JP2004234896A

JP2004234896A - Inspection method of secondary battery

Info

Publication number: JP2004234896A
Application number: JP2003019008A
Authority: JP
Inventors: Shumei Nishijima; 主明西島; Naoto Torata; 直人虎太; Koichi Ui; 幸一宇井
Original assignee: Sharp Corp
Current assignee: Sharp Corp
Priority date: 2003-01-28
Filing date: 2003-01-28
Publication date: 2004-08-19

Abstract

<P>PROBLEM TO BE SOLVED: To provide an inspection method of a secondary battery capable of distinguishing defects of the secondary battery in a shorter time, more easily, more simply, and more accurately. <P>SOLUTION: In the method of inspecting the secondary battery constituted of a positive electrode containing a lithium transition metal oxide capable of storing and discharging lithium ions, a negative electrode containing a carbon material capable of storing and discharging lithium ions, a separator consisting of an insulator separating the positive electrode and the negative electrode and an electrolyte containing lithium salt, a charging current value at constant-current charging in a charging process comprising a first constant-current charging after an assembly of the battery and a following constant-voltage charging is set at 5 to 20 CmA. The inspection method of the secondary battery distinguishes defects of the battery either by (1) measuring a current value of the battery at the constant voltage charging and/or temperature of the battery at the charging process, or by (2) measuring a voltage value of the battery at a post-aging process after the charging process. <P>COPYRIGHT: (C)2004,JPO&NCIPI

Description

【０００１】
【発明の属する技術分野】
本発明は、二次電池の検査方法に関し、より詳細には、容易かつ短時間で電池の不良を検査することができる二次電池の検査方法に関する。
【０００２】
【従来の技術】
経済性等の面から、ポータブル機器の電源として二次電池が多く使われている。二次電池には様々な種類があり、最も一般的に普及しているのがニッケル−カドミウム電池である。また、ニッケル水素電池も普及しつつあるが、ニッケル−カドミウム電池やニッケル水素電池よりも出力電圧が高く、高エネルギー密度であるリチウム二次電池が、近年、主力になりつつある。
【０００３】
しかし、リチウム二次電池は、エネルギー密度が他の電池に比較して高いがゆえに性能にばらつきが生じやすく、また、電解質に有機化合物を用いているため、電解質が漏れ出したり、破裂したりし、使用者に危害を及ぼす恐れがある。このため、リチウム二次電池の製造段階で、できる限り不良電池を選別しなければならない。
【０００４】
通常、リチウム二次電池は、電池を組み立てた後、活性化又は化成と呼ばれる１回目の充電工程が必要となる。この充電工程では、電池がある一定の電位に到達するまで一定の電流値、例えば、０．１ＣｍＡ以下の小さな電流値で充電し、設定した任意の電圧に到達した後は、その電位を超えないように充電電流を減衰させて充電を行う、定電流−定電圧充電が一般的に行われる。このような組み立て後の１回目の充電によって、リチウムの一部が正極に捕捉され、正極が新たなリチウム化合物（例えば、Ｌｉ_ｘＶ_２Ｏ_５、Ｌｉ_ｘＭｏＳ_２、Ｌｉ_ｘＴｉＳ_２又はＬｉ_ｘＮｂＳｅ_３（ｘは各正極で異なる０より大きく、３．０より小さい値））に変化し、その後、この化合物が正極として働く。正極中に含まれるリチウムが負極に移動することにより正極の組成が変化し（例えば、ＬｉＣｏＯ_２→ＬｉｘＣｉＯ_２、ＬｉＭｎ_２Ｏ_４→Ｌｉ_ｘＭｎ_２Ｏ_４（ｘは各正極で異なる０より大きく、３．０より小さい値））、その後この化合物が正極として働く。そのため、充電方法によって電池の性能にバラツキが生じやすい。また、組み立て後１回目の充電時には、未だ十分に電解液が電池の各部材に十分に行き渡っていないため、電池内での反応が不均一であり、性能のバラツキが生じやすい。さらに、反応が過剰に進行した部分では、負極側にリチウムが樹脂状結晶として析出するデンドライト析出を引き起こす。析出が激しい場合には、この結晶は正極と負極とを遮っているセパレータを突き破り、正極と接触し、マイクロショートを引き起こして端子電圧の電圧差が大きくなり、さらには、発熱や熱暴走を起こすことがある。そのため、通常、リチウム二次電池の製造工程では、組み立て後、一定時間電解液が電池の各部分に十分行き渡るまで放置した後に１回目の充電が行われる。
【０００５】
また、充電後、電池に充電又は放電などの操作を行わずに電池の端子を開放して放置するエージング工程を行い、電池を安定化させる。特許文献１には、組み立て後１回目の充電後に一週間エージングを行い、エージング前後の端子電位差から、マイクロショートが原因で発生する不良電池の識別をする方法が提案されている。また、特許文献２には、微小な電流を用いた組み立て後１回目の充電の後、電池の電位の減衰曲線から、短絡が原因で発生する不良電池を識別する方法が提案されている。
【０００６】
【特許文献１】
特開２００１−２２８２２４号公報
【特許文献２】
特開２０００−２８６９０号公報
【０００７】
【発明が解決しようとする課題】
しかし、上記の方法では、品質の安定した電池を提供することができるが、エージング時間が長期間におよび、電池を活性化させるための充電処理が別途必要になるという課題がある。
本発明は上記課題に鑑みなされたものであり、より短時間で、容易、簡便かつ高精度に二次電池の不良を判別することができる二次電池の検査方法を提供することを目的とする。
【０００８】
【課題を解決するための手段】
本発明によれば、リチウムイオンを吸蔵放出可能なリチウム遷移金属酸化物を含む正極と、リチウムイオンを吸蔵放出可能な炭素材料を含む負極と、前記正極と前記負極を隔てる絶縁物からなるセパレータと、リチウム塩を含む電解質とから構成される二次電池を検査する方法であって、前記電池の組み立て後の１回目の定電流充電と、それに続く定電圧充電とからなる充電工程において、定電流充電での充電電流値を５〜２０ＣｍＡに設定し、▲１▼定電圧充電での電池の電流値及び／又は充電工程における電池の温度を測定することにより電池の不良を判別するか、あるいは▲２▼充電工程後のエージング工程における電池の電圧値を測定することにより電池の不良を判別する二次電池の検査方法が提供される。
【０００９】
【発明の実施の形態】
本発明の二次電池の検査方法は、本質的に、二次電池を組み立てた後の初回の充電、エージング工程において、電池の電流値、電池の温度及び／又は電池の電圧値を測定することにより電池の不良を判別する方法である。
本発明においては、二次電池は、上述したように、電池を組み立てた後に初回の充電を行って電池を活性化させ、その後にエージングを行って、電池の製造工程中に発生した不良電池を選別する。なお、初回の充電は、電池の容量に対して満充電を行う必要はなく、適当な充電量、例えば、３０〜７０％程度で充電を終了してもよい。電池の活性化は、例えば、図１に示したように、一定の電位に達するまでは一定の電流値で充電し（図１中、Ａ）、設定された任意の電圧に達した後は、その電位を越えないように充電電流を減衰させる（図１中、Ｂ）、いわゆる定電流（Ａ）−定電圧（Ｂ）充電で行われる。また、エージングとは、電池の端子を開放状態にして放置することによって行われる。
【００１０】
本発明の二次電池の検査方法では、初回の充電における定電流充電後の電流値の減衰の異常を容易に検出すること、電流値の増大に伴う過度の発熱や電解質の劣化等のダメージ等を考慮して、５〜２０ＣｍＡに設定する。ここで、ＣｍＡとは、電池の公称容量を１時間で放電するのに必要な電流値を表す。例えば、１５００ｍＡｈの電池であれば、１５００ｍＡが１ＣｍＡに相当し、この電池では、５ＣｍＡは７５００ｍＡとなる。このように、初回の定電流充電における電流値を５〜２０ＣｍＡと比較的大きな電流値で行うことによって、非常に短時間で定電流充電を終了させることができる。しかも、このような比較的大きな電流値で充電を行っても、性能の劣化はなく、十分に活性化されていることを確認している。
【００１１】
したがって、定電流充電を上述の範囲で行い、その後に定電圧充電における電池の電流値を測定するのみで、その電流値が図１とは異なる挙動を示す場合に、その電池を不良と判別することができる。例えば、電池に内部短絡が生じている場合には、図２に示すように、電流が突然上昇するという現象が観察される。よって、定電圧充電時における単位時間当たりの電流の減衰量、つまり、電流値の減衰を時間で微分した値を算出し、その値が正になったときには、電流の上昇が発生したとして、その電池を不良と判別することができる。なお、電流値の値は、急激な上昇の場合のみならず、緩やかな上昇である場合、上昇と降下とが交互に発生する場合、急激な降下が認められる場合等にも、何らかの異常が生じていると推測され、不良と判別することができる。また、この電流値は、経時的に連続して測定することが好ましいが、任意の時間間隔で測定するのみでもよい。さらに、充電工程の間は、特に電池を加熱したり、冷却したりする必要はないが、電池の不良を判別するにあたり、極端に高い温度や低い温度や保管中の過度の温度変化は電位の測定に誤差を生じる恐れがあるために、ある程度の温度範囲内、例えば、任意の温度±５℃以下の範囲、１０℃以下の範囲が挙げられ、室温±５℃以下の範囲がより好ましい。
【００１２】
また、本発明においては、充電工程における電池表面の温度を測定するのみでも、図３に示すような温度と異なる挙動を示す場合に、電池の良／不良を判別することができる。つまり、通常、図３に示すように、初回の充電を行う場合、充電開始直後から電池の温度が上昇し、所定時間後、例えば、約１分後に最大温度に到達し、その後、電池の温度は緩やかに降下する。電池に内部短絡が生じている場合には、例えば、図４に示すように、一旦降下していた電池表面の温度が、突然上昇するという現象が観察される。よって、充電時における単位時間当たりの電池表面温度の増減量を測定し、充電開始以降、最初の温度上昇は正常であり、２回目以降に単位時間当たりの温度の増減量が正になった場合、その電池は異常が生じており、不良と判別することができる。また、充電工程における電池の表面温度が、好ましくは２回目以降の温度上昇において、所定温度以上となったものを不良と判別してもよい。所定温度としては、例えば、４０℃程度、４５℃程度、５０℃程度又は６０℃程度とすることができる。なお、温度は、１回目の温度上昇が過度に急激である場合（例えば、通常の温度よりも１０℃程度以上高い場合）、１回目の温度上昇が適当な範囲で、適当な時期に起こらない場合、温度降下が急激に現われる場合、上昇と降下とが交互に発生する場合等にも、インピーダンス異常等、何らかの異常が生じていると推測され、不良と判別することができる。また、この電池の温度は、経時的に連続して測定することが好ましいが、任意の時間間隔で測定するのみでもよい。さらに、充電工程の間の温度は、上述したのと同様に、ある程度の温度範囲内とすることが好ましい。
【００１３】
さらに、本発明においては、充電工程の後のエージング工程における電池の電圧値を測定するのみでも、電池の不良を判別することができる。電池に内部短絡が生じている場合、単位時間あたりの電圧変化は内部短絡のないものに比較して大きくなる。本発明では、初回の充電工程において、５ＣｍＡ以上という比較的大きな電流を電池に流すため、電池内での分極が必然的に大きくなり、充電終了直後の電位降下は大きいものとなり、よって、容易に電池の不良を判別できる。つまり、通常、図５のＡに示すように、電位降下が現われるが、電池に内部短絡が生じている場合には、図５のＢに示すように、電位降下の程度が大きく現われる。したがって、エージングの開始後の所定時間内における電位降下の程度が所定の値以下となる場合、単位時間あたりの電位降下の減少量が所定の値以上となる場合、電位降下が過度である場合、電位の降下がスムーズに進行しなかったり、電池が上昇した場合等に何らかの異常が生じていると推測され、不良と判別することができる。なお、エージングの時間は特に限定されるものではなく、電池の不良の検出しやすさを考慮して、２０分間以上、さらに３０分間以上とすることが好ましい。また、このエージングにおける電位降下は、経時的に連続して電位を測定することが好ましいが、任意の時間間隔で測定するのみでもよい。さらに、エージングの間の温度は、上述したのと同様に、ある程度の温度範囲内とすることが好ましい。
【００１４】
本発明の検査方法においては、上述した電流値の測定、温度の測定、電圧値の測定のみを個別に行ってもよいし、これらを組み合わせて行ってもよい。具体的には、電流値の測定と温度の測定、電流値の測定と電圧値の測定、温度の測定と電圧値の測定、電流値の測定と温度の測定と電圧値の測定との組み合わせが挙げられる。このように組み合わせることにより、より精度よく電池の不良を判別することができる。
【００１５】
本発明の検査方法を実施することができる電池は、具体的には、正極と、負極と、セパレータと、電解質とから構成される二次電池、特にリチウム二次電池が挙げられる。二次電池としては、円筒型、平板型、コイン型等どのような形状のものでもよい。
正極材料としては、リチウムイオンを吸蔵放出可能なリチウム遷移金属酸化物が挙げられるが、硫化物、遷移金属酸化物等であってもよい。
負極材料としては、リチウムイオンを吸蔵放出可能な炭素材料が挙げられるが、金属酸化物などのリチウムを吸蔵、放出できる物質であれば、どのような材料でも使用することができる。
【００１６】
セパレータは、正極と負極とを隔てて、絶縁することができるものであればよく、当該分野で公知の絶縁物を用いることができる。
電解質は、その種類に関して特に限定されるものではなく、液体状の有機溶媒、ゲル状あるいはポリマー状態の電解質、無機固体電解質等のいずれであってもよい。
以下に本発明の二次電池の検査方法を詳細に説明する。
【００１７】
まず、下記の手順に従ってリチウム二次電池を作成した。
正極活物質として、リチウム酸コバルトＬｉＣｏＯ_２を用いた。ＬｉＣｏＯ_２は公知の方法で合成を行った。合成したＬｉＣｏＯ_２は、Ｘ線源としてターゲットＣｕの封入管からの出力２ｋＷのＣｕＫ線を使用したＸ線回折測定、ヨードメトリー法によるコバルトの価数分析及びＩＣＰによる元素分析により、ＬｉＣｏＯ_２であることを確認した。
このようにして得られた正極活物質を乳鉢にて粉砕し、これに導電剤として約１０ｗｔ％のアセチレンブラックと、結着剤として約１０ｗｔ％のテフロン（登録商標）樹脂粉末とを混合した。この混合物をＮ−メチル−２−ピロリドン等の溶剤に溶解してスラリー状にし、これをアルミニウム箔の両面にドクターブレード法で塗布し、乾燥した後に、プレスを行って正極を作製した。
【００１８】
負極活物質として、天然黒鉛粉末を使用した。この天然黒鉛粉末に結着剤として約１０ｗｔ％のテフロン（登録商標）樹脂粉末を混合した。この混合物をＮ−メチル−２−ピロリドン等の溶剤に溶解してスラリー状にし、これを銅箔の両面に塗布し、乾燥した後に、プレスを行って負極を作製した。
上記のようにして作製した正極と負極との間に多孔質ポリエチレン製のセパレータをはさみ、電極を捲回した後に金属性の容器に挿入し、そこに１モル／リットルのＬｉＰＦ_６を溶解させた５０体積％のエチレンカーボネートと５０体積％のジエチルカーボネートとを電解質として含浸させた。その後、金属容器の開口部を樹脂キャップで封口し、二次電池を完成させた。この電池を電池Ａとする。
【００１９】
また、比較のために、セパレータと電極との間に２００メッシュのアルミニウム粉末１ｍｇを散布した電池を、擬似的に内部短絡を発生させたものとして作製した。この電池を電池Ｂとする。
さらに、比較のために、電解液を０．１モル／リットルのＬｉＰＦ_６を溶解させた以外は、電池Ａと同様にして電池を、高インピーダンスの状態を発生させたものとして作製した。この電池を電池Ｃとする。
【００２０】
このように作製した電池Ａ、電池Ｂ、電池Ｃそれぞれ３個ずつ用いて、電池の電位、電池に流れる電流値及び電池の表面温度を測定しながら２５℃の環境下で初回充電を行った。なお、これらの電池の電極活物質の重量から計算される電池容量に基づいて、１０ＣｍＡでの定電流充電を９０秒間行い、定電圧での充電電位を４．２Ｖになるように、電流を通電した。また、充電が開始されてから１５分後に充電を終了し、室温にて２４時間、開放電圧を測定しながらエージングを行った。その結果を表１に示す。
【００２１】
【表１】

正常な電池Ａに比較して電池Ｂの内２つは、１回目の充電中の定電圧充電中に本来なら時間とともに減衰する電流がある時点で急激に上昇した。また、電池Ｃは全て電池Ａに比較して電流値の減衰が激しく、また温度上昇も大きいこともわかった。さらに、電池Ｂの内１回目の充電で正常に見えた電池もエージング工程で電位の減少が見られた。
この結果から、本発明の検査方法によって、確実に不良電池を検出できることがわかった。
さらに、電池Ａ、電池Ｂ、電池Ｃの各３個ずつについて、０．２ＣｍＡ定電流充電を４時間行い、引き続き４．２Ｖの定電圧充電を、電流値が０．０５ＣｍＡになった時点まで行って、充電完了として充電を行う以外は、上記と同様に初回充電を行った。その結果を図６及び表２に示す。
【００２２】
【表２】

図６からは、電池Ｂの内１つにのみ電流の減衰に異常が見られたが、電池Ｂののこりの２つは正常であるように見える。またこの方法では、電池Ｃの異常は検出できなかった。
表１及び表２の比較から、本発明の二次電池の検査方法では、正確な不良電池の判別ができることが確認された。
【００２３】
【発明の効果】
本発明によれば、初回充電工程において、定電流充電での充電電流値を５〜２０ＣｍＡに設定するため、従来の０．１ＣｍＡ程度の充電電流値での充電に比較して、非常に短時間で充電を行うことが可能となり、電池不良の判別を迅速に行うことができる。しかも、上記の範囲の充電電流値に設定して充電を行うことにより、定電圧充電での電池の電流値及び／又は充電工程における電池の温度を測定するという非常に簡便な方法により、高価な製造装置等を必要としないために、容易に電池不良の判別を行うことができる。したがって、製造コストの低減を実現することができ、性能の良好な二次電池を安価で供給することが可能となる。
特に、定電圧充電での電池の電流値及び／又は充電工程における電池の温度を測定することに加え、エージング工程における電池の電圧値の測定を組み合わせることにより、より高精度かつ確実に電池の不良を判別することが可能となり、性能の高い二次電池のみを簡便に判別することができる。
【図面の簡単な説明】
【図１】本発明の二次電池の検査方法を正常な電池に適用した場合の初回充電工程における電池の電位と電流の経時変化を示す図である。
【図２】内部短絡が発生した電池での初回充電工程における電池の電流の経時変化を示す図である。
【図３】本発明の二次電池の検査方法を正常な電池に適用した場合の初回充電工程における電池の表面温度の経時変化を示す図である。
【図４】内部短絡が発生した電池での初回充電工程における電池の表面温度の経時変化を示す図である。
【図５】本発明の二次電池の検査方法を正常な電池及び内部短絡が発生した電池に適用した場合のエージング工程における電池の開放電圧の経時変化を示す図である。
【図６】従来の方法を正常な電池等により適用した場合の初回充電工程における電池の電流の経時変化を示す図である。[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to a secondary battery inspection method, and more particularly, to a secondary battery inspection method capable of easily and quickly inspecting a battery for defects.
[0002]
[Prior art]
From the viewpoint of economy and the like, secondary batteries are often used as power supplies for portable devices. There are various types of secondary batteries, and a nickel-cadmium battery is most commonly used. In addition, although nickel-metal hydride batteries are becoming widespread, lithium secondary batteries having a higher output voltage and higher energy density than nickel-cadmium batteries and nickel-metal hydride batteries have recently become the mainstay.
[0003]
However, lithium secondary batteries have a high energy density compared to other batteries, so their performance tends to vary.In addition, since organic compounds are used for the electrolyte, the electrolyte may leak or burst. May cause harm to the user. For this reason, it is necessary to select defective batteries as much as possible at the stage of manufacturing the lithium secondary battery.
[0004]
Usually, a lithium secondary battery requires a first charging step called activation or formation after the battery is assembled. In this charging step, the battery is charged with a constant current value, for example, a small current value of 0.1 CmA or less until the battery reaches a certain potential, and does not exceed that potential after reaching a set arbitrary voltage. In this manner, constant current-constant voltage charging, in which charging is performed by attenuating the charging current, is generally performed. By the first charging after such assembling, part of lithium is captured by the positive electrode, and the positive electrode is made of a new lithium compound (for example, Li _x V ₂ O ₅ , Li _x MoS ₂ , Li _x TiS _2, or Li _x). NbSe _{3, where} x is greater than 0 and less than 3.0, different for each cathode, and then this compound acts as the cathode. Lithium contained in the positive electrode moves to the negative electrode to change the composition of the positive electrode (for example, LiCoO ₂ → LixCiO ₂ , LiMn ₂ O ₄ → Li _x Mn ₂ O ₄ (x is different from 0 for each positive electrode, This value then serves as the positive electrode. Therefore, the performance of the battery tends to vary depending on the charging method. In addition, at the time of the first charging after the assembly, the electrolyte in the battery is not sufficiently distributed to each member of the battery, so that the reaction in the battery is not uniform, and the performance tends to vary. Further, in a portion where the reaction has progressed excessively, dendritic precipitation occurs in which lithium is precipitated as resinous crystals on the negative electrode side. If the precipitation is severe, this crystal breaks through the separator blocking the positive electrode and the negative electrode, contacts the positive electrode, causes a micro short circuit, increases the terminal voltage difference, and further generates heat and thermal runaway Sometimes. Therefore, in the manufacturing process of the lithium secondary battery, the first charging is usually performed after the assembly is allowed to stand for a certain period of time until the electrolyte sufficiently spreads to each part of the battery.
[0005]
Further, after charging, an aging step of leaving the battery terminals open without performing operations such as charging or discharging the battery is performed, thereby stabilizing the battery. Patent Literature 1 proposes a method in which aging is performed for one week after charging for the first time after assembly, and a defective battery caused by a micro short circuit is identified based on a terminal potential difference before and after aging. Further, Patent Document 2 proposes a method of identifying a defective battery caused by a short circuit from a decay curve of the battery potential after the first charge after assembly using a small current.
[0006]
[Patent Document 1]
JP 2001-228224 A [Patent Document 2]
JP 2000-28690 A
[Problems to be solved by the invention]
However, the above-mentioned method can provide a battery with stable quality, but has a problem that the aging time is long and a charging process for activating the battery is separately required.
SUMMARY OF THE INVENTION The present invention has been made in view of the above problems, and has as its object to provide a secondary battery inspection method that can easily, easily, and accurately determine a defective secondary battery in a shorter time. .
[0008]
[Means for Solving the Problems]
According to the present invention, a positive electrode including a lithium transition metal oxide capable of storing and releasing lithium ions, a negative electrode including a carbon material capable of storing and releasing lithium ions, and a separator including an insulator separating the positive electrode and the negative electrode A method for inspecting a secondary battery composed of an electrolyte containing a lithium salt, wherein a constant current charge is performed in a first constant current charge after assembling the battery and a subsequent constant voltage charge. The charging current value in charging is set to 5 to 20 CmA, and (1) the battery failure is determined by measuring the current value of the battery in constant voltage charging and / or the temperature of the battery in the charging process, or 2) There is provided a method for inspecting a secondary battery, which determines a battery failure by measuring a voltage value of the battery in an aging process after the charging process.
[0009]
BEST MODE FOR CARRYING OUT THE INVENTION
The method for testing a secondary battery according to the present invention essentially measures a battery current value, a battery temperature, and / or a battery voltage value in an initial charging and aging process after assembling the secondary battery. This is a method of determining a battery failure using the following.
In the present invention, as described above, the secondary battery is activated for the first time after assembling the battery to activate the battery, and then subjected to aging to remove a defective battery generated during the battery manufacturing process. Sort out. It is not necessary to perform the full charge for the capacity of the battery in the first charge, and the charge may be terminated with an appropriate charge amount, for example, about 30 to 70%. For example, as shown in FIG. 1, the battery is charged with a constant current value until reaching a certain potential (A in FIG. 1), and after reaching a set arbitrary voltage, as shown in FIG. The charging is performed by a constant current (A) -constant voltage (B) charge in which the charging current is attenuated (B in FIG. 1) so as not to exceed the potential. Aging is performed by leaving the terminals of the battery open and leaving it to stand.
[0010]
In the method of inspecting a secondary battery according to the present invention, it is possible to easily detect abnormality in current value decay after constant-current charging during initial charging, and to cause damage such as excessive heat generation and electrolyte deterioration due to an increase in current value. Is set in consideration of 5 to 20 CmA. Here, CmA represents a current value required to discharge the nominal capacity of the battery in one hour. For example, in the case of a battery of 1500 mAh, 1500 mA corresponds to 1 CmA, and in this battery, 5 CmA is 7500 mA. As described above, by performing the first constant current charging with a relatively large current value of 5 to 20 CmA, the constant current charging can be completed in a very short time. Moreover, it has been confirmed that even when charging is performed with such a relatively large current value, the performance is not degraded and that the battery is sufficiently activated.
[0011]
Therefore, when the constant current charging is performed in the above-described range, and then the current value of the battery in the constant voltage charging is measured, and the current value shows a behavior different from that in FIG. 1, the battery is determined to be defective. be able to. For example, when an internal short circuit occurs in the battery, a phenomenon in which the current suddenly increases is observed as shown in FIG. Therefore, the amount of current decay per unit time during constant-voltage charging, that is, a value obtained by differentiating the decay of the current value with time is calculated, and when the value becomes positive, it is determined that a rise in current has occurred. The battery can be determined to be defective. It should be noted that, not only when the current value rises sharply, but also when the current rises slowly, when the rise and fall alternate, and when a sharp fall is recognized, some abnormality occurs. And it can be determined to be defective. The current value is preferably measured continuously over time, but may be measured only at an arbitrary time interval. In addition, during the charging process, it is not necessary to heat or cool the battery, but when determining whether the battery is defective, an extremely high or low temperature or an excessive temperature change during storage may cause the potential to change. Since an error may occur in the measurement, the temperature may be within a certain temperature range, for example, an arbitrary temperature range of ± 5 ° C. or less, a range of 10 ° C. or less, and more preferably a room temperature ± 5 ° C. or less.
[0012]
Further, in the present invention, it is possible to determine whether the battery is good or defective by measuring the temperature of the battery surface in the charging step only when the behavior is different from the temperature as shown in FIG. That is, as shown in FIG. 3, when performing the first charge, the temperature of the battery usually rises immediately after the start of the charge, reaches the maximum temperature after a predetermined time, for example, about 1 minute, and thereafter, Descends slowly. When an internal short circuit occurs in the battery, for example, as shown in FIG. 4, a phenomenon is observed in which the temperature of the battery surface that has once dropped suddenly rises. Therefore, the amount of increase or decrease in the battery surface temperature per unit time during charging is measured, and the first temperature rise is normal after the start of charging, and the amount of increase or decrease in temperature per unit time becomes positive after the second time. The battery has an abnormality and can be determined to be defective. Further, when the surface temperature of the battery in the charging step becomes higher than or equal to a predetermined temperature, preferably in the second or subsequent temperature rise, the battery may be determined to be defective. The predetermined temperature can be, for example, about 40 ° C., about 45 ° C., about 50 ° C., or about 60 ° C. When the first temperature rise is excessively rapid (for example, when the temperature is higher than the normal temperature by about 10 ° C. or more), the first temperature rise does not occur at an appropriate time within an appropriate range. In this case, even when the temperature drop suddenly appears, or when the temperature rises and falls alternately, it is estimated that some abnormality such as an impedance abnormality has occurred, and it can be determined that the temperature is defective. The temperature of the battery is preferably measured continuously over time, but may be measured only at an arbitrary time interval. Further, the temperature during the charging step is preferably within a certain temperature range, as described above.
[0013]
Further, in the present invention, it is possible to determine the battery failure only by measuring the battery voltage value in the aging step after the charging step. When an internal short circuit occurs in the battery, the voltage change per unit time is larger than that without the internal short circuit. In the present invention, in the first charging step, a relatively large current of 5 CmA or more is passed through the battery, so that the polarization in the battery is inevitably increased, and the potential drop immediately after the end of charging is large. Battery failure can be determined. That is, normally, a potential drop appears as shown in FIG. 5A, but when an internal short circuit occurs in the battery, a large degree of the potential drop appears as shown in FIG. 5B. Therefore, if the degree of the potential drop within a predetermined time after the start of aging is equal to or less than a predetermined value, if the amount of decrease in the potential drop per unit time is equal to or more than a predetermined value, if the potential drop is excessive, When the potential drop does not proceed smoothly or when the battery rises, it is presumed that some abnormality has occurred, and it can be determined to be defective. The aging time is not particularly limited, and is preferably 20 minutes or more, and more preferably 30 minutes or more, in consideration of easy detection of battery failure. The potential drop in this aging is preferably measured continuously over time, but may be measured only at an arbitrary time interval. Further, the temperature during aging is preferably within a certain temperature range, as described above.
[0014]
In the inspection method of the present invention, only the measurement of the current value, the measurement of the temperature, and the measurement of the voltage value described above may be individually performed, or may be performed in combination. Specifically, the combination of current value measurement and temperature measurement, current value measurement and voltage value measurement, temperature measurement and voltage value measurement, and current value measurement and temperature measurement and voltage value measurement are combined. No. With such a combination, it is possible to more accurately determine a battery failure.
[0015]
Specific examples of the battery that can carry out the inspection method of the present invention include a secondary battery including a positive electrode, a negative electrode, a separator, and an electrolyte, particularly a lithium secondary battery. The secondary battery may have any shape such as a cylindrical type, a flat type, and a coin type.
Examples of the positive electrode material include lithium transition metal oxides capable of inserting and extracting lithium ions, but sulfides and transition metal oxides may be used.
Examples of the negative electrode material include a carbon material capable of inserting and extracting lithium ions, and any material such as a metal oxide can be used as long as it can insert and extract lithium.
[0016]
The separator may be any as long as it can insulate the positive electrode and the negative electrode from each other, and an insulator known in the art can be used.
The electrolyte is not particularly limited with respect to its kind, and may be any of a liquid organic solvent, a gel or polymer electrolyte, an inorganic solid electrolyte, and the like.
Hereinafter, the inspection method of the secondary battery of the present invention will be described in detail.
[0017]
First, a lithium secondary battery was prepared according to the following procedure.
Lithium cobaltate LiCoO ₂ was used as a positive electrode active material. LiCoO ₂ was synthesized by a known method. Synthesized LiCoO ₂ is, X-ray diffraction measurement using CuK ray output 2kW from inclusion tube target Cu as an X-ray source, by elemental analysis by valence analysis and ICP cobalt by iodometry, is LiCoO ₂ It was confirmed.
The positive electrode active material thus obtained was pulverized in a mortar, and about 10% by weight of acetylene black as a conductive agent and about 10% by weight of Teflon (registered trademark) resin powder as a binder were mixed. This mixture was dissolved in a solvent such as N-methyl-2-pyrrolidone to form a slurry, which was applied to both surfaces of an aluminum foil by a doctor blade method, dried, and then pressed to produce a positive electrode.
[0018]
Natural graphite powder was used as a negative electrode active material. About 10 wt% of Teflon (registered trademark) resin powder was mixed with the natural graphite powder as a binder. This mixture was dissolved in a solvent such as N-methyl-2-pyrrolidone to form a slurry, which was applied to both surfaces of a copper foil, dried, and then pressed to produce a negative electrode.
A porous polyethylene separator was sandwiched between the positive electrode and the negative electrode produced as described above, and the electrode was wound and inserted into a metal container, where 1 mol / liter of LiPF ₆ was dissolved. 50% by volume of ethylene carbonate and 50% by volume of diethyl carbonate were impregnated as electrolytes. Thereafter, the opening of the metal container was sealed with a resin cap, and a secondary battery was completed. This battery is referred to as battery A.
[0019]
Further, for comparison, a battery in which 1 mg of 200-mesh aluminum powder was sprayed between the separator and the electrode was produced as a pseudo-internal short circuit. This battery is referred to as battery B.
Further, for comparison, a battery was prepared in the same manner as the battery A, except that the electrolyte solution was dissolved in 0.1 mol / liter of LiPF ₆ , in which a high impedance state was generated. This battery is referred to as battery C.
[0020]
Using the three batteries A, B, and C thus manufactured, the first charge was performed in an environment of 25 ° C. while measuring the potential of the battery, the value of the current flowing through the battery, and the surface temperature of the battery. In addition, based on the battery capacity calculated from the weight of the electrode active material of these batteries, constant current charging at 10 CmA was performed for 90 seconds, and current was supplied so that the charging potential at a constant voltage became 4.2 V. did. The charging was terminated 15 minutes after the start of charging, and aging was performed at room temperature for 24 hours while measuring the open-circuit voltage. Table 1 shows the results.
[0021]
[Table 1]

Compared with the normal battery A, two of the batteries B rapidly increased at a point in time when a current that normally attenuates with time during constant voltage charging during the first charging. Further, it was also found that the current value of all of the batteries C greatly decreased compared to the battery A, and that the temperature rise was large. Further, among the batteries B, those which appeared normal in the first charge were also found to have a reduced potential in the aging step.
From these results, it was found that a defective battery can be reliably detected by the inspection method of the present invention.
Further, for each of the three batteries A, B, and C, a constant current charge of 0.2 CmA was performed for 4 hours, and then a constant voltage charge of 4.2 V was performed until the current value reached 0.05 CmA. Then, the initial charge was performed in the same manner as described above, except that the charge was completed. The results are shown in FIG.
[0022]
[Table 2]

From FIG. 6, it is found that only one of the batteries B has abnormal current decay, but the remaining two of the batteries B appear to be normal. Further, with this method, no abnormality of the battery C could be detected.
From a comparison between Tables 1 and 2, it was confirmed that the method for inspecting a secondary battery according to the present invention can accurately determine a defective battery.
[0023]
【The invention's effect】
According to the present invention, in the initial charging step, the charging current value in the constant current charging is set to 5 to 20 CmA. , And the battery failure can be quickly determined. Moreover, by setting the charging current value within the above range and performing the charging, a very simple method of measuring the current value of the battery in constant voltage charging and / or the temperature of the battery in the charging step is expensive. Since a manufacturing device or the like is not required, a battery failure can be easily determined. Therefore, a reduction in manufacturing cost can be realized, and a secondary battery with good performance can be supplied at low cost.
In particular, by combining the measurement of the battery current value in the constant-voltage charging and / or the battery temperature in the charging process and the measurement of the battery voltage value in the aging process, the battery failure can be more accurately and reliably performed. Can be determined, and only a high-performance secondary battery can be easily determined.
[Brief description of the drawings]
FIG. 1 is a diagram showing changes over time in the potential and current of a battery in an initial charging step when the method for testing a secondary battery of the present invention is applied to a normal battery.
FIG. 2 is a diagram showing a temporal change of a battery current in an initial charging step for a battery in which an internal short circuit has occurred.
FIG. 3 is a diagram showing a change over time in the surface temperature of a battery in an initial charging step when the inspection method for a secondary battery of the present invention is applied to a normal battery.
FIG. 4 is a diagram showing a change over time in the surface temperature of a battery in an initial charging step for a battery in which an internal short circuit has occurred.
FIG. 5 is a diagram showing a change over time of the open-circuit voltage of a battery in an aging process when the method of testing a secondary battery according to the present invention is applied to a normal battery and a battery having an internal short circuit.
FIG. 6 is a diagram showing a change over time of a battery current in an initial charging step when a conventional method is applied to a normal battery or the like.

Claims

A positive electrode containing a lithium transition metal oxide capable of inserting and extracting lithium ions, a negative electrode containing a carbon material capable of inserting and extracting lithium ions, a separator made of an insulator separating the positive electrode and the negative electrode, and an electrolyte containing a lithium salt A method for inspecting a secondary battery comprising:
In the charging process including the first constant current charging after the assembly of the battery and the subsequent constant voltage charging, the charging current value in the constant current charging is set to 5 to 20 CmA, and the current of the battery in the constant voltage charging is set. A method for inspecting a secondary battery, comprising determining a battery failure by measuring a value and / or a temperature of the battery in a charging step.

The inspection method for a secondary battery according to claim 1, wherein the constant voltage charging is performed for 3 minutes to 20 minutes.

3. The inspection method for a secondary battery according to claim 1, wherein, in the charging step, the battery is determined to be defective based on an amount of current decay per unit time after the potential reaches a constant potential.

4. The method for inspecting a secondary battery according to claim 3, wherein a battery having a positive attenuation amount is determined to be defective.

The method for inspecting a secondary battery according to any one of claims 1 to 4, wherein the battery in which the temperature of the battery in the charging step has reached 40C or higher is determined to be defective.

The inspection method for a secondary battery according to any one of claims 1 to 5, wherein a battery having a positive value twice or more in temperature change per unit time in the charging step is determined to be defective.

The inspection method for a secondary battery according to any one of claims 1 to 6, further comprising determining a battery failure by measuring a voltage value of the battery in an aging process after the charging process.

A positive electrode containing a lithium transition metal oxide capable of inserting and extracting lithium ions, a negative electrode containing a carbon material capable of inserting and extracting lithium ions, a separator made of an insulator separating the positive electrode and the negative electrode, and an electrolyte containing a lithium salt A method for inspecting a secondary battery comprising:
In the charging process including the first constant current charging after the assembly of the battery and the subsequent constant voltage charging, the charging current value in the constant current charging was set to 5 to 20 CmA, and the battery was subjected to an aging process after the charging process. A method for inspecting a secondary battery, comprising determining a battery failure by measuring a voltage value.