【０００１】
【発明の属する技術分野】
本発明はニッケル水素蓄電池に関し、特に複数の単電池を内蔵するとともにその電槽が相互に連通されているニッケル水素蓄電池に関するものである。
【０００２】
【従来の技術】
所要の電力容量が得られるように複数の単電池を接続した集合型二次電池において、単電池間の接続抵抗を含む単電池当たりの内部抵抗を小さくして、電池の発熱を抑制し、高出力化や寿命特性の向上を図ることができるものとして、本出願人は先に、図４に示すように、複数（図示例では６つ）の単電池２を内蔵したニッケル水素蓄電池１を提案している。
【０００３】
図４において、３は角形電槽で、幅の狭い短側面と幅の広い長側面とを有する直方体状の単電池２の電槽４をその短側面を隔壁５として共用して相互に一体的に連接して構成されている。各電槽４内には、水酸化ニッケルを有する矩形状の正極板と、水素を吸脱する水素吸蔵合金を有する矩形状の負極板を、セパレータを介して積層して構成された極板群６が電解液とともに収容され、単電池２が構成されている。極板群６はその両側に正極板と負極板のリード部が突出され、それぞれに集電体７が溶接等にて接続されている。
【０００４】
両端の電槽４の外側の短側面と各電槽４、４間の隔壁５の上部に接続穴８が形成され、隣接する単電池２の隔壁５の両側に位置する正極と負極の集電体７、７同士が接続穴８を介して接続されている。また、両端の電槽４の外側の短側面の接続穴８に正極又は負極の接続端子９が装着され、短側面壁を介して対向する集電体７と接続されている。かくして、角形電槽３に内蔵された複数の単電池２が直列接続され、両端の接続端子９、９間に出力される。
【０００５】
また、隣接する電槽４、４同士がその上端部で連通路１０にて互いに連通され、任意の電槽４の上端に電槽４の内部圧力が一定以上になったときに圧力を解放するための単一の安全弁１１が任意の電槽４の上端に配設されている。このように、隣接する電槽４、４同士を連通することで、安全弁１１の数を低減してコスト低下と冷却性能の向上を図っている。
【０００６】
【発明が解決しようとする課題】
ところで、上記のような構成のニッケル水素蓄電池１においては、長期間の使用中に劣化が進行した特定の単電池２から発生した酸素ガスは、連通路１０を通って他の単電池２に移動することにより、充電時に負極に吸蔵された水素と化合して水になる（酸素と水素のリコンビネーション反応）ことによって、劣化した単電池２の酸化劣化が抑制され、各単電池間の容量バランスが確保されて集合型二次電池の寿命を向上できるという効果が得られる。しかしながら、上記のような単電池２の劣化または冷却性能の低下に基づく単電池２温度の上昇などにより、単電池２からの酸素発生が継続した場合には、単電池２、２間で放電リザーブ量にバラツキが生じる。この放電リザーブ量のバラツキは直ちに放電容量のバラツキには結びつかないが、放電リザーブ量のバラツキが拡大して負極板の放電リザーブ量が極端に減少した場合には、放電容量にバラツキが生じ、集合型二次電池の容量劣化が発生する恐れがある。
【０００７】
本発明は、上記従来の問題点に鑑み、相互に連通された単電池間で放電容量のばらつきの発生を防止できるニッケル水素蓄電池を提供することを目的としている。
【０００８】
【課題を解決するための手段】
本発明のニッケル水素蓄電池は、隔壁を介して連接されかつ内部空間が相互に連通された複数の電槽を有する角形電槽と、水酸化ニッケルを有する正極板と水素を吸脱する水素吸蔵合金を有する負極板をセパレータを介して構成された極板群とを備え、各電槽に極板群を電解液とともに収容して単電池を構成しかつ角形電槽内で単電池を直列接続したニッケル水素蓄電池において、電槽間の連通路を少なくとも酸素ガスの透過を防止するガス不透過膜にて遮蔽したものであり、電槽間での酸素ガスの移動が防止されていることで、各電槽毎に酸素と水素のリコンビネーション反応が独立して行われ、電槽間での酸素と水素のリコンビネーション反応の速度差によって放電リザーブにばらつきを生じるのを防止できる。
【０００９】
また、ガス不透過膜が、酸素ガスの透過速度に比して水素ガスの透過速度の高い合成樹脂フィルムから成ると、水素ガスの移動によって各電槽の内圧が均等になり、安全弁を何れかの電槽にのみ配設するだけで任意の単電池の異常時にその圧力を確実に放出して角形電槽の破裂を防止することができ、コスト低下と冷却性能の向上を図ることができる。
【００１０】
【発明の実施の形態】
以下、本発明のニッケル水素蓄電池の一実施形態について、図１〜図３を参照して説明する。
【００１１】
図１において、１はニッケル水素蓄電池で、角形電槽３内に複数の単電池２が内蔵され、内部で直列接続されている。角形電槽３は、幅の狭い短側面と幅の広い長側面とを有する直方体状の単電池２の電槽４をその短側面を隔壁５として共用して相互に一体的に連接して構成され、かつ各電槽４の上面開口が一体の蓋体３ａにて密閉されている。そして、各電槽４内に極板群６が電解液とともに収容されて単電池２が構成されている。
【００１２】
極板群６は、複数枚の正極板と複数枚の負極板とを交互に配置するとともに、各正極板に横方向に開口部を有する袋状のセパレータを被せることにより正極板と負極板の間にセパレータを介装した状態で積層して構成され、正極板と負極板の一側部を互いに反対側に突出させて正極と負極のリード部が設けられ、両側のリード部にそれぞれ集電体７が接合されている。なお、極板群６は、帯状の正極板と負極板を互いに反対側の側縁にリード部を突出させてセパレータを介して積層し、これを平たく巻回して構成してもよい。
【００１３】
正極板は、Ｎｉの発泡メタルにリード部を除いて水酸化ニッケルを充填して構成され、そのリード部は発泡メタルを加圧して圧縮するとともにその一面にリード板を超音波溶接でシーム溶接して構成されている。また、負極板は、Ｎｉのパンチングメタルにリード部を除いて水素吸蔵合金を含む負極構成物質を塗着して構成されている。水素吸蔵合金は、セリウム族希土類元素の混合物であるミッシュメタル（以下、Ｍｍと記す）と、Ｎｉ、Ｃｏ、Ｍｎ、Ａｌなどの金属（Ｎｉに代表させてＮｉと表示する）との合金にて構成されている。その組成をＭｍＡ ＮｉＢ としてその組成比Ａ：Ｂは、１：５．１５〜５．４０、好適には１：５．２５〜５．３５に設定されている。
【００１４】
両端の電槽４の外側の短側面と各電槽４、４間の隔壁５の上部に接続穴８が形成され、隣接する単電池２の隔壁５の両側に位置する正極と負極の集電体７、７同士が接続穴８を介して接続されている。また、両端の電槽４の外側の短側面の接続穴８に正極又は負極の接続端子９が装着され、短側面壁を介して対向する集電体７と接続されている。かくして、角形電槽３に内蔵された複数の単電池２が直列接続され、両端の接続端子９、９間に出力される。
【００１５】
蓋体３ａには、隣接する電槽４、４同士を互いに連通する連通路１０が設けられ、かつ任意の電槽４に対応する位置に、各電槽４の内部圧力が一定以上になったときに圧力を解放するための単一の安全弁１１が配設されている。また、連通路１０の各電槽４に対する開口部は、少なくとも酸素ガスの透過を防止するガス不透過膜１２にて遮蔽されている。このガス不透過膜１２としては、例えば（株）クラレ製の「商品名エバールフィルム」など、図２に示すように、酸素ガスや水蒸気に対する透過速度が水素ガスに対する透過速度に対して著しく小さい特性を有する合成樹脂フィルムが好適に用いられる。
【００１６】
以上の構成のニッケル水素蓄電池１においては、連通路１０をガス不透過膜１２にて遮蔽して、電槽４、４間での酸素ガスの移動を防止していることで、各電槽４毎に酸素と水素のリコンビネーション反応が独立して行われ、各単電池２での酸素と水素のリコンビネーション反応の速度差によって、酸素ガスが電槽４、４間で移動し、放電リザーブにばらつきを生じるのを防止できる。
【００１７】
また、何れかの単電池２に異常が発生してその電槽４の内部圧力が所定値以上になった場合、各電槽４間に設けられた連通路１０を通って水素ガスが移動することで圧力が各電槽４に伝達され、任意の電槽４の上端に配設された安全弁１１からその圧力を速やかにかつ円滑に逃がすことができ、角形電槽３の破裂を確実に防止することができる。また、安全弁１１の数を低減でき、また各安全弁に接続される多数の排出チューブによって冷却媒体の流通が阻害されるということもないので、コスト低下を図れるとともに冷却性能の向上を図ることができる。
【００１８】
具体例について説明すると、自動車駆動用の組電池に用いられるニッケル水素蓄電池１について、本発明に基づいて連通路１０をガス不透過膜１２で遮蔽したニッケル水素蓄電池と、従来例のように連通路１０を開放したニッケル水素蓄電池とをそれぞれ１０個づつ用い、これらを直列接続した状態で、環境温度０．２５、４０及び５０℃の条件下で５０サイクル充放電を行った後、各ニッケル水素蓄電池１の各単電池２毎の放電リザーブ量を測定し、放電リザーブの平均値に対するリサーブバラツキの割合を求めた。
【００１９】
放電リザーブ量の測定に当たっては、各ニッケル水素蓄電池を１Ｖになるまで放電し、次に各単電池２の電槽４の上部に穴をあけて電解液を補充し、電槽内の電解液中にＨｇ／ＨｇＯ参照極を浸漬させ、次に放電容量を測定しながら電池を過放電し、次のように定義される放電リザーブ量を測定した。
【００２０】
放電リザーブ量＝（負極の電位から参照極の電位を差し引いた電位差が−０．７Ｖになるまでの放電容量）−（単電池の電圧が０Ｖになるまでの放電容量）
こうして測定した本発明に基づいたニッケル水素蓄電池と従来例のニッケル水素蓄電池における放電リザーブの平均値に対するリザーブばらつきの割合を図３に示す。図３に示すように、１０個のニッケル水素蓄電池の平均値では、本発明により放電リザーブバラツキを大幅に低減できることが分かる。
【００２１】
【発明の効果】
本発明のニッケル水素蓄電池によれば、電槽間の連通路を少なくとも酸素ガスの透過を防止するガス不透過膜にて遮蔽したので、電槽間での酸素ガスの移動が防止され、そのため各単電池毎に酸素と水素のリコンビネーション反応が独立して行われ、単電池間での酸素と水素のリコンビネーション反応の速度差によって放電リザーブにばらつきを生じるのを防止できる。特に高温時において効果が大きい。このことによりニッケル水素蓄電池の長寿命化を図ることができる。
【００２２】
また、ガス不透過膜が、酸素ガスの透過速度に比して水素ガスの透過速度の高い合成樹脂フィルムから成ると、水素ガスの移動によって各電槽の内圧が均等になり、安全弁を何れかの電槽にのみ配設するだけで任意の単電池の異常時にその圧力を確実に放出して角形電槽の破裂を防止することができ、コスト低下と冷却性能の向上を図ることができる。
【図面の簡単な説明】
【図１】本発明の一実施形態のニッケル水素蓄電池の概略構成を示す部分縦断面図である。
【図２】同実施形態におけるガス不透過膜の水素ガスと酸素ガスの透過特性を示すグラフである。
【図３】同実施形態と従来例のニッケル水素蓄電池における放電リザーブばらつきを示すグラフである。
【図４】従来例のニッケル水素蓄電池の概略構成を示す縦断面図である。
【符号の説明】
１ ニッケル水素蓄電池
２ 単電池
３ 角形電槽
４ 電槽
５ 隔壁
６ 極板群
１０ 連通路
１２ ガス不透過膜[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to a nickel-metal hydride storage battery, and more particularly to a nickel-metal hydride storage battery having a plurality of cells built therein and having their battery cases communicated with each other.
[0002]
[Prior art]
In an assembled secondary battery in which a plurality of cells are connected to obtain a required power capacity, the internal resistance per cell including the connection resistance between the cells is reduced to suppress the heat generation of the battery, The applicant has previously proposed a nickel-metal hydride storage battery 1 having a plurality of (six in the illustrated example) single cells 2 as shown in FIG. are doing.
[0003]
In FIG. 4, reference numeral 3 denotes a rectangular battery case, and the battery case 4 of the rectangular parallelepiped unit cell 2 having a narrow short side surface and a wide long side surface is shared with each other by using the short side as a partition 5. It is configured to be connected. Each battery case 4 has an electrode plate group formed by stacking a rectangular positive electrode plate having nickel hydroxide and a rectangular negative electrode plate having a hydrogen storage alloy for absorbing and desorbing hydrogen via a separator. 6 are accommodated together with the electrolytic solution to constitute the cell 2. The electrode group 6 has lead portions of a positive electrode plate and a negative electrode plate protruding on both sides thereof, and a current collector 7 is connected to each of them by welding or the like.
[0004]
A connection hole 8 is formed in the outer short side surface of the battery case 4 at both ends and on the upper part of the partition wall 5 between the battery cases 4, 4, and the current collection of the positive electrode and the negative electrode located on both sides of the partition wall 5 of the adjacent cell 2 The bodies 7 are connected to each other through a connection hole 8. A connection terminal 9 of a positive electrode or a negative electrode is attached to a connection hole 8 on a short side outside the battery case 4 at both ends, and is connected to a current collector 7 facing the opposite side via a short side wall. Thus, the plurality of cells 2 contained in the rectangular battery case 3 are connected in series and output between the connection terminals 9 at both ends.
[0005]
Adjacent battery containers 4, 4 communicate with each other at their upper ends through a communication path 10, and release the pressure when the internal pressure of battery container 4 at the upper end of an arbitrary battery container 4 becomes constant or higher. A single safety valve 11 is provided at the upper end of any battery case 4. In this way, by connecting the adjacent battery cases 4, 4, the number of the safety valves 11 is reduced, and cost reduction and cooling performance are improved.
[0006]
[Problems to be solved by the invention]
By the way, in the nickel-metal hydride storage battery 1 configured as described above, oxygen gas generated from a specific cell 2 that has deteriorated during long-term use moves to another cell 2 through the communication path 10. By doing so, the hydrogen absorbed in the negative electrode during charging combines with the hydrogen to form water (recombination reaction of oxygen and hydrogen), thereby suppressing the oxidative deterioration of the deteriorated cell 2 and the capacity balance between the cells. Is secured and the life of the collective secondary battery can be improved. However, when the generation of oxygen from the cells 2 continues due to the temperature rise of the cells 2 due to the deterioration of the cells 2 or the deterioration of the cooling performance as described above, the discharge reserve between the cells 2 and 2 is reduced. The amount varies. This variation in the discharge reserve does not immediately lead to a variation in the discharge capacity. The capacity of the secondary battery may be deteriorated.
[0007]
An object of the present invention is to provide a nickel-metal hydride storage battery that can prevent the occurrence of variations in discharge capacity between mutually connected single cells in view of the above conventional problems.
[0008]
[Means for Solving the Problems]
A nickel-metal hydride storage battery according to the present invention includes a rectangular battery container having a plurality of battery containers connected to each other via a partition wall and having an internal space communicated with each other, a positive electrode plate having nickel hydroxide, and a hydrogen storage alloy absorbing and desorbing hydrogen. A negative electrode plate having an electrode group formed with a separator interposed therebetween was provided, and the electrode group was housed in each battery container together with the electrolytic solution to form a unit cell, and the unit cells were connected in series in the rectangular container. In the nickel-metal hydride storage battery, the communication path between the battery cases is shielded by a gas impermeable membrane that prevents at least the permeation of oxygen gas, and the movement of oxygen gas between the battery cases is prevented. The recombination reaction of oxygen and hydrogen is performed independently for each battery case, and it is possible to prevent the discharge reserve from being varied due to the difference in the speed of the recombination reaction between oxygen and hydrogen between the battery cases.
[0009]
In addition, when the gas impermeable membrane is made of a synthetic resin film having a high hydrogen gas transmission rate compared to the oxygen gas transmission rate, the internal pressure of each battery case becomes uniform due to the movement of the hydrogen gas, and the safety valve is set to one of the above. By simply arranging only the battery case, the pressure can be reliably released in the event of an abnormality of an arbitrary cell to prevent the rectangular battery case from being ruptured, thereby reducing costs and improving cooling performance.
[0010]
BEST MODE FOR CARRYING OUT THE INVENTION
Hereinafter, an embodiment of a nickel-metal hydride storage battery of the present invention will be described with reference to FIGS.
[0011]
In FIG. 1, reference numeral 1 denotes a nickel-metal hydride storage battery, in which a plurality of cells 2 are built in a rectangular battery case 3 and are connected in series inside. The rectangular battery case 3 is formed by connecting a battery case 4 of a rectangular parallelepiped unit cell 2 having a narrow short side surface and a wide long side surface to one another integrally with the short side surface serving as a partition wall 5. The upper surface opening of each battery case 4 is sealed by an integral lid 3a. The electrode group 6 is accommodated in each battery case 4 together with the electrolytic solution, thereby forming the unit cell 2.
[0012]
The electrode plate group 6 is configured such that a plurality of positive plates and a plurality of negative plates are alternately arranged, and a bag-shaped separator having an opening in a lateral direction is covered on each positive plate, thereby forming a space between the positive plate and the negative plate. Positive and negative electrode leads are provided by protruding one side of the positive electrode plate and one side of the negative electrode plate opposite to each other with a separator interposed therebetween. Are joined. The electrode plate group 6 may be configured by laminating a strip-shaped positive electrode plate and a negative electrode plate with a lead portion protruding from the side edge opposite to each other via a separator, and winding this flat.
[0013]
The positive electrode plate is constructed by filling nickel foam with nickel hydroxide except for the lead part.The lead part is compressed by pressing the foamed metal, and the lead plate is seam-welded to one side by ultrasonic welding. It is configured. The negative electrode plate is formed by applying a negative electrode constituent material including a hydrogen storage alloy to a punched metal of Ni except for a lead portion. The hydrogen storage alloy is an alloy of a misch metal (hereinafter, referred to as Mm), which is a mixture of a cerium group rare earth element, and a metal such as Ni, Co, Mn, or Al (represented by Ni as represented by Ni). It is configured. The composition ratio A of the composition as Mm A Ni B: B is 1: 5.15 to 5.40, preferably 1: is set to 5.25 to 5.35.
[0014]
A connection hole 8 is formed in the outer short side surface of the battery case 4 at both ends and on the upper part of the partition wall 5 between the battery cases 4, 4, and the current collection of the positive electrode and the negative electrode located on both sides of the partition wall 5 of the adjacent cell 2 The bodies 7 are connected to each other through a connection hole 8. A connection terminal 9 of a positive electrode or a negative electrode is attached to a connection hole 8 on a short side outside the battery case 4 at both ends, and is connected to a current collector 7 facing the opposite side via a short side wall. Thus, the plurality of cells 2 contained in the rectangular battery case 3 are connected in series and output between the connection terminals 9 at both ends.
[0015]
The lid 3a is provided with a communication path 10 that connects the adjacent battery cases 4, 4 to each other, and the internal pressure of each battery case 4 becomes equal to or higher than a certain value at a position corresponding to an arbitrary battery case 4. Sometimes a single relief valve 11 for releasing pressure is provided. Further, the opening of the communication passage 10 with respect to each battery case 4 is shielded by a gas impermeable film 12 for preventing at least the permeation of oxygen gas. As shown in FIG. 2, the gas impermeable membrane 12 has a characteristic that the transmission rate for oxygen gas and water vapor is significantly smaller than the transmission rate for hydrogen gas, as shown in FIG. 2 such as "EVAL FILM" manufactured by Kuraray Co., Ltd. Is preferably used.
[0016]
In the nickel-metal hydride storage battery 1 having the above configuration, the communication passage 10 is shielded by the gas impermeable membrane 12 to prevent the movement of oxygen gas between the containers 4, 4. The recombination reaction of oxygen and hydrogen is performed independently for each cell, and the oxygen gas moves between the battery containers 4 and 4 due to the difference in the rate of the recombination reaction of oxygen and hydrogen in each cell 2 and the discharge reserve Variations can be prevented.
[0017]
Further, when an abnormality occurs in any one of the cells 2 and the internal pressure of the battery case 4 exceeds a predetermined value, the hydrogen gas moves through the communication path 10 provided between the battery cases 4. As a result, the pressure is transmitted to each battery case 4, and the pressure can be quickly and smoothly released from the safety valve 11 disposed at the upper end of any battery case 4, thereby reliably preventing the rectangular battery case 3 from bursting. can do. Further, the number of the safety valves 11 can be reduced, and the circulation of the cooling medium is not hindered by the large number of discharge tubes connected to each safety valve, so that the cost can be reduced and the cooling performance can be improved. .
[0018]
A specific example will be described. For a nickel-metal hydride storage battery 1 used for a battery pack for driving an automobile, a nickel-metal hydride storage battery in which a communication passage 10 is shielded by a gas impermeable membrane 12 based on the present invention, and a communication passage like a conventional example. Each of the nickel-metal hydride storage batteries was charged and discharged for 50 cycles under the conditions of an ambient temperature of 0.25, 40 and 50 ° C. in a state where each of the nickel-metal hydride storage batteries was connected in series with ten nickel-metal hydride storage batteries. The discharge reserve amount of each of the single cells 2 of No. 1 was measured, and the ratio of the reserve variation to the average value of the discharge reserve was determined.
[0019]
In measuring the discharge reserve amount, each nickel-metal hydride storage battery was discharged until it reached 1 V, and then a hole was made in the upper part of the battery case 4 of each cell 2 to replenish the electrolyte solution, and the electrolyte solution in the battery case was refilled. Then, the Hg / HgO reference electrode was immersed in the battery, and then the battery was overdischarged while measuring the discharge capacity, and the discharge reserve defined as follows was measured.
[0020]
Discharge reserve amount = (discharge capacity until potential difference obtained by subtracting reference electrode potential from negative electrode potential becomes −0.7 V) − (discharge capacity until cell voltage becomes 0 V)
FIG. 3 shows the ratio of the reserve variation to the average value of the discharge reserve in the nickel-metal hydride storage battery based on the present invention and the conventional nickel-metal hydride storage battery thus measured. As shown in FIG. 3, it can be seen that the average value of the ten nickel-metal hydride batteries can significantly reduce the discharge reserve variation according to the present invention.
[0021]
【The invention's effect】
According to the nickel-metal hydride storage battery of the present invention, since the communication path between the battery cases is shielded by the gas impermeable film for preventing at least oxygen gas from permeating, the movement of the oxygen gas between the battery cases is prevented. The recombination reaction of oxygen and hydrogen is performed independently for each unit cell, and it is possible to prevent the discharge reserve from being varied due to the difference in the rate of the recombination reaction between oxygen and hydrogen between the unit cells. The effect is particularly great at high temperatures. This can extend the life of the nickel-metal hydride storage battery.
[0022]
Further, when the gas impermeable membrane is made of a synthetic resin film having a high hydrogen gas transmission rate compared to the oxygen gas transmission rate, the internal pressure of each battery case becomes uniform by the movement of the hydrogen gas, and the safety valve is set to one of the above. By simply arranging only the battery case, it is possible to reliably release the pressure in the event of an abnormality of an arbitrary cell to prevent the rectangular battery case from being ruptured, thereby reducing costs and improving cooling performance.
[Brief description of the drawings]
FIG. 1 is a partial longitudinal sectional view showing a schematic configuration of a nickel-metal hydride storage battery according to an embodiment of the present invention.
FIG. 2 is a graph showing hydrogen gas and oxygen gas permeation characteristics of a gas impermeable membrane in the same embodiment.
FIG. 3 is a graph showing variations in discharge reserve in the nickel hydride storage batteries of the embodiment and the conventional example.
FIG. 4 is a longitudinal sectional view showing a schematic configuration of a conventional nickel-metal hydride storage battery.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 1 Nickel-metal hydride storage battery 2 Single cell 3 Rectangular battery case 4 Battery case 5 Partition wall 6 Electrode group 10 Communication passage 12 Gas impermeable membrane
