Electrode active material for secondary battery, method for producing same, and alkaline manganese secondary battery

Abstract

The present disclosure provides: an active material for a manganese oxide-zinc secondary battery, with which it is possible to achieve a manganese oxide-zinc secondary battery that is improved in terms of both the cycle characteristics and the utilization rate of an electrode active material in comparison to conventional active materials for a zinc secondary battery; and a method for producing the active material for a manganese oxide-zinc secondary battery. An electrode active material for a secondary battery according to the present disclosure is characterized by including a manganese oxide and a conductive assistant, and is also characterized in that the conductive assistant is present in at least a part of the manganese oxide surface, and the manganese / carbon area ratio of the conductive assistant is not less than 0.30 but less than 1.0.

Description

Electrode active material for secondary battery, method for producing same, and alkaline manganese secondary battery

[0001] The present disclosure relates to a manganese oxide-zinc-based secondary battery active material, more specifically to an electrode active material for a secondary battery, a method for producing the same, and an alkaline manganese secondary battery containing the electrode active material for a secondary battery in the positive electrode.

[0002] Lithium ion secondary batteries, which are the mainstream of secondary batteries, have issues in terms of safety and cost, and high safety and low cost are required. Compared to lithium ion secondary batteries, secondary batteries that do not use a non-aqueous electrolyte solution and are therefore high in safety and low in cost have been studied, including secondary batteries that use manganese dioxide as a positive electrode active material, zinc as a negative electrode active material, and an aqueous zinc sulfate solution as an aqueous electrolyte solution (manganese dioxide-zinc secondary batteries) (for example, Patent Document 1).

[0003] Japanese Patent Application Publication No. 2-132773

[0004] However, the positive electrode active material in the manganese dioxide-zinc secondary battery disclosed in Patent Document 1 is a state in which electrolytic manganese dioxide and a conductive additive simply coexist, and both the utilization rate and cycle characteristics of the manganese dioxide are low.

[0005] An object of the present disclosure is to provide a manganese oxide-zinc-based secondary battery active material, which can provide a manganese oxide-zinc-based secondary battery having improved electrode active material utilization and cycle characteristics compared to conventional zinc-based secondary battery active materials, and a method for producing the same.

[0006] The present inventors have investigated electrode active materials for manganese oxide-zinc secondary batteries and have found that, by controlling the state of the conductive additive and manganese oxide, when used as a secondary battery active material for manganese oxide-zinc secondary batteries, it is possible to obtain a manganese oxide-zinc secondary battery that achieves both high utilization of the electrode active material and excellent cycle characteristics.

[0007] That is, the present invention is the invention as recited in the claims, and the gist of the present disclosure is as follows. [1] An electrode active material for a secondary battery, comprising manganese oxide and a conductive additive, the conductive additive being present on at least a portion of the surface of the manganese oxide, and characterized in that the conductive additive has a manganese / carbon area ratio of 0.30 or more and less than 1.00. [2] The electrode active material for a secondary battery according to [1], wherein the manganese oxide is manganese dioxide. [3] The electrode active material for a secondary battery according to [1] or [2], wherein the conductive additive is acetylene black. [4] The electrode active material for a secondary battery according to [1] or [2], wherein the manganese oxide content is 70.0 mass % or more and 99.9 mass % or less. [5] A method for producing the electrode active material for a secondary battery according to [1] or [2], comprising a mixing step of mixing the manganese oxide and the conductive additive while applying compression, shear, and impact. [6] A positive electrode active material for a secondary battery comprising the electrode active material for a secondary battery according to [1] or [2]. [7] A positive electrode having the positive electrode active material for a secondary battery according to [6]. [8] An alkaline manganese secondary battery having the positive electrode according to [7].

[0008] The present disclosure provides a manganese oxide-zinc secondary battery active material and a method for producing the same, which can yield a manganese oxide-zinc secondary battery with improved electrode active material utilization and cycle characteristics.

[0009] FIG. 1 is a schematic diagram illustrating how to determine the areas of manganese regions and carbon regions.

[0010] The present embodiment provides an electrode active material for a secondary battery (hereinafter referred to as "the active material"), characterized in that it contains manganese oxide and a conductive additive, the mass ratio of the manganese oxide to the conductive additive is 90:10 to 99:1, the conductive additive is present on at least a portion of the surface of the manganese oxide, and the manganese / carbon area ratio (Mn / C area ratio) determined by EDS mapping is 0.30 or more and less than 1.0.

[0011] The active material contains manganese oxide and a conductive additive, and functions as an active material for a secondary battery.

[0012] The manganese oxide contained in the present active material may be a compound containing manganese and oxygen, such as MnO, Mn ２ O ３ , MnO ２ and Mn ３ O ４ and MnO ２ (manganese dioxide) is preferred, and electrolytic manganese dioxide is more preferred.

[0013] The conductive additive contained in the present active material may be at least one of crystalline carbon and amorphous carbon, and examples thereof include one or more selected from the group consisting of acetylene black, ketjen black, denka black, graphite, and carbon nanotubes, with acetylene black being preferred.

[0014] The mass ratio of manganese oxide to conductive additive contained in this active material is 90:10 to 99:1, and preferably 93:7 to 97:3, or 94:6 to 96:4. If the manganese oxide ratio is 90% or less, the energy density decreases, resulting in a decrease in battery capacity when used in a battery. Furthermore, if the conductive additive ratio is 1% or less, the conductive path becomes insufficient. As a result, the utilization rate of the manganese oxide decreases, resulting in a decrease in battery capacity when used in a battery.

[0015] In this active material, a conductive additive is present on at least a portion of the surface of the manganese oxide, and in particular, the conductive additive is present on at least a portion of the surface of the manganese oxide in a state that satisfies the manganese / carbon area ratio (Mn / C area ratio) described below. In the electrode composite, the manganese oxide and the conductive additive simply coexist, or the conductive additive is attached to the manganese oxide. In contrast, in this active material, the manganese oxide and the conductive additive are closely coated and interact with each other, creating a so-called composite state. This is thought to result in a synergistic effect between the manganese oxide and the conductive additive, improving both the utilization rate and cycle characteristics of the electrode active material of a manganese oxide-zinc secondary battery that uses this active material as an electrode active material.

[0016] The utilization rate of the electrode active material is a value indicating the degree of contribution of the electrode active material to the discharge capacity of the secondary battery. For example, a utilization rate of the electrode active material of 100% indicates that the discharge capacity of the secondary battery is the same as the theoretical capacity of the electrode active material.

[0017] The active material has a manganese / carbon area ratio (hereinafter simply referred to as "Mn / C area ratio") of the conductive additive determined by EDS mapping of 0.30 or more and less than 1.00. When an active material with a Mn / C area ratio of less than 0.30 is used as an electrode, the conductive additive is not sufficiently bonded to the manganese oxide, and a good conductive path is not formed. As a result, when used in a battery, the energy density and cycle characteristics are reduced. On the other hand, when an active material with a Mn / C area ratio of 1.00 or more is used as an electrode, the conductive path is insufficient, resulting in a low utilization rate of the manganese oxide. As a result, when used in a battery, the battery capacity is reduced. The Mn / C area ratio of the active material is preferably 0.30 or more, or preferably 0.40 or more, and preferably less than 1.00, or preferably 0.95 or less. Preferred Mn / C area ratios of the active material include 0.30 or more and less than 1.00, and 0.40 or more and 0.95 or less.

[0018] The Mn / C area ratio in this embodiment can be determined by a scanning electron microscope (hereinafter also referred to as "cross-sectional SEM") observation image of the cross section of the active material and an analysis by energy dispersive X-ray spectroscopy (hereinafter also referred to as "EDS"). That is, a cross-sectional SEM observation image of the active material, an EDS mapping image of manganese, and an EDS mapping image of carbon are obtained, and the Mn / C area ratio can be determined from these images using the following formula: Mn / C area ratio = S Ｍｎ / S Ｃ

[0019] In the above formula, S Ｍｎ is the area [μm ２ ] and S Ｃ is the area of ​​the carbon region corresponding to the active material in the EDS mapping diagram of carbon [μm ２ ].

[0020] The region detected in the manganese mapping diagram corresponding to the present active material observed in the cross-sectional SEM observation image can be taken as the manganese region, and the area calculated by the following method can be taken as the area of ​​the manganese region. That is, for the manganese region corresponding to each particle of the present active material, parallel straight lines (hereinafter also referred to as "division lines") are drawn at equal intervals in a certain direction, and the manganese region is divided into 10 to 100 regions (hereinafter also referred to as "divided regions"). The divided regions are approximated as trapezoids, and the area S calculated by the following formula is Ｍｎ is the area of ​​the manganese region of each particle.

[0021] S Ｍｎ [μm ２ ] = {(Lm １ +Lm ｎ＋１ ) / 2 + (Lm ２ +Lm ３ +...+Lm ｒ +Lm ｒ＋１ +...+Lm ｎ )×d

[0022] In the above formula, Lm ｎ (n = 1, 2, ... 99) is the length [μm] of the intersection between the n-th dividing line and the manganese region, and d is the interval [μm] between the dividing lines. The same operation was performed on 25 ± 10 particles, and each S Ｍｎ The arithmetic mean value of the area of ​​the manganese region (S Ｍｎ ) can be used.

[0023] Similarly, the area detected in the mapping diagram of carbon corresponding to the present active material observed in the SEM observation image can be regarded as the carbon area, and the area S calculated by the following formula Ｃ is the area of ​​the carbon region of each particle.

[0024] S Ｃ [μm ２ ]={(Lc １ +Lc ｎ＋１ ) / 2 + (Lc ２ +Lc ３ +...+Lc ｒ +Lc ｒ＋１ +...+Lc ｎ )×d In the above formula, Lc ｎ(n = 1, 2, ... 99) is the length [μm] of the intersection between the n-th dividing line and the carbon region, and d is the interval [μm] between the dividing lines. The same operation was performed on 25 ± 10 particles, and each S Ｃ The area of ​​the carbon region (S Ｃ ) can be used.

[0025] Cross-sectional SEM observation images and EDS mapping images may be observed and measured using a general cross-sectional SEM equipped with an EDS unit (for example, JSM-7600F, manufactured by JEOL Ltd.) under the following conditions: Acceleration voltage: 5 kV Magnification: 500-10,000 times

[0026] The manganese oxide content of the present active material is 70.0% by mass or more, or 75.0% by mass or more, and 99.9% by mass or less, or 99.0% by mass or less, and is preferably 70.0% by mass or more and 99.9% by mass or less, or 75.0% by mass or more and 99.0% by mass or less. A manganese oxide content of 70.0% by mass or more can be expected to provide sufficient charge / discharge capacity.

[0027] The manganese oxide content of the present active material can be determined by a method in accordance with JIS K 1467 5.2 using a general potentiometric titrator (for example, AT-610, manufactured by Kyoto Electronics Manufacturing Co., Ltd.).

[0028] The content of the conductive additive in the present active material is 0.10% by mass or more or 1.00% by mass or more, and may be 30.00% by mass or less or 25.00% by mass or less, and is preferably 0.10% by mass or more and 30.00% by mass or less, or 1.00% by mass or more and 25.00% by mass or less.

[0029] The content of the conductive additive in the present active material may be calculated using the following formula: Content of conductive additive (mass %)=100−(Content of manganese oxide (mass %))

[0030] The shape of the active material is not particularly limited as long as it can be used as a positive electrode active material, but it is preferably powder, and more preferably powder having one or more shapes selected from the group consisting of spherical, approximately spherical, polyhedral, and irregular shapes. Note that the approximately spherical shape does not necessarily have to be an ideal sphere (true sphere), and examples thereof include an oval sphere, a sphere with a missing part, a distorted sphere, and a sphere with an irregular surface.

[0031] The BET specific surface area of ​​this active material is 0.100 m ２ / g or more, or 1.00m ２ / g or more and 100m ２ / g or less, or 80m ２ / g or less, and ２ / g or more 100m ２ / g or less, or 1.00m ２ / g or more 80m ２ / g or less is preferable.

[0032] The BET specific surface area of ​​the active material can be measured by a common measuring device (e.g., Gemini VII 2390a, manufactured by Shimadzu Corporation) using a mixed gas of 30% nitrogen and 70% helium as the adsorption gas, according to the one-point method defined in 7.3 of JIS Z8830.

[0033] Before measuring the BET specific surface area, the active material can be pretreated by placing it in a glass cell for measuring the BET specific surface area and dehydrating it at 150° C. for 20 minutes in a nitrogen flow atmosphere.

[0034] The active material is an electrode active material for secondary batteries, and is suitable as a positive electrode active material for secondary batteries, and further as a positive electrode active material for manganese oxide-zinc secondary batteries.

[0035] Such a manganese oxide-zinc secondary battery is a secondary battery that includes manganese oxide as a positive electrode active material and zinc or a zinc compound or both as a negative electrode active material, and is also an alkaline manganese secondary battery.

[0036] When the present active material is used as an electrode active material, it may be made into an electrode mixture and an electrode by a known manufacturing method. For example, a method for manufacturing a positive electrode of a manganese oxide-zinc battery including the present active material includes mixing the present active material, a conductive additive, and a binder solution to obtain a positive electrode mixture slurry, which is then applied to a current collector and dried.

[0037] The method for producing the active material includes a mixing step in which manganese oxide and a conductive additive are mixed while being subjected to compression, shearing, and impact.

[0038] In the mixing step, manganese oxide and conductive additive are mixed while being subjected to compression, shear, and impact. This allows the conductive additive to adhere to the manganese oxide, rather than simply adhering to it, and allows the manganese oxide and conductive additive to interact with each other and form an adhesive coating. Conventionally, when preparing an electrode mixture, manganese oxide (electrode active material) and conductive additive are mixed. However, the mixing during preparation of the electrode mixture is performed without applying loads such as shear or impact to prevent changes in the properties of the electrode active material. Therefore, in conventional electrode mixtures, manganese oxide and conductive additive simply coexist. In contrast, in the mixing step of the present disclosure, manganese oxide and conductive additive are mixed while being subjected to compression, shear, and impact. This applies a strong load to the manganese oxide and conductive additive, and the resulting active material may have the conductive additive present in a high density on at least a portion of the surface of the manganese oxide.

[0039] The manganese oxide to be subjected to the mixing step may be any of the manganese compounds described above, and is preferably electrolytic manganese dioxide.

[0040] The average secondary particle size of the manganese oxide is 1 μm or more or 5 μm or more, and 80 μm or less or 60 μm or less, and is preferably 1 μm or more and 80 μm or less, or 5 μm or more and 60 μm or less.

[0041] The average secondary particle diameter of manganese oxide can be calculated using a general particle analysis software (e.g., Nano Hunter NS2K-Pro, manufactured by Nano Systems Co., Ltd.) from an SEM image obtained by measurement using a general scanning electron microscope (e.g., JSM-7600F, manufactured by JEOL Ltd.) under the following conditions: Acceleration voltage: 5 kV Magnification: 500x-30,000x

[0042] A specific method for calculating the average secondary particle diameter is to import a trace of particles corresponding to the observed manganese oxide into the image analysis software, and after binarization processing, the circle-equivalent diameter calculated from the area of ​​the particles can be used as the average secondary particle diameter.

[0043] The manganese oxide to be subjected to the mixing step may be any of the above-mentioned conductive additives, and is preferably acetylene black.

[0044] The particle size of the conductive additive in the present active material is 0.010 μm or more, or 0.020 μm or more, and 0.500 μm or less, or 0.350 μm or less, and is preferably 0.010 μm or more and 0.500 μm or less, or 0.020 μm or more and 0.350 μm or less.

[0045] The mass proportions of the manganese oxide and conductive aid used in the mixing step may be the same as those of the target active material, and when the total mass of the manganese oxide and conductive aid used in the mixing step is taken as 100 mass%, the mass proportion of the manganese oxide may be 70.0 mass% or more or 75.0 mass% or more, and 99.9 mass% or less or 99.0 mass% or less, with 70.0 mass% or more and 99.9 mass% or less, or 75.0 mass% or more and 99.0 mass% or less being preferred.

[0046] On the other hand, the mass proportion of the conductive additive is 0.100 mass% or more or 1.00 mass% or more, and can be 30 mass% or less or 25 mass% or less, and is preferably 0.100 mass% or more and 30 mass% or less, or 1.00 mass% or more and 25 mass% or less.

[0047] Examples of the mixing method used in the mixing step include a mixing method using an apparatus (e.g., Nobilta (registered trademark), manufactured by Hosokawa Micron) that mixes the manganese oxide and the conductive additive while applying compression, shear, and impact to them using the force generated by the rotation of a rotor.

[0048] The method for producing the active material may include, after the mixing step, at least one of a crushing step of crushing the active material and a classification step of classifying the active material.

[0049] The crushing is carried out for the purpose of crushing and dispersing the composite particles that have aggregated and become coarse after the mixing step, and examples of the crushing include crushing using one or more mills selected from the group consisting of a pin mill, a jet mill, a hammer mill, and a ball mill, and crushing using a pin mill is preferred.

[0050] The classification is carried out for the purpose of making the particle size of the active material uniform, and examples thereof include classification using one or more methods selected from the group consisting of sieves, air force, and solvents, with sieve classification being preferred.

[0051] The present disclosure will be described below with reference to examples, but the present disclosure is not limited to the following.

[0052] (Mn / C area ratio) SEM observation diagrams and EDS mapping diagrams were observed and measured using an SEM (JSM-7600F, manufactured by JEOL Ltd.) equipped with an EDS unit under the following conditions. Using the obtained EDS mapping diagram, the Mn / C area ratio was calculated by the method described above. Acceleration voltage: 5 kV Magnification: 2000x Mapping elements: carbon, manganese

[0053] Example 1: Electrolytic manganese dioxide (average secondary particle diameter 50 μm) and acetylene black (average secondary particle diameter 0.035 μm) were weighed out at a mass ratio of 95:5 (199.5 g of electrolytic manganese dioxide: 10.5 g of acetylene black). After weighing, they were mixed under the following conditions while applying compression, shear, and impact using a powder processing device Nobilta (registered trademark) (product name: NOB-130, manufactured by Hosokawa Micron).

[0054] The clearance between the rotor and casing of the powder processing device was set to 3 mm, and the temperature of the cooling water flowing through the cooling jacket was set to 18°C. The above-mentioned electrolytic manganese dioxide and acetylene black were charged, and powder processing was carried out for 30 minutes while adjusting the rotation speed so that the load power was 1.8 kW to 2.2 kW to maintain a constant compression pressure. The rotation speed was 5300 to 6100 rpm. The powder after processing was removed to obtain an active material containing electrolytic manganese dioxide and acetylene black, which was used as the active material of this example.

[0055] The manganese oxide (electrolytic manganese dioxide) content in the active material of this example was 95% by mass. Furthermore, the Mn / C area ratio of the active material of this example was 0.79, confirming that acetylene black was present on the surface of the electrolytic manganese dioxide in a state of interaction. This is thought to improve the utilization of the active material of this example in the electrode, further improving the electrode's packing ability and suppressing excessive consumption of the electrolyte, thereby improving cycle characteristics.

[0056] The present disclosure provides a manganese oxide-zinc-based secondary battery active material and a method for producing the same, which can provide a manganese oxide-zinc-based secondary battery having improved electrode active material utilization and cycle characteristics compared to conventional zinc-based secondary battery active materials.

Claims

1. An electrode active material for a secondary battery, comprising manganese oxide and a conductive aid, wherein the conductive aid is present on at least a part of the surface of the manganese oxide, and the manganese / carbon area ratio of the conductive aid is 0.30 or more and less than 1.

00.

2. The electrode active material for a secondary battery according to claim 1, wherein the manganese oxide is manganese dioxide.

3. The electrode active material for a secondary battery according to claim 1 or 2, wherein the conductive aid is acetylene black.

4. The electrode active material for a secondary battery according to claim 1 or 2, wherein the content of the manganese oxide is 70.0% by mass or more and 99.9% by mass or less.

5. A method for producing an electrode active material for a secondary battery according to claim 1 or 2, having a mixing step of mixing the manganese oxide and the conductive aid while applying compression, shear, and impact.

6. A positive electrode active material for a secondary battery containing the electrode active material for a secondary battery according to claim 1 or 2.

7. A positive electrode having the positive electrode active material for a secondary battery according to claim 6.

8. An alkaline manganese secondary battery provided with the positive electrode according to claim 7.

Images