Oxidation method of high-valence low-resistance cobalt-coated spherical nickel

Abstract

The invention provides an oxidation method of high-valence low-resistance cobalt-coated spherical nickel, which comprises the following steps: preparing spherical nickel hydroxide with the surface coated with cobalt hydroxide by using a complex precipitation method, carrying out oxidation reaction in an oxidation reactor for a certain time, carrying out secondary oxidation, washing and drying on the product obtained by primary oxidation, and thus obtaining a high-valence cobalt-coated spherical nickel product. The average valence state of cobalt of the cobalt-coated spherical nickel product prepared through the preparation method is larger than or equal to 3.2, the tabletting resistance of the material is smaller than or equal to 2 ohm, and the 1C gram capacity is larger than or equal to 240 g / mAh.

Description

Technical Field

[0001] The invention belongs to the field of chemical engineering and new materials, and specifically relates to an oxidation method for high-valence low-resistance covered cobalt ball nickel. Background Art

[0002] Spherical nickel hydroxide is the most commonly used positive electrode active material in nickel-based alkaline batteries. However, nickel hydroxide itself is a semiconductor, and its poor conductivity directly limits the battery's high-current charge and discharge performance. In order to improve the conductivity of nickel hydroxide, researchers have adopted a variety of strategies to improve its performance.

[0003] When using positive active materials, nickel-hydrogen secondary batteries often have the problem of irrecoverable positive electrode capacity under high current discharge, deep discharge, short circuit and other conditions. The main reason is that when nickel hydroxide is deeply discharged, the conductive network material β-CoOOH on the surface of nickel hydroxide will also undergo a partial reduction reaction. The reduced 2-valent cobalt will form cobalt complex ions in the battery electrolyte, causing cobalt dissolution, thereby causing the incompleteness of the β-CoOOH conductive network. Further research shows that another crystal form of γ-CoOOH can form a state higher than 3.0 valence, and the reduction potential in alkaline electrolyte is lower, and it is not easy to be reduced to 2.0 valence, which can improve the integrity of the cobalt layer on the surface of nickel hydroxide.

[0004] At present, the most commercialized method is to coat a layer of cobalt hydroxide on the surface of spherical nickel hydroxide, and a nickel hydroxide positive electrode active material coated with cobalt oxyhydroxide has been developed. However, in the current traditional oxidation process, due to insufficient oxidation, local over-alkalinity and poor stirring intensity, the average valence of cobalt in the oxidized material is low, the resistance value is high, and the coating layer falls off (Scanning electron microscopy is shown below) Figure 1 ). Simple oxygen oxidation cannot completely oxidize cobalt hydroxide into cobalt oxyhydroxide, and the oxidation depth is not enough, resulting in low discharge capacity. Summary of the invention

[0005] In view of the problems existing in the above background technology, the present invention provides a method for oxidizing high-valent low-resistance cobalt-coated nickel balls, which can avoid the shedding of the coating layer.

[0006] The technical solution adopted by the present invention is as follows: A method for oxidizing high-valence low-resistance cobalt-coated nickel balls, comprising the following steps: 1) Take the spherical nickel hydroxide coated with cobalt hydroxide and add it into the oxidation reactor. Under stirring conditions, preheat it to 150-180℃, then add 1~5M sodium hydroxide solution, and then introduce oxygen for primary oxidation. The oxygen flow rate is 3-6m 3 / h, oxygen flow time 15-30min; 2) Add the material after the primary oxidation in step 1) into the reactor, add deionized water at a solid-liquid ratio of 2:1-1:2, stir and mix well, add the oxidant, heat to 40-90°C and perform oxidation reaction for 5-20 minutes; 3) The product obtained in step 2) is washed with deionized water until the pH value is 9-11, dried at 90-120° C., and passed through a 300-mesh sieve to obtain a high-valent, low-resistance cobalt-coated nickel spherical product.

[0007] In step 1), the cobalt content of the spherical nickel hydroxide coated with cobalt hydroxide is 2.0-4.0%; the cobalt content of the spherical nickel hydroxide matrix is ​​0.8-1.0%, the zinc content is 2.8-4.0%, and the nickel content is 53-55%.

[0008] In step 1), the stirring frequency in the preheating stage is 5-15 Hz, the stirring frequency in the alkali addition stage is 30-50 Hz, and the stirring frequency in the oxidation stage is 15-30 Hz.

[0009] In step 2), the oxidant is one of sodium persulfate or hydrogen peroxide, and the amount added is 0.2% to 2% of the mass of the material after the primary oxidation.

[0010] Compared with the prior art, the present invention has the following advantages: 1. The one-time oxidation preparation method of the present invention significantly improves the shedding phenomenon of the surface coating layer due to the design of different stirring frequencies during oxidation preheating, addition of alkali metal hydroxide, and oxygenation; 2. After the primary oxidation, the material of the present invention is subjected to secondary oxidation, which increases the oxidation depth, and the cobalt valence state after oxidation is ≥3.2; 3. The product prepared by the present invention has a reduced sheet resistance from 5-10Ω to 0.5-2Ω, thereby improving the conductivity of the product. The 1C gram capacity of the battery prepared by the material is ≥240mAh / g. BRIEF DESCRIPTION OF THE DRAWINGS

[0011] Figure 1 This is an electron microscope photograph of cobalt-coated spherical nickel hydroxide in the prior art.

[0012] Figure 2 This is an electron microscope photograph of the cobalt-coated spherical nickel hydroxide prepared in Example 1 of the present invention.

[0013] Figure 3 This is an electron microscope photograph of the cobalt-coated spherical nickel hydroxide prepared in Example 2 of the present invention.

[0014] Figure 4 This is an electron microscope photograph of the cobalt-coated spherical nickel hydroxide prepared in Example 3 of the present invention.

[0015] Figure 5This is an electron microscope photograph of the cobalt-coated spherical nickel hydroxide prepared in Example 4 of the present invention. DETAILED DESCRIPTION

[0016] The present invention is further explained below with reference to specific embodiments.

[0017] Example 1 A method for oxidizing high-valence low-resistance cobalt-coated nickel balls, comprising the following steps: (1) Preparation of spherical nickel hydroxide coated with cobalt hydroxide: According to the existing method for preparing spherical nickel hydroxide coated with cobalt hydroxide (such as CN99103011.7, a process for coating cobalt hydroxide on the surface of spherical nickel hydroxide), spherical nickel hydroxide coated with cobalt hydroxide is prepared. The cobalt content of the spherical nickel hydroxide coated with cobalt hydroxide is 0.8-1.0%, the zinc content is 2.8-4.0%, and the nickel content is 53-55%; the cobalt coating amount is 2.0-4.0%.

[0018] (2) Primary oxidation The surface-coated spherical nickel hydroxide prepared in step 1 was added to the oxidation reactor. Under stirring conditions, it was first preheated to 160°C, and then a 2.5M sodium hydroxide solution was added at a solid-liquid mass ratio of 1:2. Then oxygen was introduced for primary oxidation at an oxygen flow rate of 5m 3 / h, oxygen flow time 30min; During primary oxidation, the stirring frequencies are different in different stages. In the preheating stage, a low stirring frequency of 15Hz is set to prevent the material coating from being damaged. In the alkali addition stage, a high stirring frequency of 45Hz is set to ensure uniform dispersion of the liquid alkali. In the oxygenation stage, in order to ensure that the coating is not damaged and that the oxidation is sufficient, the stirring frequency is set to 30Hz.

[0019] (3) Secondary oxidation Take 1 kg of the material after primary oxidation, add 1 L of deionized water, stir evenly, then add 0.02 kg of sodium persulfate, and the reaction time is 10 min.

[0020] (4) Washing and drying The product obtained in step 3 is washed with deionized water to pH=9, dried at 100°C, and sieved to obtain a high-valent, low-resistance cobalt-coated nickel spherical product.

[0021] The product prepared by this method was detected by scanning electron microscopy, and the surface coating layer was less detached. (The scanning electron microscopy is as follows Figure 2 ) After battery testing, the sample prepared by this method has a 1C gram capacity of 243.5mAh / g. (Discharge rate, 1C means 1 times, specifically, it takes 1 hour to fully charge.) The resistance test showed that the sheet resistance of the sample prepared by this method was 1.2Ω.

[0022] After cobalt valence detection, the cobalt valence of the sample prepared by this method was 3.34.

[0023] Example 2 Steps (1) and (2) are the same as in Example 1.

[0024] (3) Secondary oxidation: Take 1000 kg of oxidized material, add 1000 L of deionized water, stir evenly, then add 10 kg of sodium persulfate, and the reaction time is 20 min.

[0025] (4) Drying: The product obtained in step 3 is washed with deionized water to a pH of 11, dried at 50-150°C, and sieved to obtain a high-valent, low-resistance cobalt-coated nickel spherical product.

[0026] The product prepared by the method has no caking phenomenon, and when the product is sieved, there is very little material on the sieve.

[0027] Scanning electron microscopy showed that the surface coating of the product prepared above was less detached. (Scanning electron microscopy is as follows Figure 3 ).

[0028] After battery testing, the sample prepared by this method had a 1C gram capacity of 243.8 mAh / g.

[0029] The resistance test showed that the sheet resistance of the sample prepared by this method was 1.6Ω.

[0030] After cobalt valence detection, the cobalt valence of the sample prepared by this method was 3.36.

[0031] Example 3 The preparation was carried out using substantially the same steps and process conditions as in Example 1, except that the oxidant used in the secondary oxidation stage was hydrogen peroxide, the addition amount was 0.1 L, and the reaction time was 15 min.

[0032] The product prepared by the method has no caking phenomenon, and when the product is sieved, there is very little material on the sieve.

[0033] Scanning electron microscopy showed that the surface coating of the product prepared above was less detached. (Scanning electron microscopy is as follows Figure 4 ) After battery testing, the sample prepared by this method had a 1C gram capacity of 243.4 mAh / g.

[0034] The resistance test showed that the sheet resistance of the sample prepared by this method was 1.2Ω.

[0035] After cobalt valence detection, the cobalt valence of the sample prepared by this method was 3.37.

[0036] Example 4 The preparation was carried out using substantially the same steps and process conditions as in Example 2, except that the oxidant used in the secondary oxidation stage was hydrogen peroxide, the addition amount was 100 L, and the reaction time was 30 min.

[0037] The product prepared by the method has no caking phenomenon, and when the product is sieved, there is very little material on the sieve.

[0038] Scanning electron microscopy showed that the surface coating of the product prepared above was less detached. (Scanning electron microscopy is as follows Figure 5 ).

[0039] After battery testing, the sample prepared by this method had a 1C gram capacity of 243.8 mAh / g.

[0040] The resistance test showed that the sheet resistance of the sample prepared by this method was 1.1Ω.

[0041] After cobalt valence detection, the cobalt valence of the sample prepared by this method was 3.33.

Claims

1. A method for oxidizing high-valence low-resistance cobalt-coated nickel balls, characterized in that: The following steps are involved: 1) Take the spherical nickel hydroxide coated with cobalt hydroxide and add it into the oxidation reactor. Under stirring conditions, preheat it to 150-180℃, then add 1-5mol / L sodium hydroxide solution, and then introduce oxygen for primary oxidation. The oxygen flow rate is 3-6m 3 / h, oxygen flow time 15-30min; 2) Add the material after the primary oxidation in step 1) into the reactor, add deionized water at a solid-liquid ratio of 2:1-1:2, stir and mix well, add the oxidant, heat to 40-90°C and perform oxidation reaction for 5-20 minutes; 3) The product obtained in step 2) is washed with deionized water until the pH value is 9-11, dried at 90-120° C., and passed through a 300-mesh sieve to obtain a high-valent, low-resistance cobalt-coated nickel spherical product.

2. A method for oxidizing high-valence low-resistance cobalt-coated nickel balls as claimed in claim 1, characterized in that: In step 1), the cobalt content of the spherical nickel hydroxide coated with cobalt hydroxide is 2.0-4.0%; the cobalt content of the spherical nickel hydroxide matrix is ​​0.8-1.0%, the zinc content is 2.8-4.0%, and the nickel content is 53-55%.

3. A method for oxidizing high-valence low-resistance cobalt-coated nickel balls as claimed in claim 1, characterized in that: In step 1), the stirring frequency in the preheating stage is 5-15 Hz, the stirring frequency in the alkali addition stage is 30-50 Hz, and the stirring frequency in the oxidation stage is 15-30 Hz.

4. A method for oxidizing high-valence low-resistance cobalt-coated nickel balls as claimed in claim 1, characterized in that: In step 2), the oxidant is one of sodium persulfate or hydrogen peroxide, and the amount added is 0.2% to 2% of the mass of the material after the primary oxidation.

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