CN113942993B - Method for preparing hard carbon microspheres - Google Patents

Abstract

The invention relates to the technical field of preparation of battery cathode materials, and discloses a method for preparing hard carbon microspheres, which comprises the steps of firstly mixing starch with oligomeric phenolic resin, then solidifying to obtain a starch-based hard carbon precursor of which the surface is coated with a polymer, and then pyrolyzing to obtain the hard carbon microspheres.

Description

Method for preparing hard carbon microspheres

Technical Field

The invention relates to the technical field of preparation of battery cathode materials, in particular to a preparation method of an amorphous carbon coated hard carbon cathode material for a battery.

Background

Lithium ion batteries are currently mainly used in the fields of electronic products, electric automobiles, electrochemical energy storage and the like. The cathode material is one of the main components of the lithium ion battery, and the currently commercialized cathode material of the lithium ion battery is mainly a carbon material. The carbon material has the advantages of high specific capacity, low electrode potential, long cycle life and the like.

Carbon exists in several allotropes, and is used in lithium ion batteries as a carbon material of mainly graphite and disordered structures, and these materials are mainly graphite, artificial graphite, soft carbon and hard carbon. With the development of the fields of electronic equipment, electric vehicles and the like, the requirements on lithium ion batteries are continuously improved. Hard carbon is increasingly being focused by more researchers due to its good power characteristics and safety.

The precursor of the hard carbon material mainly comprises biomass, high polymer material and fossil fuel. The starch is used as a natural polymer material, is a biomass material with very rich yield, and has the characteristics of low cost and reproducibility. The spherical hard carbon cathode material has better electrochemical performance and processability, and the starch particles are naturally spherical. In order to keep the morphology of the starch particles as the precursor of the hard carbon material in the sintering process, the surface of the starch is coated to prevent fusion and agglomeration of the starch microspheres, and finally the hard carbon material with better sphericity is obtained.

The related technical staff of lithium batteries have prepared hard carbon materials from potato starch as a raw material through a long-time stabilization process to obtain better electrochemical performance, but the technical route has longer stabilization time, is difficult to apply industrially, and a method for preparing spherical hard carbon after coating precursors by similar technical means is not reported yet.

In the prior art, the publication number is CN103811717A, the publication time is 2014 and 21 days, the name is "core-shell structured power lithium ion battery anode material and preparation method thereof", chinese patent literature of the invention discloses a core-shell structured power lithium ion battery anode material for an electric automobile and preparation method thereof, the material comprises a graphite inner core and a shell, the shell is of a single-layer structure or a double-layer structure, and is formed by primary coating or secondary coating through a solid-phase coating method, wherein the shell of the single-layer structure is a mixed carbide layer of hard carbon and soft carbon, the shell of the double-layer structure is composed of an inner layer and an outer layer, the inner layer is a mixed carbide layer of hard carbon and soft carbon, the outer layer is a pure soft carbon carbide layer, the crushed mixed coating of the hard carbon and soft carbon is uniformly mixed with isotropic graphite in a conical mixer, and is carbonized under inert atmosphere, and then the shell formed by cooling, crushing and screening is obtained. However, in the prior art, the modification method of the graphite material is to coat by adding amorphous carbon, but the method is to physically stir and mix, and the sphericity of the material cannot be ensured.

Disclosure of Invention

The invention aims at solving the problems in the prior art and provides a preparation method for preparing spherical hard carbon, wherein the method comprises the steps of firstly preparing starch with polymer coated on the surface through emulsion polymerization, then obtaining spherical hard carbon precursor with polymer coated on the surface through stabilization, and finally obtaining the spherical hard carbon through high-temperature carbonization.

The invention provides a method for preparing hard carbon microspheres, which comprises the following steps:

step 1, weighing a predetermined amount of starch as a precursor A;

step 2, dissolving phenolic resin in a solvent to prepare a mixed solvent, adding the mixed solvent into the precursor A obtained in the step 1, stirring and mixing, heating to 60-80 ℃ for stirring and mixing until the solvent evaporates and the phenolic resin is solidified, and obtaining a starch-based hard carbon precursor B of which the surface is coated with a polymer;

and 3, pyrolyzing the precursor B obtained in the step 2 in a nitrogen environment to obtain the hard carbon microspheres.

Preferably, the starch in the preferred step 1 is one or a mixture of several of potato starch, wheat starch, tapioca starch and corn starch in any ratio.

Further, in the step 2, the phenolic resin is a phenolic resin oligomer which can be dissolved and dispersed in a solvent.

Preferably, in the step 2, the solvent is one of tetrahydrofuran, dimethylformamide or dimethylacetamide.

More preferably, in the step 2, the mass ratio of the precursor a to the phenolic resin is (1:1) - (1:5).

More specifically, in the step 2, after the mixed solvent is added to the precursor a, stirring and mixing are performed for 6-10 hours.

Preferably, in the step 3, the precursor B obtained in the step 2 is pyrolyzed under a nitrogen atmosphere, specifically:

firstly, heating the precursor B from room temperature of 20-25 ℃ to 150-250 ℃ at a heating rate of 1-5 ℃/min, and preserving heat for 1-3 hours;

then, heating the precursor B to 500-800 ℃ at a heating rate of 1-5 ℃/min and preserving heat for 1-3 hours;

and finally, heating the precursor B to 1000-1400 ℃ at a heating rate of 1-5 ℃/min, preserving heat for 1-3 hours, and cooling the precursor B to room temperature of 20-25 ℃ along with a furnace.

Compared with the prior art, the technical scheme of the invention has at least the following advantages:

1. according to the technical scheme, the hard carbon precursor is coated by curing the phenolic resin, and the coating effect is better than that of a common mechanical mixing method;

2. according to the technical scheme, the hard carbon precursor is coated to prevent aggregation of starch particles, so that the obtained product has uniform size;

3. according to the technical scheme, the prepared hard carbon microsphere has higher charge and discharge capacity through testing.

Drawings

The foregoing and the following detailed description of the invention will become more apparent when read in conjunction with the following drawings in which:

fig. 1 is a schematic representation of various types of fire extinguishing agents in an example of a 40Ah lithium battery.

Detailed Description

The technical solution for achieving the object of the present invention will be further described with reference to several specific examples, but it should be noted that the technical solution claimed in the present invention includes but is not limited to the following examples.

Example 1

The embodiment provides a preparation method of an amorphous carbon cathode material, which comprises the following steps:

example 1

A method of making hard carbon microspheres comprising the steps of:

step 1, weighing 200g of wheat starch as a precursor A;

step 2, adding 200g of phenolic resin into tetrahydrofuran as a solvent, preparing a mixed solvent after the phenolic resin is dissolved, adding 200g of precursor A in the step 1 into the mixed solvent, stirring and mixing, heating to 60 ℃ after stirring and mixing for 6 hours, evaporating the solvent at the temperature, and solidifying the phenolic resin to obtain a mixture precursor B of the phenolic resin and starch;

and 3, pyrolyzing the precursor B obtained in the step 2 in a nitrogen environment to obtain hard carbon microspheres, wherein the pyrolysis parameters are as follows:

the precursor B is heated up from room temperature 25 ℃ to 150 ℃ at a heating rate of 5 ℃ per minute and is kept warm for 1 hour, then the precursor B is heated up to 500 ℃ at a heating rate of 5 ℃ per minute and is kept warm for 1 hour, finally the precursor B is heated up to 1000 ℃ at a heating rate of 5 ℃ and is kept warm for 1 hour, and then the precursor B is cooled down to room temperature 25 ℃ along with a furnace.

Example 2

A method of making hard carbon microspheres comprising the steps of:

step 1, 200g of potato starch is weighed as a precursor A.

Step 2, adding 400g of phenolic resin into tetrahydrofuran as a solvent, preparing a mixed solvent after the phenolic resin is dissolved, adding 200g of precursor A in the step 1 into the mixed solvent, stirring and mixing, heating to 65 ℃ after stirring and mixing for 8 hours, evaporating the solvent at the temperature, and solidifying the phenolic resin to obtain a mixture precursor B of the phenolic resin and starch;

and 3, pyrolyzing the precursor B obtained in the step 2 in a nitrogen environment to obtain hard carbon microspheres, wherein the pyrolysis parameters are as follows: precursor B was warmed from room temperature 25 ℃ to 200 ℃ at a warming rate of 2 ℃ per minute and incubated for 1.5 hours, then warmed to 650 ℃ at a warming rate of 2 ℃ per minute and incubated for 2 hours, finally warmed to 1100 ℃ at a warming rate of 2 ℃ for 1.5 hours, then cooled to room temperature 25 ℃ with the furnace.

Example 3

A method of making hard carbon microspheres comprising the steps of:

step 1, weighing 200g of tapioca starch as a precursor A;

step 2, adding 300g of phenolic resin into tetrahydrofuran as a solvent, preparing a mixed solvent after the phenolic resin is dissolved, adding 200g of precursor A in the step 1 into the mixed solvent, stirring and mixing, heating to 70 ℃ after stirring and mixing for 6 hours, evaporating the solvent at the temperature, and solidifying the phenolic resin to obtain a mixture precursor B of the phenolic resin and starch;

and 3, pyrolyzing the precursor B obtained in the step 2 in a nitrogen environment to obtain hard carbon microspheres, wherein the pyrolysis parameters are as follows: the precursor B is heated from room temperature 25 ℃ to 200 ℃ at a heating rate of 3 ℃ per minute and is kept warm for 2 hours, then the precursor B is heated to 700 ℃ at a heating rate of 3 ℃ per minute and is kept warm for 1 hour, finally the precursor B is heated to 1300 ℃ at a heating rate of 3 ℃ and is kept warm for 1 hour, and finally the precursor B is cooled to room temperature 25 ℃ along with a furnace.

Example 4

A method of making hard carbon microspheres comprising the steps of:

step 1, weighing 200g of corn starch as a precursor A;

step 2, adding 350g of phenolic resin into tetrahydrofuran as a solvent, preparing a mixed solvent after the phenolic resin is dissolved, adding 200g of precursor A in the step 1 into the mixed solvent, stirring and mixing, heating to 60 ℃ after stirring and mixing for 7 hours, evaporating the solvent at the temperature, and solidifying the phenolic resin to obtain a mixture precursor B of the phenolic resin and starch;

and 3, pyrolyzing the precursor B obtained in the step 2 in a nitrogen environment to obtain hard carbon microspheres, wherein the pyrolysis parameters are as follows: the precursor B is heated up from room temperature 25 ℃ to 200 ℃ at a heating rate of 2 ℃ per minute and is kept warm for 2 hours, then the precursor B is heated up to 650 ℃ at a heating rate of 2 ℃ per minute and is kept warm for 2 hours, finally the precursor B is heated up to 1250 ℃ at a heating rate of 2 ℃ and is kept warm for 1 hour, and finally the precursor B is cooled down to room temperature 25 ℃ along with a furnace.

The hard carbon microspheres prepared in the above examples 1-4 are mixed with carbon black serving as a conductive agent and polyvinylidene fluoride (PVDF) serving as an adhesive according to a mass ratio of 8:1:1, are added with N-methyl pyrrolidone (NMP) to prepare slurry, are uniformly coated on copper foil, are dried in 100 oC vacuum for 12 hours, and are uniformly pressed by a tablet press to obtain the pole piece to be tested.

Lithium sheets are used as counter electrodes, electrolyte is a solution of Ethyl Carbonate (EC) +dimethyl carbonate (DMC) (volume ratio 1:1) of LiPF6 with concentration of 1mol/L, a battery diaphragm with model number celgard2325 is adopted as a diaphragm, and a CR2032 button battery is assembled in a glove box in argon atmosphere.

The button cell is subjected to constant current charge and discharge test in the voltage range of 0-2.5V, the first lithium intercalation specific capacity can reach 376.5mAh/g under the multiplying power of 0.1C, the first lithium deintercalation specific capacity can reach 323.2mAh/g, and the first charge and discharge efficiency can reach 85.8%.

In contrast, the comparison material was obtained by pyrolysis of pure starch under the same process conditions as in step 3 of examples 1-4 above. The specific capacity of the first lithium intercalation of the comparative material is only 287.3mAh/g, the specific capacity of the first lithium deintercalation is only 235.1mAh/g, and the first charge and discharge efficiency is only 81.8%.

The hard carbon microsphere negative electrode material prepared by the method has higher charge and discharge capacity and higher first charge and discharge efficiency.

Claims (5)

1. A method for preparing hard carbon microspheres, comprising the steps of:

step 1, weighing a predetermined amount of starch as a precursor A;

step 2, dissolving phenolic resin in a solvent to prepare a mixed solvent, adding the mixed solvent into the precursor A obtained in the step 1, stirring and mixing, heating to 60-80 ℃ for stirring and mixing until the solvent evaporates and the phenolic resin is solidified, and obtaining a starch-based hard carbon precursor B of which the surface is coated with a polymer, wherein the solvent is one of tetrahydrofuran, dimethylformamide or dimethylacetamide;

step 3, pyrolyzing the precursor B obtained in the step 2 in a nitrogen environment to obtain hard carbon microspheres;

the starch in the step 1 is one or a mixture of several of potato starch, wheat starch, tapioca starch and corn starch in any ratio.

2. A method of preparing hard carbon microspheres according to claim 1, wherein: in the step 2, the phenolic resin is a phenolic resin oligomer which can be dissolved and dispersed in a solvent.

3. A method of preparing hard carbon microspheres according to claim 1, wherein: in the step 2, the mass ratio of the precursor A to the phenolic resin is (1:1) - (1:5).

4. A method of preparing hard carbon microspheres according to claim 1, 2 or 3, wherein: in the step 2, after the mixed solvent is added to the precursor A, stirring and mixing are performed for 6-10 hours.

5. A method of preparing hard carbon microspheres according to claim 1, wherein: in the step 3, the precursor B obtained in the step 2 is pyrolyzed in a nitrogen environment, specifically:

firstly, heating the precursor B from room temperature of 20-25 ℃ to 150-250 ℃ at a heating rate of 1-5 ℃/min, and preserving heat for 1-3 hours;

then, heating the precursor B to 500-800 ℃ at a heating rate of 1-5 ℃/min and preserving heat for 1-3 hours;

and finally, heating the precursor B to 1000-1400 ℃ at a heating rate of 1-5 ℃/min, preserving heat for 1-3 hours, and cooling the precursor B to room temperature of 20-25 ℃ along with a furnace.

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