KR20160011097A - Electrode, battery and method of manufacturing the electrode - Google Patents

Abstract

The present invention relates to: an electrode having high electrical conductivity and high discharge capacity; a manufacturing method thereof; and a battery comprising the electrode, wherein the battery has high energy density. The present invention comprises: a step of preparing a mixed solution by mixing sulfur with a solution that polyacrylonitrile is dissolved; a step of forming the mixed solution into a composition of a predetermined shape; and a step of heat-treating the formed composition.

Description

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method of manufacturing an electrode,

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an electrode, a method of manufacturing the same, and a battery including the electrode. More particularly, the present invention relates to an electrode that can be manufactured in various shapes, a method of manufacturing the same, and a battery including the electrode.

As a next-generation battery, batteries using sulfur as an active material (lithium-sulfur battery, sodium-sulfur battery, etc.) have been actively studied due to their high theoretical energy density.

When sulfur is used as an active material, an electrode having a high discharge capacity can be produced. However, since sulfur is an insulator, conventionally, a conductive material and a binder were used in the production of an electrode.

However, the actual discharge capacity of the thus produced electrode is lower than the theoretical discharge capacity. The reason for this is that the prepared electrode contains a conductive material, a binder, and the like in addition to sulfur, which is an active material participating in an actual cell reaction.

Therefore, in order to realize an actual high performance sulfur battery close to the theoretical energy density, it is necessary to increase the ratio of sulfur in the electrode, and in the absence of the conductive material and the binder, the electrode is made of 100% active material (sulfur).

In addition, as various types of electronic devices have been developed and popularized, not only a high energy density electronic device is required but also a need for a battery having a complicated shape such as a linear or gear type such as a thread or a fiber has also been increased.

It is an object of the present invention to provide an electrode having a high discharge capacity, a method of manufacturing the electrode, and a high energy density battery including the electrode, which can be manufactured in various shapes.

According to an aspect of the present invention, there is provided a method of manufacturing an electrode, comprising: preparing a mixed solution by mixing sulfur with a solution of polyacrylonitrile; Forming a mixed solution into a composition of a predetermined shape, and heat treating the formed composition.

In this case, in the forming step, the composition may be formed by casting the mixed solution.

Meanwhile, in the forming step, the mixed solution may be injected through a nozzle.

Meanwhile, the composition may be formed by electrospinning the mixed solution.

Meanwhile, the method of manufacturing an electrode according to an embodiment of the present invention may further include passing the composition to molten sulfur to increase the sulfur concentration of the composition before the heat treatment step.

Meanwhile, the method of manufacturing an electrode according to an embodiment of the present invention may further include implanting ions into the heat-treated composition.

On the other hand, the solution in which the polyacrylonitrile is dissolved may be one in which the polyacrylonitrile is dissolved in a dimethylformamide solvent.

Meanwhile, an electrode according to an embodiment of the present invention is formed of a composition of a predetermined shape in which a solution in which polyacrylonitrile is dissolved and sulfur is mixed, without a binder and a conductive material .

In this case, the shape of the electrode may be an actual shape, a web shape, or a fabric shape.

On the other hand, the electrode may be flexible.

Meanwhile, a battery according to an embodiment of the present invention includes an anode, a cathode, and an electrolyte disposed between the anode and the cathode, and the anode may be any of the electrodes according to various embodiments described above.

In this case, the anode, the electrolyte and the cathode may be flexible.

According to the various embodiments described above, a sulfur-polyacrylonitrile composite electrode which is a new concept electrode having a high electric conductivity and a high discharge capacity can be produced. And a high energy density battery having various shapes can be manufactured by using it.

FIG. 1 is a flowchart illustrating a method of manufacturing an electrode according to an embodiment of the present invention. FIG.
Figures 2 through 3 illustrate various types of electrode images produced in accordance with various embodiments of the present invention,
Fig. 4 is an image obtained by observing a heat-treated sulfur-polyacrylonitrile electrode by a scanning electron microscope (SEM)
5 through 7 illustrate the structure of an electrode according to an embodiment of the present invention in various ways. As a result,
Figure 8 is an image showing flexible characteristics of an electrode according to an embodiment of the present invention,
9 is a graph showing an image of an electrode manufactured by a casting method according to an embodiment of the present invention,
FIG. 10 is a view for explaining the comparison of the flexible characteristics of the electrodes according to the embodiment of the present invention and the electrodes according to the comparative example,
FIG. 11 is a graph showing the results of an activation treatment performed by an electrochemical method according to an embodiment of the present invention,
12 through 17 illustrate the results of charge and discharge of batteries manufactured according to various embodiments of the present invention,
18 is a view for explaining a comparison of capacities per electrode of a battery manufactured according to an embodiment of the present invention and a battery manufactured according to a comparative example.

According to various embodiments of the present invention, it is possible to manufacture an electrode using sulfur as an active material without a conductive material and a binder. The conductive material is used for imparting conductivity to the electrode. When sulfur is used as the active material, a carbon material is generally used as a conductive material. As the binder, for example, polyvinylidene fluoride, polyvinyl alcohol, or the like has been used as a component for assisting in bonding between the active material and the conductive material and bonding to the current collector. Since the electrodes prepared according to various embodiments of the present invention do not include other additives such as conductive materials and binders, they can be manufactured in various shapes.

Various embodiments of the present invention will be described in detail with reference to the drawings.

1 is a flow chart for explaining an electrode manufacturing method according to an embodiment of the present invention.

Referring to FIG. 1, in order to manufacture an electrode, a mixed solution is prepared by mixing sulfur with a solution of polyacrylonitrile (S110), and the mixed solution is formed into a predetermined shape (S120), and the formed composition is subjected to heat treatment (S130). An ion implantation step may be further performed to impart electrical conductivity and electrochemical activity to the electrode formed after the heat treatment.

In the step (S110) of mixing sulfur into a solution of polyacrylonitrile, the manner of adding sulfur varies. For example, there may be a method in which sulfur is dissolved and added, a method in which sulfur is added and a method in which sulfur is added and dispersed.

A method of dissolving sulfur is a method in which a solution of polyacrylonitrile in a solvent of N, N-dimethylformamide (DMF) and a solution of sulfur in 1-methyl-2-pyrrolidinone (NMP) DMSO), and carbon disulfide (CS ₂ ) may be mixed to prepare a sulfur-polyacrylonitrile solution.

The method of reducing sulfur includes a solution prepared by dissolving polyacrylonitrile in a dimethylformamide solvent and a solution of sodium polysulfide (Na ₂ S _x ), sodium thiosulfate (Na ₂ S ₂ O ₃ ), sodium Solutions are prepared by mixing solutions such as sodium sulfite (Na ₂ SO ₃ ).

As a method of dispersing sulfur, a sulfur-polyacrylonitrile solution can be prepared by adding sulfur to a solution of polyacrylonitrile in a dimethylformamide solvent, followed by ball milling and stirring.

When the mixed solution is prepared as described above, the mixed solution is formed into a composition having a predetermined shape (S120).

Methods that can be used in various embodiments of the present invention include, for example, a dry spinning method using nozzles, a wet spinning method, an electrospinning method, a casting method, and the like. In addition, any method for obtaining a desired shape, such as film processing or fiber processing, is available.

 As the nozzle spraying method, a composition in the form of an emulsion can be obtained through a nozzle, and a composition in the form of an emulsion or a web can be obtained by the electrospinning method. And the thus-obtained emulsion composition may be woven.

In the wet spinning method using a nozzle, specifically, a mixed solution in which sulfur and polyacrylonitrile are mixed is injected into the ethanol solution through the nozzle, and the polyacrylonitrile in the mixed solution is dissolved in the ethanol solution The solvent is replaced with ethanol (i.e., a solvent such as DMF, which is a solvent of polyacrylonitrile, is dissolved in ethanol). As a result, there is no solvent capable of dissolving the polyacrylonitrile to become a solid, resulting in a solid composition in the form of an emulsion corresponding to the nozzle diameter. Thereafter, the gelatinous composition is separated from the ethanol solution in which the gelatinous composition is injected. Next, through a drying process, a final seal-type composition can be obtained.

In the case of the electrospinning method, a high voltage is applied between the mixed solution of polyacrylonitrile and sulfur and the collector to spray the mixed solution. When the mixed solution is injected into a collector in which voltage is applied, an actual and web type composition can be obtained according to the intensity of the voltage.

In the case of the casting method, a mixed solution obtained by mixing polyacrylonitrile and sulfur may be filled in various types of molds, and then a composition having a shape similar to a mold may be obtained through a drying process.

After the composition is processed into a desired shape, the composition is subjected to heat treatment (S130). A compound in which sulfur and polyacrylonitrile are bonded through heat treatment can be formed. The temperature conditions for the heat treatment can be determined according to the melting point of sulfur (about 118 ° C) and the temperature conditions under which the bond between sulfur and polyacrylonitrile occurs.

According to one embodiment, the heat treatment may be performed by continuously heating to a temperature at which the bonding of sulfur and polyacrylonitrile occurs. For example, to 2800 ° C. On the other hand, it was confirmed that the composition had a flexible characteristic from 450 ° C or higher.

Alternatively, it can be repeatedly performed while increasing the heating temperature. For example, after heating the composition to near the melting point of sulfur, the heating is stopped, and further sulfur is added to the composition, followed by heating to a temperature at which the bond of sulfur and polyacrylonitrile is established. That is, the heat treatment can be performed by dividing the temperature section into two sections. According to one embodiment, the first temperature interval is from 110 ° C to 200 ° C with sulfur mixed with polyacrylonitrile, and the second heat treatment is a reaction between sulfur and polyacrylonitrile to produce a new compound Section, the temperature is from 200 ° C to 2800 ° C.

Thus, it is possible to increase the sulfur content of the composition by adding sulfur to the composition before performing the heat treatment. As an example of the method of adding sulfur, sulfur may be added by passing the present composition prepared in the form of an emulsion into a crucible in which sulfur is melted. Alternatively, the sulfur content may be increased by spraying the sulfur powder onto the composition.

This is because, since the solubility of sulfur is low, the sulfur concentration in the mixed solution may not be sufficient, so that sulfur is further added to the composition formed before the heat treatment step.

The heat treatment may be performed in an atmosphere of oxygen (O ₂ ), argon (Ar), and nitrogen (N ₂ ). It was confirmed that when the heat treatment temperature was 450 ° C or higher, the composition exhibited flexible properties.

The thus heat-treated composition can be used as an electrode for a sodium battery, a sodium battery, or the like. On the other hand, in order to improve the electrical conductivity and the electrochemical activity of the electrode thus obtained, an activation treatment step may be further performed.

Specifically, the activation treatment refers to implanting ions to impart electrical conductivity and electrochemical activity to the electrode. The method of performing the activation treatment can be divided into a chemical method and an electrochemical method.

The chemical method is to immerse the electrode in a solution in which ions such as Li ⁺ , Na ⁺ , Mg ⁺ , and Fe ⁺ are dissolved for a predetermined time or more, thereby injecting ions into the electrode.

The electrochemical method is a method in which a heat-treated composition is used as an electrode, and an electrode such as Li, Na, Mg or the like is used as a counter electrode thereof, and electrochemical ions are injected into the activation process.

Hereinafter, in order to facilitate the understanding of the present invention, a method of manufacturing an electrode according to some embodiments and an electrode manufactured by the manufacturing method will be described.

Electrode Preparation Example 1

First, 1.666 g of sulfur was added to a solution of 0.833 g of polyacrylonitrile in 16 ml of dimethylformamide, followed by mixing by ball milling.

Next, the mixed solution mixed by ball milling is injected into the ethanol solution through a nozzle having an inner diameter of 0.45 mm to obtain an emulsion composition.

After molding in the above-mentioned manner, the resultant was dried in an oven at 60 ° C. in order to remove the remaining ethanol, heated at 10 ° C./min to 200 ° C. in an argon atmosphere to dissolve sulfur to be mixed well with the polyacrylonitrile, And then heated to 450 ° C at a rate of 10 ° C per minute and maintained at 450 ° C for 6 hours.

FIG. 2 shows the result of confirming that the electrode of the actual shape (diameter: 46.15 μm) manufactured in the electrode manufacturing example 1 has a flexible property. It can be confirmed that even if bent by applying a force, the electrode does not crack and bends well.

Electrode Fabrication Example 2

First, 1.666 g of sulfur was added to a solution of polyacrylonitrile (6 g) dissolved in 48.6 ml of dimethylformamide, followed by stirring at 80 ° C.

Then, 4 ml of the mixed solution prepared by stirring was injected into a syringe, and a nozzle having an inner diameter of 0.51 mm was connected to prepare a web-type composition using an electrospinning apparatus. The conditions of the electrospinning device were 20 kV applied voltage, 2.5 ml / h ejection speed, 180 rpm of the integrated device, and 18 cm between the syringe and the integrated device. The prepared composition is shown in Fig. It was confirmed that sulfur was dispersed in the web with white.

Next, the remaining dimethylformamide in the web-like composition is dried and then heat treated to obtain a web-like sulfur-polyacrylonitrile electrode. Before heat treatment, 2 g of sulfur was added to increase the content of sulfur in the web electrode. At this time, up to 32 g of sulfur added can be added. The heat treatment was performed in an argon atmosphere.

The heat treatment conditions were 150 ° C to 600 ° C. FIG. 4 is an SEM image of a sulfur-polyacrylonitrile electrode subjected to heat treatment at each temperature, and Table 1 below shows an elemental analyzer to determine the sulfur content.

Table 1

 It can be seen that as the temperature of the heat treatment condition increases, the content of sulfur decreases. During the two-stage heat treatment, that is, after the first heat treatment up to 200 ° C, the temperature during the second heat treatment is increased to a maximum of 70.04% at around 250 ° C.

Fig. 5 is a result of an X-ray diffraction analysis of the crystal structure of an electrode heated to 450 deg. C continuously after heat treatment to 200 deg. Before the heat treatment, a crystalline peak of sulfur was observed, but after the heat treatment, the crystalline peak of sulfur disappeared and only an amorphous peak was observed. From these results, it can be seen that a new compound, not a yellow or polyacrylonitrile, was formed through the heat treatment process.

6, the carbon-nitrogen triple bond peak of the polyacrylonitrile disappeared, the carbon-nitrogen double bond peak appeared, and the carbon-carbon double bond As a result, a newly formed conductive sulfur-polymer compound has an aromatic structure and contains sulfur. Referring to FIG. 7, which shows the Raman experiment results of the electrode structure heated to 450 ° C., the G and D bands of carbon, which were not observed in polyacrylonitrile or sulfur, were observed.

Referring to FIG. 8, electrodes continuously heat-treated at 450 ° C. were punched out with a punch having a diameter of 1 cm ² , and the properties of the electrodes were confirmed by applying a force.

Electrode Fabrication Example 3

First, 1.333 g of sulfur was added to a solution of 0.666 g of polyacrylonitrile in 12 ml of dimethylformamide, followed by mixing by ball milling.

Then, the mixture solution mixed by ball milling was put into a plate mold and a ring mold as shown in Fig. 9 to obtain a cast product.

Then, the composition cast in various forms was heated to 200 ° C at a rate of 10 ° C / min, maintained for 10 minutes, and then heated to 320 ° C to prepare a sulfur-polyacrylonitrile electrode. The heat treatment was performed in an argon atmosphere.

Electrode Preparation Comparative Example 1

As a comparative example, an Elemental S electrode was prepared.

The elemental S electrode was prepared by putting 20 wt% of sulfur, 20 wt% of a conductive material (Super-P), 20 wt% of a binder (polyfluorinated vinylidene: PVdF) and NMP, For 3 hours to obtain a homogeneous slurry, which was then applied to an aluminum foil.

As another comparative example, a general sulfur-polyacrylonitrile (SPAN) electrode was prepared.

SPAN General electrodes are prepared by mixing sulfur and polyacrylonitrile in a 4: 1 ratio using a mortar and then heat-treating in an argon atmosphere at 320 ° C. The SPAN composite thus prepared was charged with 80 wt% of conductive material (MWCNT), 20 wt% of binder (β-cyclodextrin) and 20 wt% of distilled water (7 ml) Mixing to obtain a homogeneous slurry, and then coating it on an aluminum foil.

As shown in Fig. 10, the electrodes prepared above were punched to a diameter of 1 cm < ^{2 &} gt ;. Preparation of Electrode When the elemental S electrode prepared in Comparative Example 1 and the SPAN general electrode were bent 10 times, the aluminum foil was bent and the electrode was separated. However, the electrode manufactured in the electrode manufacturing example 2 was not separated from the electrode and exhibited a flexible property.

Hereinafter, the activation process for injecting ions into the electrode manufactured as described above will be described in more detail.

Electrode Activation Treatment Example 1

Preparation of Electrode The electrode prepared in Example 2 was impregnated with a solution containing lithium ions for 3 days and then dried in a vacuum chamber in an Ar atmosphere.

Electrode activation treatment Example 2

An activation process was performed by repeating the process of electrochemically injecting and extracting lithium ions into the electrode prepared in Example 2 five times. The change of the charge curve before and after the activation treatment is shown in Fig. The charge capacity increased significantly after the activation treatment.

The results of the measurement of the resistance value before and after the activation treatment of the electrode of Example 2 are shown in Table 2 below.

Table 2

It can be seen that the resistance value after the activation treatment was reduced from 2.1 G? To more than 1 G? As compared with before the activation treatment.

Electrode activation treatment Example 3

An activation process of electrochemically injecting sodium ion into the electrode prepared in Example 2 once was performed.

The battery thus prepared can be used as an anode. A flexible material can be used for the negative electrode in the same manner as the positive electrode in order to give the battery a flexible property. The electrolyte can also be made of a flexible material such as a polymer electrolyte. Several specific examples of the manufacture of a battery using the electrode and lithium, sodium, and carbon will be described below.

Lithium battery manufacturing Example 1

Electrode Activation Treatment with an Anode The electrode prepared in Example 2 was used and a lithium foil was used as a cathode. The separation membrane was contacted with both electrodes using Celgard Co. 2400 (Celgard Co.). The electrolyte was prepared by dissolving lithium salt LiPF ₆ at a concentration of 1 M in a mixed solution of ethylene carbonate (EC) and diethyl carbonate (DEC) at a volume ratio of 1: 1.

The thus produced battery was subjected to discharging and charging 35 times at a voltage of 1 V to 3 V at a current of 130.94 μA, and the results are shown in FIGS. 12 to 13. The discharge capacity per electrode was more than 500 mAh / g, and the discharge capacity did not decrease according to the cycle.

Preparation of sodium battery Example 2

Electrode Activation Treatment with an Anode The electrode prepared in Example 2 was used and sodium foil was used as a cathode. The separation membrane was contacted with Celgard 2400 (Celgard Co.). Electrolytes were prepared by dissolving sodium salt NaPF ₆ at 1 M in a solution of EC and DEC in a volume ratio of 1: 1.

14 to 15 show the result of seven times of discharging and charging at a voltage range of 0.7 V to 2.8 V with a current of 14.81 μA. The initial discharge capacity was 340 mAh / g and the discharge capacity after 7 cycles was 333 mAh / g. And about 98% capacity retention rate.

Battery Manufacturing Example 3

The electrode prepared according to the above-mentioned electrode preparation example 2 was used as the anode, and the carbon felt containing the lithium / sodium ion as the cathode was used. As a separator, a glass filter (Whatman ™) was used to suppress contact between both electrodes. The electrolyte used was an electrolytic solution in which sodium carbonate NaPF ₆ was dissolved at 1 M in a solution of ethylene carbonate and diethylene carbonate in a volume ratio of 1: 1.

FIG. 16 to FIG. 17 show the results of 100 discharging and charging the battery thus manufactured at a current density of 0.1 C and a voltage range of 0.7 V to 2.8 V. FIG. The initial irreversible capacity showed a value of 1491 mAh / g. From the second cycle to the 100th cycle, the capacity was maintained at about 750 mAh / g. At this time, it is possible to manufacture a flexible battery having flexibility properties in both the positive electrode and the negative electrode.

Battery Manufacturing Comparative Example 1

The electrode prepared in Example 2 of the SPAN web was finely cut, and 20 wt% of conductive material (Super-P), 20 wt% of binder (PVdF) and NMP were placed and ball milling was performed at 300 rpm For 3 hours to obtain a homogeneous slurry, which was then applied to an aluminum foil.

Preparation of Electrode The capacities of the SPAN general electrode prepared in Comparative Example 1, the SPAN common electrode prepared in Comparative Example 1, and the electrode prepared in Example 2 were compared. Referring to FIG. 18, it was confirmed that the electrode of Example 2 exhibited a higher capacity than the other common electrodes.

The electrode according to the various embodiments described above is flexible and can be applied to a wearable device such as a watch, a necklace, or a medical patch. In addition, since the shape of this electrode can be varied depending on how it is processed, it can be manufactured in a complicated shape according to the type of device to be applied, and this electrode is suitable for batteries of various sizes ranging from a nanosize battery to a large- Do.

In addition, the electrodes according to various embodiments of the present invention have a variety of shapes, and the discharge capacity is large because the ratio of sulfur as an active material in the electrode is high.

While the present invention has been particularly shown and described with reference to exemplary embodiments thereof, it is clearly understood that the same is by way of illustration and example only and is not to be construed as limiting the scope of the invention as defined by the appended claims. It will be understood by those skilled in the art that various changes in form and details may be made therein without departing from the spirit and scope of the present invention.

Claims (12)

In the electrode manufacturing method,
Preparing a mixed solution by mixing sulfur with a solution of polyacrylonitrile;
Forming the mixed solution into a composition of a predetermined shape; And
And heat treating the formed composition. The method according to claim 1,
Wherein the forming comprises:
Wherein the composition is formed by casting the mixed solution. The method according to claim 1,
Wherein the forming comprises:
And spraying the mixed solution through a nozzle. The method according to claim 1,
Wherein the forming comprises:
Wherein the composition is formed by electrospinning the mixed solution. The method according to claim 1,
Further comprising passing the composition through the molten sulfur to increase the sulfur concentration of the composition prior to the heat treatment step. The method according to claim 1,
And injecting ions into the thermally treated composition. ≪ Desc / Clms Page number 20 > The method according to claim 1,
The solution, in which the polyacrylonitrile is dissolved,
Wherein the polyacrylonitrile is dissolved in a dimethylformamide solvent. In the electrode,
The binder and the conductive material are not included,
Wherein a solution in which polyacrylonitrile is dissolved and a mixed solution in which sulfur is mixed are formed of a composition of predetermined shape. 9. The method of claim 8,
The shape of the electrode,
Wherein the electrode is in the form of a solid, a web, or a fabric. 9. The method of claim 8,
Wherein the electrode is flexible. In the battery,
anode;
cathode; And
And an electrolyte disposed between the anode and the cathode,
Wherein the positive electrode is an electrode according to any one of claims 8 to 10. 12. The method of claim 11,
Wherein the positive electrode, the electrolyte and the negative electrode are flexible.

Images