JP4009537B2

JP4009537B2 - Charge control device, battery management system, battery pack, and secondary battery deterioration determination method using the same

Info

Publication number: JP4009537B2
Application number: JP2003007545A
Authority: JP
Inventors: 俊之仲辻
Original assignee: Panasonic Corp; Matsushita Electric Industrial Co Ltd
Current assignee: Panasonic Corp; Panasonic Holdings Corp
Priority date: 2003-01-15
Filing date: 2003-01-15
Publication date: 2007-11-14
Anticipated expiration: 2023-01-15
Also published as: JP2004222427A

Description

【０００１】
【発明の属する技術分野】
本発明は例えば、電池式電気機器、携帯用電子機器、非常用電源、補助電源、若しくは自動車に内蔵され電源として用いられ、又は電力貯蔵に用いられる二次電池に対し、その充電を制御するための装置に関する。特に、その装置による二次電池の劣化判定方法に関する。
【０００２】
【従来の技術】
二次電池の有効な利用には、その最大容量までの充電が望ましい。
しかし、過充電は、例えば、電解液の分解によるガスの発生、又は電解液の漏れ等の原因となり、二次電池の安全性を損なうので好ましくない。更に、過充電及び過剰な充電電流は二次電池を著しく劣化させるので好ましくない。
従って、二次電池の充電には厳密な制御が必要であり、すなわち、電池電圧と充電電流とが高精度で管理されなければならない。
【０００３】
二次電池に対する充電制御は、充電器、電子機器本体、又は電池管理システムに内蔵された充電制御装置により行われる。ここで、電池管理システムとは、二次電池と共通の電池パック内に収められ、その二次電池の状態を監視しかつ制御し、又は充電器等、外部の制御装置へ通知するための装置をいう。
充電制御装置は充電期間中、電池電圧、充電電流、及び電池温度を監視し、所定の充電条件に合うように制御する。ここで、充電条件とは、充電期間中、例えば電池電圧、充電電流、及び電池温度が満たすべき条件（例えば、変化パターン又は変動の許容範囲等）をいう。更に、電池電圧等の監視は、充電制御装置により直接行われても、電池管理システムを通して行われても良い。
電池電圧等が充電条件を大きく外れ、特に異常な増大を示すとき、充電制御装置は充電電流を遮断し、充電を中止する。
【０００４】
充電制御装置は通常、二次電池を満充電（完全充電ともいう)、すなわち実質的な最大容量まで充電されたときの電池状態、に達するまで充電する。二次電池の満充電は、電池電圧、充電電流、及び電池温度の測定値、又はそれらの一定時間内での変化量に基づき検知される。充電制御装置は満充電の検知時、充電電流を遮断し、充電を終了する。以下、充電制御装置による満充電の検知のように、充電終了を判断するための条件を充電終止条件という。充電終止条件は上記の充電条件の一部として含まれる。
【０００５】
充電制御装置は更に、例えば満充電まで充電された二次電池の充電状態を、放電開始まで実質的に満充電に維持する。具体的には、満充電までの充電が終了した後、二次電池の充電状態を監視する。二次電池の充電状態が例えば自己放電により満充電（100％）から所定値（例えば約5％）だけ下がるごとに、充電制御装置は二次電池の充電を再開し、二次電池の充電状態を満充電（100％）へ戻す。このように（例えば放電深度約5％程度の）ごく浅い充放電の反復により、二次電池の充電状態が満充電に実質的に維持される。
【０００６】
充電制御装置は上記の充電条件を二次電池の充電特性に応じて定める。二次電池の充電特性は二次電池の種類ごとに異なるので、具体的な充電条件、特に充電終止条件は二次電池の種類ごとに異なる。
ニッケル−カドミウム蓄電池の充電は定電流方式で行われる。電池電圧は充電開始から徐々に上昇し、満充電でピークを迎え、以後降下する。このような充電特性に基づき、充電制御装置は、一定時間内の電池電圧の変化量が正から負へ転じることを充電終止条件として定める（−ΔＶ方式)。
【０００７】
ニッケル−水素蓄電池の充電は定電流方式で行われる。電池温度の時間微分は充電開始から徐々に減少し、満充電で増大に転じ、過充電領域では増大する。このような充電特性に基づき、充電制御装置は、一定の微小時間内の電池温度の変化量の急増を充電終止条件として定める（dT／dt方式)。
【０００８】
リチウムイオン二次電池では、ニッケル−カドミウム蓄電池及びニッケル−水素蓄電池に比べ、過充電による危険性が高い。そこで、リチウムイオン二次電池の充電は定電流定電圧方式（ＣＣＣＶ方式）で行われる。充電開始からしばらくは定電流制御が行われ、充電電流値が所定値に維持される。定電流制御期間では電池電圧が上昇する。充電が進み、電池電圧が所定の上限に達するとき、定電流制御は定電圧制御へ切り換えられ、充電電圧値がその上限値に維持される。定電圧制御期間では充電電流は徐々に減少する。充電電流値が所定の閾値（以下、充電終止電流値という）を下回るとき、充電が終了する。このように、ＣＣＣＶ方式ではその充電条件の一つとして、電池電圧の上限値が設定される。それにより過充電が確実に回避される。
【０００９】
二次電池の充電特性は、その二次電池の種類の他に、その電池状態の履歴にも依存し変化する。例えば、充放電サイクル数の増大に伴い二次電池は劣化し、特にその電池容量が減少する。従って、従来の充電制御装置は、充放電サイクル数に応じ充電条件を修正し、充放電サイクル数の増大に関わらず過充電を確実に回避しなければならない。
【００１０】
二次電池の充放電サイクル数に基づき充電条件を修正する充電制御装置としては、次のようなものが知られる（特許文献１参照)。その充電制御装置は、例えばノート型パーソナルコンピュータ（以下、ノートＰＣと略す)、又は電池パック内の電池管理システムに組み込まれる。
図4は、二次電池41の充電に関するノートＰＣ3と電池パック40との従来の構成を示すブロック図である。ここで、電池パック40内の二次電池41は例えばリチウムイオン二次電池である。ノートＰＣ3内の充電器制御部32と電池管理システム42内の制御部43とは協働し、ＣＣＣＶ方式に従い二次電池41の充電を制御する。充電器31は商用交流電源1からＡＣアダプタ2を通し電力を入力する。更に、充電器制御部32の制御下でその入力電力を変換し、出力電圧又は出力電流を所定値に安定に維持し、電池パック40へ供給する。
【００１１】
電池パック40では、二次電池41が充電器31からの電力供給により充電される。
二次電池41の充電期間中、電池管理システム42では電池状態監視部が二次電池41の状態を監視する。ここで、電池状態監視部は電流検出部44、温度検出部45、及び電圧検出部46の三つのセンサを含む。電流検出部44は充電電流を、電流検出用抵抗44Aによる電圧降下量から計測する。温度検出部45は電池温度を、二次電池41に近接したサーミスタ45Aの抵抗値から計測する。電圧検出部46は二次電池41の両端間の電圧を計測し、セル当たりの電池電圧を換算する。
制御部43は、電流検出部44、温度検出部45、及び電圧検出部46のそれぞれから測定値を一定の時間間隔で入力し、それらの測定値をノートＰＣ3内の充電器制御部32へ通知する。充電器制御部32は通知された電池状態に基づき、充電器31の出力電圧又は出力電流を制御する。
【００１２】
一方、制御部43は充電期間中、充電電流の測定値を積算し、充電電気量を算定する。更にその充電電気量を充電後も保持する。複数回の充電にわたる充電電気量の累積が所定の電池容量と実質的に等しいとき、例えばその電池容量の0.9倍を超えるとき、制御部43は充放電サイクル数を1だけ加算する。ここで、電池容量は、例えば制御部43により二次電池41の放電ごとに放電電流の積算値から学習された値である。こうして、充放電サイクル数が放電深度による重み付きでカウントされる。
【００１３】
上記の重み付き充放電サイクル数が所定の閾値（例えば50）を超えるとき、制御部43は充電器制御部32へ通知する。その通知に応じ、充電器制御部32は、例えばＣＣＣＶ方式での電池電圧の上限値を所定量だけ低減させる（例えば、4.20V／セルから0.10V／セルだけ下げる)。それにより、一回の充電当たりの充電電気量の実質的な上限が下がる。
こうして、充放電サイクル数の増大に伴い二次電池41が劣化し、その電池容量が減少するときでも、過充電が確実に回避される。
【００１４】
【特許文献１】
特開２００１−３０９５６８号公報
【００１５】
【発明が解決しようとする課題】
特許文献１で開示される充電制御装置は二次電池の劣化を、上記の重み付き充放電サイクル数で評価し、判定する。しかし、二次電池の劣化判定はそのような重み付き充放電サイクル数だけでは一般に不十分である。
例えば、二次電池がごく浅い充放電の連続で高充電状態（電池容量に対する残存容量の割合が高い状態）に維持されるとき、又は過放電により完全放電状態近く（以下、過放電状態という）に維持されるとき、電池内部のキャリアが正負いずれかの電極に集中し、大きな負荷を与え続ける。その結果、二次電池は大きく劣化する。一方、高充電状態又は過放電状態の持続期間中では充電電気量及び放電電気量がいずれも一般にわずかであるので、上記の重み付き充放電サイクル数はわずかしか増大しない。こうして、二次電池の劣化の程度と重み付き充放電サイクル数との対応にずれが生じる。
【００１６】
特にリチウムイオン二次電池では、高充電状態に維持されるとき、多数のリチウム原子が負極のグラファイト層に集中し、そのグラファイト層を痛める。その損傷は特に高温下で激しい。従って、リチウムイオン二次電池では、高充電状態の持続期間が長いほど、又はその持続期間中の電池温度が高いほど、劣化が著しい。
例えば、ノートＰＣが商用交流電源で駆動されるとき、ＣＰＵ等が高熱を発する状況下で内蔵の二次電池は高充電状態に維持される。従って、その二次電池としてリチウムイオン二次電池を安全に使用するには、高充電状態の持続期間の長さとその持続期間中の電池温度とに基づき、二次電池の劣化が正確に評価されなければならない。
【００１７】
二次電池の劣化の程度は更に、過放電状態での放電率と電池温度とにも大きく依存する。すなわち、二次電池が放電により過放電状態へ突入するとき、その時点での放電率が高く又は電池温度が低いほど、電池内部のキャリアが大きな負荷を電極に与えるので、二次電池の劣化が著しい。従って、二次電池の劣化判定の精度の向上には、過放電状態での放電率及び電池温度の履歴に基づく劣化の評価が有効である。
【００１８】
本発明は、二次電池の劣化の程度を正確に評価し、それにより二次電池の劣化に応じ過充電を確実に回避できる充電制御装置、及びその二次電池の劣化判定方法の提供を目的とする。
【００１９】
【課題を解決するための手段】
本発明の一つの観点による充電制御装置は、
(A) 二次電池の充電時、その電池電圧、充電電流、及び電池温度を監視し、それらの測定値又は一定時間内の変化量が所定の充電条件を満たすか否か、を判定するための充電条件監視部；
(B) 二次電池の充電状態が一定値に実質的に維持されるとき、その充電状態の持続期間中、その二次電池の電池温度を監視し、かつその持続期間の長さを評価し、その持続期間中の電池温度の測定値とその持続期間の長さとに基づき二次電池の劣化係数を決定するための劣化評価部；並びに、
(C) 二次電池の劣化係数に応じ充電条件を補正するための充電条件補正部；
を有する。
【００２０】
充電制御装置とは、例えば充電器、電子機器本体、又は電池管理システムに内蔵され、二次電池の充電を制御するための装置をいう。
ここで、電池管理システムは、二次電池と共通の電池パック内に収められ、内部の電池状態監視部によりその二次電池の状態を監視しかつ制御し、又は充電器等、外部の制御装置へ通知するための装置である。電池状態監視部は、その二次電池について、(a) 電池電圧を測るための電圧検出部、(b) 電池電流を測るための電流検出部、及び、(c) 電池温度を測るための温度検出部、を含み、それらの検出部により得られた二次電池の電池電圧、電池電流、及び電池温度を充電制御装置に対し提供する。
充電制御装置は電池電圧、充電電流、及び電池温度の監視を、充電条件監視部により直接行っても良い。又は外部のセンサ、例えば電池管理システム内の電池状態監視部を通し行っても良い。
【００２１】
充電条件とは、二次電池の充電期間中、電池電圧、充電電流、及び電池温度が満たすべき条件（例えば、変化パターン又は変動の許容範囲）をいう。充電条件は特に、例えば満充電の検知条件等、充電終了を判断するための条件（以下、充電終止条件という）を含む。
例えば、−ΔＶ方式では、充電電流の目標値、及び一定時間内の電池電圧の変化量に対する閾値が、充電条件として含まれる。dT／dt方式では、充電電流の目標値、及び一定時間内の電池温度の変化量に対する閾値が、充電条件として含まれる。ＣＣＣＶ方式では、充電電流の目標値、電池電圧の上限値、及び充電終止電流値が、充電条件として含まれる。
【００２２】
二次電池の充電状態とは、電池容量に対する残存容量の割合をいう。「二次電池の充電状態が一定値に実質的に維持される」とは、二次電池の充電状態の変動がその一定値を含む所定の範囲内に制御されることをいう。
例えば、充電制御装置は二次電池を満充電まで一旦充電した後、その二次電池の充電状態を放電開始まで実質的に満充電に維持する。具体的には、満充電までの充電が終了した後、二次電池の充電状態を監視する。二次電池の充電状態が例えば自己放電により満充電から所定値だけ下がるごとに、充電制御装置は二次電池の充電を再開し、二次電池の充電状態を満充電へ戻す。
このように、二次電池の充電状態が一定値から所定値だけ下がるごとに、充電制御装置は二次電池の充電を再開し、二次電池の充電状態を一定値へ戻す。そのような充電の反復により、二次電池の充電状態が一定値に実質的に維持される。
以下、上記の一定値から所定値だけ低い充電状態を維持限界という。充電状態の維持限界は上記の充電条件の一部として含まれる。
【００２３】
充電状態は、例えば、電池電流の積算値、すなわち充電電気量又は放電電気量と、電池容量とから算定される。その他に、二次電池固有の充放電特性に基づき電池状態（電池電圧、電池電流、及び電池温度の組）と充電状態との対応関係が二次電池の製造時に記憶され、その対応関係から、電池状態の測定値に対応する充電状態が決定されても良い。
【００２４】
二次電池の劣化係数とはその二次電池の劣化の程度を数値化したものをいう。好ましくは、電池容量の製造時での値（以下、初期値という）と実際の値との比で定義される。すなわち、劣化が進むほど電池容量は低減するので、劣化係数は小さい。
【００２５】
二次電池は主に充放電時の負荷により劣化する。しかし、その劣化係数は充放電サイクル数だけでは一意には決まらず、例えば放電深度と電池温度との履歴に依存する。特に、高充電状態と過放電状態とのそれぞれの持続期間の長さとその持続期間中の電池温度とに依存する。
例えば、リチウムイオン二次電池は、ごく浅い充放電の連続により高充電状態に維持されるとき、又は過放電により完全放電状態近くに維持されるとき、50％程度の浅い充放電の反復時より、大きく劣化する。更に、高充電状態の持続期間では電池温度が高いほど、過放電状態の持続期間では電池温度が高いほど、それぞれリチウムイオン二次電池の劣化は著しい。
【００２６】
上記の充電制御装置では、二次電池の充電状態が一定値に実質的に維持されるごとに、劣化評価部がその持続期間の長さを評価し、かつその持続期間中の電池温度を計測する。更にその評価値と測定値とに基づき二次電池の劣化係数を決定する。それにより、二次電池の劣化を従来の装置より高精度に評価できる。
ここで、劣化評価部は上記持続期間の長さを、好ましくは、その持続時間で評価する。その他に、二次電池の充電状態の一定値から維持限界への降下回数で評価しても良い。
【００２７】
充電状態、その持続期間の長さ、及びその持続期間中の電池温度を変数とするときの劣化係数の関数形は、二次電池の種類ごとに例えば実験で決定される。劣化評価部はその関数に基づき、例えば、充電状態、その持続期間の長さ、及びその持続期間中の電池温度の組別に対応する劣化係数を予め算定し、そのリストを記憶する。劣化評価部はそのリストを参照し、充電状態、持続期間の長さ、及び電池温度の測定値の組に対応する劣化係数を決定する。
劣化評価部はその他に、劣化係数の関数形を特徴づける係数群を実験で予め決定しておき、二次電池の高充電状態又は過放電状態の持続期間ごとに、その充電状態、その持続期間の長さ、及びその持続期間中の電池温度と上記の係数群とから劣化係数を算定しても良い。
【００２８】
上記の充電制御装置では更に、充電条件補正部が、劣化評価部により決定された劣化係数に応じ充電条件を補正する。その補正により特に、充電電流の上限、又は充電期間中の電池電圧の上限を低減させる。例えば、ＣＣＣＶ方式では、定電流制御期間での充電電流の目標値若しくは電池電圧の上限値を所定量だけ低減させ、又は充電終止電流値を所定量だけ増加させる。こうして、二次電池の劣化による電池容量の減少に適切に応じ、過充電及び過剰な充電電流の発生が確実に回避される。
【００２９】
充電条件補正部は更に、上記の二次電池の劣化係数に応じ上記の充電状態の維持限界を所定値だけ下げても良い。それにより、特に二次電池が高充電状態に維持されるとき、その持続期間中での放電深度が増大する。その結果、その持続期間中での電極の負担が軽減し、二次電池の劣化の進行を緩め得る。
【００３０】
劣化評価部により決定される二次電池の劣化係数は、二次電池の充電制御だけでなく、その放電制御に用いられても良い。例えば、二次電池の放電時、二次電池の充電状態が実質的に0％まで降下し、又は電池電圧が所定の下限（放電終止電圧）まで降下する場合、二次電池内の電池管理システム又は外部の放電制御装置は放電電流を遮断する。それにより、二次電池の過放電を防ぐ。ここで、二次電池は劣化によりその放電特性を変化させる。従って、実質的に0％の充電状態に対応する電池状態又は放電終止電圧のそれぞれの値を上記の二次電池の劣化係数に応じ補正することで、過放電を確実に回避できる。
【００３１】
本発明のもう一つの観点による充電制御装置は、
(A) 二次電池の充電時、その電池電圧、充電電流、及び電池温度を監視し、それらの測定値又は一定時間内の変化量が所定の充電条件を満たすか否か、を判定するための充電条件監視部；
(B) 二次電池の放電によりその二次電池の充電状態又は電池電圧が所定の閾値まで降下するときその二次電池の放電率と電池温度とを計測し、その放電率と電池温度との測定値に基づきその二次電池の劣化係数を決定するための劣化評価部；並びに、
(C) その二次電池の劣化係数に応じ充電条件を補正するための充電条件補正部；を有する。
【００３２】
二次電池の劣化係数は放電深度と電池温度との履歴の他に、過放電状態での放電率と電池温度との履歴に依存する。例えばリチウムイオン二次電池では、過放電状態での放電率が高く又は電池温度が低いほど、劣化が著しい。
上記の充電制御装置では、劣化評価部が二次電池の充電状態又は電池電圧に対する上記の閾値を、例えば過放電状態への突入時点又はその手前での値に対応させる。具体的には例えば、充電状態に対する閾値を約0％に設定し、又は電池電圧に対する閾値を放電終止電圧値に設定する。それにより、過放電状態での放電率と電池温度との測定値に基づき二次電池の劣化係数を決定する。こうして、二次電池の劣化を従来の装置より高精度に評価できる。
【００３３】
過放電状態での放電率と電池温度とを変数とするときの劣化係数の関数形は、二次電池の種類ごとに、例えば実験で決定される。劣化評価部はその関数に基づき、例えば放電率と電池温度との組別に対応する劣化係数を予め算定し、そのリストを記憶する。劣化評価部はそのリストを参照し、放電率と電池温度との測定値の組に対応する劣化係数を決定する。
劣化評価部はその他に、劣化係数の関数形を特徴づける係数群を実験で予め決定しておき、二次電池の過放電状態への突入時ごとに、その放電率、電池温度、及び上記の係数群から劣化係数を算定しても良い。
【００３４】
上記の充電制御装置では更に、充電条件補正部が劣化評価部により決定された劣化係数に応じ充電条件を補正する。その補正により特に、充電電流の上限、又は充電期間中の電池電圧の上限を低減させる。それにより、二次電池の劣化による電池容量の減少に適切に応じ、過充電及び過剰な充電電流の発生を確実に回避する。
【００３５】
上記の充電制御装置では、放電により二次電池の充電状態又は電池電圧が上記の閾値まで降下するときの放電率の測定値が所定値以上である回数（以下、過放電検出回数という）を劣化評価部が数え、その過放電検出回数に基づき二次電池の劣化係数を決定しても良い。
二次電池が高放電率で過放電状態へ突入するとき、その二次電池の正極にかかる負荷が特に重い。すなわち、高放電率での過放電は二次電池の劣化を特に大きく促進する。
上記の充電制御装置は劣化係数の決定に過放電検出回数を反映させることで、高放電率での過放電による劣化を重点的に評価する。それにより、劣化の評価の精度を向上できる。
【００３６】
本発明の一つの観点による二次電池の劣化判定方法は、
(A) 二次電池が実質的に一定の充電状態に維持されるとき、その充電状態の持続期間中、二次電池の電池温度を監視し、かつ持続期間の持続時間を計測するステップ；及び、
(B) 持続期間中の電池温度の測定値と持続時間とに基づき二次電池の劣化係数を決定するステップ；
を有する。
【００３７】
例えば、充電器、電子機器本体、又は電池パック内の電池管理システムに内蔵される充電制御装置が、この二次電池の劣化判定方法を実施する。
ここで、二次電池の充電状態及び劣化係数は上記のものと同様に定義される。
充電状態は上記と同様、例えば、充電電気量又は放電電気量と、電池容量とから算定される。その他に、電池状態（電池電圧、電池電流、及び電池温度の組）と充電状態との対応関係から、電池状態の測定値に対応する充電状態が決定されても良い。
【００３８】
二次電池の劣化係数は充放電サイクル数だけでは一意には決まらず、その他に例えば、放電深度と電池温度との履歴に依存する。特に、高充電状態と過放電状態とのそれぞれの持続期間の長さとその持続期間中の電池温度とに依存する。
上記の劣化判定方法では、二次電池の充電状態が一定値に実質的に維持されるごとにその持続期間の長さが評価され、かつその持続期間中の電池温度が計測される。更にその評価値と測定値とに基づき二次電池の劣化係数が決定される。それにより、二次電池の劣化が従来の判定方法より高精度に評価される。
ここで、上記持続期間の長さは、好ましくは、その持続時間で評価される。その他に、二次電池の充電状態の一定値から維持限界への降下回数で評価されても良い。
【００３９】
充電状態、その持続期間の長さ、及びその持続期間中の電池温度を変数とするときの劣化係数の関数形は、二次電池の種類ごとに例えば実験で決定される。
上記の劣化判定方法では、その関数に基づき、例えば、充電状態、その持続期間の長さ、及びその持続期間中の電池温度の組別に、対応する劣化係数のリストが予め設定される。劣化係数の決定ステップではそのリストが参照され、充電状態、持続期間の長さ、及び電池温度の測定値の組に対応する劣化係数が決定される。
そのリストの他に、劣化係数の関数形を特徴づける係数群が実験で設定されても良い。劣化係数の決定ステップでは、その係数群、充電状態、その持続期間の長さ、及びその持続期間中の電池温度から劣化係数が算定される。
【００４０】
上記の劣化判定方法により決定される二次電池の劣化係数は、例えば二次電池の充電制御に利用される。すなわち、充電制御装置が二次電池の充電条件を、上記の劣化係数に応じ補正する。その補正により特に充電電流の上限又は充電期間中の電池電圧の上限が低減する。例えばＣＣＣＶ方式では、定電流制御期間での充電電流の目標値若しくは電池電圧の上限値が所定量だけ低減し、又は充電終止電流値が所定量だけ増加する。こうして、二次電池の劣化による電池容量の減少に適切に応じ、過充電及び過剰な充電電流の発生が確実に回避される。
【００４１】
上記の劣化判定方法により決定される二次電池の劣化係数は、二次電池の放電制御に用いられても良い。例えば、二次電池の放電時、二次電池の充電状態が実質的に0％まで降下し、又は電池電圧が所定の下限（放電終止電圧）まで降下する場合、二次電池内の電池管理システム又は外部の放電制御装置は放電電流を遮断する。それにより、二次電池の過放電を防ぐ。ここで、二次電池は劣化によりその放電特性を変化させる。従って、実質的に0％の充電状態に対応する電池状態又は放電終止電圧のそれぞれの値を上記の二次電池の劣化係数に応じ補正することで、過放電を確実に回避できる。
【００４２】
本発明のもう一つの観点による二次電池の劣化判定方法は、
(A) 二次電池の放電によりその二次電池の充電状態又は電池電圧が所定の閾値まで降下するとき、その二次電池の放電率と電池温度とを計測するステップ；及び、
(B) その放電率と電池温度との測定値に基づきその二次電池の劣化係数を決定するステップ；
を有する。
【００４３】
二次電池の劣化係数は放電深度と電池温度との履歴の他に、過放電状態での放電率と電池温度との履歴に依存する。例えばリチウムイオン二次電池では、過放電状態での放電率が高く又は電池温度が低いほど、劣化が著しい。
上記の劣化判定方法では、二次電池の充電状態又は電池電圧に対する上記の閾値が、例えば過放電状態への突入時点又はその手前での値に対応する。具体的には例えば、充電状態に対する閾値が約0％に設定し、又は電池電圧に対する閾値が放電終止電圧値に設定される。それにより、過放電状態での放電率と電池温度との測定値に基づき二次電池の劣化係数が決定される。こうして、二次電池の劣化が従来の判定方法より高精度に評価される。
【００４４】
過放電状態での放電率と電池温度とを変数とするときの劣化係数の関数形は、二次電池の種類ごとに、例えば実験で決定される。上記の劣化判定方法では、その関数に基づき、例えば放電率と電池温度との組別に対応する劣化係数のリストが予め設定される。劣化係数の決定ステップではそのリストが参照され、放電率と電池温度との測定値の組に対応する劣化係数が決定される。
そのリストの他に、劣化係数の関数形を特徴づける係数群が実験で設定され、その係数群、放電率、及び電池温度から劣化係数が算定されても良い。
【００４５】
上記の劣化判定方法により決定される二次電池の劣化係数は、例えば二次電池の充電制御に利用される。すなわち、充電制御装置が二次電池の充電条件を、上記の劣化係数に応じ補正する。その補正により充電電流の上限又は充電期間中の電池電圧の上限が低減する。それにより、二次電池の劣化による電池容量の減少に適切に応じ、過充電及び過剰な充電電流の発生が確実に回避される。
【００４６】
上記の劣化判定方法により決定される二次電池の劣化係数は、二次電池の放電制御に用いられても良い。すなわち、実質的に0％の充電状態に対応する電池状態又は放電終止電圧のそれぞれの値を上記の二次電池の劣化係数に応じ補正することで、過放電を確実に回避できる。
【００４７】
上記の二次電池の劣化判定方法は更に、
(A) 放電により二次電池の充電状態又は電池電圧が上記の閾値まで降下するときの放電率の測定値が所定値以上である回数（以下、過放電検出回数という）を数えるステップ；及び、
(B) その過放電検出回数に基づき二次電池の劣化係数を決定するステップ；
を有しても良い。
高放電率での過放電は二次電池の劣化を特に大きく促進する。上記の劣化判定方法では、過放電検出回数に基づく劣化係数の決定ステップを通し、高放電率での過放電による劣化が重点的に評価される。それにより、劣化の評価の精度が向上する。
【００４８】
【発明の実施の形態】
以下、本発明の最適な実施の形態について、図面を参照しつつ説明する。
【００４９】
《実施形態１》
本発明の実施形態１による充電制御装置は、ノートＰＣ用電池パック内の電池管理システムに、その制御部として搭載される。
図1は、二次電池41の充電に関するノートＰＣ3と電池パック4との構成を示すブロック図である。
ノートＰＣ3は充電器31と充電器制御部32とを含む。
電池パック4は二次電池41と電池管理システム5とを含む。
二次電池41は例えばリチウムイオン二次電池である。ノートＰＣ3と電池パック4内の電池管理システム5とは協働し、ＣＣＣＶ方式に従い二次電池41を充電する。
【００５０】
ノートＰＣ3内の充電器31は、ＡＣアダプタ2を通し商用交流電源1へ接続される。それにより、ＡＣアダプタ2から直流電力を入力する。更に、充電器制御部32の制御下でその入力電力を変換し、出力電圧又は出力電流を所定値に安定に維持し、電池パック4へ供給する。
充電器制御部32は所定の充電条件に従い、充電器31の出力電圧と出力電流とを制御する。ここで、その充電条件は電池パック4内の電池管理システム5により指定される。更に、充電期間中、電池管理システム5からのフィードバックに基づき、充電器31の出力について、充電条件による目標値からのずれを補償する。
【００５１】
例えばＣＣＣＶ方式では、定電流制御期間での充電電流の目標値と充電電圧の実質的な上限値、及び、定電圧制御期間での充電終止電流値が充電条件として含まれる。充電器制御部32は、充電初期では定電流制御を実行し、充電器の出力電流を充電電流の目標値に安定に維持する。電池電圧の上限への到達が電池管理システム5から通知されるとき、充電器制御部32は定電流制御を定電圧制御へ切り替え、充電器の出力電圧を電池電圧の上限値（例えば初期の二次電池41では約4.20V／セル）に安定に維持する。充電電流の充電終止電流値までの降下が電池管理システム5から通知されるとき、充電器制御部32は充電器31の出力を遮断し、二次電池41の充電を終了する。
【００５２】
電池パック4内の電池管理システム5は、電池状態監視部と制御部51とを含む。電池状態監視部は電流検出部44、温度検出部45、及び電圧検出部46の三つのセンサを含む。電流検出部44は充電電流を、電流検出用抵抗44Aによる電圧降下量から計測する。温度検出部45は電池温度を、二次電池41に近接したサーミスタ45Aの抵抗値から計測する。電圧検出部46は二次電池41の両端間の電圧を計測し、セル当たりの電池電圧を換算する。ここで、電圧検出部45は二次電池41のセルごとに電圧を直接計測しても良い。
【００５３】
制御部51はＣＰＵとメモリ（例えば、ＲＡＭとフラッシュメモリ）とを含む（図示せず)。
メモリは充放電制御プログラムと二次電池41に関する情報とを記憶する。その二次電池41に関する情報には、例えば、電池電圧、電池電流、電池温度、及び充電状態の履歴、電池容量の初期値と放電ごとの学習値、充放電サイクル数、電池状態と充電状態との対応関係を示すリスト、並びに、充電条件が含まれる。
【００５４】
ＣＰＵはメモリに記憶されたプログラムを実行する。それにより、制御部51は二次電池41の充放電制御について、以下のような機能を発揮する。例えば、
(A) 二次電池41の充電時、その充電条件を二次電池41の充電特性に応じて設定し、充電器制御部32に対し通知する。
(B) 所定のクロック数をカウントするごとに、電流検出部44、温度検出部45、及び電圧検出部46のそれぞれから測定値を入力し、電池電圧、電池電流、及び電池温度の変化を監視する。
(C) 特に、電池電圧、電池電流、及び電池温度の変動が所定の許容範囲内に収まっているか否かを判定する。それらの変動のいずれかがその許容範囲から大きく外れたときは、それをノートＰＣ3へ通知し、例えば電池電流を遮断させる。こうして、制御部51は二次電池41の保護回路としての機能を果たす。
【００５５】
(D) 充電開始から充電電流の測定値を積算し、充電電気量をリアルタイムに算定する。同様に、放電開始から放電電流の測定値を積算し、放電電気量をリアルタイムに算定する。更に、それらの充放電電気量と電池容量とから、二次電池41の充電状態をリアルタイムに決定する。ここで、電池状態と充電状態との対応関係から、各時点の電池状態に対応する充電状態が決定されても良い。
(E) 二次電池41の放電ごとに、放電電気量の総量から電池容量を学習する。
(F) 電池パック4の使用開始以後、二次電池41の充電状態の変化を監視し、二次電池41の充放電サイクル数をカウントする。
(G) 二次電池41の電池状態をノートＰＣ3へリアルタイムに通知する。特に充電期間中では二次電池41の電池状態を充電器制御部32へ通知する。例えば、二次電池41の電池状態が満充電に対応するとき、充電器制御部32は二次電池41の充電を終了する。
【００５６】
(H) 例えば満充電まで充電された二次電池41の充電状態を、放電開始まで実質的に満充電に維持する。具体的には、満充電までの充電が終了した後、二次電池41の充電状態を監視する。二次電池41の充電状態が例えば自己放電により満充電（100％）から所定の維持限界（例えば約95％）まで降下するとき、その降下を制御部51は充電器制御部32へ通知する。充電器制御部32はその通知に応じて二次電池41の充電を再開し、二次電池41の充電状態を満充電（100％）へ戻す。こうして、放電深度約5％程度のごく浅い充放電の反復により、二次電池41の充電状態が満充電に実質的に維持される。
【００５７】
一般に二次電池の電極には充電時に大きな負荷がかかる。その負荷は特に過充電及び過剰な充電電流により過大となり、二次電池の寿命を著しく短縮させる。
二次電池としてリチウムイオン二次電池が使用されるとき、その電解液は可燃性の有機溶媒である。もし過充電又は過剰な充電電流により二次電池が過熱されると、可燃性ガスの発生等でその安全性が著しく損なわれる。
従って、二次電池の寿命を長く維持しかつその使用の安全性を高く維持するには、二次電池の過充電及び過剰な充電電流の発生が確実に回避されなければならない。
実施形態１による制御部51は、充電条件監視部51A、劣化評価部51B、及び充電条件補正部51Cのそれぞれとして以下の機能を実現する。それらの機能により、二次電池41に対する過充電及び過剰な充電電流の発生を確実に回避する。
【００５８】
充電条件監視部51Aは、二次電池41の充電時、電流検出部44、温度検出部45、及び電圧検出部46のそれぞれの測定値を監視する。更に、それらの測定値が充電条件を満たすか否か、を判定し、その判定内容を充電器制御部32へ通知する。
充電条件監視部51Aは、具体的には例えば、充電初期では充電電流値とその目標値とのずれを計測し、そのずれを充電器制御部32へフィードバックする。その一方で、電池電圧値をその上限値と比較し、両方が実質的に一致するとき、その一致を即座に充電器制御部32へ通知する。
充電条件監視部51Aは更に、充電後期では電池電圧値とその上限値とのずれを計測し、そのずれを充電器制御部32へフィードバックする。その一方で、充電電流を充電終止電流値と比較し、両方が実質的に一致するとき、その一致を即座に充電器制御部32へ通知する。
【００５９】
制御部51は充電条件を二次電池41の充電特性に応じて設定する。一方、二次電池41の充電特性はその二次電池41の劣化により変化する。特に、二次電池41の電池容量が減少する。従って、制御部51は、二次電池41の劣化の程度を正確に評価し、その劣化の程度に応じ充電条件を適切に修正しなければならない。
そこで、制御部51はまず劣化評価部51Bとして機能し、二次電池41の劣化の程度を次のように評価する。
【００６０】
劣化評価部51Bは二次電池41の劣化の程度を表す指標、すなわち劣化係数を、電池容量の初期値とその実際の値との比として定義する。二次電池41の劣化が進むほど電池容量は低減するので、劣化係数は小さい。
二次電池41の劣化係数は、充放電サイクル数の他に、例えば放電深度と電池温度との履歴に依存する。二次電池41として特にリチウムイオン二次電池が使用されるとき、ごく浅い充放電の連続による高充電状態の持続期間が長いほど、二次電池41の劣化係数は小さい。更に、その持続期間中の電池温度が高いほど、劣化係数は小さい。
【００６１】
劣化評価部51Bは二次電池41の充電状態を監視する。例えば、二次電池41は充電終了から放電開始までの間、実質的に満充電に維持される。すなわち、二次電池41の充電状態は上記の通り、満充電（100％)〜維持限界（例えば約95％）の範囲内の高い値（すなわち高充電状態）に維持される。劣化評価部51Bはその高充電状態の持続期間中、二次電池41の電池温度を監視し、かつその持続期間の長さを評価する。
ここで、劣化評価部51Bは高充電状態の持続期間の長さを、例えばその持続時間で評価する。その他に、高充電状態の持続期間中、二次電池41の充電状態が満充電（100％）から維持限界（約95％）へ降下する回数を劣化評価部51Bがカウントし、その回数で持続期間の長さを評価しても良い。
【００６２】
劣化評価部51Bは、高充電状態の持続期間中の電池温度の測定値とその持続期間の長さの評価値とに基づき、二次電池41の劣化係数を次のように決定する。
二次電池41に対し、高充電状態の持続期間の長さがその持続時間で評価されるとき、その持続時間とその持続期間中の電池温度とを変数とする劣化係数の関数形は実験で決定される。劣化評価部51Bはその関数に基づき、高充電状態の持続時間とその持続期間中の電池温度との組別に対応する劣化係数を予め算定し、そのリストを記憶する。
【００６３】
表1は二次電池41について、その使用開始時から通算の高充電状態の持続時間とその持続期間中の平均電池温度との組別に対応する劣化係数を示す表である。表1の(a)及び(b)はそれぞれ、充電条件の一つ、電池電圧の上限値が4.20V／セル及び4.16V／セルに設定されるときの劣化係数を示す。ここで、二次電池41の電池容量の初期値は、電池電圧の上限値が4.20V／セルに設定されるときの値である。従って、電池電圧の上限値が4.16V／セルに設定されるときの電池容量は初期値の約96％に等しい。
【００６４】
【表１】

【００６５】
劣化評価部51Bが高充電状態の持続期間の長さを、その持続期間中での充電状態の満充電（100％）から維持限界（約95％）への降下回数で評価するときは、劣化評価部51Bはその降下回数とその持続期間中の電池温度との組別に対応する劣化係数を示す表を記憶する。この表は、表1と同様に、実験で決定される。
【００６６】
二次電池41が所定の負荷に対する放電（例えば、ノートＰＣ3の電池駆動）により高充電状態から脱するとき、劣化評価部51Bは表1を参照し、それまでの高充電状態の持続による劣化係数を決定する。
【００６７】
図2は、実施形態１での劣化評価部51Bによる二次電池41に対する劣化判定方法を示すフローチャートである。
二次電池41が満充電まで充電されるとき、劣化評価部51Bは起動する。
＜ステップS1＞
劣化評価部51Bは電流検出部44を通し、電池電流の向きと大きさとをチェックする。それにより、二次電池41が放電中か否かを判断する。
電池電流が放電電流であり、かつその大きさ（又は放電率）が所定の閾値を超えるとき、二次電池41は放電中であると劣化評価部51Bは判断し、処理をステップS5へ分岐させる。それ以外のとき、処理はステップS2へ分岐する。
【００６８】
＜ステップS2＞
二次電池41の充電状態（ＳＯＣ）が計測され、その測定値が所定の維持限界（例えば約95％）以上であるか否かが判定される。ＳＯＣがその維持限界以上であるときは、処理がステップS3へ進む。それ以外のとき、すなわちＳＯＣが維持限界を下回るとき、処理がステップS1へ戻る。
＜ステップS3＞
劣化評価部51Bはその起動時からの経過時間を計測する。ここで、その計時がまだ開始されていないときは、その計時が開始される。
＜ステップS4＞
劣化評価部51Bは温度検出部45を通し、二次電池41の電池温度を計測する。更に、その測定値を記憶し、処理をステップS1へ戻す。
こうして、二次電池41が満充電（100％)〜維持限界（約95％）の範囲内の高充電状態に維持される間、劣化評価部51BはステップS1〜S4のループを反復する。
【００６９】
＜ステップS5＞
劣化評価部51Bはその起動時からの経過時間の計測を停止する。更に、その測定値を、二次電池41の使用開始時から通算の高充電状態の持続時間へ加算する。
＜ステップS6＞
劣化評価部51Bは、二次電池41の使用開始以降、高充電状態の持続期間中に計測された電池温度のサンプルの全てについて、その平均値を算定する。
＜ステップS7＞
劣化評価部51Bは表1を参照する。それにより、電池電圧の上限値、高充電状態の通算持続時間、及びその持続期間中の平均電池温度の組に対応する劣化係数を決定する。
【００７０】
上記の通り、実施形態１による電池管理システム5では、二次電池41が高充電状態の持続期間を経るごとに、劣化評価部51Bがその高充電状態の持続期間の長さを評価し、かつその持続期間中の電池温度を計測する。更に、その評価値と測定値とに基づき二次電池41の劣化係数を決定する。こうして、劣化係数の決定に放電深度と電池温度との履歴、特にごく浅い充放電の反復による高充電状態の持続とその持続期間中の電池温度との履歴が反映される。その結果、二次電池41の劣化の程度が従来の装置より高精度に評価される。
【００７１】
制御部51は次に、充電条件補正部51Cとして次のように機能する。
充電条件補正部51Cは、劣化評価部51Bにより決定された二次電池41の劣化係数に基づき、充電条件の補正の必要性を判定する。その補正が必要と判定されるとき、充電条件補正部51Cは、定電流制御期間での充電電流の目標値若しくは電池電圧の上限値を所定量だけ低減させ、又は充電終止電流値を所定量だけ増加させる。
具体的には、劣化係数が所定値まで減少するごとに、例えば、95％、90％、85％、・・・と5％刻みで減少するごとに、充電条件補正部51Cは電池電圧の上限値を約0.05V／セルずつ下げる。
こうして、二次電池41の劣化による電池容量の減少に適切に応じ、過充電及び過剰な充電電流の発生が確実に回避される。
【００７２】
制御部51は二次電池41の劣化係数を、充電条件の補正の他に、充電状態の維持限界の修正に利用しても良い。例えば、充電条件補正部51は、二次電池41の劣化係数に応じ満充電（100％）に対する維持限界（約95％）を所定値（例えば5％）だけ下げても良い。それにより、高充電状態の持続期間中での放電深度が増大する。その結果、その持続期間中での電極の負担が軽減し、二次電池41の劣化の進行を緩め得る。
【００７３】
《実施形態２》
本発明の実施形態２による充電制御装置は、実施形態１と同様、ノートＰＣ用電池パック内の電池管理システムに、その制御部として搭載される。
実施形態２について、二次電池41の充電に関するノートＰＣ3と電池パック4との構成は実施形態１と同様である。従って、実施形態１と同様な構成の詳細は、図1と実施形態１での説明とを援用する。
【００７４】
実施形態２による電池管理システム5の制御部51は特に、劣化評価部51Bとしての機能について実施形態１と異なる。
二次電池41の劣化係数は、放電深度と電池温度との履歴の他に、過放電状態での放電率と電池温度との履歴に依存する。二次電池41として特にリチウムイオン二次電池が使用されるとき、過放電状態での放電率が高く又は電池温度が低いほど、二次電池41の劣化係数は小さい。
【００７５】
実施形態２による劣化評価部51Bは二次電池41の放電時、二次電池41の充電状態又は電池電圧を監視する。二次電池41の充電状態が例えば約0％まで降下するとき、又は二次電池41の電池電圧が例えば放電終止電圧まで降下するとき、劣化評価部51Bは放電率と電池温度とを計測する。更に、その放電率と電池温度との測定値を過放電状態での放電率と電池温度とみなし、それらに基づき二次電池41の劣化係数を次のように決定する。
【００７６】
二次電池41に対し、過放電状態での放電率と電池温度とを変数とする劣化係数の関数形は実験で決定される。劣化評価部51Bはその関数に基づき、放電率と電池温度との組別に対応する劣化係数を予め算定し、そのリストを記憶する。
表2は、二次電池41について、過放電状態での放電率と電池温度との組別に対応する劣化係数を示す表である。表2では、二次電池41の電池電圧が放電終止電圧（例えば約3.0V／セル）まで降下するときの放電率と電池温度とがそれぞれ、過放電状態での放電率と電池温度とみなされる。
二次電池41の放電終了時、劣化評価部51Bは表2を参照し、その放電による劣化係数を決定する。
【００７７】
【表２】

【００７８】
表2では、二次電池41の使用期間の長さが充放電サイクル数で評価される。
二次電池41の使用期間の長さはその他に、劣化評価部51Bによる過放電検出回数、又はノートＰＣ3によるハイバネーション回数で評価されても良い。
ここで、過放電検出回数とは、所定値以上の高放電率での放電により電池電圧が所定の下限値（例えば放電終止電圧）以下まで降下する回数をいう。劣化評価部51Bは上記の劣化係数の決定時、過放電状態での放電率とみなされた測定値を所定値（例えば約1.0C）と比較する。更に、その測定値がその所定値以上であるとき、過放電検出回数を1だけ増やす。
【００７９】
一方、ノートＰＣ3によるハイバネーションとはノートＰＣ3による休止状態への退避処理をいう。ノートＰＣ3は例えば、二次電池41による駆動時、二次電池41の充電状態が実質的に0％（正確には0％よりごくわずかだけ高い値、例えば0.5％又は1％等）を超えて降下するとき、ハイバネーションを実行する。それにより、電力不足による不意なシステムダウンを回避する。
劣化評価部51Bは二次電池41の放電時、例えば充電状態を監視し、実質的に0％を超えて降下するごとにハイバネーション回数を1だけ増やす。その他に、劣化評価部51Bは、ノートＰＣ3からハイバネーションの実行を通知されるごとにハイバネーション回数を1だけ増やしても良い。
【００８０】
二次電池41が高放電率で過放電を生じるとき、その正極の負荷が特に重い。すなわち、高放電率での過放電は二次電池41の劣化を特に大きく促進する。
劣化評価部51Bは、二次電池41の使用期間の長さを上記の過放電検出回数又はハイバネーション回数で評価することで、二次電池41の劣化係数の決定に高放電率での過放電を重点的に反映させる。こうして、劣化の評価の精度が向上する。
【００８１】
図3は、実施形態２での劣化評価部51Bによる二次電池41に対する劣化判定方法を示すフローチャートである。
二次電池41の充電状態が放電により所定値（例えば、約10％）まで降下するとき、劣化評価部51Bは起動する。
＜ステップS10＞
劣化評価部51Bは電流検出部44、温度検出部45、及び電圧検出部46を通し、二次電池41の電池状態を監視する。
＜ステップS11＞
劣化評価部51Bは、放電電流と電池温度との測定値の組に対応する放電終止電圧を決定し、その放電終止電圧と電池電圧の測定値とを比較する。電池電圧の測定値が放電終止電圧以下であるとき、劣化評価部51Bは処理をステップS12へ分岐させる。それ以外のとき、劣化評価部51Bは処理をステップS10へ戻す。
【００８２】
＜ステップS12＞
劣化評価部51Bは電流検出部44を通し、二次電池41の放電率を計測する。その測定値が過放電状態での放電率とみなされる。
＜ステップS13＞
劣化評価部51Bは温度検出部45を通し、二次電池41の電池温度を計測する。その測定値が過放電状態での電池温度とみなされる。
＜ステップS14＞
劣化評価部51Bは表2を参照し、その時点での充放電サイクル数、及び、過放電状態での放電率と電池温度との組に対応する劣化係数を決定する。
【００８３】
実施形態２による電池管理システム5では上記の通り、二次電池41の放電により、その電池電圧が放電終止電圧まで降下するごとに、劣化評価部51Bがその時点での放電率と電池温度とを計測する。更に、それらの測定値を過放電状態での放電率と電池温度とみなし、それらに基づき二次電池41の劣化係数を決定する。こうして、過放電状態での放電率と電池温度とが劣化係数の決定に反映される。その結果、二次電池41の劣化の程度が従来の装置より高精度に評価される。
【００８４】
制御部51は次に、充電条件補正部51Cとして次のように機能する。
充電条件補正部51Cは、劣化評価部51Bにより決定された二次電池41の劣化係数に基づき、充電条件の補正の必要性を判定する。その補正が必要と判定されるとき、充電条件補正部51Cは、定電流制御期間での充電電流の目標値若しくは電池電圧の上限値を所定量だけ低減させ、又は充電終止電流値を所定量だけ増加させる。
具体的には、劣化係数が所定値まで減少するごとに、例えば、95％、90％、85％、・・・と5％刻みで減少するごとに、充電条件補正部51Cは電池電圧の上限値を約0.05V／セルずつ下げる。
こうして、二次電池41の劣化による電池容量の減少に適切に応じ、過充電及び過剰な充電電流の発生が確実に回避される。
【００８５】
【発明の効果】
二次電池の劣化係数は充放電サイクル数だけでは一意には決まらず、一定の充電状態の持続時間とその持続期間中の電池温度、及び過放電状態での放電率と電池温度とに大きく依存する。
本発明の一つの観点による充電制御装置では、劣化評価部が実質的に一定の充電状態の持続期間ごとにその持続時間とその持続期間中の電池温度とを計測し、それらの測定値に基づき二次電池の劣化係数を決定する。
本発明のもう一つの観点による充電制御装置では、劣化評価部が過放電状態での放電率と電池温度との測定値に基づき二次電池の劣化係数を決定する。
従って、これらの充電制御装置のいずれもが、二次電池の劣化を従来の装置より高精度に評価できる。
【００８６】
本発明による充電制御装置では更に、充電条件補正部が、劣化評価部により決定された劣化係数に応じ充電条件を補正する。その補正により特に、充電電流の上限、又は充電期間中の電池電圧の上限を低減させる。こうして、二次電池の劣化による電池容量の減少に適切に応じ、過充電及び過大な充電電流の発生が確実に回避される。
【００８７】
本発明による充電制御装置では、劣化評価部が電池電圧の監視により過放電検出回数を数え、その過放電検出回数に基づき二次電池の劣化係数を決定しても良い。それにより、高放電率での過放電による劣化が重点的に評価されるので、二次電池に対する劣化評価の精度が向上する。
【図面の簡単な説明】
【図１】本発明の実施形態１について、二次電池41の充電に関するノートＰＣ3と電池パック4との構成を示すブロック図である。
【図２】本発明の実施形態１について、劣化評価部51Bによる二次電池41に対する劣化判定方法を示すフローチャートである。
【図３】本発明の実施形態２について、劣化評価部51Bによる二次電池41に対する劣化判定方法を示すフローチャートである。
【図４】二次電池41の充電に関するノートＰＣ3と電池パック40との従来の構成を示すブロック図である。
【符号の説明】
1 商用交流電源
41 二次電池
44A 電流検出用抵抗
45A サーミスタ[0001]
BACKGROUND OF THE INVENTION
The present invention controls, for example, charging of a battery-powered electric device, a portable electronic device, an emergency power source, an auxiliary power source, or a secondary battery used as a power source built in an automobile or used for power storage. Relating to the device. In particular, the present invention relates to a secondary battery deterioration determination method using the apparatus.
[0002]
[Prior art]
Charging up to its maximum capacity is desirable for effective use of secondary batteries.
However, overcharging is not preferable because, for example, gas generation due to decomposition of the electrolytic solution or leakage of the electrolytic solution is caused, and the safety of the secondary battery is impaired. Furthermore, overcharging and excessive charging current are undesirable because they significantly deteriorate the secondary battery.
Therefore, strict control is required for charging the secondary battery, that is, the battery voltage and the charging current must be managed with high accuracy.
[0003]
The charge control for the secondary battery is performed by a charger, an electronic device main body, or a charge control device built in the battery management system. Here, the battery management system is a device that is housed in a battery pack that is shared with the secondary battery, monitors and controls the state of the secondary battery, or notifies an external control device such as a charger. Say.
The charging control device monitors the battery voltage, the charging current, and the battery temperature during the charging period, and performs control so as to meet predetermined charging conditions. Here, the charging condition refers to a condition (for example, a change pattern or an allowable range of variation) that the battery voltage, the charging current, and the battery temperature should satisfy during the charging period. Further, monitoring of the battery voltage or the like may be performed directly by the charge control device or may be performed through the battery management system.
When the battery voltage or the like greatly deviates from the charging condition, and particularly shows an abnormal increase, the charging control device cuts off the charging current and stops charging.
[0004]
The charge control device normally charges the secondary battery until it reaches full charge (also called full charge), that is, a battery state when charged to a substantially maximum capacity. The full charge of the secondary battery is detected based on the measured values of the battery voltage, the charging current, and the battery temperature, or the amount of change within a certain time. When the full charge is detected, the charge control device cuts off the charge current and ends the charge. Hereinafter, a condition for determining the end of charging, such as detection of full charge by the charge control device, is referred to as a charge termination condition. The charge termination condition is included as part of the above charge condition.
[0005]
The charge control device further maintains, for example, the state of charge of the secondary battery that has been charged until full charge is substantially fully charged until the start of discharge. Specifically, after charging up to full charge is completed, the charge state of the secondary battery is monitored. Whenever the charge state of the secondary battery drops by a predetermined value (for example, about 5%) from full charge (100%) due to, for example, self-discharge, the charge control device restarts the charge of the secondary battery, and the charge state of the secondary battery To full charge (100%). In this way, the charging state of the secondary battery is substantially maintained at full charge by repeating very shallow charging / discharging (for example, about 5% of discharge depth).
[0006]
The charging control device determines the above charging conditions according to the charging characteristics of the secondary battery. Since the charging characteristics of the secondary battery differ for each type of secondary battery, the specific charging conditions, particularly the charge termination conditions, differ for each type of secondary battery.
The nickel-cadmium battery is charged by a constant current method. The battery voltage gradually increases from the start of charging, reaches a peak at full charge, and then decreases. Based on such charge characteristics, the charge control device determines that the change amount of the battery voltage within a certain time shifts from positive to negative as a charge termination condition (−ΔV method).
[0007]
The nickel-hydrogen storage battery is charged by a constant current method. The time derivative of the battery temperature gradually decreases from the start of charging, starts increasing at full charge, and increases in the overcharge region. Based on such charging characteristics, the charging control apparatus determines a sudden increase in the amount of change in battery temperature within a certain minute time as a charge termination condition (dT / dt method).
[0008]
Lithium ion secondary batteries have a higher risk of overcharging than nickel-cadmium storage batteries and nickel-hydrogen storage batteries. Therefore, charging of the lithium ion secondary battery is performed by a constant current constant voltage method (CCCV method). Constant current control is performed for a while from the start of charging, and the charging current value is maintained at a predetermined value. The battery voltage rises during the constant current control period. When charging proceeds and the battery voltage reaches a predetermined upper limit, the constant current control is switched to the constant voltage control, and the charging voltage value is maintained at the upper limit value. The charging current gradually decreases during the constant voltage control period. When the charging current value falls below a predetermined threshold value (hereinafter referred to as a charging end current value), charging ends. Thus, in the CCCV method, the upper limit value of the battery voltage is set as one of the charging conditions. Thereby, overcharging is reliably avoided.
[0009]
The charging characteristics of the secondary battery change depending on the battery state history in addition to the type of the secondary battery. For example, as the number of charge / discharge cycles increases, the secondary battery deteriorates, and in particular, its battery capacity decreases. Therefore, the conventional charge control device must correct the charging conditions according to the number of charge / discharge cycles, and reliably avoid overcharge regardless of the increase in the number of charge / discharge cycles.
[0010]
The following is known as a charge control device for correcting the charging condition based on the number of charge / discharge cycles of the secondary battery (see Patent Document 1). The charge control device is incorporated into, for example, a notebook personal computer (hereinafter abbreviated as a notebook PC) or a battery management system in a battery pack.
FIG. 4 is a block diagram showing a conventional configuration of the notebook PC 3 and the battery pack 40 relating to charging of the secondary battery 41. As shown in FIG. Here, the secondary battery 41 in the battery pack 40 is, for example, a lithium ion secondary battery. The charger controller 32 in the notebook PC 3 and the controller 43 in the battery management system 42 cooperate to control charging of the secondary battery 41 according to the CCCV method. The charger 31 inputs power from the commercial AC power source 1 through the AC adapter 2. Further, the input power is converted under the control of the charger control unit 32, the output voltage or the output current is stably maintained at a predetermined value, and supplied to the battery pack 40.
[0011]
In the battery pack 40, the secondary battery 41 is charged by supplying power from the charger 31.
During the charging period of the secondary battery 41, the battery state monitoring unit monitors the state of the secondary battery 41 in the battery management system 42. Here, the battery state monitoring unit includes three sensors: a current detection unit 44, a temperature detection unit 45, and a voltage detection unit 46. The current detection unit 44 measures the charging current from the amount of voltage drop caused by the current detection resistor 44A. The temperature detector 45 measures the battery temperature from the resistance value of the thermistor 45A adjacent to the secondary battery 41. The voltage detector 46 measures the voltage across the secondary battery 41 and converts the battery voltage per cell.
The control unit 43 inputs measurement values from the current detection unit 44, temperature detection unit 45, and voltage detection unit 46 at regular time intervals, and notifies the measurement values to the charger control unit 32 in the notebook PC 3. To do. The charger control unit 32 controls the output voltage or output current of the charger 31 based on the notified battery state.
[0012]
On the other hand, during the charging period, the control unit 43 integrates the measured values of the charging current and calculates the amount of charge electricity. Furthermore, the amount of charged electricity is retained after charging. When the accumulated amount of charge over a plurality of times of charging is substantially equal to a predetermined battery capacity, for example, when the battery capacity exceeds 0.9 times, the control unit 43 adds 1 to the number of charge / discharge cycles. Here, the battery capacity is a value learned from the integrated value of the discharge current for each discharge of the secondary battery 41 by the control unit 43, for example. Thus, the number of charge / discharge cycles is counted with a weight depending on the depth of discharge.
[0013]
When the number of weighted charge / discharge cycles exceeds a predetermined threshold (for example, 50), the control unit 43 notifies the charger control unit 32. In response to the notification, the charger control unit 32 reduces the upper limit value of the battery voltage in, for example, the CCCV method by a predetermined amount (for example, decreases from 4.20 V / cell by 0.10 V / cell). Thereby, the substantial upper limit of the amount of charged electricity per charge is lowered.
In this way, even when the secondary battery 41 deteriorates as the number of charge / discharge cycles increases and the battery capacity decreases, overcharge is reliably avoided.
[0014]
[Patent Document 1]
JP 2001-309568 A
[0015]
[Problems to be solved by the invention]
The charge control device disclosed in Patent Document 1 evaluates and determines the deterioration of the secondary battery based on the number of weighted charge / discharge cycles. However, it is generally insufficient to determine the deterioration of the secondary battery only with such weighted charge / discharge cycles.
For example, when a secondary battery is maintained in a highly charged state (a state in which the ratio of the remaining capacity to the battery capacity is high) with continuous shallow charge / discharge, or near a complete discharge state (hereinafter referred to as an overdischarge state) due to overdischarge. The carrier inside the battery concentrates on either the positive or negative electrode and continues to apply a large load. As a result, the secondary battery is greatly deteriorated. On the other hand, since the amount of charge electricity and the amount of discharge electricity are generally small during the duration of the high charge state or the overdischarge state, the number of weighted charge / discharge cycles increases only slightly. Thus, there is a difference in the correspondence between the degree of deterioration of the secondary battery and the number of weighted charge / discharge cycles.
[0016]
In particular, in a lithium ion secondary battery, when a high charge state is maintained, a large number of lithium atoms concentrate on the graphite layer of the negative electrode and damage the graphite layer. The damage is particularly severe at high temperatures. Therefore, in the lithium ion secondary battery, the longer the duration of the high charge state, or the higher the battery temperature during the duration, the more serious the deterioration.
For example, when the notebook PC is driven by a commercial AC power supply, the built-in secondary battery is maintained in a high charge state under a situation where the CPU or the like generates high heat. Therefore, in order to safely use a lithium ion secondary battery as the secondary battery, the deterioration of the secondary battery is accurately evaluated based on the length of the duration of the high charge state and the battery temperature during the duration. There must be.
[0017]
The degree of deterioration of the secondary battery further depends greatly on the discharge rate in the overdischarged state and the battery temperature. That is, when the secondary battery enters an overdischarged state due to discharge, the higher the discharge rate at that time or the lower the battery temperature, the larger the carrier in the battery gives the load to the electrode, so the secondary battery deteriorates. It is remarkable. Therefore, evaluation of deterioration based on the discharge rate in the overdischarge state and the history of the battery temperature is effective in improving the accuracy of determining the deterioration of the secondary battery.
[0018]
An object of the present invention is to provide a charge control device capable of accurately evaluating the degree of deterioration of a secondary battery and thereby reliably avoiding overcharge according to the deterioration of the secondary battery, and a method for determining the deterioration of the secondary battery. And
[0019]
[Means for Solving the Problems]
A charge control device according to one aspect of the present invention is as follows.
(A) When charging a secondary battery, the battery voltage, charging current, and battery temperature are monitored to determine whether the measured value or the amount of change within a certain time satisfies a predetermined charging condition. Charging condition monitoring unit;
(B) When the state of charge of the secondary battery is substantially maintained at a constant value, the battery temperature of the secondary battery is monitored and the length of the duration is evaluated during the duration of the state of charge. A degradation evaluation unit for determining a degradation coefficient of the secondary battery based on the measured value of the battery temperature during the duration and the length of the duration; and
(C) a charging condition correction unit for correcting the charging condition according to the deterioration coefficient of the secondary battery;
Have
[0020]
The charge control device refers to a device that is built in, for example, a charger, an electronic device body, or a battery management system and controls charging of a secondary battery.
Here, the battery management system is housed in a battery pack common to the secondary battery, and the state of the secondary battery is monitored and controlled by an internal battery state monitoring unit, or an external control device such as a charger. It is a device for notifying to. For the secondary battery, the battery status monitoring unit comprises (a) a voltage detection unit for measuring battery voltage, (b) a current detection unit for measuring battery current, and (c) a temperature for measuring battery temperature. The battery voltage, the battery current, and the battery temperature of the secondary battery obtained by the detection units are provided to the charge control device.
The charging control device may directly monitor the battery voltage, the charging current, and the battery temperature by the charging condition monitoring unit. Or you may carry out through an external sensor, for example, the battery condition monitoring part in a battery management system.
[0021]
The charging condition refers to a condition (for example, a change pattern or an allowable range of fluctuation) that the battery voltage, the charging current, and the battery temperature should satisfy during the charging period of the secondary battery. In particular, the charging condition includes a condition for determining the end of charging, such as a full charging detection condition (hereinafter referred to as a charging termination condition).
For example, in the −ΔV method, a charging current target value and a threshold value for the amount of change in battery voltage within a certain time are included as charging conditions. In the dT / dt method, a charging current target value and a threshold value for the amount of change in battery temperature within a predetermined time are included as charging conditions. In the CCCV method, a charging current target value, a battery voltage upper limit value, and a charging end current value are included as charging conditions.
[0022]
The state of charge of the secondary battery refers to the ratio of the remaining capacity to the battery capacity. “The charge state of the secondary battery is substantially maintained at a constant value” means that the change in the charge state of the secondary battery is controlled within a predetermined range including the constant value.
For example, the charge control device once charges the secondary battery until full charge, and then maintains the charge state of the secondary battery substantially fully charged until the start of discharge. Specifically, after charging up to full charge is completed, the charge state of the secondary battery is monitored. Each time the state of charge of the secondary battery drops by a predetermined value from full charge due to, for example, self-discharge, the charge control device resumes charging of the secondary battery and returns the state of charge of the secondary battery to full charge.
Thus, every time the state of charge of the secondary battery falls from the constant value by a predetermined value, the charge control device resumes charging the secondary battery and returns the state of charge of the secondary battery to the constant value. By repeating such charging, the state of charge of the secondary battery is substantially maintained at a constant value.
Hereinafter, the state of charge that is lower than the predetermined value by a predetermined value is referred to as a maintenance limit. The state of charge maintenance limit is included as part of the above charging conditions.
[0023]
The state of charge is calculated from, for example, the integrated value of the battery current, that is, the amount of charge or discharge, and the battery capacity. In addition, the correspondence between the battery state (battery voltage, battery current, and battery temperature) and the state of charge based on the charge / discharge characteristics unique to the secondary battery is stored when the secondary battery is manufactured. A state of charge corresponding to the measured value of the battery state may be determined.
[0024]
The deterioration coefficient of a secondary battery is a value obtained by quantifying the degree of deterioration of the secondary battery. Preferably, it is defined by a ratio between a battery capacity manufacturing value (hereinafter referred to as an initial value) and an actual value. That is, since the battery capacity decreases as the deterioration progresses, the deterioration coefficient is small.
[0025]
Secondary batteries are mainly deteriorated by the load during charging and discharging. However, the deterioration coefficient is not uniquely determined only by the number of charge / discharge cycles, and depends on, for example, the history of discharge depth and battery temperature. In particular, it depends on the duration of each of the high charge state and the overdischarge state and the battery temperature during that duration.
For example, when a lithium-ion secondary battery is maintained in a high charge state due to a very shallow charge / discharge sequence, or is maintained close to a complete discharge state due to overdischarge, the lithium ion secondary battery is more than 50% shallow charge / discharge repeated. Deteriorates greatly. Furthermore, the deterioration of the lithium ion secondary battery is more remarkable as the battery temperature is higher in the duration of the high charge state and the battery temperature is higher in the duration of the overdischarge state.
[0026]
In the charge control device described above, each time the state of charge of the secondary battery is substantially maintained at a constant value, the deterioration evaluation unit evaluates the length of the duration and measures the battery temperature during the duration. To do. Further, the deterioration coefficient of the secondary battery is determined based on the evaluation value and the measured value. Thereby, degradation of the secondary battery can be evaluated with higher accuracy than the conventional device.
Here, the deterioration evaluation unit evaluates the length of the duration, preferably by the duration. In addition, you may evaluate by the frequency | count of the fall to the maintenance limit from the fixed value of the charge condition of a secondary battery.
[0027]
The function form of the deterioration coefficient when the state of charge, the length of the duration, and the battery temperature during the duration are used as variables is determined by experiment, for example, for each type of secondary battery. Based on the function, for example, the deterioration evaluating unit calculates in advance a deterioration coefficient corresponding to each set of the state of charge, the length of the duration, and the battery temperature during the duration, and stores the list. The deterioration evaluation unit refers to the list and determines a deterioration coefficient corresponding to the set of the measured value of the state of charge, the length of the duration, and the battery temperature.
In addition, the degradation evaluation unit previously determines a coefficient group that characterizes the functional form of the degradation coefficient in advance by experiment, and for each duration of the secondary battery in a high charge state or overdischarge state, its charge state, its duration The degradation coefficient may be calculated from the length of the battery, the battery temperature during the duration thereof, and the coefficient group.
[0028]
In the above charging control apparatus, the charging condition correction unit further corrects the charging condition according to the deterioration coefficient determined by the deterioration evaluation unit. The correction particularly reduces the upper limit of the charging current or the upper limit of the battery voltage during the charging period. For example, in the CCCV method, the target value of the charging current or the upper limit value of the battery voltage in the constant current control period is reduced by a predetermined amount, or the charging end current value is increased by a predetermined amount. Thus, overcharge and excessive charging current can be reliably avoided in response to a decrease in battery capacity due to deterioration of the secondary battery.
[0029]
The charging condition correction unit may further reduce the maintenance limit of the charging state by a predetermined value according to the deterioration coefficient of the secondary battery. Thereby, especially when the secondary battery is maintained in a high charge state, the depth of discharge during the duration increases. As a result, the burden on the electrode during the duration can be reduced, and the progress of deterioration of the secondary battery can be relaxed.
[0030]
The deterioration coefficient of the secondary battery determined by the deterioration evaluation unit may be used not only for charge control of the secondary battery but also for discharge control thereof. For example, when the secondary battery is discharged, the state of charge of the secondary battery drops to substantially 0%, or the battery voltage drops to a predetermined lower limit (end-of-discharge voltage). Alternatively, an external discharge control device cuts off the discharge current. Thereby, overdischarge of the secondary battery is prevented. Here, the secondary battery changes its discharge characteristics due to deterioration. Therefore, overdischarge can be reliably avoided by correcting each value of the battery state or discharge end voltage corresponding to the 0% state of charge in accordance with the deterioration coefficient of the secondary battery.
[0031]
A charge control device according to another aspect of the present invention provides:
(A) When charging a secondary battery, the battery voltage, charging current, and battery temperature are monitored to determine whether the measured value or the amount of change within a certain time satisfies a predetermined charging condition. Charging condition monitoring unit;
(B) When the charging state or battery voltage of the secondary battery drops to a predetermined threshold due to the discharge of the secondary battery, the discharge rate and the battery temperature of the secondary battery are measured, and the discharge rate and the battery temperature are A degradation evaluation unit for determining a degradation coefficient of the secondary battery based on the measured value; and
(C) a charging condition correction unit for correcting the charging condition according to the deterioration coefficient of the secondary battery.
[0032]
The deterioration coefficient of the secondary battery depends on the history of the discharge rate and the battery temperature in the overdischarge state in addition to the history of the depth of discharge and the battery temperature. For example, in a lithium ion secondary battery, the deterioration is more remarkable as the discharge rate in the overdischarge state is higher or the battery temperature is lower.
In the above-described charging control device, the deterioration evaluation unit associates the above-described threshold value for the charging state or the battery voltage of the secondary battery with, for example, the value at the time of entering the over-discharge state or before that. Specifically, for example, the threshold for the state of charge is set to about 0%, or the threshold for the battery voltage is set to the discharge end voltage value. Thereby, the deterioration coefficient of the secondary battery is determined based on the measured values of the discharge rate and the battery temperature in the overdischarge state. In this way, the deterioration of the secondary battery can be evaluated with higher accuracy than the conventional apparatus.
[0033]
The function form of the deterioration coefficient when the discharge rate in the overdischarge state and the battery temperature are variables are determined, for example, by experiment for each type of secondary battery. Based on the function, the deterioration evaluation unit calculates in advance, for example, a deterioration coefficient corresponding to each combination of the discharge rate and the battery temperature, and stores the list. The deterioration evaluation unit refers to the list and determines a deterioration coefficient corresponding to a set of measured values of the discharge rate and the battery temperature.
In addition, the degradation evaluation unit previously determines a coefficient group that characterizes the functional form of the degradation coefficient by experiment, and each time the secondary battery enters the overdischarge state, its discharge rate, battery temperature, and the above The deterioration coefficient may be calculated from the coefficient group.
[0034]
In the above-described charging control device, the charging condition correction unit corrects the charging condition according to the deterioration coefficient determined by the deterioration evaluation unit. The correction particularly reduces the upper limit of the charging current or the upper limit of the battery voltage during the charging period. Accordingly, overcharge and excessive charging current are reliably avoided in response to a decrease in battery capacity due to deterioration of the secondary battery.
[0035]
In the above charge control device, the number of times that the measured value of the discharge rate when the charge state of the secondary battery or the battery voltage drops to the above threshold value due to discharge is equal to or greater than a predetermined value (hereinafter referred to as the number of overdischarge detections) The evaluation unit may count and determine the deterioration coefficient of the secondary battery based on the number of overdischarge detections.
When a secondary battery enters an overdischarge state at a high discharge rate, the load applied to the positive electrode of the secondary battery is particularly heavy. That is, the overdischarge at a high discharge rate greatly accelerates the deterioration of the secondary battery.
The above charging control apparatus focuses on the deterioration due to overdischarge at a high discharge rate by reflecting the number of overdischarge detections in the determination of the deterioration coefficient. Thereby, the accuracy of degradation evaluation can be improved.
[0036]
A method for determining deterioration of a secondary battery according to one aspect of the present invention includes:
(A) monitoring the battery temperature of the secondary battery and measuring the duration of the duration of the secondary battery when the secondary battery is maintained at a substantially constant charge state; and ,
(B) determining a degradation coefficient of the secondary battery based on the measured value and the duration of the battery temperature during the duration;
Have
[0037]
For example, a charging control device built in a battery management system in a battery charger, an electronic device main body, or a battery pack implements the secondary battery deterioration determination method.
Here, the state of charge and the deterioration coefficient of the secondary battery are defined in the same manner as described above.
Similarly to the above, the state of charge is calculated from, for example, the amount of charged electricity or discharged electricity, and the battery capacity. In addition, the charge state corresponding to the measured value of the battery state may be determined from the correspondence relationship between the battery state (a set of the battery voltage, the battery current, and the battery temperature) and the charge state.
[0038]
The deterioration coefficient of the secondary battery is not uniquely determined only by the number of charge / discharge cycles, and depends on, for example, the history of the depth of discharge and the battery temperature. In particular, it depends on the duration of each of the high charge state and the overdischarge state and the battery temperature during that duration.
In the above degradation determination method, each time the state of charge of the secondary battery is substantially maintained at a constant value, the length of the duration is evaluated, and the battery temperature during the duration is measured. Further, the deterioration coefficient of the secondary battery is determined based on the evaluation value and the measured value. Thereby, the deterioration of the secondary battery is evaluated with higher accuracy than the conventional determination method.
Here, the length of the duration is preferably evaluated by the duration. In addition, you may evaluate by the frequency | count of the fall to the maintenance limit from the fixed value of the charge condition of a secondary battery.
[0039]
The function form of the deterioration coefficient when the state of charge, the length of the duration, and the battery temperature during the duration are used as variables is determined by experiment, for example, for each type of secondary battery.
In the above deterioration determination method, a list of corresponding deterioration coefficients is set in advance for each set of, for example, the state of charge, the length of the duration, and the battery temperature during the duration based on the function. The list is referred to in the determination step of the deterioration coefficient, and the deterioration coefficient corresponding to the set of the measured value of the state of charge, the length of the duration, and the battery temperature is determined.
In addition to the list, a coefficient group that characterizes the function form of the deterioration coefficient may be set by experiment. In the determination step of the deterioration coefficient, the deterioration coefficient is calculated from the coefficient group, the state of charge, the length of the duration, and the battery temperature during the duration.
[0040]
The deterioration coefficient of the secondary battery determined by the above-described deterioration determination method is used for charge control of the secondary battery, for example. In other words, the charging control device corrects the charging condition of the secondary battery according to the deterioration coefficient. The correction particularly reduces the upper limit of the charging current or the upper limit of the battery voltage during the charging period. For example, in the CCCV method, the target value of the charging current or the upper limit value of the battery voltage in the constant current control period is reduced by a predetermined amount, or the charging end current value is increased by a predetermined amount. Thus, overcharge and excessive charging current can be reliably avoided in response to a decrease in battery capacity due to deterioration of the secondary battery.
[0041]
The deterioration coefficient of the secondary battery determined by the above-described deterioration determination method may be used for discharge control of the secondary battery. For example, when the secondary battery is discharged, the state of charge of the secondary battery drops to substantially 0%, or the battery voltage drops to a predetermined lower limit (end-of-discharge voltage). Alternatively, an external discharge control device cuts off the discharge current. Thereby, overdischarge of the secondary battery is prevented. Here, the secondary battery changes its discharge characteristics due to deterioration. Therefore, overdischarge can be reliably avoided by correcting each value of the battery state or discharge end voltage corresponding to the 0% state of charge in accordance with the deterioration coefficient of the secondary battery.
[0042]
A method for determining deterioration of a secondary battery according to another aspect of the present invention includes:
(A) measuring the discharge rate and battery temperature of the secondary battery when the charge state or battery voltage of the secondary battery drops to a predetermined threshold due to the discharge of the secondary battery; and
(B) determining a deterioration coefficient of the secondary battery based on the measured values of the discharge rate and the battery temperature;
Have
[0043]
The deterioration coefficient of the secondary battery depends on the history of the discharge rate and the battery temperature in the overdischarge state in addition to the history of the depth of discharge and the battery temperature. For example, in a lithium ion secondary battery, the deterioration is more remarkable as the discharge rate in the overdischarge state is higher or the battery temperature is lower.
In the above-described deterioration determination method, the above-described threshold value with respect to the state of charge of the secondary battery or the battery voltage corresponds to, for example, a value at the time of entering or overcoming the overdischarge state. Specifically, for example, the threshold for the state of charge is set to about 0%, or the threshold for the battery voltage is set to the end-of-discharge voltage value. Thereby, the deterioration coefficient of the secondary battery is determined based on the measured values of the discharge rate and the battery temperature in the overdischarge state. Thus, the deterioration of the secondary battery is evaluated with higher accuracy than the conventional determination method.
[0044]
The function form of the deterioration coefficient when the discharge rate in the overdischarge state and the battery temperature are variables are determined, for example, by experiment for each type of secondary battery. In the above deterioration determination method, a list of deterioration coefficients corresponding to, for example, combinations of discharge rate and battery temperature is preset based on the function. In the deterioration coefficient determination step, the list is referred to, and a deterioration coefficient corresponding to a set of measured values of the discharge rate and the battery temperature is determined.
In addition to the list, a coefficient group that characterizes the functional form of the deterioration coefficient may be set by experiment, and the deterioration coefficient may be calculated from the coefficient group, the discharge rate, and the battery temperature.
[0045]
The deterioration coefficient of the secondary battery determined by the above-described deterioration determination method is used for charge control of the secondary battery, for example. In other words, the charging control device corrects the charging condition of the secondary battery according to the deterioration coefficient. The correction reduces the upper limit of the charging current or the upper limit of the battery voltage during the charging period. Accordingly, it is possible to reliably avoid the occurrence of overcharging and excessive charging current in response to a decrease in battery capacity due to deterioration of the secondary battery.
[0046]
The deterioration coefficient of the secondary battery determined by the above-described deterioration determination method may be used for discharge control of the secondary battery. That is, overdischarge can be reliably avoided by correcting each value of the battery state or discharge end voltage corresponding to a substantially 0% charged state according to the deterioration coefficient of the secondary battery.
[0047]
The method for determining the deterioration of the secondary battery is further
(A) counting the number of times that the measured value of the discharge rate when the state of charge of the secondary battery or the battery voltage drops to the threshold value due to discharge is equal to or greater than a predetermined value (hereinafter referred to as overdischarge detection count); and
(B) determining a deterioration coefficient of the secondary battery based on the number of overdischarge detections;
You may have.
Overdischarge at a high discharge rate greatly accelerates the deterioration of the secondary battery. In the above deterioration determination method, the deterioration due to overdischarge at a high discharge rate is preferentially evaluated through a step of determining a deterioration coefficient based on the number of overdischarge detections. Thereby, the accuracy of evaluation of deterioration is improved.
[0048]
DETAILED DESCRIPTION OF THE INVENTION
DESCRIPTION OF EXEMPLARY EMBODIMENTS Hereinafter, exemplary embodiments of the invention will be described with reference to the drawings.
[0049]
Embodiment 1
The charge control device according to the first embodiment of the present invention is mounted as a control unit in a battery management system in a battery pack for notebook PCs.
FIG. 1 is a block diagram showing the configuration of the notebook PC 3 and the battery pack 4 relating to charging of the secondary battery 41. As shown in FIG.
The notebook PC 3 includes a charger 31 and a charger controller 32.
The battery pack 4 includes a secondary battery 41 and a battery management system 5.
The secondary battery 41 is, for example, a lithium ion secondary battery. The notebook PC 3 and the battery management system 5 in the battery pack 4 cooperate to charge the secondary battery 41 according to the CCCV method.
[0050]
The charger 31 in the notebook PC 3 is connected to the commercial AC power source 1 through the AC adapter 2. Thereby, DC power is input from the AC adapter 2. Further, the input power is converted under the control of the charger control unit 32, and the output voltage or output current is stably maintained at a predetermined value and supplied to the battery pack 4.
The charger control unit 32 controls the output voltage and output current of the charger 31 according to predetermined charging conditions. Here, the charging condition is specified by the battery management system 5 in the battery pack 4. Further, during the charging period, based on the feedback from the battery management system 5, the output of the charger 31 is compensated for deviation from the target value due to the charging conditions.
[0051]
For example, in the CCCV method, the charging current target value and the substantial upper limit value of the charging voltage in the constant current control period, and the charging end current value in the constant voltage control period are included as charging conditions. The charger control unit 32 performs constant current control at the initial stage of charging, and stably maintains the output current of the charger at the target value of the charging current. When the battery management system 5 notifies that the upper limit of the battery voltage has been reached, the charger control unit 32 switches the constant current control to the constant voltage control, and changes the output voltage of the charger to the upper limit value of the battery voltage (for example, the initial two The secondary battery 41 is stably maintained at about 4.20 V / cell). When the battery management system 5 notifies that the charging current has dropped to the charging end current value, the charger control unit 32 cuts off the output of the charger 31 and ends the charging of the secondary battery 41.
[0052]
The battery management system 5 in the battery pack 4 includes a battery state monitoring unit and a control unit 51. The battery state monitoring unit includes three sensors: a current detection unit 44, a temperature detection unit 45, and a voltage detection unit 46. The current detection unit 44 measures the charging current from the amount of voltage drop caused by the current detection resistor 44A. The temperature detector 45 measures the battery temperature from the resistance value of the thermistor 45A adjacent to the secondary battery 41. The voltage detector 46 measures the voltage across the secondary battery 41 and converts the battery voltage per cell. Here, the voltage detection unit 45 may directly measure the voltage for each cell of the secondary battery 41.
[0053]
The control unit 51 includes a CPU and a memory (for example, a RAM and a flash memory) (not shown).
The memory stores a charge / discharge control program and information related to the secondary battery 41. Information on the secondary battery 41 includes, for example, battery voltage, battery current, battery temperature, and charge state history, battery capacity initial value and learning value for each discharge, number of charge / discharge cycles, battery state and charge state, and so on. A list showing the correspondence relationship between the charging condition and the charging condition is included.
[0054]
The CPU executes a program stored in the memory. Thereby, the control unit 51 performs the following functions for charge / discharge control of the secondary battery 41. For example,
(A) When charging the secondary battery 41, the charging condition is set according to the charging characteristics of the secondary battery 41 and notified to the charger control unit 32.
(B) Every time a predetermined number of clocks are counted, measurement values are input from the current detection unit 44, temperature detection unit 45, and voltage detection unit 46, and changes in battery voltage, battery current, and battery temperature are monitored. To do.
(C) In particular, it is determined whether or not battery voltage, battery current, and battery temperature fluctuations are within predetermined tolerances. When any of these fluctuations deviates significantly from the allowable range, this is notified to the notebook PC 3, and for example, the battery current is cut off. Thus, the control unit 51 functions as a protection circuit for the secondary battery 41.
[0055]
(D) Accumulate the measured charge current from the start of charging and calculate the amount of charge in real time. Similarly, the measured values of discharge current are integrated from the start of discharge, and the amount of discharge electricity is calculated in real time. Furthermore, the charge state of the secondary battery 41 is determined in real time from the charge / discharge amount of electricity and the battery capacity. Here, the charging state corresponding to the battery state at each time point may be determined from the correspondence between the battery state and the charging state.
(E) Each time the secondary battery 41 is discharged, the battery capacity is learned from the total amount of discharged electricity.
(F) After the start of use of the battery pack 4, the change in the charging state of the secondary battery 41 is monitored, and the number of charge / discharge cycles of the secondary battery 41 is counted.
(G) The battery state of the secondary battery 41 is notified to the notebook PC 3 in real time. In particular, during the charging period, the battery state of the secondary battery 41 is notified to the charger control unit 32. For example, when the battery state of the secondary battery 41 corresponds to full charge, the charger control unit 32 finishes charging the secondary battery 41.
[0056]
(H) For example, the state of charge of the secondary battery 41 charged to full charge is maintained substantially fully charged until the start of discharge. Specifically, the charging state of the secondary battery 41 is monitored after charging up to full charge is completed. When the state of charge of the secondary battery 41 drops from full charge (100%) to a predetermined maintenance limit (eg, about 95%) due to self-discharge, for example, the controller 51 notifies the charger controller 32 of the drop. The charger control unit 32 resumes charging of the secondary battery 41 in response to the notification, and returns the charged state of the secondary battery 41 to full charge (100%). In this way, the charging state of the secondary battery 41 is substantially maintained at full charge by repeating very shallow charging / discharging at a depth of about 5%.
[0057]
Generally, a large load is applied to the electrode of the secondary battery during charging. The load is particularly excessive due to overcharging and excessive charging current, which significantly shortens the life of the secondary battery.
When a lithium ion secondary battery is used as the secondary battery, the electrolyte is a flammable organic solvent. If the secondary battery is overheated due to overcharging or excessive charging current, its safety is significantly impaired due to generation of flammable gas.
Therefore, in order to maintain the life of the secondary battery for a long time and to keep the safety of its use high, the secondary battery must be reliably prevented from being overcharged and excessively charged.
The control unit 51 according to the first embodiment realizes the following functions as the charging condition monitoring unit 51A, the deterioration evaluation unit 51B, and the charging condition correction unit 51C. With these functions, it is possible to reliably avoid overcharging the secondary battery 41 and generating excessive charging current.
[0058]
The charging condition monitoring unit 51A monitors the measured values of the current detection unit 44, the temperature detection unit 45, and the voltage detection unit 46 when the secondary battery 41 is charged. Further, it is determined whether or not those measured values satisfy the charging condition, and the determination content is notified to the charger control unit 32.
Specifically, for example, the charging condition monitoring unit 51A measures a deviation between the charging current value and the target value at the initial stage of charging, and feeds back the deviation to the charger control unit 32. On the other hand, the battery voltage value is compared with the upper limit value, and when both substantially match, the match is immediately notified to the charger control unit 32.
Further, the charging condition monitoring unit 51A measures the deviation between the battery voltage value and the upper limit value in the later stage of charging, and feeds back the deviation to the charger control unit 32. On the other hand, the charging current is compared with the end-of-charge current value, and when both substantially match, the match is immediately notified to the charger control unit 32.
[0059]
The control unit 51 sets the charging condition according to the charging characteristics of the secondary battery 41. On the other hand, the charging characteristics of the secondary battery 41 change due to deterioration of the secondary battery 41. In particular, the battery capacity of the secondary battery 41 is reduced. Therefore, the control unit 51 must accurately evaluate the degree of deterioration of the secondary battery 41 and appropriately correct the charging conditions according to the degree of deterioration.
Therefore, the control unit 51 first functions as the deterioration evaluation unit 51B, and evaluates the degree of deterioration of the secondary battery 41 as follows.
[0060]
The deterioration evaluation unit 51B defines an index representing the degree of deterioration of the secondary battery 41, that is, a deterioration coefficient, as a ratio between the initial value of the battery capacity and its actual value. Since the battery capacity decreases as the deterioration of the secondary battery 41 progresses, the deterioration coefficient is small.
The deterioration coefficient of the secondary battery 41 depends on, for example, the history of the depth of discharge and the battery temperature in addition to the number of charge / discharge cycles. In particular, when a lithium ion secondary battery is used as the secondary battery 41, the deterioration factor of the secondary battery 41 is smaller as the duration of the high charge state due to the continuous shallow charge / discharge is longer. Furthermore, the higher the battery temperature during its duration, the smaller the degradation factor.
[0061]
The deterioration evaluation unit 51B monitors the state of charge of the secondary battery 41. For example, the secondary battery 41 is substantially fully charged from the end of charging to the start of discharging. That is, as described above, the charged state of the secondary battery 41 is maintained at a high value (that is, a high charged state) within the range of full charge (100%) to a maintenance limit (for example, about 95%). The degradation evaluation unit 51B monitors the battery temperature of the secondary battery 41 during the duration of the high charge state and evaluates the length of the duration.
Here, the degradation evaluating unit 51B evaluates the length of the duration of the high charge state, for example, by the duration. In addition, the degradation evaluation unit 51B counts the number of times that the state of charge of the secondary battery 41 falls from the full charge (100%) to the maintenance limit (about 95%) during the duration of the high charge state. You may evaluate the length of a period.
[0062]
Deterioration evaluation unit 51B determines the deterioration coefficient of secondary battery 41 based on the measured value of the battery temperature during the duration of the high charge state and the evaluation value of the length of the duration as follows.
For secondary battery 41, when the duration of the high charge state is evaluated by its duration, the function form of the degradation coefficient with the duration and the battery temperature during that duration as variables is experimental. It is determined. Based on the function, deterioration evaluation unit 51B calculates in advance a deterioration coefficient corresponding to each combination of the duration of the high charge state and the battery temperature during the duration, and stores the list.
[0063]
Table 1 is a table showing the degradation coefficients corresponding to the combinations of the duration of the high charge state from the start of use of the secondary battery 41 and the average battery temperature during the duration. (A) and (b) of Table 1 show deterioration factors when one of the charging conditions and the upper limit value of the battery voltage are set to 4.20 V / cell and 4.16 V / cell, respectively. Here, the initial value of the battery capacity of the secondary battery 41 is a value when the upper limit value of the battery voltage is set to 4.20 V / cell. Therefore, the battery capacity when the upper limit value of the battery voltage is set to 4.16 V / cell is equal to about 96% of the initial value.
[0064]
[Table 1]

[0065]
When the degradation evaluation unit 51B evaluates the duration of the high charge state by the number of drops from the full charge (100%) to the maintenance limit (approximately 95%) during the duration The evaluation unit 51B stores a table indicating the degradation coefficient corresponding to each set of the number of drops and the battery temperature during the duration. This table, like Table 1, is determined experimentally.
[0066]
When the secondary battery 41 is released from the high charge state by discharging to a predetermined load (for example, battery driving of the notebook PC 3), the deterioration evaluation unit 51B refers to Table 1, and the deterioration coefficient due to the continuation of the high charge state until then. To decide.
[0067]
FIG. 2 is a flowchart showing a deterioration determination method for the secondary battery 41 by the deterioration evaluation unit 51B in the first embodiment.
When the secondary battery 41 is fully charged, the deterioration evaluation unit 51B is activated.
<Step S1>
The deterioration evaluation unit 51B passes the current detection unit 44 and checks the direction and magnitude of the battery current. Thereby, it is determined whether or not the secondary battery 41 is being discharged.
When the battery current is a discharge current and the magnitude (or discharge rate) exceeds a predetermined threshold, the deterioration evaluation unit 51B determines that the secondary battery 41 is discharging, and branches the process to step S5. . Otherwise, the process branches to step S2.
[0068]
<Step S2>
The state of charge (SOC) of the secondary battery 41 is measured, and it is determined whether or not the measured value is equal to or greater than a predetermined maintenance limit (for example, about 95%). When the SOC is equal to or greater than the maintenance limit, the process proceeds to step S3. In other cases, that is, when the SOC falls below the maintenance limit, the process returns to step S1.
<Step S3>
The deterioration evaluation unit 51B measures the elapsed time from the start-up. Here, when the timing has not been started yet, the timing is started.
<Step S4>
The deterioration evaluating unit 51B measures the battery temperature of the secondary battery 41 through the temperature detecting unit 45. Further, the measurement value is stored, and the process returns to step S1.
In this way, while the secondary battery 41 is maintained in a high charge state within the range of full charge (100%) to the maintenance limit (about 95%), the deterioration evaluation unit 51B repeats the loop of steps S1 to S4.
[0069]
<Step S5>
The degradation evaluation unit 51B stops measuring the elapsed time from the activation. Further, the measured value is added to the total duration of the high charge state from the start of use of the secondary battery 41.
<Step S6>
The deterioration evaluation unit 51B calculates the average value of all the battery temperature samples measured during the duration of the high charge state after the use of the secondary battery 41 is started.
<Step S7>
The deterioration evaluation unit 51B refers to Table 1. Thereby, the deterioration coefficient corresponding to the set of the upper limit value of the battery voltage, the total duration of the high charge state, and the average battery temperature during the duration is determined.
[0070]
As described above, in the battery management system 5 according to the first embodiment, each time the secondary battery 41 passes through the duration of the high charge state, the degradation evaluation unit 51B evaluates the length of the duration of the high charge state, and Measure the battery temperature during its duration. Further, the deterioration coefficient of the secondary battery 41 is determined based on the evaluation value and the measured value. In this way, the history of the depth of discharge and the battery temperature, particularly the history of the high charge state due to repeated very shallow charge / discharge and the battery temperature during the duration, is reflected in the determination of the deterioration coefficient. As a result, the degree of deterioration of the secondary battery 41 is evaluated with higher accuracy than the conventional device.
[0071]
Next, the control unit 51 functions as the charging condition correction unit 51C as follows.
The charging condition correction unit 51C determines the necessity of correcting the charging condition based on the deterioration coefficient of the secondary battery 41 determined by the deterioration evaluation unit 51B. When it is determined that the correction is necessary, the charging condition correction unit 51C reduces the target value of the charging current or the upper limit value of the battery voltage in the constant current control period by a predetermined amount, or the charging end current value by a predetermined amount. increase.
Specifically, every time the deterioration coefficient decreases to a predetermined value, for example, every 95%, 90%, 85%,... Decrease the value by about 0.05V / cell.
Thus, overcharge and excessive charging current can be reliably avoided in response to a decrease in battery capacity due to deterioration of the secondary battery 41.
[0072]
The control unit 51 may use the deterioration coefficient of the secondary battery 41 for correcting the maintenance limit of the charged state in addition to correcting the charging condition. For example, the charging condition correction unit 51 may lower the maintenance limit (about 95%) with respect to full charge (100%) by a predetermined value (for example, 5%) according to the deterioration coefficient of the secondary battery 41. This increases the depth of discharge during the duration of the high charge state. As a result, the burden on the electrode during the duration can be reduced, and the progress of deterioration of the secondary battery 41 can be relaxed.
[0073]
<< Embodiment 2 >>
As in the first embodiment, the charge control device according to the second embodiment of the present invention is mounted on the battery management system in the laptop battery pack as the control unit.
In the second embodiment, the configuration of the notebook PC 3 and the battery pack 4 relating to the charging of the secondary battery 41 is the same as that of the first embodiment. Therefore, the details of the configuration similar to that of the first embodiment are referred to FIG. 1 and the description of the first embodiment.
[0074]
In particular, the control unit 51 of the battery management system 5 according to the second embodiment differs from the first embodiment in terms of the function as the deterioration evaluation unit 51B.
The deterioration coefficient of the secondary battery 41 depends on the history of the discharge rate in the overdischarge state and the battery temperature in addition to the history of the depth of discharge and the battery temperature. In particular, when a lithium ion secondary battery is used as the secondary battery 41, the higher the discharge rate in the overdischarged state or the lower the battery temperature, the smaller the deterioration coefficient of the secondary battery 41.
[0075]
The deterioration evaluation unit 51B according to the second embodiment monitors the charging state or battery voltage of the secondary battery 41 when the secondary battery 41 is discharged. When the state of charge of the secondary battery 41 drops to, for example, about 0%, or when the battery voltage of the secondary battery 41 drops to, for example, the discharge end voltage, the deterioration evaluation unit 51B measures the discharge rate and the battery temperature. Further, the measured values of the discharge rate and the battery temperature are regarded as the discharge rate and the battery temperature in the overdischarge state, and based on these, the deterioration coefficient of the secondary battery 41 is determined as follows.
[0076]
For the secondary battery 41, the function form of the deterioration coefficient with the discharge rate in the overdischarge state and the battery temperature as variables is determined by experiment. Based on the function, deterioration evaluation unit 51B calculates in advance a deterioration coefficient corresponding to each combination of discharge rate and battery temperature, and stores the list.
Table 2 is a table showing deterioration factors corresponding to the combinations of the discharge rate in the overdischarge state and the battery temperature for the secondary battery 41. In Table 2, the discharge rate and battery temperature when the battery voltage of the secondary battery 41 drops to the discharge end voltage (for example, about 3.0 V / cell) are regarded as the discharge rate and battery temperature in the overdischarge state, respectively. .
At the end of the discharge of the secondary battery 41, the deterioration evaluation unit 51B refers to Table 2 and determines the deterioration coefficient due to the discharge.
[0077]
[Table 2]

[0078]
In Table 2, the length of the usage period of the secondary battery 41 is evaluated by the number of charge / discharge cycles.
In addition, the length of the usage period of the secondary battery 41 may be evaluated by the number of overdischarge detections by the deterioration evaluation unit 51B or the number of hibernations by the notebook PC 3.
Here, the number of overdischarge detections refers to the number of times that the battery voltage drops below a predetermined lower limit value (for example, discharge end voltage) due to discharge at a high discharge rate equal to or higher than a predetermined value. When determining the deterioration coefficient, the deterioration evaluating unit 51B compares a measured value regarded as a discharge rate in an overdischarge state with a predetermined value (for example, about 1.0 C). Further, when the measured value is equal to or greater than the predetermined value, the number of overdischarge detections is increased by one.
[0079]
On the other hand, hibernation by the notebook PC 3 refers to a process of evacuating to a sleep state by the notebook PC 3. For example, when the notebook PC 3 is driven by the secondary battery 41, the state of charge of the secondary battery 41 substantially exceeds 0% (exactly, a value slightly higher than 0%, such as 0.5% or 1%). Performs hibernation when descending. Thereby, an unexpected system down due to power shortage is avoided.
When the secondary battery 41 is discharged, the deterioration evaluating unit 51B monitors, for example, the state of charge, and increases the number of hibernations by 1 each time the battery drops substantially exceeding 0%. In addition, the degradation evaluation unit 51B may increase the number of hibernations by 1 each time the notebook PC 3 is notified of the execution of hibernation.
[0080]
When the secondary battery 41 overdischarges at a high discharge rate, the load on the positive electrode is particularly heavy. That is, overdischarge at a high discharge rate particularly greatly promotes deterioration of the secondary battery 41.
The degradation evaluation unit 51B evaluates the length of the usage period of the secondary battery 41 by the number of times of overdischarge detection or the number of hibernations described above, so that overdischarge at a high discharge rate is performed in determining the degradation coefficient of the secondary battery 41. Focus on it. Thus, the accuracy of deterioration evaluation is improved.
[0081]
FIG. 3 is a flowchart showing a deterioration determination method for the secondary battery 41 by the deterioration evaluation unit 51B in the second embodiment.
When the charged state of the secondary battery 41 drops to a predetermined value (for example, about 10%) due to discharge, the deterioration evaluation unit 51B is activated.
<Step S10>
The deterioration evaluation unit 51B monitors the battery state of the secondary battery 41 through the current detection unit 44, the temperature detection unit 45, and the voltage detection unit 46.
<Step S11>
Deterioration evaluation unit 51B determines a discharge end voltage corresponding to a set of measured values of discharge current and battery temperature, and compares the discharge end voltage with the measured value of battery voltage. When the measured value of the battery voltage is equal to or lower than the end-of-discharge voltage, deterioration evaluation unit 51B branches the process to step S12. In other cases, the degradation evaluating unit 51B returns the process to step S10.
[0082]
<Step S12>
The deterioration evaluation unit 51B measures the discharge rate of the secondary battery 41 through the current detection unit 44. The measured value is regarded as the discharge rate in the overdischarge state.
<Step S13>
The deterioration evaluating unit 51B measures the battery temperature of the secondary battery 41 through the temperature detecting unit 45. The measured value is regarded as the battery temperature in the overdischarged state.
<Step S14>
The degradation evaluation unit 51B refers to Table 2 and determines the degradation coefficient corresponding to the combination of the number of charge / discharge cycles at that time and the discharge rate in the overdischarge state and the battery temperature.
[0083]
In the battery management system 5 according to the second embodiment, as described above, every time the battery voltage drops to the discharge end voltage due to the discharge of the secondary battery 41, the deterioration evaluation unit 51B calculates the discharge rate and the battery temperature at that time. measure. Further, these measured values are regarded as the discharge rate and battery temperature in the overdischarge state, and the deterioration coefficient of the secondary battery 41 is determined based on them. Thus, the discharge rate in the overdischarge state and the battery temperature are reflected in the determination of the deterioration coefficient. As a result, the degree of deterioration of the secondary battery 41 is evaluated with higher accuracy than the conventional device.
[0084]
Next, the control unit 51 functions as the charging condition correction unit 51C as follows.
The charging condition correction unit 51C determines the necessity of correcting the charging condition based on the deterioration coefficient of the secondary battery 41 determined by the deterioration evaluation unit 51B. When it is determined that the correction is necessary, the charging condition correction unit 51C reduces the target value of the charging current or the upper limit value of the battery voltage in the constant current control period by a predetermined amount, or the charging end current value by a predetermined amount. increase.
Specifically, every time the deterioration coefficient decreases to a predetermined value, for example, every 95%, 90%, 85%,... Decrease the value by about 0.05V / cell.
Thus, overcharge and excessive charging current can be reliably avoided in response to a decrease in battery capacity due to deterioration of the secondary battery 41.
[0085]
【The invention's effect】
The deterioration factor of secondary batteries is not uniquely determined only by the number of charge / discharge cycles, and depends largely on the duration of a constant charge state, the battery temperature during that duration, and the discharge rate and battery temperature in the overdischarge state. To do.
In the charge control device according to one aspect of the present invention, the deterioration evaluation unit measures the duration and the battery temperature during the duration for each duration of the substantially constant charge state, and based on the measured values. Determine the degradation coefficient of the secondary battery.
In the charge control device according to another aspect of the present invention, the deterioration evaluation unit determines the deterioration coefficient of the secondary battery based on the measured values of the discharge rate and the battery temperature in the overdischarge state.
Therefore, any of these charge control devices can evaluate the deterioration of the secondary battery with higher accuracy than the conventional device.
[0086]
In the charging control apparatus according to the present invention, the charging condition correction unit corrects the charging condition according to the deterioration coefficient determined by the deterioration evaluation unit. The correction particularly reduces the upper limit of the charging current or the upper limit of the battery voltage during the charging period. In this way, it is possible to reliably avoid overcharge and generation of an excessive charge current in response to a decrease in battery capacity due to deterioration of the secondary battery.
[0087]
In the charge control device according to the present invention, the deterioration evaluation unit may count the number of overdischarge detections by monitoring the battery voltage, and determine the deterioration coefficient of the secondary battery based on the number of overdischarge detections. Thereby, since deterioration due to overdischarge at a high discharge rate is mainly evaluated, the accuracy of deterioration evaluation for the secondary battery is improved.
[Brief description of the drawings]
FIG. 1 is a block diagram showing configurations of a notebook PC 3 and a battery pack 4 related to charging of a secondary battery 41 in Embodiment 1 of the present invention.
FIG. 2 is a flowchart showing a deterioration determination method for a secondary battery 41 by a deterioration evaluation unit 51B according to the first embodiment of the present invention.
FIG. 3 is a flowchart illustrating a deterioration determination method for a secondary battery 41 by a deterioration evaluation unit 51B according to the second embodiment of the present invention.
4 is a block diagram showing a conventional configuration of a notebook PC 3 and a battery pack 40 relating to charging of a secondary battery 41. FIG.
[Explanation of symbols]
1 Commercial AC power supply
41 Secondary battery
44A current detection resistor
45A thermistor

Claims

(A) At the time of charging a secondary battery, the battery voltage, charging current, and battery temperature are monitored to determine whether the measured value or the amount of change within a predetermined time satisfies a predetermined charging condition. Charging condition monitoring unit;
(B) When the state of charge of the secondary battery is substantially maintained at a constant value, the battery temperature of the secondary battery is monitored during the duration of the state of charge, and the length of the duration is evaluated. A degradation evaluation unit for determining a degradation coefficient of the secondary battery based on the measured value of the battery temperature during the duration and the length of the duration; and
(C) a charging control device comprising: a charging condition correction unit for correcting the charging condition according to a deterioration coefficient of the secondary battery;
Each time the state of charge of the secondary battery drops from the constant value to a value lower by a predetermined value (hereinafter referred to as a maintenance limit), the charging of the secondary battery is resumed, whereby the state of charge of the secondary battery is When the deterioration evaluation unit substantially maintains a constant value, the deterioration evaluation unit evaluates the length of the duration by the number of drops from the constant value to the maintenance limit of the state of charge of the secondary battery, Charge control device.

The charging control device according to claim 1, wherein the charging condition correction unit lowers a maintenance limit of the charging state by a predetermined value in accordance with a deterioration coefficient of the secondary battery.

(A) Charging conditions for monitoring the battery voltage, charging current, and battery temperature when charging a secondary battery and determining whether the measured value or the amount of change within a certain time satisfies a predetermined charging condition Monitoring unit;
(B) When the charge state or battery voltage of the secondary battery drops to a predetermined threshold due to the discharge of the secondary battery, the discharge rate and the battery temperature of the secondary battery are measured, and the discharge rate and the battery temperature are measured. A degradation evaluation unit for determining a degradation coefficient of the secondary battery based on the value; and
(C) A charge control device comprising: a charge condition correction unit for correcting the charge condition according to a deterioration coefficient of the secondary battery.

The charge control device according to claim 3, wherein the deterioration evaluation unit counts the number of times the measured value of the discharge rate is equal to or greater than a predetermined value, and determines the deterioration coefficient of the secondary battery based on the number of times.

(A) The charge control device according to any one of claims 1 to 4; and
(B) Regarding the secondary battery, (a) A voltage detector for measuring battery voltage, (b) A current detector for measuring battery current, and (c) A battery state monitoring unit for providing a battery voltage, a battery current, and a battery temperature of the secondary battery obtained by the detection unit to the charge control device. ;
A battery management system.

A battery pack comprising the battery management system according to claim 5 and the secondary battery.

(A) Monitoring the battery temperature of the secondary battery and evaluating the duration of the secondary battery during the duration of the charge state when the state of charge of the secondary battery is substantially maintained at a constant value; and ,
(B) Determining a deterioration coefficient of the secondary battery based on a measured value of the battery temperature during the duration and a length of the duration;
Each time the state of charge of the secondary battery drops from the constant value to a value lower by a predetermined value (hereinafter referred to as the maintenance limit), the charging of the secondary battery is resumed, whereby the state of charge of the secondary battery is When the secondary battery deterioration coefficient is determined to be substantially maintained at a constant value, the duration of the secondary battery is determined by the number of drops from the constant value to the maintenance limit of the state of charge of the secondary battery. A method for judging deterioration of a secondary battery, characterized by being evaluated.

(A) Measuring a discharge rate and a battery temperature of the secondary battery when a charge state of the secondary battery or a battery voltage drops to a predetermined threshold due to the discharge of the secondary battery; and
(B) Determining a deterioration coefficient of the secondary battery based on measured values of the discharge rate and the battery temperature.

(A) Counting the number of times the measured value of the discharge rate is greater than or equal to a predetermined value; and
(B) Determining a degradation coefficient of the secondary battery based on the number of times;
The deterioration determination method for a secondary battery according to claim 8, further comprising: