Silicon-carbon negative electrode material for high-rate lithium-ion battery, preparation method thereof and application

Abstract

The present invention discloses a silicon-carbon anode material for high-rate lithium-ion batteries, its preparation method and application, belonging to the field of new energy technologies. The silicon-carbon anode material provided by the present invention comprises a porous carbon framework and a silicon-based material dispersed inside the porous carbon framework; moreover, element A is doped in the porous carbon framework, element A includes at least one of N, P, B and F, and the mass percentage of element A in the porous carbon framework is 0.5-15%; and / or, element B is doped in the silicon-based material; element B includes at least one of Li, Mg, Ti, Cr, Mn, Fe, Co, Ni, Cu, Zn, Ge, As and Sn, and the mass percentage of element B in the silicon-based material is 0.2-23%. The silicon-carbon anode material provided by the present invention can effectively improve its rate performance, cycle performance and first efficiency. The present invention also provides a preparation method and an application of the above-mentioned silicon-carbon anode material.

Description

Technical Field

[0001] The present invention relates to the technical field of new energy, and in particular to a silicon-carbon negative electrode material for high-rate lithium-ion batteries, a preparation method thereof, and an application thereof. Background Art

[0002] In the current power battery and consumer battery markets, lithium-ion batteries have become the absolute mainstream energy storage system due to their huge advantages in terms of voltage, life, self-discharge, and energy density. Whether it is power batteries or consumer batteries, there is an endless demand for improving battery life. The energy density (ED) (volume energy density VED, mass energy density GED) of lithium-ion batteries is the ultimate indicator on the premise that other basic performance requirements are met. In addition, the charge and discharge performance of different energy storage units at high power has been challenged with the continuous increase in the demand for fast charging in electric vehicles and consumer electronics. Among them, the lithium intercalation ability of the negative electrode material, that is, the rate performance, directly determines the energy replenishment efficiency of the energy storage unit.

[0003] In the lithium-ion battery system, the positive electrode material has reached the limit of capacity utilization in the process of industrial use, or the improvement ratio is not high (for example, lithium iron phosphate 150 / 175 mAh / g, nickel cobalt manganese ternary positive electrode 190 / 205 mAh / g, lithium manganate 142 / 148 mAh / g); the graphite negative electrode has also reached the compromise bottleneck of capacity and initial efficiency (355 / 372 mAh / g). In this context, silicon negative electrodes have gradually been used in consumer batteries and are beginning to develop towards power batteries. It has a specific capacity of up to 4200 mAh / g, which is more than ten times that of the graphite specific capacity of 372 mAh / g. However, because it can accommodate a large number of lithium ions for alloying reactions, during the lithium deintercalation process of battery cycling, a volume expansion of >300% will occur. Therefore, in the current situation where the rate performance requirements of battery cells are getting higher and higher, the problem faced by silicon negative electrode materials can be summarized as follows: The requirement to improve ED makes it inevitable for silicon negative electrode materials to partially replace graphite, but the high-rate demand is another constraint that limits the large-scale use of silicon negative electrodes besides their expansion.

[0004] The silicon anode routes mainly include the silicon oxide route, the prelithiated silicon oxide route, and the silicon carbon route. Among them, the silicon-based anode material obtained by the silicon oxide route has too low initial efficiency (~76%), resulting in a large loss of active lithium ions in the cathode. That is to say, the use of the silicon oxide route has limited improvement in ED. To make up for the low initial efficiency problem of the silicon oxide route, prelithiated silicon oxide materials have been developed. However, the lithium source used in the prelithiation process is expensive, and the improvement of the initial efficiency has also approached the limit (82%). However, the excessive formation of SEI during the battery cell cycle will continuously increase the impedance on the anode side of the battery cell, reduce the rate performance, and increase the risk of thermal runaway. Among silicon-based materials, the method of reducing the particle size can be used to alleviate its volume expansion problem and improve the rate performance. Traditional silicon carbon materials are prepared by the grinding method. The smallest size of the silicon particles obtained can be flake materials with a thickness of 20 nm and a length of 100 nm. However, this size limit still cannot solve the structural impact on the battery cell caused by its lithium intercalation expansion. Overall, the upper limit of the specific capacity per gram of the silicon-based anode materials prepared by the above three ideas is about 420 mAh / g.

[0005] In summary, for the silicon-based anode materials provided by the traditional technology, the specific capacity per gram, cycle performance, and rate performance all need to be improved. Summary of the Invention

[0006] The present invention aims to solve at least one of the technical problems existing in the prior art. For this purpose, the present invention provides a silicon carbon anode material for high-rate lithium-ion batteries, which can effectively improve its rate performance, cycle performance, and initial efficiency.

[0007] The present invention also provides a preparation method for the above silicon carbon anode material.

[0008] The present invention also provides an application of the above silicon carbon anode material.

[0009] According to an embodiment of the first aspect of the present invention, there is provided a silicon carbon anode material for high-rate lithium-ion batteries. The silicon carbon anode material includes a porous carbon skeleton and a silicon-based material dispersed inside the porous carbon skeleton; and,

[0010] Element A is doped in the porous carbon skeleton. Element A includes at least one of N, P, B, and F. The mass percentage of element A in the porous carbon skeleton is 0.5 to 15%;

[0011] And / or, element B is doped in the silicon-based material; element B includes at least one of Li, Mg, Ti, Cr, Mn, Fe, Co, Ni, Cu, Zn, Ge, As, and Sn. The mass percentage of element B in the silicon-based material is 0.2 to 23%.

[0012] The silicon carbon anode material according to the embodiment of the present invention has at least the following beneficial effects:

[0013] Dispersing silicon-based materials in a porous carbon framework can maximize the dispersion degree of the silicon-based materials and minimize the impact on the structure of lithium-ion batteries. However, at the same time, this dispersion method will inevitably introduce more interfacial barriers through which lithium ions are difficult to shuttle due to the high dispersion degree. The present invention solves the above problems through the coordination between the types and amounts of doped elements, providing a higher lithium-ion migration rate:

[0014] (1) The porous carbon framework, such as the porous carbon framework produced by pyrolysis of biomass raw materials, is actually a mixture of highly ordered graphite microcrystalline regions and highly disordered amorphous carbon regions. The doping of element A can regulate the interface between the two ordered components and increase the binding strength between the two existences. In addition, among element A, the doping of N element can improve the electronic conductivity of the porous carbon framework; the doping of B and P elements can broaden the ion migration channels of the carbon component and increase the lithium-ion migration rate; F can shrink the carbon component lattice, enhance the rigidity strength of the carbon component, and reduce the lithium intercalation expansion of the material. Overall, introducing element A into the porous carbon can improve the interlayer spacing of the graphite microcrystals that make up the porous carbon framework, provide an electronic conductivity network, an ion transport network / interface, and expansion inhibition, and increase the lithium-ion migration rate in the framework.

[0015] Among element B, Li itself plays a role in supplementing lithium elements and increases the initial Coulomb efficiency of the material; other types of elements B such as Mg, Ti, and Cr can all regulate the lattice structure of the silicon component, reduce the lattice energy loss when lithium ions are embedded in the silicon-based material, make the spatial resistance and electrical repulsion of the lithium-ion deintercalation and intercalation behavior smaller, and improve the rate performance of the material;

[0016] That is, simply doping element A or simply doping element B can significantly improve the rate performance of the obtained silicon-carbon negative electrode material; and there is a significant synergistic effect between element A and element B: on the one hand, a small amount of chemical bonds formed at the contact points between element A and element B at the carbon-silicon two-phase interface can promote the lithium-ion migration rate in the two phases and further improve the rate performance of the material; on the other hand, the improved silicon-based material and the improved porous carbon framework ensure the high rate performance, cycle performance, and initial efficiency of the entire silicon-carbon negative electrode material.

[0017] (2) Although the doping of element A and / or element B is helpful for improving the rate performance of the obtained silicon-carbon negative electrode material, if the doping amount of element A is excessive, it will affect the pore structure and electronic structure of the porous carbon framework; if the doping amount of element B is excessive, it will affect the lithium intercalation capacity of the silicon-based material; that is, the present invention obtains a silicon-carbon negative electrode material with the optimal comprehensive performance such as rate by limiting the doping amounts of element A and element B.

[0018] According to some embodiments of the present invention, the element A is selected from N.

[0019] According to some embodiments of the present invention, the mass percentage of element A in the porous carbon framework is 1-9%. For example, it can be specifically about 2%, 2.5%, 3%, 4%, 5%, 6%, 7%, 8% or about 8.5%.

[0020] According to some embodiments of the present invention, element B is selected from Ge.

[0021] According to some embodiments of the present invention, the mass percentage of element B in the silicon-based material is 1-8%. For example, it can be specifically about 2%, 3%, 3.5%, 4%, 5%, 6%, 7% or about 7.5%.

[0022] According to some embodiments of the present invention, in the silicon-carbon negative electrode material, the sum of the mass percentages of element silicon and element carbon is ≥93%.

[0023] According to some embodiments of the present invention, in the silicon-carbon negative electrode material, the mass percentage of the silicon-based material is 25-75%. In the silicon-carbon negative electrode material, the lithium intercalation capacity is mainly contributed by the silicon-based material. If the proportion of the silicon-based material is low, it will lead to a decline in the performance of the obtained silicon-carbon negative electrode material in terms of capacity, efficiency, etc.; if the proportion of the silicon-based material is too high, the porosity of the obtained silicon-carbon negative electrode material will be significantly reduced, and the increased volume after lithium intercalation in the silicon-based material is difficult to be accommodated, which will significantly affect the performance in terms of cycling, etc. Therefore, by limiting the proportion of the silicon-based material, the present invention obtains a silicon-carbon negative electrode material with excellent comprehensive capacity.

[0024] According to some embodiments of the present invention, in the silicon-carbon negative electrode material, the mass percentage of the silicon-based material is 45-50%. Further specifically, it can be about 46%, 46.5% or about 47%.

[0025] According to some embodiments of the present invention, the particle size of the porous carbon framework satisfies at least one of the following indexes:

[0026] 0.75μm < D n10 < 2.3μm;

[0027] 2.5μm < D V10 < 5.9μm; For example, it can be specifically about 2.7μm, 3μm, 4μm, 5μm or about 5.5μm;

[0028] 6.3μm < D V50 < 11μm; For example, it can be specifically about 7μm, 7.5μm, 8μm, 9μm or about 10μm;

[0029] 11.4μm < D V90 < 20μm;

[0030] 21.3μm < D V99< 35 μm; for example, specifically, it can be about 22 μm, 23 μm, 24 μm, 26 μm, 27 μm, 28 μm, 29 μm, 30 μm, 31 μm, 32 μm, 33 μm or about 34 μm;

[0031] 35 μm < D VMAX < 100 μm.

[0032] According to some embodiments of the present invention, the particle size of the silicon-carbon negative electrode material satisfies at least one of the following indexes:

[0033] 0.75 μm < D n10 < 2.3 μm;

[0034] 2.5 μm < D V10 < 5.9 μm;

[0035] 6.3 μm < D V50 < 11 μm;

[0036] 11.4 μm < D V90 < 20 μm;

[0037] 21.3 μm < D V99 < 35 μm;

[0038] 35 μm < D VMAX < 100 μm.

[0039] In actual production, the silicon-carbon negative electrode material will basically inherit the particle size parameters of the porous carbon skeleton, and even if a shell layer is coated, since the shell layer is very thin, it will basically not affect the particle size parameters of the porous carbon skeleton; therefore, in fact, the particle size parameters of the porous carbon skeleton and the silicon-carbon negative electrode material are basically the same.

[0040] According to some embodiments of the present invention, the silicon-carbon negative electrode material further includes a shell layer, and the shell layer is coated on the surface of the silicon-carbon negative electrode material.

[0041] According to some embodiments of the present invention, the material of the shell layer includes at least one of carbon, metal oxide, fast ion conductor and organic polymer. Thereby, at least to a certain extent, the side reaction between the electrolyte and the silicon-based material can be avoided, and the cycle life of the silicon-carbon negative electrode material can be prolonged.

[0042] According to some embodiments of the present invention, in the coin cell, when the charging cut-off voltage is 2.0 V and the discharging cut-off voltage is 0.005 V; the first efficiency FCE of the silicon-carbon negative electrode material 2.0V is in the range of 84.5% < FCE 2.0V< 96.5%. For example, it can specifically be 86 - 95%. More specifically, it can be approximately 90%, 91%, 91.5%, 92%, 92.5%, 93%, 93.5%, 94% or approximately 94.5%.

[0043] According to some embodiments of the present invention, in the button cell, when the charging cut-off voltage is 0.8V and the discharging cut-off voltage is 0.005V; the first efficiency FCE of the silicon-carbon negative electrode material 0.8V ranges from 76.5% < FCE 0.8V < 85.5%. For example, it can specifically be 78 - 84.5%. More specifically, it can be approximately 80%, 81%, 82%, 82.5%, 83% or approximately 84%.

[0044] According to some embodiments of the present invention, compared with the undoped silicon-carbon negative electrode material, the silicon-carbon negative electrode material obtained by doping element A alone has a rate performance improvement of 1% - 20%. For example, it can specifically be approximately 1.3%, 1.5%, 2%, 5%, 10% or approximately 15%.

[0045] According to some embodiments of the present invention, compared with the undoped silicon-carbon negative electrode material, the silicon-carbon negative electrode material obtained by doping element B alone has a rate performance improvement of 1% - 25%. For example, it can specifically be approximately 1.3%, 1.5%, 2%, 3%, 5%, 10%, 15% or approximately 20%.

[0046] According to some embodiments of the present invention, compared with the undoped silicon-carbon negative electrode material, the silicon-carbon negative electrode material obtained by doping element A and element B simultaneously has a rate performance improvement of 1% - 45%. For example, it can specifically be approximately 2%, 3%, 3.5%, 4%, 5%, 10%, 20%, 30% or approximately 40%.

[0047] Unless otherwise specified, the rate performance mentioned in the present invention is the ratio of the discharge specific capacity per gram at 0.33C and 0.1C within the voltage range of 0.005 - 2.0V.

[0048] According to the embodiments of the second aspect of the present invention, a preparation method of the silicon-carbon negative electrode material is provided, and the preparation method includes the following steps:

[0049] S1. Mix the carbon source and the precursor of element A, and thermally decompose to obtain the porous carbon framework under the condition of isolating water and oxygen;

[0050] S2. Use a gas including the silicon source and the precursor of element B as the mixed gas source, and perform chemical vapor deposition with the porous carbon framework as the substrate.

[0051] The preparation method according to the embodiments of the present invention has at least the following beneficial effects:

[0052] (1) The present invention uses carbon source pyrolysis to produce a porous carbon framework, which has the advantages of wide source of preparation raw materials, low cost, good isotropy, controllable performance, easy modification of pore structure, and better uniformity and dispersion of the silicon-based material distribution therein.

[0053] Furthermore, in the present invention, the precursor of element A and the carbon source are mixed and then pyrolyzed, which improves the uniformity of doping of element A in the porous carbon framework.

[0054] (2) The present invention uses chemical vapor deposition to produce silicon-based materials, which is a bottom-up method for constructing micro-nano particles. Compared with the traditional top-down construction methods such as grinding, the particle size of the silicon-based materials is smaller, and it is limited by the pore diameter of the porous carbon framework, and the maximum dispersion distribution of the silicon-based materials in the porous carbon framework can be achieved. Thus, the stress impact on the battery caused by the volume change of the silicon-based material during charge and discharge is further alleviated. Specifically, compared with the top-down method, the silicon-carbon composite material prepared by the present invention can reduce the volume change ratio by 50%.

[0055] Furthermore, during the process of using chemical vapor deposition, some of the silicon-based materials will also chemically react with the porous carbon framework to generate Si-C bonds, thereby reducing the graphitization degree of the porous carbon framework and improving the initial efficiency of the obtained silicon-carbon composite material.

[0056] Even further, in the present invention, the precursor of element B and the silicon source are used together as a mixed gas source, which can improve the uniformity of the doping distribution of element B in the silicon-based material.

[0057] According to some embodiments of the present invention, in step S1, the precursor of element A includes at least one of melamine, urea, phosphoric acid, lithium phosphate, lithium dihydrogen phosphate, lithium hydrogen phosphate, ammonium phosphate, boric acid, lithium borate, ammonium borate, lithium fluoride, hexamethylenetetramine, and ammonium fluoride.

[0058] According to some embodiments of the present invention, in step S1, the carbon source includes at least one of biomass carbon sources and other carbon sources.

[0059] The biomass carbon source includes at least one of corn straw, wheat straw, rice straw, peanut straw, soybean straw, sorghum straw, cotton straw, reed straw, calamus, Spartina alterniflora, sesame straw, wood powder, peanut shell, coconut shell, rice husk, walnut shell, oak shell, sugarcane bagasse, red artemisia residue, soybean residue, pine needles, pine cones, apple branches, pear branches, peach branches, eucalyptus branches, pig manure, cow manure, sheep manure, chicken manure, kitchen waste, apples, and bananas.

[0060] The other carbon source includes at least one of benzene rings, C═C double bonds, nitrogen atoms, sulfur atoms, cycloalkyl groups, heterocycles, and bridged rings.

[0061] According to some embodiments of the present invention, the other carbon source includes a polymer of resorcinol and melamine. Among them, the polymerization of the polymer is carried out in the presence of a radical initiator. The radical initiator includes at least one of AIBN (CAS: 78-67-1) and K2S2O8 (CAS: 7727-21-1).

[0062] The mass ratio between the resorcinol and the radical initiator is 10-200:1. For example, it can be specifically about 20:1, 30:1, 40:1, 50:1, 60:1, 70:1, 80:1, 90:1, 100:1 or about 150:1.

[0063] The mass ratio between the melamine and the radical initiator is 10-100:1. For example, it can be specifically about 15:1, 50:1, 75:1 or about 85:1.

[0064] The polymerization is carried out in a protective atmosphere; the protective atmosphere includes at least one of nitrogen and argon.

[0065] The temperature of the polymerization is 250-350 °C. For example, it can be specifically about 300 °C.

[0066] The duration of the polymerization is 1.5-2.5 h. For example, it can be specifically about 2 h.

[0067] Thus, polymerization, crosslinking and other reactions occur between the raw materials for the preparation of the polymerization reaction, increasing the molecular weight. It provides a basis for subsequently generating a porous carbon skeleton with stable structure and uniform material.

[0068] According to some embodiments of the present invention, in step S1, the mass ratio between the element A precursor and the carbon source is 1-30:100. For example, it can be specifically 1.5-20:100. More specifically, it can be about 2:100, 5:100, 6:100, 10:100 or about 15:100.

[0069] When the carbon source is selected from the polymer of resorcinol and melamine, in step S1, it includes mixing the element A precursor, resorcinol and melamine and then polymerizing to obtain a mixture of the element A precursor and the carbon source, and then pyrolyzing to obtain the porous carbon skeleton. Thus, the dispersion uniformity of the element A in the porous carbon skeleton can be improved.

[0070] According to some embodiments of the present invention, in step S1, the temperature of the pyrolysis is 700-900 °C. For example, it can be specifically 800-850 °C.

[0071] According to some embodiments of the present invention, in step S1, the duration of the pyrolysis is 3 to 8 hours. For example, specifically, it can be about 4 to 6 hours. More specifically, it can be about 5 hours.

[0072] According to some embodiments of the present invention, in step S1, after the pyrolysis, pore modification is further included for the obtained product. This can more conveniently accommodate the silicon-based material deposited in step S2.

[0073] According to some embodiments of the present invention, the method of pore modification includes at least one of physical method and chemical method.

[0074] The pore modification is carried out in a physical activation device. The physical activation device includes chamber-type devices such as horizontal rotary furnaces and vertical fluidized beds.

[0075] The pore modification is carried out using carbon dioxide and water vapor. The volume ratio of carbon dioxide to water vapor is 1:1.

[0076] The temperature of the pore modification is 700 to 1000 °C. For example, specifically, it can be about 850 °C.

[0077] Since the silicon-based material is controlled to be deposited in the pore channels inside the porous carbon framework during the normal production process and basically does not affect the particle size, the particle size of the silicon-carbon negative electrode material is affected by the particle size of the porous carbon framework and the thickness of the shell. Therefore, considering the particle size, it is necessary to carry out pulverization before and / or after the pore modification to obtain a porous carbon framework with a suitable particle size.

[0078] According to some embodiments of the present invention, in step S2, the element B precursor includes at least one of lithium germanium hydride, lithium nitrate, magnesium nitrate, titanium tetrachloride, manganese nitrate, cadmium nitrate, iron nitrate, cobalt nitrate, iron sulfate, ferrous sulfate, cobalt sulfate, nickel sulfate, copper sulfate, nickel nitrate, copper nitrate, zinc nitrate, arsenic tetrachloride, tin nitrate, and tin tetrachloride.

[0079] According to some embodiments of the present invention, in step S2, the mass ratio of the element B precursor to the silicon source is 1 - 15:100. For example, specifically, it can be 2 - 10:100. More specifically, it can be about 3:100, 4:100, 5:100, 6:100, 7:100, 8:100, or about 9:100.

[0080] According to some embodiments of the present invention, in step S2, the silicon source is in a gaseous state at 450 °C. Thus, during the chemical vapor deposition process, the silicon source can first disperse in the porous carbon framework, and then crack into a silicon-based material under thermal conditions; in this way, in-situ deposition is achieved, and compared with the traditional grinding method, the bonding strength between the porous carbon framework and the silicon-based material is improved, and the pores in the former also have a certain limiting effect on the particle size of the latter.

[0081] According to some embodiments of the present invention, in step S2, the silicon source includes at least one of silane and substituted silane.

[0082] According to some embodiments of the present invention, the silicon source includes SiH 4 、Si 2 H 6 、Si 2 H 4 、Si 3 H 8 、Si 3 H 6 、Si 3 H 4 、Si 4 H 10 、Si 4 H 8 、Si 4 H 6 、Si 5 H 12 、Si 5 H 10 、Si 5 H 8 、Si 5 H 6 、Si 6 H 14 、Si 6 H 12 、Si 6 H 10 、Si 6 H 8 、Si 6 H 6 、Si 7 H 16 、Si 7 H 14 、Si 7 H 12 、Si 7 H 10 、Si 7 H 8 、Si 7 H 6 、Si 8 H 18 、Si 8 H 16 、Si 8 H 14 、Si 8 H 12 、Si 8 H 10 、Si 8 H 8 、Si9 H 20 、 Si 9 H 18 、 Si 9 H 16 、 Si 9 H 14 、 Si 9 H 12 、 Si 9 H 10 、 Si 9 H 8 、 Si 10 H 22 、 Si 10 H 20 、 Si 10 H 18 、 Si 10 H 16 、 Si 10 H 14 and Si 10 H 10 at least one of

[0083] According to some embodiments of the present invention, the substituted silane is a product obtained by substituting H in the silane with a heteroatom. The heteroatom includes at least one of B, N, F, P, S, and Cl.

[0084] According to some embodiments of the present invention, in step S2, the temperature of the chemical vapor deposition is 450 - 800 °C.

[0085] According to some embodiments of the present invention, in step S2, the duration of the chemical vapor deposition is 3 - 12 h.

[0086] According to some embodiments of the present invention, in step S2, the duration of the chemical vapor deposition is 4 - 8 h. For example, it can be specifically about 4.5 h, 5 h, 6 h, 7 h, or about 7.5 h. According to some embodiments of the present invention, in step S2, the mixed gas source further includes a carrier gas.

[0087] According to some embodiments of the present invention, the volume percentage of the silicon source in the mixed gas source is 10 - 45%.

[0088] According to some embodiments of the present invention, the volume percentage of the silicon source in the mixed gas source is 20 - 40%. For example, it can be specifically 25 - 35%.

[0089] According to some embodiments of the present invention, the carrier gas includes at least one of nitrogen and argon.

[0090] According to some embodiments of the present invention, the preparation method further includes wrapping a shell layer on the surface of the material obtained in step S2 after step S2.

[0091] According to some embodiments of the present invention, the method for coating the shell layer is chemical vapor deposition.

[0092] According to some embodiments of the present invention, in the chemical vapor deposition for coating the shell layer, the gas flow used includes the precursor of the shell.

[0093] According to some embodiments of the present invention, the precursor of the shell includes at least one of hydrocarbons, metal oxide precursors, fast ion conductor precursors, and organic polymer precursors.

[0094] The hydrocarbon may specifically be at least one of alkanes, alkenes, alkynes, and aromatic hydrocarbons. More specifically, it may be acetylene.

[0095] The flow rate of the hydrocarbon is 1.5 - 7.5 L / min. For example, it may specifically be about 4 L / min.

[0096] In the chemical vapor deposition for coating the shell layer, the temperature is 350 - 750 °C. For example, it may specifically be 550 - 600 °C. This temperature can affect the crystallization performance of the obtained shell layer; within this range, most of the shell layer is amorphous carbon, thereby improving the wetting effect on the electrolyte.

[0097] The duration of the chemical vapor deposition for coating the shell layer is 0.5 - 6 h. For example, it may specifically be about 2 h. This duration and the flow rate of the hydrocarbon jointly affect the thickness of the shell layer. The shell layer obtained within this range can not only provide a protective effect, but also avoid reducing the specific capacity per gram of the silicon-carbon negative electrode material, and more importantly, avoid reducing other performances such as the first efficiency.

[0098] According to an embodiment of the third aspect of the present invention, a lithium-ion battery is provided, and the preparation raw materials of the lithium-ion battery include the silicon-carbon negative electrode material described above.

[0099] Since the lithium-ion battery adopts all the technical solutions of the silicon-carbon negative electrode material in the above embodiments, it at least has all the beneficial effects brought by the technical solutions of the above embodiments. Further, high-rate samples among similar materials often mean higher initial Coulomb efficiency under the same rate conditions. Negative electrode materials with high Coulomb efficiency, especially silicon-carbon negative electrode materials whose Coulomb efficiency is lower than that of graphite negative electrode materials at the present stage, have better active lithium ion utilization efficiency, which can better ensure their large-scale application in the battery cell; that is, a lithium-ion battery with the preparation raw materials including the silicon-based negative electrode material will have high Coulomb efficiency, rate performance, and cycle performance.

[0100] According to some embodiments of the present invention, the lithium-ion battery includes at least one of a lithium-ion half-cell and a lithium-ion full-cell.

[0101] According to some embodiments of the present invention, the lithium-ion battery includes a negative electrode.

[0102] The negative electrode includes a negative electrode current collector and a negative electrode coating provided on the surface of the negative electrode current collector. The negative electrode coating includes a negative electrode active material, and the negative electrode active material includes the silicon-carbon negative electrode material.

[0103] When the lithium-ion battery is a button-type lithium-ion half-cell and the charge-discharge voltage range is 0.005V to 2V, the ratio of the lithium intercalation capacity at 0.33C to the lithium intercalation capacity at 0.05C is ≥95%. For example, it can specifically be about 95.5%, 96%, 97%, 98% or about 99%.

[0104] When the lithium-ion battery is a button-type lithium-ion half-cell, the charge-discharge voltage range is 0.005V to 2V, and the charge-discharge rate is 0.33C, the number of cycles when the lithium intercalation capacity decays to 90% is ≥1000 cycles. For example, it can specifically be about 1050 cycles, 1100 cycles, 1150 cycles, 1200 cycles, 1250 cycles, 1300 cycles or about 1400 cycles.

[0105] According to an embodiment of the fourth aspect of the present invention, there is provided an application of the lithium-ion battery in the fields of 3C batteries, power batteries, and energy storage batteries.

[0106] Since the application adopts all the technical solutions of the lithium-ion battery of the above embodiments, it has at least all the beneficial effects brought by the technical solutions of the above embodiments.

[0107] Unless otherwise specified, no doping is carried out in the present invention, which means that no additional element A precursor and / or element B precursor is added during the preparation process; that is, pollution and doping elements inherently present in the carbon source are not considered.

[0108] Unless otherwise specified, the meaning of "about" in the present invention actually allows an error range of ±2%. For example, about 100 is actually 100 ± 2% × 100.

[0109] Unless otherwise specified, "between... and..." in the present invention includes the numerical values. For example, "between 2 and 3" includes the endpoint values 2 and 3.

[0110] Other features and advantages of the present invention will be described in the subsequent specification, and, in part, will be obvious from the specification, or will be understood by practicing the present invention. BRIEF DESCRIPTION OF THE DRAWINGS

[0111] The above and / or additional aspects and advantages of the present invention will become obvious and easy to understand from the description of the embodiments in conjunction with the following drawings, wherein:

[0112] Figure 1It is the SEM image of the silicon-carbon anode material obtained in Comparative Example 1 of the present invention. Detailed implementation mode

[0113] The following will clearly and completely describe the concept and technical effects of the present invention in combination with embodiments to fully understand the purpose, features, and effects of the present invention. Obviously, the described embodiments are only a part of the embodiments of the present invention, not all embodiments. Based on the embodiments of the present invention, other embodiments obtained by those skilled in the art without creative efforts all belong to the scope protected by the present invention.

[0114] In the description of the present invention, the description referring to terms such as "one embodiment", "some embodiments", "schematic embodiments", "examples", "specific examples", or "some examples" means that the specific features, structures, materials, or characteristics described in connection with the embodiment or example are included in at least one embodiment or example of the present invention. In this specification, the schematic expressions of the above terms do not necessarily refer to the same embodiment or example. Moreover, the specific features, structures, materials, or characteristics described can be combined in a suitable manner in any one or more embodiments or examples.

[0115] Example 1

[0116] In this example, a silicon-carbon anode material was prepared. The specific steps are as follows:

[0117] D1. Resorcinol, melamine, A precursor (hexamethylenetetramine), and AIBN free radical initiator were taken in a mass ratio of 71:24:5:2 and placed in a suitable heating container. They were mixed and polymerized at 300 °C for 2 h; then, under the protection of an inert gas, they were continuously heated and pyrolyzed at 850 °C for 5 h to obtain blocky carbon.

[0118] D2. After the porous carbon skeleton precursor obtained in step D1 was preliminarily crushed into millimeter-sized particles (jaw crushing), in a physical activation device (horizontal rotary furnace), a mixed gas of water vapor and carbon dioxide (volume ratio 1:1) was used to activate and create pores in the particles at 850 °C. After pore creation, the total pore volume was ~0.7 cc / g.

[0119] D3. The material obtained in step D2 was subjected to air jet milling and classification to obtain a porous carbon skeleton. The particle size distribution of the porous carbon skeleton was as follows: Dv10 = 2.7 μm; Dv50 = 7.9 μm; Dv99 = 28 μm.

[0120] D4. The carbon skeleton obtained in step D3 was placed in a chemical vapor deposition chamber. Using SiH 4 as the silicon source and N 2 as the carrier gas, in the mixed gas, SiH 4The volume ratio is 35%. Chemical vapor deposition of silicon is carried out at 600 °C for a total of 6 h to obtain nuclei.

[0121] D5. Place the nuclei obtained in step D4 in the chemical vapor deposition chamber continuously, introduce a gaseous hydrocarbon source (acetylene is used in this embodiment), and perform CVD coating (carbon deposition). Control the carbon coating amount by controlling the flow rate of the introduced hydrocarbon gas to be 4 L / min, the temperature to be 550 °C, and the deposition time to be 2 h.

[0122] Example 2

[0123] In this example, a silicon-carbon anode material was prepared. The specific difference from Example 1 is as follows:

[0124] In step D1, the mass ratio of the precursor of element A to the carbon source is 20:100, and the ratio among resorcinol, melamine, and the free radical initiator is the same as that in Example 1.

[0125] Example 3

[0126] In this example, a silicon-carbon anode material was prepared. The specific difference from Example 1 is as follows:

[0127] (1) In step D1, the substance to be pyrolyzed does not include the precursor of element A.

[0128] (2) In step D4, a precursor of element B was introduced, specifically germane, and the introduced amount was 4% of the mass of the silicon source.

[0129] Example 4

[0130] In this example, a silicon-carbon anode material was prepared. The specific difference from Example 1 is as follows:

[0131] (1) In step D1, the substance to be pyrolyzed does not include the precursor of element A.

[0132] (2) In step D4, a precursor of element B was introduced, specifically germane, and the introduced amount was 9% of the mass of the silicon source.

[0133] Example 5

[0134] In this example, a silicon-carbon anode material was prepared. The specific difference from Example 1 is as follows:

[0135] (1) In step D1, the mass ratio of the precursor of element A to the carbon source is 5:95.

[0136] (2) In step D4, a precursor of element B was introduced, specifically germane, and the introduced amount was 4% of the mass of the silicon source.

[0137] Comparative Example 1

[0138] In this example, a silicon-carbon anode material was prepared. The specific difference from Example 1 is as follows:

[0139] In step D1, the substance to be pyrolyzed does not include the precursor of element A.

[0140] Comparative Example 2

[0141] In this example, a silicon-carbon anode material was prepared. The specific difference from Comparative Example 1 is as follows:

[0142] In step D4, the duration of chemical vapor deposition is 4.5 h.

[0143] Comparative Example 3

[0144] In this example, a silicon-carbon anode material was prepared. The specific difference from Comparative Example 1 is as follows:

[0145] In step D4, the duration of chemical vapor deposition is 7.5 h.

[0146] Comparative Example 4

[0147] In this example, a silicon-carbon anode material was prepared. The specific difference from Comparative Example 1 is as follows:

[0148] In step D4, the duration of chemical vapor deposition is 3 h.

[0149] Comparative Example 5

[0150] In this example, a silicon-carbon anode material was prepared. The specific difference from Example 1 is as follows:

[0151] In step D1, the mass ratio of the precursor of element A to the carbon source is 25:100.

[0152] Comparative Example 6

[0153] In this example, a silicon-carbon anode material was prepared. The specific difference from Example 3 is as follows:

[0154] In step D4, the introduction amount of germane is 30% of the mass of the silicon source.

[0155] In the test example, the morphologies of the silicon-carbon anode materials obtained in the examples and comparative examples were also tested. The specific test method was scanning electron microscopy. The results showed that the morphologies and shapes of the silicon-carbon anode materials obtained in the examples and comparative examples were similar. The morphology corresponding to Comparative Example 1 is as shown in Figure 1 shown.

[0156] In this example, the elemental content in the obtained silicon-carbon anode material was tested by ICP-AES. Specifically: the prepared silicon-carbon anode material was placed in an aqueous solution with a HF mass concentration of 10%, and slowly stirred at 150 rpm for 24 h. After suction filtration, a clear solution containing silicon-based components and a porous carbon skeleton were obtained. The clear solution was fixed to a concentration that met the test standard (determined according to the instrument's detection limit) and then tested to obtain the content ratio of elements B and Si. The mass of the silicon-based component was calculated as follows: the total mass of the silicon-carbon anode material before acid etching minus the mass of the dried residue after acid etching. The residue after acid etching was washed, dried, digested with strong alkali, and prepared into an aqueous solution with an appropriate concentration for testing to obtain the mass percentage of element A in the porous carbon skeleton.

[0157] In this example, button cells including the silicon-carbon anode materials prepared in the examples and comparative examples were fabricated, and the electrochemical performance of the button cells was tested. Specifically:

[0158] Test electrode: It consists of an aluminum foil and a coating applied on the aluminum foil. In the slurry used to prepare the coating, the silicon-carbon anode material: carbon nanotube slurry (solid content 1%, where CNTs account for 40% and CMC accounts for 60%): PAA-Li (lithiated PAA binder): Super p conductive carbon black = 84:1:10:5. The silicon-carbon anode material was from the examples or comparative examples respectively. The coating surface density was 7-8 mg / cm 2 ;

[0159] Battery case: 2430 type button battery case, and a shrapnel, nickel foam or gasket was set between the test electrode or counter electrode and the battery case to avoid open circuit and accurately reflect the test results; a separator was set between the test electrode and the counter electrode to avoid short circuit.

[0160] Electrolyte: A carbonate solution of 1M lithium hexafluorophosphate, containing 15% FEC + 1-2% VC.

[0161] Counter electrode: Lithium metal sheet.

[0162] Test voltage range: The voltage range was 2V to 0.005V;

[0163] First efficiency and specific capacity test process:

[0164] After the button cell was assembled, it was left standing for 8 h to 12 h; charged at 0.05C to 5 mV and left standing for 5 min; charged at 50 μA to 5 mV and left standing for 5 min; charged at 10 μA to 5 mV and left standing for 5 min; discharged at 0.05C to the target voltage and left standing for 5 min. Obtained: the specific capacity of the silicon-carbon anode material, first efficiency = discharge amount / charge amount. Among them, the first efficiency when the charging cut-off voltage of the button cell was 2V was denoted as FCE 2.0V ; the first efficiency calculated based on the discharge capacity at a charging voltage of 0.8V was denoted as FCE 0.8V。

[0165] Test method for the percentage increase in the thickness of the fully lithiated electrode:

[0166] After performing the "lithiation at 10 μA to 5 mV and standing for 5 min" in the above process once, disassemble the coin cell, take out the electrode, measure the thickness of the electrode coating using a micrometer, divide it by the thickness of the electrode coating before assembling the coin cell, and subtract 1 from the obtained value to get the percentage.

[0167] Test method for the attenuation of the coin cell capacity: After performing the first efficiency and specific capacity tests 5 times, use the following test scheme for lithiation / delithiation cycles: lithiation at 0.33C to 5 mV and standing for 10 min; delithiation at 0.33C to 2V and standing for 10 min, for several times until the capacity retention rate ≤ 90% (compared with the first week at 0.33C rate). And calculate the percentage of the specific lithiation capacity in the first week at 0.33C to the specific lithiation capacity in the first week to obtain the lithiation rate ratio at 0.33C.

[0168] Test method for the rate:

[0169] The test voltage is 0.005 - 2.0V; cycle the coin cell 10 times at current rates of 0.1C, 0.2C, 0.33C, and 0.5C respectively to obtain the lithiation / delithiation specific capacities at different rates of the coin cell test level for the silicon-carbon negative electrode material (average value for 10 weeks). Typically, comparing the discharge specific capacity at 0.33C to that at 0.1C can reflect the rate performance differences of different silicon-carbon negative electrode materials.

[0170] For all the above rate currents, 1C current is 1700 mAh / g), and the test results of each item are shown in Table 1.

[0171] Table 1 Performance of the silicon-carbon negative electrode materials obtained in the examples and comparative examples

[0172]

[0173]

[0174] In Table 1, W Si represents the mass percentage of the silicon-based material in the silicon-carbon negative electrode material; Wa represents the mass percentage of element A in the porous carbon framework; Wb is the mass percentage of element B in the silicon-based material.

[0175] In Table 1, although no additional element A precursor or element B precursor was added to some embodiments or comparative examples, the results still showed the presence of certain element A and element B; the reason for the above results is that the carbon source used in the specific implementation manner, including melamine, itself has a certain content of N, so even if no element A precursor is added, some element A doping will still be shown, but the content is relatively small; in addition, some element B contamination may exist in the preparation instrument, so even if no element B precursor is added, a very small amount of element B doping will appear in the product.

[0176] By comparing comparative examples 1 to 4, it can be seen that the same porous carbon skeleton can be used to adjust the content of silicon-based materials in the obtained silicon-carbon composite material by adjusting the duration of chemical vapor deposition in step D4, thereby adjusting the electrochemical properties of the obtained silicon-carbon negative electrode material. The results show that because the silicon-based material has a high lithium insertion capacity and at the same time brings a large volume expansion, it causes a more violent expansion and contraction of the test electrode during the lithium insertion and extraction process of the silicon-carbon negative electrode material, and inevitably leads to an increase in the possibility of loss of electron and ion contact during the cycle process, resulting in a decrease in cycle performance. However, more silicon-based material deposition will also make more full use of the pores of the porous carbon skeleton and improve the first effect of the obtained silicon-carbon negative electrode material. On the other hand, exceeding the composite amount of the porous carbon skeleton to the silicon-based material will inevitably form a layer of pure silicon layer on the surface of the material. This layer is unstable in the electrolyte and is prone to form a large amount of unstable SEI, resulting in the loss of active lithium ions from the positive electrode and the increase of impedance, which deteriorates the overall performance of the material. Insufficient silicon-based material deposition will expose the low first efficiency and excessive SEI generation of the porous carbon skeleton, resulting in a decrease in the rate performance of the material.

[0177] Comparing Examples 1-2, Comparative Example 1 and Comparative Example 5, it can be seen that: as the content of Element A in the porous carbon framework increases, the initial efficiency of the obtained silicon-carbon anode material first increases and then decreases. This is because Element A forms a certain amount of C-A covalent bonds with carbon elements in the porous carbon framework. The presence of a certain amount of non-C-C bonds in the porous carbon framework can adjust the lattice structure of the carbon framework, transform a certain amount of layered two-dimensional ion channels into three-dimensional ion channels, increase the lithium-ion transport rate in the material, and improve the rate performance of Examples 1-2. The increase in the lithium-ion transport rate improves the initial efficiency of the silicon-carbon anode material. Moreover, the presence of a small amount of Element A in the porous carbon framework does not significantly affect the structural strength of its framework and does not significantly deteriorate the lithium insertion / extraction expansion of the silicon-carbon anode material. However, the content of Element A in Comparative Example 5 is too high, which significantly reduces the two-dimensional lithium-ion channels in the porous carbon framework, increases the tortuosity of the lithium-ion migration path in the porous carbon framework, and instead reduces the lithium-ion transport rate. At the same time, due to the presence of excessive impurity elements, the high-strength porous carbon framework structure formed by the stacking of graphite microcrystals is also damaged at the microcrystal level, resulting in a decrease in the framework strength, a decline in the ability to inhibit silicon lithium insertion expansion, and an increase in the impedance of lithium insertion / extraction due to the large amount of SEI generated by particle fragmentation, reducing the rate performance and gradually shortening the cycle life. Typically: the presence of a large amount of N will form C 3 N 4 substances with relatively low electronic conductivity, reducing the electronic conductivity of the carbon framework, thus lowering the Coulomb efficiency and rate performance of the material.

[0178] Comparing Examples 3-4, Comparative Example 1 and Comparative Example 6, it can be seen that as the content of Element B in the silicon-based material increases, the initial efficiency of the obtained silicon-carbon anode material of the present invention first increases and then decreases. This is because the electronic conductivity of Element B is higher than that of silicon, and its doping in the silicon-based material can improve the lattice of the silicon-based material, enhance its electronic conductivity, and broaden the lithium-ion transport channels in the silicon-based material, thereby achieving the simultaneous improvement of the lithium-ion transport rate: Therefore, the doping of Element B has a slight advantage over the doping of Element A in terms of improving the initial efficiency, as reflected by the slightly higher rate of Examples 3-4 than that of Examples 1-2. In addition, due to the doping of Element B in the silicon-based material, it is equivalent to breaking the stronger Si-Si bonds in advance for lithium ions, resulting in lower volume expansion during lithium-ion insertion, which is more conducive to the large-scale use of such silicon-carbon materials under the same design and ensures the cycle life of the battery cells. However, the excessive use of Element B in Comparative Example 6 easily forms agglomerations of Element B in the silicon-based material (the doping upper limits of different elements are different). Although the metal agglomerates can act as electronic conductivity dopants inside the silicon-based material to improve the initial efficiency of the silicon-carbon anode material, they have no advantage in improving the expansion and cycle performance of the silicon-carbon anode material and may even show a deteriorating trend.

[0179] Comparing Comparative Example 1 and Examples 1 to 5, it can be seen that the co-doping of Element A and Element B has an obvious synergistic effect, especially in terms of high-rate cycle life, and this synergistic effect is obvious; the reasons for the above synergistic effect include that both Element A and Element B can improve their electronic conductivity and lithium-ion conduction rate. The unique role of Element A is to increase the strength of the porous carbon skeleton to inhibit the lithium intercalation expansion of silicon element, and the unique role of Element B is to pre-expand the lattice of the silicon-based material, reduce the absolute amount of its lithium intercalation expansion, and reduce the stress impact on the porous carbon skeleton. The synergistic effect of the two can regulate the performance parameters of such silicon-carbon anode materials.

[0180] In summary, due to the improvement of the performance by Element A and Element B, the silicon-carbon anode material provided by the present invention has excellent high-rate cycle performance, rate performance, first efficiency, etc., and is expected to be widely used in the preparation of energy storage batteries, 3C batteries and power batteries.

[0181] The embodiments of the present invention have been described in detail above in conjunction with the accompanying drawings. However, the present invention is not limited to the above embodiments. Within the scope of knowledge possessed by those of ordinary skill in the art, various changes can be made without departing from the gist of the present invention. In addition, without conflict, the embodiments of the present invention and the features in the embodiments can be combined with each other.

Claims

1. A silicon-carbon negative electrode material for a high-rate lithium-ion battery, characterized in that: The silicon-carbon negative electrode material comprises a porous carbon skeleton and a silicon-based material dispersed inside the porous carbon skeleton; and, The porous carbon skeleton is doped with element A, the element A is N, and the mass percentage of the element A in the porous carbon skeleton is 0.5% to 9%; The silicon-based material is doped with element B; the element B is Ge, and the mass percentage of the element B in the silicon-based material is 0.2% to 8%.

2. The silicon-carbon negative electrode material according to claim 1, characterized in that: The mass percentage of the element A in the porous carbon skeleton is 1-9%; and / or the mass percentage of the element B in the silicon-based material is 1-8%.

3. The silicon-carbon negative electrode material according to claim 1 or 2, characterized in that: The silicon-carbon negative electrode material also includes a shell layer, and the shell layer is wrapped on the surface of the silicon-carbon negative electrode material.

4. A method for preparing the silicon-carbon negative electrode material according to any one of claims 1 to 3, characterized in that: The preparation method comprises the following steps: S1. mixing a carbon source and an element A precursor, and pyrolyzing them under conditions of water and oxygen isolation to obtain the porous carbon skeleton; S2. Using a gas including a silicon source and an element B precursor as a mixed gas source and the porous carbon skeleton as a matrix, chemical vapor deposition is performed.

5. The preparation method according to claim 4, characterized in that: In step S1, the element A precursor is hexamethylenetetramine; and / or the mass ratio of the element A precursor to the carbon source is 1 to 30:

100.

6. The preparation method according to claim 4, characterized in that: In step S2, the element B precursor is germane; and / or the mass ratio of the element B precursor to the silicon source is 1 to 15:

100.

7. The preparation method according to claim 4, characterized in that: In step S2, the silicon source is in gas phase at 450°C; and / or, in step S2, the temperature of chemical vapor deposition is 450-800°C.

8. The preparation method according to claim 4, characterized in that: In step S2, the duration of the chemical vapor deposition is 3 to 12 hours; and / or, the preparation method further comprises, after step S2, wrapping a shell layer on the surface of the material obtained in step S2.

9. A lithium ion battery, characterized in that: The raw materials for preparing the lithium-ion battery include the silicon-carbon negative electrode material as described in any one of claims 1 to 3.

10. Application of the lithium-ion battery according to claim 9 in the fields of 3C batteries, power batteries and energy storage batteries.

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