JPH0628167B2 - Secondary battery rebalancing method - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to a rebalancing method for a secondary battery, and more specifically, it produces hydrogen as a by-product on the negative electrode side at the end of charging to produce a positive electrode active material halide solution (hereinafter referred to as positive electrode). Liquid) is an overcharged state of the redox flow type secondary battery rebalancing method.

[Conventional technology]

Taking an iron-chromium secondary battery as an example, the redox flow type secondary battery flows an aqueous solution of chromium ions (Cr ²⁺ ) and an aqueous solution of trivalent iron ions (Fe ³⁺ ) in a discharged state. By passing it through the positive electrode chamber and the negative electrode chamber that are partitioned by the diaphragm of the electrolytic cell, Fe ³⁺ receives one electron at the positive electrode and becomes divalent Fe ²⁺ , and Cr ²⁺ turns 1 electron at the negative electrode.
The lost trivalent Cr ³⁺ becomes an electron exchanged between the negative electrode and the positive electrode, works through an external circuit, and releases electric power. On the other hand, if the reverse operation is performed, charging is performed. The transfer of electrons (oxidation and reduction in a broad sense) is performed by separate electrodes, the electrons flow through an external circuit to release electric energy, and the chemical energy is converted into electric energy.

In the redox flow type secondary battery, a small amount of hydrogen gas is produced as a by-product from the negative electrode (chromium) side, but the positive electrode liquid and the negative electrode active material halide solution (hereinafter referred to as the negative electrode liquid).
There will be a difference in the charge and discharge depth. This difference widens as the charge and discharge are repeated, the overcharged state of the positive electrode liquid (excess of Fe ³⁺ ) progresses, and the capacity of the battery decreases. In order to avoid this, it is necessary to provide a rebalance device to consume hydrogen generated from the negative electrode, and reduce Fe ³⁺ in the positive electrode liquid to bring the positive and negative electrode liquids into a normal charged state. . Such a method of eliminating the imbalance of the charge / discharge depth of the positive electrode liquid and the negative electrode liquid is called a rebalancing method of the secondary battery.

As a conventional rebalancing method, (1) Fe ³⁺ -H ₂ fuel cell method (positive electrode solution and, Fe ³⁺ -H ₂ fuel cell provided separately-product and hydrogen respectively at the negative electrode of the redox flow type battery Of excess F in the positive electrode liquid by flowing through the positive electrode and the negative electrode of
e ³⁺ is reduced and the hydrogen is consumed),
(2) Br ₂ mediator method (when the positive electrode solution of a redox flow battery contains bromide ions, the positive electrode solution in an overcharged state is branched and circulated to both the anode and the cathode of a separately provided electrolytic cell, and bromine is supplied from the anode. And the excess Fe ³⁺ is reduced at the cathode. The positive electrode liquids merged again after electrolysis eliminate the overcharged state. Bromine produced and by-product at the negative electrode of the redox flow battery Hydrogen is allowed to flow through the positive electrode and the negative electrode of a separately provided Br ₂ —H ₂ fuel cell to react with each other, and the generated hydrogen bromide is absorbed in the positive electrode liquid of the redox flow type battery), (3) Cl
₂ Mediator method (When the positive electrode solution of a redox flow battery contains chloride ions, an overcharged positive electrode solution is branched and flowed to both the anode and cathode of a separate electrolytic cell to electrolyze chlorine from the anode. At the same time, excess Fe ³⁺ is reduced at the cathode, and the overcharged state is eliminated in the positive electrode liquids that have been merged again after electrolysis.
Hydrogen, which is a by-product of the negative electrode of the flow-type battery, is provided separately from C.
l ₂ -H ₂ fuel is reacted by circulating to the positive electrode and the negative electrode of the battery, to absorb the hydrogen chloride generated in the positive electrode liquid of the redox flow type battery), etc. are known.

In the above-mentioned (1) Fe ³⁺ -H ₂ fuel cell method, rebalancing is performed in a one-step process, while platinum and the like used as a catalyst for the hydrogen electrode are oxidized and eluted by Fe ³⁺ , and this eluate is When it comes into contact with the negative electrode liquid, it is reduced to serve as a hydrogen generation catalyst, which significantly accelerates the reaction between divalent chromium ions and hydrogen ions (self-discharge reaction). That is, the catalyst (such as platinum) of the fuel cell may be eluted and contaminate the positive electrode liquid and the negative electrode liquid.

Further, in the (2) Br ₂ mediator method and the (3) Cl ₂ mediator method, a catalyst such as platinum is required on the hydrogen electrode side similarly to the Fe ³⁺ -H ₂ fuel cell, but bromine (or chlorine) is required. ) And hydrogen as gases to the fuel cell, and the reaction product hydrogen bromide (or hydrogen chloride)
Also returns to the system as a gas, so there is no liquid junction between the fuel cell and the positive and negative electrode liquids, so even if the catalyst such as platinum elutes, the redox flow type secondary battery is prevented from being contaminated with platinum. To be done. However, in these methods, since the electrolytic reduction reaction is forcibly promoted, although the followability and stability of Fe ³⁺ reduction are excellent, the electric power required for electrolysis is required. Even under the rebalance condition, the output of the secondary battery main body reaches, for example, 0.5 to 2%, which causes a decrease in the secondary battery charge / discharge efficiency. In addition, in these fuel cells, the polarization including the mass transfer of the bromine electrode (or chlorine electrode) tends to be rate-determining, so the rated current density is several mA.
It is necessary to make the reaction as small as cm ^-2 or less so that the reaction proceeds smoothly. Also, catalysts such as platinum do not contaminate redox flow type batteries, but Br ₂ (or C
L ₂ ) easily oxidizes and elutes. As a result, for example, it is necessary to increase the area of the electrode supporting platinum, which causes a problem of significantly increasing the manufacturing cost.

[Problems to be solved by the invention]

An object of the present invention is not to elute the catalyst such as platinum at the hydrogen electrode of the rebalancing fuel cell, which is excellent in stability, and does not reduce the charging / discharging efficiency of the secondary battery due to operation of the rebalancing device. An object of the present invention is to provide a rebalancing method for a secondary battery that is low in cost and does not lead to enlargement of equipment.

[Means for solving problems]

The first aspect of the present invention is a secondary charging and discharging operation in which a halide solution of a positive electrode active material and a negative electrode active material (a positive electrode solution and a negative electrode solution) is respectively supplied from a positive electrode solution tank and a negative electrode solution tank to a positive electrode and a negative electrode of a battery body. The oxidation state of the positive electrode active material in the halide solution of the positive electrode active material, which occurs when hydrogen is by-produced from the negative electrode during charging of a battery, is compared with the reduction state of the negative electrode active material in the halide solution of the negative electrode active material. In the rebalancing method of the secondary battery, which eliminates the difference in charge / discharge state between the halide solution of the positive electrode active material and the halide solution of the negative electrode active material, which is excessive, the first stage separate from the secondary battery. And a second-stage fuel cell is provided, and the positive electrode active material halide solution containing the active material in excess of the oxidation state is supplied to the positive electrode of the first-stage rebalancing fuel cell, and the negative electrode is used as a secondary electrode. Hydrogen is supplied to the negative electrode of the second-stage rebalancing fuel cell, and the first-stage rebalancing is performed between the negative electrode of the first-stage rebalancing fuel cell and the positive electrode of the second-stage rebalancing fuel cell. The first-stage rebalance is performed by circulating the halide solution of the redox couple, which emits electrons at the negative electrode of the balancing fuel cell to become an oxidant and takes in the electrons at the positive electrode of the second-stage rebalancing fuel cell to become a reductant. And a positive electrode active material in excess of the oxidation state is reduced by the fuel cell for use in the fuel cell, and the by-produced hydrogen is oxidized into hydrogen ions by the fuel cell for second-stage rebalancing.

In a second aspect of the present invention, in the first method, the power generated by the first-stage rebalancing fuel cell is used as a power source of a circulation pump that circulates the redox pair halide solution and the by-produced hydrogen is used as the first source. It is characterized by being used as a power source for a blower which is supplied to the negative electrode of a two-stage rebalancing fuel cell.

As described above, this type of secondary battery is called a redox flow type battery. In the present invention, a halide solution of the positive electrode active material and the negative electrode active material of the redox flow battery (a positive electrode solution and a negative electrode solution) means a positive electrode active material and a negative electrode active material whose redox state is reversibly changed by charging and discharging. A solution containing a halide ion (eg, chloride ion and / or bromide ion) dissolved therein, which is used as a positive electrode active material such as FeCl ₃ / FeCl ₂
As a negative electrode active material, for example, CrCl ₂ / CrC
l ₃ pairs are used.

Further, in the present invention, the redox pair halide solution is used as a mediator to dissolve an oxidation / reduction body (redox) pair having a reversible equilibrium potential located between the electrode potential of the positive electrode active material and the electrode potential of the negative electrode active material, Solution and a solution containing the same halide ion as the negative electrode solution. At this time, the equilibrium potential of the redox vs. halide solution is 0 to +0.4.
It is preferable to use a redox pair that serves as VvsRHE (reversible hydrogen electrode standard) from the viewpoint of avoiding elution of a catalyst metal such as platinum and improving stability, and these redox pairs include Ti ⁴⁺ / Ti ³⁺ , Sn. ^{4 +} / Sn ²⁺ etc.
Particularly, Ti ⁴⁺ / Ti ³⁺ is preferable because it does not affect precipitation even when mixed in the negative electrode liquid. Hereinafter, in the present invention,
The redox-halide solution is also referred to as a mediator solution.

INDUSTRIAL APPLICABILITY The rebalancing method of the present invention is also effective as a rebalancing method for a solution-type positive electrode active material type secondary battery involving hydrogen generation such as a zinc-chlorine battery, a zinc-bromine battery, a bromine-chromium battery, and a chlorine-chromium battery. is there.

Hereinafter, the present invention will be described in more detail with reference to the drawings.

〔Example〕

FIG. 1 is an explanatory diagram of a two-stage fuel cell type rebalance device according to the present invention. This device comprises a positive electrode liquid tank 4 and a negative electrode liquid tank 5 connected to a secondary battery body (for example, an iron-chromium redox flow type secondary battery) 9, and a mediator tank for storing a redox-halide solution (mediator solution). 3, a first-stage fuel cell 1 having a positive electrode chamber and a negative electrode chamber partitioned by a diaphragm, to which the mediator solution and the Fe ³⁺ excess positive electrode liquid overcharged in the positive electrode liquid tank 4 are respectively supplied, A negative electrode partitioned by a diaphragm, to which a mediator solution containing a redox pair (hereinafter referred to as a mediator) oxidized in the first-stage fuel cell 1 and H ₂ gas produced as a by-product on the negative electrode side of the main battery are respectively supplied. A second stage fuel cell 2 having a chamber and a positive electrode chamber. In such a configuration, the mediator solution is supplied to the negative electrode of the first-stage fuel cell 1 by the mediator liquid feed pump 6, where an oxidation reaction is performed, and the mediator in the mediator solution releases electrons to oxidize. Become a body. The mediator solution containing the oxidant is sent to the positive electrode of the second stage fuel cell 2, where a reduction reaction is performed, and the mediator is returned to the mediator tank 3 as a reducer. On the other hand, the positive electrode liquid is supplied to the positive electrode of the first-stage fuel cell 1, receives the electrons emitted by the mediator, undergoes a reduction reaction of Fe ³⁺ + e → Fe ²⁺ , and is returned to the positive electrode liquid tank 4. Further, by-produced H ₂ gas in the secondary battery negative electrode side is supplied to the negative electrode of the second stage fuel cell 2 by the H ₂ gas blower from negative electrolyte tank 5, H ₂
→ H ⁺ + e oxidation reaction is carried out and it becomes hydrogen ion,
It moves to the positive electrode (mediator electrode) of the second stage fuel cell 2 through the diaphragm.

The electric power generated by the first-stage fuel cell 1 is voltage-controlled by a load 8 and consumed as power for the mediator liquid-sending pump 6 and the H ₂ gas blower 7. The second-stage fuel cell 2 is energized through a short circuit or a small load.

In the rebalancing method of the present invention, Ti is used as a mediator.
^{4 +} / Ti ³⁺ , Sn ⁴⁺ / Sn ²⁺ etc. Equilibrium potential is 0 to +0.4
It is preferable to use a redox pair that results in VvsRHE. As a result, the catalyst (such as platinum) does not elute at the hydrogen electrode and becomes stable. Also, unlike the conventional Br ₂ or Cl ₂ mediator method, electrolysis power is not required, and the power of the mediator liquid feed pump 6 and the H ₂ gas blower 7 is covered by the power of the first-stage fuel cell for rebalancing. You can Therefore, the power consumption of the rebalancing process in the present invention is about 1/10 of the equipment of the conventional Br ₂ mediator method or Cl ₂ mediator method, which is about the same as that of the Fe ³⁺ -H ₂ fuel cell equipment. You can do it now.

〔The invention's effect〕

According to the present invention, a two-stage fuel cell is provided, an excess positive electrode active material is reduced by the first-stage rebalancing fuel cell, and hydrogen by-produced by the second-stage rebalancing fuel cell is consumed. By doing so, used as a catalyst of the hydrogen electrode of the rebalancing fuel cell, for example, because it is possible to avoid contact between the platinum and the positive electrode liquid of the secondary battery body, there is no elution of the catalyst metal in the hydrogen electrode, It is possible to stably rebalance the positive electrode liquid and the negative electrode liquid of the secondary battery body. Further, by using the electric power generated by the rebalancing fuel cell as the power source of the rebalancing liquid feed pump and the air blowing blower, the rebalancing device is operated without lowering the charge / discharge efficiency of the secondary battery body. be able to. Therefore, it is possible to adjust the charge depth of the positive and negative electrode liquids of the secondary battery at low cost without requiring an expensive structural material.

[Brief description of drawings]

FIG. 1 is an explanatory diagram of a two-stage fuel cell type rebalance device according to the present invention. 1 ... First-stage fuel cell, 2 ... Second-stage fuel cell, 3 ...
Mediator tank, 4 ...... cathode solution tank, 5 ...... negative electrolyte tank, 6 ...... mediator liquid feed pump, 7 ...... H ₂
Gas blower, 8 ... Load, 9 ... Rechargeable battery body.

Claims (2)

[Claims] 1. A secondary battery that is charged and discharged while supplying a halide solution of a positive electrode active material and a negative electrode active material to a positive electrode and a negative electrode of a battery main body from a positive electrode liquid tank and a negative electrode liquid tank, respectively. The positive electrode active state in which the oxidation state of the positive electrode active material in the halide solution of the positive electrode active material caused by by-product is excessive with respect to the reduction state of the negative electrode active material in the halide solution of the negative electrode active material. In a method of rebalancing a secondary battery, which eliminates a difference in charge / discharge state between a halide solution of a substance and the negative electrode active material halide solution, a first-stage fuel cell and a second-stage fuel cell are provided separately from the secondary battery. Supplying the positive electrode active material halide solution containing the active material in excess of the oxidation state to the positive electrode of the first-stage rebalancing fuel cell, and generating hydrogen by-produced in the negative electrode in the second-stage rebalan. To the negative electrode of the first-stage rebalancing fuel cell and between the negative electrode of the first-stage rebalancing fuel cell and the positive electrode of the second-stage rebalancing fuel cell. Is released to become an oxidant, and the halide solution of the redox couple, which becomes a reductant by taking in electrons at the positive electrode of the second-stage rebalancing fuel cell, is circulated to circulate the first
A secondary battery, wherein the positive electrode active material in an excessive oxidation state is reduced by a stage rebalancing fuel cell, and the by-produced hydrogen is oxidized into hydrogen ions by the second stage rebalancing fuel cell. Rebalancing method. 2. Hydrogen is discharged from the negative electrode during charging of a secondary battery that is charged and discharged while supplying a halide solution of the positive electrode active material and the negative electrode active material from the positive electrode liquid tank and the negative electrode liquid tank, respectively, to the positive electrode and the negative electrode of the battery body. The positive electrode active state in which the oxidation state of the positive electrode active material in the halide solution of the positive electrode active material caused by by-product is excessive with respect to the reduction state of the negative electrode active material in the halide solution of the negative electrode active material. In a method of rebalancing a secondary battery, which eliminates a difference in charge / discharge state between a halide solution of a substance and a halide solution of the negative electrode active material, a first-stage fuel cell and a second-stage fuel cell are provided separately from the secondary battery. Supplying a positive electrode active material halide solution containing the active material in excess of oxidation state to the positive electrode of the first-stage rebalancing fuel cell, and generating hydrogen by-produced in the negative electrode in the second-stage rebalan. To the negative electrode of the first-stage rebalancing fuel cell and between the negative electrode of the first-stage rebalancing fuel cell and the positive electrode of the second-stage rebalancing fuel cell. Is released to become an oxidant, and the halide solution of the redox pair, which becomes an reductant by taking in electrons at the positive electrode of the second-stage rebalancing fuel cell, is circulated to circulate the first solution.
The above-mentioned positive electrode active material in excess of oxidation state is reduced by the fuel cell for stage rebalancing, and the by-produced hydrogen is oxidized into hydrogen ions by the fuel cell for second stage rebalancing, and for the first stage rebalancing. Using the electric power generated in the fuel cell as a power source for a circulation pump that circulates the redox pair halide solution and as a power source for a blower that supplies the by-produced hydrogen to the negative electrode of the second-stage rebalancing fuel cell. Rechargeable battery rebalancing method featuring.