WO2017164561A1

WO2017164561A1 - Method for fabricating nickel sulfide electrode for lithium secondary battery

Info

Publication number: WO2017164561A1
Application number: PCT/KR2017/002807
Authority: WO
Inventors: 이동규; 전환진; 안치원
Original assignee: 한국과학기술원
Priority date: 2016-03-22
Filing date: 2017-03-15
Publication date: 2017-09-28
Also published as: KR101802301B1; KR20170110186A

Abstract

The present invention provides a method for fabricating a nickel sulfide electrode for lithium secondary batteries, comprising the steps of: (i) preparing a three-dimensional current collector; (ii) electroless plating the three-dimensional current collector with nickel; and (iii) sulfurizing the nickel-plated three-dimensional current collector. The lithium secondary battery fabricated using the electrode according to the present invention can retain a high discharge capacity and a high energy density.

Description

Manufacturing method of nickel sulfide electrode for lithium secondary battery

The present invention relates to a method for manufacturing a nickel sulfide electrode for a lithium secondary battery, and more particularly, electroless plating nickel on a three-dimensional current collector and then sulfiding to synthesize a nickel sulfide compound to provide high discharge capacity and energy density. It relates to a method for producing a nickel sulfide electrode for a lithium secondary battery.

BACKGROUND OF THE INVENTION In recent years, with the proliferation of portable electronic devices such as laptops and smart phones, the use of secondary batteries for supplying power to these devices is increasing. Such secondary batteries are being developed to be capable of charging at high speed and to have a large capacity for long time use. In addition, stability is required at the same time to prevent risks such as explosion and ignition even at high charge and long time use.

The lithium secondary battery is largely composed of a positive electrode, an electrolyte, a negative electrode, and a separator. During discharge, lithium cations (Li +) move from the cathode to the anode, and electrons generated as lithium (Li) is ionized also move from the cathode to the anode, and when charging, the opposite moves. The driving force of the lithium cation (Li +) movement is generated by chemical stability according to the potential difference between the two electrodes. The capacity of the battery (AH) is determined by the amount of lithium cations (Li +) that move from cathode to anode and from cathode to cathode.

Currently, a commercially available cathode active material for lithium ion batteries is LiCoO ₂ . However, since the theoretical energy density is low, there is a limit to increasing the energy density of the battery. In addition, there are risks of explosiveness due to various factors, and various cathode active materials are being studied to replace them. Due to these demands, high theoretical capacities, high theoretical energy densities, and inexpensive metal sulfides (MS _x , M = Ti, Mo, Cu, Ni, Fe) are spotlighted as alternative materials. Among them, lithium / nickel sulfide battery using nickel sulfide has high theoretical capacity (NiS: 590mAh / g, Ni ₃ S ₂ : 462mAh / g, NiS ₂ : 870mAh / g) and has better charge and discharge efficiency than other metal sulfides. It has the advantage of having cycle characteristics. It also shows high energy density (1102 Wh / kg-NiS).

Conventional methods of preparing nickel sulfide include preparing electrodes using nickel sulfide or nickel purchased (Electrochimica Acta 76 (2012) 145-151), (Ceramics International 40 (2014) 8351-8356), or mechanical synthesis methods ( Journal of Alloys and Compounds 351 (2003) 273-278), Journal of Alloys and Compounds 349 (2003) 290-296), Journal of Alloys and Compounds 361 (2003) 247-251, and Thermals Letters 60 (2006) 643-645), and Solid State Ionics 179 (2008) 2379-2382.

In Korean Patent No. 10-0406979 (name of the invention: a method of manufacturing an electrode for a lithium secondary battery using a nickel / sulfur compound, hereinafter referred to as the prior art 1), 10 to 70% by weight of nickel is used as the active material. A sulfur compound, a carbon powder as the electric conductor, an ion conductor and a binder are weighed and stirred in a solvent to prepare a slurry, and the slurry is dried to obtain a cathode electrode. A method of manufacturing an electrode for a lithium secondary battery is disclosed.

Prior art 1 undergoes a multi-step process, such as a process of mixing the conductive material, the polymer binder together, and then applying to the current collector and drying. Nickel sulfide electrode manufactured according to the prior art 1 has a first problem that the distance of electrons to the electrode surface or the distance that the lithium ions diffuse into the electrode is relatively long as well as the thickness of the electrode becomes thick, and the polymer binder is electrically The second problem is that the conductivity is very low and the resistance of the electrode is increased, and the third problem is that the reaction area is narrow and the amount of the active material is small because it is applied to the two-dimensional current collector.

The technical problem to be achieved by the present invention is not limited to the technical problem mentioned above, and other technical problems not mentioned above may be clearly understood by those skilled in the art from the following description. There will be.

In order to achieve the above technical problem, the present invention comprises the steps of (i) manufacturing a three-dimensional current collector; (ii) electroless plating nickel on the three-dimensional current collector; (iii) sulfiding the nickel plated three-dimensional current collector; It provides a nickel sulfide electrode manufacturing method for a lithium secondary battery comprising a.

In addition, the electroless plating in the step (ii) may be carried out for a time of 8 minutes to 16 minutes under the condition that the temperature is 75 ℃ ~ 95 ℃ and pH is 8 ~ 10.

In addition, the sulfidation treatment in the step (iii) may be performed for a time of 15 minutes to 40 minutes under the condition that the temperature is 70 ℃ ~ 90 ℃.

In addition, the step (i), (i-1) preparing a mixed solution containing the current collector precursor; (i-2) preparing a current collector precursor fiber by electrospinning the mixed solution;

(i-3) oxidative stabilizing the current collector precursor fibers; (i-4) carbonizing the oxidatively stabilized current collector precursor fibers to produce a three-dimensional current collector; It may include.

In the step (i-2), the electrospinning is performed by discharging the mixed solution at a rate of 1 ml / h to 3 ml / h under an applied voltage of 15 kV to 25 kV and a distance from the syringe to the collector of 15 cm to 20 cm. Can be.

In addition, the current collector may be one of polyacrylonitrile (PAN), Rayon or Pitch.

In addition, the oxidative stabilization in the step (i-3) may be carried out at an elevated temperature of 5 ℃ / min in the oxygen atmosphere and finally maintained for 2 to 4 hours at a temperature of 220 ℃ ~ 280 ℃.

In addition, the carbonization in the step (i-4) can be carried out at an elevated temperature of 5 ℃ / min in the argon atmosphere and finally maintained for 2 to 4 hours at a temperature of 900 ℃ ~ 1100 ℃.

In addition, the three-dimensional current collector may be a carbon felt or carbon mat containing a carbon fiber having a diameter of 100nm ~ 500nm.

In addition, the three-dimensional current collector may have a density of 0.6 g / cm ³ to 1.8 g / cm ³ .

In addition, the present invention provides a nickel sulfide electrode for a lithium secondary battery manufactured by the method according to the present invention.

In addition, the nickel sulfide electrode for the lithium secondary battery may be flexible.

In addition, the thickness of the nickel sulfide electrode for the lithium secondary battery may be 1μm ~ 25μm.

In addition, the present invention is an anode; cathode; Electrolyte; Separator; It includes, and the positive electrode provides a lithium secondary battery, characterized in that the nickel sulfide electrode for lithium secondary battery according to the present invention.

The method for manufacturing a nickel sulfide electrode for a lithium secondary battery according to the present invention has a first effect of reducing the thickness of the electrode compared to the prior art, thereby reducing the path of electrons and ions, and does not require a separate additional material such as a conductive material or a binder. Therefore, the second effect of reducing the resistance of the electrode, the third effect of using a three-dimensional current collector having a light weight and high electrical conductivity to increase the reaction area and have a flexible property and can be produced in various shapes and electroless plating Spherical nickel particles prepared by the method and a nickel sulfide compound having a petal shape by the sulfidation method have a large surface area and have a fourth effect of obtaining high discharge capacity and energy density.

The effects of the present invention are not limited to the above-described effects, but should be understood to include all the effects deduced from the configuration of the invention described in the detailed description or claims of the present invention.

1 is a flowchart illustrating a method of manufacturing a nickel sulfide electrode for a lithium secondary battery according to an embodiment of the present invention.

2 is a flowchart illustrating a method of manufacturing a three-dimensional current collector manufactured according to an embodiment of the present invention.

Figure 3 is a three-dimensional carbon felt current collector photograph prepared according to an embodiment of the present invention.

Figure 4 is a view showing the SEM image of the plating time of the three-dimensional carbon felt collector electroless plating nickel according to an embodiment of the present invention.

5 is a view showing a SEM image of the plating time of the nickel sulfide electrode for lithium secondary batteries prepared by sulfidation according to an embodiment of the present invention.

6 is a discharge graph of each plating time of a lithium secondary battery manufactured according to an embodiment of the present invention.

7 is a graph showing the discharge cycle for each plating time of a lithium secondary battery manufactured according to an embodiment of the present invention.

8 is a view showing a SEM image of the plating temperature of the three-dimensional carbon felt current collector subjected to the electroless plating of nickel according to an embodiment of the present invention.

FIG. 9 is a view showing SEM images of plating temperatures of nickel sulfide electrodes for lithium secondary batteries manufactured by sulfidation according to an embodiment of the present invention.

10 is a discharge graph of each plating temperature of a lithium secondary battery manufactured according to an embodiment of the present invention.

11 is a graph showing the discharge cycle for each plating temperature of the lithium secondary battery manufactured according to an embodiment of the present invention.

The present invention comprises the steps of (i) preparing a three-dimensional current collector; (ii) electroless plating nickel on the three-dimensional current collector; (iii) sulfiding the nickel plated three-dimensional current collector; It provides a nickel sulfide electrode manufacturing method for a lithium secondary battery comprising a.

Hereinafter, with reference to the accompanying drawings will be described the present invention. As those skilled in the art would realize, the described embodiments may be modified in various different ways, all without departing from the spirit or scope of the present invention. In the drawings, parts irrelevant to the description are omitted in order to clearly describe the present invention, and like reference numerals designate like parts throughout the specification.

Throughout the specification, when a part is said to be "connected (connected, contacted, coupled)" with another part, it is not only "directly connected" but also "indirectly connected" with another member in between. "Includes the case. In addition, when a part is said to "include" a certain component, this means that it may further include other components, without excluding the other components unless otherwise stated.

The terminology used herein is for the purpose of describing particular embodiments only and is not intended to be limiting of the invention. Singular expressions include plural expressions unless the context clearly indicates otherwise. As used herein, the terms "comprise" or "have" are intended to indicate that there is a feature, number, step, action, component, part, or combination thereof described on the specification, and one or more other features. It is to be understood that the present invention does not exclude the possibility of the presence or the addition of numbers, steps, operations, components, components, or a combination thereof.

Hereinafter, exemplary embodiments of the present invention will be described in detail with reference to the accompanying drawings.

1 is a flowchart illustrating a method of manufacturing a nickel sulfide electrode for a lithium secondary battery according to an embodiment of the present invention. Referring to Figure 1, the present invention (i) step of manufacturing a three-dimensional current collector (S100); (ii) electroless plating nickel on the three-dimensional current collector (S200); (iii) sulfiding the nickel plated three-dimensional current collector (S300); It provides a nickel sulfide electrode manufacturing method for a lithium secondary battery comprising a.

Hereinafter, the present invention will be described in detail in the manner described in detail for each step of the method for manufacturing a nickel sulfide electrode for a lithium secondary battery according to the present invention.

First, a three-dimensional current collector is manufactured.

2 is a flowchart illustrating a method of manufacturing a three-dimensional current collector manufactured according to an embodiment of the present invention. Referring to Figure 2, the first step, (i-1) preparing a mixed solution containing the current collector precursor (S110); (i-2) preparing a current collector precursor fiber by electrospinning the mixed solution (S120); (i-3) oxidative stabilizing the current collector precursor fibers (S130); (i-4) carbonizing the oxidative stabilized current collector precursor fibers to produce a three-dimensional current collector (S140); It may include.

Figure 3 is a three-dimensional carbon felt current collector photograph prepared according to an embodiment of the present invention. Referring to FIG. 3, the white felt on the left side was performed to prepare the current collector precursor fiber by electrospinning, and the center of the left felt was oxidatively stabilized (S130), and the right side was carbonized ( S140).

First, a mixed solution containing the current collector precursor is prepared. The current collector is a material for manufacturing a carbon fiber constituting a three-dimensional current collector, and may be one of a conductive polymer, polyacrlonitrile (PAN), Rayon, or Pitch. However, not limited to this, it is preferable to use a PAN. Dissolving the current collector precursor in a solvent to prepare a mixed solution, the solvent is not limited as long as the current collector precursor is dissolved, but dimethylformamide (N, N-Dimethylformamide, DMF), dimethylacetamide (DMAC), tetrahydro Preference is given to using at least one organic solvent selected from the group consisting of furan (THF), dioxane or dimethyl sulfoxide (DMSO).

Next, the mixed solution is electrospun to prepare current collector precursor fibers. Electrospinning is a method for producing nanoscale fibers using an electric field, which is simpler than the conventionally known methods and has the advantage of easy control of the shape and size of the nanofibers. The electrospinning may be performed by discharging the mixed solution at a rate of 1 ml / h to 3 ml / h under an applied voltage of 15 kV to 25 kV and a distance from a syringe to a collector of 15 cm to 20 cm.

If the applied voltage is less than 15kV, there may be a problem that the diameter of the fiber is thickened and lumps are generated. If it is more than 25kV may have a problem that the mixed solution is collected in the collector in the form of agglomerates and agglomerates, not fibrous form.

In addition, in order to obtain uniform nano-sized fibers, the discharge rate is preferably in the range of 1 ml / h to 3 ml / h.

Next, the prepared current collector precursor fiber is oxidatively stabilized. Oxidation stabilization improves interplanar stability and is a critical factor in chemical reaction rate. Oxidation stabilization is a process for easily controlling the next carbonization reaction.

Oxidation stabilization may be carried out while maintaining the current collector precursor fibers at an elevated temperature of 5 ° C./min in an oxygen atmosphere and finally at a temperature of 220 ° C. to 280 ° C. for 2 to 4 hours. If the temperature is less than 220 ℃, it may be difficult to remove some impurities remaining in the spun the current collector precursor fiber, if the temperature exceeds 280 ℃ carbon components and oxides in the current collector precursor fiber can be dehydrated.

Next, the three-dimensional current collector is manufactured by carbonizing the oxidatively stabilized current collector precursor fibers. The carbonization process is to produce a fiber made of carbon, so that the physical properties of the fiber, such as strength and elastic modulus, can be changed in a considerable range in the carbonization process, so that the carbonization conditions can be set differently according to the use. The carbonization may be performed at an elevated temperature of 5 ° C./min in an argon atmosphere and finally maintained at a temperature of 900 ° C. to 1100 ° C. for 2 to 4 hours.

If the carbonization temperature is less than 900 ℃ there is a possibility that the carbonization is not made completely, if the temperature exceeds 1100 ℃ there is a problem that the energy consumption increases.

The three-dimensional current collector manufactured through the above step may be a carbon felt or carbon mat including carbon fibers having a diameter of 100 nm to 500 nm. When the diameter is less than 100 nm, carbon fibers are brittle and the spacing between the fibers increases, so that durability and conductivity of the 3D current collector may be lowered. If the diameter is more than 500nm, the oxidation stability of the carbon fiber is not properly performed, heat fusion may occur at the next carbonization step, and the specific surface area may be reduced, thereby reducing energy density or discharge capacity during electrode production.

In addition, the three-dimensional current collector may have a density of 0.6 g / cm ³ to 1.8 g / cm ³ . When the density is less than 0.6 g / cm ³ , the pore size is large and the strength of the carbon fiber is low, so durability of the three-dimensional current collector may be a problem, and electrical conductivity may be lowered even when manufacturing the electrode, and the density is 1.8 g / cm. If it is more than ³ , the strength is improved, but the pore size becomes smaller, resulting in a poor migration path between the electrolyte and the ions.

The three-dimensional current collector is light in weight and excellent in electrical conductivity, and thus does not require a separate material such as a conductive material or a binder in the manufacture of a nickel sulfide electrode according to the manufacturing method according to the present invention, thereby obtaining high discharge capacity and energy density. There is.

Second, nickel is electroless plated on the three-dimensional current collector.

The prior art applied a compound of Ni and S by adding a conductive material and a polymer binder on a two-dimensional current collector such as a copper plate. The nickel sulfide thus prepared not only thickens the electrode but also moves electrons to the electrode surface. The distance or distance at which lithium ions diffuse into the electrode is relatively long. In addition, the polymer binder has a very low electrical conductivity, which increases the resistance of the electrode. In order to solve this problem, the present invention is electroless plated Ni to the entire three-dimensional current collector. Electroless plating is a plating method using a chemical reaction rather than an electrical reaction. In other words, it is electroless plating and plated on metals and nonmetals. The reason why nickel (Ni) is used in the electroless plating method is that the cation is easily formed as a transition metal, has good hardness and flexibility, and has superior properties to other transition metals.

First, a plating solution is prepared for electroless plating. A main component of the plating solution includes a nickel salt, a reducing agent, and a complexing agent, and nickel ions of the nickel salt form spherical nickel particles in the three-dimensional current collector by the reducing agent in the plating solution. .

Nickel chloride hexahydrate (NiCl ₂ · 6H ₂ O) is preferable as the nickel salt that is a source of nickel ions that can be used in the present invention, and sodium hypophosphite monohydrate (NaH) as the reducing agent. ₂ PO ₂ · H ₂ O), the sodium citrate (sodium citrate dihydrate, Na ₃ C ₆ H ₅ O ₇ · 2H ₂ O) may be used as the complexing agent. In addition, ammonium chloride (ammonium chloride, NH ₄ Cl) may be used as a substance for adjusting pH.

In addition, the electroless plating may be performed for a time of 8 minutes to 16 minutes under the condition that the temperature is 75 ℃ ~ 95 ℃ and pH is 8 ~ 10.

When electroless plating, temperature and pH are important parameters. Higher temperature and PH values result in faster plating and lower surface resistance. On the contrary, if the temperature and PH value are lowered, the plating speed will be slower and the surface resistance will be higher. If the plating temperature is less than 75 ° C or the pH is less than 8, the plating speed is slow, the manufacturing time is long, and the surface resistance is high, the electrical conductivity is reduced. As a result, discharge capacity and charge / discharge efficiency can be reduced. If the plating temperature exceeds 95 ° C. or the pH exceeds 10, the plating speed is increased and the nickel particles are plated too thick and the specific surface area may be reduced. As a result, the discharge capacity can be reduced.

Plating time is also an important parameter for the production of nickel sulfide electrodes with high discharge capacity and energy density. If the plating time is less than 8 minutes, a sufficient amount of nickel is not plated on the 3D current collector, so that the discharge capacity is lowered. If the plating time is more than 16 minutes, the thickness of the plated nickel becomes thick and the spherical nickel particles aggregate together. The specific surface area decreases, making the area in contact with the electrolyte too small, resulting in poor electrochemical properties.

Nickel particles prepared by the electroless plating method have a spherical shape on the carbon fiber and have a large surface area and excellent crystallinity.

Third, the nickel-plated three-dimensional current collector is sulfided.

At this time, ammonium polysulfide ((NH ₄ ) ₂ S _x ) may be used as a solvent, and sulfur powder may be used as a source of sulfur ions. First, ammonium polysulfide and sulfur powder are mixed, and when the sulfiding temperature is set, the nickel-plated 3D current collector is immersed in a solution and sulfided.

The sulfidation treatment in this step may be carried out for a time of 15 minutes to 40 minutes at a temperature of 70 ℃ ~ 90 ℃. If the temperature is less than 70 ℃ sulfur powder may not be completely dissolved in the solution, if it exceeds 90 ℃ manufacturing time and energy may be consumed a lot.

In addition, when the sulfidation time is less than 15 minutes, sufficient nickel sulfide is not formed, thereby reducing the discharge capacity and the charging and discharging efficiency, and when the time is more than 40 minutes, the nickel sulfide layer is thickened and the specific surface area decreases to form electrons. The movement of ions may not be easy.

Through the sulfidation process, a nickel sulfide compound having a petal shape on all surfaces of the nickel plated layer is manufactured to increase the surface area and reduce the electron or ion migration path.

In addition, the present invention provides a nickel sulfide electrode for a lithium secondary battery manufactured by the method according to the present invention. In addition, the nickel sulfide electrode for the lithium secondary battery may be flexible. Therefore, the electrode can be manufactured in various shapes, and can be utilized for various applications using lithium secondary batteries.

In addition, the thickness of the nickel sulfide electrode for the lithium secondary battery may be 1μm ~ 25μm. If the thickness is less than 1 μm, the amount of the electrode active material is too small, so that the discharge capacity is low and may not exhibit the characteristics of the secondary battery. The discharge efficiency can be lowered.

The nickel sulfide electrode for a lithium secondary battery manufactured according to the present invention does not need an additional material such as a conductive material or a polymer binder, which is a problem of the prior art, thereby reducing the thickness and reducing the migration path of electrons and ions, and thus high discharge capacity and energy density. Can be obtained.

Hereinafter, Examples, Comparative Examples and Experimental Examples will be described.

Example 1

[Production of 3D Carbon Felt Current Collector by Electrospinning]

First, 10 wt.% Of polyacrylonitrile (PAN) is added to dimethylformamide (N, N-Dimethylformamide, DMF) to dissolve at 80 ° C. for 2 hours to prepare a mixed solution.

Next, fill the 10ml syringe with 1ml of mixed solution for electrospinning, and then join the 21 G (outer diameter: 0.80 mm inner diameter: 0.50 mm) nozzles. Insert the syringe into the syringe pump and perform electrospinning. At this time, the process variable voltage is 19kV, discharge speed is 2.5ml / h, the distance from the syringe to the collector is 18cm and the collector's rotation speed is 200RPM. The environmental variable is temperature at room temperature and humidity at 45%.

The polyacrylonitrile fiber felt prepared by the electrospinning is put into a quartz tube heat treatment furnace to undergo oxidation stabilization and carbonization. Oxidation stabilization is maintained at a temperature of 250 ° C. for 3 hours. The temperature increase rate is 5 ℃ / min and the gas atmosphere is oxygen. Next, the carbonization process is maintained for 3 hours at a temperature of 1000 ℃. The temperature increase condition is 5 ℃ / min and the gas atmosphere is 99.999% argon. A three-dimensional carbon felt current collector is manufactured through the carbonization process.

[Nickel Electroless Plating on 3D Carbon Felt Current Collector]

Fill the beaker with 1 liter of distilled water and place it on a hotplate to rotate the solution using a magnetic bar. Next, 45 g of nickel chloride hexahydrate (NiCl ₂ · 6H ₂ O, 96%), which is a source of nickel ions, sodium hypophosphite monohydrate (NaH ₂ PO ₂ · H ₂ O, 95) %,) 11g, sodium citrate (sodium citrate dihydrate, Na ₃ C ₆ H ₅ O ₇ · 2H ₂ O, 99%) 100g, and ammonium chloride (ammonium chloride, NH ₄ Cl, 50 g of 98.5%) was added. The temperature was fixed at 90 ° C. and the pH at 9.

Next, Ni was plated by dipping the prepared 3D carbon felt current collector in the solution. At this time, the plating time is 10 minutes. After the plating was washed with distilled water and dried at 70 ℃ oven for 24 hours.

[Sulfide Treatment to Produce Nickel Sulfide Electrode for Lithium Secondary Battery]

Fill the beaker with (NH ₄ ) ₂

S

_x 200 ml and place on a hotplate to rotate the solution using a magnetic bar. When the temperature is over 40 ℃, 1.5g of sulfur powder is added. When the temperature reaches 80 ° C., the nickel-plated 3D carbon felt current collector is immersed in a solution and maintained for 30 minutes. Then, washed with distilled water and dried in an oven at 70 ℃ for 24 hours to prepare a nickel sulfide electrode for lithium secondary batteries.

[Production of lithium secondary battery with nickel sulfide electrode for lithium secondary battery]

The prepared nickel sulfide was directly used as an electrode as an anode without any additional material. Lithium foil was used as a negative electrode. As a separator, Celgard 2400 (celgard Co.) was used. The purpose of use is to avoid direct contact between cathode and anode. As the electrolyte, a liquid electrolyte prepared by dissolving 0.5 M LiTFSI salt after mixing the organic solvent DME and DOL in a volume ratio of 1: 1. The cell used was Swazilaxel, and the lamination order was laminated with a lithium foil punched to 1 cm ² , followed by a separator and a nickel sulfide electrode. The electrolyte was put in 5μl between each material to prepare a lithium secondary battery.

Example 2

A lithium secondary battery was manufactured in the same manner as in Example 1, except that the nickel electroless plating time was 15 minutes.

Comparative Example 1

A lithium secondary battery was manufactured in the same manner as in Example 1, except that the nickel electroless plating time was 5 minutes.

Comparative Example 2

A lithium secondary battery was manufactured in the same manner as in Example 1, except that the nickel electroless plating time was 20 minutes.

Example 3

A lithium secondary battery was manufactured in the same manner as in Example 1, except that the nickel electroless plating temperature was 75 ° C.

Comparative Example 3

A lithium secondary battery was manufactured in the same manner as in Example 1, except that the nickel electroless plating temperature was set to 50 ° C.

[Comparative Example 4]

A lithium secondary battery was manufactured in the same manner as in Example 1, except that the nickel electroless plating temperature was 110 ° C.

Experimental Example 1

Nickel electroless plated 3D carbon felt current collectors prepared in Examples 1, 2, Comparative Example 1 and Comparative Example 2 and nickel sulfide electrodes for sulfided lithium secondary batteries were observed by scanning electron microscope (SEM). .

Figure 4 is a view showing the SEM image of the plating time of the three-dimensional carbon felt collector electroless plating nickel according to an embodiment of the present invention. Referring to FIG. 4, the first three-dimensional carbon felt current collector shows the appearance of a bundle of carbon fibers. In Comparative Example 1 treated with nickel plating for 5 minutes, only a small amount of nickel particles were seen, and in Example 1 treated with 10 minutes Silver is plated with spherical particles along the carbon fiber, it can be seen that the entire surface area is the largest. In Example 2 after 15 minutes of treatment, the spherical size of the nickel particles was increased so that the particles were in contact with each other, and the surface area was slightly reduced. In Comparative Example 2, the particles were bonded to each other to form a thick nickel layer, thereby confirming that the surface area was considerably reduced. Can be.

5 is a view showing a SEM image of the plating time of the nickel sulfide electrode for lithium secondary batteries prepared by sulfidation according to an embodiment of the present invention. Referring to FIG. 5, Examples 1 to 2 show nickel sulfide compounds having petal shapes on all surfaces of nickel plated, whereas Comparative Example 1 shows only carbon fiber bundles, and Comparative Example 2 is petal shaped. The appearance of the plate rather than the appearance can be seen that the surface area is reduced.

Experimental Example 2

The lithium secondary batteries prepared in Examples 1, 2, Comparative Example 1 and Comparative Example 2 were subjected to 20 discharge experiments in a voltage range of 0.8V to 3.2V at a current density of 100mA / g.

6 is a discharge graph of each plating time of a lithium secondary battery manufactured according to an embodiment of the present invention. Referring to FIG. 6, Examples 1 and 2 exhibited significantly higher flat voltages of 1.8 V and 1.4 V and a discharge capacity of 560 mAh / g close to the theoretical capacity, compared to Comparative Examples 1 and 2. have.

7 is a graph showing the discharge cycle for each plating time of a lithium secondary battery manufactured according to an embodiment of the present invention. Referring to FIG. 7, Example 1 and Example 2 showed stable cycle characteristics starting from a high discharge capacity within 20 discharges. On the other hand, Comparative Example 1 and Comparative Example 2 can confirm the cycle characteristics that the discharge capacity itself is not as good as the other examples.

Experimental Example 3

Nickel electroless plated 3D carbon felt current collectors prepared in Examples 1, 3, Comparative Example 3 and Comparative Example 4 and nickel sulfide electrodes for sulfided lithium secondary batteries were observed by scanning electron microscopy (SEM). .

8 is a view showing a SEM image of the plating temperature of the three-dimensional carbon felt current collector subjected to the electroless plating of nickel according to an embodiment of the present invention. Referring to FIG. 8, in the case of Comparative Example 3 subjected to nickel plating at a plating temperature of 50 ° C. and Comparative Example 4 subjected to nickel plating at 110 ° C., it was confirmed that almost no nickel particles were present in the carbon fiber bundles. In Example 3 subjected to nickel plating at 75 ° C., it can be confirmed that a small amount of nickel particles are plated. In Example 1 plated at 90 ℃ nickel is plated with spherical particles along the carbon fiber can be seen that the total surface area is the widest.

9 is a view showing a SEM image of the plating time of the nickel sulfide electrode for a lithium secondary battery prepared by sulfidation according to an embodiment of the present invention. Referring to FIG. 9, Example 1 shows a nickel sulfide compound having a petal shape on all surfaces where nickel is plated, and in Example 3, a nickel sulfide compound having a petal shape may be confirmed, whereas Comparative Examples 3 and 4 may be used. It can be seen that only the shape of the carbon fiber bundle appears.

Experimental Example 4

The lithium secondary batteries prepared in Examples 1, 3, Comparative Example 3 and Comparative Example 4 were subjected to ten discharge experiments in a voltage range of 0.8V to 3.2V at a current density of 100mA / g.

10 is a discharge graph of each plating temperature of a lithium secondary battery manufactured according to an embodiment of the present invention. Referring to FIG. 10, it can be seen that Examples 1 and 3 exhibit flat voltages of 1.8 V and 1.4 V which are significantly higher than those of the related art, and a discharge capacity close to theoretical capacity (560 mAh / g). In contrast, Comparative Example 3 and Comparative Example 4 did not perform the discharge experiment itself.

11 is a graph showing the discharge cycle for each plating temperature of the lithium secondary battery manufactured according to an embodiment of the present invention. Referring to FIG. 11, it was confirmed that Example 1 and Example 3 can maintain the discharge capacity and efficiency, starting from a high discharge capacity and showing stable cycle characteristics within 10 discharges.

The foregoing description of the present invention is intended for illustration, and it will be understood by those skilled in the art that the present invention may be easily modified in other specific forms without changing the technical spirit or essential features of the present invention. will be. Therefore, it should be understood that the embodiments described above are exemplary in all respects and not restrictive. For example, each component described as a single type may be implemented in a distributed manner, and similarly, components described as distributed may be implemented in a combined form.

The scope of the present invention is represented by the following claims, and it should be construed that all changes or modifications derived from the meaning and scope of the claims and their equivalents are included in the scope of the present invention.

Claims

(i) manufacturing a three-dimensional current collector;

(ii) electroless plating nickel on the three-dimensional current collector;

(iii) sulfiding the nickel plated three-dimensional current collector; Nickel sulfide electrode manufacturing method for a lithium secondary battery comprising a.
The method according to claim 1,

The electroless plating in the step (ii) is a method of manufacturing a nickel sulfide electrode for a lithium secondary battery, characterized in that carried out for a time of 8 minutes to 16 minutes at a temperature of 75 ℃ ~ 95 ℃ and pH of 8 to 10.
The method according to claim 1,

The sulfidation process in the step (iii) is a method of manufacturing a nickel sulfide electrode for lithium secondary battery, characterized in that carried out for a time of 15 minutes to 40 minutes at a temperature of 70 ℃ ~ 90 ℃.
The method according to claim 1,

In step (i),

(i-1) preparing a mixed solution containing a current collector precursor;

(i-2) preparing a current collector precursor fiber by electrospinning the mixed solution;

(i-3) oxidative stabilizing the current collector precursor fibers;

(i-4) carbonizing the oxidatively stabilized current collector precursor fibers to produce a three-dimensional current collector; Nickel sulfide electrode manufacturing method for a lithium secondary battery comprising a.
The method according to claim 4,

Electrospinning in the step (i-2) is performed by discharging the mixed solution at a rate of 1ml / h ~ 3ml / h under the condition that the applied voltage is 15kV ~ 25kV and the distance from the syringe to the collector 15cm ~ 20cm A method of manufacturing a nickel sulfide electrode for a lithium secondary battery.
The method according to claim 4,

The current collector is a polyacrylonitrile (PAN) series, rayon (Rayon) series or pitch (Ni) sulfide electrode manufacturing method for a lithium secondary battery, characterized in that one of.
The method according to claim 4,

In the step (i-3), oxidative stabilization is performed at an elevated temperature of 5 ° C./min in an oxygen atmosphere to be finally maintained at a temperature of 220 ° C. to 280 ° C. for 2 to 4 hours. Manufacturing method.
The method according to claim 4,

In the step (i-4), carbonization is performed in an argon atmosphere at a temperature increase rate of 5 ° C./min and finally maintained at 900 ° C. to 1100 ° C. for 2 to 4 hours to manufacture nickel sulfide electrodes for lithium secondary batteries. Way.
The method according to claim 4,

The three-dimensional current collector is a method of manufacturing a nickel sulfide electrode for lithium secondary battery, characterized in that the carbon felt or carbon mat containing carbon fibers having a diameter of 100nm ~ 500nm.
The method according to claim 4,

The three-dimensional current collector has a density of 0.6g / cm 3 ~ 1.8g / cm 3 The nickel sulfide electrode manufacturing method for a lithium secondary battery.
The nickel sulfide electrode for lithium secondary batteries manufactured by the method of any one of Claims 1-10.
The method according to claim 11,

Nickel sulfide electrode for lithium secondary battery, characterized in that the flexible.
The method according to claim 11,

Nickel sulfide electrode for lithium secondary battery, characterized in that the thickness is 1μm ~ 25μm.
anode;

cathode;

Electrolyte;

Separator; Including,

The positive electrode is a lithium secondary battery of the lithium secondary battery of claim 11, characterized in that the lithium secondary battery.