Negative electrode material and preparation method thereof, secondary battery and electronic equipment

Abstract

The invention provides a negative electrode material and a preparation method thereof, a secondary battery and electronic equipment, the negative electrode material comprises silicon carbon particles, the oxygen content of the silicon carbon particles is X%, 3 < = X < = 10, each silicon carbon particle comprises an internal region and a surface region, the surface region refers to a region less than 20nm away from the surface of the silicon carbon particle, and the surface region refers to a region less than 20nm away from the surface of the silicon carbon particle. The internal region refers to the other region except the surface region in the silicon carbon particles, the oxygen content of the internal region is X1%, and 3 < = X1 < = 10. According to the negative electrode material provided by the invention, the specific capacity and the first coulombic efficiency of the negative electrode material can be improved, and the I TC cycle expansion of the secondary battery is reduced.

Description

Technical Field

[0001] This application relates to the field of electrochemical energy storage, and in particular to a negative electrode material, a preparation method of the negative electrode material, a secondary battery using the negative electrode material, and an electronic device using the secondary battery. Background Art

[0002] Lithium-ion batteries have the advantages of high energy density, high working voltage, good safety, and environmental friendliness, and are widely used in consumer electronics fields such as mobile phones and laptop computers. However, the negative electrodes of traditional commercial lithium-ion batteries are basically limited to graphite materials, and their low capacity (LiC6, 372 mAh g -1 ) has greatly hindered the improvement of energy density. In recent years, silicon-based materials have gradually entered the industrialization track of lithium-ion battery negative electrodes with their high specific capacity (Li 15 Si4, 3579 mAh g -1 ), rich resource reserves, and reasonable lithiation platform (<0.4V vs. Li / Li + ) and are considered to be the most promising negative electrode materials for the next generation.

[0003] Despite the above advantages, silicon-based materials will undergo large volume changes during the lithiation / delithiation process, resulting in a decline in the cycle performance of lithium-ion batteries, and causing the negative electrode active material particles in the electrode to pulverize and fail, which hinders the full play of the electrochemical performance of silicon-based materials. To address this problem, in the prior art, silicon-based materials are usually nano-sized and compounded with porous carbon. Although it can prevent the negative electrode active material particles from breaking to a certain extent, the expansion performance of secondary batteries still needs to be improved in actual applications. Summary of the Invention

[0004] This application provides a negative electrode material, a preparation method thereof, a secondary battery, and an electronic device.

[0005] In the first aspect of this application, a negative electrode material is provided. The negative electrode material includes silicon-carbon particles. The oxygen content of the silicon-carbon particles is X%, 3 ≤ X ≤ 10. The silicon-carbon particles include an internal region and a surface region. The surface region refers to the region less than 20 nm away from the surface of the silicon-carbon particles. The internal region refers to the other regions in the silicon-carbon particles except for the surface region. The oxygen content of the internal region is X1%, 3 ≤ X1 ≤ 10.

[0006] In this application, when the oxygen content and the internal region in the silicon-carbon particles are within appropriate ranges, it indicates that the internal region of the silicon-carbon particles uniformly contains oxygen, and the distribution of oxygen in the silicon-carbon particles is relatively uniform. The presence of the above oxygen content in the silicon-carbon particles and the distribution of oxygen content in the internal region can convert the nanosilicon in the silicon-carbon particles into SiOx, reduce the reaction activity of some silicon, thereby reducing the degree of reaction between silicon and water, and further reducing the generation of hydrogen by the reaction between the nanosilicon inside the silicon-carbon particles and water during the preparation of the anode slurry, improving the specific capacity and initial Coulomb efficiency of the silicon-carbon particles. At the same time, when the oxygen content in the internal region is within the above range, it can further enhance the structural stability of the silicon-carbon particles. During the charge and discharge process of the secondary battery containing silicon-carbon particles, lithiated LiSixOy can further alleviate the volume change of silicon, reduce the pulverization of the silicon-carbon particles and the shedding of the electrode material, thereby improving the expansion performance of the silicon-carbon particles. And when the secondary battery is in a fully charged state, LiSixOy can also inhibit the reaction between the electrolyte and the silicon-lithium alloy, reduce the consumption of the electrolyte and active lithium, thereby effectively reducing the cycle expansion of the secondary battery during the cycle (ITC cycle) after high-temperature full-charge storage.

[0007] Based on the first aspect, in some possible implementation manners, the silicon-carbon particles include porous carbon and silicon particles, and at least part of the silicon particles are located in the pores of the porous carbon. The porous carbon serves as the skeleton of the silicon-carbon particles, enabling the silicon-carbon particles to have good electrical conductivity and cycle stability. And the porous carbon, as the substrate for silicon deposition, can inhibit the volume expansion of silicon during the lithium insertion process, thereby reducing the expansion stress and improving the cycle performance and expansion performance of the silicon-carbon particles.

[0008] Based on the first aspect, in some possible implementation manners, the oxygen content in the surface region is X2%, where 2 ≤ X2 ≤ 8. This is conducive to fully converting the nanosilicon in the surface region into SiOx, reducing the degree of reaction between silicon and water, thereby reducing the generation of hydrogen, and further improving the specific capacity and initial Coulomb efficiency of the negative electrode material; within the above range, it is also conducive to forming LiSixOy after lithiation, reducing the contact between the electrolyte and the silicon-lithium alloy, and inhibiting the expansion of the silicon-lithium alloy during the lithiation process, thereby reducing the ITC cycle expansion of the secondary battery.

[0009] Based on the first aspect, in some possible implementation manners, 0.6 ≤ X1 / X2 ≤ 2.5. The oxygen content in the silicon-carbon particles is uniformly distributed, which is conducive to enabling the negative electrode material to have good specific capacity and initial Coulomb efficiency, and is also conducive to reducing the ITC cycle expansion of the secondary battery.

[0010] Based on the first aspect, in some possible implementation manners, the oxygen content of the silicon-carbon particles satisfies: 4 ≤ X ≤ 6 and 3 ≤ X1 ≤ 6. This is conducive to further improving the specific capacity and initial Coulomb efficiency of the negative electrode material and further reducing the ITC cycle expansion of the secondary battery.

[0011] Based on the first aspect, in some possible implementation manners, the differential capacity curve of the negative electrode material during de-lithiation has a first peak and a second peak at 200 mV to 320 mV and 600 mV to 900 mV respectively, and the peak intensity ratio of the first peak and the second peak is I1, where 1.7 ≤ I1 ≤ 3.8. This is beneficial for converting the nano-silicon in the silicon-carbon particles into SiOx, reducing the reaction activity of part of the silicon, enabling the negative electrode material to have good specific capacity and first Coulomb efficiency, and also beneficial for alleviating the volume change of silicon, and also beneficial for reducing the consumption of electrolyte and active lithium when the secondary battery is fully charged, further reducing the ITC cycle expansion of the secondary battery.

[0012] Based on the first aspect, in some possible implementation manners, in the X-ray photoelectron spectroscopy of the silicon-carbon particles, there are a Si-O peak and a Si-Si peak at 101 eV to 104 eV and 96 eV to 99 eV respectively, and the peak intensity ratio of the Si-O peak and the Si-Si peak is I2, where 0.8 ≤ I2 ≤ 1.5. This is beneficial for reducing the gas generation of the slurry during the preparation of the anode slurry, reducing the loss of the first Coulomb efficiency and specific capacity of the silicon-carbon particles, and when the secondary battery is fully charged, LiSixOy can also inhibit the reaction between the electrolyte and the silicon-lithium alloy, reduce the consumption of the electrolyte and active lithium, and reduce the ITC cycle expansion of the secondary battery.

[0013] The second aspect of the present application provides a method for preparing silicon-carbon particles in a negative electrode material, including the following steps: S1) providing a porous carbon framework, introducing silane gas into the porous carbon framework, and after silicon deposition on the porous carbon framework, sequentially switching the silane gas to a carbon dioxide mixed gas, silane gas, and a carbon dioxide mixed gas to obtain a core body, where the flow rate of each introduction of the carbon dioxide mixed gas is 50 sccm to 300 sccm, the introduction time is 1 h to 20 h, the reaction temperature is 400 °C to 500 °C, the carbon dioxide mixed gas includes carbon dioxide and an inert gas, and in the carbon dioxide mixed gas, the mass percentage of carbon dioxide is 2% to 20%; S2) introducing an alkane gas into the core body to form a carbon layer on the core body to obtain silicon-carbon particles. In the above preparation method, the porous carbon framework is subjected to alternating deposition of silane-carbon dioxide gas to form a core body, and then a carbon-coated carbon layer is formed through an alkane to obtain silicon-carbon particles. During the above preparation process, the uniformity of the oxygen content in the internal region can be improved and it is also beneficial for obtaining an appropriate content of oxygen in the silicon-carbon particles, thereby improving the specific capacity and first Coulomb efficiency of the negative electrode material and reducing the ITC cycle expansion of the secondary battery.

[0014] A third aspect of the present application provides a secondary battery, which includes a negative electrode plate, a positive electrode plate, and an electrolyte. The negative electrode plate further includes the negative electrode material described above or the negative electrode material obtained by the preparation method described above, and the negative electrode material further includes graphite. Graphite has a certain flexibility, and its cooperation with silicon-carbon particles can relieve the overall volume expansion of the negative electrode material layer. At the same time, graphite and silicon-carbon particles as the negative electrode material can also make full use of the advantages of both silicon-carbon particles and graphite to achieve better electrochemical performance.

[0015] Based on the third aspect, in some possible implementation manners, the average circularity of the silicon-carbon particles is C1, and the average circularity of the graphite is C2, and |C1 - C2| ≤ 0.2. The average circularity of the silicon-carbon particles and the graphite is similar, and the morphological difference between the silicon-carbon particles and the graphite is small. The proportion of tips and irregular regions in the negative electrode material is small. During the stirring process of preparing the anode slurry, the influence on the surface layer of the silicon-carbon particles is reduced, the exposed interface of the nano-silicon in the silicon-carbon particles is reduced, and the generation of SEI film by-products is reduced, so as to reduce the loss of the first Coulomb efficiency and specific capacity of the silicon-carbon particles, thereby improving the first Coulomb efficiency and specific capacity of the negative electrode material and reducing the ITC cycle expansion of the secondary battery.

[0016] Based on the third aspect, in some possible implementation manners, the electrolyte includes ethylene carbonate and propylene carbonate. Based on the mass of the electrolyte, the mass percentage content of ethylene carbonate is D1%, and the mass percentage content of propylene carbonate is D2%, and 9 ≤ D1 + D2 ≤ 35. This is beneficial to further improving the specific capacity and first Coulomb efficiency of the negative electrode material and reducing the ITC cycle expansion of the secondary battery.

[0017] Based on the third aspect, in some possible implementation manners, 12 ≤ D1 + D2 ≤ 25; this can further improve the specific capacity and first Coulomb efficiency of the negative electrode material and reduce the ITC cycle expansion of the secondary battery.

[0018] Based on the third aspect, in some possible implementation manners, the electrolyte includes ethylene carbonate and fluoroethylene carbonate. Based on the mass of the electrolyte, the mass percentage content of ethylene carbonate is D1%, and the mass percentage content of fluoroethylene carbonate is D3%, and 0.83 ≤ D3 / D1 ≤ 1.75. This is beneficial to further improving the specific capacity and first Coulomb efficiency of the negative electrode material and reducing the ITC cycle expansion of the secondary battery.

[0019] Based on the third aspect, in some possible implementation manners, 1 ≤ D3 / D1 ≤ 1.5, which can further improve the specific capacity and first Coulomb efficiency of the negative electrode material and reduce the ITC cycle expansion of the secondary battery.

[0020] A fourth aspect of the present application provides an electronic device, including a secondary battery. The secondary battery powers a load in the electronic device. The secondary battery including a negative electrode tab has a low ITC cycle expansion, which is beneficial to improving the service life of the electronic device. Detailed implementation manners

[0021] The technical solutions in the embodiments of the present application will be clearly and detailedly described below. Obviously, the described embodiments are some, but not all, of the embodiments of the present application. Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by those of ordinary skill in the technical field to which this application belongs. The terms used in the specification of this application are only for the purpose of describing specific embodiments, and are not intended to limit this application.

[0022] During the preparation of the anode slurry, a large stirring linear velocity will cause friction and collision between the silicon-based material particles and between the particles and the stirring rod / tank wall. After the carbon layer on the surface of the silicon-based material is damaged, the nano-silicon inside the silicon-based material reacts with water to generate hydrogen, which affects the specific capacity and the first Coulomb efficiency of the silicon-based material, and even affects the subsequent coating process, resulting in phenomena such as anode pinholes / tailing.

[0023] In the application of silicon-based lithium-ion batteries, it is necessary to meet the conditions of cycling (ITC cycle) after full charge storage under high-temperature working conditions. The expansion of silicon-based lithium-ion batteries themselves is larger than that of graphite lithium-ion batteries, and high-temperature working conditions and high-temperature full charge storage conditions will further cause the expansion of lithium-ion batteries to increase. Therefore, suppressing gas generation during anode slurry preparation and reducing ITC expansion are crucial for the application of silicon-based lithium-ion batteries.

[0024] Therefore, an embodiment of the present application provides a secondary battery, which includes a housing, an electrode assembly, and an electrolyte. The electrode assembly and the electrolyte are both located inside the housing.

[0025] The housing can be a packaging bag obtained by encapsulating with a packaging film (such as an aluminum-plastic film), such as when the secondary battery is a soft-pack battery. In other embodiments, the secondary battery can also be a steel-shell battery, an aluminum-shell battery, etc.

[0026] The electrode assembly includes a positive electrode tab, a negative electrode tab, and a separator. The separator is disposed between the positive electrode tab and the negative electrode tab. The electrode assembly can be a laminated structure, which is formed by alternately laminating the positive electrode tab, the separator, and the negative electrode tab. In other embodiments, the electrode assembly can also be a wound structure, which is formed by laminating and winding the positive electrode tab, the separator, and the negative electrode tab.

[0027] Negative electrode tab

[0028] The negative electrode plate includes a negative electrode current collector and a negative electrode material layer provided on at least one surface of the negative electrode current collector. The negative electrode current collector can be at least one of copper foil, nickel foil, stainless steel foil, titanium foil, composite current collector, carbon-based current collector, etc. The negative electrode material layer includes a negative electrode material.

[0029] An embodiment of the present application provides a negative electrode material. The negative electrode material includes silicon-carbon particles. The oxygen content of the silicon-carbon particles is X%, 3 ≤ X ≤ 10. The silicon-carbon particles include an internal region and a surface region. The surface region refers to the region within a distance less than 20 nm from the surface of the silicon-carbon particles. The internal region refers to the other regions in the silicon-carbon particles except for the surface region. The oxygen content of the internal region is X1%, 3 ≤ X1 ≤ 10.

[0030] In the present application, when the oxygen content in the silicon-carbon particles and the internal region are within a suitable range, it indicates that the internal region of the silicon-carbon particles uniformly contains oxygen, and the distribution of oxygen in the silicon-carbon particles is relatively uniform. The existence of the above oxygen content in the silicon-carbon particles and the distribution of the oxygen content in the internal region can convert the nano-silicon in the silicon-carbon particles into SiOx, reduce the reaction activity of part of the silicon, thereby reducing the degree of reaction between silicon and water, and further reducing the generation of hydrogen gas by the reaction of nano-silicon inside the silicon-carbon particles and water during the preparation of the anode slurry, improving the specific capacity and first Coulomb efficiency of the silicon-carbon particles. At the same time, when the oxygen content of the internal region is within the above range, it can further enhance the structural stability of the silicon-carbon particles. During the charge and discharge process of the secondary battery containing the silicon-carbon particles, lithiated LiSixOy can further relieve the volume change of silicon, reduce the pulverization of the silicon-carbon particles and the shedding of the electrode material, thereby improving the expansion performance of the silicon-carbon particles. And when the secondary battery is in a fully charged state, LiSixOy can also inhibit the reaction between the electrolyte and the silicon-lithium alloy, reduce the consumption of the electrolyte and active lithium, and thus effectively reduce the cycle expansion of the secondary battery during the cycle after full charge storage (ITC cycle).

[0031] If the oxygen content in the silicon-carbon particles is small, or the oxygen content in the internal region is small, such as less than 3, it will cause some nano-silicon in the silicon-carbon particles not to be converted into SiOx. During the preparation of the anode slurry, the exposed nano-silicon is likely to react with water to generate hydrogen gas, which will reduce the first Coulomb efficiency and specific capacity of the negative electrode material, and will also increase the possibility of pinholes / tailing phenomena in the anode coating; the small oxygen content is also likely to cause the nano-silicon not to be fully converted into SiOx, resulting in insufficient converted LiSixOy during the charge and discharge process of the secondary battery, which is not conducive to reducing the ITC cycle expansion of the secondary battery.

[0032] If the oxygen content in the silicon-carbon particles is relatively high, or the oxygen content in the internal region is relatively high, such as greater than 10, the relatively high oxygen content will generate more LiSixOy during the lithiation process, increasing the consumption of irreversible lithium in the first cycle of the anode material, and reducing the specific capacity and first Coulombic efficiency of the anode material; the relatively high oxygen content is also not conducive to reducing the ITC cycle expansion of the secondary battery.

[0033] In some embodiments, the oxygen content X of the silicon-carbon particles can be 3, 4, 5, 6, 7, 8, 9, 10 or any value within the range formed by any two of the above values.

[0034] In some embodiments, the oxygen content X1 in the internal region of the silicon-carbon particles can be 3, 4, 5, 6, 7, 8, 9, 10 or any value within the range formed by any two of the above values.

[0035] In some embodiments, the silicon-carbon particles include porous carbon and silicon particles, and at least part of the silicon particles are located in the pores of the porous carbon. The porous carbon serves as the framework of the silicon-carbon particles, enabling the silicon-carbon particles to have good electrical conductivity and cycle stability. Moreover, the porous carbon serves as the substrate for silicon deposition, which can inhibit the volume expansion of silicon during the lithium insertion process, thereby reducing the expansion stress and improving the cycle performance and expansion performance of the silicon-carbon particles. In some embodiments, part of the silicon particles can be located in the pores of the porous carbon, and another part of the silicon particles are located on the surface of the porous carbon.

[0036] In some embodiments, the oxygen content in the surface region is X2%, and 2 ≤ X2 ≤ 8. When the oxygen content in the surface region is within the above range, it is conducive to fully converting the nano-silicon in the surface region into SiOx, reducing the degree of reaction between silicon and water caused by the huge shear force during the anode slurrying process, thereby reducing the generation of hydrogen and further improving the specific capacity and first Coulombic efficiency of the anode material; within the above range, it is also conducive to forming LiSixOy after lithiation, reducing the contact between the electrolyte and the internal silicon-lithium alloy, and inhibiting the expansion of the silicon-lithium alloy during the lithiation process, thereby reducing the ITC cycle expansion of the secondary battery. In some embodiments, the oxygen content X2 in the surface region of the silicon-carbon particles can be 2, 3, 4, 5, 6, 7, 8 or any value within the range formed by any two of the above values.

[0037] In some embodiments, 0.6 ≤ X1 / X2 ≤ 2.5. In the silicon-carbon particles, the ratio of the oxygen content in the surface region to that in the internal region can reflect the uniformity of the oxygen content distribution between the internal region and the surface region of the silicon-carbon particles. When the oxygen content in the internal region and the external region of the silicon-carbon particles satisfies the above range, the oxygen content distribution in the silicon-carbon particles is uniform, which is beneficial to endowing the anode material with good specific capacity and first Coulombic efficiency, and also beneficial to further reducing the ITC cycle expansion of the secondary battery. In some embodiments, the ratio of X1 / X2 can be 0.6, 0.7, 0.8, 0.9, 1.2, 1.4, 1.5, 1.8, 2, 2.3, 2.5 or any value within the range formed by any two of the above values.

[0038] In some embodiments, the oxygen content of the silicon-carbon particles satisfies: 4 ≤ X ≤ 6 and 3 ≤ X1 ≤ 6, which is beneficial to further improving the specific capacity and first Coulombic efficiency of the anode material and further reducing the ITC cycle expansion of the secondary battery.

[0039] In some embodiments, the differential capacity curve of the anode material during lithium deintercalation has a first peak and a second peak at 200 mV to 320 mV and 600 mV to 900 mV respectively, and the peak intensity ratio of the first peak to the second peak is I1, and 1.7 ≤ I1 ≤ 3.8. The differential capacity-voltage curve of the anode material during lithium deintercalation can be understood as follows: taking the charge-discharge specific capacity of the anode material as the abscissa and the voltage as the ordinate, the charge-discharge curve of the anode material can be obtained. Then, taking the first derivative of the lithium deintercalation specific capacity of the anode material with respect to the voltage as the ordinate and the voltage as the abscissa, the differential capacity-voltage curve of the anode material during lithium deintercalation can be obtained. The differential capacity-voltage curve can reflect the capacity contained in the anode material within a unit voltage range. If the capacity at a certain voltage plateau is high, it means that a very large amount of capacity will be contributed within a very small voltage fluctuation range, which will be manifested as a characteristic peak on the curve. Each characteristic peak represents an electrochemical reaction, and at the same time, the peak height of each characteristic peak also represents the magnitude of the capacity contribution of the corresponding electrochemical reaction.

[0040] The first peak of the negative electrode material is the de-lithiation characteristic peak of the transformation of LixSi (x is about 3.5) to LiySi (y is about 2); the second peak is the partially reversible de-lithiation characteristic peak of the transformation of LiSixOy to SiOx. Among them, the ratio of the first peak to the second peak can reflect the influence of the oxygen content in the negative electrode material on the de-lithiation reaction of the negative electrode material. When I1 is within the above range, it indicates that the oxygen content in the negative electrode material is appropriate, which is conducive to converting the nano-silicon in the silicon-carbon particles into SiOx, reducing the reaction activity of some silicon, enabling the negative electrode material to have good specific capacity and first Coulomb efficiency, and also conducive to alleviating the volume change of silicon, and also conducive to reducing the consumption of electrolyte and active lithium in the fully charged state of the secondary battery, further reducing the ITC cycle expansion of the secondary battery. In some embodiments, I1 can be 1.7, 1.9, 2.0, 2.3, 2.5, 2.7, 3.0, 3.5, 3.8 or any value within the range formed by any two of the above values.

[0041] In some embodiments, in the X-ray photoelectron spectrum of the silicon-carbon particles, there are Si-O peaks and Si-Si peaks at 101 eV to 104 eV and 96 eV to 99 eV respectively, and the peak intensity ratio of the Si-O peak to the Si-Si peak is I2, and 0.8 ≤ I2 ≤ 1.5. In the X-ray photoelectron spectrum, the intensity of the Si-O peak at 101 eV to 104 eV can reflect the proportion of the content of SiOx in the surface area of the silicon-carbon particles, and the intensity of the Si-Si peak at 96 eV to 99 eV can reflect the proportion of the content of Si in the surface area of the silicon-carbon particles. When the peak intensity ratio I2 is within the above appropriate range, it is conducive to reducing the gas generation of the slurry during the preparation of the anode slurry, reducing the loss of the first Coulomb efficiency and specific capacity of the silicon-carbon particles, and in the fully charged state of the secondary battery, LiSixOy can also inhibit the reaction between the electrolyte and the silicon-lithium alloy, reduce the consumption of the electrolyte and active lithium, and reduce the ITC cycle expansion of the secondary battery. In some embodiments, I2 can be 0.8, 0.9, 1.0, 1.1, 1.2, 1.3, 1.4, 1.5 or any value within the range formed by any two of the above values.

[0042] In some embodiments, the negative electrode material further includes graphite. The average circularity of the silicon-carbon particles is C1, and the average circularity of the graphite is C2, where |C1 - C2| ≤ 0.2. The negative electrode material contains graphite, and the graphite includes at least one of natural graphite and artificial graphite. Since graphite has a certain flexibility, its combination with the silicon-carbon particles can relieve the overall volume expansion of the negative electrode material layer. At the same time, both the graphite and the silicon-carbon particles as the negative electrode material can also make full use of the advantages of both the silicon-carbon particles and the graphite to achieve better electrochemical performance. The inventors found that the smaller |C1 - C2| is, the closer the average circularity of the silicon-carbon particles and the graphite is, the smaller the morphological difference between the silicon-carbon particles and the graphite is, and the smaller the proportion of the tip and irregular regions in the negative electrode material is. During the stirring process of preparing the anode slurry, it is beneficial to reduce the friction and collision between the silicon-carbon particles in the negative electrode material and between the silicon-carbon particles and the stirring rod / tank wall, reduce the influence on the surface layer of the silicon-carbon particles, reduce the exposed interface of the nanosilicon in the silicon-carbon particles, and reduce the generation of by-products of the SEI film, thereby reducing the generation of gas, reducing the loss of the first Coulomb efficiency and specific capacity of the silicon-carbon particles, and thus improving the first Coulomb efficiency and specific capacity of the negative electrode material and reducing the ITC cycle expansion of the secondary battery. In some embodiments, the value of |C1 - C2| can be 0, 0.05, 0.1, 0.15, 0.2, or any value within the range formed by any two of the above values. In some embodiments, |C1 - C2| ≤ 0.1.

[0043] In some embodiments, the electrolyte includes ethylene carbonate and propylene carbonate. Based on the mass of the electrolyte, the mass percentage content of ethylene carbonate is D1%, and the mass percentage content of propylene carbonate is D2%, where 9 ≤ D1 + D2 ≤ 35. The inclusion of ethylene carbonate and propylene carbonate in the electrolyte is beneficial to improving the specific capacity and the first Coulomb efficiency of the negative electrode material and reducing the ITC cycle expansion of the secondary battery. When the sum of the contents of ethylene carbonate and propylene carbonate is within the above range, it is beneficial to further improve the specific capacity and the first Coulomb efficiency of the negative electrode material and reduce the ITC cycle expansion of the secondary battery. In some embodiments, the sum of D1 + D2 can be 9, 10, 11, 12, 15, 18, 20, 23, 25, 27, 30, 32, 35, or any value within the range formed by any two of the above values. In some embodiments, 12 ≤ D1 + D2 ≤ 25.

[0044] In some embodiments, the electrolyte includes ethylene carbonate and fluoroethylene carbonate. Based on the mass of the electrolyte, the mass percentage of ethylene carbonate is D1%, and the mass percentage of fluoroethylene carbonate is D3%, where 0.83 ≤ D3 / D1 ≤ 1.75. The inclusion of ethylene carbonate and fluoroethylene carbonate in the electrolyte helps to increase the specific capacity and initial Coulombic efficiency of the anode material and reduce the ITC cycle expansion of the secondary battery. When the content ratio of fluoroethylene carbonate to ethylene carbonate is within the above range, it is beneficial to further increase the specific capacity and initial Coulombic efficiency of the anode material and reduce the ITC cycle expansion of the secondary battery. In some embodiments, the ratio of D3 / D1 can be 0.83, 0.9, 1.0, 1.1, 1.2, 1.3, 1.4, 1.5, 1.6, 1.7, 1.75 or any value within the range formed by any two of the above values. In some embodiments, 1.0 ≤ D3 / D1 ≤ 1.5.

[0045] This application also provides a method for preparing silicon-carbon particles in an anode material, comprising the following steps:

[0046] S1) Provide a porous carbon framework, introduce silane gas into the porous carbon framework. After silicon deposition on the porous carbon framework, sequentially switch the silane gas to a carbon dioxide mixed gas, silane gas, and carbon dioxide mixed gas to obtain a core body.

[0047] This step specifically includes the following specific embodiments:

[0048] At a temperature of 400°C to 500°C, deposit the porous carbon framework in a silane mixed gas for 1 h to 20 h, and then switch the gas source to a carbon dioxide mixed gas for oxidation for 1 h to 20 h. Repeat the above operations twice to form a deposition cycle of silane - carbon dioxide oxidation - silane - carbon dioxide gas oxidation to obtain a core body.

[0049] In some embodiments, the temperature for depositing silicon on the porous carbon framework each time can be 400°C, 430°C, 450°C, 470°C, 500°C or any value within the range formed by any two of the above values. The time for depositing silicon each time can be 1 h, 2 h, 5 h, 7 h, 8 h, 10 h, 12 h, 14 h, 15 h, 17 h, 19 h, 20 h or any value within the range formed by any two of the above values.

[0050] In some embodiments, the temperature for oxidizing and depositing silicon on the porous carbon framework with carbon dioxide mixed gas each time can be 400 °C, 430 °C, 450 °C, 470 °C, 500 °C, or any value within the range formed by any two of the above values. The oxidation time of the carbon dioxide mixed gas each time can be 1 h, 2 h, 5 h, 7 h, 8 h, 10 h, 12 h, 14 h, 15 h, 17 h, 19 h, 20 h, or any value within the range formed by any two of the above values.

[0051] Among them, the heating rate of slow heating can be, but is not limited to, 0.5 °C / min to 5 °C / min. The silane mixed gas contains 2% to 20% by mass of silane and 80% to 98% of inert gas (such as, but not limited to, argon). The flow rate of the silane mixed gas introduced is 100 sccm to 500 sccm. In some embodiments, the flow rate of the silane mixed gas introduced can be 100 sccm, 150 sccm, 200 sccm, 300 sccm, 400 sccm, 500 sccm, or any value within the range formed by any two of the above values.

[0052] Among them, the carbon dioxide mixed gas contains 2% to 20% by mass of carbon dioxide and 80% to 98% of inert gas (such as, but not limited to, argon). The flow rate of the carbon dioxide mixed gas introduced is 50 sccm to 300 sccm. In some embodiments, the flow rate of the carbon dioxide mixed gas introduced can be 50 sccm, 100 sccm, 150 sccm, 200 sccm, 300 sccm, or any value within the range formed by any two of the above values.

[0053] In the above steps, the silane mixed gas is introduced. In the atmosphere of the silane mixed gas, the silane mixed gas deposits silicon on the porous carbon framework for the first time. Then, the atmosphere of the silane mixed gas is switched to the carbon dioxide mixed gas, and the carbon dioxide mixed gas oxidizes the porous carbon framework that has undergone silicon deposition for the first time, which can improve the uniformity of the oxygen content distribution in the porous carbon framework and increase the oxygen content. After that, the carbon dioxide mixed gas is switched to the silane mixed gas. In the atmosphere of the silane mixed gas, the silane mixed gas deposits silicon on the porous carbon framework for the second time. Finally, the silane mixed gas is switched to the carbon dioxide mixed gas again, and the carbon dioxide mixed gas oxidizes the porous carbon framework that has undergone two silicon depositions for the second time to obtain a core body. The temperature, the time of introducing carbon dioxide, and the flow rate of introducing carbon dioxide of the porous carbon framework after two carbon dioxide oxidations can be the same.

[0054] In the above process, during the first oxidation process, the mass fraction, flow rate, time of carbon dioxide introduction, and reaction temperature all affect the oxygen content X of the silicon-carbon particles and the oxygen content X1 in the internal region. The more carbon dioxide is introduced, or the longer the time, or the higher the temperature, or the greater the flow rate, all contribute to increasing the oxygen content in the internal region of the silicon-carbon particles. During the second oxidation process, the mass fraction, flow rate, time of carbon dioxide introduction, and reaction temperature all affect the oxygen content X2 in the surface region of the silicon-carbon particles. The more carbon dioxide is introduced, or the longer the time, or the higher the temperature, or the greater the flow rate, all contribute to increasing the oxygen content in the surface region of the silicon-carbon particles.

[0055] S2) Introduce an alkane gas into the core body to form a carbon layer on the core body, obtaining silicon-carbon particles.

[0056] Specifically: at a temperature of 500 °C to 1000 °C, then switch the carbon dioxide atmosphere to an alkane mixture gas, and maintain it for 2 h to 20 h to form a carbon coating layer covering the core body, and then switch the alkane mixture gas atmosphere to an inert atmosphere (such as but not limited to a nitrogen atmosphere) and cool it to room temperature to obtain the silicon-carbon particles. Among them, the alkane mixture gas contains 5% to 100% by mass of an alkane (such as but not limited to acetylene) and 0% to 95% of an inert gas (such as but not limited to argon). The flow rate of the introduced alkane mixture gas is 100 sccm to 500 sccm. In some embodiments, the flow rate of the introduced alkane mixture gas can be 100 sccm, 150 sccm, 200 sccm, 300 sccm, 400 sccm, 500 sccm, or any value within the range composed of any two of the above values.

[0057] The negative electrode material layer further includes a binder and a conductive agent. The binder is used to bond the negative electrode material particles to facilitate the formation of a film layer, and at the same time can also improve the bonding force between the negative electrode material layer and the negative electrode current collector. In some embodiments, the binder may include but not be limited to polyvinyl alcohol, hydroxypropyl cellulose, diacetyl cellulose, polyvinyl chloride, carboxylated polyvinyl chloride, polyvinyl fluoride, a polymer containing ethylene oxide, polyvinylpyrrolidone, polyurethane, polytetrafluoroethylene, polyvinylidene 1,1-difluoroethylene, polyethylene, polypropylene, styrene-butadiene rubber, acrylated styrene-butadiene rubber, epoxy resin, or nylon, etc.

[0058] The conductive agent in the negative electrode material layer, the conductive agent includes but not limited to carbon-based materials, metal-based materials, conductive polymers, or any combination thereof. In some embodiments, the carbon-based materials may include but not be limited to natural graphite, artificial graphite, carbon black, acetylene black, Ketjen black, carbon fiber, or any combination thereof. In some embodiments, the metal-based materials may include but not be limited to metal powder or metal fiber, such as copper, nickel, aluminum, or silver. In some embodiments, the conductive polymer may be a polyphenylene derivative.

[0059] Separator

[0060] There are no particular limitations on the material and shape of the separator used in the secondary battery of the present application, and it can be any technology disclosed in the prior art. In some embodiments, the separator includes a polymer or an inorganic substance formed of a material that is stable to the electrolyte of the present application.

[0061] For example, the separator may include a substrate layer and a surface treatment layer. The substrate layer is a non-woven fabric, a film or a composite film having a porous structure, and the material of the substrate layer is selected from at least one of polyethylene, polypropylene, polyethylene terephthalate and polyimide. Specifically, a polypropylene porous film, a polyethylene porous film, a polypropylene non-woven fabric, a polyethylene non-woven fabric or a polypropylene-polyethylene-polypropylene porous composite film can be selected.

[0062] A surface treatment layer is provided on at least one surface of the substrate layer. The surface treatment layer can be a polymer layer or an inorganic layer, or a layer formed by mixing a polymer and an inorganic substance. The inorganic layer includes inorganic particles and a binder, and the inorganic particles are selected from at least one of alumina, silica, magnesia, titanium oxide, hafnium dioxide, tin oxide, cerium dioxide, nickel oxide, zinc oxide, calcium oxide, zirconium oxide, yttrium oxide, silicon carbide, boehmite, aluminum hydroxide, magnesium hydroxide, calcium hydroxide and barium sulfate. The binder is selected from at least one of polyvinylidene fluoride, a copolymer of vinylidene fluoride and hexafluoropropylene, polyamide, polyacrylonitrile, polyacrylate, polyacrylic acid, polyacrylate salt, polyvinylpyrrolidone, polyethylene alkoxide, polymethyl methacrylate, polytetrafluoroethylene and polyhexafluoropropylene. The polymer layer contains a polymer, and the material of the polymer is selected from at least one of polyamide, polyacrylonitrile, acrylate polymer, polyacrylic acid, polyacrylate salt, polyvinylpyrrolidone, polyethylene alkoxide, polyvinylidene fluoride, poly(vinylidene fluoride-hexafluoropropylene).

[0063] Electrolyte

[0064] According to some embodiments of the present application, the electrolyte includes an organic solvent, a lithium salt and an optional additive. The organic solvent in the electrolyte of the present application can be any organic solvent known in the prior art that can be used as a solvent for the electrolyte. There is no limitation on the electrolyte used in the electrolyte of the present application, and it can be any electrolyte known in the prior art. The additive of the electrolyte according to the present application can be any additive known in the prior art that can be used as an electrolyte additive.

[0065] In some embodiments, the organic solvent includes, but is not limited to: ethylene carbonate (EC), propylene carbonate (PC), diethyl carbonate (DEC), ethyl methyl carbonate (EMC), dimethyl carbonate (DMC), propylene carbonate or ethyl propionate. In some embodiments, the organic solvent includes an ether solvent, such as at least one of 1,3-dioxolane (DOL) and dimethoxyethane (DME). In some embodiments, the lithium salt includes at least one of an organic lithium salt or an inorganic lithium salt. In some embodiments, the lithium salt includes, but is not limited to: lithium hexafluorophosphate (LiPF6), lithium tetrafluoroborate (LiBF4), lithium difluorophosphate (LiPO2F2), lithium bis(trifluoromethanesulfonyl)imide LiN(CF3SO2)2 (LiTFSI), lithium bis(fluorosulfonyl)imide Li(N(SO2F)2) (LiFSI), lithium bis(oxalato)borate LiB(C2O4)2 (LiBOB) or lithium difluoro(oxalato)borate LiBF2(C2O4) (LiDFOB). In some embodiments, the additive includes at least one of fluoroethylene carbonate and adiponitrile.

[0066] Positive electrode sheet

[0067] The positive electrode sheet includes a positive electrode current collector and a positive electrode active layer provided on the positive electrode current collector. The positive electrode current collector can use aluminum foil, nickel foil, etc. The positive electrode active layer contains a positive electrode active material, and the positive electrode active material includes a compound that reversibly intercalates and deintercalates lithium ions (i.e., a lithiated intercalation compound). In some embodiments, the positive electrode active material may include a lithium transition metal composite oxide. The lithium transition metal composite oxide contains lithium and at least one element selected from cobalt, manganese, and nickel. In some embodiments, the positive electrode active material may include, but is not limited to, at least one of lithium cobaltate, lithium nickel manganese cobaltate, lithium nickel manganese aluminate, lithium iron phosphate, lithium vanadium phosphate, lithium cobalt phosphate, lithium manganese phosphate, lithium manganese iron phosphate, lithium iron silicate, lithium vanadium silicate, lithium cobalt silicate, lithium manganese silicate, spinel-type lithium manganate, spinel-type lithium nickel manganate, and lithium titanate.

[0068] The positive electrode active layer further contains a binder for bonding the positive electrode active material particles to facilitate the formation of a film layer and at the same time improve the bonding force between the positive electrode active layer and the positive electrode current collector. In some embodiments, the binder may include, but is not limited to, at least one of polyvinyl alcohol, hydroxypropyl cellulose, diacetyl cellulose, polyvinyl chloride, carboxylated polyvinyl chloride, polyvinyl fluoride, a polymer containing ethylene oxide, polyvinylpyrrolidone, polyurethane, polytetrafluoroethylene, polyvinylidene 1,1-difluoroethylene, polyethylene, polypropylene, styrene-butadiene rubber, acrylated styrene-butadiene rubber, epoxy resin, or nylon, etc.

[0069] The positive electrode active layer may further include a conductive material, which includes but is not limited to carbon-based materials, metal-based materials, conductive polymers, or any combination thereof. In some embodiments, the carbon-based materials may include but are not limited to natural graphite, artificial graphite, carbon black, acetylene black, Ketjen black, carbon fiber, or any combination thereof. In some embodiments, the conductive polymer may be a polyphenylene derivative.

[0070] The above secondary battery is applied to an electronic device to supply power to a load in the electronic device. Moreover, the above secondary battery including the negative electrode sheet has excellent ITC cycle expansion performance, which is beneficial to improving the service life of the electronic device. Among them, the electronic device may include but is not limited to laptop computers, pen input computers, mobile computers, e-book players, portable telephones, portable fax machines, portable copiers, portable printers, head-mounted stereo headphones, video recorders, liquid crystal televisions, portable cleaners, portable CD players, mini discs, transceivers, electronic notebooks, calculators, memory cards, portable recorders, radios, backup power supplies, motors, automobiles, motorcycles, motorized bicycles, bicycles, lighting fixtures, toys, game consoles, clocks, power tools, flashlights, cameras, large household storage batteries, and lithium-ion capacitors, etc.

[0071] The present application is described below through specific examples and comparative examples. Those skilled in the art should understand that the preparation methods described in the present application are only examples, and any other suitable preparation methods are within the scope of the present application.

[0072] Example 1-1

[0073] (1) Preparation of silicon-carbon particles:

[0074] Under an argon atmosphere, 100 g of a porous carbon framework (the particle size Dv50 of the porous carbon is 6 μm to 10 μm) is heated to 420 °C at a rate of 2 °C / min, and then the argon atmosphere is switched to a silane mixture gas (by mass percentage, 20% silane and 80% argon), and the first silicon deposition is carried out at 420 °C / 200 sccm for 5 h; then, the silane mixture gas atmosphere is switched to a carbon dioxide mixture gas (by mass percentage, 5% carbon dioxide and 95% argon), and the first oxidation is carried out at 400 °C / 50 sccm for 2.4 h; after that, the carbon dioxide mixture gas atmosphere is switched to a silane mixture gas (by mass percentage, 20% silane and 80% argon), and the second silicon deposition is carried out at 420 °C / 200 sccm for 5 h; finally, the silane mixture gas atmosphere is switched to a carbon dioxide mixture gas (by mass percentage, 5% carbon dioxide and 95% argon), and the second oxidation is carried out at 400 °C / 50 sccm for 2 h to form a core body.

[0075] After switching the carbon dioxide mixed gas atmosphere to acetylene mixed gas (20% acetylene and 80% argon by mass percentage) and continuing to deposit for 10 h at 500 °C, the acetylene mixed gas was switched to nitrogen, and then the temperature was lowered to room temperature of 25 °C to obtain silicon-carbon particles.

[0076] (2) Preparation of the negative electrode sheet: Mix the negative electrode material (a mixture of artificial graphite and the above-mentioned silicon-carbon particles with a weight ratio of 80:20), carbon nanotubes, polymethyl acrylate, and sodium carboxymethyl cellulose in a weight ratio of 97:1:1:1, add deionized water as a solvent, and formulate a negative electrode slurry with a solid content of 40 wt%. After stirring evenly with a vacuum mixer, the negative electrode slurry is obtained. The negative electrode slurry is evenly coated on one surface of a negative electrode current collector copper foil with a thickness of 12 μm and dried at 85 °C to obtain a negative electrode sheet with a single-sided coated negative electrode material layer. When coating, the coating weight of the negative electrode material layer is 10 mg / cm 2 . Then repeat the above steps on the other surface of the copper foil to obtain a negative electrode sheet with a double-sided coated negative electrode material layer. Then, through cold pressing, slicing, and slitting, it is dried under vacuum conditions at 120 °C for 12 h to obtain a negative electrode sheet with a specification of 78 mm × 875 mm. After welding the tab, it is ready for use. Among them, the compaction density of the negative electrode material layer after cold pressing is 1.7 g / cm 3 ; The negative electrode material includes artificial graphite and the above-prepared silicon-carbon material, and the mass ratio of artificial graphite to silicon-carbon particles is 80:20.

[0077] (3) Preparation of the positive electrode sheet: Mix the positive electrode active material lithium cobalt oxide, conductive carbon black Super P, and positive electrode binder polyvinylidene fluoride in a mass ratio of 97:1.4:1.6, add N-methylpyrrolidone as a solvent, and formulate a positive electrode slurry with a solid content of 72 wt%. After stirring evenly with a vacuum mixer, the positive electrode slurry is obtained. The positive electrode slurry is evenly coated on one surface of a positive electrode current collector aluminum foil with a thickness of 12 μm and dried at 85 °C to obtain a positive electrode sheet with a single-sided coated positive electrode material layer. When coating, the coating weight of the positive electrode material layer is 19 mg / cm 2 . Then repeat the above steps on the other surface of the aluminum foil to obtain a positive electrode sheet with a double-sided coated positive electrode material layer. Then, through cold pressing, slicing, and slitting, it is dried under vacuum conditions at 85 °C for 4 h to obtain a positive electrode sheet with a specification of 74 mm × 867 mm. After welding the tab, it is ready for use. Among them, the compaction density of the positive electrode material layer after cold pressing is 4.2 g / cm 3 .

[0078] (4) Preparation of electrolyte: Under a dry argon atmosphere, LiPF6 was added to a mixed solution of 1,3 - propane sultone (1,3 - PS), propyl propionate (PP), ethyl propionate (EP), fluoroethylene carbonate (FEC), propylene carbonate (PC), and ethylene carbonate (EC). Among them, based on the mass of the electrolyte, the mass ratio of LiPF6 was 12.5%, the mass ratio of 1,3 - PS was 3%, the mass ratio of PC was 8%, the mass ratio of EC was 10%, the mass ratio of FEC was 10%, and the balance was EP and PP, and the mass ratio of EP to PP was 1:3.

[0079] (5) Preparation of separator: A porous polyethylene film with a thickness of 7μm (provided by Celgard) was used as the separator.

[0080] (6) Preparation of lithium - ion full cell: The positive electrode sheet, separator, negative electrode sheet, and separator were stacked in sequence, with the separator placed between the positive electrode sheet and the negative electrode sheet to play a role in isolation, and then wound to obtain an electrode assembly. The electrode assembly was placed in an aluminum - plastic film packaging bag, dried at 80°C, and then injected with electrolyte. After vacuum packaging, standing, forming, shaping, and capacity testing processes, a soft - package lithium - ion battery was obtained.

[0081] (7) Preparation method of lithium - ion coin - type half - cell:

[0082] Preparation of the negative electrode sheet of the coin - type half - cell: Silicon - carbon particles, sodium carboxymethylcellulose, and conductive carbon black were fully stirred and mixed in an appropriate amount of deionized water at a weight ratio of 80:10:10 to form a uniform negative electrode slurry, where the solid content of the negative electrode slurry was 40wt%. This slurry was coated on a negative electrode current collector copper foil, dried at 85°C, and then after cold pressing, slicing, and slitting, it was dried in a vacuum at 120°C for 12 hours to obtain the negative electrode sheet of the coin - type half - cell.

[0083] Preparation of lithium - ion coin - type half - cell: Using the electrolyte prepared in each example or comparative example as the electrolyte of the coin - type half - cell, a 7μm polypropylene / polyethylene composite separator was used, and a lithium sheet and the negative electrode sheet of the coin - type half - cell were used as counter electrodes respectively, and coin - type half - cells were assembled in a glove box.

[0084] Examples 1 - 2 to Examples 1 - 11

[0085] The differences between Examples 1 - 2 to Examples 1 - 11 and Example 1 - 1 are that during the preparation of silicon - carbon particles, the time of introducing carbon dioxide twice was changed, and the remaining steps were the same as those in Example 1 - 1. The specific preparation parameters can be referred to in Table 1 and Table 2.

[0086] Examples 2 - 1 to Examples 2 - 14

[0087] Examples 2-1 to 2-14 are different from Example 1-1 in that the times of introducing carbon dioxide twice during the preparation of silicon-carbon particles are changed, and the remaining steps are the same as those in Example 1-1. The specific preparation parameters can be referred to Table 3 and Table 4.

[0088] Examples 2-15 to 2-18

[0089] Examples 2-15 to 2-18 are different from Example 2-4 in that the average circularity of the silicon-carbon particles and graphite particles in the preparation of the negative electrode material is changed, and the remaining steps are the same as those in Example 1-1. The specific preparation parameters can be referred to Table 5.

[0090] Comparative Example 1

[0091] Comparative Example 1 is different from Example 1-1 in that during the second oxidation, the reaction temperature of carbon dioxide and the introduction amount of carbon dioxide are adjusted. For the specific preparation parameters, please refer to Table 1 and Table 2, and the rest are the same as those in Example 1-1.

[0092] Comparative Example 2

[0093] Comparative Example 2 is different from Example 1-1 in that the introduction time of carbon dioxide during the first oxidation, and during the second oxidation, the introduction amount and introduction time of carbon dioxide are adjusted. For the specific preparation parameters, please refer to Table 1 and Table 2, and the rest are the same as those in Example 1-1.

[0094] Comparative Example 3

[0095] Comparative Example 3 is different from Example 1-1 in that carbon dioxide is not introduced during both oxidation processes. For the specific preparation parameters, please refer to Table 1 and Table 2, and the rest are the same as those in Example 1-1.

[0096] Comparative Example 4

[0097] Comparative Example 4 is different from Example 1-1 in that the introduction time and the mass ratio of carbon dioxide during the first oxidation are adjusted, and the second oxidation of carbon dioxide is not carried out. For the specific preparation parameters, please refer to Table 1 and Table 2, and the rest are the same as those in Example 1-1.

[0098] Examples 3-1 to 3-8

[0099] Examples 3-1 to 3-8 are different from Example 2-1 in that the components of the electrolyte in the lithium-ion battery are adjusted. Except for adjusting the parameters of the relevant electrolyte components according to Table 6, the rest are the same as those in Example 2-1.

[0100] Relevant test methods for the negative electrode material

[0101] (1) Test method for the oxygen content of silicon-carbon particles:

[0102] The oxygen content was tested using a nitrogen-oxygen-hydrogen analyzer. Weighed 0.2 g of silicon carbide material particle sample, mixed it evenly with a flux (graphite), placed it in a graphite crucible, and put it on the instrument sampler. The high-temperature furnace was heated to 2500 °C. The silicon carbide material particle sample was melted in an argon stream, and oxygen was released in the form of CO or CO2. The carrier gas transported it to the detection system. CO / CO2 passed through an infrared detector, and the absorbance was proportional to the oxygen content. The oxygen content could be obtained through the data system.

[0103] (2) Test method for the oxygen content in the surface area and internal area of silicon carbide material particles:

[0104] Under an argon atmosphere, the silicon carbide material particles were cross-sectionally cut using focused ion beam cutting (FIB) to obtain the thin sample slices to be analyzed. The internal area and surface area of the silicon carbide material particles were observed and calibrated through TEM. The oxygen content in the internal area and surface area of the silicon carbide material particles was obtained by using TEM-EDX to take regions multiple times (5 times, taking the average value).

[0105] (3) Test method for the differential capacity curve of lithium deintercalation of the anode material:

[0106] After the lithium-ion coin half-cell was discharged at a small current of 0.05C / 50μA / 10μA in three stages to 0.005V, the first discharge capacity of the lithium-ion coin half-cell was recorded; then it was charged at a constant current of 0.1C to 1.5V, and the first charge capacity of the lithium-ion coin half-cell was recorded. The first reversible specific capacity of the anode material from 0.005V to 1.5V = the first charge capacity of the button cell / the mass of the anode material. Then, the two sets of data of specific capacity - voltage in the charging stage were processed by the slope function (to obtain DQ / DV corresponding to each voltage). One data was taken every 15 points. With voltage as the abscissa and DQ / DV as the ordinate, the differential capacity curve of lithium deintercalation of the anode material could be obtained.

[0107] (4) Test method for X-ray photoelectron spectroscopy:

[0108] XPS was used to analyze the components of the surface Si layer of the silicon carbide material particles. The silicon carbide material particles were stuck on the double-sided tape of the sample stage and put into the sample chamber for testing.

[0109] Peak deconvolution calculation: a. The raw data was charge-calibrated based on the standard value of 284.8 eV of foreign contaminated carbon. b. The energy spectrum was peak-deconvolution fitted through the XPS peaks. Peak deconvolution rule: For the split orbits of the same element, their full width at half maximum should be as close as possible. The Gaussian-Lorentz ratio of each data should be kept consistent (generally directly using the default value of 80). c. The integral intensity ratio of the peak-deconvolution fitted spectrum was calculated through a scientific drawing software (Origin).

[0110] (5) Test of the average circularity of silicon-carbon material particles and graphite:

[0111] Use a ZEISS-SEM (sigma-02-33) scanning electron microscope to observe the particle samples of the anode active material. Randomly select 20 silicon-carbon material particles (or graphite), and calculate their perimeter equivalent diameter and area equivalent diameter respectively. The sphericity of each silicon-carbon material particle (or graphite) = perimeter equivalent diameter / area equivalent diameter. Calculate the arithmetic mean of the sphericities of 20 silicon-carbon material particles (or graphite) as the sphericity of the silicon-carbon material particles (or graphite).

[0112] Performance test of lithium-ion batteries:

[0113] (1) Specific capacity / first Coulombic efficiency test:

[0114] Test: After the lithium-ion coin half-cell is discharged at a small current of 0.05C / 50μA / 10μA in three stages to 0.005V, record the first discharge capacity of the lithium-ion coin half-cell; then charge it at a constant current of 0.1C to 1.5V, and record the first charge capacity of the lithium-ion coin half-cell. The first reversible specific capacity of the anode material from 0.005V to 1.5V = first charge capacity of the lithium-ion coin half-cell / mass of the anode material.

[0115] (2) ITC cycle expansion test:

[0116] At 45°C, charge the lithium-ion full cell at a constant current density of 2C to 4.28V, charge it at a constant current density of 1.5C to 4.45V, then charge it at a constant voltage until the current density is 0.5C, charge it at a constant current density of 0.5C to 4.53V, then charge it at a constant voltage until the current density is 0.05C. At this time, the SOC of the lithium-ion full cell is 100%, then keep it warm for 24h and discharge it at a current density of 0.5C to 3.0V. Repeat this charge-discharge cycle 50 times. Apply a pressure of 1000g on the surface of the lithium-ion battery and use PPG laser to measure the thickness of the lithium-ion battery. The thickness of the fully charged full cell after 50 cycles is T1. Based on the thickness of the half-charged (50% SOC) lithium-ion battery, the thickness is T0, and calculate the expansion rate. ITC cycle expansion rate = (T1 - T0) / T0.

[0117] Among them, the preparation conditions and test results of each example and comparative example are recorded in Tables 1 to 6.

[0118] Table 1

[0119]

[0120]

[0121] Table 2

[0122]

[0123] Combining Table 1 and Table 2, compared with the comparative examples, in Examples 1-1 to 1-11, during the preparation of the silicon-carbon particle material, when the time of introducing carbon dioxide is changed twice and the oxygen content in the silicon-carbon particles and the oxygen content in the internal region both meet a specific range, the specific capacity and the first Coulombic efficiency of the negative electrode material can be improved, and the ITC cycle expansion of the secondary battery can be reduced.

[0124] In addition, when the oxygen content in the surface region also meets a specific range, the specific capacity and the first Coulombic efficiency of the negative electrode material can be further improved, and the ITC cycle expansion of the secondary battery can be reduced.

[0125] Table 3

[0126]

[0127]

[0128] Table 4

[0129]

[0130]

[0131] Combining Table 3 and Table 4, in the above examples, during the preparation of the silicon-carbon particle material, when the time of introducing carbon dioxide is changed twice, when the ratio of X1 / X2 in the silicon-carbon particles, the differential capacity curve of the negative electrode material, and the ratio of the Si-O peak to the Si-Si peak are respectively within a specific range, the gravimetric capacity and the first Coulombic efficiency of the negative electrode material can be further improved, and the ITC cycle expansion of the secondary battery can be reduced.

[0132] Table 5

[0133]

[0134] In Table 5, during the process of the negative electrode material, when the difference in the average circularity of graphite and silicon-carbon particles meets a specific range, the specific capacity and the first Coulombic efficiency of the negative electrode material can be further improved, and the ITC cycle expansion of the secondary battery can be reduced.

[0135] Table 6

[0136]

[0137] In Table 6, when the electrolytic solution contains ethylene carbonate and propylene carbonate, and the sum of the mass percentage contents D1 + D2 satisfies a suitable range, and the electrolytic solution contains ethylene carbonate and fluoroethylene carbonate, and the mass ratio D3 / D1 satisfies a suitable range, it is possible to further improve the first Coulombic efficiency of the negative electrode material while taking into account excellent specific capacity, and reduce the ITC cycle expansion of the secondary battery.

[0138] The above disclosure is only the preferred embodiment of the present application, and of course it cannot be used to limit the present application. Therefore, equivalent changes made according to the present application still fall within the scope covered by the present application.

Claims

1. A negative electrode material, characterized in that, It includes silicon-carbon particles, the oxygen content of the silicon-carbon particles is X%, 3 ≤ X ≤ 10. The silicon-carbon particles include an internal region and a surface region. The surface region refers to the region within 20 nm from the surface of the silicon-carbon particles, and the internal region refers to the other regions in the silicon-carbon particles except the surface region. The oxygen content of the internal region is X1%, 3 ≤ X1 ≤ 10.

2. The negative electrode material according to claim 1, wherein The silicon-carbon particles include porous carbon and silicon particles, and at least part of the silicon particles are located in the pores of the porous carbon.

3. The negative electrode material according to claim 1, characterized in that, The oxygen content of the surface region is X2%, 2 ≤ X2 ≤ 8.

4. The negative electrode material according to claim 3, characterized in that, 0.6 ≤ X1 / X2 ≤ 2.

5.

5. The negative electrode material according to any one of claims 1 to 4, characterized in that, The negative electrode material satisfies at least one of the following conditions: (1) The oxygen content of the silicon-carbon particles satisfies: 4 ≤ X ≤ 6 and 3 ≤ X1 ≤ 6; (2) The de-lithiation differential capacity curve of the negative electrode material has a first peak and a second peak at 200 mV to 320 mV and 600 mV to 900 mV respectively, and the peak intensity ratio of the first peak and the second peak is I1, 1.7 ≤ I1 ≤ 3.8; (3) In the X-ray photoelectron spectrum of the silicon-carbon particles, there are Si-O peaks and Si-Si peaks at 101 eV to 104 eV and 96 eV to 99 eV respectively, and the peak intensity ratio of the Si-O peak and the Si-Si peak is I2, 0.8 ≤ I2 ≤ 1.

5.

6. A method for preparing silicon-carbon particles in a negative electrode material according to any one of claims 1 to 5, characterized in that, It includes the following steps: S1) Provide a porous carbon skeleton, introduce silane gas into the porous carbon skeleton. After silicon deposition on the porous carbon skeleton, sequentially switch the silane gas to a carbon dioxide mixed gas, the silane gas, and the carbon dioxide mixed gas to obtain a core body. Wherein, the flow rate of each introduction of the carbon dioxide mixed gas is 50 sccm to 300 sccm, the introduction time is 1 h to 20 h, the reaction temperature is 400 °C to 500 °C. The carbon dioxide mixed gas includes carbon dioxide and an inert gas. In the carbon dioxide mixed gas, the mass percentage of carbon dioxide is 2% to 20%; S2) Introduce an alkane gas into the core body to form a carbon layer on the core body to obtain the silicon-carbon particles.

7. A secondary battery, comprising a negative electrode sheet, a positive electrode sheet, and an electrolyte, characterized in that, The negative electrode sheet further includes the negative electrode material according to any one of claims 1 to 5 or the negative electrode material obtained by the preparation method according to claim 6. The negative electrode material further includes graphite.

8. The secondary battery according to claim 7, wherein The average circularity of the silicon-carbon particles is C1, and the average circularity of the graphite is C2, |C1 - C2| ≤ 0.

2.

9. The secondary battery according to claim 7, characterized in that, The electrolyte satisfies at least one of the following conditions: (1) The electrolyte includes ethylene carbonate and propylene carbonate. Based on the mass of the electrolyte, the mass percentage of ethylene carbonate is D1%, and the mass percentage of propylene carbonate is D2%, 9 ≤ D1 + D2 ≤ 35. Preferably, 12 ≤ D1 + D2 ≤ 25; (2) The electrolyte solution includes ethylene carbonate and fluoroethylene carbonate. Based on the mass of the electrolyte solution, the mass percentage of ethylene carbonate is D1%, and the mass percentage of fluoroethylene carbonate is D3%, where 0.83 ≤ D3 / D1 ≤ 1.

75. Preferably, 1 ≤ D3 / D1 ≤ 1.

5.

10. An electronic device, characterized in that, Comprising a secondary battery according to any one of claims 7 to 9.

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