KR102326851B1 - Cathode electrode for lithium secondary battery and manufacturing method thereof - Google Patents

Abstract

The present invention discloses a negative electrode for a lithium secondary battery and a method for manufacturing the same. The manufacturing method of the present invention comprises the steps of mixing polyamic acid (PAA) and a silicone active material to produce a slurry, coating the resulting slurry on an anode current collector, and applying the coated anode current collector to different environments It includes the step of drying multiple times under conditions.

Description

Anode for lithium secondary battery and manufacturing method thereof

The present invention relates to a lithium secondary battery, and more particularly, to a negative electrode for a lithium secondary battery comprising a polyamic acid (PAA) and a silicon active material and a method for manufacturing the same.

A lithium ion secondary battery is one of energy storage devices for storing energy.

A lithium ion secondary battery has a higher energy density than a nickel-cadmium battery, has a non-memory effect, is eco-friendly, has a long life cycle, and can output a high voltage. Above all, since it can be miniaturized, it is widely used in small portable electronic products such as mobile phones, tablet PCs and camcorders.

A conventional lithium ion secondary battery includes a positive electrode, a negative electrode, a separator, and an electrolyte as main components. The positive electrode contains lithium oxide, the negative electrode contains a carbon compound such as graphite that can store lithium ions, the separator prevents direct contact between the positive electrode and the negative electrode, and the electrolyte prevents lithium ions from moving between the positive and negative electrodes. serves as a medium for

Recently, a technology for increasing the reversible capacity of a lithium ion secondary battery by changing the negative electrode of a lithium ion secondary battery from a carbon-based material to a silicon-based material is being studied.

However, the negative electrode of the lithium ion secondary battery is also manufactured by evenly mixing the active material and the conductive material and then coating it on the current collector, and there is a problem in that a lot of cost and time is consumed for such mixing and coating.

Korean Patent Publication No. 10-2014-0120751 (2014.10.14.)

An object of the present invention is to provide a negative electrode for a lithium secondary battery and a method for manufacturing the same, which are manufactured by including polyamic acid and a silicon active material without using a conductive material.

In order to achieve the above object, the method for manufacturing a negative electrode for a lithium secondary battery according to the present invention comprises the steps of mixing polyamic acid (PAA) and a silicon active material to produce a slurry, and applying the resulting slurry to a negative electrode current collector. coating, and drying the coated negative electrode current collector a plurality of times under different environmental conditions.

In addition, in the generating step, the slurry is characterized in that it comprises 10% to 30% by weight of the polyamic acid and 70% to 90% by weight of the silicone active material.

In addition, the drying step may include a first drying step of drying for 1 hour to 3 hours at a temperature of 70° C. to 90° C. in an atmospheric condition, and a nitrogen (N ₂ ) 4 at a temperature of 600° C. to 800° C. in an atmosphere. It is characterized in that it comprises a second drying step of drying for hours to 6 hours.

In addition, the first drying step is characterized in that the N-methyl-2-piperidone (N-methyl-2-piperidone, NMP) contained in the slurry is removed.

In addition, the second drying step is characterized in that a portion of the polyamic acid in the slurry is carbonized (carbonization).

In addition, when the anode prepared by drying the plurality of times is analyzed by Raman spectroscopy, amorphous carbon is confirmed.

In addition, when the anode prepared by drying the plurality of times is analyzed by infrared spectroscopy, absorption is observed at a ^{carbonyl group of 1630 cm -1 .}

The negative electrode for a lithium secondary battery according to the present invention includes a negative electrode current collector and a negative electrode layer formed on at least one surface of the negative electrode current collector and coated with a slurry containing polyamic acid and a silicon active material.

The negative electrode for a lithium secondary battery of the present invention and its manufacturing method do not use a conductive material, but include polyamic acid and a silicon active material, so that it is possible to shorten the process time and reduce the cost of raw materials compared to the negative electrode using a conventional conductive material.

In addition, it is possible to increase the initial efficiency and improve the life characteristics.

1 is a view for explaining a lithium secondary battery according to an embodiment of the present invention.
2 is a flowchart for explaining a method of manufacturing a negative electrode for a lithium secondary battery according to an embodiment of the present invention.
3 is a view for explaining the analysis result of the Raman and infrared spectroscopy of the negative electrode for a lithium secondary battery according to an embodiment of the present invention.
4 is a view for explaining the evaluation of the room temperature battery characteristics of the negative electrode for a lithium secondary battery according to an embodiment of the present invention.
5 is a view for explaining the evaluation of the lifespan characteristics of a negative electrode for a lithium secondary battery according to an embodiment of the present invention.

Hereinafter, embodiments of the present invention will be described in detail with reference to the accompanying drawings. First, in adding reference numerals to the components of each drawing, it should be noted that the same components are given the same reference numerals as much as possible even though they are indicated on different drawings. In addition, in describing the present invention, if it is determined that a detailed description of a related known configuration or function is obvious to those skilled in the art or may obscure the gist of the present invention, the detailed description thereof will be omitted.

1 is a view for explaining a lithium secondary battery according to an embodiment of the present invention.

Referring to FIG. 1 , in the lithium secondary battery 100 , the negative electrode 10 and the positive electrode 30 are disposed with respect to the separator 20 , and the electrolyte is interposed between the negative electrode 10 and the positive electrode 30 .

The negative electrode 10 is made of polyamic acid and a high-capacity silicone active material without using a conductive material. The negative electrode 10 includes a negative electrode current collector 11 and a negative electrode layer 12 . The negative electrode 10 is a negative electrode layer 12 is formed by mixing polyamic acid and a silicone active material, coating the mixed slurry on the negative electrode current collector 11, and then drying it twice under different environmental conditions. In this case, the negative electrode layer 12 may be formed on at least one surface of the negative electrode current collector 11 . The negative electrode current collector 11 may be made of lithium (Li) metal, and in addition, copper (Cu), a carbon-based material, or the like may be used. For example, the carbon-based material may be graphite, hard carbon, or the like.

The positive electrode 30 is an active material, LiMO ₂ (M = V, Cr, Co, Ni), LiM ₂ O ₄ (M = Mn, Ti, V), LiMPO ₄ (M = Co, Ni, Fe, Mn), LiNi ₁ -xCoxO ₂ (0<x<1), LiNi ₂ -xMnxO ₄ (0<x<2) and Li[NiMnCo]O ₂ containing lithium transition metal oxides or sulfur compounds, such as, or using a porous air electrode can Such a positive active material may have a layered structure, a spinel structure, or an olivine structure, depending on the type of active material used.

The electrolyte may be formed of a liquid electrolyte or a solid electrolyte, and in particular, when a liquid electrolyte is used, the separator 20 for supporting the organic electrolyte may be formed between the negative electrode 10 and the positive electrode 30 .

The organic electrolyte contains a lithium salt and an organic solvent. Lithium salts include, but are not limited to, lithium hexafluorophosphate (LiPF ₆ ), lithium perchlorate (LiClO ₄ ), lithium tetrafluoroborate (LiBF ₄ ), lithium trifluoromethanesulfonate (LiCF ₃ SO ₃ ), lithium hexafluoroacetate (LiAsF ₆ ), lithium bistrifluoromethanesulfonylimide (LiTFSI), lithium bisoxalatoborate (LiBOB), and slurries of two or more thereof. The organic solvent is a non-limiting example, and may be selected from ethylene carbonate, propylene carbonate, ethylmethyl carbonate, dimethyl carbonate, diethyl carbonate, ethyl propionate, and slurries of two or more thereof. The organic solvent may include dimethyl carbonate (DC), ethylmethyl carbonate (EMC), etc. in a basic solvent containing ethylene carbonate (EC) and propylene carbonate (PC). have.

The separator 20 may be disposed between the negative electrode 10 and the positive electrode 30 . The separator 20 includes at least one selected from a polyolefin-based resin, a fluorine-based resin, a polyester-based resin, a polyacrylonitrile resin, or a microporous film made of a cellulose-based material, or an inorganic material such as a ceramic is coated on these films it could be For example, the polyolefin-based resin may include polyethylene, polypropylene, and the like, the fluorine-based resin may include polyvinylidene fluoride, polytetrafluoroethylene, and the like, and the polyester-based resin may include polyethylene terephthalate, polybutyl Renterephthalate and the like may be included.

Meanwhile, the lithium secondary battery 100 may be manufactured in a dry room or in a glove box in an inert gas atmosphere in order to minimize the influence of moisture and active gas in the atmosphere.

When the lithium secondary battery 100 is manufactured in the form of a coin cell, the positive electrode 30, the separator 20, and the negative electrode 10 are configured in a stacked manner. Can be used. Thereafter, a terminal tab is attached to the negative electrode 10 and the positive electrode 30, which are passages of external electron flow, and the packaging is performed. When packaging is completed, the lithium secondary battery 100 may be completed by injecting electrolyte and sealing in a vacuum.

2 is a flowchart for explaining a method of manufacturing a negative electrode for a lithium secondary battery according to an embodiment of the present invention.

1 and 2, the negative electrode 10 does not use a conductive material, and includes polyamic acid and a silicon active material, thereby shortening the process time and reducing raw material costs compared to the negative electrode using a conventional conductive material. have.

In step S10, a slurry is produced by mixing the polyamic acid and the silicone active material. At this time, the slurry contains 10 wt% to 30 wt% of polyamic acid, and 70 wt% to 90 wt% of a silicone active material. Preferably, the slurry may contain 15 wt% to 25 wt% of a polyamic acid and 75 wt% to 85 wt% of a silicone active material. More preferably, the slurry contains 19% by weight of polyamic acid and 81% by weight of a silicone active material.

In step S30, the slurry produced in step S10 is coated on the negative electrode current collector 11. The negative electrode current collector 11 is supported in the slurry and the surface thereof is coated. Preferably, the slurry may be coated on the negative electrode current collector 11 to a constant thickness.

In steps S50 and S70, the negative electrode current collector 11 coated in step S30 is dried to form the negative electrode layer 12. At this time, the negative electrode current collector is dried a plurality of times under different environmental conditions. That is, the steps S50 and S70 are different environmental conditions.

In step S50, the negative electrode current collector 11 coated in step S30 is first dried. The first drying is dried for 1 hour to 3 hours at a temperature of 70° C. to 90° C. under atmospheric conditions. Preferably, the first drying may be performed for 1 hour 30 minutes to 2 hours 30 minutes at a temperature of 75° C. to 85° C. in an atmospheric condition. More preferably, the first drying may be performed for 2 hours at a temperature of 80° C. under atmospheric conditions. The first drying removes N-methyl-2-piperidone (NMP) contained in the slurry.

In step S70, the first dried negative electrode current collector in step S50 is second dried. The second drying is drying under an environmental condition different from that of the first drying. That is, the second drying is performed at a temperature of 600° C. or higher in a _{nitrogen (N 2 ) atmosphere for 4 hours or more.} Preferably, the second drying may be performed in a nitrogen atmosphere at a temperature of 600° C. to 800° C. for 4 hours to 6 hours. More preferably, the second drying may be performed in a nitrogen atmosphere at a temperature of 700° C. for 5 hours. In the second drying, a portion of the polyamic acid in the slurry is carbonized. When the second drying is completed, the negative electrode 10 including the polyamic acid and the silicone active material is completed.

On the other hand, the negative electrode 10 can maximize the conductivity and adhesion of the carbon body formed from the polyamic acid through drying a plurality of times. Through this, the cathode 10 may smoothly implement electrode characteristics.

Hereinafter, analysis and characteristic evaluation of the negative electrode 10 manufactured by the above-described manufacturing method will be described.

3 is a view for explaining the analysis results of the Raman and infrared spectroscopy of the negative electrode for a lithium secondary battery according to an embodiment of the present invention. FIG. 3(a) is a view for explaining the result of analyzing the cathode 10 by Raman spectroscopy, and FIG. 3(b) is a view for explaining the result of analyzing the cathode 10 by infrared spectroscopy.

1 and 3, the degree of adhesion between the current collector and the slurry of the negative electrode 10 was confirmed through Raman spectroscopy and infrared spectroscopy.

The negative electrode 10 confirmed the presence of amorphous carbon through FIG. 3(a), and through FIG. 3(b), mechanical properties such as preserving adhesion by ^{a conventional carbonyl group (1630cm -1 ) functional group.} was confirmed to be maintained. That is, it can be seen that the ^{anode 10 absorbs light at 1630 cm -1} of the carbonyl group.

4 is a view for explaining the evaluation of the room temperature battery characteristics of the negative electrode for a lithium secondary battery according to an embodiment of the present invention. Here, the evaluation conditions are 2.5 to 0.005V (vs. Li/Li+), 0.1C/0.1C.

1 and 4 , the first charging and discharging of the negative electrode 10 are shown as a profile, and through this, the negative electrode 10 can be applied to a lithium secondary battery by evaluating the battery characteristics at room temperature. Confirmed.

As a result, the charging and discharging behavior of the battery was confirmed at an average charging voltage of about 0.43V and an average discharge voltage of about 0.09V, and an initial charge-discharge efficiency of about 80% with a discharge capacity of about 2500 (mAh/g) confirmed that there is.

Accordingly, it was confirmed that the negative electrode 10 had improved initial charge/discharge efficiency compared to the conventional negative electrode.

5 is a view for explaining the evaluation of the lifespan characteristics of a negative electrode for a lithium secondary battery according to an embodiment of the present invention. Here, the evaluation conditions are 1.4 to 0.005V (vs. Li/Li+), 0.2C/0.2C.

Referring to FIGS. 1 and 5 , it was confirmed whether the negative electrode 10 was applicable to a lithium secondary battery through evaluation of lifespan characteristics at room temperature.

As a result, it was confirmed that excellent life characteristics were exhibited at the level of 80%@ 24 cycles compared to the initial 0.2C discharge capacity.

Therefore, it was confirmed that the negative electrode 10 has an improved lifespan at room temperature compared to the conventional negative electrode.

Although preferred embodiments of the present invention have been illustrated and described above, the present invention is not limited to the specific preferred embodiments described above, and in the technical field to which the present invention belongs, without departing from the gist of the present invention as claimed in the claims Any person skilled in the art can make various modifications, of course, and such modifications are within the scope of the claims.

10: cathode
11: anode current collector
12: cathode layer
20: separator
30: positive electrode
100: lithium secondary battery

Claims (8)

generating a slurry by mixing polyamic acid (PAA) and a silicone active material;
coating the generated slurry on an anode current collector;
Including; drying the coated anode current collector a plurality of times under different environmental conditions;
The step of drying the plurality of times,
A first drying step of drying for 1 hour 30 minutes to 2 hours 30 minutes at a temperature of 75 ° C. to 85 ° C. in the standby state; and
a second drying step of drying for 4 to 6 hours at a temperature of 600°C to 800°C in a nitrogen (N2) atmosphere;
A method for manufacturing a negative electrode for a lithium secondary battery, comprising: The method of claim 1,
In the generating step,
The slurry is a method of manufacturing a negative electrode for a lithium secondary battery, characterized in that it comprises 10% to 30% by weight of the polyamic acid, and 70% to 90% by weight of the silicon active material. delete The method of claim 1,
The first drying step,
A method for manufacturing a negative electrode for a lithium secondary battery, characterized in that the N-methyl-2-piperidone (NMP) contained in the slurry is removed. The method of claim 1,
The second drying step is,
A method for manufacturing a negative electrode for a lithium secondary battery, characterized in that a part of the polyamic acid in the slurry is carbonized. The method of claim 1,
When the anode prepared by drying the plurality of times is analyzed by Raman spectroscopy, amorphous carbon is confirmed. The method of claim 1,
When the anode prepared by drying the plurality of times is analyzed by infrared spectroscopy, light absorption is observed at a ^{carbonyl group of 1630 cm -1 .} delete

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