CN102637903A - Formation method of lithium ion battery - Google Patents

Abstract

The invention belongs to the technical field of lithium ion batteries, and in particular relates to a formation method of lithium ion batteries, which comprises the following steps: vacuumizing the battery to be injected and performing the first liquid injection; opening the battery after the first liquid injection Formation, the formation current is 0.1C ~ 1.5C; the battery after formation is injected and packaged for the second time, and the electrolyte solution for the second injection contains a high-temperature additive, and the high-temperature additive is propylene sulfite, At least one of vinyl sulfate, succinonitrile and adiponitrile. Compared with the prior art, the formation method of the present invention overcomes the leakage of the electrolyte caused by the rapid gas production during the high-current formation through two liquid injections, and also avoids the influence of one-time addition of electrolyte additives on the SEI membrane components , thus improving the low-temperature performance of the cell, and at the same time, the additives injected after the formation make the cell have high-temperature performance, and at the same time greatly shorten the formation time, greatly improve the process efficiency, and reduce production costs.

Description

A kind of formation method of lithium ion battery

technical field

The invention belongs to the technical field of lithium-ion batteries, and in particular relates to a high-current formation method of lithium-ion batteries.

Background technique

Lithium-ion secondary battery, as a green battery, has the advantages of high working voltage, high specific energy and long cycle life. It has been developed rapidly in recent years. The application in is more and more extensive. The expansion of battery application fields and the increase in battery demand have prompted battery manufacturers to simplify the process flow, reduce process time to improve production efficiency to meet market requirements, and continuously improve the comprehensive electrochemical performance of batteries to meet application requirements. With the improvement of production mechanization in the battery industry, the formation process has become an important step that currently restricts the production efficiency of lithium-ion batteries.

The formation step of lithium-ion batteries is an important process in battery manufacturing, which is related to the performance of the battery in terms of capacity, cycle life, and high-temperature storage. During the formation process of the battery, the organic electrolyte will be reduced and decomposed on the surface of the negative electrode, and an SEI (Solid Electrolyte Interface, solid electrolyte) film will be formed on the surface of the negative electrode. The formation of a uniform and stable SEI film is beneficial to various electrochemical performances of the battery. The composition of the electrolyte directly affects the formation of the SEI film: when the electrolyte contains additives with different functions, it is not easy to form an ideal SEI film during formation.

In order to obtain a better SEI film, traditional formation uses a small current to charge for tens of hours, and the production efficiency is extremely low.

In order to improve the efficiency of the formation process, the world patent publication number WO2010/081422A1 introduces a large current pre-charge to accelerate the generation of side reaction gases so as to shorten the formation time. However, in this process, the same electrolyte is injected twice before and after formation, and the interaction of the additives of the electrolyte during high-current charging is not considered. Therefore, the charging effect is not ideal, and the low-temperature performance of the battery cell is relatively poor.

In order to improve the quality and battery performance of the SEI film formed during the formation process, the Chinese patent with publication number CN101640285A improves the low temperature and cycle performance of the battery by pouring different electrolytes before and after the formation. However, this process needs to stand still for 2 to 3 days after liquid injection, and uses a small current for formation. The entire formation process takes a long time. The liquid injection hole needs to be sealed to prevent the electrolyte from leaking due to long-term exposure. After formation, the liquid injection hole needs to be opened. Carry out secondary liquid injection, the production efficiency is low.

In view of this, it is indeed necessary to provide a lithium-ion battery formation method that can greatly shorten the formation time and greatly increase the production capacity, while ensuring that the battery has better high-temperature performance and low-temperature performance.

Contents of the invention

The purpose of the present invention is to provide a lithium ion battery formation method that can greatly shorten the formation time and greatly increase the production capacity, and at the same time ensure that the battery has better high-temperature performance and low-temperature performance.

In order to achieve the above object, the present invention adopts following technical scheme:

A method for forming a lithium ion battery, comprising the steps of:

Vacuumize the liquid-filled battery and perform the first liquid injection; vacuum before liquid injection is to ensure that the gas in the pores of the pole piece is removed, which is conducive to the rapid infiltration of the electrolyte injected by the first liquid injection and shortens the standing time.

The battery after the first liquid injection is opened for formation, and the formation current is 0.1C to 1.5C; during the formation process, a large current of 0.1C to 1.5C is used to charge to a certain amount of electricity, thereby forming an SEI film on the surface of the negative electrode. The opening is formed to facilitate the rapid discharge of the gas generated by the formation, so as to avoid the accumulation of gas inside the battery, which will cause the battery to expand, and the shell to bulge and deform. In addition, the open formation also facilitates the addition of the second electrolyte, shortening the process time.

The battery after formation is injected and packaged for the second time. The electrolyte of the second injection contains high-temperature additives, and the high-temperature additives are propylene sulfite, vinyl sulfate, succinonitrile and adiponitrile. at least one of . The additive can form a protective layer on the surface of the negative electrode or the positive electrode to prevent the decomposition of the SEI film at high temperature or the oxidation of the electrolyte by the positive electrode active material, which will cause the cell to swell.

The addition of high-temperature additives can improve the high-temperature performance of the battery. The present invention chooses to inject the electrolyte solution containing high-temperature additives after the formation process, because if the electrolyte solution containing high-temperature additives is injected before the formation process, the quality of the SEI film will be affected, and the low-temperature performance of the battery core will be deteriorated. Therefore, adopting the formation method of the present invention can not only shorten the formation time, but also ensure the formation of a relatively uniform SEI film when the battery is formed at a high current, and can improve the comprehensive electrochemical performance (including high-temperature performance and low-temperature performance) of the battery.

As an improvement to the formation method of the lithium-ion battery of the present invention, based on the total weight of the electrolyte, the weight content of the high-temperature additive is 0.1-5 wt%. Experimental results show that if the amount of high-temperature additives in the electrolyte exceeds 5%, the discharge performance of the battery and the cycle performance of the battery cell will deteriorate.

As an improvement to the formation method of the lithium-ion battery of the present invention, based on the total weight of the electrolyte, the weight content of the high-temperature additive is 0.5-3 wt%.

As an improvement to the formation method of the lithium-ion battery of the present invention, based on the total weight of the electrolyte, the weight content of the high-temperature additive is 2 wt%.

As an improvement of the formation method of the lithium ion battery of the present invention, the negative pressure of the vacuum is -0.01Mpa～-0.1Mpa, so as to ensure that the gas in the pores of the pole piece is drawn out, which is beneficial to the first liquid injection. The rapid infiltration of the electrolyte shortens the standing time before formation.

As an improvement of the formation method of the lithium-ion battery of the present invention, the amount of the electrolyte injected in the first liquid injection is 65-85% of the total amount of the electrolyte. Too much electrolyte will cause overflow of the entrained electrolyte when the gas generated by the formation is discharged, causing loss and affecting the appearance of the battery. If the amount of electrolyte is insufficient, the ion channel will be blocked during formation due to insufficient electrolyte in the pole piece, and the formation effect will be deteriorated.

As an improvement of the formation method of the lithium-ion battery of the present invention, the amount of the electrolyte injected in the second liquid injection is 15-35% of the total amount of the electrolyte.

As an improvement of the formation method of the lithium ion battery of the present invention, the charging time of the opening formation is 3-60 Min. This formation method reduces the formation time to less than 60 minutes while ensuring the performance of the battery cell, and overcomes the volatilization of the electrolyte caused by the traditional low-current long-term formation, which is conducive to a clean and environmentally friendly production process.

As an improvement of the formation method of the lithium-ion battery of the present invention, the pre-charge capacity during the opening formation process is 8% to 60% of the rated capacity of the battery. Experiments have found that when the precharge amount reaches about 10% of the total battery current, the formation gas reaches the maximum, and the SEI film has been formed.

As an improvement of the formation method of the lithium ion battery of the present invention, the formation current is 0.5C-1.5C.

In addition, the entire chemical conversion process is carried out in a dry room or a glove box. Avoid the negative impact of moisture and other impurities in the external environment on the battery to ensure the performance of the battery.

Compared with prior art, beneficial effect of the present invention:

Utilizing the formation method of the present invention, the liquid-injected battery is firstly vacuumed to discharge the gas in the pores of the pole piece, which facilitates the rapid infiltration of the injected electrolyte into the pole piece with a porous structure and shortens the standing time before formation; through two The liquid injection method overcomes the problem of electrolyte leakage caused by rapid gas generation during high-current formation, and also avoids the impact of adding high-temperature additives on the SEI film components before formation, thereby improving the low-temperature performance of the battery. At the same time, injection after formation The high-temperature additives make the battery have high-temperature performance. In addition, the method of high-current formation can obtain electrical properties similar to or even better than those of traditional low-current long-term formation batteries, and at the same time greatly shorten the formation time. The chemical conversion process that takes one to several days to complete in the traditional method can be completed in only one or two hours by this method, which greatly improves the process efficiency and reduces the production cost, which is of great economic significance.

Detailed ways

Example 1

Preparation of the positive electrode sheet: LiCoO ₂ (lithium cobaltate), Super-P (conductive carbon black), PVDF (polyylidene fluoride resin) and NMP (N,N-dimethyl pyrrolidone) and stir evenly to obtain the slurry coated with the positive electrode sheet. Viscosity was adjusted by NMP during stirring. Then the slurry was uniformly coated on both sides of a 14 micron thick positive electrode current collector (aluminum foil) according to a certain width, and finally cold pressed and sliced to obtain positive electrode sheets.

Preparation of the negative electrode sheet: MCMB (a kind of anode graphite, mesophase pitch-based carbon microspheres), Super-P (conductive carbon black), CMC (water-based binder, carboxymethyl cellulose), SBR ( Styrene ButadieneRubber (a kind of rubber) was mixed with deionized water in a mass ratio of 94:1:2:3 and stirred evenly to obtain a negative electrode coating slurry. The viscosity was adjusted by deionized water during stirring. Then, the slurry was coated on both sides of a 9-micron-thick negative electrode current collector (copper foil) according to a certain width, and the negative electrode sheet was obtained through cold pressing and slicing.

Preparation of the battery: Wind the positive electrode, negative electrode and 16 micron thick polyethylene separator film obtained above to form a battery cell, and put the battery cell into a battery case (aluminum-plastic composite film). The electrolyte formula is 1mol/L LiPF ₆ solution, its solvent is the mixed solvent of EC, PC and DEC, wherein the volume ratio of ethylene carbonate (EC), propylene carbonate (PC), diethyl carbonate (DEC) is 1:1:1. In the dry room, vacuum inject 3.0 g of the above electrolyte solution into the battery case for the first liquid injection. After standing for half an hour, charge with a current of 0.5C for 15 minutes for opening formation, and the charging capacity is 12.5% of the rated capacity of the battery. Next, 0.038 g of adiponitrile (AN) was added to 0.762 g of the above-mentioned electrolyte and mixed evenly, and then the electrolyte containing AN additive was injected into the cell casing for the second injection, and quickly sealed to make a 053450 lithium-ion battery.

Example 2

Lithium-ion batteries were prepared according to the method described in Example 1. The difference was that the amount of electrolyte solution injected during the first liquid injection was 2.47 grams, and after standing for half an hour, it was charged with a current of 0.1C for 60 minutes for opening formation, and the charging capacity was 10% of the battery's rated capacity. Then add 0.19 grams of succinonitrile (SN) to 1.14 grams of the above-mentioned electrolyte and mix evenly, then inject the electrolyte containing the SN additive into the cell shell for the second injection, and quickly seal it to make a 053450 lithium-ion battery .

Example 3

Lithium-ion batteries were prepared according to the method described in Example 1. The difference was that the amount of electrolyte solution injected during the first liquid injection was 3.23 grams, and after standing for half an hour, it was charged with a current of 1.5C for 3 minutes for opening formation, and the charging capacity was 8% of the battery's rated capacity. Then add 0.038 grams of ethylene sulfate (DTD) to 0.532 grams of the above electrolyte and mix evenly, then inject the electrolyte containing DTD additive into the cell shell for the second injection, and quickly seal it to make a 053450 lithium-ion battery .

Example 4

Lithium-ion batteries were prepared according to the method described in Example 1. The difference was that the amount of electrolyte solution injected during the first liquid injection was 3.04 grams, and after standing for half an hour, it was charged with a current of 1C for 30 minutes for opening formation, and the charging capacity of the battery was 50% of rated capacity. Then add 0.114 grams of propylene sulfite (PS) to 0.646 grams of the above-mentioned electrolyte and mix evenly, then inject the electrolyte containing PS additive into the cell shell for the second injection, and quickly seal it to make a 053450 lithium-ion battery. Battery.

Example 5

Lithium-ion battery was prepared according to the method described in Example 1, the difference was that the amount of electrolyte injected during the first liquid injection was 2.85 grams, and after standing for half an hour, it was charged with a current of 0.5C for 30 minutes for opening formation, and the charging capacity was 25% of the battery's rated capacity. Next, add 0.114 grams of propylene sulfite (PS) and 0.038 grams of succinonitrile (SN) to 0.798 grams of the above electrolyte and mix evenly, then inject the electrolyte containing PS and SN additives into the battery case for the second injection Liquid, quickly sealed, made of 053450 lithium-ion batteries.

Example 6

Lithium-ion battery was prepared according to the method described in Example 1, the difference was that the amount of electrolyte injected during the first liquid injection was 2.85 grams, and after standing for half an hour, it was charged with a current of 0.5C for 30 minutes for opening formation, and the charging capacity was 45% of the battery's rated capacity. Then add 0.114 grams of propylene sulfite (PS) and 0.038 grams of adiponitrile (AN) to 0.798 grams of the above electrolyte and mix evenly, then inject the electrolyte containing PS and AN additives into the battery case for the second injection , Quickly sealed, made of 053450-type lithium-ion batteries.

Example 7

Lithium-ion battery was prepared according to the method described in Example 1, the difference was that the amount of electrolyte injected during the first liquid injection was 2.85 grams, and after standing for half an hour, it was charged with a current of 0.5C for 30 minutes for opening formation, and the charging capacity was 35% of the battery's rated capacity. Then add 0.076 grams of vinyl sulfate (DTD) and 0.038 grams of succinonitrile (SN) to 0.836 grams of the above electrolyte and mix evenly, then inject the electrolyte containing DTD and SN additives into the battery case for the second injection , Quickly sealed, made of 053450-type lithium-ion batteries.

Example 8

Lithium-ion battery was prepared according to the method described in Example 1, the difference was that the amount of electrolyte injected during the first liquid injection was 2.85 grams, and after standing for half an hour, it was charged with a current of 0.5C for 30 minutes for opening formation, and the charging capacity was 60% of the battery's rated capacity. Then add 0.076 gram of ethylene sulfate (DTD) and 0.038 gram of adiponitrile (AN) to 0.836 gram of the above-mentioned electrolyte and mix evenly, then inject the electrolyte containing DTD and AN additives into the cell casing for the second injection, Quickly sealed to make a 053450 lithium-ion battery.

Comparative example 1

Lithium-ion batteries were prepared in the manner described in Example 1, except that the electrolyte injected for the second time was the same as the first time, and did not contain high-temperature additives.

Comparative example 2

A lithium-ion battery was prepared in the manner described in Example 1, except that the electrolyte solution containing 0.038 g of adiponitrile (AN) was injected into the battery case at one time, and the weight of the electrolyte solution was 3.8 g.

Comparative example 3

Lithium-ion batteries were prepared according to the method described in Example 1, except that the traditional low-current formation method was used for formation, and the battery was charged at 0.035C for 800 minutes, and the charging capacity was 50% of the rated capacity of the battery.

Battery performance comparison

The batteries of Examples 1 to 8 and Comparative Examples 1 to 3 were tested as follows:

(1) Low temperature cycle test

The batteries of Examples 1 to 8 and Comparative Examples 1 to 3 were placed in a low temperature environment (10° C.) to perform a capacity cycle test. The test method: firstly test the first discharge capacity of the battery. Then charge at 0.8C constant current to 4.2V, then switch to constant voltage charging, until the current is 0.05C, then discharge at 0.5C to 3V, and repeat 200 cycles, test the discharge capacity at this time, and calculate the capacity retention rate of the battery , the calculation formula of capacity retention rate is as follows:

Capacity retention = (C1-C2)/C1×100%

The results are shown in Table 1. It can be seen from Table 1 that the low-temperature performance of the batteries of Examples 1 to 8 is similar to that of the battery of Comparative Example 1 without high-temperature additives, and is significantly better than that of the battery of Comparative Example 2 with additives added at one time . In addition, the battery formed with high current in Example 1 and the battery formed with low current in Comparative Example 3 have comparable low-temperature performance.

(2) Normal temperature and high temperature cycle test

The batteries prepared in Examples 1 to 8 and Comparative Examples 1 to 3 were placed in a normal temperature environment (25° C.) and a high temperature environment (45° C.) to carry out a capacity cycle test. The test method: first test the first discharge capacity of the battery, and then test it at 1C Constant current charge to 4.2V, then switch to constant voltage charge, to a current of 0.05C, then discharge to 3V at 1C, and repeat 500 cycles, test the discharge capacity at this time, and calculate the capacity retention rate of the battery, the calculation of the capacity retention rate The formula is as follows:

Capacity retention = (C1-C2)/C1×100%

The results are shown in Table 1. It can be seen from Table 1 that the high temperature performance of the batteries of Examples 1 to 8 is better than that of the battery of Comparative Example 2 containing additives added at one time, and the high temperature performance of the battery of Comparative Example 1 without additives is very poor. In addition, the battery formed by high current in Example 1 and the battery formed by low current in Comparative Example 3 have comparable high temperature performance.

Table 1: The cycle performance comparison of Examples 1 to 8 and Comparative Examples 1 to 3

In summary, using the formation method of the present invention, through two liquid injections, it overcomes the defect that the high-current formation is difficult to form an ideal SEI film, which leads to poor cell cycle, and ensures that the lithium-ion battery has good high and low temperature performance. , and at the same time greatly shorten the formation time, greatly increase production capacity, and reduce production costs.

It should be noted that, according to other embodiments of the present invention, the positive electrode active material may also be Li _z CoO ₂ , Li _z NiO ₂ , Li _z MnO ₂ , Li _z Co _1-(x+y) Ni _{x Mny} O ₂ , Li _z Ni _x Mn _1-x O ₂ , Li _z Co _x Ni _{1 -x} O ₂ , LiVPO ₄ , Li ₂ MnO ₃ or Li _z Mn _x M _1-x O ₄ etc. (where: x, y, x One or more of +y<1, z≥1). The negative electrode active material can also be hard carbon, soft carbon, Li ₄ Ti ₅ O ₁₂ , Sn, Si or a mixture thereof in any proportion. The isolation film can be polypropylene isolation film, polyethylene isolation film, or polypropylene and polyethylene composite polymer isolation film, or polyvinylidene fluoride, vinylidene fluoride-hexafluoropropylene copolymer, polymethyl methacrylate 1. A polymer gel-state isolation membrane formed from polyethylene glycol, or a composite isolation membrane of the aforementioned composite polymer isolation membrane and the aforementioned gel-state isolation membrane. The electrolyte salt in the electrolyte may be LiPF ₆ , LiClO ₄ , LiBF ₄ , LiAsF ₆ , LiCl, LiBr, LiBOB, CF ₃ SO ₃ Li, CH ₃ SO ₃ Li, LiB(C ₆ H ₅ ) ₄ or combinations thereof. The organic solvent in the electrolyte can be EC, PC, DEC, DMC, FEC, VC, tetrahydrofuran, γ-butyrolactone, diethyl ethyl ester, methyl sulfoxide, dioxolane, acetonitrile or a combination thereof.

It should be noted that, according to the disclosure and teaching of the above specification, those skilled in the art to which the present invention pertains may also make changes and modifications to the above implementation manners. Therefore, the present invention is not limited to the specific embodiments disclosed and described above, and some equivalent modifications and changes to the present invention should also fall within the protection scope of the claims of the present invention. In addition, although some specific terms are used in this specification, these terms are only for convenience of description and do not constitute any limitation to the present invention.

Claims (10)

1. a method for forming lithium ion battery, is characterized in that, comprises the steps: Vacuumize the liquid-filled battery and perform the first liquid injection; Perform opening formation on the battery after the first liquid injection, and the formation current is 0.1C ~ 1.5C; The battery after formation is injected and packaged for the second time. The electrolyte of the second injection contains high-temperature additives, and the high-temperature additives are propylene sulfite, vinyl sulfate, succinonitrile and adiponitrile. at least one of . 2 . The method for forming a lithium-ion battery according to claim 1 , characterized in that: based on the total weight of the electrolyte, the weight content of the high-temperature additive is 0.1-5 wt%. 3 . The method for forming a lithium-ion battery according to claim 2 , characterized in that: based on the total weight of the electrolyte, the weight content of the high-temperature additive is 0.5-3 wt%. 4. The formation method of lithium ion battery according to claim 3, characterized in that: based on the total weight of the electrolyte, the weight content of the high temperature additive is 2wt%. 5 . The formation method of lithium ion battery according to claim 1 , characterized in that: the negative pressure of the vacuuming is -0.01Mpa～-0.1Mpa. 6 . The method for forming a lithium ion battery according to claim 1 , wherein the amount of electrolyte solution injected in the first liquid injection is 65% to 85% of the total amount of electrolyte solution used. 7 . 7 . The method for forming a lithium ion battery according to claim 1 , characterized in that: the amount of electrolyte solution injected in the second liquid injection is 15-35% of the total amount of electrolyte solution used. 8 . The formation method of lithium ion battery according to claim 1 , characterized in that: the charging time of opening formation is 3-60 Min. 9 . The formation method of lithium ion battery according to claim 1 , characterized in that: the pre-charged capacity during the opening formation process is 8% to 60% of the rated capacity of the battery. 10 . The formation method of lithium ion battery according to claim 1 , wherein the formation current is 0.5C˜1.5C. 11 .