CN110589796B

CN110589796B - Carbon powder chemically synthesized by molten salt and preparation method and application thereof

Info

Publication number: CN110589796B
Application number: CN201910927347.3A
Authority: CN
Inventors: 宋秋实; 谢志刚; 谢宏伟; 宁志强; 尹华意
Original assignee: Northeastern University China
Current assignee: Northeastern University China
Priority date: 2019-09-27
Filing date: 2019-09-27
Publication date: 2020-11-24
Anticipated expiration: 2039-09-27
Also published as: CN110589796A

Abstract

A fused salt chemical synthesis carbon powder and a preparation method and application thereof belong to the field of carbon material chemical synthesis. The preparation method of the fused salt chemical synthesis carbon powder comprises weighing dry CaC according to the proportion₂Powdered, dried CaCO₃Putting the powder and the dehydrated molten salt raw material into a crucible, putting the crucible into a closed reactor, and introducing inert gas for protection; heating the closed reactor to the reaction temperature, and preserving the temperature for 5 min-10 h to carry out carbonization reaction to obtain a carbon product; and (3) carrying out ultrasonic cleaning on the carbon product, carrying out solid-liquid separation, removing molten salt, and drying to obtain carbon powder. The carbon powder material is used as a negative electrode carbon material of a lithium ion electrode, and has the advantages of improving the battery capacity and the cycle performance. The product of the method only generates calcium oxide except carbon, does not generate other toxic and harmful substances, and has green and environment-friendly process, and simple and easy operation.

Description

Carbon powder chemically synthesized by molten salt and preparation method and application thereof

Technical Field

The invention belongs to the field of chemical synthesis of carbon materials, and particularly relates to carbon powder synthesized by molten salt chemistry, and a preparation method and application thereof.

Background

The carbon material has various forms such as graphite, amorphous carbon, diamond, carbon nanotubes, graphene and the like, and different synthesis methods such as natural graphite high-temperature sintering, organic carbon pyrolysis, vapor deposition, epitaxial growth, electrolysis and the like are also needed for preparing the corresponding carbon material. The above methods all have certain advantages, but there are some technical problems to be overcome. For example, high temperature of over 1800 ℃ is generally required for high temperature sintering of natural graphite and high temperature cracking of organic carbon, the requirement on heating equipment is high, and the energy consumption is also high; vapor deposition, epitaxial growth require delicate, expensive equipment and complex operations; the electrolysis method has low efficiency and more side reactions. Therefore, the development of a simple, feasible and low-cost carbon material preparation method has good practical significance.

Calcium carbide is widely applied to the chemical fields of PVC, vinyl acetate, rubber, acetylene and the like. The calcium carbide is the main component of natural calcium carbide. In addition, industrial calcium carbide is mainly produced by the high-temperature reaction of coke and calcium oxide. Calcium carbonate is also an important inorganic chemical raw material, and is often used in many industries such as coating, rubber, plastic and paper making. Calcium carbonate can be obtained from natural limestone by mechanical grinding, crushing and other procedures (ground calcium carbonate); or prepared by chemical methods such as calcination, separation, precipitation, etc. (light calcium carbonate, active calcium carbonate and nano calcium carbonate).

Lithium Ion Batteries (LIBs) have the advantages of high energy density, no memory effect, long cycle life, environmental friendliness and the like, are widely applied to the fields of portable machinery, electronics, automobiles, aviation and the like, and are one of the most widely applied secondary batteries so far. The cathode material is a main component of the lithium ion battery and generates Li in the charging and discharging processes of the battery⁺And ion intercalation and deintercalation reactions. Common lithium ion battery negative electrode materials include carbon-based, silicon-based, tin-based, titanium-based oxides, transition metal sulfides, and the like. Among them, carbon-based negative electrode materials represented by graphite are typical intercalation materials, have the characteristics of good conductivity, low intercalation potential, low price and the like, and are the earliest and most widely applied commercialized negative electrode materials. Although, the theoretical specific capacity of graphite is 372mAh g^-1Although lower than other negative electrode materials (4200 mAh g for silicon)^-1) But also has the advantages of small volume expansion, good stability and the like. At present, the battery carbon negative electrode of the lithium ion battery mainly comprises graphites (including modified graphite, artificial graphite and the like), amorphous carbons (including soft carbon, hard carbon and the like), and nanocarbons (including carbon nanotubes, graphene and C)₆₀Etc.). However, the preparation of these carbon materials generally requires a complicated synthesis process, and requires severe conditions such as high temperature and high vacuum.

Disclosure of Invention

Based on the prior art, the invention aims to provide a carbon powder synthesized by molten salt chemistry, a preparation method and application thereof. The invention takes calcium carbide and calcium carbonate as raw materials, takes molten Ca-based halide molten salt as a reaction medium, and carries out carbonization reaction at a certain temperature and time to prepare the carbon powder material. And removing the reacted product and the molten salt mixture from the melt, cooling, washing with ultrasonic water, and drying to obtain the carbon powder material. The carbon powder material is used as a negative electrode carbon material of a lithium ion electrode, and has the advantages of improving the battery capacity and the cycle performance. The product of the method only generates calcium oxide except carbon, does not generate other toxic and harmful substances, and has green and environment-friendly process, and simple and easy operation.

The invention relates to a preparation method of carbon powder chemically synthesized by molten salt, which comprises the following steps:

step 1: molten salt dehydration treatment

Vacuum drying the raw material of the molten salt, and cooling the raw material of the molten salt to room temperature along with the furnace to obtain a dehydrated raw material of the molten salt; the molten salt is calcium-based halide molten salt, and when the molten salt is a mixture, the mixing proportion of the molten salt is the mixing proportion of the mixed substances to form eutectic salt;

step 2: preparation of calcium carbide and calcium carbonate

(1) Weighing CaC₂Crushing and drying under inert atmosphere to obtain dried CaC with particle size of 1 μm-5mm₂Powder;

(2) weighing CaCO₃Drying the powder to obtain dry CaCO₃Powder;

and step 3: chemical synthesis of carbon powder by molten salt

(1) Weighing dry CaC according to the proportion₂Powdered, dried CaCO₃Putting the powder and the dehydrated molten salt raw material into a crucible, putting the crucible into a closed reactor, and introducing inert gas for protection; wherein, according to CaCO₃Complete reaction, CaCO₃+2CaC₂Chemical formula of → 3CaO +5C, CaC₂The addition amount is 1-100 wt.% of CaCO in stoichiometric excess₃The mass of the calcium halide accounts for the mass percentage of the calcium halide in the dehydrated molten salt raw material0.1-20%, preferably 5-10%;

(2) heating the closed reactor to the reaction temperature, and preserving the temperature for 5 min-10 h to carry out carbonization reaction to obtain a carbon product; wherein the reaction temperature is higher than the melting point of the dehydrated molten salt raw material;

and 4, step 4: post-treatment

And (3) carrying out ultrasonic cleaning on the carbon product, carrying out solid-liquid separation, removing molten salt, and drying to obtain carbon powder.

In the step 1, the vacuum drying process comprises the following steps: the drying temperature is 200-400 ℃, and the drying time is 24-48 h.

In the step 1, the calcium-based halide molten salt is one of calcium halide, a mixture of calcium halide and alkali metal halide, a mixture of calcium halide and alkaline earth metal halide, or a mixture of calcium halide, alkaline earth metal halide and alkali metal halide.

In the molten salt of calcium-based halide, the calcium-based halide is preferably CaCl₂、CaBr₂、CaF₂Preferably CaCl₂。

The alkali metal halogen compound is one or more of NaCl, KCl, LiCl, NaBr, KBr, LiBr, NaF, KF and LiF.

The alkaline earth metal halide is MgCl₂、MgF₂、CaCl₂、CaF₂、SrCl₂、SrF₂、BaCl₂、BaF₂One or more of them.

In the step 2(1), CaC₂For analytically pure calcium carbide or industrial calcium carbide, analytically pure calcium carbide is preferred.

In the step 2(1), CaC₂The crushing mode is manual crushing and mechanical grinding, and mechanical crushing is preferred.

In the step 2(1), the CaC is dried₂The particle size of the powder is preferably 50 μm to 200. mu.m.

In the step 2(1), the drying temperature is 80-120 ℃.

In the step 2(2), the CaCO₃Is heavy calcium carbonate and lightCalcium carbonate, activated calcium carbonate and nano calcium carbonate, preferably light calcium carbonate and nano calcium carbonate.

In the step 2(2), the CaCO₃The particle size of the powder is 0.05-200 μm, preferably 0.1-20 μm.

In the step 2(2), the drying temperature is 100-300 ℃, preferably 120-150 ℃.

In the step 3(1), CaCO is preferably used in a molar ratio₃：CaC₂＝(1～2)：(2～4)。

In the step 3(1), the CaC is dried₂Powdered, dried CaCO₃Placing the powder and the dehydrated molten salt raw material in a crucible, and selecting the following five modes:

the first method comprises the following steps: uniformly mixing all the raw materials and placing the mixture in a crucible;

secondly, each raw material is laid in a crucible layer by layer; the layer-by-layer tiling is preferably distributed layer-by-layer from the bottom of the crucible upwards in the order of dry CaC₂Powder, dehydrated molten salt raw material and dried CaCO₃The tiling mode of the powder;

thirdly, after two raw materials are uniformly mixed, the mixture is flatly paved with the other raw material layer by layer;

fourthly, repeatedly spreading part of raw materials layer by layer and then placing the raw materials in the crucible;

fifthly, at least two of the four materials are mixed and placed in the crucible.

In the step 3(2), the temperature rise rate of the temperature rise is 0.5-15 ℃/min.

In the step 3(2), the reaction temperature is higher than the melting point of the dehydrated molten salt raw material, and the reaction temperature is preferably 600-1000 ℃.

In the step 4, the ultrasonic cleaning adopts the existing hydrochloric acid cleaning to remove the unreacted CaC₂And cleaning with clear water to remove the molten salt after reaction, wherein the ultrasonic frequency is 10-30 KHz.

The pH value of the clear water is 5-7, and the hydrochloric acid is a hydrochloric acid solution with the substance concentration of 0.5-2 mol/L.

In the step 4, the solid-liquid separation is preferably centrifugal separation, and the rotation speed of the centrifugal separation is preferably 200-1000 r/min.

A carbon powder chemically synthesized by fused salt is prepared by the preparation method.

The average particle size of the carbon powder chemically synthesized by the molten salt prepared by the invention is 0.1-50 mu m, and the carbon powder tends to a single structure with a spherical shape from a composite structure with at least two shapes of flower shape, tubular shape, sheet shape and spherical shape along with the rise of the reaction temperature.

The application of the carbon powder chemically synthesized by the molten salt is to use the carbon powder chemically synthesized by the molten salt as a negative electrode carbon material of a lithium ion battery, and the prepared lithium ion battery has the specific cyclic charge-discharge capacity of more than 400mAh g^-1The specific cyclic charge-discharge capacity of the graphite is superior to that of a common graphite material (the theoretical capacity of the common graphite is 372mAh g^-1)。

A lithium ion battery cathode material comprises the carbon powder chemically synthesized by the molten salt.

An electrode plate is prepared by adopting the lithium ion battery negative electrode material.

A lithium ion battery comprises the electrode pole piece.

The invention relates to a carbon powder synthesized by molten salt chemistry, a preparation method and application thereof, and the principle is as follows:

calcium carbonate and calcium carbide are two inorganic substances containing carbon elements respectively and are also common chemical raw materials. Wherein, the carbon element in the calcium carbonate is in an oxidation state and is tetravalent; the carbon element in the calcium carbide is in a reduction state and is in a negative valence state. According to thermodynamic calculation, calcium carbonate and calcium carbide can react at 600-1000 ℃ to generate simple substance carbon and calcium oxide. The standard Gibbs free energies of the reactions were all less than-400 kJ/mol. However, since the reactants and the product are in a pure solid state, diffusion of the product into elemental carbon and calcium carbide after the contact reaction may block the contact of the reactants, preventing the reaction from proceeding sufficiently. The calcium-based halide molten salt is used as a reaction medium, has high solubility for CaO as a product, and can quickly dissolve the generated calcium oxide, and the liquid molten salt can be suspended in the calcium-based halide molten salt by using simple carbonThereby removing the barrier between the reactants calcium carbide and calcium carbonate and allowing the reaction to proceed rapidly. In addition, the calcium carbonate and the calcium oxide have higher solubility in the calcium-based halide molten salt, so that the calcium carbonate and the calcium oxide can be used for ensuring that

Ions and

the dissolved state exists in the molten salt, and the reaction process can be effectively regulated and controlled by controlling the concentration, proportion and distribution of reactants, the composition of the molten salt, the reaction time and the like, so that the structure and the appearance of a product are controlled.

The invention relates to a carbon powder chemically synthesized by molten salt and a preparation method thereof, which have the beneficial effects that:

1. the method can realize the high-efficiency and high-quality preparation of the carbon powder at a lower temperature, and the equipment is simple to operate.

2. The industrial raw materials of calcium carbonate and calcium carbide are used as reaction raw materials, so that the sources of carbon materials can be widened, the transitional consumption of natural graphite and the complex process of pyrolysis can be reduced, the carbon powder material with controllable structure and shape can be prepared, the raw materials are rich and easy to obtain, no toxic or harmful substances are generated in the reaction process, and the recovery is facilitated.

3. The melting environment of the calcium-based halide molten salt has high solubility for calcium oxide which is one of the products, so that the reaction product is removed in time, and dynamic conditions can be provided for the full reaction.

4. The melting can enable carbon-containing ions in reactants to exist in the molten salt, so that chemical reaction and product regulation are realized.

5. According to the invention, calcium carbide and calcium carbonate are used as raw materials, a molten salt medium environment is utilized, and a chemical method is used for preparing the carbon powder material, so that the high-quality carbon powder material can be prepared at a lower temperature. The reaction product is only calcium oxide except carbon, does not generate other toxic and harmful substances, has the characteristics of low cost, environment-friendly process, environmental friendliness, high product quality and the like, and utilizes certain solubility of calcium carbonate and calcium carbide in calcium-based molten salt to convert the carbonization reaction from a solid phase to a liquid phase reaction, so that the reaction is easier to carry out.

Drawings

FIG. 1 is an XRD pattern of a carbon powder chemically synthesized by molten salt in example 1 of the present invention;

FIG. 2 is an SEM photograph of a carbon powder chemically synthesized by molten salt in example 1 of the present invention;

FIG. 3 is an XRD pattern of the carbon powder chemically synthesized by molten salt in example 2 of the present invention;

FIG. 4 is an SEM photograph of carbon powder chemically synthesized by molten salt in example 2 of the present invention

FIG. 5 is a flow chart of molten salt chemical synthesis of a carbon anode material of a lithium ion battery in example 15 of the present invention;

FIG. 6 shows the cycling performance of the carbon anode material of the lithium ion battery chemically synthesized by molten salt in example 15 of the present invention;

FIG. 7 is a graph showing rate capability of a carbon anode material of a lithium ion battery chemically synthesized by molten salt in example 15 of the present invention;

Detailed Description

The present invention will be described in further detail with reference to examples.

In the embodiment of the invention, the calcium-based halide molten salt is used as analytically pure and has the purity of 99 percent;

the alumina crucible adopted in the embodiment of the invention is a commercial product, the purity is 99%, the diameter is 40-200 mm, and the alumina crucible adopted in the embodiment is 50mm and 100 mm;

the Ar argon adopted in the embodiment of the invention is commercially available high-purity argon with the purity of 99.999 percent;

in the embodiment of the invention, CaCl is adopted as the molten salt₂、CaCl₂-NaCl、CaCl₂-LiCl、CaCl₂-LiCl-KCl molten salt System, CaCl₂The working temperature of the furnace is 800 +/-5-1000 +/-5 ℃; CaCl₂In a molten salt system of NaCl, in molar ratio, CaCl₂: NaCl 52:48, and the working temperature is 600 +/-5-1000 +/-5 ℃; CaCl₂In a molten salt system of-LiCl, in molar ratio of CaCl₂：LiCl＝36:64；CaCl₂-LiCl-KIn the Cl system, according to the molar ratio of CaCl₂: LiCl: KCl is 35:52:13, and the working temperature is 500 +/-5-950 +/-5 ℃.

In the embodiment of the invention, the mass of the molten salt is 50-1000 g;

in the embodiment of the invention, the frequency of the applied ultrasonic field is 10-30 KHz;

in the embodiment of the invention, the pH value of water adopted for ultrasonic cleaning is between 5 and 7;

in the embodiment of the invention, the ultrasonic cleaning frequency is 10-30 KHZ;

in the embodiment of the invention, the centrifugal separation rotating speed is 600 r/min.

Comparative example 1

A preparation method of carbon powder chemically synthesized by molten salt comprises the following steps:

step 1, preparation of calcium carbide and calcium carbonate raw materials and assembly of reaction device

Weighing 10g of CaCO₃And drying for 24h at 300 ℃. Weighing 13gCaC₂Crushing in inert atmosphere and drying at 80 deg.c.

Step 2, carbon powder synthesis reaction

(1) According to the CaC starting from the bottom of the crucible₂、CaCO₃The reactor is closed, high-purity argon is introduced, and meanwhile, circulating cooling water is introduced to a sealing flange of the closed reactor.

(2) Heating to 850 ℃ according to the temperature of 3 ℃/min, and preserving the heat for 4h to obtain a reaction product.

Step 3, post-treatment

And removing the cooled product out of the reactor, and repeatedly ultrasonically cleaning the product by using clear water with the pH value of 7 to remove salt, wherein the ultrasonic oscillation frequency is 20 kHZ. Then, 2mol/L hydrochloric acid is used for washing, residual acid is washed by clear water, and a product is obtained after centrifugation and drying. After the reaction, the black matter in the crucible is very little, and the yield of the carbon element after cleaning and recovery is lower than 10 percent, which indicates that the reactant is basically not reacted.

Example 1

step 1, molten salt dehydration treatment

Weighing 50g of CaCl₂Molten salt is dried for 24 hours in a crucible furnace at 300 ℃ to obtain dried and dehydrated molten salt;

step 2, preparation of calcium carbide and calcium carbonate raw materials and assembly of reaction device

Weighing 10g of CaCO₃And drying the mixture for 24 hours at 300 ℃ to obtain the dry molten salt. Weighing 13gCaC₂Crushing in inert atmosphere and drying at 80 deg.c.

Step 3, carbon powder synthesis reaction

(1) According to the CaC starting from the bottom of the crucible₂、CaCl₂And CaCO₃The reactor is closed, high-purity argon is introduced, and meanwhile, circulating cooling water is introduced to a sealing flange of the closed reactor.

(2) Heating up to 700 ℃ according to the temperature of 3 ℃/min, and preserving the heat for 4h to obtain a reaction product.

Step 4, post-treatment

And removing the cooled product out of the reactor, and repeatedly ultrasonically cleaning the product by using clear water with the pH value of 7 to remove salt, wherein the ultrasonic oscillation frequency is 20 kHZ. Then, 2mol/L hydrochloric acid is used for washing insoluble substances such as CaO, residual acid is washed by clear water, and the product is obtained after centrifugation and drying. The phase and morphology of the resulting product are shown in FIGS. 1 and 2, respectively. The product obtained by the reaction mainly consists of amorphous carbon, and the product is in a tubular, flaky and granular structure. The yield of the carbon element is more than 85 percent.

Example 2

A method for preparing carbon powder by molten salt chemical synthesis, which is different from the method in example 1 in that:

(1) the temperature used in step 2 was 900 ℃.

The structure of the resulting product is a composite structure comprising amorphous carbon and graphitic phase, and its XRD is shown in fig. 3, and its SEM is shown in fig. 4, and as can be seen from fig. 4, its morphology is uniform spherical particles.

Example 3

(1) the molten salt used in the step 1 is CaCl₂NaCl eutectic mixed molten salt with the mass of 500g is uniformly mixed with the two kinds of molten salt before drying;

(2) CaCO in step 2₃Mass 70g, CaC₂The mass is 91 g;

(3) in the step 3(1), the diameter of the corundum crucible is 100 mm;

(4) in step 3(1) CaC₂、CaCl₂NaCl and CaCO₃The mixing mode of (A) is uniform mixing;

(4) in the step 3(2), the reaction temperature is 650 ℃, and the reaction time is 6 h.

Example 4

(1) the molten salt used in the step 1 is CaCl₂-LiCl eutectic mixed molten salt, the molten salts being mixed homogeneously before drying;

(2) CaCO in step 2₃Mass 2g, CaC₂The mass is 2.6 g;

(3) in step 3(1) CaC₂、CaCl₂-LiCl and CaCO₃And spreading layer by layer from the bottom of the crucible.

(4) In the step 3(2), the reaction temperature is 750 ℃, and the reaction time is 4 h.

Example 5

(1) the molten salt used in the step 1 is CaCl₂-LiCl-KCl eutectic mixed molten salt with the mass of 100g is uniformly mixed with the molten salt before drying;

(2) CaCO in step 2₃3.5g, CaC₂4.55 g;

(3) in step 3(1) CaC₂、CaCl₂-LiCl-KCl and CaCO₃And (4) uniformly mixing.

(4) In the step 3(2), the reaction temperature is 700 ℃, and the reaction time is 5 h.

Example 6

(1) the mass of the molten salt used in the step 1 is 1000 g;

(2) CaCO in step 2₃40g, CaC₂Is 64 g;

(3) in the step 3(1), the diameter of the corundum crucible is 150 mm;

(3) in step 3(1) CaC₂、CaCl₂And CaCO₃And (4) uniformly mixing.

Example 7

(1) CaCO in step 3(1)₃、CaCl₂And CaC₂The crucible is spread layer by layer from the bottom of the crucible.

Example 8

(1) in step 3(1), CaC is used from the bottom of the crucible₂(0.5 part by mass) of CaCl₂(one third of the total mass), CaCO₃(0.5 part by mass) of CaCl₂(one third of the total mass), CaC₂(0.5 part by mass) of CaCl₂(one third of the total mass) and CaCO₃(0.5 parts by mass) are layered one upon another.

Example 9

A method for preparing carbon powder by molten salt chemical synthesis, which is different from the method in example 3 in that:

(1) CaCO in step 3(1)₃、CaCl₂NaCl and CaC₂The crucible is spread layer by layer from the bottom of the crucible.

Example 10

(1) in step 3(1), CaC is used from the bottom of the crucible₂(0.5 part by mass) of CaCl₂NaCl (one third of the total mass), CaCO₃(0.5 part by mass) of CaCl₂NaCl (one third of the total mass), CaC₂(0.5 part by mass) of CaCl₂NaCl (III)In parts by total mass) and CaCO₃(0.5 parts by mass) are layered one upon another.

Example 11

A method for preparing carbon powder by molten salt chemical synthesis, which is different from the method in example 4 in that:

(1) CaCO in step 3(1)₃、CaCl₂-LiCl and CaC₂The crucible is spread layer by layer from the bottom of the crucible.

Example 12

(1) in step 3(1), CaC is used from the bottom of the crucible₂(0.5 part by mass) of CaCl₂-LiCl (one third of the total mass), CaCO₃(0.5 part by mass) of CaCl₂-LiCl (one third of the total mass), CaC₂(0.5 part by mass) of CaCl₂-LiCl (one third of the total mass) and CaCO₃(0.5 parts by mass) are layered one upon another.

Example 13

(1) CaCO in step 3(1)₃、CaCl₂-LiCl-KCl and CaC₂The crucible is spread layer by layer from the bottom of the crucible.

Example 14

(1) in step 3(1), CaC is used from the bottom of the crucible₂(0.5 part by mass) of CaCl₂-LiCl-KCl (one third of the total mass), CaCO₃(0.5 part by mass) of CaCl₂-LiCl-KCl (one third of the total mass), CaC₂(0.5 part by mass) of CaCl₂-LiCl-KCl (one third of the total mass) and CaCO₃(0.5 parts by mass) are layered one upon another.

Example 15

The method for preparing the carbon cathode material of the lithium ion battery in the molten salt has the process flow shown in figure 5, and comprises the following steps

Step 1: the carbon powder obtained in example 1 was taken as a carbon material;

step 2: battery assembly and testing

Preparing the obtained carbon material, acetylene black and PVDF into slurry in an NMP medium according to the mass ratio of 8:1:1 to obtain a lithium ion battery cathode material;

and coating the lithium ion battery negative electrode material on copper foil, and drying in vacuum at 80 ℃ for 12h to obtain the electrode plate.

The electrode plate and the lithium plate are used as counter electrodes, the polypropylene film is used as a diaphragm, the electrolyte is 1MLLiPF6/(EC: DEC ═ 1:1), the battery case model is 2025, the battery is charged and discharged at a current density of 0.5C, and the cycle life test is carried out within a voltage range of 1-2.5V.

Fig. 6 and 7 are the cycle performance and rate performance, respectively, of the carbon anode material. Therefore, the material has good cycle and rate performance, and the capacity is obviously higher than that of common graphite (the theoretical capacity of the common graphite is 372mAh g)^-1). Although the stability of the battery needs to be improved, the material is amorphous carbon, graphite and a complex at present, and the micro-morphology is the mixture of various particles such as fibers, spheres, petals and the like, so that the structure and the morphology of a final product can be adjusted by regulating and controlling the reaction, and the material with high cycle performance and better stability is obtained.

Example 16

A method for preparing a carbon negative electrode material of a lithium ion battery in molten salt, which is similar to example 15, and is different from the following steps:

(1) the molten salt used in the step 1(1) is CaCl₂NaCl eutectic mixed molten salt with the mass of 200g and CaCl before drying₂Mixing NaCl evenly;

(2) CaCO in step 1(2)₃Is nano CaCO₃The mass is 14 g;

(3) in step 1(3), CaC₂The mass is 18.2 g;

(4) in step 2(1) CaC₂、CaCl₂NaCl and CaCO₃The mixing mode of (A) is uniform mixing;

(4) in the step 2(2), the reaction temperature is 650 ℃, and the reaction time is 6 h.

Example 17

(1) the molten salt used in the step 1(1) is CaCl₂-LiCl eutectic mixed molten salt, the molten salts being mixed homogeneously before drying;

(2) light CaCO in step 1(2)₃The mass of the powder is 2g,

(3) in step 1(3), CaC₂The mass is 2.6 g;

(4) in step 2(1) CaC₂、CaCl₂-LiCl and CaCO₃Spreading layer by layer from the bottom of the crucible;

(4) in the step 2(2), the reaction temperature is 750 ℃, and the reaction time is 4 h.

Example 18

(1) CaCl used in step 1(1)₂The mass is 800 g;

(2) CaCO in step 1(2)₃Is heavy calcium carbonate with the mass of 160g,

(3) in step 1(3), CaC₂The mass is 60 g;

(4) in the step 2(1), the diameter of the corundum crucible is 150 mm;

(5) in step 2(1) CaC₂、CaCl₂And CaCO₃And (4) uniformly mixing.

(6) In the step 2(2), the reaction temperature is 950 ℃, and the reaction time is 8 h.

Example 19

(1) CaCl used in step 1(1)₂The mass is 800 g;

(2) CaCO in step 1(2)₃Is heavy calcium carbonate with the mass of 160g,

(3) in step 1(3), CaC₂The mass is 60 g;

(4) in the step 2(1), the diameter of the corundum crucible is 150 mm;

(5) step (ii) of2(1) in CaCl₂And CaCO₃Mixing uniformly, then according to CaC₂And the mixture is spread layer by layer from the bottom to the top of the crucible.

(6) In the step 2(2), the reaction temperature is 1000 ℃, and the reaction time is 4 h.

Example 20

(1) in step 2(1), CaC is used from the bottom of the crucible₂(0.5 part by mass) of CaCl₂(one third of the total mass), CaCO₃(0.5 part by mass) of CaCl₂(one third of the total mass), CaC₂(0.5 part by mass) of CaCl₂(one third of the total mass) and CaCO₃(0.5 parts by mass) are layered one upon another.

(2) In the step 2(2), the reaction temperature is 900 ℃, and the reaction time is 2 h.

Example 21

A method for preparing a carbon negative electrode material of a lithium ion battery in molten salt, which is similar to example 16, and is different from the following steps:

(1) the molten salt used in the step 1(1) is CaCl₂The mass of the NaCl eutectic mixed molten salt is 1000 g;

(2) step 1(2) Nano CaCO₃The mass is 280 g;

(3) in step 1(3), CaC₂The mass is 109.2 g;

(4) in step 2(1) CaC₂、CaCl₂NaCl and CaCO₃Mixing in a layer-by-layer tiling mode;

(4) in the step 2(2), the reaction temperature is 800 ℃, and the reaction time is 10 h.

Example 22

(1) CaCl in step 2(1)₂NaCl and CaCO₃Mixing uniformly, then according to CaC₂And the mixture is spread layer by layer from the bottom to the top of the crucible.

(2) In the step 2(2), the reaction temperature is 900 ℃, and the reaction time is 7 h.

Example 23

(2) In the step 2(2), the reaction time is 3 h.

Example 24

A method for preparing a carbon negative electrode material of a lithium ion battery in molten salt, which is similar to example 17, and is different from the following steps:

(1) the molten salt used in the step 1(1) is CaCl₂The mass of the LiCl eutectic mixed molten salt is 500 g;

(2) active CaCO in step 1(2)₃The mass is 140 g;

(3) in step 1(3), CaC₂The mass is 65 g;

(4) in step 2(1) CaC₂、CaCl₂-LiCl and CaCO₃Uniformly mixing;

(4) in the step 2(2), the reaction temperature is 850 ℃ and the reaction time is 8 h.

Example 25

(1) CaCl in step 2(1)₂-LiCl and CaCO₃Mixing uniformly, then according to CaC₂And the mixture is spread layer by layer from the bottom to the top of the crucible.

(2) In the step 2(2), the reaction time is 5 h.

Example 26

(1) in step 2(1), starting from the bottom of the crucibleCaC₂(0.5 part by mass) of CaCl₂-LiCl (one third of the total mass), CaCO₃(0.5 part by mass) of CaCl₂-LiCl (one third of the total mass), CaC₂(0.5 part by mass) of CaCl₂-LiCl (one third of the total mass) and CaCO₃(0.5 parts by mass) are layered one upon another.

(2) In the step 2(2), the reaction time is 2 h.

Claims

1. A preparation method of carbon powder chemically synthesized by molten salt is characterized by comprising the following steps:

step 1: molten salt dehydration treatment

Vacuum drying the raw material of the molten salt, and cooling the raw material of the molten salt to room temperature along with the furnace to obtain a dehydrated raw material of the molten salt; the molten salt is one of calcium halide, a mixture of calcium halide and alkali metal halogen compounds, or a mixture of calcium halide and alkaline earth metal halogen compounds, or a mixture of calcium halide, alkaline earth metal halogen compounds and alkali metal halogen compounds; when the molten salt is a mixture, the mixing proportion is the mixing proportion of the mixed substances to form eutectic salt;

step 2: preparation of calcium carbide and calcium carbonate

(2) weighing CaCO₃Drying the powder to obtain dry CaCO₃Powder;

and step 3: chemical synthesis of carbon powder by molten salt

(1) Weighing dry CaC according to the proportion₂Powdered, dried CaCO₃Putting the powder and the dehydrated molten salt raw material into a crucible, putting the crucible into a closed reactor, and introducing inert gas for protection; wherein, according to CaCO₃Complete reaction, CaCO₃+2CaC₂Chemical formula of → 3CaO +5C, CaC₂The addition amount is 1-100 wt.% of CaCO in stoichiometric excess₃The mass of the calcium halide accounts for 0.1-20% of the mass of the calcium halide in the dehydrated molten salt raw material;

and 4, step 4: post-treatment

2. The method as claimed in claim 1, wherein calcium halide is CaCl in molten salt₂、CaBr₂、CaF₂One or more of the above;

the alkali metal halogen compound is one or more of NaCl, KCl, LiCl, NaBr, KBr, LiBr, NaF, KF and LiF;

the alkaline earth metal halide is MgCl₂、MgF_2、CaCl₂、CaF₂、SrCl₂、SrF₂、BaCl₂、BaF₂One or more of them.

3. The method for preparing carbon powder by chemical synthesis using molten salt according to claim 1, wherein in the step 2(1), CaC₂Analyzing pure calcium carbide or industrial calcium carbide; the drying temperature is 80-120 ℃.

4. The method for preparing carbon powder by chemical synthesis using molten salt as claimed in claim 1, wherein the CaCO is used in step 2(2)₃Heavy calcium carbonate, light calcium carbonate, active calcium carbonate and nano calcium carbonate; the CaCO₃The particle size of the powder is 0.05-200 μm; the drying temperature is 100-300 ℃.

5. The method for preparing the carbon powder through molten salt chemical synthesis according to claim 1, wherein in the step 3(2), the reaction temperature is 600-1000 ℃.

6. A molten salt chemically synthesized carbon powder characterized by being prepared by the preparation method of any one of claims 1 to 5.

7. The carbon powder for molten salt chemical synthesis as claimed in claim 6, wherein the average particle size of the prepared carbon powder for molten salt chemical synthesis is 0.1-50 μm, and the carbon powder for molten salt chemical synthesis tends to be a single structure with a spherical shape from a composite structure with at least two of flower-shaped, tubular, sheet-shaped and spherical shapes with the increase of reaction temperature.

8. A lithium ion battery negative electrode material, characterized in that the lithium ion battery negative electrode material comprises the molten salt chemically synthesized carbon powder of claim 6.

9. An electrode plate, characterized by being prepared by the lithium ion battery negative electrode material of claim 8.

10. A lithium ion battery, characterized in that, the lithium ion battery comprises the electrode plate of claim 9, the prepared lithium ion battery has a specific charge-discharge capacity of more than 400mAh g^-1。