Secondary battery and electric device

Abstract

The application provides a secondary battery and a power utilization device. The secondary battery comprises a negative electrode sheet and an electrolyte, the negative electrode sheet comprises a silicon-carbon composite material with a three-dimensional network cross-linked pore structure, and the electrolyte comprises a lithium sulfoximine salt. Through the cooperation between the three-dimensional network cross-linked pore structure of the silicon-carbon composite material and the lithium sulfoximine salt in the electrolyte, the high-temperature cycle performance and storage performance of the battery are improved.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of secondary batteries, in particular to a secondary battery and a power consumption device. BACKGROUND

[0002] In recent years, secondary batteries are widely used in energy storage power systems such as hydroelectric, thermal, wind and solar power stations, and in many fields such as electric tools, electric bicycles, electric motorcycles, electric vehicles, military equipment, aerospace, etc.

[0003] With the gradual increase of market demand for battery energy, the use of high-capacity electrode materials has become the consensus in the field. However, many electrode materials with high theoretical capacity have poor cycle performance and thermal stability. How to improve the cycle performance of the battery, especially at high temperature, through the mutual cooperation of each component of the battery is a technical problem that needs to be solved in the field. SUMMARY

[0004] The present application is made in view of the above-mentioned problems, and aims to provide a secondary battery. Through the matching of the electrolyte and the negative electrode material, the thermal stability and chemical stability of the electrolyte are improved, and the cycle capacity retention rate and the storage capacity retention rate at high temperature of the battery are improved.

[0005] The first aspect of the present application provides a secondary battery, comprising a negative electrode sheet and an electrolyte, the negative electrode sheet comprising a silicon-carbon composite material with a three-dimensional network cross-linked pore structure; the electrolyte comprising a lithium sulfoximide salt.

[0006] The silicon-carbon composite material with a three-dimensional network cross-linked pore structure has a stable porous framework and good mechanical strength, and can effectively reduce the volume change of silicon before and after charging and discharging while loading a high silicon content. At the same time, the lithium sulfoximide salt can easily enter the pore structure of the silicon-carbon composite material, generating a solid electrolyte film containing sulfur-containing oxides and nitrogen-containing oxides at the silicon-based material interface, thereby improving the high-temperature cycle performance and storage performance of the battery.

[0007] In any embodiment, the pore volume per unit mass of the silicon-carbon composite material is Vm, with a unit of cm 3 / g; in the electrolyte, the mass fraction of the lithium sulfoximide salt based on the total mass of the electrolyte is EL, with a unit of g / g, EL: Vm is 0.1-10, preferably 0.5-6.

[0008] When the ratio EL: Vm between the pore volume Vm of the silicon-carbon composite material and the mass fraction EL of the lithium sulfoximide salt in the electrolyte satisfies the above range, the amount of the lithium sulfoximide salt and the pore volume Vm of the silicon-carbon composite material form a mutual cooperation, which improves the high-temperature cycle performance and high-temperature storage performance of the battery.

[0009] In any embodiment, the pore volume of the silicon-carbon composite material per unit mass is Vm, which is 0.01-0.3, and optionally 0.04-0.15 cm 3 / g.

[0010] When the pore volume of the silicon-carbon composite material satisfies the above range, the mechanical strength thereof can be ensured, the loading amount of silicon can be ensured, and the high-temperature performance of the battery can be improved through effective cooperation with the lithium sulfonylimide salt in the electrolyte.

[0011] In any embodiment, the specific surface area of the silicon-carbon composite material per unit mass is SSA, which is m 2 / g, and in the electrolyte, the mass ratio of the lithium sulfonylimide salt based on the total mass of the electrolyte is EL, which is g / g, and EL:SSA is 0.002-0.2, and optionally 0.01-0.08.

[0012] When the ratio EL:SSA between the mass ratio of the lithium sulfonylimide salt in the electrolyte and the specific surface area SSA of the silicon-carbon composite material satisfies the above range, the lithium sulfonylimide salt can be effectively embedded in the pore structure of the silicon-carbon composite material, fully contact the silicon-carbon composite material, improve the interface stability, and improve the high-temperature performance of the battery.

[0013] In any embodiment, the specific surface area SSA of the silicon-carbon composite material is 2-10 m 2 / g; and optionally 3-7 m 2 / g.

[0014] When the specific surface area SSA of the silicon-carbon composite material satisfies the above range, the specific surface area of the silicon-carbon composite material is large, and the kinetic performance of the material is good.

[0015] In any embodiment, in the electrolyte, the mass ratio of the lithium sulfonylimide salt based on the total mass of the electrolyte is EL, which is g / g, and the total pore volume of pores with a pore size less than or equal to 100 nm in the silicon-carbon composite material is V1 cm 3 / g, and EL:V1 is 1-100, and optionally 7-62.

[0016] When the ratio EL:V1 between the mass ratio EL of the lithium sulfonylimide salt in the electrolyte and the total pore volume V1 of pores with a pore size less than or equal to 100 nm in the silicon-carbon composite material satisfies the above range, the lithium sulfonylimide salt can effectively enter the pore structure of the silicon-carbon composite material, improve the stability of the electrode / electrolyte interface, and thus improve the high-temperature storage life of the battery.

[0017] In any embodiment, V1 of the silicon-carbon composite material is ≥0.001 cm 30.005~0.01 cm 3 / g.

[0018] When V1 of the silicon-carbon composite material satisfies the above range, the silicon-carbon composite material can not only have good mechanical strength, but also effectively cooperate with the lithium sulfonimide salt in the electrolyte, thereby improving the cycle performance of the battery.

[0019] In any embodiment, the lithium sulfonimide salt is represented by Formula I,

[0020] Formula I

[0021] wherein R1, R2 are each independently selected from halogen, halogen-substituted or unsubstituted C1-C6 alkyl.

[0022] In any embodiment, the lithium sulfonimide salt is at least one selected from lithium bisfluorosulfonimide , lithium bistrifluoromethanesulfonimide , lithium (fluorosulfonyl)(trifluoromethylsulfonyl)imide .

[0023] The above lithium sulfonimide salt can not only improve the thermal stability and chemical stability of the electrolyte, but also generate components containing S and N elements in the interfacial film, thereby improving the high-temperature stability of the electrode / electrolyte interface and further improving the high-temperature cycle performance and storage performance of the battery.

[0024] In any embodiment, the silicon-carbon composite material comprises carbon matrix particles and silicon nanoparticles, the carbon matrix particles have a three-dimensional network cross-linked pore structure; and the silicon nanoparticles are at least partially embedded in the three-dimensional network cross-linked pore structure of the carbon matrix particles.

[0025] The carbon matrix particles of the present application have a stable porous framework structure, strong support capacity, high stress capacity, excellent mechanical properties and electrical conductivity; the carbon matrix particles comprise a three-dimensional network cross-linked pore structure, which provides more space for embedding silicon-based nanoparticles, can be used for storing a large amount of silicon, and effectively improves the silicon loading capacity of the silicon-carbon composite material. After the carbon matrix particles are combined with the silicon-based nanoparticles, the electrical conductivity of the silicon-carbon composite material can be improved, the volume effect of silicon during the process of deintercalating lithium can be relieved, the stress change of the silicon-based nanoparticles can be fully borne, the structural stability of the silicon-carbon composite material can be ensured, and the cycle performance and lithium storage capacity of the silicon-carbon composite material can be improved. Therefore, when the silicon-carbon composite material is applied to a secondary battery, the cycle performance and energy density of the secondary battery can be improved.

[0026] In any embodiment, the mass ratio of the silicon nanoparticles in the silicon-carbon composite material is greater than or equal to 40%, and can be 40-60%.

[0027] The negative electrode material of the secondary battery of the present application realizes high loading of silicon nanoparticles in the negative electrode material by using a carbon-based material having a three-dimensional network cross-linked pore structure, so that the silicon-carbon composite material has high capacity and can further improve the energy density of the battery.

[0028] In any embodiment, the silicon nanoparticles comprise one or more of silicon oxide compounds, amorphous silicon, crystalline silicon and silicon-carbon composite.

[0029] In any embodiment, the carbon matrix comprises one or more of graphite, soft carbon and hard carbon.

[0030] In any embodiment, the total volume of pores with a pore size greater than 100 nm in the carbon matrix particles is denoted as Vc1 cm3 / g, and the total volume of pores with a pore size less than or equal to 100 nm in the carbon matrix particles is denoted as Vc2 cm3 / g. 3 In any embodiment, the total volume of pores with a pore size greater than 100 nm in the carbon matrix particles is denoted as Vc1 cm3 / g, and the total volume of pores with a pore size less than or equal to 100 nm in the carbon matrix particles is denoted as Vc2 cm3 / g. 3 In any embodiment, the carbon matrix particles satisfy: 1 < Vc2 / Vc1 ≤ 30; optionally, 3 ≤ Vc2 / Vc1 ≤ 25.

[0031] By adjusting the total pore volume ratio of pores of a specific size in the porous carbon matrix particles, the pore size distribution of the carbon matrix particles can be moderate, which is conducive to the entry of silicon nanoparticles into the pores of the carbon matrix particles, and the silicon-carbon composite material can have a certain mechanical strength, maintain its structural stability during the cycle process, and optimize its cycle performance.

[0032] In any embodiment, the powder compaction density of the silicon-carbon composite material after 1 powder pressing under a force of 20000 N is denoted as P11 g / cm3. 3 The ratio of the compaction density of the silicon-carbon composite material after 20 powder pressings under a force of 20000 N to the compaction density of the silicon-carbon composite material after 1 powder pressing under a force of 20000 N is denoted as P21 / P11. 3 The ratio of the compaction density of the silicon-carbon composite material after 20 powder pressings under a force of 20000 N to the compaction density of the silicon-carbon composite material after 1 powder pressing under a force of 20000 N is denoted as P21 / P11.

[0033] When the ratio of P21 / P11 satisfies the above range, the silicon-carbon composite material has high specific capacity and good pressure resistance, which improves the structural stability of the negative electrode film layer, so that the secondary battery containing the material has high energy density and good cycle performance.

[0034] In any embodiment, the powder compaction density of the silicon-carbon composite material after 1 powder pressing under a force of 20000 N is denoted as P11 g / cm3. 3 The ratio of the compaction density of the silicon-carbon composite material after 20 powder pressings under a force of 20000 N to the compaction density of the silicon-carbon composite material after 1 powder pressing under a force of 20000 N is denoted as P21 / P11.

[0035] The powder compaction density P11 of the silicon-carbon composite material after 1 time of powder pressing under a force of 20,000 N 3 When the above range is satisfied, the negative electrode film layer has a high compaction density, thereby making the secondary battery have a high energy density.

[0036] In any embodiment, the secondary battery includes at least one of a lithium ion battery, a sodium ion battery, a magnesium ion battery, and a potassium ion battery.

[0037] A second aspect of the present application provides an electric device including the secondary battery of the first aspect. BRIEF DESCRIPTION OF DRAWINGS

[0038] Figure 1 is a schematic diagram of a secondary battery according to an embodiment of the present application;

[0039] Figure 2 is Figure 1 is an exploded view of a secondary battery according to an embodiment of the present application;

[0040] Figure 3 is a schematic diagram of an electric device using a secondary battery according to an embodiment of the present application as a power source.

[0041] REFERENCE NUMERALS

[0042] 1 secondary battery; 11 housing; 12 electrode assembly; 13 cover plate. DETAILED DESCRIPTION

[0043] Hereinafter, embodiments of the present application, which specifically disclose a binder, a production method, an electrode, a battery, and an electric device, will be described in detail with appropriate reference to the accompanying drawings. However, there will be cases where unnecessary detailed description is omitted. For example, there will be cases where detailed description of matters that are already well known, repeated description of substantially identical structures, are omitted. This is to avoid the following description from becoming unnecessarily lengthy and to facilitate understanding by those skilled in the art. Furthermore, the accompanying drawings and the following description are provided so that those skilled in the art can fully understand the present application, and are not intended to limit the subject matter recited in the claims.

[0044] The ranges disclosed herein are intended to be "open" ranges, i.e., the upper and lower limits of the range are not included. The ranges are also intended to include any and all sub-ranges of the range, i.e., all combinations of any two of the range limits, unless otherwise indicated. For example, a range of "1 to 10" is intended to include any number from 1 to 10, including the integers 1 and 10. Unless otherwise indicated, the use of "or" in the disclosed aspects herein is the inclusive, and not the exclusive use. Only the context, and not the number of times an item is used, can determine that it is the exclusive use. For example, the phrase "A uses B or C" means that A can use B, or A can use C, or A can use both B and C. Also, the use of the term "one" or "a" or "the" is intended to be singular as well as plural, unless only the singular form is used. For example, the phrase "one or more of A, B, and C" means that A, B, or C can be present, and that one of A, B, and C can be present, and that two of A, B, and C can be present, and that all of A, B, and C can be present.

[0045] All embodiments and optional embodiments of the present application can be combined with each other to form new technical solutions, unless otherwise specified.

[0046] All technical features and optional technical features of the present application can be combined with each other to form new technical solutions, unless otherwise specified.

[0047] All steps of the present application can be performed in sequence or randomly, preferably in sequence, unless otherwise specified. For example, the method comprises steps (a) and (b), which means that the method can comprise steps (a) and (b) in sequence, or steps (b) and (a) in sequence. For example, the method can further comprise step (c), which means that step (c) can be added to the method in any order, for example, the method can comprise steps (a), (b) and (c), or steps (a), (c) and (b), or steps (c), (a) and (b), etc.

[0048] Unless otherwise specified, "includes" and "comprises" mentioned in the present application are open-ended, and can also be closed. For example, "includes" and "comprises" can mean that other components not listed can also be included or contained, or only the listed components can be included or contained.

[0049] If not specifically stated, the term "or" in this application is inclusive. For example, the phrase "A or B" means "A, B, or both A and B." More specifically, any of the following satisfy the condition "A or B": A is true (or present) and B is false (or not present); A is false (or not present) and B is true (or present); or both A and B are true (or present).

[0050] With the popularization of the application range of secondary batteries, the requirements for the performance of secondary batteries, such as energy density, are gradually improved. Silicon-based materials have high specific capacity and are suitable for negative electrode materials of high-energy-density batteries. However, the silicon-based materials have a large volume expansion rate during the charging and discharging process, especially under high-temperature conditions, which leads to the deterioration of the battery performance.

[0051] Based on this, the present application provides a secondary battery, which comprises: a negative electrode sheet and an electrolyte, the negative electrode sheet comprises a silicon-carbon composite material with a three-dimensional network cross-linked pore structure; and the electrolyte comprises a lithium sulfoximine salt.

[0052] In this context, the three-dimensional network cross-linked pore structure generally refers to a structure in which two or more pores are interconnected or interlaced and share pore volume in the pore structure formed by the carbon matrix particles in the silicon-carbon composite material.

[0053] The pore structure of the silicon-carbon composite material can be tested by using devices and methods known in the art. For example, it can be tested by using a scanning electron microscope (such as ZEISS Sigma 300). As an example, the following steps can be performed: first, cut the negative electrode sheet containing the silicon-carbon composite material into a certain size of sample to be tested (for example, 6 mm x 6 mm), clamp the sample to be tested with two pieces of conductive and heat-conductive sheet (such as copper foil), and fix the sample to be tested and the sheet with glue (such as double-sided tape) for a certain period of time (such as 1 hour) with a certain mass (such as about 400 g) of flat iron, so that the gap between the sample to be tested and the copper foil is as small as possible, then trim the edges with scissors, and stick them on the sample stage with conductive glue, and the sample slightly protrudes from the edge of the sample stage. Then, lock the sample stage on the sample holder, turn on the argon ion cross-section polisher (such as IB-19500CP) power and vacuum (for example, 10 Pa -4 Pa), set the argon flow (for example, 0.15 MPa) and voltage (for example, 8 KV) and polishing time (for example, 2 hours), adjust the sample stage to the swing mode to start polishing, and after polishing, use a scanning electron microscope (such as ZEISS Sigma 300) to obtain the ion polishing cross-section morphology (CP) picture of the sample to be tested.

[0054] The silicon-carbon composite material with three-dimensional network cross-linked pore structure has stable porous framework and good mechanical strength, and can effectively reduce the volume change of silicon before and after charging and discharging while loading high silicon content. At the same time, lithium sulfonimide salt can easily enter the pore structure of the silicon-carbon composite material, generating a solid electrolyte film containing sulfur-containing oxides and nitrogen-containing oxides at the silicon-based material interface, thereby improving the high-temperature cycle performance and storage performance of the battery.

[0055] In some embodiments, the pore volume of the silicon-carbon composite material per unit mass is Vm, and the unit is cm 3 / g; in the electrolyte, the mass fraction of the lithium sulfonimide salt in the total mass of the electrolyte is EL, the unit is g / g, and the ratio EL:Vm between the pore volume Vm of the silicon-carbon composite material and the mass fraction EL of the lithium sulfonimide salt in the electrolyte is 0.1-10, preferably 0.5-6.

[0056] In some embodiments, the ratio EL:Vm between the pore volume Vm of the silicon-carbon composite material and the mass fraction EL of the lithium sulfonimide salt in the electrolyte can be selected from 0.1, 0.2, 0.3, 0.4, 0.5, 0.6, 0.7, 0.8, 0.9, 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 or 10.

[0057] The pore volume Vm of the silicon-carbon composite material can be calculated by the following formula: Vm=1 / ρreal×α / (1-α), wherein ρreal represents the true density of the silicon-carbon composite material, and α represents the porosity of the silicon-carbon composite material. The porosity refers to the ratio of the volume of the intragranular pores to the total volume of the carbon matrix particles. The porosity can be measured by the gas displacement method according to GB / T24586. The porosity W=(L1-L2) / L1*100%, wherein L1 is the apparent volume of the sample, and L2 is the true volume of the sample. The true density is the meaning known in the art, which refers to the actual mass of unit volume of solid matter in the state of absolute compaction, i.e. the density after removing the internal voids or intergranular voids of the material; it can be tested by the instruments and methods known in the art. For example, the test method can refer to GB / T 24586-2009, and the test instrument can use a true density tester. As an example, the following steps can be operated: place a clean and dry sample cup on the balance, zero, add a certain amount of powder sample to the sample cup (for example, the sample can occupy 1 / 2 of the volume of the sample cup), record the mass of the sample taken, place the sample cup with the sample in the true density tester, introduce helium gas, detect the pressure of the gas in the sample chamber and the expansion chamber, and then calculate the true volume according to the Boyle's law, and further calculate the true density.

[0058] When the ratio EL:Vm between the mass ratio EL of the lithium sulfonimide salt in the electrolyte and the pore volume Vm of the silicon-carbon composite material satisfies the above range, the amount of the lithium sulfonimide salt added and the pore volume Vm of the silicon-carbon composite material can be matched, and the high-temperature cycle performance and high-temperature storage performance of the battery can be improved.

[0059] In some embodiments, the pore volume per unit mass of the silicon-carbon composite material is Vm, which is 0.01-0.3 cm 3 / g, and can be 0.04-0.15 cm 3 / g.

[0060] In some embodiments, the pore volume per unit mass of the silicon-carbon composite material can be 0.01, 0.015, 0.02, 0.025, 0.03, 0.035, 0.04, 0.045, 0.05, 0.055, 0.06, 0.065, 0.07, 0.075, 0.08, 0.085, 0.09, 0.095, 0.01, 0.015, 0.02, 0.025, or 0.3 cm 3 / g.

[0061] When the pore volume of the silicon-carbon composite material satisfies the above range, the mechanical strength, the load amount of silicon, and the high-temperature performance of the battery can be improved through effective cooperation with the lithium sulfonimide salt in the electrolyte.

[0062] In some embodiments, the specific surface area per unit mass of the silicon-carbon composite material is SSA, and the unit is m 2 / g, and the mass ratio of the lithium sulfonimide salt in the electrolyte is EL, and the unit is g / g. The ratio EL:SSA between the mass ratio of the lithium sulfonimide salt in the electrolyte and the specific surface area SSA of the silicon-carbon composite material is 0.002-0.2, and can be 0.01-0.08.

[0063] In this document, the specific surface area SSA is the meaning known in the art, and the surface area is usually expressed in m 2The unit g / g indicates that the method and instrument known in the art can be used for testing. For example, the method can be tested by referring to GB / T 19587-2017, using an inert gas (such as nitrogen) adsorption specific surface area analysis test method, and using the BET (Brunauer Emmett Teller) method for calculation, wherein the nitrogen adsorption specific surface area analysis test can be performed by a Tri-Star 3020 specific surface area pore size analyzer of the American Micromeritics Company. In some embodiments, the ratio EL:SSA between the mass percentage of the lithium sulfonylimide salt in the electrolyte and the specific surface area SSA of the silicon-carbon composite material can be selected as 0.005, 0.006, 0.007, 0.008, 0.009, 0.01, 0.015, 0.02, 0.025, 0.03, 0.035, 0.04, 0.045, 0.05, 0.055, 0.06, 0.065, 0.07, 0.075, 0.08, 0.085, 0.09, 0.095, 0.1, 0.11, 0.12, 0.13, 0.14, or 0.15.

[0064] When the ratio EL:SSA between the mass percentage of the lithium sulfonylimide salt in the electrolyte and the specific surface area SSA of the silicon-carbon composite material is within the above range, the lithium sulfonylimide salt can be effectively embedded in the pore structure of the silicon-carbon composite material, fully contact the silicon-carbon composite material, improve the interface stability, and improve the high-temperature performance of the battery.

[0065] In some embodiments, the specific surface area SSA of the silicon-carbon composite material is 2-10 m 2 / g; and can be selected as 3-7 m 2 / g.

[0066] When the specific surface area SSA of the silicon-carbon composite material satisfies the above range, the specific surface area of the silicon-carbon composite material is large, and the kinetic performance of the material is good.

[0067] In some embodiments, in the electrolyte, the mass percentage of the lithium sulfonylimide salt based on the total mass of the electrolyte is EL, the unit is g / g, the total pore volume of the pores with a pore size less than or equal to 100 nm in the silicon-carbon composite material is V1 cm 3 / g, and EL:V1 is 1-100, which can be selected as 7-62.

[0068] The pore volume test method of different pore sizes can refer to GB / T 19587-2004, using the BJH (Barret joyner Halenda) method for mesopore pore size distribution test, using the gas adsorption-desorption method under the micro-mesopore model, and selecting the adsorption branch data to determine and count the total pore volume V1 of the pores with a pore size less than or equal to 100 nm.

[0069] In some embodiments, the ratio EL of the mass percentage of lithium sulfonamide salt in the electrolyte to the total pore volume V1 of pores with a pore size of less than or equal to 100 nm in the silicon-carbon composite material is: V1 can be selected as 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 15, 20, 25, 30, 35, 40, 45, 50, 55, 60, 65, 70, 75, 80, 85, 90, 95 or 100.

[0070] When the mass percentage of lithium sulfonamide in the electrolyte EL is within the range of V1:EL, the ratio between EL and V1 of the total pore volume of pores with a diameter of less than or equal to 100 nm in the silicon-carbon composite material can be satisfied, lithium sulfonamide can effectively enter the pore structure of the silicon-carbon composite material, improve the stability of the electrode / electrolyte interface, and thus improve the high-temperature storage life of the battery.

[0071] In some embodiments, the silicon-carbon composite material has a V1 ≥ 0.001 cm⁻¹. 3 / g, which can be selected from 0.005 to 0.01 cm 3 / g.

[0072] In some embodiments, the V1 of the silicon-carbon composite material can be selected as 0.001, 0.002, 0.003, 0.004, 0.005, 0.006, 0.007, 0.008, 0.009, or 0.01 cm. 3 / g.

[0073] When the V1 of the silicon-carbon composite material meets the above-mentioned range, the silicon-carbon composite material can not only have good mechanical strength, but also effectively cooperate with the lithium sulfonamide salt in the electrolyte, thereby improving the cycle performance of the battery. In some embodiments, the lithium sulfonamide salt is shown in Formula I.

[0074] Formula I

[0075] R1 and R2 are each independently selected from halogens, halogen-substituted or unsubstituted C1-C6 alkyl groups.

[0076] In some embodiments, the lithium sulfonylimide salt is selected from lithium difluorosulfonylimide. Lithium bis(trifluoromethanesulfonylimide) (Fluorosulfonyl)(trifluoromethanesulfonyl)iminolithium At least one of them.

[0077] The aforementioned lithium sulfonamide salts can not only improve the thermal and chemical stability of the electrolyte, but also generate components containing S and N elements in the interfacial film, thereby improving the high-temperature stability of the electrode / electrolyte interface and thus improving the high-temperature cycle performance and storage performance of the battery.

[0078] In some embodiments, the silicon-carbon composite material comprises: carbon matrix particles having a three-dimensionally networked pore structure, and silicon nanoparticles at least partially embedded in the three-dimensionally networked pore structure of the carbon matrix particles.

[0079] The carbon matrix particles of the present application have a stable porous framework structure, strong support capacity, high stress capacity, excellent mechanical properties and electrical conductivity; the carbon matrix particles comprise a three-dimensionally networked pore structure, which provides more space for embedding silicon-based nanoparticles, and can be used for storing a large amount of silicon, thereby effectively increasing the loading of silicon in the silicon-carbon composite material. After the carbon matrix particles are combined with the silicon-based nanoparticles, the electrical conductivity of the silicon-carbon composite material can be improved, the volume effect of silicon during the process of deintercalating lithium can be alleviated, the stress change of the silicon-based nanoparticles can be fully borne, the structural stability of the silicon-carbon composite material can be ensured, and the cycle performance and lithium storage capacity of the silicon-carbon composite material can be improved. Therefore, when the silicon-carbon composite material is applied to a secondary battery, the cycle performance and energy density of the secondary battery can be improved.

[0080] In some embodiments, the mass ratio of the silicon nanoparticles in the silicon-carbon composite material is greater than or equal to 40%, and can be 40-60%.

[0081] In some embodiments, the mass ratio of the silicon nanoparticles in the silicon-carbon composite material can be 40%, 45%, 50%, 55% or 60%.

[0082] The mass of the silicon nanoparticles in the silicon-carbon composite material can be tested by methods and devices known in the art, for example, the EPA 6010D-2014 standard can be referred to for determination; specifically, ICP-OES (elemental analysis-inductively coupled plasma atomic emission spectrometry) can be used for testing, the solid to be tested is first dissolved into a liquid with a strong acid, then the liquid is introduced into an ICP light source by atomization, and further the gaseous atoms to be tested are ionized and excited in a strong magnetic field after returning to the ground state from the excited state; the energy released in the above process is recorded as different characteristic spectral lines for trace element quantitative analysis.

[0083] The negative electrode material used in the secondary battery of the present application realizes high loading of silicon nanoparticles in the negative electrode material by using carbon-based materials having a three-dimensionally networked pore structure, so that the silicon-carbon composite material has high capacity and can further improve the energy density of the battery.

[0084] In some embodiments, the silicon nanoparticles comprise one or more of silicon oxide compounds, amorphous silicon, crystalline silicon and silicon-carbon composites.

[0085] In some embodiments, the carbon matrix comprises one or more of graphite, soft carbon and hard carbon.

[0086] In some embodiments, the total volume of pores with a pore size greater than 100 nm in the carbon matrix particles is denoted as Vc1 cm 3 / g, and the total volume of pores with a pore size less than or equal to 100 nm in the carbon matrix particles is denoted as Vc2 cm 3 / g, then the carbon matrix particles satisfy: 1 < Vc2 / Vc1≤30; optionally, 3≤Vc2 / Vc1≤25.

[0087] In some embodiments, Vc2 / Vc1 is 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20, 21, 22, 23, 24, or 25.

[0088] By adjusting the proportion of the total pore volume of pores of a specific size in the porous carbon matrix particles, the pore size distribution of the carbon matrix particles can be moderate, which is conducive to the entry of silicon nanoparticles into the pores of the carbon matrix particles, and the silicon-carbon composite material can have a certain mechanical strength, maintain its structural stability during the cycle process, and optimize its cycle performance.

[0089] In some embodiments, the powder compaction density of the silicon-carbon composite material tested after 1 powder pressing under an action force of 20000 N is P11 g / cm 3 The compaction density of the silicon-carbon composite material tested after 20 powder pressings under an action force of 20000 N is denoted as P21 g / cm 3 The ratio of P21 / P11 satisfies: 1.00 < P21 / P11≤1.20, optionally, 1.02≤P21 / P11≤1.10.

[0090] In some embodiments, P21 / P11 can be optionally 1.01, 1.02, 1.03, 1.04, 1.05, 1.06, 1.07, 1.08, 1.09, 1.10, 1.11, 1.12, 1.13, 1.14, 1.15, 1.16, 1.17, 1.18, 1.19, 1.20.

[0091] When the ratio of P21 / P11 satisfies the above range, the silicon-carbon composite material has higher specific capacity and better pressure resistance, which improves the structural stability of the negative electrode film layer, so that the secondary battery containing the material has higher energy density and better cycle performance.

[0092] In some embodiments, the powder compaction density of the silicon-carbon composite material tested after 1 powder pressing under an action force of 20000 N is P11 g / cm 3 satisfies: 1.10≤P11≤1.40, optionally, 1.12≤P11≤1.35.

[0093] In some embodiments, P11 can be optionally 1.10, 1.11, 1.12, 1.13, 1.14, 1.15, 1.16, 1.17, 1.18, 1.19, 1.20, 1.21, 1.22, 1.23, 1.24, 1.25, 1.26, 1.27, 1.28, 1.29, 1.30, 1.31, 1.32, 1.33, 1.34, 1.35, 1.36, 1.37, 1.38, 1.39, or 1.40.

[0094] The powder compaction density P11 of the silicon-carbon composite material after 1 time of powder pressing under a force of 20000 N 3 When the above range is satisfied, the negative electrode film layer has a high compaction density, thereby making the secondary battery have a high energy density and cycle performance.

[0095] In some embodiments, the secondary battery comprises a negative electrode tab, the negative electrode tab comprising a negative electrode current collector and a negative electrode film layer disposed on at least one surface of the negative electrode current collector, the negative electrode film layer comprising a negative electrode active material.

[0096] As an example, the negative electrode current collector has two surfaces opposite in the thickness direction thereof, and the negative electrode film layer is disposed on either one or both of the two opposite surfaces of the negative electrode current collector.

[0097] In some embodiments, the negative electrode current collector can adopt a metal foil or a composite current collector. For example, as the metal foil, a copper foil can be adopted. The composite current collector can comprise a high polymer material base layer and a metal layer formed on at least one surface of the high polymer material base layer. The composite current collector can be formed by forming a metal material (copper, copper alloy, nickel, nickel alloy, titanium, titanium alloy, silver, silver alloy, etc.) on a high polymer material base layer (such as a base layer of polypropylene (PP), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polystyrene (PS), polyethylene (PE), etc.).

[0098] In some embodiments, the negative electrode film layer can further optionally comprise a binder. The binder can be selected from at least one 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).

[0099] In some embodiments, the negative electrode film layer can further optionally comprise a conductive agent. The conductive agent can be selected from at least one of superconducting carbon, acetylene black, carbon black, ketjen black, carbon dots, carbon nanotubes, graphene, and carbon nanofibers.

[0100] In some embodiments, the negative electrode film layer can also optionally include other auxiliary agents, such as thickening agents (e.g., sodium carboxymethyl cellulose (CMC-Na)) and the like.

[0101] In some embodiments, the negative electrode sheet can be prepared by dispersing the above-mentioned 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 (e.g., deionized water) to form a negative electrode slurry; coating the negative electrode slurry on a negative electrode current collector, and after processes such as drying, cold pressing, and the like, obtaining the negative electrode sheet.

[0102] In some embodiments, the secondary battery includes a positive electrode sheet, which includes a positive electrode current collector and a positive electrode film layer disposed on at least one surface of the positive electrode current collector, the positive electrode film layer including the positive electrode active material of the first aspect of the present application.

[0103] As an example, the positive electrode current collector has two surfaces opposite in the thickness direction of the positive electrode current collector, and the positive electrode film layer is disposed on either one or both of the two opposite surfaces of the positive electrode current collector.

[0104] In some embodiments, the positive electrode current collector can be a metal foil or a composite current collector. For example, as the metal foil, an aluminum foil can be used. 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 formed by forming a metal material (aluminum, aluminum alloy, nickel, nickel alloy, titanium, titanium alloy, silver, silver alloy, and the like) on a polymer material base material (e.g., a base material of polypropylene (PP), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polystyrene (PS), polyethylene (PE), and the like).

[0105] In some embodiments, the positive electrode active material can be a positive electrode active material for a battery known in the art. As an example, the positive electrode active material can include at least one of a lithium-containing phosphate of olivine structure, a lithium transition metal oxide, and a modified compound of each thereof. However, the present application is not limited to these materials, and other conventional materials that can be used as a positive electrode active material for a battery can also be used. These positive electrode 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, lithium cobalt oxide (e.g., LiCoO2), lithium nickel oxide (e.g., LiNiO2), lithium manganese oxide (e.g., LiMnO2, LiMn2O4), lithium nickel cobalt oxide, lithium manganese cobalt oxide, lithium nickel manganese oxide, lithium nickel cobalt manganese oxide (e.g., LiNi 1 / 3 Co 1 / 3 Mn 1 / 3 O2 (which can also be referred to as NCM 333 ), LiNi 0.5 Co0.2 Mn 0.3 O2(also can be referred to as NCM 523 ), LiNi 0.5 Co 0.25 Mn 0.25 O2(also can be referred to as NCM 211 ), LiNi 0.6 Co 0.2 Mn 0.2 O2(also can be referred to as NCM 622 ), LiNi 0.8 Co 0.1 Mn 0.1 O2(also can be referred to as NCM 811 ), lithium nickel cobalt aluminum oxide (such as LiNi 0.85 Co 0.15 Al 0.05 O2), and modified compounds thereof. Examples of lithium-containing phosphates of olivine structure can include, but are not limited to, at least one of lithium iron phosphate (such as LiFePO4(also can be referred to as LFP)), a composite of lithium iron phosphate and carbon, lithium manganese phosphate (such as LiMnPO4), a composite of lithium manganese phosphate and carbon, lithium manganese iron phosphate, a composite of lithium manganese iron phosphate and carbon.

[0106] In some embodiments, the positive electrode active material is a nickel-rich material, the molar proportion of nickel element in transition metals in the positive electrode active material is higher than 85%.

[0107] In some embodiments, the positive electrode film layer can further optionally include a binder. As an example, the binder can include at least one of polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), a vinylidene-fluoride-tetrafluoroethylene-propylene terpolymer, a vinylidene-fluoride-hexafluoropropylene-tetrafluoroethylene terpolymer, a tetrafluoroethylene-hexafluoropropylene copolymer, and a fluorine-containing acrylate resin.

[0108] In some embodiments, the positive electrode film layer can further optionally include a conductive agent. As an example, the conductive agent can include at least one of super P, acetylene black, carbon black, ketjen black, carbon dots, carbon nanotubes, graphene, and carbon nanofibers.

[0109] 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 (such as N-methylpyrrolidone) to form a positive electrode slurry; coating the positive electrode slurry on a positive electrode current collector, and after processes such as drying, cold pressing, etc., the positive electrode tab can be obtained.

[0110] In some embodiments, the secondary battery further comprises a separator. The type of the separator is not particularly limited in the present application, and any known porous separator having good chemical stability and mechanical stability can be used.

[0111] In some embodiments, the material of the separator can be selected from at least one of glass fiber, non-woven fabric, polyethylene, polypropylene, and polyvinylidene fluoride. The separator can be a single-layer film or a multi-layer composite film, and is not particularly limited. When the separator is a multi-layer composite film, the materials of the layers can be the same or different, and are not particularly limited.

[0112] In some embodiments, the secondary battery comprises at least one of a lithium-ion battery, a sodium-ion battery, a magnesium-ion battery, and a potassium-ion battery.

[0113] In one embodiment of the present application, a power device is provided, which comprises the secondary battery of any of the embodiments.

[0114] The shape of the secondary battery is not particularly limited in the present application, and can be cylindrical, square, or any other shape. For example, Figure 1 is a square structure of the secondary battery 1 as an example.

[0115] In some embodiments, with reference to Figure 2 , the outer package can comprise a housing 11 and a cover plate 13. The housing 11 can comprise 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 housing 11 has an opening communicating with the receiving cavity, and the cover plate 13 can be arranged on the opening to close the receiving cavity. The positive electrode sheet, the negative electrode sheet, and the separator can be formed into an electrode assembly 12 by 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 secondary battery 1 can be one or more, which can be selected by those skilled in the art according to specific actual needs.

[0116] The power device comprises the secondary battery provided by the present application. The secondary battery can be used as a power source of the power device, or as an energy storage unit of the power device. The power device can comprise a mobile device (such as a mobile phone, a notebook computer, etc.), an electric vehicle (such as 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.), an electric train, a ship and a satellite, an energy storage system, etc., but is not limited thereto.

[0117] Figure 3 is a power device as an example. The power device is a pure electric vehicle, a hybrid electric vehicle, or a plug-in hybrid electric vehicle, etc. In order to meet the high power and high energy density requirements of the power device for the secondary battery, a battery pack or a battery module can be used.

[0118] As another example, the device can be a mobile phone, a tablet, a notebook computer, etc. The device generally requires thinness, and a secondary battery can be used as a power source.

[0119] Examples

[0120] Hereinafter, the embodiments of the present application will be described. The embodiments described below are exemplary and are for the purpose of explanation of the present application and should not be understood as a limitation of the present application. In the embodiments, the specific techniques or conditions not mentioned are performed according to the techniques or conditions described in the literature in the art or according to the product manual. The reagents or instruments not mentioned by the manufacturer are all conventional products that can be obtained on the market.

[0121] I. Preparation method

[0122] Example 1

[0123] (1) Preparation of silicon-carbon composite material

[0124] A gas containing a silicon precursor is provided to carbon matrix particles having a three-dimensional network crosslinked pore structure;

[0125] Silicon nanoparticles attached to the carbon matrix particles are generated from the silicon precursor by chemical vapor deposition to obtain a silicon-carbon composite material. The silicon precursor is silane, and the carbon matrix is hard carbon.

[0126] The total volume of pores with a pore size of 100 nm or less in the carbon matrix particles is denoted as Vc2 cm 3 / g, and the total volume of pores with a pore size of more than 100 nm in the carbon matrix particles is denoted as Vc1 cm 3 / g, and Vc2 / Vc1 is 10.5. The tap density P11 of the silicon-carbon composite material after 1 tap under a force of 20,000 N is 1.11 g / cm 3 / g, and the ratio of the tap density P21 of the silicon-carbon composite material after 20 taps under a force of 20,000 N to P11 is 1.02.

[0127] (2) Preparation of negative electrode sheet

[0128] The negative active material (silicon-carbon composite), conductive carbon black, thickening agent carboxymethyl cellulose sodium (CMC), and binder styrene-butadiene rubber emulsion (SBR) are mixed in a weight ratio of 96.5:1.0:1.0:1.5 in an appropriate amount of deionized water to form a uniform negative electrode slurry. The negative electrode slurry is coated on the negative electrode current collector, and after drying and other processes, a negative electrode sheet is obtained.

[0129] (3) Preparation of positive electrode sheet

[0130] Aluminum foil with thickness of 8 μm was used as the positive current collector. The positive active material LiNi 0.8 Co 0.1 Mn 0.1 O2(NCM 811 ), conductive agent acetylene black, binder polyvinylidene fluoride (PVDF) were dissolved in solvent N-methyl pyrrolidone (NMP) in weight ratio of 93:2:5, and after fully stirring and mixing uniformly, the positive electrode slurry was obtained; then the positive electrode slurry was uniformly coated on the positive current collector, and after drying, cold pressing, and slitting, the positive electrode sheet was obtained.

[0131] (4) Preparation of electrolyte

[0132] Vinyl carbonate (EC), methyl ethyl carbonate (EMC), and diethyl carbonate (DEC) were mixed in volume ratio of 1:1:1 to obtain an organic solvent, and then the fully dried lithium salt LiPF6 was dissolved in the mixed organic solvent to prepare an electrolyte with a concentration of 1 mol / L, and 8 wt% of lithium sulfonylimide salt was added as an additive.

[0133] (5) Isolation film

[0134] A polypropylene film was used as the isolation film.

[0135] (6) Preparation of battery

[0136] The positive electrode sheet, the isolation film, and the negative electrode sheet were stacked in order, with the isolation film between the positive and negative electrode sheets to play a role of isolation, and then the bare cell was obtained by winding. The bare cell was welded with a tab, and was put into an aluminum shell and baked at 80°C to remove water. Then, the electrolyte was injected and sealed to obtain a non-charged battery. The non-charged battery was subjected to the processes of standing, hot and cold pressing, formation, shaping, capacity testing, and the like in sequence to obtain the lithium ion battery product of Example 1.

[0137] Examples 2-3

[0138] The preparation method of the battery of Examples 2-3 was similar to that of Example 1, but the type of additive was adjusted, and the specific parameters are shown in Table 1.

[0139] Examples 4-7

[0140] The preparation method of the battery of Examples 4-7 was similar to that of Example 1, but the amount of lithium sulfonylimide salt added was adjusted, and the specific parameters are shown in Table 1.

[0141] Examples 8-11

[0142] The preparation method of the batteries of Examples 8-11 is similar to that of Example 1, but the pore parameters of the silicon-carbon composite material and the addition amount of the lithium sulfonimide salt are adjusted synchronously, and the specific parameters are shown in Table 1.

[0143] Comparative Example 1

[0144] Comparative Example 1 is basically the same as Example 1, but no lithium sulfonimide salt is added to the electrolyte.

[0145] Comparative Example 2

[0146] Comparative Example 2 is basically the same as Example 1, but the pore structure of the carbon matrix particles of Comparative Example 2 is a honeycomb pore structure.

[0147] II. Test Methods

[0148] 1. Silicon-carbon composite material

[0149] 1) Structure characterization of silicon-carbon composite material

[0150] The pore structure of the silicon-carbon composite material can be tested using equipment and methods known in the art. For example, it can be tested by using a scanning electron microscope (e.g., ZEISS Sigma 300). As an example, the following steps can be followed: first, cut the negative electrode sheet containing the silicon-carbon composite material into a certain size of the sample to be tested (e.g., 6 mm x 6 mm), clamp the sample to be tested with two pieces of conductive and heat-conductive sheet (such as copper foil), and fix the sample to be tested and the sheet with glue (such as double-sided tape) for a certain time (such as 1 h) with a certain mass (such as about 400 g) of flat iron block, so that the gap between the sample to be tested and the copper foil is as small as possible, then trim the edges with scissors, and stick them on the sample stage with conductive glue, and the sample slightly protrudes from the edge of the sample stage. Then, lock the sample stage on the sample holder, turn on the argon ion cross-section polisher (e.g., IB-19500CP) power and vacuum (e.g., 10 Pa -4Pa), set the argon gas flow (e.g., 0.15 MPa) and voltage (e.g., 8 KV) and polishing time (e.g., 2 hours), adjust the sample stage to the swing mode to start polishing, and after polishing, use a scanning electron microscope (e.g., ZEISS Sigma 300) to obtain the ion polishing cross-section morphology (CP) picture of the sample to be tested.

[0151] 2) Porosity of silicon-carbon composite material

[0152] After the battery is disassembled, the negative electrode film layer is scraped and the binder is removed after high-temperature ablation to obtain silicon-carbon composite material powder, which is measured according to GB / T24586 using gas displacement method. Porosity P = (V1-V2) / V1*100%, wherein V1 is the apparent volume of the sample, and V2 is the true volume of the sample.

[0153] 3) Specific surface area of silicon-carbon composite material SSA

[0154] The specific surface area is tested by gas adsorption method according to the test standard GB / T 19587-2017, as follows: taking the silicon-carbon composite material as a sample, the sample tube is immersed in liquid nitrogen at-196℃, the adsorption amount of nitrogen on the surface of the solid at different pressures is measured at 0.05-0.30 relative pressure, the monolayer adsorption amount of the sample is obtained based on the BET multilayer adsorption theory and its formula, and thus the specific surface area of the negative electrode active material is calculated.

[0155] The calculation formula of BET is as follows:

[0156]

[0157] In the formula, n a The amount of adsorbed gas, unit: mol / g; p / p0-relative pressure; nm-monolayer adsorption amount; C represents a revised parameter, which is used to limit the number of adsorption layers on the surface of the adsorbent.

[0158] 4) Pore size of silicon-carbon composite material

[0159] The pore size is tested by gas adsorption method according to the test standards GB / T 19587-2017 & GB / T 21650.2-2008, as follows: taking the silicon-carbon composite material as a sample, the sample tube is immersed in liquid nitrogen at-196℃, nitrogen is adsorbed on the material to be tested at a relative pressure of 0-1, and the pore size distribution of the porous material is characterized based on the relationship diagram of the volume of each pore size and the corresponding partial pressure.

[0160] 5) Powder compaction density

[0161] According to GB / T 24533-2009, an electronic pressure testing machine (such as UTM7305) is used for testing: a certain mass G of the powder sample to be tested is placed on a compaction special mold (bottom area S), different pressures (20000N or 50000N can be used in the present application) are set, the pressure is maintained for 20s, the pressure is removed, and the thickness H of the powder after being pressed under the pressure is read on the device after waiting for 10s, and the compaction density under the pressure is calculated, that is, the compaction density of the material under the pressure is G / (H*S).

[0162] 6) True density of silicon-carbon composite material

[0163] Referring to GB / T 24586-2009, a true density tester can be used as the testing instrument. As an example, the procedure can be as follows: Place a clean, dry silicon-carbon composite material sample cup on a balance, zero the balance, add a certain amount of powder sample to the sample cup (for example, the sample can occupy 1 / 2 of the sample cup's volume), record the mass of the sample, place the sample cup containing the sample in a true density tester for a sealed test, introduce helium gas, measure the gas pressure in the sample chamber and expansion chamber, and then calculate the true volume according to Bohr's law, and subsequently calculate the true density.

[0164] 7) Characterization of silicon and carbon element distribution in silicon-carbon composite materials

[0165] Elemental analysis of the ion-polished cross-section was performed using energy dispersive spectroscopy (EDS) according to the GB-T17359-2012 testing standard to determine the elemental distribution of the particle cross-section.

[0166] 2. Battery performance

[0167] 1) High-temperature cycling capacity retention

[0168] At 45°C, the secondary batteries prepared in each embodiment and comparative example were charged at a constant current rate of 0.5 C to the charging cutoff voltage of 4.25V, then charged at a constant voltage until the current ≤0.05C, allowed to stand for 5 minutes, and then discharged at a constant current rate of 0.33 C to the discharge cutoff voltage of 2V, allowed to stand for 5 minutes. This constitutes one charge-discharge cycle. The batteries were subjected to cyclic charge-discharge tests according to this method, and the capacity retention rate of the lithium-ion battery after 800 cycles was calculated.

[0169] 2) High-temperature storage performance

[0170] The secondary batteries prepared in each embodiment and comparative example were charged at a constant current rate of 0.5 C to the charging cutoff voltage of 4.25V, then charged at a constant voltage rate until the current ≤0.05C, allowed to stand for 5 minutes, and then discharged at a constant current rate of 0.33 C to the discharge cutoff voltage of 2V, allowed to stand for 5 minutes. This constitutes one charge-discharge cycle. Then, the batteries were charged at a constant current rate of 0.5 C to the charging cutoff voltage of 4.25V, followed by constant voltage charging until the current ≤0.05C. After being stored at 60°C for 100 days, charge-discharge cycle tests were performed, and the capacity retention rate of the lithium-ion batteries after high-temperature storage was calculated.

[0171] III. Analysis of Test Results for Each Embodiment and Comparative Example

[0172] Secondary batteries for each embodiment and comparative example were prepared according to the above method, and various parameters were measured. The results are shown in Table 1 below.

[0173] Table 1

[0174]

[0175] According to the results of Table 1, the batteries of Examples 1-11, in which the negative active material is a three-dimensional network cross-linked pore structure silicon-carbon composite material and the electrolyte contains a lithium sulfonimide salt, exhibit more excellent high-temperature cycle capacity retention and more excellent high-temperature storage capacity retention than the battery of Comparative Example 1, in which the negative active material is a three-dimensional network cross-linked pore structure silicon-carbon composite material and the electrolyte does not contain a lithium sulfonimide salt, and the battery of Comparative Example 2, in which the negative active material is a honeycomb pore structure silicon-carbon composite material and the electrolyte contains a lithium sulfonimide salt.

[0176] In the comparative example, the negative electrode is a honeycomb pore structure silicon-carbon composite material, and the silicon particles are not easily deposited inside the honeycomb pore structure. Therefore, the mass content of silicon-based particles in the honeycomb pore structure silicon-carbon composite material is low, only 7%, and the silicon element is concentrated on the surface of the composite material, and the carbon matrix is difficult to play a role in limiting the expansion of silicon-based particles, and the cycle performance of the battery is poor.

[0177] As can be seen from the comparison of Examples 4-5 and Examples 6-7, controlling the ratio EL:Vm between the pore volume Vm of the silicon-carbon composite material and the mass ratio EL of the lithium sulfonimide salt in the electrolyte in the range of 0.5-7 can improve the cycle capacity retention and high-temperature storage capacity retention of the battery.

[0178] As can be seen from Examples 8-11, further controlling EL:SSA to be 0.01-0.08 or EL:V1 to be 7-62 further improves the cycle performance of the battery.

[0179] It should be noted that the present application is not limited to the above-described embodiments. The above-described embodiments are only examples, and embodiments having the same technical idea and playing the same role and effect within the scope of the technical solutions of the present application are all included in the technical scope of the present application. In addition, within the scope of the main idea of the present application, various modifications that can be thought of by those skilled in the art, other modes constructed by combining part of the components of the embodiments are also included in the scope of the present application.

Claims

1. A secondary battery characterized by comprising: The secondary battery includes a negative electrode tab including a silicon-carbon composite material having a three-dimensional network cross-linked pore structure; and an electrolyte including a lithium sulfonylimide salt, The pore volume of the silicon-carbon composite material per unit mass is Vm, and the unit is cm 3 / g; in the electrolyte, the mass ratio of the lithium sulfonylimide salt in the electrolyte based on the total mass of the electrolyte is EL, the unit is g / g, and the specific surface area of the silicon-carbon composite material per unit mass is SSA, the unit is m 2 / g, wherein a ratio EL:Vm between a pore volume Vm per unit mass of the silicon-carbon composite material and a mass ratio EL of the lithium sulfonylimide salt in the electrolyte is 0.1 to 10; and / or a ratio EL:SSA between the mass ratio EL of the lithium sulfonylimide salt in the electrolyte and a specific surface area SSA per unit mass of the silicon-carbon composite material is 0.002 to 0.

2.

2. The secondary battery according to claim 1, wherein The pore volume of the silicon-carbon composite per unit mass is Vm, in cm 3 / g; a mass ratio EL of the lithium sulfonylimide salt in the electrolyte is EL (g / g) based on a total mass of the electrolyte, a ratio EL:Vm between a pore volume Vm per unit mass of the silicon-carbon composite material and the mass ratio EL of the lithium sulfonylimide salt in the electrolyte is 0.5 to 6.

3. The secondary battery according to claim 2, characterized by The pore volume per unit mass of the silicon-carbon composite is Vm, which is 0.01-0.3 cm3 / g. 3 / g.

4. The secondary battery according to claim 3, characterized by The pore volume per unit mass of the silicon-carbon composite is Vm, which is 0.04-0.15 cm3 / g. 3 / g.

5. The secondary battery according to any one of claims 1 to 4, wherein a ratio EL:SSA between the mass ratio EL of the lithium sulfonylimide salt in the electrolyte and a specific surface area SSA per unit mass of the silicon-carbon composite material is 0.01 to 0.

08.

6. The secondary battery according to any one of claims 1 to 5, characterized by, The specific surface area SSA of the silicon-carbon composite material is 2-10 m 2 / g.

7. The secondary battery according to claim 6, characterized by The specific surface area SSA of the silicon-carbon composite material is 3-7 m 2 / g.

8. The secondary battery according to any one of claims 1 to 7, characterized by, In the electrolyte, the mass ratio of the lithium sulfoximide salt is EL, unit: g / g, based on the total mass of the electrolyte, the total pore volume of the pores with a pore size less than or equal to 100 nm in the silicon-carbon composite material is V1 cm 3 / g, EL:V1 is 1~100.

9. The secondary battery according to claim 8, characterized by In the electrolyte, the mass ratio of the lithium sulfoximide salt is EL, unit: g / g, based on the total mass of the electrolyte, the total pore volume of the pores with a pore size less than or equal to 100 nm in the silicon-carbon composite material is V1 cm 3 / g, EL:V1 is 7~62.

10. The secondary battery according to claim 8 or 9, characterized by V1 of the silicon-carbon composite material is ≥ 0.001 cm 3 / g.

11. The secondary battery according to claim 10, characterized by The V1 of the silicon-carbon composite material is 0.005-0.01 cm 3 / g.

12. The secondary battery according to any one of claims 1 to 11, characterized by the lithium sulfonylimide salt is represented by Formula I, Formula I wherein R1, R2 each independently includes at least one of a halogen, a halogen-substituted or unsubstituted C1-C6 alkyl group.

13. The secondary battery according to any one of claims 1 to 12, characterized by the lithium sulfonylimide salt is selected from at least one of lithium bisfluorosulfonylimide, lithium bistrifluoromethanesulfonylimide, lithium (fluorosulfonyl)(trifluoromethanesulfonyl)imide.

14. The secondary battery according to any one of claims 1 to 13, characterized by, the silicon-carbon composite material includes: carbon matrix particles having a three-dimensional network cross-linked pore structure; and silicon nanoparticles at least partially embedded in the three-dimensional network cross-linked pore structure of the carbon matrix particles.

15. The secondary battery according to claim 14, characterized by a mass ratio of the silicon nanoparticles in the silicon-carbon composite material is greater than or equal to 40%.

16. The secondary battery according to claim 15, characterized by a mass ratio of the silicon nanoparticles in the silicon-carbon composite material is 40 to 60%.

17. The secondary battery according to any one of claims 14 to 16, characterized by, the silicon nanoparticles include one or more of a silicon oxide compound, amorphous silicon, crystalline silicon, and a silicon-carbon composite.

18. The secondary battery according to any one of claims 14 to 17, characterized by, the carbon matrix includes one or more of graphite, soft carbon, and hard carbon.

19. The secondary battery according to any one of claims 14 to 18, characterized by, The total volume of pores having a pore diameter greater than 100 nm in the carbon matrix particles is denoted as Vc1 cm 3 / g, and the total volume of pores having a pore diameter less than or equal to 100 nm in the carbon matrix particles is denoted as Vc2 cm 3 / g, then the carbon matrix particles satisfy: 1 < Vc2 / Vc1 < 30.

20. The secondary battery according to claim 19, characterized by The total volume of pores having a pore diameter greater than 100 nm in the carbon matrix particles is denoted as Vc1 cm 3 / g, and the total volume of pores having a pore diameter less than or equal to 100 nm in the carbon matrix particles is denoted as Vc2 cm 3 / g, then the carbon matrix particles satisfy: 3≤Vc2 / Vc1≤25.

21. The secondary battery according to any one of claims 1 to 20, characterized by The ratio of the powder compacted density P11 g / cm3 of the silicon-carbon composite material tested after 1 powder pressing under an action force of 20000 N to the powder compacted density P21 g / cm3 of the silicon-carbon composite material tested after 20 powder pressings under an action force of 20000 N satisfies: 3 The ratio of the powder compacted density P11 g / cm3 of the silicon-carbon composite material tested after 1 powder pressing under an action force of 20000 N to the powder compacted density P21 g / cm3 of the silicon-carbon composite material tested after 20 powder pressings under an action force of 20000 N satisfies: 3 The ratio of the powder compacted density P11 g / cm3 of the silicon-carbon composite material tested after 1 powder pressing 1.00 < P21 / P11 ≤ 1.

20.

22. The secondary battery according to claim 21, characterized by The ratio of the powder compacted density P11 g / cm3 of the silicon-carbon composite material tested after 1 powder pressing under an action force of 20000 N to the powder compacted density P21 g / cm3 of the silicon-carbon composite material tested after 20 powder pressings under an action force of 20000 N satisfies: 3 The ratio of the powder compacted density P11 g / cm3 of the silicon-carbon composite material tested after 1 powder pressing under an action force of 20000 N to the powder compacted density P21 g / cm3 of the silicon-carbon composite material tested after 20 powder pressings under an action force of 20000 N satisfies: 3 The ratio of the powder compacted density P11 g / cm3 of the silicon-carbon composite material tested after 1 powder pressing 1.02 ≤ P21 / P11 ≤ 1.

10.

23. The secondary battery according to any one of claims 1 to 22, characterized by The silicon-carbon composite material has a powder compacting density P11 g / cm3 tested after 1 time of powder pressing under an acting force of 20000 N 3 satisfies: 1.10≤P11≤1.

40.

24. The secondary battery according to claim 23, characterized by The silicon-carbon composite material has a powder compacting density P11 g / cm3 tested after 1 time of powder pressing under an acting force of 20000 N 3 satisfies: 1.12≤P11≤1.

35.

25. The secondary battery according to any one of claims 1 to 24, characterized by the secondary battery includes at least one of a lithium ion battery, a sodium ion battery, a magnesium ion battery, and a potassium ion battery.

26. An electrical device, comprising: the secondary battery includes the secondary battery according to any one of claims 1 to 25.

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