Secondary battery and electric device

Abstract

The application provides a secondary battery. 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 dimethyl carbonate. Through the cooperation of the three-dimensional network cross-linked pore structure of the silicon-carbon composite material and the dimethyl carbonate in the electrolyte, the volume effect of the active material in the charging and discharging process is inhibited, the interface stability is improved, the internal resistance of the battery is reduced, and the cycle capacity retention rate and the charging and discharging performance at high rate 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 utilization 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] Electrode active materials with high specific capacity often have poor cycle performance and kinetic performance. How to improve the energy density of the battery while taking into account excellent cycle performance and kinetic 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 made in view of the above-mentioned problems, and aims to provide a secondary battery. By matching the electrolyte with the negative electrode material, the volume effect of the active material during charging and discharging is inhibited, the interface stability is improved, the internal resistance of the battery is reduced, and the cycle capacity retention rate and rate performance 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 comprises a silicon-carbon composite material with a three-dimensional network cross-linked pore structure, and the electrolyte comprises dimethyl carbonate.

[0006] The silicon-carbon composite material with a three-dimensional network cross-linked pore structure has a stable porous skeleton 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 dimethyl carbonate matched in the electrolyte can improve the backflow speed of the electrolyte during charging and discharging, promote the transmission of ions at the active material / electrolyte interface, effectively reduce the battery polarization impedance, and thus improve the cycle performance and rate performance of the battery.

[0007] In any embodiment, the pore volume of the silicon-carbon composite material per unit mass is Vm, in cm3 / g; the mass percentage of the dimethyl carbonate in the electrolyte is EL g / g based on the total mass of the electrolyte, and the ratio EL:Vm between the pore volume Vm of the silicon-carbon composite material and the mass percentage EL of the dimethyl carbonate in the electrolyte is 0.5-20, preferably 2-13. 3 / g; the mass percentage of the dimethyl carbonate in the electrolyte is EL g / g based on the total mass of the electrolyte, and the ratio EL:Vm between the pore volume Vm of the silicon-carbon composite material and the mass percentage EL of the dimethyl carbonate in the electrolyte is 0.5-20, preferably 2-13.

[0008] When the ratio EL:Vm between the mass ratio EL of dimethyl carbonate in the electrolyte and the pore volume Vm of the silicon-carbon composite material satisfies the above range, the amount of added dimethyl carbonate and the pore volume Vm of the silicon-carbon composite material can be matched, the cycle capacity retention rate of the battery can be improved, and the rate performance of the battery can be improved.

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

[0010] When the pore volume Vm per unit mass of the silicon-carbon composite material is within the above range, the small-molecule dimethyl carbonate can easily enter the pore structure of the silicon-carbon composite material and match with it, the internal resistance of the battery can be reduced, and the cycle performance of the battery can be improved.

[0011] In any embodiment, the mass ratio EL of dimethyl carbonate in the electrolyte based on the total mass of the electrolyte is EL g / g, and the ratio EL:SSA between the mass ratio EL of dimethyl carbonate in the electrolyte and the specific surface area SSA of the silicon-carbon composite material is 0.01-0.5, and optionally 0.05-0.25.

[0012] When the ratio EL:SSA between the mass ratio EL of dimethyl carbonate in the electrolyte and the specific surface area SSA of the silicon-carbon composite material satisfies the above range, the dimethyl carbonate can effectively enter the pore structure of the silicon-carbon composite material, fully contact the silicon-carbon composite material, improve the migration rate of ions at the electrode / electrolyte interface, reduce the internal resistance of the battery, and improve the cycle performance and high-rate capacity 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, the kinetic performance of the secondary battery is good, and the rate performance is high.

[0015] In any embodiment, the mass ratio EL of dimethyl carbonate in the electrolyte based on the total mass of the electrolyte is EL g / g, the total pore volume V1 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 the ratio EL:V1 between the mass ratio EL of dimethyl carbonate 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 is 10-200, and optionally 30-120.

[0016] The small molecule dimethyl carbonate can easily enter the pore structure of the silicon-carbon composite material, form a mutual fit with the silicon-carbon composite material, further improve the migration rate of ions in the electrode active material, and improve the cycle performance and rate performance of the battery.

[0017] In any embodiment, the silicon-carbon composite material comprises carbon matrix particles and silicon nanoparticles, the carbon matrix has a three-dimensionally network-crosslinked pore structure, and the silicon nanoparticles are at least partially embedded in the three-dimensionally network-crosslinked pore structure of the carbon matrix particles.

[0018] The carbon matrix of the present application has a stable porous framework structure, strong support capability, high stress capability, excellent mechanical properties and electrical conductivity; the carbon matrix comprises a three-dimensionally network-crosslinked pore structure, and has 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 is 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 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.

[0019] 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%.

[0020] The negative electrode material used in the secondary battery of the present application realizes high loading capacity of silicon nanoparticles in the negative electrode material by using a carbon matrix material having a three-dimensionally network-crosslinked pore structure, so that the silicon-carbon composite material has high capacity and can further improve the energy density of the battery.

[0021] In any embodiment, the silicon nanoparticles comprise one or more of silicon oxide compounds, pre-lithiated silicon oxide compounds, amorphous silicon, crystalline silicon and silicon-carbon composites.

[0022] In any embodiment, the carbon matrix comprises one or more of graphite, soft carbon and hard carbon.

[0023] The above material, when prepared into a porous structure, is beneficial to embedding silicon-based nanoparticles in the pores of the porous structure, and has relatively high structural stability.

[0024] 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 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 3If the carbon matrix particles are 1 < Vc2 / Vc1 ≤ 30, then 3 ≤ Vc2 / Vc1 ≤ 25.

[0025] By controlling the total pore volume ratio of pores of a specific size in porous carbon matrix particles, the pore size distribution of the carbon matrix particles can be made moderate, which is conducive to silicon nanoparticles entering the pores of the carbon matrix particles. It can also make the specific surface area of ​​silicon-carbon composite particles moderate and improve their reversible capacity.

[0026] In any embodiment, the powder compaction density P11 g / cm³ of the silicon-carbon composite material after undergoing one powder compaction test under a force of 20000N is measured. 3 The compaction density of the silicon-carbon composite material after 20 cycles of powder compaction under a force of 20000N is recorded as P21 g / cm³. 3 The ratio satisfies: 1.00 < P21 / P11 ≤ 1.20, and optionally, 1.02 ≤ P21 / P11 ≤ 1.10.

[0027] When the ratio of P21 / P11 meets the above range, the silicon-carbon composite material has both high specific capacity and good compressive strength, which improves the structural stability of the negative electrode film. As a result, the secondary battery containing this material has both high energy density and good cycle performance.

[0028] In any embodiment, the powder compaction density P11 g / cm³ of the silicon-carbon composite material after undergoing one powder compaction test under a force of 20000N is measured. 3 It satisfies: 1.10≤P11≤1.40, and optionally, 1.12≤P11≤1.35.

[0029] The compacted density P11 of the silicon-carbon composite material after one compaction under a force of 20000N is measured. 3 When the above range is met, the negative electrode film layer has a high compaction density, which in turn enables the secondary battery to have a high energy density.

[0030] In any embodiment, the conductivity of the electrolyte is 8–12 ms / cm, and can be selected as 9–11 ms / cm.

[0031] When the conductivity of the electrolyte is within the above range, the migration rate of ions in the electrolyte can be ensured, thereby improving the cycle performance and cycle efficiency of the battery.

[0032] In any embodiment, the secondary battery includes at least one of lithium-ion batteries, sodium-ion batteries, magnesium-ion batteries, and potassium-ion batteries.

[0033] A second aspect of this application provides an electrical device comprising the secondary battery of the first aspect. Attached Figure Description

[0034] Figure 1 This is a schematic diagram of a secondary battery according to one embodiment of this application;

[0035] Figure 2 yes Figure 1 An exploded view of a secondary battery according to an embodiment of this application is shown.

[0036] Figure 3 This is a schematic diagram of an electrical device that uses a secondary battery as a power source according to one embodiment of this application.

[0037] Explanation of reference numerals in the attached figures:

[0038] 1. Secondary battery; 11. Housing; 12. Electrode assembly; 13. Cover plate. Detailed Implementation

[0039] The following detailed description, with appropriate reference to the accompanying drawings, discloses embodiments of the adhesive, preparation method, electrode, battery, and power device of this application. However, unnecessary details may be omitted. For example, detailed descriptions of well-known matters and repetitive descriptions of essentially identical structures may be omitted. This is to avoid unnecessarily lengthy descriptions and to facilitate understanding by those skilled in the art. Furthermore, the accompanying drawings and the following description are provided for the purpose of enabling those skilled in the art to fully understand this application and are not intended to limit the subject matter of the claims.

[0040] The "range" disclosed in this application is defined by a lower limit and an upper limit. A given range is defined by selecting a lower limit and an upper limit, which define the boundaries of a particular range. Ranges defined in this way can include or exclude endpoints and can be arbitrarily combined; that is, any lower limit can be combined with any upper limit to form a range. For example, if ranges of 60-120 and 80-110 are listed for a specific parameter, it is expected that ranges of 60-110 and 80-120 are also included. Furthermore, if minimum range values ​​of 1 and 2 are listed, and if maximum range values ​​of 3, 4, and 5 are listed, then the following ranges are all expected: 1-3, 1-4, 1-5, 2-3, 2-4, and 2-5. In this application, unless otherwise stated, the numerical range "ab" represents a shortened representation of any combination of real numbers between a and b, where a and b are real numbers. For example, the numerical range "0-5" indicates that all real numbers between "0-5" have been listed in this article; "0-5" is simply a shortened representation of these numerical combinations. Furthermore, when a parameter is stated as an integer ≥2, it is equivalent to disclosing that the parameter is, for example, an integer such as 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, etc.

[0041] If not particularly specified, all the embodiments and optional embodiments of the present application can be combined with each other to form new technical solutions.

[0042] If not particularly specified, all the technical features and optional technical features of the present application can be combined with each other to form new technical solutions.

[0043] If not particularly specified, all the steps of the present application can be performed in sequence or randomly, and preferably in sequence. For example, the method comprises steps (a) and (b), which means that the method can comprise steps (a) and (b) performed in sequence, or steps (b) and (a) performed in sequence. For example, the method also comprises 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.

[0044] If not particularly specified, the "comprising" and "including" mentioned in the present application are open-ended and can also be closed. For example, the "comprising" and "including" can mean that other components not listed can also be included, or only the listed components can be included.

[0045] If not particularly specified, in the present application, the term "or" is inclusive. For example, the phrase "A or B" means "A, B, or both A and B". More specifically, any one of the following conditions satisfies the condition "A or B": A is true (or exists) and B is false (or does not exist); A is false (or does not exist) and B is true (or exists); or A and B are both true (or exist).

[0046] 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 for high-energy-density batteries. However, the silicon-based material has a large volume expansion rate during charging and discharging, 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.

[0047] 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 dimethyl carbonate.

[0048] In this paper, 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 volume in the pore structure formed by the silicon-carbon composite material, especially the carbon matrix particles.

[0049] The pore structure of the silicon-carbon composite material can be tested using equipment and methods known in the art. For example, testing can be performed 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 (e.g., copper foil), and use glue (e.g., double-sided tape) to fix the sample to be tested between the sheets. A certain mass (e.g., about 400 g) of flat iron is used to press for a certain period of time (e.g., 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 the sample to a sample stage with conductive glue, with the sample slightly protruding from the edge of the sample stage. Then, place the sample stage into 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 to 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.

[0050] The silicon-carbon composite material having 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 content of silicon. At the same time, dimethyl carbonate can increase the backflow speed of the electrolyte during the charging and discharging process, promote the transmission of ions at the active material / electrolyte interface, reduce the interface deterioration due to polarization, and improve the cycle performance of the battery and the charging and discharging capacity under high rate conditions.

[0051] In some embodiments, the silicon-carbon composite material has a pore volume Vm cm 3 / g, and Vm is defined by the following formula: wherein p 真 represents the true density of the silicon-carbon composite material, a represents the porosity of the silicon-carbon composite material; the mass ratio of dimethyl carbonate in the electrolyte is EL g / g, and the ratio EL:Vm between the pore volume Vm of the silicon-carbon composite material and the mass ratio EL of dimethyl carbonate in the electrolyte is 0.5-20, preferably 2-13.

[0052] In some embodiments, the ratio EL:Vm between the pore volume Vm of the silicon-carbon composite material and the mass ratio EL of dimethyl carbonate 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, 1.1, 1.2, 1.3, 1.4, 1.5, 1.6, 1.7, 1.8, 1.9, 2, 2.5, 3, 3.5, 4, 4.5, 5, 5.5, 6, 6.5, 7, 7.5, 8, 8.5, 9, 9.5, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, or 20.

[0053] The pore volume Vm of the silicon-carbon composite material can be calculated by the following formula: wherein, p 真 represents the true density of the silicon-carbon composite material, and a 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 a well-known meaning in the art, which refers to the actual mass of solid matter per unit volume of the material in an absolutely dense state, i.e., the density after removing the internal voids or intergranular voids of the material; it can be tested by using 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 performed: place a clean and dry sample cup on a balance, zero, add a certain amount of powder sample into 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.

[0054] When the ratio EL:Vm between the pore volume Vm of the silicon-carbon composite material and the mass ratio EL of dimethyl carbonate in the electrolyte satisfies the above range, the addition amount of dimethyl carbonate and the pore volume Vm of the silicon-carbon composite material can form a mutual cooperation, the cycle capacity retention rate of the battery can be improved, and the rate performance of the battery can be improved.

[0055] In some embodiments, the pore volume per unit mass Vm of the silicon-carbon composite material is 0.01-0.3, which can be selected from 0.04-0.15 cm 3 / g.

[0056] In some embodiments, the pore volume of the silicon-carbon composite per unit mass Vm can be selected from 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, 0.20, 0.21, 0.22, 0.23, 0.24, 0.25, 0.26, 0.27, 0.28, 0.29, 0.3 cm3 / g. 3 / g.

[0057] When the pore volume of the silicon-carbon composite per unit mass Vm is within the above range, the small molecule dimethyl carbonate can easily enter the pore structure of the silicon-carbon composite and interact therewith, reducing the internal resistance of the battery and improving the cycle performance of the battery.

[0058] In some embodiments, the ratio EL:SSA between the mass percentage of dimethyl carbonate in the electrolyte and the specific surface area SSA of the silicon-carbon composite is 0.01-0.5, which can be selected from 0.05-0.25.

[0059] In some embodiments, the mass percentage of dimethyl carbonate in the electrolyte based on the total mass of the electrolyte is EL g / g, and the specific surface area of the silicon-carbon composite is SSA, and EL:SSA can be selected from 0.01, 0.02, 0.03, 0.04, 0.05, 0.06, 0.07, 0.08, 0.09, 0.1, 0.15, 0.2, 0.25, 0.3, 0.35, 0.4, 0.45 or 0.5.

[0060] In this context, the specific surface area SSA is the meaning known in the art, and the surface area is usually expressed in m 2 / g, which can be tested by methods and instruments known in the art. For example, it can be tested by the inert gas (e.g. nitrogen) adsorption specific surface area analysis test method according to GB / T 19587-2017, and the BET (Brunauer Emmett Teller) method is used for calculation, wherein the nitrogen adsorption specific surface area analysis test can be performed by a Tri-Star 3020 type specific surface area pore size analyzer of the American Micromeritics company.

[0061] When the ratio EL:SSA between the mass percentage of dimethyl carbonate in the electrolyte and the specific surface area SSA of the silicon-carbon composite satisfies the above range, the dimethyl carbonate can effectively enter the pore structure of the silicon-carbon composite and fully contact the silicon-carbon composite, thereby improving the migration rate of ions at the electrode / electrolyte interface, reducing the internal resistance of the battery, and improving the cycle performance and high-rate capacity of the battery.

[0062] In some embodiments, the specific surface area SSA of the silicon-carbon composite material is 2-10 m 2 / g; or 3-7 m 2 / g.

[0063] The specific surface area SSA of the silicon-carbon composite material can be 2 m 2 / g, 3 m 2 / g, 4 m 2 / g, 5 m 2 / g, 6 m 2 / g, 7 m 2 / g, 8 m 2 / g, 9 m 2 / g, or 10 m 2 / g, or a range formed by any two of the above values.

[0064] 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 coulombic efficiency of the battery.

[0065] In some embodiments, the mass percentage of the dimethyl carbonate in the electrolyte based on the total mass of the electrolyte is EL 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 the ratio EL:V1 between the mass percentage EL of the dimethyl carbonate in the electrolyte and the total pore volume V1 of the pores with a pore size less than or equal to 100 nm in the silicon-carbon composite material is 10-200, or 30-120.

[0066] The pore volume of pores with different sizes can be tested according to GB / T 19587-2004, using the BJH (Barret joyner Halenda) method for testing the mesopore size distribution, and using the gas adsorption-desorption method under the micropore-mesopore model to test and select 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.

[0067] In some embodiments, the ratio EL:V1 between the mass percentage EL of the dimethyl carbonate in the electrolyte and the total pore volume V1 of the pores with a pore size less than or equal to 100 nm in the silicon-carbon composite material is 10, 15, 20, 25, 30, 35, 40, 45, 50, 55, 60, 65, 70, 75, 80, 85, 90, 95, 100, 110, 120, 130, 140, 150, 160, 170, 180, 190, or 200.

[0068] The small molecule dimethyl carbonate can easily enter the pore structure of the silicon-carbon composite material, form a mutual fit with the silicon-carbon composite material, further improve the migration rate of ions in the electrode active material, and improve the cycle performance and rate performance of the battery.

[0069] In some embodiments, the silicon-carbon composite material has a V1≥0.001 cm 3 / g, and optionally 0.005-0.01 cm 3 / g.

[0070] In some embodiments, the silicon-carbon composite material has a V1of 0.005, 0.006, 0.007, 0.008, 0.009, or 0.01 cm 3 / g.

[0071] When the V1of the silicon-carbon composite material is within the above range, the small molecule dimethyl carbonate can easily enter the pore structure of the silicon-carbon composite material, form a mutual fit with the silicon-carbon composite material, further improve the migration rate of ions in the electrode active material, and improve the cycle performance and rate performance of the battery.

[0072] In some embodiments, the silicon-carbon composite material comprises carbon matrix particles and silicon nanoparticles, the carbon matrix has a three-dimensionally network-crosslinked pore structure, and the silicon nanoparticles are at least partially embedded in the three-dimensionally network-crosslinked pore structure of the carbon matrix particles.

[0073] The carbon matrix of the present application has a stable porous framework structure, strong support capability, high stress capability, excellent mechanical properties, and excellent electrical conductivity; the carbon matrix comprises a three-dimensionally network-crosslinked pore structure, and has a large 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 is 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 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 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.

[0074] In some embodiments, the mass ratio of the silicon nanoparticles in the silicon-carbon composite material is greater than or equal to 40%, and optionally 40-60%.

[0075] In some embodiments, the mass ratio of the silicon nanoparticles in the silicon-carbon composite material is 40%, 45%, 50%, 55%, or 60%.

[0076] 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 optical 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 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; the energy released in the above process is recorded as different characteristic spectral lines for trace element quantitative analysis.

[0077] The negative electrode material used in the secondary battery of the present application realizes 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.

[0078] In some embodiments, the silicon nanoparticles include one or more of silicon oxide compounds, pre-lithiated silicon oxide compounds, amorphous silicon, crystalline silicon, and silicon-carbon composites.

[0079] In some embodiments, the carbon matrix includes one or more of graphite, soft carbon, and hard carbon.

[0080] When the above-mentioned material is prepared into a porous structure, it is beneficial for the silicon-based nanoparticles to be embedded in the pores of the porous structure, and the structural stability is relatively high.

[0081] 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, 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, and r represents the short diameter of the silicon-carbon composite material.

[0082] The silicon element content can be determined by inductively coupled plasma (ICP) emission spectroscopy, specifically as follows: take the silicon-carbon composite material as a sample, digest the sample with aqua regia and hydrofluoric acid HF, take the 15 min digested solution and the completely digested solution for ICP testing, and the silicon content in the 45 min digested solution is the silicon content in the "peripheral region of the silicon-carbon composite material".

[0083] 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 area" of the silicon-carbon composite material.

[0084] When A1 and B1 meet the above range, the mass of the silicon nanoparticles attached to the inside of the carbon matrix particles is relatively high, which can significantly improve the capacity of the negative electrode active material, and the voltage of metal ion intercalation is low, which is beneficial to the intercalation of metal ions, thereby further improving the capacity retention rate of the secondary battery during charging and discharging at high rate.

[0085] 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 meet: 1

[0086] 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 beneficial to the entry of silicon nanoparticles into the pores of the carbon matrix particles, and the specific surface area of the silicon-carbon composite particles can be moderate, thereby improving the reversible capacity.

[0087] In some embodiments, the powder compaction density P11 g / cm 3 of the silicon-carbon composite material after 1 powder pressing under the action of 20000N is tested, and the compaction density P21 g / cm 3 of the silicon-carbon composite material after 20 powder pressings under the action of 20000N is tested, and the ratio of P21 / P11 satisfies: 1.00

[0088] When the ratio of P21 / P11 meets the above range, the silicon-carbon composite material has higher gravimetric capacity and better pressure resistance, which improves the structural stability of the negative electrode film layer, thereby making the secondary battery containing the material have higher energy density while having better cycle performance.

[0089] In some embodiments, the powder compaction density P11 g / cm 3 of the silicon-carbon composite material after 1 powder pressing under the action of 20000N satisfies: 1.10

[0090] The powder compaction density P11 of the silicon-carbon composite material after 1 time of powder pressing under a force of 20000 N is g / cm3 3 When the above range is met, the negative electrode film layer has a high compaction density, thereby making the secondary battery have a high energy density.

[0091] In some embodiments, the conductivity of the electrolyte is 8-12 ms / cm, and optionally 9-11 ms / cm.

[0092] In some embodiments, the conductivity of the electrolyte is optionally 8, 9, 10, 11 or 12 ms / cm.

[0093] When the conductivity of the electrolyte is within the above range, the migration rate of ions in the electrolyte can be ensured, and the cycle performance and cycle efficiency of the battery are improved.

[0094] 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.

[0095] For example, the negative electrode current collector has two opposite surfaces in the thickness direction thereof, and the negative electrode film layer is disposed on any one or both of the two opposite surfaces of the negative electrode current collector.

[0096] In some embodiments, the negative electrode 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 comprise 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 and 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.).

[0097] 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).

[0098] 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.

[0099] 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)), etc.

[0100] 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, etc., a negative electrode sheet can be obtained.

[0101] 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.

[0102] As an example, the positive electrode current collector has two surfaces opposite in the thickness direction thereof, and the positive electrode film layer is disposed on either one or both of the two opposite surfaces of the positive electrode current collector.

[0103] In some embodiments, the positive electrode current collector can adopt 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, and silver alloy, etc.) on a polymer material base material (such as a base material of polypropylene (PP), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polystyrene (PS), polyethylene (PE), etc.).

[0104] In some embodiments, the positive electrode active material can adopt 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 the following materials: lithium-containing phosphate of olivine structure, lithium transition metal oxide, and their respective modified compounds. 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 or in combination of two or more. Among them, examples of the lithium transition metal oxide can include, but are not limited to, lithium cobalt oxide (such as LiCoO2), lithium nickel oxide (such as LiNiO2), lithium manganese oxide (such as LiMnO2, LiMn2O4), lithium nickel cobalt oxide, lithium manganese cobalt oxide, lithium nickel manganese oxide, lithium nickel cobalt manganese oxide (such as 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.

[0105] 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%.

[0106] 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 acrylic ester resin.

[0107] 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.

[0108] 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.

[0109] 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.

[0110] 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.

[0111] 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.

[0112] In one embodiment of the present application, a power device is provided, which comprises the secondary battery of any of the embodiments.

[0113] 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.

[0114] 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.

[0115] 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.

[0116] 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.

[0117] 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.

[0118] Examples

[0119] 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 commercially.

[0120] Primary and secondary batteries

[0121] Example 1

[0122] (1) Preparation of silicon-carbon composite material

[0123] A gas containing a silicon precursor is provided to carbon substrate particles having a three-dimensional network cross-linked pore structure; silicon nanoparticles attached to the carbon substrate 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 substrate is hard carbon.

[0124] (2) Preparation of negative electrode sheet

[0125] The negative electrode 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, and stirred 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.

[0126] (3) Preparation of positive electrode sheet

[0127] An aluminum foil with a thickness of 8 μm is used as the positive electrode current collector. The positive electrode 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 after being stirred and mixed uniformly, a positive electrode slurry is obtained. The positive electrode slurry is then uniformly coated on the positive electrode current collector, and after drying, cold pressing, and slitting, a positive electrode sheet is obtained.

[0128] (4) Preparation of electrolyte

[0129] Ethylene carbonate (EC), diethyl carbonate (DEC), and methyl ethyl carbonate (EMC) were mixed in a volume ratio of 1:1:1 to obtain an organic solvent, and then a fully dried lithium salt LiPF6 was dissolved in the mixed organic solvent to prepare an electrolyte with a concentration of 1 mol / L, and 30 wt% of dimethyl carbonate was added and uniformly mixed.

[0130] (5) separator

[0131] A polypropylene film was used as the separator.

[0132] (6) Preparation of the battery

[0133] The positive electrode sheet, the separator, and the negative electrode sheet were stacked in order, with the separator between the positive and negative electrode sheets to serve as a separator, and then wound to obtain a bare cell. The bare cell was welded with tabs, and the bare cell was loaded 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, and capacity testing in sequence to obtain the lithium ion battery product of Example 1.

[0134] Examples 2-5

[0135] The preparation method of the battery of Examples 2-5 was similar to that of Example 1, but the mass ratio EL of dimethyl carbonate in the electrolyte was adjusted. The specific parameters are shown in Table 1.

[0136] Examples 6-9

[0137] The preparation method of the battery of Examples 6-9 was similar to that of Example 1, but the mass ratio EL of dimethyl carbonate in the electrolyte and the related parameters of the silicon-carbon composite material were adjusted at the same time.

[0138] Comparative Example 1

[0139] The preparation method of the battery of Comparative Example 1 was similar to that of Example 1, but no dimethyl carbonate was added to the electrolyte.

[0140] Comparative Example 2

[0141] The preparation method of the battery of Comparative Example 2 was similar to that of Example 1, but the pore structure of the carbon matrix particles of Comparative Example 2 was a honeycomb pore structure.

[0142] II. Test Methods

[0143] 1. Silicon-carbon composite material

[0144] 1) Structure characterization of the silicon-carbon composite material

[0145] The pore structure of the silicon-carbon composite material can be tested using equipment and methods known in the art. For example, testing can be performed 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 fix the sample to be tested with the sheet with glue (such as double-sided tape) for a certain period of time (e.g., 1 hour) with a certain mass (e.g., about 400 g) of flat iron to make the gap between the sample to be tested and the copper foil as small as possible, then trim the edges with scissors, and stick them on the sample stage with conductive glue, with the sample slightly protruding 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., 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 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.

[0146] 2) Porosity of the silicon-carbon composite material

[0147] After disassembling the battery, the negative electrode film layer is obtained, the negative electrode film layer is removed after high-temperature ablation of the binder to obtain a silicon-carbon composite material powder, and the porosity is measured according to GB / T24586 using a gas displacement method. The porosity P = (V1-V2) / V1*100%, wherein V1 is the apparent volume of the sample, and V2 is the true volume of the sample.

[0148] 3) Specific surface area SSA of the silicon-carbon composite material

[0149] The specific surface area is tested according to the test standard GB / T19587-2017 using a gas adsorption method, as follows: the silicon-carbon composite material is taken as the sample, the sample tube is immersed in liquid nitrogen at -196°C, the adsorption amount of nitrogen on the surface of the solid at different pressures is measured under a relative pressure of 0.05-0.30, the monolayer adsorption amount of the sample is calculated based on the BET multilayer adsorption theory and its formula, and thus the specific surface area of the negative electrode active material is calculated.

[0150] The calculation formula of BET is as follows:

[0151]

[0152] 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.

[0153] 4) Pore size of silicon-carbon composite

[0154] Pore size is tested by gas adsorption method according to GB / T 19587-2017 & GB / T 21650.2-2008 test standard, which is as follows: take silicon-carbon composite as sample, immerse the sample tube in liquid nitrogen at -196℃, adsorb nitrogen on the material to be tested under the relative pressure of 0-1, and characterize the pore size distribution of the porous material based on the relationship between the volume of each pore size and the corresponding partial pressure.

[0155] 5) Compacted density of powder

[0156] According to GB / T 24533-2009, use an electronic pressure testing machine (such as UTM7305) to test: place a certain mass G of the powder sample to be tested on a compaction special mold (bottom area S), set different pressures (20000N or 50000N can be used in this application), keep pressure for 20s, remove the pressure, wait for 10s, read the thickness H of the powder after compaction under the pressure on the device, and calculate the compaction density under the pressure, the compaction density of the material under the pressure = G / (H*S).

[0157] 6) True density of silicon-carbon composite

[0158] According to GB / T 24586-2009, the test instrument can use a true density tester. As an example, the following steps can be followed: place a clean and dry silicon-carbon composite sample cup on a 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, 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.

[0159] 7) Distribution of silicon and carbon elements in silicon-carbon composite

[0160] Use energy spectrum ion polishing section element analysis according to GB-T 17359-2012 test standard to test the element distribution of the particle section.

[0161] 2, Electrolyte

[0162] 1) Conductivity test of electrolyte

[0163] Use a conductivity meter to test the electrolyte at 25℃, and the model of the conductivity meter is Mettler conductivity meter S230.

[0164] 3, Battery performance

[0165] 1) Cycle capacity retention rate

[0166] The secondary batteries prepared in each example and comparative example were charged at a constant current of 0.5C rate to a charge cut-off voltage of 4.25V at 25°C, then charged at a constant voltage until the current was less than or equal to 0.05C, and then rested for 5min, and then discharged at a constant current of 0.33C rate to a discharge cut-off voltage of 2V, and then rested for 5min, which was one charge-discharge cycle. The batteries were tested by the above method for cycle charge-discharge, and the capacity retention rate of the lithium ion battery after 800 cycles was calculated.

[0167] 2) Cycle capacity retention rate at high rate

[0168] The secondary batteries prepared in each example and comparative example were charged at a constant current of 0.5C rate to a charge cut-off voltage of 4.25V at 25°C, then charged at a constant voltage until the current was less than or equal to 0.05C, and then rested for 5min, and then discharged at a constant current of 0.33C rate to a discharge cut-off voltage of 2V, and then rested for 5min, which was one charge-discharge cycle. Then the batteries were charged at a constant current of 2C rate to a charge cut-off voltage of 4.25V, and then discharged at a constant current of 0.33C rate to a discharge cut-off voltage of 2V, and the batteries were tested by the above method for cycle charge-discharge, and the capacity retention rate of the lithium ion battery after 800 cycles was calculated.

[0169] 3) Battery internal resistance test

[0170] The secondary batteries prepared in each example and comparative example and the lithium ion battery cycled 800 times at 2C rate at 25°C were charged at a constant current of 1C to 4.3V at 25°C. Then, the batteries were charged at a constant voltage of 4.3V until the current was less than 0.05C, and then discharged at 1C for 30min, i.e. the battery capacity was adjusted to 50% SOC. Then, the positive and negative probes of the TH2523A AC internal resistance tester were respectively contacted with the positive and negative electrodes of the battery, and the internal resistance value of the battery was read by the internal resistance tester, which were respectively recorded as the initial battery internal resistance (mΩ) and the battery internal resistance after 800 times (mΩ).

[0171] III. Analysis of test results of each example and comparative example

[0172] The secondary batteries of each example and comparative example were prepared according to the above method, and each parameter was measured, and the results are shown in Table 1 below.

[0173] Table 1

[0174]

[0175] According to the results in Table 1, the negative electrode active material of the batteries in Examples 1-9 is a silicon-carbon composite material with a three-dimensional network cross-linked pore structure, and the electrolyte contains dimethyl carbonate. Compared with the battery in Comparative Example 1 with a silicon-carbon composite material with a three-dimensional network cross-linked pore structure and no dimethyl carbonate in the electrolyte, the battery in Comparative Example 2 with a silicon-carbon composite material with a honeycomb pore structure and dimethyl carbonate in the electrolyte, the battery in Comparative Example 3 with diethyl carbonate, and the battery in Comparative Example 4 with methyl ethyl carbonate, the batteries in Examples 1-9 exhibit lower internal resistance, higher cycle capacity retention, and better high-rate charge-discharge performance.

[0176] In the comparative example, the negative electrode is a silicon-carbon composite material with a honeycomb pore structure. Silicon particles are not easily deposited inside the honeycomb pore structure. Therefore, the mass content of silicon-based particles in the silicon-carbon composite material with a honeycomb pore structure is low, only 7%. Moreover, the silicon element is concentrated on the surface of the composite material. The carbon matrix is ​​unable to restrict the expansion of silicon-based particles, resulting in poor cycle performance of the battery.

[0177] A comparison of Examples 2-3 and Examples 4-5 shows that controlling the ratio EL:Vm between the pore volume Vm of the silicon-carbon composite material and the mass percentage EL of dimethyl carbonate in the electrolyte to be in the range of 0.5 to 20 can significantly improve the rate performance of the battery while improving the battery cycle capacity retention rate.

[0178] As can be seen from Examples 6-9, controlling EL:SSA to 0.05-0.25 or EL:V1 to 30-120 can further improve the cycle performance and rate performance of the battery.

[0179] It should be noted that this application is not limited to the above-described embodiments. The above embodiments are merely examples, and any embodiments with the same structure and effect as the technical concept within the scope of this application are included in the technical scope of this application. Furthermore, various modifications that can be conceived by those skilled in the art to the embodiments, and other ways of constructing by combining some of the constituent elements of the embodiments, without departing from the spirit of this application, are also included in the scope of this application.

Claims

1. A secondary battery characterized by comprising: The secondary battery according to any one of claims 1 to 8, wherein The negative electrode sheet includes a silicon-carbon composite material having a three-dimensionally networked crosslinked pore structure; and The electrolyte includes dimethyl carbonate, The mass ratio of the dimethyl carbonate in the electrolyte based on the total mass of the electrolyte is EL g / g, the specific surface area of the silicon-carbon composite material is SSA, and EL:SSA is 0.01 to 0.

5.

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; The mass ratio of the dimethyl carbonate in the electrolyte based on the total mass of the electrolyte is EL g / g, The ratio EL:Vm between the pore volume per unit mass Vm of the silicon-carbon composite material and the mass ratio EL of the dimethyl carbonate in the electrolyte is 0.5 to 20.

3. The secondary battery according to claim 2, wherein The ratio EL:Vm between the pore volume per unit mass Vm of the silicon-carbon composite material and the mass ratio EL of the dimethyl carbonate in the electrolyte is 2 to 13.

4. The secondary battery according to claim 2 or 3, 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.

5. The secondary battery according to claim 4, 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.

6. The secondary battery according to any one of claims 1 to 5, characterized by The mass ratio of the dimethyl carbonate in the electrolyte based on the total mass of the electrolyte is EL g / g, the specific surface area of the silicon-carbon composite material is SSA, and EL: SSA is 0.05 to 0.

25.

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

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

9. The secondary battery according to any one of claims 1 to 8, characterized by, The mass ratio of the dimethyl carbonate in the electrolyte based on the total mass of the electrolyte is EL g / g, the total pore volume of pores having a pore diameter of 100 nm or less in the silicon-carbon composite material is VI cm3 / g, and the ratio EL:VI between the mass ratio EL of the dimethyl carbonate in the electrolyte and the total pore volume VI of pores having a pore diameter of 100 nm or less in the silicon-carbon composite material is 10 to 200.

10. The secondary battery according to claim 9, characterized by The mass ratio of the dimethyl carbonate in the electrolyte based on the total mass of the electrolyte is EL g / g, the total pore volume of pores having a pore diameter of 100 nm or less in the silicon-carbon composite material is VI cm3 / g, and the ratio EL:VI between the mass ratio EL of the dimethyl carbonate in the electrolyte and the total pore volume VI of pores having a pore diameter of 100 nm or less in the silicon-carbon composite material is 30 to 120.

11. The secondary battery according to claim 9 or 10, characterized by VI of the silicon-carbon composite material is 0.001 cm3 / g or more.

12. The secondary battery according to claim 11, characterized by VI of the silicon-carbon composite material is 0.005 to 0.01 cm3 / g.

13. The secondary battery according to any one of claims 1 to 12, characterized by, The silicon-carbon composite material includes carbon base particles having a three-dimensionally networked crosslinked pore structure, and silicon nanoparticles at least partially embedded in the three-dimensionally networked crosslinked pore structure of the carbon base particles.

14. The secondary battery according to claim 13, characterized by The mass ratio of the silicon nanoparticles in the silicon-carbon composite material is 40% or more.

15. The secondary battery according to claim 14, characterized by The mass ratio of the silicon nanoparticles in the silicon-carbon composite material is 40 to 60%.

16. The secondary battery according to any one of claims 13 to 15, characterized by The silicon nanoparticles include one or more of a silicon oxide compound, amorphous silicon, crystalline silicon, and a silicon-carbon composite.

17. The secondary battery according to any one of claims 13 to 16, characterized by The carbon base includes one or more of graphite, soft carbon, and hard carbon.

18. The secondary battery according to any one of claims 13 to 17, characterized by, The total volume of pores with a pore size greater than 100 nm in the carbon matrix particles is denoted as Vc1 cm3 / g, 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, and the carbon matrix particles satisfy: 1 < Vc2 / Vc1 ≤ 30.

19. The secondary battery according to claim 18, characterized by The total volume of pores with a pore size greater than 100 nm in the carbon matrix particles is denoted as Vc1 cm3 / g, 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, and the carbon matrix particles satisfy: 3 ≤ Vc2 / Vc1 ≤ 25.

20. The secondary battery according to any one of claims 1 to 19, characterized by The ratio of the powder compacting 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 compacting 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 compacting 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 compacting 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 compacting density P11 g / cm3 of the silicon-carbon composite material tested after 1 powder pressing 1.00 < P21 / P11 ≤ 1.

20.

21. The secondary battery according to claim 20, characterized by The ratio of the powder compacting 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 compacting 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 compacting 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 compacting 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 compacting density P11 g / cm3 of the silicon-carbon composite material tested after 1 powder pressing 1.02 ≤ P21 / P11 ≤ 1.

10.

22. The secondary battery according to any one of claims 1 to 19, 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.

23. The secondary battery according to claim 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: 1.12≤P11≤1.

35.

24. The secondary battery according to any one of claims 1 to 23, characterized by The conductivity of the electrolyte is 8-12 ms / cm.

25. The secondary battery according to claim 24, characterized by The conductivity of the electrolyte is 9-11 ms / cm.

26. The secondary battery according to any one of claims 1 to 25, 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.

27. An electrical device, comprising: 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.

Images