KR19990000506A - Anode active material composition for nickel-hydrogen battery and manufacturing method of anode for nickel-hydrogen battery using same - Google Patents

Abstract

Binders, shock absorbers, water repellents, and the like selected from the group consisting of a negative electrode active material for nickel-hydrogen batteries, acrylonitrile-rubber, styrene-butadiene rubber, butadiene rubber, acrylate butadiene rubber, chloroprene, acrylic emulsion and mixtures thereof When the negative electrode active material composition for nickel-hydrogen batteries including the thickener is applied to a two-dimensional conductive substrate, a high density hydrogen storage alloy electrode may be manufactured. Therefore, it is possible to maintain the stable adhesion state of the alloy to increase the life of the pole plate, to minimize the amount of binder, to increase the discharge voltage, and to secure the three-phase interface on the surface of the pole plate, thereby reducing the internal pressure of the battery to enable sealing. have.

Description

Anode active material composition for nickel-hydrogen battery and manufacturing method of anode for nickel-hydrogen battery using same

[Industrial use]

The present invention relates to a negative electrode active material composition for nickel-hydrogen batteries, and more particularly, to a negative electrode active material composition for a nickel-hydrogen battery capable of producing a high capacity battery and a method for producing a negative electrode for nickel-hydrogen batteries using the same.

[Prior art]

Recently, with the trend toward miniaturization and lightening of new portable electronic devices such as camera-integrated VTRs, audio, laptop personal computers, portable telephones, and the like, there is a need for a technology for increasing the performance and capacity of batteries used as power sources for these devices. In particular, efforts are being made to develop technologies that reduce manufacturing costs of these batteries, particularly in economic terms. Generally, batteries include primary cells used for single use, such as manganese batteries, alkaline batteries, mercury batteries, and silver oxide batteries, Ni-MH (nickel-metal hydride) batteries using lead-acid batteries and metal hydrides as negative active materials, and sealed types. Rechargeable batteries such as nickel-cadmium batteries and lithium-metal batteries, lithium-ion batteries (LIB: Lithium Ion Battery), lithium group batteries such as Lithium Polymer Battery (LPB), and the like; It can be divided into fuel cell, solar cell and the like.

Among them, primary batteries have a small capacity, short lifespan, and cannot be recycled, causing environmental pollution. On the other hand, secondary batteries can be recharged and used for a long time, and voltage is much higher than that of primary batteries. It is excellent in terms of efficiency and efficiency, and generates less waste, which is also excellent in environmental protection.

Among the secondary batteries described above, nickel-based batteries are most used because they have the most established recycling technology and are excellent in terms of environmental protection.

Among the nickel-based batteries, Ni-Cd batteries are well known and used in various fields. However, Ni-Cd batteries have a problem of causing environmental pollution due to cadmium. Recently, nickel-hydrogen batteries using high-density and non-polluting hydrogen storage alloy electrodes are used. There is a growing interest in. The hydrogen storage alloy electrode uses a hydrogen storage alloy having a characteristic of absorbing and releasing hydrogen at low pressure in a battery. In order to manufacture a sealed nickel-hydrogen secondary battery using the hydrogen storage alloy electrode, the following methods have been used so far.

1) Method of manufacturing electrode plate by sintering powder of hydrogen storage alloy together with electrically conductive conductive agent

2) A method of injecting or loading a hydrogen storage alloy into a porous substrate having an electrically conductive three-dimensional structure such as foamed nickel

3) A method of attaching a hydrogen storage alloy with a polymer binder such as PTFE (polytetrafluoroethylene) to a porous substrate having an electrically conductive two-dimensional structure

In the first method, the sintering method oxidizes the surface of the hydrogen storage alloy during the sintering process, thereby suppressing the adsorption and release of hydrogen, thereby lowering the conductivity of the electrode and lowering the discharge voltage. Will be imported.

Second, the method of using the 3D porous substrate may show advantageous properties in many aspects of the battery, but the capacity of the hydrogen storage alloy is severely limited compared to the volume occupied by the electrode plate, so the capacity of the battery must be designed small. In addition, there is a problem in price competitiveness because the price of the three-dimensional porous substrate is quite expensive.

Third, the method of using the porous substrate of the two-dimensional structure is advantageous to increase the energy density of the electrode by the efficient use of the electrode plate space, but it is difficult to bind the alloy to the current collector of the two-dimensional structure due to the weak adhesive force There is this. In order to bind the hydrogen storage alloy to the current collector having a two-dimensional structure, a large amount of polymer binder must be added. Since the binder is an insulator, the conductivity of the electrode plate is lowered, thereby lowering the discharge voltage. In addition, due to the thickening of the binder film, it is difficult to absorb and release hydrogen gas into and out of the alloy. As a result, the hydrogen balance pressure and the reaction rate are lowered, resulting in an increase in battery pressure and a decrease in high rate charge and discharge characteristics. have.

The present invention is to solve the above problems, an object of the present invention is first, by using a binder having excellent binding effect by attaching a hydrogen storage alloy to a two-dimensional porous substrate nickel that can increase the energy density of the entire battery It is to provide a negative electrode active material composition for a hydrogen battery, and second, to provide a method for producing a negative electrode for a nickel-hydrogen battery that can produce a high capacity nickel-hydrogen battery negative electrode using the same.

[Means for solving the problem]

The present invention to achieve the above object is a negative electrode active material for nickel-hydrogen battery; Shock absorbers; Water repellents; Thickeners and acrylonitrile-rubbers, styrene-butadiene rubbers, butadiene rubbers, acrylate butadiene rubbers chloroprene, acrylic emulsions It provides a negative electrode active material for a nickel-hydrogen battery comprising a binder selected from the group consisting of) and mixtures thereof.

In the present invention described above, the amount of the binder is preferably 0.2 to 3% by weight based on the negative electrode active material.

In the present invention, the water repellent is a fluorine resin having a surface energy of 10 to 20 dyne / cm, or a fluorine resin having an amorphous form, or the dispersion solvent is C ₃ F ₈ , C ₄ F ₁₀ , C ₅ F ₁₂ , C ₅ F ₁₁ NO, C ₆ F ₁₄ , C ₇ F ₁₆ , C ₈ F ₁₈ , CCl ₃ F, CCl ₂ F ₂ , C ₂ F ₃ Cl ₃ , C ₂ Cl ₃ F ₄ , C ₂ ClF ₅ It is preferable that it is a fluororesin which is a fluorocarbon solution chosen from.

In the present invention described above, the shock absorbing agent uses nickel powder having a tapped density of 1.3 g / cm 3 in an amount of 3 to 5 wt% based on the weight of the alloy, or carbon black as described above. It is preferable to use in an amount of 0.05 to 0.4% by weight based on the weight.

In the present composition, the nickel-hydrogen battery negative electrode active material is selected from the group consisting of CeO ₂ , Y ₂ O ₃ , Ca (OH) ₂ , Yb ₂ O ₃ The antioxidant alloy is 1 to the weight of the hydrogen storage alloy It is preferable to coat in an amount of -5% by weight.

In the present invention, the thickener is preferably selected from the group consisting of methyl cellulose, carboxymethyl cellulose, hydroxypropyl methyl cellulose.

A binder for the negative electrode active material composition of a nickel-hydrogen battery comprising a compound selected from the group consisting of acrylonitrile-rubber, styrene-butadiene rubber, butadiene rubber, acrylate butadiene rubber, chloroprene and acrylic emulsion or a mixture thereof. to provide.

The present invention also provides a method for producing a negative electrode for a nickel-hydrogen battery, including a step of coating a current collector with the negative electrode active material composition for a nickel-hydrogen battery.

In the present invention described above, it is preferable that the current collector uses a metal plate having a two-dimensional structure with electrical conductivity in which regular holes are dug.

[Action]

The sealed nickel-hydrogen secondary battery has a negative electrode charge / discharge reservoir to suppress an increase in internal pressure due to hydrogen gas not absorbed in the negative electrode plate during charging and oxygen generated from the positive electrode during overcharge, and also to protect the battery during overcharge and overdischarge. Must be given separately. For this reason, the capacity of the cathode is designed to be larger than that of the anode. Therefore, in order to increase the energy density of the entire battery, it is advantageous to have a high energy density of the negative electrode plate, and a method of manufacturing the electrode plate capable of satisfying this condition is a method of coating the active material of the negative electrode on a porous metal plate having an electrically conductive two-dimensional structure.

Unlike the positive electrode active material composition using nickel hydroxide, the negative electrode active material composition using the hydrogen storage alloy does not need a separate conductive agent because the conductivity is very good. However, a separate strong binder was needed because the mixture was kneaded and fixed on a two-dimensional thin plate.

The inventors have studied various polymers as binders for attaching hydrogen storage alloys to electrically conductive two-dimensional porous metal substrates and found that polymers having the following physical properties are useful as binders. First of all, it should be stable to alkaline aqueous solution of battery, stable to some temperature, and easy to handle chemically and physically. In addition, when a large number of binders are used, the internal pressure of the battery increases and problems such as deterioration of high rate charge / discharge characteristics occur. In addition, when the pole plate group is inserted into the sealed battery, it is bent in the form of a cylinder, so the flexibility and elasticity that can withstand a certain physical impact on the pole plate are required. In addition, since the mixture to be the electrode plate must be applied to the current collector in a dough state, it must be able to be dispersed in an aqueous liquid. The inventors have found that SBR (styrene-butadiene-rubber), BR (butadiene-rubber: butadiene-rubber), NBR (acrylonitrile-butadiene-rubber), CR (chloroprene: As a result of using aqueous dispersions such as chloroprene) and acrylic aqueous emulsions as binders to bind hydrogen storage alloys to current collectors having a two-dimensional structure, the present inventors have found that the above properties are satisfied.

All of the above materials had similar effects, but especially SBR, NBR, and acrylic emulsions showed excellent characteristics. In addition, the amount of the solid content is preferably 0.2 to 3% by weight relative to the alloy. If a larger amount is added, the conductivity of the electrode plate is lowered in proportion to the discharge voltage, and the thickness of the binder film becomes thicker, which makes it difficult to absorb and release hydrogen gas into and out of the alloy. As a result, the hydrogen balance pressure is increased and the reaction rate is lowered. This results in an increase in battery pressure and a decrease in high rate charge / discharge characteristics. On the contrary, when the alloy is insufficient, the alloy has a poor binding force on the current collector substrate, and the electrode plate is extremely weak to physical and chemical impacts.

In addition, the hydrogen storage alloy is required to increase the durability of the alloy and to increase the oxygen overvoltage of the anode because it causes micro-degradation and surface oxidation due to repeated electrode reactions. To this end, CeO ₂ was coated on the surface of the metal and had an effect of inhibiting oxidation at high temperatures.

In addition, since a viscosity of a certain viscosity or more is required to apply the mixture of the alloy and the binder to the electrode plate, CMC (carboxy methyl cellulose sodium salt: carboxy methyl cellulose sodium salt), which is generally used, was used as a thickener.

In addition, the lower the viscosity of the slurry (mixture of the mixture), the greater the fluidity, the easier it is to handle the slurry, but the greater the specific gravity of the alloy, the greater the specific gravity of the slurry as a whole, the greater the need to prevent flow down when applied to the current collector substrate There is a problem to increase the viscosity of the slurry. In addition, there is a problem that the viscosity of the slurry must be high in order for the slurry to be applied to the current collector due to the relatively high specific gravity of the slurry mainly composed of an alloy. In order to increase the viscosity of the slurry, it is necessary to increase the amount of CMC, which is added thickener, and to reduce the amount of water. However, when the viscosity of the slurry is high, the mixture is not dispersed well and much care and equipment are required to handle the slurry itself during the process. For example, if the viscosity is high, many bubbles are generated, and thus a method of removing bubbles is additionally required. In addition, as the electrode reaction continues, the absorption and release of hydrogen into and out of the hydrogen storage alloy is continuously performed. As a result, the shrinkage and expansion of the alloy lead to the micronization of the alloy and the phenomenon of the alloy falling off from the electrode plate. do. In particular, in the absence of a buffer as a shock absorber around the alloy, one alloy shock wave spreads over the entire electrode plate to accelerate the dropping of the active material. In order to improve this phenomenon, a material having a very low density but not impairing the conductivity of the battery is required. Nickel powder, graphite powder, and carbon black are examined to find that nickel powder and carbon black are suitable as shock absorbers for the above-mentioned applications. It was.

In addition, the hydrogen gas and the oxygen gas generated during charging basically need to be efficiently absorbed from the negative electrode so that the internal pressure of the battery does not increase and the battery can be sealed. To this end, it is possible to increase the three-phase interface of the alloy, the electrolyte and the gas on the surface of the negative electrode, so that a method of coating the surface of the negative electrode with a water repellent having a water repellent effect was examined. Fluorine resins with low surface tension were effective as water repellents. Among them, morphologically fluorine resins such as FC722, 3M's product, were dispersed in a low surface tension perfluorocarbon solvent such as PF5060. It was found that immersion coating of CVD was most advantageous in forming a uniform film over the entire electrode plate while reducing the thickness of the coating, and the effect of reducing the pressure resistance of the battery was also the greatest, and side effects due to the formation of an insulator film on the negative electrode surface were minimized.

EXAMPLE

Hereinafter, preferred examples and comparative examples of the present invention are described. However, the following examples are only one preferred embodiment of the present invention and the present invention is not limited to the following examples.

(Example 1)

An SBR suspension having 48% solids concentration as a binder was added to 100 g of hydrogen storage alloy (ce rich Mm as a composition formula of MmNi _3.55 Al _0.3 Mn _0.4 Co _0.75 ) to adjust the amount of solids to 1 g. Subsequently, 0.2 g of CMC was added as a thickener, and 0.6 g of Ketjen Black, a shock absorber, was added for the purpose of lowering the specific gravity of the slurry and absorbing the physical electrochemical impact of the plates. ) 0.2 wt% was added to prepare a negative electrode active material composition for a nickel-hydrogen battery. The rolled electrode plate was immersed in this composition to prepare a negative electrode for a nickel-hydrogen battery. This was inserted into a battery can together with a nickel anode, a separator, and an electrolyte to prepare a 4 / 5A size 1800mAh battery. The N / P ratio at this time was 1.6.

(Example 2)

An acrylic emulsion was added in the same manner as in Example 1, except that the amount of the solid emulsion was 1 g.

(Example 3)

3% by weight of CeO ₂ was added to the hydrogen storage alloy, and the mixture was stirred in a ball mill (ball mill) for 24 hours, except that the hydrogen storage alloy was used in the same manner as in Example 1.

(Example 4)

For the purpose of lowering the specific gravity of the slurry and absorbing the physical electrochemical impact of the electrode plate, it was prepared in the same manner as in Example 1 except that 3g of nickel powder having a low specific gravity fiber form was added instead of Ketjen Black.

(Comparative Example 1)

It was prepared in the same manner as in Example 1 except that PTFE (polytetrafluoroethylene) was used as the water repellent.

(Comparative Example 2)

It was prepared in the same manner as in Example 1 except that 2 g of PTFE was added as a binder.

(Comparative Example 3)

A battery was manufactured in the same manner as in Example 1, except that Catchen Black was not added. However, additives other than the alloy were reduced by a certain amount by calculating the volume ratio by the ratio of the loss of Caten Black.

The utilization rate, lifespan, and internal pressure of the batteries prepared according to the methods of Examples and Comparative Examples described above were measured, and the results are shown in Table 1 below.

TABLE 1

Utilization [%] Cycle life Internal pressure [kgf / ㎠] Example 1 105 552 5 Example 2 105 531 6 Example 3 108 632 5 Comparative Example 1 105 411 16 Comparative Example 2 80 252 14 Comparative Example 3 110 352 7

(Utilization: Measured capacity per unit weight of the negative electrode alloy with half cell, expressed as a percentage based on 270mAh / g)

Lifespan: Cycles from 1C charge / discharge to 90% of initial capacity)

As described above, when the negative electrode active material composition for nickel-hydrogen battery of the present invention is applied to a two-dimensional conductive substrate, a high density hydrogen storage alloy electrode can be manufactured. Therefore, the stable life of the alloy increases the life span of the pole plate, the discharge voltage is high by minimizing the amount of binder, and the internal pressure of the battery is reduced due to the sufficient securing of three-phase interface on the surface of the pole plate, enabling the sealing. There is.

Claims (16)

Negative electrode active materials for nickel-hydrogen batteries; Shock absorbers; Water repellents; Thickeners; A binder selected from the group consisting of acrylonitrile-rubber, styrene-butadiene rubber, butadiene rubber, acrylate butadiene rubber, chloroprene and acrylic emulsion and mixtures thereof; A negative electrode active material composition for a nickel-hydrogen battery containing. The composition of claim 1, wherein the amount of the binder is 0.2 to 3% by weight based on the negative electrode active material. The composition according to claim 1, wherein the water repellent is a fluorine resin having a surface energy of 10 to 20 dyne / cm. The composition of claim 1 wherein the water repellent is a fluororesin in amorphous form. The composition of claim 1, wherein the water repellent is a fluororesin in which the dispersing solvent is a fluorocarbon solution. The method of claim 5, wherein the fluorine carbon is C ₃ F ₈ , C ₄ F ₁₀ , C ₅ F ₁₂ , C ₅ F ₁₁ NO, C ₆ F ₁₄ , C ₇ F ₁₆ , C ₈ F ₁₈ , CCl ₃ F, CCl ₂ F ₂ , C ₂ F ₃ Cl ₃ , C ₂ Cl ₃ F ₄ , C ₂ ClF _{5 The} composition is selected from the group consisting of. The negative electrode active material composition of claim 1, wherein the shock absorber is nickel powder or carbon black. The composition of claim 7, wherein the nickel powder has a density of 1.3 g / cm 3 and uses 3 to 5 wt% based on the weight of the alloy. 8. The composition of claim 7, wherein the carbon black uses 0.05 to 0.4 wt% based on the weight of the alloy. The composition of claim 1, wherein the negative active material for the nickel-hydrogen battery is a hydrogen storage alloy. The composition of claim 10, wherein the hydrogen storage alloy is coated with an antioxidant alloy selected from the group consisting of CeO ₂ , Y ₂ O ₃ , Ca (OH) ₂ , Yb ₂ O ₃ . The composition of claim 11, wherein the coating amount of the antioxidant alloy is 1 to 5% by weight based on the weight of the hydrogen storage alloy. The composition of claim 1 wherein the thickener is selected from the group consisting of methylcellulose, carboxymethylcellulose, hydroxypropyl methylcellulose. A binder for the negative electrode active material of a nickel-hydrogen battery comprising a compound selected from the group consisting of acrylonitrile-rubber, styrene-butadiene rubber, butadiene rubber, acrylate butadiene rubber, chloroprene and acrylic emulsion or a mixture thereof. Coating the current collector with the negative electrode active material composition for a nickel-hydrogen battery of claim 1; The manufacturing method of the negative electrode for nickel-hydrogen batteries containing a process. The manufacturing method according to claim 15, wherein the current collector is a metal plate having a two-dimensional structure having electrical conductivity with regular holes.