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　　一、鋰離子電池容量衰減現象分析

　　正負極、電解液及隔膜是組成鋰離子電池的重要成分。鋰離子電池的正負極分別發生鋰的嵌入脫出反應，其正負極的嵌鋰量成為影響鋰離子電池容量的主要因素。因此，必須維持鋰離子電池正負極容量的平衡性，才能確保電池具備最佳性能。

　　通(tong)常來說，鋰離(li)子(zi)電(dian)(dian)池(chi)(chi)常用(yong)有(you)機溶劑和電(dian)(dian)解質(zhi)(zhi)(鋰鹽)組成的(de)電(dian)(dian)解質(zhi)(zhi)溶液(ye)，該電(dian)(dian)解質(zhi)(zhi)溶液(ye)應(ying)當具備足(zu)夠(gou)的(de)導(dao)電(dian)(dian)性、穩定性，并且能(neng)夠(gou)與(yu)電(dian)(dian)極(ji)(ji)實現(xian)相容。對(dui)于隔(ge)膜來說，其(qi)性能(neng)是決定電(dian)(dian)池(chi)(chi)內阻及界面結構(gou)的(de)主要因素，對(dui)電(dian)(dian)池(chi)(chi)容量衰(shuai)減變化情(qing)況有(you)著(zhu)直接的(de)影響(xiang)。若(ruo)隔(ge)膜的(de)質(zhi)(zhi)量和性能(neng)優越，將會顯著(zhu)提升鋰離(li)子(zi)電(dian)(dian)池(chi)(chi)的(de)容量和綜合(he)性能(neng)。一般情(qing)況下，隔(ge)膜在電(dian)(dian)池(chi)(chi)中主要起著(zhu)分隔(ge)電(dian)(dian)池(chi)(chi)正極(ji)(ji)和電(dian)(dian)池(chi)(chi)負(fu)極(ji)(ji)的(de)作用(yong)，避免正負(fu)極(ji)(ji)發生(sheng)接觸而導(dao)致電(dian)(dian)池(chi)(chi)短路，同時還能(neng)夠(gou)放行電(dian)(dian)解質(zhi)(zhi)離(li)子(zi)，以充分發揮(hui)電(dian)(dian)池(chi)(chi)效用(yong)。

　　鋰電池中的化學反應不僅僅包括鋰離子嵌入和脫出過程中的氧化還原反應，還包括諸如負極表面SEI膜的生產和破壞、電解液的分解以及活性材料的結構變化和溶解等副反應，這些副反應都是造成鋰離子電池容量衰減的原因。

　　電池(chi)循環過程(cheng)中發生(sheng)容(rong)量衰減和損失(shi)是必然現(xian)象(xiang)，因此，為了提高電池(chi)容(rong)量和性能，國(guo)內外各領域的(de)學者充分研(yan)究(jiu)了鋰(li)(li)電池(chi)容(rong)量損失(shi)的(de)機理。目前，可知(zhi)引起鋰(li)(li)離子(zi)電池(chi)容(rong)量衰減的(de)主要因素包(bao)括正負極(ji)(ji)(ji)表(biao)面(mian)形成SEI鈍化(hua)膜、金屬鋰(li)(li)沉積、電極(ji)(ji)(ji)活性材料的(de)溶(rong)解、陰陽(yang)極(ji)(ji)(ji)氧(yang)化(hua)還原反(fan)應或副反(fan)應的(de)發生(sheng)、結構變化(hua)及(ji)相變化(hua)等(deng)。當前，對鋰(li)(li)離子(zi)電池(chi)容(rong)量衰減變化(hua)及(ji)其(qi)原因仍(reng)然在不斷研(yan)究(jiu)的(de)過程(cheng)中。

　　二、過充電

　　2.1 負極過充反(fan)應(ying)

　　能夠作(zuo)為(wei)鋰離(li)子電(dian)池(chi)負(fu)極(ji)的活性材(cai)(cai)(cai)料(liao)種類(lei)較(jiao)多，以碳系負(fu)極(ji)材(cai)(cai)(cai)料(liao)，硅基、錫基負(fu)極(ji)材(cai)(cai)(cai)料(liao)、鈦酸鋰負(fu)極(ji)材(cai)(cai)(cai)料(liao)等為(wei)主要材(cai)(cai)(cai)料(liao)。不(bu)同(tong)(tong)類(lei)型的碳材(cai)(cai)(cai)料(liao)具有(you)(you)不(bu)同(tong)(tong)的電(dian)化(hua)學性能，其中，石墨(mo)具有(you)(you)導電(dian)性能較(jiao)高(gao)、層狀結(jie)構優(you)良、結(jie)晶(jing)度高(gao)的優(you)勢(shi)，較(jiao)為(wei)適合鋰的嵌(qian)入(ru)和(he)脫出，同(tong)(tong)時石墨(mo)材(cai)(cai)(cai)料(liao)價格實惠、存量較(jiao)多，因(yin)此，應用較(jiao)為(wei)廣泛。

　　當(dang)鋰離子(zi)(zi)電(dian)(dian)池(chi)(chi)首次充放電(dian)(dian)時，溶劑分子(zi)(zi)會(hui)在(zai)石墨表面發生(sheng)分解反應，并形成名為(wei)SEI的(de)鈍化膜，這一反應會(hui)引發電(dian)(dian)池(chi)(chi)容量損失，并且屬(shu)于(yu)不可(ke)逆(ni)的(de)過程(cheng)。鋰離子(zi)(zi)電(dian)(dian)池(chi)(chi)過充電(dian)(dian)過程(cheng)中，負(fu)極(ji)表面會(hui)發生(sheng)金屬(shu)鋰沉積現(xian)象，該情況(kuang)容易發生(sheng)在(zai)正(zheng)極(ji)活性(xing)材(cai)料相對于(yu)負(fu)極(ji)活性(xing)材(cai)料過量的(de)情況(kuang)下(xia)。同時，若在(zai)高倍率條件下(xia)，也有可(ke)能產生(sheng)金屬(shu)鋰沉積現(xian)象。

　　通常來說，形成(cheng)金(jin)(jin)屬(shu)鋰(li)導(dao)致(zhi)鋰(li)電(dian)池(chi)(chi)容(rong)量(liang)衰(shuai)減變化(hua)(hua)(hua)的原(yuan)因主要包括以下方面(mian)：第(di)一，導(dao)致(zhi)電(dian)池(chi)(chi)中(zhong)可循(xun)(xun)環鋰(li)量(liang)降低;第(di)二，金(jin)(jin)屬(shu)鋰(li)與電(dian)解(jie)質或溶劑發(fa)生副(fu)反應，形成(cheng)其他副(fu)產物;第(di)三，金(jin)(jin)屬(shu)鋰(li)主要沉(chen)積在(zai)負(fu)極(ji)(ji)和隔(ge)膜(mo)(mo)之間(jian)，從而造成(cheng)隔(ge)膜(mo)(mo)孔(kong)隙堵(du)塞，導(dao)致(zhi)電(dian)池(chi)(chi)內阻增加。石墨(mo)(mo)材料的不(bu)同，鋰(li)離子電(dian)池(chi)(chi)容(rong)量(liang)衰(shuai)減變化(hua)(hua)(hua)的影響機理(li)也存在(zai)一定差異。天(tian)然(ran)石墨(mo)(mo)的比表面(mian)積較(jiao)高，因此，發(fa)生自放電(dian)反應將(jiang)會導(dao)致(zhi)鋰(li)電(dian)池(chi)(chi)容(rong)量(liang)損失(shi)，并且天(tian)然(ran)石墨(mo)(mo)作為電(dian)池(chi)(chi)負(fu)極(ji)(ji)，其電(dian)化(hua)(hua)(hua)學(xue)反應阻抗(kang)也比人造石墨(mo)(mo)要高。另外，循(xun)(xun)環過程(cheng)(cheng)中(zhong)負(fu)極(ji)(ji)層(ceng)狀(zhuang)結構解(jie)離、極(ji)(ji)片(pian)制作過程(cheng)(cheng)中(zhong)導(dao)電(dian)劑分散情(qing)況、儲存過程(cheng)(cheng)中(zhong)電(dian)化(hua)(hua)(hua)學(xue)反應阻抗(kang)的增加等因素，都是導(dao)致(zhi)鋰(li)電(dian)池(chi)(chi)容(rong)量(liang)損失(shi)的重要因素。

　　2.2 正極過充反應

　　正極(ji)過充電主要在正極(ji)材(cai)料占比過低的(de)情況下發(fa)生，導致(zhi)電極(ji)間容(rong)量失衡(heng)，致(zhi)使(shi)鋰電池(chi)容(rong)量發(fa)生不可(ke)逆的(de)損失，并且正極(ji)材(cai)料和電解液分解出來的(de)氧氣及可(ke)燃(ran)氣體的(de)并存和不斷積累，可(ke)能會(hui)給鋰電池(chi)的(de)使(shi)用帶(dai)來安(an)全隱患。

　　2.3 電解液在(zai)高電壓下發生反(fan)應

　　若鋰(li)(li)(li)電(dian)(dian)(dian)池充(chong)(chong)電(dian)(dian)(dian)電(dian)(dian)(dian)壓過高，將會導致(zhi)(zhi)電(dian)(dian)(dian)解(jie)(jie)(jie)液發(fa)生(sheng)氧化反(fan)(fan)應，并生(sheng)成部分副產物，將電(dian)(dian)(dian)極微孔(kong)堵塞，阻(zu)礙(ai)了(le)鋰(li)(li)(li)離子的(de)遷(qian)移，從而(er)造成循環(huan)容(rong)(rong)量(liang)衰減(jian)變化。電(dian)(dian)(dian)解(jie)(jie)(jie)質濃(nong)度(du)和電(dian)(dian)(dian)解(jie)(jie)(jie)液的(de)穩(wen)(wen)定性的(de)變化趨勢成反(fan)(fan)比，電(dian)(dian)(dian)解(jie)(jie)(jie)質濃(nong)度(du)越高，電(dian)(dian)(dian)解(jie)(jie)(jie)液穩(wen)(wen)定性越低(di)，進而(er)對鋰(li)(li)(li)離子電(dian)(dian)(dian)池容(rong)(rong)量(liang)產生(sheng)影響(xiang)。在充(chong)(chong)電(dian)(dian)(dian)過程(cheng)中，電(dian)(dian)(dian)解(jie)(jie)(jie)液會發(fa)生(sheng)一定消(xiao)耗(hao)，因(yin)此，需要(yao)在裝配時進行補(bu)充(chong)(chong)，導致(zhi)(zhi)電(dian)(dian)(dian)池活性材(cai)料減(jian)少，并影響(xiang)電(dian)(dian)(dian)池初始容(rong)(rong)量(liang)。

　　三、電解液分解

　　電(dian)(dian)(dian)(dian)解(jie)液(ye)(ye)包括電(dian)(dian)(dian)(dian)解(jie)質(zhi)(zhi)(zhi)、溶劑(ji)和(he)添加劑(ji)，其性(xing)質(zhi)(zhi)(zhi)會對(dui)電(dian)(dian)(dian)(dian)池(chi)(chi)的(de)(de)(de)使用年(nian)限(xian)、比(bi)容(rong)(rong)量、倍率充放電(dian)(dian)(dian)(dian)性(xing)能(neng)和(he)安全性(xing)能(neng)等產(chan)(chan)生(sheng)(sheng)影(ying)(ying)響。電(dian)(dian)(dian)(dian)解(jie)液(ye)(ye)中(zhong)(zhong)電(dian)(dian)(dian)(dian)解(jie)質(zhi)(zhi)(zhi)和(he)溶劑(ji)的(de)(de)(de)分(fen)解(jie)都會引起電(dian)(dian)(dian)(dian)池(chi)(chi)容(rong)(rong)量發(fa)(fa)(fa)生(sheng)(sheng)損(sun)失。在(zai)首次充放電(dian)(dian)(dian)(dian)時(shi)(shi)，溶劑(ji)等物質(zhi)(zhi)(zhi)在(zai)負(fu)極(ji)(ji)表面(mian)生(sheng)(sheng)成SEI膜會形成不可(ke)逆的(de)(de)(de)容(rong)(rong)量損(sun)失，但(dan)這是必然情況(kuang)(kuang)。若電(dian)(dian)(dian)(dian)解(jie)液(ye)(ye)中(zhong)(zhong)存在(zai)水或氟化氫(qing)等雜質(zhi)(zhi)(zhi)時(shi)(shi)，可(ke)能(neng)會使電(dian)(dian)(dian)(dian)解(jie)質(zhi)(zhi)(zhi)LiPF6在(zai)溫度較高(gao)的(de)(de)(de)情況(kuang)(kuang)下發(fa)(fa)(fa)生(sheng)(sheng)分(fen)解(jie)，并且生(sheng)(sheng)成的(de)(de)(de)產(chan)(chan)物與(yu)正(zheng)極(ji)(ji)材料反應(ying)(ying)，導致(zhi)電(dian)(dian)(dian)(dian)池(chi)(chi)容(rong)(rong)量受到(dao)影(ying)(ying)響。同時(shi)(shi)，部分(fen)產(chan)(chan)物還(huan)會與(yu)溶劑(ji)發(fa)(fa)(fa)生(sheng)(sheng)反應(ying)(ying)，并對(dui)負(fu)極(ji)(ji)表面(mian)的(de)(de)(de) SEI膜的(de)(de)(de)穩定性(xing)造(zao)成影(ying)(ying)響，會造(zao)成鋰離子電(dian)(dian)(dian)(dian)池(chi)(chi)性(xing)能(neng)衰減。除此之外(wai)，若電(dian)(dian)(dian)(dian)解(jie)液(ye)(ye)分(fen)解(jie)的(de)(de)(de)產(chan)(chan)物不與(yu)電(dian)(dian)(dian)(dian)解(jie)液(ye)(ye)相容(rong)(rong)，將會在(zai)遷移過(guo)程中(zhong)(zhong)阻塞正(zheng)極(ji)(ji)孔隙，從而導致(zhi)電(dian)(dian)(dian)(dian)池(chi)(chi)容(rong)(rong)量衰減。總的(de)(de)(de)來說(shuo)，電(dian)(dian)(dian)(dian)解(jie)液(ye)(ye)和(he)電(dian)(dian)(dian)(dian)池(chi)(chi)的(de)(de)(de)正(zheng)負(fu)極(ji)(ji)之間副(fu)(fu)反應(ying)(ying)的(de)(de)(de)發(fa)(fa)(fa)生(sheng)(sheng)，以(yi)及產(chan)(chan)生(sheng)(sheng)的(de)(de)(de)副(fu)(fu)產(chan)(chan)物，都是造(zao)成電(dian)(dian)(dian)(dian)池(chi)(chi)容(rong)(rong)量衰減的(de)(de)(de)主要因素。

　　四、自放電

　　鋰(li)(li)離子(zi)(zi)電(dian)(dian)池在一(yi)般情況下(xia)，會(hui)(hui)(hui)發生(sheng)容(rong)量(liang)損(sun)(sun)耗現(xian)象，這一(yi)過程(cheng)被稱(cheng)為自(zi)放(fang)電(dian)(dian)，分(fen)為可(ke)逆容(rong)量(liang)損(sun)(sun)失(shi)(shi)和(he)不可(ke)逆容(rong)量(liang)損(sun)(sun)失(shi)(shi)。溶(rong)劑(ji)氧化速(su)率對(dui)自(zi)放(fang)電(dian)(dian)速(su)率產(chan)生(sheng)直(zhi)接影響，正負(fu)極活性材料(liao)可(ke)能在充電(dian)(dian)過程(cheng)中和(he)溶(rong)質發生(sheng)反應(ying)，導致鋰(li)(li)離子(zi)(zi)遷(qian)移(yi)完成容(rong)量(liang)失(shi)(shi)衡及不可(ke)逆衰(shuai)減，因此，可(ke)以看出減少活性材料(liao)表(biao)面積(ji)可(ke)以降低容(rong)量(liang)損(sun)(sun)失(shi)(shi)速(su)率，且(qie)溶(rong)劑(ji)的分(fen)解會(hui)(hui)(hui)影響電(dian)(dian)池貯存壽命(ming)。另外，隔膜漏(lou)電(dian)(dian)也會(hui)(hui)(hui)導致容(rong)量(liang)損(sun)(sun)失(shi)(shi)，但這種可(ke)能性較低。自(zi)放(fang)電(dian)(dian)現(xian)象若長期存在，會(hui)(hui)(hui)導致金屬(shu)鋰(li)(li)沉(chen)積(ji)，并進(jin)一(yi)步導致正負(fu)極容(rong)量(liang)的衰(shuai)減變化。

　　五、電極不穩定性

　　充(chong)電(dian)(dian)過(guo)程(cheng)中(zhong)，電(dian)(dian)池(chi)(chi)正極(ji)的活(huo)性(xing)材料不穩(wen)定，會導(dao)致其(qi)與(yu)電(dian)(dian)解質發生反(fan)應(ying)，并影(ying)響電(dian)(dian)池(chi)(chi)容(rong)量(liang)。其(qi)中(zhong)，正極(ji)材料結構(gou)缺陷、充(chong)電(dian)(dian)電(dian)(dian)勢過(guo)高、炭黑含量(liang)都是(shi)影(ying)響電(dian)(dian)池(chi)(chi)容(rong)量(liang)的主要(yao)因素。

　　六、總結

　　綜上所述，鋰離子電池屬于具有良好性能、污染較低的“綠色電池”，被廣泛應用于我國各行各業之中，但鋰離子電池的使用壽命會受到正極材料結構、炭黑含量、電極穩定性、自放電、電池內阻增加、電解質分解等因素的影響，導致電池容量衰減過快。