CN119695121A - Silicon-carbon material and secondary battery containing the same - Google Patents
Silicon-carbon material and secondary battery containing the same Download PDFInfo
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- CN119695121A CN119695121A CN202411905431.2A CN202411905431A CN119695121A CN 119695121 A CN119695121 A CN 119695121A CN 202411905431 A CN202411905431 A CN 202411905431A CN 119695121 A CN119695121 A CN 119695121A
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Abstract
The invention relates to the technical field of battery materials, in particular to a silicon-carbon material and a secondary battery comprising the same. The silicon-carbon material provided by the invention comprises porous carbon and a silicon-based material positioned in the pores of the porous carbon, wherein the silicon content in the silicon-carbon material is 20-70 wt%, and when the relationship between the specific surface area BET 1(m2/g of the silicon-carbon material and the median particle diameter Dv50 1 (mu m) and the median particle diameter Dv50 2 (mu m) of the porous carbon is 0.8-BET 1×(Dv502/Dv501 -6.5 is satisfied, the expansion and contraction effects of a silicon negative electrode can be effectively relieved, and the silicon-carbon material has higher reversible specific capacity, so that the silicon-carbon material provided by the invention can be used as a negative electrode active material of a secondary battery.
Description
Technical Field
The invention relates to the technical field of battery materials, in particular to a silicon-carbon material and a secondary battery comprising the same.
Background
The cathode material is one of the most critical materials in the lithium ion battery technology, the currently marketed graphite cathode has reached the technical bottleneck due to low gram capacity, and the silicon cathode material has been valued by researchers due to the advantages of high gram capacity, abundant resources and the like. However, the silicon negative electrode material has a high expansion ratio and poor conductivity, which are factors that restrict its wide application.
Disclosure of Invention
In view of the above, the present invention provides a silicon-carbon material to solve the problem of short cycle life of the existing silicon-based anode material.
In a first aspect, the invention provides a silicon-carbon material, which comprises porous carbon and a silicon-based material positioned in pores of the porous carbon, wherein the silicon content in the silicon-carbon material is 20-70 wt%, and the specific surface area BET 1 of the silicon-carbon material, the median particle diameter Dv50 1 of the silicon-carbon material and the median particle diameter Dv50 2 of the porous carbon meet the following conditions:
0.8≤BET1×(Dv502/Dv501)≤6.5;
Wherein BET 1 is in m 2/g,Dv501 and Dv50 2 are in μm.
In an alternative embodiment, the silicon-carbon material provided by the invention has a silicon content of 48wt.% to 55wt.% and satisfies 1.0.ltoreq.BET 1×(Dv502/Dv501.ltoreq.3.0.
In an alternative embodiment, the present invention provides a silicon carbon material satisfying 0.3m 2/g≤BET1≤5m2/g.
In an alternative embodiment, the present invention provides a silicon carbon material satisfying 0.5m 2/g≤BET1≤2m2/g.
In an alternative embodiment, the silicon carbon material provided by the invention satisfies Dv50.ltoreq. 50 1.ltoreq.20μm.
In an alternative embodiment, the silicon carbon material provided by the invention satisfies that Dv50 1.ltoreq.10μm is 2 μm or less.
In an alternative embodiment, the silicon-carbon material provided by the invention comprises one or more of amorphous silicon, crystalline silicon and a composite of crystalline silicon and amorphous silicon.
In an alternative embodiment, the present invention provides a silicon carbon material having a pore volume of less than 0.5cm 3/g.
In an alternative embodiment, the present invention provides a silicon carbon material having a pore volume of less than 0.1cm 3/g.
In an alternative embodiment, the present invention provides a silicon carbon material having a true density of 1.5g/cm 3～3g/cm3.
In an alternative embodiment, the silicon carbon material provided by the invention has a tap density ρ td of 0.5g/cm 3≤ρtd≤1.2g/cm3.
In an alternative embodiment, the present invention provides a silicon carbon material having a compaction density ρ cd of 0.5g/cm 3≤ρcd≤2g/cm3 at a 5T pressure.
In an alternative embodiment, the present invention provides a silicon carbon material having a raman spectrum with an I D/IG of less than 2.
In an alternative embodiment, the silicon-based material is filled with 10% -90% of the porous carbon pore volume.
In an alternative embodiment, the silicon-based material provided by the invention fills 20% -60% of the porous carbon pore volume.
In an alternative embodiment, the porous carbon has a specific surface area BET 2 of 200m 2/g≤BET2≤4000m2/g.
In an alternative embodiment, the porous carbon has a specific surface area BET 2 of 500m 2/g≤BET2≤2000m2/g.
In an alternative embodiment, the porous carbon has a pore volume of 0.4cm 3/g～2.5cm3/g.
In an alternative embodiment, the porous carbon has a porosity of 50% -90%.
In an alternative embodiment, the porous carbon has a true density of 1g/cm 3～3g/cm3.
In an alternative embodiment, the silicon-carbon material provided by the invention further comprises a coating layer, wherein the coating layer comprises one or more of a carbon coating layer, an oxide coating layer, a metal salt coating layer and a polymer coating layer.
In an alternative embodiment, the thickness of the coating layer is 5 nm-500 nm.
In an alternative embodiment, the mass of the coating layer accounts for 1% -20% of the total mass of the silicon carbon material.
In a second aspect, the invention also provides a negative electrode plate, which comprises a current collector and a membrane arranged on the surface of the current collector, wherein the membrane comprises the silicon-carbon material in the first aspect.
In a third aspect, the present invention also provides a secondary battery, including a positive electrode tab, a negative electrode tab according to the second aspect of the present invention, and an electrolyte between the positive electrode tab and the negative electrode tab.
In a fourth aspect, the invention also provides electric equipment, which comprises the secondary battery of the third aspect of the invention.
Compared with the prior art, the technical scheme of the invention has the following beneficial effects:
The invention provides a silicon-carbon material, which comprises porous carbon and a silicon-based material positioned in the pores of the porous carbon, and the inventor researches that when the silicon content in the silicon-carbon material is proper, and the specific surface area BET 1(m2/g and the median particle diameter Dv50 1 (mu m) of the silicon-carbon material and the median particle diameter Dv50 2 (mu m) of the porous carbon meet 0.8-BET 1×(Dv502/Dv501 -6.5, the silicon-carbon negative electrode material can effectively relieve the expansion and contraction effects of a silicon negative electrode and has higher reversible specific capacity.
Detailed Description
The following examples are provided for a better understanding of the present invention and are not limited to the preferred embodiments described herein, but are not intended to limit the scope of the invention, any product which is the same or similar to the present invention, whether in light of the present teachings or in combination with other prior art features, falls within the scope of the present invention.
The specific experimental procedures or conditions are not noted in the examples and may be followed by the operations or conditions of conventional experimental procedures described in the literature in this field. The reagents or apparatus used were conventional reagent products commercially available without the manufacturer's knowledge.
In order to solve the problems in the related art, according to a first aspect of the present invention, there is provided a silicon-carbon material comprising porous carbon and a silicon-based material located in pores of the porous carbon, wherein the silicon content in the silicon-carbon material is 20wt.% to 70wt.%, and the specific surface area BET 1 of the silicon-carbon material satisfies the following conditions with respect to the median particle diameter Dv50 1 of the silicon-carbon material and the median particle diameter Dv50 2 of the porous carbon:
0.8≤BET1×(Dv502/Dv501)≤6.5;
Wherein BET 1 is in m 2/g,Dv501 and Dv50 2 are in μm.
The inventors of the present invention have made extensive studies and found that when the silicon content in the silicon-carbon material is appropriate and the specific surface area BET 1(m2/g and the median particle diameter Dv50 1 (μm) of the silicon-carbon material and the median particle diameter Dv50 2 (μm) of the porous carbon satisfy 0.8.ltoreq.BET 1×(Dv502/Dv501.ltoreq.6.5, the silicon-carbon negative electrode material can effectively alleviate the expansion and contraction effects of the silicon negative electrode and has a higher reversible specific capacity. In particular, BET 1×(Dv502/Dv501) may have a value of, but is not limited to, 0.8, 1.0, 1.5, 2.0, 2.5, 3.0, 3.5, 4.0, 4.5, 5.0, 5.5, 6.0, 6.5. The silicon content in the silicon carbon material may be, but is not limited to, 20wt.%, 30wt.%, 40wt.%, 48wt.%, 55wt.%, 60wt.%, 70wt.%.
Further, the inventor researches find that when the silicon content in the silicon-carbon material is 48wt.% to 55wt.%, and the silicon-carbon material satisfies 1.0.ltoreq.BET 1×(Dv502/Dv501.ltoreq.3.0, the expansion and contraction effect of the silicon anode is smaller and the reversible specific capacity is higher.
In an alternative embodiment, the specific surface area BET 1 of the silicon carbon material provided by the present invention satisfies 0.3m 2/g≤BET1≤5m2/g, preferably 0.5m 2/g≤BET1≤2m2/g. The inventor researches and discovers that the silicon-carbon product with high specific surface area can cause excessive consumption of electrolyte and unstable solid electrolyte interface film caused by volume expansion in the circulating process, so that the silicon-carbon material has the specific surface area, can avoid the problems of excessive consumption of electrolyte, unstable solid electrolyte interface film and the like, and improves the stability of the battery. In particular, the BET 1 value may be, but is not limited to 0.3m2/g、0.5m2/g、1.0m2/g、1.5m2/g、2.0m2/g、2.5m2/g、3m2/g、3.5m2/g、4m2/g、4.5m2/g、5m2/g.
In an alternative embodiment, the present invention provides a silicon carbon material having a median particle diameter Dv50 1 satisfying 1 μm.ltoreq.Dv50 1.ltoreq.20 μm, preferably 2 μm.ltoreq.Dv50 1.ltoreq.10 μm. The inventors have found that the silicon carbon material has good processability when the median particle diameter Dv50 1 satisfies the above conditions. In particular, the values of Dv50 1 may be, but are not limited to, 1 μm, 2 μm, 5 μm, 8 μm, 10 μm, 13 μm, 15 μm, 17 μm, 20 μm.
In an alternative embodiment, the silicon-based material in the silicon-carbon material provided by the invention is filled with 10% -90%, preferably 20% -60% of the pore volume of the porous carbon, and the pore volume of the silicon-carbon material is smaller than 0.5cm 3/g, preferably smaller than 0.1cm 3/g, more preferably smaller than 0.01cm 3/g after filling. The inventor researches that when the pore volume of the silicon-carbon material meets the above conditions, pores exist in the porous carbon, so that space is reserved for the volume expansion of the silicon-based material, and the cycle performance is improved. Specifically, the pore volume of the filled silicon-carbon material may be, but is not limited to, a value of 0.45cm3/g、0.4cm3/g、0.3cm3/g、0.2cm3/g、0.1cm3/g、0.05cm3/g、0.01cm3/g、0.005cm3/g.
In an alternative embodiment, the present invention provides a silicon carbon material having a true density of 1.5g/cm 3～3g/cm3 and a true density of 1g/cm 3～3g/cm3 of porous carbon. True density refers to the actual mass of solid matter per unit volume of material in an absolutely dense state, i.e., the density after removal of internal or inter-particle voids. Specifically, the true density of the silicon carbon material may be, but is not limited to, 1.5cm 3/g、2.0cm3/g、2.5cm3/g、3cm3/g, and the true density of the porous carbon may be, but is not limited to, 1.0cm 3/g、1.5cm3/g、2.0cm3/g、2.5cm3/g、3cm3/g.
In an alternative embodiment, the silicon carbon material provided by the invention has a tap density ρ td of 0.5g/cm 3≤ρtd≤1.2g/cm3. Specifically, the tap density ρ td of the silicon carbon material may be, but is not limited to, 0.5cm 3/g、0.8cm3/g、1.0cm3/g、1.2cm3/g.
In an alternative embodiment, the present invention provides a silicon carbon material having a compaction density ρ cd of 0.5g/cm 3≤ρcd≤2g/cm3 at a 5T pressure. Specifically, the compaction density ρ cd of the silicon-carbon material at 5T pressure may be, but is not limited to 0.5g/cm3、0.8g/cm3、1.0g/cm3、1.2g/cm3、1.5g/cm3、1.8g/cm3、2.0g/cm3.
In an alternative embodiment, the present invention provides a silicon carbon material having a raman spectrum with an I D/IG of less than 2. Specifically, I D/IG in the raman spectrum of the silicon-carbon material may be, but is not limited to, 1.9, 1.5, 1.0, 0.8, 0.6, 0.4, 0.2.
In an alternative embodiment, the porous carbon has a specific surface area BET 2 that satisfies 200m 2/g≤BET2≤4000m2/g, preferably 500m 2/g≤BET2≤2000m2/g, which ensures a high number of sites for silane contact with the porous carbon and facilitates deposition of silicon-based materials. In particular, the specific surface area BET 2 of the porous carbon may be, but is not limited to 200m2/g、500m2/g、800m2/g、1000m2/g、2000m2/g、3000m2/g、4000m2/g.
In an alternative embodiment, the porous carbon has a pore volume of 0.4cm 3/g～2.5cm3/g, and if the amount of silicon deposited is too low for Kong Rongtai hours, a large Kong Rongtai would result in the porous carbon being brittle and not strong enough to inhibit the volume expansion of the silicon during charge and discharge. In particular, the pore volume of the porous carbon may be, but is not limited to 0.4cm3/g、0.8cm3/g、1.2cm3/g、1.6cm3/g、2.0cm3/g、2.2cm3/g、2.5cm3/g.
In an alternative embodiment, the porosity of the porous carbon is 50% -90%, wherein the micropore ratio is between 10% -30%, and the Kong Zhanbi is between 50% -85%. The inventors have found that porous carbon having a pore size in this range is more prone to deposition of silicon-based materials. Specifically, the porosity of the porous carbon may be, but is not limited to, 50%, 60%, 70%, 80%, 90%, the micropore ratio may be, but is not limited to, 10%, 20%, 30%, and Kong Zhanbi may be, but is not limited to, 50%, 60%, 70%, 80%, 95%.
In an alternative embodiment, the porous carbon has a true density of 1g/cm 3～3g/cm3. Specifically, the true density of the porous carbon may be, but is not limited to, 1g/cm 3、1.5g/cm3、2g/cm3、2.5g/cm3、3g/cm3.
It is understood that the specific surface area BET 2, pore volume, porosity, true density, etc. of the porous carbon described in the present invention refer to structural parameters of the porous carbon raw material itself, not parameters of the porous carbon after the silicon carbon material is formed.
In an alternative embodiment, the silicon carbon material further comprises a coating layer, the coating layer comprising one or more of a carbon coating layer, an oxide coating layer, a metal salt coating layer, and a polymer coating layer.
In an alternative embodiment, the thickness of the coating layer is 5 nm-500 nm. In particular, the thickness of the cladding layer may be, but is not limited to, 5nm, 10nm, 50nm, 100nm, 200nm, 300nm, 400nm, 500nm.
In an alternative embodiment, the mass of the coating layer accounts for 1% -20% of the total mass of the silicon-carbon material. Specifically, the mass of the coating layer accounts for 1%, 5%, 10%, 15% and 20% of the total mass of the silicon-carbon material, but is not limited to the silicon-carbon material.
In an alternative embodiment, the silicon-carbon material is prepared by depositing a silicon-based material in porous carbon, the silicon-based material being produced by cracking a silicon-containing gas. The method is simple and feasible, and can be used for mass production.
In an alternative embodiment, the preparation method of the silicon carbon material comprises the steps of heating porous carbon to 300-800 ℃ in a moving state, introducing silicon-containing gas for reaction, controlling the flow rate of the silicon-containing gas to be 50 mL/min-50L/min, controlling the pressure to be-3-101 kPa and the introducing time to be 0.5-50 h, wherein the mass ratio of the silicon-containing gas to the porous carbon is 2-20:1 in a certain period of time when the reaction is carried out. According to the invention, through comprehensive regulation and control of deposition temperature, concentration, pressure, flow and time, the silicon-based material is ensured to be deposited in the pores of the porous carbon, so that the expansion and contraction effects of the silicon negative electrode are effectively relieved, and the cycle life of the silicon negative electrode is prolonged.
In an alternative embodiment, in the preparation method of the silicon-carbon material, the silicon-containing gas comprises silane, wherein the silane is at least one selected from monosilane, disilane, trisilane, dichlorosilane, trichlorosilane, tetrachlorosilane and trimethylsilane, and besides, the silicon-containing gas can also comprise chlorosilane, such as at least one of dichlorosilane, trichlorosilane and tetrachlorosilane.
The mass of the silicon-containing gas required for the reaction also depends on the conversion of silane (chlorosilane), which can be calculated from the mass of silicon-based material deposited in porous carbon/the mass of silane (chlorosilane), and also by analyzing the mass flow rate of the silicon-containing gas at the reactor inlet and the concentration (mol/h) of silane (chlorosilane) and hydrogen in the off-gas, the conversion of silane (chlorosilane) being greater than 50% in the present invention. In a preferred embodiment, the mass ratio of the silicon-containing gas to the porous carbon is 3-10:1.
In an alternative embodiment, in the method for preparing a silicon-carbon material, the boiling point of the silicon-containing gas is 20 ℃ to 800 ℃.
In an alternative embodiment, in the method for preparing a silicon-carbon material, the content of silane in the silicon-containing gas is 1.25wt.% to 100wt.%.
In an alternative embodiment, in the method for preparing a silicon carbon material, the porous carbon is fluidized by a carrier gas and is in countercurrent contact with the silicon-containing gas, so that the flow rate of the fluid is 0.1m/s to 0.5m/s, preferably 0.18m/s to 0.22m/s.
In an alternative embodiment, in the preparation method of the silicon carbon material, the flow rate of the carrier gas is 65mL/min to 50L/min.
In an alternative embodiment, in the method for preparing a silicon-carbon material, the carrier gas is at least one of hydrogen, argon, and nitrogen.
In an alternative embodiment, in the method for preparing a silicon-carbon material, the volume flow ratio of the carrier gas to the silicon-containing gas is 18-24:1, preferably 20-23:1.
In an alternative embodiment, in the method for preparing a silicon-carbon material, the heating temperature is 400 ℃ to 700 ℃.
In an alternative embodiment, in the preparation method of the silicon carbon material, the introducing time is 1h to 20h.
In an alternative embodiment, the preparation method of the silicon-carbon material further comprises the steps of determining the deposition rate of the silicon-based material by monitoring the volume percentage of hydrogen (monosilane is cracked to generate the silicon-based material and hydrogen) in the tail gas of the reactor along with the reaction time when the silicon-containing gas is monosilane, and determining the deposition amount of the silicon-based material according to the pore volume of the porous carbon and the requirement of preparing the silicon-carbon material with high silicon content or low silicon content so as to ensure that silicon is deposited in the pores of the porous carbon, and meanwhile, certain pores are reserved to avoid volume expansion, so that the silicon content is generally controlled to be between 10 and 90 percent, preferably between 20 and 60 percent of the pore volume of the porous carbon.
In an alternative embodiment, the preparation method of the silicon-carbon material further comprises the step of passivating the deposited material by adopting passivation gas, wherein the passivation temperature is 100-700 ℃, and the passivation time is 0.1-12 h, preferably 0.1-6 h. And introducing passivation gas for enough time to enable the passivation gas to perform self-terminated hydrosilylation reaction with the surface of the amorphous silicon nano particles to obtain passivated silicon-carbon composite particles so as to prevent the silicon-based material from being in direct contact with electrolyte and reduce irreversible capacity.
The passivation gas used in the invention is an organic compound, and can be a non-oxygen-containing passivation gas or an oxygen-containing passivation gas, wherein the non-oxygen-containing gas comprises alkene or alkyne, such as acetylene, propylene, ethylene, butylene and the like, and the oxygen-containing gas comprises at least one of ethanol, dimethyl carbonate, ethylene carbonate, propylene carbonate, methyl ethyl carbonate, diethyl carbonate, vinylene carbonate, allyloxyethanol, diallyl carbonate, allylmethyl carbonate, allylethyl carbonate, allylglycidyl ether, allyloxy (polyethylene oxide) methyl ether and allyloxytrimethylsilane.
In an alternative embodiment, in the preparation method of the silicon-carbon material, carbon source gas is used for carbon coating of the deposited or passivated material, so that the conductivity can be improved and the expansion can be buffered at the same time. The reaction temperature of the carbon coating step is 600-1200 ℃, the reaction time is 3-360 min, and the carbon source gas is selected from alkene or alkyne, such as acetylene, propylene, ethylene, butylene and the like.
In an alternative embodiment, in the preparation method of the silicon carbon material, the flow rate of the carbon source gas is 0.1L/min to 15L/min.
In an alternative embodiment, in the preparation method of the silicon carbon material, the thickness of the carbon coating layer is 1 nm-120 nm, preferably 2 nm-50 nm.
In an alternative embodiment, in the preparation method of the silicon carbon material, the mass of the carbon coating layer in each silicon carbon material particle accounts for 1% -20% of the total mass of the particle.
In an alternative embodiment, the porous carbon is activated from a coke feedstock. The coke raw material can be one or more of petroleum coke, pitch coke, needle coke and coal coke.
In an alternative embodiment, the porous carbon is prepared by pyrolysis and activation in sequence. The polymer material may be an organic polymer, an inorganic polymer, or a synthetic polymer, such as a polymer gel formed by polymerization of a phenol compound (phenol, resorcinol, catechol, hydroquinone, phloroglucinol, or a combination thereof) and an aldehyde compound (formaldehyde, acetaldehyde, propionaldehyde, butyraldehyde, benzaldehyde, cinnamaldehyde, or a combination thereof) and then pyrolysis, or a polymer gel formed by polymerization of bisphenol a and hexamethylenetetramine and pyrolysis. The pyrolysis step is to pyrolyze the polymer material in an inert atmosphere at a temperature of 650-1100 ℃ to obtain a pyrolyzed carbon material.
The invention activates the porous carbon material obtained by pyrolysis, thereby adjusting the pore structure of the porous carbon. In the activation step, the activation temperature is 650-1100 ℃, and the activated porous carbon material is obtained by adopting at least one of carbon dioxide and water vapor as the activation gas.
In an alternative embodiment, the activated porous carbon is subjected to heat treatment under an inert atmosphere at a treatment temperature of 500-3000 ℃ for 0.5-24 hours to adjust the pore size distribution of the porous carbon, so that the porous carbon prepared by the method has a porosity of 50-90%, wherein the micropore ratio is 10-30%, and the center Kong Zhanbi is 50-85%, and thus the deposition of the silicon-based material is easier.
In an alternative embodiment, the activated or heat treated porous carbon is subjected to chemical vapor deposition by using a carbon source, wherein the reaction pressure is 0.2-0.3 MPa, the reaction temperature is 700-800 ℃, and the reaction time is 0.5-20 h. By further depositing carbon on the porous carbon, partial pores are filled or sealed, and pores with the size below 1nm in the specific porous carbon are sealed, so that the mesoporosity of the porous carbon is improved.
According to a second aspect of the present invention, there is also provided a negative electrode tab comprising a current collector and a membrane provided on a surface of the current collector, the membrane comprising the silicon carbon material of the first aspect.
According to a third aspect of the present invention, there is also provided a secondary battery comprising a positive electrode tab, a negative electrode tab according to the second aspect of the present invention, and an electrolyte between the positive electrode tab and the negative electrode tab. Based on the characteristics of the silicon-carbon material, the secondary battery provided by the invention has the advantages of high specific capacity, long cycle life and good reaction kinetics.
According to a fourth aspect of the present invention, the present invention further provides an electric device, including the secondary battery according to the third aspect of the present invention.
The invention is described in further detail below in connection with specific examples which are not to be construed as limiting the scope of the invention as claimed.
The testing method comprises the following steps:
1. Particle size was measured using Mastersizer 3000 laser diffraction technique. According to a particle size distribution laser diffraction method GB/T190772016, the particle size distribution of the modified graphite material sample is measured. Dv50 particle size corresponding to a cumulative particle size distribution percentage of one sample reaching 50%. Its physical meaning is that the particle size is greater than 50% of its particle size, and less than 50% of its particle size, dv50 also being called median particle size.
2. Specific surface area (BET) was measured according to GB/T195872017 by the nitrogen adsorption specific surface area analytical test method and calculated by BET (Brunauer EmmettTeller) method.
3. Silicon content is defined by the formula silicon content = 100% (mass of silicon contained in the silicon-carbon material)/(mass of silicon-carbon material) in mass%. The sample cup was filled with a sample, and the silicon content (Si element content) was calculated as mass% by the basic parameter method (FP method) by the following method. The fluorescent X-ray device comprises NEX CG manufactured by Rigaku, tube voltage of 50kV, tube current of 1.00mA, sample cup of phi 32 mL CH1530, sample weight of 2-3 g and sample height of 5-18 mm, wherein the sample cup is filled with the sample, the method is adopted for measuring, and the silicon content in the composite particles is calculated in mass percent by using a basic parameter (FP method).
4. Pore volume and porosity were analyzed for micropores and mesopores using Micromeretics ASAP 2460,2460. At the temperature of liquid nitrogen, the equilibrium adsorption quantity of nitrogen on the surface of the object is related to the characteristics of aperture and the like, and the aperture calculation can be performed by fitting various models in combination with the law that the adsorption quantity changes along with the relative pressure in the adsorption process. Report generated by software is generated by BJH Desorptioncumulative volume of pores modelPore volume and porosity are calculated over the pore size range.
5. Tap Density measurement of powder tap Density was performed on a test instrument, a Baite tap Density meter, using GB/T5162-2006.
6. Coating layer thickness, namely carrying out section treatment on the material by using FIB-SEM equipment, and measuring in SEM to obtain the average coating layer thickness.
7.I D/IG test by Raman spectrum test, the ratio I D/IG of the peak intensity I D of the composite anode material in the range of 1300cm -1～1400cm-1 to the peak intensity I G of the composite anode material in the range of 1580cm -1～1620cm-1 is measured.
8. True density the true density of the material was tested according to GB/T24533-2019, and the test equipment used a true density tester (Bei Shide, 3H-2000 TD).
9. Compacted density the compacted density of the material was tested according to GB/T24533-2019, using a compacted density meter (minox, CARVER, 4350).
Example 1
The embodiment provides a preparation method of a silicon-carbon material, which comprises the following steps:
(1) Preparation of porous carbon
Petroleum coke is used as a carbon precursor, petroleum coke and KOH (solid activator) are uniformly mixed according to the mass ratio of 1:2, the mixture is placed in a rotary furnace to be heated to 800 ℃ at the heating rate of 4 ℃ per minute after being mixed, N 2 is used as a shielding gas, water vapor is introduced after the temperature is raised to 850 ℃, the flow rate of the water vapor is 0.16mL/g/s, the heat is preserved for 3 hours, and then the vapor is closed, so that the porous carbon material is obtained. The porous carbon was crushed to have a Dv50 2 of 7.4 μm, a specific surface area of 2000m 2/g, and a pore volume of 0.96cm 3/g.
(2) Deposition of silicon-based materials
1Kg of porous carbon is weighed into a reactor, purged, discharged oxygen and detected by a leakage point, then the temperature is raised, monosilane (SiH 4) is used as a silicon source, nitrogen is used as a carrier gas, the flow rate of the silicon source is 3L/min, and the flow rate of the carrier gas is 12L/min. Reacting in a chemical vapor deposition furnace at 500 ℃ for 6 hours, depositing nano silicon into the porous carbon gaps, controlling the pressure of a fluidized bed to be-2 kPa, then controlling the temperature to be 580 ℃, introducing acetylene gas at 3L/min, controlling the time of introducing the acetylene gas to be 60min, and controlling the pressure of the fluidized bed to be 6kPa. And stopping introducing acetylene gas, and keeping introducing inert gas until the reaction product is cooled to room temperature to obtain silicon carbon particles, thereby obtaining the anode active material. The chemical vapor deposition furnace is vertical fluidized bed equipment.
The silicon-carbon material prepared in this embodiment includes an active material and a coating layer on at least a portion of the surface of the active material, the active material including a porous carbon matrix and amorphous silicon filled in pores of the porous carbon matrix. Wherein the coating layer is a carbon layer. The silicon content in the silicon-carbon material was 51wt.%, the Dv50 1 of the silicon-carbon material was 7.8 μm, and the specific surface area of the silicon-carbon material was 1.5m 2/g;BET1×(Dv502/Dv501) =1.42.
Example 2
The difference between this example and example 1 is that the silicon source flow rate is 2L/min, the carrier gas flow rate is 30L/min, and the reaction time of chemical vapor deposition is 12h. The silicon content in the silicon-carbon material was 70wt.%, the Dv50 1 of the silicon-carbon material was 8.1 μm, and the specific surface area of the silicon-carbon material was 0.9m 2/g;BET1×(Dv502/Dv501) =0.82.
Example 3
The difference between this example and example 1 is that the silicon source flow is 10L/min, the chemical vapor deposition temperature is 520 ℃, and the reaction time of the chemical vapor deposition is 4 hours. The silicon content in the silicon-carbon material was 20wt.%, the Dv50 1 of the silicon-carbon material was 7.5 μm, and the specific surface area of the silicon-carbon material was 6.5m 2/g;BET1×(Dv502/Dv501) =6.41.
Example 4
This example differs from example 1 only in that the fluidized bed pressure was controlled to-1 kPa. The silicon content in the silicon-carbon material was 60wt.%, the Dv50 1 of the silicon-carbon material was 7.8 μm, and the specific surface area of the silicon-carbon material was 1.2m 2/g;BET1×(Dv502/Dv501) =1.14.
Example 5
This example differs from example 1 only in that the silicon source flow is 5L/min and the reaction time for chemical vapor deposition is 4 hours. The silicon content in the silicon-carbon material was 45wt.%, the Dv50 1 of the silicon-carbon material was 7.6 μm, and the specific surface area of the silicon-carbon material was 3.1m 2/g;BET1×(Dv502/Dv501) =3.02.
Example 6
This example differs from example 1 only in that the porous carbon was crushed to a particle size of Dv50 2 to 5.5 μm. The silicon content in the silicon-carbon material was 53wt.%, the Dv50 1 of the silicon-carbon material was 5.9 μm, and the specific surface area of the silicon-carbon material was 1.4m 2/g;BET1×(Dv502/Dv501) =1.31.
Example 7
This example differs from example 1 only in that the porous carbon was crushed to a particle size of 9.8 μm in Dv50 2. The silicon content in the silicon-carbon material was 48wt.%, the Dv50 1 of the silicon-carbon material was 10.3 μm, and the specific surface area of the silicon-carbon material was 1.6m 2/g;BET1×(Dv502/Dv501) =1.52.
Comparative example 1
This comparative example differs from example 1 only in that the carrier gas flow rate was 200L/min. The silicon content in the silicon-carbon material was 5wt.%, dv50 1 of the silicon-carbon material was 7.4 μm, and the specific surface area of the silicon-carbon material was 1750m 2/g;BET1×(Dv502/Dv501) =1750.
Comparative example 2
The comparative example is different from example 1 only in that the silicon source flow rate is 1L/min, the carrier gas flow rate is 30L/min, and the reaction time of chemical vapor deposition is 16h. The silicon content in the silicon-carbon material was 75wt.%, the Dv50 1 of the silicon-carbon material was 8.1 μm, and the specific surface area of the silicon-carbon material was 0.5m 2/g;BET1×(Dv502/Dv501) =0.46.
Electrochemical performance test
Preparing a button half battery, namely weighing the anode active materials, the conductive additive carbon black and the adhesive (sodium carboxymethylcellulose and styrene-butadiene rubber in a mass ratio of 1:1) obtained in each example and comparative example according to a mass ratio of 94:2:4, preparing slurry by using a beater to obtain anode slurry, coating the anode slurry on the surface of an anode current collector (particularly copper foil), drying and cutting the anode slurry sequentially, and assembling the anode slurry and a lithium metal sheet in a glove box to form the button battery. And (3) performing constant-current charge-discharge mode test by using a charge-discharge instrument at a constant temperature of 25+/-2 ℃, wherein the discharge cut-off voltage is 0.005V, the charge cut-off voltage is 2V, and the first-week charge-discharge test is performed at a current density of 1C/10, so as to obtain reversible specific capacity and first coulomb efficiency. First coulombic efficiency = first charge capacity/first discharge capacity x 100%.
Preparing a full battery, namely preparing a composite body with the specific capacity of 450mAg/h by using the anode active materials prepared in each example and comparative example and graphite, preparing anode slurry by using a conductive additive and an adhesive according to the mass ratio of 94:2:4, coating the anode slurry on a current collector (specifically a copper foil) to obtain an anode pole piece, fully stirring and uniformly mixing an anode active material LiCoO 2, conductive carbon black and a binder polyvinylidene fluoride (PVDF) in an N-methylpyrrolidone solvent system according to the weight ratio of 96.7:1.7:1.6, coating the anode pole piece on an Al foil, drying and cold pressing to obtain an anode pole piece, taking a polypropylene porous polymeric film as an isolating film, sequentially laminating the anode pole piece, the isolating film and the anode pole piece, enabling the isolating film to be positioned between the anode pole piece and the anode pole piece, and winding the anode pole piece to obtain a bare cell. And placing the bare cell in an outer package, injecting the prepared electrolyte, packaging, and performing technological processes such as formation, degassing, trimming and the like to obtain the full cell. The electrolyte is a formula of a common adaptive silicon negative electrode electrolyte in the market.
And (3) testing the expansion rate of the battery, namely, using a charge-discharge instrument to perform constant-current charge-discharge testing on all the batteries at the temperature of 25 ℃, wherein the discharge cut-off voltage is 2.75V, the charge cut-off voltage is 4.2V, and the charge-discharge testing is performed at the current density of 1 ℃. After 100 cycles, the cell expansion ratios were measured using an in situ expansion analysis system, and the results are summarized in table 1. And the capacity retention after 300 cycles was recorded, the capacity retention=the discharge capacity at 300 th cycle/the discharge capacity at 1 st cycle×100%.
Table 1 electrochemical data
As can be seen from the data in table 1, when the silicon content in the silicon-carbon material provided by the embodiment of the invention is 20wt.% to 70wt.%, and the relationship between the specific surface area BET 1(m2/g of the silicon-carbon material and the median particle diameter Dv50 1 (μm) and the median particle diameter Dv50 2 (μm) of porous carbon satisfies 0.8-BET 1×(Dv502/Dv501 -6.5, the silicon-carbon material provided by the invention can effectively relieve the expansion and contraction effects of the silicon negative electrode, and has a higher reversible specific capacity, so that the silicon-carbon material provided by the invention can be used as the negative electrode active material of the secondary battery.
It is apparent that the above examples are given by way of illustration only and are not limiting of the embodiments. Other variations or modifications of the above teachings will be apparent to those of ordinary skill in the art. It is not necessary here nor is it exhaustive of all embodiments. While still being apparent from variations or modifications that may be made by those skilled in the art are within the scope of the invention.
Claims (10)
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