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

Abstract

The present application provides a lithium-ion battery cell, a lithium-ion battery, and an electric device. The lithium-ion battery cell comprises a positive electrode sheet, a negative electrode sheet, and an electrolyte, wherein 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 positive electrode active material of the positive electrode active layer comprising a lithium-containing phosphate; the negative electrode sheet comprises a negative electrode current collector and a negative electrode active layer located on at least one surface of the negative electrode current collector, and the negative electrode active material of the negative electrode active layer comprises a silicon-carbon composite material, which silicon-carbon composite material comprises a silicon material and a carbon material, with the silicon material being distributed within the carbon material or the carbon material being distributed within the silicon material; and in the electrolyte, the mass percentage of fluoroethylene carbonate (FEC) in the electrolyte is less than or equal to 10%. In the lithium-ion battery cell, the lithium-containing phosphate, the silicon material, and FEC can be effectively compatible, such that the lithium-ion battery can balance both a higher energy density and better cycle performance.

Description

Lithium ion battery cell, lithium ion battery and electric device

[0001] Related applications

[0002] The present application claims priority to the Chinese patent application No. 2024110351328, filed on July 30, 2024, entitled "Lithium ion battery cell, lithium ion battery and electric device", the contents of which are hereby incorporated by reference in its entirety. TECHNICAL FIELD

[0003] The present application relates to the technical field of battery, in particular to a lithium ion battery cell, a lithium ion battery and an electric device. BACKGROUND

[0004] In recent years, batteries such as lithium ion batteries are widely used in energy storage power systems such as hydraulic, thermal, wind and solar power stations, and in many fields such as electric tools, electric bicycles, electric motorcycles, electric vehicles, military equipment, aerospace, etc. With the continuous expansion of the use range of batteries such as lithium ion batteries, higher requirements are also put forward for the performance of the batteries.

[0005] In the selection of battery materials, lithium-containing phosphates such as lithium iron phosphate are widely used in positive electrode materials of batteries because of their lower price and better cycle performance. Although these lithium-containing phosphates have the above advantages, when they are used as positive electrode materials in batteries, the energy density of the batteries is low. For example, taking lithium iron phosphate as an example, its theoretical specific capacity is 170 milliampere hours per gram (mAh / g), and in the traditional battery system, the specific capacity of lithium iron phosphate can be close to 163 mAh / g, that is, the specific capacity of lithium iron phosphate has been developed to a level close to its theoretical specific capacity, but for the battery system, the energy density of the battery still needs to be improved. SUMMARY

[0006] The first aspect of the present application provides a lithium ion battery cell. The lithium ion battery cell comprises a positive electrode sheet, a negative 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 positive electrode active material of the positive electrode active layer comprising a lithium-containing phosphate; the negative electrode sheet comprises a negative electrode current collector and a negative electrode active layer located on at least one surface of the negative electrode current collector, the negative electrode active material of the negative electrode active layer comprising a silicon-carbon composite material; the silicon-carbon composite material comprises a silicon material and a carbon material, the silicon material being distributed inside the carbon material or the carbon material being distributed inside the silicon material; in the electrolyte, the mass percentage of fluoroethylene carbonate (FEC) in the electrolyte is less than or equal to 10%.

[0007] In the lithium ion battery cell, the use of silicon material in the negative active material can improve the energy density of the battery cell. Since the silicon material generally has a large expansion rate, more FEC film-forming additives need to be used to improve the film-forming performance so that the battery cell has good cycle performance. However, FEC is sensitive to moisture in the battery and is prone to side reactions with water to deteriorate battery performance. Lithium-containing phosphates generally contain more moisture. This makes it difficult for lithium-containing phosphates, silicon materials, and FEC to be effectively compatible. In the lithium ion battery cell of the present application, the carbon material in the silicon-carbon composite material can provide a certain buffering effect for the expansion of the silicon material, so that the silicon-carbon composite material has a lower expansion rate than the traditional silicon material, especially when the silicon material in the silicon-carbon composite material is distributed inside the carbon material or the carbon material is distributed inside the silicon material, the silicon-carbon composite material has a lower expansion rate. Therefore, the silicon-carbon composite material can reduce the dependence of silicon material on FEC on the basis of improving the energy density of the battery cell, so that the amount of FEC in the electrolyte can be reduced to less than 10%. When the amount of FEC is reduced, the compatibility of FEC with lithium-containing phosphates is improved. Therefore, in the lithium ion battery cell of the present application, lithium-containing phosphates, silicon materials, and FEC can be effectively compatible, thereby enabling lithium ion batteries containing lithium-containing phosphates to have both high energy density and good cycle performance.

[0008] In some embodiments, the carbon material includes a carbon base, and the carbon base includes a porous carbon material and / or a fibrous carbon material. The porous carbon material and / or the fibrous carbon material can provide more attachment sites for the silicon material, facilitate buffering of the expansion of the silicon material, and be conducive to further reducing the expansion of the silicon-carbon composite material.

[0009] In some embodiments, the silicon-carbon composite material includes a porous carbon material and silicon material located in the pores of the porous carbon material. The porous carbon material can provide a certain buffering effect for the expansion of the silicon material, reduce the overall expansion rate of the silicon-carbon composite material, further reduce the dependence of the silicon-carbon composite material on fluoroethylene carbonate, and better promote the compatibility of the silicon-carbon composite material with lithium-containing phosphates.

[0010] In some embodiments, the porous carbon material includes a porous hard carbon. The porous hard carbon can provide good support for the expansion of the silicon material, reduce the overall expansion rate of the silicon-carbon composite material, and further promote the compatibility of the silicon-carbon composite material with lithium-containing phosphates. In addition, the porous hard carbon can maintain good particle integrity during the cycle of the battery cell, has a low risk of breaking and pulverizing, and can promote the improvement of the cycle performance of the battery cell.

[0011] In some embodiments, the specific surface area of the porous carbon material is 1350 square meters per gram (m2 / g) to 2200 m2 / g. The specific surface area of the porous carbon material in this range can provide suitable attachment sites for the silicon material, so that the negative electrode sheet maintains a relatively stable structure during the cycle process, which is conducive to improving the cycle performance of the battery cell.

[0012] In some embodiments, the pore volume of the porous carbon material is 0.55 cubic centimeters per gram (cm3 / g) to 1 cm3 / g, and optionally, the pore volume of the micropores with a pore size less than or equal to 2 nanometers (nm) in the porous carbon material is 0.4 cm3 / g to 0.8 cm3 / g. The pore volume of the porous carbon in this range can promote the uniform growth of the silicon material, so that the distribution of the silicon material in the silicon-carbon composite material has better uniformity, so that the negative electrode sheet maintains a relatively stable structure during the cycle process, which is conducive to maintaining the good cycle performance of the battery cell. Further optionally, the average pore size of the pores of the porous carbon material is 1.5 nm to 5 nm.

[0013] In some embodiments, the mass percentage of the silicon material in the silicon-carbon composite material is 32% to 55%. The mass percentage of the silicon material in the silicon-carbon composite material in this range can make the silicon-carbon composite material have a higher energy density, while controlling the overall expansion rate of the silicon-carbon composite material in a more suitable range, further reducing the dependence on fluoroethylene carbonate, and promoting the compatibility between the lithium-containing phosphate and fluoroethylene carbonate.

[0014] In some embodiments, the silicon material includes elemental silicon. Optionally, the grain size of the elemental silicon is less than or equal to 5.5 nm. The elemental silicon has a higher initial efficiency, which can promote the improvement of the initial efficiency of the battery cell.

[0015] In some embodiments, the silicon-carbon composite material further includes a carbon coating layer, and the carbon coating layer at least coats the surface of the silicon material or the carbon substrate. By coating the silicon material with the carbon coating layer, the contact between the electrolyte and the silicon material can be reduced, the exposure of new silicon interfaces during the cycle process is reduced, and the dependence of the silicon-carbon composite material on fluoroethylene carbonate is further reduced, which promotes the compatibility of the silicon-carbon composite material with the lithium-containing phosphate. Optionally, the silicon material is located between the carbon substrate and the carbon coating layer.

[0016] In some embodiments, the silicon-carbon composite material includes a fibrous carbon material and nano-silicon particles and / or nano-silicon layers distributed on the fibrous carbon material.

[0017] In some embodiments, the mass percentage of fluoroethylene carbonate in the electrolyte is 1% to 10%. Using less fluoroethylene carbonate can make the lithium-containing phosphate and the silicon-carbon composite material better compatible, can control the consumption of active lithium while giving full play to the advantages of the lithium-containing phosphate and the silicon-carbon composite material, and achieve a better initial coulombic efficiency. Alternatively, the mass percentage of fluoroethylene carbonate in the electrolyte is 3% to 8%.

[0018] In some embodiments, the electrolyte contains a cyclic carbonate, and the mass percentage of fluoroethylene carbonate in the electrolyte is 0.

[0019] In some embodiments, the unit volume capacity of the negative electrode sheet is 500 milliampere-hour per cubic centimeter (mAh / cm 3 ) to 880 mAh / cm 3 , and the unit volume capacity of the negative electrode sheet is the product of the density of the negative electrode active layer and the gram capacity of the negative electrode active material. Setting the unit volume capacity of the negative electrode sheet in a more appropriate range can make the battery cell have both high energy density and high initial coulombic efficiency.

[0020] In some embodiments, the density of the negative electrode active layer is 1.5 grams per cubic centimeter (g / cm 3 ) to 1.75 g / cm 3 , and the density of the negative electrode active layer is 1.55 g / cm 3 to 1.6 g / cm 3 .

[0021] In some embodiments, the mass percentage of the silicon-carbon composite material in the negative electrode active material is 1% to 5%.

[0022] In some embodiments, the negative electrode active material further includes graphite, and the mass ratio of the graphite and the silicon-carbon composite material is 99:1 to 95:5.

[0023] In some embodiments, the unit volume capacity of the negative electrode sheet is 500 mAh / cm 3 to 600 mAh / cm 3 , the electrolyte contains a cyclic carbonate, and the mass percentage of fluoroethylene carbonate in the electrolyte is 0. When the unit volume capacity of the negative electrode sheet is low, the density of the negative electrode active layer and / or the mass percentage of the silicon-carbon composite material in the negative electrode active material is low. At this time, in the negative electrode sheet, the low density of the active layer can make the negative electrode sheet have high porosity and can make the negative electrode sheet exhibit good kinetic performance. At the same time, the low mass percentage of the silicon-carbon composite material in the negative electrode active material can reduce the dependence on fluoroethylene carbonate, and even no fluoroethylene carbonate can be used. When no fluoroethylene carbonate is used, the battery cell can have a high initial coulombic efficiency.

[0024] In some embodiments, the density of the negative electrode active layer is 1.35 g / cm³. 3 ~1.6g / cm 3 Optionally, it can be 1.45 g / cm³. 3 ~1.55g / cm 3 .

[0025] In some embodiments, the silicon-carbon composite material accounts for more than 5% and less than or equal to 10% of the mass percentage of the negative electrode active material.

[0026] In some embodiments, the negative electrode active material further includes graphite, and the mass ratio of the graphite and silicon-carbon composite material is greater than or equal to 90:10 and less than 95:5.

[0027] In some implementations, the volumetric capacity of the negative electrode is greater than 600 mAh / cm³. 3 And less than or equal to 670mAh / cm 3 The mass percentage of fluoroethylene carbonate in the electrolyte is greater than 0 and less than or equal to 3%. In this case, the volumetric capacity of the negative electrode can be greater than 600 mAh / cm³. 3 And less than or equal to 670mAh / cm 3 The corresponding system enables the battery cell to have a high initial coulombic efficiency.

[0028] In some embodiments, the density of the negative electrode active layer is 1.3 g / cm³. 3 ~1.6g / cm 3 Optionally, it can be 1.4 g / cm³. 3 ~1.55g / cm 3 .

[0029] In some embodiments, the silicon-carbon composite material accounts for a mass percentage of more than 10% and less than or equal to 25% of the negative electrode active material.

[0030] In some embodiments, the negative electrode active material further includes graphite, and the mass ratio of the graphite and silicon-carbon composite material is greater than or equal to 75:25 and less than 90:10.

[0031] In some implementations, the volumetric capacity of the negative electrode is greater than 670 mAh / cm³. 3 And less than or equal to 880mAh / cm 3 The mass percentage of fluoroethylene carbonate in the electrolyte is greater than 3% and less than or equal to 10%. In this case, the volumetric capacity of the negative electrode can be greater than 670 mAh / cm³. 3 And less than or equal to 880mAh / cm 3The corresponding system makes the battery monomer have a higher first coulomb efficiency. Optionally, the mass percentage of fluoroethylene carbonate in the electrolyte is 5% to 8%.

[0032] In some embodiments, the silicon-carbon composite material has a gram capacity of 1400 mAh / g to 2300 mAh / g. When the silicon-carbon composite material has a gram capacity of 1400 mAh / g to 2300 mAh / g, the volume energy density and cycle life of the battery monomer can be better balanced. Optionally, the silicon-carbon composite material has a gram capacity of 1600 mAh / g to 2000 mAh / g.

[0033] In some embodiments, the silicon-carbon composite material has a Dv50 of 3 microns (μm) to 15 μm. When the silicon-carbon composite material has a Dv50 of 3 μm to 15 μm, the battery monomer can have better cycle performance. Optionally, the silicon-carbon composite material has a Dv50 of 6 μm to 10 μm.

[0034] In some embodiments, the negative electrode active material further includes graphite. Optionally, the mass percentage of graphite in the negative electrode active material is 75% to 99%.

[0035] In some embodiments, the graphite has a Dv50 of 5 μm to 20 μm, and optionally 10 μm to 18 μm.

[0036] In some embodiments, the lithium-containing phosphate includes at least one of lithium iron phosphate, a composite of lithium iron phosphate and carbon, lithium manganese iron phosphate, and a composite of lithium manganese iron phosphate and carbon.

[0037] In some embodiments, the positive electrode active layer has a density of 2.3 g / cm 3 to 2.9 g / cm 3 . The density of the positive electrode active layer in this range can make the positive electrode sheet have a higher unit volume capacity, and also enable the positive electrode sheet to maintain a relatively stable structure during cold pressing, reducing the risk of damage to the positive electrode sheet. At the same time, the density of the positive electrode active layer in this range can make the battery monomer have a higher first coulomb efficiency. Optionally, the density of the positive electrode active layer is 2.6 g / cm 3 to 2.8 g / cm 3 .

[0038] In some embodiments, the lithium-containing phosphate has a water content of 200 parts per million (ppm) to 300 ppm. The water in the lithium-containing phosphate is difficult to be completely removed. During the cycling of the battery cell, the water is prone to react with water to produce byproducts and consume active lithium, resulting in a decrease in the first coulombic efficiency of the battery cell. Generally, FEC needs to be added to the electrolyte to improve the stability of the solid electrolyte interface film (SEI film) in the battery cell using silicon material. In the embodiments of the present application, FEC can be used without or in a small amount, so that the silicon-carbon composite material and the lithium-containing phosphate can be well adapted, and the battery cell can have a high first coulombic efficiency while improving the energy density of the battery cell.

[0039] In some embodiments, the lithium salt in the electrolyte includes at least one of a fluorine-containing lithium phosphate salt and a fluorine-containing lithium sulfonimide salt.

[0040] In some embodiments, the fluorine-containing lithium phosphate salt includes lithium hexafluorophosphate.

[0041] In some embodiments, the fluorine-containing lithium sulfonimide salt includes at least one of lithium bisfluorosulfonimide and lithium bistrifluoromethylsulfonimide.

[0042] The second aspect of the present application provides a lithium ion battery. The battery includes a battery cell.

[0043] The third aspect of the present application provides a power utilization device. The power utilization device includes a lithium ion battery. BRIEF DESCRIPTION OF DRAWINGS

[0044] For better description and illustration of the embodiments or examples provided by the present application, one or more drawings can be referred to. Additional details or examples used to describe the drawings should not be considered as limiting the scope of the disclosed application, the presently described embodiments or examples, and any one of the best modes of the application presently understood. Moreover, the same reference numerals are used to represent the same components throughout the drawings. In the drawings:

[0045] FIG. 1 is a schematic diagram of a silicon-carbon composite material according to an embodiment of the present application.

[0046] FIG. 2 is a schematic diagram of a silicon-carbon composite material according to another embodiment of the present application.

[0047] FIG. 3 is a schematic diagram of a battery cell according to an embodiment of the present application.

[0048] FIG. 4 is an exploded view of the battery cell according to an embodiment of the present application shown in FIG. 3.

[0049] FIG. 5 is a schematic diagram of a power utilization device using the battery cell according to an embodiment of the present application as a power source.

[0050] Explanation of reference signs: 1, battery cell; 11, case; 12, electrode assembly; 13, cover plate; 2, electric device; 3, silicon-carbon composite material; 31, porous carbon material; 311, pore; 32, silicon material; 4, silicon-carbon composite material; 41, fibrous carbon material; 42, nano-silicon particle; 43, nano-silicon layer. DETAILED DESCRIPTION

[0051] For the purposes of this application, reference will be made to the accompanying drawings in which the preferred embodiments of the application are illustrated. The application may, however, be embodied in many different forms and should not be construed as limited to the embodiments set forth herein. Rather, these embodiments are provided so that this disclosure will be thorough and complete, and fully convey the scope of the application to those skilled in the art.

[0052] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this application belongs. The terminology used in the description of the application herein is for the purpose of describing particular embodiments only and is not intended to be limiting of the application. As used herein, the term "and / or" includes any and all combinations of one or more of the associated listed items.

[0053] "Ranges" disclosed herein are to be understood to be shorthand for describing a group of sub-ranges ranging from the lower limit of the range up to a second arbitrary sub-range within the disclosed range, and thereafter up to the upper limit of the range. This is because the end values of the sub-ranges are used only to define the boundary of the range itself, and they are not to be interpreted as also representing possible or even preferred sub-ranges. In other words, all statements in the specification that contain a numerical range should be interpreted to apply to the broader range as well as to the individual sub-ranges. For example, a statement that a range or sub-range "A to B" should be interpreted to apply to the broader range of "A to B," and to the individual sub-ranges "A to C," "A to D," "C to B," and "D to B," where C and D are real numbers between A and B. The statement "A to B" is not to be interpreted as a preference for A to B over C to B or D to B, even though this is the only range that can be explicitly recited.

[0054] In the present application, "a plurality of", "a plurality of kinds", and the like, if not specifically limited, refer to a number greater than 2 or equal to 2. For example, "one or more" means one or more than two.

[0055] If not specifically stated, all embodiments and optional embodiments of the present application can be combined with each other to form new technical solutions.

[0056] In the present application, the phrase "embodiments" means that the specific features, structures or properties described in connection with the embodiments can be included in at least one embodiment or embodiment of the present application. The appearance of this phrase in various places in the specification does not necessarily refer to the same embodiment, nor is it an independent or alternative embodiment to other embodiments. Those skilled in the art understand explicitly and implicitly that the embodiments described herein can be combined with other embodiments. The phrase "embodiments" in the present application has a similar understanding.

[0057] Those skilled in the art can understand that in the method of each embodiment or embodiment, the writing order of each step does not mean 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. If not specifically stated, all steps of the present application can be performed sequentially or randomly. For example, the method comprises steps (a) and (b), which means that the method can comprise steps (a) and (b) performed sequentially, or steps (b) and (a) performed sequentially. For example, the method can also include step (c), which means that step (c) can be added to the method in any order, for example, the method can include steps (a), (b) and (c), or steps (a), (c) and (b), or steps (c), (a) and (b), etc.

[0058] In the present application, the open technical features or technical solutions described by the words "contain", "include", "comprise" and the like, if not otherwise stated, do not exclude additional members from the listed members, which can be considered as providing both a closed feature or solution composed of the listed members, and an open feature or solution including additional members in addition to the listed members. For example, A includes a1, a2 and a3, if not otherwise stated, it can also include other members, or it can not include additional members, which can be considered as providing the feature or solution that "A is composed of a1, a2 and a3", and also providing the feature or solution that "A includes a1, a2 and a3, and also includes other members".

[0059] In the present application, "A, such as B", if not otherwise stated, means that B is a non-limiting example of A, and it can be understood that A is not limited to B.

[0060] In the present application, "optionally", "optional" or "option" means optional, i.e. selected from either of the two parallel schemes "with" or "without". If there are multiple "optionally" in a technical solution, each "optionally" is independent of each other unless otherwise specified, and there is no contradiction or mutual restriction.

[0061] An embodiment of the present application provides a lithium ion battery cell. The battery cell comprises a positive electrode sheet, a negative electrode sheet and an electrolyte. The positive electrode sheet comprises a positive electrode current collector and a positive electrode active layer on at least one surface of the positive electrode current collector, and the positive electrode active material of the positive electrode active layer comprises lithium-containing phosphate. The negative electrode sheet comprises a negative electrode current collector and a negative electrode active layer on at least one surface of the negative electrode current collector, and the negative electrode active material of the negative electrode active layer comprises a silicon-carbon composite material. The silicon-carbon composite material comprises a silicon material and a carbon material, and the silicon material is distributed inside the carbon material or the carbon material is distributed inside the silicon material. In the electrolyte, the mass percentage of fluoroethylene carbonate in the electrolyte is less than or equal to 10%.

[0062] The silicon material has a high gram capacity, and the use of the silicon material in the negative electrode active material can improve the energy density of the battery cell. Since the silicon material generally has a large expansion rate, a large amount of FEC film-forming additive is required to improve the film-forming performance so that the battery cell has good cycle performance. However, FEC is sensitive to moisture in the battery and is prone to side reactions with water to deteriorate battery performance. Lithium-containing phosphate generally contains a large amount of moisture. Thus, it is difficult to effectively compatibilize lithium-containing phosphate, silicon material and FEC. In the present embodiment, the carbon material in the silicon-carbon composite material can buffer the expansion of the silicon material to some extent, so that the silicon-carbon composite material has a lower expansion rate than the traditional silicon material, and especially when the silicon material is distributed inside the carbon material or the carbon material is distributed inside the silicon material, the silicon-carbon composite material has a lower expansion rate. Therefore, the silicon-carbon composite material can reduce the dependence of silicon material on FEC on the basis of improving the energy density of the battery cell, so that the amount of FEC in the electrolyte can be reduced to less than 10%. When the amount of FEC is reduced, the compatibility of FEC with lithium-containing phosphate is improved. Therefore, in the lithium ion battery cell of the present application, lithium-containing phosphate, silicon material and FEC can be effectively compatibilized, and thus a lithium ion battery comprising lithium-containing phosphate can have both high energy density and good cycle performance.

[0063] Further, in the present embodiment, the amount of FEC is small, the amount of byproduct produced by the reaction of FEC with water and the consumption of active lithium are small, and thus the battery cell can maintain a high initial coulombic efficiency.

[0064] It can be understood that in the embodiment, the silicon material is distributed inside the carbon material or the carbon material is distributed inside the silicon material, wherein the "inside" can be in the pores of the material, at the surface folds, recesses, or inside the solid material, etc.

[0065] Optionally, the FEC accounts for 0, 0.5%, 1%, 1.5%, 2%, 2.5%, 3%, 3.5%, 4%, 4.5%, 5%, 5.5%, 6%, 6.5%, 7%, 7.5%, 8%, 8.5%, 9%, 9.5%, 10% or any value within the range formed by any two of the above values of the mass percentage of FEC in the electrolyte. The mass percentage of FEC in the electrolyte is selected within the range of less than or equal to 10%, which can make the battery cell have better negative electrode film-forming property and lower side reaction, and promote the improvement of the energy density of the battery cell and the maintenance of higher initial efficiency.

[0066] In some embodiments, the carbon material includes a carbon base, and the carbon base includes a porous carbon material and / or a fibrous carbon material. The porous carbon material and / or the fibrous carbon material can provide more attachment sites for the silicon material, facilitate the buffering of the expansion of the silicon material, and be conducive to further reducing the expansion of the silicon-carbon composite material. As an example, the fibrous carbon material can be in the form of a wire, a tube, a rod, etc. Specifically, the fibrous carbon material can be a carbon nanotube, a carbon nanofiber, or a composite structure formed by any combination thereof.

[0067] Referring to FIG. 1, in some embodiments, the silicon-carbon composite material 3 includes a porous carbon material 31 and a silicon material 32 located in the pores 311 of the porous carbon material 31. The porous carbon material can provide a certain buffering for the expansion of the silicon material, reduce the overall expansion rate of the silicon-carbon composite material, further reduce the dependence of the silicon-carbon composite material on FEC, and better promote the compatibility of the silicon-carbon composite material with the lithium-containing phosphate. At the same time, the reduction of the overall expansion rate of the silicon-carbon composite material can reduce the expansion of the negative electrode sheet during the cycle process, so that the negative electrode sheet can maintain a relatively stable structure during the cycle process, thereby being conducive to maintaining good cycle performance of the battery cell.

[0068] Optionally, the porous carbon material includes a porous hard carbon. The porous hard carbon can provide good support for the expansion of the silicon material, reduce the overall expansion rate of the silicon-carbon composite material, and further promote the compatibility of the silicon-carbon composite material with the lithium-containing phosphate. In addition, the porous hard carbon can also maintain good particle integrity during the cycle process of the battery cell, and has a low risk of breaking and pulverizing, which can promote the improvement of the cycle performance of the battery cell.

[0069] In some embodiments, the specific surface area of ​​the porous carbon material is between 1350 m² / g and 2200 m² / g. Within this range, the specific surface area of ​​the porous carbon material can provide suitable attachment sites for the silicon material, allowing the negative electrode to maintain a relatively stable structure during cycling, which is beneficial for improving the cycle performance of the battery cell. Optionally, the specific surface area of ​​the porous carbon material can be 1350 m² / g or 1400 m² / g. 2 / g, 1500m 2 / g, 1600m 2 / g、1700m 2 / g, 1800m2 / g, 1900m2 / g, 2000m2 / g, 2100m2 / g, 2200m2 / g, and any value within the range of any two of the above values.

[0070] In some embodiments, the pore volume of the porous carbon material is 0.55 cm³ / g to 1 cm³ / g. 3 / g. Optionally, the pore volume of micropores with a pore size less than or equal to 2 nm in the porous carbon material is 0.4 cm³. 3 / g~0.8cm 3 / g. The pore volume of porous carbon within this range can promote the uniform growth of silicon materials, resulting in better uniformity of silicon material distribution in silicon-carbon composites. This allows the negative electrode sheet to maintain a relatively stable structure during cycling, thus contributing to better cycle performance of the battery cell. Optionally, the pore volume of the porous carbon material can be 0.55 cm³. 3 / g, 0.6cm 3 / g, 0.65cm 3 / g, 0.7cm 3 / g, 0.75cm 3 / g, 0.8cm 3 / g, 0.85cm 3 / g, 0.9cm 3 / g, 0.95cm³ / g, 1cm 3 / g and any value within the range formed by any two of the above values. Further optionally, the pore volume of micropores with a pore size less than or equal to 2 nm in the porous carbon material can be 0.4 cm³. 3 / g, 0.45cm 3 / g, 0.5cm 3 / g, 0.55cm 3 / g, 0.6cm 3 / g, 0.65cm 3 / g, 0.7cm³ / g, 0.75cm 3Further optionally, the average pore size of the pores of the porous carbon material is 1.5 nm to 5 nm. Optionally, the average pore size of the pores of the porous carbon material can be 1.5 nm, 2 nm, 2.5 nm, 3 nm, 3.5 nm, 4 nm, 4.5 nm, 5 nm, and any value within a range defined by any two of the aforementioned values.

[0071] In some embodiments, the silicon-carbon composite material includes carbon nanofibers and a silicon material on the carbon nanofibers. Further, the silicon-carbon composite material includes carbon nanotubes. The addition of carbon nanotubes can improve the stability of the structure of the silicon-carbon composite material.

[0072] In some embodiments, the silicon material accounts for 32% to 55% of the mass percentage of the silicon-carbon composite material. The mass percentage of the silicon material in the silicon-carbon composite material within this range can allow the silicon-carbon composite material to have a higher energy density, while controlling the overall expansion rate of the silicon-carbon composite material within a more suitable range, further reducing the dependence on FEC, and promoting the compatibility between the lithium-containing phosphate and FEC. Optionally, the mass percentage of the silicon material in the silicon-carbon composite material can be 32%, 35%, 40%, 45%, 50%, 55%, and any value within a range defined by any two of the aforementioned values.

[0073] In some embodiments, the silicon material includes elemental silicon, which has a high first efficiency and can promote the improvement of the first efficiency of the battery cell. Optionally, the silicon material includes nanometer elemental silicon. Further optionally, the nanometer elemental silicon has a grain size of less than or equal to 5.5 nm.

[0074] Further, the silicon-carbon composite material further includes a carbon coating layer, which at least coats the surface of the silicon material or the carbon substrate. By coating the silicon material with the carbon coating layer, the contact between the electrolyte and the silicon material can be reduced, the exposure of new silicon interfaces during the cycle process can be reduced, the dependence of the silicon-carbon composite material on FEC can be further reduced, and the compatibility between the silicon-carbon composite material and the lithium-containing phosphate can be promoted. Optionally, the silicon material is located between the carbon substrate and the carbon coating layer.

[0075] In some embodiments, the silicon-carbon composite material can be prepared by depositing the silicon material in the pores of the porous carbon material through gas phase deposition.

[0076] Optionally, the method for preparing the silicon-carbon composite material comprises the following steps: heating the porous carbon material in a reactor to 500 degrees Celsius (℃) under an argon atmosphere, and maintaining the temperature for 2 hours (h) to desorb the air adsorbed in the porous carbon. A mixture of silane and argon gas is introduced into the reactor at a flow rate of 4 liters per minute (L / min), wherein the volume ratio of silane to argon is 1:4. Then, the temperature of the reactor is increased to 600℃, and a mixture of acetylene and argon gas is introduced into the reactor at a flow rate of 3 L / min, wherein the volume ratio of acetylene to argon is 1:4, to perform coating treatment on the silicon-carbon particles. In some embodiments, the silicon-carbon composite material prepared has a first cycle disengagement capacity of 1400 mAh / g to 2300 mAh / g.

[0077] Referring to FIG. 2, in some embodiments, the silicon-carbon composite material 4 comprises a fibrous carbon material 41, and nano-silicon particles 42 and / or a nano-silicon layer 43 distributed on the fibrous carbon material 41.

[0078] In some embodiments, the fluorinated ethylene carbonate accounts for 1% to 10% of the mass percentage of the electrolyte. Using less fluorinated ethylene carbonate can make the lithium-containing phosphate and the silicon-carbon composite material better compatible, can control the consumption of active lithium while giving full play to the advantages of the lithium-containing phosphate and the silicon-carbon composite material, and achieve a better first coulombic efficiency. Optionally, the fluorinated ethylene carbonate accounts for 3% to 8% of the mass percentage of the electrolyte. Optionally, when the fluorinated ethylene carbonate accounts for 1% to 10% of the mass percentage of the electrolyte, the electrolyte can further comprise a cyclic carbonate, a chain carbonate, or the like.

[0079] In some embodiments, the electrolyte comprises a cyclic carbonate, and the fluorinated ethylene carbonate accounts for 0% of the mass percentage of the electrolyte.

[0080] In some embodiments, the unit volume capacity of the negative electrode sheet is 500 mAh / cm 3 to 880 mAh / cm 3 The unit volume capacity of the negative electrode sheet is the product of the density of the active layer of the negative electrode sheet and the gram capacity of the negative active material.

[0081] For the battery monomer, the increase of the unit volume capacity of the negative electrode sheet can improve the energy density of the battery monomer. However, due to the composition of the negative electrode sheet, the increase of the unit volume capacity of the negative electrode sheet is often subject to certain constraints. For example, in the negative electrode sheet, the unit volume capacity can be increased by increasing the density of the active layer of the negative electrode sheet and increasing the proportion of silicon-carbon composite material in the negative active material. When the density of the active layer of the negative electrode sheet increases, the degree of extrusion of the silicon-carbon composite material will increase, the risk of crushing of the silicon-carbon composite material will increase, the reaction site will increase to increase the film forming consumption, and the porosity of the negative electrode sheet will also decrease, which may cause the first coulomb efficiency of the battery monomer to decrease. Therefore, setting the unit volume capacity of the negative electrode sheet in a more appropriate range can make the battery monomer have higher energy density and higher first coulomb efficiency. Optionally, the unit volume capacity of the negative electrode sheet is 500 mAh / cm 3 ~ 880 mAh / cm 3 . Further optionally, the unit volume capacity of the negative electrode sheet is 500 mAh / cm 3 , 550 mAh / cm 3 , 600 mAh / cm 3 , 650 mAh / cm 3 , 700 mAh / cm 3 , 750 mAh / cm 3 , 800 mAh / cm 3 , 850 mAh / cm 3 , 880 mAh / cm 3 , and any value within the range formed by any two of the above values. Still further optionally, the unit volume capacity of the negative electrode sheet is 650 mAh / cm 3 ~ 750 mAh / cm 3 Within the range of the unit volume capacity, the battery monomer can exhibit better comprehensive performance in terms of first coulomb efficiency and energy density.

[0082] In some embodiments, the unit volume capacity of the negative electrode sheet can be adjusted by a suitable active layer density and a proportion of silicon-carbon composite material. Optionally, the density of the active layer of the negative electrode sheet is 1.5 g / cm 3 ~ 1.75 g / cm 3 . For example, the density of the active layer of the negative electrode sheet can be 1.5 g / cm 3 , 1.55 g / cm 3 , 1.6 g / cm 3 , 1.65 g / cm 3 , 1.7 g / cm 3 , 1.75 g / cm 3and any value within a range derived from any two of the above values. Further optionally, the density of the active layer of the negative electrode tab is 1.55 g / cm 3 ~ 1.6 g / cm 3 Optionally, the mass percentage of the silicon-carbon composite in the negative electrode active material is 1%~5%. For example, the mass percentage of the silicon-carbon composite in the negative electrode active material can be 1%, 1.5%, 2%, 2.5%, 3%, 3.5%, 4%, 4.5%, 5%, and any value within a range derived from any two of the above values. Further optionally, the negative electrode active material further comprises graphite, and the mass ratio of the graphite and the silicon-carbon composite is 99:1~95:5. For example, the mass ratio of the graphite and the silicon-carbon composite can be 99:1, 98:2, 97:3, 96:4, 95:5, and any ratio within a range derived from any two of the above ratios.

[0083] In some embodiments, the unit volume capacity of the negative electrode tab is 500 mAh / cm 3 ~ 600 mAh / cm 3 The electrolyte comprises a cyclic carbonate, and the mass percentage of the fluoroethylene carbonate in the electrolyte is 0. When the unit volume capacity of the negative electrode tab is low, the density of the active layer of the negative electrode tab and / or the mass percentage of the silicon-carbon composite in the negative electrode active material is low. At this time, in the negative electrode tab, the low active layer density can make the negative electrode tab have high porosity, and can make the negative electrode tab exhibit good kinetic performance. At the same time, the low mass percentage of the silicon-carbon composite in the negative electrode active material reduces the dependence on the fluoroethylene carbonate, and even the fluoroethylene carbonate can not be used. When the fluoroethylene carbonate is not used, the battery monomer can have high initial coulomb efficiency.

[0084] When the mass percentage of the silicon-carbon composite in the negative electrode active material is low, the negative electrode tab can be designed to have a high compaction density to make the battery monomer have a high energy density under the corresponding system when the unit volume capacity of the negative electrode tab is 500 mAh / cm 3 ~ 600 mAh / cm 3 For example, when the mass percentage of the silicon-carbon composite in the negative electrode active material is 1%, the density of the active layer of the negative electrode tab can be set to a high value of 1.75 g / cm 3 When the mass percentage of the silicon-carbon composite in the negative electrode active material is 5%, the density of the active layer of the negative electrode tab can be set to a relatively low value of 1.5 g / cm 3 .

[0085] In some embodiments, the density of the active layer of the negative electrode tab is 1.35 g / cm 3 ~ 1.6 g / cm 3For example, the density of the active layer of the negative electrode can be 1.35 g / cm³. 3 1.4g / cm 3 1.45g / cm 3 1.5g / cm 3 1.55g / cm 3 1.6g / cm 3 And any value within the range formed by any two of the above values. Further optionally, the density of the active layer of the negative electrode is 1.45 g / cm³. 3 ~1.55g / cm 3 Optionally, the silicon-carbon composite material accounts for a mass percentage of greater than 5% and less than or equal to 10% of the negative electrode active material. For example, the mass percentage of silicon-carbon composite material in the negative electrode active material can be 5.1%, 5.5%, 6%, 6.5%, 7%, 7.5%, 8%, 8.5%, 9%, 9.5%, 10%, or any value within the range of any two of the above values. Further optionally, the mass ratio of graphite to silicon-carbon composite material is greater than or equal to 90:10 and less than 95:5. For example, the mass ratio of graphite to silicon-carbon composite material can be 90:10, 91:9, 92:8, 93:7, 94:6, or any ratio within the range of any two of the above ratios.

[0086] In some implementations, the volumetric capacity of the negative electrode is greater than 600 mAh / cm³. 3 And less than or equal to 670mAh / cm 3 The mass percentage of fluoroethylene carbonate in the electrolyte is greater than 0 and less than or equal to 3%. In this case, the volumetric capacity of the negative electrode can be greater than 600 mAh / cm³. 3 And less than or equal to 670mAh / cm 3 The corresponding system enables the battery cell to have a high initial coulombic efficiency.

[0087] It is understandable that the unit volume capacity of the negative electrode is greater than 600mAh / cm³. 3 And less than or equal to 670mAh / cm 3 In the corresponding system, when the mass percentage of silicon-carbon composite material in the negative electrode active material is slightly greater than 5%, the density of the active layer of the negative electrode sheet can be set to a higher value of 1.6 g / cm³. 3 When the silicon-carbon composite material accounts for 10% of the mass of the negative electrode active material, the density of the active layer of the negative electrode sheet can be set to a relatively low value of 1.35 g / cm³. 3 .

[0088] In some embodiments, the density of the active layer of the negative electrode is 1.3 g / cm³. 3 ~1.6g / cm3 For example, the density of the active layer of the negative electrode 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 And any value within the range formed by any two of the above values. Optionally, it is 1.4 g / cm³. 3 ~1.55g / cm 3 Optionally, the silicon-carbon composite material accounts for a mass percentage of greater than 10% and less than or equal to 25% of the negative electrode active material. For example, the mass percentage of silicon-carbon composite material in the negative electrode active material can be 11%, 12%, 15%, 18%, 20%, 22%, 25%, or any value within the range of any two of the above values. Further optionally, the negative electrode active material also includes graphite, and the mass ratio of graphite to silicon-carbon composite material is greater than or equal to 75:25 and less than 90:10. For example, the mass ratio of graphite to silicon-carbon composite material can be 80:20, 83:17, 85:15, 88:12, or any ratio within the range of any two of the above ratios.

[0089] In some implementations, the volumetric capacity of the negative electrode is greater than 670 mAh / cm³. 3 And less than or equal to 880mAh / cm 3 The mass percentage of fluoroethylene carbonate in the electrolyte is greater than 3% and less than or equal to 10%. In this case, the volumetric capacity of the negative electrode can be greater than 670 mAh / cm³. 3 And less than or equal to 880mAh / cm 3 The corresponding system enables the battery cell to exhibit a high initial coulombic efficiency. Optionally, fluoroethylene carbonate accounts for 5% to 8% of the electrolyte by mass.

[0090] It is understandable that the unit volume capacity of the negative electrode is greater than 670mAh / cm³. 3 And less than or equal to 880mAh / cm 3 In the corresponding system, when the mass percentage of silicon-carbon composite material in the negative electrode active material is slightly greater than 10%, the density of the active layer of the negative electrode sheet can be set to a higher value of 1.6 g / cm³. 3 When the silicon-carbon composite material accounts for 25% of the mass of the negative electrode active material, the density of the active layer of the negative electrode sheet can be set to a relatively low value of 1.3 g / cm³. 3 .

[0091] In some embodiments, the silicon-carbon composite has a gravimetric capacity of 1400 mAh / g to 2300 mAh / g. The gravimetric capacity of the silicon-carbon composite is related to the content of the silicon material in the pores of the porous carbon. When the gravimetric capacity of the silicon-carbon composite is 1400 mAh / g to 2300 mAh / g, the volume energy density and the cycle life of the battery cell can be better balanced. Optionally, the gravimetric capacity of the silicon-carbon composite can be 1400 mAh / g, 1500 mAh / g, 1600 mAh / g, 1700 mAh / g, 1800 mAh / g, 1900 mAh / g, 2000 mAh / g, 2100 mAh / g, 2200 mAh / g, 2300 mAh / g, and any value within a range defined by any two of the above values. Further optionally, the gravimetric capacity of the silicon-carbon composite is 1600 mAh / g to 2000 mAh / g.

[0092] In some embodiments, the silicon-carbon composite has a Dv50 of 3 μm to 15 μm. When the Dv50 of the silicon-carbon composite is 3 μm to 15 μm, the battery cell can have better cycle performance. Optionally, the Dv50 of the silicon-carbon composite can be 3 μm, 4 μm, 5 μm, 6 μm, 7 μm, 8 μm, 9 μm, 10 μm, 11 μm, 12 μm, 13 μm, 14 μm, 15 μm, and any value within a range defined by any two of the above values. Further optionally, the Dv50 of the silicon-carbon composite is 6 μm to 10 μm.

[0093] In some embodiments, the negative active material further comprises graphite. Optionally, the mass percentage of graphite in the negative active material is 75% to 99%. Optionally, in the negative active material, when the mass percentage of the silicon-carbon composite in the negative active material is 1% to 5%, the mass percentage of graphite in the negative active material is 95% to 99%. When the mass percentage of the silicon-carbon composite in the negative active material is 5% to 10%, the mass percentage of graphite in the negative active material is 90% to 95%. When the mass percentage of the silicon-carbon composite in the negative active material is 10% to 25%, the mass percentage of graphite in the negative active material is 75% to 90%.

[0094] In some embodiments, the graphite has a Dv50 of 5 μm to 20 μm. Optionally, the Dv50 of the graphite can be 5 μm, 6 μm, 7 μm, 8 μm, 9 μm, 10 μm, 11 μm, 12 μm, 13 μm, 14 μm, 15 μm, 16 μm, 17 μm, 18 μm, 19 μm, 20 μm, and any value within a range defined by any two of the above values. Further optionally, the Dv50 of the graphite is 10 μm to 18 μm.

[0095] In the present application, Dv50 refers to the particle size corresponding to the cumulative particle size distribution number of 50% in the volume cumulative distribution curve, and its physical meaning is that the particles with a particle size smaller than or larger than it account for 50%. As an example, Dv50 can be obtained by referring to the test method of GB / T 19077-2016, using the particle size distribution curve obtained by a laser diffraction particle size distribution measuring instrument Mastersizer 3000.

[0096] In some embodiments, the lithium-containing phosphate includes at least one of lithium iron phosphate, a composite of lithium iron phosphate and carbon, lithium manganese iron phosphate, and a composite of lithium manganese iron phosphate and carbon. Optionally, the lithium-containing phosphate includes a lithium-containing phosphate of olivine structure.

[0097] In some embodiments, the density of the positive electrode active layer is 2.3 g / cm 3 ~ 2.9 g / cm 3 . The density of the positive electrode active layer in this range can make the positive electrode sheet have a higher unit volume capacity, and also enable the positive electrode sheet to maintain a relatively stable structure during cold pressing, reducing the risk of damage to the positive electrode sheet. At the same time, the density of the positive electrode active layer in this range can make the battery monomer have a higher first coulomb efficiency. Optionally, the density of the positive electrode active layer can be any value in the range of 2.3 g / cm 3 , 2.4 g / cm 3 , 2.5 g / cm 3 , 2.6 g / cm 3 , 2.7 g / cm 3 , 2.8 g / cm 3 , 2.9 g / cm 3 and any two of the above values. Further optionally, the density of the positive electrode active layer is 2.6 g / cm 3 ~ 2.8 g / cm 3 .

[0098] In some embodiments, the lithium-containing phosphate has a moisture content of 200 ppm to 300 ppm. It is difficult to completely remove the moisture in the lithium-containing phosphate. During the cycling of the battery cell, these moisture contents are prone to react with water to produce byproducts and consume active lithium, resulting in a decrease in the initial coulombic efficiency of the battery cell. Generally, FEC needs to be added to the electrolyte in a battery cell using silicon material to improve the stability of the solid electrolyte interface film. In these embodiments of the present application, FEC can be used without or in small amounts, so that the silicon-carbon composite material and the lithium-containing phosphate can be well adapted to each other, improving the energy density of the battery cell while ensuring a high initial coulombic efficiency of the battery cell. In some embodiments, the lithium salt in the electrolyte includes at least one of a fluorine-containing lithium phosphate salt and a fluorine-containing lithium sulfonimide salt. Optionally, the fluorine-containing lithium phosphate salt includes lithium hexafluorophosphate. The fluorine-containing lithium sulfonimide salt includes at least one of lithium bisfluorosulfonimide and lithium bistrifluoromethylsulfonimide.

[0099] The present application also provides a lithium ion battery in another embodiment. The battery includes the above-mentioned lithium ion battery cell.

[0100] The present application also provides an electric device in another embodiment. The electric device includes the above-mentioned lithium ion battery.

[0101] The battery cell, battery and electric device of the present application are described below with reference to the accompanying drawings.

[0102] Generally, the battery cell includes a positive electrode sheet, a negative electrode sheet, an electrolyte and a separator. During the charging and discharging of the battery, active ions are inserted and extracted between the positive electrode sheet and the negative electrode sheet. The electrolyte plays a role in conducting ions between the positive electrode sheet and the negative electrode sheet. The separator is arranged between the positive electrode sheet and the negative electrode sheet, mainly playing a role in preventing the short circuit of the positive and negative electrodes, while allowing ions to pass through.

[0103] Positive electrode sheet

[0104] The positive electrode sheet includes a positive current collector and a positive active layer arranged on at least one surface of the positive current collector, the positive active layer including a positive active material.

[0105] As a non-limiting example, the positive current collector has two opposite surfaces in the thickness direction of itself, and the positive active layer is arranged on any one or both of the two opposite surfaces of the positive current collector.

[0106] In some embodiments, the positive current collector can employ a metal foil or a composite current collector. For example, as a metal foil, an aluminum foil can be employed. The composite current collector can include a polymer material base layer and a metal layer formed on at least one surface of the polymer material base layer. The composite current collector can be obtained by forming a metal material on a polymer material base material. Non-limiting examples of the metal material in the positive current collector can include one or more of aluminum, an aluminum alloy, nickel, a nickel alloy, titanium, a titanium alloy, silver, a silver alloy, and the like. Non-limiting examples of the polymer material base material in the positive current collector can include one or more of a polypropylene (PP), a polyethylene terephthalate (PET), a polybutylene terephthalate (PBT), a polystyrene (PS), a polyethylene (PE), and the like.

[0107] In some embodiments, the lithium-containing phosphate can further include one or more of lithium manganese phosphate, a composite material of lithium manganese phosphate and carbon. Alternatively, the positive active material can further include a positive active material for a battery as known in the art. As non-limiting examples, the positive active material can further include one or more of lithium transition metal oxides and respective modified compounds thereof. However, the present application is not limited to these materials, and other conventional materials that can be used as positive active materials for batteries can also be used. These positive active materials can be used alone or in combination of two or more. Examples of the lithium transition metal oxide can include, but are not limited to, one or more of lithium cobalt oxide, lithium nickel oxide, lithium manganese oxide, lithium nickel cobalt oxide, lithium manganese cobalt oxide, lithium nickel manganese oxide, lithium nickel cobalt manganese oxide, lithium nickel cobalt aluminum oxide, and modified compounds thereof. Non-limiting examples of the lithium cobalt oxide can include LiCoO2; non-limiting examples of the lithium nickel oxide can include LiNiO2; non-limiting examples of the lithium manganese oxide can include LiMnO2, LiMn2O4, and the like; non-limiting examples of the lithium nickel cobalt manganese oxide can include LiNi 1 / 3 Co 1 / 3 Mn 1 / 3 O2(abbreviated as NCM 333 ), LiNi 0.5 Co 0.2 Mn 0.3 O2(abbreviated as NCM 523 ), LiNi 0.5 Co 0.25 Mn 0.25 O2(abbreviated as NCM 211 ), LiNi 0.6 Co 0.2 Mn 0.2 O2(abbreviated as NCM 622 ), LiNi 0.8 Co 0.1Mn 0.1 O2 (referred to as: NCM 811 ), etc. Non-limiting examples of lithium nickel cobalt aluminum oxides can include LiNi 0.8 Co 0.15 Al 0.05 O2.

[0108] In some embodiments, the positive electrode active layer further optionally includes a binder. As non-limiting examples, the binder can include one or more of polyvinylidene fluoride (referred to as: PVDF), polytetrafluoroethylene (referred to as: PTFE), a vinylidene fluoride-tetrafluoroethylene-propylene terpolymer, a vinylidene fluoride-hexafluoropropylene-tetrafluoroethylene terpolymer, a tetrafluoroethylene-hexafluoropropylene copolymer, and a fluorine-containing acrylate resin.

[0109] In some embodiments, the positive electrode active layer further optionally includes a conductive agent. As non-limiting examples, the conductive agent can include one or more of super P, acetylene black, carbon black, ketjen black, carbon dots, carbon nanotubes, graphene, and carbon nanofibers.

[0110] In some embodiments, the positive electrode tab can be prepared by dispersing the above-mentioned components for preparing the positive electrode tab, such as the positive electrode active material, the conductive agent, the binder, and any other components, in a solvent to form a positive electrode slurry; coating the positive electrode slurry on at least one side surface of the positive electrode current collector, and after processes such as drying, cold pressing, etc., the positive electrode tab can be obtained. The type of the solvent can be selected from, but is not limited to, any of the aforementioned embodiments, such as N-methyl pyrrolidone (referred to as: NMP). The surface of the positive electrode current collector coated with the positive electrode slurry can be on a single surface of the positive electrode current collector, or on both surfaces of the positive electrode current collector. The surface of the positive electrode current collector coated with the positive electrode slurry can be on a single surface of the positive electrode current collector, or on both surfaces of the positive electrode current collector. The solid content of the positive electrode slurry can be 40% by weight (referred to as: wt%) to 80 wt%. The viscosity of the positive electrode slurry at room temperature can be adjusted to 5000 millipascal-seconds (referred to as: mPa·s) to 25000 mPa·s.

[0111] Negative electrode tab

[0112] The negative electrode tab includes a negative electrode current collector and a negative electrode active layer disposed on at least one surface of the negative electrode current collector, the negative electrode active layer including a negative electrode active material.

[0113] As non-limiting examples, the negative electrode current collector has two opposite surfaces in the thickness direction of itself, and the negative electrode active layer is disposed on any one or both of the two opposite surfaces of the negative electrode current collector.

[0114] In some embodiments, the negative current collector can employ a metal foil or a composite current collector. For example, as a metal foil, a copper foil can be employed. The composite current collector can include a polymer material base layer and a metal layer formed on at least one surface of the polymer material base layer. The composite current collector can be obtained by forming a metal material on a polymer material base layer. Non-limiting examples of the metal material in the negative current collector can include one or more of copper, copper alloy, nickel, nickel alloy, titanium, titanium alloy, silver, silver alloy, and the like. Non-limiting examples of the polymer material base layer in the negative current collector can include one or more of polypropylene (PP), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polystyrene (PS), polyethylene (PE), and the like.

[0115] In some embodiments, the negative active material includes a silicon-carbon composite material and graphite. Optionally, the graphite includes one or more of artificial graphite and natural graphite. Further optionally, the negative active material can also employ a negative active material for a battery known in the art. As a non-limiting example, the negative active material can include one or more of soft carbon, hard carbon, a tin-based material, and lithium titanate, and the like. The tin-based material can include one or more of elemental tin, a tin oxide compound, and a tin alloy. However, the present application is not limited to these materials, and other conventional materials that can be used as a negative active material for a battery can also be used. The negative active material can be used alone or in combination with two or more types.

[0116] In some embodiments, the negative active layer can also optionally include a binder. The binder can 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).

[0117] In some embodiments, the negative active layer can also optionally include a conductive agent. The conductive agent can include one or more of super conductive carbon, acetylene black, carbon black, ketjen black, carbon dots, carbon nanotubes, graphene, and carbon nanofibers.

[0118] In some embodiments, the negative active layer can also optionally include other auxiliary agents, such as a thickening agent, and the like. The thickening agent can include sodium carboxymethyl cellulose (CMC-Na).

[0119] In some embodiments, the negative electrode sheet can be prepared by dispersing the components for preparing the negative electrode sheet, such as the negative electrode active material, the conductive agent, the binder, and any other components, in a solvent, for example, deionized water, to form a negative electrode slurry, coating the negative electrode slurry on at least one side surface of the negative electrode current collector, and drying, cold-pressing, or the like to obtain the negative electrode sheet. The surface of the negative electrode current collector to which the negative electrode slurry is coated can be one surface of the negative electrode current collector or both surfaces of the negative electrode current collector. The solid content of the negative electrode slurry can be 40 wt% to 60 wt%. The viscosity of the negative electrode slurry at room temperature can be adjusted to 2,000 mPa·s to 15,000 mPa·s.

[0120] Electrolyte

[0121] The electrolyte has a function of conducting ions between the positive electrode sheet and the negative electrode sheet. The type of the electrolyte is not particularly limited in the present application, and can be selected as needed. For example, the electrolyte can be liquid, gel, or all-solid.

[0122] In some embodiments, the electrolyte uses an electrolyte solution. The electrolyte solution includes an electrolyte salt and a solvent.

[0123] In some embodiments, the electrolyte salt can include one or more of lithium hexafluorophosphate (LiPF6), lithium tetrafluoroborate (LiBF4), lithium perchlorate (LiClO4), lithium hexafluoroarsenate (LiAsF6), lithium bisfluorosulfonylimide (LiFSI), lithium bis-trifluoromethanesulfonylimide (LiTFSI), lithium trifluoromethanesulfonate (LiTFS), lithium difluorophosphate (LiPO2F2), lithium difluoro-oxalato-borate (LiDFOB), lithium bis-oxalato-borate (LiBOB), lithium difluoro-bis-oxalato-phosphate (LiDFOP), and lithium tetrafluoro-oxalato-phosphate (LiTFOP).

[0124] In some embodiments, the solvent can include ethylene carbonate (EC), the chemical formula of which is propylene carbonate (PC), the chemical formula of which is methyl ethyl carbonate (EMC), diethyl carbonate (DEC), dimethyl carbonate (DMC), dipropyl carbonate (DPC), methyl propyl carbonate (MPC), ethyl propyl carbonate (EPC), butylene carbonate, the chemical formula of which is one or more of fluoroethylene carbonate (abbreviation: FEC), methyl formate, methyl acetate, ethyl acetate, propyl acetate, methyl propionate, ethyl propionate, propyl propionate, methyl butyrate, ethyl butyrate, 1,4-butyrolactone, sulfolane, dimethyl sulfone, methyl ethyl sulfone, and diethyl sulfone.

[0125] Optionally, when the electrolyte contains a cyclic carbonate, the cyclic carbonate can be one or more of EC and PC. When the electrolyte contains a chain carbonate, the chain carbonate can be one or more of EMC, DEC, and DMC.

[0126] In some embodiments, the electrolyte can also optionally include an additive. For example, the additive can include a negative electrode film-forming additive, a positive electrode film-forming additive, and can also include an additive capable of improving certain properties of the battery, such as an additive for improving overcharge performance of the battery, an additive for improving high-temperature or low-temperature performance of the battery, etc.

[0127] In some embodiments, the additive in the electrolyte can also include, but is not limited to, one or more of difluoroethylene carbonate (abbreviation: DFEC), trifluoromethyl ethylene carbonate (abbreviation: TFPC), etc.

[0128] Separator film

[0129] In some embodiments, the secondary battery further includes a separator film. The type of the separator film is not particularly limited in the present application, and any publicly known porous structure separator film having good chemical stability and mechanical stability can be used.

[0130] In some embodiments, the material of the separator film can include one or more of glass fiber, non-woven fabric, polyethylene, polypropylene, and polyvinylidene fluoride. The separator film can be a single-layer film or a multi-layer composite film, and is not particularly limited. When the separator film is a multi-layer composite film, the materials of the respective layers can be the same or different, and are not particularly limited.

[0131] In some embodiments, the thickness of the separator film is 6 μm to 40 μm, and can be optionally 12 μm to 20 μm.

[0132] In some embodiments, the positive electrode sheet, the negative electrode sheet, and the separator film can be used to make an electrode assembly through a winding process or a stacking process.

[0133] In some embodiments, the battery cell can include an outer package. The outer package can be used to package the electrode assembly and the electrolyte described above.

[0134] In some embodiments, the outer packaging of the battery cell can be a hard shell, such as a hard plastic shell, an aluminum shell, a steel shell, etc. The outer packaging of the battery cell can also be a soft pack, such as a pouch soft pack. The material of the soft pack can be plastic, and further, non-limiting examples of the plastic can include one or more of polypropylene, polybutylene terephthalate, and polybutylene succinate, etc.

[0135] The secondary battery includes at least one battery cell. The secondary battery can include one or more battery cells.

[0136] In the present application, unless otherwise specified, the "battery cell" refers to a basic unit capable of realizing mutual conversion between chemical energy and electrical energy, and further, generally includes at least a positive electrode sheet, a negative electrode sheet, and an electrolyte. During the charging and discharging process of the battery, active ions are embedded and extracted between the positive electrode sheet and the negative electrode sheet. The electrolyte plays a role in conducting active ions between the positive electrode sheet and the negative electrode sheet.

[0137] The shape of the battery cell is not particularly limited in the present application, and can be cylindrical, square, or any other shape. For example, FIG. 3 is a battery cell 1 of a square structure as an example.

[0138] In some embodiments, referring to FIG. 4, the outer packaging can include a shell 11 and a cover plate 13. Among them, the shell 11 can include a bottom plate and a side plate connected to the bottom plate, and the bottom plate and the side plate enclose a receiving cavity. The shell 11 has an opening communicating with the receiving cavity, and the cover plate 13 can be provided on the opening to close the receiving cavity. The positive electrode sheet, the negative electrode sheet, and the separator can form an electrode assembly 12 through a winding process or a stacking process. The electrode assembly 12 is packaged in the receiving cavity. The electrolyte is impregnated in the electrode assembly 12. The number of electrode assemblies 12 contained in the battery cell 1 can be one or more, and a person skilled in the art can select according to the actual needs.

[0139] The battery can be a battery module or a battery pack.

[0140] The battery module includes at least one battery cell. The number of battery cells contained in the battery module can be one or more, and a person skilled in the art can select a suitable number according to the application and capacity of the battery module.

[0141] In the battery module, the plurality of battery cells can be arranged in sequence along the length direction of the battery module. Of course, they can also be arranged in any other manner. Further, the plurality of battery cells can be fixed by fasteners.

[0142] Optionally, the battery module can also include a housing having a receiving space, and the plurality of battery cells are received in the receiving space.

[0143] In some embodiments, the battery module described above can also be assembled into a battery pack, and the number of battery modules contained in the battery pack can be one or more, and a person skilled in the art can select a suitable number according to the application and capacity of the battery pack.

[0144] In the battery pack, a battery box and a plurality of battery modules arranged in the battery box can be included. The battery box includes an upper box body and a lower box body, and the upper box body can be arranged on the lower box body and form a closed space for accommodating the battery modules. The plurality of battery modules can be arranged in the battery box in any manner.

[0145] In addition, the application also provides a power utilization device, which includes the battery provided by the application. The battery can be used as a power supply of the power utilization device, or can be used as an energy storage unit of the power utilization device. The power utilization device can include a mobile device, an electric vehicle, an electric train, a ship and a satellite, an energy storage system, etc., but is not limited thereto. Among them, the mobile device can be a mobile phone, a notebook computer, etc.; the electric vehicle can be a pure electric vehicle, a hybrid electric vehicle, a plug-in hybrid electric vehicle, an electric bicycle, an electric scooter, an electric golf cart, an electric truck, etc., but is not limited thereto.

[0146] As the power utilization device, a secondary battery can be selected according to the use requirement thereof.

[0147] FIG. 5 is a power utilization device 2 as an example. The power utilization device is a pure electric vehicle, a hybrid electric vehicle, or a plug-in hybrid electric vehicle, etc. In order to meet the requirement of high power and high energy density of the battery for the power utilization device, a battery pack or a battery module can be used.

[0148] As another example of the device, it can be a mobile phone, a tablet computer, a notebook computer, etc. The device usually requires thinning, and a battery can be used as a power supply.

[0149] In order to make the technical problems, technical solutions and beneficial effects solved by the application clearer, the application will be further described in detail below in combination with embodiments and drawings. Obviously, the described embodiments are only a part of the embodiments of the application, rather than all the embodiments. The description of the at least one exemplary embodiment below is actually only illustrative, but not as any limitation on the application and its application. Based on the embodiments in the application, all other embodiments obtained by a person skilled in the art without creative labor fall within the scope of protection of the application.

[0150] If a specific technology or condition is not specified in the embodiments, it is performed according to the technology or condition described in the literature in the art or according to the product instruction. If the reagent or instrument used is not specified by the manufacturer, it is a conventional product that can be obtained by market purchase.

[0151] Embodiment 1

[0152] (1) Preparation of silicon-carbon composite material

[0153] The porous hard carbon was heated to 500°C in an argon atmosphere in a reactor for 2 hours to desorb the air adsorbed in the porous carbon. A mixture of silane and argon was introduced into the reactor at a flow rate of 4 L / min, with a volume ratio of silane to argon being 1:4, and then the temperature of the rotary kiln was increased to 600°C, and a mixture of acetylene and argon was introduced at a flow rate of 3 L / min, with a volume ratio of acetylene to argon being 1:4 to coat the silicon-carbon particles. The specific surface area of the porous hard carbon was 1650 m 2 / g, the pore volume was 0.78 cm 3 / g, the micropore volume of pores with a pore size of less than or equal to 2 nm was 0.6 cm 3 / g, and the average pore size of the pores was 1.8 nm. The mass percentage of elemental silicon in the silicon-carbon composite material was 47%, the grain size of the elemental silicon was ≤5.5 nm, the gravimetric capacity of the silicon-carbon composite material was 1800 mAh / g, and the Dv50 of the silicon-carbon composite material was 9 μm.

[0154] (2) Preparation of positive electrode sheet

[0155] The positive electrode active material lithium iron phosphate (abbreviation: LiFePO4), the conductive agent acetylene black, and the binder polyvinylidene fluoride were mixed in a weight ratio of 97.9:0.5:1.6, and dissolved in the solvent N-methyl pyrrolidone (abbreviation: NMP) to prepare a positive electrode slurry. The water content of the positive electrode active material lithium iron phosphate was 200 ppm. Then, the positive electrode slurry was coated on the current collector aluminum foil, and after drying, cold pressing, edge cutting, sheet cutting, and striping were performed to obtain a positive electrode sheet. The density of the positive electrode active layer in the positive electrode sheet was 2.8 g / cm 3 .

[0156] (3) Preparation of negative electrode sheet

[0157] The negative electrode active material, the conductive agent carbon black, the thickening agent CMC, the binder, and the single-arm carbon nanotube were mixed in a weight ratio of 96.4:0.5:1:2:0.1, and dissolved in the solvent deionized water to prepare a negative electrode slurry, and the negative electrode slurry was obtained under the action of a vacuum stirrer. Then, the negative electrode slurry was coated on the current collector copper foil, and after drying, cold pressing, edge cutting, sheet cutting, and striping were performed to obtain a negative electrode sheet. The negative electrode active material was a silicon-carbon composite material and artificial graphite. The related parameters of the silicon-carbon composite material and the artificial graphite are shown in Table 1. The Dv50 of the artificial graphite was 16 μm.

[0158] (4) Preparation of electrolyte

[0159] In an argon atmosphere glove box with water content <10 ppm, ethylene carbonate, methyl ethyl carbonate, dimethyl carbonate were mixed in a volume ratio of 3:3:4, then lithium hexafluorophosphate (abbreviation: LiPF6) was uniformly dissolved in the solvent, and then FEC was added to obtain an electrolyte. The molar concentration of LiPF6 in the electrolyte was 1 mol / L, and the mass percentage of FEC in the electrolyte is shown in Table 1.

[0160] (5) Separator film

[0161] A porous polyethylene (abbreviation: PP) film was used as a separator film.

[0162] (6) Preparation of battery monomer

[0163] The positive electrode sheet, the separator film, and the negative electrode sheet were prepared in order, and the separator film was placed between the positive electrode sheet and the negative electrode sheet to play a role of isolation, then the electrode assembly was obtained by winding, hot pressing shaping, and welding. The electrode assembly was placed in a square aluminum shell, vacuum dried, and then injected with an electrolyte, and then placed, formation tested, aged, and capacity tested, and finally a battery monomer with a volume of 0.411 L was obtained.

[0164] Examples 2-14 and Comparative Example 1

[0165] Compared with Example 1, the mass percentage of FEC in the electrolyte, the mass percentage of silicon-carbon composite material in the negative electrode active material, the density of the negative electrode active layer, and the unit volume capacity of the negative electrode sheet were different in Examples 2-14 and Comparative Example 1, and the specific values are shown in Tables 1-5. The density of the positive electrode active layer in Examples 1-13 and Comparative Example 1 was 2.8 g / cm 3 , and the density of the positive electrode active layer in Example 14 was 2.4 g / cm 3 .

[0166] Example 15

[0167] Compared with Example 1, the difference between Example 15 was that the silicon-carbon composite material in Example 1 was replaced by sanding silicon-carbon. The sanding silicon-carbon included silicon material and carbon material coated on the surface of the silicon material. The Dv50 of the sanding silicon-carbon was 9 μm.

[0168] Comparative Example 2

[0169] Compared with Example 1, the difference between Comparative Example 2 was that the silicon-carbon composite material was replaced by equal mass of silicon-oxygen material. The Dv50 of the silicon-oxygen material was 9 μm.

[0170] Test Example

[0171] (1) The unit volume capacity of the negative electrode sheet is tested, and the test method is as follows: the active material layer of any one face of the double-face negative electrode sheet is cleaned, and the remaining single-face negative electrode sheet is punched into a small circular sheet with a radius of 7 millimeters (referred to as mm) using a mold, the area S = 0.49π square millimeters (referred to as mm 2 ), the thickness h of the active layer is tested by using a micrometer, the volume is obtained according to the formula V = Sh, the single-face negative electrode sheet with a volume of V is dried and then transferred to a glove box to make a lithium half-battery, and then the delithiation capacity Q of the above circular sheet is tested by using a Wuhan Blue Electric test device, and finally the unit volume capacity of the negative electrode sheet is obtained by Q ÷ V.

[0172] (2) The first coulombic efficiency and the volume energy density of the battery monomer are tested, and the test method is as follows:

[0173] The battery monomer is placed in a negative pressure environment at 45°C for 20 minutes, and then charged to 20% state of charge (referred to as SOC) at a rate of 0.05 coulomb (referred to as C), and the theoretical cell capacity C can be calculated according to the size of the cathode after winding, and the formation capacity C0 is obtained, and then the battery monomer is placed in an environment at 45°C for 48 hours, and then transferred to a normal temperature and pressure environment and charged to 3.65 volts (referred to as V) at a rate of 0.2C, and then charged to 0.05C at 3.65V, and then the charging capacity C1 is obtained. Finally, discharge to 2V at a rate of 0.1C at normal temperature and pressure, and obtain the discharge capacity C2, and obtain the discharge energy E, the unit of E is watt-hour (referred to as wh).

[0174] The first coulombic efficiency of the battery monomer = C2 ÷ (C0 + C1) * 100%.

[0175] The volume energy density of the battery monomer = E ÷ 0.411.

[0176] (3) The cycle retention rate of the battery monomer is tested, and the test method is as follows:

[0177] The cell is placed in an environment at 25°C, and charged to 80% C2 at a rate of 1C2, and charged to 3.65V at a rate of 0.33C2, and then charged to 0.05C2 at 3.65V, and then discharged to 10% C2 at a rate of 1C, and the above steps are repeated for 9 times, and the discharge capacity C10 is obtained by discharging to 2V in the 10th charging step. Repeat the above steps until the cell is cycled 1000 times to obtain the 2V discharge capacity C1000, and calculate the capacity retention rate of the battery monomer after 1000 cycles. The capacity retention rate = C1000 ÷ C10 * 100%.

[0178] Table 1

[0179] As can be seen from Table 1, when the negative active material comprises the silicon-carbon composite material, the battery cell has higher energy density and better cycle performance when the mass percentage of FEC in the electrolyte is less than or equal to 10%. Further, as can be seen from Example 1 and Example 15, when the silicon-carbon composite material comprises the porous carbon material and the silicon material in the pores of the porous carbon material, the battery cell has better cycle performance while having higher volumetric energy density.

[0180] Table 2

[0181] As can be seen from Table 2, when the mass percentage of the silicon-carbon composite material in the negative active material is 1% to 5% and the mass percentage of FEC in the electrolyte is 0, the battery cell has higher initial coulombic efficiency.

[0182] Table 3

[0183] As can be seen from Table 3, when the mass percentage of the silicon-carbon composite material in the negative active material is greater than 5% and less than or equal to 10% and the mass percentage of FEC in the electrolyte is greater than 0 and less than or equal to 3%, the battery cell has higher initial coulombic efficiency.

[0184] Table 4

[0185] As can be seen from Table 4, when the mass percentage of the silicon-carbon composite material in the negative active material is greater than 10% and less than or equal to 25% and the mass percentage of FEC in the electrolyte is greater than 3% and less than or equal to 10%, the battery cell has higher initial coulombic efficiency.

[0186] Table 5

[0187] As can be seen from Table 5, when the density of the positive active layer is in the appropriate range, the battery cell has higher initial coulombic efficiency.

[0188] The technical features of the above-described embodiments can be combined in any manner. To make the description concise, all possible combinations of the technical features in the above-described embodiments are not described, but it should be considered that any combination of the technical features is within the scope of the present disclosure.

[0189] The above-described embodiments only express several implementation manners of the present application, and the description is relatively specific and detailed, but it should not be understood as a limitation on the patent scope of the present application. It should be noted that, for those skilled in the art, some modifications and improvements can be made without departing from the concept of the present application, and these are within the protection scope of the present application. Therefore, the patent protection scope of the present application should be subject to the appended claims.

Claims

A lithium ion battery cell includes a positive electrode sheet, a negative electrode sheet, and an electrolyte; the positive electrode sheet includes a positive electrode current collector and a positive electrode active layer on at least one surface of the positive electrode current collector, and a positive electrode active material of the positive electrode active layer includes a lithium-containing phosphate; the negative electrode sheet includes a negative electrode current collector and a negative electrode active layer on at least one surface of the negative electrode current collector, and a negative electrode active material of the negative electrode active layer includes a silicon-carbon composite material; the silicon-carbon composite material includes a silicon material and a carbon material, and the silicon material is distributed inside the carbon material or the carbon material is distributed inside the silicon material; The fluorinated ethylene carbonate accounts for less than or equal to 10% of the electrolyte. The lithium-ion battery cell according to claim 1, wherein The carbon material includes a carbon base, and the carbon base includes a porous carbon material and / or a fibrous carbon material. The lithium-ion battery cell according to claim 2, wherein The silicon-carbon composite material includes a porous carbon material and a silicon material in pores of the porous carbon material. The lithium-ion battery cell according to claim 3, wherein The porous carbon material includes a porous hard carbon. The lithium-ion battery cell according to claim 3 or 4, wherein The porous carbon material satisfies at least one of the following characteristics: (1) the specific surface area of the porous carbon material is 1350 m 2 / g ~ 2200 m 2 / g; (2) the porous carbon material has a pore volume of 0.55 cm 3 / g to 1 cm 3 / g; (3) The average pore diameter of the porous carbon material is 1.5 nm to 5 nm. The lithium-ion battery cell according to any one of claims 3 to 5, wherein The micropores in the porous carbon material have a pore volume of 0.4 cm3 / g or less for micropores having a pore diameter of less than or equal to 2 nm 3 / g to 0.8 cm3 / g 3 / g. The lithium-ion battery cell according to any one of claims 3 to 6, wherein The silicon material accounts for 32% to 55% of the silicon-carbon composite material. The lithium-ion battery cell according to any one of claims 3 to 7, wherein The silicon material includes elemental silicon. The lithium-ion battery cell according to claim 8, wherein, The grain size of the elemental silicon is less than or equal to 5.5 nm. The lithium-ion battery cell according to any one of claims 2 to 9, wherein The silicon-carbon composite material further includes a carbon coating layer, and the carbon coating layer at least coats the surface of the silicon material or the carbon base. The lithium-ion battery cell of claim 10, wherein, The silicon material is between the carbon base and the carbon coating layer. The lithium-ion battery cell according to claim 1 or 2, wherein The silicon-carbon composite material includes a fibrous carbon material, and nano-silicon particles and / or a nano-silicon layer are distributed on the fibrous carbon material. The lithium-ion battery cell according to any one of claims 1 to 12, wherein The fluorinated ethylene carbonate accounts for 1% to 10% of the electrolyte. The lithium-ion battery cell of claim 13, wherein, The fluorinated ethylene carbonate accounts for 3% to 8% of the electrolyte. The lithium-ion battery cell according to any one of claims 1 to 12, wherein The electrolyte contains a cyclic carbonate, and the fluorinated ethylene carbonate accounts for 0% of the electrolyte. The lithium-ion battery cell according to any one of claims 1 to 12, wherein The unit volume capacity of the negative electrode tab is 500 mAh / cm 3 ~ 880 mAh / cm 3 The unit volume capacity of the negative electrode tab is the product of the density of the negative electrode active layer and the gram capacity of the negative electrode active material. The lithium-ion battery cell of claim 16, wherein, The density of the negative active layer is 1.5 g / cm 3 ~ 1.75 g / cm 3 . The lithium-ion battery cell of claim 17, wherein, The density of the negative active layer is 1.55 g / cm 3 ~ 1.6 g / cm 3 . The lithium-ion battery cell according to claim 17 or 18, wherein The silicon-carbon composite material accounts for 1% to 5% of the negative electrode active material. The lithium-ion battery cell of claim 19, wherein, The negative electrode active material further includes graphite, and the mass ratio of the graphite to the silicon-carbon composite material is 99:1 to 95:

5. The lithium-ion battery cell according to any one of claims 17 to 20, wherein The unit volume capacity of the negative electrode plate is 500 mAh / cm 3 ~ 600 mAh / cm 3 The electrolyte contains a cyclic carbonate, and the mass percentage of the fluoroethylene carbonate in the electrolyte is 0. The lithium-ion battery cell of claim 16, wherein, The density of the negative active layer is 1.35 g / cm 3 ~ 1.6 g / cm 3 . The lithium-ion battery cell of claim 22, wherein, The density of the negative active layer is 1.45 g / cm 3 ~ 1.55 g / cm 3 . The lithium-ion battery cell according to claim 22 or 23, wherein The silicon-carbon composite material accounts for more than 5% and less than or equal to 10% of the negative electrode active material. The lithium-ion battery cell of claim 24, wherein, The negative electrode active material further includes graphite, and the mass ratio of the graphite to the silicon-carbon composite material is more than or equal to 90:10 and less than 95:

5. The lithium-ion battery cell according to any one of claims 22 to 25, wherein The unit volume capacity of the negative electrode plate is greater than 600 mAh / cm 3 and less than or equal to 670 mAh / cm 3 The mass percentage of the fluoroethylene carbonate in the electrolyte is greater than 0 and less than or equal to 3%. The lithium-ion battery cell of claim 16, wherein, The density of the negative active layer is 1.3 g / cm 3 ~ 1.6 g / cm 3 . The lithium-ion battery cell of claim 27, wherein, The density of the negative active layer is 1.4 g / cm 3 ~ 1.55 g / cm 3 . The lithium-ion battery cell according to claim 27 or 28, wherein The silicon-carbon composite material accounts for more than 10% and less than or equal to 25% of the negative electrode active material. The lithium-ion battery cell of claim 29, wherein, The negative electrode active material further includes graphite, and the mass ratio of the graphite to the silicon-carbon composite material is more than or equal to 75:25 and less than 90:

10. The lithium-ion battery cell according to any one of claims 27 to 30, wherein The unit volume capacity of the negative electrode plate is greater than 670 mAh / cm 3 and less than or equal to 880 mAh / cm 3 The mass percentage of the fluoroethylene carbonate in the electrolyte is greater than 3% and less than or equal to 10%. The lithium-ion battery cell of claim 31, wherein, The fluorinated ethylene carbonate accounts for 5% to 8% of the electrolyte. The lithium-ion battery cell according to any one of claims 1 to 32, wherein The silicon-carbon composite material has a gram capacity of 1400 mAh / g to 2300 mAh / g. The lithium-ion battery cell of claim 33, wherein, The silicon-carbon composite material has a gram capacity of 1600 mAh / g to 2000 mAh / g. The lithium-ion battery cell according to any one of claims 1 to 34, wherein The silicon-carbon composite material has a Dv50 of 3 μm to 15 μm. The lithium-ion battery cell of claim 35, wherein, The Dv50 of the silicon-carbon composite material is 6 μm to 10 μm. The lithium-ion battery cell according to any one of claims 1 to 19, 21 to 36, wherein The negative active material further comprises graphite. The lithium-ion battery cell of claim 37, wherein, The mass percentage of the graphite in the negative active material is 75% to 99%. The lithium-ion battery cell according to claim 37 or 38, wherein The Dv50 of the graphite is 5 μm to 20 μm. The lithium-ion battery cell of claim 39, wherein, The Dv50 of the graphite is 10 μm to 18 μm. The lithium-ion battery cell according to any one of claims 1 to 40, wherein The lithium-containing phosphate includes at least one of lithium iron phosphate, a composite of lithium iron phosphate and carbon, lithium manganese iron phosphate, and a composite of lithium manganese iron phosphate and carbon. The lithium-ion battery cell according to any one of claims 1 to 41, wherein The density of the positive electrode active layer is 2.3 g / cm 3 ~ 2.9 g / cm 3 . The lithium-ion battery cell of claim 42, wherein, The density of the positive electrode active layer is 2.6 g / cm 3 ~ 2.8 g / cm 3 . The lithium-ion battery cell according to any one of claims 1 to 43, wherein The moisture content in the lithium-containing phosphate is 200 ppm to 300 ppm. The lithium-ion battery cell according to any one of claims 1 to 44, wherein The lithium salt in the electrolyte includes at least one of a fluorine-containing lithium phosphate salt and a fluorine-containing lithium sulfonimide salt. The lithium-ion battery cell of claim 45, wherein, The fluorine-containing lithium phosphate salt includes lithium hexafluorophosphate. The lithium-ion battery cell according to claim 45 or 46, wherein The fluorine-containing lithium sulfonimide salt includes at least one of lithium bisfluorosulfonimide and lithium bistrifluoromethylsulfonimide. A lithium ion battery cell according to any one of claims 1 to 47. An electric device according to claim 48.

Images