JP3449176B2 - Method for producing positive electrode active material for alkaline secondary battery - Google Patents

Description

Description: BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for producing a positive electrode active material which can be used for a high capacity alkaline secondary battery. 2. Description of the Related Art In recent years, with the spread of portable devices, higher capacity of alkaline secondary batteries has been demanded. In particular, a nickel-hydrogen secondary battery is a secondary battery consisting of a positive electrode made of an active material mainly composed of nickel hydroxide and a negative electrode made of a hydrogen storage alloy as an active material, and has a high capacity and high reliability. It is spreading rapidly. Hereinafter, a positive electrode of a conventional alkaline secondary battery will be described. The positive electrode for an alkaline secondary battery is roughly classified into a sintered type and a non-sintered type. In the former, a porous nickel sintered substrate obtained by sintering nickel powder and having a porosity of about 80% is impregnated with a nickel salt solution such as a nickel nitrate aqueous solution and then immersed in an alkaline aqueous solution. It is manufactured by producing a nickel hydroxide active material in a sintered substrate. Since it is difficult for this electrode to increase the porosity of the substrate any more, the amount of the filled active material cannot be increased, and there is a limit to increasing the capacity. As the latter non-sintered type positive electrode, for example, a sponge-like porous substrate made of nickel metal and having a three-dimensionally continuous porosity of 95% or more disclosed in Japanese Patent Application Laid-Open No. 50-36935 is disclosed. Is filled with nickel hydroxide as an active material, which is currently widely used as a positive electrode of a high capacity secondary battery. In this non-sintered positive electrode, it has been proposed to fill a porous substrate with spherical nickel hydroxide from the viewpoint of increasing the capacity. This means that the pore size of the sponge-like porous substrate is 200 to 50.
0 μm, and the pore size is several μm to several tens μm.
m spherical nickel hydroxide. In this configuration, the charge / discharge reaction of nickel hydroxide near the nickel metal skeleton where the conductive network is maintained proceeds smoothly, but the reaction of nickel hydroxide separated from the skeleton does not sufficiently proceed. Therefore, in order to improve the utilization of the filled nickel hydroxide in this non-sintered positive electrode, a conductive agent is used in addition to nickel hydroxide as an active material, thereby electrically connecting spherical nickel hydroxide particles. Connected to As the conductive agent, a cobalt compound such as cobalt hydroxide or cobalt monoxide, metallic cobalt, metallic nickel or the like is used. Thus, the non-sintered positive electrode can be filled with the active material at a high density, and the capacity can be increased as compared with the sintered positive electrode. Further, as a method for producing a positive electrode active material for a high capacity nickel-hydrogen secondary battery, which meets the market demand for high capacity, excellent overdischarge characteristics and improved cycle characteristics, a cobalt compound is used as an active material. JP-A-8-148145 discloses a method of coating a nickel oxide and subjecting the cobalt compound to an alkali oxidation treatment to obtain a higher cobalt oxide.
An improvement of the manufacturing method is disclosed in Japanese Patent Application Laid-Open No. 9-73900. In this method, an alkaline aqueous solution is sprayed while fluidizing or dispersing nickel hydroxide powder coated with a cobalt compound in heated air.
As a result, it is possible to improve the battery characteristics such as the active material utilization rate and the high-rate discharge characteristics as compared with the conventional manufacturing method in which a cobalt compound is added as an external additive, and to manufacture a high energy density alkaline secondary battery. it can. However, in the positive electrode active material for an alkaline secondary battery produced by the method described in the above-mentioned publication, the oxidation of a cobalt compound coated on the surface of a nickel hydroxide active material is performed. The condition is inadequate and there is still room for improvement. [0008] By efficiently converting the cobalt compound coated on the surface of the nickel hydroxide active material into a higher-order cobalt compound, the utilization of the active material in the alkaline secondary battery can be improved, the high-rate discharge characteristics can be improved, and the resistance can be improved. Overdischarge characteristics can be improved. In order to efficiently oxidize the above-mentioned cobalt compound into a higher oxide, it is possible to control the oxidized state. The oxidation of the cobalt compound is an important parameter for the oxidation temperature, the concentration of the alkaline solution, the oxygen supply amount in the oxidation atmosphere, and the oxidation time. This oxidation reaction is oxidation of a cobalt compound, that is, cobalt hydroxide in this case, but the oxidation of cobalt hydroxide can be considered as two processes. In the first process, when cobalt hydroxide is placed in an alkaline solution, a divalent cobalt complex ion (HCo
Dissolves as O ₂ ⁻ ). This cobalt complex ion is trivalent cobalt oxyhydroxide (CoOOH) when oxygen is present.
And is precipitated as a precipitate. This reaction is represented by (Equation 1) and (Equation 2). Formula 1 Co (OH) ₂ + OH ⁻ = HCoO ₂ ⁻ + H ₂ O Formula 2 HCoO ₂ ⁻ + 1 / 2H ₂ O + 1/402 ₂ = CoOOH + OH ⁻ 2 The second process is a process in which divalent cobalt hydroxide is oxidized into trivalent cobalt oxyhydroxide by solid-phase reaction while generating water in an atmosphere containing alkali and oxygen. This reaction is represented by the following equation (Equation 3):
(Equation 4) is obtained. [0012] [Formula 3] ^{_{Co (OH) 2 + OH -}} = CoOOH + H 2 O + e - [0013] [Formula 4] _{1/40 2 + 1 / 2H 2 O} + e - = OH - thus efficiently To oxidize cobalt hydroxide,
The process needs to be well controlled. The first process relies on the solubility of cobalt hydroxide in alkaline solutions. The solubility of cobalt hydroxide in an alkaline solution depends on the concentration of the alkaline solution.
ppm. Therefore, in order to completely dissolve cobalt hydroxide in an alkaline solution, a large amount of an alkaline solution as a solvent is required. Therefore, it is extremely difficult to oxidize to higher-order cobalt oxyhydroxide only by this reaction. In addition, the cobalt complex ion dissolved in this reaction becomes insufficiently oxidized and has low conductivity as shown by Co ₃ O ₄ if oxygen is insufficient. In the second process, when oxygen is supplied in the presence of an alkali, cobalt hydroxide is oxidized and changed to cobalt oxyhydroxide. At that time, in the presence of oxygen, the reaction of (Equation 4) occurs first, and the reaction of (Equation 3) occurs continuously, and oxidation of cobalt hydroxide occurs. In order for this reaction to proceed smoothly, it is necessary to increase the OH ^- concentration and to appropriately remove generated water from the reaction system. As described above, it is clear that water and oxygen play important roles in any of the reactions. Therefore, it is possible to produce a desired high-order cobalt oxide only by properly controlling water and oxygen, and it is possible to provide a nickel-hydrogen secondary battery having a high energy density. Means for Solving the Problems To solve the above problems, a method for producing a positive electrode active material according to the present invention comprises nickel hydroxide as a main component, and comprises Co, Mn, Fe, Al, Cr, Zn, M
g, Cu, in which at least one element selected from the group consisting of a solid solution is coated with a cobalt compound on the surface of a particle is heated on the wall surface of an airtight container provided with a heating and stirring means, and is placed inside the container. The method is characterized by comprising a step of charging, a step of charging an alkaline aqueous solution into a container while stirring the powder, and a step of continuously feeding heated air into an airtight container. The airtight container is provided with a heating means and a stirring means because nickel hydroxide powder coated with a cobalt compound is brought into efficient contact with the inner surface of the airtight container, and heat is transmitted by gas (here, air). To efficiently heat the powder to the reaction temperature. By this step, the temperature of the nickel hydroxide can be uniformly raised to a predetermined temperature. Next, an alkaline aqueous solution is introduced while stirring the nickel hydroxide powder. In this step, the alkaline aqueous solution can be uniformly mixed with the nickel hydroxide powder by dripping the alkaline aqueous solution with stirring. Continue to send heated air,
An object of the present invention is to efficiently discharge excess water generated by the oxidation reaction of cobalt to the outside of the system and supply a necessary and sufficient amount of oxygen to the reaction system. Another reason for sending heated air is that latent heat of evaporation is exposed when excess water evaporates, and the air is heated to compensate for the decrease in temperature at the reaction surface. According to the production method of the present invention, a higher-order cobalt compound can be produced by controlling the oxidizing atmosphere, and a nickel-hydrogen secondary battery having high energy density and excellent battery characteristics can be produced. It is possible to do. DETAILED DESCRIPTION OF THE INVENTION The first aspect of the present invention comprises nickel hydroxide as a main component, and Co, Mn, Fe, Al, C
A powder in which at least one element selected from the group consisting of r, Zn, Mg, and Cu is dissolved as a solid solution and the surface of which is coated with a cobalt compound is placed in a heated airtight container equipped with heating and stirring means. The method is characterized by comprising a step of charging, a step of charging an alkaline aqueous solution into a container while stirring the powder, and a step of continuously feeding heated air into an airtight container. Preferably, the heating temperature of the airtight container is 90-1.
It is characterized by a temperature of 30 ° C. The temperature at which the closed vessel is heated is to give the heat necessary for controlling the oxidation reaction to the powder and the alkaline solution. At a temperature of 90 ° C. or less, the evaporated water or alkali mist is condensed on the closed vessel wall to form a powder. Agglomerates and solidifies. Therefore, the temperature must be above 90 ° C. 130 ° C
At a temperature exceeding 130 ° C., the reaction occurs violently, and the cobalt complex ion dissolved at the interface between the cobalt coating layer and the nickel hydroxide diffuses into the nickel, disturbing the crystals on the surface of the nickel hydroxide active material, This is because the utilization rate decreases. Claim 3 defines the concentration of the alkaline aqueous solution to be greater than 40% by weight. Since the oxidation reaction of the present invention is a reaction that occurs near the boiling point of the aqueous alkaline solution, the evaporation rate of water in the alkaline solution is high. However, as one of the processes of the oxidation reaction of the present invention, cobalt hydroxide is dissolved in an aqueous alkali solution,
Since a cobalt complex ion is generated and furthermore, this ion reacts with oxygen to form a higher-order cobalt compound, it is preferable that the solution amount is large. Therefore, the higher the concentration of the aqueous alkali solution, the higher the boiling point and the lower the evaporation rate, so that the amount of liquid at a predetermined temperature can be increased. As another oxidation process, the higher the OH 2 ^- concentration, the more the oxidation proceeds. Therefore, the higher the concentration of the alkaline solution, the better. A fourth aspect of the present invention is to limit the kind of the alkaline aqueous solution, and is characterized in that it is a single or mixed aqueous solution of sodium hydroxide or potassium hydroxide. FIG. 1 is a schematic cross-sectional view of the reactor used in the present invention. 1 is an airtight container, 2 is a heating means, 3 is a mixing and stirring blade, and 4 is a rotating means of the stirring blade, for example, a motor. Reference numeral 5 denotes a pipe for introducing heated air into the airtight container, and reference numeral 6 denotes a heating air blowing means including a blower 7 and a heater 8. This blowing means is provided with a function of controlling the amount of air blow, temperature and humidity. Reference numeral 9 denotes a pipe for exhaust air, and reference numeral 10 denotes an exhaust air processing unit for processing exhaust air, which has a function of measuring the exhaust air 11 and the amount, temperature, and humidity of the exhaust air. Reference numeral 12 denotes an inlet for introducing an alkaline aqueous solution into the airtight container, and a valve for controlling injection is provided near the inlet. (Embodiment 1) The operation will be described in more detail with reference to FIG.
Nickel hydroxide whose surface was coated with cobalt hydroxide was used as a positive electrode active material for an alkaline secondary battery. Coating amount of cobalt hydroxide is 10w with respect to the weight of nickel hydroxide.
t%. The alkaline aqueous solution used was a sodium hydroxide aqueous solution having a concentration of 45 wt%. First, the surface temperature of the inner wall of the airtight container is set to 100 ° C. by the heating means 2 provided in the wall of the airtight container.
And Next, 1 kg of nickel hydroxide coated with cobalt hydroxide was charged into the airtight container. The rotating blades 4 rotated the stirring blades 3 to stir the cobalt hydroxide-coated nickel hydroxide. Next, while the stirring blade 3 was being rotated, 80 cc of a 45 wt% sodium hydroxide aqueous solution was introduced from the alkaline aqueous solution inlet 12. Then the valve was closed. After stirring for about 2 minutes, blower 7 equipped with heating means
And heated air at 115 ° C. was fed into the airtight container. The air volume at this time was 2.5 m ³ / min, and the humidity was 0.01 (kg).
H ₂ O / kg dry-air). About 3 in this state
When the heated air was fed for 0 minutes, it became almost dry and the reaction was completed. The dry state was confirmed by monitoring the temperature and humidity on the exhaust side. The powder obtained by this process was an active material in which cobalt was uniformly oxidized without agglomerated particles.
Since the obtained powder contained an excess alkali component, it was washed with water to obtain a positive electrode active material. The obtained powder is A
And (Comparative Example) FIG. 2 is a schematic view of a batch type fluidized-bed drying apparatus. Reference numeral 13 denotes a cylindrical device housing. Reference numeral 14 denotes a blower for sending heated air into the apparatus housing, 15 denotes a heater for heating the blown air, and 16 denotes a pipe connecting the blower and the housing. Reference numeral 17 denotes a stirring blade for stirring the powder, and reference numeral 18 denotes a rotating means including a motor, for example, for rotating the stirring blade. 19 is a two-fluid nozzle for spraying an alkaline aqueous solution, 20 is a piping for transferring compressed air when spraying the alkaline solution, 21 is a piping for transferring the alkaline aqueous solution, 22 is a tank for storing the alkaline aqueous solution, A compressor that creates air. 2
Reference numeral 3 denotes an airflow rectifying plate for flowing the powder. Reference numeral 24 denotes a filter for preventing fine particles from being discharged to the outside of the housing when the powder flows. Reference numeral 25 denotes a pipe connecting the housing and the air blower 26 for exhausting the air inside the housing 13. The operation when the present apparatus is used will be described in more detail. Nickel hydroxide coated with cobalt hydroxide was used as a positive electrode active material for an alkaline secondary battery. The coating amount of cobalt hydroxide is 1 to the weight of nickel hydroxide.
0 wt%. The aqueous alkaline solution used was a sodium hydroxide aqueous solution having a concentration of 45 wt%. First, 1 kg of cobalt hydroxide-coated nickel hydroxide was charged into the housing. Next, the stirring blade 17 is rotated by the rotating means 18. Then, blower 1
4 and the blower 26 are moved to generate an updraft in the cylindrical housing 13. At this time, the blown air was heated by the heater 15. The heated air that has passed through the current plate causes fluidization of the supplied nickel hydroxide powder coated with cobalt hydroxide. While the powder is fluidized, a predetermined amount of an alkaline aqueous solution is sprayed from a two-fluid nozzle. By the end of the spraying, the aqueous alkaline solution permeates the surface of the particles and acts on the heated air to turn the cobalt hydroxide on the surface into a higher oxide. After the end of spraying, the mixture is allowed to flow in heated air for about 15 minutes. Thereafter, the device was stopped and the powder was taken out of the housing. The obtained powder was washed with water because it contained an excessive amount of an alkaline component, and was used as an active material of a positive electrode. Let the obtained powder be B. (Embodiment as Battery) Powders A and B were used as positive electrode active materials. A foam metal was used for the positive electrode substrate. To this foamed metal, 0.5 wt% of polytetrafluoroethylene (PTFE) and water were added to powders A and B, respectively, and pastes were prepared and filled. Thereafter, it was dried and subsequently rolled. The dimensions of the positive electrode plate were 35 mm in height, 120 mm in width, and 0.78 mm in thickness after rolling. The theoretical capacity of this cathode (289 assuming that nickel hydroxide is a one-electron reaction)
(calculated as mAh / g) was 1600 mAh. Next, the paste prepared by adding AB ₅ type hydrogen storage alloy, 1 wt% of carbon material, 1 wt% of PTFE and water was applied to a punching metal, dried, and then rolled. The dimensions of the negative electrode plate are 35 mm in height and 145 in width.
mm, and the thickness after rolling was 0.39 mm. The theoretical capacity of this electrode (the quantity of electricity per unit weight of the hydrogen storage alloy is 28
(Calculated as 0 mAh / g) was 2900 mAh. As the separator, a non-woven fabric made of polypropylene was used. The above positive electrode, negative electrode, and separator were arranged in the order of positive electrode, separator, negative electrode, and separator, and the whole was spirally wound, inserted into a battery case of 4/5 A size, and a predetermined amount of an alkaline electrolyte was injected. Thereafter, the battery was sealed with a sealing plate to form a sealed nickel-hydrogen secondary battery. The electrolyte used here was a 7-8N aqueous potassium hydroxide solution. A battery using the powder A is referred to as a battery A, and a battery using the powder B is referred to as a battery B. This battery was charged at 160 mA for 15 hours,
After leaving for 1 hour, the battery was discharged at 320 mA until the discharge voltage reached 1V. After performing this cycle twice, aging was performed in a temperature atmosphere of 45 ° C. for 3 days. After aging, the battery was charged at 160 mA for 15 hours in a temperature atmosphere of 20 ° C., left for 1 hour, and then discharged at 320 mA until the discharge voltage reached 1 V. Utilization rate (actual discharge capacity / positive electrode theoretical capacity) Of battery A is 105
%, And that of the battery B was 100%. As an overdischarge resistance test, 72 at 1600 mA
After charging for 60 minutes and leaving for 60 minutes, the battery was discharged at 1600 mA until the discharge voltage reached 1V. The capacity of the fifth cycle in which this cycle is performed five times is defined as the initial capacity. The batteries A and B, whose capacity has been confirmed, are connected to a 1Ω resistor at 45
It was stored for 1 month in an environment of ° C. After returning the stored batteries A and B to room temperature, the same charge and discharge as in the initial capacity check were performed.
The percentage obtained by dividing these capacities by the initial capacity of each battery is defined as a capacity recovery rate. The capacity recovery rate is almost 100% for Battery A, whereas it is almost 90% for Battery B.
The active material utilization rate, high rate discharge characteristics, and capacity recovery rate of the battery A are excellent. As described above, in the nickel-hydrogen secondary battery using the active material obtained by the method for producing a cathode active material for an alkaline secondary battery according to the present invention, it is possible to increase the capacity. At the same time, the over-discharge resistance can be dramatically improved, and the industrial value is immeasurable.

[Brief description of the drawings] FIG. 1 is a schematic sectional view of a reaction apparatus according to a first embodiment. FIG. 2 is a schematic diagram of a batch type fluidized drying apparatus according to a comparative example. [Explanation of symbols] 1 airtight container 2 heating means 3 mixing and stirring blades 4 Stirring blade rotating means 5 Piping 6 heating air blowing means 7 Blower 8 heater 9 Piping 10 Exhaust air treatment means 11 exhaust fan 12 Inlet 13 Case 14 Blower 15 heater 16 Piping 17 stirring blades 18 rotating means 19 Two-fluid nozzle 20, 21 piping 22 tank, compressor 23 Rectifier plate 24 Filter 25 Piping 26 exhaust fan

──────────────────────────────────────────────────の Continuing on the front page (72) Inventor Fumio Kato 1006 Kazuma Kadoma, Osaka Prefecture Matsushita Electric Industrial Co., Ltd. (56) References JP-A-9-50805 (JP, A) JP-A-9-50808 (JP, A) JP-A-9-73900 (JP, A) JP-A-9-82319 (JP, A) JP-A-9-147905 (JP, A) JP-A-6-163035 (JP, A) JP-A-8-236112 (JP, A) (58) Fields investigated (Int. Cl. ⁷ , DB name) H01M 4/52 H01M 4/32

Claims (1)

(57) [Claims] (1) Nickel hydroxide as a main component, Co, M
A powder in which at least one element selected from the group consisting of n, Fe, Al, Cr, Zn, Mg, and Cu is dissolved as a solid solution and the surface of which is coated with a cobalt compound is heated and agitated, and the wall surface is heated to 90%. a step of introducing a 130 heated hermetic container ° C., with stirring powdered sodium hydroxide
Or concentrated aqueous solution of potassium hydroxide alone or mixed
Adding an alkaline aqueous solution having a degree of more than 40% by weight into a container, and subsequently placing the mixture in an airtight container at 90 to 130 ° C.
A method for producing a positive electrode active material for an alkaline secondary battery, comprising the step of: