JP2018166072A - Power storage element - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a power storage element in which both of deterioration in capacity after repetition of charge and discharge and increase of inner resistance are suppressed.SOLUTION: A power storage element such as a nickel hydride secondary battery includes: a separator with fibers having a thickness of 4 μm or less; and an electrolytic solution containing zinc.SELECTED DRAWING: None

Description

  The present invention relates to a power storage element such as a nickel metal hydride storage battery.

  Conventionally, a nickel-metal hydride storage battery including a positive electrode having nickel hydroxide as an active material, a negative electrode having a hydrogen storage alloy, and an electrolytic solution is known (for example, Patent Document 1).

  In the battery described in Patent Document 1, the hydrogen storage alloy of the negative electrode has an atomic ratio of 0.015 to 0 with respect to Misch metal containing at least 60 to 90 wt% La, Ni, Co, Mn, and Misch metal. A rare earth-based hydrogen storage alloy containing Mg in the range of 0.1 as a constituent element. A surface treatment is applied to the rare earth-based hydrogen storage alloy. The electrolytic solution contains a zinc compound.

JP 2001-291510 A

In the battery described in Patent Document 1, the capacity may decrease or the internal resistance may increase after repeated charging and discharging.
This embodiment makes it a subject to provide the electrical storage element in which both the capacity | capacitance fall after repeating charging / discharging and an internal resistance raise were suppressed.

  The electrical storage element of this embodiment contains the separator which has a fiber with a thickness of 4 micrometers or less, and the electrolyte solution containing zinc. With the above-described configuration, both the decrease in capacity and the increase in internal resistance after repeated charge / discharge are suppressed.

  According to the present embodiment, it is possible to provide a power storage device in which both the decrease in capacity and the increase in internal resistance after repeated charge / discharge are suppressed.

FIG. 1 is a cross-sectional view of a storage element (nickel metal hydride storage battery) according to this embodiment.

  Hereinafter, an embodiment of a power storage device according to the present invention will be described with reference to FIG. There exists a secondary battery in an electrical storage element. In the present embodiment, a chargeable / dischargeable secondary battery will be described as an example of a power storage element. In addition, the name of each component (each component) of this embodiment is a thing in this embodiment, and may differ from the name of each component (each component) in background art.

  The electricity storage device 1 of the present embodiment is an alkaline storage battery containing an alkaline electrolyte. More specifically, the electric storage element 1 is a nickel-metal hydride storage battery that has a nickel compound as an active material for a positive electrode and uses a hydrogen storage alloy as an active material for a negative electrode. This type of power storage element 1 supplies electric energy. The electric storage element 1 is used singly or in plural. Specifically, the storage element 1 is used as a single unit when the required output and the required voltage are small. On the other hand, when at least one of the required output and the required voltage is large, the power storage element 1 is used in a power storage device (module) in combination with another power storage element 1. In the power storage device, the power storage element 1 used in the power storage device supplies electric energy.

  As shown in FIG. 1, the power storage element 1 includes an electrode group 2 including a positive electrode 21, a negative electrode 22, and a separator 23, and a case 3 that houses the electrode group 2. In addition to the electrode group 2 and the case 3, the power storage element 1 includes an electrolytic solution, a connection member 5 that electrically connects the positive electrode 21 of the electrode group 2 and a part of the case 3, and the like.

  The electrode group 2 is formed by winding a laminate in which the positive electrode 21 and the negative electrode 22 are laminated with the separator 23 being insulated from each other.

  The positive electrode 21 has a current collecting plate and a mixture adhering to the current collecting plate. The current collecting plate is, for example, a metal plate such as foamed nickel. The mixture contains, for example, a particulate active material or a conductive agent. In the present embodiment, the positive electrode 21 is formed by applying a mixture to a foamed nickel plate as a current collector plate. In addition, the thickness of the positive electrode 21 is usually 300 μm or more and 1200 μm or less.

  The current collector plate of the positive electrode 21 of the present embodiment is, for example, a nickel foam plate. The current collector plate is strip-shaped.

The positive electrode mixture contains a particulate active material (active material particles), a particulate conductive agent, and a binder. The mixture mass per unit area in the positive electrode is usually 100 mg / cm ² or more and 500 mg / cm ² or less.

  The positive electrode mixture includes particles containing nickel hydroxide as active material particles. Since a part of nickel hydroxide changes to nickel oxyhydroxide with charging, the above particles may contain nickel oxyhydroxide. The particle diameter of the particles is usually 5 μm or more and 15 μm or less. The positive electrode mixture usually contains 95% by mass to 99% by mass of the active material.

  The positive electrode mixture contains, for example, polytetrafluoroethylene (PTFE), polyvinylidene fluoride (PVdF), ethylene-propylene-diene terpolymer (EPDM), sulfonated EPDM, styrene butadiene rubber (SBR), and the like as a binder. To do. The positive electrode mixture usually contains 0.1% by mass or more and 0.8% by mass or less of a binder. The positive electrode mixture may contain a cellulose derivative such as methylcellulose or a polysaccharide such as xanthan gum as a thickener for the mixture at the time of production.

  The mixture of positive electrodes contains a carbonaceous material, a metal material, etc. as a electrically conductive agent. Examples of the carbonaceous material include graphite such as natural graphite and artificial graphite, carbon black such as ketjen black (registered trademark) and acetylene black, carbon whisker, carbon fiber, and vapor grown carbon fiber. Examples of the metal material include nickel, gold, and cobalt compounds. The positive electrode mixture usually contains 0 to 5% by mass of a conductive agent. The conductive agent is usually in the form of particles.

  The negative electrode 22 has a current collector plate and a mixture adhering to the current collector plate. The current collector plate is, for example, a metal plate (such as a perforated steel plate) having a plurality of holes in the thickness direction. The mixture contains, for example, a particulate hydrogen storage alloy or a conductive agent. In the present embodiment, the negative electrode 22 is formed by applying a mixture to a perforated steel plate as a current collector plate. In addition, the thickness of the negative electrode 22 is usually 200 μm or more and 800 μm or less.

  The current collector plate of the negative electrode 22 of the present embodiment is, for example, a perforated steel plate subjected to nickel plating.

The negative electrode mixture contains a particulate hydrogen storage alloy, a particulate conductive agent, and a binder. The mass per unit area of the negative electrode mixture is usually 100 mg / cm ² or more and 500 mg / cm ² or less.

The negative electrode mixture includes, for example, hydrogen storage alloy particles containing a rare earth element. The hydrogen storage alloy is, for example, an alloy of AB type ₅ (rare earth-Ni system), AB _3.0-3.8 type (rare earth- _Mg -Ni system), or AB ₂ type (Laves phase). As the hydrogen storage alloy, for example, an alloy having a composition of Mm _1.0 Ni _4.0 Co _0.7 Al _0.3 Mn _0.3 is employed. Note that Mm is a misch metal [lanthanum (La), cerium (Ce), praseodymium (Pr), neodymium (Nd), etc.] that is a mixture of rare earth elements. The particle size of the hydrogen storage alloy is usually 30 μm or more and 60 μm or less. The negative electrode mixture usually contains 95% by mass or more and 99% by mass or less of a hydrogen storage alloy.

It is preferable that the particles of the hydrogen storage alloy have been treated with an alkaline aqueous solution. As the alkaline aqueous solution (treatment liquid), it is preferable to use any one of potassium hydroxide (KOH), sodium hydroxide (NaOH), lithium hydroxide (LiOH), or a mixed solution. The concentration of the alkaline aqueous solution is preferably 7 mol / L or more and 12 mol / L or less, the temperature in the treatment is preferably 80 ° C. or more and less than the boiling point, and the treatment time is 1 hour or more and 4 hours or less. preferable. In particular, when the hydrogen storage alloy is AB _3.0-3.8 type (rare earth- _Mg -Ni-Al system) and does not contain Co which is easily corroded by alkali, the concentration is 10 mol / L or more with an alkaline aqueous solution containing KOH. It is preferable that the treatment time is 1 hour or more at a temperature of 110 ° C. or more using an alkaline aqueous solution. With such treatment conditions, a dense Ni layer can be formed on the particle surface of the hydrogen storage alloy, thereby improving the corrosion resistance of the hydrogen storage alloy and improving the cycle life.

  The negative electrode mixture contains the same binder as that of the positive electrode mixture described above. The negative electrode mixture usually contains 0.1% by mass or more and 2.0% by mass or less of a binder. The negative electrode mixture may contain a cellulose derivative such as methylcellulose or a polysaccharide such as xanthan gum as a thickener for the mixture during production. The negative electrode mixture usually contains 0.01% by mass to 0.5% by mass of a thickener.

  The negative electrode mixture contains the same conductive agent as that of the positive electrode mixture described above. The negative electrode mixture usually contains 0 to 5% by mass of a conductive agent. The conductive agent is usually in the form of particles.

  In the electrode group 2 of the present embodiment, the positive electrode 21 and the negative electrode 22 configured as described above are wound in a state where they are insulated by the separator 23. That is, in the electrode group 2 of this embodiment, the laminated body of the positive electrode 21, the negative electrode 22, and the separator 23 is wound. The separator 23 is an insulating member. The separator 23 is disposed between the positive electrode 21 and the negative electrode 22. Thereby, in the electrode group 2 (specifically, a laminated body), the positive electrode 21 and the negative electrode 22 are insulated from each other. The separator 23 holds the electrolytic solution in the case 3.

  The separator 23 has a strip shape. The separator 23 is disposed between the positive electrode 21 and the negative electrode 22 in order to prevent a short circuit between the positive electrode 21 and the negative electrode 22.

The separator 23 has at least fibers having a thickness of 4 μm or less (hereinafter also referred to as ultrafine fibers). The thickness of the ultrafine fiber is usually 1 μm or more. The thickness of the ultrafine fiber may be 2 μm or more. Further, the thickness of the ultrafine fiber may be 3 μm or less.
Since the separator 23 includes comparatively thin ultrafine fibers, the contact between the fibers increases by the amount of the thin fiber, and the separator 23 can sufficiently hold the electrolyte. It is considered that the decrease in the capacity and the increase in the internal resistance are suppressed even after the charge / discharge is repeated as long as the separator 23 can hold the electrolytic solution sufficiently.

  The separator 23 may include a fiber (ultrafine fiber) having a thickness of 4 μm or less and a fiber (hereinafter also referred to as normal fiber) having a thickness of 10 μm or more. Usually, the thickness of the fiber is preferably 20 μm or less. Usually, the thickness of the fiber may be 10 μm or more and 25 μm or less.

  The thickness of each fiber in the separator 23 is obtained by observing the separator 23 with a scanning electron microscope or an optical microscope and calculating the thickness of each fiber from the magnification of the observation image based on the thickness measured in the observation image. To be determined. In addition, the thickness of each fiber is determined by measuring the thickness of 5 points selected at random other than the tip, and averaging them.

  The mass ratio of the ultrafine fibers to the normal fibers in the separator 23 may be 5 or more and 40 or less.

  The separator 23 is porous. The separator 23 is, for example, a woven fabric or a non-woven fabric. Examples of the material of the separator 23 include a polymer compound, glass, and ceramic. Examples of the polymer compound include polyesters such as polyacrylonitrile (PAN), polyamide (PA), and polyethylene terephthalate (PET), and polyolefins (PO) such as polypropylene (PP) and polyethylene (PE).

  The case 3 includes a case main body 31 having a circular opening, and a disc-shaped lid portion 32 that closes (closes) the opening of the case main body 31. The case 3 further includes a gasket 33 disposed between the opening peripheral portion of the case body 31 and the peripheral portion of the lid portion 32. Case 3 accommodates electrode group 2 and the electrolytic solution in the internal space. Case 3 is formed of a metal having resistance to the electrolytic solution. Examples of the material of the case 3 include iron-based metal materials such as iron and steel. The case 3 is formed of, for example, a metal plate whose surface is subjected to nickel plating or galvanization.

  The gasket 33 is made of, for example, an insulating synthetic resin. The case 3 is formed by joining the peripheral edge of the opening of the case main body 31 and the peripheral edge of the disc-shaped lid 32 with the gasket 33 being overlapped. By the gasket 33, the case main body 31 and the lid portion 32 are electrically insulated. The case 3 has an internal space defined by the case main body 31 and the lid portion 32. In this embodiment, the opening peripheral part of the case main body 31 and the peripheral part of the cover part 32 are joined by crimping.

  The case body 31 has a cylindrical shape (that is, a bottomed cylindrical shape) in which an end in the direction opposite to the opening direction is closed. The case main body 31 has a hollow cylindrical side wall portion and a disc-shaped bottom portion that closes one opening of the side wall portion (an opening opposite to the opening of the case main body 31). Inside the case main body 31, the electrode group 2 is accommodated so that the winding axis direction of the electrode group 2 and the cylindrical axis direction of the side wall portion are the same direction. The bottom portion of the case body 31 functions as a negative electrode terminal when the negative electrode 22 is electrically connected.

  The lid portion 32 is a disk-shaped member that closes the opening of the case main body 31. The center part of the cover part 32 protrudes outward. The protruding portion functions as a positive electrode terminal by being electrically connected to the positive electrode 21 via the connecting member 5 having elasticity.

  The lid 32 has a safety valve 321 that can discharge the gas in the case 3 to the outside. The safety valve 321 discharges gas from the inside of the case 3 to the outside when the internal pressure of the case 3 rises to a predetermined pressure.

  The electrolytic solution is an alkaline (for example, pH 14 to 15) aqueous solution. The electrolytic solution is obtained by dissolving an electrolyte in water. The electrolyte is an alkali metal hydroxide such as potassium hydroxide or sodium hydroxide. The electrolytic solution of the present embodiment is obtained by dissolving potassium hydroxide, sodium hydroxide, or the like in water so that the concentration of alkali metal is 6 to 9M.

The electrolytic solution contains zinc. Specifically, the electrolytic solution contains zinc dissolved in the electrolytic solution. The dissolved zinc is usually in an ionic state (Zn ²⁺ , [Zn (OH) ₄ ] ^2−, etc.). For example, the electrolytic solution is prepared by dissolving zinc oxide or zinc hydroxide.
When the electrolytic solution contains zinc, it is possible to suppress the β-nickel oxyhydroxide of the positive electrode 21 from being changed to γ-nickel oxyhydroxide. When β-nickel oxyhydroxide is changed to a γ-form, swelling of the positive electrode active material becomes relatively large, and the capacity may decrease or the internal resistance may increase after repeated charge and discharge. On the other hand, the zinc in the electrolyte prevents the β-nickel oxyhydroxide from changing to a γ-form, which may cause the capacity to decrease or the internal resistance to increase after repeated charge and discharge. Can be suppressed.
Moreover, it can suppress that the hydrogen storage alloy of the negative electrode 22 corrodes because electrolyte solution contains zinc. Also by this, it can suppress that a capacity | capacitance falls or an internal resistance raises after charging / discharging is repeated.

  The electrolytic solution may contain zinc in an amount of 0.05 mol / L to 1.0 mol / L in terms of Zn. The Zn conversion is to express the zinc content in the electrolytic solution in terms of the amount of zinc element (Zn).

  Next, the manufacturing method of the electrical storage element 1 of the said embodiment is demonstrated.

  In the manufacturing method of the electrical storage element 1, first, the positive electrode 21 is produced by apply | coating the mixture containing an active material to current collector plates, such as a nickel foam board. Moreover, the negative electrode 22 is produced by apply | coating the mixture containing an active material to current collector plates, such as a perforated steel plate. Next, the positive electrode 21, the separator 23, and the negative electrode 22 are overlapped to form the electrode group 2. Subsequently, the electrode group 2 is put in the case 3 and the electrolytic solution is put in the case 3 to assemble the power storage device 1.

  In producing the positive electrode 21, a mixture containing an active material is applied and filled on the current collector plate. The mixture usually further contains rare earth oxides such as Y and Yb, a binder, and a solvent (water). By changing the coating amount of the mixture, the mass of the mixture per unit area can be adjusted. As a method for applying the mixture, a general method is adopted. And the water in a mixture is volatilized by a drying process.

  In producing the negative electrode 22, a mixture containing an active material is applied to the current collector plate. The mixture usually further includes a conductive agent, a binder, and a solvent (water). By changing the coating amount of the mixture, the mass of the mixture per unit area can be adjusted. As a method for applying the mixture, a general method is adopted. And the water in a mixture is volatilized by a drying process. A commercially available product can be used as the separator 23.

  In the formation of the electrode group 2, the electrode group 2 is formed by winding a laminate in which the separator 23 is sandwiched between the positive electrode 21 and the negative electrode 22. Specifically, the positive electrode 21, the separator 23, and the negative electrode 22 are overlapped to form a laminate. The electrode assembly 2 is formed by winding the laminate.

  The electrolytic solution can be prepared, for example, by dissolving potassium hydroxide or sodium hydroxide in water and further dissolving a zinc compound such as zinc oxide. The composition of the electrolytic solution can be confirmed by analysis using ICP or ion chromatograph.

  In assembling the electricity storage device 1, the electrode group 2 is placed in the case body 31 of the case 3, and the electrolytic solution is placed in the case body 31. The opening of the case body 31 is closed with the lid portion 32 by caulking.

  The electricity storage device 1 of the present embodiment configured as described above includes a separator 23 having a fiber having a thickness of 4 μm or less, and an electrolytic solution containing zinc. With such a configuration, both the decrease in capacity and the increase in internal resistance after repeated charge / discharge are suppressed.

  In addition, the electrical storage element of this invention is not limited to the said embodiment, Of course, a various change can be added in the range which does not deviate from the summary of this invention. For example, the configuration of another embodiment can be added to the configuration of a certain embodiment, and a part of the configuration of a certain embodiment can be replaced with the configuration of another embodiment. Furthermore, a part of the configuration of an embodiment can be deleted.

  In the said embodiment, although the electrical storage element 1 provided with the electrode group 2 by which a laminated body was wound was demonstrated in detail, the electrical storage element of this invention may be provided with the laminated body which is not wound. Specifically, the storage element may include an electrode group in which a positive electrode, a separator, a negative electrode, and a separator, each formed in a rectangular shape, are stacked a plurality of times in this order. The shape of the electricity storage element 1 is not particularly limited, and is, for example, a cylindrical shape, a rectangular parallelepiped shape, a sheet shape, or the like.

  In the above embodiment, the case where the power storage element 1 is used as a chargeable / dischargeable alkaline storage battery (for example, a nickel metal hydride storage battery) has been described, but the type and size (capacity) of the power storage element 1 are arbitrary. Moreover, in the said embodiment, although the nickel hydride storage battery was demonstrated as an example of the electrical storage element 1, it is not limited to this.

  The power storage element 1 (for example, a battery) may be used in a power storage device (a battery module when the power storage element is a battery). The power storage device includes at least two power storage elements 1 and a bus bar member that electrically connects two (different) power storage elements 1 to each other. In this case, the technique of the present invention may be applied to at least one power storage element.

  As shown below, an alkaline storage battery (nickel metal hydride storage battery) was manufactured.

Example 1
(1) Preparation of positive electrode 5 wt% cobalt hydroxide is coated on the surface of nickel hydroxide particles containing 3 wt% zinc and 0.06 wt% cobalt in solid solution, What carried out the air oxidation process for 1 hour at 110 degreeC using 18M sodium hydroxide aqueous solution was used as a positive electrode active material. A paste is prepared by mixing an aqueous solution in which a thickener (carboxymethylcellulose) is dissolved, an active material, and 1% by mass of ytterbium oxide with respect to the active material, and the substrate surface density is 320 g / m ² . The paste was filled in foamed nickel and dried. Then, a 2400 mAh positive electrode plate was produced by pressing to a predetermined thickness (0.63 mm).

(2) Production of Negative Electrode Powder of hydrogen storage alloy (La _0.62 Y _0.13 Mg _0.15 Ni _3.45 Al _0.15 composition) pulverized so as to have an average particle diameter D50 of 60 μm at 110 ° C. Stir vigorously in 10M aqueous potassium hydroxide for 2 hours. Thereafter, washing with water was repeated until the pH reached 10. As a result of measuring the treated alloy powder with a vibrating sample magnetometer, the magnetization was 0.7 Am ² / kg. 100 parts by mass of the dried powder and an aqueous solution in which a thickener (methylcellulose) was dissolved were mixed, and 1 part by mass of a binder (styrene butadiene rubber) was added to prepare a paste. The prepared paste was applied to both sides of a 35 μm thick perforated steel plate (opening ratio 50%) and dried, and then pressed to a thickness of 0.26 mm to produce a 3100 mAh negative electrode plate.

(3) Separator A non-woven fabric having a basis weight of 40 g / m ² subjected to a sulfonation treatment was used as a separator. The separator contained PP fibers (ultrafine fibers) having a thickness of 2 to 3 μm and PP / PE fibers (normal fibers) having a thickness of 15 to 20 μm. The mass ratio of ultrafine fibers to normal fibers was 30%.

(4) Preparation of electrolytic solution As the electrolytic solution, one prepared by the following method was used. KOH, NaOH, and LiOH were added to water as a solvent to prepare an electrolytic solution so that the concentration was K / Na / Li = 2.5 / 5 / 0.5 mol / L. Furthermore, ZnO was added and dissolved so as to have a concentration of 0.5 mol / L to prepare an electrolytic solution.

(5) Arrangement of electrode group in case A battery was manufactured by a general method using the above positive electrode, the above negative electrode, the above electrolytic solution, a separator, and a case.
First, a sheet-like material in which a separator was disposed between the positive electrode and the negative electrode and laminated was wound. Next, the wound electrode group was placed in a hollow cylindrical case body in which nickel was plated on iron. Subsequently, the positive electrode was electrically connected to the lid of the case. On the other hand, the negative electrode was brought into contact with the side surface of the case (battery can) to energize. Furthermore, the above electrolytic solution was put in a 2.3 g case. Finally, a lid was attached to the case body and caulked to seal the case to produce a 2,400 mAh battery.

(Comparative Example 1)
A battery was manufactured in the same manner as in Example 1 except that the battery was manufactured without adding zinc oxide to the electrolytic solution.

(Comparative Example 2)
A battery was manufactured in the same manner as in Example 1 except that the battery was manufactured using a separator having only normal fibers.

(Comparative Example 3)
A battery was manufactured in the same manner as in Example 1 except that the battery was manufactured without adding zinc oxide to the electrolytic solution and that the battery was manufactured using a separator having only ordinary fibers.

(Initialization)
About the battery of an Example and each comparative example, initialization was performed in the following procedures. Charging was performed at 20 ° C. under the condition of 0.1 ItA (240 mA) for 12 hours, and then discharging was performed under the condition of 0.2 ItA (480 mA) until reaching 1 V, and this was repeated for 2 cycles. Thereafter, it was stored at 40 ° C. for 48 hours. Then, charging is performed for 16 hours at 20 ° C. under the condition of 0.1 ItA (240 mA), paused for 1 hour, discharged until 1 V is satisfied under the condition of 0.2 ItA (480 mA), and this is repeated for 3 cycles. Ended.

(Capacitance measurement and internal resistance after 100 cycle test)
At 20 ° C., -dV = 5 mV was charged at 0.5 ItA (1200 mA), paused for 0.5 hour, discharged until 1 V was obtained under the condition of 1 ItA (2400 mA), and this was repeated 100 cycles. Thereafter, discharging was performed under the condition of 0.2 ItA (480 mA) until the voltage became 1 V.
Then, charging was performed at 20 ° C. under the condition of 0.1 ItA (240 mA) for 16 hours, paused for 1 hour, discharged to 1 V under the condition of 0.2 ItA (480 mA), and the discharge capacity was measured. Moreover, the internal resistance of 1 kHz was measured at 20 degreeC using the contact resistance meter of the battery in the discharge state.

(Cycle life)
At 20 ° C., charge -dV = 5 mV at 0.5 ItA (1200 mA), pause for 0.5 hour, discharge until 1 V at 1 ItA (2400 mA), and 60% of the discharge capacity of the first cycle The number of cycles at the time was defined as the cycle life.

  As can be seen from Table 1, in the battery of the example, both the decrease in capacity and the increase in internal resistance after repeated charge and discharge were significantly suppressed. Further, the cycle life of the battery of the example was significantly longer than the cycle life of the battery of the comparative example.

1: Power storage element (nickel metal hydride storage battery),
2: Electrode group,
21: positive electrode, 22: negative electrode, 23: separator,
3: Case, 31: Case main body, 32: Cover part.

Claims (1)

A separator having a fiber with a thickness of 4 μm or less;
An electricity storage device comprising an electrolyte solution containing zinc.

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