KR101627372B1 - Nanosheet-shaped nickel metal by mechanochemical reduction, and fabrication method of positive electrode of Ni-based alkaline storage battery using the same - Google Patents

Abstract

The present invention relates to a nano-sheet-shaped nickel metal by mechanochemical reduction, and a method of preparing a nickel-based alkaline secondary battery using the same. More specifically, the present invention relates to a method for preparing a nickel salt mixture by mixing a nickel salt with NaBH ₄ ; Applying shear stress to the nickel salt mixture; And forming a nano-sheet-like nickel metal as a result of the shear stress applied. The method of manufacturing a nano-sheet-like nickel metal by mechanochemical reduction, . ≪ / RTI >
According to the present invention as described above, the nano-sheet-like nickel metal produced by the mechanochemical reduction method is added to a positive electrode made of nickel hydroxide (Ni (OH) ₂ ) powder to improve the electric conductivity (impedance spectroscopy standard) It is anticipated that the effect of suppressing the voltage drop of the anode and improving the discharge efficiency of the battery at the time of discharging is expected.

Description

[0001] The present invention relates to a method of manufacturing a positive electrode of a nickel-based alkaline secondary battery using nanosheet-shaped nickel metal by mechanochemical reduction, and a method of manufacturing a positive electrode of nickel-based alkaline secondary battery using the nickel-

The present invention relates to a nano-sheet-shaped nickel metal by mechanochemical reduction, and a method of preparing a nickel-based alkaline secondary battery using the same. More specifically, the present invention relates to a method for preparing a nickel salt mixture by mixing a nickel salt with NaBH ₄ ; Applying shear stress to the nickel salt mixture; And forming a nano-sheet-like nickel metal as a result of the shear stress applied. The method for producing a nano-sheet-like nickel metal by mechanochemical reduction, The method comprising:

Recently, the demand for light weight / high energy density, longevity and environmental friendliness of batteries used as the power source of these devices has been urgently demanded in accordance with the trend of high performance / light weight, multifunctionality and environment friendliness of mobile electronic devices including smart phones . In accordance with this trend, the use of existing nickel-cadmium batteries or lead acid batteries has become more and more strictly regulated due to environmental pollution problems. The Ni-MH battery has a higher energy density than the nickel-cadmium battery and is free from pollutants. Therefore, the Ni-MH battery has been actively studied for performance improvement as a secondary battery capable of being developed as a high performance battery.

In addition, there has been a recent blackout due to inconsistency in power demand-supply, and the need for an energy storage system as an emergency power source in terms of efficient power utilization, high quality power, and stable power supply in the mid- to long- Is increasing. An energy storage system (ESS) is a system that stores produced power and supplies it at the time when power is most needed to improve energy efficiency. Battery is a key component to store electricity. Research on NaS batteries and flow cells is under way, but the results are insufficient.

Of these, the NaS cell is a battery using high-temperature sulfur and molten sodium at 300 ° C or higher, and NGK of Japan installed the actual ESS. However, it is necessary to operate the equipment at a high temperature and disadvantage of using sulfur which is a harmful substance And the V-type or Ni-Zn type Redox Flow battery is a battery that charges / discharges by forcibly circulating a positive-negative electrode electrolyte. It is advantageous in that the investment cost is low, but the disadvantage is that the conversion efficiency is low and the operation cost is high.

Nickel hydroxide (Ni (OH) ₂ ) powder is used as a positive electrode active material of a nickel-based alkaline _secondary battery including a Ni-MH battery. However, since a binding force between powders is weak, However, this has a problem in that the overall electrical conductivity is further deteriorated by adding a binder having a poor electrical conductivity to the anode composed of nickel hydroxide (Ni (OH) ₂ ) which is originally poor in electrical conductivity.

Therefore, in order to overcome such a problem, an anode is prepared by adding metal nickel powder or cobalt oxide (CoO) or the like. When CoO is added, the oxygen overpotential is increased to reduce the amount of oxygen generated in the anode. (Japanese Patent Laid-Open Nos. 2006-525645 and 2013-243142).

When CoO is added to the cathode active material, CoO is converted to cobalt hydroxide (Co (OH) ₂ ) in the electrolyte and oxidized to cobalt oxyhydroxide (CoOOH), so that the cobalt oxyhydroxide reacts with the nickel hydroxide particles and between the nickel hydroxide and the collector Thereby improving the electrical conductivity of the substrate. However, since the amount of CoO to be added at this time is very high, it is inevitable to add a small amount of CoO. Therefore, when a small amount of CoO is added, the electrical conduction path is uneven, thereby deteriorating the reliability of battery performance.

In order to overcome the problem of lowering the electrical conductivity of the electrode due to the binder added to supplement the weak bonding force of the nickel hydroxide (Ni (OH) ₂ ) powder used as the positive electrode active material of the nickel-based alkaline _secondary battery as described above As a result, it has been proposed that the nano-sheet-like nickel metal produced by the mechanical chemical reduction method is added to a positive electrode made of nickel hydroxide (Ni (OH) ₂ ) powder to improve the electrical conductivity of the positive electrode, And to improve the discharge efficiency of the battery.

Another object of the present invention is to replace the expensive CoO to lower the manufacturing cost and to manufacture a positive electrode having excellent electrical properties nevertheless.

In order to achieve the above-mentioned object,

Comprising: a mixture of a nickel salt with NaBH ₄ to prepare a nickel salt mixture; Applying shear stress to the nickel salt mixture; The present invention also provides a method of manufacturing a nanosheet-shaped nickel metal by mechanochemical reduction, wherein the nanosheet-shaped nickel metal is produced as a result of the shear stress.

The nickel salt is a hydrochloric acid nickel (NiCl ₂ 6H ₂ O), nickel sulfate (NiSO ₄揃 6H ₂ O), or nickel nitrate (Ni (NO ₃ ) ₂揃 6H ₂ O).

In the step of preparing the nickel salt mixture, it is preferable to further add a decomposition retarding solvent.

The decomposition retarding solvent is preferably at least one selected from the group consisting of isopropyl alcohol, t-butyl alcohol and diglyme.

It is preferable that the NaBH ₄ has a value at least twice as much as that of the nickel salt based on the molar concentration.

In the step of preparing the nano-sheet-like nickel metal, the heat treatment is preferably performed in a hydrogen atmosphere.

The heat treatment is preferably performed under the conditions of a temperature of 300 to 450 DEG C and a heat treatment time of 30 minutes to 2 hours.

In the step of producing the nano-sheet-like nickel metal as a result of the shear stress, the method may further include a step of forming an amorphous nano-sheet-like nickel metal, followed by filtration to remove impurities.

Further, the present invention is produced by the above-mentioned method,

The present invention also provides a nano-sheet-like nickel metal produced by mechanochemical reduction characterized by having crystalline properties.

The present invention also relates to a process for producing a mixture comprising: mixing a raw material containing Ni (OH) ₂ , graphite, carbon black, nickel nanosheets and a binder to form a mixture; Immersing the mixture in a nickel foam; And a step of compressing and drying the nickel-based alkaline secondary battery using the nickel-metal-like nano-sheet by mechanical chemical reduction.

The nickel nanosheets are preferably mixed at least 5% by weight based on the weight of the mixture.

Further, the present invention is produced by the above method,

And the electrode resistance by impedance spectroscopy is 1 Ω · cm or less. The present invention also provides a nickel-based alkaline secondary battery using nanosheet-shaped nickel metal by mechanochemical reduction.

According to the present invention as described above, the nano-sheet-like nickel metal produced by the mechanochemical reduction method is added to a positive electrode made of nickel hydroxide (Ni (OH) ₂ ) powder to improve the electric conductivity of the positive electrode, It is expected that the voltage drop suppression and the discharge efficiency of the battery are improved.

In addition, the present invention is expected to have an action effect of replacing expensive CoO to lower the cost of manufacture, and nevertheless making it possible to produce a positive electrode having excellent electrical properties.

1 is a graph showing the results of X-ray diffraction analysis of a nickel nano-sheet before and after a heat treatment according to an embodiment of the present invention.
2 is a transmission electron micrograph of a nickel nanosheet before and after a heat treatment according to an embodiment of the present invention.
3 is a graph showing impedance analysis results of a positive electrode to which a nickel nanosheet is added according to an embodiment of the present invention.
4 is a graph showing the results of charging / discharging tests on a positive electrode to which 5 wt% of nickel nanosheet is added according to an embodiment of the present invention.
FIG. 5 is a graph showing a charge / discharge test result on a positive electrode to which 10 wt% of nickel nano-sheet is added according to an embodiment of the present invention.
6 is a graph showing the results of charging / discharging tests on a positive electrode to which a nickel nano-sheet is not added according to a comparative example.

Hereinafter, the present invention will be described in more detail with reference to the accompanying drawings and preferred embodiments.

The present invention hydrochloric acid nickel (NiCl ₂ · 6H ₂ O), nickel sulfate (NiSO ₄ · 6H ₂ O) or nickel nitrate _{(Ni (NO 3) 2 ·} 6H 2 O) , such as the NaBH ₄ and the mixture that acts as a reducing agent, a nickel salt comprising one embodiment For example, a solvent for delaying the decomposition of NaBH ₄ such as isopropyl alcohol in a mixing apparatus in which shear stress acts, etc., preferably for at least 30 minutes to produce an amorphous nano-sheet-like nickel metal metal, NaCl and other impurities are removed to synthesize amorphous nano-sheet-like nickel metal. The amorphous nickel is heat-treated at 400 ° C for 1 hour in a 3% hydrogen atmosphere to produce nano-sheet-like metal nickel powder to prepare a synthesis method of a metal powder which is characterized and the nickel metal nano-sheet shape, and then, to this nickel preferably powdered nickel hydroxide (Ni (OH) ₂₎ min. By addition to produce a positive electrode to provide a method that can improve the discharge efficiency of suppressing the voltage drop of a nickel-alkaline secondary battery positive electrode and the battery.

In the heat treatment process, a temperature range of 300 to 450 ° C. can be applied. In order to crystallize the nickel metal, a temperature of at least 300 ° C. is required. In order to prevent a decrease in the specific surface area associated with the activity, Therefore, there is a critical significance in the above range.

In addition, the NaBH ₄ should be added at a molar concentration of at least twice the molar concentration of the nickel salt. If the molar concentration is lower than the molar concentration, the reducing ability of nickel may be deteriorated.

The present invention relates to a method for producing nickel (Ni (OH) ₂ ) powders by adding nickel metal nanosheet-shaped nickel metal produced by mechanochemical reduction represented by the following reaction formula to a nickel hydroxide Can be suppressed and the discharge efficiency of the battery can be improved.

Ni ^{2 +} X + 2NaBH ₄ → Ni ⁰ + 2NaX + B ₂ H ₆ + H ₂ (X = Cl ^- , (NO ₃ ) ^-, etc.) --- (1)

Ni ^{2 +} Y + 2NaBH ₄ → Ni ⁰ + Na ₂ Y + B ₂ H ₆ + H ₂ (Y = (SO ₄ ) ² -

≪ Example 1 >

In order to synthesize Ni (OH) ₂ having a high specific surface area, which is a main material of an anode, a nickel cation raw material component is preferably injected into a fine droplet of 5 μm or less by ultrasonic atomization. However, it is preferable to use an ultrasonic spray method in order to improve the efficiency of the synthesis. Cobalt (Co) may be added to the Ni (OH) ₂ .

More specifically, by adopting a nickel hydroxide synthesis method by chemical precipitation in an alkali solution, 0.97 M of purity 99.5% NiSO ₄ .6H ₂ O and 0.03 M of Co (NO ₃ ) ₂ .6H ₂ O as a nickel cation raw material For example, a nickel salt solution for use in ultrasonic spraying was prepared by dissolving in 1 L of distilled water.

As a raw material for the alkaline solution to cause the chemical precipitation reaction, 2M purity 99.8% potassium hydroxide (KOH) was dissolved in distilled water. Thereafter, while the potassium hydroxide solution was stirred at a speed of 500 rpm, the nickel salt solution was dropletized through a 130 kHz ultrasonic atomizing nozzle and sprayed at a rate of 20 ml / min to induce a chemical precipitation reaction, Co) - added Ni (OH) ₂ precipitates were synthesized.

The precipitated Ni (OH) ₂ precipitate was filtered with distilled water until the filtrate became neutral, filtered, packed in a 500 ml PTFE vessel and heated in an autoclave at 120 ° C for 24 hours Hydrothermally synthesized. The resultant hydrothermal synthesis was filtered again with distilled water and ethanol to remove impurities such as alkali ion component and hydroxide ion and dried at 80 ° C for 24 hours to finally obtain cobalt (Co) -added Ni (OH) ₂ powder.

The above numerical values are preferably adopted, but are not limited to the above values as long as the Ni (OH) ₂ powder added with the desired Co can be obtained. The PTFE material may also be replaced by other materials.

The nanosheet-shaped nickel metal for producing the positive electrode was prepared by a mechanochemical reduction method, as described above.

The crystal structure of nickel before and after the heat treatment was analyzed by X-ray diffraction analysis and the shape of metallic nickel powder was analyzed by transmission electron microscope (TEM), which are shown in FIG. 1 and FIG. 2, respectively.

As can be seen from FIG. 1, the nickel immediately before the synthesis, before the heat treatment, shows amorphous, and the powder subjected to the heat treatment in a 3% hydrogen atmosphere at 400 ° C for 1 hour shows nickel crystalline quality.

It can also be confirmed that the shape of the nickel synthesized from FIG. 2 shows a nanosheet shape. More specifically, the TEM photograph shown in Fig. 2 (a) means a wrinkled sheet shape of a nano-sized scale. In the case of a typical manufacturing method, a mechanochemical reduction method of applying shear stress as in the present invention, Of nickel metal is produced.

Ni (OH) ₂ powder and nano sheet-like nickel metal synthesized under the above conditions were mixed so that Ni (OH) ₂ : graphite: carbon black: nickel nanosheet was 50: 40: 5: 5 by weight, And PTFE as a binder was added and mixed as an aqueous solution so as to be 5 wt% based on the weight of the mixture.

Here, the content of Ni (OH) ₂ , graphite and carbon black can be controlled within a known content range, but it is preferable that at least 5 parts by weight of the nickel nanosheet according to an embodiment of the present invention is added. This is because the addition of the nickel metal effectively suppresses the voltage drop of the anode and improves the discharge efficiency of the battery significantly above the upper weight portion.

Thereafter, the mixture was dipped in nickel pores having a pore density of 110 ppi (pore per inch) using the mixture as a current collector, pressed at a pressure of 3 MPa at 80 ° C for 15 minutes, and dried to obtain a nickel- Each composition is shown in Table 1, and electrode resistance measurement results by impedance analysis are shown in FIG. 3, respectively.

Item Ni (OH) 2
(weight%) Graphite
(weight%) Ni
(weight%) Carbon black
(weight%) PTFE
(weight%) One 50 45 0 5 5 2 50 40 5 5 5 3 50 35 10 5 5

As shown in FIG. 3, when 5 wt% of nano-sheet-like nickel metal was added, the electrode resistance value was 0.6 Ω · cm, which was 40% lower than that when nano-sheet-like nickel metal was not added. The resistance reduction effect was confirmed.

The cell was constituted by using a nickel hydroxide foam having a pore density of 110 ppi (pore per inch) and a potassium hydroxide (KOH) solution having a concentration of 8M as an electrolyte, and a charge / discharge test was conducted. Charging and discharging conditions were carried out under relatively high-speed charging and discharging conditions (2C) capable of charging and discharging the total electrochemical charging and discharging capacity of the anode in 0.5 hour, and the results are shown in Table 2 and FIG.

Discharge capacity
(mAh / g) Discharge efficiency
(%) Discharge energy density
(mW / g) Discharge energy density efficiency (%) 0 wt% addition 238.2 82.4 361.1 67.5 5 wt% addition 240.3 83.3 381.1 71.2 10 wt% added 252.5 87.4 420 78.5

As can be seen from Table 2, the discharge efficiency of the nickel-based alkaline secondary battery was somewhat increased. In particular, the discharge energy efficiency was significantly improved by about 4% from 67.5% to 71.2% when no nano-sheet nickel metal was added can confirm.

Meanwhile, as shown in FIG. 4, it can be confirmed that the discharge energy efficiency is improved due to the suppression of the voltage drop of the anode due to the addition of the nano-sheet-shaped nickel metal.

≪ Example 2 >

Ni (OH) ₂ powder and nano-sheet-like nickel metal were prepared according to the above <Example 1>.

Ni (OH) ₂ powder and nano-sheet-like nickel metal synthesized under the above conditions were mixed so that Ni (OH) ₂ : graphite: carbon black: nickel nanosheet was 50: 35: 5: 10 by weight, And PTFE as a binder was added and mixed as an aqueous solution so as to be 5 wt% based on the weight of the mixture.

The mixture was immersed in nickel pores having a pore density of 110 ppi (pore per inch) using the mixture as a current collector, pressed at a pressure of 3 MPa at 80 캜 for 15 minutes and dried to prepare a nickel-based alkaline secondary battery cathode Each composition is shown in Table 1, and an electrode resistance measurement result by impedance analysis is shown in Fig.

As can be seen from Fig. 3, when the electrode resistance was 10% by weight in the case of addition of 10% by weight of the nano-sheet-like nickel metal, the resistance was decreased by 90% The resistance reduction effect can be confirmed.

The configuration of the cathode and the cell, and the charge-discharge test were performed in accordance with Example 1, and the results are shown in Table 2 and FIG.

As can be seen from Table 2, the discharging efficiency of the nickel-based alkaline secondary battery was 87.4% and the discharging energy efficiency was 78.5%, which was higher than that of Example 1 in which 5 parts by weight of the nano- The effect of addition of sheet-like nickel metal is more clearly shown.

Meanwhile, as shown in FIG. 5, it can be confirmed that the voltage drop of the anode is further suppressed according to the second embodiment, thereby improving the discharge efficiency and the discharge energy efficiency.

&Lt; Comparative Example 1 &

The cobalt (Co) -added Ni (OH) ₂ powder was prepared according to the above <Example 1>.

Ni (OH) ₂ : graphite: carbon black having a weight ratio of 50: 45: 5 was added to the cobalt (Co) -containing Ni (OH) ₂ powder synthesized under the above- Then, PTFE was added and mixed as an aqueous solution so that 5 parts by weight of PTFE was contained as a binder.

Thereafter, the mixture was dipped in nickel pores having a pore density of 110 ppi (pore per inch) using the mixture as a current collector, pressed at a pressure of 3 MPa at 80 ° C for 15 minutes, and dried to obtain a nickel- Each composition is shown in Table 1, and electrode resistance measurement results by impedance analysis are shown in FIG. 3, respectively.

As shown in FIG. 3, it was confirmed that the electrode resistance without addition of the nano-sheet-like nickel metal exhibits 1.0 Ω · cm and exhibits a higher electrode resistance than the electrode prepared by adding the nano-sheet-like nickel metal .

On the other hand, the structure of the cathode and the cell was performed in accordance with Example 1, and the results are shown in Table 2 and FIG.

As can be seen from Table 2, the discharge efficiency and the discharge energy density efficiency are the lowest.

In addition, as shown in FIG. 6, in the case of this comparative example, a very large voltage drop appears at the anode, which indicates that the discharge efficiency and the discharge energy efficiency are poor.

While the present invention has been particularly shown and described with reference to exemplary embodiments thereof, it is to be understood that the invention is not limited to the disclosed exemplary embodiments, but, on the contrary, the invention is not limited thereto.

Claims (12)

delete delete delete delete delete delete delete delete delete Ni (OH) ₂ , graphite, carbon black, nickel nanosheets and a binder to prepare a mixture;
Immersing the mixture in a nickel foam;
Pressing and pressing after the immersion;
Wherein the nickel-based alkaline secondary battery is manufactured by a mechanochemical reduction method using nickel metal in the form of nanosheets. 11. The method of claim 10,
Wherein the nickel nanosheets are mixed at least 5 wt% with respect to the weight of the mixture. 11. A process for producing a polyurethane foam according to claim 10 or claim 11,
Characterized in that the electrode resistance by impedance spectroscopy is 1 Ω · cm or less. The positive electrode of nickel-based alkaline secondary battery using nanosheet-shaped nickel metal by mechanochemical reduction.

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