Secondary battery

Abstract

To provide a secondary battery in which charge / discharge capacity is enhanced by lowering the internal resistance.SOLUTION: The positive electrode includes a positive electrode active material 40 containing at least one of nickel hydroxide and manganese dioxide, and the negative electrode includes a negative electrode current collector 10 and a negative electrode active material 20, in which the negative electrode active material contains a porous-carbon as a porous-material 110 and a hydrophilic-carbon conductive powder as a carbon-based conductive assistant 140, and an amount of Zn contained in the negative electrode is 15wt% or less.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present disclosure relates to secondary batteries, and more particularly to alkaline secondary batteries. [Background technology]

[0002] In recent years, the importance of batteries has rapidly increased in many industries, and various new battery systems that have advantages mainly in terms of capacity, energy density, and rechargeability have been developed and improved.

[0003] Patent Document 1 discloses an alkaline secondary battery equipped with a zinc electrode using a zinc negative electrode mixture containing a zinc-containing compound and a conductive additive, the zinc negative electrode mixture containing particles having an average particle diameter of 1000 μm or less and an aspect ratio (length / width) of 1.1 or more. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Japanese Patent Application Laid-Open No. 2014-026951 Summary of the Invention [Problem to be solved by the invention]

[0005] The secondary battery disclosed in Patent Document 1 uses a carbon material or the like as a conductive additive. Table 1 shows the HSP (Hansen solubility parameter) values, which are the surface compatibility indexes of carbon materials used in general manufacturing methods, and water and alcohol-based solvents used as ink solvents. In the table, δ D is the energy derived from the dispersion forces between molecules, and δ P is the energy resulting from intermolecular dipole interactions, and δ H is the energy derived from the hydrogen bonding forces between molecules. [Table 1]

[0006] Carbon materials have a particularly high δ P and δ H Because the carbon materials have significantly different properties, they are poorly compatible with these solvents. Therefore, carbon materials have low dispersibility in these solvents and tend to aggregate. As a result, secondary batteries using carbon materials as conductive additives have problems such as high internal resistance and difficulty in increasing charge / discharge capacity because a sufficient conductive network is not formed.

[0007] The present disclosure has been made to solve such problems, and has an object to provide a secondary battery that reduces internal resistance and improves charge / discharge capacity. [Means for solving the problem]

[0008] The secondary battery according to the present disclosure includes a positive electrode, a negative electrode, and a separator disposed between the positive electrode and the negative electrode, wherein the positive electrode includes a positive electrode active material containing at least one of nickel hydroxide and manganese oxide, and the negative electrode includes a negative electrode current collector and a negative electrode active material, wherein the negative electrode active material includes porous carbon as a porous material and a hydrophilic carbon conductive powder as a carbon-based conductive additive, and the amount of Zn contained in the negative electrode is 15 wt % or less. This makes it possible to provide a secondary battery with reduced internal resistance and improved charge / discharge capacity.

[0009] The carbon-based conductive additive may further contain multi-walled carbon nanotubes, thereby providing a secondary battery with reduced internal resistance and improved charge / discharge capacity.

[0010] The negative electrode current collector may contain a metal selected from Cu, Fe, and Ni, or an alloy containing at least one of them, thereby providing a secondary battery with reduced internal resistance and improved charge / discharge capacity.

[0011] Furthermore, the hydrophilic conductive carbon powder may have functional groups such as hydroxyl groups or carboxyl groups on a portion of its surface, thereby providing a secondary battery with reduced internal resistance and improved charge / discharge capacity. [Effects of the Invention]

[0012] According to the present disclosure, a secondary battery with reduced internal resistance and improved charge / discharge capacity can be provided. [Brief explanation of the drawings]

[0013] [Figure 1] 1 is a schematic diagram illustrating an example of a secondary battery according to a first embodiment. [Figure 2] 1 is a graph showing evaluation results of secondary batteries of Examples and Comparative Examples. DETAILED DESCRIPTION OF THE INVENTION

[0014] Hereinafter, embodiments of the present disclosure will be described with reference to the drawings. Fig. 1(a) is a diagram showing an example structure of a secondary battery 1 according to the present disclosure. The secondary battery 1 shown in the example of Fig. 1(a) has a configuration including a negative electrode current collector 10, a negative electrode active material 20, a positive electrode current collector 30, a positive electrode active material 40, and a separator 50, some of which are immersed in an electrolyte solution 60. In the present disclosure, the negative electrode current collector 10 and the negative electrode active material 20 are referred to as the negative electrode, and the positive electrode current collector 30 and the positive electrode active material 40 are referred to as the positive electrode.

[0015] Fig. 1(b) is an enlarged view of the area surrounded by the dotted line in Fig. 1(a), namely, the vicinity of the surface of the negative electrode current collector 10. As shown in Fig. 1(b), a porous material 110, an additive 120, a binder 130, and a carbon-based conductive additive 140 are formed on the surface of the negative electrode current collector 10. Hereinafter, the porous material 110, the additive 120, the binder 130, and the carbon-based conductive additive 140 will be referred to as a negative electrode active material 20.

[0016] The negative electrode current collector 10 may be made of any material as long as it is electrically conductive, such as metal or graphite. Metal is preferred from the viewpoints of electrical conductivity and workability. The metal may be a metal selected from Cu, Fe, or Ni, or stainless steel or an alloy containing at least one of the above metals. Furthermore, the metal may be surface-treated by plating, reflow plating, etching, or the like. Plated metals are preferred from the viewpoint of operating potential. An example of the negative electrode current collector 10 is a Cu foil plated with Ni, which can suppress Cu elution. Furthermore, Sn- or In-based plating may be applied to suppress side reactions.

[0017] The shape of the negative electrode current collector 10 is not particularly limited, but metal foil or punched metal can be used, and physical irregularities may be added to the surface.

[0018] The negative electrode active material 20 is disposed on the surface of the negative electrode current collector 10, and includes a porous material 110, an additive 120, a binder 130, and a carbon-based conductive additive 140.

[0019] The porous material 110 preferably contains porous carbon, which is carbon powder particles that have a large specific surface area and exhibit high hydrophilicity. Examples of porous carbon include activated carbon, graphite, and hard carbon. The porous carbon has a density of 1.5 to 2.2 g / cm. 2 True density and 500m 2 / g~5000m 2 The average particle size and pore distribution of the porous carbon are not particularly limited, and the porous carbon may have a single particle size or may contain different particle sizes.

[0020] The additive 120 is preferably powder particles of bismuth oxide (Bi2O3) and indium oxide (In2O3). The average particle size of the bismuth oxide is preferably less than 1 μm, and the average particle size of the indium oxide is preferably less than 50 μm. The additive 120 may further include an organic additive such as oxalic acid.

[0021] The additive 120 may contain zinc oxide (ZnO), but in the secondary battery according to the present disclosure, the amount of Zn contained in the negative electrode is preferably 15 wt% or less. By setting the amount of Zn to 15 wt% or less, input / output characteristics are improved, especially at high currents.

[0022] The binder 130 is preferably made of styrene butadiene rubber (SBR) or polytetrafluoroethylene (PTFE) because of its chemical stability.

[0023] The carbon-based conductive additive 140 is preferably a carbon conductive powder that has high hydrophilicity, extremely high dispersibility in a solvent, a particle size of 0.01 to 1 μm, and an average particle size of about 0.1 μm.

[0024] In addition to the carbon conductive powder, MWCNT (Multi-Walled Carbon Nanotube), VGCF (Vapor Growth Carbon Fiber), and SWCNT (Single Wall Nanotube) may also be added.

[0025] The hydrophilicity and dispersibility referred to here are expressed in terms of sedimentation properties, and refer to a state in which 80% or more of the carbon conductive powder does not sediment even when left in pure water for a long period of time, for example, 24 hours or more. Furthermore, it is preferable that the carbon conductive powder has functional groups such as hydroxyl groups or carboxyl groups on a portion of its surface. This makes the carbon conductive powder more likely to have high hydrophilicity and dispersibility.

[0026] The method for forming the negative electrode active material 20 is not limited, but examples include a method in which the porous material 110, additive 120, binder 130, carbon-based conductive additive 140, and surfactant as a dispersion aid are mixed to produce an ink, which is then applied to the negative electrode active material 20, dried, and pressed to form the ink. The weight ratio of the ink is preferably 90 parts porous material 110, approximately 10 parts carbon-based conductive additive, 3 parts or less additive 120, 7 parts or less binder 130, and 0.1 parts or less dispersion aid. The solvent is preferably about 99 parts water and 1 part alcohol-based solvent, but this may be changed as desired depending on the viscosity and target thickness.

[0027] The positive electrode current collector 30 is preferably made of Ni, Ni-plated steel sheet, or porous nickel. The positive electrode active material 40 preferably contains at least one of nickel hydroxide (Ni(OH)2) and manganese oxide (Mn2O3). When the theoretical capacity of the positive electrode is taken as 1, the theoretical capacity of the negative electrode active material 20 is preferably 0.5 to 2.0.

[0028] The separator 50 preferably uses either or both of a hydrophilic or hydrophilized nonwoven fabric and a microporous film such as polypropylene (PP).

[0029] The electrolyte 60 is preferably an aqueous potassium hydroxide (KOH) solution with a concentration of 3M to 7M, in which zinc oxide or tin oxide, or other inorganic salts are dissolved in a weight ratio range of 0 to 15 wt %.

[0030] In the secondary battery 1 according to the present disclosure, by using a highly hydrophilic carbon conductive powder as the carbon-based conductive additive 140 contained in the negative electrode active material 20, dispersibility in the solvent is improved, a sufficient conductive network is formed, the internal resistance is reduced, and the charge / discharge capacity is improved. [Example]

[0031] The secondary battery according to the present disclosure will be described in detail with reference to examples and comparative examples, but the secondary battery according to the present disclosure is not limited to the following examples.

[0032] <Example 1-1> A 30 μm thick Ni foil was used as the negative electrode current collector, and the specific surface area was 1000 m 2 Black ink was prepared by mixing activated carbon powder with an average particle size of 60 μm, hydrophilic conductive carbon powder with an average particle size of approximately 0.1 μm, fine Bi2O3 particles with an average particle size of 3 μm, high-purity reagent In2O3, SBR dispersion, and Gemini surfactant E40 in a solids weight ratio of 90:10:2.5:0.03:7:0.05, adding pure water to give a viscosity of 10 Pa·s, stirring, and degassing.

[0033] The black ink was uniformly applied to the negative electrode current collector, dried, and roll-pressed, and a 120 μm-thick tin-plated copper foil was joined to the tab end using a resistance welder to form a negative electrode.

[0034] The positive electrode was a composite electrode of nickel Celmet and Co-coated Ni(OH)2, and was selected so that the capacity ratio of the negative electrode to the positive electrode (negative electrode capacity ÷ positive electrode capacity) was approximately 1.5. 100 μm Ni foil was welded to the terminal.

[0035] The positive electrode was entirely wrapped in a 120 μm thick hydrophilic nonwoven fabric, and two negative electrodes were used to sandwich one positive electrode, forming a secondary battery according to the present disclosure.

[0036] The secondary battery was placed in a case, and 0.2 wt%, 2.5 wt%, and 0.3 wt% of LiOH, NaOH, and ZnO were added to a 6M KOH solution as an electrolyte, respectively. After appropriate amounts were dropped, the case was sealed and left to stand for a certain period of time to prepare a single cell.

[0037] This single cell was subjected to one cycle of 0.2C CC charge (Cutoff: 1.65V) and 0.2C CC discharge (Cutoff: 1.1V) and two cycles of 0.5C CC charge (Cutoff: 1.65V) and 0.5C CC discharge (Cutoff: 1.1V) to activate the battery.

[0038] <Example 1-2> The basic structure and materials were the same as in Example 1, and in addition to the hydrophilic carbon conductive powder, multi-walled carbon nanotubes were added at 1 part based on the above solid content weight ratio.

[0039] <Examples 1-3> The basic structure and materials were the same as in Example 1, and in addition to the hydrophilic carbon conductive powder, multi-walled carbon nanotubes were added at 2 parts by weight based on the above solid content ratio.

[0040] <Example 2> The basic configuration and materials were the same as in Example 1-1, but the surfactant was changed from Gemini surfactant E40 to Gemini surfactant E100.

[0041] Example 3 The basic configuration and materials were the same as in Example 1-1, and no surfactant was added as a dispersion aid. Pure water was added as the ink solvent, and 1 part of ethanol was added based on the above solid content weight ratio.

[0042] Example 4 The basic configuration and materials were the same as in Example 1-1, and no surfactant was added as a dispersion aid. Pure water was added as the ink solvent, and 1 part of IPA (isopropanol) was added based on the solid content weight ratio.

[0043] <Example 5> The basic configuration and materials were the same as in Example 1-1, except that Gemini surfactant E40 was used as the surfactant, and pure water was used as the ink solvent, with 1 part of ethanol added relative to the above solid weight ratio.

[0044] <Comparative Example 1> The carbon-based conductive aid was changed from hydrophilic carbon conductive powder to hydrophobic acetylene black, and the ink was prepared using pure water as the solvent only without adding a surfactant as a dispersion aid.

[0045] <Comparative Example 2> The ink was prepared by changing the carbon-based conductive additive from hydrophilic carbon conductive powder to hydrophobic acetylene black (AB), and using sodium laurylbenzenesulfonate (LAS) as a surfactant.

[0046] <Comparative Example 3> The ink was prepared by changing the carbon-based conductive aid from hydrophilic carbon conductive powder to hydrophobic acetylene black, and using Softazoline CPB (registered trademark), an amidobetaine-type amphoteric surfactant, as the surfactant.

[0047] The produced inks were evaluated for performance as follows. [Ink status] The state of the coating film when the ink was applied to the negative electrode current collector was visually evaluated and classified according to the following criteria. A: Good C: Poor coating [Air bubbles in the ink] After stirring and degassing, the occurrence of bubbles in the ink was visually evaluated and classified according to the following criteria. A: None B: Somewhat remaining C: Occurrence [Coating condition] The ink was applied to the negative electrode current collector, and the state of the coating film after drying was visually evaluated and classified according to the following criteria. A: Good B: Slightly rough C: Rough [Paint film cracking] The ink was applied to the negative electrode current collector, and after drying, cracks in the coating were visually evaluated and classified according to the following criteria. A: None B: Slightly C: Significant

[0048] The evaluation results are shown in Table 2. [Table 2] *1: Indicates the ratio of battery capacity when the battery capacity of Comparative Example 1 is set to 100

[0049] The battery capacity of Example 1-1 was significantly increased compared to Comparative Example 1. This indicates that the use of highly dispersible hydrophilic conductive carbon powder formed a sufficient conductive network, reduced internal resistance, and improved charge / discharge capacity.

[0050] For Example 2, properties almost the same as those for Example 1-1 were obtained. This shows that good properties can be obtained even if the type of surfactant is changed.

[0051] For Example 3, properties were obtained that were approximately the same as those for Examples 1-1 and 2. This shows that good properties can be obtained even when ethanol is added instead of a surfactant.

[0052] For Example 4, properties were obtained that were approximately the same as those for Examples 1-1, 2, and 3. This shows that good properties can be obtained even when IPA is added instead of a surfactant.

[0053] It can be seen that Example 5 exhibits even better properties than Examples 1-1, 2, 3, and 4, and the coating film state is also good, and high electrical properties and high coating film performance are obtained.

[0054] By comparing the results of Comparative Examples 1, 2, and 3 with Example 1, it is clear that highly dispersible hydrophilic conductive carbon powder has a significant effect on charge / discharge capacity.

[0055] Next, an example of the results of charge / discharge measurements is shown in Figure 2. Improvements in charge and discharge were confirmed in Examples 1-1 to 1-3 compared to Comparative Example 1. Furthermore, it was found that the discharge characteristics were particularly improved in Examples 1-2 and 1-3, in which multi-walled carbon nanotubes were added.

[0056] The present disclosure is not limited to the above-described embodiment, and can be modified as appropriate within the scope of the present disclosure. [Explanation of symbols]

[0057] 1 Secondary battery 10 Negative electrode current collector 20 Negative electrode active material 30 Positive electrode current collector 40 Cathode active material 50 Separator 60 Electrolyte 110 Porous materials 120 Additives 130 Binder 140 Carbon-based conductive additives

Claims

1. a positive electrode, a negative electrode, and a separator disposed between the positive electrode and the negative electrode; the positive electrode comprises a positive electrode active material containing at least one of nickel hydroxide and manganese oxide; the negative electrode includes a negative electrode current collector and a negative electrode active material, the negative electrode active material includes porous carbon as a porous material and hydrophilic carbon conductive powder as a carbon-based conductive additive, The amount of Zn contained in the negative electrode is 15 wt% or less. Secondary battery.

2. The carbon-based conductive additive further contains multi-walled carbon nanotubes. The secondary battery according to claim 1 .

3. the negative electrode current collector contains a metal selected from Cu, Fe, and Ni, or an alloy containing at least one of them; The secondary battery according to claim 1 .

4. The hydrophilic carbon conductive powder has a functional group such as a hydroxyl group or a carboxyl group on a part of its surface. The secondary battery according to claim 3 .

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