Silicon-carbon material and preparation method thereof, and lithium ion battery

Abstract

The application discloses a silicon-carbon material and a preparation method thereof and a lithium ion battery. The preparation method comprises the following steps: S1, drying a slurry of a carbon-containing material precursor and an iron salt to obtain a first precursor; wherein the iron salt comprises an organic trivalent iron salt; S2, carbonizing and activating the first precursor to obtain a second precursor; S3, performing first vapor deposition on the second precursor to obtain a third precursor; wherein the first deposition gas used in the first vapor deposition comprises a silicon source gas and a carrier gas; the silicon source gas comprises silane, and the carrier gas comprises nitrogen; S4, performing second vapor deposition on the third precursor to obtain the silicon-carbon material; wherein the second deposition gas used in the second vapor deposition comprises a carbon source gas. The preparation method can optimize the strength and other performances of the obtained silicon-carbon material, and after being used in the lithium ion battery, the performances of the lithium ion battery such as the rate, expansion and cycle can be comprehensively optimized and improved.

Description

TECHNICAL FIELD

[0001] The present application relates to a silicon-carbon material, a preparation method thereof and a lithium ion battery. BACKGROUND

[0002] With the development of the times, the current lithium ion battery technology is increasingly difficult to meet people's needs for production and life, and people urgently need a lithium ion battery with super-high energy density, super-high cycle performance, super-high rate performance, and super-high environmental adaptability. For the existing technology, the emergence and development of silicon-carbon negative electrode material is undoubtedly a powerful lever to promote the development of high-performance lithium ion batteries.

[0003] However, the existing silicon-carbon negative electrode material, although its specific capacity is high, is low in strength and not pressure-resistant because it is usually prepared by depositing silane on a porous carbon material. In addition, the low-temperature deposition technology easily leads to poor rate performance of the obtained battery. Generally speaking, the expansion amount of the silicon-carbon negative electrode material after lithium intercalation is often limited by the strength of the porous carbon. The porous carbon with low expansion amount has high strength, and the porous carbon with high expansion amount has low strength. In addition, the porous carbon is usually obtained by activating hard carbon. Although activation is conducive to the development of graphitization, the rate performance of the obtained battery is still poor. Moreover, it is difficult to activate a carbon material precursor with too high graphitization, and the layered structure contained therein also affects the uniformity of silane deposition.

[0004] Limited by the contradictions among the strength performance, rate performance, expansion performance, cycle performance, and environmental adaptability, in order to obtain a lithium ion battery with excellent comprehensive performance, the silicon-carbon material needs to be matched with various components in the positive and negative electrode formulations and electrolyte formulations, especially additives for improving related performance, or needs to be matched with various advanced technologies such as extremely low copper foil, extremely low electrode thickness, laser drilling technology, laser cleaning technology, middle ear placement technology, double-layer coating, multi-tab, full-tab, and even full-tab technology.

[0005] Therefore, from the perspective of materials, there is an urgent need for a silicon-carbon material with high strength and which can comprehensively improve the rate performance, expansion performance, cycle performance, and environmental adaptability when used in a battery. SUMMARY

[0006] In order to solve the defect that the lithium ion battery using the porous silicon-carbon material in the prior art cannot simultaneously consider multiple excellent performances, the present application provides a silicon-carbon material, a preparation method thereof, and a lithium ion battery. The preparation method can optimize the strength and other performances of the obtained silicon-carbon material, and when used in a lithium ion battery, it can comprehensively optimize and improve the rate, expansion, cycle, and other performances.

[0007] To achieve the above purpose, the present application adopts the following technical solutions.

[0008] The application provides a preparation method of a silicon-carbon material, which comprises the following steps:

[0009] S1, a slurry of a carbon material precursor and an iron salt is dried to obtain a first precursor; wherein the iron salt comprises an organic trivalent iron salt;

[0010] S2, the first precursor is carbonized and activated to obtain a second precursor;

[0011] S3, the second precursor is subjected to first vapor deposition to obtain a third precursor;

[0012] wherein the first deposition gas used in the first vapor deposition comprises a silicon source gas and a carrier gas; the silicon source gas comprises silane, and the carrier gas comprises nitrogen;

[0013] S4, the third precursor is subjected to second vapor deposition to obtain the silicon-carbon material;

[0014] wherein the second deposition gas used in the second vapor deposition comprises a carbon source gas.

[0015] In the application, the inventors have found that, by adding an organic trivalent iron salt in the preparation of a porous carbon, the porous carbon thus prepared can realize the following functions simultaneously in the subsequent silane deposition and carbon deposition processes: increasing the mesopore ratio of the material, doping nitrogen in the silicon deposition process, and more controllably growing carbon nanotubes in situ, thus achieving multiple purposes at one time, and optimizing the conductivity and strength of the obtained silicon-carbon material through a simple process, and then, when used in lithium ion batteries, comprehensively optimizing and improving the rate, expansion, cycle and other performances of the lithium ion batteries.

[0016] In the application, in step S1, the organic trivalent iron salt has a certain complexing effect and has good compatibility with the carbon material precursor, so that the organic trivalent iron salt can be extremely uniformly dispersed in the carbon material precursor with high viscosity, and in the drying process, the pores of macropores and above are first eliminated in the carbon material precursor, thereby improving the overall strength of the material.

[0017] In some embodiments, in step S1, the organic trivalent iron salt comprises iron acetate and / or iron citrate.

[0018] In some embodiments, in step S1, the molar amount of iron in the iron salt is 0.01-1 mol / kg, for example 0.02 mol / kg, 0.04 mol / kg, 0.06 mol / kg, 0.08 mol / kg, 0.12 mol / kg, 0.14 mol / kg, 0.16 mol / kg or 0.25 mol / kg, based on the mass of the carbon material precursor.

[0019] In the present application, in step S1, the carbon material precursor can be a carbon source for preparing carbon material in the art, preferably including resin and / or biomass.

[0020] Preferably, the resin includes one or more of phenolic resin, epoxy resin, urea-formaldehyde resin, melamine-formaldehyde resin, furan resin, silicone resin, polyester resin, polyamide resin, acrylic resin, polyurethane, vinyl resin, hydrocarbon resin and polyether resin.

[0021] Preferably, the biomass includes one or more of lignin, cellulose, hemicellulose and chitin.

[0022] In some embodiments, in step S1, the carbon material precursor includes one or more of phenolic resin, lignin and chitin.

[0023] In some embodiments, in step S1, the carbon material precursor includes phenolic resin, and the slurry further includes a curing agent.

[0024] Preferably, the curing agent includes urotropine.

[0025] Preferably, the mass ratio of the curing agent to the phenolic resin is (0.005-1):1, for example 0.06:1.

[0026] In some embodiments, in step S1, the solvent in the slurry includes ethanol.

[0027] In some embodiments, in step S1, the mass ratio of the solvent in the slurry to the carbon material precursor is (1-20):1, for example 2:1.

[0028] In some embodiments, in step S1, the drying method is spray drying.

[0029] In some embodiments, in step S1, the drying temperature is 70-200℃, for example 130℃.

[0030] In some embodiments, in step S1, the particle size of the first precursor is 4-16μm, for example 8μm.

[0031] In the present application, in step S2, during carbonization, due to the low residual carbon rate of the organic ferric salt, mesopores are preferentially generated around the organic ferric salt, and the organic ferric salt is also converted into ferroferric oxide accordingly; further, due to the opening characteristics of the mesopores, good micropore dispersion structures are further generated around the mesopores during activation, which can greatly inhibit expansion; finally, the ferroferric oxide generated by carbonization of the organic ferric salt is dispersed in the surface of the porous carbon and / or the pore channels of the mesopores in the form of nanoparticles.

[0032] In some embodiments, in step S2, the carbonization is performed in a protective gas.

[0033] Preferably, the protective gas is nitrogen.

[0034] Preferably, the flow rate of the protective gas is 0.5-5 L·kg -1 ·min -1 , for example 1 L·kg -1 ·min -1 .

[0035] In some embodiments, in step S2, the carbonization comprises a heating-up stage and a holding stage.

[0036] Preferably, the heating-up rate of the heating-up stage is 1-10 ℃ / min, for example 4 ℃ / min.

[0037] Preferably, the temperature of the holding stage is 300-550 ℃, for example 500 ℃.

[0038] Preferably, the time of the holding stage is 0.5-5 h, for example 2 h.

[0039] In some embodiments, in step S2, the carbonization further comprises cross-linking the first precursor before the carbonization.

[0040] Preferably, the cross-linking comprises a heating-up stage and a holding stage.

[0041] Preferably, the heating-up rate of the heating-up stage is 1-10 ℃ / min, for example 4 ℃ / min.

[0042] Preferably, the temperature of the holding stage is 100-300 ℃, for example 200 ℃.

[0043] Preferably, the time of the holding stage is 0.5-2 h, for example 1 h.

[0044] In some embodiments, in step S2, the activation is performed by gas activation and / or alkali activation.

[0045] Preferably, the gas activation is CO2 activation or water vapor activation.

[0046] In some embodiments, in step S2, the activation is performed by CO2 activation.

[0047] Preferably, the flow rate of the CO2 is 0.1-10 L·kg -1 ·min -1 , for example 2 L·kg -1·min -1 .

[0048] wherein the CO2 activation time is preferably 2-20h, for example 9h.

[0049] wherein the CO2 activation temperature is preferably 300-500℃.

[0050] In some embodiments, in step S2, the specific surface area of the second precursor (i.e. porous carbon) is 1800m 2 / g-2100m 2 / g, the specific surface area of micropores accounts for 75-98%, the specific surface area of mesopores accounts for 2%-25%, and the pore volume is 0.6cm 3 / g-1.5cm 3 / g.

[0051] In the present application, in step S3, the first vapor deposition is performed in the presence of silane and nitrogen, which can simultaneously achieve the deposition of silicon, the doping of nitrogen and the reduction of metal oxide. In the first vapor deposition process, hydrogen is generated by the cracking of silane. On the one hand, based on the principle of Haber process for synthesizing ammonia, the hydrogen and nitrogen are catalyzed by the ferroferric oxide to synthesize ammonia, which solidifies the nitrogen while the similar cracking temperature between ammonia and silane enables the nitrogen atoms to be successfully doped into the silicon nanoparticles, especially into the silicon nanoparticles with larger particle size, so that the silicon is converted from a semiconductor to a conductor to form an N-type semiconductor, thereby reducing the ohmic resistance of the silicon nanoparticles; at the same time, part of the nitrogen atoms generate Li-N irreversible compounds in the first lithium intercalation process, which expand the crystal lattice stripe structure of the silicon nanoparticles, so that the lithium ion migration resistance is reduced, thereby facilitating the improvement of the energy density and rate performance of the battery. On the other hand, the hydrogen can also act as a reducing agent to reduce part or all of the ferroferric oxide distributed in the porous carbon into nano-iron element, so that carbon nanotubes and carbon-coated materials are in-situ grown in the second vapor deposition in step S4.

[0052] In some embodiments, in step S3, the volume ratio of the silicon source gas to the carrier gas is (0.05-1):1, for example 0.25:1.

[0053] In some embodiments, in step S3, the silane (general formula: Si n H 2n+2 ) can include one or more of monosilane (SiH4), disilane (Si2H6), trisilane (Si3H8) and tetrasilane (Si4H 10 ).

[0054] In some embodiments, in step S3, the flow rate of the first deposition gas is 0.1-2L·kg -1 ·min-1 for example 0.5 L·kg -1 · min -1 .

[0055] In some embodiments, in step S3, the temperature of the first vapor deposition is 400-500 °C, for example 500 °C.

[0056] In some embodiments, in step S3, the absolute pressure of the first vapor deposition is 0.1-50 MPa, for example 1 MPa or 5 MPa.

[0057] In some embodiments, in step S3, the time of the first vapor deposition is 4-16 h, for example 8 h. The time of the first vapor deposition affects the amount of silicon deposition, and also affects the degree of reduction of the iron sesquioxide. Preferably, the time of the first vapor deposition is such that the iron sesquioxide is completely reduced to iron.

[0058] In the present application, both the iron sesquioxide and the iron can be catalysts for the carbon nanotubes. Because of the presence of oxygen atoms in the iron sesquioxide, its interaction with the carbon material is stronger, resulting in the growth of carbon nanotubes in a top growth mode, while the interaction between the iron and the carbon material is weaker, resulting in the growth of carbon nanotubes in a bottom growth mode. Compared with the top growth mode, the growth speed of carbon nanotubes in the bottom growth mode is faster, so longer carbon nanotubes are grown first, and then carbon coating is performed. In the top growth mode, because the catalyst is in the mesoporous, the contact between the catalyst and the carbon source gas is not close, so the growth speed is slow, and the carbon shell grown later can break the top of the carbon nanotubes, resulting in uneven coating, and also causing bubbling during the later acid washing, and reducing the specific capacity and rate performance, etc. In addition, in the bottom growth mode, the catalyst is on the outside of the material, while in the top growth mode, the catalyst is on the inside of the material, and the former is more conducive to water washing and demagnetization, while the latter is easy to lose more material during demagnetization, reducing the yield and increasing the cost, etc.

[0059] In some embodiments, in step S4, the carbon source gas includes one or more of alkyne, alkane, alkene, aromatic compound, and carbohydrate.

[0060] In some embodiments, in step S4, the second deposition gas further includes a carrier gas.

[0061] Preferably, the carrier gas includes nitrogen.

[0062] Preferably, the volume ratio of the carbon source gas to the carrier gas is (0.05-1):1, for example 0.25:1.

[0063] In some embodiments, in step S4, the flow rate of the second deposition gas is 0.1-50 L·kg-1 ·min -1 , for example 5 L·kg -1 ·min -1 .

[0064] In some embodiments, in step S4, the temperature of the second vapor deposition is 400-800℃, for example 500℃.

[0065] In some embodiments, in step S4, the time of the second vapor deposition is 2-40h, for example 10h.

[0066] In some embodiments, in step S4, the second vapor deposition further comprises a step of washing and drying.

[0067] In some embodiments, the washing comprises a step of first washing with hydrochloric acid and then washing with water. The purpose of the washing is mainly to remove iron-containing substances.

[0068] In the operation of the hydrochloric acid washing, the mass of the hydrochloric acid is preferably 1-100:1, for example 20:1, of the product obtained by the second vapor deposition.

[0069] In the operation of the hydrochloric acid washing, the concentration of the hydrochloric acid is preferably 0.0001-12.9 mol / L, for example 0.1 mol / L.

[0070] In the operation of the hydrochloric acid washing, the number of times of the hydrochloric acid washing is preferably 1-10, for example 2.

[0071] In the operation of the hydrochloric acid washing, the soaking time with the hydrochloric acid is preferably 5-500min, for example 30min.

[0072] In the operation of the water washing, the mass of the water is more preferably 1-30, for example 3, times of the product obtained by the hydrochloric acid washing.

[0073] In the operation of the water washing, the number of times of the water washing is more preferably 1-10, for example 3.

[0074] In some embodiments, the drying is performed by using a double-cone dryer.

[0075] The present application also provides a silicon-carbon material prepared by the method for preparing a silicon-carbon material as described above.

[0076] In the present application, the silicon-carbon material can comprise a core-shell structure, the core-shell structure comprising an inner core, an outer shell, and carbon nanotubes; the inner core comprising porous carbon and silicon particles, the silicon particles being distributed on the surface and / or in the pores of the porous carbon; the outer shell comprising a carbon layer, the carbon layer being coated on the surface of the inner core.

[0077] In the core-shell structure, the distribution mode of the carbon nanotubes can comprise one or more of the following modes ①-⑤:

[0078] ① the carbon nanotubes are distributed in the pores of the porous carbon,

[0079] ② the carbon nanotubes are distributed on the surface of the porous carbon;

[0080] ③ the carbon nanotubes extend from the surface of the porous carbon and penetrate through the outer shell;

[0081] ④ the carbon nanotubes extend from the pores of the porous carbon and penetrate through the outer shell;

[0082] ⑤ the carbon nanotubes extend from the inside of the outer shell and penetrate through the outer shell.

[0083] In some embodiments, the silicon content of the silicon-carbon material is 45%-55%, for example 48.0%, 50.18%, 50.35%, 50.54%, 50.69%, 50.67%, 50.75%, 50.65%, 50.2%, or 51.49%.

[0084] In some embodiments, the carbon content of the silicon-carbon material is 45%-55%, for example 49.82%, 49.65%, 49.46%, 49.31%, 49.33%, 49.25%, 49.35%, 49.8%, 48.51%, or 52.0%.

[0085] In some embodiments, the powder conductivity of the silicon-carbon material is 10-1000 s / cm, for example 11.4 s / cm, 13.2 s / cm, 32.2 s / cm, 54.1 s / cm, 87.3 s / cm, 134.2 s / cm, 189.6 s / cm, 205.3 s / cm, 213.2 s / cm, 801 s / cm, or 91.2 s / cm.

[0086] In some embodiments, the D50 particle size of the silicon-carbon material is 7.5-8.5 μm, for example 7.7 μm, 7.8 μm, 7.9 μm, or 8 μm.

[0087] In some embodiments, the specific surface area of the silicon-carbon material is 3-5 m 2 / g, for example 3.4 m 2 / g, 3.6 m2 / g, 3.8m 2 / g, 4m 2 / g, 4.1m 2 / g or 4.3m 2 / g.

[0088] The present application also provides a lithium ion battery comprising the silicon-carbon material as described above.

[0089] On the basis of common general knowledge in the art, the above-mentioned preferred conditions can be combined arbitrarily, thereby obtaining various preferred examples of the present application.

[0090] The reagents and raw materials used in the present application are commercially available.

[0091] The positive progress effect of the present application is that:

[0092] The present application integrates the nitrogen-doped silicon nanoparticles, the mesopore etching control, the mesopore strengthening, and the growth of carbon nanotubes on the surface of silicon-carbon. By using a simple process, the conductivity and the pressure strength of the obtained silicon-carbon material can be comprehensively optimized. When used in a lithium ion battery, the expansion can be effectively relieved while ensuring a high capacity, and the initial efficiency, the rate performance, and the cycle performance of the lithium ion battery can be comprehensively optimized. BRIEF DESCRIPTION OF DRAWINGS

[0093] Figure 1 It is a structural schematic diagram of the distribution of mesopores and micropores in the preparation process of the silicon-carbon material in the present application.

[0094] Figure 2 It is a structural schematic diagram of the silicon-carbon material with top-grown carbon nanotubes in Examples 1-4.

[0095] Figure 3 It is a structural schematic diagram of the silicon-carbon material with bottom-grown carbon nanotubes in Examples 5-8. DETAILED DESCRIPTION

[0096] The present application will be further described by way of examples, but the present application is not limited to the examples. In the following examples, the experimental methods not specified in the examples are selected according to conventional methods and conditions, or according to the instructions of the products.

[0097] Example 1

[0098] The silicon-carbon material is prepared according to the following steps:

[0099] S1, Preparation of the first precursor:

[0100] 1 kg of phenolic resin (type 2153, provided by Hubei Hengye Technology Co., Ltd.), 2 kg of ethanol, 60 g of urotropine (HMT), and 5 g of iron citrate (the molar amount of iron is 0.02 mol) were mixed in a high-speed dispersion homogenizer at a dispersion speed of 2000 r / min for 60 min. Spray drying was performed at 130℃ until the particle diameter was 8 μm, and a first precursor was obtained.

[0101] S2, preparation of a second precursor (i.e., porous carbon):

[0102] (1) Crosslinking: The first precursor was placed in a rotary furnace at a rotation speed of 10 r / min, and a nitrogen gas was introduced at a flow rate of 2 L·kg -1 min -1 -1 with a temperature increasing rate of 4℃ / min. After being raised to 200℃, the temperature was kept constant for 1 h.

[0103] (2) Carbonization: The temperature increasing rate was kept at 4℃ / min, and the nitrogen gas was introduced at a flow rate of 1 L·kg -1 min -1 -1. After being raised to 500℃, the temperature was kept constant for 2 h.

[0104] (3) Activation: CO2 was introduced, and the second precursor (i.e., porous carbon) was obtained after activation in a CO2 atmosphere for 9 h at a flow rate of 2 L·kg -1 min -1 -1 and a furnace temperature of 500℃. At this time, the iron citrate had been converted into nano-sized ferric oxide.

[0105] S3, preparation of a third precursor:

[0106] First vapor deposition: The atmosphere was switched to a mixture of silane and nitrogen gas (20% silane and 80% nitrogen gas by volume percentage) at a flow rate of 0.5 L·kg -1 min -1 -1 and an absolute pressure of 1 MPa, and silicon deposition, nitrogen doping, and reduction of metal oxides were performed at 500℃ for 8 h.

[0107] S4, preparation of a silicon-carbon material:

[0108] (1) Second vapor deposition: The atmosphere was switched to a mixture of acetylene and nitrogen gas (20% acetylene and 80% nitrogen gas by mass percentage) at a flow rate of 5 L·kg -1 min -1 -1, and deposition was performed at 500℃ for 10 h.

[0109] Subsequently, the atmosphere was switched to nitrogen gas, and then the temperature was lowered to room temperature (25℃).

[0110] (2) Washing and drying: then 0.1 mol / L hydrochloric acid was used to soak the product obtained in the previous step at 20 times the amount (by mass), for 30 min, filtration, repeated washing 2 times; then deionized water was used to continue washing 3 times. The powder washed by deionized water was dried by a double-cone drying machine, and then sealed and stored, to obtain the silicon-carbon material of the present example.

[0111] Example 2

[0112] On the basis of Example 1, only the amount of iron citrate in step S1 was changed to 10 g (the molar amount of iron was 0.04 mol), and the remaining steps and parameters were the same as Example 1, to prepare the silicon-carbon material of Example 2.

[0113] Example 3

[0114] On the basis of Example 1, only the amount of iron citrate in step S1 was changed to 15 g (the molar amount of iron was 0.06 mol), and the remaining steps and parameters were the same as Example 1, to prepare the silicon-carbon material of Example 3.

[0115] Example 4

[0116] On the basis of Example 1, only the amount of iron citrate in step S1 was changed to 20 g (the molar amount of iron was 0.08 mol), and the remaining steps and parameters were the same as Example 1, to prepare the silicon-carbon material of Example 4.

[0117] Example 5

[0118] On the basis of Example 1, only the amount of iron citrate in step S1 was changed to 25 g (the molar amount of iron was 0.1 mol), and the remaining steps and parameters were the same as Example 1, to prepare the silicon-carbon material of Example 5.

[0119] Example 6

[0120] On the basis of Example 1, only the amount of iron citrate in step S1 was changed to 30 g (the molar amount of iron was 0.12 mol), and the remaining steps and parameters were the same as Example 1, to prepare the silicon-carbon material of Example 6.

[0121] Example 7

[0122] On the basis of Example 1, only the amount of iron citrate in step S1 was changed to 35 g (the molar amount of iron was 0.14 mol), and the remaining steps and parameters were the same as Example 1, to prepare the silicon-carbon material of Example 7.

[0123] Example 8

[0124] On the basis of example 1, only the amount of iron citrate in step S1 is changed to 40 g (the molar amount of iron is 0.16 mol), and the remaining steps and parameters are the same as example 1, to prepare the silicon-carbon material of example 8.

[0125] Example 9

[0126] On the basis of example 1, only the iron citrate in step S1 is changed to iron acetate, and the amount is 37.2 g (the molar amount of iron is 0.25 mol), and the remaining steps and parameters are the same as example 1, to prepare the silicon-carbon material of example 9.

[0127] Example 10

[0128] On the basis of example 1, the amount of iron citrate in step S1 is changed to 20 g (the molar amount of iron is 0.08 mol), and the absolute pressure in step S3 is changed to 5 MPa, and the remaining steps and parameters are the same as example 1, to prepare the silicon-carbon material of example 10.

[0129] Example 11

[0130] On the basis of example 1, only the absolute pressure in step S3 is changed to 0.1 MPa, and the remaining steps and parameters are the same as example 1, to prepare the silicon-carbon material of example 11.

[0131] Comparative example 1

[0132] On the basis of example 1, no iron citrate is added in step S1, and silane is used to replace the mixed gas of silane and nitrogen in step S3, and the remaining steps and parameters are the same as example 1, to prepare the silicon-carbon material of comparative example 3.

[0133] Comparative example 2

[0134] On the basis of example 1, no iron citrate is added in step S1, and 60 g of melamine is added instead, and the remaining steps and parameters are the same as example 1, to prepare the silicon-carbon material of comparative example 2.

[0135] Comparative example 3

[0136] On the basis of example 1, silane is used to replace the mixed gas of silane and nitrogen in step S3, and the remaining steps and parameters are the same as example 1, to prepare the silicon-carbon material of comparative example 3.

[0137] Comparative example 4

[0138] On the basis of example 1, 60 g of melamine is added in the slurry in step S1, and silane is used to replace the mixed gas of silane and nitrogen in step S3, and the remaining steps and parameters are the same as example 1, to prepare the silicon-carbon material of comparative example 4.

[0139] Effect example

[0140] The following effect tests were performed on the intermediate products and the final silicon-carbon materials in Examples 1-11 and Comparative Examples 1-4, respectively:

[0141] 1. Electrochemical performance test

[0142] (1) Preparation of button cell

[0143] Preparation of negative electrode slurry and electrode sheet: The negative electrode formulation was designed as CMC:PAA:SBR:SP:CNTs:silicon-carbon material:graphite = 0.5:2.5:1:0.1:15:80.9. The negative electrode slurry preparation time sequence was graphite→ CMC→ silicon-carbon material→ SP→ CNTs, followed by dispersion for 3 h at a rotation speed of 300 r / min for self-rotation and 1000 r / min for revolution of a planetary disperser, then injection of deionized water (only 80% of the required amount) with a solid content of 40%, dispersion for 1 h at a rotation speed of 500 r / min for self-rotation and 600 r / min for revolution, addition of PAA and dispersion for 1 h at a rotation speed of 500 r / min for self-rotation and 500 r / min for revolution, injection of the remaining 20% deionized water, and finally addition of SBR and dispersion for 1 h at a rotation speed of 300 r / min for self-rotation and 300 r / min for revolution. The coated current collector was an 8 μm thick copper foil, which was coated on both sides, with the coated side facing the negative electrode of the button cell. The active material thickness was about 40 μm for single-sided coating, and the tap density was 1.8 g / cm 3 (the electrode sheet was punched into a unit circle, the weight was tested, the copper foil weight was subtracted, and the tap density was obtained by dividing the thickness), wherein the coating speed was 40 cm / S, the baking temperature was 80°C, and the drying time was 400 s.

[0144] Preparation of battery electrolyte: the electrolyte composition was as follows in terms of mass percentage: formula EC 10%, PC 15%, DEC 20%, PP 30%, LiPF6 15%, FEC 6%, PS 2.5%, and LiODFB 1.5%.

[0145] Preparation of half-cell: the positive electrode was the single negative electrode sheet as above, the negative electrode was a lithium sheet, and 0.5 g of the electrolyte as above was used to assemble a CR2450 button cell, with a voltage string port of 0-1.5 V. The entire cell assembly was performed in a glove box to avoid contact with air.

[0146] (2) Test parameters and steps

[0147] ①Gravimetric capacity and cycle failure number

[0148] 1.5 V gravimetric capacity:

[0149] The above button cell is discharged at a constant voltage of 0.1 V / h to 0.000 V, and then charged at 0.1 V / h to 1.5 V, and the charging capacity is recorded; after obtaining the capacity, the capacity per gram of active material in the electrode is used to obtain the gram capacity at 0.1 C 1.5 V.

[0150] 0.5C 1.5V cycle failure number (measured at 25℃ and 45℃ respectively):

[0151] Reassemble a button cell, and perform constant current charge-discharge test at 0.5C of the charging capacity, repeatedly charge-discharge 0v to 1.5v, terminate when the discharge gram capacity is 60% of the 1.5V gram capacity, and record the number of cycles, which is the cycle failure number under the test condition.

[0152] 1C 1.5V cycle failure number (measured at 25℃ and 45℃ respectively):

[0153] Reassemble a button cell, and perform constant current charge-discharge test at 1C of the charging capacity, repeatedly charge-discharge 0v to 1.5v, terminate when the discharge gram capacity is 60% of the 1.5V gram capacity, and record the number of cycles, which is the cycle failure number under the test condition.

[0154] ②Rate retention rate

[0155] 25℃ different rate retention rate (%): 1C rate cycle failure number / 0.5C rate cycle failure number at 25℃.

[0156] 45℃ different rate retention rate (%): 1C rate cycle failure number / 0.5C rate cycle failure number at 45℃.

[0157] 0.5C hot box cycle retention rate (%): 0.5C 45℃ cycle failure number / 0.5C 25℃ cycle failure number.

[0158] 45℃, 25℃ rate difference (%): 45℃ different rate retention rate-25℃ different rate retention rate.

[0159] ③Initial efficiency

[0160] The above button cell is discharged at a constant voltage of 0.1 V / h to 0.000 V, and then charged at 0.1 / h to 1.5 V, and the charge-discharge capacity is recorded, and the initial efficiency is obtained from the delithiation capacity / lithiation capacity.

[0161] ④Lithium intercalation expansion amount (measured at 25℃ and 45℃ respectively)

[0162] Lithium intercalation expansion amount: (thickness of the saturated lithium intercalation electrode - thickness of the copper foil) / (thickness of the non-lithium intercalation electrode - thickness of the copper foil) - 1.

[0163] 2. Physicochemical property test of the obtained intermediate product and silicon-carbon material itself

[0164] ① Particle size test: laser particle size analyzer was used.

[0165] ② Specific surface area and pore volume test: ASAP2020 of Micromeritics was used.

[0166] ③ Carbon content and silicon content test: high-frequency carbon-sulfur analyzer (model DK-606) was used.

[0167] ④ Iron content test: inductively coupled plasma spectrometer (ICP, model Agilent 5800, provided by Agilent) was used.

[0168] ⑤ Raman spectrum test (Raman): in the Raman spectrum curve of the silicon-carbon material, there are two characteristic peaks, the peak between 1310-1360 cm -1 is a disordered peak (D peak); the peak between 1560-1610 cm -1 is a graphite peak (G peak). The integral area ratio of D peak to G peak (ID / IG) can represent the degree of disorder or graphitization of the silicon-carbon material. The smaller the ID / IG, the lower the degree of disorder and the higher the degree of graphitization, and the stronger the role of the obtained material in buffering the lithium intercalation expansion of silicon.

[0169] ⑥ Powder conductivity test: powder conductivity meter (model FT-8100) was used, based on the four-probe test principle, and the test standard was GB / T 1552-1995. A known amount of solid powder of the material to be tested was compressed to a set pressure value or pressure under the action of hydraulic power, and the conductivity of the solid powder was measured online.

[0170] The results are shown in Tables 1-3, respectively.

[0171] Table 1

[0172]

[0173]

[0174] Table 2

[0175]

[0176] Table 3

[0177]

[0178]

[0179] As can be seen from the results of Table 1-Table 3, the silicon-carbon materials obtained in Examples 1-11 have at least lower ID / IG than Comparative Examples 1-4, and when used in batteries, have at least better cycle performance while having excellent anti-swelling performance, and preferably also have higher initial efficiency, higher cycle performance, higher rate performance and higher thermal cycle performance; indicating that the silicon-carbon materials obtained in Examples 1-11 of the present application can comprehensively optimize the various performances of the obtained batteries.

[0180] Specifically, in Examples 1-11 of the present application, due to the complexation of the iron salt, the pores of the carbon material precursor with a pore size of greater than or equal to 50 nm are first eliminated, and the overall strength is improved. During carbonization, due to the low residual carbon rate of the iron salt, mesopores are preferentially generated around the iron salt, and the iron salt is also converted into metal oxides attached to the mesopores. Further, during activation, due to the opening characteristics of the mesopores, a good micropore dispersion structure is further generated around the mesopores, and the metal oxides are also dispersed on the surface of the mesopores, as shown in FIG. 1. Figure 1 When the silicon source gas and nitrogen gas are introduced for the first gas phase deposition, silicon and doped nitrogen are deposited at the same time, and hydrogen gas is generated during the deposition of silane. On the one hand, based on the principle of Haber synthesis of ammonia, hydrogen and nitrogen synthesize ammonia, and while the nitrogen is solidified, the ammonia and silane have similar cracking temperatures, so that the nitrogen atoms are successfully doped into the silicon nanoparticles, reducing the resistance. On the other hand, hydrogen can also act as a reducing agent to reduce part of the metal oxides on the surface of the mesopores to metal elements, and then when the carbon source gas is introduced for the second gas phase deposition, carbon nanotubes and carbon coating are in-situ grown, and carbon nanotubes are in-situ grown from the metal elements as much as possible in a bottom growth manner. Among them, the oxides (ferric oxide) corresponding to the iron salt and the elemental iron are both catalysts for carbon nanotubes, but when the amount of iron salt is small, the amount of ferric oxide is relatively large. Due to the presence of oxygen atoms, the interaction between ferric oxide and carbon material is stronger, resulting in the growth of carbon nanotubes mainly in a top growth manner, as shown in FIG. 2. Figure 2 When the amount of iron salt is large, the amount of elemental iron is relatively large, and the interaction between iron and carbon material is smaller, resulting in the growth of carbon nanotubes mainly in a bottom growth manner, as shown in FIG. 3. Figure 3 With the gradual increase of the amount of iron salt, the overall improved performance is better, and when the amount reaches that of Example 4, the effect is optimal.

[0181] In Comparative Example 1, without adding iron salt and without doping nitrogen, the effective generation of mesopores, the effective growth of carbon nanotubes and the effective reduction of ohmic resistance are not performed, the ID / IG is obviously higher, the conductivity is obviously lower, and when used in batteries, the anti-swelling performance is obviously poorer, and the initial efficiency, cycle performance, etc. are all obviously decreased.

[0182] In the case of not adding iron salt and doping nitrogen in a conventional form (i.e. directly adding a nitrogen source in the carbon material precursor) in Comparative Example 2, effective generation of mesopores and effective growth of carbon tubes are not performed, ID / IG is obviously higher, conductivity is obviously lower, anti-swelling performance is obviously poorer after being used in a battery, and initial efficiency, cycle performance and the like are obviously decreased; it is shown that in the case of not adding iron salt, even if nitrogen is doped in a conventional manner, the effect after doping nitrogen in a trace amount in the embodiment of the present application with iron salt cannot be achieved.

[0183] In Comparative Example 3, even if iron salt is added, in the case of not doping nitrogen, ID / IG is obviously higher, conductivity is obviously lower, anti-swelling performance is obviously poorer after being used in a battery, and initial efficiency, cycle performance and the like are obviously decreased; it is shown that doping nitrogen in a trace amount also has a great influence.

[0184] In Comparative Example 4, even if iron salt is added, in the case of doping nitrogen in a conventional form (i.e. directly adding a nitrogen source in the carbon material precursor), ID / IG is obviously higher, conductivity is obviously lower, it is shown that the way of doping nitrogen in a trace amount also has a great influence, even if the nitrogen source is added in a conventional form, the effect after doping nitrogen in a trace amount during deposition cannot be achieved.

Claims

1. A method for preparing a silicon-carbon material, characterized by, The preparation method of the silicon-carbon material comprises the following steps: S1, dry the slurry of the carbon material precursor and the iron salt to obtain a first precursor; wherein the iron salt comprises an organic trivalent iron salt; S2, carbonize and activate the first precursor to obtain a second precursor; S3, perform first vapor deposition on the second precursor to obtain a third precursor; wherein the first deposition gas used in the first vapor deposition comprises a silicon source gas and a carrier gas; the silicon source gas comprises silane, and the carrier gas comprises nitrogen; S4, perform second vapor deposition on the third precursor to obtain the silicon-carbon material; wherein the second deposition gas used in the second vapor deposition comprises a carbon source gas.

2. The method for preparing silicon-carbon material as described in claim 1, characterized in that, In step S1, the organic trivalent iron salt comprises ferric acetate and / or ferric citrate; and / or, in step S1, the molar amount of iron in the iron salt is 0.01-1 mol / kg based on the mass of the carbon material precursor; and / or, in step S1, the drying is performed by spray drying; and / or, in step S1, the drying temperature is 70-200°C; and / or, in step S1, the particle size of the first precursor is 4-16 μm.

3. The method for preparing silicon-carbon material as described in claim 2, characterized in that, In step S1, the molar amount of iron in the iron salt is 0.02 mol / kg, 0.04 mol / kg, 0.06 mol / kg, 0.08 mol / kg, 0.12 mol / kg, 0.14 mol / kg, 0.16 mol / kg or 0.25 mol / kg based on the mass of the carbon material precursor; and / or, in step S1, the drying temperature is 130°C; and / or, in step S1, the particle size of the first precursor is 8 μm.

4. The method for preparing silicon-carbon material as described in claim 1, characterized in that, In step S1, the carbon material precursor comprises resin and / or biomass; and / or, in step S1, the solvent in the slurry comprises ethanol; and / or, in step S1, the mass ratio of the solvent in the slurry to the carbon material precursor is (1-20):

1.

5. The method for preparing silicon-carbon material as described in claim 4, characterized in that, In step S1, the resin comprises one or more of phenolic resin, epoxy resin, urea-formaldehyde resin, melamine-formaldehyde resin, furan resin, silicone resin, polyester resin, polyamide resin, acrylic resin, polyurethane, vinyl resin, hydrocarbon resin and polyether resin; and / or, in step S1, the biomass comprises one or more of lignin, cellulose, hemicellulose and chitin; and / or, in step S1, the mass ratio of the solvent in the slurry to the carbon material precursor is 2:

1.

6. The method for preparing silicon-carbon material as described in claim 5, characterized in that, In step S1, the carbon material precursor comprises phenolic resin, and the slurry further comprises a curing agent.

7. The method of making a silicon-carbon material of claim 6, wherein, In step S1, the curing agent comprises urotropine; and / or, in step S1, the mass ratio of the curing agent to the phenolic resin is (0.005-1):

1.

8. The method for preparing silicon-carbon material as described in claim 7, characterized in that, In step S1, the mass ratio of the curing agent to the phenolic resin is 0.06:

1.

9. The method for preparing silicon-carbon material as described in claim 1, characterized in that, In step S2, the carbonization is performed in a protective gas; and / or, in step S2, the carbonization comprises a heating stage and a holding stage; and / or, in step S2, the carbonization further comprises crosslinking the first precursor before the carbonization.

10. The method for preparing silicon-carbon material as described in claim 9, characterized in that, In step S2, during the carbonization process, the protective gas is nitrogen. And / or, in step S2, in the carbonization, the flow rate of the protective gas is 0.5-5 L kg -1 ·min -1 ; And / or, in step S2, during the carbonization process, the heating rate during the heating stage is 1-10℃ / min; And / or, in step S2, during the carbonization process, the temperature of the heat preservation stage is 300-550℃; And / or, in step S2, the heat preservation stage during carbonization lasts for 0.5-5 hours; And / or, in step S2, the crosslinking includes a heating stage and a heat preservation stage.

11. The method of making a silicon-carbon material of claim 10, wherein, In step S2, the flow rate of the protective gas is 1 L-kg -1 ·min -1 ; And / or, in step S2, during the carbonization process, the heating rate during the heating stage is 4°C / min; And / or, in step S2, the temperature of the heat preservation stage during carbonization is 500°C; And / or, in step S2, the heat preservation stage during carbonization lasts for 2 hours; And / or, in step S2, during the crosslinking process, the heating rate during the heating phase is 1-10℃ / min; And / or, in step S2, during the crosslinking process, the temperature of the heat preservation stage is 100-300℃; And / or, in step S2, the heat preservation stage during the crosslinking process lasts for 0.5-2 hours.

12. The method of making a silicon-carbon material of claim 11, wherein, In step S2, during the crosslinking process, the heating rate during the heating stage is 4°C / min; And / or, in step S2, during the crosslinking process, the temperature of the heat preservation stage is 200°C; And / or, in step S2, the heat preservation stage during the crosslinking process lasts for 1 hour.

13. The method of claim 1, wherein the silicon-carbon material is prepared by the steps of: In step S2, the activation methods include gas activation and / or alkali activation. ​ 14. The method of making a silicon-carbon material of claim 13, wherein, In step S2, the gas activation is CO2 activation or water vapor activation.

15. The method of claim 14, wherein the silicon-carbon material is prepared by In the CO2 activation in step S2, the flow rate of the CO2 is 0.1-10 L·kg -1 ·min -1 ; And / or, in step S2, the CO2 activation time is 2-20 hours; And / or, in step S2, the CO2 activation temperature is 300-500℃.

16. The method of making a silicon-carbon material of claim 15, wherein, In the CO2 activation in step S2, the flow rate of the CO2 is 2 L-kg -1 ·min -1 ; And / or, in step S2, the CO2 activation time is 9 hours.

17. The method for preparing silicon-carbon material as described in claim 1, characterized in that, In step S3, the volume ratio of the silicon source gas to the carrier gas is (0.05-1):1; And / or, in step S3, the silane includes one or more of methylsilane, disilane, propane, and butane; And / or, in step S3, the flow rate of the first deposition gas is 0.1-2 L·kg -1 ·min -1 ; And / or, in step S3, the temperature of the first vapor deposition is 400-500℃; And / or, in step S3, the absolute pressure of the first vapor deposition is 0.1-50 MPa; And / or, in step S3, the time for the first vapor deposition is 4-16 hours.

18. The method of making a silicon-carbon material of claim 17, wherein, In step S3, the volume ratio of the silicon source gas to the carrier gas is 0.25:1; And / or, in step S3, the flow rate of the first deposition gas is 0.5 L·kg -1 ·min -1 ; And / or, in step S3, the temperature of the first vapor deposition is 500°C; And / or, in step S3, the absolute pressure of the first vapor deposition is 1 MPa or 5 MPa; And / or, in step S3, the time for the first vapor deposition is 8 hours.

19. The method of making a silicon-carbon material of claim 1, wherein, In step S4, the carbon source gas includes one or more of alkynes, alkanes, alkenes, aromatic compounds, and carbohydrates; And / or, in step S4, the second deposition gas further includes a carrier gas; And / or, in step S4, the flow rate of the second deposition gas is 0.1-50 L kg -1 ·min -1 ; And / or, in step S4, the temperature of the second vapor deposition is 400-800°C; And / or, in step S4, the second vapor deposition is performed for 2-40 hours. And / or, in step S4, the second vapor deposition is followed by a washing and drying step.

20. The method of making a silicon-carbon material of claim 19, wherein, In step S4, the carrier gas in the second deposition gas comprises nitrogen. And / or, in step S4, the volume ratio of the carbon source gas to the carrier gas in the second deposition gas is (0.05-1):

1. And / or, in step S4, the flow rate of the second deposition gas is 5 L kg -1 ·min -1 ; And / or, in step S4, the second vapor deposition is performed at a temperature of 500°C. And / or, in step S4, the second vapor deposition is performed for 10 hours. And / or, in step S4, the washing step comprises a hydrochloric acid washing step followed by a water washing step.

21. The method of making a silicon-carbon material of claim 20, wherein, In step S4, the volume ratio of the carbon source gas to the carrier gas in the second deposition gas is 0.25:

1.

22. A silicon-carbon material, characterized in that, The silicon-carbon material is prepared by the method of any one of claims 1-21.

23. The silicon-carbon material of claim 22, wherein, The silicon-carbon material comprises a core-shell structure, the core-shell structure comprising an inner core, an outer shell, and carbon nanotubes; the inner core comprises porous carbon and silicon particles, the silicon particles being distributed on the surface and / or in the pores of the porous carbon; the outer shell comprises a carbon layer, the carbon layer being coated on the surface of the inner core; And / or, the silicon content of the silicon-carbon material is 45%-55%. And / or, the carbon content of the silicon-carbon material is 45%-55%. And / or, the powder conductivity of the silicon-carbon material is 10-1000 s / cm. And / or, the D50 particle size of the silicon-carbon material is 7.5-8.5 μm. and / or the silicon-carbon material has a specific surface area of 3-5 m 2 / g.

24. The silicon-carbon material of claim 23, wherein, The distribution mode of the carbon nanotubes comprises one or more of the following modes ①-⑤: ① the carbon nanotubes are distributed in the pores of the porous carbon, ② the carbon nanotubes are distributed on the surface of the porous carbon; ③ the carbon nanotubes extend from the surface of the porous carbon and penetrate through the outer shell; ④ the carbon nanotubes extend from the pores of the porous carbon and penetrate through the outer shell; ⑤ the carbon nanotubes extend from the inside of the outer shell and penetrate through the outer shell; And / or, the silicon content of the silicon-carbon material is 48.0%, 50.18%, 50.35%, 50.54%, 50.69%, 50.67%, 50.75%, 50.65%, 50.2%, or 51.49%. And / or, the carbon content of the silicon-carbon material is 49.82%, 49.65%, 49.46%, 49.31%, 49.33%, 49.25%, 49.35%, 49.8%, 48.51%, or 52.0%. And / or, the powder conductivity of the silicon-carbon material is 11.4 s / cm, 13.2 s / cm, 32.2 s / cm, 54.1 s / cm, 87.3 s / cm, 134.2 s / cm, 189.6 s / cm, 205.3 s / cm, 213.2 s / cm, 801 s / cm, or 91.2 s / cm. And / or, the D50 particle size of the silicon-carbon material is 7.7 μm, 7.8 μm, 7.9 μm, or 8 μm. and / or the silicon-carbon material has a specific surface area of 3.4 m2 / g 2 / g, 3.6 m 2 / g, 3.8 m 2 / g, 4 m 2 / g, 4.1 m 2 / g, or 4.3 m 2 / g.

25. A lithium-ion battery, characterized by, The lithium ion battery comprises the silicon-carbon material of any one of claims 22-24.

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