Porous carbon material, preparation method of porous carbon material, silicon carbon material and application of silicon carbon material

Abstract

The invention relates to a porous carbon material and a preparation method thereof, a silicon carbon material and an application thereof, when a button cell assembled by the porous carbon material and lithium metal is charged at a current of 0.05 C in a voltage range of 0.005 V to 2V, the charging specific capacity in a voltage range of 0.005 V to 0.15 V is 43 mAh / g to 132 mAh / g; the charging specific capacity in a voltage range of 0.005 V to 0.8 V is in a range of 152 mAh / g to 253.4 mAh / g; the voltage capacity differential dQ / dV curve of the button cell has a first characteristic peak from 0.005 V to 0.15 V, and the peak height is not less than 260 mAh / g / V. The porous carbon material with the above characteristics can improve the overall capacity and first efficiency of the silicon-carbon negative electrode material, and improve the cycle performance of the secondary battery.

Description

Technical Field

[0001] This application belongs to the technical field of energy storage, and particularly relates to a porous carbon material and its preparation method, a silicon-carbon material and its application. Background Art

[0002] The traditional graphite anode material only has a theoretical energy density of 372 mAh / g, which restricts its further development and application. In recent years, the high energy density of silicon materials, 4200 mAh / g, has attracted wide attention. Currently, common silicon-carbon materials mostly use amorphous porous carbon materials with nanoscale pores as the framework, and nanosilicon crystals are deposited inside the pores by chemical vapor deposition. The silicon-carbon material is formed by an amorphous porous carbon material matrix and amorphous nanosilicon crystals to jointly form an energy storage carrier. As a candidate material for a new generation of high-energy-density lithium-ion batteries, it combines the high theoretical capacity of silicon and the good electrical conductivity of carbon materials. In theory, it can improve the energy density of the battery and shows great potential in enhancing the battery energy storage capacity.

[0003] However, silicon-carbon materials still face the technical challenge of a relatively low initial Coulomb efficiency in practical applications. Moreover, silicon will undergo volume expansion during the lithium intercalation process, which will not only lead to battery capacity attenuation but also damage the battery structure and affect the cycle performance. Therefore, how to effectively improve the initial Coulomb efficiency of silicon-carbon materials and their cycle performance in battery applications has become an urgent technical problem to be solved in the current battery material field. Summary of the Invention

[0004] In view of this, this application provides a porous carbon material and its preparation method, a silicon-carbon material and its application. The porous carbon material itself has a relatively high reversible capacity, so it can improve the overall capacity and initial efficiency of the silicon-carbon anode material and improve the cycle performance of secondary batteries.

[0005] The present application provides a porous carbon material. The porous carbon material is assembled with lithium metal into a button cell. When the button cell is charged at a current of 0.05C in the voltage range of 0.005V to 2V, the specific charge capacity in the voltage range of 0.005V to 0.15V is 43mAh / g to 132mAh / g; the specific charge capacity in the voltage range of 0.005V to 0.8V is 152mAh / g to 253.4mAh / g; the voltage-capacity differential dQ / dV curve of the button cell has a first characteristic peak located at 0.005V to 0.15V, and the peak height of the first characteristic peak is not less than 260mAh / g / V. Among them, the porous carbon material can provide a certain specific charge capacity in the lower voltage range of 0.005V to 0.15V. Moreover, the voltage-capacity differential dQ / dV curve has a first characteristic peak located at 0.005V to 0.15V and a relatively high peak height of not less than 260mAh / g / V, reflecting that the porous carbon material has a fast and large lithium-ion insertion ability in this voltage range, indicating that the porous carbon material has good lithium-ion transport ability in the low voltage range of 0.005V to 0.15V and can increase the capacity under the low voltage platform, which is beneficial to improving the lithium-ion insertion and extraction rate, especially improving the electrochemical performance of the secondary battery under high-rate conditions; in addition, providing the above specific charge capacity in the voltage range of 0.005V to 0.8V, on the one hand, indicates that the porous carbon material has a high capacity contribution during the charging process in this voltage range, so as to further improve the overall capacity and energy density of the silicon-carbon material, and the capacity in this voltage range is beneficial to improving the initial Coulomb efficiency of the silicon-carbon material. On the other hand, it shows that the porous carbon material has a structure for lithium deintercalation and intercalation in the above voltage range. The process of lithium-ion insertion and extraction in this lower voltage range is relatively gentle, which is beneficial to reducing the stress on the material, better buffering the expansion of nano-silicon, and enhancing the structural stability, thereby improving the cycle performance of the silicon-carbon material and the secondary battery.

[0006] In some embodiments, the true density of the porous carbon material is 2.003g / cm 3 to 2.230g / cm 3; and at least a part of the porous carbon material has a lattice structure. In this application, a lattice structure is provided in the porous carbon material, and lithium ions can be embedded into the interlayer of the lattice structure like in graphite materials, providing a certain lithium storage capacity for the porous carbon material. Moreover, the lattice structure can also improve the diffusion rate of lithium ions, thereby improving the rate performance of the secondary battery. Furthermore, when the true density of the porous carbon material satisfies the above range, it indicates that there is an appropriate amount of closed pore structure in the porous carbon material. These closed pore structures are not connected to the outer surface, but through the diffusion channels provided by the lattice structure, lithium ions can diffuse into the closed pore structures and be embedded in the closed pore structures to form lithium metal clusters to achieve controllable lithium intercalation, thereby further enhancing the reversible lithium storage capacity of the porous carbon material and reducing the waste of the lithium storage volume inside the porous carbon material. Porous carbon material. In addition, when the closed pore structure is formed, it will preferentially close the pores with small pore diameters, so as to ensure that more nanosilicon is deposited inside the pores with relatively large pore diameters, thereby better providing a buffer for the expansion of nanosilicon, reducing the expansion and side reactions of the negative electrode material, and improving the cycle performance of the secondary battery. Therefore, through the cooperation of the lattice structure and the closed pore structure in this application, the reversible lithium storage capacity and the lithium ion diffusion rate of the porous carbon material can be improved, enabling the porous carbon material to provide a relatively high charging specific capacity in the voltage range of 0.005V to 0.8V, and the voltage-capacity differential dQ / dV curve has a corresponding first characteristic peak, thereby improving the first Coulomb efficiency of the silicon-carbon material, as well as the rate performance and cycle performance of the secondary battery.

[0007] In some embodiments, the peak height of the first characteristic peak is from 260 mAh / g / V to 1927 mAh / g / V. When this condition is satisfied, the first Coulomb efficiency, rate performance, and cycle performance of the secondary battery can be further improved.

[0008] In some embodiments, the porous carbon material satisfies at least one of the following:

[0009] (1) When the coin cell is charged at a current of 0.05C in the voltage range of 0.005V to 2V, the charging specific capacity in the voltage range of 0.005V to 0.15V is from 75 mAh / g to 132 mAh / g, and the charging specific capacity in the voltage range of 0.005V to 0.8V is from 174 mAh / g to 253.4 mAh / g;

[0010] (2) The peak height of the first characteristic peak is from 760 mAh / g / V to 1927 mAh / g / V. When the porous carbon material satisfies the above conditions and is combined with its closed pores and lattice structure, the first Coulomb efficiency, rate performance, and cycle performance of the secondary battery can be further improved.

[0011] In some embodiments, the specific surface area of the porous carbon material is 1752 m 2 / g to 2035 m2 / g; and / or, the pore volume of the porous carbon material is 0.68 cm 3 / g to 0.91 cm 3 / g. When the porous carbon material meets the above conditions, the contact area between the porous carbon material and the electrolyte can be increased, which is beneficial to making full use of the lithium ions embedded in the microcrystalline structure and the lithium ion channels of its closed pores, and can further improve the initial Coulomb efficiency, rate performance and cycle performance of the secondary battery.

[0012] In some embodiments, the porous carbon material includes type I pores and type II pores. The pore diameter of the type I pores is P1 nm, and the pore diameter of the type II pores is P2 nm, where 0 < P1 ≤ 2 nm and 2 < P1 ≤ 10 nm; based on the sum of the pore volume of the type I pores and the pore volume of the type II pores, the proportion of the pore volume of the type I pores is 92.4% to 98.2%. Preferably, the proportion of the pore volume of the type I pores is 93.2% to 96.5%. When the porous carbon material has the above pore size distribution characteristics, it can provide more diffusion channels for lithium ions. Cooperating with the microcrystalline structure can further improve the diffusion ability of lithium ions, and can further improve the initial Coulomb efficiency and rate performance of the secondary battery; the above pore size distribution cooperates with the closed pore structure to jointly buffer the volume change of silicon during charge and discharge, improve the stability of the battery structure, and thus enable the secondary battery to exhibit more excellent cycle performance.

[0013] This application also provides a preparation method of the aforementioned porous carbon material, including the following steps:

[0014] Step S1: Dispersing a catalytic metal element to obtain a dispersion system; performing a polymerization reaction on a polymerization monomer in the dispersion system to obtain a porous carbon material precursor; the catalytic metal element includes at least one of iron, cobalt, nickel, vanadium, chromium, manganese, zinc, tin, calcium, magnesium, and aluminum; the mass proportion of the catalytic metal element in the porous carbon material precursor is 0.004% to 0.500%; the polymerization monomer includes a phenolic compound and an aldehyde compound;

[0015] Step S2: Carbonizing the porous carbon material precursor at T1 °C for t1 hours to obtain a carbonized material, where 750 °C ≤ T1 ≤ 1200 °C and 1 ≤ t1 ≤ 10;

[0016] Step S3: Mixing the carbonized material with an activator, and then performing an activation treatment at T2 °C for t2 hours to obtain an activated material, where 700 °C ≤ T2 ≤ 1100 °C and 1 ≤ t2 ≤ 6;

[0017] Step S4: Wash the activated material and then dry it. Calcinate the dried activated material in a mixed gas atmosphere of alkane (such as methane) and inert gas (such as nitrogen) at T3 °C for t3 hours to obtain the porous carbon material; 600 °C ≤ T3 ≤ 1400 °C, 2 ≤ t3 ≤ 8, and the volume ratio of alkane to inert gas is 1:(5 - 10).

[0018] In this application, a catalytic metal is added to the porous carbon material precursor. Combining with the high-temperature conditions of subsequent carbonization and activation treatments, it can catalyze the formation of a lattice structure inside the porous carbon material, improving the lithium storage capacity and the diffusion rate of lithium ions. After the activation is completed, the alkane gas and calcination treatment can make the porous carbon material form a closed pore structure, further enhancing the reversible lithium storage capacity of the porous carbon material, as well as improving the buffering effect on the expansion of nanosilicon, and improving the initial Coulomb efficiency, cycle performance, and rate performance of the secondary battery.

[0019] This application further provides a silicon-carbon material, which includes a porous carbon material, nanosilicon located inside the porous carbon material, and a carbon layer located on the surface of the porous carbon material; the porous carbon material includes the aforementioned porous carbon material or the porous carbon material prepared by the aforementioned preparation method. Based on the porous carbon material therein, the silicon-carbon material of this application can have a higher lithium storage capacity and initial Coulomb efficiency, and can improve the cycle performance and rate performance of the secondary battery.

[0020] This application further provides a secondary battery, which includes a positive electrode, a negative electrode, and an electrolyte. In some embodiments, the negative electrode includes a negative electrode current collector and a negative electrode material layer located on at least part of the surface of the negative electrode current collector, and the negative electrode material layer includes the aforementioned silicon-carbon material.

[0021] In some embodiments, the electrolyte includes ethylene carbonate and fluoroethylene carbonate; based on the mass of the electrolyte, the mass percentage of ethylene carbonate is C1%, and the mass percentage of fluoroethylene carbonate is C2%, 0.5 ≤ C2 / C1 ≤ 2; preferably, 1 ≤ C2 / C1 ≤ 1.5. Adjusting the mass percentage of ethylene carbonate and fluoroethylene carbonate in the electrolyte to meet the above range can improve the film-forming effect of the electrolyte and the wettability to the negative electrode material, thereby promoting the formation of a stable solid electrolyte interface film (SEI film) on the surface of the aforementioned silicon-carbon material or porous carbon material, reducing electrolyte side reactions, and at the same time reducing the diffusion resistance of lithium ions, further improving the cycle performance and rate performance of the secondary battery.

[0022] In some embodiments, the electrolyte includes a first lithium salt selected from at least one of lithium bis(trifluoromethanesulfonyl)imide, lithium bis(fluorosulfonyl)imide, and lithium trifluoromethanesulfonate; the electrolyte includes a second lithium salt selected from at least one of lithium tetrafluoroborate and lithium difluorophosphate; based on the mass of the electrolyte, the mass percentage of the first lithium salt is S1%, and the mass percentage of the second lithium salt is S2%, where 0.2 ≤ S2 / S1 ≤ 2; preferably, 0.4 ≤ S2 / S1 ≤ 1.6. By regulating the electrolyte to include the above-mentioned first lithium salt and second lithium salt, the compactness and stability of the SEI film can be improved, and the ionic conductivity of the electrolyte can be increased. When combined with the above-mentioned negative electrode system, the cycle performance and rate performance of the secondary battery can be further improved.

[0023] The present application also provides an electronic device including the aforementioned secondary battery. Based on the porous carbon material contained in the negative electrode of the secondary battery, the electronic device of the present application has strong battery life and high safety performance. BRIEF DESCRIPTION OF THE DRAWINGS

[0024] Figure 1 It is a charge-discharge cycle curve graph of the porous carbon materials provided in Example 1-1 and Comparative Example 1-1 of the present application;

[0025] Figure 2 It is a voltage-capacity differential dQ / dV curve graph of the porous carbon materials provided in Example 1-1 and Comparative Example 1-1 of the present application. DETAILED DESCRIPTION OF THE EMBODIMENTS

[0026] In order to make the objectives, technical solutions, and advantages of the present application clearer, the present application will be further described in detail below with reference to the embodiments. It should be understood that the specific embodiments described herein are only used to explain the present application and are not used to limit the present application.

[0027] The silicon-carbon material is formed by using a porous carbon material as a matrix and jointly forming an energy storage carrier with nano-silicon. Since the porous carbon material itself is amorphous, the capacity it provides is limited. Although the high specific surface area of the porous carbon material provides more active sites, it also increases the loss of irreversible lithium ions during the first charge-discharge process, thereby reducing the first Coulomb efficiency. Therefore, the capacity and first Coulomb efficiency of the silicon-carbon material cannot be fully exerted.

[0028] The present application provides a porous carbon material. The porous carbon material is assembled with lithium metal into a button cell. When the button cell is charged at a current of 0.05C in the voltage range of 0.005V to 2V, the specific charge capacity in the voltage range of 0.005V to 0.15V is 43mAh / g to 132mAh / g, preferably 43mAh / g to 132mAh / g, such as values within the range composed of 43mAh / g, 50mAh / g, 60mAh / g, 70mAh / g, 80mAh / g, 90mAh / g, 100mAh / g, 110mAh / g, 132mAh / g or any two of them; the specific charge capacity in the voltage range of 0.005V to 0.8V is 152mAh / g to 253.4mAh / g, preferably 174mAh / g to 253.4mAh / g, such as values within the range composed of 152mAh / g, 160mAh / g, 174mAh / g, 170mAh / g, 180mAh / g, 190mAh / g, 200mAh / g, 210mAh / g, 220mAh / g, 230mAh / g, 240mAh / g, 250mAh / g, 253.4mAh / g or any two of them.

[0029] The voltage-capacity differential dQ / dV curve of the button cell has a first characteristic peak located at 0.005V to 0.15V, and the peak height of the first characteristic peak is 260mAh / g / V to 1927mAh / g / V. Preferably, the peak height of the first characteristic peak is 760mAh / g / V to 1927mAh / g / V. Exemplarily, the peak height of the first characteristic peak can be 260mAh / g / V, 330mAh / g / V, 620mAh / g / V, 740mAh / g / V, 1090mAh / g / V, 1240mAh / g / V, 1540mAh / g / V, 1760mAh / g / V, 1927mAh / g / V or values within the range composed of any two of them.

[0030] The inventors found that when the porous carbon material meets the above characteristics, it can provide a certain charge specific capacity in the lower voltage range of 0.005V to 0.15V. This part of the capacity helps to improve the first Coulombic efficiency of the porous carbon material and the silicon-carbon material. The voltage-capacity differential dQ / dV curve has a first characteristic peak located at 0.005V to 0.15V and has a relatively high peak height, reflecting the rapid and large-scale lithium-ion insertion ability of the porous carbon material in this voltage range, indicating that the porous carbon material has good lithium-ion transport ability in the above low voltage range. This can promote the stable formation of the SEI film in the low voltage range, which is beneficial to reducing side reactions and improving the first Coulombic efficiency of the porous carbon material and the silicon-carbon material. In addition, providing the above charge specific capacity in the voltage range of 0.005V to 0.8V, on the one hand, indicates that the porous carbon material has a relatively high capacity contribution during the entire charging process, thus being able to further improve the overall capacity and energy density of the silicon-carbon material. On the other hand, it indicates that the porous carbon material has a pore structure for lithium deintercalation and intercalation in the above voltage range, and this structure can better buffer the expansion of nano-silicon and enhance the structural stability, thereby improving the cycle performance of the silicon-carbon material and the secondary battery.

[0031] In some embodiments, the true density of the porous carbon material is 2.003 g / cm 3 to 2.230 g / cm 3 ; and at least part of the region of the porous carbon material has a lattice structure. Exemplarily, the true density of the porous carbon material can be selected from 2.003 g / cm 3 , 2.012 g / cm 3 , 2.032 g / cm 3 , 2.055 g / cm 3 , 2.093 g / cm 3 , 2.127 g / cm 3 , 2.137 g / cm 3 , 2.162 g / cm 3 , 2.193 g / cm 3 , 2.230 g / cm 3Or a value within the range composed of any two of them. When the true density of the porous carbon material satisfies the above range, it indicates that there are some closed pore structures in the porous carbon material. And when the porous carbon material has a lattice structure, it can provide lithium ion insertion sites and diffusion paths, enabling lithium ions to diffuse into the closed pore structures through the lattice structure and perform controllable lithium insertion in the closed pore structures by forming lithium clusters, thereby improving the lithium storage capacity. After the two cooperate, the reversible lithium storage capacity of the porous carbon material can be improved, enabling the porous carbon material to provide a certain charging specific capacity within the aforementioned voltage range, and the voltage-capacity differential dQ / dV curve has a corresponding first characteristic peak. Among them, the microcrystalline structure can also increase the diffusion rate of lithium ions, and thus can improve the rate performance of the secondary battery. When the closed pore structure is formed, it will preferentially close the pores with small pore diameters, so as to ensure that more nano-silicon is deposited inside the pores with relatively large pore diameters, thereby better providing a buffer for the expansion of nano-silicon, reducing the expansion and side reactions of the negative electrode material, and improving the cycle performance of the secondary battery.

[0032] In some embodiments, the conductivity of the porous carbon material is from 5 S / cm to 20 S / cm, such as 5 S / cm, 6 S / cm, 7 S / cm, 8 S / cm, 9 S / cm, 10 S / cm, 11 S / cm, 12 S / cm, 13 S / cm, 14 S / cm, 15 S / cm, 16 S / cm, 17 S / cm, 18 S / cm, 19 S / cm, 20 S / cm or a value within the range composed of any two of them. The microcrystalline structure in the porous carbon material can increase the diffusion rate of lithium ions and increase the conductivity to the above range. Cooperating with the closed pore structure, it can further improve the initial Coulomb efficiency, rate performance and cycle performance of the secondary battery.

[0033] In some embodiments, the specific surface area of the porous carbon material is 1752 m 2 / g to 2035 m 2 / g. For example, it can be 1752 m 2 / g, 1770 m 2 / g, 1900 m 2 / g, 1990 m 2 / g, 2035 m 2 / g or a value within the range composed of any two of them. When the porous carbon material meets the above conditions and cooperates with its closed pore and microcrystalline structures, it can further improve the initial Coulomb efficiency, rate performance and cycle performance of the secondary battery.

[0034] In some embodiments, the pore volume of the porous carbon material is 0.68 cm 3 / g to 0.91 cm 3 / g. For example, it can be 0.68 cm 3 / g, 0.73 cm 3 / g, 0.79 cm 3 / g, 0.81 cm 3 / g, 0.84 cm 3 / g, 0.88 cm 3 / g, 0.91 cm 3 / g, or a value within the range formed by any two of them. The porous carbon material satisfies the above conditions and, in combination with its closed pore and microcrystalline structure, can further improve the initial Coulomb efficiency, rate performance, and cycling performance of the secondary battery.

[0035] In some embodiments, the porous carbon material includes a first type of pores and a second type of pores. The pore diameter of the first type of pores is P1 nm, and the pore diameter of the second type of pores is P2 nm, where 0 < P1 ≤ 2 nm and 2 < P1 ≤ 10 nm; based on the sum of the pore volume of the first type of pores and the pore volume of the second type of pores, the proportion of the pore volume of the first type of pores is 92.4% to 98.2%. Exemplarily, based on the sum of the pore volume of the first type of pores and the pore volume of the second type of pores, the proportion of the pore volume of the first type of pores is 92.4%, 93.5%, 93.6%, 94.7%, 95.0%, 96.0%, 96.9%, 97.2%, 97.9%, 98.1%, 98.2%, or a value within the range formed by any two of them. When the porous carbon material has the above pore size distribution characteristics, it can provide more diffusion channels for lithium ions, and in combination with the microcrystalline structure, it can further improve the diffusion ability of lithium ions, and can further improve the initial Coulomb efficiency and rate performance of the secondary battery; the above pore size distribution in combination with the closed pore structure can jointly buffer the volume change of silicon during charge and discharge, improve the stability of the battery structure, so that the secondary battery exhibits more excellent cycling performance.

[0036] This application also provides a preparation method of the aforementioned porous carbon material, including the following steps:

[0037] Step S1: Dispersing a catalytic metal single substance to obtain a dispersion system; carrying out a polymerization reaction of the polymerization monomer in the dispersion system to obtain a porous carbon material precursor; the catalytic metal includes at least one of iron, cobalt, nickel, vanadium, chromium, manganese, zinc, tin, calcium, magnesium, and aluminum; the porous carbon material precursor contains a catalytic metal single substance, and the mass proportion of the catalytic metal single substance in the porous carbon material precursor is 0.004% to 0.500%; the polymerization monomer includes a phenolic compound and an aldehyde compound;

[0038] Step S2: Carbonizing the porous carbon material precursor at T1 °C for t1 hours to obtain a carbonized material, where 750 °C ≤ T1 ≤ 1200 °C and 1 ≤ t1 ≤ 10;

[0039] Step S3: Mix the carbonized material with the activator, and then carry out activation treatment at T2 °C for t2 hours to obtain an activated material, where 700 °C ≤ T2 ≤ 1100 °C and 1 ≤ t2 ≤ 6;

[0040] Step S4: Wash the activated material and then dry it; roast the dried activated material at T3 °C in an atmosphere of a mixed gas of alkane and inert gas for t3 hours to obtain a porous carbon material; 600 °C ≤ T3 ≤ 1400 °C, 2 ≤ t3 ≤ 8, and the volume ratio of alkane to inert gas is 1:(5 - 10).

[0041] In this application, a catalytic metal is added to the porous carbon material precursor. Combining with the high-temperature conditions of subsequent carbonization treatment and activation treatment, it can catalyze the formation of a lattice structure inside the porous carbon material, improve the lithium storage capacity and the diffusion rate of lithium ions; after the activation is completed, the alkane gas and roasting treatment can make the porous carbon material form a closed pore structure, further improving the reversible lithium storage capacity of the porous carbon material, as well as enhancing the buffering effect on the expansion of nanosilicon, and improving the first Coulomb efficiency, cycle performance and rate performance of the secondary battery.

[0042] In this application, the dispersion system is used to provide a solvent system for the polymerization reaction, and the catalytic metal is added to the porous carbon material precursor during the polymerization reaction. This application does not make special limitations on the dispersion system, as long as the purpose of this application can be achieved. Exemplarily, a catalyst for catalyzing the polymerization reaction of monomers, such as alkalis like sodium hydroxide and potassium hydroxide, can also be added to the dispersion system.

[0043] In some embodiments, the temperature T1 °C of the carbonization treatment satisfies: 750 °C ≤ T1 ≤ 1200 °C. For example, T1 can be selected from 750, 770, 830, 850, 950, 950, 1040, 1060, 1110, 1150, 1200 or values within the range composed of any two of them. The time of the carbonization treatment is t1 hours, 1 ≤ t1 ≤ 10. For example, t1 can be selected from 1, 2, 3, 4, 5, 6, 7, 8, 10 or values within the range composed of any two of them.

[0044] In some embodiments, the temperature of the activation treatment is T2 °C, and T2 satisfies: 700 °C ≤ T2 ≤ 1100 °C. For example, T2 can be selected from 700, 740, 770, 800, 870, 890, 950, 980, 1050, 1070, 1100 or values within the range composed of any two of them. The time of the activation treatment is t2 hours, 1 ≤ t2 ≤ 6. For example, t2 can be selected from 1, 2, 3, 4, 5, 6 or values within the range composed of any two of them.

[0045] In some embodiments, the temperature T3 °C of the calcination treatment satisfies: 600 °C ≤ T3 ≤ 1400 °C. For example, T3 can be selected from 600, 680, 730, 860, 880, 970, 1080, 1140, 1220, 1370, 1400 or values within the range composed of any two of them. The time of the calcination treatment is t3 hours, 2 ≤ t3 ≤ 8. For example, t3 can be selected from 2, 3, 4, 5, 6, 7, 8 or values within the range composed of any two of them.

[0046] In some embodiments, the washing treatment can be carried out using deionized water and / or acid solution.

[0047] The present application further provides a silicon-carbon material, which includes a porous carbon material, nano-silicon located inside the porous carbon material, and a carbon layer located on the surface of the porous carbon material; the porous carbon material includes the aforementioned porous carbon material or the porous carbon material prepared by the aforementioned preparation method. Based on the porous carbon material therein, the silicon-carbon material of the present application can have a higher lithium storage capacity and first Coulombic efficiency, and can improve the cycle performance and rate performance of the secondary battery. Among them, the carbon layer can cover a part of the surface of the porous carbon material or can be located on the entire surface of the porous carbon material. When the proportion of the surface of the porous carbon material covered by the carbon layer increases, the cycle performance and rate performance of the secondary battery can be further improved.

[0048] In the present application, the silicon-carbon material can be prepared by subjecting the porous carbon material to silane chemical vapor deposition. For example, a method including the following steps can be used: The porous carbon material is heated to 400 °C to 600 °C in an inert atmosphere, and then silane gas is introduced for chemical vapor deposition and kept warm for 2 h to 8 h. After that, the temperature is controlled at 450 °C to 650 °C, and acetylene gas is switched, and the reaction is carried out for 1 h to 4 h to obtain the silicon-carbon material.

[0049] The present application further provides a secondary battery, which includes a positive electrode, a negative electrode, and an electrolyte. In some embodiments, the negative electrode includes a negative electrode current collector and a negative electrode material layer located on at least part of the surface of the negative electrode current collector, and the negative electrode material layer includes the aforementioned silicon-carbon material.

[0050] Secondary battery

[0051] The secondary battery of the present application is not particularly limited. According to the type of electron transport substance, it is divided into various categories. For example, when the electron transport substance is lithium (Li, including ions), the secondary battery is a lithium-ion battery; when the electron transport substance is sodium (Na, including ions), the secondary battery is a sodium-ion battery. Hereinafter, the present application will be described by taking the secondary battery as an example in combination with the embodiments of the present application. It should be noted that in the specific embodiments of the present application, the secondary battery is used as an example of the secondary battery to explain the present application, but the secondary battery of the present application is not limited to the secondary battery.

[0052] According to an embodiment of the present application, a secondary battery may include an electrode assembly and an electrolyte. The electrode assembly may include a packaging material and an electrode component disposed inside the packaging material, and the electrolyte may be filled in the internal space formed by the packaging material. The packaging material may protect the electrode component from external impacts and prevent the electrolyte from leaking to the outside. According to the shape of the packaging material, the electrode assembly may be divided into a prismatic shape, a cylindrical shape, or a soft-pack type.

[0053] The electrode assembly includes a positive electrode, a negative electrode, and a separator, as well as other components known in the art in secondary batteries, and the present application does not limit the above other components. Among them, the separator may be disposed between the positive electrode and the negative electrode.

[0054] The present application does not particularly limit the manufacturing method of the secondary battery. For example, it may include the following steps: stacking the positive electrode, the separator, and the negative electrode in sequence, and performing operations such as winding and folding as needed to obtain the electrode assembly, placing the electrode assembly into the packaging material, injecting the electrolyte into the packaging material and sealing it to obtain the secondary battery.

[0055] Positive electrode

[0056] In the present application, there is no particular limitation on the positive electrode as long as the object of the present application can be achieved. The positive electrode includes a positive electrode current collector and a positive electrode material layer disposed on at least one surface of the positive electrode current collector; the above "positive electrode material layer disposed on at least one surface of the positive electrode current collector" means that the positive electrode material layer may be located on one surface of the positive electrode current collector along its own thickness direction, or may be located on two surfaces of the positive electrode current collector along its own thickness direction. It should be noted that the "surface" here may be the entire area of the surface of the positive electrode current collector, or may be a partial area of the surface of the positive electrode current collector. The present application has no particular limitation as long as the object of the present application can be achieved.

[0057] The present application has no particular limitation on the type, size, and shape of the positive electrode current collector as long as it does not cause chemical changes in the electrode assembly and has conductivity. For example, the positive electrode current collector may use substances such as stainless steel, aluminum, nickel, titanium, calcined carbon, or substances obtained by surface treatment of the surface of aluminum or stainless steel with carbon, nickel, titanium, or silver, etc. In the present application, the positive electrode current collector may also contain non-metallic elements. For example, the non-metallic elements include at least one of fluorine, phosphorus, boron, chlorine, silicon, and sulfur.

[0058] The positive electrode current collector may have an appropriate thickness as needed. Although there is no particular limitation, the positive electrode current collector may have a thickness in the range of 1 μm to 500 μm, or may have a thickness in the range of 1 μm to 300 μm, or may have a thickness in the range of 1 μm to 100 μm, or may have a thickness in the range of 1 μm to 50 μm, or may have a thickness in the range of 1 μm to 20 μm.

[0059] Unless otherwise specifically stated, the terms thickness (or height), width, and length used in this application refer to average values and can be measured by measuring instruments capable of separately measuring the thickness (or height), width, and length and according to methods in the art.

[0060] The positive electrode current collector may form fine irregularities on its surface, thereby further enhancing the adhesion force with the positive electrode material layer. For example, the form of the positive electrode current collector may be one or more selected from a film, a sheet, a foil, a net, a porous body, a foam, and a non-woven fabric.

[0061] In this application, the positive electrode material layer includes a positive electrode active material. There is no particular limitation on the type of the positive electrode active material in this application as long as the object of this application can be achieved. For example, the positive electrode active material may include lithium nickel cobalt manganese oxide (LiNi 0.90 Co 0.05 Mn 0.05 O2 (NCM 955 ), NCM 811 , NCM 622 , NCM 523 , NCM 111 ), lithium nickel cobalt aluminate, lithium iron phosphate, lithium vanadium phosphate, lithium cobalt phosphate, lithium manganese phosphate, lithium manganese iron phosphate, lithium-rich manganese-based material, lithium cobalt oxide (LiCoO2), lithium iron silicate, lithium vanadium silicate, lithium cobalt silicate, lithium manganese silicate, spinel-type manganese oxide, spinel-type nickel manganese oxide, and lithium titanate. In this application, the positive electrode active material may further include a non-metallic element. For example, the non-metallic element includes at least one of fluorine, phosphorus, boron, chlorine, silicon, or sulfur. In this application, there is no particular limitation on the thickness of the positive electrode current collector and the positive electrode material layer as long as the object of this application can be achieved.

[0062] In some embodiments, the positive electrode material layer may further include a positive electrode binder. There is no particular limitation on the type of the positive electrode binder in this application as long as the object of this application can be achieved. For example, the positive electrode binder may include, but is not limited to, at least one of polyvinylidene fluoride, polytetrafluoroethylene, polyolefins, sodium carboxymethyl cellulose, lithium carboxymethyl cellulose, modified polyvinylidene fluoride, modified styrene-butadiene rubber (SBR), polyacrylate ester, polyvinyl alcohol, polyacrylic acid, or polyurethane. In some embodiments, the polyolefin binder includes at least one of polyethylene or polypropylene.

[0063] In some embodiments, the positive electrode material layer may further include a conductive agent. There is no particular limitation on the type of the conductive agent in the positive electrode material layer in the present application, as long as the object of the present application can be achieved. In some exemplary embodiments, the conductive agent includes carbon-based materials, such as natural graphite or artificial graphite, carbon black, acetylene black, Ketjen black, channel black, furnace black, lamp black, thermal cracking carbon black, or carbon fiber; conductive polymers, such as polyphenylene derivatives; conductive metal oxides, such as zinc oxide, titanium oxide, etc.; conductive whiskers, such as potassium titanate, etc.; or a mixture formed by any combination of these substances.

[0064] In the present application, the positive electrode material layer can be formed by coating the positive electrode slurry on at least one surface of the positive electrode current collector and drying, and calendering can be performed after drying as needed. The positive electrode slurry contains the above-mentioned positive electrode active material, positive electrode binder, and conductive agent. In addition, the positive electrode slurry may further contain a solvent. There is no particular limitation on the type of the solvent in the present application, as long as the object of the present application can be achieved. For example, N-methyl-2-pyrrolidone can be used as the solvent.

[0065] There is no particular limitation on the mass ratio of the positive electrode active material, conductive agent, and positive electrode binder in the positive electrode material layer in the present application. Those skilled in the art can select according to actual needs, as long as the object of the present application can be achieved, and these mass ratios can apply known mass ratios.

[0066] Negative electrode

[0067] There is no particular limitation on the negative electrode in the present application, as long as the object of the present application can be achieved. For example, the negative electrode includes a negative electrode current collector and a negative electrode material layer provided on at least one surface of the negative electrode current collector. In the present application, the negative electrode material layer can be provided on one surface in the thickness direction of the negative electrode current collector, or can be provided on two surfaces in the thickness direction of the negative electrode current collector. It should be noted that the "surface" here can be the entire area of the negative electrode current collector or a partial area of the negative electrode current collector. There is no particular limitation in the present application, as long as the object of the present application can be achieved.

[0068] There is no particular limitation on the type, size, and shape of the negative electrode current collector in the present application, as long as it does not cause chemical changes in the battery cell and has conductivity. For example, the negative electrode current collector can use substances such as stainless steel, copper, nickel, titanium, calcined carbon, or substances obtained by surface treatment of the surface of copper or stainless steel with carbon, nickel, titanium, or silver, etc.

[0069] The negative electrode current collector may have an appropriate thickness as needed. Although not particularly limited, the negative electrode current collector may have a thickness in the range of 1 μm to 500 μm, or may have a thickness in the range of 1 μm to 300 μm, or may have a thickness in the range of 1 μm to 100 μm, or may have a thickness in the range of 1 μm to 50 μm, or may have a thickness in the range of 1 μm to 20 μm, or may have a thickness in the range of 5 μm to 10 μm.

[0070] The negative electrode current collector may form fine unevenness on the surface, thereby further enhancing the adhesion to the negative electrode material layer. For example, the form of the negative electrode current collector may be one or more selected from a film, a sheet, a foil, a net, a porous body, a foam, and a non-woven fabric.

[0071] The negative electrode material layer of the present application includes a negative electrode active material, and the negative electrode active material includes the above-mentioned silicon-carbon material. Based on the mass of the negative electrode material layer, the mass ratio of potassium element is C ppm, 1 ≤ C ≤ 100. For example, C may be 1, 8, 12, 24, 41, 49, 66, 77, 86, 95, 100 or a value within the range composed of any two of them. When the mass ratio of potassium element in the negative electrode material layer is adjusted to satisfy the above range, the ion conductivity of the secondary battery can be further improved and the swelling performance can be suppressed.

[0072] In some embodiments, the negative electrode active material may further include other materials, such as, but not limited to, carbon materials such as graphite (artificial graphite, natural graphite or graphitized carbon fiber) or amorphous carbon; metals that can be alloyed with lithium such as Si, Al, Sn, Pb, Zn, Bi, In, Mg, Ga, Cd, Si alloy, Sn alloy or Al alloy, or alloys formed by them and lithium; SiO β (0 < β ≤ 2), metal oxides that can be doped or de-doped with lithium such as SnO, SnO2, vanadium oxides, lithium vanadium oxides, or alloys formed by them and lithium; or composites containing the metal and carbon materials such as Si-C composites or Sn-C composites; or lithium titanate with a spinel structure, lithiated TiO2-Li4Ti5O 12 , and any one or a mixture of two or more of them can be used. Specifically, carbon materials such as low-crystalline carbon and high-crystalline carbon can be used. Representative low-crystalline carbon is soft carbon and hard carbon. Examples of high-crystalline carbon can be amorphous, plate-shaped, sheet-shaped, spherical or fibrous natural graphite or artificial graphite, primary graphite, pyrolytic carbon, mesophase pitch-based carbon fiber, carbon microspheres (mesophase carbon microspheres), mesophase pitch, and high-temperature calcined carbon such as petroleum and coal-based coke (coke derived from petroleum or coal tar pitch), etc.

[0073] The negative electrode material layer in the present application further includes a negative electrode binder. There is no particular limitation on the type of the negative electrode binder in the present application, as long as the object of the present application can be achieved. For example, the negative electrode binder may include, but is not limited to, at least one selected from polyvinylidene fluoride (PVDF), polyvinyl alcohol, styrene-butadiene rubber (SBR), polyethylene oxide, carboxymethyl cellulose (CMC), hydroxypropyl cellulose, cellulose acetate, diacetyl cellulose, cellulose acetate butyrate, cellulose acetate propionate, cyanoethyl pullulan, cyanoethyl polyvinyl alcohol, cyanoethyl cellulose, cyanoethyl sucrose, pullulan, polymethyl methacrylate, polybutyl acrylate, polyacrylonitrile, polyvinyl pyrrolidone, polyvinyl acetate, ethylene-vinyl acetate copolymer, polyarylate, polyvinyl chloride, carboxylated polyvinyl chloride, polyvinyl fluoride, polymers containing ethylene oxide, polyurethane, polytetrafluoroethylene, polyethylene, polypropylene, polyacrylic acid, styrene-butadiene rubber, acrylated styrene-butadiene rubber, epoxy resin or nylon.

[0074] There is no particular limitation on the type of the conductive agent in the negative electrode material layer in the present application, as long as the object of the present application can be achieved. In some exemplary embodiments, the conductive agent includes carbon-based materials, such as graphite like natural graphite or artificial graphite, carbon black such as acetylene black, Ketjen black, channel black, furnace black, lamp black, thermal cracking carbon black, or carbon fiber; metal-based materials, such as metal powders or metal fibers of copper, nickel, aluminum, silver, etc.; conductive polymers, such as polyphenylene derivatives; conductive metal oxides, such as zinc oxide, titanium oxide, etc.; conductive whiskers, such as potassium titanate, etc.; or mixtures formed by any combination of these substances.

[0075] There is no particular limitation on the mass ratio of the negative electrode active material, the negative electrode conductive agent, and the negative electrode binder in the negative electrode material layer in the present application. Those skilled in the art can select according to actual needs as long as the object of the present application can be achieved, and these mass ratios can adopt well-known mass ratios.

[0076] In the present application, the negative electrode material layer can be formed by coating the negative electrode slurry on at least one surface of the negative electrode current collector and drying, and calendering can be performed after drying as needed. The negative electrode slurry contains the above-mentioned negative electrode active material and negative electrode binder, and can further contain a conductive agent as needed. In addition, the negative electrode slurry can also contain a solvent. There is no particular limitation on the type of the solvent in the present application, as long as the object of the present application can be achieved. For example, deionized water can be used as the solvent.

[0077] Separator

[0078] The separator of the present application is a film used to prevent short circuit between the positive electrode and the negative electrode while allowing the passage of electron transport substances. There is no particular limitation on the separator in the present application, as long as the object of the present application can be achieved. For example, the material of the separator may include, but is not limited to, at least one of polyolefins (PO) mainly composed of polyethylene (PE) and polypropylene (PP), polyesters (such as polyethylene terephthalate (PET) film), cellulose, polyimide (PI), polyamide (PA), spandex, and aramid; the type of the separator may include at least one of woven film, non-woven film, microporous film, composite film, rolled film, and spun film.

[0079] According to some embodiments of the present application, the separator may include a substrate layer and a surface treatment layer. The substrate layer may be a non-woven fabric, a film, or a composite film having a porous structure, and the material of the substrate layer may include at least one of polyethylene, polypropylene, polyethylene terephthalate, and polyimide. Optionally, a polypropylene porous film, a polyethylene porous film, a polypropylene non-woven fabric, a polyethylene non-woven fabric, or a polypropylene-polyethylene-polypropylene porous composite film may be used.

[0080] Optionally, a surface treatment layer is provided on at least one surface of the substrate layer. The surface treatment layer may be a polymer layer, an inorganic layer, or a layer formed by mixing a polymer and an inorganic substance. For example, the inorganic layer includes inorganic particles and a binder. There is no particular limitation on the inorganic particles in the present application. For example, it may include at least one of alumina, silica, magnesia, titania, hafnium dioxide, tin dioxide, cerium dioxide, nickel oxide, zinc oxide, calcium oxide, zirconium oxide, yttrium oxide, silicon carbide, boehmite, aluminum hydroxide, magnesium hydroxide, calcium hydroxide, and barium sulfate. There is no particular limitation on the binder in the present application. For example, it may be at least one of the above-mentioned positive electrode binders or negative electrode binders. The polymer layer contains a polymer. There is no particular limitation on the polymer in the present application. For example, the polymer includes at least one of polyamide, polyacrylonitrile, acrylate polymer, polyacrylic acid, polyacrylate, polyvinylpyrrolidone, polyethylene ether, polyvinylidene fluoride, and poly(vinylidene fluoride-hexafluoropropylene). In the present application, the thickness of the separator is not particularly limited as long as the object of the present application can be achieved. For example, the thickness of the separator may be 5 μm to 500 μm.

[0081] Electrolyte

[0082] In the present application, the electrolyte refers to a medium that causes the movement of electron transport substances to smoothly carry out the electrochemical reaction between the positive electrode and the negative electrode. The electrolyte may use commonly used organic liquid electrolytes, inorganic liquid electrolytes, gel-type polymer electrolytes, molten-type inorganic electrolytes, etc., but is not limited thereto. A solid electrolyte such as a gel-type polymer electrolyte may also be used to replace the electrolyte. A battery using a solid electrolyte is usually called a solid-state battery or an all-solid-state battery. The liquid electrolyte (electrolyte) usually contains a non-aqueous solvent and a lithium salt.

[0083] In some embodiments, the electrolyte includes ethylene carbonate and fluoroethylene carbonate; based on the mass of the electrolyte, the mass percentage of ethylene carbonate is C1%, and the mass percentage of fluoroethylene carbonate is C2%, where 0.5 ≤ C2 / C1 ≤ 2; preferably, 1 ≤ C2 / C1 ≤ 1.5. Exemplarily, the value of C2 / C1 can be 0.5, 0.8, 0.9, 1.1, 1.2, 1.4, 1.5, 1.8, 1.9, 2, or a value within the range formed by any two of them. Adjusting the mass percentages of ethylene carbonate and fluoroethylene carbonate in the electrolyte to meet the above range can improve the film-forming effect of the electrolyte and its wettability to the anode material, thereby promoting the formation of a stable solid electrolyte interface film (SEI film) on the surface of the above silicon-carbon material or porous carbon material, reducing side reactions of the electrolyte, and at the same time reducing the diffusion resistance of lithium ions, further improving the cycle performance and rate performance of the secondary battery.

[0084] In some embodiments, 5 ≤ C1 ≤ 12. For example, the value of C1 can be 5, 6, 7, 8, 9, 10, 11, 12, or a value within the range formed by any two of them. In some embodiments, 2.5 ≤ C2 ≤ 20. For example, the value of C2 can be 2.5, 3, 6, 7, 9, 12, 14, 16, 17, 19, 20, or a value within the range formed by any two of them. Meeting the above conditions further improves the cycle performance and rate performance of the secondary battery.

[0085] In some embodiments, the electrolyte includes a first lithium salt, and the first lithium salt is selected from at least one of lithium bis(trifluoromethanesulfonyl)imide, lithium bis(fluorosulfonyl)imide, and lithium trifluoromethanesulfonate; the electrolyte includes a second lithium salt, and the second lithium salt is selected from at least one of lithium tetrafluoroborate and lithium difluorophosphate; based on the mass of the electrolyte, the mass percentage of the first lithium salt is S1%, and the mass percentage of the second lithium salt is S2%, where 0.2 ≤ S2 / S1 ≤ 2; preferably, 0.4 ≤ S2 / S1 ≤ 1.6. Exemplarily, the value of S2 / S1 can be 0.2, 0.4, 0.5, 0.7, 0.9, 1.1, 1.4, 1.5, 1.7, 1.9, 2, or a value within the range formed by any two of them. Adjusting the electrolyte to include the above first lithium salt and second lithium salt can improve the compactness and stability of the SEI film and increase the ionic conductivity of the electrolyte. Cooperating with the above anode system can further improve the cycle performance and rate performance of the secondary battery.

[0086] In some embodiments, 0.5 ≤ S1 ≤ 5. For example, the value of S1 can be 0.5, 0.6, 1.1, 1.6, 2.2, 2.7, 3.1, 3.6, 4.0, 4.9, 5, or a value within the range composed of any two of them. In some embodiments, 0.2 ≤ S2 ≤ 1.2. For example, the value of S2 can be 0.2, 0.3, 0.4, 0.5, 0.6, 0.7, 0.8, 0.9, 1.0, 1.1, 1.2, or a value within the range composed of any two of them. Meeting the above conditions further improves the cycle performance and rate performance of the secondary battery.

[0087] According to some embodiments of the present application, the lithium salt may include but is not limited to: lithium hexafluorophosphate (LiPF6), lithium tetrafluoroborate (LiBF4), lithium difluorophosphate (LiPO2F2), lithium bis(oxalato)borate {LiB(C2O4)2, LiBOB}, lithium difluoro(oxalato)borate {LiBF2(C2O4), LiDFOB}, LiNO3, LiClO4, LiB(C6H5)4, LiCH3SO3, LiCF3SO3, LiC(SO2CF3)3, Li2SiF6, or at least one of lithium difluoroborate. The present application does not limit the content of the lithium salt in the electrolyte as long as the object of the present application can be achieved.

[0088] The present application has no particular limitation on the non-aqueous solvent. For example, the non-aqueous solvent may include, but is not limited to, at least one of carbonate compounds, carboxylate compounds, ether compounds or other organic solvents. The above-mentioned carbonate compounds may include, but are not limited to, at least one of linear carbonate compounds, cyclic carbonate compounds or fluorinated carbonate compounds. The above-mentioned linear carbonate compounds may include, but are not limited to, at least one of dimethyl carbonate (DMC), diethyl carbonate (DEC), dipropyl carbonate, methylpropyl carbonate, ethylpropyl carbonate or ethylmethyl carbonate (EMC). The above-mentioned cyclic carbonates may include, but are not limited to, at least one of propylene carbonate (PC), butylene carbonate or ethylene ethylene carbonate. The above-mentioned fluorinated carbonate compounds may include, but are not limited to, at least one of 1,2-difluoroethylene carbonate, 1,1-difluoroethylene carbonate, 1,1,2-trifluoroethylene carbonate, 1,1,2,2-tetrafluoroethylene carbonate, 1-fluoro-2-methylethylene carbonate, 1-fluoro-1-methylethylene carbonate, 1,2-difluoro-1-methylethylene carbonate, 1,1,2-trifluoro-2-methylethylene carbonate or trifluoromethyl ethylene carbonate. The above-mentioned carboxylate compounds may include, but are not limited to, at least one of methyl formate, methyl acetate, ethyl acetate, n-propyl acetate, tert-butyl acetate, methyl propionate, ethyl propionate, propyl propionate, γ-butyrolactone, decanolide, valerolactone or caprolactone. The above-mentioned ether compounds may include, but are not limited to, at least one of 1,3-dioxolane (DOL), ethylene glycol dimethyl ether (1,2-dimethoxyethane, DME), dibutyl ether, tetraethylene glycol dimethyl ether, diethylene glycol dimethyl ether, 1,2-diethoxyethane, 1-ethoxy-1-methoxyethane, 2-methyltetrahydrofuran or tetrahydrofuran.

[0089] Electronic device

[0090] The present application provides an electronic device including the above secondary battery. The electronic device of the present application is not particularly limited and may be any electronic device known in the prior art. For example, the electronic device may include, but is not limited to, laptop computers, pen-input computers, mobile computers, e-book players, mobile phones, portable fax machines, portable copiers, portable printers, head-mounted stereo headphones, video recorders, liquid crystal televisions, hand-held cleaners, portable CD players, minidiscs, transceivers, electronic notebooks, calculators, memory cards, portable recorders, radios, backup power supplies, motors, automobiles, motorcycles, motorized bicycles, bicycles, lighting fixtures, toys, game consoles, clocks, power tools, flashlights, cameras, large household batteries and lithium ion capacitors.

[0091] Measurement method

[0092] The physical properties mentioned in this application can be measured by the following methods, and the physical properties in the following examples and comparative examples are measured by the following methods.

[0093] Charge-discharge cycle curve and voltage-capacity differential dQ / dV curve test

[0094] Mix the porous carbon material (96 wt%) with conductive agent carbon black (1.5 wt%), binder polymethyl acrylate (1.5 wt%), and thickener sodium carboxymethyl cellulose (1 wt%), and then add water and stir evenly to obtain a slurry. Then coat the slurry on a copper foil with a coating thickness of 50 μm, and then dry it to obtain a pole piece. After that, using metallic lithium as the counter electrode, stack the pole piece (cut into a diameter of 18 mm), separator (12-μm-thick polyethylene microporous membrane), and a lithium piece with a diameter of 18 mm and a thickness of 0.6 mm in sequence, add the electrolyte of Example 1-1, and encapsulate it in a button-type stainless steel shell to obtain a button cell.

[0095] Then discharge the button cell at a constant current of 0.1C to 0.005V, then let it stand for 5 min, and then discharge it at a constant current of 0.05C to 0.005V; after standing for 5 min, discharge it at a constant current of 0.02C to 0.005V, and after standing for 5 min, discharge it at a constant current of 0.01C to 0.005V; after standing for 5 min, charge it at a constant current of 0.05C to 2V; record the charging specific capacity of the porous carbon material at 0.15V and 0.8V during the charging process. Then process the data obtained from the above charge-discharge cycles to obtain the voltage-capacity differential dQ / dV curve of the porous carbon material.

[0096] Figure 1 It is the charge-discharge cycle curve graph of the porous carbon materials provided by Example 1-1 and Comparative Example 1-1 of this application; Figure 2 It is the voltage-capacity differential dQ / dV curve graph of the porous carbon materials provided by Example 1-1 and Comparative Example 1-1 of this application.

[0097] Replace the above-mentioned porous carbon material with a silicon-carbon material, perform the test according to the above charge-discharge process, and then calculate the first Coulomb efficiency of the silicon-carbon material = charging specific capacity at 0.8V / total discharge capacity.

[0098] True density test

[0099] Weigh the porous carbon material and place it in a true density meter. Introduce helium gas according to the procedure, detect the gas pressures in the expansion chamber and the sample chamber, calculate the true volume v of the sample according to Boyle's law PV = nRT, and calculate the true density of the porous carbon material according to ρ = m / v.

[0100] Specific surface area, pore volume, and pore size distribution test

[0101] The porous carbon material was tested using a physical adsorption instrument (model: ipore 620). The process included: taking 0.15 g of the porous carbon material as a sample and placing it in a sample tube. First, degas the sample at 200 °C for 6 h, and then test the adsorption amount of argon by the sample under different pressures to draw the isothermal adsorption curve of the sample. Then, use BET fitting to calculate the specific surface area of the sample, and use non-local density functional theory (NLDFT) fitting to calculate the pore volume and pore size distribution of the sample, and further calculate the pore volume ratio of type I pores and type II pores based on the pore volume.

[0102] Performance test

[0103] Rate performance test of lithium-ion full battery

[0104] Take the lithium-ion full battery of the example / control to be tested, let it stand for 5 min at a test temperature of 25 °C, then charge the lithium-ion full battery at a constant current of 0.7C to 4.45V, and then charge it at a constant voltage of 4.45V to 0.05C; let it stand for 5 min, and then discharge it at a constant current of 0.2C to 3.0V, and record the 0.2C discharge capacity; then let it stand for 5 min, repeat the above charging process, and then discharge it at a constant current of 2C, and record the 2C discharge capacity. Rate capacity retention = 2C discharge capacity / 0.2C discharge capacity × 100%.

[0105] Cycle performance test of lithium-ion full battery

[0106] At a test temperature of 25 °C, let the lithium-ion full battery to be tested stand for 5 min, and record the initial thickness MMC0 of the lithium-ion full battery. Charge the lithium-ion full battery at a constant current of 3.4C to 4.25V, then charge it at 2C to 4.4V, then charge it at 1C to 4.50V, and then charge it at a constant voltage of 4.50V to 0.05C; let it stand for 5 min, and then discharge it at a constant current of 0.5C to 3.0V, let it stand for 5 min, and record the discharge capacity C1 of the lithium-ion full battery. After 400 cycles of the above 3.4C step charge / 0.5C discharge charge-discharge cycle process, record the thickness MMC1 and discharge capacity C2 of the lithium-ion full battery.

[0107] Cycle capacity retention (%) = C2 / C1 × 100%.

[0108] Cycle thickness expansion rate (%) = (MMC1 - MMC0) / MMC0 × 100%.

[0109] Next, taking the lithium-ion battery as an example, the solution of the present application will be described in combination with the following specific examples. Unless otherwise specified, the raw materials used in the following examples are all from ordinary commercially available products, and the devices or equipment used are all purchased from conventional market sales channels.

[0110] Example 1-1

[0111] Preparation of porous carbon materials and silicon-carbon materials:

[0112] Step S1, dispersing nickel in water, then sequentially adding phenol, sodium hydroxide and formaldehyde thereto, performing polymerization reaction, and obtaining a phenolic resin material as a porous carbon material precursor, wherein the molar ratio of phenol, formaldehyde and sodium hydroxide is 1:2.1:0.1. The phenolic resin material contains a catalytic metal nickel, and the mass of the nickel accounts for 0.2% based on the mass of the phenolic resin material.

[0113] Step S2: Carbonizing the phenolic resin material containing 0.2 wt % nickel at 900° C. in a nitrogen atmosphere for 4 hours to obtain a carbonized material.

[0114] Step S3, then the carbonized material and the activator potassium hydroxide (KOH) are uniformly mixed in a mass ratio of 1:2.5, and then activation treatment is performed at 950° C. in a nitrogen atmosphere for 2 hours to obtain an activated material.

[0115] Step S4, washing the activated material with deionized water, then adding hydrochloric acid to neutralize the excess alkali, then washing the impurities with deionized water, and then drying the water at 150°C; calcining the dried activated material at 900°C in a mixed gas atmosphere of methane and nitrogen for 4 hours to obtain a porous carbon material. The volume ratio of methane to nitrogen is 1:10.

[0116] Step S5, placing the porous carbon material in a reactor, introducing silane gas at 440°C, reacting for 6 hours, then raising the temperature to 500°C, switching to acetylene gas, reacting for 2 hours, and obtaining a silicon-carbon material.

[0117] Preparation of lithium-ion full battery:

[0118] Preparation of negative electrode:

[0119] Silicon-carbon material and artificial graphite are mixed in a mass ratio of 1:5 to obtain negative electrode material. The negative electrode material (96wt%), conductive agent carbon black (1.5wt%), binder polymethyl acrylate (1.5wt%), and thickener sodium carboxymethyl cellulose (1wt%) are mixed, and then deionized water is added and stirred evenly to prepare a negative electrode slurry. The negative electrode slurry is evenly coated on one surface of the copper foil, and after drying, the above steps are repeated on the other surface of the copper foil to obtain a negative electrode sheet coated with a negative electrode material layer on both sides. The coated copper foil is dried, pressurized, and cut into a specified size, and the pole ears are welded to make a negative electrode.

[0120] Preparation of positive electrode:

[0121] Lithium cobalt oxide (97 wt%), conductive agent carbon black (1.5 wt%), and binder polyvinylidene fluoride (1.5 wt%) are mixed in N-methylpyrrolidone to prepare the positive electrode slurry. The positive electrode slurry is uniformly coated on one surface of the aluminum foil, and after drying, the coating step is repeated on the other surface of the aluminum foil, thus obtaining a positive electrode tab with a positive electrode material layer coated on both sides. The coated aluminum foil is dried, pressure-treated, and then cut into a specified size, and the tab is welded to fabricate the positive electrode.

[0122] Preparation of the separator: A 12-μm-thick polyethylene microporous membrane is selected as the separator.

[0123] Preparation of the electrolyte:

[0124] In a glove box under an argon atmosphere with a water content of less than 10 ppm, dimethyl carbonate and diethyl carbonate (mass ratio 1:1) are mixed to obtain the base solvent. Then, ethylene carbonate, fluoroethylene carbonate, and lithium hexafluorophosphate are added to the above base solvent, and after mixing evenly, the electrolyte is obtained. Based on the mass of the electrolyte, the mass ratio of lithium hexafluorophosphate is 12.5%, the mass ratio of ethylene carbonate is 10%, the mass ratio of fluoroethylene carbonate is 10%, and the balance is dimethyl carbonate and diethyl carbonate (mass ratio 1:1).

[0125] Battery fabrication:

[0126] The positive electrode, separator, and negative electrode are stacked in sequence, with the separator placed between the positive electrode and the negative electrode to play an isolation role, and then wound to obtain an electrode assembly. The electrode assembly is placed in an outer packaging aluminum-plastic film, baked, and then the above electrolyte is injected. After vacuum packaging, standing, forming, shaping, capacity testing, and other processes, a lithium-ion full battery is obtained.

[0127] In Table 1, for Examples 1-2 to 1-6 and Examples 2-1 to 2-4, except that the type or content of the catalytic metal is inconsistent with that of Example 1-1, the remaining reaction conditions are the same as those of Example 1-1.

[0128] Table 1

[0129]

[0130]

[0131] In Table 2, for Comparative Example 1-1, except that no catalytic metal is added, other conditions are the same as those of Example 1-1; for Comparative Example 1-2, except that the carbonization temperature T1 is inconsistent with that of Comparative Example 1-1, other conditions are the same. For Examples 3-1 to 3-4, except that the carbonization temperature T1 is changed, the rest is the same as that of Example 1-1. For Examples 3-5 and 3-6, except that the carbonization treatment time is changed, the rest is the same as that of Example 1-1.

[0132] Table 2

[0133]

[0134] In Examples 4-1 to 4-5 in Table 3, except for adjusting the temperature T3 and time t3 of the calcination treatment, the rest are the same as those in Example 1-1.

[0135] Table 3

[0136]

[0137] The test results of the above examples and comparative examples are shown in Table 4 below.

[0138] Table 4

[0139]

[0140]

[0141] From the performance test results of Examples 1-1 to 1-6, it can be seen that as the mass ratio of the catalytic metal increases, the charge specific capacity of the coin cells assembled with the porous carbon material in the voltage range of 0.005 V to 0.15 V and the charge specific capacity in the voltage range of 0.005 V to 0.8 V (hereinafter simply referred to as the "0.15 V and 0.8 V capacities of the porous carbon material") both increase. It can be seen that by introducing a catalytic metal into the porous carbon material precursor in this application, the rearrangement of carbon can be promoted, enabling the carbon to form ordered local graphite microcrystals, which can increase the capacity of the porous carbon material. By regulating the mass ratio of the catalytic metal, the order degree of the porous carbon material and the pore-forming effect during the later activation process can be balanced; combined with the closed pore structure formed by the disordered stacking of carbon in the calcination treatment process, the capacity can be further improved.

[0142] From Examples 2-1 to 2-4 and Comparative Example 1-1, it can be seen that in this application, when transition metals such as Fe, Co, and V are selected as the catalytic metal, the 0.15 V and 0.8 V capacities of the porous carbon material can be increased.

[0143] From the test results of Examples 3-1 to 3-4, it can be seen that: when the temperature of the carbonization treatment is increased, the 0.15 V and 0.8 V capacities of the porous carbon material show a trend of first increasing and then decreasing. This is mainly because the increase in temperature is beneficial to increasing the order degree of carbon microcrystals, but too high a temperature will instead reduce the closed pores, thereby reducing the 0.15 V and 0.8 V capacities of the porous carbon material. From the comparison between Examples 3-5 to 3-6 and Example 1-1, it can be seen that adjusting the time of the carbonization treatment can affect the 0.15 V and 0.8 V capacities of the porous carbon material.

[0144] From the results of Examples 4-1 to 4-5 and Example 1-1, it can be seen that increasing the temperature of the roasting treatment can increase some closed pores, thereby increasing the 0.15V and 0.8V capacities of the porous carbon material. If the carbon temperature is too high or the reaction time is too long, the pores of the porous carbon material will fuse more severely, resulting in a decrease in the amount of closed pores, and thus a decrease in the 0.15V and 0.8V capacities of the porous carbon material.

[0145] Based on the comprehensive results in Table 1, it can be known that the present application regulates the porous carbon material to provide a charging specific capacity in the voltage ranges of 0.005V to 0.15V and 0.005V to 0.8V, and the peak height of the first characteristic peak located in the range of 0.005V to 0.15V in the voltage-capacity differential dQ / dV curve meets the above range, which can improve the lithium-ion transport ability of the porous carbon material in the above voltage ranges. This can improve the first Coulombic efficiency of the silicon-carbon material and the cycling performance and rate performance of the secondary battery. In particular, when the true density of the porous carbon material is controlled to be 2.003 g / cm 3 to 2.230 g / cm 3 and there is a lattice structure in at least part of the porous carbon material, the rate performance and cycling performance of the secondary battery can be improved, and the first Coulombic efficiency of the silicon-carbon material can be increased.

[0146] Particularly, when the specific surface area, pore volume, and the proportion of the pore volume of a certain type of pores of the porous carbon material are regulated to meet the above ranges, the rate performance and cycling performance of the secondary battery can be further improved, and the first Coulombic efficiency of the silicon-carbon material can be increased.

[0147] The differences between Examples 5-1 to 5-3 and Example 1-1 in Table 5 are as follows: the mass ratios of ethylene carbonate and fluoroethylene carbonate in the electrolyte are adjusted. The specific adjustment parameters and performance test results are shown in Table 5 below. At the same time, the content of the base solvent is adjusted adaptively, where the mass ratio of dimethyl carbonate and diethyl carbonate remains unchanged.

[0148] Table 5

[0149]

[0150] As can be seen from Table 5, when the present application regulates the mass ratio C1% of ethylene carbonate and the mass ratio C2% of fluoroethylene carbonate in the electrolyte to satisfy 0.5 ≤ C2 / C1 ≤ 2, the cycling performance and rate performance of the secondary battery can be further improved. In particular, when 1 ≤ C2 / C1 ≤ 1.5, the cycling performance and rate performance of the secondary battery can be further improved.

[0151] The differences between Examples 6-1 to 6-4 and Example 5-2 in Table 6 are as follows: adjust the mass ratios of the first lithium salt and the second lithium salt in the electrolyte. The specific adjusted parameters and performance test results are shown in Table 6 below. At the same time, adaptively adjust the content of the base solvent, wherein the mass ratio of dimethyl carbonate to diethyl carbonate remains unchanged.

[0152] Table 6

[0153]

[0154]

[0155] It can be seen from Table 6 that the mass ratio S1% of the first lithium salt and the mass ratio S2% of the second lithium salt in the regulated electrolyte satisfy: 0.2 ≤ S2 / S1 ≤ 2, which can further improve the cycling performance and rate performance of the secondary battery. In particular, when 0.4 ≤ S2 / S1 ≤ 1.6 is satisfied, the cycling performance and rate performance of the secondary battery can be further improved.

[0156] The above are only the preferred embodiments of the present application and are not intended to limit the present application. Any modifications, equivalent replacements, and improvements made within the principles of the present application shall be included within the protection scope of the present application.

Claims

1. A porous carbon material, characterized in that: The porous carbon material and lithium metal are assembled into a button battery. When the button battery is charged at a current of 0.05C in a voltage range of 0.005V to 2V, the charging specific capacity in the voltage range of 0.005V to 0.15V is 43mAh / g to 132mAh / g, and the charging specific capacity in the voltage range of 0.005V to 0.8V is 152mAh / g to 253.4mAh / g; The voltage capacity differential dQ / dV curve of the button battery has a first characteristic peak located between 0.005V and 0.15V, and the peak height of the first characteristic peak is not less than 260mAh / g / V.

2. The porous carbon material according to claim 1, characterized in that The porous carbon material satisfies at least one of the following: (1) The true density of the porous carbon material is 2.003 g / cm 3 Up to 2.230g / cm 3 ; and at least a portion of the porous carbon material has a lattice structure; (2) The peak height of the first characteristic peak is 260 mAh / g / V to 1927 mAh / g / V.

3. The porous carbon material according to claim 1, characterized in that The porous carbon material satisfies at least one of the following: (1) When the button battery is charged at a current of 0.05C in a voltage range of 0.005V to 2V, the charge specific capacity in a voltage range of 0.005V to 0.15V is 75mAh / g to 132mAh / g, and the charge specific capacity in a voltage range of 0.005V to 0.8V is 174mAh / g to 253.4mAh / g; (2) The peak height of the first characteristic peak is 760 mAh / g / V to 1927 mAh / g / V.

4. The porous carbon material according to any one of claims 1 to 3, characterized in that The specific surface area of ​​the porous carbon material is 1752 m 2 / g to 2035m 2 / g; and / or, The pore volume of the porous carbon material is 0.68 cm 3 / g to 0.91cm 3 / g.

5. The porous carbon material according to claim 4, characterized in that: The porous carbon material includes a first type of pores and a second type of pores, the pore size of the first type of pores is P1 nm, the pore size of the second type of pores is P2 nm, 0<P1≤2nm, 2<P1≤10nm; Based on the sum of the pore volume of the first type of pores and the pore volume of the second type of pores, the pore volume of the first type of pores accounts for 92.4% to 98.2%, preferably, the pore volume of the first type of pores accounts for 93.2% to 96.5%.

6. The method for preparing a porous carbon material according to any one of claims 1 to 5, characterized in that: The following steps are involved: Step S1, dispersing a catalytic metal element to obtain a dispersed system; The polymerizable monomer is subjected to a polymerization reaction in the dispersed system to obtain a porous carbon material precursor, wherein the catalytic metal element comprises at least one of iron, cobalt, nickel, vanadium, chromium, manganese, zinc, tin, calcium, magnesium, and aluminum; the mass proportion of the catalytic metal element in the porous carbon material precursor is 0.004% to 0.500%; the polymerizable monomer comprises a phenolic compound and an aldehyde compound; Step S2, carbonizing the porous carbon material precursor at T1°C for t1 hours to obtain a carbonized material, wherein 750°C≤T1≤1200°C, 1≤t1≤10; Step S3, mixing the carbonized material with an activating agent, and then performing an activation treatment at T2°C for t2 hours to obtain an activated material, wherein 700°C≤T2≤1100°C, 1≤t2≤6; Step S4, washing the activated material and then drying it; calcining the dried activated material at T3°C in a mixed gas atmosphere of alkane and inert gas for t3 hours to obtain the porous carbon material; 600°C≤T3≤1400°C, 2≤t3≤8, the volume ratio of the alkane to the inert gas is 1:(5~10).

7. A silicon-carbon material, characterized in that: The silicon-carbon material comprises a porous carbon material, nano-silicon located inside the porous carbon material, and a carbon layer located on the surface of the porous carbon material; The porous carbon material includes the porous carbon material according to any one of claims 1 to 5 or the porous carbon material prepared by the preparation method according to claim 6.

8. A secondary battery comprising a positive electrode, a negative electrode and an electrolyte, characterized in that: The negative electrode comprises a negative electrode current collector and a negative electrode material layer located on at least a portion of the surface of the negative electrode current collector, and the negative electrode material layer comprises the silicon-carbon material according to claim 7.

9. The secondary battery according to claim 8, characterized in that: The electrolyte includes ethylene carbonate and fluoroethylene carbonate; Based on the mass of the electrolyte, the mass proportion of the ethylene carbonate is C1%, the mass proportion of the fluoroethylene carbonate is C2%, 0.5≤C2 / C1≤2; preferably, 1≤C2 / C1≤1.

5.

10. The secondary battery according to claim 8, characterized in that: The electrolyte includes a first lithium salt, the first lithium salt being selected from at least one of lithium bis(trifluoromethylsulfonyl)imide, lithium bis(fluorosulfonyl)imide and lithium trifluoromethylsulfonate; The electrolyte includes a second lithium salt, wherein the second lithium salt is selected from at least one of lithium tetrafluoroborate and lithium difluorophosphate; Based on the mass of the electrolyte, the mass proportion of the first lithium salt is S1%, the mass proportion of the second lithium salt is S2%, 0.2≤S2 / S1≤2; preferably, 0.4≤S2 / S1≤1.

6.

11. An electronic device, characterized in that: A secondary battery comprising the secondary battery according to any one of claims 8 to 10.

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