鋰電池容量
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電一樣,熟(shu)悉了(le)解鋰電池(chi)容量的(de)學問(wen),也(ye)許(xu)對使用和設計鋰電池(chi)供電包(bao)括設計電池(chi)充電器來說,很(hen)有必要。
現在好多關注鋰電(dian)池放電(dian)的(de)(de)人,都(dou)有這樣(yang)的(de)(de)體會,就(jiu)是當鋰電(dian)池從充(chong)滿電(dian)壓4.2V放電(dian)到3.7V時,時間很長,但一(yi)旦過了3.7V就(jiu)放電(dian)很快(kuai)了,沒(mei)錯,確(que)實(shi)這樣(yang)。
下面翻閱一(yi)些鋰電池的一(yi)些資(zi)料,給大家做一(yi)個總(zong)結。
先說(shuo)一下電(dian)(dian)(dian)池(chi)的(de)放電(dian)(dian)(dian)平臺,就是指充滿(man)電(dian)(dian)(dian)的(de)鋰(li)電(dian)(dian)(dian)池(chi)在放電(dian)(dian)(dian)時,電(dian)(dian)(dian)池(chi)的(de)電(dian)(dian)(dian)壓(ya)變化狀(zhuang)態。
電(dian)(dian)(dian)(dian)(dian)池(chi)恒流放電(dian)(dian)(dian)(dian)(dian),電(dian)(dian)(dian)(dian)(dian)池(chi)電(dian)(dian)(dian)(dian)(dian)壓要經歷三個(ge)過程,即(ji)下降、穩定、再下降,在(zai)這三個(ge)過程中,穩定期是最長的(de)(de)。穩定時間越(yue)長,說(shuo)明電(dian)(dian)(dian)(dian)(dian)池(chi)的(de)(de)放電(dian)(dian)(dian)(dian)(dian)平(ping)臺(tai)(tai)越(yue)高。放電(dian)(dian)(dian)(dian)(dian)平(ping)臺(tai)(tai)的(de)(de)高低,與(yu)電(dian)(dian)(dian)(dian)(dian)池(chi)制(zhi)造工藝(yi)息息相關。就(jiu)是因為各(ge)個(ge)鋰電(dian)(dian)(dian)(dian)(dian)池(chi)廠(chang)家的(de)(de)市(shi)場定位不(bu)一樣,技術工藝(yi)手段(duan)不(bu)同,其控制(zhi)的(de)(de)放電(dian)(dian)(dian)(dian)(dian)平(ping)臺(tai)(tai)就(jiu)不(bu)一樣,質量也就(jiu)有很大差別(bie)。
一(yi)(yi)般地,一(yi)(yi)節18650的(de)(de)鋰電(dian)池(chi)滿電(dian)壓4.2V,當(dang)用(yong)1C的(de)(de)電(dian)流(liu)放電(dian)放到3.7V,放了60分鐘,那么我們就說電(dian)池(chi)的(de)(de)使用(yong)容量是(shi)2200mAh,在這(zhe)段時(shi)間里 根(gen)據充電(dian)電(dian)池(chi)特性,做出一(yi)(yi)個圖如下,可以(yi)更好理解電(dian)池(chi)容量和電(dian)壓電(dian)流(liu)時(shi)間與放電(dian)平臺(tai)關系(xi):
鋰電池電池容量與放電平臺(tai)理解(jie)示意圖
容量(C)=放電電流(liu)×電池放電平臺時(shi)間
對于1節容(rong)量(liang)為2200mAh的18650鋰電(dian)池來說,1C放電(dian)到(dao)3.7V用時1小時,
容量(C)=2200mA×1小時=2200mAh
那么問(wen)題(ti)就(jiu)來了,對(dui)于好一點的鋰電池,一般在我們(men)做產品測試時會在3.7V以后電壓下(xia)降的很(hen)快,那么在短時間(jian)內放的電量就(jiu)很(hen)少。
相(xiang)反不(bu)好(hao)的(de)(de)(de)電池在4.2V到3.7V放(fang)電的(de)(de)(de)時候(hou),電壓(ya)下降的(de)(de)(de)很(hen)快,而在3.7V以后電壓(ya)又(you)下降的(de)(de)(de)有很(hen)慢,這種電池是性能不(bu)好(hao)的(de)(de)(de)一般容量也非常低(di)。那(nei)么好(hao)的(de)(de)(de)鋰電池的(de)(de)(de)放(fang)電平臺就是3.7V。
就(jiu)一般而言,在恒壓條件下,充到(dao)電(dian)(dian)壓為4.2V,電(dian)(dian)流小于0.01C時停充電(dian)(dian),然后擱置10分鐘(zhong),在任何(he)倍率的(de)放電(dian)(dian)電(dian)(dian)流下,放電(dian)(dian)至3.7V時,電(dian)(dian)池放電(dian)(dian)所經歷的(de)一個時間長度(du),是衡量電(dian)(dian)池好壞的(de)重要指標。
不(bu)過,不(bu)要(yao)一味(wei)地追求高(gao)平(ping)臺,有時候平(ping)臺電(dian)(dian)壓高(gao),容(rong)量卻下降了,因為(wei),不(bu)同倍率條件下,平(ping)臺電(dian)(dian)壓是不(bu)同的,因此(ci),平(ping)臺的問題應從多方考慮。既(ji)要(yao)容(rong)量高(gao),又要(yao)在指定(ding)電(dian)(dian)壓持續時間(jian)長,才算真正的好(hao)電(dian)(dian)池。
什么又是放電率的呢?
放(fang)(fang)(fang)電(dian)率F:[1/時],意思(si)是 "N小(xiao)時充(chong)(chong)(放(fang)(fang)(fang))電(dian)率,常(chang)常(chang)只說"數",而不說單位(wei);F也(ye)稱做 "N小(xiao)時充(chong)(chong)(放(fang)(fang)(fang))電(dian)率", F =1/(N小(xiao)時), 一般可以這(zhe)樣計(ji)算:I=0.1 X [1/(N小(xiao)時)] X C
舉例(li),電(dian)池容量時(shi)2200mAh,以 0.1C 的電(dian)流充電(dian),相當于明確(que): 對電(dian)池的充電(dian)電(dian)流 I=0.1[1/時(shi)]X2200[毫安(an)時(shi)]=220[毫安(an)]
借助上面的鋰電池電池容量(liang)與(yu)放電(dian)(dian)(dian)平(ping)臺(tai)理解(jie)(jie)示(shi)意圖,能比(bi)較好的(de)(de)(de)理解(jie)(jie)充電(dian)(dian)(dian)電(dian)(dian)(dian)池容量(liang)和(he)電(dian)(dian)(dian)池的(de)(de)(de)放電(dian)(dian)(dian)平(ping)臺(tai)的(de)(de)(de)道理,也(ye)可以說是(shi)(shi)(shi)衡量(liang)電(dian)(dian)(dian)池高(gao)功率的(de)(de)(de)工作(zuo)(zuo)時(shi)間(jian)(jian),同(tong)樣兩(liang)個(ge)(ge)(ge)電(dian)(dian)(dian)池容量(liang)是(shi)(shi)(shi)相(xiang)同(tong)的(de)(de)(de),充滿電(dian)(dian)(dian)后(hou)假設同(tong)時(shi)從4.2V放到(dao)3.7V,但是(shi)(shi)(shi)一個(ge)(ge)(ge)時(shi)間(jian)(jian)長(chang),一個(ge)(ge)(ge)時(shi)間(jian)(jian)短,就是(shi)(shi)(shi)時(shi)間(jian)(jian)長(chang)的(de)(de)(de)電(dian)(dian)(dian)池平(ping)臺(tai)高(gao),就是(shi)(shi)(shi)高(gao)電(dian)(dian)(dian)壓的(de)(de)(de)時(shi)間(jian)(jian)工作(zuo)(zuo)時(shi)間(jian)(jian)長(chang),比(bi)如這兩(liang)個(ge)(ge)(ge)電(dian)(dian)(dian)池用在手(shou)(shou)機(ji)上,待機(ji)時(shi)間(jian)(jian)是(shi)(shi)(shi)相(xiang)同(tong)的(de)(de)(de),但兩(liang)個(ge)(ge)(ge)手(shou)(shou)機(ji)一起(qi)打電(dian)(dian)(dian)話(hua),平(ping)臺(tai)時(shi)間(jian)(jian)長(chang)的(de)(de)(de)電(dian)(dian)(dian)池通(tong)(tong)知時(shi)間(jian)(jian)會長(chang),平(ping)臺(tai)時(shi)間(jian)(jian)短的(de)(de)(de)電(dian)(dian)(dian)池通(tong)(tong)話(hua)時(shi)間(jian)(jian)會短 二,對于(yu)這個(ge)(ge)(ge)圖,另(ling)一個(ge)(ge)(ge)含義,對理解(jie)(jie)鋰電(dian)(dian)(dian)池的(de)(de)(de)電(dian)(dian)(dian)量(liang)管理監測也(ye)很(hen)有意義。
比如,目前,對充電電池進行電量(liang)監控方法,一般有兩(liang)種。
測量電池電壓方法。當充電器在充電(dian)時(shi)(shi)檢測電(dian)池電(dian)壓(ya)(ya),當電(dian)壓(ya)(ya)達(da)到規定電(dian)壓(ya)(ya)值時(shi)(shi)就(jiu)認為(wei)充滿。如(ru)鋰電(dian)池的(de)(de)(de)(de)電(dian)壓(ya)(ya)充到4.2V時(shi)(shi)就(jiu)認為(wei)充滿。檢測電(dian)壓(ya)(ya)的(de)(de)(de)(de)電(dian)壓(ya)(ya)表精度要達(da)到正負1%的(de)(de)(de)(de)精度。因鋰電(dian)池過充電(dian)要損壞。如(ru)果(guo)想監視電(dian)池充放電(dian)的(de)(de)(de)(de)話,書(shu)上有很成(cheng)熟的(de)(de)(de)(de)電(dian)路可以參考,如(ru)果(guo)只是測量(liang)一下的(de)(de)(de)(de)話那就(jiu)好辦了,根據容量(liang)計算一下負載(zai)電(dian)阻,用標準放電(dian)電(dian)流放電(dian),這時(shi)(shi)再(zai)檢測電(dian)壓(ya)(ya),只要能達(da)到或接近標稱的(de)(de)(de)(de)放電(dian)時(shi)(shi)間就(jiu)行。
測量電池電壓這種方法(fa),有很多不(bu)(bu)足。例如對于(yu)不(bu)(bu)同廠商(shang)生產的電池,其開路(lu)電壓與容量之間的關系各不(bu)(bu)相同等(deng)。優點是設計成本比較低(di)。
還有一個常用(yong)的(de)監(jian)測(ce)剩(sheng)余電(dian)(dian)(dian)量(liang)的(de)方法是,在一些要求(qiu)比較精確電(dian)(dian)(dian)池(chi)容(rong)量(liang)的(de)地方, 了解(jie)電(dian)(dian)(dian)池(chi)剩(sheng)余容(rong)量(liang)用(yong)估(gu)算電(dian)(dian)(dian)池(chi)使用(yong)時間,通(tong)過測(ce)量(liang)流(liu)入/流(liu)出電(dian)(dian)(dian)池(chi)的(de)凈電(dian)(dian)(dian)荷(he)來估(gu)算電(dian)(dian)(dian)池(chi)剩(sheng)余容(rong)量(liang)。對(dui)流(liu)入/流(liu)出電(dian)(dian)(dian)池(chi)的(de)總電(dian)(dian)(dian)流(liu)進(jin)行積分,也(ye)就(jiu)是求(qiu)圖中曲線下的(de)面積,得到的(de)凈電(dian)(dian)(dian)荷(he)數即為剩(sheng)余容(rong)量(liang)。
這就電(dian)池容量計(ji)算的(de)方法(fa)是目前認為是比(bi)較(jiao)精確的(de)計(ji)算電(dian)池電(dian)量的(de)方法(fa)。當然設(she)計(ji)成本也是比(bi)較(jiao)高的(de)。