies one or more of the following characteristics: (1) The positive electrode active material accounts for 90% to 99% of the mass of the positive electrode active layer; (2) The positive electrode active material includes lithium phosphate; optionally, the lithium phosphate accounts for 80% to 100% of the mass of the positive electrode active material.

13. A lithium-ion battery cell, comprising a positive electrode and an electrolyte; the positive electrode comprises a positive current collector and a positive active layer located on at least one surface of the positive current collector, wherein the specific surface area of ​​the positive active material of the positive active layer is 5 m² / s. 2 / g~30m 2 / g, the coating weight of the positive electrode active layer is 12mg / cm³. 2 ~32mg / cm 2 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 electrolyte also includes a water-removing additive; Optionally, the dehydration additive satisfies one or more of the following characteristics: (1) The water-removing additive accounts for 0.1% to 2% of the mass of the electrolyte; (2) The dehydration additives include one or more of cyanide additives, isocyanate additives and silicon oxide additives.

15. The lithium-ion cell according to any one of claims 13 to 14, wherein, The film-forming additives also include cyclic carbonates; Optionally, the cyclic carbonate satisfies one or more of the following characteristics: (1) The cyclic carbonate accounts for 2% to 10% of the mass of the electrolyte; (2) The cyclic carbonates include one or more of vinylene carbonate, vinyl sulfate and fluoroethylene carbonate.

16. An electrical device comprising a lithium-ion battery according to any one of claims 1 to 12.

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