Lithium-doped porous carbon material, negative electrode material, preparation method and application

Abstract

The invention discloses a lithium-doped porous carbon material, a negative electrode material, a preparation method and application, the lithium-doped porous carbon material comprises porous carbon and lithium, the porous carbon comprises through holes, the proportion of the through holes in the porous carbon is 40-60%, and the lithium is at least partially dispersed and distributed in the through holes of the porous carbon. And lithium doping is carried out on the porous carbon material, so that active lithium loss in the initial cycle process can be compensated, and the first efficiency and the capacity of the silicon-carbon negative electrode material prepared from the porous carbon material can be effectively improved. A battery using the lithium-doped porous carbon material can effectively relieve lithium ions consumed after SEI is generated in the cycle process, the performance of the battery is improved, meanwhile, the silicon nanoparticles are embedded in the through holes, and improvement of the structural stability of the silicon-carbon negative electrode material is facilitated.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of negative electrode materials, in particular to a lithium-doped porous carbon material, a negative electrode material, a preparation method and application. BACKGROUND

[0002] With the rapid development of society, the capacity performance of graphite negative electrode materials has been difficult to meet the growing market demand. Under this background, researchers urgently need to develop new negative electrode materials to meet the demand for high-performance energy storage. Silicon (Si) material is considered as a promising negative electrode material candidate due to its theoretical specific capacity of up to 4200 mAh / g. However, this material still faces many challenges in practical application, including significant volume expansion effect, low first-cycle coulombic efficiency, and poor lithium ion / electron conduction performance, etc. These factors seriously restrict the commercialization process of lithium-doped silicon-carbon materials.

[0003] In view of the above technical bottlenecks, domestic and foreign research teams have carried out a lot of exploratory work, mainly including: conductive matrix composite modification, ion / electron transport channel construction, and nanostructure design, etc. Innovative strategies. In the review paper published in the journal Green Energy & Environment [Prelithiation strategies for silicon-based anode in high energy density lithium-ion battery] by Jia et al., it is pointed out that the current mainstream research scheme is to pre-dope lithium-containing compounds in the negative electrode material to compensate for the loss of active lithium in the initial cycle process, in order to improve the cycle stability of the battery. However, existing research results show that the modification effect of this strategy has not yet reached the expected level.

[0004] In view of this, the present application is proposed. SUMMARY

[0005] The purpose of the present application is to provide a lithium-doped porous carbon material, a negative electrode material, a preparation method and application, which is beneficial to improve the cycle stability of the negative electrode material prepared from the lithium-doped porous carbon material.

[0006] The present application is implemented as follows:

[0007] In a first aspect, the present application provides a lithium-doped porous carbon material, comprising a porous carbon and lithium, the porous carbon containing through holes, the through hole ratio in the porous carbon being 40% to 60%, and the lithium being at least partially dispersedly distributed in the through holes of the porous carbon.

[0008] In an optional embodiment, at least one of the following characteristics i-v is met:

[0009] i. the pore volume of the porous carbon is 1.5 cm 3 / g ~ 3.5 cm 3 / g;

[0010] ii. the average pore size of the porous carbon is 3 nm ~ 10 nm;

[0011] iii. the mass fraction of lithium in the lithium-doped porous carbon material is 0.1% ~ 5%;

[0012] iv. the pore volume of the lithium-doped porous carbon material is 0.8 cm 3 / g ~ 1.2 cm 3 / g;

[0013] v. the lithium-doped porous carbon material comprises porous carbon and lithium and lithium-carbon composite particles dispersedly distributed on the inner wall of the through hole of the porous carbon.

[0014] In a second aspect, the present application provides a preparation method of a lithium-doped porous carbon material, comprising:

[0015] primary lithium doping, performing primary lithium doping on the porous carbon to obtain a primary-doped porous carbon;

[0016] secondary lithium doping, mixing the primary-doped porous carbon with a lithium salt and a resin, and then performing carbonization to obtain a secondary-doped porous carbon;

[0017] activation, performing activation on the secondary-doped porous carbon to obtain the lithium-doped porous carbon material.

[0018] In optional embodiments, at least one of the following features a ~ f is met:

[0019] a. the through hole accounts for 40% ~ 60% in the porous carbon;

[0020] b. the pore volume of the porous carbon is 1.5 cm 3 / g ~ 3.5 cm 3 / g;

[0021] c. the average pore size of the porous carbon is 3 nm ~ 10 nm;

[0022] d. the primary lithium doping and / or the secondary lithium doping is performed by an impregnation method;

[0023] e. the lithium source used in the primary lithium doping and / or the secondary lithium doping comprises at least one of machine lithium and inorganic lithium;

[0024] f. the activation method comprises a chemical activation method or a physical activation method.

[0025] In an optional embodiment, the primary lithium doping comprises: subjecting the porous carbon to a primary impregnation in a first impregnation solution comprising a lithium salt, followed by a primary drying, to obtain a primary doped porous carbon;

[0026] And / or, the secondary lithium doping comprises: subjecting the primary doped porous carbon to a secondary impregnation in a second impregnation solution comprising a lithium salt and a resin, followed by a secondary drying and carbonization, to obtain a secondary doped carbon material.

[0027] In an optional embodiment, at least one of the following features (1) to (15) is satisfied:

[0028] (1) In the primary lithium doping step, the mass ratio of lithium element to carbon element in the first impregnation solution is 1:(10-500);

[0029] (2) The primary impregnation step is performed under a protective gas condition;

[0030] (3) The primary impregnation step is performed at a temperature of 45-120°C and a gauge pressure of 0-10 MPa;

[0031] (4) The primary impregnation step is performed under stirring, the stirring time is 2-24 h, and the stirring rate is 100-1000 rpm;

[0032] (5) The temperature of the primary drying step is -30- -50°C, and the time is 48-96 h;

[0033] (6) The organic lithium comprises at least one of lithium trifluoromethanesulfonate, lithium bis(oxalato)borate, butyl lithium, and phenyl lithium;

[0034] (7) The inorganic lithium comprises at least one of lithium carbonate, lithium perchlorate, lithium hydroxide, lithium tetrafluoroborate, lithium hexafluoroarsenate, and lithium hexafluorophosphate;

[0035] (8) In the first impregnation solution, the solvent is selected from any one or more of water, aromatic hydrocarbons, alcohols, ether solvents, N-methylpyrrolidone, and N,N-dimethylformamide;

[0036] (9) In the second impregnation solution, the mass ratio of lithium element to resin is 1:(20-600);

[0037] (10) In the second impregnation solution, the mass fraction of the resin is 35-70%;

[0038] (11) In the second impregnation solution, the solvent is selected from at least one of acetone, alcohol, and water.

[0039] (12) In the secondary lithium doping step, the second impregnation solution covers the primary doped porous carbon;

[0040] (13) the secondary lithium doping step comprises: placing the primary doped porous carbon in a reactor for negative pressure treatment, then adding the second impregnation solution into the reactor and performing pressure treatment;

[0041] (14) the temperature of the secondary drying step is 60-120℃, and the time is 4-72h;

[0042] (15) the temperature of the carbonization step is 450-1200℃, the time is 2-12h, the heating rate is 1-10℃ / min, and the carbonization step is performed in the presence of a protective gas.

[0043] In an optional embodiment, the gauge pressure of the negative pressure treatment step is -0.01Kpa to -0.001Kpa;

[0044] And / or, the negative pressure treatment step and / or the pressure treatment step is performed under stirring at a stirring rate of 100-500rpm;

[0045] And / or, the gauge pressure of the pressure treatment step is 0-6MPa, the time is 12-96h, and the pressure treatment is performed in the presence of a protective gas;

[0046] And / or, the primary impregnation step satisfies Δ JZ / TP is 0.25-5; wherein, ΔJZ is the change in the normalized lithium content per unit temperature*pressure, T is the temperature of the primary impregnation step in unit of ℃, and P is the absolute pressure of the primary impregnation step in unit of MPa.

[0047] In an optional embodiment, the activation step adopts a water vapor activation mode, the activation temperature is 900-1100℃, the water vapor flow rate is 45-55L / min, and the activation time is 40-60h.

[0048] In a third aspect, the present application provides a preparation method of a lithium-doped silicon-carbon material, comprising: introducing a silicon-containing gas source into a reactor containing the lithium-doped porous carbon material as described in the foregoing embodiments to perform silicon deposition, to obtain the lithium-doped silicon-carbon material.

[0049] In an optional embodiment, the lithium-doped porous carbon material is first crushed to a D50 of 4.5-8.5μm and a particle size concentration degree of ≤2 before being placed in the reactor;

[0050] And / or, the silicon-containing gas source comprises at least one of silane, trichlorosilane, silicon tetrafluoride, silicon tetrachloride, and dichlorosilane;

[0051] And / or, the deposition temperature of the silicon deposition step is 350-500 DEG C, the flow rate of the silicon-containing gas source is 100-1000 L / h, and the deposition time is 24-96 h.

[0052] In a fourth aspect, the present application provides a lithium-doped silicon-carbon material, which is prepared by the method for preparing a lithium-doped silicon-carbon material according to the preceding embodiments, and the mass fraction of lithium in the lithium-doped silicon-carbon material is 0.1-5%.

[0053] In a fifth aspect, the present application provides a negative electrode sheet comprising the lithium-doped silicon-carbon material according to the preceding embodiments.

[0054] In a sixth aspect, the present application provides a battery comprising the negative electrode sheet according to the preceding embodiments.

[0055] The present application has the following beneficial effects:

[0056] Lithium doping of the porous carbon material can compensate for the loss of active lithium during the initial cycle, and can effectively improve the initial efficiency and capacity of the silicon-carbon negative electrode material prepared therefrom.

[0057] The battery using the lithium-doped porous carbon material according to the present application can effectively alleviate the consumption of lithium ions after the formation of SEI during the cycle, and improve the performance thereof, and the silicon nanoparticles are embedded in the through holes, which is beneficial to the improvement of the structural stability of the silicon-carbon negative electrode material. BRIEF DESCRIPTION OF DRAWINGS

[0058] In order to more clearly illustrate the technical solutions of the embodiments of the present application, the following will briefly introduce the drawings needed to be used in the embodiments. It should be understood that the following drawings only show some embodiments of the present application, and therefore should not be regarded as a limitation on the scope. For those skilled in the art, other related drawings can also be obtained without creative labor on the basis of these drawings.

[0059] Figure 1 The figure is the immersion effect of the porous carbon under different conditions for one-time immersion;

[0060] Figure 2 The figure is the SEM of the lithium-doped silicon-carbon material prepared in Example 1. DETAILED DESCRIPTION

[0061] In order to make the purpose, technical solutions and advantages of the embodiments of the present application more clear, the technical solutions in the embodiments of the present application will be described clearly and completely. The specific conditions are not specified in the embodiments, and are carried out according to the conventional conditions or the conditions recommended by the manufacturer. The reagents or instruments used are not specified by the manufacturer, and are all conventional products that can be obtained by market purchase.

[0062] The embodiment of the present application provides a lithium-doped porous carbon material, which comprises porous carbon and lithium, the porous carbon contains through holes, the ratio of the through holes in the porous carbon is 40%-60%, for example, 40%, 42%, 44%, 46%, 48%, 50%, 52%, 54%, 56%, 58%, 60%, and the lithium is at least partially dispersed in the through holes of the porous carbon.

[0063] The lithium-doping of the porous carbon material can compensate for the active lithium loss in the initial cycle process, and can effectively improve the initial efficiency and capacity of the silicon-carbon negative electrode material prepared therefrom.

[0064] The battery using the lithium-doped porous carbon material in the present application can effectively alleviate the consumption of lithium ions after the formation of SEI in the cycle process, and improve the performance, and the silicon nanoparticles are inlaid in the through holes, which is beneficial to the improvement of the structural stability of the silicon-carbon negative electrode material.

[0065] In the present application, the ratio of the through holes refers to the volume ratio of the through hole volume to the total pore volume.

[0066] In the optional embodiment, at least one of the following characteristics i-v is met:

[0067] i. The pore volume of the porous carbon is 1.5 cm 3 / g-3.5 cm 3 / g, for example, 1.5 cm3 / g, 1.7 cm3 / g, 1.9 cm3 / g, 2.1 cm 3 / g, 2.3 cm 3 / g, 2.5 cm 3 / g, 2.7 cm 3 / g, 2.9 cm 3 / g, 3.1 cm 3 / g, 3.3 cm 3 / g, 3.5 cm 3 / g;

[0068] ii. The average pore diameter of the porous carbon is 3 nm-10 nm, for example, 3 nm, 3.8 nm, 4.6 nm, 5.4 nm, 6.2 nm, 7.0 nm, 7.8 nm, 8.6 nm, 9.4 nm, 10 nm;

[0069] iii. The mass fraction of lithium in the lithium-doped porous carbon material is 0.1%-5%, for example, 0.1%, 0.6%, 1.1%, 1.6%, 2.1%, 2.6%, 3.1%, 3.6%, 4.1%, 4.6%, 5%;

[0070] iv. The pore volume of the lithium-doped porous carbon material is 0.8 cm 3 / g-1.2 cm 3 / g, for example 0.8 cm3 / g, 0.84 cm3 / g, 0.88 cm3 / g 3 / g, 0.92 cm 3 / g, 0.96 cm 3 / g, 1.0 cm 3 / g, 1.04 cm 3 / g, 1.08 cm 3 / g, 1.12 cm 3 / g, 1.16 cm 3 / g, 1.2 cm 3 / g.

[0071] v. the lithium-doped porous carbon material comprises porous carbon, lithium dispersedly distributed on the inner wall of the through hole of the porous carbon, and a porous carbon skeleton generated in situ on the porous carbon, wherein the porous carbon skeleton comprises lithium-carbon compounds.

[0072] The porous carbon has a suitable pore volume and pore size, which is conducive to providing more storage sites for lithium, and facilitating the entry of lithium into the pore structure during lithium doping, thereby facilitating the increase of the amount of lithium doping.

[0073] The amount of lithium doping is in the range of 0.1% to 5%, which can balance the cycle stability and capacity of the silicon-carbon negative electrode material prepared therefrom, and is conducive to promoting the application of the silicon-carbon negative electrode in high-energy-density batteries.

[0074] The pore volume of the lithium-doped porous carbon material is 0.8 to 1.2 cm 3 / g, which is conducive to the subsequent deposition of silicon in the pore structure to increase the capacity of the silicon-carbon negative electrode material.

[0075] For the structure of the lithium-doped porous carbon material, the skeleton of the lithium-doped porous carbon material in the present application comprises a porous carbon base skeleton and dispersedly distributed lithium and / or lithium-carbon compounds, which is more conducive to the improvement of the conductivity of the silicon-carbon negative electrode material prepared therefrom and the buffering of the volume expansion of the silicon particles, thereby facilitating the improvement of the structural stability.

[0076] The present application also provides a preparation method of a lithium-doped porous carbon material, comprising:

[0077] primary lithium doping, performing primary lithium doping on the porous carbon to obtain a once-doped porous carbon;

[0078] secondary lithium doping, mixing the once-doped porous carbon with a lithium salt and a resin, and then carbonizing to obtain a twice-doped porous carbon;

[0079] activation, activating the twice-doped porous carbon to obtain the lithium-doped porous carbon material.

[0080] In the preparation method of the lithium-doped porous carbon material, lithium is introduced into the porous carbon by the first lithium doping, and the carbon skeleton is formed while the lithium doping is performed by the second lithium doping. After the carbon skeleton is activated, the porous carbon skeleton is formed, and then the lithium-doped porous carbon material with good structural stability is obtained.

[0081] In optional embodiments, at least one of the following features a-f is satisfied:

[0082] a. The ratio of through holes in the porous carbon is 40-60%, for example, 40%, 42%, 44%, 46%, 48%, 50%, 52%, 54%, 56%, 58%, or 60%;

[0083] b. The pore volume of the porous carbon is 1.5 cm 3 / g-3.5 cm 3 / g, for example, 1.5 cm3 / g, 1.7 cm3 / g, 1.9 cm3 / g, 2.1 cm 3 / g, 2.3 cm 3 / g, 2.5 cm 3 / g, 2.7 cm 3 / g, 2.9 cm 3 / g, 3.1 cm 3 / g, 3.3 cm 3 / g, 3.5 cm 3 / g;

[0084] c. The average pore size of the porous carbon is 3-10 nm, for example, 3 nm, 3.8 nm, 4.6 nm, 5.4 nm, 6.2 nm, 7.0 nm, 7.8 nm, 8.6 nm, 9.4 nm, or 10 nm;

[0085] d. The first lithium doping and / or the second lithium doping is performed by the impregnation method;

[0086] e. The lithium source used in the first lithium doping and / or the second lithium doping includes at least one of machine lithium and inorganic lithium;

[0087] f. The activation method includes a chemical activation method and a physical activation method.

[0088] When the impregnation method is used for doping, the ratio of through holes, the pore volume, and the average pore size of the porous carbon have a great influence on the entry of the impregnation solution, which in turn affects the content of lithium doping.

[0089] In optional embodiments, the first lithium doping includes: placing the porous carbon in a first impregnation solution including a lithium salt for first impregnation, and then performing first drying to obtain the first-doped porous carbon. In the first doping step, lithium mainly exists on the surface of the through holes of the porous carbon.

[0090] In an optional embodiment, the secondary lithium doping comprises: placing the primary doped porous carbon into a second impregnation solution comprising a lithium salt and a resin for secondary impregnation, followed by secondary drying and carbonization to obtain a secondary doped carbon material. In the secondary doping step, the second impregnation solution fills the inside of the through holes of the porous carbon and at least partially coats the surface of the porous carbon. After carbonization, a carbon skeleton is formed in the through holes and part of the surface of the porous carbon, and lithium is doped in the carbon skeleton. After a subsequent activation step, a porous carbon skeleton is formed.

[0091] In an optional embodiment, at least one of the following features (1) to (15) is satisfied:

[0092] (1) In the primary lithium doping step, the mass ratio of lithium element in the first impregnation solution to carbon element in the porous carbon is 1:(10-500), for example, 1:10, 1:50, 1:100, 1:200, 1:300, 1:400, 1:500;

[0093] (2) The primary impregnation step is carried out under a protective gas condition;

[0094] (3) The temperature of the primary impregnation step is 45℃-120℃, for example, 45℃, 53℃, 61℃, 69℃, 77℃, 85℃, 93℃, 101℃, 109℃, 117℃, 120℃; and the pressure is 0MPa-10MPa, for example, 0MPa, 1MPa, 2MPa, 3MPa, 4MPa, 5MPa, 6MPa, 7MPa, 8MPa, 9MPa, 10MPa;

[0095] (4) The primary impregnation step is carried out under stirring conditions, the stirring time is 2h-24h, for example, 45℃, 53℃, 61℃, 69℃, 77℃, 85℃, 93℃, 101℃, 109℃, 117℃, 120℃; and the stirring rate is 100rpm-1000rpm, for example, 100rpm, 200rpm, 300rpm, 400rpm, 500rpm, 600rpm, 700rpm, 800rpm, 900rpm, 1000rpm;

[0096] (5) The temperature of the primary drying step is -30℃--50℃, for example, -30℃, -32℃, -34℃, -36℃, -38℃, -40℃, -42℃, -44℃, -46℃, -48℃, -50℃; and the time is 48h-96h, for example, 48h, 53h, 58h, 63h, 68h, 73h, 78h, 83h, 88h, 93h, 96h;

[0097] (6) The organic lithium comprises at least one of lithium trifluoromethanesulfonate, lithium bis(oxalato)borate, butyl lithium and phenyl lithium;

[0098] (7) the inorganic lithium comprises at least one of lithium carbonate, lithium perchlorate, lithium hydroxide, lithium tetrafluoroborate, lithium hexafluoroarsenate and lithium hexafluorophosphate;

[0099] (8) in the first impregnation solution, the solvent is selected from any one or more of water, aromatic hydrocarbons, alcohol, ether solvent, N-methyl pyrrolidone and N,N-dimethylformamide;

[0100] (9) in the second impregnation solution, the mass ratio of lithium element to resin is 1:(20-600), for example 1:20, 1:84, 1:148, 1:212, 1:276, 1:340, 1:404, 1:468, 1:532, 1:596, 1:600;

[0101] (10) in the second impregnation solution, the mass fraction of resin is 35%-70%, for example 35%, 39%, 43%, 47%, 51%, 55%, 59%, 63%, 67%, 70%;

[0102] (11) in the second impregnation solution, the solvent is selected from at least one of acetone, alcohol and water.

[0103] (12) in the secondary lithium doping step, the second impregnation solution covers the once-doped porous carbon;

[0104] (13) the secondary lithium doping step comprises: placing the once-doped porous carbon in a reactor for negative pressure treatment, then adding the second impregnation solution into the reactor and performing pressure treatment;

[0105] (14) the temperature of the secondary drying step is 60-120°C, for example 60°C, 66°C, 72°C, 78°C, 84°C, 90°C, 96°C, 102°C, 108°C, 114°C, 120°C; and the time is 4-72h, for example 4h, 11h, 18h, 25h, 32h, 39h, 46h, 53h, 60h, 67h, 72h;

[0106] (15) the temperature of the carbonization step is 450-1200°C, for example 450°C, 530°C, 610°C, 690°C, 770°C, 850°C, 930°C, 1010°C, 1090°C, 1170°C, 1200°C; the time is 2-12h, for example 2h, 3h, 4h, 5h, 6h, 7h, 8h, 9h, 10h, 11h, 12h; the heating rate is 1-10°C / min, for example 1°C / min, 2°C / min, 3°C / min, 4°C / min, 5°C / min, 6°C / min, 7°C / min, 8°C / min, 9°C / min, 10°C / min; and the carbonization step is performed in the presence of a protective gas.

[0107] Specifically, the first impregnation step is carried out under the condition of increasing temperature and pressure, which is more conducive to the penetration of the impregnation solution into the pore structure of the porous carbon, and is conducive to increasing the lithium doping amount in the first lithium doping step.

[0108] In an optional embodiment, the first impregnation step satisfies Δ JZ / TP is 0.25-5, for example, 0.25, 0.75, 1.25, 1.75, 2.25, 2.75, 3.25, 3.75, 4.25, 4.75, 5; wherein, Δ JZ is the change amount of the normalized lithium content under unit temperature*pressure; T is the temperature of the first impregnation step, in units of ℃; P is the absolute pressure of the first impregnation step, in units of MPa. It should be noted that during the first impregnation process, the impregnation effect is improved by adjusting the impregnation temperature and the impregnation pressure, so that the lithium content after the first impregnation is significantly improved; wherein, Δ JZ = M TP / M0 is normalized, M TP is the lithium content in the lithium-doped porous carbon material at a temperature of T and a gauge pressure of P, and M0 is the lithium content in the lithium-doped porous carbon material at a temperature of 25℃ and a gauge pressure of 0MPa, i.e. the pressure is atmospheric pressure.

[0109] In the second lithium doping step, first, a negative pressure treatment is carried out to extract the gas in the pores of the porous carbon, and then a second impregnation solution is added for pressure treatment, so that the second impregnation solution can enter the small and deep pore structure of the porous carbon, which is conducive to repairing cracks in the porous carbon structure and improving the stability of the porous carbon structure. At the same time, it can also increase the bonding area between the porous carbon and the subsequent formed porous carbon skeleton, thereby improving the bonding strength between them, which is conducive to improving the structural stability of the material.

[0110] In an optional embodiment, the gauge pressure of the negative pressure treatment step is -0.01Kpa to -0.001Kpa, for example, -0.01kPa, -0.009kPa, -0.008kPa, -0.007kPa, -0.006kPa, -0.005kPa, -0.004kPa, -0.003kPa, -0.002kPa, -0.001kPa;

[0111] And / or, the negative pressure treatment step and / or the pressure treatment step is carried out under stirring conditions, and the stirring rate is 100rpm-500rpm, for example, 100rpm, 140rpm, 180rpm, 220rpm, 260rpm, 300rpm, 340rpm, 380rpm, 420rpm, 460rpm, 500rpm;

[0112] and / or, the pressure treatment step has a gauge pressure of 0 MPa to 6 MPa, for example, 0 MPa, 0.6 MPa, 1.2 MPa, 1.8 MPa, 2.4 MPa, 3.0 MPa, 3.6 MPa, 4.2 MPa, 4.8 MPa, 5.4 MPa, 6 MPa; a time of 12 h to 96 h, for example, 12 h, 21 h, 30 h, 39 h, 48 h, 57 h, 66 h, 75 h, 84 h, 93 h, 96 h; and the pressure treatment is performed in the presence of a protective gas.

[0113] The gauge pressure of the negative pressure and pressure treatment steps is within the above range, which is conducive to extracting the gas in the carbon material and pressing the second impregnating solution into the deep and fine pore structure of the porous carbon; if the absolute value of the gauge pressure of the negative pressure or pressure treatment step is too large, the porous carbon may be subjected to excessive pressure fluctuation and cracks or other defects may be generated or intensified.

[0114] In an optional embodiment, the activation step is performed by using steam activation, the activation temperature is 900 ℃ to 1100 ℃, for example, 900 ℃, 920 ℃, 940 ℃, 960 ℃, 980 ℃, 1000 ℃, 1020 ℃, 1040 ℃, 1060 ℃, 1080 ℃, 1100 ℃; the steam flow rate is 45 L / min to 55 L / min, for example, 45 L / min, 46 L / min, 47 L / min, 48 L / min, 49 L / min, 50 L / min, 51 L / min, 52 L / min, 53 L / min, 54 L / min, 55 L / min; and the activation time is 40 h to 60 h, for example, 40 h, 42 h, 44 h, 46 h, 48 h, 50 h, 52 h, 54 h, 56 h, 58 h, 60 h.

[0115] After the activation step, a rich pore structure is formed in the carbon skeleton on the porous carbon, forming a porous carbon skeleton.

[0116] The embodiment of the present application also provides a preparation method of a lithium-doped silicon-carbon material, which comprises: introducing a silicon-containing gas source into a reactor in which the lithium-doped porous carbon material in the above embodiment is placed to perform silicon deposition, so as to obtain the lithium-doped silicon-carbon material.

[0117] In an optional embodiment, the lithium-doped porous carbon material is first crushed to have a D50 of 4.5 μm to 8.5 μm, for example, D50: 4.5 μm, 4.9 μm, 5.3 μm, 5.7 μm, 6.1 μm, 6.5 μm, 6.9 μm, 7.3 μm, 7.7 μm, 8.1 μm, 8.5 μm, before being placed in the reactor; and the particle size concentration degree is ≤2, and the particle size concentration degree is (D10+D90) / D50; a suitable particle size is conducive to the lithium-doped silicon-carbon material having both structural stability and cycle stability.

[0118] In an optional embodiment, the silicon-containing gas source comprises at least one of silane, trichlorosilane, silicon tetrafluoride, silicon tetrachloride, and dichlorosilane;

[0119] And / or, the deposition temperature of the silicon deposition step is 350-500℃, for example, 350℃, 365℃, 380℃, 395℃, 410℃, 425℃, 440℃, 455℃, 470℃, 485℃, 500℃; the flow rate of the silicon-containing gas source is 100-1000L / h, for example, 100L / h, 200L / h, 300L / h, 400L / h, 500L / h, 600L / h, 700L / h, 800L / h, 900L / h, 1000L / h; the deposition time is 24-96h, for example, 24h, 32h, 40h, 48h, 56h, 64h, 72h, 80h, 88h, 96h.

[0120] Silicon is deposited to the pores and part of the surface of the lithium-doped porous carbon material, the lithium-doped porous carbon material has good structural stability, and the deposited silicon is beneficial to improve the capacity of the lithium-doped silicon-carbon material, so that the lithium-doped silicon-carbon material has both structural stability and capacity.

[0121] The embodiment of the present application further provides a lithium-doped silicon-carbon material, which is prepared by the preparation method of the lithium-doped silicon-carbon material described in the foregoing embodiment, and the mass fraction of lithium in the lithium-doped silicon-carbon material is 0.1%-5%, for example, 0.1%, 0.6%, 1.1%, 1.6%, 2.1%, 2.6%, 3.1%, 3.6%, 4.1%, 4.6%, 5%.

[0122] The embodiment of the present application further provides a negative electrode sheet comprising the lithium-doped silicon-carbon material described in the foregoing embodiment.

[0123] The embodiment of the present application further provides a battery comprising the negative electrode sheet described in the foregoing embodiment.

[0124] The features and performances of the present application are further described in detail below in combination with examples.

[0125] Example 1

[0126] The embodiment provides a preparation method of a lithium-doped silicon-carbon material, which specifically comprises the following steps:

[0127] 1) 10L of an aqueous solution of lithium carbonate with a concentration of 0.175mol / L is mixed with 500g of a porous carbon with a ratio of through holes of 40%, an average pore size of 6nm, and a pore volume of 2.5cm 3 / g, which is prepared by a template method, to obtain solution A.

[0128] 2) Put solution A into a high-pressure reactor, and stir at 300 rpm under the conditions of 3 MPa gauge pressure and 80℃ for 12 h to obtain solution B.

[0129] 3) Put solution B into a freeze dryer, and vacuum dry at ~50℃ for 48 h to obtain the lithium-doped porous carbon material.

[0130] 4) Take 30 mL of lithium perchlorate aqueous solution with a concentration of 50 mol / L, and stir in 2 kg of resin-ethanol solution (phenol-formaldehyde resin solution with a mass fraction of 60%) for 12 h to obtain a mixed solution.

[0131] 5) Take 500 g of the lithium-doped porous carbon material after freeze drying, and vacuumize in a negative pressure bottle (~0.01 KPa) while stirring at 300 rpm, then slowly add the mixed solution into the bottle until the material is covered, and stir during the process to obtain a composite material.

[0132] 6) Put the composite material into a high-pressure reactor, and stir at 300 rpm under the conditions of 4 MPa gauge pressure for 24 h, then perform solid-liquid separation to obtain a second-doped composite material.

[0133] 7) Dry the second-doped composite material at 80℃ under vacuum for 24 h.

[0134] 8) Put the dried material into a box furnace, and heat to 1000℃ at a rate of 5℃ / min, and keep the temperature for 6 h to complete carbonization.

[0135] 9) Perform steam activation on the carbonized material to obtain a second lithium-doped porous carbon material, wherein the pore volume of the second lithium-doped porous carbon material is 1.0 cm 3 / g, the activation temperature is 1000℃, the water vapor is introduced at a flow rate of 50 L / min, and the introduction time is 48 h.

[0136] 10) After crushing the second lithium-doped porous carbon material to a D50 of 8 μm and a particle size concentration of 1.5, put it into a CVD furnace, introduce silane gas at a flow rate of 800 L / h at 400℃, and the introduction time is 48 h to obtain a lithium-doped silicon-carbon material, and the SEM image is as shown in Figure 2 .

[0137] Example 2

[0138] The difference from Example 1 is only that the amount of lithium carbonate solution in step 1) is changed to 20 L.

[0139] Example 3

[0140] The difference from Example 1 is only that the gauge pressure in step 2) is changed to 1 MPa.

[0141] Example 4

[0142] The difference from Example 1 is only that the stirring time in step 2) is changed to 24 h.

[0143] Example 5

[0144] The difference from Example 1 is only that the lithium carbonate solution is replaced by a lithium hydroxide solution with a concentration of 0.35 mol / L.

[0145] Example 6

[0146] The difference from Example 1 is only that the lithium carbonate solution used is replaced by a lithium bistrifluoromethanesulfonimide solution with a concentration of 0.35 mol / L.

[0147] Example 7

[0148] The difference from Example 1 is only that the average pore size is changed to 10 nm.

[0149] Example 8

[0150] The difference from Example 1 is only that the porous carbon in step 1) is replaced by a porous carbon with a porosity of 40%, a pore size of 6 nm and a pore volume of 1.25 cm 3 / g, which is prepared by a template method.

[0151] Example 9

[0152] The difference from Example 1 is only that the porous carbon in step 1) is replaced by a porous carbon with a porosity of 40%, a pore size of 6 nm and a pore volume of 3.5 cm 3 / g, which is prepared by a template method.

[0153] Comparative Example 1

[0154] The difference from Example 1 is only that the pressure in step 2) is reduced to atmospheric pressure.

[0155] Comparative Example 2

[0156] The difference from Example 1 is only that the temperature in step 2) is reduced to 25°C.

[0157] Comparative Example 3

[0158] The difference from Example 1 is only that the pressure in step 6) is reduced to atmospheric pressure.

[0159] Comparative Example 4

[0160] The difference from Example 1 is only that steps 4) to 7) are removed and the porous carbon material doped with lithium elements is directly carbonized.

[0161] Comparative Example 5

[0162] The difference from Example 1 is that steps 1) to 3) are removed, and 500 g of porous carbon with a porosity of 40%, a pore size of 6 nm, and a pore volume of 2.5 cm 3 / g is used to replace the lithium element-doped porous carbon material in step 5).

[0163] Comparative Example 6

[0164] The difference from Example 1 is that the secondary lithium-doped porous carbon material in step 10) is not crushed, but directly subjected to silicon deposition.

[0165] Comparative Example 7

[0166] The difference from Example 1 is that the pressure in step 2) is reduced to atmospheric pressure, and the temperature is reduced to 25°C.

[0167] Comparative Example 8

[0168] The difference from Example 1 is that steps 4) to 7) are removed, the lithium element-doped porous carbon material is directly subjected to carbonization, and the concentration of the lithium carbonate solution in step 1) is 0.80 mol / L.

[0169] Comparative Example 9

[0170] The difference from Example 1 is that steps 1) to 3) are removed, and 500 g of porous carbon with a porosity of 40%, a pore size of 6 nm, and a pore volume of 2.5 cm 3 / g is used to replace the lithium element-doped porous carbon material in step 5), and the mass of the lithium perchlorate aqueous solution in step 4) is changed to 180 mL.

[0171] Comparative Example 10

[0172] The difference from Example 1 is that step 5) is not subjected to vacuum treatment, and 500 g of the lithium element-doped porous carbon material after freeze-drying is placed in a negative pressure bottle, and then the above-mentioned mixed solution is slowly added into the bottle until it is higher than the material, and stirring is performed during the process to obtain the composite material.

[0173] According to the mass ratio of active material: SP: CMC: SBR = 92: 2: 2: 4, lithium-doped silicon-carbon material, SP, CMC and SBR were weighed and uniformly mixed in deionized water to prepare a slurry; the uniformly mixed slurry was coated on an aluminum foil current collector, the aluminum foil current collector was cut before coating, an aluminum foil disc with a diameter of 14 mm was prepared and weighed as m2, then the slurry-coated current collector was baked in an 80°C oven for 1 h, cooled to room temperature, and the roll gap was adjusted for roll pressing. The roll-pressed electrode was cut to prepare a small disc with a diameter of 14 mm and weighed as m1, and (m1-m2) * 0.92 was the mass of the active material, denoted as m3. The weighed small disc was placed in an 80°C oven for vacuum baking for 12 h. The vacuum-baked small disc was transferred to a glove box, lithium pieces were used as the counter electrode and auxiliary electrode, 1M NaPF6 solution was used as the electrolyte, the volume ratio of EC: DMC: DEC mixed solvent was 2: 2: 1, and glass fiber was used as the separator. A lithium ion button cell was assembled in a glove box with oxygen and water content less than 0.01 ppm. The assembled button lithium ion battery was allowed to stand for 12 h. The button lithium ion battery after standing was tested for electrochemical performance on a Wuhan Blue Electric Battery Test System, specifically: at 25°C, first discharged at 0.1C to 0.005V, then discharged at 0.08C to 0.001V, discharged at 0.05C to 0.001V, discharged at 0.02C to 0.001V, and stood for 10 min; then charged at 0.1C to 1.5V and stood for 10 min. The charge and discharge capacity after the first cycle was recorded, and the first coulombic efficiency (referred to as first efficiency) was calculated.

[0174] The thickness H1 before charging and the thickness H2 after charging of the negative electrode sheet before and after the first charge and discharge were measured by TEM, and the expansion rate was (H2-H1) / H1.

[0175] The D50 of the lithium-doped silicon-carbon material was detected by Malvern 3000.

[0176] The mass fraction of lithium element was detected by X-ray photoelectron spectroscopy. The pore volume was determined by gas adsorption method.

[0177] Table 1

[0178]

[0179]

[0180] According to Table 1, the expansion rate of the silicon-carbon material prepared in each embodiment of the application is less than that of the comparative example, indicating that the lithium-doped porous carbon material and the silicon-carbon material prepared in the application have good structural stability.

[0181] Further, it can be seen from the comparison of Example 1 and Examples 2-5 and Comparative Examples 1, 2 and 7 that appropriately increasing the amount of the first impregnation solution or prolonging the stirring time of the first impregnation is conducive to increasing the lithium doping amount, and the lithium doping amount of the first impregnation is reduced, but if the temperature and pressure of the first impregnation are too low, the lithium doping amount will be significantly reduced. Moreover, with the increase of the lithium doping amount, the first coulombic efficiency and the expansion rate tend to increase, and the capacity first increases and then decreases.

[0182] The comparison of Examples 5 and 6 with Example 1 shows that both organic lithium source and inorganic lithium source can be used for lithium doping of the porous carbon material.

[0183] Example 7 has an increased average pore size compared to Example 1, which is more conducive to the entry of lithium into the pore structure, thereby facilitating the increase of the lithium doping amount.

[0184] The comparison of Comparative Examples 3 and 10 with Example 1 shows that vacuumizing first and then pressurizing is more conducive to increasing the lithium doping amount, and the structure stability of the obtained silicon-carbon material is better.

[0185] The comparison of Comparative Examples 4 and 5 with Example 1 shows that there is a synergistic effect between the first impregnation and the second impregnation, which is conducive to increasing the lithium doping amount, and the second impregnation can also significantly improve the structure stability of the silicon-carbon material.

[0186] The comparison of Comparative Examples 8 and 9 with Example 1 shows that single lithium supplementing can achieve the effect (lithium content) of double lithium supplementing, but there is a large difference in performance.

[0187] To study the influencing factors of the first impregnation, the temperature and the pressure were adjusted based on Example 1, the product of the temperature and the absolute pressure was taken as the horizontal coordinate, the normalized lithium content of the lithium-doped silicon-carbon material prepared was taken as the vertical coordinate, and the green curve in FIG. 1 was fitted; the product of the temperature and the atmospheric pressure was taken as the horizontal coordinate based on Comparative Example 1, and the normalized lithium content of the lithium-doped silicon-carbon material prepared was taken as the vertical coordinate, and the red curve in FIG. 1 was fitted; the product of the absolute pressure and the temperature was taken as the horizontal coordinate based on Comparative Example 2, and the normalized lithium content of the lithium-doped silicon-carbon material prepared was taken as the vertical coordinate, and the blue curve in FIG. 1 was fitted. It can be seen from FIG. 1 that compared with only increasing the temperature or only increasing the pressure, simultaneously increasing the temperature and the pressure is conducive to improving the impregnation effect. Figure 1 Figure 1 Figure 1 Figure 1

[0188] ​​​​The above merely provides the preferred embodiments of the present application, and is not used to limit the present application. For those skilled in the art, the present application can have various modifications and changes. Any modifications, equivalent replacements, improvements, etc. made within the principles and technical scope of the present application shall fall into the scope of the present application.

Claims

1. A lithium-doped porous carbon material, characterized in that: The invention comprises porous carbon and lithium, wherein the porous carbon comprises through-holes, the through-holes account for 40% to 60% of the porous carbon, and the lithium is at least partially dispersed in the through-holes of the porous carbon.

2. The porous carbon material according to claim 1, wherein Satisfy at least one of the following characteristics i-v: i. The pore volume of the porous carbon is 1.5 cm 3 / g~3.5cm 3 / g; ii. The average pore size of the porous carbon is 3nm to 10nm; iii. The mass fraction of lithium in the lithium-doped porous carbon material is 0.1% to 5%; iv. The pore volume of the lithium-doped porous carbon material is 0.8 cm 3 / g~1.2cm 3 / g; v. The lithium-doped porous carbon material comprises porous carbon and lithium and lithium-carbon composite particles dispersedly distributed on the inner walls of the porous carbon pores.

3. A method for preparing a lithium-doped porous carbon material, characterized in that: include: primary lithium doping, performing lithium doping on the porous carbon to obtain primary doped porous carbon; Secondary lithium doping: the primary doped porous carbon is mixed with lithium salt and resin and then carbonized to obtain secondary doped porous carbon; Activation: activating the secondary doped porous carbon to obtain the lithium-doped porous carbon material.

4. The method for preparing a lithium-doped porous carbon material according to claim 3, wherein: Satisfy at least one of the following characteristics a to f: a. The porous carbon has a through-hole ratio of 40% to 60%; b. The pore volume of the porous carbon is 1.5 cm 3 / g~3.5cm 3 / g; c. The average pore size of the porous carbon is 3 nm to 10 nm; d. using an impregnation method for primary lithium doping and / or secondary lithium doping; e. The primary lithium doping and / or secondary lithium doping lithium source comprises at least one of organic lithium and inorganic lithium; f. The activation method includes chemical activation or physical activation.

5. The method for preparing lithium-doped porous carbon material according to claim 4, characterized in that: The primary lithium doping comprises: placing the porous carbon in a first impregnation solution comprising a lithium salt for a primary impregnation, followed by a primary drying to obtain the primary doped porous carbon; And / or, the secondary lithium doping comprises: placing the primary doped porous carbon in a second impregnation solution comprising a lithium salt and a resin for secondary impregnation, followed by secondary drying and carbonization to obtain a secondary doped carbon material.

6. The method for preparing a lithium-doped porous carbon material according to claim 5, wherein: Satisfy at least one of the following characteristics (1) to (15): (1) In the primary lithium doping step, the mass ratio of lithium element in the first impregnation solution to carbon element in the porous carbon is 1:(10-500); (2) the primary impregnation step is carried out under protective gas conditions; (3) The temperature of the first impregnation step is 45°C to 120°C and the gauge pressure is 0 MPa to 10 MPa; (4) The primary impregnation step is carried out under stirring conditions, with a stirring time of 2 h to 24 h and a stirring rate of 100 rpm to 1000 rpm; (5) The temperature of the primary drying step is -30°C to -50°C, and the time is 48h to 96h; (6) The organic lithium comprises at least one of lithium trifluoromethanesulfonate, lithium bis(oxalatoborate), butyl lithium and phenyl lithium; (7) The inorganic lithium comprises at least one of lithium carbonate, lithium perchlorate, lithium hydroxide, lithium tetrafluoroborate, lithium hexafluoroarsenate and lithium hexafluorophosphate; (8) In the first impregnation solution, the solvent is selected from any one or more of water, aromatic hydrocarbons, alcohols, ether solvents, N-methylpyrrolidone and N,N-dimethylformamide; (9) In the second impregnation solution, the mass ratio of lithium element to resin is 1:(20-600); (10) In the second impregnation liquid, the mass fraction of the resin is 35% to 70%; (11) In the second impregnation solution, the solvent is selected from at least one of acetone, alcohol and water; (12) In the secondary lithium doping step, the second impregnation solution does not cover the primary doped porous carbon; (13) The secondary lithium doping step comprises: placing the primary doped porous carbon in a reactor and subjecting it to negative pressure treatment, and then adding the second impregnation solution into the reactor and subjecting it to pressure treatment; (14) The temperature of the secondary drying step is 60°C to 120°C, and the time is 4h to 72h; (15) The carbonization step is carried out at a temperature of 450°C to 1200°C, for a time of 2 h to 12 h, at a heating rate of 1°C / min to 10°C / min, and in the presence of a protective gas.

7. The method for preparing a lithium-doped porous carbon material according to claim 6, wherein: The gauge pressure of the negative pressure treatment step is -0.01Kpa to -0.001Kpa; and / or, the negative pressure treatment step and / or the pressurized treatment step is performed under stirring conditions, with a stirring rate of 100 rpm to 500 rpm; And / or, the gauge pressure of the pressure treatment step is 0 MPa to 6 MPa, the time is 12 hours to 96 hours, and the pressure treatment is carried out in the presence of a protective gas; and / or, a single impregnation step satisfies Δ JZ / TP is 0.25~5; among them, Δ J Z is the normalized change in lithium content per unit temperature*pressure, T is the temperature of the first impregnation step, in °C; P is the absolute pressure of the first impregnation step, in MPa.

8. The method for preparing a lithium-doped porous carbon material according to claim 3, wherein: The activation step adopts a water vapor activation method, the activation temperature is 900° C. to 1100° C., the water vapor flow rate is 45 L / min to 55 L / min, and the activation time is 40 h to 60 h.

9. A method for preparing a lithium-doped silicon-carbon material, characterized in that: include: A silicon-containing gas source is introduced into a reactor containing the lithium-doped porous carbon material according to claim 1 or 2 to carry out silicon deposition, thereby obtaining the lithium-doped silicon-carbon material.

10. The method for preparing lithium-doped silicon-carbon material according to claim 9, characterized in that: The lithium-doped porous carbon material is crushed to a D50 of 4.5 μm to 8.5 μm and a particle size concentration of ≤2 before being placed in the reactor; And / or, the silicon-containing gas source includes at least one of silane, trichlorosilane, silicon tetrafluoride, silicon tetrachloride and dichlorosilane; And / or, the deposition temperature of the silicon deposition step is 350° C. to 500° C., the flow rate of the silicon-containing gas source is 100 L / h to 1000 L / h, and the deposition time is 24 h to 96 h.

11. A lithium-doped silicon-carbon material, characterized in that: The lithium-doped silicon-carbon material is prepared by the preparation method of the lithium-doped silicon-carbon material according to claim 9 or 10, wherein the mass fraction of lithium in the lithium-doped silicon-carbon material is 0.1% to 5%.

12. A negative electrode sheet, characterized in that: Including the lithium-doped silicon-carbon material according to claim 11.

13. A battery, characterized in that: Including the negative electrode sheet according to claim 12.

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