熱(re)失(shi)(shi)(shi)控是鋰(li)(li)(li)離子(zi)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)池(chi)(chi)(chi)使用中(zhong)zui為嚴重的(de)(de)(de)安(an)全(quan)事故，熱(re)失(shi)(shi)(shi)控往往是由于鋰(li)(li)(li)離子(zi)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)池(chi)(chi)(chi)在(zai)(zai)發(fa)(fa)生了擠壓變形、穿刺(ci)(ci)(ci)或(huo)者(zhe)(zhe)高溫炙烤等(deng)導(dao)(dao)致(zhi)隔(ge)膜被(bei)破壞引(yin)發(fa)(fa)正負極(ji)短路(lu)，或(huo)者(zhe)(zhe)由于電(dian)(dian)(dian)(dian)(dian)(dian)(dian)池(chi)(chi)(chi)外部(bu)短路(lu)，導(dao)(dao)致(zhi)鋰(li)(li)(li)離子(zi)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)池(chi)(chi)(chi)內(nei)部(bu)短時間(jian)內(nei)積累了大量熱(re)量，引(yin)發(fa)(fa)正負極(ji)活性物質和電(dian)(dian)(dian)(dian)(dian)(dian)(dian)解(jie)液等(deng)發(fa)(fa)生分解(jie)，導(dao)(dao)致(zhi)鋰(li)(li)(li)離子(zi)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)池(chi)(chi)(chi)起火和爆炸，嚴重威脅使用者(zhe)(zhe)的(de)(de)(de)生命和財產安(an)全(quan)。因此(ci)(ci)在(zai)(zai)鋰(li)(li)(li)離子(zi)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)池(chi)(chi)(chi)安(an)全(quan)測試中(zhong)一般都會要(yao)(yao)求鋰(li)(li)(li)離子(zi)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)池(chi)(chi)(chi)通過(guo)過(guo)充、過(guo)放、短路(lu)和擠壓、針(zhen)刺(ci)(ci)(ci)等(deng)實驗(yan)，但(dan)是隨著(zhu)動力電(dian)(dian)(dian)(dian)(dian)(dian)(dian)池(chi)(chi)(chi)能量密度和電(dian)(dian)(dian)(dian)(dian)(dian)(dian)池(chi)(chi)(chi)容(rong)量的(de)(de)(de)不斷提升，電(dian)(dian)(dian)(dian)(dian)(dian)(dian)池(chi)(chi)(chi)通過(guo)針(zhen)刺(ci)(ci)(ci)實驗(yan)變得越來越困難，因此(ci)(ci)在(zai)(zai)工(gong)信部(bu)發(fa)(fa)布的(de)(de)(de)《電(dian)(dian)(dian)(dian)(dian)(dian)(dian)動汽車用鋰(li)(li)(li)離子(zi)動力蓄電(dian)(dian)(dian)(dian)(dian)(dian)(dian)池(chi)(chi)(chi)安(an)全(quan)要(yao)(yao)求》中(zhong)規定針(zhen)刺(ci)(ci)(ci)實驗(yan)暫(zan)不執行(xing)(xing)。但(dan)是新版的(de)(de)(de)要(yao)(yao)求只是對針(zhen)刺(ci)(ci)(ci)實驗(yan)暫(zan)不執行(xing)(xing)，后續(xu)是否(fou)會恢復還未可知，如果廠(chang)家實現了大容(rong)量、高能量密度的(de)(de)(de)動力電(dian)(dian)(dian)(dian)(dian)(dian)(dian)池(chi)(chi)(chi)順利通過(guo)針(zhen)刺(ci)(ci)(ci)實驗(yan)，那么必(bi)將(jiang)在(zai)(zai)競爭中(zhong)取得顯著(zhu)的(de)(de)(de)優勢。今天我們就來談(tan)一談(tan)那些給鋰(li)(li)(li)離子(zi)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)池(chi)(chi)(chi)熱(re)失(shi)(shi)(shi)控裝上“剎車”的(de)(de)(de)技(ji)術。

1.電解液阻燃劑

電(dian)(dian)解液(ye)阻燃(ran)(ran)(ran)劑是(shi)一種(zhong)非常有效的(de)(de)減少電(dian)(dian)池(chi)(chi)熱失控(kong)(kong)(kong)風險的(de)(de)方(fang)法，但是(shi)這(zhe)(zhe)些阻燃(ran)(ran)(ran)劑往往會對鋰離(li)(li)子(zi)電(dian)(dian)池(chi)(chi)的(de)(de)電(dian)(dian)化(hua)學性能產生(sheng)嚴重的(de)(de)影(ying)響，因此難(nan)以在(zai)實際中應用(yong)。為了解決這(zhe)(zhe)一問題，美國加州大(da)學圣迭戈分校的(de)(de)Yu Qiao團(tuan)隊【1】采(cai)用(yong)膠囊(nang)封(feng)裝的(de)(de)方(fang)式將(jiang)阻燃(ran)(ran)(ran)劑DBA（二(er)芐胺）儲存(cun)在(zai)微型(xing)膠囊(nang)的(de)(de)內(nei)部(bu)，分散在(zai)電(dian)(dian)解液(ye)中，在(zai)平時(shi)不會對鋰離(li)(li)子(zi)電(dian)(dian)池(chi)(chi)的(de)(de)電(dian)(dian)性能產生(sheng)影(ying)響，但是(shi)當電(dian)(dian)池(chi)(chi)受到擠壓等外(wai)力破壞時(shi)，這(zhe)(zhe)些膠囊(nang)中的(de)(de)阻燃(ran)(ran)(ran)劑就會釋放出來，對電(dian)(dian)池(chi)(chi)進行“毒(du)化(hua)”引起(qi)電(dian)(dian)池(chi)(chi)失效，從而避免熱失控(kong)(kong)(kong)的(de)(de)發生(sheng)。2018年Yu Qiao團(tuan)隊【2】再次利用(yong)了上(shang)述技術，采(cai)用(yong)了乙二(er)醇和乙二(er)胺作為阻燃(ran)(ran)(ran)劑，封(feng)裝后裝入(ru)鋰離(li)(li)子(zi)電(dian)(dian)池(chi)(chi)內(nei)部(bu)使(shi)得鋰離(li)(li)子(zi)電(dian)(dian)池(chi)(chi)在(zai)針刺實驗(yan)中zui高溫(wen)度下降(jiang)了70%，顯著(zhu)降(jiang)低了鋰離(li)(li)子(zi)電(dian)(dian)池(chi)(chi)熱失控(kong)(kong)(kong)的(de)(de)風險。

上(shang)面提(ti)到(dao)的(de)(de)方法都是(shi)自毀式的(de)(de)，也就是(shi)說該(gai)阻(zu)(zu)燃(ran)劑一(yi)旦發生(sheng)(sheng)作用，整(zheng)個鋰(li)(li)離(li)(li)(li)子(zi)(zi)電(dian)(dian)池(chi)就要(yao)報廢(fei)了，而日本東京大學的(de)(de)Atsuo Yamada團隊【3】開發了一(yi)種不會影(ying)響(xiang)鋰(li)(li)離(li)(li)(li)子(zi)(zi)電(dian)(dian)池(chi)性能的(de)(de)阻(zu)(zu)燃(ran)電(dian)(dian)解液(ye)(ye)，該(gai)電(dian)(dian)解液(ye)(ye)采用了高(gao)(gao)濃度的(de)(de)NaN(SO2F)2(NaFSA) or LiN(SO2F)2 (LiFSA)作為鋰(li)(li)鹽，同(tong)時向其中添加了常見的(de)(de)阻(zu)(zu)燃(ran)劑磷酸*酯TMP，顯著(zhu)提(ti)高(gao)(gao)了鋰(li)(li)離(li)(li)(li)子(zi)(zi)電(dian)(dian)池(chi)的(de)(de)熱穩定性，更(geng)厲害的(de)(de)是(shi)阻(zu)(zu)燃(ran)劑的(de)(de)添加并沒(mei)有對(dui)鋰(li)(li)離(li)(li)(li)子(zi)(zi)電(dian)(dian)池(chi)循(xun)(xun)環(huan)性能產生(sheng)(sheng)影(ying)響(xiang)，采用該(gai)電(dian)(dian)解液(ye)(ye)的(de)(de)電(dian)(dian)池(chi)能夠穩定循(xun)(xun)環(huan)1000次以上(shang)（C/5循(xun)(xun)環(huan)1200次，容量保持率95%）。

通過添加劑使(shi)得鋰離(li)子電(dian)(dian)池(chi)具有(you)阻(zu)燃(ran)特性(xing)是(shi)避免鋰離(li)子電(dian)(dian)池(chi)發(fa)生(sheng)熱失(shi)控的(de)(de)其中(zhong)一種(zhong)途徑，也有(you)人另辟(pi)蹊徑，試圖從根源上避免外力導(dao)致的(de)(de)鋰離(li)子電(dian)(dian)池(chi)內短路的(de)(de)發(fa)生(sheng)，從而達(da)到(dao)釜(fu)底(di)抽薪的(de)(de)目的(de)(de)，*杜(du)絕(jue)熱失(shi)控的(de)(de)發(fa)生(sheng)。針對動力電(dian)(dian)池(chi)在(zai)使(shi)用中(zhong)可能(neng)面臨(lin)暴力沖擊的(de)(de)情(qing)況，美國橡樹嶺國家實驗室的(de)(de)Gabriel M. Veith設(she)計了(le)一種(zhong)具有(you)剪切增稠(chou)特性(xing)的(de)(de)電(dian)(dian)解(jie)(jie)液(ye)(ye)【4】，該電(dian)(dian)解(jie)(jie)液(ye)(ye)利(li)用了(le)非牛頓流體的(de)(de)特性(xing)，在(zai)正常(chang)狀(zhuang)態(tai)下，電(dian)(dian)解(jie)(jie)液(ye)(ye)呈(cheng)現的(de)(de)是(shi)液(ye)(ye)體狀(zhuang)態(tai)，但是(shi)在(zai)遭遇(yu)突(tu)然的(de)(de)沖擊時則會呈(cheng)現固體狀(zhuang)態(tai)，變得異常(chang)堅固，甚至能(neng)夠(gou)達(da)到(dao)防彈的(de)(de)效(xiao)果，從根源上避免了(le)在(zai)動力電(dian)(dian)池(chi)發(fa)生(sheng)碰(peng)撞(zhuang)時電(dian)(dian)池(chi)內短路導(dao)致熱失(shi)控的(de)(de)風(feng)險。

2.電池結構

接下我們來從電(dian)池(chi)(chi)單體層面上(shang)看看如何給熱(re)(re)(re)失控(kong)踩下剎車，目前(qian)鋰離(li)子(zi)電(dian)池(chi)(chi)在結(jie)構設(she)計中(zhong)都對熱(re)(re)(re)失控(kong)的(de)問(wen)題進行(xing)了(le)考(kao)慮，例如在18650電(dian)池(chi)(chi)的(de)上(shang)蓋中(zhong)一般都會有泄壓閥，在熱(re)(re)(re)失控(kong)時能夠及時將電(dian)池(chi)(chi)內部(bu)過高(gao)的(de)壓力進行(xing)釋放，其次電(dian)池(chi)(chi)上(shang)蓋中(zhong)會有正溫度(du)系數材料PTC，在熱(re)(re)(re)失控(kong)溫度(du)上(shang)升時PTC材料的(de)電(dian)阻顯著(zhu)增大，以減少(shao)電(dian)流減少(shao)產熱(re)(re)(re)。此外(wai)，在單體電(dian)池(chi)(chi)結(jie)構設(she)計時還需要考(kao)慮正負極之間的(de)防短路(lu)設(she)計，避(bi)免因(yin)為(wei)誤操(cao)作、金屬(shu)多(duo)余物等因(yin)素導(dao)致電(dian)池(chi)(chi)發生外(wai)短路(lu)，引起安全事故(gu)。

其(qi)次(ci)在電(dian)芯(xin)設計時，需要(yao)采(cai)用(yong)更加安全的(de)(de)(de)隔(ge)膜，例如在高溫下自(zi)動閉孔的(de)(de)(de)三層(ceng)復(fu)合隔(ge)膜，但(dan)是近年來(lai)隨著電(dian)池能量密(mi)度的(de)(de)(de)不(bu)斷(duan)提升、隔(ge)膜薄型化的(de)(de)(de)趨勢下三層(ceng)復(fu)合隔(ge)膜已經逐漸被淘汰，取而代(dai)之的(de)(de)(de)陶(tao)瓷涂(tu)層(ceng)隔(ge)膜，陶(tao)瓷涂(tu)層(ceng)能夠對隔(ge)膜起到支撐作用(yong)，減少隔(ge)膜在高溫下的(de)(de)(de)收(shou)縮，提高鋰離子(zi)電(dian)池的(de)(de)(de)熱(re)穩定(ding)性，減少鋰離子(zi)電(dian)池發生熱(re)失控的(de)(de)(de)風險。

3.電池(chi)組熱(re)安全(quan)設計

動力電(dian)(dian)池(chi)(chi)在(zai)使用中往往都是(shi)由數十只、數百只甚至是(shi)數千只電(dian)(dian)池(chi)(chi)通過串并聯組成，例如(ru)特斯拉的(de)(de)(de)(de)(de)Model S的(de)(de)(de)(de)(de)電(dian)(dian)池(chi)(chi)組中就(jiu)由多(duo)達7000只以上的(de)(de)(de)(de)(de)18650組成，如(ru)果(guo)其中的(de)(de)(de)(de)(de)一(yi)只電(dian)(dian)池(chi)(chi)發(fa)生熱失(shi)控(kong)，就(jiu)可能會在(zai)電(dian)(dian)池(chi)(chi)組內蔓延(yan)，引(yin)(yin)起(qi)嚴重的(de)(de)(de)(de)(de)后(hou)果(guo)。例如(ru)，2013年1月發(fa)生在(zai)美國波(bo)士頓的(de)(de)(de)(de)(de)一(yi)架日本航(hang)空(kong)公司(si)的(de)(de)(de)(de)(de)波(bo)音787客機鋰(li)離子電(dian)(dian)池(chi)(chi)起(qi)火事(shi)件，根據美國國家運輸安全委(wei)員(yuan)會的(de)(de)(de)(de)(de)調查(cha)，就(jiu)是(shi)由于電(dian)(dian)池(chi)(chi)組中的(de)(de)(de)(de)(de)一(yi)只7h方形鋰(li)離子電(dian)(dian)池(chi)(chi)發(fa)生熱失(shi)控(kong)后(hou)引(yin)(yin)發(fa)了相鄰的(de)(de)(de)(de)(de)電(dian)(dian)池(chi)(chi)熱失(shi)控(kong)，這(zhe)次事(shi)件后(hou)波(bo)音公司(si)要(yao)求(qiu)在(zai)所有(you)的(de)(de)(de)(de)(de)電(dian)(dian)池(chi)(chi)組上都要(yao)增加防止(zhi)熱失(shi)控(kong)擴散的(de)(de)(de)(de)(de)措施。

為了避免熱(re)失(shi)(shi)(shi)控在(zai)鋰離(li)(li)子(zi)電(dian)(dian)(dian)(dian)池(chi)(chi)(chi)(chi)(chi)(chi)內(nei)部(bu)蔓延，美國Allcell Technology公司開(kai)發(fa)了一款(kuan)基于相變材(cai)(cai)料(liao)(liao)(liao)(liao)的(de)(de)(de)鋰離(li)(li)子(zi)電(dian)(dian)(dian)(dian)池(chi)(chi)(chi)(chi)(chi)(chi)熱(re)失(shi)(shi)(shi)控隔離(li)(li)材(cai)(cai)料(liao)(liao)(liao)(liao)PCC【5】。PCC材(cai)(cai)料(liao)(liao)(liao)(liao)填充在(zai)單體(ti)鋰離(li)(li)子(zi)電(dian)(dian)(dian)(dian)池(chi)(chi)(chi)(chi)(chi)(chi)之間，在(zai)鋰離(li)(li)子(zi)電(dian)(dian)(dian)(dian)池(chi)(chi)(chi)(chi)(chi)(chi)組(zu)正常工作(zuo)的(de)(de)(de)情況下，電(dian)(dian)(dian)(dian)池(chi)(chi)(chi)(chi)(chi)(chi)組(zu)產生的(de)(de)(de)熱(re)量可以通過PCC材(cai)(cai)料(liao)(liao)(liao)(liao)快(kuai)速傳(chuan)遞到電(dian)(dian)(dian)(dian)池(chi)(chi)(chi)(chi)(chi)(chi)組(zu)外，在(zai)鋰離(li)(li)子(zi)電(dian)(dian)(dian)(dian)池(chi)(chi)(chi)(chi)(chi)(chi)發(fa)生熱(re)失(shi)(shi)(shi)控時(shi)，PCC材(cai)(cai)料(liao)(liao)(liao)(liao)可以通過其內(nei)部(bu)的(de)(de)(de)石蠟(la)材(cai)(cai)料(liao)(liao)(liao)(liao)熔(rong)化吸(xi)收大量的(de)(de)(de)熱(re)量，阻止(zhi)電(dian)(dian)(dian)(dian)池(chi)(chi)(chi)(chi)(chi)(chi)溫度進一步上升，從而(er)避免熱(re)失(shi)(shi)(shi)控在(zai)電(dian)(dian)(dian)(dian)池(chi)(chi)(chi)(chi)(chi)(chi)組(zu)內(nei)部(bu)擴散。在(zai)針刺實驗中(zhong)，一個由18650電(dian)(dian)(dian)(dian)池(chi)(chi)(chi)(chi)(chi)(chi)組(zu)成的(de)(de)(de)4并10串的(de)(de)(de)電(dian)(dian)(dian)(dian)池(chi)(chi)(chi)(chi)(chi)(chi)組(zu)，沒有使(shi)用(yong)PCC材(cai)(cai)料(liao)(liao)(liao)(liao)時(shi)，一只電(dian)(dian)(dian)(dian)池(chi)(chi)(chi)(chi)(chi)(chi)熱(re)失(shi)(shi)(shi)控zui終引發(fa)了電(dian)(dian)(dian)(dian)池(chi)(chi)(chi)(chi)(chi)(chi)組(zu)中(zhong)20只電(dian)(dian)(dian)(dian)池(chi)(chi)(chi)(chi)(chi)(chi)發(fa)生熱(re)失(shi)(shi)(shi)控，而(er)采用(yong)PCC材(cai)(cai)料(liao)(liao)(liao)(liao)的(de)(de)(de)電(dian)(dian)(dian)(dian)池(chi)(chi)(chi)(chi)(chi)(chi)組(zu)中(zhong)，一只電(dian)(dian)(dian)(dian)池(chi)(chi)(chi)(chi)(chi)(chi)熱(re)失(shi)(shi)(shi)控并未引發(fa)其他電(dian)(dian)(dian)(dian)池(chi)(chi)(chi)(chi)(chi)(chi)組(zu)熱(re)失(shi)(shi)(shi)控。

鋰(li)離子(zi)電(dian)池熱(re)(re)失(shi)(shi)控是我(wo)們(men)zui不愿意看到、極力避(bi)免的(de)鋰(li)離子(zi)電(dian)池安全(quan)事故，提(ti)高(gao)鋰(li)離子(zi)電(dian)池的(de)安全(quan)性(xing)(xing)、避(bi)免熱(re)(re)失(shi)(shi)控的(de)發生(sheng)需要從電(dian)池配方設(she)計、結(jie)構(gou)設(she)計和(he)電(dian)池組的(de)熱(re)(re)管理設(she)計上多管齊下，共同提(ti)高(gao)鋰(li)離子(zi)電(dian)池熱(re)(re)穩定(ding)性(xing)(xing)，減少熱(re)(re)失(shi)(shi)控發生(sheng)的(de)可能性(xing)(xing)。