Secondary battery and electric device

Abstract

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; the electrolyte comprises a first component, the first component comprises one or more of compounds represented by formula I and formula II, and the structural formula of formula I or formula II is as follows: wherein R1, R2, R3 and R4 comprise at least one of a hydrogen atom, a fluorine atom, a fluorine-substituted or unsubstituted C1-C4 alkyl group, and formula I contains fluorine elements. Through the cooperation of the three-dimensional network cross-linked pore structure of the silicon-carbon composite material and the first component in the electrolyte, the volume effect of the active material in the charging and discharging process is inhibited, the internal resistance of the battery is reduced, and the cycle capacity retention rate of the battery is 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 supply systems such as hydropower, thermal power, wind power and solar power stations, and in many fields such as electric tools, electric bicycles, electric motorcycles, electric vehicles, military equipment, aerospace, etc.

[0003] Electrode active materials with high specific capacity often have poor cycle performance. How to improve the energy density of the battery while taking into account excellent cycle performance 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 carried out 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 internal resistance of the battery is reduced, and the cycle capacity retention rate of the battery is improved.

[0005] The first aspect of the present application provides a secondary battery, characterized in that it 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; the electrolyte comprises a first component, the first component comprises one or more of the compounds represented by formula I and formula II,

[0006]

[0007] wherein R1, R2, R3, R4 include at least one of a hydrogen atom, a fluorine atom, a fluorine-substituted or unsubstituted C1-C4 alkyl group, and formula I contains a fluorine element.

[0008] 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 first component in the electrolyte has an electron-withdrawing group F or an electron-rich double bond structure, which will further promote the formation of a ring radical polymer or ring-opening polymerization of its cyclic structure, timely forming a solid electrolyte interface film (SEI film) on the silicon-based material, which is conducive to inhibiting the destruction of the volume effect of silicon on the interface structure during the charging and discharging process, reducing the interface impedance, and improving the cycle stability of the battery.

[0009] In any embodiment, the specific surface area of the silicon-carbon composite material is SSA m 2 / g, and the mass fraction of the first component based on the total mass of the electrolyte is EL g / g, EL:SSA is 0.005-0.4, which can be optionally 0.014-0.2.

[0010] When the ratio EL:SSA between the mass percentage of the first component in the electrolyte and the specific surface area SSA of the silicon-carbon composite material satisfies the above range, the first component can be effectively embedded in the pore structure of the silicon-carbon composite material, fully contact the silicon-carbon composite material, improve the ion migration rate at the electrode / electrolyte interface, reduce the battery internal resistance, and improve the cycle capacity retention rate of the battery.

[0011] In any embodiment, the mass percentage of the first component is EL g / g, based on the total mass of the electrolyte,

[0012] In the outer peripheral region of the silicon-carbon composite material, the mass percentage of silicon in the silicon-carbon composite material is B1, based on the total mass of the silicon-carbon composite material, wherein the outer peripheral region of the silicon-carbon composite material is a region extending within r / 2 from the outer surface of the silicon-carbon composite material to the interior of the silicon-carbon composite material, and r represents the short diameter of the silicon-carbon composite material,

[0013] EL:B1 is 0.01-2, which can be 0.15-1.2.

[0014] When the ratio between the mass percentage of the first component in the electrolyte and the mass percentage B1 of silicon in the silicon-carbon composite material, based on the total mass of the silicon-carbon composite material, satisfies the above range, it is beneficial to alleviate the volume expansion of silicon during charging and discharging, improve the structural stability of the silicon-carbon composite material, and thus improve the cycle stability of the battery.

[0015] In any embodiment, the total pore volume of pores with a pore size greater than 100 nm in the silicon-carbon composite material is V1 cm 3 / g, and the ratio EL:V1 between the mass percentage EL of the first component in the electrolyte and the total pore volume V1 of pores with a pore size greater than 100 nm in the silicon-carbon composite material is 10-500, which can be preferably 20-300.

[0016] When the ratio EL:V1 between the mass percentage EL of the first component in the electrolyte and the total pore volume V1 of pores with a pore size greater than 100 nm in the silicon-carbon composite material satisfies the above range, the first component can be smoothly embedded in the pore structure of the silicon-carbon composite material, form a mutual cooperation with it, further improve the ion migration rate in the electrode active material, reduce the battery internal resistance, and improve the cycle capacity retention rate of the battery.

[0017] In any embodiment, the compound represented by formula I includes one or more of the following compounds:

[0018]

[0019] The compound represented by formula II includes one or more of the following compounds:

[0020]

[0021] The compound represented by the above formula I and the compound represented by formula II have an electron-withdrawing group F or an electron-rich double bond structure, which can further promote the cyclic formation of the ring free radical polymerization or the ring-opening polymerization, inhibit the destruction of the interface structure by the volume effect of silicon in the charging and discharging process, and improve the cycle stability.

[0022] In any embodiment, in the peripheral region of the silicon-carbon composite material, the mass percentage content A1 of the carbon element of the silicon-carbon composite material relative to the total mass of the silicon-carbon composite material and the mass percentage content B1 of the silicon element of the silicon-carbon composite material relative to the total mass of the silicon-carbon composite material satisfy 0.8≤B1 / A1≤2.5, and optionally, 1≤B1 / A1≤1.5.

[0023] When the mass percentage content A1 of the carbon element of the silicon-carbon composite material relative to the total mass of the silicon-carbon composite material and the mass percentage content B1 of the silicon element of the silicon-carbon composite material relative to the total mass of the silicon-carbon composite material satisfy the above range in the peripheral region of the silicon-carbon composite material, the mass of silicon in the pore structure of the silicon-carbon composite material is relatively high, which can significantly improve the capacity of the negative active material, and the voltage of metal ion intercalation is low, which is conducive to the intercalation of metal ions, thereby improving the rate cycle performance of the secondary battery. At the same time, the three-dimensional network cross-linked pore structure can inhibit the volume expansion of silicon during the cycle process, improve the structure stability of the negative active material, and thus improve the cycle performance of the battery.

[0024] In any embodiment, the mass percentage content A of the carbon element of the silicon-carbon composite material relative to the total mass of the silicon-carbon composite material has a decreasing trend along the direction from the geometric center of the silicon-carbon composite material to the outer surface of the silicon-carbon composite material, and the mass percentage content B of the silicon element of the silicon-carbon composite material relative to the total mass of the silicon-carbon composite material has an increasing trend along the direction from the geometric center of the silicon-carbon composite material to the outer surface of the silicon-carbon composite material.

[0025] Since the silicon-carbon composite material can be irregularly shaped, the geometric center of the silicon-carbon composite material can be equivalent to the geometric center of a rectangular parallelepiped tangent to it. Along the direction from the geometric center of the silicon-carbon composite material to the outer surface of the silicon-carbon composite material, the mass percentage content A of the carbon element gradually decreases, the mass percentage content B of the silicon element gradually increases, and the content of silicon in the pore structure of the silicon-carbon composite material gradually increases, and the content of silicon is relatively high, which can significantly improve the capacity of the negative active material.

[0026] In any embodiment, the specific surface area SSA of the silicon-carbon composite material satisfies: 2m 2 / g≤SSA≤10m 2 / g; optionally, 3m 2 / g≤SSA≤7m 2 / g.

[0027] 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, the kinetic performance of the material is good, and the first coulombic efficiency of the battery is improved.

[0028] In any embodiment, the silicon-carbon composite material comprises carbon matrix particles and silicon nanoparticles, the carbon matrix particles comprise a three-dimensional network cross-linked pore structure, and at least a part of the silicon nanoparticles is arranged in the three-dimensional network cross-linked pore structure.

[0029] 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 lithium extraction 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 stability 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.

[0030] In any embodiment, the silicon nanoparticles comprise one or more of a silicon oxide compound, a pre-lithiated silicon oxide compound, amorphous silicon, crystalline silicon and a silicon-carbon composite, and are optionally amorphous silicon.

[0031] In any embodiment, the carbon matrix comprises one or more of graphite, soft carbon and hard carbon.

[0032] In any embodiment, the mass ratio of the silicon nanoparticles in the silicon-carbon composite material is greater than or equal to 40%, and is optionally 40-60%.

[0033] 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 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.

[0034] In any embodiment, the silicon-carbon composite material has a powder compaction density P11 g / cm3 after 1 powder pressing under an acting force of 20,000 N. 3The ratio of the compacted density P21 g / cm 3 tested after the silicon-carbon composite material is powder-pressed 20 times under a force of 20,000 N satisfies: 1.00 < P21 / P11 ≤ 1.20. Optionally, 1.02 ≤ P21 / P11 ≤ 1.10.

[0035] When the ratio of P21 / P11 satisfies the above range, the silicon-carbon composite material has good compressive resistance while having a high specific capacity, improving the structural stability of the negative electrode film layer, so that the secondary battery containing this material has good cycle performance while having a high energy density.

[0036] In any implementation manner, the powder compacted density P11 g / cm 3 tested after the silicon-carbon composite material is powder-pressed once under a force of 20,000 N satisfies: 1.10 ≤ P11 ≤ 1.40. Optionally, 1.12 ≤ P11 ≤ 1.35.

[0037] When the powder compacted density P11 g / cm 3 tested after the silicon-carbon composite material is powder-pressed once under a force of 20,000 N satisfies the above range, the negative electrode film layer has a high compacted density, so that the secondary battery has a high energy density.

[0038] In any implementation manner, 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.

[0039] The second aspect of the present application provides an electrical device including the secondary battery of the first aspect. Brief Description of the Drawings

[0040] Figure 1 is a schematic diagram of a secondary battery according to an embodiment of the present application;

[0041] Figure 2 is Figure 1 ... a decomposition diagram of the secondary battery according to an embodiment of the present application shown; ...

[0042] Figure 3 is a schematic diagram of an electrical device using the secondary battery according to an embodiment of the present application as a power source.

[0043] Description of the Reference Numerals:

[0044] 1 Secondary battery; 11 Housing; 12 Electrode assembly; 13 Cover plate. Detailed Embodiments

[0045] Hereinafter, specific embodiments of the binder, the production method, the electrode, the battery, and the electric device of the present application 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 known to those skilled in the art, repeated description of substantially identical configurations, is 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 to enable those skilled in the art to fully understand the present application, and are not intended to limit the subject matter recited in the claims.

[0046] The ranges disclosed herein are defined by their lower and upper limits. Ranges can be inclusive or exclusive of their endpoints, and all ranges and sub-ranges are combinable. For example, if a range is listed as 60-120 and 80-110, it is understood that 60-110 and 80-120 are also expressly stated. Moreover, if a range is listed as 1-2 and 3-5, it is understood that 1-5, 1-3, 2-5, and 2-3 are also expressly stated. In the present application, unless otherwise indicated, a numerical range "a-b" is intended to indicate any and all sub-ranges between (and including) the minimum value a and the maximum value b in which each and every value from a to b is encompassed. For example, the numerical range "0-5" is intended to indicate the entire range of values from 0 to 5, inclusive of all integer and fractional values therebetween. Additionally, if a parameter is stated to be an integer ≥ 2, it is understood that the parameter is also disclosed to be, for example, an integer 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, etc.

[0047] Unless otherwise specified, all embodiments and optional embodiments of the present application can be combined with each other to form new technical solutions.

[0048] Unless otherwise specified, all technical features and optional technical features of the present application can be combined with each other to form new technical solutions.

[0049] If not specified otherwise, all steps of the application can be carried out in sequence or randomly, preferably in sequence. For example, the method comprises steps (a) and (b) 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) 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.

[0050] If not specified otherwise, the terms "comprising" and "including" as used in the present application are open-ended and also include the case where the other components are not present. For example, the terms "comprising" and "including" can mean that the method can further comprise or include other components not listed.

[0051] If not specified otherwise, the term "or" in the present 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).

[0052] 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, which leads to poor cycle performance of the battery, and the solid electrolyte interface film (SEI film) on the surface of the silicon-based material is repeatedly regenerated with the expansion of the silicon-based material, which increases the internal resistance of the battery and reduces the kinetic performance.

[0053] Based on this, the application provides a secondary battery, which comprises a negative electrode sheet and an electrolyte, wherein the negative electrode sheet comprises a silicon-carbon composite material having a three-dimensional network cross-linked pore structure; and the electrolyte comprises a first component, wherein the first component comprises one or more of the compounds represented by formula I and formula II,

[0054]

[0055] wherein R1, R2, R3, R4 comprise at least one of a hydrogen atom, a fluorine atom, a fluorine-substituted or unsubstituted C1-C4 alkyl group, and formula I contains a fluorine element.

[0056] 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 staggered and share pore volumes with each other in the pore structure formed by the silicon-carbon composite material, especially the carbon matrix particles.

[0057] The pore structure of the silicon-carbon composite material can be tested using devices and methods known in the art. For example, it can be tested by using a scanning electron microscope (e.g., ZEISS Sigma300). 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 (e.g., 6mm x 6mm), 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 with the sheet with glue (such as double-sided tape). A certain mass (such as about 400g) of flat iron is pressed for a certain period of time (such as 1h), so that the gap between the sample to be tested and the copper foil is as small as possible. Then, use scissors to trim the edges, and stick them on the sample stage with conductive glue. The sample slightly protrudes from the edge of the sample stage. Then, lock the sample stage into the sample holder, turn on the argon ion cross-section polisher (e.g., IB-19500CP) power and vacuum (e.g., 10Pa-4Pa), set the argon flow (e.g., 0.15MPa) and voltage (e.g., 8KV) and polishing time (e.g., 2 hours), adjust the sample stage to the swing mode to start polishing. After polishing, use a scanning electron microscope (e.g., ZEISS Sigma300) to obtain the ion polishing cross-section morphology (CP) picture of the sample to be tested.

[0058] 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 first component in the electrolyte has an electron-withdrawing group F or an electron-rich double bond structure, which will further promote its cyclic generation of ring free radical polymerization or ring-opening polymerization, and can timely form a solid-state electrolyte film on the silicon-based material, which is conducive to inhibiting the destruction of the volume effect of silicon on the interface structure during the charging and discharging process, reducing the interface impedance, and improving the cycle stability of the battery.

[0059] In some embodiments, the specific surface area of the silicon-carbon composite material is SSA m 2 / g, and the mass ratio of the first component based on the total mass of the electrolyte is EL g / g, EL:SSA is 0.005-0.4, which can be optionally 0.014-0.2.

[0060] In some embodiments, the specific surface area of the silicon-carbon composite material is SSA m 2EL g / g, the mass percentage of the first component in the total mass of the electrolyte is EL g / g, EL: SSA can be 0.001, 0.002, 0.003, 0.004, 0.005, 0.006, 0.007, 0.008, 0.009, 0.01, 0.02, 0.03, 0.04, 0.05, 0.06, 0.07, 0.08, 0.09, 0.1, 0.11, 0.12, 0.13, 0.14, 0.15, 0.16, 0.17, 0.18, 0.19, 0.2, 0.25, 0.3, 0.35, 0.4, 0.45, or 0.5.

[0061] In this context, the specific surface area SSA is of the meaning known in the art, typically the surface area is expressed in m2 / g and can be tested using methods and instruments known in the art. For example, it can be tested according to GB / T 19587-2017, using the inert gas (e.g. nitrogen) adsorption specific surface area analysis test method and calculated using the BET (Brunauer Emmett Teller) method, 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 Micromeritics company in the United States. 2 2 In this context, the specific surface area SSA is of the meaning known in the art, typically the surface area is expressed in m2 / g and can be tested using methods and instruments known in the art. For example, it can be tested according to GB / T 19587-2017, using the inert gas (e.g. nitrogen) adsorption specific surface area analysis test method and calculated using the BET (Brunauer Emmett Teller) method, 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 Micromeritics company in the United States.

[0062] When the ratio EL:SSA between the mass percentage of the first component in the electrolyte and the specific surface area SSA of the silicon-carbon composite material satisfies the above range, the first component can be effectively embedded in the pore structure of the silicon-carbon composite material, fully contacting the silicon-carbon composite material, and through the effective cooperation of the amount of the first component and the specific surface area of the silicon-based material, the timely formation of the SEI film on the silicon-carbon composite material is realized, the internal resistance of the battery is reduced, and the cycle capacity retention rate of the battery is improved.

[0063] In some embodiments, the mass percentage of the first component in the total mass of the electrolyte is EL g / g, and in the peripheral region of the silicon-carbon composite material, the mass percentage of silicon in the silicon-carbon composite material is B1, wherein the peripheral region of the silicon-carbon composite material is a region extending within r / 2 from the outer surface of the silicon-carbon composite material to the interior of the silicon-carbon composite material, r represents the short diameter of the silicon-carbon composite material, and EL:B1 is 0.01-2, which can be 0.15-1.2.

[0064] The silicon element content can be determined by inductively coupled plasma (ICP) test, specifically as follows: taking the silicon-carbon composite material as a sample, using aqua regia and hydrofluoric acid HF to digest the sample, taking the 15 min digested solution and the completely digested solution for ICP test, and the silicon content in the 45 min digested solution is the silicon content of the "outer peripheral region" of the silicon-carbon composite material.

[0065] In some embodiments, the ratio EL:B1 between the mass percentage of the first component in the electrolyte and the mass percentage content B1 of the silicon element in the silicon-carbon composite material relative to the total mass of the silicon-carbon composite material can be 0.01, 0.02, 0.03, 0.04, 0.05, 0.06, 0.07, 0.08, 0.09, 0.1, 0.11, 0.12, 0.13, 0.14, 0.15, 0.16, 0.17, 0.18, 0.19, 0.2, 0.3, 0.4, 0.5, 0.6, 0.7, 0.8, 0.9, 1, 1.2, 1.4, 1.6, 1.8, or 2.

[0066] The silicon element in the outer peripheral region of the silicon-carbon composite material is not easily bound by the carbon skeleton and has more significant volume expansion than the silicon element in the inner region. When the ratio between the mass percentage of the first component in the electrolyte and the mass percentage content B1 of the silicon element in the silicon-carbon composite material relative to the total mass of the silicon-carbon composite material satisfies the above range, it is beneficial to quickly form an SEI film on the silicon element in the outer peripheral region of the silicon-carbon composite material through the first component, relieve the volume expansion of silicon during the charging and discharging process, improve the structural stability of the silicon-carbon composite material, and thus improve the cycle stability of the battery.

[0067] In some embodiments, the total pore volume of the pores with a pore size greater than 100 nm in the silicon-carbon composite material is V1 cm 3 The ratio EL:V1 between the mass percentage EL of the first component in the electrolyte and the total pore volume V1 of the pores with a pore size greater than 100 nm in the silicon-carbon composite material is 10-500, and can be 20-300.

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

[0069] In some embodiments, the total pore volume of the pores with a pore size greater than 100 nm in the silicon-carbon composite material is V1 cm 3The ratio EL:Q1 between the mass fraction EL of the first component in the electrolyte and the total pore volume V1 of the pores with a pore size greater than 100 nm in the silicon-carbon composite material can be preferably 10, 20, 30, 40, 50, 60, 70, 80, 90, 100, 150, 200, 250, 300, 350, 400, 450, or 500.

[0070] When the ratio EL:V1 between the mass fraction EL of the first component in the electrolyte and the total pore volume V1 of the pores with a pore size greater than 100 nm in the silicon-carbon composite material satisfies the above range, the first component can be smoothly embedded in the pore structure of the silicon-carbon composite material, form a mutual cooperation with it, further improve the migration rate of ions in the electrode active material, reduce the internal resistance of the battery, and improve the cycle capacity retention rate of the battery.

[0071] In some embodiments, the compound of Formula I includes one or more of the following compounds:

[0072]

[0073] The compound of Formula II includes one or more of the following compounds:

[0074]

[0075] The compounds of Formula I and Formula II described above have an electron-withdrawing group F or an electron-rich double bond structure, which can further promote the formation of SEI film through ring-opening polymerization or ring formation to form a ring free radical polymerization, inhibit the destruction of the interface structure by the volume effect of silicon during the charging and discharging process, and improve the cycle stability.

[0076] In some embodiments, in the peripheral region of the silicon-carbon composite material, the mass percentage content A1 of the carbon element in the silicon-carbon composite material relative to the total mass of the silicon-carbon composite material and the mass percentage content B1 of the silicon element in the silicon-carbon composite material relative to the total mass of the silicon-carbon composite material satisfy 0.8≤B1 / A1≤2.5, and optionally, 1≤B1 / A1≤1.5.

[0077] The carbon element content can be tested by infrared absorption method carbon-sulfur content analysis according to GB / T20123-2006 test standard, and the specific method is as follows: taking the silicon-carbon composite material as a sample, the carbon content at 20 min is the carbon content of the "outer peripheral region" of the silicon-carbon composite material. When the mass percentage content A1 of the carbon element of the silicon-carbon composite material relative to the total mass of the silicon-carbon composite material and the mass percentage content B1 of the silicon element of the silicon-carbon composite material relative to the total mass of the silicon-carbon composite material in the outer peripheral region of the silicon-carbon composite material meet the above range, the mass of silicon in the pore structure of the silicon-carbon composite material is relatively high, which can significantly improve the capacity of the negative active material, and the voltage of the metal ion insertion is relatively low, which is beneficial to the insertion of the metal ion, thereby improving the rate cycle performance of the secondary battery. At the same time, the three-dimensional network cross-linked pore structure can inhibit the volume expansion of silicon during the cycle process, improve the structure stability of the negative active material, and thus improve the cycle performance of the battery.

[0078] In some embodiments, the mass percentage content A of the carbon element of the silicon-carbon composite material relative to the total mass of the silicon-carbon composite material has a decreasing trend along the direction from the geometric center of the silicon-carbon composite material to the outer surface of the silicon-carbon composite material, and the mass percentage content B of the silicon element of the silicon-carbon composite material relative to the total mass of the silicon-carbon composite material has an increasing trend along the direction from the geometric center of the silicon-carbon composite material to the outer surface of the silicon-carbon composite material.

[0079] Since the silicon-carbon composite material can be irregularly shaped, the geometric center of the silicon-carbon composite material can be equivalent to the geometric center of a rectangular parallelepiped tangent to it. Along the direction from the geometric center of the silicon-carbon composite material to the outer surface of the silicon-carbon composite material, the mass percentage content A of the carbon element gradually decreases, the mass percentage content B of the silicon element gradually increases, and the content of silicon in the pore structure of the silicon-carbon composite material gradually increases, and the content of silicon is relatively high, which can significantly improve the capacity of the negative active material.

[0080] And the increasing content of silicon element from the outer surface to the center makes the inhibition of the expansion of silicon element by the carbon material more significant, thereby further improving the cycle performance of the battery.

[0081] In some embodiments, the specific surface area SSA of the silicon-carbon composite material satisfies: 2m 2 / g≤SSA≤10m 2 / g; optionally, 3m 2 / g≤SSA≤7m 2 / g.

[0082] In some embodiments, the specific surface area SSA of the silicon-carbon composite material is optionally 2m 2 / g, 3m 2 / g, 4m 2 / g, 5m 2 / g, 6m2 / g, 7m 2 / g, 8m 2 / g, 9m 2 / g or 10m 2 / g, or a range formed by any two of the above values.

[0083] 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, which is beneficial to improve the initial coulomb efficiency of the battery.

[0084] In some embodiments, the silicon-carbon composite material comprises: carbon matrix particles and silicon nanoparticles, the carbon matrix particles comprise a three-dimensional network cross-linked pore structure, and at least a part of the silicon nanoparticles is arranged in the three-dimensional network cross-linked pore structure.

[0085] 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 deintercalation of 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 stability 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.

[0086] In some embodiments, the silicon nanoparticles comprise one or more of silicon oxide compounds, pre-lithiated silicon oxide compounds, amorphous silicon, crystalline silicon and silicon-carbon composites, and can be amorphous silicon.

[0087] In some embodiments, the carbon matrix comprises one or more of graphite, soft carbon and hard carbon.

[0088] 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%.

[0089] In some embodiments, the mass ratio of the silicon nanoparticles in the silicon-carbon composite material can be 40%, 45%, 50%, 55% or 60%.

[0090] 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, according to the EPA 6010D-2014 standard; specifically, ICP-OES (elemental analysis-inductively coupled plasma atomic emission spectrometry) can be used for testing, in which the solid to be tested is first dissolved into a liquid with a strong acid, and then the liquid is introduced into the ICP light source by atomization, and further, the gaseous atoms to be tested are ionized and excited in a strong magnetic field, and then return to the ground state from the excited state; in the above process, energy is released and recorded as different characteristic spectral lines for quantitative analysis of trace elements.

[0091] The negative electrode material used in the secondary battery of the present application achieves a high loading amount 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 a high capacity, and the energy density of the battery can be further improved.

[0092] In some embodiments, the powder compaction density P11 of the silicon-carbon composite material after 1 time of powder pressing under the action of 20000N meets: 1.10≤P11≤1.40, and more preferably, 1.12≤P11≤1.35. 3 The ratio of the compaction density P21 of the silicon-carbon composite material after 20 times of powder pressing under the action of 20000N to the compaction density P11 of the silicon-carbon composite material after 1 time of powder pressing under the action of 20000N meets: 1.00 3 ≤P21 / P11≤1.20, and more preferably, 1.02≤P21 / P11≤1.10.

[0093] When the ratio of P21 / P11 meets the above range, the silicon-carbon composite material has a higher specific capacity while also having good pressure resistance, which improves the structural stability of the negative electrode film layer, so that the secondary battery containing the material has a higher energy density while also having good cycle performance.

[0094] In some embodiments, the powder compaction density P11 of the silicon-carbon composite material after 1 time of powder pressing under the action of 20000N meets: 1.10≤P11≤1.40, and more preferably, 1.12≤P11≤1.35. 3

[0095] The powder compaction density P11 of the silicon-carbon composite material after 1 time of powder pressing under the action of 20000N meets: 1.10≤P11≤1.40, and more preferably, 1.12≤P11≤1.35. 3 When the powder compaction density P11 of the silicon-carbon composite material after 1 time of powder pressing under the action of 20000N meets the above range, the negative electrode film layer has a higher compaction density, so that the secondary battery has a higher energy density.

[0096] In some embodiments, the secondary battery includes a negative electrode sheet, and the negative electrode sheet includes a negative electrode current collector and a negative electrode film layer disposed on at least one surface of the negative electrode current collector, and the negative electrode film layer includes a negative electrode active material.

[0097] ​As an example, the negative current collector has two surfaces opposite in the thickness direction thereof, and the negative film layer is provided on either one or both of the two surfaces of the negative current collector.

[0098] In some embodiments, the negative current collector can be a metal foil or a composite current collector. For example, as the metal foil, a copper 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 (copper, copper alloy, nickel, nickel alloy, titanium, titanium alloy, silver, silver alloy, etc.) on a polymer material base layer such as a base layer of polypropylene (PP), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polystyrene (PS), polyethylene (PE), etc.

[0099] In some embodiments, the negative film layer can further optionally include 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).

[0100] In some embodiments, the negative film layer can further optionally include 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.

[0101] In some embodiments, the negative film layer can further optionally include other auxiliary agents, such as thickening agents (e.g., sodium carboxymethyl cellulose (CMC-Na)) and the like.

[0102] 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 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 the negative current collector, and after processes such as drying, cold pressing, etc., the negative electrode sheet can be obtained.

[0103] In some embodiments, the secondary battery includes a positive electrode sheet including a positive current collector and a positive film layer provided on at least one surface of the positive current collector, the positive film layer including the positive active material of the first aspect of the present application.

[0104] As an example, the positive current collector has two surfaces opposite in the thickness direction thereof, and the positive film layer is provided on either one or both of the two surfaces of the positive current collector.

[0105] In some embodiments, the positive electrode 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 formed by forming a metal material (aluminum, aluminum alloy, nickel, nickel alloy, titanium, titanium alloy, silver, silver alloy, etc.) on a polymer material base material (e.g., a base material of polypropylene (PP), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polystyrene (PS), polyethylene (PE), etc.).

[0106] In some embodiments, the positive electrode active material can employ 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 an 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 only one or two or more can be used in combination. Among them, 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(also referred to simply as NCM 333 ), LiNi 0.5 Co o0.2 Mn 0.3 O2(also referred to simply as NCM 523 ), LiNi 0.5 Co 0.25 Mn 0.25 O2(also referred to simply as NCM 211 ), LiNi 0.6 Co o0.2 Mn 0.2 O2(also referred to simply as NCM 622 ), LiNi 0.8 Co 0.1 Mn 0.1 O2(also referred to simply as NCM 811 ), lithium nickel cobalt aluminum oxide (e.g., LiNi 0.85 Co 0.15 Al 0.05O2) and modified compounds thereof, etc. Examples of the lithium-containing phosphate of olivine structure can include, but are not limited to, at least one of lithium iron phosphate (such as LiFePO4 (which can also 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, and a composite of lithium manganese iron phosphate and carbon.

[0107] 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%.

[0108] In some embodiments, the positive electrode film layer further optionally includes 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.

[0109] In some embodiments, the positive electrode film layer further optionally includes 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.

[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 (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., obtaining the positive electrode tab.

[0111] 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 known porous structure separator film with good chemical stability and mechanical stability can be selected.

[0112] In some embodiments, the material of the separator film can be selected from at least one 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 layers can be the same or different, and are not particularly limited.

[0113] In some embodiments, 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.

[0114] In one embodiment of the present application, a power utilization device is provided, including the secondary battery of any embodiment.

[0115] The shape of the secondary battery is not particularly limited, and can be cylindrical, square, or any other shape. For example, Figure 1 is a square structure as an example of the secondary battery 1.

[0116] In some embodiments, referring to Figure 2 , the outer package can include a housing 11 and a cover plate 13. The housing 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 housing 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 the 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 secondary battery 1 can be one or more, and the skilled person in the art can select according to the specific actual needs.

[0117] The power device includes the secondary battery provided by the present application. The secondary battery can be used as a power source of the power device, or can be used as an energy storage unit of the power device. The power device can include 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.

[0118] 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.

[0119] The device as another example can be a mobile phone, a tablet computer, a notebook computer, etc. The device usually requires thinning, and a secondary battery can be used as a power source.

[0120] Examples

[0121] Hereinafter, the embodiments of the present application are described. The embodiments described below are exemplary and are only used to explain the present application, and cannot be understood as a limitation of the present application. If the 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 from the market.

[0122] One, secondary battery

[0123] Example 1

[0124] (1) Preparation of silicon-carbon composite material

[0125] A gas containing a silicon precursor is supplied to carbon substrate particles having a three-dimensional network crosslinked pore structure;

[0126] Silicon nanoparticles are generated from the silicon precursor by chemical vapor deposition to adhere to the carbon substrate particles, to obtain a silicon-carbon composite material.

[0127] (2) Preparation of negative electrode sheet

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

[0129] (3) Preparation of positive electrode sheet

[0130] An aluminum foil with a thickness of 8 μm is used as a positive electrode current collector. A positive active material LiNi 0.8 Co 0.1 Mn 0.1 O2(NCM 811 ), a conductive agent acetylene black, and a binder polyvinylidene fluoride (PVDF) are dissolved in a solvent N-methyl pyrrolidone (NMP) in a weight ratio of 93:2:5, and are sufficiently stirred and mixed to obtain a positive electrode slurry. The positive electrode slurry is then uniformly coated on the positive electrode current collector, and is subjected to processes such as drying, cold pressing, and slitting, to obtain a positive electrode sheet.

[0131] (4) Preparation of electrolyte

[0132] Ethylene carbonate (EC), methyl ethyl carbonate (EMC), and diethyl carbonate (DEC) are mixed in a volume ratio of 1:1:1 to obtain an organic solvent, and then a sufficiently dried lithium salt LiPF6 is dissolved in the mixed organic solvent to prepare an electrolyte having a concentration of 1 mol / L. 10 wt% of a compound A-1 is added as an additive.

[0133]

[0134] (5) Separator

[0135] A polypropylene film is used as a separator.

[0136] (6) Preparation of battery

[0137] The positive electrode sheet, the separator, and the negative electrode sheet are stacked in order with the separator between the positive and negative electrode sheets to function as a separator, and then wound to obtain a bare cell. The bare cell is welded with tabs, and is put into an aluminum case, and is baked at 80°C to remove water. Then, an electrolyte is injected and sealed to obtain a non-charged battery. The non-charged battery is subjected to a series of processes of standing, hot and cold pressing, formation, shaping, and capacity test to obtain the lithium ion battery product of Example 1.

[0138] Examples 2-4

[0139] The preparation method of the battery of Example 2-4 is similar to that of Example 1, but the type of additive is adjusted.

[0140] The electrolyte additive of Example 2

[0141]

[0142] The electrolyte additive of Example 3

[0143]

[0144] The electrolyte additive of Example 4

[0145]

[0146] Examples 5-8

[0147] The preparation method of the battery of Examples 5-8 is similar to that of Example 1, but the content of the electrolyte additive is adjusted so that EL:SSA, EL:B1, and EL:V1 are changed. The specific parameters are shown in Table 1.

[0148] Examples 9-12

[0149] The preparation method of the battery of Examples 9-12 is similar to that of Example 1, but the deposition position of the silicon-based particles in the silicon-carbon composite material is adjusted to adjust the value of EL:B1. The specific parameters are shown in Table 1.

[0150] Examples 13-16

[0151] The preparation method of the battery of Examples 13-16 is similar to that of Example 1, but the ratio of large and small pores in the silicon-carbon composite material is adjusted to adjust the value of EL:V1. The specific parameters are shown in Table 1.

[0152] Comparative Example 1

[0153] The preparation method of the battery of Comparative Example 1 is similar to that of Example 1, but the first component is not added to the electrolyte.

[0154] Comparative Example 2

[0155] The battery of Comparative Example 2 was prepared in a similar manner to Example 1, except that the carbon matrix particles of Comparative Example 2 had a honeycomb pore structure.

[0156] Comparative Example 3

[0157] The battery of Comparative Example 3 was prepared in a similar manner to Example 3, except that the carbon matrix particles of Comparative Example 3 had a honeycomb pore structure.

[0158] Comparative Example 4

[0159] The battery of Comparative Example 4 was prepared in a similar manner to Example 4, except that the carbon matrix particles of Comparative Example 4 had a honeycomb pore structure.

[0160] II. Test Methods

[0161] 1. Silicon-carbon composite material

[0162] 1) Structure characterization of silicon-carbon composite material

[0163] 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 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 use glue (such as double-sided tape) to fix the sample to be tested between the sheets. A certain mass (such as about 400 g) of flat iron is used to press for a certain period of time (such as 1 h), so that the gap between the sample to be tested and the copper foil is as small as possible. Then use scissors to trim the edges, and stick them on a sample stage with conductive glue, with the sample slightly protruding from the edge of the sample stage. Then mount the sample stage on the sample holder and lock it in place, turn on the argon ion cross-section polisher (e.g., IB-19500CP) power and vacuum (e.g., 10 Pa-4 Pa), 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 and start polishing. 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.

[0164] 2) Specific surface area SSA of silicon-carbon composite material

[0165] The specific surface area is tested by gas adsorption method according to the test standard GB / T 19587-2017, as follows: the battery is disassembled, the negative electrode powder is scraped, and the binder is removed by high-temperature ablation, and then the powder material is taken as the silicon-carbon composite material sample, the sample tube is immersed in liquid nitrogen at-196 ℃, the adsorption amount of nitrogen on the solid surface under different pressures is measured under 0.05-0.30 relative pressure, the monolayer adsorption amount of the sample is calculated based on the BET multilayer adsorption theory and its formula, and then the specific surface area of the negative electrode active material is calculated.

[0166] The calculation formula of BET is as follows:

[0167]

[0168] 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.

[0169] 3) Pore size of silicon-carbon composite material

[0170] The pore size is tested by gas adsorption method according to the test standards GB / T 19587-2017 and GB / T 21650.2-2008, as follows: the silicon-carbon composite material is taken as the sample, the sample tube is immersed in liquid nitrogen at-196 ℃, nitrogen is adsorbed on the material to be tested under 0-1 relative pressure, 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.

[0171] 4) Powder compaction density

[0172] Referring 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 compaction under the pressure is read on the device after waiting for 10s, and the compaction density under the pressure is calculated, the compaction density of the material under the pressure = G / (H*S).

[0173] 5) Silicon and carbon element distribution characterization in silicon-carbon composite material

[0174] The ion polishing section element analysis is used, and the element distribution of the particle section is tested according to the test standard GB-T 17359-2012.

[0175] 6) Silicon element content test in silicon-carbon composite material

[0176] The silicon element content is determined by inductively coupled plasma (ICP) test. Specifically, the silicon-carbon composite material is taken as a sample, the sample is digested with aqua regia and hydrofluoric acid HF, and the ICP test is performed on the 15 min digested solution and the completely digested solution. The silicon content in the 45 min digested solution is the silicon content of the "outer peripheral region" of the silicon-carbon composite material, and the difference between the silicon contents in the completely and 1 h digested solutions is the silicon content of the "central region" of the silicon-carbon composite material.

[0177] 7) Carbon element content test in the silicon-carbon composite material

[0178] The carbon-sulfur content is analyzed by infrared absorption method according to the test standard GB / T20123-2006. Specifically, the silicon-carbon composite material is taken as a sample, and the carbon content at 20 min is the carbon content of the "outer peripheral region" of the silicon-carbon composite material. The difference between the carbon contents at 20 min and at the end of the test is the carbon content of the "outer peripheral region" of the silicon-carbon composite material.

[0179] 8) Short diameter r test of the silicon-carbon composite material

[0180] The short diameter r is determined according to the three-axis characterization method. Specifically, the short diameter r is determined on the planar projection of the silicon-carbon composite material.

[0181] 2, Battery performance

[0182] 1) Room temperature cycle capacity retention rate

[0183] The secondary batteries prepared from each example and the comparative example are charged at a rate of 0.5C to a charge cut-off voltage of 4.25V at 25°C, then charged at a constant voltage until the current is less than 0.05C, and then left for 5 min. Then, the batteries are discharged at a rate of 0.33C to a discharge cut-off voltage of 2V, and then left for 5 min. This is one charge-discharge cycle. The batteries are tested by the above method for cycle charge-discharge, and the capacity retention rate of the lithium ion battery after 800 cycles is calculated.

[0184] 2), Battery internal resistance

[0185] The lithium ion batteries prepared from each example and the comparative example and the lithium ion batteries cycled for 800 times at 25°C are charged at a rate of 1C to 4.3V at 25°C; then, charged at a constant voltage of 4.3V until the current is less than 0.05C, and then discharged at a rate of 1C for 30 min, i.e., the battery is adjusted to 50% SOC. Then, the positive and negative probes of the TH2523A alternating current internal resistance tester are respectively contacted with the positive and negative electrodes of the battery, and the internal resistance value of the battery is read by the internal resistance tester, which is recorded as the initial battery internal resistance (mΩ) and the battery internal resistance (mΩ) after 800 cycles, respectively.

[0186] III. Analysis of test results of each embodiment and comparative example

[0187] Secondary batteries of each embodiment and comparative example were prepared according to the above method, and each parameter was measured, and the results are shown in Table 1 below.

[0188] Table 1

[0189]

[0190] According to the results in Table 1, the batteries of Examples 1-16 have a negative active material of a three-dimensional network cross-linked pore structure silicon-carbon composite material, and the electrolyte contains a compound represented by Formula I or Formula II, and compared with the batteries of Comparative Example 1 in which the electrolyte does not contain a compound represented by Formula I or Formula II, and the batteries of Comparative Examples 2-4 in which the negative active material is a honeycomb pore structure silicon-carbon composite material and the electrolyte contains a compound represented by Formula I or Formula II, the batteries of Examples 1-16 exhibit lower internal resistance and higher cycle capacity retention rate.

[0191] 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, so 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.

[0192] As can be seen from the comparison of Examples 5-6 and Examples 7-8, controlling the ratio EL:SSA between the mass ratio EL of the first component in the electrolyte and the specific surface area of the silicon-carbon composite material in the range of 0.014-0.2 is beneficial to reduce the internal resistance of the battery and improve the cycle capacity retention rate of the battery.

[0193] As can be seen from Examples 9-12, further controlling EL:B1 in the range of 0.15-1.2 is beneficial to further reduce the internal resistance of the battery and improve the cycle capacity retention rate of the battery.

[0194] As can be seen from Examples 13-16, further controlling EL:V1 in the range of 20-300 is beneficial to further reduce the internal resistance of the battery and improve the cycle capacity retention rate of the battery.

[0195] It should be noted that the present application is not limited to the above embodiments. The above 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, and other ways 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 comprises a negative electrode tab comprising a silicon-carbon composite material having a three-dimensional network cross-linked pore structure; and an electrolyte comprising a first component, the first component comprising one or more of compounds represented by Formula I, Formula II, Formula I Formula II wherein R1, R2, R3, R4 comprise at least one of a hydrogen atom, a fluorine atom, a fluorine-substituted or unsubstituted C1-C4 alkyl group, and Formula I contains a fluorine element; a ratio EL:V1 between a mass ratio EL of the first component in the electrolyte and a total pore volume V1 of pores with a pore size greater than 100 nm in the silicon-carbon composite material is 10-500.

2. The secondary battery according to claim 1, characterized by a ratio EL:V1 between a mass ratio EL of the first component in the electrolyte and a total pore volume V1 of pores with a pore size greater than 100 nm in the silicon-carbon composite material is 20-300.

3. The secondary battery according to claim 1 or 2, characterized in that The specific surface area of the silicon-carbon composite material is SSA m 2 / g, a mass ratio of the first component is EL g / g based on a total mass of the electrolyte, EL:SSA is 0.005-0.

4.

4. The secondary battery according to claim 3, characterized by a mass ratio of the first component is EL g / g based on a total mass of the electrolyte, EL: SSA is 0.014-0.

2.

5. The secondary battery according to any one of claims 1 to 4, characterized in that a mass ratio of the first component is EL g / g based on a total mass of the electrolyte, in a peripheral region of the silicon-carbon composite material, a mass percentage content B1 of silicon element in the silicon-carbon composite material relative to a total mass of the silicon-carbon composite material, wherein the peripheral region of the silicon-carbon composite material is a region extending within r / 2 from an outer surface of the silicon-carbon composite material to an inner part of the silicon-carbon composite material, r representing a short diameter of the silicon-carbon composite material, EL:B1 is 0.01-2.

6. The secondary battery according to claim 5, characterized in that EL:B1 is 0.15-1.

2.

7. The secondary battery according to any one of claims 1 to 6, characterized by, the compound represented by Formula I comprises one or more of the following compounds: 、 、 、 、 、 、 、 、 、 、 ； the compound represented by Formula II comprises one or more of the following compounds: 、 、 、 、 、 。 8. The secondary battery according to any one of claims 5 to 7, characterized by, in the peripheral region of the silicon-carbon composite material, a mass percentage content A1 of carbon element in the silicon-carbon composite material relative to a total mass of the silicon-carbon composite material and a mass percentage content B1 of silicon element in the silicon-carbon composite material relative to a total mass of the silicon-carbon composite material satisfy 0.8≤B1 / A1≤2.

5.

9. The secondary battery according to claim 8, characterized by in the peripheral region of the silicon-carbon composite material, a mass percentage content A1 of carbon element in the silicon-carbon composite material relative to a total mass of the silicon-carbon composite material and a mass percentage content B1 of silicon element in the silicon-carbon composite material relative to a total mass of the silicon-carbon composite material satisfy 1≤B1 / A1≤1.

5.

10. The secondary battery according to any one of claims 1 to 9, characterized by A mass percentage content A of carbon element of the silicon-carbon composite material with respect to a total mass of the silicon-carbon composite material has a decreasing tendency in a direction from a geometric center of the silicon-carbon composite material to an outer surface of the silicon-carbon composite material, and a mass percentage content B of silicon element of the silicon-carbon composite material with respect to the total mass of the silicon-carbon composite material has an increasing tendency in the direction from the geometric center of the silicon-carbon composite material to the outer surface of the silicon-carbon composite material.

11. The secondary battery according to any one of claims 1 to 10, wherein The specific surface area SSA of the silicon-carbon composite material satisfies: 2 m 2 / g≤SSA≤10 m 2 / g.

12. The secondary battery according to claim 11, wherein The specific surface area SSA of the silicon-carbon composite material satisfies: 3 m 2 / g≤SSA≤7 m 2 / g.

13. The secondary battery according to any one of claims 1 to 12, characterized by, The silicon-carbon composite material includes: carbon matrix particles including a three-dimensionally network-crosslinked pore structure; and silicon nanoparticles, at least a part of which is disposed in the three-dimensionally network-crosslinked pore structure.

14. The secondary battery according to claim 13, characterized by The silicon nanoparticles include one or more of a silicon oxide compound, amorphous silicon, crystalline silicon, and a silicon-carbon composite.

15. The secondary battery according to claim 14, characterized by The silicon nanoparticles include amorphous silicon.

16. The secondary battery according to any one of claims 13 to 15, characterized by, The carbon matrix particles include one or more of graphite, soft carbon, and hard carbon.

17. The secondary battery according to any one of claims 13 to 16, characterized by, A mass ratio of the silicon nanoparticles in the silicon-carbon composite material is greater than or equal to 40%.

18. The secondary battery according to claim 17, characterized by A mass ratio of the silicon nanoparticles in the silicon-carbon composite material is 40 to 60%.

19. The secondary battery according to any one of claims 1 to 18, 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 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 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 compacted density P21 g / cm3 of the silicon-carbon composite material tested after 20 powder pressings under an action force of 20000 N satisfies:​ 1.00 < P21 / P11 ≤ 1.

20.

20. The secondary battery according to claim 19, characterized by The compaction density P11 g / cm³ of the silicon-carbon composite material was tested after one compaction under a force of 20000 N. 3 The compaction density P21 g / cm³ of the silicon-carbon composite material was measured after 20 cycles of powder compaction under a force of 20000 N. 3 The ratio satisfies: 1.02 ≤ P21 / P11 ≤ 1.

10.

21. The secondary battery according to any one of claims 1 to 20, 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.

22. The secondary battery according to claim 21, 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.

23. The secondary battery according to any one of claims 1 to 22, 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.

24. An electrical device, comprising: A secondary battery according to any one of claims 1 to 23. A secondary battery according to any one of claims 1 to 23.

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