WO2016169149A1

WO2016169149A1 - Recycling method for graphite fine powder to act as lithium ion battery negative electrode material

Info

Publication number: WO2016169149A1
Application number: PCT/CN2015/085813
Authority: WO
Inventors: 鲍海友; 田东; 张贵萍; 谌江宏; 鲍丹
Original assignee: 深圳市斯诺实业发展有限公司
Priority date: 2015-04-24
Filing date: 2015-07-31
Publication date: 2016-10-27
Also published as: CN104779372A

Abstract

Provided is a recycling method for a graphite fine powder to act as a lithium ion battery negative electrode material, said method comprising the following steps: step A: using "tailings" generated during the production of a lithium battery graphite negative electrode material as a raw material, adding a binding agent and a pore-forming agent, performing kneading and granulation at a certain temperature, performing roll-pressing or pressing, and performing carbonisation at a high temperature; step B: crushing, shaping and pelletising the carbonised material, obtaining a spherical or oval graphite powder which satisfies a particle size range requirement, performing high temperature graphitisation, and simultaneously adding the "tailings" collected again in the crushing/pelletising process to step A to act as the raw material and be recycled; step C: performing granularity blending on the pellitised powder, and filling the powder into gaps between particles. The preparation method of the present invention has a safe and controllable process, the recycling of the low value graphite "tailings" is implemented, and the prepared negative electrode material has good performance and exhibits good cycling, rate charge and discharge, and low temperature performance.

Description

Method for recycling graphite fine powder as anode material of lithium ion battery

Technical field

The invention belongs to the field of energy and relates to a method for a negative electrode material, in particular to an ultrafine graphite powder--"tail material" produced in the production process of a graphite anode material as a raw material, which is recycled by treatment and used as lithium. A method of ion battery anode material.

Background technique

With the development of the automotive industry, the depletion of non-renewable fossil fuels such as oil and natural gas has received increasing attention, and air pollution and room temperature effects have become global problems. In order to solve the energy problem and achieve low-carbon environmental protection, based on the current development level of energy technology, electric vehicle technology has gradually become the focus of global economic development. The United States, Japan, Germany, China and other countries have successively restricted the use of fuel vehicles and vigorously developed electric vehicles. As the core component of electric vehicles, the power battery has also ushered in a great development opportunity. Power battery refers to the battery used in electric vehicles, including lithium ion batteries, lead acid batteries, fuel cells, etc. Among them, lithium ion batteries have higher specific energy, higher specific power, less self-discharge, long service life and good safety. Other advantages have become the focus of current development in various countries. The graphite material as the anode material of the lithium ion battery has the advantages of low lithium insertion/deintercalation potential, suitable reversible capacity, abundant resources, and low price, and is an ideal anode material for lithium ion batteries.

As a strategic resource, graphite is not only widely used in general industrial and consumer fields, but also widely used in some special industrial fields. However, the low-end and disorderly development caused by the increasingly expanding market demand has adversely affected China's resource protection and industrial upgrading. In the production process, graphite is required to be pulverized by a pulverizer for a plurality of times, and then spheroidized by a spheroidizing machine. The use of such a process has the disadvantages of low utilization rate of raw materials and poor environment. Since each pulverization and spheroidization needs to be collected after grading, the intermediate semi-finished products are processed for the next time, and each grading will reduce the utilization rate of raw materials. Therefore, the final yield of such a negative electrode material production method is 40% to 50%. The remaining 50% to 60% becomes a “tailing material”. The graphite fine powder “tailing material” has small particle size, high specific surface area and low tap density, and can no longer be used as a negative electrode material for lithium ion batteries. Very low, mainly used in steel metallurgy and other aspects as a recarburizer, which not only increases production costs, but also causes waste of resources.

At the same time, various conventional modification methods for graphite are mainly based on surface carbon coating. By coating a layer of pyrolytic carbon on the surface of the graphite, the effect of the organic solvent and the graphite body can be effectively prevented, thereby preventing lithium. Peeling and pulverization of the graphite layer caused by co-insertion of ions and electrolyte. As the coating material for the surface layer, only the resin-based hard carbon precursor or the asphalt-based soft carbon precursor is used alone.

The main advantage of using resin as the coating material is that the resin has good fluidity at low temperature, not only can coat the surface, but also easily penetrate into the graphite particles through micropores in the graphite to improve the tap density and electrons of the graphite particles. The conductivity is beneficial, and can also be cured by heating, introducing a catalyst or ultraviolet irradiation. The resin will not melt and deform during the pyrolysis process, nor will it cause significant expansion, and the order of the amorphous carbon formed after pyrolysis of the resin is low. The structure is relatively loose, and lithium ions can be relatively freely embedded and extracted therein without a large influence on the structure thereof, so that pulverization is less likely to occur. However, the affinity of the resin material and the graphite is poor, so the carbon material obtained by pyrolysis thereof is not firmly bonded to the graphite, the carbon material obtained by pyrolysis of the resin has a low yield, is brittle, and has a large amount of volatiles during pyrolysis of the resin. The specific surface area is high, the adhesion of the resin is strong, and the coated particles are easily bonded together, and the coating layer is easily broken during the heat treatment, and the resin has too many small molecules in the resin during the heat treatment. During the overflow process, excessive voids are formed on the surface of the coated material, resulting in an excessively large specific surface area of the coated graphite, resulting in an excessively large irreversible capacity for the first time.

These problems affect the cycle efficiency, cycle stability, and compressibility of the graphite electrode of the resin-coated graphite material. When asphalt, petroleum tar, coal tar or a mixture thereof is used to coat graphite, the pitch pyrolysis carbon has a smaller specific surface area than the resin pyrolytic carbon coated graphite, has better affinity with graphite, and has a firmer structure, but the asphalt coating In the heating process, it is deformed by melting. If the amount is too much, the coated graphite particles are easily bonded to each other. If the amount is too small, the coating is not uniform, and the heating process is easy to expand, which affects the electrical properties of the graphite.

Summary of the invention

In order to solve the above technical problems, the present invention provides a method for doping a graphite fine powder as a negative electrode material, comprising the following steps:

Step A: The “tailing material” produced in the production process of the lithium battery anode material is used as a raw material, a binder and a pore-forming agent are added, and kneading and granulation are carried out at a temperature higher than the softening point of the asphalt at 20 to 50° C., and then the roll is performed. Pressing or pressing, carbonizing at a high temperature of 800 to 1000 ° C;

Step B: the carbonized material is pulverized and shaped to obtain spherical or elliptical graphite powder according to the particle size range; high temperature graphitization is performed at 2600 ° C or higher, and the pulverization/spheroidization process can be performed at the same time. The collected "tails" are added to step A as a raw material for recycling;

Step C: Performing particle size distribution on the graphitized powder, adding a certain proportion of graphite anode powder, and filling the gap between the particles by physical mixing to increase the bulk density.

Among them, the graphite powder is continuously vibrated by a tap density measuring instrument, and the bulk density of the powder can be measured. However, since the shape of the powder is close to a spherical shape or an elliptical shape, the contact between the powder particles is point contact or small-area contact, in which any void is left, and at the same time the limitations of the pulverization and spheroidizing equipment, the tap density of the powder is still Hard to improve. By adding a certain amount of fine powder to the powder after the spheroidizing treatment, it is filled into the voids, and the unit bulk density of the entire material can be further increased.

A lithium-ion battery is a rechargeable battery that relies on lithium ions to move between the positive and negative electrodes to work. During charge and discharge, Li+ is intercalated and deintercalated between the two electrodes: when charging the battery, Li+ is deintercalated from the positive electrode, and the electrolyte is embedded in the negative electrode, and the negative electrode is in a lithium-rich state; And the graphite negative electrode material due to good layered structure for embedding a lithium - prolapse interlayer insertion compound of formula LiC _x, and has excellent charge and discharge platform, thus being widely used. While graphite is used as a negative electrode material for lithium ion batteries, the SEI film is formed through the interface reaction between the graphite and the electrolyte during the first charge process, resulting in loss of irreversible capacity. Therefore, the theoretical capacity of the graphite negative electrode material is 372 mAh/g. However, in actual use, its capacity is generally 330-360 mAh/g, which is lower than the theoretical capacity. The irreversible capacity loss caused by SEI film production is directly related to the specific surface area of the graphite anode material. The specific surface area of graphite is large, the range of contact between electrolyte and graphite is large, and the generated SEI is too much, resulting in irreversible capacity loss. . At the same time, since graphite is especially co-embedded with the electrolyte in the electrolyte containing PC, the graphite sheet peels off and a new end face is formed, resulting in further SEI formation, resulting in a continuous decrease in cycle performance. Therefore, the currently widely used graphite coating modification is to coat a modified layer for the specific surface area of graphite to reduce the specific surface area of the material, thereby improving the first discharge efficiency of graphite, increasing its capacity and circulation. Stability performance.

The tailings produced in the production process of graphite anode materials have fine particles (D50 is generally 1-7 μm), high specific surface area (SSA≥10 m2/g), and low tap density (Tap≤0.6 g/cm3), although The structure itself is a graphite layer structure with a certain capacity, but as a negative electrode material, it has the disadvantages of low volume specific energy, low capacity, poor material processing performance, etc. Therefore, the treatment method for tailings in the industry is mainly applied to steel metallurgy. Used as a recarburizer. However, with the continuous promotion and rapid development of electric vehicles, the market demand for graphite anode materials has also shown a rapid growth trend. As the output of anode materials continues to expand, the number of tailings increases, so the tailings are High value-added processing and recycling have a broad Market prospects.

The invention adopts the above technical solutions, and has the advantages that: 1. The tailings produced in the industrial production of graphite anode materials have small particle size and large specific surface area, and the general treatment method in the industry is carried out as a refining agent with low added value. deal with. However, due to its small particle size, the channel resistance between lithium ions entering the graphite layer can be shortened, and the superior rate performance and low temperature performance are exhibited. 2. Adding bitumen and resin as binder, kneading and granulating at a certain temperature, polymerizing small particles of graphite, and then rolling or pressing to make the internal structure further dense, increase its bulk density, and then carbonize at high temperature. The asphalt and the resin form pyrolytic carbon, and the small molecules in the resin are formed into pores inside the material by the heat overflow, and these micropores are favorable for expanding the contact range of graphite and lithium ion deintercalation. 3. Graphitization transforms the interior of the material from the disordered overlap of the two-dimensional space to the orderly overlap of the three-dimensional space, which makes the structural structure of the material tend to be complete, further improving the cycle stability and product consistency of the material. 4. Control the particle size Dmax of the product, the particle size index Dmax of the anode material powder is a very important technical parameter, especially in the application of automotive power battery, this index plays a very important role in the safety performance of the power battery. If there are graphite particles with large particle size in the powder of the material, during the rapid charging process of the power battery, the channel between the lithium ions entering the graphite layer increases, and the embedded current is too large, which causes lithium deposition on the surface, forming dendrites, and thorns. Wearing a diaphragm creates a safety hazard. 5. Through the particle size adjustment in the later stage, the difficulty of further improving the tap density by the mechanical treatment is avoided, and the volumetric energy density is improved.

Preferably, the heating rate in step A is 1 to 10 ° C / min.

Preferably, the raw material has a particle diameter D50 of 1 to 7 μm; a tap density of ≤0.6 g/cm ³ and a specific surface area of ≥10 m 2 /g.

Preferably, the binder in the step A adopts modified asphalt, and the modified asphalt adopts one or more of coal asphalt, petroleum asphalt, mesophase pitch and modified asphalt.

Preferably, the pore forming agent in the step A is one or more of a phenol resin, an epoxy resin, a polyvinyl alcohol, a polyvinyl chloride resin, and a polyamide resin.

Preferably, the weight ratio of graphite: binder: pore former in the step A is 100: 0.1 to 0.4: 0.01 to 0.1. Preferably, in the step C, the particle size ratio is adjusted, and the weight ratio of the carbonized graphite to the added graphite powder is 1:0.05 to 0.2, wherein the added graphite powder has a smaller particle diameter than that obtained in the step B.

In the step B, the average particle diameter D50 obtained after pulverization and spheroidization is 8 to 25 μm, and Dmax ≤ 55.

As a core component of new energy vehicles, power batteries are more common than ordinary lithium used in daily life. Sub-batteries have more stringent standards and requirements for materials such as high rate charge and discharge performance, good high and low temperature performance, long cycle performance, high safety performance and low cost. The tailings are precisely because of their smaller particle size, and the path of lithium ions entering and leaving the graphite layer is reduced, so that it has very excellent rate charge and discharge performance.

The use of tailings as raw materials saves the cost of raw materials. By “granulating” the tailings, adding bitumen as a binder, the tailings particles are polymerized, and the defects such as low bulk density and high specific surface area are changed, and then rolling or Press to further increase its density. As a pore-forming agent, the resin has too many small molecules in the resin during the heat treatment process. Micropores are formed inside the material during the overflow process, and then the pulverization and shaping treatment can be used to obtain suitable particle size and isotropy of the anode material. Powder. The micropores facilitate the absorption and maintenance of the electrolyte, and the isotropic property has the advantage of co-intercalation with the PC electrolyte to ensure the performance of high and low temperature performance. After high-temperature graphitization, the added asphalt and resin are converted from disordered carbon layer structure to ordered structure, while improving the overall purity of the material, reducing its magazine content, ensuring batch consistency, increasing material cycle stability and Security performance.

The preparation method of the invention is safe and controllable, realizes the recycling of waste, and the prepared negative electrode material has good performance and exhibits good electrical properties.

DRAWINGS

1 is a 500-fold scanning electron micrograph of the material prepared in Example 1.

2 is a 1000x scanning electron micrograph of the material prepared in Example 1.

3 is a 2000x scanning electron micrograph of the material prepared in Example 1.

4 is a graph showing the tap density of the material prepared in Example 1.

Fig. 5 is a graph showing the rate discharge performance of a battery prepared by using the anode material of the present invention.

Fig. 6 is a graph showing the cycle retention ratio of a battery prepared by using the negative electrode material of the present invention.

Fig. 7 is a graph showing the high and low temperature discharge capacity retention ratio of a battery prepared by using the anode material of the present invention.

detailed description

The preferred embodiments of the present invention are further described in detail below with reference to the accompanying drawings:

Example 1

100Kg artificial graphite "tailing" (particle diameter D50 = 3.46μm, tap density 0.47g / cm ³ , specific surface area 15.6m2 / g) as raw materials, according to graphite: asphalt: pore forming agent = 100: 0.2: 0.05 Proportion, weigh 0.2Kg of modified coal bitumen (softening point 120 ° C), 0.05Kg of epoxy resin (softening point 80 ° C), put together into the kneading machine with heating device, while mixing, kneading The machine was heated to 140 ° C (20 ° C higher than the asphalt softening point). Mix together for 120 min, then use the kneaded material to inform the tablet press to press and increase the bulk density. The pressed material was raised to 900 ° C at a heating rate of 10 ° C / min under an inert gas atmosphere, and kept for one hour, and then cooled to room temperature.

The high-temperature carbonized material is coarsely crushed and spheroidized to control the particle size Dmax of the material to obtain a powder having a particle diameter D50 of 16.52 μm, a tap density of 0.89 g/cm ³ and a specific surface area of 5.1 m 2 /g. High temperature graphitization (2600 ° C) treatment, further improve the material properties, the internal structure of the material from the disordered carbon to the ideal structure of graphite, tested (particle size D50 is 14.3μm, tap density is 1.04g / cm ^3, specific surface area 2.9 m2/g), finally, artificial graphite (particle diameter D50 of 11.3 μm, tap density of 1.10 g/cm ^{3 ,} specific surface area of 1.6 m 2 /g) was added in a ratio of 1:0.1, and finally, the present example was obtained. The obtained negative electrode material.

The physical property test of Embodiment 1 is shown in Table 1:

Table 1

Example 2

100Kg artificial graphite "tailings" (particle diameter D50 = 2.31μm, tap density 0.37g / cm ³ , specific surface area 18.6m2 / g) as raw materials, by weight graphite: asphalt: pore forming agent = 100: 0.1: 0.1 proportion, weigh 0.1Kg of modified coal bitumen (softening point 150 ° C), 0.1Kg of phenolic resin (softening point 110 ° C), together into the kneading machine with heating device, while mixing, will The kneader was heated to 170 °C. Mix together for 140 min, then use the kneaded material to inform the tablet press to press to increase the bulk density. The pressed material was raised to 950 ° C at a heating rate of 5 ° C / min under an inert gas atmosphere, and kept for one hour, and then cooled to room temperature.

The high-temperature carbonized material is coarsely crushed and spheroidized to control the particle diameter Dmax, and a powder having a particle diameter D50 of 12.71 μm, a tap density of 0.94 g/cm ^{3 and a} specific surface area of 5.8 m 2 /g is obtained. High temperature graphitization (2800 ° C) treatment, further improve the material properties, the internal structure of the material from the disordered carbon to the ideal structure of graphite, tested (particle size D50 is 12.27μm, tap density is 1.02g / cm ^3, specific surface area 3.1m2/g), finally adding artificial graphite (particle diameter D50 of 10.31μm, tap density of 1.10g/cm ^{3 ,} specific surface area: 1.9m2/g) at a ratio of 1:0.05, and finally obtaining the present embodiment. The obtained negative electrode material.

The physical property test of Embodiment 2 is shown in Table 2:

Table 2

Example 3

100Kg artificial graphite "tailings" (particle diameter D50=6.16μm, tap density 0.59g/cm ³ , specific surface area 14.54m2/g) as raw materials, by weight graphite: asphalt: pore former = 100:0.4: 0.1 proportion, weigh 0.4Kg of modified coal pitch (softening point 100 ° C), 0.1Kg of polyamide resin (softening point 80 ° C), together into the kneading machine with heating device, while mixing, The kneader was heated to 130 °C. Mix together for 150 min, then use the kneaded material to inform the tablet press to press and increase the bulk density. The pressed material was raised to 1000 ° C at a heating rate of 10 ° C / min under an inert gas atmosphere, and kept for half an hour, and then cooled to room temperature.

The high-temperature carbonized material is coarsely crushed and spheroidized to control the particle diameter Dmax, and a powder having a particle diameter D50 of 15.92 μm, a tap density of 0.93 g/cm ^{3 and a} specific surface area of 3.2 m 2 /g is obtained. High temperature graphitization (2600 °C) treatment, further improve the material properties, and transform the internal structure of the material from disordered carbon to graphite ideal structure. The particle size D50 is 15.35μm, the tap density is 0.98g/cm ^{3 , and the} specific surface area 2.7 m2/g), and finally artificial graphite (particle diameter D50 of 11.3 μm, tap density of 1.10 g/cm ^{3 ,} specific surface area of 1.6 m 2 /g) was mixed at a ratio of 1:0.09 to finally obtain the present example. The obtained negative electrode material.

The physical property test of Embodiment 3 is shown in Table 3:

table 3

Electrochemical performance test

To test the properties of the negative electrode material prepared by the method of the present invention, the test was carried out by a half-cell test method using the negative electrode materials of the above examples and comparative examples: acetylene black: PVDF (polyvinylidene fluoride) = 93:3:4 (weight ratio) ), adding appropriate amount of NMP (N-methylpyrrolidone) into a slurry, coating on copper foil, drying at 110 ° C for 8 hours to make a negative electrode sheet; using lithium metal sheet as a counter electrode, the electrolyte is 1 mol / L LiPF6/EC+DEC+DMC=1:1:1, the polypropylene microporous membrane is a membrane and assembled into a battery. The charge and discharge voltage is 0-2.0V, and the charge-discharge rate is 0.2C. The battery performance can be tested. The test results are shown in Table 4.

Table 4

In order to detect the rate performance of the negative electrode material of the present invention in the power battery, the production of the 4244130 soft-packed finished battery was used for the detection of the rate charge and discharge.

Using the negative electrode materials of the above examples and comparative examples: SP: SBR (solid content: 50%): CMC = 94: 2.5: 1.5: 2 (weight ratio), adding appropriate amount of deionized water, mixing and evenly slurrying, applied to copper On the foil, vacuum drying at 90 ° C; LiFePO4 powder: SP: KS-6: PVDF = 92: 3.5: 2: 2.5 (weight ratio), mixed with NMP as a solvent, and then applied to aluminum foil. Vacuum drying at 100 ° C; the dried positive and negative pole pieces are subjected to rolling, cutting, winding, injecting, sealing, and forming processes to prepare a lithium iron phosphate powered type 4244130 soft package finished battery ( The nominal capacity is 2.5Ah), the diaphragm is Celgard2400, and the electrolyte is 1M LiPF6/DMC:EC:DEC. The power performance test device is used to detect the rate performance. The test results are shown in Table 3.

table 3

1 to 3, a scanning electron micrograph of the negative electrode material obtained in Example 1 of the present invention can be seen from FIG. 4, and the tap density of the material is as high as 1.28 g/cm 3 , which is known from FIG. 5 and is prepared from the material. Power The high-rate discharge of the battery is 50C/1C, and the capacity retention rate is 89.61%. As can be seen from Fig. 6, the battery 2C charge and discharge 3800 times capacity retention rate is 81.91%. As can be seen from Fig. 7, the high-low temperature performance of the battery, -40 ° C The discharge efficiency can reach 82.3%. It can be seen from the above that the materials prepared by the invention have excellent performance in various aspects, can meet the requirements of various aspects of the power battery of the new energy vehicle, and have broad market prospects.

The above is a further detailed description of the present invention in connection with the specific preferred embodiments, and the specific embodiments of the present invention are not limited to the description. It will be apparent to those skilled in the art that the present invention may be made without departing from the spirit and scope of the invention.

Claims

A method for recycling graphite fine powder as a negative electrode material for a lithium ion battery, comprising the following steps:

Step A: The “tailing material” produced in the production process of the lithium battery anode material is used as a raw material, a binder and a pore-forming agent are added, and kneading and granulation are carried out at a temperature higher than the softening point of the asphalt at 20 to 50° C., and then the roll is performed. Pressing or pressing, carbonizing at a high temperature of 800 to 1000 ° C;

Step B: the carbonized material is pulverized and shaped to obtain spherical or elliptical graphite powder according to the particle size range; high temperature graphitization is performed at 2600 ° C or higher, and the pulverization/spheroidization process can be performed at the same time. The collected "tails" are added to step A as a raw material for recycling;

Step C: Performing particle size distribution on the graphitized powder, adding a certain proportion of graphite anode powder, and filling the gap between the particles by physical mixing to increase the bulk density.
The method according to claim 1, wherein said raw material has a particle diameter D50 of from 1 to 7 μm; a tap density of ≤ 0.6 g/cm 3 and a specific surface area of ≥ 10 m 2 /g.
The method according to claim 1, wherein the powder obtained after the pulverization and the spheroidization in the step B has an average particle diameter D50 of 8 to 25 μm and a Dmax ≤ 55.
The method according to claim 1, wherein the binder in the step A is a modified asphalt, and the modified asphalt is one of coal pitch, petroleum pitch, mesophase pitch, modified pitch or Several.
The method according to claim 1, wherein the pore forming agent in the step A is one or more of a phenol resin, an epoxy resin, a polyvinyl alcohol, a polyvinyl chloride resin, and a polyamide resin.
The method according to claim 1, wherein the weight ratio of the graphite: binder: pore former in the step A is 100: 0.1 to 0.4: 0.01 to 0.1.
The method according to claim 1, wherein in the step C, the weight ratio of the carbonized graphite to the added graphite powder is 1:0.05 to 0.2, wherein the graphite negative electrode powder is added. The diameter is smaller than the powder obtained after pulverization and spheroidization in step B.
The method of claim 1 wherein said step A has a rate of temperature increase of from 1 to 10 ° C/min.