JP4040315B2

JP4040315B2 - Sodium-sulfur battery

Info

Publication number: JP4040315B2
Application number: JP2002022963A
Authority: JP
Inventors: 孝志安藤
Original assignee: NGK Insulators Ltd
Current assignee: NGK Insulators Ltd
Priority date: 2002-01-31
Filing date: 2002-01-31
Publication date: 2008-01-30
Anticipated expiration: 2022-01-31
Also published as: JP2003223927A

Description

【０００１】
【発明の属する技術分野】
本発明は、電力貯蔵用等の二次電池として利用されるナトリウム−硫黄電池に関して、陰極金具の熱サイクルによる疲労劣化を緩和し、かつ陰極金具と絶縁リングとの接合面の剥離によるナトリウムの侵入を防止したことを特徴とするナトリウム−硫黄電池に関するものである。
【０００２】
【従来の技術】
電力の平準化やピークカットなどの機能を実現するための電力貯蔵システムにナトリウム−硫黄電池が使用されているが、そのナトリウム−硫黄電池の構造は、図６にその断面図を模式的に示した通りのものである。
【０００３】
製造時におけるその電池構造は、有底筒状のベータアルミナ固体電解質管９がその上端外周面でα−アルミナの絶縁リング１の内周面とガラス接合され、更に、絶縁リング１の上面に接合された陰極金具２及びその陰極金具２に溶接された陰極蓋４と絶縁リング１とベータアルミナ固体電解質管９とで区画された陰極室が、有底筒状の金属製安全管１２とその安全管１２内側にナトリウム及び少量のアジ化ナトリウムを収納したナトリウム収納容器１３を配設しており、一方、陽極室は、絶縁リング１の下面に接合された陽極金具８と、その陽極金具８に溶接された陽極容器１０と、更にはその陽極容器１０に溶接された底蓋１１と、絶縁リング１と、ベータアルミナ固体電解質管９とで区画され、硫黄を含浸したカーボンマットが配設され、その上部には窒素などの不活性ガスが充填された構造である。
【０００４】
各部材による単電池組み立て後、電池作動温度までの昇温過程で、ナトリウム収納容器１３内のナトリウムは溶融し、ナトリウム収納容器１３内の上部に内包されていたアジ化ナトリウムの分解で発生した窒素ガスの圧力によりナトリウム収納容器１３の底部に設けられている小孔より溶融ナトリウムが陰極室内に流出して陰極室内を充填状態にする。
【０００５】
２９０℃〜３８５℃の温度で電池は作動し、ナトリウムはベータアルミナ固体電解質管９中をナトリウムイオンとしてイオン伝導し、陽極室の溶融硫黄と反応し、多硫化ナトリウムを生成して放電反応が進行する。充電の際は逆の反応が進み、陰極室に溶融ナトリウムが戻される。
【０００６】
上述の構成のナトリウム−硫黄電池において、その構成部材であるα−アルミナ製の絶縁リング１とＡｌ又はＡｌ合金製の陰極金具２は熱圧接合されて単電池が組立てられる。
【０００７】
熱圧接合部材の要部断面図を図３に示す。絶縁リング１と陰極金具２の熱圧接合方法は、絶縁リング１の上面にリング状の金属とセラミックの接合部材１６を載置した後、絶縁リング１に陰極金具２を挿嵌し、陰極金具２の外フランジ部２ｂの底面を金属とセラミックの接合部材１６上面に当接させる。次いで、ステンレス製リング板１４を挿嵌して陰極金具２の外フランジ部２ｂ上面に載置する。加熱した炉内雰囲気中で押圧治具１５によって絶縁リング１の上面に陰極金具２の外フランジ部２ｂを加圧接合する。
【０００８】
この際、陰極金具２の外フランジ部２ｂはＡｌ合金であるから柔らかく、金属とセラミックの接合部材１６と共に圧延されながら絶縁リング１の上面に熱圧接合される。絶縁リング１の内周面上部に位置する絶縁リング１と陰極金具２の下方円筒部２ｃとの隙間は、加圧の際にはみ出した金属とセラミックの接合部材１６で充填される。
【０００９】
熱圧接合後、押圧治具１５を陰極金具２から離脱させる際、ステンレス製リング板１４と押圧治具１５は接合しないので、押圧治具１５は容易に離脱できる。一方、ステンレス製リング板１４は陰極金具２と接合した状態であり、図４に示される通り、ステンレス製リング板１４は陰極金具２の外フランジ部２ｂに接合されたままの状態で残る。その後、図５に示される通り、陰極蓋４が陰極金具２の上端縁に溶接され、電池として組立てられてきた。
【００１０】
ステンレス製リング板１４は押圧治具１５との離脱性の改善のみを目的としたものであり、本発明者らは、経済性から厚み０．１２ｍｍ〜０．２ｍｍのＳＵＳ３０４製リング板１４を用いてきた。電池組立て後は何らの機能を有せず電池としては無用の部材である。
【００１１】
この様にして組立てられた単電池を集合電池として７年間運転させ、７年間運転後の電池を解体し、調査解析した。その結果、図７に示される通り、陰極金具２の上方円筒部２ａから外フランジ部２ｂへの屈曲部近傍Ｂ点に微細な亀裂が発生しており、又絶縁リング１内周面上端部近傍Ａ点においても接合部にナトリウムの侵入が発生していた。図８に局部拡大断面図を示す。陰極金具２の上方円筒部２ａから外フランジ部２ｂへの屈曲部近傍Ｂ点に発生する微細な亀裂は斜め下方方向に入っており、更に、陰極金具２は絶縁リング１の内周面上端部近傍Ａ点で少し上方に離脱し、陰極金具２と絶縁リング１の熱圧接合部にナトリウムの侵入が観察された。尚、用いる陰極金具２はアルミニウム合金の冷間鍛造品であり、円筒部と外フランジ部は一体品である。
【００１２】
この様な屈曲部近傍Ｂ点における微細な亀裂の発生、及び絶縁リング１の内周面上端部近傍Ａ点における陰極金具２の離脱とそれに伴うナトリウムの侵入についての発生原因は、α−アルミナ絶縁リング１の膨張係数が７〜８×１０^-6／℃に対し、アルミニウム合金製の陰極金具２及び陰極蓋４は２５〜２６×１０^-6／℃と極めてその差は大きく、電池の運転時における充電及び放電に伴う昇降温、及び電池立ち上げ時の昇温、更には定期点検修理時の室温までの降温及び作動温度までの昇温のヒートサイクルの際に、その温度変化に伴って陰極金具２の上方円筒部２ａが膨張、収縮するが、絶縁リング１内に挿嵌されている部分の下方円筒部２ｃは熱膨張係数の小さい絶縁リング１で拘束され、膨張収縮の動きが抑止される。
【００１３】
この結果、陰極金具２の屈曲部近傍Ｂ点を起点として陰極金具２の上方円筒部２ａが傾動を繰返し、屈曲部近傍Ｂ点に金属疲労を生じ、その結果、亀裂が発生したものと推定される。又、絶縁リング１の内周面上端部近傍Ａ点における陰極金具２の離脱も同じ要因によるものと推定される。
【００１４】
特開平３−１８７１６０号公報では、リング状のα−アルミナ製抑止体を陰極金具の円筒部外周面に当接する発明を提案しているが、リング状のα−アルミナ製抑止体はそれ自体極めてコストが高く、又、陰極金具の円筒部に当接させるには高度な寸法精度を要求され、リング状のα−アルミナ製抑止体は高強度であるから、その研磨加工コストも極めて高い。この様な理由から適用することは困難である。又、比較的低コストなムライト製抑止体の適用は強度不足のためムライト製抑止体にクラックが発生するとの問題を生じ適用できない。
【００１５】
【発明が解決しようとする課題】
本発明は、上述した問題点に鑑みてなされたものであり、その目的とするところは、電池として長期間運転しても、陰極金具に亀裂が発生せず、又、陰極金具と絶縁リングの接合部にもナトリウムが侵入せず、低コストであって、長期の耐久性と信頼性に優れたナトリウム−硫黄電池を提供するものである。
【００１６】
【課題を解決するための手段】
本発明によれば、有底筒状の固体電解質管と固体電解質管の開口端部の外周面と接合された絶縁リングと絶縁リングの上面に接合された陰極金具と陰極金具に溶接された陰極蓋とで区画された陰極室内にナトリウムが収納され、一方、該固体電解質管外周面と絶縁リングと絶縁リングの底面に接合された陽極金具と陽極金具に溶接された円筒状の陽極容器とで区画された陽極室に電子導電材と共に硫黄が収納されて構成されるナトリウム−硫黄電池において、陰極金具がアルミニウム又はアルミニウム合金製で、その形状が円筒部の途中に外フランジ部を有する形状であり、外フランジ部底面で絶縁リングの上面と接合した陰極金具であって、電池運転時における熱膨張収縮による陰極金具円筒部の傾動を抑止する板厚３．０〜８．０ｍｍのリング状の金属製抑止体を陰極金具円筒部の外周面に当接又は近接させて設けると共に、金属製抑止体の底面が外フランジ部の上面に接合されていることを特徴とするナトリウム−硫黄電池が提供される。
【００１７】
本発明においては、前記リング状の金属製抑止体の板厚が４．０〜６．０ｍｍの範囲であることが最も好ましい。
【００１８】
又、本発明においては、前記リング状の金属製抑止体の内周面上端縁及び下端縁に面取りが施されていることが好ましい。又、前記リング状の金属製抑止体がフェライト系ステンレスであることが好ましい。又、前記リング状の金属製抑止体と陰極金具の外フランジ部との接合がろう付け接合であることが好ましい。
【００１９】
【発明の実施の形態】
以下、本発明の実施の形態について説明するが、本発明は以下の実施の形態に限定されるものではないことはいうまでもない。
本発明をその一実施態様である図１に基づいて説明する。
【００２０】
図１は、本発明のナトリウム−硫黄電池の構成部材であるα−アルミナ製の絶縁リング１と、陰極金具２と、リング状の金属製抑止体３との電池組み立て後の要部拡大断面図を示す。陰極金具２の形状は、円筒部（上方を２ａ、下方を２ｃと符号）の途中に外フランジ部２ｂを有する形状であって、冷間鍛造で製作されたアルミニウム又はアルミニウム合金の一体品である。
【００２１】
本発明のナトリウム−硫黄電池の特徴は、ステンレス製リング板１４を用いる代わりにリング状の金属製抑止体３を用いる点を特徴とするものである。
【００２２】
リング状の金属製抑止体３は、厚み（ｔ）が２．０〜８．０ｍｍの範囲にある肉厚状のリング状金属体であって、そのリング状の金属製抑止体３の内周面３ａは陰極金具２の上方円筒部２ａに当接しているか又は近接した状態にあり、かつ底面で陰極金具２の外フランジ部２ｂの上面に接合している。
尚、リング状の金属製抑止体３の陰極金具２の上方円筒部２ａへの挿入の容易性と金属加工コストの点から近接した状態が好ましい。
【００２３】
厚みが２．０〜８．０ｍｍの範囲にある肉厚状であってリング状の金属製抑止体３の内周面３ａが陰極金具２の上方円筒部２ａに当接しているか又は近接した状態にあって、かつ底面が陰極金具２の外フランジ部２ｂの上面に接合した構成であることにより、電池の運転時における充電及び放電に伴う昇降温及び室温と電池作動温度間の熱サイクルにより発生する陰極金具２の屈曲点Ｂ点を起点とした上方円筒部２ａの傾動が金属製抑止体３によって抑止される。
【００２４】
その結果、屈曲点Ｂ点における金属疲労により生じる亀裂の発生がおさえられ、更に、絶縁リング１の内周面上端部近傍Ａ点における陰極金具２の離脱も防止され、陰極金具２と絶縁リング１の接合面６にＮａが侵入するのを防止するとの格別の効果が得られる。
【００２５】
この場合、金属製抑止体３の厚み（ｔ）が２ｍｍより薄い場合は陰極金具２の上方円筒部２ａの傾動に対する抑止効果が低下し、８ｍｍを超えると電池の重量が増加し、又、コストの点で好ましくない。上方円筒部２ａと当接又は近接状態にする際も寸法精度を要求される。厚みが４．０〜６．０ｍｍの範囲であることが最も効果が高くかつ経済的であり好ましい。
【００２６】
又、リング状の金属製抑止体３の内周面３ａ上端縁Ｃ点及び下端縁Ｄ点に半径１ｍｍ〜３ｍｍの面取りを施すことが好ましい。上方円筒部２ａの傾動が金属製抑止体３によって抑止される際の上方円筒部２ａへの金属製抑止体３の当たりが緩和され、陰極金具円筒部に亀裂が発生することを防止するからである。更に、絶縁リング１の内周面上端部近傍Ａ点に対応する陰極金具２の屈曲部Ｅ点に半径０．２ｍｍ以上の面取りを施すことが好ましい。
【００２７】
尚、近接とは、電池組立て後、電池として運転した際に、電池の運転時における充電及び放電に伴う昇降温及び室温と作動温度間の熱サイクルにより、陰極金具２の屈曲部近傍Ｂ点を起点として発生する陰極金具２の傾動をリング状の金属製抑止体３が抑止する程度の隙間が得られるように陰極金具２の上方円筒部２ａ外周面とリング状の金属製抑止体３の内周面３ａが配設された状態を意味する。
【００２８】
図１に示す本発明のナトリウム−硫黄電池における中間組立て部材の製造方法は、図３に示す従来の熱圧接合方法において、ステンレス製リング板１４を用いる代わりにリング状の金属製抑止体３を用いる点を除いて全て同一である。リング状の金属製抑止体３も押圧治具１５に対する離脱性効果を有する。
【００２９】
図１に示す本発明のナトリウム−硫黄電池における中間組立て部材において、リング状の金属製抑止体３の材質は、廉価である所定厚さのオーステナイト系ステンレス（ＳＵＳ３０４）を用いても良いが、熱膨張係数がα−アルミナ絶縁リングに近く、剛性の高いものが好ましい。例えば、フェライト系ステンレス（例えばＳＵＳ４３０）熱膨張係数１１×１０^-6／℃が廉価であり、特に好ましい。他にはコバール（Ｆｅ−Ｎｉ−Ｃｏ）熱膨張係数４．４〜５．２×１０^-6／℃、４２合金（Ｆｅ−４２Ｎｉ）熱膨張係数４．０〜４．７×１０^-6／℃、などが挙げられる。
【００３０】
尚、リング状の金属製抑止体３と陰極金具２の外フランジ部２ｂの上面との接合面５は、圧着接合でも良いが、ろう材を用いたろう付け接合が接合強度を向上し、陰極金具２の上方円筒部２ａの傾動を長期に亘り安定して抑止できる点で好ましい。
【００３１】
本発明のナトリウム−硫黄電池を構成する他の構成部材による電池構造は図６に示すナトリウム−硫黄電池と同一である。即ち、絶縁リング１に陰極金具２を熱圧接合した後、有底筒状の金属製安全管１２とその安全管１２内側にナトリウム及び少量のアジ化ナトリウムを収納したナトリウム収納容器１３を配設し、次いで、減圧雰囲気中で陰極金具２に陰極蓋４を溶接する。
【００３２】
陽極室に関しては、絶縁リング１の底面に陽極金具８を熱圧接合し、有底筒状のベータアルミナ固体電解質管９の上端部外周面を絶縁リング１の内周面にガラス接合し、陽極金具８に円筒状の陽極容器１０を溶接後、硫黄を含浸したカーボンマット（電子導電材）を陽極陽器１０内に配設し、次いで、底蓋１１を溶接して電池を組立てる。
【００３３】
【実施例】
図１において、リング状の金属製抑止体３のみを４通りに変えて製作した本発明のナトリウム−硫黄電池を実施例１〜４として各２本作製し、試験した。実施例１〜４において、陰極金具２の構成及び絶縁リング１との接合状態、更に、リング状の金属製抑止体３と陰極金具２の外フランジ部２ｂとの接合状態も各々同一条件で熱圧接合して製作したものであり同一である。
【００３４】
即ち、陰極金具２は、円筒部（２ａ，２ｂ）の肉厚が２．５ｍｍ、上方円筒部（２ａ）から外フランジ部（２ｂ）への屈曲部Ｂ点が半径０．３ｍｍの面取りが施されたものを用い、絶縁リング１との接合面６における接合距離（Ｓ）は３．０ｍｍである。
【００３５】
ここで、絶縁リング１との接合面６における接合距離（Ｓ）は、外フランジ部２ｂの先端までの距離ではない。熱圧接合の際、金属とセラミックの接合部材１６も陰極金具２の外フランジ部２ｂと共に絶縁リング１上面に圧延により押し伸ばされるが、陰極金具２の外フランジ部２ｂと絶縁リング１の接合は、この接合部材１６が介在されている箇所で行われる。従って、接合距離（Ｓ）は圧延により押し伸ばされた接合部材１６の先端までの距離である。
リング状の金属製抑止体３の底面と陰極金具２の外フランジ部２ｂ上面との接合面５は金属間接合用ろう材を用いてろう付け接合した。
【００３６】
本発明の実施例１〜４について各２本の電池を、４００℃で７年間運転した後、各電池を解体し、観察調査した結果を各々表１に示す。
尚、表１に示す測定値は、各部位の状態を光学顕微鏡で観察し、Ｎａの侵入距離及び亀裂の長さについて測定した測定値の内、最大測定値を示す。又、この７年間の運転の間に４００℃から室温までの降温、及び室温から４００℃までの昇温、即ち、室温⇔４００℃のヒートサイクルを７回行った。
【００３７】
実施例１はＳＵＳ３０４、板厚３．０ｍｍのリング状の金属製抑止体３を用いた実施例であって、絶縁リング１の内周面上端部近傍Ａ点における陰極金具２の剥離は小さく、Ｎａの侵入は０．１１ｍｍと僅かであった。又、陰極金具２の上方円筒部２ａから外フランジ部２ｂの屈曲部近傍Ｂ点に発生した亀裂の長さは０．０２ｍｍと微細な亀裂にとどまっている。実施例２はＳＵＳ３０４、板厚５．０ｍｍのリング状の金属製抑止体３を用いた実施例であって、絶縁リング１の内周面上端部近傍Ａ点における接合面６へのＮａの侵入は０．０７ｍｍと極めて僅かであった。又、陰極金具２の上方円筒部２ａから外フランジ部２ｂの屈曲部近傍Ｂ点には亀裂の発生が観察されなかった。
【００３８】
実施例３はＳＵＳ４３０、板厚３．０ｍｍのリング状の金属製抑止体３を用いた実施例であって、絶縁リング１の内周面上端部近傍Ａ点における接合面６へのＮａの侵入は０．０７ｍｍと極めて僅かであり、又、陰極金具２の上方円筒部２ａから外フランジ部２ｂへの屈曲部近傍Ｂ点に発生した亀裂の長さは０．０１ｍｍ極めて小さな亀裂であった。実施例４はＳＵＳ４３０、板厚５．０ｍｍのリング状の金属製抑止体３を用いた実施例であって、絶縁リング１の内周面上端部近傍Ａ点における接合面６へのＮａの侵入は観察されなかった。又、陰極金具２の上方円筒部２ａから外フランジ部２ｂの屈曲部近傍Ｂ点においても亀裂の発生は観察されなかった。
【００３９】
【表１】

【００４０】
一方、リング状の金属製抑止体３の代わりに従来のステンレス製リング板１４を用いて作成した従来のナトリウム−硫黄電池についても、実施例１と同一の各部材を用い、同一条件で熱圧接合し、同一期間運転した後、電池を解体し、観察調査した。その結果を表１に示す。尚、表１に示す数値は各部位の状態を光学顕微鏡で観察し、Ｎａの侵入距離及び亀裂の長さを測定し、最大測定値を示す。
【００４１】
従来例１は、ＳＵＳ３０４，板厚０．５ｍｍ、従来例２は、ＳＵＳ３０４，板厚１．５ｍｍ、従来例３は、ＳＵＳ４３０，板厚０．５ｍｍ、従来例３は、ＳＵＳ４３０で板厚１．５ｍｍのリング板１４を用いた実施態様であって、各実施態様について電池各２本作製し、供試体とした。
【００４２】
従来例１〜４について、いずれも図８に示す通りの状態に損傷を受けていた。絶縁リング１の内周面上端部近傍Ａ点にはＮａがかなり侵入しており、各従来例における最大Ｎａ侵入距離は２．１１〜２．５２ｍｍの範囲であった。又、陰極金具２の上方円筒部２ａから外フランジ部２ｂへの屈曲部近傍Ｂ点にも亀裂が発生しており、亀裂の各従来例における最大長さは０．２１〜０．２８ｍｍの範囲であった。
【００４３】
リング状の金属製抑止体３は本発明の主旨を逸脱しない範囲において、各種の実施態様が可能である。例えば、図２に示す通りの円筒部とフランジ部を有した形状とすることも可能である。
【００４４】
【発明の効果】
以上説明したように、電池運転時における熱膨張収縮による陰極金具の上方円筒部の傾動を抑止するリング状の金属製抑止体を陰極金具円筒部に当接又は近接させて設けると共にリング状の金属製抑止体を絶縁リング上面に接合させたことにより、長期に亘り電池を運転しても、陰極金具と絶縁リングとの熱圧接合部へのＮａの侵入は防止され、更に、陰極金具円筒部から外フランジ部への屈曲部における亀裂の発生が防止される。又、抑止体は金属製であり、α−アルミナリングなどの高強度セラミック製品に比較し、安価であり、加工も容易である。
【図面の簡単な説明】
【図１】本発明の絶縁リングと陰極金具とリング状の金属製抑止体とから構成される電池局部構造の要部断面図を示す。
【図２】本発明の別の実施態様である電池局部構造の要部断面図を示す。
【図３】従来の熱圧接合する工程において、絶縁リングと、金属とセラミックスの接合材と、陰極金具と、ステンレス製リング板とを配設し、押圧治具で押圧する要部断面図を示す。
【図４】従来の熱圧接合後の絶縁リングと陰極金具とステンレス製リング板とから構成される中間電池部材の要部断面図を示す。
【図５】従来の陰極金具に陰極蓋を溶接して電池を組立てることを説明する要部断面図を示す。
【図６】従来のナトリウム−硫黄電池を示す模式的断面図である。
【図７】従来のナトリウム−硫黄電池を長年運転した際に、陰極金具に発生する亀裂及び陰極金具と絶縁リングの熱圧接合面へのＮａの侵入を説明する図である。
【図８】亀裂が発生した部位及び陰極金具と絶縁リングの熱圧接合面へのＮａの侵入部位を示す局部拡大断面図を示す。
【符号の説明】
１…絶縁リング、２…陰極金具、２ａ…上方円筒部、２ｂ…外フランジ部、２ｃ…下方円筒部、３…リング状の金属製抑止体、３ａ…内周面、４…陰極蓋、５…陰極金具と金属製抑止体の接合面、６…陰極金具と絶縁リングとの接合面、７…陰極金具と陰極蓋の溶接箇所、８…陽極金具、９…固体電解質管、１０…陽極容器、１１…底蓋、１２…安全管、１３…ナトリウム収納容器、１４…ステンレス製リング板、１５…押圧治具、１６…金属とセラミックの接合部材。[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a sodium-sulfur battery used as a secondary battery for power storage or the like, which alleviates fatigue deterioration due to the thermal cycle of the cathode metal fitting and invades sodium due to peeling of the joint surface between the cathode metal fitting and the insulating ring. The present invention relates to a sodium-sulfur battery characterized in that
[0002]
[Prior art]
A sodium-sulfur battery is used in a power storage system for realizing functions such as power leveling and peak cut. The structure of the sodium-sulfur battery is schematically shown in FIG. That's right.
[0003]
The battery structure at the time of manufacture is such that a bottomed cylindrical beta-alumina solid electrolyte tube 9 is glass-bonded to the inner peripheral surface of the α-alumina insulating ring 1 at the outer peripheral surface of the upper end and further bonded to the upper surface of the insulating ring 1. The cathode chamber 2 partitioned by the cathode fitting 2 and the cathode lid 4 welded to the cathode fitting 2, the insulating ring 1, and the beta alumina solid electrolyte tube 9 is a bottomed cylindrical metal safety tube 12 and its safety. A sodium storage container 13 storing sodium and a small amount of sodium azide is disposed inside the tube 12, while the anode chamber is connected to the anode fitting 8 joined to the lower surface of the insulating ring 1 and the anode fitting 8. A welded anode vessel 10, and further, a bottom lid 11 welded to the anode vessel 10, an insulating ring 1, and a beta alumina solid electrolyte tube 9, are provided with a carbon mat impregnated with sulfur. At its upper portion a structure that inert gas is filled, such as nitrogen.
[0004]
After assembling the cell by each member, the sodium in the sodium storage container 13 is melted in the process of raising the temperature to the battery operating temperature, and nitrogen generated by decomposition of sodium azide contained in the upper part of the sodium storage container 13 Due to the pressure of the gas, molten sodium flows into the cathode chamber from a small hole provided in the bottom of the sodium container 13 and fills the cathode chamber.
[0005]
The battery operates at a temperature of 290 ° C. to 385 ° C., and sodium conducts ions in the beta alumina solid electrolyte tube 9 as sodium ions, reacts with molten sulfur in the anode chamber, generates sodium polysulfide, and the discharge reaction proceeds. To do. The reverse reaction proceeds during charging, and the molten sodium is returned to the cathode chamber.
[0006]
In the sodium-sulfur battery having the above-mentioned configuration, the α-alumina insulating ring 1 and the cathode fitting 2 made of Al or Al alloy, which are constituent members, are hot-pressure bonded to assemble a unit cell.
[0007]
FIG. 3 shows a cross-sectional view of the main part of the hot-pressure bonding member. The insulating ring 1 and the cathode metal fitting 2 are heat-pressure bonded by placing a ring-shaped metal / ceramic bonding member 16 on the upper surface of the insulating ring 1 and then inserting the cathode metal fitting 2 into the insulating ring 1. The bottom surface of the outer flange portion 2b is brought into contact with the top surface of the metal / ceramic bonding member 16. Next, the stainless steel ring plate 14 is inserted and placed on the upper surface of the outer flange portion 2 b of the cathode metal fitting 2. The outer flange portion 2b of the cathode metal fitting 2 is pressure bonded to the upper surface of the insulating ring 1 by a pressing jig 15 in a heated furnace atmosphere.
[0008]
At this time, since the outer flange portion 2b of the cathode metal fitting 2 is made of Al alloy, it is soft and is hot-pressure bonded to the upper surface of the insulating ring 1 while being rolled together with the metal-ceramic bonding member 16. The gap between the insulating ring 1 located at the upper part of the inner peripheral surface of the insulating ring 1 and the lower cylindrical portion 2c of the cathode metal fitting 2 is filled with a metal-ceramic bonding member 16 that protrudes during pressurization.
[0009]
Since the stainless steel ring plate 14 and the pressing jig 15 are not joined when the pressing jig 15 is detached from the cathode metal fitting 2 after the hot press bonding, the pressing jig 15 can be easily detached. On the other hand, the stainless steel ring plate 14 is in a state of being joined to the cathode metal fitting 2, and the stainless steel ring plate 14 remains in a state of being joined to the outer flange portion 2b of the cathode metal fitting 2 as shown in FIG. Thereafter, as shown in FIG. 5, the cathode lid 4 is welded to the upper edge of the cathode fitting 2 and assembled as a battery.
[0010]
The stainless steel ring plate 14 is only for the purpose of improving the detachability from the pressing jig 15, and the present inventors use a ring plate 14 made of SUS304 having a thickness of 0.12 mm to 0.2 mm for the sake of economy. I came. After the battery is assembled, it has no function and is a useless member as a battery.
[0011]
The unit cell assembled in this way was operated as an assembled battery for 7 years, and the battery after 7 years of operation was disassembled and investigated and analyzed. As a result, as shown in FIG. 7, a fine crack is generated at the point B near the bent portion from the upper cylindrical portion 2a to the outer flange portion 2b of the cathode metal fitting 2, and the vicinity of the upper end portion of the inner peripheral surface of the insulating ring 1 Also at point A, sodium intrusion occurred in the joint. FIG. 8 shows a local enlarged sectional view. A fine crack generated at a point B near the bent portion from the upper cylindrical portion 2a of the cathode metal fitting 2 to the outer flange portion 2b enters the diagonally downward direction, and the cathode metal fitting 2 further has an upper end on the inner peripheral surface of the insulating ring 1. At a point A in the vicinity, it was separated slightly upward, and sodium penetration was observed at the hot-pressure junction between the cathode metal fitting 2 and the insulating ring 1. The cathode fitting 2 to be used is a cold forged product of aluminum alloy, and the cylindrical portion and the outer flange portion are an integrated product.
[0012]
The occurrence of such fine cracks at the point B near the bent portion and the cause of the detachment of the cathode metal fitting 2 at the point A near the upper end of the inner peripheral surface of the insulating ring 1 and the accompanying sodium intrusion are caused by α-alumina insulation. While the ring 1 has an expansion coefficient of 7-8 × 10 ⁻⁶ / ° C., the aluminum alloy cathode metal fitting 2 and the cathode lid 4 have an extremely large difference of 25-26 × 10 ⁻⁶ / ° C. The temperature rises and falls during charging and discharging, and the temperature rises when the battery is started up. Although the upper cylindrical portion 2a of the metal fitting 2 expands and contracts, the lower cylindrical portion 2c of the portion inserted into the insulating ring 1 is restrained by the insulating ring 1 having a small thermal expansion coefficient, and the expansion and contraction movement is suppressed. The
[0013]
As a result, it is estimated that the upper cylindrical portion 2a of the cathode metal fitting 2 repeatedly tilted starting from the point B near the bent portion of the cathode metal fitting 2, causing metal fatigue at the point B near the bent portion, resulting in cracks. The Further, the separation of the cathode metal fitting 2 at the point A in the vicinity of the upper end of the inner peripheral surface of the insulating ring 1 is estimated to be due to the same factor.
[0014]
Japanese Patent Application Laid-Open No. 3-187160 proposes an invention in which a ring-shaped α-alumina deterring body is brought into contact with the outer peripheral surface of the cylindrical portion of the cathode metal fitting. The cost is high, and a high degree of dimensional accuracy is required to contact the cylindrical portion of the cathode metal fitting. Since the ring-shaped α-alumina deterrent has high strength, its polishing cost is extremely high. For this reason, it is difficult to apply. Moreover, the application of a relatively low cost mullite deterrent cannot be applied due to the problem of cracking in the mullite deterred due to insufficient strength.
[0015]
[Problems to be solved by the invention]
The present invention has been made in view of the above-described problems, and the object of the present invention is that no cracks occur in the cathode metal fittings even when the battery is operated for a long period of time. The present invention provides a sodium-sulfur battery that does not allow sodium to enter the junction, is low in cost, and has excellent long-term durability and reliability.
[0016]
[Means for Solving the Problems]
According to the present invention, a bottomed cylindrical solid electrolyte tube, an insulating ring joined to the outer peripheral surface of the open end of the solid electrolyte tube, a cathode fitting joined to the upper surface of the insulating ring, and a cathode welded to the cathode fitting Sodium is housed in a cathode chamber partitioned by a lid, and on the other hand, an outer peripheral surface of the solid electrolyte tube, an insulating ring, an anode fitting joined to the bottom of the insulating ring, and a cylindrical anode container welded to the anode fitting In a sodium-sulfur battery configured by storing sulfur together with an electronic conductive material in a partitioned anode chamber, the cathode fitting is made of aluminum or an aluminum alloy, and the shape thereof has an outer flange portion in the middle of the cylindrical portion. , a cathode bracket joined with outer flange bottom surface and the upper surface of the insulating ring, the thickness 3.0~8.0mm to suppress tilting of the cathode metal cylinder due to thermal expansion and contraction during battery operation A metal-containing deterrent body is provided in contact with or close to the outer peripheral surface of the cylindrical part of the cathode metal fitting, and the bottom surface of the metal deterrent body is joined to the upper surface of the outer flange portion. A battery is provided.
[0017]
In the present invention, it is most preferable that the thickness of the ring-shaped metal inhibitor is in the range of 4.0 to 6.0 mm.
[0018]
Moreover, in this invention, it is preferable that the chamfering is given to the inner peripheral surface upper end edge and lower end edge of the said ring-shaped metal suppression body. Moreover, it is preferable that the said ring-shaped metal inhibitor is a ferritic stainless steel. Moreover, it is preferable that joining of the said ring-shaped metal suppression body and the outer flange part of a cathode metal fitting is brazing joining.
[0019]
DETAILED DESCRIPTION OF THE INVENTION
Hereinafter, although embodiment of this invention is described, it cannot be overemphasized that this invention is not limited to the following embodiment.
The present invention will be described with reference to FIG.
[0020]
FIG. 1 is an enlarged cross-sectional view of a main part after assembling a battery of an α-alumina insulating ring 1, a cathode metal fitting 2, and a ring-shaped metal deterrent 3, which are constituent members of the sodium-sulfur battery of the present invention. Indicates. The shape of the cathode metal fitting 2 is a shape having an outer flange portion 2b in the middle of the cylindrical portion (the upper portion is denoted by 2a and the lower portion is denoted by 2c), and is an integrated product of aluminum or aluminum alloy manufactured by cold forging. .
[0021]
The feature of the sodium-sulfur battery of the present invention is that a ring-shaped metal deterrent 3 is used instead of the stainless steel ring plate 14.
[0022]
The ring-shaped metal restraining body 3 is a thick ring-shaped metal body having a thickness (t) in the range of 2.0 to 8.0 mm, and the inner circumference of the ring-shaped metal restraining body 3 The surface 3a is in contact with or close to the upper cylindrical portion 2a of the cathode metal fitting 2, and is joined to the upper surface of the outer flange portion 2b of the cathode metal fitting 2 at the bottom surface.
It is preferable that the ring-shaped metal deterrent 3 is close to the cathode member 2 in terms of ease of insertion into the upper cylindrical portion 2a and metal processing costs.
[0023]
Thickness in the range of 2.0 to 8.0 mm, and the inner peripheral surface 3a of the ring-shaped metal deterrent 3 is in contact with or close to the upper cylindrical portion 2a of the cathode metal fitting 2 And the bottom surface is joined to the upper surface of the outer flange portion 2b of the cathode metal fitting 2, and is generated by the temperature rise and fall associated with charging and discharging during battery operation and the thermal cycle between the room temperature and the battery operating temperature. The tilting of the upper cylindrical portion 2 a starting from the bending point B of the cathode metal fitting 2 is suppressed by the metal deterrence body 3.
[0024]
As a result, generation of cracks caused by metal fatigue at the bending point B is suppressed, and further, the cathode metal fitting 2 is prevented from being detached at the point A near the upper end of the inner peripheral surface of the insulating ring 1. The special effect of preventing Na from entering the bonding surface 6 is obtained.
[0025]
In this case, if the thickness (t) of the metal deterrence body 3 is less than 2 mm, the deterrence effect on the tilting of the upper cylindrical portion 2a of the cathode metal fitting 2 is reduced, and if it exceeds 8 mm, the weight of the battery increases, and the cost increases. This is not preferable. Dimensional accuracy is also required when making contact with or close to the upper cylindrical portion 2a. A thickness in the range of 4.0 to 6.0 mm is most effective and economical.
[0026]
Further, it is preferable to chamfer the inner peripheral surface 3a of the ring-shaped metal deterrence body 3 at the upper end edge C point and the lower end edge D point with a radius of 1 mm to 3 mm. This is because the contact of the metal deterrent body 3 with the upper cylindrical portion 2a when the tilting of the upper cylindrical portion 2a is deterred by the metal deterrent body 3 is alleviated, and cracks are prevented from occurring in the cathode metal fitting cylindrical portion. is there. Furthermore, it is preferable to chamfer a radius of 0.2 mm or more at the bent portion E point of the cathode metal fitting 2 corresponding to the point A near the upper end of the inner peripheral surface of the insulating ring 1.
[0027]
The proximity means that when the battery is assembled and then operated as a battery, the point B near the bent portion of the cathode metal fitting 2 is determined by the temperature rise and fall associated with charging and discharging during battery operation and the thermal cycle between the room temperature and the operating temperature. The outer circumferential surface of the upper cylindrical portion 2a of the cathode metal fitting 2 and the ring-shaped metal inhibition body 3 are provided so that a gap is obtained to the extent that the ring-shaped metal inhibition body 3 inhibits the tilt of the cathode metal fitting 2 generated as a starting point. This means a state in which the peripheral surface 3a is disposed.
[0028]
The manufacturing method of the intermediate assembly member in the sodium-sulfur battery of the present invention shown in FIG. 1 uses a ring-shaped metal deterrent 3 in place of using the stainless steel ring plate 14 in the conventional hot-pressure joining method shown in FIG. All are the same except for the point of use. The ring-shaped metal deterrent 3 also has a detachable effect with respect to the pressing jig 15.
[0029]
In the intermediate assembly member of the sodium-sulfur battery of the present invention shown in FIG. 1, the material of the ring-shaped metal restraining body 3 may be austenitic stainless steel (SUS304) having a predetermined thickness, which is inexpensive, A material having an expansion coefficient close to that of the α-alumina insulating ring and high rigidity is preferred. For example, a ferritic stainless steel (for example, SUS430) having a thermal expansion coefficient of 11 × 10 ⁻⁶ / ° C. is inexpensive and particularly preferable. In addition, the coefficient of thermal expansion of Kovar (Fe—Ni—Co) is 4.4 to 5.2 × 10 ⁻⁶ / ° C., and the coefficient of thermal expansion of 42 alloy (Fe-42Ni) is 4.0 to 4.7 × 10 ⁻⁶ / ° C, and the like.
[0030]
The bonding surface 5 between the ring-shaped metal deterrent body 3 and the upper surface of the outer flange portion 2b of the cathode metal fitting 2 may be crimped, but brazing using a brazing material improves the bonding strength, and the cathode metal fitting. 2 is preferable in that tilting of the upper cylindrical portion 2a can be stably suppressed over a long period of time.
[0031]
The battery structure of other constituent members constituting the sodium-sulfur battery of the present invention is the same as that of the sodium-sulfur battery shown in FIG. That is, after the cathode metal fitting 2 is hot-pressure bonded to the insulating ring 1, a bottomed cylindrical metal safety tube 12 and a sodium storage container 13 containing sodium and a small amount of sodium azide are disposed inside the safety tube 12. Then, the cathode lid 4 is welded to the cathode metal fitting 2 in a reduced pressure atmosphere.
[0032]
As for the anode chamber, the anode fitting 8 is hot-pressure bonded to the bottom surface of the insulating ring 1, and the outer peripheral surface of the upper end portion of the bottomed cylindrical beta alumina solid electrolyte tube 9 is glass bonded to the inner peripheral surface of the insulating ring 1. After welding the cylindrical anode container 10 to the metal fitting 8, a carbon mat (electronic conductive material) impregnated with sulfur is disposed in the anode anode 10, and then the bottom lid 11 is welded to assemble the battery.
[0033]
【Example】
In FIG. 1, two sodium-sulfur batteries of the present invention manufactured by changing only the ring-shaped metal deterrent 3 in four ways were prepared and tested as Examples 1-4. In Examples 1 to 4, the structure of the cathode metal fitting 2 and the bonding state with the insulating ring 1 and the bonding state between the ring-shaped metal deterrent 3 and the outer flange portion 2b of the cathode metal fitting 2 were heated under the same conditions. It is manufactured by pressure bonding and is the same.
[0034]
That is, the cathode fitting 2 is chamfered with a cylindrical portion (2a, 2b) having a thickness of 2.5 mm and a bent portion B point from the upper cylindrical portion (2a) to the outer flange portion (2b) having a radius of 0.3 mm. The joint distance (S) at the joint surface 6 with the insulating ring 1 is 3.0 mm.
[0035]
Here, the joining distance (S) at the joining surface 6 with the insulating ring 1 is not the distance to the tip of the outer flange portion 2b. At the time of hot-pressure bonding, the metal-ceramic bonding member 16 is also rolled to the upper surface of the insulating ring 1 together with the outer flange portion 2b of the cathode metal fitting 2, but the bonding between the outer flange portion 2b of the cathode metal fitting 2 and the insulating ring 1 is performed. This is performed at a location where the joining member 16 is interposed. Therefore, the joining distance (S) is the distance to the tip of the joining member 16 that has been stretched by rolling.
The joint surface 5 between the bottom surface of the ring-shaped metal restraining body 3 and the top surface of the outer flange portion 2b of the cathode metal fitting 2 was brazed and joined using a brazing material for intermetallic joining.
[0036]
Table 1 shows the results of disassembling and observing each of the two batteries for Examples 1 to 4 of the present invention after operating at 400 ° C. for 7 years.
In addition, the measured value shown in Table 1 shows the maximum measured value among the measured values which observed the state of each site | part with the optical microscope, and measured about the penetration | invasion distance of Na and the length of the crack. Further, during this 7-year operation, the temperature was lowered from 400 ° C. to room temperature and the temperature was raised from room temperature to 400 ° C., that is, a heat cycle from room temperature to 400 ° C. was performed 7 times.
[0037]
Example 1 is an example using SUS304, a ring-shaped metal restraining body 3 having a plate thickness of 3.0 mm, and the peeling of the cathode metal fitting 2 at the point A near the upper end of the inner peripheral surface of the insulating ring 1 is small. The penetration of Na was as small as 0.11 mm. Further, the length of the crack generated from the upper cylindrical portion 2a of the cathode metal fitting 2 to the point B near the bent portion of the outer flange portion 2b is 0.02 mm, which is only a minute crack. Example 2 is an example using SUS304 and a ring-shaped metal deterrent 3 having a plate thickness of 5.0 mm, and Na intrusions into the joint surface 6 at the point A near the upper end of the inner peripheral surface of the insulating ring 1. Was as very small as 0.07 mm. Further, no cracks were observed from the upper cylindrical portion 2a of the cathode metal fitting 2 to the point B near the bent portion of the outer flange portion 2b.
[0038]
Example 3 is an example using SUS430 and a ring-shaped metal deterrent 3 having a plate thickness of 3.0 mm, and the penetration of Na into the joint surface 6 at the point A near the upper end of the inner peripheral surface of the insulating ring 1. Is 0.07 mm, which is very small, and the length of the crack generated at the point B near the bent portion from the upper cylindrical portion 2a to the outer flange portion 2b of the cathode metal fitting 2 was 0.01 mm. Example 4 is an example using SUS430, a ring-shaped metal deterrent 3 having a plate thickness of 5.0 mm, and Na intrusions into the joint surface 6 at the point A near the upper end of the inner peripheral surface of the insulating ring 1. Was not observed. Also, no cracks were observed from the upper cylindrical portion 2a of the cathode metal fitting 2 to the point B near the bent portion of the outer flange portion 2b.
[0039]
[Table 1]

[0040]
On the other hand, for the conventional sodium-sulfur battery prepared using the conventional stainless steel ring plate 14 instead of the ring-shaped metal deterrent 3, the same members as in Example 1 were used under the same conditions. After joining and operating for the same period, the battery was disassembled and observed. The results are shown in Table 1. In addition, the numerical value shown in Table 1 observes the state of each site | part with an optical microscope, measures the penetration | invasion distance of Na, and the length of a crack, and shows the maximum measured value.
[0041]
Conventional Example 1 is SUS304, plate thickness 0.5 mm, Conventional Example 2 is SUS304, plate thickness 1.5 mm, Conventional Example 3 is SUS430, plate thickness 0.5 mm, Conventional Example 3 is SUS430 and plate thickness 1. It is an embodiment using a ring plate 14 of 5 mm, and for each embodiment, two batteries were produced and used as test specimens.
[0042]
About the prior art examples 1-4, all were damaged in the state as shown in FIG. Na penetrates considerably at the point A in the vicinity of the upper end of the inner peripheral surface of the insulating ring 1, and the maximum Na penetration distance in each conventional example is in the range of 2.11 to 2.52 mm. In addition, a crack is also generated at a point B near the bent portion from the upper cylindrical portion 2a of the cathode metal fitting 2 to the outer flange portion 2b, and the maximum length of each conventional crack is 0.21 to 0.28 mm. Met.
[0043]
Various embodiments of the ring-shaped metal deterrent 3 are possible without departing from the spirit of the present invention. For example, a shape having a cylindrical portion and a flange portion as shown in FIG. 2 may be used.
[0044]
【The invention's effect】
As described above, the ring-shaped metal depressing body that suppresses the tilt of the upper cylindrical portion of the cathode metal fitting due to thermal expansion and contraction during battery operation is provided in contact with or close to the cathode metal fitting cylindrical portion, and the ring-shaped metal By joining the manufacturing restrainer to the upper surface of the insulating ring, even if the battery is operated for a long time, the intrusion of Na into the hot-pressure bonded portion between the cathode metal fitting and the insulating ring is prevented. Occurrence of cracks at the bent portion from the outer flange portion to the outer flange portion is prevented. Further, the restraining body is made of metal, and is inexpensive and easy to process as compared with high-strength ceramic products such as α-alumina rings.
[Brief description of the drawings]
FIG. 1 is a cross-sectional view of a main part of a battery local structure composed of an insulating ring, a cathode metal fitting, and a ring-shaped metal deterrent body according to the present invention.
FIG. 2 is a cross-sectional view of a main part of a battery local structure according to another embodiment of the present invention.
FIG. 3 is a cross-sectional view of a main part in which an insulating ring, a metal / ceramic bonding material, a cathode metal fitting, and a stainless steel ring plate are disposed and pressed by a pressing jig in a conventional hot-pressure bonding process. Show.
FIG. 4 is a cross-sectional view of a main part of an intermediate battery member composed of an insulating ring, a cathode fitting, and a stainless steel ring plate after conventional hot-pressure bonding.
FIG. 5 is a cross-sectional view of an essential part for explaining that a battery is assembled by welding a cathode lid to a conventional cathode metal fitting.
FIG. 6 is a schematic cross-sectional view showing a conventional sodium-sulfur battery.
FIG. 7 is a diagram for explaining cracks that occur in the cathode metal fitting and Na intrusion into the hot-press bonding surface of the cathode metal fitting and the insulating ring when a conventional sodium-sulfur battery is operated for many years.
FIG. 8 is a local enlarged cross-sectional view showing a site where a crack has occurred and a site where Na penetrates into the hot-press bonding surface of the cathode metal fitting and the insulating ring.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 1 ... Insulating ring, 2 ... Cathode metal fitting, 2a ... Upper cylindrical part, 2b ... Outer flange part, 2c ... Lower cylindrical part, 3 ... Ring-shaped metal suppression body, 3a ... Inner peripheral surface, 4 ... Cathode cover, 5 ... Joint surface of cathode metal fitting and metal deterrent, 6 ... Joint surface of cathode metal fitting and insulating ring, 7 ... Welded portion of cathode metal fitting and cathode lid, 8 ... Anode metal fitting, 9 ... Solid electrolyte tube, 10 ... Anode container DESCRIPTION OF SYMBOLS 11 ... Bottom cover, 12 ... Safety tube, 13 ... Sodium storage container, 14 ... Stainless steel ring board, 15 ... Pressing jig, 16 ... Metal-ceramic joining member.

Claims

A bottomed cylindrical solid electrolyte tube, an insulating ring joined to the outer peripheral surface of the open end of the solid electrolyte tube, a cathode fitting joined to the upper surface of the insulating ring, and a cathode lid welded to the cathode fitting Sodium is stored in the partitioned cathode chamber, and on the other hand, an outer peripheral surface of the solid electrolyte tube, the insulating ring, an anode fitting joined to the bottom surface of the insulating ring, and a cylindrical anode container welded to the anode fitting In a sodium-sulfur battery configured by storing sulfur together with an electronic conductive material in a partitioned anode chamber,
The cathode fitting is made of aluminum or an aluminum alloy, and the shape of the cathode fitting is a shape having an outer flange part in the middle of the cylindrical part, and the cathode fitting joined to the upper surface of the insulating ring at the bottom of the outer flange part. A ring-shaped metal deterrent body having a plate thickness of 3.0 to 8.0 mm that suppresses tilting of the cathode fitting cylindrical portion due to thermal expansion and contraction at the time is provided in contact with or close to the outer peripheral surface of the cathode fitting cylindrical portion. A sodium-sulfur battery characterized in that the bottom surface of the metallic deterrent body is joined to the upper surface of the outer flange portion.

2. The sodium-sulfur battery according to claim 1 , wherein a thickness of the ring-shaped metal inhibitor is in a range of 4.0 to 6.0 mm .

2. The sodium-sulfur battery according to claim 1, wherein the upper end edge and the lower end edge of the inner peripheral surface of the ring-shaped metal restraining body are chamfered .

2. The sodium-sulfur battery according to claim 1, wherein the ring-shaped metal inhibitor is ferritic stainless steel .

2. The sodium-sulfur battery according to claim 1, wherein the ring-shaped metal deterrent body and the outer flange portion of the cathode metal fitting are brazed .