CN105236393B - A kind of spherical porous artificial plumbago negative pole material and preparation method thereof - Google Patents

Abstract

The invention provides a spherical porous artificial graphite negative electrode material. The obtained artificial graphite material is a spherical particle bonded by graphite nanocrystal particles less than 0.5 micron. The spherical particle size is 5-15 micron, and a large amount of porosity. The preparation method of the artificial graphite is to obtain anthracite coal after ball milling, impurity removal, dispersion, coating and high temperature heat treatment. The purity of the artificial graphite material obtained by the present invention is as high as 99.99%, and the 0.5C reversible capacity of the material reaches 390mAh g ^-1 by adjusting the degree of graphitization and introducing coated carbon with a special structure; the porous spherical structure is composed of a large number of graphite nanocrystalline particles, both It has a larger specific surface area, which not only has a larger specific surface area, but also facilitates the penetration of the electrolyte into the interior of the spherical particles. Commercially available.

Description

A kind of spherical porous artificial graphite negative electrode material and preparation method thereof

technical field

The invention relates to a porous spherical artificial graphite negative electrode material for a lithium secondary battery and a preparation method thereof, belonging to the field of electrochemistry.

Background technique

Since Sony applied lithium-ion batteries to the commercial market, lithium-ion batteries have been widely used due to their high specific capacity, high energy density, high operating voltage and long cycle life. The development of lithium-ion batteries largely depends on the development of high-performance positive and negative electrode materials. Searching for anode materials with superior performance can improve the performance of lithium-ion batteries to a certain extent.

At present, commercial lithium-ion battery anode materials mainly use carbon materials, and there are two kinds of natural graphite anodes and artificial graphite anodes. The negative electrode material obtained by natural graphite through spheroidization, purification, coating, and high-temperature sintering has a higher degree of graphitization than artificial graphite negative electrode, and has the advantages of good processing performance and high discharge specific capacity. However, when natural graphite is processed as negative electrode material The utilization rate of graphite is low (<40%), and the negative electrode material has disadvantages such as poor cycle stability, poor high and low temperature performance, poor compatibility with electrolyte, and poor rate performance. The biggest bottleneck in electric vehicles. At present, the anode material of commercial lithium-ion batteries is mainly artificial graphite, which has the advantages of good cycle stability, high particle sphericity, excellent high and low temperature performance, and good safety performance, but it also has low discharge specific capacity and low production cost. advanced defects. Comprehensive consideration, artificial graphite will still be the mainstream application of lithium-ion battery anode materials in the future.

Contents of the invention

The invention provides a method for preparing a spherical porous artificial graphite negative electrode material, using anthracite as a raw material, which greatly reduces the production cost of the material, and at the same time, the microspheres with a porous structure obtained by the method can not only significantly improve the reversible capacity of the material , can also effectively improve its rate performance, this method is simple and easy, and is suitable for industrial production.

The technical solution of the present invention is: a high-quality anthracite selected from a spherical porous artificial graphite negative electrode material, with a carbon content greater than 97%, through ball milling, liquid phase purification, spray granulation (coating), high-temperature sintering and other processes to obtain the described Material, the obtained artificial graphite material is spherical particles bonded by graphite nanocrystal particles less than 0.5 micron, the spherical particle size is 5-15 micron, and a large number of pores are distributed in the spherical particles.

A specific preparation method of porous spherical artificial graphite negative electrode material:

In the first step, the anthracite coal with a carbon content greater than 97% is subjected to mechanical ball milling, and the average particle size of the anthracite particles is controlled within 0.5 microns by adjusting the ball milling parameters to obtain anthracite fine powder;

In the second step, place the ball-milled anthracite fine powder in 2-5mol/L mixed acid (hydrochloric acid/nitric acid mixed in equimolar ratio), heat to 60-80°C, and stir for 3-5 hours to remove metals in anthracite Impurities. After the reaction is finished, it is directly used for spray granulation after filtering and washing until the filtrate is neutral;

The third step is to mix the anthracite purified in the second step with the dispersant, defoamer, adhesive and coating precursor according to a certain ratio, and mix and disperse on the planetary ball mill. The solid content of the slurry is controlled at 30%-50% %between;

In the fourth step, the obtained slurry is atomized, granulated and dried on a spray granulator to obtain anthracite spherical particles with uniform particle size and regular surface (average particle size 5-15 microns);

The fifth step is to place the obtained anthracite spherical particles in a medium-frequency induction graphitization furnace, and carry out high-temperature graphitization (2600-3000°C, 5-8 hours) with nitrogen gas. After the material is cooled and sieved, a spherical porous artificial graphite negative electrode is obtained. Material.

The anthracite accounts for 90-97% (mass ratio) in the artificial graphite negative electrode material, and the binder and coating precursor pyrolytic carbon account for 3-10% (mass ratio).

The above-mentioned dispersant is water or alcohol. If water is used as the dispersant, polyvinyl alcohol (PVA) or sodium carboxymethyl cellulose (CMC) is used as the binder. When alcohol is used as the dispersant, polyvinyl butyral is used. (PVB) as the binder; the defoamer is n-octanol, and the coating precursor is sucrose, glucose or citric acid; the purity of the obtained spherical porous artificial graphite negative electrode material can reach 99.99%.

Compared with the existing graphite negative electrode materials, the porous spherical artificial graphite negative electrode material prepared by the present invention has the following remarkable characteristics:

1. The purity of the material is high. The purity of the porous spherical artificial graphite anode material can be increased to 99.99% through liquid phase purification and high-temperature graphitization. By adjusting the degree of graphitization and introducing coated carbon with a special structure, the reversible capacity of the material at 0.5C can reach 390mAh g ^-1 ;

2. The porous spherical structure is composed of a large number of graphite nanocrystalline particles, which not only has a large specific surface area, but also facilitates the penetration of the electrolyte into the spherical particles. It provides more reaction sites for the electrochemical reaction and shortens the time for lithium ions. The diffusion distance in graphite particles significantly improves the high-rate cycle performance of the material;

3. The preparation process is simple and easy for industrial production;

4. The material preparation cost is low.

5. As a new type of material, the present invention can also be used in the preparation process of other inorganic functional materials that have special requirements on material sphericity (fluidity) and porosity.

Description of drawings

The present invention will be further described below in conjunction with accompanying drawings and examples.

Fig. 1 is the X-ray diffraction spectrum of the porous spherical artificial graphite negative electrode material prepared with anthracite as raw material.

Figure 2 is a scanning electron micrograph of a porous spherical artificial graphite negative electrode material prepared from anthracite.

Fig. 3 is the charging and discharging voltage curve of the battery prepared with the porous spherical artificial graphite negative electrode material.

Figure 4 is a high-rate (0.5C) cycle performance curve of a battery prepared with a porous spherical artificial graphite anode material.

specific implementation plan

Comparative example : the anthracite is mechanically crushed, shaped, and classified to obtain spherical anthracite powder with an average particle size of about 15 microns, and the spherical anthracite is sintered at high temperature (3000°C) in a graphitization furnace (5-8 hours), and after cooling in the furnace Sieve (300 mesh) for use. The resulting material and polyvinylidene fluoride (PVdF) were made into slurry in N-methylpyrrolidone (NMP) medium at a mass ratio of 9:1, coated on copper foil, dried, punched and pressed into the working electrode. The metal lithium foil is used as the counter electrode, the polypropylene film (Celgard 2325) is used as the separator, and 1MLiPF ₆ /(PC+DMC) (1:1) is used as the electrolyte for constant current charge and discharge test (0.5C), and the voltage range is 0- between 1.5V. The first charge (delithiation) capacity is 312.8 mAh g ^-1 , the coulombic efficiency is 92.1%, the charge capacity after 100 cycles is 284.2 mAh g ^-1 , and the capacity retention rate is 90%. The low capacity of the material indicates that the purity of anthracite is difficult to improve only through high-temperature sintering, and the capacity of the uncoated material decays quickly after graphitization.

Example 1 : Add anthracite coal powder obtained by mechanical ball milling into 2-5mol/L mixed acid (hydrochloric acid/nitric acid equimolar ratio), heat to 60-80°C, stir for 3-5 hours, filter and wash until the filtrate is neutral . The filtered anthracite is mixed with water, defoamer, sucrose (5%), polyvinyl alcohol or carboxymethyl cellulose sodium salt (2-5%), and planetary ball mill for 6-8 hours to obtain slurry (solid content 30% ), the slurry is sintered in a graphitization furnace at high temperature (2600°C) for 5-8 hours after spray granulation, and sieved (300 mesh) after cooling with the furnace. The electrode preparation method, battery assembly and test conditions are the same as those of the comparative example. The first charge (lithium removal) capacity is 342.3 mAh g ^-1 , and the coulombic efficiency is 91.4%%. After 100 cycles, the charge (lithium insertion) capacity is 325.4 mAh g ^-1 , and the capacity retention rate is 95%. It shows that after the anthracite is purified by mixed acid, spray granulation and high temperature sintering, the reversible capacity of the obtained material is improved, and the sucrose pyrocarbon coating makes the cycle stability of the material significantly improved.

Example 2 : Add anthracite coal powder obtained by mechanical ball milling into 2-5mol/L mixed acid (hydrochloric acid/nitric acid equimolar ratio), heat to 60-80°C, stir for 3-5 hours, filter and wash until the filtrate is neutral . The filtered anthracite is mixed with water, defoamer, sucrose (8%), polyvinyl alcohol or sodium carboxymethyl cellulose (2-5%), and planetary ball milling for 6-8 hours to obtain a slurry (solid content 40% ), the slurry is sintered in a graphitization furnace at high temperature (2800°C) for 5-8 hours after spray granulation, and sieved (300 mesh) after cooling with the furnace. The electrode preparation method, battery assembly and test conditions are the same as those of the comparative example. The first charge (lithium removal) capacity is 362.6mAh g ^-1 , and the coulombic efficiency is 92.4%. After 100 cycles, the charge (lithium insertion) capacity is 365.8mAh g ^-1 , and the capacity retention rate is 101%. It shows that increasing the content of coated carbon and further increasing the graphitization temperature can improve the reversible capacity of the material, and the unique porous structure makes it experience no capacity fading after 100 cycles.

Example 3 : Add anthracite coal powder obtained by mechanical ball milling into 2-5mol/L mixed acid (hydrochloric acid/nitric acid equimolar ratio), heat to 60-80°C, stir and react for 3-5 hours, filter and wash until the filtrate is neutral . The filtered anthracite is mixed with ethanol, defoamer, citric acid (10%), polyvinyl butyral (2-5%), planetary ball mill for 6-8 hours to obtain a slurry (solid content 45%), and the slurry is passed through After spray granulation, sinter at high temperature (2900°C) for 5-8 hours in a graphitization furnace, and sieve (300 mesh) after cooling with the furnace. The electrode preparation method, battery assembly and test conditions are the same as those of the comparative example. The first charge (lithium removal) capacity is 372.3mAh g ^-1 , the coulombic efficiency is 92.6%%, the charge (lithium insertion) capacity after 100 cycles is 391.2mAh g ^-1 , and the capacity retention rate is 105%. The capacity of the material exceeds the capacity limit of graphite negative electrode (372mAh g ^-1 ), indicating that the coated carbon and suitable graphite layer spacing (regulated by graphitization temperature) provide more active potential for lithium ion intercalation/extraction. The characterization and charge and discharge experiments of the artificial graphite obtained in this experiment are shown in Figures 1-4 of the specification.

It can be seen from Figure 1 that after high-temperature sintering, anthracite undergoes carbonization and graphitization transformation, and the main diffraction peaks in the diffraction pattern are consistent with graphitized carbon.

It can be seen from Figure 2 that the obtained artificial graphite material is bonded into a spherical shape (5-15 microns) by graphite nanocrystalline particles of about 0.5 microns, and a large number of pores are distributed in the spherical particles.

It can be seen from Figure 3 that the discharge (lithium intercalation) process of the porous spherical artificial graphite anode material mainly occurs below 0.2V (except for the first cycle), and the charge (delithiation) process mainly occurs below 0.3V, showing a typical graphite anode voltage curve feature.

It can be seen from Figure 4 that the first delithiation capacity of porous spherical artificial graphite anode material is 372mAh g ^-1 , and the reversible capacity after 100 cycles is maintained at about 390mAh g ^-1 , and there is no obvious capacity fading phenomenon. The increase in capacity shows that graphitized anthracite provides more lithium storage sites for lithium ions, and the porous structure enables the material to perform ion migration quickly under high-rate cycle conditions, avoiding rapid capacity decay caused by excessive internal resistance of the battery.

Example 4 : Add the anthracite coal powder obtained by mechanical ball milling into 2-5mol/L mixed acid (hydrochloric acid/nitric acid equimolar ratio), heat to 60-80°C, stir and react for 3-5 hours, filter and wash until the filtrate is neutral . The filtered anthracite is mixed with water, defoamer, glucose (12%), polyvinyl alcohol or carboxymethyl cellulose sodium salt (2-5%), and planetary ball mill for 6-8 hours to obtain slurry (solid content 50% ), the slurry is sintered in a graphitization furnace at high temperature (3000°C) for 5-8 hours after spray granulation, and sieved (300 mesh) after cooling with the furnace. The electrode preparation method, battery assembly and test conditions are the same as those of the comparative example. The first charge (lithium removal) capacity is 368.7mAh g ^-1 , the coulombic efficiency is 92.8%%, the charge (lithium insertion) capacity after 100 cycles is 376.9mAh g ^-1 , and the capacity retention rate is 102%. It shows that further increasing the coating carbon content and raising the graphitization temperature is not conducive to improving the reversible capacity of the material and improving the cycle stability of the material.

Claims (4)

1. the preparation method of a spherical porous artificial plumbago negative pole material, it is characterized in that, described spherical porous Delanium is the spheroidal particle become by the Nano graphite crystalline substance particles stick less than 0.5 micron, this spheroidal particle particle diameter is 5-15 micron, a large amount of hole is distributed in spheroidal particle, the raw material of this Delanium is that phosphorus content is more than 97% anthracite mine, and the preparation method of this spherical porous artificial plumbago negative pole material is as follows:

The first step, carries out mechanical ball milling process by phosphorus content more than 97% anthracite mine, by regulation ball milling parameter, controls anthracite mean particle size, within 0.5 micron, to obtain anthracite micropowder；

Second step, is placed in the anthracite micropowder after ball milling in the nitration mixture of 2-5mol/L, is heated to 60-80 DEG C, after stirring is reacted 3-5 hour, is neutrality through filtering, washing to filtrate, obtains the anthracite purified；

3rd step, after the anthracite purified by second step mixes with dispersant, defoamer, bonding agent and cladding presoma, carries out mixing dispersion on planetary ball mill, obtains slurry, and wherein, the solid content of slurry controls between 30%-50%；

4th step, carries out the slurry in step 3 on sponging granulator being atomized, pelletize and dried, obtains the anthracite spheroidal particle that even particle size, surface are regular, and the spherical mean particle size of this anthracite is 5-15 micron；

5th step, is placed in gained anthracite spheroidal particle in Medium frequency induction graphitizing furnace, carries out high temperature graphitization 5-8 hour at 2600-3000 DEG C after logical nitrogen, i.e. obtains spherical porous artificial plumbago negative pole material after material cooling, screening.

The preparation method of spherical porous artificial plumbago negative pole material the most according to claim 1, it is characterised in that the nitration mixture in step 2 is the nitration mixture that hydrochloric acid/nitric acid equimolar ratio carries out being mixed to get.

The preparation method of spherical porous artificial plumbago negative pole material the most according to claim 1, it is characterised in that described dispersant is water or ethanol；

If dispersant is water, then bonding agent is PVAC polyvinylalcohol or sanlose CMC；

If dispersant is ethanol, then bonding agent is polyvinyl butyral PVB；

Described defoamer is n-octyl alcohol；

Described cladding presoma is sucrose, glucose or citric acid.

It is 3-10% that the preparation method of spherical porous artificial plumbago negative pole material the most according to claim 1, it is characterised in that the anthracite mass ratio that accounts in artificial plumbago negative pole material is 90-97%, binding agent and cladding presoma pyrolytic carbon account for mass ratio.