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)電一樣，熟(shu)悉了解鋰電池容量的學問，也許(xu)對使用和設計(ji)鋰電池供(gong)電包括(kuo)設計(ji)電池充電器來說(shuo)，很(hen)有必要。

現在好多(duo)關注(zhu)鋰(li)電池放電的(de)人，都有這(zhe)樣(yang)的(de)體會(hui)，就是當(dang)鋰(li)電池從充滿電壓4.2V放電到(dao)3.7V時(shi)(shi)，時(shi)(shi)間很長，但一旦過了(le)3.7V就放電很快了(le)，沒錯(cuo)，確實這(zhe)樣(yang)。

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

先說(shuo)一下電(dian)池(chi)的(de)放(fang)電(dian)平臺(tai)，就是指充滿(man)電(dian)的(de)鋰電(dian)池(chi)在放(fang)電(dian)時，電(dian)池(chi)的(de)電(dian)壓變化狀態。

電(dian)(dian)池(chi)恒(heng)流(liu)放電(dian)(dian)，電(dian)(dian)池(chi)電(dian)(dian)壓(ya)要經歷(li)三個過程，即下降、穩(wen)定(ding)、再下降，在這三個過程中，穩(wen)定(ding)期是(shi)最長(chang)(chang)的(de)(de)。穩(wen)定(ding)時間越長(chang)(chang)，說明(ming)電(dian)(dian)池(chi)的(de)(de)放電(dian)(dian)平(ping)臺越高(gao)。放電(dian)(dian)平(ping)臺的(de)(de)高(gao)低，與電(dian)(dian)池(chi)制(zhi)(zhi)造(zao)工藝息息相關。就(jiu)是(shi)因為各個鋰(li)電(dian)(dian)池(chi)廠家的(de)(de)市場(chang)定(ding)位不(bu)一樣，技術(shu)工藝手段不(bu)同，其(qi)控制(zhi)(zhi)的(de)(de)放電(dian)(dian)平(ping)臺就(jiu)不(bu)一樣，質量也就(jiu)有很(hen)大(da)差別。

一般地，一節18650的(de)鋰電(dian)池滿電(dian)壓4.2V，當用1C的(de)電(dian)流放電(dian)放到3.7V，放了60分鐘，那么我(wo)們就說電(dian)池的(de)使用容量是2200mAh，在(zai)這段時間里 根據充電(dian)電(dian)池特性，做出一個圖(tu)如下，可以更好理解電(dian)池容量和電(dian)壓電(dian)流時間與放電(dian)平臺關系：

鋰電(dian)池電(dian)池容量與放電(dian)平(ping)臺理解示意圖

容(rong)量（C）=放電電流×電池放電平(ping)臺時間

對于1節容量為2200mAh的18650鋰電(dian)池來說(shuo)，1C放電(dian)到3.7V用時(shi)1小(xiao)時(shi)，

容(rong)量（C）=2200mA×1小時=2200mAh

那(nei)么(me)問題就(jiu)來了，對于好一點的鋰電(dian)池，一般在我(wo)們做產品測(ce)試時(shi)會在3.7V以后電(dian)壓下降的很快，那(nei)么(me)在短(duan)時(shi)間內(nei)放的電(dian)量就(jiu)很少。

相反不(bu)好(hao)的(de)電(dian)(dian)池在4.2V到3.7V放電(dian)(dian)的(de)時候(hou)，電(dian)(dian)壓(ya)下(xia)(xia)降(jiang)的(de)很(hen)快，而在3.7V以后電(dian)(dian)壓(ya)又下(xia)(xia)降(jiang)的(de)有很(hen)慢，這種電(dian)(dian)池是(shi)性能不(bu)好(hao)的(de)一般容(rong)量(liang)也非常(chang)低。那么(me)好(hao)的(de)鋰電(dian)(dian)池的(de)放電(dian)(dian)平(ping)臺就是(shi)3.7V。

就(jiu)一般而言(yan)，在(zai)恒壓條件下，充到電(dian)(dian)(dian)壓為(wei)4.2V，電(dian)(dian)(dian)流小于0.01C時(shi)停(ting)充電(dian)(dian)(dian)，然后擱置10分鐘，在(zai)任何倍率的(de)放(fang)電(dian)(dian)(dian)電(dian)(dian)(dian)流下，放(fang)電(dian)(dian)(dian)至3.7V時(shi)，電(dian)(dian)(dian)池(chi)放(fang)電(dian)(dian)(dian)所經歷的(de)一個時(shi)間長度，是衡量(liang)電(dian)(dian)(dian)池(chi)好壞的(de)重要指標。

不(bu)(bu)過(guo)，不(bu)(bu)要一味地追(zhui)求高(gao)平臺(tai)，有時候平臺(tai)電壓(ya)高(gao)，容量卻下降了，因(yin)為，不(bu)(bu)同(tong)倍率條件(jian)下，平臺(tai)電壓(ya)是(shi)不(bu)(bu)同(tong)的(de)，因(yin)此(ci)，平臺(tai)的(de)問(wen)題(ti)應從多(duo)方(fang)考(kao)慮。既要容量高(gao)，又要在(zai)指定電壓(ya)持(chi)續時間(jian)長，才算真正(zheng)的(de)好電池。

什么又(you)是放電率(lv)的(de)呢？

放(fang)(fang)電率(lv)F：[1/時]，意思是(shi) "N小(xiao)時充（放(fang)(fang)）電率(lv)，常常只(zhi)說(shuo)"數",而不說(shuo)單位;F也(ye)稱(cheng)做 "N小(xiao)時充（放(fang)(fang)）電率(lv)", F =1/(N小(xiao)時)， 一般可以這樣計算：I=0.1 X [1/(N小(xiao)時)] X C

舉例,電池(chi)容量(liang)時2200mAh,以 0.1C 的電流充電,相當于明(ming)確: 對(dui)電池(chi)的充電電流 I=0.1[1/時]X2200[毫安時]=220[毫安]

借助上面的鋰電池電池容(rong)量與放電(dian)(dian)平(ping)臺(tai)(tai)理解示意圖(tu)，能比(bi)較(jiao)好的理解充電(dian)(dian)電(dian)(dian)池(chi)容(rong)量和電(dian)(dian)池(chi)的放電(dian)(dian)平(ping)臺(tai)(tai)的道理，也可以(yi)說是(shi)衡量電(dian)(dian)池(chi)高功率的工(gong)作(zuo)時(shi)(shi)(shi)間(jian)(jian)(jian)(jian),同(tong)樣兩(liang)個電(dian)(dian)池(chi)容(rong)量是(shi)相(xiang)同(tong)的,充滿電(dian)(dian)后假(jia)設同(tong)時(shi)(shi)(shi)從4.2V放到3.7V,但是(shi)一個時(shi)(shi)(shi)間(jian)(jian)(jian)(jian)長(chang),一個時(shi)(shi)(shi)間(jian)(jian)(jian)(jian)短,就是(shi)時(shi)(shi)(shi)間(jian)(jian)(jian)(jian)長(chang)的電(dian)(dian)池(chi)平(ping)臺(tai)(tai)高,就是(shi)高電(dian)(dian)壓的時(shi)(shi)(shi)間(jian)(jian)(jian)(jian)工(gong)作(zuo)時(shi)(shi)(shi)間(jian)(jian)(jian)(jian)長(chang),比(bi)如這(zhe)兩(liang)個電(dian)(dian)池(chi)用在手機上,待機時(shi)(shi)(shi)間(jian)(jian)(jian)(jian)是(shi)相(xiang)同(tong)的,但兩(liang)個手機一起(qi)打電(dian)(dian)話,平(ping)臺(tai)(tai)時(shi)(shi)(shi)間(jian)(jian)(jian)(jian)長(chang)的電(dian)(dian)池(chi)通知時(shi)(shi)(shi)間(jian)(jian)(jian)(jian)會長(chang),平(ping)臺(tai)(tai)時(shi)(shi)(shi)間(jian)(jian)(jian)(jian)短的電(dian)(dian)池(chi)通話時(shi)(shi)(shi)間(jian)(jian)(jian)(jian)會短 二，對于這(zhe)個圖(tu)，另一個含義(yi)，對理解鋰電(dian)(dian)池(chi)的電(dian)(dian)量管理監測也很有意義(yi)。

比如，目前，對充電電池進行電量監控(kong)方法，一(yi)般有兩種。

測量電池電壓方法。當充電器在充(chong)(chong)電(dian)(dian)(dian)時(shi)(shi)檢測電(dian)(dian)(dian)池電(dian)(dian)(dian)壓(ya)，當(dang)電(dian)(dian)(dian)壓(ya)達(da)(da)到規定(ding)電(dian)(dian)(dian)壓(ya)值時(shi)(shi)就(jiu)認為充(chong)(chong)滿。如鋰電(dian)(dian)(dian)池的(de)(de)(de)(de)電(dian)(dian)(dian)壓(ya)充(chong)(chong)到4.2V時(shi)(shi)就(jiu)認為充(chong)(chong)滿。檢測電(dian)(dian)(dian)壓(ya)的(de)(de)(de)(de)電(dian)(dian)(dian)壓(ya)表精度要(yao)達(da)(da)到正負(fu)1%的(de)(de)(de)(de)精度。因鋰電(dian)(dian)(dian)池過充(chong)(chong)電(dian)(dian)(dian)要(yao)損壞。如果想監視電(dian)(dian)(dian)池充(chong)(chong)放電(dian)(dian)(dian)的(de)(de)(de)(de)話(hua)，書上有很成熟的(de)(de)(de)(de)電(dian)(dian)(dian)路可以(yi)參(can)考，如果只是測量一下(xia)的(de)(de)(de)(de)話(hua)那就(jiu)好辦了，根(gen)據容量計算(suan)一下(xia)負(fu)載電(dian)(dian)(dian)阻(zu)，用標準(zhun)放電(dian)(dian)(dian)電(dian)(dian)(dian)流放電(dian)(dian)(dian)，這(zhe)時(shi)(shi)再檢測電(dian)(dian)(dian)壓(ya)，只要(yao)能達(da)(da)到或接近標稱的(de)(de)(de)(de)放電(dian)(dian)(dian)時(shi)(shi)間就(jiu)行。

測量(liang)電池電壓(ya)這種方(fang)法，有很(hen)多不足。例(li)如(ru)對于(yu)不同廠商(shang)生產的電池，其開路電壓(ya)與(yu)容量(liang)之間的關系各不相同等。優點是設計成(cheng)本比較低。

還有一(yi)個常用(yong)(yong)的(de)(de)(de)監測剩(sheng)余(yu)(yu)電(dian)(dian)(dian)量的(de)(de)(de)方法(fa)是，在一(yi)些要求比較精確電(dian)(dian)(dian)池容量的(de)(de)(de)地方， 了解電(dian)(dian)(dian)池剩(sheng)余(yu)(yu)容量用(yong)(yong)估算電(dian)(dian)(dian)池使用(yong)(yong)時間，通(tong)過測量流(liu)入/流(liu)出(chu)電(dian)(dian)(dian)池的(de)(de)(de)凈電(dian)(dian)(dian)荷來估算電(dian)(dian)(dian)池剩(sheng)余(yu)(yu)容量。對(dui)流(liu)入/流(liu)出(chu)電(dian)(dian)(dian)池的(de)(de)(de)總(zong)電(dian)(dian)(dian)流(liu)進行積分，也就(jiu)是求圖中曲線下(xia)的(de)(de)(de)面積，得到的(de)(de)(de)凈電(dian)(dian)(dian)荷數即為剩(sheng)余(yu)(yu)容量。

這就電(dian)(dian)池容量(liang)計(ji)(ji)算的(de)(de)方法是目前(qian)認為是比較精確的(de)(de)計(ji)(ji)算電(dian)(dian)池電(dian)(dian)量(liang)的(de)(de)方法。當(dang)然設計(ji)(ji)成(cheng)本也(ye)是比較高(gao)的(de)(de)。