隨著鋰(li)離(li)子電(dian)池(chi)(chi)在手機(ji)、電(dian)腦、汽車(che)、儲能等領域的(de)廣泛應(ying)用(yong)(yong)，人們對(dui)電(dian)池(chi)(chi)的(de)安全性(xing)(xing)(xing)、能量密(mi)度(du)(du)和功率(lv)密(mi)度(du)(du)性(xing)(xing)(xing)能的(de)需求(qiu)(qiu)越來越高。為了(le)提高鋰(li)離(li)子電(dian)池(chi)(chi)的(de)能量密(mi)度(du)(du)和功率(lv)密(mi)度(du)(du)，一些鋰(li)電(dian)新材料和新技術亟待開發(fa)。鋰(li)離(li)子電(dian)池(chi)(chi)生(sheng)產(chan)由(you)多個工(gong)藝過程組(zu)成，為了(le)得到安全可(ke)靠性(xing)(xing)(xing)高且性(xing)(xing)(xing)能一致(zhi)性(xing)(xing)(xing)好(hao)的(de)電(dian)池(chi)(chi)，需要對(dui)每一個生(sheng)產(chan)工(gong)藝制定嚴格的(de)監控(kong)措施(shi)，確(que)保不良品不流入市(shi)場。為了(le)節約生(sheng)產(chan)成本，提升生(sheng)產(chan)效率(lv)，電(dian)池(chi)(chi)企業更加希望能在前(qian)(qian)工(gong)序(xu)(xu)(xu)階段就能快速識別(bie)出(chu)異常，及(ji)時做(zuo)出(chu)相應(ying)改善措施(shi)。目前(qian)(qian)大多數電(dian)池(chi)(chi)企業在前(qian)(qian)工(gong)序(xu)(xu)(xu)常用(yong)(yong)的(de)監控(kong)方法主要包括監控(kong)以下參數：漿料黏度(du)(du)、漿料固含量、涂布質量、壓實密(mi)度(du)(du)，這些方法雖然可(ke)以一定程度(du)(du)上監控(kong)出(chu)工(gong)序(xu)(xu)(xu)波動，但(dan)還不足(zu)(zu)以滿足(zu)(zu)監控(kong)成品電(dian)芯一致(zhi)性(xing)(xing)(xing)的(de)要求(qiu)(qiu)。極(ji)片(pian)是(shi)電(dian)(dian)池前端(duan)工(gong)序的(de)(de)(de)(de)(de)(de)一個重要(yao)輸出，極(ji)片(pian)的(de)(de)(de)(de)(de)(de)電(dian)(dian)子(zi)電(dian)(dian)阻（電(dian)(dian)導(dao)率)影(ying)響全電(dian)(dian)池的(de)(de)(de)(de)(de)(de)功率性(xing)、可靠性(xing)及安(an)全性(xing)，同時(shi)它又與攪(jiao)拌、涂(tu)布和(he)輥壓工(gong)序息(xi)息(xi)相關，因此，測(ce)量極(ji)片(pian)電(dian)(dian)阻的(de)(de)(de)(de)(de)(de)變(bian)化可以(yi)(yi)較好地評價極(ji)片(pian)制(zhi)作過程中(zhong)電(dian)(dian)子(zi)導(dao)電(dian)(dian)網絡的(de)(de)(de)(de)(de)(de)性(xing)能，評估電(dian)(dian)極(ji)微觀(guan)結(jie)構(gou)的(de)(de)(de)(de)(de)(de)均勻性(xing)以(yi)(yi)及監控極(ji)片(pian)制(zhi)作工(gong)藝的(de)(de)(de)(de)(de)(de)穩定性(xing)，助力(li)改(gai)進極(ji)片(pian)的(de)(de)(de)(de)(de)(de)配方以(yi)(yi)及攪(jiao)拌、涂(tu)布和(he)輥壓工(gong)藝的(de)(de)(de)(de)(de)(de)控制(zhi)參數。
目前，測試極片電子電阻主要有兩種原理：四探針法和兩探針法。四探針法只能表征極片表面涂層的電阻，忽略了涂層和集流體的界面電阻，與極片在電池中的實際使用情況不符，因此不用于測試鋰離子電池極片電阻1-2。兩探針法能表征極片的整體穿透內阻，包含涂層電阻、涂層與集流體界面電阻以及集流體本身電阻，測試時的電子傳導路徑與極片在電池中實際使用時的電子傳導路徑相同，大多數企業和科研工作者采用該方法進行極片電阻表征2-4。本文使用(yong)的方法(fa)(fa)是在兩(liang)探針法(fa)(fa)的基礎上做(zuo)進(jin)(jin)一步改進(jin)(jin)，采用(yong)四線(xian)法(fa)(fa)加可(ke)控壓(ya)雙(shuang)圓盤電(dian)極(ji)，測試極(ji)片(pian)電(dian)子(zi)(zi)電(dian)阻(zu)，監控涂布(bu)和(he)輥壓(ya)工序極(ji)片(pian)電(dian)阻(zu)的變化，將電(dian)芯的風險控制提(ti)前至極(ji)片(pian)端(duan)，從而為鋰離子(zi)(zi)電(dian)池(chi)研發和(he)生產保駕護航(hang)。
1.工藝監控案例
1.1 極片批次穩定性監控
極片電阻受導電劑分散、涂布重量、冷壓參數等多種因素影響，其中導電劑對電阻的影響非常顯著3。正極導電劑的分散情況與漿料配方、攪拌條件、涂布/烘干條件等眾多復雜工藝控制參數有關，導電劑分散不均將極大惡化電池動力學性能，但不均勻性很難通過極片外觀、粘接力等常規監控手段發現，往往容易被忽略，造成不可挽回的損失。
在電(dian)(dian)(dian)芯(xin)(xin)(xin)研發(fa)初(chu)期，通過對三(san)元(yuan)極(ji)(ji)(ji)(ji)片(pian)(pian)(pian)(pian)電(dian)(dian)(dian)阻(zu)的(de)(de)(de)大(da)量(liang)測(ce)(ce)試和監控，初(chu)步制定正(zheng)常(chang)(chang)(chang)極(ji)(ji)(ji)(ji)片(pian)(pian)(pian)(pian)電(dian)(dian)(dian)阻(zu)范圍為0.2~0.4Ω，在電(dian)(dian)(dian)芯(xin)(xin)(xin)導入量(liang)產(chan)階段后，對不(bu)同批次(ci)(ci)極(ji)(ji)(ji)(ji)片(pian)(pian)(pian)(pian)進(jin)行電(dian)(dian)(dian)阻(zu)監控。如圖2（a）是(shi)對6個批次(ci)(ci)極(ji)(ji)(ji)(ji)片(pian)(pian)(pian)(pian)進(jin)行的(de)(de)(de)極(ji)(ji)(ji)(ji)片(pian)(pian)(pian)(pian)電(dian)(dian)(dian)阻(zu)測(ce)(ce)試，黑(hei)色數(shu)據(ju)點(dian)代(dai)表單次(ci)(ci)測(ce)(ce)試電(dian)(dian)(dian)阻(zu)值(zhi)，紅(hong)色數(shu)據(ju)點(dian)代(dai)表電(dian)(dian)(dian)阻(zu)均值(zhi)，綠(lv)色數(shu)據(ju)點(dian)代(dai)表電(dian)(dian)(dian)阻(zu)COV。從電(dian)(dian)(dian)阻(zu)數(shu)據(ju)可發(fa)現有(you)3個批次(ci)(ci)電(dian)(dian)(dian)芯(xin)(xin)(xin)極(ji)(ji)(ji)(ji)片(pian)(pian)(pian)(pian)電(dian)(dian)(dian)阻(zu)大(da)于0.4Ω，明顯超出(chu)規格，進(jin)一步對正(zheng)常(chang)(chang)(chang)和異(yi)常(chang)(chang)(chang)批次(ci)(ci)的(de)(de)(de)極(ji)(ji)(ji)(ji)片(pian)(pian)(pian)(pian)進(jin)行SEM形貌分析，如圖2（b）和2（c），正(zheng)常(chang)(chang)(chang)批次(ci)(ci)極(ji)(ji)(ji)(ji)片(pian)(pian)(pian)(pian)中(zhong)導電(dian)(dian)(dian)碳(tan)(tan)的(de)(de)(de)分布較均勻，而異(yi)常(chang)(chang)(chang)批次(ci)(ci)極(ji)(ji)(ji)(ji)片(pian)(pian)(pian)(pian)的(de)(de)(de)導電(dian)(dian)(dian)碳(tan)(tan)出(chu)現明顯的(de)(de)(de)團聚現象，由于測(ce)(ce)試極(ji)(ji)(ji)(ji)片(pian)(pian)(pian)(pian)電(dian)(dian)(dian)阻(zu)時是(shi)隨機選取極(ji)(ji)(ji)(ji)片(pian)(pian)(pian)(pian)不(bu)同位置(zhi)，導電(dian)(dian)(dian)碳(tan)(tan)分布不(bu)均會(hui)導致無導電(dian)(dian)(dian)碳(tan)(tan)的(de)(de)(de)位置(zhi)處極(ji)(ji)(ji)(ji)片(pian)(pian)(pian)(pian)電(dian)(dian)(dian)阻(zu)明顯增大(da)。因此，通過監控極(ji)(ji)(ji)(ji)片(pian)(pian)(pian)(pian)電(dian)(dian)(dian)阻(zu)的(de)(de)(de)變(bian)化(hua)可在極(ji)(ji)(ji)(ji)片(pian)(pian)(pian)(pian)端(duan)快速識別(bie)異(yi)常(chang)(chang)(chang)極(ji)(ji)(ji)(ji)片(pian)(pian)(pian)(pian)，避免不(bu)良(liang)極(ji)(ji)(ji)(ji)片(pian)(pian)(pian)(pian)流入下一工(gong)序，節約生產(chan)成本。
1.2 極片涂布均(jun)勻性監控
為(wei)了提升電池能量密度，硅(gui)碳(tan)(tan)(tan)混合(he)(he)材(cai)料(liao)作(zuo)為(wei)鋰離子(zi)電池負極(ji)材(cai)料(liao)的(de)(de)研究(jiu)逐漸增多，如何控制(zhi)硅(gui)碳(tan)(tan)(tan)混合(he)(he)材(cai)料(liao)在極(ji)片中的(de)(de)分布均勻性對負極(ji)的(de)(de)膨脹以及(ji)電位分布有顯著影響。監(jian)控不同工藝(yi)參數條件下極(ji)片電阻的(de)(de)變化可評估(gu)硅(gui)碳(tan)(tan)(tan)材(cai)料(liao)混合(he)(he)均勻性。
如圖(tu)(tu)(tu)3是兩(liang)種混(hun)料(liao)(liao)(liao)(liao)(liao)工(gong)藝(yi)的(de)(de)極(ji)(ji)(ji)片(pian)(pian)進行(xing)的(de)(de)極(ji)(ji)(ji)片(pian)(pian)電(dian)阻(zu)(zu)(zu)測試和(he)SEM形貌表征結果。由(you)圖(tu)(tu)(tu)3（a）可(ke)看(kan)出混(hun)料(liao)(liao)(liao)(liao)(liao)1的(de)(de)極(ji)(ji)(ji)片(pian)(pian)電(dian)阻(zu)(zu)(zu)均(jun)(jun)值和(he)COV均(jun)(jun)明(ming)顯(xian)高于混(hun)料(liao)(liao)(liao)(liao)(liao)2組，說明(ming)混(hun)料(liao)(liao)(liao)(liao)(liao)1的(de)(de)均(jun)(jun)勻(yun)性差于混(hun)料(liao)(liao)(liao)(liao)(liao)2 的(de)(de)極(ji)(ji)(ji)片(pian)(pian)。結合圖(tu)(tu)(tu)3（b）和(he)3（c）SEM形貌分析(xi)可(ke)看(kan)出，混(hun)料(liao)(liao)(liao)(liao)(liao)1組極(ji)(ji)(ji)片(pian)(pian)中硅(gui)(gui)(gui)碳的(de)(de)混(hun)合不(bu)均(jun)(jun)勻(yun)，有較多(duo)單獨的(de)(de)硅(gui)(gui)(gui)顆粒存在，因此導致極(ji)(ji)(ji)片(pian)(pian)電(dian)阻(zu)(zu)(zu)均(jun)(jun)值增(zeng)大，且不(bu)同位(wei)置處的(de)(de)極(ji)(ji)(ji)片(pian)(pian)電(dian)阻(zu)(zu)(zu)差異較大，從(cong)而電(dian)阻(zu)(zu)(zu)COV較大，而混(hun)料(liao)(liao)(liao)(liao)(liao)2組中硅(gui)(gui)(gui)碳混(hun)合相對均(jun)(jun)勻(yun)，電(dian)阻(zu)(zu)(zu)的(de)(de)均(jun)(jun)值和(he)COV均(jun)(jun)較小，進一步證(zheng)明(ming)混(hun)料(liao)(liao)(liao)(liao)(liao)2對應的(de)(de)混(hun)料(liao)(liao)(liao)(liao)(liao)工(gong)藝(yi)較好。
2.總(zong)結(jie)
本文使(shi)用的(de)四線法(fa)(fa)加可(ke)(ke)控(kong)壓(ya)雙(shuang)圓盤電(dian)(dian)極(ji)(ji)的(de)方(fang)法(fa)(fa)測(ce)試極(ji)(ji)片(pian)(pian)電(dian)(dian)阻，能(neng)較好的(de)應用于監控(kong)極(ji)(ji)片(pian)(pian)工藝的(de)穩(wen)定(ding)性(xing)和均勻性(xing)，且極(ji)(ji)片(pian)(pian)電(dian)(dian)阻數(shu)據可(ke)(ke)實時連接BIS或MES系統，實現數(shu)據的(de)可(ke)(ke)記錄、可(ke)(ke)追溯。目前已有多(duo)家(jia)材料(liao)和電(dian)(dian)池企業將(jiang)該方(fang)法(fa)(fa)導入產線工藝監控(kong)，對工藝參數(shu)及工藝穩(wen)定(ding)性(xing)進行快(kuai)速有效的(de)評估(gu)，將(jiang)電(dian)(dian)芯的(de)風險控(kong)制提前至極(ji)(ji)片(pian)(pian)端，加速鋰離(li)子電(dian)(dian)池研發和生產進度，滿足市場需求。
