JP2008269913A - Method for manufacturing nickel positive electrode for alkaline storage battery - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a method for stably manufacturing a nickel hydroxide electrode excellent in life time characteristics for an alkaline storage battery in which a cobalt oxide layer having high density and high conductivity is formed on a surface of a porous nickel sintered substrate, thereby assuring conductivity by improvement of oxidation resistance of the sintered substrate. <P>SOLUTION: The method for manufacturing a nickel positive electrode for an alkaline storage battery includes a first step drying a porous nickel sintered substrate after immersing it in a cobalt nitrate solution, a second step changing cobalt nitrate into cobalt hydroxide by immersing the porous nickel sintered substrate processed in the first step into aqueous alkaline solution, a third step changing the cobalt hydroxide into cobalt oxide by steam-heating of the porous nickel sintered substrate processed in the second step, and a forth step fixing nickel salt by immersing the porous nickel sintered substrate processed in the third step into an acid nickel salt impregnation liquid. The method is characterized in that the aqueous cobalt nitrate solution contains alkaline cations in the first step. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to a method for producing a sintered nickel positive electrode for an alkaline storage battery, and more particularly to improvement of a nickel sintered substrate.

  Alkaline storage batteries can withstand severe charging and discharging compared to lithium ion secondary batteries, and are therefore widely used as auxiliary power sources for electric vehicles and main power sources for electric tools. In particular, a sintered nickel positive electrode having a high utilization factor and high conductivity of an active material is widely used from the viewpoint of improving discharge characteristics and cycle characteristics.

  A sintered nickel positive electrode is obtained by immersing a porous nickel sintered substrate, which is an active material holding body, in an acidic nickel salt impregnating solution such as nickel nitrate, and placing nickel salt in the pores of the porous nickel sintered substrate. After impregnation, the nickel salt is fixed to the sintered substrate in the drying process, and then the nickel sintered substrate is immersed in an alkaline solution to replace the nickel salt with nickel hydroxide, and the active material is filled. It is common to repeat the operation multiple times.

  The reason why the porous nickel sintered substrate is filled with the active material a plurality of times is because a desired amount of the active material filling cannot be obtained by a single active material filling operation. The active material filling amount can be secured. In order to increase the filling efficiency of the active material and increase the amount of the active material filled in the substrate by a single filling operation, a high concentration acidic nickel salt impregnating solution is generally used. Specifically, an aqueous nickel nitrate solution having a specific gravity of about 1.7 to 1.8 g / ml is used. However, since the specific gravity of the aqueous nickel nitrate solution cannot be 1.7 to 1.8 g / ml at room temperature, It is common to use it warm.

  However, the acidic nickel salt impregnating solution with high concentration and low pH is highly corrosive, so if the porous nickel sintered substrate is immersed for a long time during the filling operation of the active material, the corrosion progresses, the mechanical strength decreases and the concentration increases. Electricity decreases. Since the nickel positive electrode made of this porous nickel sintered substrate is brittle, there has been a problem that when an alkaline storage battery using this is repeatedly charged and discharged, the nickel positive electrode swells and the life characteristics are lowered.

In order to solve this problem, cobalt hydroxide is formed on the surface of a porous nickel sintered substrate, and then the substrate is heated in the presence of alkali and oxygen to convert cobalt hydroxide into cobalt oxyhydroxide or There has been proposed a method (for example, Patent Document 1) in which an acidic nickel salt is impregnated after the surface of a porous nickel sintered substrate is coated by changing to cobalt oxide. Furthermore, if the anticorrosion effect on the electrolytic solution is insufficient in the method of Patent Document 1, first, the porous nickel sintered substrate is immersed and dried in an acidic salt impregnating solution containing cobalt as a main component, to thereby obtain a porous nickel sintered substrate. A cobalt compound is attached to the surface in a solid state and then dipped in an alkaline cobalt aqueous solution to cover the defective portion (pinhole) in the previous step, and then heated to oxidize cobalt complex ions (HCoO2 ⁻ ). It is considered that a method of depositing and covering the surface of the porous nickel sintered substrate (for example, Patent Document 2) is effective.
JP 63-216268 A Japanese Patent Laid-Open No. 05-089876

However, even if the method of Patent Document 2 is used, the porous nickel sintered substrate is locally sintered by repeating the charge / discharge cycle, although the effect of inhibiting the corrosion from the high temperature, high concentration impregnating liquid is seen. In some cases, the conductivity between the substrate and the active material is lowered, and the life performance of the battery is lowered.

  The present invention was made to solve this problem, and formed a dense and highly conductive cobalt oxide layer on the surface of a porous nickel sintered substrate to improve the oxidation resistance of the sintered substrate. An object of the present invention is to stably provide a nickel hydroxide electrode for an alkaline storage battery having excellent life performance by suppressing a decrease in conductivity between the sintered substrate and the active material.

  In order to solve the above-mentioned problems, a method for producing a nickel positive electrode for an alkaline storage battery of the present invention comprises a first step of immersing a porous nickel sintered substrate in a cobalt nitrate aqueous solution and then drying the first step, and a first step. A second step of changing the cobalt nitrate to cobalt hydroxide by immersing the passed porous nickel sintered substrate in an alkaline aqueous solution, and hydroxylating by steam heating the porous nickel sintered substrate having undergone the second step A third step of changing cobalt to cobalt oxide, and a fourth step of fixing the nickel salt by immersing the porous nickel sintered substrate that has undergone the third step in an acidic nickel salt impregnating solution. In the step, an alkali cation is included in the cobalt nitrate aqueous solution.

  As a result of intensive studies by the inventors, in order to efficiently obtain a high-order cobalt oxide having high conductivity, an appropriate amount of an alkaline aqueous solution is provided on the surface of the cobalt hydroxide particles to form a funicular state, and a high temperature. It was found that a solid, liquid, and gas three-phase interface was formed underneath, and that alkali cations should be sufficiently present when cobalt hydroxide was eluted as a cobalt complex ion. In the case of the present invention, the alkali cation is contained in the cobalt aqueous solution in the first step and fixed together with the cobalt salt, so that the alkali cation is uniformly and abundant in the vicinity of the cobalt complex ion eluted in the third step. Therefore, the surface of the porous nickel sintered substrate after this step can be efficiently coated with a high-order cobalt oxide having high conductivity and uniformity. Thus, it is considered that an alkaline storage battery having better life characteristics than the conventional techniques such as Patent Documents 1 and 2 can be provided without imposing an excessive burden on the production facility.

  According to the present invention, since the surface of the porous nickel sintered substrate can be uniformly coated with the higher cobalt oxide containing alkali cations, the oxidation resistance of the substrate can be improved and the substrate and the active material can be improved. As a result, the conductivity of the alkaline storage battery can be improved.

  Hereinafter, the best mode for carrying out the present invention will be described in detail.

  The first invention includes a first step of drying after a porous nickel sintered substrate is immersed in a cobalt nitrate aqueous solution, and a step of immersing the porous nickel sintered substrate that has undergone the first step in an alkaline aqueous solution. A second step of changing cobalt nitrate to cobalt hydroxide by a third step, a third step of changing the cobalt hydroxide to cobalt oxide by steam heating the porous nickel sintered substrate that has undergone the second step, And a fourth step of fixing the nickel salt by immersing the porous nickel sintered substrate that has undergone the step 3 in an acidic nickel salt impregnating solution. In the first step, an alkali cation is included in the cobalt nitrate aqueous solution. It is related with the manufacturing method of the nickel positive electrode for alkaline storage batteries characterized by the above-mentioned.

In the third step, cobalt oxyhydroxide having high crystallinity and low conductivity is produced when cobalt hydroxide is oxidized without being dissolved in an alkaline aqueous solution, and becomes conductive when oxidation conditions are insufficient. Poor cobalt tetroxide is produced. However, when cobalt hydroxide elutes as cobalt complex ions in an aqueous alkali solution and reacts with oxygen (Co (OH) ₂ + OH ⁻ → HCoO ₂ ⁻ + H ₂ O, HCoO ₂ ⁻ + 1 / 4O ₂ + 1 / 2H ₂ O → CoOOH + OH) ^- ) Cobalt oxyhydroxide with low crystallinity and high conductivity is produced. If a large amount of alkali cations can be contained here, higher-order cobalt oxyhydroxide having higher conductivity is generated.

  If an attempt is made to contain a large amount of alkali cations in the second step in order to obtain this effect, it is necessary to increase the concentration of the aqueous alkali solution used when changing nitrates to hydroxides. Further, if a large amount of alkali cations are included in the third step, it is necessary to impose severe conditions such as increasing the temperature of steam heating. Any of these options may raise productivity costs including maintenance of production facilities.

  Here, an appropriate amount of an alkaline aqueous solution is provided on the surface of the cobalt hydroxide particles to form a Funicular state, and a three-phase interface of solid, liquid, and gas is formed at a high temperature, and when cobalt hydroxide is eluted as a cobalt complex ion, It was found that a high-order cobalt oxide with high conductivity can be obtained efficiently by sufficiently containing cations.

  In the case of the present invention, the alkali cation is contained in the cobalt aqueous solution in the first step and fixed together with the cobalt salt, so that the alkali cation is uniformly and abundant in the vicinity of the cobalt complex ion eluted in the third step. Therefore, the surface of the porous nickel sintered substrate after this step can be efficiently coated with a high-order cobalt oxide having high conductivity and uniformity. Thereby, while the corrosion resistance in the following 4th process improves, the fall of the electroconductivity with a porous nickel sintered substrate and an active material can be suppressed.

  A second invention is characterized in that, in the first invention, the first to third steps are repeated at least two cycles, the fourth step is performed, and the alkali cation is included only in the first cycle.

  In the first step after the second cycle, an alkali cation is substantially not included. Therefore, the conductivity of the higher cobalt oxide formed after the second cycle is determined in the first to third steps of the first cycle. Although it is lower than the highly conductive high-order cobalt oxide containing a large amount of alkali cations formed, it is difficult to elute because the surface area is relatively small. On the other hand, the highly conductive high-order cobalt oxide that directly covers the porous nickel sintered substrate is microcrystallized and has a large surface area, so that the corrosion of the porous nickel sintered substrate is suppressed in the fourth step. Is accompanied by a large amount of elution, making it difficult to ensure the conductivity between the porous nickel sintered substrate and the active material. In order to avoid this phenomenon, it is necessary to increase the coating amount of the high-order cobalt oxide containing a large amount of alkali cations, but a lot of high-cost cobalt is used. Therefore, by forming a high-order cobalt oxide having a low conductivity but a relatively small surface area (that is, difficult to elute) on the high-conductivity high-order cobalt oxide formed in the first cycle, one cycle is obtained. It functions as a sacrificial coating that protects the highly conductive higher cobalt oxide formed in the eye.

  In the second invention, alkali cations are not substantially contained in the first step after the second cycle. Specifically, 0.01 is a level at which splashes from adjacent steps are mixed. It is preferable to set it as the weight% or less.

  A third invention is characterized in that, in the first invention, at least one of potassium ion, sodium ion and lithium ion is contained as an alkali cation. These alkali cations are preferable because they are taken into the crystal lattice of the cobalt oxide when the cobalt compound is oxidized, and the effect of increasing the conductivity of the higher cobalt oxide by increasing the interval of the crystal lattice.

  The fourth invention is characterized in that, in the first invention, the amount of alkali cations after the third step is 2.5 wt% or more and 20 wt% or less with respect to cobalt ions. When this value is less than 2.5% by weight, the content of the alkali cation in the higher cobalt oxide is lowered and the effect of the present invention is diminished. On the other hand, when this value exceeds 20% by weight, cobalt oxyhydroxide having an excessively long c-axis is increased, and the filling property of the active material is lowered.

  Next, constituent features other than those described above will be described in detail.

  The porous nickel sintered substrate can be produced by drying and sintering processes using nickel powder, water, a thickener, and a punching core as raw materials. The preferable range of the thickness is 400 to 600 μm, and the preferable range of the pore volume ratio is 80 to 90%.

  The suitable range of the concentration in the cobalt nitrate aqueous solution used in the first step is 0.5 to 1.5 mol / L, and the preferred range of the drying temperature is 90 to 110 ° C. Further, as the alkaline aqueous solution used in the second step, an aqueous solution such as sodium hydroxide is specifically suitable, the preferred range of the concentration is 10 to 30% by weight, and the preferred range of the temperature is 60 to 90 ° C. is there. Further, as the acidic nickel salt impregnating liquid used in the fourth step, specifically, an aqueous solution such as nickel nitrate is preferable, and a preferable range of specific gravity is 1.5 to 1.8 g / ml.

  Examples of the present invention will be described below.

Example 1
(1) Production of Porous Nickel Sintered Substrate A metallic paste was prepared by adding carboxymethyl cellulose as a thickener and surfactant and water as an antifoaming agent to metal nickel powder and kneading. This nickel paste is applied to an iron punching core material plated with nickel having a thickness of 60 μm, and then sintered at 900 ° C. to 1100 ° C. in a nitrogen atmosphere. Was made.

(2) 1st process After immersing the above-mentioned porous nickel sintered board in what dissolved 0.04 mol / L sodium nitrate in cobalt nitrate aqueous solution of specific gravity 1.13, it dried at 100 ° C for 30 minutes. .

(3) Second step The porous nickel sintered substrate that has undergone the first step is immersed in a 25% by weight sodium hydroxide aqueous solution at 80 ° C., thereby containing sodium on the surface of the porous nickel sintered substrate. Cobalt hydroxide was produced.

(4) Third step The surface of the porous nickel sintered substrate that has undergone the second step is put into a high-temperature bath while being wet with an aqueous sodium hydroxide solution until the temperature in the high-temperature bath reaches 160 ° C. The temperature rose. When the temperature reached 160 ° C., high-temperature steam at 150 ° C. was introduced into the high-temperature bath for 5 minutes, and humidification was performed until the relative humidity reached 18% without lowering the temperature in the high-temperature bath (humidification stage). Then, it exhausted, without lowering | hanging the temperature in a high temperature tank, and the relative humidity in a high temperature tank was gradually reduced over 10 minutes (dehumidification stage). Thus, a porous nickel sintered substrate covered with cobalt oxide containing dense sodium was prepared by using cobalt hydroxide generated on the surface of the porous nickel sintered substrate as a high-order cobalt oxide. From the measurement result of atomic absorption analysis (ICP), the content ratio of sodium ion to cobalt ion was measured and found to be 5% by weight.

(5) Fourth Step The porous nickel sintered substrate that has undergone the third step is made into an acidic mixed aqueous solution of nickel nitrate and cobalt nitrate (nickel nitrate: cobalt nitrate = 100: 1, specific gravity 1.7) at 80 ° C. After dipping, the nickel nitrate and cobalt nitrate are fixed in the pores of the porous nickel sintered substrate by drying at 100 ° C., and then immersed in a sodium hydroxide aqueous solution at 80 ° C. and 25 wt%, Nickel nitrate and cobalt nitrate were each replaced with hydroxide. This is washed with hot water at 80 ° C. to remove the alkali, and dried at 100 ° C., and then filled with an active material (nickel hydroxide). did.

(3) Production of battery This nickel positive electrode was cut into a length of 260 mm and a height of 35 mm. On the other hand, with respect to 100 parts by weight of the hydrogen storage alloy represented by the general formula MmNi _3.55 Co _0.75 Mn _0.4 Al _0.3 (Mm represents a mixture of rare earths with misch metal), 0.15 wt. %, Carbon black as a conductive agent, 0.3% by weight, 0.8 part by weight of a styrene-butadiene copolymer as a binder, and water as a dispersion medium to prepare a pace, and this paste has a thickness of 60 μm Then, it was applied to both surfaces of an iron punched core material plated with nickel with a porosity of 42%, dried and pressurized to produce a negative electrode having a length of 310 mm, a width of 35 mm, a thickness of 0.3 mm, and a capacity of 3000 mAh. . The positive electrode a, the negative electrode and a polypropylene nonwoven fabric separator were combined and wound in a spiral shape, inserted into an SC-sized cylindrical metal case, and 40 g / l lithium hydroxide was added to a potassium hydroxide aqueous solution having a specific gravity of 1.30. After injecting a predetermined amount of the dissolved electrolyte, the case was sealed to constitute an alkaline storage battery with a nominal capacity of 2.0 Ah. This is Example 1.

(Examples 2 to 5)
Compared to Example 1, the concentration of sodium nitrate used in the first step was 0.02 mol / L (Example 2), 0.08 mol / L (Example 3), 0.16 mol / L (Example 4). And 0.18 mol / L (Example 5), and the content ratio of sodium ions to cobalt ions determined from ICP measurement results was 2.5% by weight (Example 2), 10.0% by weight (Examples). 3) An alkaline storage battery was produced using a nickel positive electrode produced in the same manner as in Example 1 except that the content was 20.0% by weight (Example 4) and 21.0% by weight (Example 5). Let this be Examples 2-5.

(Examples 6 to 7)
In contrast to Example 1, 0.04 mol / L sodium nitrate used in the first step was changed to 0.05 mol / L potassium nitrate (Example 6) and 0.05 mol / L lithium nitrate (Example 7). This was carried out except that the content ratio of potassium ions to cobalt ions determined from ICP measurement results was 4.5% by weight (Example 6) and the content ratio of lithium ions was 3.5% by weight (Example 7). An alkaline storage battery was produced using a nickel positive electrode produced in the same manner as in Example 1. Let this be Examples 6-7.

(Example 8)
The same porous nickel sintered substrate as in Example 1 was processed in the following order.
(1) First to third steps similar to Example 1 (2) First step similar to Example 1 except that sodium nitrate is not included (3) Second to fourth similar to Example 1 Process An alkaline storage battery was produced using a nickel positive electrode produced in the same manner as in Example 1 except that this porous nickel sintered substrate was used. This is Example 8.

(Comparative Example 1)
Compared to Example 1, an alkaline storage battery was produced using a nickel positive electrode produced in the same manner as in Example 1 except that sodium nitrate was not included in the first step. This is referred to as Comparative Example 1. The content ratio of sodium ions to cobalt ions determined from ICP measurement results was 2.0% by weight.

  With respect to the battery of each example manufactured by the above method, the battery is charged to 120% of the theoretical capacity at a current value of 2.0 A at an ambient temperature of 20 ° C., and discharged until the battery voltage reaches 0.8 V at a current value of 2.0 A. The cycle was repeated. The number of cycles when the discharge capacity deteriorated to 80% of the initial discharge capacity was determined, and the number of cycles of Comparative Example 1 was set to 100, and the number of cycles of each battery was indicated by an index. The results are shown in (Table 1).

（表１）に示した結果から、第１の工程で硝酸コバルト水溶液にアルカリカチオンを混合させた各実施例の電池は、比較例１と比べて寿命特性が向上した。比較例１ではアルカリカチオンが内部まで十分取り込まれていないのに対し、各実施例では第１の工程でアルカリカチオンを硝酸コバルト水溶液中に混合しており、多孔性ニッケル焼結基板に定着されるコバルト硝酸塩の内部までアルカリカチオンが十分取り込まれた状態となるので、その後の酸化過程でアルカリカチオンを含有した高次コバルト酸化物を多く生成することができる。このアルカリカチオンを含有した高次コバルト酸化物は、結晶性が低く、微細化しているために多くの結晶子界面が形成される。導電性の高い高次コバルト酸化物としての側面と、結晶子界面が電子伝導面として機能する側面との双方が、多孔性ニッケル焼結基板の良好な導電性に寄与する一方、電解液に対する腐食抑制効果も相まって、寿命特性が向上したものと考えられる。この効果はアルカリカチオンがナトリウムイオン、カリウムイオン、リチウムイオンのいずれでも同様である。

From the results shown in (Table 1), the battery of each example in which the alkali cation was mixed with the cobalt nitrate aqueous solution in the first step had improved life characteristics as compared with Comparative Example 1. In Comparative Example 1, the alkali cations are not sufficiently taken up to the inside, whereas in each Example, the alkali cations are mixed in the cobalt nitrate aqueous solution in the first step and fixed to the porous nickel sintered substrate. Since the alkali cations are sufficiently taken up to the inside of the cobalt nitrate, many higher order cobalt oxides containing alkali cations can be generated in the subsequent oxidation process. This high-order cobalt oxide containing an alkali cation has low crystallinity and is miniaturized, so that many crystallite interfaces are formed. Both the side surface as a highly conductive higher cobalt oxide and the side surface where the crystallite interface functions as an electron conducting surface contribute to the good conductivity of the porous nickel sintered substrate, while corrosion against the electrolyte Combined with the suppression effect, it is considered that the life characteristics are improved. This effect is the same regardless of whether the alkali cation is a sodium ion, a potassium ion or a lithium ion.

  However, in Example 2 where the alkali cation content was low, the life characteristics were slightly lowered due to the influence of the decrease in the corrosion resistance in the fourth step. Further, Example 5 having a high content of alkali cations also had a slight decrease in life characteristics, but this phenomenon was caused by the fact that the c-axis of cobalt oxyhydroxide was excessively long, so that the filling property of the active material was reduced and It is presumed that the positive electrode voids were reduced and the electrolyte solution was not sufficiently distributed. Therefore, the amount of alkali cations after the third step is preferably 2.5% by weight or more and 20% by weight or less with respect to cobalt ions.

Furthermore, in Example 8, the result of a more favorable battery characteristic was obtained by coat | covering the cobalt oxide layer with little content of an alkali cation on the surface of the higher order cobalt oxide containing the alkali cation. While cobalt oxide containing alkali cations is highly conductive,
Since the crystals are finer, the surface area is larger, and in the fourth step, although it has a corrosion resistance effect, it elutes into a high-temperature and high-concentration nickel nitrate aqueous solution. As in Example 9, the surface of a high-order cobalt oxide containing an alkali cation is coated with a layer of cobalt oxide having a low alkali cation content (not high conductivity but high crystallinity and low surface area). As a result, it is possible to suppress the elution of higher cobalt oxide containing alkali cations in the fourth step, and to maintain a highly conductive state even after the battery configuration, further improving the life characteristics. It is thought to have improved.

  The alkaline storage battery using the nickel positive electrode that has undergone the manufacturing method of the present invention is excellent in life characteristics, and thus is useful in various applications such as an auxiliary power source for electric vehicles and a main power source for electric tools.

Claims (4)

A first step in which a porous nickel sintered substrate is dipped in a cobalt nitrate aqueous solution and then dried, and a cobalt nickel nitrate substrate which has been subjected to the first step is dipped in an alkaline aqueous solution to hydroxylate cobalt nitrate. A second step to convert to cobalt,
A third step of changing the cobalt hydroxide to cobalt oxide by steam heating the porous nickel sintered substrate that has undergone the second step;
A fourth step of fixing the nickel salt by immersing the porous nickel sintered substrate that has undergone the third step in an acidic nickel salt impregnating solution;
A method for producing a nickel positive electrode for an alkaline storage battery, comprising:
In the first step, an alkali cation is included in the aqueous cobalt nitrate solution, and the method for producing a nickel positive electrode for an alkaline storage battery. The nickel for alkaline storage batteries according to claim 1, wherein the fourth step is performed after repeating the first to third steps at least two cycles, and the alkali cation is included only in the first cycle. A method for producing a positive electrode. The method for producing a nickel positive electrode for an alkaline storage battery according to claim 1, wherein at least one of potassium ion, sodium ion and lithium ion is included as the alkali cation. 2. The nickel positive electrode for an alkaline storage battery according to claim 1, wherein the amount of the alkali cation after the third step is 2.5 wt% or more and 20 wt% or less with respect to cobalt ions. Production method.