鋰電池的電池容量

我們現在設計電子產品，很多時候也用鋰電池供電，同手機或者平板電腦用鋰電池供(gong)電(dian)一(yi)樣，熟悉了(le)解鋰(li)(li)電(dian)池容(rong)量的學問，也許對使用(yong)和設計(ji)鋰(li)(li)電(dian)池供(gong)電(dian)包括設計(ji)電(dian)池充電(dian)器(qi)來說，很有必要。

現在好(hao)多關注鋰(li)電(dian)池放(fang)電(dian)的(de)人，都有這(zhe)樣的(de)體會，就是當(dang)鋰(li)電(dian)池從充(chong)滿(man)電(dian)壓4.2V放(fang)電(dian)到(dao)3.7V時，時間很長，但一旦過(guo)了3.7V就放(fang)電(dian)很快了，沒錯，確實這(zhe)樣。

下面翻閱一(yi)些鋰電(dian)池的一(yi)些資料，給大(da)家做(zuo)一(yi)個總結。

先說一(yi)下(xia)電(dian)(dian)池(chi)的放(fang)電(dian)(dian)平臺，就是(shi)指充滿(man)電(dian)(dian)的鋰電(dian)(dian)池(chi)在(zai)放(fang)電(dian)(dian)時，電(dian)(dian)池(chi)的電(dian)(dian)壓變化狀(zhuang)態(tai)。

電(dian)池(chi)恒流放電(dian)，電(dian)池(chi)電(dian)壓要經歷三個(ge)過(guo)程，即(ji)下降、穩定(ding)、再下降，在這三個(ge)過(guo)程中，穩定(ding)期是最長(chang)的(de)(de)。穩定(ding)時間(jian)越長(chang)，說明電(dian)池(chi)的(de)(de)放電(dian)平(ping)(ping)臺(tai)越高。放電(dian)平(ping)(ping)臺(tai)的(de)(de)高低，與電(dian)池(chi)制造工藝(yi)息息相(xiang)關。就是因為各個(ge)鋰電(dian)池(chi)廠家的(de)(de)市場定(ding)位(wei)不一樣，技術工藝(yi)手段不同，其控制的(de)(de)放電(dian)平(ping)(ping)臺(tai)就不一樣，質量也就有很大(da)差別(bie)。

一般地，一節18650的(de)鋰(li)電(dian)池(chi)滿(man)電(dian)壓4.2V，當用(yong)1C的(de)電(dian)流放電(dian)放到3.7V，放了60分鐘(zhong)，那么我們就(jiu)說電(dian)池(chi)的(de)使用(yong)容量(liang)是(shi)2200mAh，在這段時間里 根據充電(dian)電(dian)池(chi)特性，做出(chu)一個(ge)圖如(ru)下(xia)，可以(yi)更好理解電(dian)池(chi)容量(liang)和電(dian)壓電(dian)流時間與放電(dian)平臺關系：

鋰電池(chi)電池(chi)容量與放電平(ping)臺理解示意(yi)圖

容(rong)量（C）=放電電流×電池放電平臺時間

對于1節容量為2200mAh的(de)18650鋰電池(chi)來說(shuo)，1C放電到3.7V用時1小時，

容量（C）=2200mA×1小時=2200mAh

那(nei)么問(wen)題就(jiu)(jiu)來(lai)了，對(dui)于好一點的鋰電池，一般在我們做產(chan)品測試時(shi)會在3.7V以后電壓下降(jiang)的很快，那(nei)么在短時(shi)間內放的電量就(jiu)(jiu)很少。

相(xiang)反不好(hao)的(de)電(dian)池(chi)(chi)在4.2V到3.7V放電(dian)的(de)時候，電(dian)壓(ya)(ya)下(xia)降(jiang)的(de)很(hen)快，而(er)在3.7V以后電(dian)壓(ya)(ya)又下(xia)降(jiang)的(de)有很(hen)慢，這種(zhong)電(dian)池(chi)(chi)是性(xing)能不好(hao)的(de)一般容量也非常低。那么(me)好(hao)的(de)鋰電(dian)池(chi)(chi)的(de)放電(dian)平臺(tai)就是3.7V。

就一般而言，在恒壓(ya)條(tiao)件下(xia)，充(chong)到電(dian)(dian)(dian)壓(ya)為4.2V，電(dian)(dian)(dian)流(liu)小于(yu)0.01C時(shi)(shi)停充(chong)電(dian)(dian)(dian)，然后(hou)擱置10分鐘，在任(ren)何(he)倍率的放電(dian)(dian)(dian)電(dian)(dian)(dian)流(liu)下(xia)，放電(dian)(dian)(dian)至3.7V時(shi)(shi)，電(dian)(dian)(dian)池放電(dian)(dian)(dian)所經(jing)歷的一個時(shi)(shi)間長度(du)，是衡量電(dian)(dian)(dian)池好(hao)壞的重要指標。

不(bu)過，不(bu)要(yao)一味地追求高平(ping)(ping)臺，有(you)時候平(ping)(ping)臺電壓(ya)(ya)高，容量(liang)卻下(xia)降了，因為(wei)，不(bu)同倍率條件下(xia)，平(ping)(ping)臺電壓(ya)(ya)是不(bu)同的，因此(ci)，平(ping)(ping)臺的問題應從多方考慮。既要(yao)容量(liang)高，又要(yao)在(zai)指定電壓(ya)(ya)持續時間長(chang)，才算真正的好電池。

什么又(you)是(shi)放(fang)電率(lv)的呢？

放電(dian)率(lv)F：[1/時(shi)]，意(yi)思是 "N小(xiao)時(shi)充（放）電(dian)率(lv)，常常只說"數",而不說單(dan)位;F也稱(cheng)做 "N小(xiao)時(shi)充（放）電(dian)率(lv)", F =1/(N小(xiao)時(shi))， 一(yi)般(ban)可以(yi)這樣計算：I=0.1 X [1/(N小(xiao)時(shi))] X C

舉例,電(dian)池(chi)容量時2200mAh,以 0.1C 的電(dian)流(liu)充電(dian),相當于明確(que): 對電(dian)池(chi)的充電(dian)電(dian)流(liu) I=0.1[1/時]X2200[毫安(an)時]=220[毫安(an)]

借助上面的鋰電池電池容量(liang)與放(fang)電(dian)(dian)(dian)平(ping)臺(tai)理(li)解示意圖(tu)，能比較好的(de)(de)(de)理(li)解充(chong)電(dian)(dian)(dian)電(dian)(dian)(dian)池(chi)容量(liang)和電(dian)(dian)(dian)池(chi)的(de)(de)(de)放(fang)電(dian)(dian)(dian)平(ping)臺(tai)的(de)(de)(de)道(dao)理(li)，也可(ke)以說是(shi)(shi)衡量(liang)電(dian)(dian)(dian)池(chi)高功率的(de)(de)(de)工(gong)作(zuo)時間(jian)(jian)(jian),同(tong)(tong)樣兩個(ge)電(dian)(dian)(dian)池(chi)容量(liang)是(shi)(shi)相同(tong)(tong)的(de)(de)(de),充(chong)滿電(dian)(dian)(dian)后假設同(tong)(tong)時從4.2V放(fang)到3.7V,但是(shi)(shi)一(yi)(yi)個(ge)時間(jian)(jian)(jian)長(chang),一(yi)(yi)個(ge)時間(jian)(jian)(jian)短(duan),就(jiu)是(shi)(shi)時間(jian)(jian)(jian)長(chang)的(de)(de)(de)電(dian)(dian)(dian)池(chi)平(ping)臺(tai)高,就(jiu)是(shi)(shi)高電(dian)(dian)(dian)壓的(de)(de)(de)時間(jian)(jian)(jian)工(gong)作(zuo)時間(jian)(jian)(jian)長(chang),比如這兩個(ge)電(dian)(dian)(dian)池(chi)用在(zai)手機(ji)上,待(dai)機(ji)時間(jian)(jian)(jian)是(shi)(shi)相同(tong)(tong)的(de)(de)(de),但兩個(ge)手機(ji)一(yi)(yi)起打電(dian)(dian)(dian)話(hua),平(ping)臺(tai)時間(jian)(jian)(jian)長(chang)的(de)(de)(de)電(dian)(dian)(dian)池(chi)通知(zhi)時間(jian)(jian)(jian)會長(chang),平(ping)臺(tai)時間(jian)(jian)(jian)短(duan)的(de)(de)(de)電(dian)(dian)(dian)池(chi)通話(hua)時間(jian)(jian)(jian)會短(duan) 二(er)，對于這個(ge)圖(tu)，另一(yi)(yi)個(ge)含義(yi)，對理(li)解鋰電(dian)(dian)(dian)池(chi)的(de)(de)(de)電(dian)(dian)(dian)量(liang)管理(li)監測也很有意義(yi)。

比(bi)如，目前，對(dui)充(chong)電(dian)(dian)電(dian)(dian)池進(jin)行電(dian)(dian)量(liang)監控方(fang)法，一般有兩種。

測量電池電壓方法。當充電器在充(chong)(chong)電(dian)(dian)(dian)(dian)(dian)時(shi)(shi)檢測(ce)電(dian)(dian)(dian)(dian)(dian)池(chi)電(dian)(dian)(dian)(dian)(dian)壓，當電(dian)(dian)(dian)(dian)(dian)壓達到規定電(dian)(dian)(dian)(dian)(dian)壓值時(shi)(shi)就(jiu)認(ren)為充(chong)(chong)滿。如鋰電(dian)(dian)(dian)(dian)(dian)池(chi)的(de)電(dian)(dian)(dian)(dian)(dian)壓充(chong)(chong)到4.2V時(shi)(shi)就(jiu)認(ren)為充(chong)(chong)滿。檢測(ce)電(dian)(dian)(dian)(dian)(dian)壓的(de)電(dian)(dian)(dian)(dian)(dian)壓表精(jing)度要達到正負1%的(de)精(jing)度。因鋰電(dian)(dian)(dian)(dian)(dian)池(chi)過(guo)充(chong)(chong)電(dian)(dian)(dian)(dian)(dian)要損壞。如果想(xiang)監視電(dian)(dian)(dian)(dian)(dian)池(chi)充(chong)(chong)放(fang)電(dian)(dian)(dian)(dian)(dian)的(de)話，書上(shang)有很成熟的(de)電(dian)(dian)(dian)(dian)(dian)路可以(yi)參考，如果只是測(ce)量一下的(de)話那就(jiu)好辦了(le)，根據容(rong)量計算一下負載電(dian)(dian)(dian)(dian)(dian)阻，用標準(zhun)放(fang)電(dian)(dian)(dian)(dian)(dian)電(dian)(dian)(dian)(dian)(dian)流放(fang)電(dian)(dian)(dian)(dian)(dian)，這(zhe)時(shi)(shi)再檢測(ce)電(dian)(dian)(dian)(dian)(dian)壓，只要能達到或接(jie)近標稱的(de)放(fang)電(dian)(dian)(dian)(dian)(dian)時(shi)(shi)間就(jiu)行。

測(ce)量電池電壓(ya)這種方法，有(you)很多不足。例如對于(yu)不同(tong)廠商生產(chan)的電池，其開路電壓(ya)與容量之間的關(guan)系各不相同(tong)等。優點(dian)是設計成本比較低(di)。

還(huan)有一(yi)個常(chang)用(yong)的(de)(de)(de)監測剩(sheng)余(yu)電(dian)(dian)(dian)量(liang)(liang)的(de)(de)(de)方法(fa)是，在一(yi)些要(yao)求比較精確電(dian)(dian)(dian)池(chi)(chi)容(rong)量(liang)(liang)的(de)(de)(de)地方， 了解電(dian)(dian)(dian)池(chi)(chi)剩(sheng)余(yu)容(rong)量(liang)(liang)用(yong)估(gu)(gu)算電(dian)(dian)(dian)池(chi)(chi)使用(yong)時(shi)間，通過測量(liang)(liang)流(liu)入(ru)/流(liu)出電(dian)(dian)(dian)池(chi)(chi)的(de)(de)(de)凈(jing)電(dian)(dian)(dian)荷來估(gu)(gu)算電(dian)(dian)(dian)池(chi)(chi)剩(sheng)余(yu)容(rong)量(liang)(liang)。對(dui)流(liu)入(ru)/流(liu)出電(dian)(dian)(dian)池(chi)(chi)的(de)(de)(de)總電(dian)(dian)(dian)流(liu)進行積分(fen)，也就是求圖中曲線下的(de)(de)(de)面積，得到的(de)(de)(de)凈(jing)電(dian)(dian)(dian)荷數即為剩(sheng)余(yu)容(rong)量(liang)(liang)。

這就(jiu)電池容量(liang)計算(suan)的方法是目前(qian)認為(wei)是比較精確的計算(suan)電池電量(liang)的方法。當然設計成本也是比較高的。