CN116199226A - Method for preparing core-shell hollow structure silicon-carbon nano negative electrode material by using lignin - Google Patents

Method for preparing core-shell hollow structure silicon-carbon nano negative electrode material by using lignin Download PDF

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CN116199226A
CN116199226A CN202211694031.2A CN202211694031A CN116199226A CN 116199226 A CN116199226 A CN 116199226A CN 202211694031 A CN202211694031 A CN 202211694031A CN 116199226 A CN116199226 A CN 116199226A
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silicon
core
preparing
negative electrode
carbon
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易峰
高波
杨博凌
吴有飞
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Dongguan Honghe New Material Co ltd
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    • B82—NANOTECHNOLOGY
    • B82Y—SPECIFIC USES OR APPLICATIONS OF NANOSTRUCTURES; MEASUREMENT OR ANALYSIS OF NANOSTRUCTURES; MANUFACTURE OR TREATMENT OF NANOSTRUCTURES
    • B82Y30/00—Nanotechnology for materials or surface science, e.g. nanocomposites
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    • B82—NANOTECHNOLOGY
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    • H01M10/05—Accumulators with non-aqueous electrolyte
    • H01M10/052—Li-accumulators
    • H01M10/0525—Rocking-chair batteries, i.e. batteries with lithium insertion or intercalation in both electrodes; Lithium-ion batteries
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
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    • H01M4/36—Selection of substances as active materials, active masses, active liquids
    • H01M4/38—Selection of substances as active materials, active masses, active liquids of elements or alloys
    • H01M4/386—Silicon or alloys based on silicon
    • H—ELECTRICITY
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    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M4/00—Electrodes
    • H01M4/02—Electrodes composed of, or comprising, active material
    • H01M4/62—Selection of inactive substances as ingredients for active masses, e.g. binders, fillers
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M4/00—Electrodes
    • H01M4/02—Electrodes composed of, or comprising, active material
    • H01M4/62—Selection of inactive substances as ingredients for active masses, e.g. binders, fillers
    • H01M4/624—Electric conductive fillers
    • H01M4/625—Carbon or graphite
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    • C01P—INDEXING SCHEME RELATING TO STRUCTURAL AND PHYSICAL ASPECTS OF SOLID INORGANIC COMPOUNDS
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    • C01P2004/60—Particles characterised by their size
    • C01P2004/64—Nanometer sized, i.e. from 1-100 nanometer
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    • C01—INORGANIC CHEMISTRY
    • C01P—INDEXING SCHEME RELATING TO STRUCTURAL AND PHYSICAL ASPECTS OF SOLID INORGANIC COMPOUNDS
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    • C01P—INDEXING SCHEME RELATING TO STRUCTURAL AND PHYSICAL ASPECTS OF SOLID INORGANIC COMPOUNDS
    • C01P2006/00—Physical properties of inorganic compounds
    • C01P2006/40—Electric properties
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    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M4/00—Electrodes
    • H01M4/02—Electrodes composed of, or comprising, active material
    • H01M2004/021—Physical characteristics, e.g. porosity, surface area
    • H—ELECTRICITY
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    • H01M4/00—Electrodes
    • H01M4/02—Electrodes composed of, or comprising, active material
    • H01M2004/026—Electrodes composed of, or comprising, active material characterised by the polarity
    • H01M2004/027—Negative electrodes
    • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
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    • Y02E—REDUCTION OF GREENHOUSE GAS [GHG] EMISSIONS, RELATED TO ENERGY GENERATION, TRANSMISSION OR DISTRIBUTION
    • Y02E60/00—Enabling technologies; Technologies with a potential or indirect contribution to GHG emissions mitigation
    • Y02E60/10—Energy storage using batteries

Abstract

The invention discloses a method for preparing a silicon-carbon nano negative electrode material with a core-shell hollow structure by using lignin, which comprises the following steps: step one, material structure design; step two, preparing lignin standard solution; step three, preparing first composite particles; uniformly dispersing the first composite particles; step five, preparing a carbon outer layer; step six, preparing a hollow layer; according to the invention, the hollow layer is arranged between the nano silicon inner core and the carbon outer layer, so that an expansion space can be provided for the nano silicon inner core, and the capacity attenuation problem caused by expansion of the silicon-carbon anode material in the charge-discharge process is effectively relieved; according to the invention, experiments show that when the weight part ratio of the nano silicon core to the metal precipitate layer to the carbon outer layer is 10:1:1, the silicon-carbon nano negative electrode material has the most stable structure and the optimal performance; the preparation method of the hollow structure silicon carbon nano negative electrode material provided by the invention has the advantages of simplicity in operation and good controllability, and is suitable for mass production.

Description

Method for preparing core-shell hollow structure silicon-carbon nano negative electrode material by using lignin
Technical Field
The invention relates to the technical field of lithium ion batteries, in particular to a method for preparing a core-shell hollow structure silicon-carbon nano negative electrode material by using lignin.
Background
Silicon has an ultra-high theoretical specific capacity (4200 mAh/g) and a lower delithiation potential (< 0.5V) compared to conventional graphite cathodes, and silicon is one of the potential choices for carbon-based negative electrode upgrades of lithium ion batteries. Silicon materials with high capacity are receiving a great deal of attention based on the current demand for high energy density batteries for portable electronic consumer products and all-electric vehicles. Silicon has disadvantages as a negative electrode material for lithium ion batteries. Silicon is a semiconductor material with itself low electrical conductivity. In the electrochemical circulation process, the lithium ions are inserted and separated to expand and contract the volume of the material by more than 300%, the generated mechanical force can gradually pulverize the material to cause structural collapse, and finally, the electrode active material is separated from the current collector to lose electrical contact, so that the cycle performance of the battery is greatly reduced. In addition, due to this volume effect, silicon has difficulty in forming a stable Solid Electrolyte Interface (SEI) film in an electrolyte. With the destruction of the electrode structure, new SEI films are continuously formed on the exposed silicon surface, and corrosion and capacity fading of silicon are aggravated. The progress of silicon negative electrode industrialization application is slow due to some physicochemical properties of silicon. Unlike the intercalation mechanism of graphite, silicon crystals exhibit a three-dimensional bulk structure of covalent tetrahedra, and charge and discharge proceed by forming Li-Si alloy with lithium. The volume expansion rate of the Li-Si alloy is up to 320%, and the powerful stress can cause the fragmentation of silicon particles, so that the silicon particles fall off from the electrode plate, and the battery cycle stability is greatly reduced and the potential safety hazard is increased.
In order to solve the problem of volume expansion during the electrochemical reaction of silicon, silicon particle nano-meter is one of the indispensable measures in many schemes. By reducing the size of silicon particles, the structure damage caused by the volume effect of silicon can be effectively avoided by nanocrystallization, so that the structural stability is improved, and the cycle performance is improved.
However, although the modification of the silicon carbon anode at present can improve the cycle performance of silicon to some extent, the advantage of high specific capacity of the silicon anode is not exerted. Therefore, the silicon-carbon negative electrode needs to be further optimized, and a negative electrode material with high specific capacity and high coulombic efficiency is developed.
Disclosure of Invention
The invention aims to provide a method for preparing a silicon-carbon nano negative electrode material with a core-shell hollow structure by using lignin, which aims to solve the problems that the existing silicon-based negative electrode material provided in the background art is poor in cycle performance, the volume expansion of silicon in the silicon-based material is large, the negative electrode material is easy to pulverize and collapse, and the actual capacity is low.
In order to achieve the above purpose, the present invention provides the following technical solutions: the method for preparing the silicon-carbon nano negative electrode material with the core-shell hollow structure by using lignin comprises the following steps: step one, material structure design; step two, preparing lignin standard solution; step three, preparing first composite particles; uniformly dispersing the first composite particles; step five, preparing a carbon outer layer; step six, preparing a hollow layer;
in the first step, the silicon-carbon nano negative electrode material with the core-shell hollow structure comprises a nano silicon core, a hollow layer and a carbon outer layer, wherein the carbon outer layer is coated on the outer surface of the nano silicon core, and the hollow layer is arranged between the nano silicon core and the carbon outer layer;
in the second step, the kraft lignin is dissolved in an organic solution to prepare a standard solution with the weight percent of 18.5 percent;
in the third step, the nano silicon core is dissolved in a metal solution, alkali is added for reaction, stirring and centrifugal water washing are carried out, and a first composite particle of the nano silicon core coated by the metal sediment is obtained;
in the fourth step, the first composite particles are gradually added into the standard solution, so that the mass ratio of the first composite particles to the lignin is 1:1, and the first composite particles are uniformly dispersed by continuously stirring while being added, so as to obtain slurry;
in the fifth step, the prepared slurry is uniformly smeared on a copper foil with the thickness of 127 mu m by a surgical knife, and is dried at room temperature and then is transferred into a vacuum oven for drying for 12 hours; calcining the dried composite particles in a tubular furnace, and then preserving the heat at 600 ℃ for 2 hours to obtain second composite particles to form a carbon outer layer;
in the sixth step, the second composite particles are reacted under an acidic condition, and the metal sediment is removed to form a hollow layer, so that the silicon-carbon nano negative electrode material with the core-shell hollow structure is obtained.
Preferably, in the first step, the diameter of the nano silicon core is 30-50nm.
Preferably, in the first step, the weight part ratio of the nano silicon inner core to the carbon outer layer is 5-10:0.5-2.
Preferably, in the first step, the nano silicon core is prepared from a silicon source by a pyrolysis method or a vapor deposition method.
Preferably, the silicon source is one of silicon tetrahydroide and trimethyldichlorosilane.
Preferably, in the second step, the organic matter is dimethylformamide.
Preferably, in the third step, the metal solution is one of a zinc ion solution, a magnesium ion solution and an iron ion solution.
Preferably, the concentration of the metal solution is 0.8-2 mol/L.
Preferably, in the fifth step, the calcination temperature is 500-700 ℃ and the calcination time is 1-4 h.
Compared with the prior art, the invention has the beneficial effects that: according to the invention, the hollow layer is arranged between the nano silicon inner core and the carbon outer layer, so that an expansion space can be provided for the nano silicon inner core, and the capacity attenuation problem caused by expansion of the silicon-carbon anode material in the charge-discharge process is effectively relieved; according to the invention, experiments show that when the weight part ratio of the nano silicon core to the metal precipitate layer to the carbon outer layer is 10:1:1, the silicon-carbon nano negative electrode material has the most stable structure and the optimal performance; the preparation method of the hollow structure silicon carbon nano negative electrode material provided by the invention has the advantages of simplicity in operation and good controllability, and is suitable for mass production.
Drawings
FIG. 1 is a step diagram of the present invention;
FIG. 2 is a diagram of a structure of a hollow structure silicon-carbon nano-anode material according to the present invention;
FIG. 3 is a flow chart of the method of the present invention;
in the figure: 1. a nano silicon core; 2. a hollow layer; 3. and a carbon outer layer.
Detailed Description
The following description of the embodiments of the present invention will be made clearly and completely with reference to the accompanying drawings, in which it is apparent that the embodiments described are only some embodiments of the present invention, but not all embodiments. All other embodiments, which can be made by those skilled in the art based on the embodiments of the invention without making any inventive effort, are intended to be within the scope of the invention.
Referring to fig. 1-3, the present invention provides a technical solution:
example 1:
the method for preparing the silicon-carbon nano negative electrode material with the core-shell hollow structure by using lignin comprises the following steps:
step one, material structure design; step two, preparing lignin standard solution; step three, preparing first composite particles; uniformly dispersing the first composite particles; step five, preparing a carbon outer layer; step six, preparing a hollow layer;
in the first step, the silicon-carbon nano negative electrode material with the core-shell hollow structure comprises a nano silicon core 1, a hollow layer 2 and a carbon outer layer 3, wherein the carbon outer layer 3 is coated on the outer surface of the nano silicon core 1, and the hollow layer 2 is arranged between the nano silicon core 1 and the carbon outer layer 3; wherein, in nano siliconCore 1 is SiH 4 Preparing Si pellets with the diameter of 20nm for a silicon source by a high-temperature pyrolysis method; the weight part ratio of the silicon core 1 to the carbon outer layer 3 is 5:1;
in the second step, the kraft lignin is dissolved in dimethylformamide solution to prepare 18.5wt% of standard solution;
wherein in the third step, the nano silicon core 1 is dissolved in 15ml of ZnCl with the concentration of 1mol/L 2 5mL of concentrated ammonia water was then slowly added to the Si and ZnCl solution 2 Continuously stirring, centrifuging and washing the obtained solution to obtain Si/ZnO pellets, namely first composite particles;
in the fourth step, the first composite particles are gradually added into the standard solution, so that the mass ratio of the first composite particles to the lignin is 1:1, and the first composite particles are uniformly dispersed by continuously stirring while being added, so as to obtain slurry;
in the fifth step, the prepared slurry is uniformly smeared on a copper foil with the thickness of 127 mu m by a surgical knife, and is dried at room temperature and then is transferred into a vacuum oven for drying for 12 hours; calcining the dried material in a tube furnace at 500-700 ℃ for 1-4 h; then, the mixture is kept at 600 ℃ for 2 hours to prepare Si/ZnO@C nanospheres, namely second composite particles;
wherein in the sixth step, the second composite particles are mixed in H 2 SO 4 Etching for 1h at 60 ℃ in the solution, removing ZnO, and forming a hollow layer 2 to obtain the hollow Si@C nanospheres, namely the silicon carbon nano negative electrode material with the core-shell hollow structure.
Example 2:
the difference from example 1 is that the diameter of the nano-silicon core 1 is 40nm, and the rest is the same as example 1.
Example 3:
the difference from example 1 is that the diameter of the nano-silicon core 1 is 60nm, and the rest is the same as example 1.
Example 4:
the difference from example 1 is that the diameter of the nano-silicon core 1 is 10nm, and the rest is the same as example 1.
Example 5:
is different from example 1 in that ZnCl 2 The concentration of the solution was 2mol/L, and the rest was the same as in example 1.
Example 6:
is different from example 1 in that ZnCl 2 The concentration of the solution was 1.5mol/L, and the rest was the same as in example 1.
Example 7:
is different from example 1 in that ZnCl 2 The concentration of the solution was 0.5mol/L, and the rest was the same as in example 1.
Example 8:
is different from example 1 in that ZnCl 2 The concentration of the solution was 0.1mol/L, and the rest was the same as in example 1.
Test example:
preparing the core-shell hollow structure silicon carbon nano negative electrode materials prepared in the above examples 1-8, preparing a lithium ion secondary battery, and then respectively performing a cycle performance test and a pole piece thickness expansion rate test to obtain optimal process conditions, wherein the results are shown in the following table 1, and the specific method is as follows:
(1) Preparation of a positive plate: uniformly mixing NCM811 anode active material, conductive agent superconducting carbon, carbon tube and binder polyvinylidene fluoride according to the mass ratio of 96:2.0:0.5:1.5 to prepare anode slurry, coating the anode slurry on one surface of a current collector aluminum foil, drying and rolling at 85 ℃, coating and drying the anode slurry on the other surface of the aluminum foil according to the method, and carrying out cold pressing treatment on the prepared pole piece with the anode active material layer coated on both sides of the aluminum foil; trimming, cutting pieces and slitting, and manufacturing a lithium ion battery positive plate after slitting;
(2) Preparing a negative plate: preparing a negative electrode slurry from the hollow silicon-carbon negative electrode material, conductive agent superconducting carbon, thickener sodium carboxymethylcellulose and binder styrene-butadiene rubber according to the mass ratio of 96.5:1.0:1.0:1.5, coating the negative electrode slurry on a current collector copper foil, drying and rolling the current collector copper foil at 85 ℃, coating and drying the negative electrode slurry on the other surface of the copper foil according to the method, and carrying out cold pressing treatment on pole pieces with negative electrode active material layers coated on the two surfaces of the prepared copper foil; trimming, cutting pieces and slitting, and manufacturing a lithium ion battery negative plate after slitting;
(3) A diaphragm: selecting a polyethylene porous film with the thickness of 7 mu m as a diaphragm;
(4) Preparation of electrolyte: dissolving lithium hexafluorophosphate (LiPF 6) in a mixed solvent of dimethyl carbonate (DEC), ethylene Carbonate (EC), ethylmethyl carbonate (EMC) and diethyl carbonate (DEC) (the mass ratio of the three is 3:5:2) to obtain an electrolyte;
(5) Preparation of the battery: winding the positive plate, the diaphragm and the negative plate into a battery core, wherein the capacity of the battery core is about 5Ah; the diaphragm is positioned between the adjacent positive plate and the negative plate, the positive electrode is led out by spot welding of an aluminum tab, and the negative electrode is led out by spot welding of a nickel tab; then placing the battery core in an aluminum-plastic packaging bag, baking, injecting the electrolyte, and finally preparing the lithium ion secondary battery through the procedures of packaging, formation, capacity division and the like;
(6) And (3) testing the cycle performance: charging the lithium ion secondary battery to 4.2V at a constant current and a constant voltage of 1C at 25+/-2 ℃, and discharging the lithium ion secondary battery to 3.0V at a constant current of 0.05C, wherein the charging cycle is a charging cycle process, and the discharging capacity is the discharging capacity of the first cycle; performing 100-cycle charge and discharge tests on the lithium ion secondary battery prepared in the step (5) according to the method, recording the discharge capacity of each cycle, and recording the test results in Table 1; wherein, cyclic capacity retention (%) =discharge capacity of 200 th cycle/discharge capacity of first cycle×100%;
(7) And (3) testing the thickness expansion rate of the pole piece: charging the lithium ion secondary battery to 4.2V at a constant current and a constant voltage of 1C at 25 ℃, and discharging the lithium ion secondary battery to 3.0V at a constant current of 0.05C, wherein the charging cycle is a charging cycle process; performing 20 cycles on the lithium ion battery prepared in the step (5) according to the conditions, testing the thickness of the pole piece before and after the cycle by using a micrometer, and recording the test results in a table 1; wherein, the expansion rate of the thickness of the pole piece is = [ (thickness before circulation after circulation)/thickness before circulation ] ×100%;
(8) Analysis of results: according to comparison of examples 1-5, when the diameter of the nano silicon core 1 is set to be 20nm, the prepared battery has a capacity retention rate of 87%, a thickness expansion rate of 1.1% and better performance, and the ratio of the nano silicon core 1 to the carbon outer layer 3 in parts by weight is close to 10:1 when the diameter is set, so that a more stable structure can be formed; as shown by comparison of examples 1 and 5-8, when the concentration of the metal solution is set to be 1mol/L, the prepared battery performance is better, because the concentration of the metal solution influences the thickness of metal precipitate of the hollow structure silicon-carbon anode material, namely the thickness of the hollow layer 2, namely the distance between the nano silicon core 1 and the carbon outer layer 3, thereby influencing the structural stability of the whole silicon-carbon anode material; since the weight ratio of the nano silicon core 1 to the metal deposit in the embodiment 1 is 10:1, the two comparisons are combined to obtain: when the weight part ratio of the nano silicon inner core 1 to the metal precipitate layer to the carbon outer layer 3 is 10:1:1, the prepared nano silicon inner core has more stable structure and better performance.
Figure BDA0004022623150000071
Figure BDA0004022623150000081
Table 1 test results table
Based on the above, the invention has the advantages that the metal sediment is deposited on the surface of the nano silicon inner core 1, the nano silicon inner core 1 coated with the metal sediment is uniformly stirred in lignin and dimethylformamide solution, then is coated on copper foil to be dried to form a carbon outer layer 3, and the metal sediment is etched and removed under an acidic condition to obtain a hollow layer 2, so that the core-shell hollow silicon-carbon nano negative electrode material is prepared, and the preparation method is simple to operate, good in controllability and capable of mass production; compared with the conventional negative plate, the negative plate prepared from the hollow structure silicon-carbon negative plate material can effectively inhibit the expansion of a silicon-carbon negative plate, and the prepared battery has higher capacity retention rate, lower thickness expansion rate, longer service life and better safety.
It will be evident to those skilled in the art that the invention is not limited to the details of the foregoing illustrative embodiments, and that the present invention may be embodied in other specific forms without departing from the spirit or essential characteristics thereof. The present embodiments are, therefore, to be considered in all respects as illustrative and not restrictive, the scope of the invention being indicated by the appended claims rather than by the foregoing description, and all changes which come within the meaning and range of equivalency of the claims are therefore intended to be embraced therein. Any reference sign in a claim should not be construed as limiting the claim concerned.

Claims (9)

1. The method for preparing the silicon-carbon nano negative electrode material with the core-shell hollow structure by using lignin comprises the following steps: step one, material structure design; step two, preparing lignin standard solution; step three, preparing first composite particles; uniformly dispersing the first composite particles; step five, preparing a carbon outer layer; step six, preparing a hollow layer; the method is characterized in that:
in the first step, the silicon-carbon nano negative electrode material with the core-shell hollow structure comprises a nano silicon core (1), a hollow layer (2) and a carbon outer layer (3), wherein the carbon outer layer (3) is coated on the outer surface of the nano silicon core (1), and a hollow layer (2) is arranged between the nano silicon core (1) and the carbon outer layer (3);
in the second step, the kraft lignin is dissolved in an organic solution to prepare a standard solution with the weight percent of 18.5 percent;
in the third step, dissolving the nano silicon inner core (1) in a metal solution, adding alkali for reaction, stirring, and centrifugally washing to obtain first composite particles coated with the nano silicon inner core (1) by metal sediment;
in the fourth step, the first composite particles are gradually added into the standard solution, so that the mass ratio of the first composite particles to the lignin is 1:1, and the first composite particles are uniformly dispersed by continuously stirring while being added, so as to obtain slurry;
in the fifth step, the prepared slurry is uniformly smeared on a copper foil with the thickness of 127 mu m by a surgical knife, and is dried at room temperature and then is transferred into a vacuum oven for drying for 12 hours; calcining the dried composite particles in a tubular furnace, and then, keeping the temperature at 600 ℃ for 2 hours to obtain second composite particles so as to form a carbon outer layer (3);
in the sixth step, the second composite particles are reacted under an acidic condition, and the metal sediment is removed to form a hollow layer (2), so that the silicon-carbon nano negative electrode material with the core-shell hollow structure is obtained.
2. The method for preparing the silicon-carbon nano negative electrode material with the core-shell hollow structure by using lignin according to claim 1, which is characterized in that: in the first step, the diameter of the nano silicon core (1) is 30-50nm.
3. The method for preparing the silicon-carbon nano negative electrode material with the core-shell hollow structure by using lignin according to claim 1, which is characterized in that: in the first step, the weight part ratio of the nano silicon core (1) to the carbon outer layer (3) is 5-10:0.5-2.
4. The method for preparing the silicon-carbon nano negative electrode material with the core-shell hollow structure by using lignin according to claim 1, which is characterized in that: in the first step, the nano silicon core (1) is prepared from a silicon source by a pyrolysis method or a vapor deposition method.
5. The method for preparing the silicon-carbon nano negative electrode material with the core-shell hollow structure by using lignin according to claim 4, which is characterized in that: the silicon source is one of silicon tetrahydroide and trimethyldichlorosilane.
6. The method for preparing the silicon-carbon nano negative electrode material with the core-shell hollow structure by using lignin according to claim 1, which is characterized in that: in the second step, the organic matter is dimethylformamide.
7. The method for preparing the silicon-carbon nano negative electrode material with the core-shell hollow structure by using lignin according to claim 1, which is characterized in that: in the third step, the metal solution is one of zinc ion solution, magnesium ion solution and iron ion solution.
8. The method for preparing the silicon-carbon nano negative electrode material with the core-shell hollow structure by using lignin according to claim 7, which is characterized in that: the concentration of the metal solution is 0.8-2 mol/L.
9. The method for preparing the silicon-carbon nano negative electrode material with the core-shell hollow structure by using lignin according to claim 1, which is characterized in that: in the fifth step, the calcining temperature is 500-700 ℃ and the calcining time is 1-4 h.
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