JP2010040375A - Anode discharge reserve reduction method of battery module - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a method of reducing discharge reserve after initial activation by supplying oxygen into a battery in order to improve a lifetime and a charge and discharge capacity of a nickel hydrogen secondary battery. <P>SOLUTION: A battery module includes a unit battery constituted as a nickel hydrogen secondary battery and an oxygen supply source to communicate with the interior of the unit battery. After the initial activation charge and discharge of the unit battery, oxygen is supplied into the unit battery from the oxygen supply source, and is made to react with hydrogen being a discharge reserve stored in the anode. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to a method for reducing the negative electrode discharge reserve of a nickel metal hydride secondary battery module by supplying oxygen into the battery.

  Conventionally, various rechargeable secondary batteries used mainly as a power source for portable devices have been proposed. Furthermore, in recent years, a battery equipped with a rechargeable battery has been developed for vehicles such as automobiles and trains in consideration of the environment. When a secondary battery is mounted on a vehicle, regenerative power generated during braking can be stored in the mounted battery and used as a power source for the vehicle, so that the energy efficiency of the vehicle can be increased. Thus, for example, a nickel metal hydride secondary battery is considered suitable as a secondary battery mounted on a vehicle from various conditions such as energy density, load fluctuation followability, durability, and manufacturing cost (Patent Document 1). .

The electrode reaction of the nickel hydride secondary battery is expressed by the following formulas (1) and (2). The rightward reaction is a charging reaction and the leftward reaction is a discharge reaction, respectively, and M represents a hydrogen storage alloy.
Positive electrode: Ni (OH) ₂ + OH ⁻ Ｎｉ NiOOH + H ₂ O + e ⁻ (1)
Negative electrode: M + H ₂ O + e ⁻ ⇔ MH + OH ⁻ (2)

By the way, in a nickel metal hydride secondary battery, generally, as shown in FIG. 1, the negative electrode charge capacity is set to be larger than the positive electrode charge capacity in advance to enable sealing. The portion of the negative electrode that exceeds the charge capacity of the positive electrode is called charge reserve. At the time of overcharging in which charging is further performed from the fully charged state, oxygen gas is generated at the positive electrode by the reaction (3) below.
OH ⁻ → 1/4 O ₂ + 1/2 H ₂ O + e ⁻ (3)
The oxygen gas generated in the positive electrode reacts with hydrogen in the hydrogen storage alloy (M) of the negative electrode by the reaction (4) below to become H ₂ O, so that the increase in pressure inside the battery is suppressed, and the battery is sealed. It can be.
MH + 1/4 O ₂ → M + 1/2 H ₂ O (4)

  On the other hand, a large discharge capacity (that is, hydrogen) is provided in advance on the negative electrode so that the positive electrode is also regulated on the discharge side. This is called discharge reserve. Usually, a nickel metal hydride secondary battery does not function sufficiently as a battery immediately after it is assembled, so it is shipped after preliminary charge / discharge (initial activation). A material such as a conductive material and a binder other than the active material is oxidized and hydrogen generated thereby is stored in the negative electrode as a discharge reserve.

However, even after the initial activation described above, the discharge reserve further increases due to oxidation of the separator and binder, corrosion of the negative electrode alloy, and the like as the normal charge / discharge cycle proceeds. When the discharge reserve increases in this way and the charge capacity of the negative electrode becomes smaller than the charge capacity of the positive electrode, hydrogen gas is generated from the negative electrode at the end of the charge, the internal pressure rapidly rises, and the gas discharge valve Operate. Moreover, since the increase in the discharge reserve is due to the decomposition of the electrolytic solution (H ₂ O), the battery life is reduced due to the dry-out of the electrolytic solution. Furthermore, in order to prevent such an adverse effect due to the increase in the discharge reserve, if the charge reserve is set to be large, an extra negative electrode material that does not substantially contribute to the battery capacity must be filled. The volume energy density of the material is inevitably reduced.

JP 2001-110381 A

  The object of the present invention is to reduce the discharge reserve after the initial activation by supplying oxygen into the battery in order to solve the above problems and improve the life and charge / discharge capacity of the nickel metal hydride secondary battery. Is to provide a way to do.

  To achieve the above object, a negative discharge reserve reduction method for a battery module according to the present invention includes a unit battery configured as a nickel hydride secondary battery and an oxygen supply source communicating with the inside of the unit battery. A method for reducing the negative discharge reserve of the battery module, wherein after the initial activation charge / discharge of the unit battery, oxygen is supplied from the oxygen supply source to the inside of the unit battery, and the discharge is occluded in the negative electrode. Reacting with hydrogen which is a reserve.

According to this configuration, the hydrogen accumulated in the negative electrode by the initial activation reacts with oxygen supplied from the oxygen supply source to become H ₂ O, and the discharge reserve of the negative electrode is reduced. Dryout can be prevented, and deterioration of battery performance, in particular, charge / discharge cycle life can be prevented. In addition, since the discharge reserve of the negative electrode in the initial stage can be reduced, it is possible to reduce the amount of charge reserve set in advance, that is, the amount of the negative electrode active material to be additionally filled, so that the charge / discharge capacity of the entire battery can be reduced. Can be increased.

  In the negative electrode discharge reserve reducing method according to the present invention, it is preferable to adjust the supply amount of oxygen from the oxygen supply source to the inside of the unit battery based on a negative electrode discharge reserve amount measured in advance. By comprising in this way, an appropriate amount of oxygen can be supplied and discharge reserve can be reduced effectively.

In the above-described negative electrode discharge reserve reduction method according to the present invention, the battery module is provided with a cooling structure for cooling the unit battery, and oxygen is supplied to the inside of the unit battery while cooling the unit battery by the cooling structure. Is preferred. Since the reaction in which hydrogen, which is the discharge reserve, reacts with oxygen to generate H ₂ O is an exothermic reaction, the battery temperature rises when the discharge reserve is reduced by this method. An increase in battery temperature causes deterioration of materials constituting the battery and a decrease in battery performance. However, such a harmful effect can be eliminated by providing a cooling structure in the battery module.

  In the method for reducing negative electrode discharge reserve according to the present invention, the cooling structure includes, for example, electrically connecting a plurality of the unit cells to the battery module and communicating the interior with each other via a communication member. The battery stack can be provided, and a heat dissipation plate having a through hole extending perpendicularly to the stacking direction of the unit cells can be provided between adjacent unit cells of the battery stack. With such a configuration, it is possible to effectively cool not only the surface of the battery stack but also the stack surface of the unit battery with a simple structure, and prevent performance deterioration of the battery module.

  A battery module according to the present invention includes a unit battery configured as a nickel metal hydride secondary battery and an oxygen supply source that communicates with the inside of the unit battery, and the negative electrode discharge reserve is reduced by the negative electrode discharge reserve reduction method described above. The ratio of the filling amount of the negative electrode active material to the filling amount of the positive electrode active material is in a range of 100 to 400% in terms of capacity. Since the negative electrode discharge reserve can be reduced by the above method, it is possible to reduce the amount equivalent to the charge reserve of the negative electrode active material previously filled in excess of the positive electrode active material. The charge / discharge capacity can be increased.

  As described above, according to the negative discharge reserve reduction method for a battery module according to the present invention, the discharge reserve after the initial activation can be reliably reduced, and the life of the battery module and the charge / discharge capacity can be improved. .

  Hereinafter, embodiments according to the present invention will be described with reference to the drawings. However, the present invention is not limited to the embodiments.

  FIG. 2 is a schematic configuration diagram illustrating a battery module to which the discharge reserve reduction method according to an embodiment of the present invention is applied. The battery module B is mounted on a train, for example, and a plurality of unit batteries C (30 in the present embodiment) stacked in the thickness direction of the unit battery C are stacked as nickel-hydrogen secondary batteries. The battery stack 1, the communication member 3 that communicates the inside of the unit battery C, and the oxygen supply source 5 that supplies oxygen to the inside of each unit battery C via the communication member 3 are provided as main components. These are covered by a housing which will be described later.

  FIG. 3 is a cross-sectional view showing an example of the structure of the unit battery C of FIG. The unit battery C includes a separator 21, an electrode body 27 including a positive electrode 23 and a negative electrode 25, and a rectangular casing 29 that houses the electrode body 27 together with an electrolytic solution. The casing 29 includes a rectangular frame member 31 made of an insulating material, and a first lid member 33 and a second lid member 35 made of a conductive material that respectively cover the two openings of the frame member 31.

  A communication port 37 is provided on the outer surface of the frame-shaped member 31 of the casing 29 to allow the inside and the outside of the unit battery C to communicate with each other. The communication port 37 has a bifurcated communication portion 37a that protrudes toward the center of the frame-shaped member 31 substantially parallel to one side of the frame-shaped member 31 provided with the communication port 37, as will be described later. In addition, a part of the gas supply system 39 of the battery module B is configured. The unit battery C in this embodiment is nickel-hydrogen that can be repeatedly charged and discharged using nickel hydroxide as a main positive electrode active material, a hydrogen storage alloy as a main negative electrode active material, and an alkaline aqueous solution as an electrolyte. It is configured as a secondary battery.

  The structure of the electrode body 27 is not particularly limited. For example, a stacked structure in which a plurality of positive electrodes 23 and a plurality of negative electrodes 25 are alternately stacked in a predetermined direction through separators 21 bent in a pleat shape. have. The first lid member 33 and the second lid member 35 of the casing 29 are formed of a nickel-plated steel plate. The positive electrode 23 is electrically connected to the first lid member 33 and the negative electrode 25 is electrically connected to the second lid member 35. Connected. That is, the first and second lid members 33 and 35 also serve as the positive electrode current collector and the negative electrode current collector of the unit battery C, respectively. The separator 21 is not limited to the pleated one shown in FIG. 3, and for example, a bag-like one may be used.

  Next, the structure of the battery module B configured using the unit battery C will be described. As shown in FIG. 2, the battery stack 1 of the battery module B in the present embodiment is obtained by stacking unit batteries C and a heat radiating plate 41 having a structure described later. In the unit cell C, one first lid member 33 and the other second lid member 35 of the adjacent unit cells C are stacked in a direction facing each other, and further, one unit cell C is in proportion to two unit cells C. And the heat sink 41 is interposed.

  In the battery module B, a gas supply system 39 for supplying oxygen gas into each unit battery C is configured and provided as follows. As shown in FIG. 2, each of the bifurcated introduction portions 37 a of each communication port 37 provided in each unit battery C is connected to one of the introduction portions 37 a of the communication ports 37 of the adjacent unit cells C, and a gas supply passage. They are sequentially connected via a flexible connecting tube 51 that forms a part of GS, and one introduction portion 37a of the terminal unit cell C is provided in an introduction tube 52 that forms a part of the gas supply passage GS. The flow rate monitoring valve F, the flow rate adjustment valve 53, and the flow path opening / closing mechanism 55 are connected to an oxygen tank 57 serving as an oxygen gas supply source. One introduction part 37a of the unit battery C at the tip is closed by a blind plug. The communication port 37, the connection tube 51 and the introduction tube 52 that are the communication members 3, the flow meter F, the flow rate adjustment valve 53, the flow path opening / closing mechanism 55, and the oxygen tank 57 constitute a gas supply system 39 of the battery module B. Yes.

  In the gas supply system 39 configured as described above, when the supply of oxygen gas is stopped by the flow path opening / closing mechanism 55 when a predetermined number of moles of oxygen gas is supplied, a necessary amount of oxygen gas is not wasted. Can be supplied. The flow rate adjusting valve 53 may be anything that can adjust the flow rate. For example, the flow rate adjusting valve 53 may be a diaphragm type flow rate adjusting valve used for an industrial process in addition to a flow rate throttle mechanism. The flow meter F may be a positive displacement type or a rotary type such as a windmill. If a positive displacement type is used, more precise measurement is possible, and the rotary flow meter has a low flow path resistance. Further, a pressure gauge P for monitoring the pressure when oxygen is supplied to the unit battery C may be provided in the gas supply system 39.

  Note that the oxygen tank 57 that is the gas supply source 5 and devices for adjusting the gas supply amount such as the flow meter F, the flow rate adjusting valve 53, and the flow path opening / closing mechanism 55 may be provided in the battery module B. All or a part of these may be disposed outside the battery module B. Of the members constituting the gas supply system 39, members other than the communication port 37, the connecting tube 51, and the oxygen tank 57 may be omitted depending on circumstances, and the configuration and specifications thereof may be changed or added. . For example, instead of the flow meter F, a differential pressure gauge (not shown) may be provided, and the flow rate adjustment valve 53 may be controlled via a flow rate regulator (not shown). At this time, if the so-called temperature / pressure correction is performed using the pressure gauge P and the thermometer provided in the reservoir, precise flow rate adjustment is possible. The flow rate regulator 53 may be provided with an integrating function so that the flow rate regulating valve 53 is closed when a predetermined number of moles of oxygen gas is supplied. With this configuration, the flow path opening / closing mechanism 55 can be omitted, and the supply amount of oxygen gas can be automatically adjusted.

  Next, the cooling structure of the battery module B according to this embodiment will be described. As shown in FIG. 4, the heat radiating plate 41 is obtained by applying nickel plating to an aluminum material, and for passing cooling air formed as a linear through hole extending in a direction orthogonal to the stacking direction X. A plurality of ventilation holes 41a. As shown in FIG. 2, in the battery module B, the heat radiating plate 41 is laminated so as to be interposed between one first lid member 23 and the other second lid member 25 of adjacent unit cells C. Yes.

  Further, as shown in FIG. 5, flow spaces 61 and 63 for flowing air as a cooling medium are formed inside the upper portion 5 a and the bottom portion 5 b of the housing 7 of the battery module B, and the bottom portion An intake fan 65 for forcibly cooling the battery stack 1 is installed on each of the front end wall and the rear end wall of 5b. The air A introduced into the circulation space 63 of the bottom portion 5b from each intake fan 65 passes through the circulation space 61 of the upper portion 5a and is exhausted to the outside through the front and rear openings. The air enters the ventilation hole 41 a and cools the unit battery C through the heat radiating plate 41. Thus, the ventilation hole 41a functions as a cooling medium passage for cooling the unit battery C. In the present embodiment, the heat radiating plate 41 is interposed in one unit cell C at a ratio of one, but the position and number of the heat radiating plates 41 interposed may be changed as appropriate. Further, as the refrigerant, in addition to the air A, a commonly used one such as oil may be used.

  Since the heat radiating plate 41 is interposed between the first lid member 23 that is one positive electrode current collector of the adjacent unit battery C and the second lid member 25 that is the other negative electrode current collector, In order to electrically connect the unit cells C, it is necessary to have electrical conductivity. In this respect, since aluminum has a relatively low electrical resistance and a relatively high thermal conductivity, aluminum has preferable characteristics as a material for forming the heat sink 41. However, since aluminum easily oxidizes and has high contact resistance, the contact resistance is reduced by applying nickel plating to the aluminum plate.

Next, a method for reducing the negative electrode discharge reserve according to an embodiment of the present invention will be described. FIG. 6 is a flowchart showing the production process of the battery module B including the method for reducing negative discharge reserve of the battery module according to the present invention. As shown in FIG. 6, after the battery module B is assembled, it is put into an initial activation process, and charging and discharging are performed for several cycles under predetermined conditions. Thereafter, oxygen is supplied into each unit cell C of the battery module B which has been charged and discharged for initial activation and placed in a discharged state, and this oxygen reacts with hydrogen which is a discharge reserve in the negative electrode. By generating H ₂ O, the discharge reserve is reduced. The amount of oxygen supplied at this time is determined based on the measurement result of the discharge reserve amount that is performed separately from the production process of the battery module B. In addition, while oxygen is supplied to the battery module B, the unit battery C constituting the battery stack 1 of the battery module B is cooled in parallel. The battery module B is shipped after the discharge reserve reduction including the discharge reserve amount measurement, oxygen supply, and battery module cooling is performed.

The measurement of the amount of negative electrode discharge reserve in this embodiment is performed as follows, for example. First, a battery module having the same specifications as the battery module B to which oxygen is actually supplied is prepared for measuring the discharge reserve amount. The battery module is charged and discharged for initial activation under the same conditions as the actual production process to be in a discharged state, and then further discharged at a low constant current. The discharge end voltage at this time is set to a value lower than −0.2 V per unit battery C, for example, −0.5 V. When discharging is performed under such conditions and the battery voltage-discharge capacity characteristics are measured, a flat voltage region P is observed in the vicinity of -0.2 V in the overdischarge region as shown in FIG. The discharge amount x (Ah) in the flat region P represents the amount of hydrogen stored as the discharge reserve. That is, at this time, in the negative electrode, the following one-electron reaction (6)
^{MH → M + H + + e} - (6)
As a result, hydrogen of the negative electrode is oxidized. Since the electric quantity of 1 mol of electrons is 96500 coulombs and 1Ah is 3600 coulombs, the discharge quantity of xAh corresponds to 3600 x / 96500 mols of hydrogen atoms.

Since the oxygen gas (O ₂ ) required to react with 1 mol of hydrogen atoms to generate H ₂ O is ¼ mol, it corresponds to the negative electrode discharge reserve amount obtained from the above measurement. The amount of oxygen gas to be used is 3600 × / (96500 × 4) = about 0.0093 × mol.

The supply of oxygen gas into each unit battery C constituting the battery stack 1 is performed as follows, for example. First, in a state where the flow path opening / closing mechanism 55 of the gas supply system 39 shown in FIG. 2 is switched to the oxygen tank 57 side, the flow rate adjustment valve 53 is set to a predetermined value, and the communication tube 51 and the communication port 37 are connected to the oxygen tank 57. Then, oxygen gas is supplied into each unit cell C through the gas, and this oxygen gas is reacted with hydrogen accumulated in the negative electrode to generate H ₂ O. The oxygen gas supply amount is controlled by, for example, determining the oxygen gas flow rate to be supplied in advance based on the measured value of the negative electrode discharge reserve and adjusting the oxygen gas supply amount to be supplied only by the predetermined gas flow rate. be able to. Alternatively, oxygen gas supply may be performed while monitoring the voltage of the entire battery module B or each unit battery C, and the supply may be stopped when the voltage drops to a predetermined voltage value.

  According to the negative electrode discharge reserve reducing method of the battery module B according to the embodiment, the following effects are obtained.

In the method for reducing negative discharge reserve of the battery module according to the present embodiment described above, the oxygen supply source in which the battery module B having the unit battery C configured as a nickel hydride secondary battery communicates with the inside of the unit battery C. 5, after the initial activation of the battery module B, oxygen gas is supplied into the unit battery C and reacted with hydrogen, which is a discharge reserve occluded in the negative electrode. Therefore, the hydrogen accumulated in the negative electrode due to the initial activation reacts with the oxygen supplied from the oxygen supply source to become H ₂ O and the discharge reserve of the negative electrode is reduced. It is possible to prevent deterioration of battery performance, particularly charge / discharge cycle life. In addition, since the discharge reserve of the negative electrode in the initial stage can be reduced, it is possible to reduce the amount of charge reserve set in advance, that is, the amount of the negative electrode active material to be additionally filled, so that the charge / discharge capacity of the entire battery can be reduced. Can be increased.

  Further, in the negative electrode discharge reserve reducing method according to the present embodiment, the supply amount of oxygen from the oxygen supply source 5 to the inside of the unit battery C is determined based on the negative electrode discharge reserve amount measured in advance and controlled. Therefore, the discharge reserve can be effectively reduced by supplying an appropriate amount of oxygen.

Furthermore, since the battery module B is provided with a cooling structure for cooling the unit cells C constituting the battery stack 1, that is, the heat radiation plate 41 having the ventilation holes 41 a, hydrogen as a discharge reserve reacts with oxygen. Thus, an increase in battery temperature due to an exothermic reaction that generates H ₂ O can be prevented. In general, an increase in battery temperature causes deterioration of the material constituting the battery, leading to a decrease in battery performance. By providing such a cooling structure for the battery module B, a battery stack with a simple structure can be obtained. It is possible to effectively cool not only the surface of 1 but also the laminated surface of the unit cells C, and prevent performance deterioration of the battery module B.

  In addition, since the battery module B according to the present embodiment can reduce the negative electrode discharge reserve by the above-described method, an amount equivalent to the charge reserve of the negative electrode active material that is previously filled in excess of the positive electrode active material is provided. The ratio of the filling amount of the negative electrode active material to the filling amount of the positive electrode active material can be reduced, and is set within a range of 100 to 400% in terms of capacity. Therefore, the charge / discharge capacity of the battery module B can be increased.

  As described above, the preferred embodiments of the present invention have been described with reference to the drawings, but various additions, modifications, or deletions can be made without departing from the spirit of the present invention. Therefore, such a thing is also included in the scope of the present invention.

It is a schematic diagram of the negative electrode charge reserve and discharge reserve of a nickel metal hydride secondary battery. It is a schematic block diagram which shows the battery module which concerns on one Embodiment of this invention. FIG. 3 is a partially broken cross-sectional view of a unit battery used in the battery module of FIG. 2. It is a perspective view which shows the heat sink used for the battery module of FIG. It is a perspective view which shows the example of the cooling structure of the battery module of FIG. It is a flowchart which shows the negative electrode discharge reserve reduction method which concerns on one Embodiment of this invention. It is a characteristic view which shows the principle of the measuring method of the discharge reserve in the negative electrode discharge reserve reducing method which concerns on one Embodiment of this invention.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Battery laminated body 3 Communication member 5 Oxygen supply source 27 Gas inlet 51 Connection tube (communication member)
52 Lead tube (communication member)
C Unit battery B Battery module

Claims (5)

A method for reducing negative discharge reserve of a battery module comprising a unit battery configured as a nickel metal hydride secondary battery and an oxygen supply source communicating with the inside of the unit battery,
After the initial activation charge / discharge of the unit battery, the negative discharge of the battery module includes supplying oxygen from the oxygen supply source to the inside of the unit battery and reacting with hydrogen which is a discharge reserve stored in the negative electrode Reserve reduction method.   2. The method of reducing negative discharge reserve in a battery module according to claim 1, wherein the supply amount of oxygen from the oxygen supply source to the inside of the unit cell is adjusted based on a negative discharge reserve amount measured in advance.   3. The negative electrode of the battery module according to claim 1, wherein the battery module includes a cooling structure that cools the unit battery, and supplies oxygen to the inside of the unit battery while cooling the unit battery by the cooling structure. Discharge reserve reduction method.   The battery module according to claim 3, wherein the battery module is provided with a battery stack in which the plurality of unit batteries are electrically connected to each other, and the inside thereof is connected to each other via a communication member. A method for reducing negative discharge reserve in a battery module, wherein a heat sink having a through hole extending perpendicularly to a stacking direction of unit cells is interposed between adjacent unit cells.   A negative electrode discharge reserve according to claim 1, comprising a unit battery configured as a nickel metal hydride secondary battery and an oxygen supply source communicating with the inside of the unit battery. The battery module in which the ratio of the filling amount of the negative electrode active material to the filling amount of the positive electrode active material is in the range of 100 to 400% in terms of capacity.

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