CN112531161B

CN112531161B - Pre-lithium negative electrode material, preparation method thereof, pre-lithium negative electrode and pre-lithium battery

Info

Publication number: CN112531161B
Application number: CN202011380909.6A
Authority: CN
Inventors: 朱金鑫; 刘浩; 娄帅宾
Original assignee: Svolt Energy Technology Co Ltd
Current assignee: Svolt Energy Technology Co Ltd
Priority date: 2020-11-30
Filing date: 2020-11-30
Publication date: 2022-04-29
Anticipated expiration: 2040-11-30
Also published as: CN112531161A

Abstract

The invention discloses a pre-lithium negative electrode material, a preparation method thereof, a pre-lithium negative electrode and a pre-lithium battery. The method comprises the following steps: 1) dispersing a negative electrode active material and metal lithium in an organic solvent to obtain a mixed solution; 2) and carrying out hydrothermal reaction on the mixed solution to obtain the pre-lithium negative electrode material. According to the invention, metal lithium is fully and uniformly embedded into the structure of the negative active material such as graphite material and the like by utilizing hydrothermal high-temperature high-pressure environment, the pre-lithium effect is good, and the pre-lithium negative material is used as the negative active material and applied to the lithium ion battery, so that the consumption of active lithium ions of the anode can be effectively reduced, and the electrochemical performance of the negative electrode, especially the first coulombic efficiency, is improved.

Description

Pre-lithium negative electrode material, preparation method thereof, pre-lithium negative electrode and pre-lithium battery

Technical Field

The invention relates to the technical field of new energy, and relates to a pre-lithium negative electrode material, a preparation method thereof, a pre-lithium negative electrode and a pre-lithium battery.

Background

The conventional lithium ion battery has the problem of loss of active lithium ions in the charge-discharge cycle process. The rate of lithium ion loss varies from battery system to battery system, for example, the rate of active lithium ion loss is faster for high nickel ternary positive electrode material/silicon oxygen negative electrode material system. In terms of mechanism, the loss of active lithium ions may be caused by structural attenuation of positive and negative active materials, interface side reactions and the like. The consequence of active lithium ion loss is reduced battery capacity and shortened cycle life.

In order to solve the above problems, the current technical means include improving the structural stability of the active species (for example, adding a stable and dense coating layer on the surface of the active material), optimizing the electrolyte formula to improve the electrochemical stability, and pre-lithium technology (including positive electrode pre-lithium or negative electrode pre-lithium). The pre-lithium technique is a direct and efficient method.

For positive pre-lithium, the main academic research is that a second positive active material, such as transition metal and lithium oxide composite material [ Sun, Y., Lee, H., Seh, Z.et. high-capacity cathode modification to offset initial lithium loss. Nat Energy 1,15008 (https:// doi. org/10.1038/nenergy.2015.8], is added during the homogenization of the positive electrode, which generally reduces the content of the first positive active material, possibly resulting in a reduction in Energy density.

For the lithium pre-preparation of the negative electrode, the mainstream technical route in the industry is lithium powder pre-preparation and lithium belt pre-preparation, for example, CN109148827A discloses a pre-lithiation method of a lithium battery electrode, which comprises the steps of heating a battery pole piece and metal lithium, and rubbing the metal lithium on the surface of the battery pole piece under the action of external force to complete the pre-lithiation of the lithium battery electrode. However, both methods need to strictly ensure the temperature and humidity of a production workshop and avoid safety accidents such as fire and even explosion caused by the contact of metal lithium with moisture. Because an additional electrode production process is required, for example, after the cathode plate is homogenized and coated, a lithium tape is firstly attached to the cathode plate or lithium powder is scattered, then rolling, die cutting, winding/laminating and liquid injection packaging are carried out, and finally battery assembly is completed. In this process, the longer the metallic lithium is exposed to the air, the more serious the metallic lithium is deteriorated (may be deteriorated by reaction with nitrogen, oxygen, or the like), resulting in a great reduction in the pre-lithiation effect.

Disclosure of Invention

In view of the above problems in the prior art, an object of the present invention is to provide a pre-lithium anode material, a preparation method thereof, a pre-lithium anode and a pre-lithium battery.

In order to achieve the purpose, the invention adopts the following technical scheme:

in a first aspect, the present invention provides a method of preparing a pre-lithium anode material, the method comprising the steps of:

(1) dispersing a negative electrode active material and metal lithium in an organic solvent to obtain a mixed solution;

(2) and (2) carrying out hydrothermal reaction on the mixed solution obtained in the step (1) to obtain a pre-lithium negative electrode material.

According to the invention, the pre-lithium negative electrode material is prepared by a novel preparation method, metal lithium is fully and uniformly embedded into the structure of negative active materials such as graphite materials and the like by utilizing a hydrothermal high-temperature high-pressure environment, the pre-lithium effect is good, and the pre-lithium negative electrode material is used as the negative active material and applied to a lithium ion battery, so that the consumption of active lithium ions of a positive electrode can be effectively reduced, the electrochemical performance of the negative electrode is improved, and especially the first coulombic efficiency is improved.

The method is controllable, safe and high in efficiency, is a pre-lithiation technology with a very promising prospect, and is applied to the negative electrode and the lithium ion battery, and during the subsequent electrode production process, homogenization, coating, rolling, cutting and the like can be carried out in a conventional production line without additional working procedures, and the temperature and the dew point environment can also be carried out under the conventional control conditions, so that the production cost is saved, the safety risk is reduced, and the industrial amplification production is easy to realize.

The following is a preferred technical solution of the present invention, but not a limitation to the technical solution provided by the present invention, and the technical objects and advantageous effects of the present invention can be better achieved and achieved by the following preferred technical solution.

Preferably, the negative active material in step (1) includes at least one of graphite, a silicon-oxygen material, a silicon-carbon material and nano-silicon, and is preferably graphite.

The graphite of the present invention is not limited in kind, and may be, for example, natural graphite or artificial graphite.

Preferably, the negative electrode active material of step (1) has a particle size of 0.2 to 20 μm, for example, 0.2, 0.5, 1, 3, 5, 8, 10, 12.5, 15, 16, 18, or 20 μm.

Preferably, the lithium metal of step (1) is selected from at least one of lithium powder and lithium ribbon.

Preferably, the mass ratio of the negative electrode active material and the metal lithium in the step (1) is 100 (0.1 to 5), for example, 100:0.1, 100:0.2, 100:0.3, 100:0.5, 100:0.7, 100:0.8, 100:1, 100:1.2, 100:1.5, 100:2, 100:2.3, 100:2.5, 100:2.8, 100:3, 100:3.3, 100:3.6, 100:4, 100:4.5, 100:5, or the like. If the content of the metal lithium is too low, the pre-lithium effect is not obvious; if the content of the metallic lithium is too large, side reactions may be caused in the subsequent application of the battery, and more preferably 100 (0.2-1).

By controlling the quality of the negative active material and the metal lithium, a series of graphite materials with different pre-lithium amounts can be obtained, and the use requirements of the subsequent lithium ion battery on different pre-lithium amounts are met.

Preferably, the organic solvent of step (1) includes at least one of n-hexane, ethylene carbonate, diethyl carbonate and ethyl methyl carbonate. However, the organic solvent is not limited to the above-mentioned organic solvents, and other organic solvents commonly used in the art to achieve the same effect may be used in the present invention.

As a preferred embodiment of the method of the present invention, the temperature of the hydrothermal reaction in step (2) is 150 to 300 ℃, for example, 150 ℃, 170 ℃, 182 ℃, 188 ℃, 190 ℃, 195 ℃, 200 ℃, 210 ℃, 215 ℃, 220 ℃, 230 ℃, 240 ℃, 250 ℃, 260 ℃, 265 ℃, 280 ℃ or 300 ℃, preferably 190 to 230 ℃.

Preferably, the temperature of the hydrothermal reaction in step (2) is higher than the melting point of lithium. This preferred embodiment is designed to facilitate melting of lithium and to facilitate better insertion of lithium into the negative electrode active material such as graphite.

Preferably, the holding time of the hydrothermal reaction in the step (2) is 2h to 70h, such as 2h, 4h, 6h, 8h, 12h, 15h, 18h, 20h, 22h, 24h, 27h, 30h, 33h, 36h, 40h, 45h, 50h, 55h, 57h, 60h, 65h or 70h, etc., preferably 40h to 60 h.

Preferably, vibration treatment is carried out during the hydrothermal reaction in the step (2).

Preferably, the vibration frequency of the vibration treatment in the three-dimensional direction is 0.03Hz to 0.1Hz, such as 0.03Hz, 0.05Hz, 0.06Hz, 0.08Hz, or 0.1Hz, and the like.

The hydrothermal treatment is carried out under a vibration condition, and is advantageous in that metallic lithium is uniformly incorporated into a negative electrode active material such as graphite.

Preferably, the hydrothermal reaction in step (2) is carried out under the protection of inert gas. For example, the autoclave may be purged with argon to ensure a strict inert atmosphere.

Preferably, the temperature is reduced after the hydrothermal reaction in the step (2) is finished.

Preferably, the organic solvent is recovered after the hydrothermal reaction in step (2).

As a further preferred technical solution of the method of the present invention, the method comprises the steps of:

s1: weighing a certain mass of graphite cathode material and a lithium belt in a glove box;

s2: pouring a certain volume of n-hexane liquid into the reaction kettle, and filling argon for inert atmosphere protection; the volume of the n-hexane liquid accounts for 45-90% of the volume of the reaction kettle (for example, 45%, 50%, 55%, 60%, 65%, 70%, 75%, 80%, 90% or the like);

s3: putting the graphite cathode material and the lithium strip in the S1 into a reaction kettle in the S2, wherein the mass ratio of the graphite cathode material to the lithium strip is 100 (0.02-0.1), and screwing the reaction kettle tightly;

s4: placing the reaction kettle in a three-dimensional oscillation oven, and setting the vibration frequency in the three-dimensional direction;

s5: vibrating for a certain time, heating the oven to the temperature of 150-300 ℃ for hydrothermal reaction, and then keeping the same vibration frequency for 2-70 h at constant temperature;

s6: after the reaction kettle is cooled, recovering and recycling the normal hexane in the kettle;

s7: and finally, taking out the powder material in the kettle to obtain the pre-lithiated graphite cathode material.

In a second aspect, the present invention provides a pre-lithium anode material prepared by the method of the first aspect, wherein the pre-lithium anode material comprises an anode active material and lithium embedded in the anode active material.

In the present invention, the chemical formula of the pre-lithium anode material can be expressed as

Structurally, the lithium atoms are located inside the negative electrode active material (e.g., graphite material), that is, the negative electrode active material is in a lithium intercalation state.

In a third aspect, the present invention provides a pre-lithium anode, characterized in that the pre-lithium anode comprises the pre-lithium anode material of the second aspect.

In a fourth aspect, the present invention provides a pre-lithium battery comprising a pre-lithium negative electrode according to the third aspect.

Compared with the prior art, the invention has the following beneficial effects:

(1) according to the invention, the pre-lithium negative electrode material is prepared by a novel preparation method, metal lithium is fully and uniformly embedded into the structure of negative active materials such as graphite materials and the like by utilizing a hydrothermal high-temperature high-pressure environment, the pre-lithium effect is good, and the pre-lithium negative electrode material is used as the negative active material and applied to a lithium ion battery, so that the consumption of active lithium ions of a positive electrode can be effectively reduced, the electrochemical performance of the negative electrode is improved, and especially the first coulombic efficiency is improved.

(2) The method is controllable, safe and high in efficiency, is a pre-lithiation technology with a very promising prospect, and is applied to the negative electrode and the lithium ion battery, and during the subsequent electrode production process, homogenization, coating, rolling, cutting and the like can be carried out in a conventional production line without additional working procedures, and the temperature and the dew point environment can also be carried out under the conventional control conditions, so that the production cost is saved, the safety risk is reduced, and the industrial amplification production is easy to realize.

Detailed Description

The technical solution of the present invention is further explained by the following embodiments.

Example 1

The embodiment provides a pre-lithium negative electrode material and a preparation method thereof, and the preparation method specifically comprises the following steps:

10g of graphite powder was weighed in a glove box together with 0.0237g of lithium tape. 100mL of n-hexane was poured into a reaction vessel (having a volume of 200mL), and then an inert atmosphere protection was performed by introducing argon gas into the reaction vessel. Adding weighed graphite powder and a lithium belt into a reaction kettle, screwing to ensure that no air enters the reaction kettle which is well sealed, then placing the reaction kettle into a three-dimensional vibration oven, setting the vibration frequency of the oven in the three-dimensional direction to be 0.05Hz, subsequently heating to 190 ℃, and keeping the constant temperature for 48 hours. And after the constant temperature is finished, reducing the temperature to 60 ℃, recovering the normal hexane in the reaction kettle, and finally taking out the powder material in the kettle.

Example 2

10g of graphite powder was weighed in a glove box with 0.0594g of lithium tape. 100mL of n-hexane was poured into a reaction vessel (having a volume of 200mL), and then an inert atmosphere protection was performed by introducing argon gas into the reaction vessel. Adding weighed graphite powder and a lithium belt into a reaction kettle, screwing to ensure that no air enters the reaction kettle which is well sealed, then placing the reaction kettle into a three-dimensional vibration oven, setting the vibration frequency of the oven in the three-dimensional direction to be 0.05Hz, subsequently heating to 200 ℃, and keeping the constant temperature for 50 h. And after the constant temperature is finished, reducing the temperature to 60 ℃, recovering the normal hexane in the reaction kettle, and finally taking out the powder material in the kettle.

Example 3

10g of graphite powder was weighed in a glove box together with 0.0878g of lithium tape. 100mL of n-hexane was poured into a reaction vessel (having a volume of 200mL), and then an inert atmosphere protection was performed by introducing argon gas into the reaction vessel. Adding weighed graphite powder and a lithium belt into a reaction kettle, screwing to ensure that no air enters the reaction kettle which is well sealed, then placing the reaction kettle into a three-dimensional vibration oven, setting the vibration frequency of the oven in the three-dimensional direction to be 0.05Hz, subsequently heating to 200 ℃, and keeping the constant temperature for 55 h. And after the constant temperature is finished, reducing the temperature to 60 ℃, recovering the normal hexane in the reaction kettle, and finally taking out the powder material in the kettle.

Example 4

10g of graphite powder and 0.0620g of lithium powder were weighed in a glove box. 100mL of n-hexane was poured into a reaction vessel (having a volume of 200mL), and then an inert atmosphere protection was performed by introducing argon gas into the reaction vessel. Adding the weighed graphite powder and the lithium belt into a reaction kettle, screwing to ensure that no air enters the reaction kettle which is well sealed, then placing the reaction kettle into a three-dimensional vibration oven, setting the vibration frequency of the oven in the three-dimensional direction to be 0.07Hz, subsequently heating to 225 ℃, and keeping the constant temperature for 42 hours. And after the constant temperature is finished, reducing the temperature to 60 ℃, recovering the normal hexane in the reaction kettle, and finally taking out the powder material in the kettle.

Example 5

The difference from example 3 is that the mass of the lithium ribbon was 0.3172g, and the other preparation methods and conditions were the same as in example 1.

Example 6

The difference from example 3 is that the mass of the lithium ribbon is 0.0135g, and other preparation methods and conditions are the same as example 1.

Example 7

The difference from example 3 is that the temperature of the reaction vessel was raised to 150 ℃ and the other preparation methods and conditions were the same as in example 1.

Example 8

The difference from example 3 is that the temperature of the reaction vessel was raised to 300 ℃ and the other preparation methods and conditions were the same as in example 1.

Comparative example 1

This comparative example is a graphite powder without prelithiation treatment.

Comparative example 2

The comparative example provides a pre-lithium negative electrode material and a preparation method thereof, and the preparation method specifically comprises the following steps:

(1) dispersing 0.0237g of a lithium belt into 50mL of polyaniline to obtain a lithium simple substance solution;

(2) dispersing 10g of graphite powder into 50 mLN-methyl pyrrolidone to obtain a negative electrode material dispersion liquid;

(3) and dropwise adding the lithium simple substance solution into the negative electrode material dispersion liquid, and performing vacuum drying to obtain the pre-lithiated negative electrode material.

And (3) testing:

the powder materials prepared in examples 1 to 8 and the pure graphite powder in comparative examples 1 to 2 were respectively used as negative electrode active materials and homogenized, wherein the content of the negative electrode active material was 96%, the content of the conductive agent super-p was 1%, the content of the binder CMC was 1.3%, and the content of the binder SBR was 1.7%. Coating and baking the obtained slurry to obtain the single-sided surface density of 8.0mg/cm²Followed by rolling to obtain a compacted density of 1.55g/cm³The electrode sheet of (1). The four electrode pole pieces are respectively assembled with button batteries and test battery headsThe specific charge-discharge capacity and the first coulombic efficiency, and the test results are shown in table 1.

TABLE 1 specific first-Charge capacity, specific first-discharge capacity, and first-coulombic efficiency of each graphite material in examples and comparative examples

	Specific capacity of first charge mAh/g	Specific capacity of first discharge mAh/g	First coulombic efficiency%
				Example 1	373.3	352.8	94.5
Example 2	361.9	352.5	97.4
				Example 3	353.5	353.1	99.9
Example 4	372.1	353.0	94.8
				Example 5	368.7	351.4	95.3
Example 6	378.2	352.0	93.1
				Example 7	379.4	351.3	92.6
Example 8	378.9	351.6	92.8
				Comparative example 1	380.2	352.1	92.6
Comparative example 2	380.0	351.7	92.5

And (3) analysis:

as shown in table 1, comparative example 1 was the original graphite powder (not subjected to pre-lithiation treatment), the first charge and discharge specific capacities were 380.2 and 352.1mAh/g, respectively, and the first coulombic efficiency was 92.6%. After the graphite powder is subjected to pre-lithiation treatment by the preparation method, the first coulombic efficiency of the graphite is improved to different degrees. The first coulombic efficiency of the prelithiated graphite in example 3 increased to 99.9%. This indicates that the prelithiation treatment can reduce the amount of active lithium ion consumption from the positive electrode, and it is believed that this part of lithium ion consumption mainly participates in the formation of the SEI film on the surface of the negative electrode.

By comparing example 3 with examples 5-6, it can be seen that a range of different pre-lithiated amounts of graphitic material can be obtained by adjusting the mass of graphite and lithium ribbon. If the using amount of the lithium belt is too small, the pre-lithium effect is not obvious; if the amount of the lithium ribbon used is too large, side reactions may be caused, which may result in a decrease in electrochemical performance.

It can be seen from the comparison between example 3 and examples 7-8 that the electrochemical performance is not improved by too high or too low hydrothermal temperature, and in example 7, the hydrothermal reaction temperature is lower than the melting point of lithium (the melting point of lithium is 180 ℃), and the amount of lithium intercalation is less, resulting in a decrease in electrochemical performance.

Compared with the comparative example 2, the method disclosed by the invention can better improve the pre-lithium effect of the material, and further improve the electrochemical performance.

The applicant states that the present invention is illustrated in detail by the above examples, but the present invention is not limited to the above detailed methods, i.e. it is not meant that the present invention must rely on the above detailed methods for its implementation. It should be understood by those skilled in the art that any modification of the present invention, equivalent substitutions of the raw materials of the product of the present invention, addition of auxiliary components, selection of specific modes, etc., are within the scope and disclosure of the present invention.

Claims

1. A method of preparing a pre-lithium anode material, the method comprising the steps of:

2. The method of claim 1, wherein the negative active material of step (1) comprises at least one of graphite, a silicon oxygen material, a silicon carbon material, and nano-silicon.

3. The method according to claim 2, wherein the negative active material of step (1) is graphite.

4. The method according to claim 1, wherein the particle size of the negative electrode active material in the step (1) is 0.2 to 20 μm.

5. The method of claim 1, wherein the lithium metal of step (1) is selected from at least one of lithium powder and lithium ribbon.

6. The method according to claim 1, wherein the mass ratio of the negative electrode active material to the metallic lithium in the step (1) is 100 (0.1-5).

7. The method according to claim 6, wherein the mass ratio of the negative electrode active material to the metallic lithium in the step (1) is 100 (0.2-1).

8. The method of claim 1, wherein the organic solvent of step (1) comprises at least one of n-hexane, ethylene carbonate, diethyl carbonate, and ethyl methyl carbonate.

9. The method according to claim 1, wherein the temperature of the hydrothermal reaction in the step (2) is 150 ℃ to 300 ℃.

10. The method according to claim 9, wherein the temperature of the hydrothermal reaction in the step (2) is 190 ℃ to 230 ℃.

11. The method of claim 1, wherein the hydrothermal reaction of step (2) is at a temperature above the melting point of lithium.

12. The method according to claim 1, wherein the hydrothermal reaction in the step (2) is carried out for 2-70 h.

13. The method according to claim 12, wherein the hydrothermal reaction in the step (2) is carried out for a holding time of 40-60 hours.

14. The method according to claim 1, wherein vibration treatment is performed during the hydrothermal reaction in the step (2).

15. The method of claim 14, wherein the vibration frequency of the vibration treatment in three dimensions is 0.03Hz to 0.1 Hz.

16. The method according to claim 1, wherein the hydrothermal reaction in step (2) is carried out under the protection of inert gas.

17. The method according to claim 1, wherein the hydrothermal reaction in step (2) is cooled after the hydrothermal reaction is completed.

18. The method according to claim 1, wherein after the hydrothermal reaction in step (2), the organic solvent is recovered.

19. Method according to claim 1, characterized in that it comprises the following steps:

s2: pouring a certain volume of n-hexane liquid into the reaction kettle, and filling argon for inert atmosphere protection; the volume of the n-hexane liquid accounts for 45-90% of the volume of the reaction kettle;

20. A pre-lithium anode material prepared according to any one of claims 1 to 19, wherein the pre-lithium anode material comprises an anode active material and lithium intercalated into the anode active material.

21. A pre-lithium anode comprising the pre-lithium anode material of claim 20.

22. A pre-lithium battery, characterized in that it comprises a pre-lithium negative electrode according to claim 21.