Silicon-carbon material, negative electrode sheet, and battery

Abstract

The present application relates to the technical field of battery, in particular to a silicon-carbon material, a negative plate comprising the silicon-carbon material and a battery. The silicon-carbon material comprises a porous carbon as a skeleton structure and a filler filled in the pores of the porous carbon, the filler in the inner layer of the silicon-carbon material comprises silicon, and the filler in the surface layer of the silicon-carbon material comprises a material containing F, P and S elements. The silicon-carbon material has the characteristics of high specific capacity, high surface structure and high electrochemical stability, can reduce the occurrence of interface side reactions, and greatly improves the cycle charge-discharge performance. The negative plate comprising the silicon-carbon material has the characteristics of slow thickness growth at high temperature. The battery comprising the negative plate has the characteristics of high average coulomb efficiency and slow thickness growth at high temperature.

Description

Technical Field

[0001] This invention relates to the field of battery technology, and more specifically to a silicon-carbon material, a negative electrode sheet comprising the silicon-carbon material, and a battery. Background Technology

[0002] Silicon has a theoretical specific capacity approximately ten times that of graphite, giving it a significant advantage in next-generation high-energy-density lithium-ion battery applications. However, silicon undergoes large volume changes during lithium insertion and extraction, making the solid electrolyte interphase (SEI) film on its surface, which provides protection, highly susceptible to rupture. This leads to continuous side reactions, rapid capacity retention decay during charge-discharge cycles, and a significant increase in thickness expansion. This phenomenon is particularly severe during high-temperature cycling.

[0003] Currently, coating is commonly used to enhance the interfacial stability of silicon-based materials. The coating materials include amorphous carbon, artificial SEI films, polymer coatings, and metal oxides. However, the volume change rate of silicon-based materials is generally greater than 50%, making it difficult for these coating structures to maintain long-term integrity. Consequently, the high-temperature cycling performance of silicon-based materials cannot meet application requirements.

[0004] Therefore, inventing a silicon-carbon material with high interfacial stability is of great significance for improving the high-temperature cycling performance of high-energy-density batteries. Summary of the Invention

[0005] The purpose of this invention is to overcome the aforementioned problems in the prior art and provide a silicon-carbon material, an anode sheet comprising the silicon-carbon material, and a battery. The silicon-carbon material of this invention possesses the characteristics of high specific capacity, high surface structure, and high electrochemical stability, which can reduce the occurrence of interfacial side reactions and greatly improve cycle charge-discharge performance. The anode sheet comprising the silicon-carbon material of this invention has the characteristic of slow thickness growth during high-temperature cycling. The battery comprising the anode sheet of this invention has the characteristics of high average coulombic efficiency and slow thickness growth during high-temperature cycling.

[0006] The inventors of this invention have discovered that by improving the interfacial stability of silicon-carbon materials, the cycle stability of the negative electrode and the battery can be improved.

[0007] Through further in-depth research, the inventors of this invention discovered that to improve the interfacial stability of silicon-carbon materials, the interfacial structural stability can be enhanced by constructing specific structures, and specific elements can be introduced to improve the interfacial electrochemical stability of silicon-carbon materials. This reduces the occurrence of interfacial side reactions, decreases the rate of increase in the thickness of the negative electrode during high-temperature cycling, improves the high-temperature cycling coulombic efficiency of the battery, and reduces the rate of thickness increase. The inventors of this invention, through extensive and in-depth research, have identified specific elements capable of improving the interfacial electrochemical stability of silicon-carbon materials.

[0008] To achieve the above objectives, the first aspect of the present invention provides a silicon-carbon material comprising porous carbon as a framework structure and a filler filling the pores of the porous carbon, wherein the filler in the inner layer of the silicon-carbon material is silicon, and the filler in the outer layer of the silicon-carbon material comprises a material containing F, P, and S elements.

[0009] A second aspect of the present invention provides a negative electrode sheet comprising the silicon-carbon material described in the first aspect of the present invention.

[0010] In one example, the negative electrode includes a negative current collector and an active material layer, the active material layer comprising the silicon-carbon material.

[0011] A third aspect of the present invention provides a battery comprising the silicon-carbon material described in the first aspect of the present invention and / or the negative electrode sheet described in the second aspect of the present invention.

[0012] By employing the above technical solution, the present invention has at least the following advantages compared with the prior art:

[0013] (1) The silicon-carbon material of the present invention has high specific capacity and high interface structure stability;

[0014] (2) The silicon-carbon material of the present invention has high specific capacity and high interfacial electrochemical stability;

[0015] (3) The silicon-carbon material of the present invention has high specific capacity and low amount of interfacial side reactions;

[0016] (4) The thickness of the negative electrode sheet of the present invention increases slowly during high-temperature cycling;

[0017] (5) The battery of the present invention has a high average coulombic efficiency during high-temperature cycling;

[0018] (6) The battery of the present invention has a slow thickness increase during high-temperature cycling.

[0019] Other features and advantages of the present invention will be described in detail in the following detailed description section. Attached Figure Description

[0020] Figure 1 The diagram shown is a structural schematic of a portion of the silicon-carbon material of the present invention.

[0021] Figure 2 The diagram shown is a structural schematic of the silicon-carbon material of the present invention.

[0022] Figure 3 The image shown is a schematic SEM cross-section of the silicon-carbon material prepared according to an embodiment of the present invention. Detailed Implementation

[0023] The following provides a detailed description of specific embodiments of the present invention. It should be understood that the specific embodiments described herein are for illustrative and explanatory purposes only and are not intended to limit the scope of the invention.

[0024] The first aspect of the present invention provides a silicon-carbon material comprising porous carbon as a framework structure and a filler filling the pores of the porous carbon, wherein the filler in the inner layer of the silicon-carbon material comprises silicon, and the filler in the outer layer of the silicon-carbon material comprises a material containing F, P and S elements.

[0025] The silicon-carbon material can be a silicon-carbon composite material.

[0026] Existing technologies improve the interfacial stability of silicon-based materials through coating, but the coating layer has low mechanical strength and weak bonding with the coated material, making it prone to cracking or falling off, thereby increasing side reactions.

[0027] The inventors of this invention have discovered that filling the pores in the surface region of a porous carbon skeleton with a specific filler can improve the interfacial structure and electrochemical stability of silicon-carbon materials during lithium insertion and extraction processes, thanks to the restraining effect of the porous carbon skeleton and the isolation effect of the filler on the electrolyte. This prevents the surface from cracking or the filler from falling off due to excessive expansion of the silicon-based material, avoids the exposure of silicon components to the electrolyte, thereby reducing the amount of side reactions between silicon and the electrolyte, reducing the thickness growth rate of the negative electrode during high-temperature cycling, improving the average coulombic efficiency of the battery during high-temperature cycling, and reducing the thickness growth rate.

[0028] In this invention, by employing the above-described methods to improve the interfacial structure and electrochemical stability of the carbon-silicon composite material, the carbon-silicon composite material has achieved better stability than existing technologies. To further enhance the effect, one or more of the technical features can be further optimized.

[0029] For example, such as Figure 1 As shown, the silicon-carbon material uses porous carbon 11 as its framework structure, with silicon filling the inner layer 12 of the porous carbon 11 pores, and materials containing F, P, and S elements filling the outer layer 13 of the porous carbon 11 pores. Figure 1 As can be seen, in the aforementioned silicon-carbon material, silicon is located in the inner layer of the material containing F, P, and S elements. Therefore, as... Figure 2 and Figure 3 As shown, the silicon-carbon materials (2, 3) have a core-shell structure, which includes a shell (22, 32) and a core (21, 31). The shell includes porous carbon and materials containing F, P, and S elements distributed in the pores of the porous carbon. The core includes porous carbon and silicon distributed in the pores of the porous carbon.

[0030] in, Figure 3 This is a schematic diagram of the SEM cross-section of the silicon-carbon material prepared according to an embodiment of the present invention. The testing method involves cutting the silicon-carbon material using an Ar ion polishing method to obtain the cross-section of the silicon-carbon material, and then observing the cross-section of the silicon-carbon material using a scanning electron microscope (SEM) in backscattered electron mode.

[0031] Porous carbon, as a framework structure, can be a single porous carbon structure or a framework structure formed by multiple porous carbons (i.e., discontinuous, such as layered structures). Using porous carbon as a framework structure can improve the interfacial mechanical strength of silicon-carbon materials, inhibit the cracking of fillers containing F, P, and S elements in the surface layer, and prevent the fillers containing F, P, and S elements in the surface layer from falling off.

[0032] In one example, the porous carbon serving as the framework structure can be a framework structure formed by a porous carbon layer, where the filler in the inner layer and the filler in the outer layer are located within the same pores of the porous carbon. This structure can further enhance the structural stability of the silicon-carbon material.

[0033] Silicon, as an inner filler in silicon-carbon materials, can partially or completely fill the pores of porous carbon.

[0034] The F, P, and S elements in the material containing F, P, and S elements can exist in the form of compounds.

[0035] In one example, the material containing F, P, and S elements is selected from one or more of lithium difluorooxalatoborate, lithium difluorobis(oxalato)phosphate, lithium difluorosulfonylimide, lithium bis(trifluoromethanesulfonylimide), lithium fluoride, sodium fluoride, lithium hexafluorophosphate, lithium dihydrogen phosphate, lithium phosphate, sodium phosphate, disodium hydrogen phosphate, sodium dihydrogen phosphate, lithium sulfate, sodium sulfate, fluoroethylene carbonate, 1,3-propanesulfonate lactone, and ethylene sulfate.

[0036] According to one specific embodiment, the weight ratio of F, P, and S elements in the material containing F, P, and S elements satisfies one or more (one, two, or three) of the following relationships: (I-1), (II-1), and (III-1):

[0037] 0.04 < m P / m F <0.35, formula (I-1);

[0038] 0.02 < m S / m F <0.25, Equation (II-1);

[0039] 0.3 < m S / mP <1, Equation (III-1).

[0040] When the F, P, and S elements in the material containing F, P, and S satisfy the above-mentioned specific ratio, the interfacial electrochemical stability of the silicon-carbon material can be further improved, and the amount of surface side reactions can be reduced.

[0041] In one example, the weight ratios of the F, P, and S elements in the filler satisfy one or more (one, two, or three) of the following relationships: (I-2), (II-2), and (III-2):

[0042] 0.15 < m P / m F <0.25, formula (I-2),

[0043] 0.08 < m S / m F <0.18, Equation (II-2),

[0044] 0.55 < m S / m P <0.8, Equation (III-2).

[0045] In one example, the filler in the surface layer of the silicon-carbon material includes Li.

[0046] According to one specific implementation, the ratio of the weight of Li to the sum of the weights of F, P, and S elements satisfies 0.1 < m. Li / (m F +m P +m S If ) < 0.45, then Equation (Ⅳ-1).

[0047] When the weight of Li element and the sum of the weights of F element, P element and S element satisfy the above specific ratio, the stability of the interface can be further improved.

[0048] In one instance, the ratio of the weight of Li to the sum of the weights of F, P, and S elements satisfies 0.25 < m. Li / (m F +m P +m S If ) < 0.4, then equation (Ⅳ-2).

[0049] In one example, the silicon-carbon material includes C, Si, F, P, and S elements.

[0050] According to one specific embodiment, based on the total weight of the silicon-carbon material, the weight content α of the C element satisfies 30wt% ≤ α ≤ 80wt% (e.g., 30wt%, 35wt%, 40wt%, 45wt%, 50wt%, 55wt%, 60wt%, 65wt%, 70wt%, 75wt%, 80wt%), and the weight content β of the Si element satisfies 15wt% ≤ β < 70wt% (e.g., 15wt%, 20wt%, 25wt%, 30wt%, 35wt%, 40wt%, 45wt%, 50wt%). The sum of the weight contents γ of the elements F, P, and S satisfies 0.5wt% ≤ γ ≤ 9wt% (e.g., 1wt%, 2wt%, 3wt%, 4wt%, 5wt%, 6wt%, 7wt%, 8wt%, 9wt%), and the sum of α, β, and γ satisfies 93wt% ≤ α + β + γ < 100wt% (e.g., 93wt%, 94wt%, 95wt%, 96wt%, 97wt%, 98wt%, 99wt%, 99.5wt%).

[0051] When α < 30% or β ≥ 70%, it indicates that the content of porous carbon is too low and the content of silicon is too high, resulting in large charge-discharge expansion and poor structural stability of the silicon-carbon material. When α > 80% or β < 15%, the specific capacity of the silicon-carbon material is low. When γ > 9%, it indicates that the content of materials containing F, P, and S elements is large, resulting in poor interfacial conductivity of the silicon-carbon material. When α + β + γ < 93%, it indicates that the materials containing F, P, and S elements contain excessive amounts of other elements, which is not conducive to ensuring the electrochemical stability of the shell.

[0052] In one example, based on the total weight of the silicon-carbon material, the weight content α of the C element satisfies 40wt% ≤ α ≤ 55wt%, the weight content β of the Si element satisfies 40wt% ≤ β ≤ 55wt%, the sum of the weight contents γ of the F, P, and S elements satisfies 2.5wt% ≤ γ ≤ 5.5wt%, and the sum of α, β, and γ satisfies 94wt% ≤ α + β + γ ≤ 97.5wt%.

[0053] In this invention, the content of each element can be determined using an X-ray energy dispersive spectroscopy (EDS) instrument.

[0054] In one example, the porous carbon is porous hard carbon. Hard carbon refers to carbon that is difficult to graphitize even at temperatures above 2500°C. The porous carbon can be obtained commercially.

[0055] In one example, the average pore size of the porous carbon is 0.5 nm to 20 nm (e.g., 0.5 nm, 1 nm, 5 nm, 10 nm, 15 nm, 20 nm). When the average pore size of the porous carbon is <0.5 nm, it is not conducive to the entry of silicon and fillers; when the average pore size of the porous carbon is >20 nm, silicon tends to aggregate and grow, and the structural stability of the silicon-carbon material deteriorates.

[0056] In one example, the porous carbon has an average pore size of 1 nm to 6 nm.

[0057] In this invention, the average pore size can be tested by the following method: the specific surface area and total pore volume of the material can be measured by nitrogen adsorption, and then the average pore size can be calculated by the following formula: average pore size = 4 × total pore volume / specific surface area.

[0058] In one example, the median particle size of the porous carbon is 1 μm-15 μm (e.g., 1 μm, 5 μm, 10 μm, 15 μm).

[0059] In one example, the median particle size of the porous carbon is 5 μm-12 μm.

[0060] In one example, the specific surface area of ​​the silicon-carbon material is <20 m². 2 / g. When the specific surface area is ≥20m² 2 At a density of / g, the silicon-carbon material has a large specific surface area and numerous surface side reactions.

[0061] In this invention, the specific surface area can be tested using the Brunauer-Emmett-Teller (BET) method.

[0062] In one example, the median particle size of the silicon-carbon material is 1 μm-15 μm (e.g., 1 μm, 5 μm, 10 μm, 15 μm). When the median particle size is less than 1 μm, the silicon-carbon material has small particles, a large specific surface area, and a large amount of surface side reactions; when the median particle size is greater than 15 μm, the silicon-carbon material has large particles, a large volume change during charging and discharging, and poor structural stability.

[0063] In this invention, the median particle size can be tested using a laser particle size analyzer. The median particle size represents the particle size of 50% of the particles in the volume-based particle size distribution that is smaller than this value.

[0064] In one example, the median particle size of the silicon-carbon material is 5 μm-12 μm.

[0065] In one example, the maximum thickness of the surface layer in the silicon-carbon material is 50-1000 nm (e.g., 50 nm, 100 nm, 200 nm, 300 nm, 400 nm, 500 nm, 600 nm, 700 nm, 800 nm, 900 nm, 1000 nm). The maximum thickness of the surface layer refers to the thickness value at the point where the surface layer of the silicon-carbon material is the thickest. When the maximum thickness of the surface layer is >1000 nm, the surface layer of the silicon-carbon material is relatively thick, the conductivity of the silicon-carbon material deteriorates, and the capacity is not easily realized.

[0066] In one example, the maximum thickness of the surface layer in the silicon-carbon material is 100-600 nm.

[0067] Because the types of elements in the surface and inner layers of the silicon-carbon material differ, the surface and inner layers can be clearly distinguished under backscattered electron mode, which is sensitive to atomic number. Figure 3 As shown, the surface layer has a different contrast than the inner layer when observed under the backscattered electron mode of a scanning electron microscope (SEM). Based on this, the thickness of the surface layer in the silicon-carbon material can be measured.

[0068] The present invention also provides a method for preparing the silicon-carbon material described in the first aspect, comprising: contacting porous carbon with a silicon source gas to carry out a pyrolysis reaction, and naturally cooling to obtain powder A; at room temperature, immersing the powder A in a NaOH solution to dissolve the silicon portion on the surface, then separating the solid and liquid, and drying the solid to obtain powder B; at room temperature, mixing the powder B with a material containing F, P, and S elements, and evaporating to dryness to obtain powder C; and calcining the powder C.

[0069] In one example, the silicon source gas is a mixture of an inert gas and a silane gas.

[0070] In one example, the silane gas is selected from one or more of silane, silane, and trichlorosilane.

[0071] According to one specific embodiment, the volume ratio of the inert gas to the silane gas is (1-20):1 (e.g., 1:1, 5:1, 10:1, 15:1, 20:1).

[0072] In one example, the volume ratio of the inert gas to the silane gas is (5-15):1.

[0073] According to one specific embodiment, the flow rate of the silicon source gas is 100-1000 sccm (e.g., 100 sccm, 200 sccm, 300 sccm, 400 sccm, 500 sccm, 600 sccm, 700 sccm, 800 sccm, 900 sccm, 1000 sccm).

[0074] In one example, the flow rate of the silicon source gas is 300-600 sccm.

[0075] According to one specific embodiment, the conditions for the pyrolysis reaction include: a temperature of 350-600℃ (e.g., 350℃, 400℃, 450℃, 500℃, 550℃, 600℃) and a reaction time of 5-15h (e.g., 5h, 6h, 7h, 8h, 9h, 10h, 11h, 12h, 13h, 14h, 15h).

[0076] In one example, the conditions for the pyrolysis reaction include a temperature of 450-550°C and a reaction time of 8-12 hours.

[0077] According to one specific embodiment, the weight ratio of the powder A to the NaOH solution is 1:(5-20) (e.g., 1:5, 1:8, 1:10, 1:12, 1:15, 1:18, 1:20).

[0078] In one example, the weight ratio of the powder A to the NaOH solution is 1:(8-15).

[0079] According to one specific embodiment, the pH of the NaOH solution is 10-14 (e.g., 10, 11, 12, 13, 14).

[0080] In one example, the pH of the NaOH solution is 11-13.

[0081] According to one specific implementation, the dissolution reaction time is 0.5-4 hours (e.g., 0.5 hours, 1 hour, 1.5 hours, 2 hours, 2.5 hours, 3 hours, 3.5 hours, 4 hours).

[0082] In one instance, the dissolution reaction took 1–2.5 hours.

[0083] According to one specific embodiment, the evaporation temperature is 70-100°C (e.g., 70°C, 80°C, 90°C, 100°C).

[0084] In one example, the evaporation temperature is 80-90°C.

[0085] According to one specific embodiment, the calcination conditions include: a temperature of 200-400℃ (e.g., 200℃, 250℃, 300℃, 350℃, 400℃) and a time of 0.5-5h (e.g., 0.5h, 1h, 1.5h, 2h, 2.5h, 3h, 3.5h, 4h, 4.5h, 5h).

[0086] In one example, the calcination conditions include a temperature of 220-320°C and a time of 1-3 hours.

[0087] A second aspect of the present invention provides a negative electrode sheet comprising the silicon-carbon material described in the first aspect of the present invention.

[0088] Except for the negative silicon-carbon material, the materials used in the negative electrode sheet can all be made in accordance with the methods in this field, and all can achieve the effect of slow thickness growth during high-temperature cycling.

[0089] In one example, the negative electrode includes a negative current collector and a negative active material layer, the negative active material layer comprising the silicon-carbon material.

[0090] According to one specific embodiment, the negative electrode active material layer further includes graphite.

[0091] In one instance, the graphite is synthetic graphite and / or natural graphite.

[0092] In one example, the negative electrode active material layer includes a conductive agent and a binder.

[0093] In one example, the conductive agent is selected from one or more of carbon black, carbon fiber, single-walled carbon nanotubes, multi-walled carbon nanotubes, and graphene.

[0094] In one example, the adhesive is selected from one or more of carboxymethyl cellulose, sodium carboxymethyl cellulose, lithium carboxymethyl cellulose, hydroxypropyl cellulose, diacetyl cellulose, polyethylene, polyvinyl alcohol, polyvinyl chloride, polyvinyl fluoride, polyvinylpyrrolidone, polytetrafluoroethylene, polypropylene, styrene-butadiene rubber, and epoxy resin.

[0095] According to one specific embodiment, based on the total weight of the negative electrode active material layer, the weight content of the silicon-carbon material is 1-50 wt% (e.g., 1 wt%, 5 wt%, 10 wt%, 15 wt%, 20 wt%, 25 wt%, 30 wt%, 35 wt%, 40 wt%, 45 wt%, 50 wt%).

[0096] In one example, the weight content of the silicon-carbon material is 5-25 wt%, based on the total weight of the negative electrode active material layer.

[0097] In one example, the graphite content is 30-98 wt% (e.g., 30 wt%, 40 wt%, 50 wt%, 60 wt%, 70 wt%, 80 wt%, 90 wt%, 95 wt%, 98 wt%), based on the total weight of the negative electrode active material layer.

[0098] In one example, the graphite content is 70-94 wt%, based on the total weight of the negative electrode active material layer.

[0099] In one example, the weight content of the conductive agent is 0.1-10 wt% (e.g., 0.1 wt%, 1 wt%, 2 wt%, 3 wt%, 4 wt%, 5 wt%, 6 wt%, 7 wt%, 8 wt%, 9 wt%, 10 wt%), based on the total weight of the negative electrode active material layer.

[0100] In one example, the weight content of the conductive agent is 0.5-4 wt%, based on the total weight of the negative electrode active material layer.

[0101] In one example, the binder has a weight content of 0.1-15 wt% (e.g., 0.1 wt%, 1 wt%, 3 wt%, 5 wt%, 7 wt%, 10 wt%, 13 wt%, 15 wt%) based on the total weight of the negative electrode active material layer.

[0102] In one example, the binder content is 0.5-6 wt% based on the total weight of the negative electrode active material layer.

[0103] The negative electrode sheet of the present invention, by including a negative electrode material containing the silicon-carbon material described in the present invention, reduces the thickness growth rate during high-temperature cycling.

[0104] A third aspect of the present invention provides a battery comprising the silicon-carbon material described in the first aspect of the present invention and / or the negative electrode sheet described in the second aspect of the present invention.

[0105] The materials used in the battery, except for the negative electrode, can all be manufactured in accordance with the methods described in this field, and can all achieve high energy density, high average coulombic efficiency during high-temperature cycling, and low thickness growth rate.

[0106] The battery can be a lithium-ion battery.

[0107] Because the battery of the present invention contains the negative electrode sheet described in the present invention, the average coulombic efficiency of the battery during high-temperature cycling is improved and the rate of thickness increase is reduced.

[0108] The present invention will be described in detail below through embodiments. The embodiments described herein are only a part of the embodiments of the present invention, and not all of them. All other embodiments obtained by those skilled in the art based on the embodiments of the present invention without inventive effort are within the scope of protection of the present invention.

[0109] The following examples illustrate the silicon-carbon material of the present invention.

[0110] Example 1

[0111] (1) Preparation of ingredients

[0112] Porous carbon: 100g of porous hard carbon, with an average pore size of 4nm and a median particle size of 7.5μm;

[0113] Silane gas: Methylsilane;

[0114] Inert gas: High-purity argon (purity ≥ 99.99%);

[0115] NaOH solution: pH 12;

[0116] Materials containing F, P, and S elements: 0.023 parts by weight of LiTFSI (lithium bis(trifluoromethanesulfonyl)imide), 0.042 parts by weight of LiF, and 0.028 parts by weight of Li3PO4.

[0117] (2) Preparation of silicon-carbon materials

[0118] Porous carbon was placed in a vapor deposition apparatus, and a mixture of inert gas and silane gas at a volume ratio of 9:1 was introduced at a flow rate of 500 sccm. The temperature was then raised to 500℃ to induce a silane gas decomposition reaction, with the reaction time controlled for 10 hours. Afterward, the mixture was allowed to cool naturally to obtain powder A. At room temperature, powder A was immersed in a NaOH aqueous solution at a weight ratio of 1:10 to dissolve the silicon on the surface of the porous carbon, with the reaction time controlled for 1 hour. After 5 hours, the mixture was filtered and dried to obtain powder B. At room temperature, powder B, LiTFSI (lithium bis(trifluoromethanesulfonyl)imide), LiF, Li3PO4, and deionized water were mixed and stirred evenly in a weight ratio of 1:0.023:0.042:0.028:20. The mixture was then evaporated at 80°C to obtain powder C. Powder C was placed in a vacuum furnace (pressure less than 0.01 MPa) and calcined at 250°C for 2 hours, followed by natural cooling to obtain silicon-carbon material.

[0119] Example 2 group

[0120] This set of examples is used to illustrate the effect of changing the weight parts of materials containing F, P, and S elements, resulting in a change in the sum of the weight contents γ of F, P, and S elements.

[0121] Example 2a

[0122] This embodiment is based on Example 1, except that the weight ratio of powder B, LiTFSI, LiF, Li3PO4, and deionized water is adjusted to 1:0.008:0.014:0.009:20, as detailed in Table 1.

[0123] Example 2b

[0124] This embodiment is based on Example 1, except that the weight ratio of powder B, LiTFSI, LiF, Li3PO4, and deionized water is adjusted to 1:0.046:0.083:0.056:20, as detailed in Table 1.

[0125] Example 3

[0126] This set of examples is used to illustrate how changing the weight parts of materials containing F, P, and S elements can cause m P / m F m S / m F m S / m P and m Li / (m F +m P +m S The effect of changing at least one of them.

[0127] Example 3a

[0128] This embodiment is based on Example 1, except that the weight ratio of powder B, LiTFSI, LiF, Li3PO4, and deionized water is adjusted to 1:0.018:0.036:0.004:20, as detailed in Table 1.

[0129] Example 3b

[0130] This embodiment is based on Example 1, except that the weight ratio of powder B, LiTFSI, LiF, Li3PO4, and deionized water is adjusted to 1:0.043:0.037:0.013:20, as detailed in Table 1.

[0131] Example 3c

[0132] This embodiment is based on Example 1, except that the weight ratio of powder B, LiTFSI, LiF, Li3PO4, and deionized water is adjusted to 1:0.002:0.028:0.026:20, as detailed in Table 1.

[0133] Example 3d

[0134] This embodiment is based on Example 1, except that the weight ratio of powder B, LiTFSI, LiF, Li3PO4, and deionized water is adjusted to 1:0.032:0.057:0.004:20, as detailed in Table 1.

[0135] Example 3e

[0136] This embodiment is based on Example 1, except that the weight ratio of powder B, LiTFSI, LiF, Li3PO4, and deionized water is adjusted to 1:0.017:0.031:0.044:20, as detailed in Table 1.

[0137] Example 3f

[0138] This embodiment is based on Example 1, except that the weight ratio of powder B, LiTFSI, LiF, Li3PO4, and deionized water is adjusted to 1:0.002:0.006:0.032:20, as detailed in Table 1.

[0139] Example 3g

[0140] This embodiment is based on Example 1, except that the weight ratio of powder B, LiTFSI, LiF, Li3PO4, and deionized water is adjusted to 1:0.047:0.022:0.025:20, as detailed in Table 1.

[0141] Example 3h

[0142] This embodiment is based on Example 1, except that the weight ratio of powder B, LiTFSI, LiF, Li3PO4, and deionized water is adjusted to 1:0.008:0.045:0.04:20, as detailed in Table 1.

[0143] Example 3i

[0144] This embodiment is based on Example 1, except that the weight ratio of powder B, LiTFSI, LiF, Li3PO4, and deionized water is adjusted to 1:0.031:0.046:0.017:20, as detailed in Table 1.

[0145] Example 4 group

[0146] This set of examples illustrates the effects of changes in the average pore size of porous carbon.

[0147] Example 4a

[0148] This embodiment is based on Embodiment 1, except that the average pore size of the porous carbon is adjusted to 10 nm, as detailed in Table 1.

[0149] Example 4b

[0150] This embodiment is based on Embodiment 1, except that the average pore size of the porous carbon is adjusted to 0.8 nm, as detailed in Table 1.

[0151] Example 5 group

[0152] This set of examples illustrates the effects of changing the median particle size of porous carbon.

[0153] Example 5a

[0154] This embodiment is based on Example 1, except that the median particle size of the porous carbon is adjusted to 2.7 μm, as detailed in Table 1.

[0155] Example 5b

[0156] This embodiment is based on Example 1, except that the median particle size of the porous carbon is adjusted to 14 μm, as detailed in Table 1.

[0157] Example 6 group

[0158] This set of examples illustrates the effects of changing the surface layer thickness when altering the dissolution reaction time.

[0159] Example 6a

[0160] This embodiment is based on Example 1, except that the dissolution reaction time is adjusted to 3 hours, as detailed in Table 1.

[0161] Example 6b

[0162] This embodiment is based on Example 1, except that the dissolution reaction time is adjusted to 0.7 h, as detailed in Table 1.

[0163] Comparative Example 1

[0164] The procedure was carried out in accordance with Example 1, except that no further steps were performed until powder A was obtained.

[0165] Comparative Example 2

[0166] The procedure was carried out in accordance with Example 1, except that no further steps were performed until powder B was obtained.

[0167] Comparative Example 3

[0168] The procedure was carried out in accordance with Example 1, except that powder A was prepared and the pyrolysis reaction time was controlled to be 5 hours. Subsequent steps were not performed.

[0169] Table 1

[0170]

[0171]

[0172] * indicates the same as in Example 1.

[0173] Preparation Example

[0174] 1. Preparation of button cells

[0175] The silicon-carbon material, sodium carboxymethyl cellulose, styrene-butadiene rubber, carbon black, and single-walled carbon nanotubes obtained in the examples and comparative examples were mixed in a mass ratio of 85:2:5.5:7:0.5. Deionized water was added, and a negative electrode slurry was obtained under vacuum stirring. The slurry was coated onto copper foil, dried at 80°C, sliced, and then transferred to a vacuum oven at 100°C for 12 hours of drying. After rolling in a drying environment, the compaction was approximately 1.4 g / cm³, and then the slurry was formed into discs with a diameter of approximately 1.2 cm using a die-cutting machine. A lithium metal sheet was used as the counter electrode, a polyethylene membrane was used as the separator, and an electrolyte (containing 13 wt% lithium hexafluorophosphate (LiPF6) and 10 wt% fluoroethylene carbonate (FEC) as the solvent) was added to assemble a coin cell.

[0176] 2. Preparation of lithium-ion batteries

[0177] (1) Preparation of negative electrode

[0178] The silicon-carbon material, artificial graphite, styrene-butadiene rubber, sodium carboxymethyl cellulose, carbon black, and single-walled carbon nanotubes obtained in the examples and comparative examples were mixed in a mass ratio of x:(95.5-x):1:2.5:0.9:0.1. Deionized water was added, and a negative electrode slurry was obtained under vacuum stirring. The negative electrode slurry was uniformly coated onto a copper foil with a thickness of 8 μm and dried to obtain a copper foil containing a negative electrode active material layer. The copper foil containing the negative electrode active material layer was transferred to a 100°C oven and dried for 10 hours at a concentration of 1.65 g / cm³. 3 The material is compacted and rolled, then cut to obtain the negative electrode sheet.

[0179] The amounts of silicon-carbon material and the areal density of the negative electrode active material layer in the examples and comparative examples were set to different values. The different values ​​of x were used to keep the total specific capacity of the negative electrode material in the negative electrode sheet constant, and the different values ​​of areal density were used to ensure that the operating state of the positive electrode sheet in the batteries prepared in each example and comparative example was similar, so that the difference in battery cycle performance was mainly affected by the negative electrode sheet. Specific values ​​for x and areal density are shown in Table 2.

[0180] Table 2

[0181]

[0182]

[0183] (2) Preparation of positive electrode

[0184] Lithium cobalt oxide, polyvinylidene fluoride, and carbon black were mixed in a mass ratio of 96:2:2. N-methylpyrrolidone was added, and the mixture was stirred under vacuum until a uniform positive electrode slurry was formed. The positive electrode slurry was then uniformly coated onto an aluminum foil with a thickness of 12 μm and dried to obtain an aluminum foil with a positive electrode coating. The areal density of the positive electrode coating was 20 mg / cm³. 2 The aluminum foil containing the positive electrode coating was transferred to an oven at 120°C and dried for 8 hours, with a yield of 4.1 g / cm³. 3 The compaction density is achieved by rolling, and then slitting to obtain the desired positive electrode sheet.

[0185] (3) Electrolyte preparation

[0186] Under an inert atmosphere, a mixed solution was prepared according to the mass ratio of EC:PC:PP:LiPF6:FEC:PS = 12:12:47:15:10:4, and stirred evenly to obtain the desired electrolyte.

[0187] (4) Lithium-ion battery manufacturing

[0188] The positive electrode sheet and separator from step (2) and the negative electrode sheet from step (1) are stacked in sequence, ensuring that the separator is positioned between the positive and negative electrodes to provide isolation. Then, the bare cell is obtained by winding. The bare cell is placed in an aluminum-plastic film shell and dried. The electrolyte from step (3) is injected into the bare cell. After processes such as encapsulation, settling, formation, secondary sealing, and sorting, the desired lithium-ion battery is obtained.

[0189] Test case

[0190] The button cells and lithium-ion batteries obtained in the examples and comparative examples were tested as follows.

[0191] 1. Performance testing of button cells

[0192] Based on the mass of the silicon-carbon material, it was discharged to 0.005V at a current of 50mA / g, left to stand for 10min, and then charged to 0.7V at 50mA / g. The charge capacity was divided by the mass of the composite material to obtain the specific capacity, and the charge capacity was divided by the discharge capacity to obtain the first effect. The test results are shown in Table 3.

[0193] 2. Performance testing of lithium-ion batteries

[0194] The test temperature was 45℃. The battery was discharged to 3V at 0.5C and allowed to stand for 10 minutes; then charged at a constant current of 2C to 3.83V, followed by a constant voltage charge to 0.02C, and allowed to stand for 10 minutes. The battery thickness was measured and used as the initial thickness t0. The battery was then charged at a constant current of 2C to 4.48V, followed by a constant voltage charge to 0.1C, and allowed to stand for 10 minutes. Finally, it was discharged at 0.5C to 3V and allowed to stand for 10 minutes. This charge-discharge cycle was repeated, and the charging capacity Q at the nth cycle (where n is a positive integer) was obtained. n Discharge capacity Q n ', with Q n ' / Q n Let Q be the Coulomb efficiency of the nth cycle. n ' / Q1' represents the capacity retention rate in the nth cycle.

[0195] Let Q n Let ξ be the number of cycles when ' / Q1' equals 90%, and let Q... n The number of cycles when ' / Q1' equals 80% is Measure the ξ and The battery thickness t at full charge during the next cycle ξ and by For the rate of increase in thickness, with the first The average coulombic efficiency of each cycle is the average coulombic efficiency, and the test results are shown in Table 3.

[0196] The smaller the thickness growth rate and the lower the average coulombic efficiency, the better the cycle performance of the lithium-ion battery, the higher the interface stability of the silicon-carbon material, the less surface side reaction occurs, and the slower the thickness growth rate of the negative electrode sheet.

[0197] The results are recorded in Table 3.

[0198] Table 3

[0199]

[0200] As can be seen from Table 3, and from the comparative examples and embodiments, the batteries made of silicon-carbon materials in the embodiments show a significantly slower thickness increase and a significantly improved average coulombic efficiency. This indicates that the silicon-carbon material of the present invention, as well as the negative electrode sheet and battery including the silicon-carbon material, improves the interface stability of the silicon-carbon material, thereby slowing down the thickness increase of the negative electrode sheet during high-temperature cycling and improving the average coulombic efficiency of the battery during high-temperature cycling.

[0201] The preferred embodiments of the present invention have been described in detail above; however, the present invention is not limited thereto. Within the scope of the inventive concept, various simple modifications can be made to the technical solutions of the present invention, including combinations of various technical features in any other suitable manner. These simple modifications and combinations should also be considered as the content disclosed in the present invention and are all within the protection scope of the present invention.

Claims

1. A silicon-carbon material, characterized in that, The silicon-carbon material comprises porous carbon as a framework structure and fillers filling the pores of the porous carbon. The filler in the inner layer of the silicon-carbon material is silicon, and the filler in the outer layer of the silicon-carbon material comprises a material containing F, P, and S elements. The types of elements differ between the outer and inner layers of the silicon-carbon material, and the weight ratios of F, P, and S elements in the F-containing material satisfy one or more of the following relationships: (I-1), (II-1), and (III-1). 0.04 < m P / m F <0.35, formula (I-1); 0.02 < m S / m F <0.25, Equation (II-1); 0.3 < m S / m P <1, Equation (III-1).

2. The silicon-carbon material according to claim 1, wherein, The silicon-carbon material includes C, Si, F, P, and S elements. Based on the total weight of the silicon-carbon material, the weight content α of the C element satisfies 30wt%≤α≤80wt%, and / or; the weight content β of the Si element satisfies 15wt%≤β<70wt%, and / or the sum of the weight contents γ of the F, P, and S elements satisfies 0.5wt%≤γ≤9wt%, and the sum of α, β, and γ satisfies 93wt%≤α+β+γ<100wt%.

3. The silicon-carbon material according to claim 2, wherein, Based on the total weight of the silicon-carbon material, the weight content α of the C element satisfies 40wt%≤α≤55wt%, the weight content β of the Si element satisfies 40wt%≤β≤55wt%, the sum of the weight contents γ of the F, P, and S elements satisfies 2.5wt%≤γ≤5.5wt%, and the sum of α, β, and γ satisfies 94wt%≤α+β+γ≤97.5wt%.

4. The silicon-carbon material according to claim 1, characterized in that, The filler in the surface layer of the silicon-carbon material includes Li.

5. The silicon-carbon material according to claim 4, characterized in that, The ratio of the weight of Li to the sum of the weights of F, P, and S elements satisfies 0.1 < m. Li / (m F +m P +m S If ) < 0.45, then Equation (Ⅳ-1).

6. The silicon-carbon material according to claim 1, wherein, The porous carbon is porous hard carbon; And / or, the average pore size of the porous carbon is 0.5 nm-20 nm; And / or, the median particle size of the porous carbon is 1 μm-15 μm; And / or, the specific surface area of ​​the silicon-carbon material is <20 m². 2 / g; And / or, the median particle size of the silicon-carbon material is 1 μm-15 μm; And / or, in the silicon-carbon material, the maximum thickness of the surface layer is 50-1000 nm.

7. The silicon-carbon material according to claim 6, wherein, The average pore size of the porous carbon is 1 nm to 6 nm. And / or; the median particle size of porous carbon is 5 μm-12 μm. And / or, the median particle size of the silicon-carbon material is 5 μm-12 μm; And / or, in the silicon-carbon material, the maximum thickness of the surface layer is 100-600 nm.

8. The silicon-carbon material according to claim 1, wherein, The materials containing F, P, and S elements include one or more of lithium difluorooxalatoborate, lithium difluorobis(oxalato)phosphate, lithium difluorosulfonylimide, lithium bis(trifluoromethanesulfonylimide), lithium fluoride, sodium fluoride, lithium hexafluorophosphate, lithium dihydrogen phosphate, lithium phosphate, sodium phosphate, disodium hydrogen phosphate, sodium dihydrogen phosphate, lithium sulfate, sodium sulfate, fluoroethylene carbonate, 1,3-propanesulfonate lactone, and ethylene sulfate, and the materials containing F, P, and S elements include F elements, P elements, and S elements.

9. A negative electrode sheet, characterized in that, The negative electrode comprises the silicon-carbon material according to any one of claims 1-8.

10. The negative electrode according to claim 9, wherein, The negative electrode sheet includes a negative electrode current collector and a negative electrode active material layer, wherein the negative electrode active material layer includes the silicon-carbon material; And / or, based on the total weight of the negative electrode active material layer, the weight content of the silicon-carbon material is 1-50 wt%.

11. A battery, characterized in that, The battery comprises the silicon-carbon material according to any one of claims 1-8 and / or the negative electrode according to claim 9 or 10.

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