為(wei)了(le)給(gei)設備提供足夠的電(dian)壓，鋰(li)電(dian)池(chi)(chi)包(bao)通常由多個電(dian)池(chi)(chi)串聯而成，但是(shi)如(ru)果電(dian)池(chi)(chi)之間的容量失配(pei)便會影響整個電(dian)池(chi)(chi)包(bao)的容量。為(wei)此(ci)，我們需(xu)要對失配(pei)的電(dian)池(chi)(chi)進行均(jun)衡。本文討論了(le)電(dian)池(chi)(chi)均(jun)衡的概念和一些注意事(shi)項。

      鋰電池包通(tong)常由一(yi)個(ge)(ge)或(huo)幾個(ge)(ge)電(dian)(dian)池(chi)(chi)組并聯(lian)，每個(ge)(ge)電(dian)(dian)池(chi)(chi)組由3到4個(ge)(ge)電(dian)(dian)池(chi)(chi)串(chuan)聯(lian)構成。這種(zhong)組合方式能同時滿足筆(bi)記本電(dian)(dian)腦(nao)、醫療設備、測試儀器(qi)及工業(ye)應用(yong)所需(xu)的電(dian)(dian)壓和功率要求。然而(er)，這種(zhong)應用(yong)普遍的配(pei)(pei)置通(tong)常并不能發(fa)揮其(qi)最大功效，因(yin)為如果某個(ge)(ge)串(chuan)聯(lian)電(dian)(dian)池(chi)(chi)的容量與其(qi)它(ta)電(dian)(dian)池(chi)(chi)不匹配(pei)(pei)將(jiang)會(hui)降低整(zheng)個(ge)(ge)電(dian)(dian)池(chi)(chi)包的容量。

電(dian)(dian)(dian)池(chi)(chi)(chi)(chi)容(rong)量(liang)的(de)(de)不(bu)匹(pi)配(pei)(pei)(pei)包括充電(dian)(dian)(dian)狀態(SOC)失(shi)配(pei)(pei)(pei)和容(rong)量(liang)/能量(liang)(C/E)失(shi)配(pei)(pei)(pei)。在兩種情況下(xia)，電(dian)(dian)(dian)池(chi)(chi)(chi)(chi)包的(de)(de)總容(rong)量(liang)都只能達到最弱電(dian)(dian)(dian)池(chi)(chi)(chi)(chi)的(de)(de)容(rong)量(liang)。在大(da)多數情況下(xia)，引起電(dian)(dian)(dian)池(chi)(chi)(chi)(chi)失(shi)配(pei)(pei)(pei)的(de)(de)原(yuan)因是工藝控制和檢測手段的(de)(de)不(bu)完善，而不(bu)是鋰(li)離(li)子本身的(de)(de)化學(xue)屬性變化。棱柱形鋰(li)電(dian)(dian)(dian)池(chi)(chi)(chi)(chi)(LiIon prismatic cell)在生(sheng)產時需要更強的(de)(de)機械壓力(li)，電(dian)(dian)(dian)池(chi)(chi)(chi)(chi)之間(jian)更容(rong)易產生(sheng)差異。此外(wai)，鋰(li)離(li)子聚合物電(dian)(dian)(dian)池(chi)(chi)(chi)(chi)也(ye)會因為(wei)采用新的(de)(de)工藝而出現電(dian)(dian)(dian)池(chi)(chi)(chi)(chi)之間(jian)的(de)(de)差異。

      采用電(dian)(dian)(dian)池均(jun)衡(heng)(heng)處理(li)技(ji)術可解決SOC和(he)C/E失(shi)配問題(ti)，從而改(gai)進(jin)(jin)串聯鋰(li)電(dian)(dian)(dian)池包的(de)性(xing)能(neng)。通過(guo)(guo)在初(chu)始調節過(guo)(guo)程(cheng)中對(dui)電(dian)(dian)(dian)池進(jin)(jin)行均(jun)衡(heng)(heng)處理(li)可以矯正電(dian)(dian)(dian)池失(shi)配問題(ti)，此后只需(xu)在充(chong)電(dian)(dian)(dian)過(guo)(guo)程(cheng)中進(jin)(jin)行均(jun)衡(heng)(heng)即可，而C/E失(shi)配則必(bi)(bi)須在充(chong)、放(fang)電(dian)(dian)(dian)過(guo)(guo)程(cheng)都(dou)進(jin)(jin)行均(jun)衡(heng)(heng)。盡管對(dui)于某個(ge)電(dian)(dian)(dian)池廠商(shang)而言其產品缺(que)陷率(lv)可能(neng)很低(di)，但為了避免出現(xian)電(dian)(dian)(dian)池使(shi)用壽命 過(guo)(guo)短的(de)問題(ti)，我們仍然有必(bi)(bi)要提供進(jin)(jin)一步的(de)質量保證。

電池均衡的定義

     工作電(dian)壓(ya)為6V 或以上的(de)(de)便攜(xie)式(shi)(shi)設備采用串聯電(dian)池包(bao)(bao)供(gong)電(dian)，這(zhe)種情(qing)況下電(dian)池包(bao)(bao)的(de)(de)總電(dian)壓(ya)為各(ge)串聯電(dian)池電(dian)壓(ya)之和。便攜(xie)式(shi)(shi)電(dian)腦的(de)(de)電(dian)池包(bao)(bao)通常由(you)三、四個(ge)電(dian)池串聯而成，標稱電(dian)壓(ya)為 10.8V或14.4V。在大多數此類應用中，單個(ge)串聯電(dian)池包(bao)(bao)無(wu)法提供(gong)設備所需能量。目前最大的(de)(de)電(dian)池(如18650)可提供(gong)2,000mAh(毫安 ?小(xiao)時)能量，而電(dian)腦需要50-60Whr(5,000-6,000mAh)的(de)(de)能量，因此必須給串聯的(de)(de)每(mei)個(ge)電(dian)池并聯三個(ge)電(dian)池。

     電(dian)(dian)(dian)(dian)(dian)池(chi)(chi)(chi)均衡(heng)是指對串聯電(dian)(dian)(dian)(dian)(dian)池(chi)(chi)(chi)包中(zhong)不同(tong)的(de)(de)電(dian)(dian)(dian)(dian)(dian)池(chi)(chi)(chi)(或(huo)電(dian)(dian)(dian)(dian)(dian)池(chi)(chi)(chi)組)采用差分電(dian)(dian)(dian)(dian)(dian)流。串聯電(dian)(dian)(dian)(dian)(dian)池(chi)(chi)(chi)包中(zhong)每個(ge)電(dian)(dian)(dian)(dian)(dian)池(chi)(chi)(chi)的(de)(de)電(dian)(dian)(dian)(dian)(dian)流通常是一樣(yang)的(de)(de)，因(yin)此必須給電(dian)(dian)(dian)(dian)(dian)池(chi)(chi)(chi)包增加(jia)額外(wai)的(de)(de)元件和電(dian)(dian)(dian)(dian)(dian)路來實(shi)現 電(dian)(dian)(dian)(dian)(dian)池(chi)(chi)(chi)均衡(heng)。只(zhi)有當電(dian)(dian)(dian)(dian)(dian)池(chi)(chi)(chi)包中(zhong)的(de)(de)電(dian)(dian)(dian)(dian)(dian)池(chi)(chi)(chi)是串聯的(de)(de)，同(tong)時(shi)串聯電(dian)(dian)(dian)(dian)(dian)池(chi)(chi)(chi)等于或(huo)大于三級(ji)時(shi)才(cai)會考慮電(dian)(dian)(dian)(dian)(dian)池(chi)(chi)(chi)均衡(heng)問題。當電(dian)(dian)(dian)(dian)(dian)池(chi)(chi)(chi)包中(zhong)所(suo)有電(dian)(dian)(dian)(dian)(dian)池(chi)(chi)(chi)都滿足(zu)下(xia)面兩個(ge)條件時(shi)，便實(shi)現了電(dian)(dian)(dian)(dian)(dian)池(chi)(chi)(chi)均衡(heng)：

1. 如(ru)(ru)果(guo)所(suo)有(you)電(dian)(dian)池的(de)(de)容量(liang)相同，那么當它們的(de)(de)相對充(chong)(chong)電(dian)(dian)狀態一樣時(shi)(shi)便實現(xian)了電(dian)(dian)池均(jun)衡(heng)。SOC通(tong)常以當前(qian)容量(liang)與額定容量(liang)的(de)(de)百分比來表(biao)示(shi)，因此，開路電(dian)(dian)壓(OCV)可作為(wei)SOC的(de)(de)一個(ge)衡(heng)量(liang)標(biao)準(zhun)。如(ru)(ru)果(guo)一個(ge)不均(jun)衡(heng)電(dian)(dian)池包(bao)中的(de)(de)所(suo)有(you)電(dian)(dian)池可以通(tong)過(guo)差分充(chong)(chong)電(dian)(dian)達(da)到滿容量(liang)(均(jun)衡(heng)點)，它們便可以進(jin)行正(zheng)常的(de)(de)充(chong)(chong)放電(dian)(dian)而無需任何額外的(de)(de)調(diao)整(zheng)，通(tong)常這種調(diao)整(zheng)是(shi)一次(ci)性(xing)的(de)(de)。用戶在使(shi)用新電(dian)(dian)池時(shi)(shi)，通(tong)常需要求對電(dian)(dian)池進(jin)行長(chang)時(shi)(shi)間充(chong)(chong)電(dian)(dian)，這個(ge)過(guo)程(cheng)實際上包(bao)括(kuo)一次(ci)完整(zheng)的(de)(de)放-充(chong)(chong)電(dian)(dian)。該過(guo)程(cheng)使(shi)負載最小化，并使(shi)電(dian)(dian)池充(chong)(chong) 電(dian)(dian)時(shi)(shi)間最長(chang)，降低對電(dian)(dian)池均(jun)衡(heng)電(dian)(dian)路的(de)(de)要求。

2. 如果電(dian)(dian)池的(de)容量不同(tong)(tong)(tong)，當(dang)SOC相同(tong)(tong)(tong)時(shi)也認為它們(men)是(shi)均衡的(de)。但SOC只是(shi)一個相對(dui)值，每(mei)個電(dian)(dian)池容量的(de)絕對(dui)值是(shi)不同(tong)(tong)(tong)的(de)。為了使容量不同(tong)(tong)(tong)的(de)電(dian)(dian)池的(de)SOC相同(tong)(tong)(tong)，每(mei)次對(dui)串聯電(dian)(dian)池進行充放電(dian)(dian)時(shi)都必須(xu)使用(yong)差分電(dian)(dian)流(liu)。正常充放電(dian)(dian)的(de)時(shi)間比(bi)初次充放電(dian)(dian)更(geng)短，并需要更(geng)大的(de)電(dian)(dian)流(liu)。

     當(dang)電(dian)(dian)(dian)(dian)池(chi)(chi)(chi)包(bao)(bao)(bao)中的(de)(de)電(dian)(dian)(dian)(dian)池(chi)(chi)(chi)不(bu)均(jun)衡時(shi)，它(ta)(ta)的(de)(de)可用(yong)容(rong)(rong)量將(jiang)減少，串(chuan)聯電(dian)(dian)(dian)(dian)池(chi)(chi)(chi)包(bao)(bao)(bao)中容(rong)(rong)量最(zui)低的(de)(de)電(dian)(dian)(dian)(dian)池(chi)(chi)(chi)將(jiang)決(jue)定電(dian)(dian)(dian)(dian)池(chi)(chi)(chi)包(bao)(bao)(bao)的(de)(de)總容(rong)(rong)量。在(zai)不(bu)均(jun)衡電(dian)(dian)(dian)(dian)池(chi)(chi)(chi)包(bao)(bao)(bao)中，一(yi)個(ge)或(huo)幾個(ge)電(dian)(dian)(dian)(dian)池(chi)(chi)(chi)會在(zai)其它(ta)(ta)電(dian)(dian)(dian)(dian)池(chi)(chi)(chi)尚需充(chong)電(dian)(dian)(dian)(dian)時(shi)便(bian)已達到(dao)最(zui)大容(rong)(rong)量。而在(zai)放(fang)電(dian)(dian)(dian)(dian)時(shi)，未(wei)完全充(chong)電(dian)(dian)(dian)(dian)的(de)(de)電(dian)(dian)(dian)(dian)池(chi)(chi)(chi)又會比其它(ta)(ta)電(dian)(dian)(dian)(dian)池(chi)(chi)(chi)先(xian)放(fang)完電(dian)(dian)(dian)(dian)，使電(dian)(dian)(dian)(dian)池(chi)(chi)(chi)包(bao)(bao)(bao)因(yin)電(dian)(dian)(dian)(dian)壓不(bu)足而提(ti)前停止供電(dian)(dian)(dian)(dian)。

通常，電(dian)池之間容量(liang)的差(cha)異(yi)低(di)于3%。如(ru)果串聯鋰電(dian)池包的某(mou)個(ge)電(dian)池不(bu)合標準，或者在封裝前放置過(guo)久，在充電(dian)器充滿電(dian)后電(dian)壓差(cha)可達150mV，從而(er)使電(dian)池包的總容量(liang)下降13-18%。

SOC均衡處理

如果電(dian)池包中所(suo)有(you)電(dian)池的(de)容(rong)量相(xiang)同，我們(men)(men)便(bian)采用SOC均衡處理。當所(suo)有(you)電(dian)池的(de)SOC值相(xiang)同時我們(men)(men)認為(wei)電(dian)池是均衡的(de)。

單個(ge)電池的充電狀態定(ding)義為：

SOC=C/CTOTAL%

單個電池的容量定義為：

C=(i×t)mAh

為了確定某個電池的容量，我們將該電池完全放電然后再用鋰電池充電器充電(dian)，并在(zai)電(dian)池(chi)(chi)充電(dian)器充電(dian)過(guo)程中的(de)不同時間進行電(dian)流測量，直到(dao)(dao)達(da)到(dao)(dao)4.20V的(de)開路電(dian)壓。最佳性能電(dian)池(chi)(chi)在(zai)該狀態(tai)下的(de)SOC為(wei)(wei)100%，SOC為(wei)(wei)50%的(de)OCV電(dian)壓通常稱為(wei)(wei)VMID，其典(dian)型值為(wei)(wei)3.67V。

為了給容量(liang)(liang)不同的電池充(chong)電使它們達到同樣的SOC，要求一些(xie)電池的充(chong)/放電量(liang)(liang)必(bi)須比(bi)其(qi)它電池多，這必(bi)須使用差分電流。我(wo)們將這個過程稱之為容量(liang)(liang)/能量(liang)(liang)最大化。

容量/能量最大化

容量(liang)(liang)/能(neng)量(liang)(liang)最(zui)大(da)化是(shi)指將電(dian)池(chi)(chi)(chi)包(bao)中所(suo)有(you)串聯電(dian)池(chi)(chi)(chi)設置為相(xiang)同(tong)的(de)SOC，即使它們的(de)容量(liang)(liang)不同(tong)。在所(suo)有(you)時間內管理SOC，使電(dian)池(chi)(chi)(chi)包(bao)的(de)輸出能(neng)量(liang)(liang)達到(dao)最(zui)大(da)。為了使輸出能(neng)量(liang)(liang)最(zui)大(da)化，所(suo)有(you)的(de)電(dian)池(chi)(chi)(chi)都必須充滿電(dian)。即，所(suo)有(you)電(dian)池(chi)(chi)(chi)的(de)SOC必須為100%。如果(guo)電(dian)池(chi)(chi)(chi)的(de)容量(liang)(liang)不同(tong)，一些電(dian)池(chi)(chi)(chi)的(de)充/放(fang)電(dian)就(jiu)會比其(qi)它電(dian)池(chi)(chi)(chi)更多(duo)。例(li)如，假設一個電(dian)池(chi)(chi)(chi)包(bao)有(you)三個串聯電(dian)池(chi)(chi)(chi)，C1＞C2=C3。均衡這個電(dian)池(chi)(chi)(chi)包(bao)的(de)唯一方法是(shi)給容量(liang)(liang)較高的(de)電(dian)池(chi)(chi)(chi)(C1)施加一個差分(fen)充電(dian)電(dian)流(liu)。

在電(dian)(dian)(dian)池(chi)(chi)包(bao)放電(dian)(dian)(dian)時也必須如此，否則當容量最(zui)小的電(dian)(dian)(dian)池(chi)(chi)達到關斷電(dian)(dian)(dian)壓時，整個(ge)電(dian)(dian)(dian)池(chi)(chi)包(bao)便會停止放電(dian)(dian)(dian)，而(er)此時其(qi)它電(dian)(dian)(dian)池(chi)(chi)仍有剩余容量，這樣使(shi)總容量降低。長此以(yi)往，容量最(zui)小的電(dian)(dian)(dian)池(chi)(chi)便會比(bi)其(qi)它電(dian)(dian)(dian)池(chi)(chi)性能(neng)衰(shuai)退更快，經過(guo)多個(ge)充/放電(dian)(dian)(dian)周期后將(jiang)加速容量損耗。

通過匹配串聯電池的電壓，將從高容量電池汲取更多電流。放電時要求通過均衡消耗掉一些額外的電壓，在最后當所有電池都達到0SOC時，從電池包中獲得的總電能相對于均衡前仍然會增加。
通常圓柱形(xing)鋰(li)離子電(dian)(dian)池(chi)(chi)(cylindrical cell)的質量控(kong)制通常都(dou)較(jiao)好，電(dian)(dian)池(chi)(chi)容(rong)量差別不超過±3%。輸入(ru)容(rong)量基本上比(bi)較(jiao)精確(que)，差別不超過幾個(ge)mAs(毫安(an)?秒)。因此，電(dian)(dian)池(chi)(chi)容(rong)量絕對值(zhi)也(ye)基本準(zhun)確(que)，SOC的差異在幾個(ge)百分(fen)點以(yi)內。