[go: up one dir, main page]
More Web Proxy on the site http://driver.im/

JP4459559B2 - Sealed battery - Google Patents

Sealed battery Download PDF

Info

Publication number
JP4459559B2
JP4459559B2 JP2003174466A JP2003174466A JP4459559B2 JP 4459559 B2 JP4459559 B2 JP 4459559B2 JP 2003174466 A JP2003174466 A JP 2003174466A JP 2003174466 A JP2003174466 A JP 2003174466A JP 4459559 B2 JP4459559 B2 JP 4459559B2
Authority
JP
Japan
Prior art keywords
diaphragm
battery
connection plate
friction stir
joined
Prior art date
Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
Expired - Lifetime
Application number
JP2003174466A
Other languages
Japanese (ja)
Other versions
JP2005011673A (en
Inventor
幹男 小熊
高久 鳥塚
欣也 青田
晃二 佐藤
Current Assignee (The listed assignees may be inaccurate. Google has not performed a legal analysis and makes no representation or warranty as to the accuracy of the list.)
Hitachi Ltd
Resonac Corp
Original Assignee
Hitachi Ltd
Shin Kobe Electric Machinery Co Ltd
Priority date (The priority date is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the date listed.)
Filing date
Publication date
Application filed by Hitachi Ltd, Shin Kobe Electric Machinery Co Ltd filed Critical Hitachi Ltd
Priority to JP2003174466A priority Critical patent/JP4459559B2/en
Publication of JP2005011673A publication Critical patent/JP2005011673A/en
Application granted granted Critical
Publication of JP4459559B2 publication Critical patent/JP4459559B2/en
Anticipated expiration legal-status Critical
Expired - Lifetime legal-status Critical Current

Links

Images

Classifications

    • YGENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
    • Y02TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
    • Y02EREDUCTION OF GREENHOUSE GAS [GHG] EMISSIONS, RELATED TO ENERGY GENERATION, TRANSMISSION OR DISTRIBUTION
    • Y02E60/00Enabling technologies; Technologies with a potential or indirect contribution to GHG emissions mitigation
    • Y02E60/10Energy storage using batteries

Landscapes

  • Gas Exhaust Devices For Batteries (AREA)
  • Connection Of Batteries Or Terminals (AREA)

Description

【0001】
【発明の属する技術分野】
本発明は、密閉型電池に係り、特に、中央に平面部を有する皿状の導電性ダイヤフラムと、上方に突起が形成され該突起の中央に平面部を有する導電性接続板とが平面部同士で電気的・機械的に接続された防爆機構を備える密閉型電池に関する。
【0002】
【従来の技術】
従来、密閉型電池は家電製品に汎用されており、最近では、密閉型電池の中でも特にリチウム電池が数多く用いられるに至っている。リチウム電池はエネルギ密度が高いことから、電気自動車(EV)又はハイブリッド車(HEV)の車載電源としても開発が進められている。しかし、密閉型電池は充電装置の故障などによって過充電状態に陥ると、電池内圧が極端に上昇することがある。このため、ダイヤフラム(防爆弁)と、ダイヤフラムより電池の内側に配置され薄肉部を有するリード板取付部材とが接合された防爆機構を有する電池が提案されている(例えば、特許文献1参照)。この電池では、電池内圧が上昇した場合に、ダイヤフラムとリード板取付部材との接合部又は薄肉部が剥離又は破断することで電流が遮断される。
【0003】
リチウム電池で防爆機構を正極側に組込む場合は、一般にアルミニウム合金製のダイヤフラムとリード板取付部材とが用いられており、ダイヤフラム及びリード板取付部材の接合には、例えば抵抗溶接やレーザ溶接が採用されている。
【0004】
【特許文献1】
特開平第7−105933号公報(図1、段落番号「0015」〜「0020」)
【0005】
【発明が解決しようとする課題】
しかしながら、上記特許文献1の技術では、電流を遮断する際に、ダイヤフラムの側が破断すると、破断部から電池内部のガスや電解液が漏出することがあるため、リード板取付部材の剥離又は破断を確保する必要があり、リード板取付部材に予め薄肉部を形成する必要があるのでコスト高となる、という問題がある。
【0006】
また、ダイヤフラム及びリード板取付部材の接合に抵抗溶接を採用する場合は、アルミニウム合金の表面に生成される酸化皮膜の影響を受けて接合が不安定になりやすく、品質の維持が困難である。
【0007】
更に、大きな充放電電流が流れる電池の場合では、抵抗溶接によって生成するナゲットを大きくする必要があるが、ナゲットの大きさは接合する板の厚さによって限界があるので、大きな充放電流が流れる電池には採用できない、という問題がある。レーザ溶接を採用する場合は多数のパルスで接合することによって大電流にも対応できるが、アルミニウム合金の表面はレーザ光の反射率が高いため効率が低い上、表面状態によって吸収されるエネルギが変動するため、抵抗溶接と同様に、接合が不安定になりやすく接合装置が高価なため低コスト化が困難である、という問題がある。
【0008】
本発明は、上記事案に鑑み、低コストで信頼性の高い防爆機構を有する密閉型電池を提供することを課題とする。
【0009】
上記課題を解決するために、本発明は、中央に平面部を有する皿状の導電性ダイヤフラムと、上方に突起が形成され該突起の中央に平面部を有する導電性接続板とが前記平面部同士で電気的・機械的に接続された防爆機構を備える密閉型電池であって、前記平面部同士は、摩擦攪拌接合によって前記接続板側から接合されており、前記接続板は、前記摩擦攪拌接合によって接合された近傍の板厚が前記ダイヤフラムの厚さより小さいことを特徴とする。
【0010】
本発明では、ダイヤフラムと接続板との平面部同士は、摩擦攪拌接合によって接合されているので、塑性流動による結晶の微細化が生じ、接合の安定性が向上し防爆機構の作動圧が一定の信頼性の高い防爆機構を得ることができると共に、平面部同士が接続板側から摩擦攪拌接合されているので、薄肉の接続板を用いることで、接合時とは別に薄肉部を形成する必要がないため、低コスト化を図ることができ、接続板の接合された近傍の板厚がダイヤフラムの厚さより小さいため、電池内圧上昇時に接続板の接合された近傍が破断するので、電池内容物の漏出を防止することができる。
【0011】
この場合において、ダイヤフラム及び接続板の平面部同士を円形状に接合すれば、接合面積を大きくすることができるので、大電流用とすることができる。
【0012】
【発明の実施の形態】
以下、図面を参照して本発明が適用可能な密閉円筒型リチウムイオン二次電池の実施の形態について説明する。
【0013】
図1に示すように、本実施形態の密閉円筒型リチウムイオン二次電池30(以下、二次電池30と略称する。)は、電極捲回群11を備えている。電極捲回群11は、負極端子を兼ねる有底円筒状の電池缶15内の中央に収容されており、正極板と負極板とをポリエチレン製微多孔薄膜のセパレータを介してガラス入り樹脂製軸芯の周りに捲回されている。
【0014】
正極は、スピネル構造を有するリチウムマンガン複合酸化物(LiMnO、LiMn)又は層状岩塩型構造を有するLiMnO、LiMnのリチウムサイト又はマンガンサイトを他の金属元素で置換又はドープしたリチウムマンガン遷移金属複合酸化物の粉末、導電材の炭素材料、結着剤のポリフッ化ビニリデン(PVDF)及び粘度調整溶媒としてn−メチルピロリドンを混合し、コーネルデスパで均一分散、混練して得た正極活物質合剤を正極集電体のアルミニウム箔の両表面に均一に塗布、乾燥、所定寸法にプレスして、集電するための一部を残し短冊状に裁断して得られたものである。
【0015】
一方、負極は、黒鉛又は炭素、結着剤のPVDF及び粘度調整溶媒としてn−メチルピロリドンを混合し、コーネルデスパで均一分散、混練して得た負極活物質合剤を負極集電体の銅箔の両表面に均一に塗布、乾燥、所定寸法にプレス、集電するための一部を残して短冊状に裁断して得られたものである。なお、集電するために残した部分には正、負極タブが形成されている。
【0016】
正極タブ及び負極タブは電極捲回群11の互いに反対側の両端面に位置するように配置されている。軸芯の下端には、集電用の負極集電リングが固定されており、負極集電リングの周縁部には負極タブが超音波溶接されている。負極集電リングは、電池缶15に抵抗溶接されている。軸芯の上端には集電用の正極集電リング18が固定されており、正極集電リング18の周縁部には正極タブが超音波溶接されている。正極集電リング18には、短冊状の正極リード板16の一端が溶接されている。正極リード板16の他端は、短冊状の正極リード板19の一端に接続されており、正極リード板19の他端は、電極捲回群11の上部に配置された上蓋20を構成するスプリッタ4の底面に溶接されている。
【0017】
図2に示すように、上蓋20は、鉄製でニッケルメッキが施された円板状の上蓋キャップ1を有している。円板の中央には上方に向けて突出した円筒状の突起が形成されている。突起の上面には開口が形成されている。上蓋キャップ1の周縁部は、ダイヤフラム2の周縁部でカシメられている。ダイヤフラム2は、アルミニウム合金製で下方に底部が形成された皿状の形状を有している。皿状の底部は平面状でありダイヤフラム2の中央に平面部を形成している。ダイヤフラム2の平面部と周縁部との間には、薄肉化されており電池内圧が所定圧に達すると開裂する開裂溝8が形成されている。ダイヤフラム2の開裂溝8と周縁部との間の下方には、ダイヤフラム2を支持する断面略T字状の樹脂製絶縁リング3が配置されている。絶縁リング3の内面側には、絶縁リング3と一体成形されたツメ10が、3箇所以上形成されている。ダイヤフラム2に沿った扁平ドーナツ形状のスプリッタ4の外周部が、ツメ10により、ダイヤフラム2の底面と所定間隔を隔てて支持されている。スプリッタ4は、アルミニウム合金製で中央に貫通穴9が形成されている。スプリッタ4の中央部は、上方に突起が形成され突起の中央に平面部を有するアルミニウム合金製の接続板6の周縁部と、ダイヤフラム2の平面部とに、ポリプロピレン樹脂製のブッシュ5を介して狭持されている。ブッシュ5は、円環状でフランジ部を有し、フランジ部がダイヤフラム2の平面部の底面に当接されている。なお、ダイヤフラム2、スプリッタ4、上蓋キャップ1及び接続板6は、プレス加工により形成されている。
【0018】
図3に示すように、ダイヤフラム2の平面部の底面と、接続板6の平面部の上面とは、スポット式に摩擦攪拌接合により電気的・機械的に接合されている(以下、この摩擦攪拌接合箇所を接合部7という。)。摩擦攪拌接合は、図4に示す合金工具鋼製で円柱状の摩擦攪拌接合ツール21を用いて行われる。ツール21を高速で回転させながら被接合部材に押しつけて摩擦熱を発生させ、摩擦熱によって被接合部材の表層を塑性流動させ、ツール21により攪拌して接合する。ツール21は、先端側に円柱状ピン12が突出しており、ピン12の基部周囲には、ツール21の角部となるショルダ部13を有している。また、ピン12を除いたツール21の先端面には、ツール21の外周から中心に向かうにつれ深くなる凹部が形成されている。ツール21は、不図示のモータに接続されており、所定回転速度で回転可能とされている。また、ツール21は、回転軸の方向に上下動可能に支持部に固定されている。ダイヤフラム2と接続板6との接続板6側からの接合時には、ツール21の上下動によりツール21のショルダ部13が接続板6に食い込み、ショルダ部13が食い込んだ部分の接続板6の残厚tが、ダイヤフラム2の板厚tdより小さくなるように設定されている。ダイヤフラム2は、二次電池30の内圧が大気圧以上の所定圧になったときに作動(接続板6側が破断しダイヤフラム2が上蓋キャップ1側に反転)するように設定されており、防爆装置として機能する。
【0019】
ダイヤフラム2のスプリッタ4が沿う部分と、スプリッタ4とが、図1に示した正極集電リング18内に収容されている。スプリッタ4の底面と正極集電リング18の内面とで画定された空間Sは、電池の高さ方向で中央部より周部の方が大きい。図1に示した正極リード片16は、空間Sの周部近傍で折り曲げられて収容されている。
【0020】
電池缶15内に非水電解液が所定量注入された後、上蓋20の周縁部と電池缶15とはガスケット17を介してカシメられて電池内が密閉されている。非水電解液には、例えば、6フッ化リン酸リチウムや4フッ化ホウ酸リチウムをエチレンカーボネート、ジメチルカーボネートなどの有機溶媒に1モル/リットル程度溶解した電解液が用いられている。
【0021】
次に、本実施形態の二次電池30の作用等について説明する。
【0022】
本実施形態の二次電池30は、ダイヤフラム2と、接続板6との平面部同士は、摩擦攪拌接合によって接合されている。このため、塑性流動による結晶の微細化を生ずるので、接合部7の安定性が向上し、ダイヤフラム2の作動圧が一定の防爆装置を得ることができる。従って、確実に一定の作動圧でダイヤフラム2が反転する信頼性の高い二次電池30を得ることができる。また、摩擦攪拌接合では、従来の溶接に比べて低温で金属部材同士を接合することができる。このため、摩擦攪拌接合時のダイヤフラム2及び接続板6の変形を抑制することができるので、変形の少ない部材を用いて信頼性に優れた防爆装置を作製することができる。
【0023】
更に、本実施形態の二次電池30は、接続板6側からツール21を押し当てて摩擦攪拌接合する。このため、摩擦攪拌接合時にツール21のショルダ部13が接続板2に食い込ませて、接続板6の残厚tをダイヤフラム2の板厚tdより小さくすることができる。従って、摩擦攪拌接合時とは別に接続板6を薄くする工程が不要なので、二次電池30の生産コストを低減することができる。
【0024】
また、本実施形態の二次電池30では、接続板6の残厚tはダイヤフラム2の板厚tdより小さい。このため、一定の作動圧で、ダイヤフラム2より接続板6の残厚tの箇所が破断するので、電池内のガスや非水電解液の漏出を防止しすることができる。従って、ガスや非水電解液による二次電池30の周辺機器の劣化を抑制することができる。
【0025】
更にまた、ダイヤフラム2の作動圧は大気圧より大きいので、一旦ダイヤフラム2が反転すれば、大気圧でダイヤフラム2は元の形状には戻らず、接続板6がダイヤフラム2に再度電気的に接触することもない。このため、安全性に優れた電池とすることができる。
【0026】
更に、二次電池30の内圧が更に上昇すると、ダイヤフラム2には薄肉化された開裂溝8が形成されているので、開裂溝8が内圧により開裂される。電池缶15内のガスは、スプリッタ4に形成された貫通穴、開裂溝8の開裂箇所、上蓋キャップ1に形成された開口を経て外部へ開放される。従って、安全に二次電池30を使用不能状態とすることができる。
【0027】
なお、本実施形態では、ダイヤフラム2及び接続板6の平面部同士を、スポット式に摩擦攪拌接合する例を示したが、図5(A)、(B)に示すように、本発明をより大型の二次電池に適用する場合には、ダイヤフラム2及び接続板6の平面部同士を重ね合わせ不図示の載置台上に載置して固定し、接続板6側からツール21を回転させながら押し当てて、ツール21による接合部27が直径Dの円形状となるように載置台を回転するようにしてもい。このようにすれば、ダイヤフラム2及び接続板6の通電断面積を大きくすることができるので、大電流用の電池とすることができる。電池は、用途に応じて要求される最大充放電電流値や通電パターンが異なるので、接合部の温度上昇が実用上問題ない範囲に収まるように直径Dを設定すればよい。
【0028】
また、本実施形態では、ダイヤフラム2、接続板6及びスプリッタ4の材質にアルミニウム合金を用いる例を示したが、これに限定されるものではなく、アルミニウム、ニッケル合金、導電性プラスチックなどの他の導電性材質を使用するようにしてもよい。
【0029】
そして、本実施形態では、先端側にピン12が突出するツール21を用いて摩擦攪拌接合する例を示したが、接続板6側を薄くすることができれば、ピン12の形状は限定されず、例えば、ピン12の長さを短くしてもよい。これにより、より薄い部材の接合に対応することができる。
【0030】
【実施例】
次に、上記実施形態に従って作製した実施例の二次電池について説明する。比較のために作製した電池についても併記する。
【0031】
(比較例1)
下表1に示すように、比較例1では、ダイヤフラムに厚さ0.6mmのアルミニウム合金A3003−H14、接続板に厚さ0.8mmのアルミニウム合金A3003−H14を用い、ショルダ径3mm、ピン径1mm、ピンの長さ1mmのツールを使用し、接続板の残厚tが0.70mm、容量6Ah、電池の外径40mm、電池の高さ110mm、最大充放電電流30Aの電池を作製した。
【0032】
【表1】

Figure 0004459559
【0033】
(比較例2)
表1に示すように、比較例2では、接続板の残厚tを0.60mmとした以外は比較例1と同様に電池を作製した。
【0034】
(実施例1)
表1に示すように、実施例1では、接続板の残厚tを0.55mmとした以外は比較例1と同様に電池を作製した。
【0035】
(実施例2)
表1に示すように、実施例2では、接続板の残厚tを0.50mmとした以外は比較例1と同様に電池を作製した。
【0036】
<試験>
上述したように作製した実施例及び比較例の電池をそれぞれ100個ずつ準備し、6Aの電流値で過充電したときの防爆装置の動作を調べた。下表2に試験結果を示す。
【0037】
【表2】
Figure 0004459559
【0038】
比較例1及び比較例2の電池では、ダイヤフラム側が破断することがあったのに対し、実施例1及び実施例2の電池では、ダイヤフラム側が破断することはなかった。従って、接続板の残厚tをダイヤフラムの板厚tdより小さくすることで、確実に接続板側を破断することができることが確かめられた。
【0039】
(比較例3)
下表3に示すように、比較例3では、ダイヤフラムに板厚1.6mmのアルミニウム合金A3003−H14、接続板に厚さ1.6mmのアルミニウム合金A3003−H14を用い、ショルダ径6mm、ピン径2mm、ピンの長さ1.8mmのツールを使用し、接続板の残厚tを1.2mm、直径Dを2mm、容量30Ah、電池の外径67mm、電池の高さ135mm、最大充放電電流300Aの電池を作製した。
【0040】
【表3】
Figure 0004459559
【0041】
(比較例4)
表3に示すように、比較例4では、直径Dを4mmとした以外は比較例3と同様に電池を作製した。
【0042】
(実施例3)
表3に示すように、実施例3では、直径Dを6mmとした以外は比較例3と同様に電池を作製した。
【0043】
(実施例4)
表3に示すように、実施例4では、直径Dを8mmとした以外は比較例3と同様に電池を作製した。
【0044】
<試験>
上述したように作製した実施例及び比較例の電池をそれぞれ10個ずつ準備し、25゜Cの恒温槽中で30A充電と300A放電を繰り返し行って接合部の温度を赤外線温度計で測定し、平均値を調べた。下表4に試験結果を示す。
【0045】
【表4】
Figure 0004459559
【0046】
表4に示すように、比較例3及び比較例4の電池では、最高温度が100゜Cを超えたのに対し、実施例3及び実施例4の電池では、100゜C以下に抑えることができ、高温による接合部の劣化のおそれがないことが判明した。また、30Aの電流で過充電したときに、防爆装置が確実に作動することも確かめられた。従って、実施例3及び実施例4の電池は、摩擦攪拌接合の直径Dを6mm以上とすることで、大電流の充放電に適すると共に、過充電時の安全性に優れていることが判明した。
【0047】
【発明の効果】
以上説明したように、本発明によれば、ダイヤフラムと接続板との平面部同士は、摩擦攪拌接合によって接合されているので、塑性流動による結晶の微細化が生じ、接合の安定性が向上し防爆機構の作動圧が一定の信頼性の高い防爆機構を得ることができると共に、平面部同士が接続板側から摩擦攪拌接合されているので、薄肉の接続板を用いることで、接合時とは別に薄肉部を形成する必要がないため、低コスト化を図ることができ、接続板の接合された近傍の板厚がダイヤフラムの厚さより小さいため、電池内圧上昇時に接続板の接合された近傍が破断するので、電池内容物の漏出を防止することができる、という効果を得ることができる。
【図面の簡単な説明】
【図1】本発明が適用可能な実施形態の密閉円筒型リチウムイオン二次電池の断面図である。
【図2】実施形態の密閉円筒型リチウムイオン二次電池の上蓋の断面図である。
【図3】密閉円筒型リチウムイオン二次電池のダイヤフラムと接続板との接合部の拡大断面図である。
【図4】実施形態の摩擦攪拌接合に用いるツールの先端部の一部破断断面図である。
【図5】本発明が適用可能な大型の密閉円筒型リチウムイオン二次電池のダイヤフラムと接続板との接合部の拡大図であり、(A)は接続板側から見た平面図、(B)は断面図である。
【符号の説明】
2 ダイヤフラム(防爆機構の一部)
6 接続板(防爆機構の一部)
7、27 接合部
20 上蓋
30 密閉円筒型リチウムイオン二次電池(密閉型電池)[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a sealed battery, and in particular, a plate-shaped conductive diaphragm having a flat portion at the center and a conductive connection plate having a protrusion formed above and having a flat portion at the center of the protrusion. The present invention relates to a sealed battery having an explosion-proof mechanism electrically and mechanically connected.
[0002]
[Prior art]
Conventionally, sealed batteries have been widely used in home appliances, and recently, lithium batteries, in particular, have been used in many cases among sealed batteries. Since the lithium battery has a high energy density, the lithium battery is being developed as an in-vehicle power source for an electric vehicle (EV) or a hybrid vehicle (HEV). However, when the sealed battery falls into an overcharged state due to a failure of the charging device or the like, the battery internal pressure may extremely increase. For this reason, a battery having an explosion-proof mechanism in which a diaphragm (explosion-proof valve) and a lead plate attachment member having a thin wall portion disposed inside the battery from the diaphragm are joined has been proposed (for example, see Patent Document 1). In this battery, when the internal pressure of the battery rises, the current is interrupted by peeling or breaking the joint or thin part between the diaphragm and the lead plate mounting member.
[0003]
When an explosion-proof mechanism is incorporated on the positive electrode side in a lithium battery, an aluminum alloy diaphragm and a lead plate mounting member are generally used. For example, resistance welding or laser welding is used to join the diaphragm and the lead plate mounting member. Has been.
[0004]
[Patent Document 1]
Japanese Patent Laid-Open No. 7-105933 (FIG. 1, paragraph numbers “0015” to “0020”)
[0005]
[Problems to be solved by the invention]
However, in the technique of Patent Document 1, when the current is interrupted, if the diaphragm side breaks, the gas or electrolyte inside the battery may leak from the breakage part. There is a problem that it is necessary to ensure and a thin portion needs to be formed in advance on the lead plate mounting member, resulting in high costs.
[0006]
Further, when resistance welding is employed for joining the diaphragm and the lead plate mounting member, the joining tends to be unstable due to the influence of an oxide film formed on the surface of the aluminum alloy, and it is difficult to maintain quality.
[0007]
Furthermore, in the case of a battery in which a large charge / discharge current flows, it is necessary to increase the nugget generated by resistance welding. However, since the nugget size is limited by the thickness of the plates to be joined, a large charge / discharge current flows. There is a problem that it cannot be used for batteries. When laser welding is used, large currents can be accommodated by joining with a large number of pulses, but the aluminum alloy surface has low efficiency due to the high reflectance of laser light, and the energy absorbed varies depending on the surface condition. Therefore, like resistance welding, there is a problem that it is difficult to reduce the cost because the joining tends to be unstable and the joining device is expensive.
[0008]
An object of the present invention is to provide a sealed battery having a low-cost and highly reliable explosion-proof mechanism in view of the above-mentioned case.
[0009]
In order to solve the above-mentioned problems, the present invention provides a plate-like conductive diaphragm having a flat portion at the center, and a conductive connecting plate having a protrusion formed above and having a flat portion at the center of the protrusion. A sealed battery having an explosion-proof mechanism electrically and mechanically connected to each other, wherein the flat portions are joined from the connecting plate side by friction stir welding, and the connecting plate is friction stir The thickness of the vicinity joined by joining is smaller than the thickness of the diaphragm.
[0010]
In the present invention, since the flat portions of the diaphragm and the connection plate are joined by friction stir welding, crystal refinement occurs due to plastic flow, the stability of the joining is improved, and the operating pressure of the explosion-proof mechanism is constant. A highly reliable explosion-proof mechanism can be obtained, and the flat portions are friction stir welded from the connecting plate side, so it is necessary to form a thin portion separately from the joining by using a thin connecting plate. Therefore, the cost of the battery can be reduced, and the thickness of the vicinity of the connection plate joined is smaller than the thickness of the diaphragm. Leakage can be prevented.
[0011]
In this case, when bonding the flat portions of the dust Iyafuramu and connecting plate into a circular shape, the bonding area can be increased, it can be for a large current.
[0012]
DETAILED DESCRIPTION OF THE INVENTION
Hereinafter, embodiments of a sealed cylindrical lithium ion secondary battery to which the present invention can be applied will be described with reference to the drawings.
[0013]
As shown in FIG. 1, the sealed cylindrical lithium ion secondary battery 30 (hereinafter abbreviated as a secondary battery 30) of the present embodiment includes an electrode winding group 11. The electrode winding group 11 is accommodated in the center of a bottomed cylindrical battery can 15 that also serves as a negative electrode terminal, and the positive electrode plate and the negative electrode plate are made of a glass-filled resin shaft through a polyethylene microporous thin film separator. It is wound around the core.
[0014]
The positive electrode is a lithium manganese complex oxide (LiMnO 2 , LiMn 2 O 4 ) having a spinel structure or LiMnO 2 having a layered rock salt structure, LiMn 2 O 4 lithium sites or manganese sites substituted or doped with other metal elements Obtained by mixing lithium manganese transition metal composite oxide powder, conductive carbon material, polyvinylidene fluoride (PVDF) binder and n-methylpyrrolidone as viscosity adjusting solvent, and uniformly dispersing and kneading with Cornel Despa. The positive electrode active material mixture was uniformly applied to both surfaces of the aluminum foil of the positive electrode current collector, dried, pressed to a predetermined size, and cut into a strip shape, leaving a part for current collection. It is.
[0015]
On the other hand, the negative electrode is obtained by mixing graphite or carbon, PVDF as a binder and n-methylpyrrolidone as a viscosity adjusting solvent, uniformly dispersing and kneading with Cornel Despa, and using the negative electrode active material mixture as copper for the negative electrode current collector. It was obtained by uniformly coating on both surfaces of the foil, drying, pressing to a predetermined size, and cutting into strips leaving a part for current collection. Note that positive and negative electrode tabs are formed in the portions left for current collection.
[0016]
The positive electrode tab and the negative electrode tab are disposed so as to be located on both end surfaces on the opposite sides of the electrode winding group 11. A negative electrode current collecting ring for current collection is fixed to the lower end of the shaft core, and a negative electrode tab is ultrasonically welded to the peripheral edge of the negative electrode current collecting ring. The negative electrode current collecting ring is resistance-welded to the battery can 15. A positive current collecting ring 18 for collecting current is fixed to the upper end of the shaft core, and a positive electrode tab is ultrasonically welded to the peripheral edge of the positive current collecting ring 18. One end of a strip-shaped positive electrode lead plate 16 is welded to the positive electrode current collecting ring 18. The other end of the positive electrode lead plate 16 is connected to one end of a strip-like positive electrode lead plate 19, and the other end of the positive electrode lead plate 19 is a splitter that constitutes an upper lid 20 disposed above the electrode winding group 11. 4 is welded to the bottom surface.
[0017]
As shown in FIG. 2, the upper lid 20 has a disk-shaped upper lid cap 1 made of iron and plated with nickel. A cylindrical projection protruding upward is formed at the center of the disk. An opening is formed on the upper surface of the protrusion. The peripheral edge of the upper lid cap 1 is crimped by the peripheral edge of the diaphragm 2. The diaphragm 2 is made of an aluminum alloy and has a dish-like shape with a bottom portion formed below. The dish-shaped bottom portion is flat and forms a flat portion in the center of the diaphragm 2. Between the flat surface portion and the peripheral edge portion of the diaphragm 2, there is formed a cleavage groove 8 that is thinned and is cleaved when the battery internal pressure reaches a predetermined pressure. A resin insulating ring 3 having a substantially T-shaped cross section for supporting the diaphragm 2 is disposed below the cleavage groove 8 and the peripheral edge of the diaphragm 2. Three or more claws 10 formed integrally with the insulating ring 3 are formed on the inner surface side of the insulating ring 3. The outer periphery of the flat donut-shaped splitter 4 along the diaphragm 2 is supported by a claw 10 at a predetermined distance from the bottom surface of the diaphragm 2. The splitter 4 is made of an aluminum alloy, and a through hole 9 is formed at the center. The central portion of the splitter 4 is formed on a peripheral portion of an aluminum alloy connecting plate 6 having a projection formed on the upper portion and having a flat portion at the center of the projection and a flat portion of the diaphragm 2 via a bush 5 made of polypropylene resin. It is pinched. The bush 5 is annular and has a flange portion, and the flange portion is in contact with the bottom surface of the flat portion of the diaphragm 2. The diaphragm 2, the splitter 4, the upper lid cap 1, and the connection plate 6 are formed by pressing.
[0018]
As shown in FIG. 3, the bottom surface of the flat surface portion of the diaphragm 2 and the top surface of the flat surface portion of the connection plate 6 are electrically and mechanically joined in a spot manner by friction stir welding (hereinafter, this friction stir welding). The joint portion is referred to as a joint portion 7). The friction stir welding is performed using a columnar friction stir welding tool 21 made of alloy tool steel shown in FIG. The tool 21 is pressed against the member to be joined while rotating at a high speed to generate frictional heat, the surface layer of the member to be joined is plastically flowed by the frictional heat, and the tool 21 is agitated and joined. The tool 21 has a cylindrical pin 12 protruding from the tip side, and has a shoulder portion 13 that becomes a corner portion of the tool 21 around the base portion of the pin 12. In addition, a concave portion that is deeper from the outer periphery to the center of the tool 21 is formed on the tip surface of the tool 21 excluding the pin 12. The tool 21 is connected to a motor (not shown) and is rotatable at a predetermined rotational speed. The tool 21 is fixed to the support portion so as to be movable up and down in the direction of the rotation axis. When the diaphragm 2 and the connection plate 6 are joined from the connection plate 6 side, the shoulder portion 13 of the tool 21 bites into the connection plate 6 by the vertical movement of the tool 21, and the remaining thickness of the connection plate 6 where the shoulder portion 13 bites in. t is set to be smaller than the plate thickness td of the diaphragm 2. The diaphragm 2 is set to operate when the internal pressure of the secondary battery 30 reaches a predetermined pressure equal to or higher than the atmospheric pressure (the connection plate 6 side is broken and the diaphragm 2 is reversed to the upper lid cap 1 side). Function as.
[0019]
The portion along the splitter 4 of the diaphragm 2 and the splitter 4 are accommodated in the positive electrode current collecting ring 18 shown in FIG. The space S defined by the bottom surface of the splitter 4 and the inner surface of the positive electrode current collecting ring 18 is larger in the circumferential portion than in the central portion in the height direction of the battery. The positive electrode lead piece 16 shown in FIG. 1 is housed by being bent near the periphery of the space S.
[0020]
After a predetermined amount of non-aqueous electrolyte is injected into the battery can 15, the peripheral portion of the upper lid 20 and the battery can 15 are crimped via a gasket 17 to seal the inside of the battery. As the nonaqueous electrolytic solution, for example, an electrolytic solution in which about 6 mol / liter of lithium hexafluorophosphate or lithium tetrafluoroborate is dissolved in an organic solvent such as ethylene carbonate or dimethyl carbonate is used.
[0021]
Next, the operation and the like of the secondary battery 30 of the present embodiment will be described.
[0022]
In the secondary battery 30 of the present embodiment, the flat portions of the diaphragm 2 and the connection plate 6 are joined by friction stir welding. For this reason, since refinement | miniaturization of the crystal | crystallization by plastic flow arises, the stability of the junction part 7 improves, and the explosion-proof device with the fixed operating pressure of the diaphragm 2 can be obtained. Therefore, it is possible to obtain a highly reliable secondary battery 30 in which the diaphragm 2 is reversed with a certain operating pressure. Moreover, in friction stir welding, metal members can be joined at a lower temperature than in conventional welding. For this reason, since the deformation of the diaphragm 2 and the connecting plate 6 at the time of friction stir welding can be suppressed, an explosion-proof device having excellent reliability can be manufactured using a member with little deformation.
[0023]
Furthermore, the secondary battery 30 of this embodiment presses the tool 21 from the connection plate 6 side and performs friction stir welding. For this reason, the shoulder part 13 of the tool 21 bites into the connection plate 2 at the time of friction stir welding, and the remaining thickness t of the connection plate 6 can be made smaller than the plate thickness td of the diaphragm 2. Accordingly, since the process of thinning the connection plate 6 is not required separately from the friction stir welding, the production cost of the secondary battery 30 can be reduced.
[0024]
Further, in the secondary battery 30 of this embodiment, the remaining thickness t of the connection plate 6 is smaller than the plate thickness td of the diaphragm 2. For this reason, since the location of the remaining thickness t of the connection plate 6 is broken from the diaphragm 2 at a constant operating pressure, leakage of gas and nonaqueous electrolyte in the battery can be prevented. Therefore, it is possible to suppress deterioration of peripheral devices of the secondary battery 30 due to gas or non-aqueous electrolyte.
[0025]
Furthermore, since the operating pressure of the diaphragm 2 is larger than the atmospheric pressure, once the diaphragm 2 is reversed, the diaphragm 2 does not return to its original shape at the atmospheric pressure, and the connecting plate 6 comes into electrical contact with the diaphragm 2 again. There is nothing. For this reason, it can be set as the battery excellent in safety | security.
[0026]
Further, when the internal pressure of the secondary battery 30 further increases, the diaphragm 2 is formed with the thinned cleavage groove 8, so that the cleavage groove 8 is cleaved by the internal pressure. The gas in the battery can 15 is released to the outside through a through hole formed in the splitter 4, a cleavage location of the cleavage groove 8, and an opening formed in the upper lid cap 1. Therefore, the secondary battery 30 can be safely disabled.
[0027]
In addition, in this embodiment, although the flat part of the diaphragm 2 and the connection board 6 was shown in the spot type friction stir welding, as shown to FIG. 5 (A) and (B), this invention is made more. When applied to a large-sized secondary battery, the flat portions of the diaphragm 2 and the connection plate 6 are overlapped and mounted on a mounting table (not shown), and the tool 21 is rotated from the connection plate 6 side. The mounting table may be rotated by pressing so that the joint 27 by the tool 21 has a circular shape with a diameter D. By doing so, the energization cross-sectional areas of the diaphragm 2 and the connection plate 6 can be increased, so that a battery for large current can be obtained. Since the battery has different maximum charge / discharge current values and energization patterns required depending on the application, the diameter D may be set so that the temperature rise at the junction is within a practically acceptable range.
[0028]
Moreover, in this embodiment, although the example which uses an aluminum alloy for the material of the diaphragm 2, the connection board 6, and the splitter 4 was shown, it is not limited to this, Other things, such as aluminum, a nickel alloy, and a conductive plastic, are shown. A conductive material may be used.
[0029]
And in this embodiment, although the example which carries out friction stir welding using the tool 21 which the pin 12 protrudes to the front end side was shown, if the connection board 6 side can be made thin, the shape of the pin 12 will not be limited, For example, the length of the pin 12 may be shortened. Thereby, it can respond to joining of a thinner member.
[0030]
【Example】
Next, the secondary battery of the Example produced according to the said embodiment is demonstrated. A battery manufactured for comparison is also shown.
[0031]
(Comparative Example 1)
As shown in Table 1 below, in Comparative Example 1, an aluminum alloy A3003-H14 having a thickness of 0.6 mm is used for the diaphragm, and an aluminum alloy A3003-H14 having a thickness of 0.8 mm is used for the connection plate. Using a tool of 1 mm and a pin length of 1 mm, a battery with a remaining thickness t of the connection plate of 0.70 mm, a capacity of 6 Ah, a battery outer diameter of 40 mm, a battery height of 110 mm, and a maximum charge / discharge current of 30 A was produced.
[0032]
[Table 1]
Figure 0004459559
[0033]
(Comparative Example 2)
As shown in Table 1, in Comparative Example 2, a battery was produced in the same manner as in Comparative Example 1 except that the remaining thickness t of the connection plate was 0.60 mm.
[0034]
Example 1
As shown in Table 1, in Example 1, a battery was manufactured in the same manner as in Comparative Example 1 except that the remaining thickness t of the connection plate was changed to 0.55 mm.
[0035]
(Example 2)
As shown in Table 1, in Example 2, a battery was produced in the same manner as in Comparative Example 1 except that the remaining thickness t of the connection plate was 0.50 mm.
[0036]
<Test>
100 batteries of Examples and Comparative Examples prepared as described above were prepared, and the operation of the explosion-proof device when overcharged with a current value of 6 A was examined. The test results are shown in Table 2 below.
[0037]
[Table 2]
Figure 0004459559
[0038]
In the batteries of Comparative Examples 1 and 2, the diaphragm side sometimes broke, whereas in the batteries of Examples 1 and 2, the diaphragm side did not break. Therefore, it was confirmed that the connection plate side can be reliably broken by making the remaining thickness t of the connection plate smaller than the plate thickness td of the diaphragm.
[0039]
(Comparative Example 3)
As shown in Table 3 below, in Comparative Example 3, an aluminum alloy A3003-H14 with a plate thickness of 1.6 mm is used for the diaphragm, and an aluminum alloy A3003-H14 with a thickness of 1.6 mm is used for the connection plate, a shoulder diameter of 6 mm, a pin diameter Using a tool of 2 mm and a pin length of 1.8 mm, the remaining thickness t of the connecting plate is 1.2 mm, the diameter D is 2 mm, the capacity is 30 Ah, the battery outer diameter is 67 mm, the battery height is 135 mm, and the maximum charge / discharge current A 300 A battery was produced.
[0040]
[Table 3]
Figure 0004459559
[0041]
(Comparative Example 4)
As shown in Table 3, in Comparative Example 4, a battery was produced in the same manner as Comparative Example 3 except that the diameter D was 4 mm.
[0042]
(Example 3)
As shown in Table 3, in Example 3, a battery was produced in the same manner as in Comparative Example 3 except that the diameter D was 6 mm.
[0043]
Example 4
As shown in Table 3, in Example 4, a battery was produced in the same manner as in Comparative Example 3 except that the diameter D was 8 mm.
[0044]
<Test>
Prepare 10 batteries for each of the examples and comparative examples prepared as described above, repeat 30A charge and 300A discharge in a thermostat at 25 ° C, and measure the temperature of the joint with an infrared thermometer. The average value was examined. The test results are shown in Table 4 below.
[0045]
[Table 4]
Figure 0004459559
[0046]
As shown in Table 4, in the batteries of Comparative Examples 3 and 4, the maximum temperature exceeded 100 ° C, whereas in the batteries of Examples 3 and 4, the temperature was suppressed to 100 ° C or less. It was found that there was no risk of deterioration of the joint due to high temperature. It was also confirmed that the explosion-proof device operates reliably when overcharged with a current of 30A. Therefore, the batteries of Example 3 and Example 4 were found to be suitable for charging / discharging of a large current and having excellent safety during overcharging by setting the diameter D of the friction stir welding to 6 mm or more. .
[0047]
【The invention's effect】
As described above, according to the present invention, since the flat portions of the diaphragm and the connection plate are joined by friction stir welding, crystal refinement occurs due to plastic flow, and the stability of the joining is improved. A reliable explosion-proof mechanism with a constant operating pressure of the explosion-proof mechanism can be obtained, and the flat portions are friction stir welded from the connection plate side, so by using a thin connection plate, Since it is not necessary to form a separate thin part, the cost can be reduced and the thickness of the vicinity of the connection plate joined is smaller than the thickness of the diaphragm. Since it breaks, the effect that the leakage of the battery contents can be prevented can be obtained.
[Brief description of the drawings]
FIG. 1 is a cross-sectional view of a sealed cylindrical lithium ion secondary battery according to an embodiment to which the present invention is applicable.
FIG. 2 is a cross-sectional view of an upper lid of the sealed cylindrical lithium ion secondary battery according to the embodiment.
FIG. 3 is an enlarged cross-sectional view of a joint portion between a diaphragm and a connection plate of a sealed cylindrical lithium ion secondary battery.
FIG. 4 is a partially broken cross-sectional view of a tip portion of a tool used for friction stir welding according to the embodiment.
FIG. 5 is an enlarged view of a joint portion between a diaphragm and a connection plate of a large sealed cylindrical lithium ion secondary battery to which the present invention can be applied, (A) is a plan view viewed from the connection plate side; ) Is a cross-sectional view.
[Explanation of symbols]
2 Diaphragm (part of explosion-proof mechanism)
6 Connection board (part of the explosion-proof mechanism)
7, 27 Joint 20 Upper lid 30 Sealed cylindrical lithium ion secondary battery (sealed battery)

Claims (2)

中央に平面部を有する皿状の導電性ダイヤフラムと、上方に突起が形成され該突起の中央に平面部を有する導電性接続板とが前記平面部同士で電気的・機械的に接続された防爆機構を備える密閉型電池であって、前記平面部同士は、摩擦攪拌接合によって前記接続板側から接合されており、前記接続板は、前記摩擦攪拌接合によって接合された近傍の板厚が前記ダイヤフラムの厚さより小さいことを特徴とする密閉型電池。Explosion-proof in which a dish-shaped conductive diaphragm having a flat portion in the center and a conductive connection plate having a protrusion formed above and having a flat portion in the center of the protrusion are electrically and mechanically connected between the flat portions. A sealed battery comprising a mechanism, wherein the flat portions are joined from the side of the connecting plate by friction stir welding, and the connecting plate has a thickness in the vicinity of the diaphragm joined by the friction stir welding. A sealed battery characterized by being smaller than the thickness of the battery. 前記平面部同士は、前記摩擦攪拌接合によって円形状に接合されたことを特徴とする請求項1に記載の密閉型電池。The sealed battery according to claim 1, wherein the flat portions are joined in a circular shape by the friction stir welding.
JP2003174466A 2003-06-19 2003-06-19 Sealed battery Expired - Lifetime JP4459559B2 (en)

Priority Applications (1)

Application Number Priority Date Filing Date Title
JP2003174466A JP4459559B2 (en) 2003-06-19 2003-06-19 Sealed battery

Applications Claiming Priority (1)

Application Number Priority Date Filing Date Title
JP2003174466A JP4459559B2 (en) 2003-06-19 2003-06-19 Sealed battery

Publications (2)

Publication Number Publication Date
JP2005011673A JP2005011673A (en) 2005-01-13
JP4459559B2 true JP4459559B2 (en) 2010-04-28

Family

ID=34097941

Family Applications (1)

Application Number Title Priority Date Filing Date
JP2003174466A Expired - Lifetime JP4459559B2 (en) 2003-06-19 2003-06-19 Sealed battery

Country Status (1)

Country Link
JP (1) JP4459559B2 (en)

Families Citing this family (5)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
JP4688605B2 (en) * 2005-08-05 2011-05-25 日立ビークルエナジー株式会社 Cylindrical secondary battery
US7508682B2 (en) 2005-09-19 2009-03-24 Hitachi, Ltd. Housing for an electronic circuit
JP4939101B2 (en) * 2006-04-18 2012-05-23 前田建設工業株式会社 Approach construction method
JP5974531B2 (en) * 2012-02-23 2016-08-23 トヨタ自動車株式会社 Manufacturing method of sealed battery
CN105684192B (en) 2013-11-05 2019-04-26 三洋电机株式会社 Enclosed-type battery seal body and enclosed-type battery

Family Cites Families (3)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
JPH07105933A (en) * 1993-10-06 1995-04-21 Hitachi Maxell Ltd Anti-explosive enclosed battery
JPH11329405A (en) * 1998-05-21 1999-11-30 At Battery:Kk Nonaqueous electrolyte secondary battery
JP2000223104A (en) * 1999-02-01 2000-08-11 Hitachi Maxell Ltd Sealed battery

Also Published As

Publication number Publication date
JP2005011673A (en) 2005-01-13

Similar Documents

Publication Publication Date Title
US10224533B2 (en) Secondary battery comprising current interrupt device
JP6662377B2 (en) Cylindrical battery
JP5171401B2 (en) Lithium secondary battery
JP5103489B2 (en) Sealed battery
JPWO2014097586A1 (en) Cylindrical secondary battery and manufacturing method thereof
JP4688688B2 (en) Secondary battery for large current discharge
JP5619033B2 (en) Sealed battery and manufacturing method thereof
JP3627645B2 (en) Lithium secondary battery
JP5334429B2 (en) Lithium secondary battery
JP5231089B2 (en) Sealed secondary battery
JP3786074B2 (en) Sealed battery
JP4586339B2 (en) Sealed battery
JP4590856B2 (en) Sealed battery
JP2003007346A (en) Secondary lithium battery and manufacturing method of the same
JP4356209B2 (en) Batteries for high power applications
JP4459559B2 (en) Sealed battery
JP4934994B2 (en) Sealed cylindrical secondary battery
JP4591012B2 (en) Sealed lithium secondary battery
JP2003243036A (en) Cylindrical lithium secondary battery
JP2009289714A (en) Lithium-ion secondary battery and method of manufacturing the same
JP2002170531A (en) Tubular secondary battery
JP2006040772A (en) Lithium ion battery
JP4688605B2 (en) Cylindrical secondary battery
JP4975993B2 (en) Sealed secondary battery
WO2024143319A1 (en) Power storage device and power storage module

Legal Events

Date Code Title Description
A621 Written request for application examination

Free format text: JAPANESE INTERMEDIATE CODE: A621

Effective date: 20060519

A977 Report on retrieval

Free format text: JAPANESE INTERMEDIATE CODE: A971007

Effective date: 20090203

A131 Notification of reasons for refusal

Free format text: JAPANESE INTERMEDIATE CODE: A131

Effective date: 20091110

A521 Request for written amendment filed

Free format text: JAPANESE INTERMEDIATE CODE: A523

Effective date: 20091215

TRDD Decision of grant or rejection written
A01 Written decision to grant a patent or to grant a registration (utility model)

Free format text: JAPANESE INTERMEDIATE CODE: A01

Effective date: 20100202

A01 Written decision to grant a patent or to grant a registration (utility model)

Free format text: JAPANESE INTERMEDIATE CODE: A01

A61 First payment of annual fees (during grant procedure)

Free format text: JAPANESE INTERMEDIATE CODE: A61

Effective date: 20100210

R150 Certificate of patent or registration of utility model

Ref document number: 4459559

Country of ref document: JP

Free format text: JAPANESE INTERMEDIATE CODE: R150

Free format text: JAPANESE INTERMEDIATE CODE: R150

FPAY Renewal fee payment (event date is renewal date of database)

Free format text: PAYMENT UNTIL: 20130219

Year of fee payment: 3

FPAY Renewal fee payment (event date is renewal date of database)

Free format text: PAYMENT UNTIL: 20140219

Year of fee payment: 4

R250 Receipt of annual fees

Free format text: JAPANESE INTERMEDIATE CODE: R250

FPAY Renewal fee payment (event date is renewal date of database)

Free format text: PAYMENT UNTIL: 20140219

Year of fee payment: 4

S111 Request for change of ownership or part of ownership

Free format text: JAPANESE INTERMEDIATE CODE: R313117

FPAY Renewal fee payment (event date is renewal date of database)

Free format text: PAYMENT UNTIL: 20140219

Year of fee payment: 4

R350 Written notification of registration of transfer

Free format text: JAPANESE INTERMEDIATE CODE: R350

S111 Request for change of ownership or part of ownership

Free format text: JAPANESE INTERMEDIATE CODE: R313113

R350 Written notification of registration of transfer

Free format text: JAPANESE INTERMEDIATE CODE: R350

R250 Receipt of annual fees

Free format text: JAPANESE INTERMEDIATE CODE: R250

S111 Request for change of ownership or part of ownership

Free format text: JAPANESE INTERMEDIATE CODE: R313111

R350 Written notification of registration of transfer

Free format text: JAPANESE INTERMEDIATE CODE: R350

R250 Receipt of annual fees

Free format text: JAPANESE INTERMEDIATE CODE: R250

R250 Receipt of annual fees

Free format text: JAPANESE INTERMEDIATE CODE: R250

R250 Receipt of annual fees

Free format text: JAPANESE INTERMEDIATE CODE: R250

EXPY Cancellation because of completion of term