A silicon-carbon composite material, a negative electrode sheet, an electrochemical device, and an electronic device

Abstract

The application belongs to the technical field of electrochemistry, and relates to a silicon-carbon composite material, a negative electrode sheet, an electrochemical device and an electronic device. The Raman spectrum of the silicon-carbon composite material satisfies 0.61 < R / R' < 0.78; wherein R is the ratio of I A and I B ; R' is the ratio of I D and I G ; I A represents the intensity of a peak at 521±5 cm ‑1 in the Raman spectrum of the silicon-carbon composite material; I B represents the intensity of a peak at 480±5 cm ‑1 in the Raman spectrum of the silicon-carbon composite material; I D represents the intensity of a peak at 1360±5 cm ‑1 in the Raman spectrum of the silicon-carbon composite material; and I G represents the intensity of a peak at 1580±5 cm ‑1 in the Raman spectrum of the silicon-carbon composite material. The silicon-carbon composite material with the above characteristics can be applied to a secondary battery negative electrode material, so that the secondary battery has obviously improved conductivity, low-temperature performance, cycle performance and expansion performance under the premise of maintaining a high specific capacity.

Description

[0001] The present invention is a divisional application of the parent case with the patent number 202311352607.1 and the invention title "A silicon-carbon composite material, a negative electrode plate, an electrochemical device and an electronic device", and the entire content of the original application is incorporated into the present application by reference. Technical Field

[0002] The present invention belongs to the field of electrochemical technology, and relates to a silicon-carbon composite material, a negative electrode plate, an electrochemical device and an electronic device. Background Art

[0003] Electrochemical devices such as lithium-ion batteries are widely used in all aspects of daily life nowadays due to their advantages such as no memory effect, small volume, light weight and environmental friendliness. In recent years, electrochemical devices have even developed rapidly in the fields of new energy vehicles and large-scale energy storage. However, among the negative electrode materials of traditional commercial electrochemical devices, taking lithium-ion batteries as an example, carbon-based materials such as graphite have low capacity, resulting in low energy density of lithium-ion batteries; while silicon-based materials are prone to volume expansion, resulting in poor cycling performance of lithium-ion batteries, which greatly limits their large-scale application in electrochemical devices.

[0004] Although carbon materials as negative electrode materials have low specific capacity, they can be used as good conductive media and buffer matrices for silicon-based materials due to their advantages such as low price, good electrical conductivity, and outstanding chemical and thermal stability. Therefore, preparing silicon-carbon composite negative electrode materials by combining silicon oxide and carbon is an effective method. For example, Yang et al. prepared uniform silicon nanoparticles@phenolic resin-based carbon composite materials with adjustable carbon layer thickness through a simple, scalable production method. Son et al. used silane gas as a silicon source, uniformly deposited a nano-silicon layer on the surface of carbon materials by CVD method, and obtained a silicon-carbon composite material with low expansion.

[0005] Although there are a large number of studies on silicon-carbon composite materials at present, there are few studies on the internal connection between the characteristics of the material itself and the cycling performance and expansion performance. Summary of the Invention

[0006] The purpose of the present invention is to provide a silicon-carbon composite material, a negative electrode plate, an electrochemical device and an electronic device. When the silicon-carbon composite material provided by the present invention is applied to the negative electrode material of a secondary battery, the secondary battery can have significantly improved electrical conductivity, low-temperature performance, cycling performance and expansion performance while maintaining a high specific capacity.

[0007] According to a first aspect of the present invention, the present invention provides a silicon-carbon composite material, the silicon-carbon composite material comprising elemental silicon and a carbon material; the Raman spectrum of the silicon-carbon composite material satisfies: 0.61 < R / R' < 0.78; wherein, the R value is I A and IB The ratio; R' is I D with I G The ratio; I A The Raman spectrum of the silicon-carbon composite material is represented by 521±5 cm⁻¹. -1 The intensity of the peak at that location; I B The Raman spectrum of the silicon-carbon composite material at 480±5 cm⁻¹ represents... -1 The intensity of the peak at that location; I D The Raman spectrum of the silicon-carbon composite material is 1360±5 cm⁻¹. -1 The intensity of the peak at that location; I G The Raman spectrum of the silicon-carbon composite material is 1580±5 cm⁻¹. -1 The intensity of the peak at that location.

[0008] Through experimental investigation, this invention unexpectedly discovered that when the R / R' value of the silicon-carbon composite material is in the range of 0.61 to 0.78, the secondary battery exhibits improved conductivity, low-temperature performance, cycle performance, and expansion performance while maintaining a high specific capacity. In other words, when the silicon-carbon composite material provided by this invention satisfies the above characteristics, the secondary battery exhibits significantly improved conductivity, low-temperature performance, cycle performance, and expansion performance while maintaining a high specific capacity.

[0009] In some embodiments of the present invention, the range of R in the Raman spectral characteristics of the silicon-carbon composite material is: 0.78≤R≤0.9; the range of R' in the Raman spectral characteristics of the silicon-carbon composite material is 1.2≤R'≤1.25.

[0010] Further experimental investigation revealed that when the R value of the silicon-carbon composite material provided by this invention is within the aforementioned range, the secondary battery exhibits significantly improved cycle performance and expansion performance while maintaining a high specific capacity. Simultaneously, when the R' value of the silicon-carbon composite material is within the aforementioned range, the secondary battery demonstrates improved cycle performance while maintaining good conductivity and low-temperature performance. In other words, when both the R value and the R' value in the Raman spectral characteristics of the silicon-carbon composite material provided by this invention satisfy the aforementioned range characteristics, the secondary battery exhibits significantly improved conductivity, low-temperature performance, cycle performance, and expansion performance while maintaining a high specific capacity.

[0011] In some embodiments of the present invention, the elemental silicon comprises at least one of silicon nanoparticles, silicon submicron particles, or silicon nanofilms. In some embodiments of the present invention, the carbon material comprises a porous carbon framework and a carbon coating layer. In the silicon-carbon composite material provided by the present invention, the elemental silicon in the silicon-carbon composite material imparts a high specific capacity to the silicon-carbon composite material, and the carbon material in the silicon-carbon composite material not only buffers the volume expansion of silicon to a certain extent, but also enhances the conductivity of the silicon-carbon composite material.

[0012] In some embodiments of the present invention, based on the mass of the silicon-carbon composite material, the ratio of the carbon content 'a' to the silicon content 'b' in the silicon-carbon composite material ranges from 0.5.

[0013] In the technical solution provided by the present invention, by adjusting the ratio of a and b and the values ​​of a and b within the above range, the silicon-carbon composite material can have a high specific capacity, while buffering the volume expansion of the silicon-carbon composite material to a certain extent and enhancing the conductivity of the silicon-carbon composite material.

[0014] ​In some embodiments of the present invention, the internal cross-sectional SEM images of the silicon-carbon composite material show that the internal surface of the particles is flat, and the pore size inside the particles is less than 50 nm. Observing the SEM images of the cross-section of the silicon-carbon composite material provided by the present invention in backscatter mode, the internal structure of the particles is flat and smooth, with small-diameter pores and no large-pore structure, and the outer surface of the particles exhibits a certain degree of silicon enrichment. The flat and smooth internal structure with small-diameter pores can improve the deposition uniformity inside the silicon-carbon composite material particles and avoid the phenomenon of low capacity caused by the absence of silicon deposition inside the silicon-carbon composite material due to large pores; at the same time, the certain degree of silicon enrichment on the outer surface of the particles can give the silicon-carbon composite material a higher specific capacity and first coulombic efficiency.

[0015] In some embodiments of the present invention, the silicon-carbon composite material satisfies at least one of the following conditions 1) to 5): 1) The size of the silicon crystals in the silicon-carbon composite material is less than 1 nm; preferably, the size of the silicon crystals in the silicon-carbon composite material is 0.8~0.95 nm; 2) Particle size D V 50 is 5 µm~10 µm, D V 99 is 15 µm to 25 µm; preferably, the particle size D V The range of 50 is 5 µm to 6.5 µm, D V 99 is 15 µm~19 µm; 3) The specific surface area of ​​the silicon-carbon composite material is 1 m². 2 / g~50 m 2 / g; preferably, the specific surface area of ​​the silicon-carbon composite material is in the range of 4 m². 2 / g~8 m 2 / g; 4) The oxygen content in the silicon-carbon composite material is 1.5 wt% to 4.0 wt%; the oxygen content range in the silicon-carbon composite material is 1.2 wt% to 3 wt%. 5) The initial delithiation specific capacity of the silicon-carbon composite material is 500 mAh / g to 2500 mAh / g; preferably, the initial delithiation specific capacity of the silicon-carbon composite material is 1400 mAh / g to 2000 mAh / g.

[0016] By controlling the size of silicon crystallites in the silicon-carbon composite material within the aforementioned range, the lithium insertion / extraction activity of the silicon crystallites can be improved, and the transport of active ions can be accelerated. Simultaneously, the smaller size of the silicon crystallites can buffer the deformation stress during charge and discharge processes, thereby improving the cycle performance and expansion properties of the silicon-carbon composite material. This can be achieved by controlling the particle size D of the silicon-carbon composite material. v 50 and D vWithin the aforementioned range, 99% of the specific surface area can improve the dispersion uniformity of the slurry and enhance the transport of active ions, thereby improving the cycle performance and expansion performance of the secondary battery. Furthermore, by controlling the specific surface area of ​​the silicon-carbon composite material within the aforementioned range, side reactions between the silicon-carbon composite material and the electrolyte can be reduced, further improving the cycle performance and expansion performance of the secondary battery. Controlling the oxygen content of the silicon-carbon composite material within the aforementioned range helps to further balance the specific capacity, cycle performance, and expansion performance of the lithium-ion battery, thereby improving the overall performance of the lithium-ion battery. When the initial delithiation specific capacity of the silicon-carbon composite material is within the aforementioned range, it is possible to balance the specific capacity of the silicon-carbon composite material with its cycle performance and expansion performance.

[0017] According to a second aspect of the present invention, the present invention also provides a method for preparing the silicon-carbon composite material, the method comprising: controlling the R value of the silicon-carbon composite material by changing at least one parameter among the following: the pyrolysis temperature of the silicon-containing gas, the flow rate of the silicon-containing gas, the time of introducing the silicon-containing gas, the time of micro-oxidation, the temperature of micro-oxidation, or the flow rate of oxygen; and / or controlling the R' value of the silicon-carbon composite material by changing at least one parameter among the following: the pyrolysis temperature of the carbon source gas, the flow rate of the carbon source gas, or the time of introducing the carbon source gas.

[0018] In some embodiments of the present invention, the method includes the following steps: (1) Silicon deposition: Using porous carbon materials as precursors and silicon-containing gas as silicon source, elemental nano-silicon is adsorbed and deposited in the pores of porous carbon through chemical vapor deposition. (2) Micro-oxidation: oxygen is introduced to micro-oxidize the nano-silicon on the shallow and outer surfaces of porous carbon; (3) Carbon deposition: After the micro-oxidation treatment is completed, carbon source gas is introduced, so that carbon source gas is deposited on the outer surface of the material obtained in step (2) and a carbon coating layer is formed, and silicon-carbon material coated with carbon coating layer is obtained. Steps (1) to (3) are all carried out under an inert gas protective atmosphere and a slightly positive pressure gas phase pressure; the slightly positive pressure condition is 0.1~5 kPa.

[0019] In some embodiments of the present invention, the method further includes: (4) Grind and sieve the silicon-carbon composite material obtained in step (3) to obtain the silicon-carbon composite material.

[0020] In some embodiments of the present invention, in step (1), the condition of the micro-positive pressure can be 1.5~2.5 kPa; in step (2), the condition of the micro-positive pressure is 0.5~1.5 kPa; in step (3), the condition of the micro-positive pressure is 2.0~3.0 kPa.

[0021] In some embodiments of the present invention, the inert gas is argon.

[0022] In some embodiments of the present invention, the silicon-containing gas may include, but is not limited to, at least one of: silane, silane, propane, tetrasilane, chlorosilane, dichlorosilane, trichlorosilane, or tetrachlorosilane; the carbon source gas may include, but is not limited to, at least one of: methane, acetylene, ethylene, ethane, propyne, propylene, propane, butyne, butene, or butane; the porous carbon material may include, but is not limited to, at least one of: activated carbon, expanded graphite, carbon molecular sieve, carbon nanofiber, or carbon nanotube; preferably, the activated carbon is obtained by activating biochar, resin carbon, coke, etc.

[0023] In some embodiments of the present invention, the specific surface area of ​​the porous carbon material is 1000 m². 2 / g to 2500 m 2 / g; the pore volume of the porous carbon material is 0.5 cm³. 3 / g to 1.5 cm 3 / g; The porous carbon material comprises 0~30% ultramicropores, 0~30% submicropores, 0~60% macropores and 0~20% mesopores.

[0024] According to a third aspect of the present invention, the present invention provides a negative electrode sheet, the negative electrode sheet comprising a negative electrode current collector and a negative electrode active material located on at least one surface of the negative electrode current collector, the negative electrode active material comprising a silicon-carbon composite material as described in the first aspect of the present invention.

[0025] In some embodiments of the present invention, the negative electrode active material further includes graphite, a conductive agent, and a binder; the mass percentage of graphite in the negative electrode active material is from 35 wt.% to 95 wt.%.

[0026] In some embodiments of the present invention, the negative electrode active material satisfies at least one of the following conditions (I) to (III): (I) Particle size D V 50 is 5 µm~15 µm, D V 99 is 15 µm~40 µm; (II) The specific surface area of ​​the negative electrode active material is 1 m². 2 / g~10 m 2 / g; (III) The initial delithiation specific capacity of the negative electrode active material is 400 mAh / g to 1000 mAh / g.

[0027] According to a fourth aspect of the present invention, the present invention provides an electrochemical device comprising the negative electrode tab according to the third aspect of the present invention.

[0028] According to a fifth aspect of the present invention, the present invention provides an electronic device comprising the electrochemical device according to the fourth aspect of the present invention.

[0029] Compared with the prior art, the present invention has the following beneficial effects: The present invention provides a silicon-carbon composite material, a negative electrode tab containing the silicon-carbon composite material, an electrochemical device, and an electronic device. The silicon-carbon composite material provided by the embodiment of the present invention, by regulating I of the silicon-carbon composite material A and I B ratio R and I D and I G the ratio of ratio R' R / R' satisfies 0.61 < R / R' < 0.78, the silicon-carbon composite material can achieve an optimal balance between crystalline silicon and amorphous silicon, and between carbon defects and carbon graphitization, thereby enabling a secondary battery to have significantly improved electrical conductivity, low-temperature performance, cycling performance and expansion performance while maintaining a high specific capacity. Description of Drawings

[0030] Figure 1 is an XRD pattern of the silicon-carbon composite material obtained in Example 1; the XRD pattern shows that elemental silicon in the silicon-carbon composite material obtained in the embodiment of the present invention exists in an amorphous form; Figure 2 is a Raman spectrum of the silicon-carbon composite material obtained in Example 1; Figure 3 is an SEM image in backscattering mode of a cross-section of the silicon-carbon composite material obtained in Example 1; Figure 4 is a first-cycle charge-discharge curve of the silicon-carbon composite material obtained in Example 1. Detailed Description

[0031] The technical solution of the present invention is further described below through specific embodiments, and the specific embodiments do not represent limitations to the protection scope of the present invention. Some non-essential modifications and adjustments made by others based on the concept of the present invention still fall within the protection scope of the present invention.

[0032] It should be noted that in the following content, the present invention is explained by taking a lithium-ion battery as an example of the secondary battery, but the secondary battery of the present invention is not limited to lithium-ion batteries.

[0033] According to a first aspect of the present invention, the present invention provides a silicon-carbon composite material, which comprises elemental silicon and a carbon material; the Raman spectrum of the silicon-carbon composite material satisfies: 0.61 < R / R' < 0.78; wherein, the R value is I A and I B ratio; R' value is I D and I G ratio; I A represents the intensity of the peak at 521±5cm -1 in the Raman spectrum of the silicon-carbon composite material; I B represents the intensity of the peak at 480±5cm -1 in the Raman spectrum of the silicon-carbon composite material; I D represents the intensity of the peak at 1360±5cm -1 in the Raman spectrum of the silicon-carbon composite material; I G represents the intensity of the peak at 1580±5cm -1 in the Raman spectrum of the silicon-carbon composite material.

[0034] I A represents the intensity of a characteristic peak of crystalline silicon at 521±5cm -1 in the Raman spectrum. The silicon-silicon bonds have a symmetric structure, which can produce strong Raman scattering. Crystalline silicon has highly consistent bond angles and bond lengths, and is arranged in an ordered manner, which can form a sharp Raman peak, and its characteristic strong scattering band is located at 521±5cm -1 ; I B represents the intensity of a characteristic peak of amorphous silicon at 480±5 cm -1 in the Raman spectrum. The structure of amorphous silicon is relatively disordered, with large ranges of bond angles, bond energies, bond lengths and rocking ranges, which forms a relatively broad Raman peak at 480±5 cm -1 , which is significantly different from the characteristic peak of crystalline silicon. Based on the intensity ratio of the peaks at 521±5 cm -1 and 480±5cm -1 , i.e., the ratio R of I A to I B , can be used to characterize the content ratio of crystalline silicon and amorphous silicon in the silicon-carbon composite material of the present application.

[0035] I A represents the intensity of the characteristic peak at 521±5cm -1 in the Raman spectrum of the silicon-carbon composite material. Specifically, I A represents the intensity of the corresponding characteristic peak between 516~527cm -1 , for example, I A represents the intensity at 516 cm-1 517 cm -1 518 cm -1 519 cm -1 520 cm -1 521 cm -1 522 cm -1 523 cm -1 524 cm -1 525 cm -1 526 cm -1 or 527cm -1 The intensity of the characteristic peak at any wavelength, or the intensity of the characteristic peak corresponding to the range between any two wavelength values ​​mentioned above.

[0036] Similarly, I B The Raman spectrum of the silicon-carbon composite material at 480±5 cm⁻¹ represents... -1 The intensity of the peak at that location. Specifically, I B The Raman spectrum of the silicon-carbon composite material is 475-485 cm⁻¹. -1 The intensity of the corresponding characteristic peaks, such as I B The Raman spectrum of the silicon-carbon composite material at 475 cm⁻¹ represents... -1 476 cm -1 477 cm -1 478 cm -1 479 cm -1 480cm -1 481 cm -1 482 cm -1 483 cm -1 484 cm -1 or 85cm -1 The intensity of the characteristic peak at any wavelength, or the intensity of the characteristic peak corresponding to the range between any two wavelength values ​​mentioned above.

[0037] The D and G peaks in the Raman spectrum are characteristic peaks of carbon atom crystals, located at 1360±5 cm⁻¹, respectively. -1 and 1580±5cm -1 Nearby. The D peak represents defects in the carbon atom crystal and is inversely proportional to the degree of order in the carbon structure; the G peak represents sp atoms of carbon. 2 Hybridized in-plane stretching vibrations represent the degree of graphitization of the carbon structure, and the intensity ratio of the D peak to the G peak in Raman spectroscopy can be used to reflect the disorder of carbon. In this invention, I D The Raman spectrum of silicon-carbon composite materials at 1360±5 cm⁻¹ -1 The intensity of the peak at I GThe Raman spectrum of the silicon-carbon composite material is 1580±5 cm⁻¹. -1 The peak intensity at 1360±5 cm⁻¹ is based on the Raman spectrum. -1 and 1580±5 cm -1 The height ratio of the peak, i.e., I D and I G The ratio R' can be used to characterize the defect level of carbon materials.

[0038] I D The Raman spectrum of the silicon-carbon composite material is 1360±5 cm⁻¹. -1 The intensity of the peak at that location. Specifically, I D The Raman spectrum of the silicon-carbon composite material is 1355~1365cm. -1 The intensity of the corresponding peaks, such as I D The Raman spectrum of the silicon-carbon composite material at 1355 cm⁻¹ represents... -1 1356 cm -1 1357 cm -1 1358 cm -1 1359 cm -1 1360 cm -1 1361 cm -1 1362 cm -1 1363 cm -1 1364 cm -1 or 1365cm -1 The intensity of the characteristic peak at any wavelength, or the intensity of the characteristic peak corresponding to the range between any two wavelength values ​​mentioned above.

[0039] I G The Raman spectrum of the silicon-carbon composite material is 1580±5 cm⁻¹. -1 The intensity of the peak at that location. Specifically, I G The Raman spectrum of the silicon-carbon composite material is 1575~1585 cm⁻¹ -1 The intensity of the corresponding peaks, such as I G The Raman spectrum of the silicon-carbon composite material at 1575 cm⁻¹ represents... -1 1576 cm -1 1577 cm -1 1578 cm -1 1579 cm -1 1579 cm -1 1580 cm -1 1581 cm -1 1582 cm -1 1583 cm -11584 cm -1 or 1585cm -1 The intensity of the characteristic peak at any wavelength, or the intensity of the characteristic peak corresponding to the range between any two wavelength values ​​mentioned above.

[0040] The inventors discovered that when the ratio of R to R' in the Raman spectral characteristics of the silicon-carbon composite material is within the range of this invention, the secondary battery can maintain a high specific capacity while also exhibiting significantly improved conductivity, low-temperature performance, cycle performance, and expansion performance. Therefore, in the design of the silicon-carbon composite material of this invention, the long-term performance of the silicon-carbon composite material can be predicted by the ratio of R to R'. Furthermore, it was found that when the R / R' value of the silicon-carbon composite material is in the range of 0.61 to 0.78, the silicon-carbon composite material possesses an optimal balance between crystalline silicon and amorphous silicon, and between carbon defects and carbon graphitization. This allows the silicon-carbon composite material to maintain a high specific capacity while exhibiting significantly improved conductivity, low-temperature performance, cycle performance, and expansion performance.

[0041] Specifically, the ratio R / R' can be 0.611, 0.612, 0.613, 0.615, 0.516, 0.617, 0.618, 0.619, 0.62, 0.63, 0.64, 0.65, 0.66, 0.67, 0.68, 0.69, 0.70, 0.71, 0.72, 0.73, 0.74, 0.75, 0.76, 0.77, 0.771, 0.772, 0.773, 0.774, 0.775, 0.776, 0.777, 0.778, or a range consisting of any two of the above values. When the R / R' value is too low, such as 0.61 or lower, although the lithium-ion battery has excellent cycle performance and expansion performance, its specific capacity, initial coulombic efficiency and conductivity all decrease significantly. When the R / R' value is too high, such as 0.78 or higher, although the lithium-ion battery has relatively high specific capacity, initial coulombic efficiency and conductivity, its cycle performance and expansion performance decrease significantly.

[0042] In some embodiments of the present invention, the range of R in the Raman spectral characteristics of the silicon-carbon composite material is: 0.78 ≤ R ≤ 0.9; the range of R' in the Raman spectral characteristics of the silicon-carbon composite material is 1.2 ≤ R' ≤ 1.25. Studies have found that when I in the Raman spectral characteristics of the silicon-carbon composite material... A with I B The ratios R and I D / I G When the R' value is within the range of this invention, the secondary battery can maintain a high specific capacity while also exhibiting significantly improved conductivity, low-temperature performance, cycle performance, and expansion performance. Therefore, in the design of the silicon-carbon composite material of this invention, I...A with I B The ratios R and I D / I G The R' value was used to predict the long-term performance of silicon-carbon composites, and it was found that when the I of the silicon-carbon composite was... A with I B The ratio R is in the range of 0.78 to 0.9, I D / I G When the R' value is in the range of 1.2 to 1.25, the silicon-carbon composite material has the best balance ratio between crystalline silicon and amorphous silicon, and between carbon defects and carbon graphitization, so that the silicon-carbon composite material has significantly improved electrical conductivity, low temperature performance, cycle performance and expansion performance while maintaining a high specific capacity.

[0043] Specifically, the silicon-carbon composite material's I A with I B The ratio R can be 0.78, 0.79, 0.80, 0.81, 0.82, 0.83, 0.84, 0.85, 0.86, 0.87, 0.88, 0.89, 0.90, or a range of any two of the above values. When the R value is too large, the crystalline silicon content of the silicon-carbon composite material is too high, which will deteriorate its cycle performance and expansion performance. Conversely, when the R value is too small, the amorphous silicon content of the silicon-carbon composite material is too high, which is detrimental to the specific capacity and initial coulombic efficiency of the silicon-carbon composite material. Specifically, the I of the silicon-carbon composite material... D / I G The ratio R' can be 1.2, 1.21, 1.22, 1.23, 1.24, 1.25, or any range of two of the above values. When the value of R' is too large, the degree of defect in the silicon-carbon composite material is too high, which will increase side reactions, reduce conductivity, and affect its cycle performance and low-temperature performance. When the value of R' is too small, although the conductivity of the silicon-carbon composite material is improved, the degree of defect is too low, which is not conducive to the volume expansion of the buffer material.

[0044] In other words, the silicon-carbon composite material provided by this invention has I A with I B The ratios R and I D / I G If the ratio R' is too large or too small, it will significantly affect the performance of the silicon-carbon composite material. For example, when the I of the silicon-carbon composite material is too large or too small, it will significantly affect the performance of the silicon-carbon composite material. A with I B The ratios R and I D / I G When the ratio R' of the silicon-carbon composite material is too low, although the lithium-ion battery exhibits excellent cycle performance and expansion performance, its specific capacity, initial coulombic efficiency, and conductivity all decrease significantly; when the ratio R' of the silicon-carbon composite material is too low, although the lithium-ion battery exhibits excellent cycle performance and expansion performance, its specific capacity, initial coulombic efficiency, and conductivity all decrease significantly; A with IB The ratios R and I D / I G When the ratio R' is too large, although lithium-ion batteries have relatively high specific capacity, initial coulombic efficiency and conductivity, their cycle performance and expansion performance are significantly reduced. At the same time, excessively large R and R' values ​​will also deteriorate the low-temperature performance of silicon-carbon composite materials.

[0045] In some embodiments of the present invention, the elemental silicon comprises at least one of silicon nanoparticles, silicon submicron particles, or silicon nanofilms. In some embodiments of the present invention, the carbon material comprises a porous carbon framework and a carbon coating layer. In the silicon-carbon composite material provided by the present invention, elemental silicon imparts a high specific capacity to the silicon-carbon composite material, and the carbon material in the silicon-carbon composite material not only buffers the volume expansion of silicon to a certain extent, but also enhances the conductivity of the silicon-carbon composite material.

[0046] In some embodiments of the present invention, based on the mass of the silicon-carbon composite material, the ratio of the carbon content 'a' to the silicon content 'b' in the silicon-carbon composite material ranges from 0.5.

[0047] ​In some embodiments of the present invention, based on the mass of the silicon-carbon composite material, the content a of carbon element in the silicon-carbon composite material ranges from 40 wt%<a<90 wt%, and the content b of silicon element in the silicon-carbon composite material ranges from 10 wt%<b<60 wt%; preferably, the content a of carbon element in the silicon-carbon composite material ranges from 50 wt%<a<64.8 wt%, and the content b of silicon element in the silicon-carbon composite material ranges from 31.9 wt%<b<46.6 wt%; more preferably, the content a of carbon element in the silicon-carbon composite material ranges from 52 wt%<a<64 wt%, and the content b of silicon element in the silicon-carbon composite material ranges from 32 wt%<b<44 wt%. Specifically, the content a of carbon element in the silicon-carbon composite material can be 50.1wt%, 50.5wt%, 51wt%, 52wt%, 52.1wt%, 52.5wt%, 53wt%, 54wt%, 55wt%, 56wt%, 57wt%, 58wt%, 59wt%, 60wt%, 61wt%, 62wt%, 63wt%, 64wt%, 64.5wt%, 64.6wt%, 64.7wt%, or a range composed of any two of the above values. Specifically, for the content b of silicon element in the silicon-carbon composite material that ranges from 31.9 wt%<b<46.6 wt%, the content b can be 32wt%, 33wt%, 34wt%, 35wt%, 36wt%, 37wt%, 38wt%, 39wt%, 40wt%, 41wt%, 42wt%, 43wt%, 44wt%, 45wt%, 46wt%, 46.1wt%, 46.2wt%, 46.3wt%, 46.4wt%, 46.5wt%, or a range composed of any two of the above values. By regulating the values of a and b within the above ranges, the silicon-carbon composite material can have a high specific capacity, while buffering the volume expansion of the silicon-carbon composite material to a certain extent and enhancing the electrical conductivity of the silicon-carbon composite material. When the content a is too high, the specific capacity of the silicon-carbon composite material will be deteriorated; when the content a is too low, the expansion resistance and electrical conductivity of the silicon-carbon composite material will be reduced. On the contrary, when the content b is too high, the expansion resistance and electrical conductivity of the silicon-carbon composite material will be reduced; when the content b is too low, the specific capacity of the silicon-carbon composite material will be deteriorated.

[0048] In some embodiments of the present invention, when observing the SEM image of the internal cross-section of the silicon-carbon composite material in backscattering mode, the internal surface of the particle is flat, the pore diameter of the pores inside the particle is less than 50 nm, and there is a certain silicon-rich phenomenon on the outer surface of the particle. For example, Figure 3The image shows a cross-section of the silicon-carbon composite material in backscattering mode (SEM). Observing the SEM image of the cross-section of the silicon-carbon composite material in backscattering mode, the particles exhibit a smooth and flat internal structure with small-diameter pores and no macroporous structures. Furthermore, the outer surface of the particles shows a certain degree of silicon enrichment. The smooth and flat internal structure with small-diameter pores improves the deposition uniformity within the silicon-carbon composite particles and avoids the phenomenon of low capacity caused by the absence of silicon deposition due to macroporous structures. Simultaneously, the degree of silicon enrichment on the outer surface of the particles contributes to the high specific capacity and initial coulombic efficiency of the silicon-carbon composite material.

[0049] In some embodiments of the present invention, the size of the silicon crystallites in the silicon-carbon composite material is less than 1 nm; preferably, the size of the silicon crystallites in the silicon-carbon composite material is 0.8~0.95 nm. Specifically, the size of the silicon crystallites in the silicon-carbon composite material can be 0.99 nm, 0.98 nm, 0.97 nm, 0.96 nm, 0.95 nm, 0.94 nm, 0.93 nm, 0.92 nm, 0.91 nm, 0.90 nm, 0.89 nm, 0.88 nm, 0.87 nm, 0.86 nm, 0.85 nm, 0.84 nm, 0.83 nm, 0.82 nm, 0.81 nm, 0.80 nm, 0.70 nm, 0.60 nm, 0.50 nm, 0.40 nm, 0.30 nm, 0.20 nm, or a range consisting of any two of the above values. By controlling the size of silicon crystals in silicon-carbon composite materials within the above-mentioned range, the lithium insertion / extraction activity of silicon crystals can be improved, the transport of active ions can be accelerated, and the smaller size of silicon crystals can buffer the deformation stress during the charging and discharging process, thereby improving the cycle performance and expansion performance of silicon-carbon composite materials.

[0050] In some embodiments of the present invention, the particle size D of the silicon-carbon composite material is... V 50 is 5μm~10μm, D V 99 is 15μm~25μm; preferably, the particle size D V The range of 50 is 5 µm to 6.5 µm, D V 99 represents 15 µm to 19 µm. Specifically, the particle size D... V 50 can be 5μm, 5.5μm, 6.0μm, 6.5μm, 7.0μm, 7.5μm, 8.0μm, 8.5μm, 9.0μm, 9.5μm, 10.0μm, or a range of any two of the above values. V99 can be 15μm, 15.5μm, 16μm, 16.5μm, 17μm, 17.5μm, 18μm, 18.5μm, 19μm, 19.5μm, 20μm, 20.5μm, 21μm, 21.5μm, 22μm, 22.5μm, 23μm, 23.5μm, 24μm, 24.5μm, 25μm, or a range of any two of the above values. The particle size D of the silicon-carbon composite material can be adjusted. v 50 and D v Within the above range, 99 can improve the dispersion uniformity of the slurry and improve the transport of active ions, thereby helping to improve the cycle performance and expansion performance of the secondary battery.

[0051] In this invention, D v 50 represents the particle size that, in the volumetric reference particle size distribution of the silicon-carbon composite material, reaches 50% of the total volumetric particle size, measured from the smallest particle size. v 99 indicates the particle size that accounts for 99% of the volumetric particle size distribution in the material's volumetric reference particle size distribution, measured from the smallest particle size.

[0052] In some embodiments of the present invention, the specific surface area of ​​the silicon-carbon composite material is 1 m². 2 / g~50m 2 / g; preferably, the specific surface area of ​​the silicon-carbon composite material is in the range of 4 m². 2 / g~8 m 2 / g. For example, the specific surface area of ​​silicon-carbon composite materials can be 1m². 2 / g、2 m 2 / g、3 m 2 / g、4 m 2 / g、5m 2 / g、6 m 2 / g、7 m 2 / g、8 m 2 / g、9 m 2 / g, 10m 2 / g, 15m 2 / g、20m 2 / g、25m 2 / g、30m 2 / g、35m 2 / g、40m 2 / g、45m 2 / g, 50m 2 / g or a range consisting of any two of the above values. Silicon-carbon composite materials possess a specific surface area within the above range, which can reduce side reactions between the silicon-carbon composite material and the electrolyte, thus improving the cycle performance and expansion performance of the secondary battery.

[0053] In some embodiments of the present invention, the oxygen content in the silicon-carbon composite material is 1.0 wt% to 4.0 wt%; preferably, the oxygen content in the silicon-carbon composite material ranges from 1.2 wt% to 3 wt%. Specifically, the oxygen content of the silicon-carbon composite material can be 1.0 wt%, 1.1 wt%, 1.2 wt%, 1.3 wt%, 1.4 wt%, 1.5 wt%, 2 wt%, 2.5 wt%, 3 wt%, 3.5 wt%, 4 wt%, or a range consisting of any two of the above values. By controlling the oxygen content of the silicon-carbon composite material within the above range, it is beneficial to further balance the specific capacity, cycle performance, and expansion performance of the lithium-ion battery, thereby improving the overall performance of the lithium-ion battery.

[0054] In some embodiments of the present invention, the initial delithiation specific capacity of the silicon-carbon composite material is 500 mAh / g to 2500 mAh / g; preferably, the initial delithiation specific capacity of the silicon-carbon composite material is 1400 mAh / g to 2000 mAh / g. Specifically, the initial delithiation specific capacity of the silicon-carbon composite material can be 500 mAh / g, 600 mAh / g, 700 mAh / g, 800 mAh / g, 900 mAh / g, 1000 mAh / g, 1100 mAh / g, 1200 mAh / g, 1300 mAh / g, 1400 mAh / g, 1500 mAh / g, 1600 mAh / g, 1700 mAh / g, 1800 mAh / g, 1900 mAh / g, 2000 mAh / g, 2100 mAh / g, 22 mAh / g, 2300 mAh / g, 2400 mAh / g, 2500 mAh / g, or a range consisting of any two of the above values. When the initial delithiation specific capacity of the silicon-carbon composite material is within the above range, it can balance the specific capacity of the silicon-carbon composite material with its cycle performance and expansion performance.

[0055] According to a second aspect of the present invention, the present invention provides a method for preparing the silicon-carbon composite material, the method comprising, but not limited to, the following steps: adjusting the R value of the silicon-carbon composite material by changing at least one parameter among the following: the pyrolysis temperature of the silicon-containing gas, the flow rate of the silicon-containing gas, the time of introducing the silicon-containing gas, the time of micro-oxidation, the temperature of micro-oxidation, or the flow rate of oxygen; and / or adjusting the R' value of the silicon-carbon composite material by changing at least one parameter among the following: the pyrolysis temperature of the carbon source gas, the flow rate of the carbon source gas, or the time of introducing the carbon source gas.

[0056] In some embodiments of the present invention, the preparation method includes, but is not limited to, the following steps: (1) Silicon deposition: Using porous carbon materials as precursors and silicon-containing gas as silicon source, elemental nano-silicon is adsorbed and deposited in the pores of porous carbon through chemical vapor deposition. (2) Micro-oxidation: oxygen is introduced to micro-oxidize the nano-silicon on the shallow and outer surfaces of porous carbon; (3) Carbon deposition: After the micro-oxidation treatment is completed, carbon source gas is introduced, so that carbon source gas is deposited on the outer surface of the material obtained in step (2) and a carbon coating layer is formed, and silicon-carbon material coated with carbon coating layer is obtained. (4) Grind and sieve the silicon-carbon composite material obtained in step (3) to obtain the silicon-carbon composite material.

[0057] Steps (1) through (3) are all performed under an inert gas protective atmosphere and a slightly positive pressure in the gas phase, wherein the slightly positive pressure is 0.1 to 5 kPa. Specifically, the slightly positive pressure can be 0.1 kPa, 0.5 kPa, 1.0 kPa, 1.5 kPa, 2.0 kPa, 2.5 kPa, 3.0 kPa, 3.5 kPa, 4.0 kPa, 4.5 kPa, 5.0 kPa, or any range of two of the above values.

[0058] In some embodiments of the present invention, in step (1), the micro-positive pressure condition can be 1.5~2.5 kPa. In step (2), the micro-positive pressure condition is 0.5~1.5 kPa. In step (3), the micro-positive pressure condition is 2.0~3.0 kPa.

[0059] In some implementations, the inert gas may be argon.

[0060] In the above preparation method, the R-value of the silicon-carbon composite material can be controlled by changing the pyrolysis temperature, the flow rate of the silicon-containing gas, and the duration of silicon-containing gas introduction. For example, increasing the pyrolysis temperature increases the R-value of the silicon-carbon composite material; decreasing the pyrolysis temperature decreases the R-value; increasing the flow rate of the silicon-containing gas increases the R-value; decreasing the flow rate decreases the R-value; extending the duration of silicon-containing gas introduction increases the R-value; shortening the duration of silicon-containing gas introduction decreases the R-value. Simultaneously, the R-value of the silicon-carbon composite material can also be controlled by changing the micro-oxidation time and the oxygen flow rate. For example, extending the micro-oxidation time decreases the R-value; shortening the micro-oxidation time increases the R-value.

[0061] Similarly, the R' value of silicon-carbon composite materials can be controlled by changing the pyrolysis temperature, the carbon source gas flow rate, and the duration of carbon source gas introduction. For example, increasing the pyrolysis temperature decreases the R' value of silicon-carbon composite materials; decreasing the pyrolysis temperature increases the R' value; increasing the carbon source gas flow rate increases the R' value; decreasing the carbon source gas flow rate slightly decreases the R' value; extending the duration of carbon source gas introduction increases the R' value; and shortening the duration of carbon source gas introduction slightly decreases the R' value.

[0062] Technicians can adjust the pyrolysis temperature, flow rate, and introduction time of the silicon-containing or carbon-source gas, as well as the micro-oxidation temperature, micro-oxidation time, and oxygen flow rate as needed. For example, the pyrolysis temperature of the silicon-containing or carbon-source gas can be 400℃~800℃, the flow rate can be 100 sccm~800 sccm, the introduction time can be 1h~20h, the oxygen flow rate can be 50 sccm~200 sccm, the micro-oxidation time can be 1h~20h, and the micro-oxidation temperature can be 50-200℃.

[0063] In some embodiments of the present invention, the silicon-containing gas may include, but is not limited to, at least one of: silane, disilane, propane, tetrasilane, chlorosilane, dichlorosilane, trichlorosilane, or tetrachlorosilane; the carbon source gas may include, but is not limited to, at least one of: methane, acetylene, ethylene, ethane, propyne, propylene, propane, butyne, butene, or butane; the porous carbon material may include, but is not limited to, at least one of: activated carbon, expanded graphite, carbon molecular sieve, carbon nanofibers, or carbon nanotubes. The activated carbon may be obtained by activating biochar, resin carbon, coke, etc.

[0064] In some embodiments of the present invention, the specific surface area of ​​the porous carbon material is 1000 m². 2 / g~2500 m 2 / g. Specifically, the specific surface area of ​​porous carbon materials can be 1000 m². 2 / g、1100 m 2 / g、1200 m 2 / g、1300 m 2 / g, 1400 m 2 / g, 1500 m 2 / g、1600 m 2 / g、1700 m 2 / g、1800 m 2 / g、1900 m 2 / g、2000 m2 / g、2100 m 2 / g、2200 m 2 / g、2300 m 2 / g、2400 m 2 / g、2500 m 2 / g or a range consisting of any two of the above values. The pore volume of the porous carbon material is 0.5 cm³. 3 / g~1.5 cm 3 / g. Specifically, the pore volume of the porous carbon material can be 0.5 cm³. 3 / g, 0.6cm 3 / g, 0.7 cm 3 / g, 0.8 cm 3 / g, 0.9 cm 3 / g, 1.0 cm 3 / g, 1.1 cm 3 / g, 1.2 cm 3 / g, 1.3 cm 3 / g, 1.4cm 3 / g, 1.5 cm 3 / g or any two of the above values. Furthermore, the pore size distribution of the porous carbon material can also be varied. In some embodiments of the present invention, the porous carbon material comprises 0-30% ultramicropores, 0-30% submicropores, 0-60% macropores, and 0-20% mesopores. Ultramicropores are defined as pores with a diameter less than 0.7 nm, submicropores are defined as pores with a diameter between 0.7 nm and 1.0 nm, macropores are defined as pores with a diameter between 1.0 nm and 2.0 nm, and mesopores are defined as pores with a diameter greater than 2 nm. When the specific surface area, pore volume, and pore size distribution of the porous carbon material are within the above ranges, it is beneficial for the adsorption and deposition of silicon-containing gases.

[0065] In some embodiments of the present invention, the pyrolysis temperature of the silicon-containing gas can be 400°C to 800°C; preferably, the pyrolysis temperature of the silicon-containing gas or carbon source gas can be 300°C to 500°C. Specifically, the pyrolysis temperature of the silicon-containing gas can be 400°C, 450°C, 500°C, 550°C, 600°C, 650°C, 700°C, 750°C, 800°C, or a range consisting of any two of the above values.

[0066] In some embodiments of the present invention, the flow rate of the silicon-containing gas can be 100 sccm to 700 sccm; preferably, the flow rate of the silicon-containing gas can be 400 sccm to 600 sccm. Specifically, the flow rate of the silicon-containing gas can be 100 sccm, 150 sccm, 200 sccm, 250 sccm, 300 sccm, 350 sccm, 400 sccm, 450 sccm, 500 sccm, 550 sccm, 600 sccm, 650 sccm, 700 sccm, or any combination of two of the above values.

[0067] In some embodiments of the present invention, the time for introducing the silicon-containing gas can be from 1 hour to 20 hours; preferably, the time for introducing the silicon-containing gas can be from 7 hours to 15 hours. Specifically, the time for introducing the silicon-containing gas can be 1 hour, 2 hours, 3 hours, 4 hours, 5 hours, 6 hours, 7 hours, 8 hours, 9 hours, 10 hours, 11 hours, 12 hours, 13 hours, 14 hours, 15 hours, 16 hours, 17 hours, 18 hours, 19 hours, 20 hours, or any range of two of the above values.

[0068] In some embodiments of the present invention, the flow rate of the oxygen introduced can be 50 sccm to 200 sccm; preferably, the flow rate of the oxygen introduced can be 100 sccm to 150 sccm. Specifically, the flow rate of the oxygen introduced can be 50 sccm, 60 sccm, 70 sccm, 80 sccm, 90 sccm, 100 sccm, 110 sccm, 120 sccm, 130 sccm, 140 sccm, 150 sccm, 160 sccm, 170 sccm, 180 sccm, 190 sccm, 200 sccm, or a range of any two of the above values.

[0069] In some embodiments of the present invention, the oxygen is introduced for a period of 1 hour to 20 hours; preferably, the oxygen is introduced for a period of 3 hours to 8 hours. Specifically, the time for introducing the silicon-containing gas can be 1 hour, 2 hours, 3 hours, 4 hours, 5 hours, 6 hours, 7 hours, 8 hours, 9 hours, 10 hours, 11 hours, 12 hours, 13 hours, 14 hours, 15 hours, 16 hours, 17 hours, 18 hours, 19 hours, 20 hours, or any combination of two of the above values.

[0070] In some embodiments of the present invention, the temperature of the micro-oxidation is 50-200°C; preferably, the temperature of the micro-oxidation is 50-150°C. Specifically, the temperature of the micro-oxidation can be 50°C, 60°C, 70°C, 80°C, 90°C, 100°C, 110°C, 120°C, 130°C, 140°C, 150°C, 160°C, 170°C, 180°C, 190°C, 200°C, or any range of two of the above values.

[0071] In some embodiments of the present invention, the pyrolysis temperature of the carbon source gas is 400°C to 800°C; preferably, the pyrolysis temperature of the carbon source gas is 450°C to 600°C. Specifically, the pyrolysis temperature of the carbon source gas can be 400°C, 450°C, 500°C, 550°C, 600°C, 650°C, 700°C, 750°C, 800°C, or any combination of two of the above values.

[0072] In some embodiments of the present invention, the flow rate of the carbon source gas is 200 sccm to 800 sccm; preferably, the flow rate of the carbon source gas is 450 sccm to 700 sccm. Specifically, the flow rate of the carbon source gas can be 200 sccm, 250 sccm, 300 sccm, 350 sccm, 400 sccm, 450 sccm, 500 sccm, 550 sccm, 600 sccm, 650 sccm, 700 sccm, 750 sccm, 800 sccm, or any combination of two of the above values.

[0073] In some embodiments of the present invention, the carbon source gas is introduced for 1 hour to 20 hours; preferably, the carbon source gas is introduced for 3 hours to 10 hours. Specifically, the time for introducing the carbon source gas can be 1 hour, 2 hours, 3 hours, 4 hours, 5 hours, 6 hours, 7 hours, 8 hours, 9 hours, 10 hours, 11 hours, 12 hours, 13 hours, 14 hours, 15 hours, 16 hours, 17 hours, 18 hours, 19 hours, 20 hours, or any range of two of the above values.

[0074] In some embodiments of the present invention, in step (1), the volume mixing ratio of silane gas to inert gas can be 5-20:80-100. In step (3), the volume mixing ratio of carbon source gas to inert gas can be 40-60:40-60.

[0075] In some embodiments of the present invention, in step (4), when the obtained silicon-carbon composite material is ground and sieved, the mesh size of the sieve used is 300-500 mesh. Specifically, the mesh size can be 300 mesh, 350 mesh, 400 mesh, 450 mesh, 450 mesh, 500 mesh, or any combination of two of the above values.

[0076] According to a third aspect of the present invention, a negative electrode sheet is provided, the negative electrode sheet comprising a negative electrode current collector and a negative electrode active material located on at least one surface of the negative electrode current collector, the negative electrode active material comprising the silicon-carbon composite material in any of the foregoing embodiments. Therefore, the negative electrode sheet comprising the silicon-carbon composite material exhibits significantly improved conductivity, low-temperature performance, cycle performance, and expansion performance while maintaining a high specific capacity.

[0077] In some embodiments of the present invention, the negative current collector in the negative electrode sheet of the present invention may include, but is not limited to, at least one of copper foil, copper alloy foil, nickel foil, stainless steel foil, titanium foil, nickel foam, copper foam, or composite current collectors (e.g., carbon-copper composite current collectors, nickel-copper composite current collectors, titanium-copper composite current collectors, etc.). The thickness of the negative current collector in the negative electrode sheet of the present invention may include, but is not limited to, 6 μm to 12 μm. The thickness of the negative electrode sheet of the present invention may include, but is not limited to, 50 μm to 150 μm.

[0078] In some embodiments of the present invention, the negative electrode active material may further include a conductive agent and a binder. The conductive agent may include, but is not limited to, at least one of: acetylene black, conductive carbon black (Super P), carbon nanotubes (CNTs), carbon fiber, flake graphite, Ketjen black, or graphene. The binder may include, but is not limited to: at least one of: sodium alginate, polyacrylate, polyimide, polyamide, polyamide-imide, polyvinylidene fluoride, polystyrene-butadiene copolymer (styrene-butadiene rubber), polyvinyl alcohol, polytetrafluoroethylene, polyacrylonitrile, sodium carboxymethyl cellulose, potassium carboxymethyl cellulose, sodium carboxymethyl cellulose, or potassium carboxymethyl cellulose. Those skilled in the art can select the appropriate mass ratio of the silicon-carbon composite material, conductive agent, and binder in the negative electrode sheet of the present invention according to actual needs.

[0079] In some embodiments of the present invention, the negative electrode active material may further include graphite, wherein the mass percentage of graphite in the negative electrode active material is from 35 wt.% to 95 wt.%. Specifically, the mass percentage of graphite in the negative electrode active material may be 35 wt.%, 40 wt.%, 45 wt.%, 50 wt.%, 55 wt.%, 60 wt.%, 65 wt.%, 70 wt.%, 75 wt.%, 80 wt.%, 85 wt.%, 95 wt.%, or any combination of two of the above values. When the mass percentage of graphite in the negative electrode active material is within the above range, the energy density and rate performance of the secondary battery can be balanced while reducing internal resistance.

[0080] In some embodiments of the present invention, the particle size D of the negative electrode active material is... V 50 is 5µm~15µm, D V 99 represents particles ranging from 15µm to 40µm. Specifically, the particle size D... V 50 can be 5μm, 5.5μm, 6.0μm, 6.5μm, 7.0μm, 7.5μm, 8.0μm, 8.5μm, 9.0μm, 9.5μm, 10.0μm, 10.5μm, 11μm, 11.5μm, 12μm, 12.5μm, 13μm, 13.5μm, 14μm, 14.5μm, 15μm, or a range of any two of the above values. D V 99 can be 15μm, 16μm, 17μm, 18μm, 19μm, 20μm, 21μm, 22μm, 23μm, 24μm, 25μm, 26μm, 27μm, 28μm, 29μm, 30μm, 31μm, 32μm, 33μm, 34μm, 35μm, 36μm, 37μm, 38μm, 39μm, 40μm, or a range of any two of the above values. In this invention, D... v 50 represents the particle size distribution, measured from the smallest particle size to 50% of the total volumetric particle size, in the volumetric particle size distribution of the negative electrode active material layer. v 99 indicates the particle size that reaches 99% of the volumetric accumulation in the particle size distribution of the negative electrode active material, starting from the smallest particle size.

[0081] In some embodiments of the present invention, the specific surface area of ​​the negative electrode active material is 1 m². 2 / g~10m 2 / g. Specifically, the specific surface area of ​​the negative electrode active material can be 1m². 2 / g、2m 2 / g、3m 2 / g、4m 2 / g、5m 2 / g、6m 2 / g、7m 2 / g、8m 2 / g、9m 2 / g, 10m 2 / g or a range consisting of any two of the above values. A negative electrode active material with a specific surface area within the above range can reduce side reactions between the negative electrode active material and the electrolyte, thus improving the cycle performance and expansion performance of the secondary battery.

[0082] In some embodiments of the present invention, the initial delithiation specific capacity of the negative electrode active material is 400 mAh / g to 1000 mAh / g. Specifically, the initial delithiation specific capacity of the negative electrode active material can be 400 mAh / g, 500 mAh / g, 600 mAh / g, 700 mAh / g, 800 mAh / g, 900 mAh / g, 1000 mAh / g, or any combination of two of the above values. When the initial delithiation specific capacity of the negative electrode active material is within the above range, the energy density, cycle performance, and expansion performance of the secondary battery can be balanced.

[0083] In some embodiments of the present invention, the negative electrode sheet can be prepared by methods known in the art, including but not limited to: mixing the silicon-carbon composite material provided by the present invention with a conductive agent and a binder to obtain a slurry, uniformly coating the slurry onto a negative current collector and drying it to obtain a negative electrode sheet.

[0084] According to a fourth aspect of the present invention, an electrochemical device is provided, comprising a negative electrode as described in any of the foregoing embodiments.

[0085] In some embodiments of the present invention, the electrochemical device of the present invention includes, but is not limited to, all types of primary batteries, secondary batteries, fuel cells, solar cells, or capacitors. In some embodiments, the electrochemical device is a lithium secondary battery.

[0086] In some embodiments of the present invention, the lithium secondary battery includes, but is not limited to: lithium metal secondary battery, lithium-ion secondary battery, lithium polymer secondary battery or lithium-ion polymer secondary battery.

[0087] In some embodiments of the present invention, the secondary battery provided by the present invention includes a positive electrode, a separator, an electrolyte, and a negative electrode as described in any of the foregoing embodiments. Therefore, the secondary battery provided by the present invention, while maintaining a high specific capacity, has significantly improved conductivity, low-temperature performance, cycle performance, and expansion performance.

[0088] In some embodiments, the positive electrode includes a positive current collector and a positive electrode material disposed on at least one surface of the positive current collector. The positive current collector may include, but is not limited to, at least one of aluminum foil, aluminum alloy foil, or composite current collectors (e.g., aluminum-carbon composite current collectors). The positive electrode material includes a positive active material, which may include, but is not limited to, at least one of lithium nickel cobalt manganese oxide (e.g., common NCM811, NCM622, NCM523, NCM111), lithium nickel cobalt aluminum oxide, lithium iron phosphate, lithium-rich manganese-based materials, lithium cobalt oxide (LiCoO2), lithium manganese oxide, lithium manganese iron phosphate, or lithium titanate. The positive electrode material also includes a conductive agent and a binder, which may be at least one of the conductive agent and binder selected from the above-described negative electrode materials.

[0089] In some embodiments, the positive electrode sheet can be prepared by methods known in the art, which may include, but are not limited to, the following steps: mixing a positive electrode active material, a conductive agent, and a binder in a solvent to obtain an active material mixture slurry, and uniformly coating the mixture slurry onto a current collector to obtain the positive electrode sheet. In some embodiments, the solvent may include, but is not limited to, N-methylpyrrolidone.

[0090] The separator of the secondary battery is used to separate the positive and negative electrode plates, prevent internal short circuits, allow electrolyte ions to pass freely, and does not affect the electrochemical charging and discharging process. In some embodiments, the material of the separator may include, but is not limited to, at least one of the following: polyethylene (PE), polyolefins (PO) mainly composed of polypropylene (PP), polyester (e.g., polyethylene terephthalate (PET) film), cellulose, polyimide (PI), polyamide (PA), spandex, or aramid. The type of separator may include, but is not limited to, at least one of the following: woven membrane, nonwoven membrane, microporous membrane, composite membrane, rolled membrane, or spun membrane.

[0091] In some embodiments, the separator of the secondary battery may include a substrate layer and a surface treatment layer located on at least one surface of the substrate layer. The substrate layer may be a nonwoven fabric, membrane, or composite membrane with a porous structure, and the material of the substrate layer may include, but is not limited to, at least one of polyethylene, polypropylene, polyethylene terephthalate, or polyimide. The surface treatment layer may be a polymer layer or an inorganic layer, or a layer formed by mixing polymers and inorganic materials. The inorganic layer includes inorganic particles and a binder, and the inorganic particles may include, but are not limited to, at least one of alumina, silicon oxide, magnesium oxide, 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, or barium sulfate; the binder may be at least one of the above binders. The polymer layer contains a polymer, and the polymer material may include, but is not limited to, at least one of the following: polyamide, polyacrylonitrile, acrylate polymer, polyacrylic acid, polyacrylate, polyvinylpyrrolidone, polyvinyl ether, or polyvinylidene fluoride or poly(vinylidene fluoride-hexafluoropropylene).

[0092] In some embodiments, the electrolyte of the secondary battery may include a lithium salt and a non-aqueous solvent. The lithium salt may be selected from at least one of LiPF6, LiBF4, LiAsF6, LiClO4, LiB(C6H5)4, LiCH3SO3, LiCF3SO3, and LiN(SO2CF3)2. In some embodiments, based on the mass of the electrolyte, the mass percentage of the lithium salt may be from 8% to 15%, specifically, the mass percentage of the lithium salt in the electrolyte may be 8%, 11%, 12.5%, 13%, 15%, or a range consisting of any two of the above values. The non-aqueous solvent may include, but is not limited to, at least one of carbonate compounds, carboxylic acid ester compounds, ether compounds, or other organic solvents.

[0093] In some embodiments, the secondary battery provided by the present invention further includes a packaging bag for containing the positive electrode, separator, negative electrode, electrolyte, and other components known in the art, which are not limited to the above-mentioned components. The present invention does not particularly limit the packaging bag; it can be any packaging bag known in the art.

[0094] In some embodiments, the method for preparing a secondary battery provided by the present invention may include, but is not limited to, the following steps: stacking a positive electrode sheet, a separator, and a negative electrode sheet in sequence, and performing operations such as winding and folding as needed to obtain a wound electrode assembly; placing the electrode assembly in a packaging bag; injecting electrolyte into the packaging bag and sealing it to obtain a secondary battery. Alternatively, the preparation method may include, but is not limited to, the following steps: stacking a positive electrode sheet, a separator, and a negative electrode sheet in sequence, then fixing the four corners of the entire stacked structure with tape to obtain a stacked electrode assembly; placing the electrode assembly in a packaging bag; injecting electrolyte into the packaging bag and sealing it to obtain a secondary battery. Furthermore, overcurrent protection components, conductive plates, etc., may be placed in the packaging bag as needed to prevent pressure rise and overcharging / discharging inside the secondary battery.

[0095] According to a fifth aspect of the present invention, an electronic device is provided, the electronic device comprising the electrochemical device in any of the foregoing embodiments. In some embodiments, the electronic device includes, but is not limited to: a laptop computer, a pen-based computer, a mobile computer, an e-book player, a portable telephone, a portable fax machine, a portable copier, a portable printer, a stereo headset, a video recorder, an LCD TV, a portable cleaner, a portable CD player, a mini CD-ROM, a transceiver, an electronic notebook, a calculator, a memory card, a portable recorder, a radio, a backup power supply, a motor, an automobile, a motorcycle, an electric bicycle, a bicycle, a lighting fixture, a toy, a game console, a clock, a power tool, a flashlight, a camera, a household large-capacity battery, or a lithium-ion capacitor, at least one of these.

[0096] Example The present invention will now be described in more detail through specific embodiments and comparative examples.

[0097] The testing methods used are as follows: Test of relevant parameters of silicon-carbon composite materials (1) Characterization method of silicon content in silicon-carbon composite materials: The silicon content in silicon-carbon composite materials was characterized using ICP (inductively coupled plasma spectroscopy) technology.

[0098] (2) Characterization methods for carbon content in silicon-carbon composite materials: The carbon content in silicon-carbon composite materials was characterized using ICP (inductively coupled plasma spectroscopy) technology.

[0099] (3) Characterization method for oxygen content in silicon-carbon composite materials: The secondary battery, after 100 cycles, was disassembled to obtain the negative electrode plate, which was then placed in a glove box to dry naturally. The powder was then carefully scraped off with a knife, and the oxygen content in the silicon-carbon composite material was determined by testing the collected powder with a German Elementar elemental analyzer.

[0100] (4) Calculation method for silicon crystallite size in silicon-carbon composite materials: XRD testing: A D8 Advance instrument was used with a Cu target (λ=1.54178 Å) at 60 kV, and tests were conducted from 2θ = 10° to 80°. After obtaining the XRD pattern of the silicon-carbon composite material, the size of the silicon crystallites in the composite material was calculated using the Debye-Scherrer formula at 2θ = 28.4°. Here, K is the Scherrer constant, D is the size of the silicon crystallites, B is the measured half-width at half-maximum (FWHM) of the diffraction peak, θ is the Bragg diffraction angle, and γ is the X-ray wavelength.

[0101] (5) Raman spectroscopy test: The HR Evolution instrument was used to perform the test with a 532 nm solid-state laser (1 MHz, 100 mV power). After obtaining the Raman spectrum of the silicon-carbon composite material, a value of 521 ± 5 cm⁻¹ was taken. -1 480±5 cm -1 1360±5 cm -1 and 1580±5 cm -1 The intensity of the peak at that point is I. A I B I D and I G .

[0102] (6) SEM test: First, the silicon-carbon composite material was polished using an IB-09010CP / ion polisher (6 kV). Then, the silicon-carbon composite material was tested using a JEOL-JSM-6700F scanning electron microscope at 5 kV and 0.8 nA in backscatter mode.

[0103] (7) D V 50 / D V 99: Using a MasterSizer 2000 instrument, the silicon-carbon composite material was tested at a detection angle from 0° to 135° to obtain the D of the silicon-carbon composite material. V 50 and D V 99 is a good value.

[0104] (8) Specific surface area: The BET specific surface area of ​​silicon-carbon composite material was tested using a TriStarⅡ3020 instrument.

[0105] (9) Conductivity test: The powder conductivity of silicon-carbon composite material was tested using a Suzhou Jinglü Electronic ST-2255 resistivity tester.

[0106] Electrical performance related parameter testing (1) Preparation process of half cell and full cell: The preparation process of the negative electrode sheet: The silicon-carbon composite material of this invention is used as the negative electrode active material, conductive carbon black as the conductive agent, and polyacrylic acid as the binder. The mass ratio of the negative electrode active material, conductive carbon black, and polyacrylic acid is 70:20:10. The aqueous solutions of the negative electrode active material, conductive agent, and binder are thoroughly mixed to obtain a slurry. The slurry is then uniformly coated onto copper foil and dried to obtain the negative electrode sheet.

[0107] The preparation process of the positive electrode sheet: Super P is used as a conductive agent and PVDF as a binder, with the mass ratio of positive electrode active material (LiFePO4), Super P, and PVDF being 70:20:10. The positive electrode active material, Super P, and PVDF solution are thoroughly mixed to obtain a slurry. The slurry is then uniformly coated onto aluminum foil and dried to obtain the positive electrode sheet.

[0108] Electrolyte and separator: In an argon-filled glove box (moisture <10 ppm, oxygen <1 ppm), ethylene carbonate (EC) and dimethyl carbonate (DMC) were mixed uniformly at a volume ratio of 1:1. LiPF6 and fluoroethylene carbonate (FEC) were slowly added to the mixed solution and stirred until homogeneous to obtain a non-aqueous electrolyte. A Celgard 2400 membrane was used as the separator.

[0109] Half-cell and full-cell assembly: The negative electrode is assembled into a coin cell in a glove box with either a lithium sheet or a positive electrode as the counter electrode, in the order of negative electrode, separator, lithium sheet or positive electrode, with the lithium sheet as the counter electrode. The positive electrode prepared above is then assembled into a coin cell.

[0110] (2) First delithiation specific capacity test: On the LAND CT2001A battery testing system, charge-discharge tests were performed on the assembled half-cells and full-cells. For the half-cell test, a working voltage range of 0.01V to 2V was used. The half-cell was discharged at a constant current of 0.1C to 0.01V, allowed to rest for 5 minutes, then discharged at a constant current of 50 μA to 0.01V, allowed to rest for 5 minutes, and then charged at a constant current of 0.1C to 2.0V, allowed to rest for 5 minutes. The initial charge capacity of the half-cell was recorded as the initial lithium delithiation specific capacity.

[0111] (3) First discharge specific capacity test of the full battery: The full cell test used a working voltage range of 2.4 V to 3.8 V. It was charged at a constant current of 0.1 C to 3.8 V, then charged at a constant voltage of 3.8 V to 50 μA cutoff, and left to stand for 5 min. It was then discharged at a constant current of 0.1 C to 2.4 V and left to stand for 5 min. The first discharge capacity of the full cell was recorded. The first discharge specific capacity of the full cell = the first discharge capacity of the full cell / the mass of the positive electrode active material (LiFePO4).

[0112] (4) Thickness expansion rate test of negative electrode sheet: The assembled full-cell electrochemical device before and after 100 cycles was disassembled, and the negative electrode was obtained separately. The thickness of the electrode was measured 12 times with vernier calipers and the average value was taken. If the copper foil thickness is a, the electrode thickness before 100 cycles is b, and the electrode thickness after 100 cycles is c, then the thickness expansion rate k of the negative electrode after 100 cycles is: k = (cb) / (ba)×100%.

[0113] (5) Low-temperature discharge capacity retention test: The assembled half-cell was discharged at 25°C with a constant current of 0.5 C to 0.01 V, allowed to stand for 5 min, then discharged at a constant current of 50 μA to 0.01 V, allowed to stand for 5 min, and charged at a constant current of 0.5 C to 2.0 V, allowed to stand for 5 min. This cycle was repeated three times, and the discharge capacity of the third cycle was recorded. Subsequently, the cell was placed at -10°C for 24 h, discharged at a constant current of 0.5 C to 0.01 V, allowed to stand for 5 min, and then discharged at a constant current of 50 μA to 0.01 V. The discharge capacity under low-temperature conditions was recorded.

[0114] Low-temperature discharge capacity retention rate (%) = (discharge capacity under low-temperature conditions / discharge capacity in the third cycle) × 100%.

[0115] (6) Half-cell capacity retention rate after 50 cycles (%): The assembled half-cell was discharged at 0.5 C constant current to 0.01 V at 25°C, allowed to stand for 5 min, then discharged at 50 μA constant current to 0.01 V, allowed to stand for 5 min, and then charged at 0.5 C constant current to 2.0 V, allowed to stand for 5 min. The discharge capacity of the first cycle was recorded. Then, the same steps were repeated for 50 charge and discharge cycles, and the discharge capacity of the 50th cycle was recorded.

[0116] Half-cell capacity retention rate after 50 cycles (%) = (discharge capacity of the 50th cycle / discharge capacity of the first cycle) × 100%.

[0117] (7) Capacity retention rate of the entire battery after 100 cycles (%): The assembled full battery was charged at 0.5 C constant current to 3.8 V at 25°C, then charged at 3.8 V constant voltage to 50 μA cutoff, allowed to stand for 5 min, and then discharged at 0.5 C constant current to 2.4 V, allowed to stand for 5 min. The discharge capacity of the first cycle was recorded. Then, the same steps were repeated for 100 charge and discharge cycles, and the discharge capacity of the 100th cycle was recorded.

[0118] Full battery capacity retention rate after 100 cycles (%) = (discharge capacity of the 100th cycle / discharge capacity of the first cycle) × 100%.

[0119] Example 1 I. Preparation of Silicon-Carbon Composite Materials (1) Select a specific surface area of ​​1804 m² 2 / g, pore volume 0.78 cm³ 3 Resin-based activated carbon with a composition of 21% ultramicropores, 22% submicropores, 52% macropores, and 5% mesopores was obtained. The resin-based activated carbon was dried and sieved through a 400-mesh sieve. 50g of the treated porous carbon material was placed in a chemical vapor deposition furnace. Under an argon protective atmosphere, the temperature was raised to 450℃. At a slightly positive pressure (2kPa) in the gas phase, a mixture of silane and argon (volume ratio 10:90) was used as the silicon source, and the reaction was continued for 10 h at a flow rate of 500 sccm. This yielded a silicon-carbon material in which elemental nano-silicon was adsorbed and deposited within the porous carbon pores. (2) In the same vapor deposition furnace, the temperature was lowered to 100°C, and oxygen was slowly introduced at a flow rate of 100 sccm under a slightly positive pressure (1 kPa) vapor pressure. The reaction was continued for 5 hours to perform micro-oxidation treatment on the shallow and outer surfaces of porous carbon nano-silicon. (3) In the same vapor deposition furnace, the temperature was raised to 500°C under the protective atmosphere of argon. Under the gas phase pressure of micro-positive pressure (2.5 kPa), a mixture of acetylene and argon with a volume ratio of 50:50 was used as the carbon source and the reaction was continued for 5 h at a flow rate of 650 sccm. This allowed the acetylene-derived carbon to be deposited on the outer surface of the silicon-carbon material obtained in step (2) and form a silicon-carbon material coated with a carbon coating layer. (4) Grind and sieve the silicon-carbon material obtained in step (3) to obtain the final silicon-carbon composite material.

[0120] II. Preparation of the negative electrode sheet The silicon-carbon composite material prepared by this invention is used as the negative electrode active material, conductive carbon black as the conductive agent, and polyacrylic acid as the binder. The silicon-carbon composite material, conductive carbon black, and polyacrylic acid are thoroughly mixed and stirred at a mass ratio of 7:2:1. An appropriate amount of deionized water is added and stirred thoroughly to form a uniform negative electrode slurry with a certain viscosity. The slurry is then uniformly coated onto the negative electrode current collector copper foil, dried thoroughly at 100°C, and then punched to obtain the negative electrode sheet.

[0121] III. Preparation of the positive electrode sheet Using LiFePO4 as the positive electrode active material, Super P as the conductive agent, and PVDF as the binder, LiFePO4, Super P, and PVDF are thoroughly mixed and stirred at a mass ratio of 7:2:1. An appropriate amount of N-methylpyrrolidone (NMP) is added and thoroughly stirred to form a uniform positive electrode slurry with a certain viscosity. This slurry is then uniformly coated onto the positive electrode current collector aluminum foil, dried thoroughly at 100°C, and then punched to obtain the positive electrode sheet.

[0122] IV. Preparation of Electrolyte In an argon-filled glove box (moisture <10 ppm, oxygen <1 ppm), ethylene carbonate (EC) and dimethyl carbonate (DMC) were mixed uniformly at a volume ratio of 1:1. LiPF6 and fluoroethylene carbonate (FEC) were slowly added to the mixed solution and stirred until homogeneous to obtain a non-aqueous electrolyte. Based on the mass of the electrolyte, the mass percentage of LiPF6 was 12.5% ​​and the mass percentage of FEC was 4.5%.

[0123] V. Separating membrane Celgard 24000 membrane was used as the separator.

[0124] VI. Preparation of Lithium-ion Batteries The above-mentioned negative electrode is used as the counter electrode with lithium sheet and positive electrode respectively. In the order of negative electrode, separator, lithium sheet or positive electrode, they are assembled into button half cell (lithium sheet as counter electrode) and full cell (positive electrode as positive electrode) in the glove box.

[0125] Examples 2 to 8 Based on Example 1, except for adjusting the relevant preparation parameters according to Table 1 in the "I. Preparation of Silicon-Carbon Composite Material" step, all other steps are the same as in Example 1.

[0126] Comparative Examples 1 to 6 Based on Example 1, except for adjusting the relevant preparation parameters according to Table 1 in the "I. Preparation of Silicon-Carbon Composite Material" step, all other steps are the same as in Example 1.

[0127] The preparation parameters, powder performance parameters, and electrical performance parameters of each embodiment and comparative example are shown in Tables 1, 2, and 3.

[0128] Table 1: Experimental parameters of Examples 1-8 and Comparative Examples 1-6

[0129] Table 2: Powder data for Examples 1-8 and Comparative Examples 1-6

[0130] Table 3: Electrochemical performance of half-cells and full-cells in Examples 1-8 and Comparative Examples 1-6

[0131] Referring to Tables 1, 2, and 3, it can be seen from the data of the examples and comparative examples that when the R / R' value is too large, such as in Comparative Examples 1 and 2 where the R / R' values ​​of the silicon-carbon composite material are 0.87 and 0.83 respectively, although the lithium-ion battery has a high initial delithiation specific capacity and conductivity, its corresponding capacity retention rate (%) and thickness expansion rate (%) are significantly reduced, that is, the cycle performance and expansion performance of the silicon-carbon composite material are significantly reduced. On the other hand, when the R / R' value is too low, such as in Comparative Examples 3 and 4 where the R / R' values ​​of the silicon-carbon composite material are 0.56 and 0.50 respectively, although the lithium-ion battery has a relatively good 50-cycle capacity retention rate (%) and 100-cycle capacity retention rate (%), its corresponding specific capacity, conductivity, low-temperature discharge capacity retention rate, initial discharge specific capacity, thickness expansion rate, and other performance characteristics are significantly reduced.

[0132] Furthermore, when the R value of the silicon-carbon composite material is too large, such as in Comparative Examples 1 and 2, where the R values ​​are 0.99 and 0.96 respectively, although the lithium-ion battery has a high initial delithiation specific capacity and conductivity, its cycle performance (capacity retention rate) and expansion performance (thickness expansion rate) are significantly reduced. When the R value is too small, such as in Comparative Examples 3 and 4, where the R values ​​of the silicon-carbon composite material are 0.71 and 0.64 respectively, although the lithium-ion battery has relatively good cycle performance (capacity retention rate), its specific capacity, conductivity, low-temperature discharge capacity retention rate, initial discharge specific capacity, and thickness expansion rate are all significantly reduced. When the R' value is too large, as in Comparative Examples 3 and 4, where the R' values ​​of the silicon-carbon composite material are 1.26 and 1.28 respectively, although the lithium-ion battery exhibits relatively good cycle performance (capacity retention), its specific capacity, conductivity, low-temperature discharge capacity retention, first discharge specific capacity, and thickness expansion rate all decrease significantly. Conversely, when the R' value is too low, as in Comparative Examples 1 and 2, where the R' values ​​of the silicon-carbon composite material are 1.14 and 1.16 respectively, although the lithium-ion battery exhibits high first delithiation specific capacity and conductivity, its cycle performance (capacity retention) and expansion performance (thickness expansion rate) decrease significantly. Furthermore, excessively low or excessively high R' values ​​further deteriorate the low-temperature performance (low-temperature discharge capacity retention) of the silicon-carbon composite material, as seen in Comparative Examples 3 and 4.

[0133] Furthermore, as can be seen from Comparative Example 5, when the R' value of the silicon-carbon composite material is 1.24 (within the scope of this invention) or 0.97 (too large and outside the scope of this invention), although the lithium-ion battery exhibits a high specific capacity, its conductivity, low-temperature performance, cycle performance, and expansion performance decrease. Similarly, as can be seen from Comparative Example 6, when the R' value of the silicon-carbon composite material is 1.30 (too large and outside the scope of this invention) or 0.79 (within the scope of this invention), although the lithium-ion battery exhibits good cycle performance and expansion performance, its conductivity, specific capacity, and low-temperature performance are significantly reduced.

[0134] The present invention has found that by simultaneously controlling the R / R' value of the silicon-carbon composite material, as well as the corresponding R and R' values ​​within the range of the present invention, lithium-ion batteries can have high specific capacity while also having improved conductivity, low-temperature performance, cycle performance, and expansion performance. That is, by adjusting the silicon-carbon composite material to simultaneously satisfy the following conditions: the R / R' value is greater than 0.61 and less than 0.78 (e.g., R / R' values ​​in the examples: 0.62, 0.66, 0.68, 0.71, 0.72, 0.74, 0.75); the corresponding R value is greater than 0.78 and less than 0.9 (e.g., R values ​​in the examples: 0.78, 0.79, 0.82, 0.86, 0.87, 0.88, 0.89, 0.90); and the corresponding R' value is greater than or equal to 1.2 and less than or equal to 1.25 (e.g., R' values ​​in the examples: 1.20, 1.21, 1.22, 1.23, 1.25). In this case, the silicon-carbon composite material has the optimal balance ratio between crystalline silicon and amorphous silicon, and between carbon defects and carbon graphitization. Therefore, while maintaining a high specific capacity, it can exhibit significantly improved electrical conductivity, low-temperature performance, cycle performance, and expansion performance.

[0135] As can be seen from Examples 1 to 8, compared with existing silicon-carbon composite materials or silicon-carbon composite materials in comparative examples, when the R / R' value and the corresponding R and R' values ​​of the silicon-carbon composite material are simultaneously controlled within the range provided by this invention, the resulting silicon-carbon composite material exhibits higher specific capacity, as well as superior conductivity, low-temperature performance, cycle performance, and expansion performance, thus demonstrating more outstanding lithium storage performance. After cycling, the oxygen content of the silicon-carbon composite material in the negative electrode sheet also affects the cycle performance of the lithium-ion battery. As can be seen from Examples 1 to 8, by controlling the oxygen content of the silicon-carbon composite material in the negative electrode sheet after cycling within the range of this invention, it is beneficial to further balance the specific capacity, cycle performance, and expansion performance of the lithium-ion battery, thereby improving the overall performance of the lithium-ion battery. The ratio of carbon material to elemental silicon in the silicon-carbon composite material, D... V 50. D V 99. Specific surface area and oxygen content also typically affect the performance of lithium-ion batteries. As can be seen from Examples 1 to 8, by controlling the ratio of carbon material to elemental silicon, the size of silicon crystallites, oxygen content, and D content in the silicon-carbon composite material... V 50. D V 99. The specific surface area and conductivity are within the scope of this invention, which is beneficial for obtaining lithium-ion batteries with excellent specific capacity, low-temperature performance, cycle performance and expansion performance.

[0136] It is understood that this invention has been described through some embodiments, and those skilled in the art will recognize that various changes or equivalent substitutions can be made to these features and embodiments without departing from the spirit and scope of this invention. Furthermore, under the teachings of this invention, these features and embodiments can be modified to adapt to specific situations and materials without departing from the spirit and scope of this invention. Therefore, this invention is not limited to the specific embodiments disclosed herein, and all embodiments falling within the scope of the claims of this invention are within the protection scope of this invention.

Claims

1. A silicon-carbon composite material, said silicon-carbon composite material comprising elemental silicon and carbon materials, characterized in that, The Raman spectrum characteristics of the silicon-carbon composite material satisfy: 0.61<R / R'<0.78; wherein, R is the ratio of I A to I B ; R' is the ratio of I D to I G ; I A represents the intensity of the peak at 521±5cm -1 in the Raman spectrum of the silicon-carbon composite material; I B represents the intensity of the peak at 480±5cm -1 in the Raman spectrum of the silicon-carbon composite material; I D represents the intensity of the peak at 1360±5cm -1 in the Raman spectrum of the silicon-carbon composite material; I G represents the intensity of the peak at 1580±5cm -1 in the Raman spectrum of the silicon-carbon composite material; The elemental silicon includes at least one of silicon nanoparticles, silicon submicron particles or silicon nanofilms; the range of R in the Raman spectrum characteristic of the silicon-carbon composite material is: 0.78≤R≤0.9; the range of R' in the Raman spectrum characteristic of the silicon-carbon composite material is 1.2≤R'≤1.

25.

2. The silicon-carbon composite material according to claim 1, characterized in that, 0.62<R / R'<0.

75.

3. The silicon-carbon composite material according to claim 1, characterized in that, Based on the mass of the silicon-carbon composite material, the ratio range of the content a of carbon element in the silicon-carbon composite material to the content b of silicon element in the silicon-carbon composite material is: 0.5<a / b<10; and / or, The range of the content a of carbon element in the silicon-carbon composite material is: 40 wt%<a<90 wt%, and the range of the content b of silicon element in the silicon-carbon composite material is: 10 wt%<b<60 wt%.

4. The silicon-carbon composite material according to claim 1, characterized in that, Based on the mass of the silicon-carbon composite material, the ratio range of the content a of carbon element in the silicon-carbon composite material to the content b of silicon element in the silicon-carbon composite material is: 1.07<a / b<2.03; and / or, The range of the content a of carbon element in the silicon-carbon composite material is: 50 wt%<a<64.8 wt%; the range of the content b of silicon element in the silicon-carbon composite material is: 31.9 wt%<b<46.6 wt%.

5. The silicon-carbon composite material according to claim 4, characterized in that, 1.1<a / b<2.

02.

6. The silicon-carbon composite material according to claim 4, characterized in that, The range of the content a of carbon element in the silicon-carbon composite material is: 52 wt%<a<64 wt%; the range of the content b of silicon element in the silicon-carbon composite material is: 32.0 wt%<b<44.0 wt%.

7. The silicon-carbon composite material according to claim 1, characterized in that, In the SEM image of the internal cross-section of the silicon-carbon composite material, the inner surface of the particle is flat, and the pore diameter of the pores inside the particle is less than 50 nm.

8. The silicon-carbon composite material according to any one of claims 1-7, characterized in that, The silicon-carbon composite material satisfies at least one of the following conditions 1) to 5): 1) the size of silicon microcrystals in the silicon-carbon composite material is less than 1 nm; 2) The particle size D of the silicon-carbon composite material V The range of 50 is 5 µm to 10 µm, D V 99 is 15 µm~25 µm; 3) The specific surface area of ​​the silicon-carbon composite material is in the range of 1 m². 2 / g~50 m 2 / g; 4) the oxygen content in the silicon-carbon composite material ranges from 1.0 wt% to 4.0 wt%; 5) the first delithiation specific capacity of the silicon-carbon composite material is 500 mAh / g to 2500 mAh / g.

9. The silicon-carbon composite material according to any one of claims 1-7, characterized in that, The silicon-carbon composite material satisfies at least one of the following conditions 1) to 5): 1) the size of silicon microcrystals in the silicon-carbon composite material is 0.8 nm to 0.95 nm; 2) The particle size D of the silicon-carbon composite material V The range of 50 is 5 µm to 6.5 µm, D V 99 is 15 µm~19 µm; 3) The specific surface area of ​​the silicon-carbon composite material is in the range of 4 m². 2 / g~8 m 2 / g; 4) the oxygen content in the silicon-carbon composite material ranges from 1.2 wt% to 3 wt%; 5) the first delithiation specific capacity of the silicon-carbon composite material is 1400 mAh / g to 2000 mAh / g.

10. A method for preparing a silicon-carbon composite material as described in any one of claims 1-9, characterized in that, The preparation method comprises: regulating the R value of the silicon-carbon composite material by changing at least one parameter among the pyrolysis temperature of silicon-containing gas, the flow rate of the silicon-containing gas, the duration of introducing the silicon-containing gas, the micro-oxidation duration, the micro-oxidation temperature, or the flow rate of introduced oxygen; and / or, regulating the R' value of the silicon-carbon composite material by changing at least one parameter among the pyrolysis temperature of carbon source gas, the flow rate of the carbon source gas, or the duration of introducing the carbon source gas.

11. A negative electrode sheet, characterized in that, The negative electrode sheet includes a negative current collector and a negative active material located on at least one surface of the negative current collector, wherein the negative active material includes a silicon-carbon composite material as described in any one of claims 1-9.

12. The negative electrode sheet according to claim 11, characterized in that, The negative electrode active material also includes graphite, conductive agent, and binder; the mass percentage of graphite in the negative electrode active material is 35 wt% to 95 wt%.

13. The negative electrode sheet according to claim 11, characterized in that, The negative electrode active material satisfies at least one of the following conditions (I) to (III): (I) Particle size D V 50 is 5 µm~15 µm, D V 99 is 15 µm~40 µm; (II) The specific surface area of ​​the negative electrode active material is 1 m². 2 / g~10 m 2 / g; (III) The initial delithiation specific capacity of the negative electrode active material is 400 mAh / g to 1000 mAh / g.

14. An electrochemical device, characterized in that, The electrochemical device includes the negative electrode as described in any one of claims 11 to 13.

15. An electronic device, characterized in that, It includes the electrochemical device as described in claim 14.

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