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極片上(shang)的(de)顆(ke)粒或微(wei)(wei)量金屬殘渣(zha)、隔膜上(shang)的(de)微(wei)(wei)小缺(que)陷、電芯在組裝過程中引入的(de)粉(fen)塵等(deng)，都會造成電芯內部微(wei)(wei)短路(lu)。

圖 1 金屬異物導致電池內部短路的原理(li)

金(jin)屬(shu)異物(wu)(wu)(wu)造成(cheng)電(dian)池內部短路(lu)的(de)基本原理有(you)兩種(zhong)(zhong)過程(cheng)，如圖1所示。第(di)一種(zhong)(zhong)情況，尺寸較大的(de)金(jin)屬(shu)顆粒直接刺穿(chuan)隔(ge)膜(mo)，導致正負(fu)(fu)極(ji)(ji)之間短路(lu)，這是物(wu)(wu)(wu)理短路(lu)。第(di)二(er)種(zhong)(zhong)情況，當金(jin)屬(shu)異物(wu)(wu)(wu)混入正極(ji)(ji)后，充電(dian)之后正極(ji)(ji)電(dian)位升(sheng)高，高電(dian)位下金(jin)屬(shu)異物(wu)(wu)(wu)發生溶(rong)解(jie)，通過電(dian)解(jie)液擴(kuo)散，然后負(fu)(fu)極(ji)(ji)低電(dian)位下溶(rong)解(jie)的(de)金(jin)屬(shu)再在負(fu)(fu)極(ji)(ji)表面析(xi)出(chu)堆積(ji)，最終刺穿(chuan)隔(ge)膜(mo)，形成(cheng)短路(lu)，這是化學(xue)溶(rong)解(jie)短路(lu)。電(dian)池工(gong)廠現場最常見的(de)金(jin)屬(shu)異物(wu)(wu)(wu)有(you)Fe、Cu、Zn、Al、Sn、不銹鋼等(deng)。

電池制(zhi)造現場容易發生異(yi)物混入(ru)電池產品的工(gong)藝包括(kuo)電極(ji)漿料(liao)混入(ru)金屬雜質(zhi)；極(ji)片切割(ge)工(gong)序產生切割(ge)毛刺(ci)或(huo)金屬碎屑,；卷繞(rao)工(gong)藝極(ji)片切斷產生毛刺(ci)或(huo)電芯內部(bu)混入(ru)金屬異(yi)物顆(ke)粒；極(ji)耳和殼體(ti)焊(han)接產生金屬屑等等，如圖(tu)2和圖(tu)3所(suo)示。

圖 2 極片(pian)激光切割碎(sui)屑

圖 3 分切毛刺

耐電壓測試檢出金屬異物
絕緣耐電(dian)(dian)壓(ya)測試一(yi)(yi)般采用安(an)規儀，在電(dian)(dian)芯(xin)熱壓(ya)整形時(shi)測試，儀器給電(dian)(dian)芯(xin)施加(jia)一(yi)(yi)個電(dian)(dian)壓(ya)，這個電(dian)(dian)壓(ya)持續一(yi)(yi)段規定(ding)的(de)時(shi)間，然后檢測其電(dian)(dian)流是否保持在規定(ding)的(de)范圍內，判斷電(dian)(dian)芯(xin)正負極內部有無短路。一(yi)(yi)般，施加(jia)電(dian)(dian)壓(ya)如圖4所示：

圖 4 絕(jue)緣耐電(dian)壓測試示意圖

在(zai)測(ce)試(shi)中(zhong)，正負極極片由(you)(you)于(yu)相互(hu)靠近，僅(jin)僅(jin)15-30μm，裸(luo)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)芯(xin)內部會(hui)形成一定(ding)的(de)(de)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)容（雜散電(dian)(dian)(dian)(dian)(dian)(dian)(dian)容），由(you)(you)于(yu)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)容量存在(zai)，測(ce)試(shi)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)壓必須由(you)(you)“零”開始(shi)，緩(huan)慢上升(sheng)，以避免充(chong)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)流(liu)(liu)(liu)過大(da)，電(dian)(dian)(dian)(dian)(dian)(dian)(dian)容量越大(da)所(suo)需的(de)(de)緩(huan)升(sheng)時(shi)(shi)間t1越長(chang)，一次所(suo)能增加的(de)(de)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)壓也(ye)越低(di)。充(chong)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)流(liu)(liu)(liu)過大(da)時(shi)(shi)，一定(ding)會(hui)引起(qi)測(ce)試(shi)器的(de)(de)誤判，使測(ce)試(shi)的(de)(de)結(jie)果不(bu)正確(que)。一旦被(bei)(bei)測(ce)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)芯(xin)的(de)(de)雜散電(dian)(dian)(dian)(dian)(dian)(dian)(dian)容被(bei)(bei)充(chong)滿，只會(hui)剩(sheng)下(xia)實(shi)際的(de)(de)漏電(dian)(dian)(dian)(dian)(dian)(dian)(dian)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)流(liu)(liu)(liu)。由(you)(you)于(yu)直(zhi)流(liu)(liu)(liu)耐壓測(ce)試(shi)會(hui)對(dui)被(bei)(bei)測(ce)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)芯(xin)充(chong)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)，所(suo)以在(zai)測(ce)試(shi)后，一定(ding)要對(dui)被(bei)(bei)測(ce)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)芯(xin)放電(dian)(dian)(dian)(dian)(dian)(dian)(dian)。

老化工藝檢出金屬異物
金屬異物在電芯內部會導致內部微短路，電池自放電，電壓下降。一般老化程序為：三元材料等電池充電到4.0-4.2V，常溫存儲 7d，高溫45℃存儲7d，檢測電池老化前后的電壓差剔除不合格品。將電池在高溫或常溫狀態下開路擱置 7 天或 28 天，通過對電池放電至截止電壓測量其放電電量來判斷其自放電性能，如圖五所示。該方法需要對電池進行長達一個月的擱置檢測，時間周期長，影響因素大，并且長時間占用了較多的設備和場地，測試過程是對人力和財力的大量浪費。

圖 5 老化(hua)不合格品(pin)檢出

總之，電池(chi)(chi)生產(chan)異物管控非常重要，車(che)間潔凈度控制(zhi)好(hao)壞可能直接(jie)影響電池(chi)(chi)安全性。