WO2010053256A2

WO2010053256A2 - Secondary battery capable of automatically supplying an electrolyte refill

Info

Publication number: WO2010053256A2
Application number: PCT/KR2009/005217
Authority: WO
Inventors: Tae Hyuk Kang; Yun Jung Kwak; Dong Pil Park
Original assignee: Energreen Co., Ltd
Priority date: 2008-11-07
Filing date: 2009-09-14
Publication date: 2010-05-14
Also published as: WO2010053256A3; KR20100051403A

Abstract

The present invention to a secondary battery in which an electrolyte refill is supplied automatically, in order to prevent decreases in volume and increases in specific gravity of the electrolyte caused by gases produced during charging, and thereby increase the service life of the battery. The secondary battery may include: a main cell that includes a positive electrode and a negative electrode and contains an electrolyte; an auxiliary cell connected with the main cell; a case that houses the main cell and the auxiliary cell; a vent that connects the main cell with the atmosphere; a gas passageway configured to equalize pressure levels in the main cell and the auxiliary cell; and an electrolyte refill passageway through which an electrolyte refill in the auxiliary cell may pass to the main cell at or above a particular pressure level. When the volume of the electrolyte is decreased and the specific gravity is increased due to the production of gases by the dissociation reactions of the electrolyte during charging, the electrolyte refill may be supplied automatically to replenish the electrolyte, and as this can delay the decrease in charge and discharge capacity, the service life of the battery may be greatly increased.

Description

SECONDARY BATTERY CAPABLE OF AUTOMATICALLY SUPPLYING AN ELECTROLYTE REFILL

The present invention relates to a secondary battery that is capable of automatically supplying an electrolyte refill. More particularly, the invention relates to a secondary battery in which an electrolyte refill is supplied automatically, in order to prevent decreases in volume and increases in specific gravity of the electrolyte caused by gases produced during charging, and thereby increase the service life of the battery.

A secondary battery is a device that converts electrical energy into chemical energy, which may be stored and later converted back into electrical energy when necessary. Nickel-based secondary batteries are widely being used as a secondary battery, examples of which include nickel-cadmium (Ni-Cd) batteries and nickel-metal hydride (Ni-MH) batteries. The nickel-metal hydride battery is currently receiving much attention due to its high energy density, low pollution, and high performance, while the nickel-zinc (Ni-Zn) battery has recently entered the market as well.

In general, charging a nickel-based secondary battery may entail a side effect of producing oxygen gas at the positive electrode and hydrogen gas at the negative electrode, causing an increase in the internal pressure of the battery. This can lead to a leakage of the electrolyte and a decrease in charge/discharge capacity, resulting in a shorter service life for the battery.

Methods of removing the gases thus produced include reducing the gases into electrolyte via a recombination reaction, such as by increasing the ratio of the capacity of the negative electrode to the capacity of the positive electrode, and discharging the gases to the outside, such as by installing a vent for the surplus gases that have not undergone recombination. However, in a secondary battery equipped with a vent, especially a low-pressure vent, the vent may be activated even at a low internal pressure. This can lead to a frequent discharging of gases, and consequently a decrease in the amount of water in the electrolyte, whereby the specific gravity of the electrolyte may be greatly increase. This in turn may incur problems of lower charge/discharge capacity, lower quality, shorter service life, etc., and in order to resolve these problems, there is a need to supply electrolyte refills at appropriate times.

Specific methods aimed at resolving the above problems include, for example, a method of applying an electrode additive, i.e. a metal such as In, Cd, Pb, etc., or an oxide thereof, to increase the hydrogen overpotential at the negative electrode; a method of using a current collector that is plated with a metal high in hydrogen overpotential; and a method of fabricating an auxiliary electrode from a catalyst material to electrochemically oxidize the hydrogen gases produced.

However, the first and second of the methods listed above may not provide a significant effect in suppressing the production of hydrogen, while the third method may entail a complicated process, because of having to install the auxiliary electrode, as well as a high fabrication cost, due to the high cost of the catalyst electrode.

As a solution to the problems described above, an aspect of the present invention aims to provide a secondary battery in which an electrolyte refill is supplied automatically, in order to prevent decreases in volume and increases in specific gravity of the electrolyte caused by gases produced during charging, and thereby increase the service life of the battery.

To achieve the above objective, an aspect of the present invention provides a secondary battery that is capable of automatically supplying an electrolyte refill. The secondary battery includes: a main cell that includes a positive electrode and a negative electrode and contains an electrolyte; an auxiliary cell connected with the main cell; a case that houses the main cell and the auxiliary cell; a vent that connects the main cell with the atmosphere; a gas passageway configured to equalize pressure levels in the main cell and the auxiliary cell; and an electrolyte refill passageway through which an electrolyte refill in the auxiliary cell may pass to the main cell at or above a particular pressure level.

The electrolyte refill passageway can include a microporous layer that allows passage for the electrolyte refill in the auxiliary cell to the main cell at or above a particular pressure level. The gas passageway can include a microporous layer that disallows passage for liquids but allows passage for gases. The microporous layer for the electrolyte refill passageway and/or the gas passageway can be a membrane or a ceramic layer.

The opening pressure of the microporous layer can be set lower than the minimum opening pressure of the vent. In certain embodiments, the opening pressure of the microporous layer can be about 70 to 99 % of the minimum opening pressure of the vent.

The main cell and the auxiliary cell can be divided by a partition. An electrolyte refill inlet can be formed in the auxiliary cell. The electrolyte refill may be distilled water or an electrolyte that contains at least one or more components of the electrolyte of the main cell. To maintain the specific gravity of the electrolyte in the main cell, the electrolyte refill can be an electrolyte that contains at least one or more components of the electrolyte of the main cell but has a specific gravity lower than that of the main cell.

Additional aspects and advantages of the present invention will be set forth in part in the description which follows, and in part will be obvious from the description, or may be learned by practice of the invention.

In a secondary battery capable of automatically supplying an electrolyte refill, according to an aspect of the present invention, an auxiliary cell holding an electrolyte refill is included inside the case. When the volume of the electrolyte is decreased and the specific gravity is increased due to the production of gases by the dissociation reactions of the electrolyte during charging, the electrolyte refill may be supplied automatically to replenish the electrolyte, and as this can delay the decrease in charge and discharge capacity, the service life of the battery may be greatly increased.

Figure 1 is a cross-sectional view of a secondary battery capable of automatically supplying an electrolyte refill according to an aspect of the present invention.

Figure 2 and Figure 3 are cross-sectional views illustrating a process of automatically supplying an electrolyte refill, in a secondary battery capable of automatically supplying an electrolyte refill according to an aspect of the present invention.

* Description of Numerals for Key Elements *

100: secondary battery 110: case

120: main cell 140: auxiliary cell

150: partition 152: gas passageway

154: electrolyte refill passageway 156: first porous layer

158: second porous layer

Figure 1 is a cross-sectional view of a secondary battery capable of automatically supplying an electrolyte refill according to an aspect of the present invention. An embodiment of the present invention will be described below with reference to Figure 1.

The secondary battery 100 capable of automatically supplementing an electrolyte refill, according to an aspect of the present invention, may include a case 110 that is divided by a partition 150 of a particular thickness into a main cell 120 and an auxiliary cell 140.

The battery may use Ni(OH)₂ for the positive-electrode active material, ZnO, calcium zincate, etc., for the negative-electrode active material, and at least one or more types of binder, such as PTFE, for example. Also, a thickening agent, such as CMC, HEC, etc., may be used to prepare a slurry, which may be coated, dried, and compressed on a plate, sheet, foam, etc., made of Ni, Cu, a copper alloy, etc., serving as a current collector. A common separator, such as Celgard 3407, can be used as a separator for negative electrodes, and a non-woven separator can be used as a separator for positive electrodes. Each of the electrodes can be encased in a separator, after which the positive electrodes and negative electrodes may be alternately stacked together to form the battery.

Among the

cells

120, 140 divided by the partition 150, the main cell 120 may serve to convert electrical energy into chemical energy or convert chemical energy into electrical energy as necessary. The main cell 120 may include many positive electrodes 122, negative electrodes 124, and separators 126, and may be filled with a supply of electrolyte 128 up to a particular height. In an upper portion of the main cell 120, there may be installed a vent 132, for discharging the gases produced during charging to the exterior, a positive electrode terminal 134, which may be connected to a multiple number of positive electrodes 122, and a negative electrode terminal 136, which may be connected to a multiple number of negative electrodes 122.

The vent 132 can be a kind of valve that opens and exhausts gas, when the gases produced during charging raise the internal pressure of the main cell 120 to above a certain pressure level. While this particular embodiment presents a structure that opens and closes by way of a coil spring 132s and a piston 132p as an example of a vent 132, the invention is not thus limited, and a variety of structures can be applied as the vent.

The auxiliary cell 140 may serve as an auxiliary tank for holding extra refill 142, which may be used to replenish the supply of electrolyte 128 filled in the main cell 120 when the amount of electrolyte 128 is reduced. In an upper portion of the auxiliary cell 140, an electrolyte inlet 144 may be formed, through which to supply the electrolyte refill from the exterior. It can be advantageous to implement the auxiliary cell 140 with about one fifth the capacity of the main cell 120, in consideration of the redundancy, fabrication costs, etc., of the secondary battery. However, the capacity of the auxiliary cell 140 may be increased or decreased according to the requirements of the user or the intentions of the manufacturer.

The partition 150 diving the main cell 120 and auxiliary cell 140 can be fabricated as a flat member that has the same material and thickness as those of the outer wall of the case 110. To prevent the electrolyte 128 and the electrolyte refill 142 from intermixing, leaking, and moving about, it can be advantageous to have the partition 150 integrated with the case 110. In an upper portion of the partition 150, a passageway 152 may be formed through which the gases produced in the main cell 120 may pass, and in a lower portion of the partition 150, a passageway 154 may be formed through which the electrolyte refill in the auxiliary cell 140 may pass.

Here, a first porous layer 156 can be coupled to the gas passageway 152 for preventing backflow of the electrolyte and the electrolyte refill due to the secondary battery being tilted, etc., while a second porous layer 158 may be formed on the electrolyte refill passageway 154 that enables the electrolyte refill 142 to pass only when the pressure level is within a particular range. In this particular embodiment, the first and second

porous layers

156, 158 may be microporous layers made from a membrane or a ceramic material. However, the invention is not limited to such materials, and any type of material can be used that enables selective permeation.

Figure 2 and Figure 3 are cross-sectional views illustrating a process of automatically supplying an electrolyte refill, in a secondary battery capable of automatically supplying an electrolyte refill according to an aspect of the present invention. A process of automatically supplying the electrolyte refill will be described below with reference to Figure 2 and Figure 3.

Similar to a regular secondary battery, the secondary battery 100 capable of automatically supplementing an electrolyte refill according to this embodiment may also produce oxygen gas at the positive electrode and hydrogen gas at the negative electrode, as a side effect of charging. Some of the gas thus produced (oxygen and hydrogen) may be reduced into the electrolyte by way of a recombination reaction, but the remainder of the gas that has not been reduced may remain in the main cell 120 to increase the internal pressure (P _m). However, when the internal pressure (P _m) of the main cell 120 rises beyond a particular pressure level, a portion of the gas that has not been removed may move through the first porous layer 156 of the gas passageway 152 to the auxiliary cell 140, so that the internal pressure (P _m) of the main cell 120 may be kept below a certain pressure level.

When the amount of gas produced is increased and the internal pressure (P _m) of the main cell 120 rises again, the internal pressure (P _a) of the auxiliary cell 140 may rise together, and as a result, the internal pressure (P _m) of the main cell 120 may equal the internal pressure (P _a) of the auxiliary cell 140. Here, due to the production of gases, the amount of electrolyte 128 in the main cell 120 may be decreased.

When the internal pressure (P _m = P _a) of the battery reaches approximately 70 to 99 % of the minimum opening pressure (P _v) of the vent 132, some of the electrolyte refill 142 may pass through the second porous layer 158 formed in the electrolyte refill passageway 154 to the main cell 120. In this way, the electrolyte 128 of the main cell 120 may be replenished by the amount decreased by gas production (see Figure 2).

Afterwards, when the internal pressure (P _m) of the main cell 120 continues to rise and eventually exceeds the minimum opening pressure (P _v) of the vent 132, the vent 132 may be opened, to exhaust some of the gas to the exterior, and at the same time, lower the internal pressure (P _m) of the main cell 120 to below the minimum opening pressure (P _v) of the vent 132, so that the movement of the electrolyte refill through the second porous layer 158 formed in the electrolyte refill passageway 154 may be stopped. Through the above process, the level of the electrolyte 128 in the main cell 120 can be kept substantially the same as that before the gases are produced (see Figure 3).

When the amount of electrolyte refill 142 is decreased below a suitable level, due to the automatic supply of electrolyte refill described above, more electrolyte refill can be added through the electrolyte refill inlet 144 formed in the auxiliary cell 140. For example, the position of the gas passageway 152 can be set as the maximum height, and the position of the electrolyte refill passageway 154 can be set as the minimum height, where the electrolyte refill may be added up to the maximum height. Here, the maximum height of the electrolyte refill 142 added to the auxiliary cell 140 may vary according to the purpose of the secondary battery. For instance, if the secondary battery is of a stationary type, the electrolyte refill may be added up to the maximum height, and if the battery is of a portable type, the electrolyte refill may be added up to about 5 mm below the maximum height.

As described above, the secondary battery 100 according to an aspect of the present invention can automatically supply the electrolyte refill 142 filled in the auxiliary cell 140, when the amount of electrolyte 128 is decreased because of the gases produced during charging, whereby the decrease of electrolyte 128 in the main cell 120 and the increase in specific gravity may be avoided. Also, the automatic supply of an electrolyte refill can delay the decrease in charge/discharge capacity, to greatly lengthen the service life of the secondary battery.

The present embodiment was applied to a Ni-Zn secondary battery. In this example, a 3-component electrolyte of KOH/NaOH/LiOH was used in a concentration of 6 to 12 M. The electrolyte was injected into a battery, aged in a vacuum for 0.5 to 1 h, aged at 20 to 60 C for 1 to 6 h, and then activated. The amount of electrolyte was 1 to 5 g (preferably 1.5 g) per negative electrode capacity, and the amount of electrolyte on the side of the electrodes was about 10 to 50 ml. The minimum operating pressure of the vent, for discharging gases produced by cell reactions, was 1.1 to 10 atm (preferably 1.5 atm), and the amount of electrolyte decreased due to the exhaust of gas was approximately 0.67 ml/day. Under these conditions, when the supply of electrolyte on the side of the electrodes was about 30 ml, the electrolyte was depleted after about 50 days of continuous charging and discharging. However, when an electrolyte refill of 100 ml was included, the period of time passed until the electrolyte was depleted was increased by about 4 times or more.

The present embodiment was applied to a Ni-MH secondary battery. In this example, a 3-component electrolyte of KOH/NaOH/LiOH was used in a concentration of 6 to 12 M. The electrolyte was injected into a battery, aged in a vacuum for 0.5 to 1 h, aged at 20 to 60 C for 1 to 6 h, and then activated. The amount of electrolyte was 1 to 5 g (preferably 2.5 g) per positive electrode capacity, and the amount of electrolyte on the side of the electrodes was about 10 to 50 ml. The minimum operating pressure of the vent, for discharging gases produced by cell reactions, was 1.1 to 10 atm (preferably 2 atm), and the amount of electrolyte decreased due to the exhaust of gas was approximately 1.5 ml/day. Under these conditions, when the supply of electrolyte on the side of the electrodes was about 30 ml, the electrolyte was depleted after about 20 days of continuous charging and discharging. However, when an electrolyte refill of 100 ml was included, the period of time passed until the electrolyte was depleted was increased by about 4 times or more.

The composition of a secondary battery capable of automatically supplying an electrolyte refill, and a process of automatically supplying an electrolyte refill, according to certain aspects of the present invention have been presented above in the written description and drawings with reference to particular embodiments. However, these embodiments are for illustrative purposes only and do not limit the invention. Those skilled in the art will well understand that various changes and modifications can be made to the embodiments without departing from the scope and spirit of the invention.

Claims

A secondary battery capable of automatically supplying an electrolyte refill, the secondary battery comprising:

a main cell including a positive electrode and a negative electrode and containing an electrolyte;

an auxiliary cell connected with the main cell;

a case housing the main cell and the auxiliary cell;

a vent connecting the main cell with the atmosphere;

a gas passageway configured to equalize pressure levels in the main cell and the auxiliary cell; and

an electrolyte refill passageway configured to allow passage for an electrolyte refill in the auxiliary cell to the main cell at or above a particular pressure level.
The secondary battery according to claim 1, wherein the electrolyte refill passageway comprises a microporous layer allowing passage for the refill in the auxiliary cell to the main cell at or above a particular pressure level.
The secondary battery according to claim 1, wherein the gas passageway comprises a microporous layer disallowing passage for liquids and allowing passage for gases.
The secondary battery according to either claim 2 or claim 3, wherein the microporous layer is a membrane or a ceramic layer.
The secondary battery according to claim 2, wherein an opening pressure of the microporous layer is set lower than a minimum opening pressure of the vent.
The secondary battery according to claim 5, wherein the opening pressure of the microporous layer is about 70 to 99 % of the minimum opening pressure of the vent.
The secondary battery according to either claim 1 or claim 2, wherein an electrolyte refill inlet is formed in the auxiliary cell.
The secondary battery according to either claim 1 or claim 2, wherein the main cell and the auxiliary cell are divided by a partition.
The secondary battery according to claim 1, wherein the electrolyte refill is distilled water or an electrolyte containing at least one or more components of the electrolyte of the main cell.
The secondary battery according to claim 1, wherein the electrolyte refill is an electrolyte containing at least one or more components of the electrolyte of the main cell but having a specific gravity lower than that of the main cell.