Silicon-carbon composite material and application thereof

Abstract

The application relates to the technical field of batteries, in particular to a silicon-carbon composite material and application thereof. The silicon-carbon composite material comprises porous carbon material and nano-silicon particles in the pores of the porous carbon material; the ratio of the intensity value of the lithium intercalation peak at 0.30-0.45 V to the strongest peak value in 0-0.25 V in the dQ / dV curve of the first lithium intercalation of the silicon-carbon composite material is less than 0.05. The silicon-carbon composite material has high compressive strength, high charge-discharge capacity and good cycle stability.

Description

Technical Field

[0001] This invention relates to the field of battery technology, and more specifically, to a silicon-carbon composite material and its applications. Background Technology

[0002] Currently, commercially available lithium-ion battery anode materials are limited to carbon materials, represented by graphite, with a maximum theoretical specific capacity of only 372 mAh / g, which is insufficient to meet the requirements of modern battery applications. Silicon materials, with a specific capacity as high as 3579 mAh / g, are considered a promising anode material and will gradually replace carbon materials in the application of lithium-ion battery anode materials.

[0003] However, silicon undergoes a volume change of approximately 300% during lithium insertion / extraction, which causes a series of problems during cycling. For example, silicon-based anode materials can crack and eventually pulverize; the volume change prevents the formation of a stable SEI layer on the electrode surface, leading to repeated SEI layer breakage and formation, consuming a large number of lithium ions. Simultaneously, silicon's inherently low electronic and ionic conductivity limits its rate performance output.

[0004] The emergence of silicon-carbon composite materials can solve the above problems to some extent. The core of silicon-carbon composite materials is to store silicon through a porous carbon framework and to buffer the volume changes during silicon-lithium intercalation through the porous structure of the carbon. However, the charge-discharge capacity and cycle stability of silicon-carbon composite materials in the current technology are not ideal.

[0005] In view of this, the present invention is hereby proposed. Summary of the Invention

[0006] Another object of the present invention is to provide a silicon-carbon composite material having excellent charge-discharge capacity and cycle stability.

[0007] Another object of the present invention is to provide a negative electrode.

[0008] Another object of the present invention is to provide a battery.

[0009] In order to achieve the above-mentioned objectives of the present invention, the following technical solution is adopted:

[0010] A silicon-carbon composite material includes a porous carbon material and nano-silicon particles located in the pores of the porous carbon material; in the dQ / dV curve of the first lithium insertion of the silicon-carbon composite material, the ratio of the intensity value of the lithium insertion peak at 0.30 to 0.45V to the strongest peak value in the range of 0 to 0.25V is less than 0.05.

[0011] In some embodiments, the ratio of the intensity of the lithium insertion peak at 0.30–0.45 V to the strongest peak at 0–0.25 V in the dQ / dV curve of the first lithium insertion of the silicon-carbon composite material is 0.

[0012] In some embodiments, the microporosity φ, pore volume Pv, and compressive strength Cs of the porous carbon material satisfy the following relationship: 550≤(Cs·φ) / Pv≤1050, wherein the microporosity φ>95% and the compressive strength Cs is 600~850MPa.

[0013] In some embodiments, the pore volume Pv is 0.7–1.2 cm. 3 / g.

[0014] In some embodiments, the microporosity φ, pore volume Pv, and compressive strength Cs of the porous carbon material satisfy the following relationship: 650 ≤ (Cs·φ) / Pv ≤ 1040; wherein the microporosity φ > 99%, the compressive strength Cs is 700–850 MPa, and the pore volume Pv is 0.8–1.1 cm³. 3 / g.

[0015] In some embodiments, the specific surface area of ​​the porous carbon material is 1700–2800 cm². 3 / g.

[0016] The method for preparing porous carbon materials as described above includes the following steps:

[0017] The carbon source is subjected to a first heat treatment in a CO2 atmosphere to obtain a first carbon material; the first carbon material is subjected to a second heat treatment with a mixture of the first carbon material and an alkaline activator to obtain a second carbon material; the second carbon material is subjected to a washing treatment and a third heat treatment to obtain the porous carbon material.

[0018] In some embodiments, the CO2 flow rate is 0.5 to 1.2 L / min.

[0019] In some embodiments, the temperature of the first heat treatment is 850–950°C, and the holding time of the first heat treatment is 9–15 hours.

[0020] In some embodiments, the alkali activator includes at least one selected from potassium hydroxide, magnesium hydroxide, sodium hydroxide, and calcium hydroxide.

[0021] In some embodiments, the mass ratio of the first carbon material to the alkaline activator is (1.5 to 6):1.

[0022] In some embodiments, the temperature of the second heat treatment is 700–850°C, and the holding time of the second heat treatment is 1–3 hours.

[0023] In some embodiments, the temperature of the third heat treatment is 850–950°C, and the holding time of the third heat treatment is 2–5 hours.

[0024] In some embodiments, the washing process includes acid washing and water washing.

[0025] In some embodiments, the mass content of the silicon nanoparticles in the silicon-carbon composite material is 45% to 65%.

[0026] In some embodiments, the surface of the silicon-carbon composite material further includes a coating layer comprising at least one of a fast ion conductor, amorphous carbon, and a polymer.

[0027] In some embodiments, the compressive strength of the silicon-carbon composite material is 820–1100 MPa.

[0028] A negative electrode comprising the aforementioned silicon-carbon composite material.

[0029] A battery comprising the aforementioned negative electrode.

[0030] An electrical device comprising the battery described above.

[0031] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0032] (1) In the silicon-carbon composite material of the present invention, the ratio of the intensity value of the lithium insertion peak at 0.30 to 0.45V to the strongest peak value in 0 to 0.25V is less than 0.05 in the dQ / dV curve of the first lithium insertion, indicating that it has high charge-discharge capacity and good cycle stability.

[0033] (2) In the silicon-carbon composite material of the present invention, the porous carbon material has a high microporosity, and the microporosity φ, pore volume Pv and compressive strength Cs of the porous carbon material satisfy the relationship 550≤(Cs·φ) / Pv≤1050. The high microporosity (microporosity φ>95%) porous carbon can effectively reduce the particle size of silicon particles in the silicon-carbon composite material, reduce the absolute expansion of silicon in the carbon matrix, and improve the cycle stability of the electrode. The high microporosity porous carbon can effectively improve the compressive strength of the porous carbon matrix, which is beneficial to reduce the occurrence of cracking of silicon-carbon composite material after rolling during electrode preparation, inhibit the generation of silicon oxide inside the particles, and thus improve the first coulombic efficiency.

[0034] (3) The battery of the present invention has the characteristics of high initial efficiency and high capacity retention rate. The capacity of the battery after 100 cycles is above 1720mAh / g, and the capacity retention rate after 100 cycles is 90% or above. Attached Figure Description

[0035] To more clearly illustrate the specific embodiments of the present invention or the technical solutions in the prior art, the drawings used in the description of the specific embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are some embodiments of the present invention. For those skilled in the art, other drawings can be obtained from these drawings without creative effort.

[0036] Figure 1 This is a pore size distribution diagram of the porous carbon material in Example 1 of the present invention;

[0037] Figure 2 This is a graph showing the compressive strength of the porous carbon material in Example 1 of the present invention.

[0038] Figure 3 This is a graph showing the compressive strength of the silicon-carbon composite material in Example 1 of the present invention.

[0039] Figure 4 This is a dQ / dV curve of the battery prepared from the silicon-carbon composite material in Example 1 of the present invention;

[0040] Figure 5 This is a dQ / dV curve of the battery prepared from the silicon-carbon composite material in Comparative Example 1 of the present invention. Detailed Implementation

[0041] The embodiments of the present invention will be described in detail below with reference to examples. However, those skilled in the art will understand that the following examples are for illustrative purposes only and should not be considered as limiting the scope of the invention. Unless otherwise specified in the examples, conventional conditions or conditions recommended by the manufacturer are followed. Reagents or instruments whose manufacturers are not specified are all commercially available conventional products.

[0042] According to one aspect of the present invention, the present invention relates to a silicon-carbon composite material, comprising a porous carbon material and nano-silicon particles located in the pores of the porous carbon material; wherein, in the dQ / dV curve of the first lithium intercalation of the silicon-carbon composite material, the ratio of the intensity value of the lithium intercalation peak at 0.30 to 0.45 V to the strongest peak value in the range of 0 to 0.25 V is less than 0.05.

[0043] Unconstrained by theory, in the dQ / dV curve of the first lithium intercalation of silicon-carbon composite materials, the peak in the 0–0.25V range corresponds to the lithium intercalation peak of silicon, and the lithium intercalation peak in the 0.30–0.45V range corresponds to the SiO peak. x The lithium intercalation peak indicates that the silicon-carbon composite material of this invention has high compressive strength, and SiO... x The intensity of the lithium intercalation peak in the silicon is much smaller than that in silicon, indicating that there is virtually no particle breakage during the rolling process of the electrode, which greatly reduces and avoids the formation of SiO2 from the reaction of elemental silicon and air in the silicon-carbon composite particles.x This leads to a decrease in capacity and initial efficiency. In some embodiments, the ratio of the intensity of the lithium insertion peak at 0.30–0.45 V to the strongest peak at 0–0.25 V in the dQ / dV curve of the silicon-carbon composite material is 0.4, 0.3, 0.2, 0.1, 0, or any value between the two in the range of dQ / dV for the initial lithium insertion.

[0044] In some embodiments, in the dQ / dV curve of the initial lithium intercalation of the silicon-carbon composite material, the ratio of the intensity of the lithium intercalation peak at 0.30–0.45 V to the strongest peak at 0–0.25 V is 0, meaning the number of lithium intercalation peaks at 0.30–0.45 V is 0. This indicates that the first derivative of the lithium intercalation dQ / dV curve at 0.30–0.45 V does not have a zero value (and the signs on both sides are reversed). Not bound by theory, in some embodiments, the dQ / dV curve of the initial lithium intercalation of the silicon-carbon composite material of the present invention shows no SiO₂ at 0.30–0.45 V. x The lithium intercalation peak is due to the high compressive strength of the silicon-carbon composite material of the present invention. During the rolling process, the electrode exhibits virtually no particle breakage, thus avoiding the formation of SiO2 from the reaction of elemental silicon in the silicon-carbon composite material particles with air. x This leads to a decrease in capacity and first-efficiency.

[0045] In some embodiments, the microporosity φ, pore volume Pv, and compressive strength Cs of the porous carbon material satisfy the following relationship: 550≤(Cs·φ) / Pv≤1050, wherein the microporosity φ>95% and the compressive strength Cs is 600~850MPa.

[0046] The porous carbon material of this invention has a high microporosity (according to the definition of the International Union of Pure and Applied Chemistry (IUPAC), micropores are pores with a diameter of less than 2 nm), and the microporosity φ, pore volume Pv, and compressive strength Cs of the porous carbon material satisfy the above-mentioned relationship, which is not subject to theoretical constraints. This can effectively reduce the particle size of silicon particles, reduce the absolute expansion of silicon inside the carbon matrix, and improve the cycling stability of the electrode. The high microporosity of the porous carbon can effectively improve the compressive strength of the porous carbon matrix, which is beneficial to reducing the occurrence of cracking of silicon-carbon composite materials after rolling during electrode preparation, inhibiting the generation of silicon oxide inside the particles, and thus improving the first coulombic efficiency. In some embodiments, the value of φ is, for example, 95.1%, 95.5%, 96%, 96.5%, 97%, 97.5%, 98%, 98.5%, 99%, 99.5%, or 100%, or any value in the range of two. In some implementations, the value of (Cs·φ) / Pv is 550, 560, 570, 580, 600, 620, 650, 680, 700, 750, 780, 800, 820, 850, 880, 900, 950, 980, 1000 or 1050, or any value between the two.

[0047] In some embodiments, the pore volume Pv of the porous carbon material of the present invention is 0.7–1.2 cm³. 3 / g, for example, 0.7cm 3 / g, 0.8cm 3 / g, 0.85cm 3 / g, 0.9cm 3 / g, 0.95cm 3 / g, 1cm 3 / g, 1.05cm 3 / g, 1.1cm 3 / g, 1.15cm 3 / g or 1.2cm 3 / g, or any value within a range of both. Unbound by theory, the microporosity of porous carbon materials is positively correlated with their compressive strength (i.e., the higher the microporosity, the greater the compressive strength); under the same microporosity, pore volume is negatively correlated with compressive strength. High-pore-volume porous carbon can increase the silicon content inside silicon-carbon composite particles, effectively improving charge-discharge capacity. The applicant of this invention discovered that when the pore volume increases to a certain value, further increases in pore volume will result in pore expansion, i.e., pore size increases and microporosity decreases. The porous carbon material of this invention has a suitable pore volume. When the pore volume of porous carbon is small, it is difficult to penetrate an appropriate amount of silicon, resulting in a low silicon content in the silicon-carbon composite material and a low reversible capacity; when the pore volume of porous carbon is large, due to the pore expansion phenomenon during the preparation process, its micropores are low (φ<95%), which in turn leads to a decrease in its compressive strength.

[0048] In some embodiments, the microporosity φ, pore volume Pv, and compressive strength Cs of the porous carbon material satisfy the following relationship: 650 ≤ (Cs·φ) / Pv ≤ 1040; wherein the microporosity φ > 99%, the compressive strength Cs is 700–850 MPa, and the pore volume Pv is 0.8–1.1 cm³. 3 / g.

[0049] In some embodiments, the porous carbon material of the present invention has a suitable surface area, with a specific surface area of ​​1700–2800 cm². 3 / g, including but not limited to 1700cm 3 / g、1800cm 3 / g、1900cm 3 / g、2000cm 3 / g、2100cm 3 / g、2500cm 3 / g、2600cm 3 / g、2800cm 3 / g, or any value within a range of both.

[0050] In some embodiments, the preparation method of the above-mentioned porous carbon material of the present invention includes the following steps:

[0051] The carbon source is subjected to a first heat treatment in a CO2 atmosphere to obtain a first carbon material; the first carbon material is subjected to a second heat treatment with a mixture of the first carbon material and an alkaline activator to obtain a second carbon material; the second carbon material is subjected to a washing treatment and a third heat treatment to obtain the porous carbon material.

[0052] The method for preparing porous carbon materials of the present invention obtains porous carbon materials with high microporosity through the combined activation of CO2 gas and alkaline activator. This method can effectively reduce the amount of KOH used for chemical activation, slow down the equipment corrosion rate, and reduce activation costs. The high microporosity porous carbon can effectively improve the compressive strength of the porous carbon matrix, which is beneficial to reducing the occurrence of cracking of silicon-carbon composite materials after rolling during electrode preparation, inhibiting the generation of silicon oxide inside the particles, and thus improving the first coulombic efficiency.

[0053] In some embodiments, the carbon source includes at least one of a polymer, petroleum coke, and pitch coke.

[0054] In some implementations, the CO2 flow rate is 0.5–1.2 L / min, including but not limited to 0.5 L / min, 0.8 L / min, 1 L / min, 1.1 L / min, 1.2 L / min, or any value in between. A suitable CO2 flow rate is used to ensure better activation.

[0055] In some embodiments, the temperature of the first heat treatment is 850–950°C, for example, 850°C, 860°C, 870°C, 900°C, 920°C, 930°C, 950°C, or any range between these two. The holding time of the first heat treatment is 9–15 hours, for example, 9 hours, 10 hours, 11 hours, 12 hours, 13 hours, 15 hours, or any range between these two. This invention employs suitable first heat treatment conditions to ensure the CO2 activation effect. In some embodiments, the first carbon material is subjected to natural cooling treatment.

[0056] In some embodiments, the alkaline activator includes at least one selected from potassium hydroxide, magnesium hydroxide, sodium hydroxide, and calcium hydroxide. In some embodiments, the mass ratio of the first carbon material to the alkaline activator is (1.5–6):1, for example, 1.5:1, 2:1, 2.5:1, 3:1, 3.5:1, 4:1, 5:1, or 6:1, or any range between the two. Using a suitable mass ratio of the first carbon material to the alkaline activator is more conducive to ensuring the activation effect.

[0057] In some embodiments, the temperature of the second heat treatment is 700–850°C, for example, 700°C, 720°C, 750°C, 780°C, 800°C, 820°C, 850°C, or any range between the two. The holding time of the second heat treatment is 1–3 hours, for example, 1 hour, 1.5 hours, 2 hours, 2.5 hours, or 3 hours, or any range between the two. This invention employs suitable second heat treatment conditions to ensure the activation effect of the alkali activator. In some embodiments, the second heat treatment is carried out under a protective gas condition, such as nitrogen or an inert gas, with a flow rate of 0.5–5 L / min. In some embodiments, the second carbon material is subjected to natural cooling.

[0058] In some embodiments, the temperature of the third heat treatment is 850–950°C, for example, 850°C, 880°C, 900°C, 920°C, 950°C, or any range between the two. The holding time of the third heat treatment is 2–5 hours, for example, 2 hours, 2.5 hours, 3 hours, 4 hours, or 5 hours, or any range between the two. This invention employs suitable third heat treatment conditions to obtain porous carbon materials with high microporosity, suitable pore volume, and compressive strength.

[0059] In some embodiments, the washing process includes acid washing and water washing. Acid washing uses 0.5–2 mol / L hydrochloric acid. Water washing involves repeated washing with deionized water until the filtrate is neutral.

[0060] In some embodiments, the silicon-carbon composite material of the present invention has a suitable silicon content, wherein the mass content of the nano-silicon particles in the silicon-carbon composite material is 45% to 65%, for example 45%, 48%, 50%, 52%, 55%, 60% or 65%, or any value between the two.

[0061] In some embodiments, the surface of the silicon-carbon composite material further includes a coating layer comprising at least one of a fast ion conductor, amorphous carbon, and a polymer. By providing the aforementioned coating layer, the electrochemical performance of the silicon-carbon composite material can be further improved.

[0062] In some embodiments, the silicon-carbon composite material of the present invention has high compressive strength, which is 820 to 1100 MPa, such as 830 MPa, 850 MPa, 900 MPa, 950 MPa, 1000 MPa, 1050 MPa, 1060 MPa, 1080 MPa, 1100 MPa, or any value in the range between the two.

[0063] According to another aspect of the present invention, the present invention relates to a method for preparing a silicon-carbon anode material, comprising the following steps: performing vapor deposition of porous carbon material in an atmosphere containing a silicon source to obtain the silicon-carbon anode material.

[0064] In some embodiments, the silicon source includes conventional siliconizing gases. Silicon sources include, but are not limited to, at least one of silane (SiH4), silane, propane, halosilane, polysilane, thiophene and its derivatives, and fluorene and its derivatives.

[0065] In some embodiments, the temperature of vapor deposition is 400–550°C, for example, but not limited to 400°C, 450°C, 480°C, 500°C, 510°C, 550°C, or any range between the two.

[0066] In some embodiments, the preparation method of silicon-carbon composite material includes: placing porous carbon material in a heat treatment apparatus, evacuating at room temperature and introducing a protective gas to replace air with the protective gas. Under the protective gas atmosphere, the temperature is increased to 400-550°C at a rate of 2-8°C / min, while a silicon source is introduced at a flow rate of 0.5-1.5 L / min, and the temperature is maintained for 2-3.5 hours before the silicon source is introduced is stopped.

[0067] In some embodiments, the method further includes: coating the silicon-carbon anode material to obtain a coating layer on the surface of the silicon-carbon anode material, the coating layer comprising at least one of amorphous carbon, a fast ion conductor, and a polymer. The coating process specifically includes: performing a third heat treatment after vapor deposition, while continuously introducing a coating source gas. This invention improves the overall performance of the final silicon-carbon anode material by further coating its surface.

[0068] In some embodiments, after the porous carbon material is vapor-deposited in an atmosphere containing a silicon source, the temperature is increased to 600-700°C at a rate of 2-8°C / min, while a coating gas source is introduced at a flow rate of 0.1-0.5L / min. After holding at this temperature for 1-3 hours, the introduction of the coating gas source is stopped.

[0069] In some implementations, the protective gas includes nitrogen, an inert gas such as helium, etc.

[0070] In some embodiments, the coating source gas includes acetylene, methane, ethane, isopropane, propane, butane, isobutane, ethylene, butene, propylene, acetylene (C2H2), vinyl chloride, chloroethane, vinyl fluoride, pentachlorofluoroethane, difluoroethane, 1,1-difluoroethylene, fluoromethane, chloromethane, difluoromethane, trifluoromethane, etc.

[0071] According to another aspect of the invention, the invention also relates to a negative electrode comprising the aforementioned silicon-carbon composite material.

[0072] In some embodiments, the negative electrode sheet includes a negative electrode current collector and a negative electrode material layer located on at least one side surface of the negative electrode current collector, wherein the negative electrode material layer contains the aforementioned silicon-carbon composite material.

[0073] According to another aspect of the invention, the invention also relates to a battery comprising the aforementioned negative electrode.

[0074] The battery of the present invention has high capacity and excellent cycle performance. In some embodiments, the battery includes the above-described negative electrode, positive electrode, separator, and electrolyte.

[0075] According to another aspect of the invention, the invention also relates to an electrical device comprising the battery described above. The electrical device may be, but is not limited to, a tablet, mobile phone, electric toy, laptop computer, power tool, ship, electric car, electric vehicle, spacecraft, etc.

[0076] The following explanation, combined with specific embodiments and comparative examples, further illustrates the point.

[0077] Example 1

[0078] A method for preparing porous carbon materials includes the following steps:

[0079] 1 kg of resin was placed in a rotary kiln, and CO2 was introduced at a rate of 1 L / min. The rotary kiln was heated to 900 °C at a rate of 5 °C / min for the first heat treatment, and held at that temperature for 12 h. After the rotary kiln cooled naturally, the material was removed and set aside. 500 g of the porous carbon obtained after the initial activation and 200 g of KOH were placed in a rotary kiln, and N2 was introduced at a rate of 1 L / min. The rotary kiln was heated to 800 °C at a rate of 5 °C / min for the second heat treatment, and held at that temperature for 1.5 h. After the rotary kiln cooled naturally, the material was removed and placed in a 1 mol / L HCl solution, stirred, filtered, and washed. After washing with hydrochloric acid, it was repeatedly washed with deionized water until the filtrate was neutral. After drying, the intermediate product was placed in a rotary kiln under a nitrogen atmosphere at 900 °C for the third heat treatment, and held at that temperature for 3 h, to obtain the final porous carbon material with high pore volume and high microporosity.

[0080] A method for preparing a silicon-carbon composite material includes the following steps:

[0081] One kilogram of the porous carbon described in this embodiment was placed in a rotary kiln. A vacuum was drawn at room temperature, and N2 was introduced to replace the air with N2. Under a nitrogen atmosphere, the temperature was increased to 450°C at a rate of 5°C / min, while SiH4 was introduced at a flow rate of 0.8 L / min. After holding at this temperature for 3 hours, the SiH4 gas valve was closed. Next, the temperature was increased to 650°C at a rate of 5°C / min, while C2H2 was introduced at a flow rate of 0.2 L / min. After holding at this temperature for 2 hours, the C2H2 gas valve was closed, yielding a silicon-carbon anode material with a silicon mass content of 60%.

[0082] Example 2

[0083] A method for preparing porous carbon materials differs from that in Example 1 in that:

[0084] The flow rate of CO2 gas is 0.5 L / min.

[0085] The preparation method of the silicon-carbon composite material in this embodiment is the same as that in Example 1, except that the porous carbon material used in this embodiment is employed.

[0086] Example 3

[0087] A method for preparing porous carbon materials differs from that in Example 1 in that:

[0088] The amount of KOH used is 100g.

[0089] The preparation method of the silicon-carbon composite material in this embodiment is the same as that in Example 1, except that the porous carbon material used in this embodiment is employed.

[0090] Example 4

[0091] A method for preparing porous carbon materials differs from that in Example 1 in that:

[0092] The amount of KOH used is 300g.

[0093] The preparation method of the silicon-carbon composite material in this embodiment is the same as that in Example 1, except that the porous carbon material used in this embodiment is employed.

[0094] Example 5

[0095] A method for preparing porous carbon materials differs from that in Example 1 in that:

[0096] The amount of KOH used is 160g.

[0097] The preparation method of the silicon-carbon composite material in this embodiment is the same as that in Example 1, except that the porous carbon material used in this embodiment is employed.

[0098] Comparative Example 1

[0099] A method for preparing porous carbon materials differs from that in Example 1 in that:

[0100] Instead of using CO2 for activation, adjust the amount of KOH used to 280g.

[0101] The preparation method of the silicon-carbon composite material in this comparative example differs from that in Example 1 in that the porous carbon material in this comparative example is used, and the SiH4 deposition time at 450°C is extended from 3h to 3.5h.

[0102] Comparative Example 2

[0103] A method for preparing porous carbon materials differs from that in Example 1 in that:

[0104] Without using KOH for activation, the CO2 gas flow rate was adjusted to 1.9 L / min.

[0105] The preparation method of the silicon-carbon composite material in this comparative example differs from that in Example 1 in that the porous carbon material in this comparative example is used, and the deposition time of SiH4 at 450°C is extended from 3h to 4h.

[0106] Comparative Example 3

[0107] A method for preparing porous carbon materials differs from that in Example 1 in that:

[0108] The flow rate of CO2 gas is 1.5 L / min.

[0109] The preparation method of the silicon-carbon composite material in this embodiment is the same as that in Example 1, except that the porous carbon material used in this embodiment is employed.

[0110] Experimental Example

[0111] I. Performance Testing of Porous Carbon Materials

[0112] The specific surface area, pore volume, microporosity, and compressive strength of the porous carbon materials in each embodiment and comparative example were tested. The test methods are as follows:

[0113] Microporosity testing method: The pore size distribution of porous carbon was obtained by fitting the nitrogen isothermal adsorption-desorption curve using the NLDFT model. The proportion of pore volume with a pore size of 2 nm or less to the total pore volume is the microporosity.

[0114] Compressive strength testing method: A micro-compression testing machine with a flat indenter diameter of 50 μm is used. The sample is clamped between two indicators, and the sample is measured in increments of 0.1 μm until it reaches 200 μm. The pressure and deformation during the sample deformation process are measured. The obtained data graph shows the compressive displacement on the horizontal axis and the pressure calculated by the instrument on the vertical axis. The compressive strength of the material is the pressure corresponding to the inflection point of the curve.

[0115] The specific surface area and pore volume were determined by nitrogen isothermal adsorption-desorption.

[0116] The performance test results of the porous carbon materials in each embodiment and comparative example are shown in Table 1. The pore size distribution diagram of the porous carbon material in Example 1 is shown below. Figure 1 As shown. The compressive strength curve of the carbon material in Example 1 is shown in the figure. Figure 2 As shown in the figure. The compressive strength curve of the silicon-carbon composite material in Example 1 is shown in the figure. Figure 3 As shown.

[0117] Table 1 Performance test results of porous carbon materials

[0118]

[0119] Table 1 shows that the microporosity of porous carbon materials is positively correlated with their compressive strength; that is, the higher the microporosity, the greater the compressive strength. Under the same microporosity, pore volume is negatively correlated with compressive strength. Furthermore, combining CO2 gas activation and alkali activation is beneficial for preparing porous carbon materials with suitable pore volume and high microporosity. When the pore volume increases to a certain value, further increases in pore volume will result in pore expansion, i.e., the pore size increases and the microporosity decreases. The microporosity φ, pore volume Pv, and compressive strength Cs of the porous carbon materials obtained in the various embodiments of this invention satisfy the relationship 550≤(Cs·φ) / Pv≤1050. The compressive strength of the porous carbon materials obtained in Comparative Examples 1-3 is too low, and the value of (Cs·φ) / Pv is too low.

[0120] II. Performance Testing of Silicon-Carbon Anode Materials

[0121] The compressive strength and silicon content of the silicon-carbon anode materials obtained in each embodiment and comparative example were tested respectively.

[0122] The compressive strength test method for silicon-carbon anode materials is the same as the test method for porous carbon materials described above.

[0123] Silicon content testing: Thermogravimetric analysis (TGA) was used. A sample of a certain mass m1 was heated to 600℃ at room temperature under air atmosphere and held for 1 hour. Then, the temperature was further increased to 1000℃ and held for 1 hour. After natural cooling, the mass m2 of the resulting sample was measured. The silicon content was 0.467 × m2 / m1.

[0124] The performance test results of the silicon-carbon anode materials in each embodiment and comparative example are shown in Table 2.

[0125] Table 2 Performance test results of silicon-carbon anode materials

[0126] Group Compressive strength (MPa) Silicon content (wt%) Example 1 965 60 Example 2 1051 45 Example 3 983 49 Example 4 830 56 Example 5 953 54 Comparative Example 1 741 60 Comparative Example 2 449 60 Comparative Example 3 618 52

[0127] As shown in Table 2, under the same pore volume and deposition process, a higher microporosity corresponds to a higher silicon content, because micropores have a stronger adsorption force on gas molecules. The methods of the various embodiments of the present invention can obtain silicon-carbon anode materials with high compressive strength and high silicon content.

[0128] III. Battery Performance Testing

[0129] The silicon-carbon composite materials used in each embodiment and comparative example were respectively prepared into half-cells, and their electrochemical performance was tested. The specific preparation method of the half-cells included: mixing the silicon-carbon composite material with binder polyacrylic acid (PAA) and conductive carbon black (SP) at a mass ratio of 70:20:10; preparing this mixture into a slurry with deionized water; uniformly coating the slurry onto copper foil; vacuum drying at 80°C for 24 hours; and then rolling to obtain the half-cell electrode, wherein the electrode's compaction density was approximately 1.0 g / cm³. 3 Its surface density is approximately 2.5 mg / cm³. 2 Using lithium foil as the counter electrode, 1 mol / L LiPF6 was dissolved in a four-component mixed solvent as the electrolyte. The volume ratio of ethylene carbonate (EC): dimethyl carbonate (DMC): vinylene carbonate (VC): fluoroethylene carbonate (FEC) in the four-component solvent was 1:1:1:1. A polypropylene microporous membrane was used as the separator, and the CR2032 coin cell was assembled in a vacuum glove box.

[0130] Electrochemical performance testing conditions: After standing for 10 min, discharge at a constant current of 0.1C to 5 mV, stand for 5 min, then discharge at a constant current of 0.02C to 5 mV, stand for 5 min, then discharge at a constant current of 0.01C to 5 mV; stand for 10 min, then charge at a constant current of 0.1C to 2.0V. Cycle 100 times.

[0131] The performance test results of the batteries in each embodiment and comparative example are shown in Table 3. The dQ / dV curve of the battery prepared from the silicon-carbon composite material in Example 1 is shown in Table 3. Figure 4 As shown in the figure. The dQ / dV curve of the battery prepared by the silicon-carbon composite material in Comparative Example 1 is shown in the figure. Figure 5 As shown.

[0132] Table 3 Battery performance test results

[0133]

[0134]

[0135] In Table 3, I SiOx / I Si The dQ / dV curve representing the initial lithium insertion, with intensity values ​​(I) in the range of 0.30–0.45 V. SiOx ) and the strongest peak value within 0 to 0.25V (I Si The ratio of ).

[0136] As shown in Table 3, the silicon-carbon anode material obtained by the method of the present invention produces batteries with high initial delithiation capacity, coulombic efficiency, and good cycle performance. The initial delithiation capacity can reach 2434 mAh / g, the coulombic efficiency can reach 93.2%, the capacity after 100 cycles is 1728 mAh / g or higher, and the capacity retention rate after 100 cycles is over 90%.

[0137] Comparing Comparative Example 1, Comparative Example 2, and Example 1, it can be seen that, with the same silicon content, the capacity and efficiency of the silicon-carbon anode material are positively correlated with the microporosity of its porous carbon matrix. Furthermore, from... Figure 4 The dQ / dV curve of the first lithium intercalation shows that no SiO2 was observed in the range of 0.30–0.45 V. x The lithium intercalation peak, and the dQ / dV curves of the first lithium intercalation in Examples 2-5, showed no SiO2 observed in the range of 0.30–0.45 V. x The lithium intercalation peak, or even if a lithium intercalation peak exists, its intensity value (I) SiOx ) and the strongest peak value within 0 to 0.25V (I Si The ratio is also less than 0.05; from Figure 5 The dQ / dV curve of the first lithium intercalation shows the appearance of SiO₂ in the range of 0.30–0.45 V. x The lithium intercalation peak is observed, and the intensity of this peak is 0.5 times that of the strongest peak in the 0–0.25V range. This is because the silicon-carbon particles have low compressive strength, and the particles fractured during the rolling process, causing the elemental silicon in the silicon-carbon particles to react with air to form silicon oxide, resulting in a decrease in capacity and initial efficiency.

[0138] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, and not to limit them. Although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some or all of the technical features therein. Such modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments of the present invention.

Claims

1. A silicon-carbon composite material, characterized in that, The material includes porous carbon material and nano-silicon particles located in the pores of the porous carbon material; in the dQ / dV curve of the first lithium intercalation of the silicon-carbon composite material, the ratio of the intensity value of the lithium intercalation peak at 0.30~0.45V to the strongest peak value in the range of 0~0.25V is less than 0.

05. The microporosity of the porous carbon material The pore volume Pv and compressive strength Cs satisfy the following relationship: 550 ≤ (Cs• ) / Pv≤1050, wherein the microporosity >95%, and the compressive strength Cs is 600~850MPa.

2. The silicon-carbon composite material according to claim 1, characterized in that, In the dQ / dV curve of the first lithium insertion of the silicon-carbon composite material, the ratio of the intensity value of the lithium insertion peak at 0.30~0.45V to the strongest peak value in the range of 0~0.25V is 0.

3. The silicon-carbon composite material according to claim 1, characterized in that, The pore volume Pv is 0.7~1.2cm. 3 / g.

4. The silicon-carbon composite material according to claim 1, characterized in that, The microporosity of the porous carbon material The pore volume Pv and compressive strength Cs satisfy the following relationship: 650 ≤ (Cs• ) / Pv≤1040; wherein, the microporosity >99%, the compressive strength Cs is 700~850MPa, and the pore volume Pv is 0.8~1.1cm. 3 / g.

5. The silicon-carbon composite material according to claim 1, characterized in that, The specific surface area of ​​the porous carbon material is 1700~2800 cm². 3 / g.

6. The silicon-carbon composite material according to claim 1, characterized in that, The mass content of nano-silicon particles in the silicon-carbon composite material is 45% to 65%.

7. The silicon-carbon composite material according to claim 1, characterized in that, The surface of the silicon-carbon composite material also includes a coating layer, which comprises at least one of a fast ion conductor, amorphous carbon, and a polymer.

8. The silicon-carbon composite material according to claim 1, characterized in that, The compressive strength of the silicon-carbon composite material is 820~1100MPa.

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

10. A battery, characterized in that, It includes the negative electrode sheet as described in claim 9.

11. An electrical appliance, characterized in that, It includes the battery as described in claim 10.

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