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)一樣，熟悉了解鋰電(dian)池(chi)容量的學問，也(ye)許對使用和設計(ji)鋰電(dian)池(chi)供(gong)電(dian)包括設計(ji)電(dian)池(chi)充(chong)電(dian)器來說，很有必要。

現在好多關注(zhu)鋰電(dian)(dian)池放(fang)電(dian)(dian)的(de)人(ren)，都有(you)這樣的(de)體會，就是(shi)當鋰電(dian)(dian)池從充滿(man)電(dian)(dian)壓4.2V放(fang)電(dian)(dian)到3.7V時，時間很(hen)長，但一旦(dan)過了3.7V就放(fang)電(dian)(dian)很(hen)快了，沒(mei)錯(cuo)，確實這樣。

下面翻閱一些(xie)(xie)鋰電池的一些(xie)(xie)資料，給大(da)家做一個總結。

先(xian)說(shuo)一(yi)下(xia)電池(chi)(chi)的(de)放電平(ping)臺，就是指充滿電的(de)鋰電池(chi)(chi)在(zai)放電時(shi)，電池(chi)(chi)的(de)電壓(ya)變化(hua)狀(zhuang)態(tai)。

電(dian)(dian)池(chi)恒(heng)流放電(dian)(dian)，電(dian)(dian)池(chi)電(dian)(dian)壓要經歷三個過程，即下降(jiang)、穩(wen)定(ding)、再下降(jiang)，在這(zhe)三個過程中，穩(wen)定(ding)期是最長的(de)。穩(wen)定(ding)時間越(yue)長，說明電(dian)(dian)池(chi)的(de)放電(dian)(dian)平臺越(yue)高(gao)。放電(dian)(dian)平臺的(de)高(gao)低，與電(dian)(dian)池(chi)制造(zao)工藝息息相關。就(jiu)是因(yin)為各個鋰電(dian)(dian)池(chi)廠家的(de)市場定(ding)位不一樣(yang)(yang)，技術工藝手段(duan)不同，其控制的(de)放電(dian)(dian)平臺就(jiu)不一樣(yang)(yang)，質量(liang)也就(jiu)有很大差別。

一(yi)(yi)(yi)般地，一(yi)(yi)(yi)節18650的鋰(li)電(dian)池(chi)滿電(dian)壓(ya)4.2V，當用1C的電(dian)流放(fang)電(dian)放(fang)到3.7V，放(fang)了60分鐘，那(nei)么我們就說電(dian)池(chi)的使用容(rong)量(liang)是2200mAh，在這段時(shi)間里 根(gen)據(ju)充(chong)電(dian)電(dian)池(chi)特性，做出一(yi)(yi)(yi)個(ge)圖(tu)如下，可以更好理解電(dian)池(chi)容(rong)量(liang)和電(dian)壓(ya)電(dian)流時(shi)間與放(fang)電(dian)平(ping)臺(tai)關系：

鋰電(dian)(dian)池電(dian)(dian)池容(rong)量與(yu)放電(dian)(dian)平臺理解示(shi)意圖(tu)

容量（C）=放電電流×電池(chi)放電平(ping)臺時間(jian)

對于1節容(rong)量(liang)為(wei)2200mAh的18650鋰電池來說，1C放電到(dao)3.7V用(yong)時1小時，

容(rong)量（C）=2200mA×1小時=2200mAh

那么(me)(me)問題就(jiu)來了，對于好(hao)一點的(de)鋰電池(chi)，一般在(zai)我(wo)們做產品(pin)測試時(shi)會(hui)在(zai)3.7V以后電壓下(xia)降的(de)很快(kuai)，那么(me)(me)在(zai)短時(shi)間內放的(de)電量(liang)就(jiu)很少。

相反不好的(de)(de)電(dian)池(chi)在(zai)(zai)4.2V到3.7V放電(dian)的(de)(de)時候，電(dian)壓下(xia)(xia)降的(de)(de)很(hen)快，而在(zai)(zai)3.7V以后電(dian)壓又下(xia)(xia)降的(de)(de)有很(hen)慢，這種電(dian)池(chi)是性能不好的(de)(de)一般容量也(ye)非(fei)常低。那么好的(de)(de)鋰電(dian)池(chi)的(de)(de)放電(dian)平(ping)臺就(jiu)是3.7V。

就(jiu)一般而言，在恒壓條件(jian)下，充到(dao)電(dian)(dian)(dian)壓為4.2V，電(dian)(dian)(dian)流(liu)小于0.01C時停充電(dian)(dian)(dian)，然后擱置(zhi)10分鐘，在任何倍率的(de)放(fang)電(dian)(dian)(dian)電(dian)(dian)(dian)流(liu)下，放(fang)電(dian)(dian)(dian)至(zhi)3.7V時，電(dian)(dian)(dian)池放(fang)電(dian)(dian)(dian)所經(jing)歷(li)的(de)一個時間長度，是(shi)衡量電(dian)(dian)(dian)池好壞(huai)的(de)重(zhong)要指標。

不過，不要(yao)(yao)一味地追(zhui)求(qiu)高平臺，有(you)時候平臺電(dian)(dian)壓(ya)高，容量卻下降了，因為，不同倍率條件下，平臺電(dian)(dian)壓(ya)是不同的，因此，平臺的問題應從(cong)多(duo)方(fang)考慮。既(ji)要(yao)(yao)容量高，又要(yao)(yao)在指定電(dian)(dian)壓(ya)持續時間(jian)長，才(cai)算真(zhen)正的好電(dian)(dian)池(chi)。

什么又是放電率的呢？

放(fang)電率(lv)F：[1/時(shi)]，意(yi)思是 "N小時(shi)充（放(fang)）電率(lv)，常常只說(shuo)"數(shu)",而不說(shuo)單(dan)位;F也稱(cheng)做(zuo) "N小時(shi)充（放(fang)）電率(lv)", F =1/(N小時(shi))， 一(yi)般可(ke)以(yi)這樣(yang)計算(suan)：I=0.1 X [1/(N小時(shi))] X C

舉例,電池容量時(shi)2200mAh,以 0.1C 的電流充電,相當于明(ming)確: 對電池的充電電流 I=0.1[1/時(shi)]X2200[毫(hao)安(an)時(shi)]=220[毫(hao)安(an)]

借助上面的鋰電池電池容量與放電(dian)(dian)(dian)(dian)平(ping)(ping)臺理(li)(li)(li)解示意圖，能比較好的(de)(de)(de)理(li)(li)(li)解充電(dian)(dian)(dian)(dian)電(dian)(dian)(dian)(dian)池(chi)(chi)(chi)容量和電(dian)(dian)(dian)(dian)池(chi)(chi)(chi)的(de)(de)(de)放電(dian)(dian)(dian)(dian)平(ping)(ping)臺的(de)(de)(de)道理(li)(li)(li)，也(ye)(ye)可以說(shuo)是衡量電(dian)(dian)(dian)(dian)池(chi)(chi)(chi)高功率的(de)(de)(de)工作時(shi)(shi)間(jian)(jian),同(tong)(tong)樣兩(liang)個(ge)(ge)(ge)電(dian)(dian)(dian)(dian)池(chi)(chi)(chi)容量是相同(tong)(tong)的(de)(de)(de),充滿(man)電(dian)(dian)(dian)(dian)后(hou)假設同(tong)(tong)時(shi)(shi)從4.2V放到3.7V,但是一個(ge)(ge)(ge)時(shi)(shi)間(jian)(jian)長,一個(ge)(ge)(ge)時(shi)(shi)間(jian)(jian)短(duan),就(jiu)是時(shi)(shi)間(jian)(jian)長的(de)(de)(de)電(dian)(dian)(dian)(dian)池(chi)(chi)(chi)平(ping)(ping)臺高,就(jiu)是高電(dian)(dian)(dian)(dian)壓的(de)(de)(de)時(shi)(shi)間(jian)(jian)工作時(shi)(shi)間(jian)(jian)長,比如這兩(liang)個(ge)(ge)(ge)電(dian)(dian)(dian)(dian)池(chi)(chi)(chi)用在(zai)手機(ji)上,待機(ji)時(shi)(shi)間(jian)(jian)是相同(tong)(tong)的(de)(de)(de),但兩(liang)個(ge)(ge)(ge)手機(ji)一起打(da)電(dian)(dian)(dian)(dian)話(hua),平(ping)(ping)臺時(shi)(shi)間(jian)(jian)長的(de)(de)(de)電(dian)(dian)(dian)(dian)池(chi)(chi)(chi)通(tong)知時(shi)(shi)間(jian)(jian)會長,平(ping)(ping)臺時(shi)(shi)間(jian)(jian)短(duan)的(de)(de)(de)電(dian)(dian)(dian)(dian)池(chi)(chi)(chi)通(tong)話(hua)時(shi)(shi)間(jian)(jian)會短(duan) 二，對于(yu)這個(ge)(ge)(ge)圖，另一個(ge)(ge)(ge)含義(yi)，對理(li)(li)(li)解鋰(li)電(dian)(dian)(dian)(dian)池(chi)(chi)(chi)的(de)(de)(de)電(dian)(dian)(dian)(dian)量管理(li)(li)(li)監測(ce)也(ye)(ye)很有(you)意義(yi)。

比如，目前，對充電電池進(jin)行電量(liang)監控方法，一(yi)般有兩種。

測量電池電壓方法。當充電器在(zai)充(chong)(chong)電(dian)(dian)時(shi)檢(jian)測(ce)電(dian)(dian)池(chi)(chi)電(dian)(dian)壓(ya)，當電(dian)(dian)壓(ya)達(da)到規定電(dian)(dian)壓(ya)值時(shi)就(jiu)(jiu)認為充(chong)(chong)滿(man)。如鋰電(dian)(dian)池(chi)(chi)的(de)(de)電(dian)(dian)壓(ya)充(chong)(chong)到4.2V時(shi)就(jiu)(jiu)認為充(chong)(chong)滿(man)。檢(jian)測(ce)電(dian)(dian)壓(ya)的(de)(de)電(dian)(dian)壓(ya)表精度要(yao)達(da)到正負1%的(de)(de)精度。因鋰電(dian)(dian)池(chi)(chi)過(guo)充(chong)(chong)電(dian)(dian)要(yao)損壞。如果(guo)想監視電(dian)(dian)池(chi)(chi)充(chong)(chong)放(fang)電(dian)(dian)的(de)(de)話，書上有很(hen)成熟的(de)(de)電(dian)(dian)路可以參考，如果(guo)只(zhi)是(shi)測(ce)量一(yi)下(xia)的(de)(de)話那就(jiu)(jiu)好(hao)辦了(le)，根(gen)據容量計算一(yi)下(xia)負載(zai)電(dian)(dian)阻(zu)，用標準(zhun)放(fang)電(dian)(dian)電(dian)(dian)流放(fang)電(dian)(dian)，這(zhe)時(shi)再檢(jian)測(ce)電(dian)(dian)壓(ya)，只(zhi)要(yao)能(neng)達(da)到或(huo)接近(jin)標稱的(de)(de)放(fang)電(dian)(dian)時(shi)間就(jiu)(jiu)行。

測量電池電壓(ya)這種方法，有很多不(bu)足。例如對(dui)于不(bu)同廠商生產(chan)的(de)電池，其開路電壓(ya)與(yu)容量之(zhi)間的(de)關系各(ge)不(bu)相同等。優點是設計(ji)成本(ben)比較低。

還有一個常用的(de)監測(ce)剩余電(dian)(dian)(dian)量(liang)的(de)方法是(shi)，在一些要(yao)求(qiu)比較精確電(dian)(dian)(dian)池(chi)(chi)容(rong)量(liang)的(de)地(di)方， 了(le)解電(dian)(dian)(dian)池(chi)(chi)剩余容(rong)量(liang)用估算電(dian)(dian)(dian)池(chi)(chi)使用時(shi)間，通過(guo)測(ce)量(liang)流(liu)入/流(liu)出(chu)(chu)電(dian)(dian)(dian)池(chi)(chi)的(de)凈電(dian)(dian)(dian)荷(he)來估算電(dian)(dian)(dian)池(chi)(chi)剩余容(rong)量(liang)。對流(liu)入/流(liu)出(chu)(chu)電(dian)(dian)(dian)池(chi)(chi)的(de)總(zong)電(dian)(dian)(dian)流(liu)進行積分，也(ye)就是(shi)求(qiu)圖中(zhong)曲線下的(de)面積，得到(dao)的(de)凈電(dian)(dian)(dian)荷(he)數即為剩余容(rong)量(liang)。

這就電(dian)池容量計(ji)算的方法是(shi)目前(qian)認為(wei)是(shi)比較精確的計(ji)算電(dian)池電(dian)量的方法。當然設(she)計(ji)成本也是(shi)比較高(gao)的。