CN111732096B

CN111732096B - Negative electrode material of high-power lithium ion battery and preparation method thereof

Info

Publication number: CN111732096B
Application number: CN201910226958.5A
Authority: CN
Inventors: 刘建红; 王兴勤; 王慧; 高亚伦; 高云
Original assignee: CITIC Guoan Mengguli Power Technology Co Ltd
Current assignee: RiseSun MGL New Energy Technology Co Ltd
Priority date: 2019-03-25
Filing date: 2019-03-25
Publication date: 2022-02-22
Anticipated expiration: 2039-03-25
Also published as: CN111732096A

Abstract

The invention provides a high-power lithium ion battery cathode material and a preparation method thereof. The graphite material serving as the negative electrode material ensures the multiplying power performance of the material by screening small-granularity coke raw materials, simultaneously utilizes the self-bonding effect of high-ash coke to be mixed with the small-granularity coke, and is pressed into blocks by a cold isostatic pressing technology, and simultaneously adopts an Acheson furnace type graphitization furnace to directly graphitize, thereby removing a crucible and increasing the charging amount of a single furnace. Compared with the conventional isostatic pressing technology, the method of the invention does not adopt a binder, reduces the problem of larger specific surface area caused by graphitization and volatilization of the binder, and simultaneously mixes and bonds large-particle size and small-particle size, thereby improving the processing performance of the material while ensuring the rate performance.

Description

Negative electrode material of high-power lithium ion battery and preparation method thereof

Technical Field

The invention relates to the field of lithium ion batteries, in particular to a negative electrode material of a high-power lithium ion battery and a preparation method thereof.

Background

With the popularization of lithium ion battery application and the expectation of consumers to lithium ion batteries, the mainstream development directions of the lithium ion batteries are divided into two categories, on one hand, the capacity of the lithium ion batteries is improved, on the other hand, the power performance of the batteries is improved on the basis of ensuring the capacity, namely, the charging time can be shortened, the charging speed performance of the batteries is greatly required, the power performance of the batteries can be improved to become a bright point promotion of various related products, a spot can be seen from the advertisement words of various products, for example, the advertisement words of an oppo mobile phone are 'charging 5 minutes, talking 2 hours', and the advertisement words of Tesla are 'charging 40 minutes, SOC 80%'. Particularly, as a lithium ion battery used on a power automobile, in addition to the requirement of endurance mileage, the charging time is an important assessment index, the charging time of a traditional fuel automobile is only a few minutes, while the charging time of the current power automobile is still more than 2 hours, and a very obvious difference exists between the charging time and the charging time. According to the new energy automobile subsidy policy of 2018, the charging rate is higher than (including) 3C, and the new energy automobile subsidy policy belongs to the fast-charging pure electric passenger vehicles. According to the Chinese data of the batteries, the output of 6486 fast-charging buses in China in 2017 is that the battery loading amount is 597.52MWh and is only 6% of the total amount of new energy buses, so that the difficulty and the urgency degree of improving the battery charging rate performance are shown.

In order to improve the power performance of the lithium ion battery, the research focus on the lithium battery negative electrode material includes the following four aspects: the first is to promote the charge rate performance of the cathode material, the second is to guarantee the cycle performance of the material while promoting the rate performance, the third is to solve the safety problem of lithium precipitation on the surface of the material in the large-current charging process, and the fourth is to reduce the cost of the material to promote the use value thereof. Long Chen et al (Porous graphite nano sheets as a high-rate anode Materials for lithium-ion batteries [ J ]. ACS Applied Materials & Interfaces,2013(5): 9537-. J.S. park et al (Edge-extended graphics for facility of degradation [ J ] ACS Nano,2012(6):10770-10775) modify the end face of graphite, add selective functional groups, can promote the capacity performance at 50C magnification. However, no matter the graphite nanosheet or the end face is modified, the manufacturing process is complex, the requirement on equipment precision is high, and the manufacturing cost is greatly increased. The two methods are only limited to small-scale experiments in laboratory stage, and have no application value in industrial large-scale production.

Disclosure of Invention

Aiming at the defects in the prior art and the targeted requirements in the field, the invention aims to improve the rate capability of the material on the basis of ensuring the specific capacity of the material, improve the processing performance of the material with small granularity, reduce the production cost of the material and expand the application range of the material.

The invention ensures the rate capability of the material by controlling the proportion of the size and the granularity of the raw materials. The processing performance of the material is ensured by controlling the coke class of the low-ash small-particle size material. The cold isostatic pressing treatment is carried out by utilizing the self-adhesiveness of the high-ash coke, so that the addition of extra binder and carbonization treatment are not needed, and the cost of the material is greatly reduced.

In order to achieve the purpose, the invention provides a high-power lithium ion battery cathode material and a preparation method thereof. The scheme of the invention aims to: by adjusting the collocation of two types of coke (petroleum coke, pitch coke, coal coke and the like) with different particle sizes, the multiplying power performance of the material is improved, the ash content of the coke is controlled, the graphitization is carried out by using a cold isostatic pressing technology without a bonding agent while the processing performance is ensured, and the cost of the material is reduced.

The specific scheme is as follows: a preparation method of a high-power lithium ion battery cathode material comprises the following steps:

step 1) two coke raw materials with different ash contents are ground and milled to respectively obtain two coke raw materials with different particle sizes, and the two coke raw materials are physically mixed according to a proportion at normal temperature.

And 2) carrying out cold isostatic pressing treatment on the mixture to obtain a square block-shaped material to be graphitized.

And 3) treating the block materials in a graphitization furnace at a high temperature of more than 2800 ℃ to obtain graphite block raw materials.

And 4) coarsely crushing the blocky graphite raw material, and grinding the blocky graphite raw material into small-granularity graphite through air flow.

And 5) mixing, sieving and demagnetizing the graphite material after the ink powder is applied to obtain the high-power lithium ion battery cathode material.

Wherein the content of the first and second substances,

in the step 1), selecting coke with ash content of 2-10% (Ad%) and grinding the coke into small-granularity coke with granularity of 2-10 mu m.

In the step 1), selecting coke with ash content of 10-20% and grinding the coke into large-particle coke with particle size of 10-30 μm.

The ratio of medium-small particle size coke to large particle size coke in the step 1) is 1: 100-100: 1 (wt%), preferably 30: 70-50: 50 (wt%).

The mixing time of the small-particle coke and the large-particle coke in the step 1) is 0.5 to 5.0 hours, preferably 1.5 to 3.0 hours.

The pressure of the cold isostatic pressing in the step 2) is 150-350MPa, preferably 200-300MPa, and the pressure maintaining time is 10-60min, preferably 25-45 min.

The size of the square block graphite in step 2) is 20 × 20cm to 100 × 100cm, preferably 50 × 50cm to 70 × 70 cm.

The graphitization processing conditions in the step 3) are as follows: slowly raising the temperature to 1000-1200 ℃ at the speed of 2-5 ℃/h, raising the temperature to 2800-3200 ℃ at the speed of 5-10 ℃/h, keeping the temperature for 1-3h, naturally cooling to below 100 ℃, and discharging.

The particle size range of the small-particle graphite obtained by the final jet milling in step 4) is 2 to 25 μm, preferably 5 to 15 μm.

The mesh number of the screen in the screening process in the step 5) is 50-400 meshes, preferably 150-300 meshes. The temperature of the demagnetizing process is controlled at 20-100 deg.C, preferably 50-70 deg.C.

The invention further provides a negative electrode material of the high-power lithium ion battery, which is prepared by the method.

Furthermore, the invention also provides a lithium ion battery which comprises the anode material.

The method comprises the steps of firstly screening and controlling ash content and particle size of raw coke, realizing the mutual matching of different properties of the same raw material, carbonizing the raw coke in the raw material pretreatment to obtain required raw materials with different gray ranges, and then grinding the raw coke with different gray levels to reach the required particle size, thereby obtaining the raw coke with the required characteristics (small particle size coke for ensuring processability and large particle size coke for ensuring adhesion); the specific surface area of the material is reduced by controlling the ash content of coke, and the processability of the material is improved; the effective raw materials are used for replacing an auxiliary agent (the conventional isostatic pressing technology needs a binder to maintain the state of a material block), the cost is reduced, and the proportion of effective components is improved.

Meanwhile, the raw coke is pressed by the cold isostatic pressing treatment and the mould, and the space occupied by the crucible is removed by directly graphitizing by adopting the Acheson furnace type graphitizing furnace, so that the furnace charging amount of the graphitizing treatment is greatly improved by the interaction of the two, the output is greatly improved under the condition of the same energy consumption, and the production cost of the material is further reduced.

In conclusion, the high-power graphite cathode material prepared by the method of the invention has the advantages of improving the processing performance of the material and reducing the cost while ensuring the rate performance.

Drawings

FIG. 1 is SEM images of example 1 (FIG. 1/b) and reference example 2 (FIG. 1/a) of the present invention.

FIG. 2 is a specific capacity curve of the materials of example 1 and reference 2 of the present invention.

Detailed Description

The technical solution of the present invention is further described and illustrated by the following specific examples, but the present invention is not limited to the following examples.

Reference example 1

1) The coke having ash content of 10% was crushed and ground to obtain a coke having a small particle size of 12.0 μm.

2) Loading into a crucible, and carrying out high-temperature graphitization in an Acheson furnace type, wherein the maximum temperature is 2800 ℃: slowly heating to 1200 ℃ at the speed of 5 ℃/h, then heating to 2800 ℃ at the speed of 10 ℃/h, keeping the temperature for 1.5h, naturally cooling to below 100 ℃, and discharging.

3) And mixing, sieving and demagnetizing the graphitized material to obtain the conventional artificial graphite.

Reference example 2

1) Crushing and grinding coke with ash content of 8% to obtain small-granularity coke with granularity of 6 mu m; the coke having an ash content of 15% was crushed and ground to obtain large-particle-size coke having a particle size of 15 μm.

2) 400kg of small-particle coke is mixed with 600kg of large-particle coke.

3) Directly carrying out high-temperature graphitization in an Acheson furnace type, wherein the maximum temperature is 2800 ℃: slowly heating to 1200 ℃ at the speed of 5 ℃/h, then heating to 2800 ℃ at the speed of 10 ℃/h, keeping the temperature for 1.5h, naturally cooling to below 100 ℃, and discharging.

4) And mixing, sieving and demagnetizing the graphitized material to obtain the high-power artificial graphite.

Reference example 3

1) 2.5g of glucose, 1.68g of Fe (NO)₃)₃ 9H₂Dissolving O and 24.11g of NaCl in 75mL of deionized water to obtain a mixed liquid;

2) carbonizing the mixed liquid at 700 ℃, and carrying out heat treatment for 2 hours under Ar gas to obtain carbonized powder;

3) dissolving the black powder in 100mL of concentrated hydrochloric acid (12mol/L), and magnetically stirring for 3 hours at 80 ℃ to obtain the two-dimensional porous graphite nanosheet material.

Reference example 4

1) 10g of natural crystalline flake graphite having a particle size of 20 μm, 40g of 4-fluorobenzoic acid, and 200g of P₂O₅And 100g of H₃PO₄Mixing to obtain a mixture;

2) heating the mixture in nitrogen atmosphere, keeping the temperature at 100 ℃ for 3 hours, and keeping the temperature at 130 ℃ for 72 hours to obtain carbide;

3) washing the carbide with distilled water for many times, dissolving in methanol solution, and freeze-drying to obtain the graphite modified material.

Example 1

2) 400kg of small-particle coke and 600kg of large-particle coke are mixed for 1.5 hours.

3) The mixed coke is molded into 50 x 50cm square graphite block by cold isostatic pressing (300Mpa for 25 min).

4) Directly graphitizing the block material in an Acheson furnace at the highest temperature of 2800 ℃: slowly heating to 1200 ℃ at the speed of 5 ℃/h, then heating to 2800 ℃ at the speed of 10 ℃/h, keeping the temperature for 1.5h, naturally cooling to below 100 ℃, and discharging.

5) The blocky graphite raw material is coarsely crushed and then is crushed into small-granularity artificial graphite with the granularity of 10 mu m (median particle size) by air jet milling.

6) And mixing, sieving and demagnetizing the milled materials to obtain the high-power artificial graphite.

Example 2

2) 500kg of small-particle coke is mixed with 500kg of large-particle coke for about 2 hours.

3) And preparing the mixed coke into a square blocky graphite raw material with the thickness of 50 x 50cm by adopting a cold isostatic pressing technology (200Mpa, keeping for 45 min).

5) The massive graphite raw material is coarsely crushed and then is milled into artificial graphite with small granularity of 10 mu m by airflow.

Example 3

1) The coke having an ash content of 6% was crushed and ground to obtain a coke having a small particle size of 6 μm. The coke having an ash content of 15% was crushed and ground to obtain a coke having a small particle size of 15 μm.

2) 400kg of small-particle coke and 600kg of large-particle coke are mixed for 3 hours.

3) And preparing the mixed coke into a square blocky graphite raw material with the thickness of 50 x 50cm by adopting a cold isostatic pressing technology (280Mpa, keeping for 30 min).

4) Directly graphitizing the block material in an Acheson furnace at the highest temperature of 2800 ℃: slowly heating to 1200 ℃ at the speed of 5 ℃/h, heating to 3000 ℃ at the speed of 10 ℃/h, keeping the temperature for 1h, naturally cooling to below 100 ℃, and discharging.

The following is a comparison of the properties of the product in the preparation and comparison of the properties of the product in the above examples.

First, there were differences in energy consumption per unit yield of the above 5 examples of the same material (reference examples 1-2 and examples 1-3) as shown in Table 1. As can be seen from table 1, by increasing the amount of the graphitization charge, the cost of the graphitization process can be effectively reduced.

TABLE 1 cost ratio differences for the processes of reference examples 1-2 and examples 1-3

Next, the materials obtained in the above examples were combined into a battery, and a performance test was performed. The results are shown in Table 2.

The experimental method comprises the following steps: the discharge capacity and charge rate were tested by assembling a button cell model CR2032 (lithium plate for the counter electrode). The method comprises the following specific steps:

a) the formula of the battery negative plate is as follows: binder (PVDF) ═ 95: 5, the compaction density of the negative plate is 1.4 g/cc;

b) the electrolyte is EC: DEC: EMC 1: 1: 1 of 1mol/L LiPF₆A solution;

c) the discharge capacity test conditions were 0.1C charged, 0.05C discharged, and the first week discharge capacity was recorded.

d) The charging multiplying power test conditions are that charging is carried out under the condition of 0.1C and discharging is carried out under the condition of 0.05C, the test is carried out for three weeks, and charging is carried out under the condition of 6C and discharging is carried out under the condition of 1C in the fourth week. In the fifth week, the cells were charged under 8C condition and discharged under 1C condition. In the sixth week, the cells were charged at 10C and discharged at 1C. In the seventh week, the cells were charged under 12C condition and discharged at 1C.

TABLE 2 comparison of test results of reference examples and examples

Table 2 reflects both the capacity and charge rate properties of the materials. Among them, the main factor affecting the charging rate performance of the lithium non-precipitating is the particle size of the raw coke (the smaller the particle size of the raw coke, the better the rate). The charging rate of the non-lithium-separation battery in reference example 1 is only 8C, that is, the battery can be charged by 8C at the maximum, lithium separation occurs when the charging rate exceeds 8C, and irreversible loss of battery capacity and potential safety hazard are caused; in the embodiment of the invention, the charging rate of the lithium-precipitating-free lithium is effectively improved by mixing the raw materials with two particle sizes.

Meanwhile, as can be seen from fig. 1 of the present invention, by comparing the electron microscopes of example 1 (fig. 1/b) with reference example 2 (fig. 1/a), it can be observed that the morphology of particle bonding is manufactured by adjusting the proportions of different ash coke types in example 1, and the rate capability of the original coke type with small particle size is ensured while the processability of the material is improved by increasing the particle size of the material.

The embodiments described above were chosen and described in order to best explain the principles of the invention, but are not intended to be exhaustive or to limit the invention to the precise forms disclosed, and many modifications and variations are possible to those skilled in the art to best utilize the invention, the scope of which is defined by the appended claims.

Claims

1. A preparation method of a negative electrode material of a high-power lithium ion battery is characterized by comprising the following steps:

(1) weighing and mixing small-particle coke and large-particle coke in proportion; wherein the mass ratio of the small-particle coke to the large-particle coke is 30: 70-50: 50; the ash content of the small-granularity coke is 2-10% and the granularity is 2-10 mu m; ash content of the large-granularity coke is 10-20% and granularity is 10-30 μm;

(2) carrying out cold isostatic pressing treatment on the mixture obtained in the step (1) to obtain a blocky material; wherein the pressure of the cold isostatic pressing is 150-350MPa, and the pressure maintaining time is 10-60 min;

(3) graphitizing the block-shaped material obtained in the step (2) to obtain block-shaped graphite;

(4) coarsely crushing the blocky graphite obtained in the step (3), and then crushing the blocky graphite into small-granularity graphite by airflow; wherein the small particle size graphite has a particle size in the range of 2-25 μm;

(5) and (4) mixing, sieving and demagnetizing the small-granularity graphite obtained in the step (4) to obtain the negative electrode material.

2. The method of claim 1, wherein the mixing time in step (1) is 0.5 to 5.0 hours.

3. The method of claim 1, wherein the mixing time in step (1) is 1.5 to 3.0 hours.

4. The method according to any one of claims 1 to 3, wherein the cold isostatic pressing in step (2) has a pressure of 200MPa and 300MPa and a dwell time of 25-45 min.

5. The method of any one of claims 1 to 3, wherein the size of the cake material in step (2) is from 20 x 20cm to 100 x 100 cm.

6. The method of any one of claims 1 to 3, wherein the size of the cake material in step (2) is from 50 x 50cm to 70 x 70 cm.

7. The method according to any one of claims 1 to 3, wherein the conditions for the graphitization treatment in step (3) are: slowly raising the temperature to 1000-1200 ℃ at the speed of 2-5 ℃/h, raising the temperature to 2800-3200 ℃ at the speed of 5-10 ℃/h, keeping the temperature for 1-3h, and then naturally lowering the temperature to below 100 ℃.

8. The method according to any one of claims 1 to 3, wherein the small particle size graphite in step (4) has a particle size in the range of 2 to 25 μm.

9. The method according to any one of claims 1 to 3, wherein the small particle size graphite in step (4) has a particle size in the range of 5 to 15 μm.

10. A negative electrode material for high power lithium ion batteries, characterized in that it is obtained according to the method of any one of claims 1 to 9.

11. A lithium ion battery, characterized in that the battery comprises the negative electrode material according to claim 10.