為了給(gei)設備提供足夠的(de)電壓，鋰(li)電池包(bao)通常(chang)由多個電池串(chuan)聯而(er)成(cheng)，但是(shi)如果電池之(zhi)間的(de)容量失配(pei)便會影響(xiang)整個電池包(bao)的(de)容量。為此，我們需要(yao)對(dui)失配(pei)的(de)電池進行(xing)均衡。本(ben)文討論了電池均衡的(de)概念和一些注意事(shi)項。

      鋰電池包(bao)通常(chang)由(you)一(yi)個(ge)或幾個(ge)電(dian)(dian)池(chi)(chi)組(zu)(zu)并(bing)聯(lian)，每個(ge)電(dian)(dian)池(chi)(chi)組(zu)(zu)由(you)3到4個(ge)電(dian)(dian)池(chi)(chi)串(chuan)聯(lian)構成。這種組(zu)(zu)合方式能(neng)同時滿(man)足筆記本電(dian)(dian)腦、醫療設備、測試儀器及工業應用(yong)所需的(de)(de)電(dian)(dian)壓和功率要求。然而(er)，這種應用(yong)普遍的(de)(de)配置(zhi)通常(chang)并(bing)不(bu)(bu)能(neng)發(fa)揮(hui)其(qi)最大功效，因為如果某個(ge)串(chuan)聯(lian)電(dian)(dian)池(chi)(chi)的(de)(de)容(rong)量與其(qi)它電(dian)(dian)池(chi)(chi)不(bu)(bu)匹配將會降低整個(ge)電(dian)(dian)池(chi)(chi)包(bao)的(de)(de)容(rong)量。

電(dian)(dian)池(chi)(chi)容量(liang)的(de)(de)不匹配(pei)(pei)包括充電(dian)(dian)狀(zhuang)態(SOC)失(shi)配(pei)(pei)和容量(liang)/能量(liang)(C/E)失(shi)配(pei)(pei)。在兩種(zhong)情(qing)況(kuang)下，電(dian)(dian)池(chi)(chi)包的(de)(de)總容量(liang)都只能達到最弱電(dian)(dian)池(chi)(chi)的(de)(de)容量(liang)。在大(da)多數(shu)情(qing)況(kuang)下，引起電(dian)(dian)池(chi)(chi)失(shi)配(pei)(pei)的(de)(de)原(yuan)因是(shi)工藝控制和檢測手段的(de)(de)不完善，而(er)不是(shi)鋰離子(zi)本(ben)身的(de)(de)化學屬性變化。棱柱形鋰電(dian)(dian)池(chi)(chi)(LiIon prismatic cell)在生產時(shi)需要更強的(de)(de)機械(xie)壓力，電(dian)(dian)池(chi)(chi)之間(jian)更容易產生差異。此(ci)外(wai)，鋰離子(zi)聚合物(wu)電(dian)(dian)池(chi)(chi)也會因為(wei)采用新(xin)的(de)(de)工藝而(er)出現電(dian)(dian)池(chi)(chi)之間(jian)的(de)(de)差異。

      采用(yong)電(dian)(dian)池均(jun)衡(heng)(heng)處(chu)理(li)技術可(ke)解決SOC和C/E失配問題，從(cong)而改進串聯鋰電(dian)(dian)池包(bao)的性能(neng)。通過(guo)(guo)在(zai)初始調節過(guo)(guo)程中對(dui)電(dian)(dian)池進行(xing)均(jun)衡(heng)(heng)處(chu)理(li)可(ke)以矯正電(dian)(dian)池失配問題，此后只(zhi)需在(zai)充電(dian)(dian)過(guo)(guo)程中進行(xing)均(jun)衡(heng)(heng)即(ji)可(ke)，而C/E失配則必(bi)須在(zai)充、放電(dian)(dian)過(guo)(guo)程都進行(xing)均(jun)衡(heng)(heng)。盡管對(dui)于(yu)某個(ge)電(dian)(dian)池廠商而言其產品缺陷(xian)率可(ke)能(neng)很低，但為了避免出現電(dian)(dian)池使用(yong)壽命(ming) 過(guo)(guo)短的問題，我們(men)仍然(ran)有必(bi)要提供進一步的質量保證。

電池均衡的定義

     工作電(dian)(dian)(dian)(dian)壓為6V 或以上的(de)(de)(de)(de)便(bian)攜式(shi)設備采用串(chuan)(chuan)(chuan)聯(lian)電(dian)(dian)(dian)(dian)池(chi)(chi)(chi)包(bao)(bao)供電(dian)(dian)(dian)(dian)，這種情況(kuang)下電(dian)(dian)(dian)(dian)池(chi)(chi)(chi)包(bao)(bao)的(de)(de)(de)(de)總電(dian)(dian)(dian)(dian)壓為各串(chuan)(chuan)(chuan)聯(lian)電(dian)(dian)(dian)(dian)池(chi)(chi)(chi)電(dian)(dian)(dian)(dian)壓之(zhi)和。便(bian)攜式(shi)電(dian)(dian)(dian)(dian)腦的(de)(de)(de)(de)電(dian)(dian)(dian)(dian)池(chi)(chi)(chi)包(bao)(bao)通常由三(san)、四個電(dian)(dian)(dian)(dian)池(chi)(chi)(chi)串(chuan)(chuan)(chuan)聯(lian)而(er)(er)成，標稱電(dian)(dian)(dian)(dian)壓為 10.8V或14.4V。在(zai)大多數此類(lei)應用中(zhong)，單(dan)個串(chuan)(chuan)(chuan)聯(lian)電(dian)(dian)(dian)(dian)池(chi)(chi)(chi)包(bao)(bao)無法提供設備所需(xu)能(neng)(neng)(neng)量。目前最大的(de)(de)(de)(de)電(dian)(dian)(dian)(dian)池(chi)(chi)(chi)(如18650)可提供2,000mAh(毫安 ?小(xiao)時)能(neng)(neng)(neng)量，而(er)(er)電(dian)(dian)(dian)(dian)腦需(xu)要50-60Whr(5,000-6,000mAh)的(de)(de)(de)(de)能(neng)(neng)(neng)量，因此必(bi)須給串(chuan)(chuan)(chuan)聯(lian)的(de)(de)(de)(de)每個電(dian)(dian)(dian)(dian)池(chi)(chi)(chi)并聯(lian)三(san)個電(dian)(dian)(dian)(dian)池(chi)(chi)(chi)。

     電(dian)(dian)(dian)(dian)(dian)池(chi)(chi)(chi)均衡是(shi)指對串聯(lian)電(dian)(dian)(dian)(dian)(dian)池(chi)(chi)(chi)包(bao)(bao)中不同的(de)(de)電(dian)(dian)(dian)(dian)(dian)池(chi)(chi)(chi)(或(huo)(huo)電(dian)(dian)(dian)(dian)(dian)池(chi)(chi)(chi)組(zu))采用差分電(dian)(dian)(dian)(dian)(dian)流。串聯(lian)電(dian)(dian)(dian)(dian)(dian)池(chi)(chi)(chi)包(bao)(bao)中每個(ge)電(dian)(dian)(dian)(dian)(dian)池(chi)(chi)(chi)的(de)(de)電(dian)(dian)(dian)(dian)(dian)流通常是(shi)一樣的(de)(de)，因此必(bi)須給電(dian)(dian)(dian)(dian)(dian)池(chi)(chi)(chi)包(bao)(bao)增加額外的(de)(de)元件和電(dian)(dian)(dian)(dian)(dian)路來實現(xian)(xian) 電(dian)(dian)(dian)(dian)(dian)池(chi)(chi)(chi)均衡。只(zhi)有(you)當(dang)電(dian)(dian)(dian)(dian)(dian)池(chi)(chi)(chi)包(bao)(bao)中的(de)(de)電(dian)(dian)(dian)(dian)(dian)池(chi)(chi)(chi)是(shi)串聯(lian)的(de)(de)，同時(shi)(shi)串聯(lian)電(dian)(dian)(dian)(dian)(dian)池(chi)(chi)(chi)等于或(huo)(huo)大于三級時(shi)(shi)才會考慮電(dian)(dian)(dian)(dian)(dian)池(chi)(chi)(chi)均衡問題。當(dang)電(dian)(dian)(dian)(dian)(dian)池(chi)(chi)(chi)包(bao)(bao)中所有(you)電(dian)(dian)(dian)(dian)(dian)池(chi)(chi)(chi)都滿足下面兩個(ge)條件時(shi)(shi)，便實現(xian)(xian)了電(dian)(dian)(dian)(dian)(dian)池(chi)(chi)(chi)均衡：

1. 如果所有電(dian)(dian)(dian)(dian)(dian)(dian)池(chi)(chi)的(de)(de)(de)(de)容(rong)(rong)量相同，那么當它(ta)們的(de)(de)(de)(de)相對(dui)(dui)充(chong)(chong)(chong)(chong)電(dian)(dian)(dian)(dian)(dian)(dian)狀(zhuang)態(tai)一(yi)樣時便實現了電(dian)(dian)(dian)(dian)(dian)(dian)池(chi)(chi)均(jun)(jun)衡(heng)。SOC通常以當前容(rong)(rong)量與額(e)定容(rong)(rong)量的(de)(de)(de)(de)百分(fen)比來表(biao)示，因(yin)此，開(kai)路電(dian)(dian)(dian)(dian)(dian)(dian)壓(ya)(OCV)可作為SOC的(de)(de)(de)(de)一(yi)個衡(heng)量標準。如果一(yi)個不均(jun)(jun)衡(heng)電(dian)(dian)(dian)(dian)(dian)(dian)池(chi)(chi)包中的(de)(de)(de)(de)所有電(dian)(dian)(dian)(dian)(dian)(dian)池(chi)(chi)可以通過差分(fen)充(chong)(chong)(chong)(chong)電(dian)(dian)(dian)(dian)(dian)(dian)達(da)到滿容(rong)(rong)量(均(jun)(jun)衡(heng)點)，它(ta)們便可以進行(xing)正常的(de)(de)(de)(de)充(chong)(chong)(chong)(chong)放電(dian)(dian)(dian)(dian)(dian)(dian)而無需(xu)任(ren)何額(e)外的(de)(de)(de)(de)調(diao)整，通常這種調(diao)整是一(yi)次性的(de)(de)(de)(de)。用(yong)戶在使(shi)(shi)用(yong)新(xin)電(dian)(dian)(dian)(dian)(dian)(dian)池(chi)(chi)時，通常需(xu)要求(qiu)對(dui)(dui)電(dian)(dian)(dian)(dian)(dian)(dian)池(chi)(chi)進行(xing)長(chang)時間(jian)充(chong)(chong)(chong)(chong)電(dian)(dian)(dian)(dian)(dian)(dian)，這個過程(cheng)(cheng)實際上包括一(yi)次完整的(de)(de)(de)(de)放-充(chong)(chong)(chong)(chong)電(dian)(dian)(dian)(dian)(dian)(dian)。該(gai)過程(cheng)(cheng)使(shi)(shi)負載最(zui)小(xiao)化，并使(shi)(shi)電(dian)(dian)(dian)(dian)(dian)(dian)池(chi)(chi)充(chong)(chong)(chong)(chong) 電(dian)(dian)(dian)(dian)(dian)(dian)時間(jian)最(zui)長(chang)，降低對(dui)(dui)電(dian)(dian)(dian)(dian)(dian)(dian)池(chi)(chi)均(jun)(jun)衡(heng)電(dian)(dian)(dian)(dian)(dian)(dian)路的(de)(de)(de)(de)要求(qiu)。

2. 如果電池的(de)(de)(de)容(rong)(rong)量不(bu)同(tong)(tong)，當SOC相(xiang)(xiang)同(tong)(tong)時(shi)也認(ren)為它(ta)們是(shi)均衡的(de)(de)(de)。但SOC只是(shi)一個相(xiang)(xiang)對值(zhi)，每個電池容(rong)(rong)量的(de)(de)(de)絕對值(zhi)是(shi)不(bu)同(tong)(tong)的(de)(de)(de)。為了使容(rong)(rong)量不(bu)同(tong)(tong)的(de)(de)(de)電池的(de)(de)(de)SOC相(xiang)(xiang)同(tong)(tong)，每次對串聯電池進(jin)行充(chong)放電時(shi)都必須使用差分電流。正(zheng)常充(chong)放電的(de)(de)(de)時(shi)間比(bi)初(chu)次充(chong)放電更(geng)短，并需(xu)要更(geng)大的(de)(de)(de)電流。

     當電(dian)(dian)(dian)(dian)池(chi)(chi)包(bao)中的(de)電(dian)(dian)(dian)(dian)池(chi)(chi)不均(jun)衡時，它(ta)的(de)可(ke)用(yong)容(rong)量(liang)將(jiang)減少，串聯電(dian)(dian)(dian)(dian)池(chi)(chi)包(bao)中容(rong)量(liang)最(zui)低(di)的(de)電(dian)(dian)(dian)(dian)池(chi)(chi)將(jiang)決定電(dian)(dian)(dian)(dian)池(chi)(chi)包(bao)的(de)總容(rong)量(liang)。在(zai)不均(jun)衡電(dian)(dian)(dian)(dian)池(chi)(chi)包(bao)中，一個或幾(ji)個電(dian)(dian)(dian)(dian)池(chi)(chi)會(hui)在(zai)其它(ta)電(dian)(dian)(dian)(dian)池(chi)(chi)尚(shang)需充(chong)電(dian)(dian)(dian)(dian)時便已達(da)到(dao)最(zui)大容(rong)量(liang)。而在(zai)放電(dian)(dian)(dian)(dian)時，未(wei)完(wan)全(quan)充(chong)電(dian)(dian)(dian)(dian)的(de)電(dian)(dian)(dian)(dian)池(chi)(chi)又會(hui)比其它(ta)電(dian)(dian)(dian)(dian)池(chi)(chi)先(xian)放完(wan)電(dian)(dian)(dian)(dian)，使電(dian)(dian)(dian)(dian)池(chi)(chi)包(bao)因電(dian)(dian)(dian)(dian)壓不足而提(ti)前停止供電(dian)(dian)(dian)(dian)。

通常，電池(chi)之間容量的(de)差異(yi)低于(yu)3%。如果(guo)串聯鋰電池(chi)包的(de)某個(ge)電池(chi)不合標準，或者(zhe)在(zai)封(feng)裝(zhuang)前放置過(guo)久，在(zai)充電器(qi)充滿電后電壓差可(ke)達150mV，從而使電池(chi)包的(de)總容量下降13-18%。

SOC均衡處理

如(ru)果電(dian)池(chi)包中所(suo)有電(dian)池(chi)的(de)容量相同，我們(men)便采用(yong)SOC均衡(heng)(heng)處理(li)。當所(suo)有電(dian)池(chi)的(de)SOC值(zhi)相同時我們(men)認為電(dian)池(chi)是均衡(heng)(heng)的(de)。

單個電(dian)池的(de)充電(dian)狀態定義為：

SOC=C/CTOTAL%

單(dan)個電池的容量定義(yi)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(chong)電(dian)(dian)(dian)，并在電(dian)(dian)(dian)池充(chong)電(dian)(dian)(dian)器充(chong)電(dian)(dian)(dian)過程中(zhong)的(de)不同(tong)時間(jian)進行電(dian)(dian)(dian)流測量，直到(dao)達到(dao)4.20V的(de)開路電(dian)(dian)(dian)壓。最佳(jia)性(xing)能(neng)電(dian)(dian)(dian)池在該狀態下的(de)SOC為(wei)(wei)100%，SOC為(wei)(wei)50%的(de)OCV電(dian)(dian)(dian)壓通常稱為(wei)(wei)VMID，其典(dian)型值為(wei)(wei)3.67V。

為(wei)了給容量(liang)不同(tong)的(de)電(dian)(dian)池充(chong)電(dian)(dian)使它們達到(dao)同(tong)樣的(de)SOC，要求一些電(dian)(dian)池的(de)充(chong)/放電(dian)(dian)量(liang)必(bi)須比其它電(dian)(dian)池多，這(zhe)必(bi)須使用差(cha)分電(dian)(dian)流。我們將這(zhe)個過程稱之(zhi)為(wei)容量(liang)/能(neng)量(liang)最大化。

容量/能量最大化

容量(liang)(liang)/能量(liang)(liang)最(zui)大(da)化是指(zhi)將電(dian)(dian)池(chi)包(bao)中所(suo)有(you)串聯電(dian)(dian)池(chi)設(she)置為(wei)相同(tong)的(de)(de)SOC，即使(shi)它們的(de)(de)容量(liang)(liang)不(bu)同(tong)。在(zai)所(suo)有(you)時間(jian)內(nei)管理(li)SOC，使(shi)電(dian)(dian)池(chi)包(bao)的(de)(de)輸出能量(liang)(liang)達到最(zui)大(da)。為(wei)了使(shi)輸出能量(liang)(liang)最(zui)大(da)化，所(suo)有(you)的(de)(de)電(dian)(dian)池(chi)都必(bi)須(xu)充滿電(dian)(dian)。即，所(suo)有(you)電(dian)(dian)池(chi)的(de)(de)SOC必(bi)須(xu)為(wei)100%。如果電(dian)(dian)池(chi)的(de)(de)容量(liang)(liang)不(bu)同(tong)，一(yi)些電(dian)(dian)池(chi)的(de)(de)充/放電(dian)(dian)就會比其它電(dian)(dian)池(chi)更多。例如，假設(she)一(yi)個(ge)電(dian)(dian)池(chi)包(bao)有(you)三個(ge)串聯電(dian)(dian)池(chi)，C1＞C2=C3。均衡(heng)這(zhe)個(ge)電(dian)(dian)池(chi)包(bao)的(de)(de)唯一(yi)方法(fa)是給(gei)容量(liang)(liang)較高的(de)(de)電(dian)(dian)池(chi)(C1)施加一(yi)個(ge)差(cha)分(fen)充電(dian)(dian)電(dian)(dian)流。

在電(dian)(dian)(dian)(dian)池包(bao)放電(dian)(dian)(dian)(dian)時(shi)也必須如此(ci)，否(fou)則當(dang)容(rong)(rong)量(liang)最(zui)小的電(dian)(dian)(dian)(dian)池達(da)到關(guan)斷電(dian)(dian)(dian)(dian)壓時(shi)，整個電(dian)(dian)(dian)(dian)池包(bao)便(bian)會停止放電(dian)(dian)(dian)(dian)，而(er)此(ci)時(shi)其(qi)(qi)它電(dian)(dian)(dian)(dian)池仍(reng)有剩(sheng)余(yu)容(rong)(rong)量(liang)，這(zhe)樣使總容(rong)(rong)量(liang)降低。長此(ci)以往，容(rong)(rong)量(liang)最(zui)小的電(dian)(dian)(dian)(dian)池便(bian)會比其(qi)(qi)它電(dian)(dian)(dian)(dian)池性能衰退更快，經過多個充/放電(dian)(dian)(dian)(dian)周期后將加速(su)容(rong)(rong)量(liang)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(tong)常圓柱形鋰離子電池(cylindrical cell)的(de)質(zhi)量控制通(tong)常都較(jiao)好，電池容(rong)量差(cha)別不超過(guo)±3%。輸入容(rong)量基本上(shang)比較(jiao)精確，差(cha)別不超過(guo)幾個mAs(毫安?秒)。因此，電池容(rong)量絕對值也基本準確，SOC的(de)差(cha)異在幾個百(bai)分點以內。