在有些應用中，較(jiao)長的(de)電(dian)池(chi)壽(shou)命、較(jiao)多的(de)充(chong)電(dian)次數(shu)或(huo)較(jiao)安全的(de)電(dian)池(chi)比電(dian)池(chi)容量更重要。本文介(jie)紹幾種可以極大延長電(dian)池(chi)壽(shou)命的(de)鋰離子電(dian)池(chi)充(chong)電(dian)和放電(dian)方法。

  幾乎所有高性能便攜式產品都會使用包括鋰離子聚合物電池在內的可再充電鋰離子電池，這是因為與其(qi)他可再充(chong)電(dian)(dian)(dian)(dian)電(dian)(dian)(dian)(dian)池相(xiang)比，鋰離子電(dian)(dian)(dian)(dian)池有(you)較高(gao)(gao)的(de)(de)能量密度、較高(gao)(gao)的(de)(de)電(dian)(dian)(dian)(dian)池電(dian)(dian)(dian)(dian)壓、自放電(dian)(dian)(dian)(dian)少、周期壽命非常(chang)長，而且(qie)環保，且(qie)充(chong)電(dian)(dian)(dian)(dian)和(he)維護簡(jian)單。另外，由于其(qi)具(ju)有(you)相(xiang)對高(gao)(gao)的(de)(de)電(dian)(dian)(dian)(dian)壓（2.9V至4.2V），因此很多(duo)便(bian)攜式產品都能用單節(jie)電(dian)(dian)(dian)(dian)池工作，從而簡(jian)化了產品總體設計。C速率等于特定條(tiao)件下的(de)(de)充(chong)電(dian)(dian)(dian)(dian)或(huo)放電(dian)(dian)(dian)(dian)電(dian)(dian)(dian)(dian)流，定義(yi)如下：I=M×Cn

  其中：I = 充電(dian)或(huo)放電(dian)電(dian)流，單位為A；M = C的(de)倍數(shu)(shu)或(huo)分(fen)數(shu)(shu)；C = 額定(ding)容量的(de)數(shu)(shu)值，單位為Ah；N = 小(xiao)時數(shu)(shu)（對應于C）。

  以(yi)1倍C速(su)率(lv)放(fang)電(dian)(dian)(dian)的(de)電(dian)(dian)(dian)池將在一個小時(shi)內(nei)釋放(fang)標稱的(de)額定容(rong)(rong)量(liang)。例如，如果標稱容(rong)(rong)量(liang)是1000mAhr,那么1C的(de)放(fang)電(dian)(dian)(dian)速(su)率(lv)對應(ying)于1000mA的(de)放(fang)電(dian)(dian)(dian)電(dian)(dian)(dian)流，C/10的(de)速(su)率(lv)對應(ying)100mA的(de)放(fang)電(dian)(dian)(dian)電(dian)(dian)(dian)流。

  通常生產商標定的電池容量都是指n=5時，即5小時放電的容量。例如，上述電池在200mA恒流放電時能夠提供5小時的工作時間。理論上該電池在1000mA恒流放電時能夠提供1小時的工作時間。然而實際上由于大電池放電時效能降低，此時的工作時間將小于1小時。
 

  給(gei)鋰離(li)子(zi)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)池(chi)(chi)(chi)充(chong)(chong)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)的(de)(de)(de)推薦方法是(shi)，向(xiang)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)池(chi)(chi)(chi)提供一(yi)(yi)個±1%限壓(ya)的(de)(de)(de)恒定(ding)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)流(liu)(liu)，直(zhi)到(dao)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)池(chi)(chi)(chi)充(chong)(chong)滿電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)，然后(hou)停止充(chong)(chong)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)。用來(lai)決定(ding)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)池(chi)(chi)(chi)何(he)時(shi)(shi)(shi)(shi)(shi)(shi)充(chong)(chong)滿電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)的(de)(de)(de)方法包(bao)括：給(gei)總的(de)(de)(de)充(chong)(chong)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)時(shi)(shi)(shi)(shi)(shi)(shi)間(jian)定(ding)時(shi)(shi)(shi)(shi)(shi)(shi)、監(jian)視充(chong)(chong)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)流(liu)(liu)或(huo)兼(jian)用這兩種方法。第一(yi)(yi)種方法采用限壓(ya)恒定(ding)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)流(liu)(liu)，變化范圍從(cong)C/2到(dao)1C,持續(xu)2.5至(zhi)(zhi)3小(xiao)時(shi)(shi)(shi)(shi)(shi)(shi)，使電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)池(chi)(chi)(chi)達(da)到(dao)100%充(chong)(chong)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)。也(ye)可以使用較低的(de)(de)(de)充(chong)(chong)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)流(liu)(liu)，但(dan)是(shi)將(jiang)需(xu)要更長時(shi)(shi)(shi)(shi)(shi)(shi)間(jian)。第二(er)種方法與第一(yi)(yi)種方法類似，只是(shi)需(xu)要監(jian)視充(chong)(chong)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)流(liu)(liu)。隨(sui)著電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)池(chi)(chi)(chi)的(de)(de)(de)充(chong)(chong)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)，電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)壓(ya)上升，這與采用第一(yi)(yi)種方法時(shi)(shi)(shi)(shi)(shi)(shi)完全相同(tong)。電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)池(chi)(chi)(chi)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)壓(ya)達(da)到(dao)編程限壓(ya)值（也(ye)稱為(wei)浮(fu)動(dong)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)壓(ya)）時(shi)(shi)(shi)(shi)(shi)(shi)，充(chong)(chong)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)流(liu)(liu)開(kai)始下降(jiang)。電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)流(liu)(liu)一(yi)(yi)開(kai)始下降(jiang)時(shi)(shi)(shi)(shi)(shi)(shi)，電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)池(chi)(chi)(chi)約充(chong)(chong)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)至(zhi)(zhi)容量的(de)(de)(de)50%至(zhi)(zhi)60%.浮(fu)動(dong)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)壓(ya)繼(ji)續(xu)提供，直(zhi)到(dao)充(chong)(chong)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)流(liu)(liu)降(jiang)至(zhi)(zhi)足(zu)夠(gou)低的(de)(de)(de)水平(ping)（C/10至(zhi)(zhi)C/20），這時(shi)(shi)(shi)(shi)(shi)(shi)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)池(chi)(chi)(chi)約充(chong)(chong)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)至(zhi)(zhi)容量的(de)(de)(de)92%至(zhi)(zhi)99%,充(chong)(chong)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)周期(qi)終(zhong)止。目前，要為(wei)標準鋰離(li)子(zi)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)池(chi)(chi)(chi)快速充(chong)(chong)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)（不到(dao)1小(xiao)時(shi)(shi)(shi)(shi)(shi)(shi)）至(zhi)(zhi)容量的(de)(de)(de)100%,還沒(mei)有一(yi)(yi)種安全的(de)(de)(de)方法。

  有些鋰離子電池充電器允許使用熱敏電阻監視電池溫度。這么做的主要目的是，如果電池溫度超出推薦的0℃至40℃窗口范圍，就禁止充電。與鎳鎘或鎳氫金屬電池不同，鋰離子電池在充電時溫度上升非常少。圖1是一個典型的鋰離子電池充(chong)(chong)(chong)電(dian)(dian)(dian)(dian)曲線，圖中顯(xian)示了(le)充(chong)(chong)(chong)電(dian)(dian)(dian)(dian)電(dian)(dian)(dian)(dian)流、電(dian)(dian)(dian)(dian)池電(dian)(dian)(dian)(dian)壓和電(dian)(dian)(dian)(dian)池容量隨時(shi)間的(de)變化。那么怎(zen)樣才能正確地為鋰離子(zi)電(dian)(dian)(dian)(dian)池充(chong)(chong)(chong)電(dian)(dian)(dian)(dian)呢？鋰離子(zi)電(dian)(dian)(dian)(dian)池最適合的(de)充(chong)(chong)(chong)電(dian)(dian)(dian)(dian)過程可以(yi)分為四個(ge)階段(duan)：涓流充(chong)(chong)(chong)電(dian)(dian)(dian)(dian)、恒(heng)流充(chong)(chong)(chong)電(dian)(dian)(dian)(dian)、恒(heng)壓充(chong)(chong)(chong)電(dian)(dian)(dian)(dian)以(yi)及充(chong)(chong)(chong)電(dian)(dian)(dian)(dian)終止。參(can)考(kao)圖1.

  階段1:涓流充電--涓流充電用來先對完全放電的電池單元進行預充（恢復性充電）。在電池電壓低于3V左右時，先采用最大0.1C的恒定電流對電池進行充電。
  階段2:恒流充電--當電池電壓上升到涓流充電閾值以上時，提高充電電流進行恒流充電。恒流充電的電流在0.2C至 1.0C之間。恒流充電時的電流并不要求十分精確，準恒定電流也可以。在線性充電器設計中，電流經常隨著電池電壓的上升而上升，以盡量減輕傳輸晶體管上的 散熱問題。大于1C的恒流充電并不會縮短整個充電周期時間，因此這種做法不可取。當以更高電流充電時，由于電極反應的過壓以及電池內部阻抗上的電壓上升，電池電壓會更快速地上升。恒流充電階段會變短，但由于下面恒壓充電階段的時間會相應增加，因此總的充電周期時間并不會縮短。
  階段3:恒壓充電-- 當電池電壓上升到4.2V時，恒流充電結束，開始恒壓充電階段。為使性能達到最佳，穩壓容差應當優于+1%.
階段4:充電終止--與鎳電池不同，并不建議對鋰離子電池連(lian)續(xu)涓流充電(dian)。連(lian)續(xu)涓流充電(dian)會導致(zhi)金(jin)屬鋰出現極板電(dian)鍍效應。這(zhe)會使電(dian)池不(bu)穩定(ding)，并(bing)且有可能導致(zhi)突(tu)然的自動快速(su)解體(ti)。

  有兩種典(dian)型的(de)充(chong)電(dian)(dian)(dian)終止(zhi)方法：采(cai)用最(zui)小充(chong)電(dian)(dian)(dian)電(dian)(dian)(dian)流判斷(duan)或采(cai)用定(ding)時(shi)器（或者兩者的(de)結(jie)合）。最(zui)小電(dian)(dian)(dian)流法監(jian)視恒(heng)(heng)壓(ya)充(chong)電(dian)(dian)(dian)階段的(de)充(chong)電(dian)(dian)(dian)電(dian)(dian)(dian)流，并在充(chong)電(dian)(dian)(dian)電(dian)(dian)(dian)流減小到0.02C至0.07C范圍時(shi)終止(zhi)充(chong)電(dian)(dian)(dian)。第二種方法從恒(heng)(heng)壓(ya)充(chong)電(dian)(dian)(dian)階段開始時(shi)計時(shi)，持續充(chong)電(dian)(dian)(dian)兩個小時(shi)后終止(zhi)充(chong)電(dian)(dian)(dian)過程。

  上述四階段的充電法完成對完全放電電池的充電約需要2.5至3小時。高級充電器還(huan)采用了(le)更多安全措施。例如如果電(dian)(dian)池溫度超出(chu)指(zhi)定窗口(kou)（通常(chang)為0℃至45℃），那么充電(dian)(dian)會暫(zan)停。

  1 決定鋰離子電池周期壽命或服務壽命的因素

  不(bu)存在任何延(yan)長(chang)(chang)或縮(suo)短電(dian)池(chi)壽命(ming)(ming)的(de)單一因素，而常(chang)(chang)常(chang)(chang)是幾種因素合起來發(fa)揮作用。就延(yan)長(chang)(chang)周期(qi)壽命(ming)(ming)而言有以下方法可以延(yan)長(chang)(chang)電(dian)池(chi)壽命(ming)(ming)：

1).采用部分放電(dian)(dian)的(de)做(zuo)法。在再(zai)充電(dian)(dian)前僅使用20%或(huo)30%的(de)電(dian)(dian)池(chi)(chi)容量會極大延長周(zhou)期壽命(ming)。作為一(yi)個一(yi)般性(xing)的(de)規則，5至10個淺放電(dian)(dian)周(zhou)期等于(yu)1個滿(man)放電(dian)(dian)周(zhou)期。盡管(guan)部分放電(dian)(dian)周(zhou)期可能達到(dao)數(shu)千次，但是保持電(dian)(dian)池(chi)(chi)處于(yu)滿(man)充電(dian)(dian)狀態也縮短電(dian)(dian)池(chi)(chi)壽命(ming)。如(ru)果可能，應該避免滿(man)放電(dian)(dian)周(zhou)期（降(jiang)至2.5V或(huo)3V,取決于(yu)化學材料(liao)）。

2).避免充電至(zhi)容(rong)量(liang)的(de)100%.選(xuan)擇一個較(jiao)低(di)(di)(di)的(de)浮動(dong)(dong)電壓(ya)(ya)可以做到這一點(dian)。降(jiang)低(di)(di)(di)浮動(dong)(dong)電壓(ya)(ya)將(jiang)提高周(zhou)期壽(shou)(shou)命(ming)和服務壽(shou)(shou)命(ming)，代價是降(jiang)低(di)(di)(di)電池(chi)容(rong)量(liang)。浮動(dong)(dong)電壓(ya)(ya)降(jiang)低(di)(di)(di)100mV至(zhi)300mV可以將(jiang)周(zhou)期壽(shou)(shou)命(ming)延長(chang)2至(zhi)5倍(bei)或更(geng)長(chang)。與(yu)其他(ta)化學材料相比(bi)，鋰(li)離子(zi)鈷(gu)化學材料對較(jiao)高浮動(dong)(dong)電壓(ya)(ya)更(geng)敏感。磷酸(suan)鋰(li)離子(zi)電池(chi)一般(ban)比(bi)更(geng)常(chang)見的(de)鋰(li)離子(zi)電池(chi)的(de)浮動(dong)(dong)電壓(ya)(ya)低(di)(di)(di)。

3). 選擇合適的充電終止方法。選擇一個采用最小充電電流終止（C/10或C/x）的充電器，通過(guo)不充電到(dao)容量的(de)100%,也可以延長(chang)電池(chi)壽(shou)命。例如，電流(liu)降(jiang)至C/5時(shi)結束充電周(zhou)期與將浮動(dong)電壓降(jiang)至4.1V的(de)效果類似。在這兩種情況下，電池(chi)都只充電至約為容量的(de)85%,這是決定電池(chi)壽(shou)命的(de)一個重要因素(su)。

4).限(xian)制(zhi)電(dian)(dian)(dian)(dian)池溫(wen)度。限(xian)制(zhi)電(dian)(dian)(dian)(dian)池的(de)極限(xian)溫(wen)度可(ke)以(yi)(yi)延長(chang)電(dian)(dian)(dian)(dian)池壽命，尤其是禁止在(zai)(zai)(zai)0℃以(yi)(yi)下充(chong)電(dian)(dian)(dian)(dian)。在(zai)(zai)(zai)0℃以(yi)(yi)下充(chong)電(dian)(dian)(dian)(dian)促進金屬在(zai)(zai)(zai)電(dian)(dian)(dian)(dian)池陽極上的(de)鍍敷(fu)，這(zhe)可(ke)能造成(cheng)內部短路(lu)，產(chan)生(sheng)熱量(liang)并(bing)使(shi)電(dian)(dian)(dian)(dian)池不(bu)穩定和(he)不(bu)安全。很多(duo)電(dian)(dian)(dian)(dian)池充(chong)電(dian)(dian)(dian)(dian)器(qi)都有測(ce)量(liang)電(dian)(dian)(dian)(dian)池溫(wen)度的(de)裝置，以(yi)(yi)確保不(bu)會(hui)在(zai)(zai)(zai)極限(xian)溫(wen)度時(shi)充(chong)電(dian)(dian)(dian)(dian)。

5).避免大(da)的充電(dian)(dian)和放電(dian)(dian)電(dian)(dian)流(liu)，因(yin)為(wei)這會縮短周(zhou)期壽(shou)命。有些化學材料更(geng)適合(he)較大(da)電(dian)(dian)流(liu)，如鋰(li)離(li)子(zi)錳和磷酸(suan)鋰(li)離(li)子(zi)電(dian)(dian)池(chi)。大(da)電(dian)(dian)流(liu)給電(dian)(dian)池(chi)施加了過大(da)的壓(ya)力。

6).避免(mian)低于2V或(huo)(huo)2.5V的深(shen)度放電(dian)(dian)，因為(wei)這會迅速永久(jiu)性損壞(huai)鋰離子電(dian)(dian)池。可能發生內(nei)部金屬鍍敷，這會引起短路，使電(dian)(dian)池不(bu)可用或(huo)(huo)不(bu)安全。大多(duo)數鋰離子電(dian)(dian)池在電(dian)(dian)池組(zu)內(nei)部都(dou)有電(dian)(dian)子電(dian)(dian)路，如(ru)(ru)果(guo)充(chong)電(dian)(dian)或(huo)(huo)放電(dian)(dian)時電(dian)(dian)池電(dian)(dian)壓低于2.5V、超(chao)過(guo)4.3V或(huo)(huo)如(ru)(ru)果(guo)電(dian)(dian)池電(dian)(dian)流超(chao)過(guo)預定門限值，該電(dian)(dian)子電(dian)(dian)路就會斷開電(dian)(dian)池連接(jie)。

  2 鋰離子充電--系統(tong)注(zhu)意事項

  要快速可靠(kao)地完成充(chong)電過程需要一(yi)個高性能的充(chong)電系統(tong)。為(wei)實現(xian)可靠(kao)且(qie)經濟高效(xiao)的解決方案，設(she)計時(shi)應當考慮到以下系統(tong)參數：

2.1 輸入源
  許多應用都采用極廉價的墻式適(shi)配器(qi)(qi)作為輸入電源。其(qi)輸出(chu)電壓(ya)主要依賴于交流輸入電壓(ya)和(he)從墻式適(shi)配器(qi)(qi)流出(chu)的負(fu)載電流。

  在美國標準的墻面插座上交流母線輸入電壓的變化范圍一般為90VRMS至132VRMS.假設額定輸入電壓為120VRMS,容差為+10%, ?25%.充電器必須為電池提供適當的穩壓措施，從而不受輸入電壓的影響。充電器的輸入電壓與交流母線電壓和充電電流成比例：
 
VO=2VIN×a-1O（REQ+RPTC）-2×VFD
  REQ是次(ci)級(ji)繞(rao)組(zu)的電(dian)阻(zu)與初級(ji)繞(rao)組(zu)反射電(dian)阻(zu)的和(he)。RPTC是PTC的電(dian)阻(zu)，VFD是橋式整流(liu)器的前向壓(ya)(ya)降。此外變壓(ya)(ya)器磁芯損失也會使輸(shu)出電(dian)壓(ya)(ya)略有降低(di)。

  利用汽車適配器(qi)(qi)充(chong)電的應用也會遇(yu)到(dao)類似的問題。汽車適配器(qi)(qi)的輸出(chu)電壓(ya)典型范圍(wei)為9V至18V.

2.2 恒流充電的速率和精度
   特定應用的拓撲結構選擇可能要由充電電流來決定。出于尺寸和成本方面的考慮，低檔和中檔的快速充電應用則傾向于采用線性解決方案，然 而線性解決方案會以熱的形式損失更多能耗。對于線性充電系統來說，恒流充電的容差變得極為重要。如果穩壓容差太大，傳輸晶體管和其他元器件都需要更大體 積，從而增加尺寸和成本。此外，如果恒流充電電流過小，整個充電周期將會延長。
2.3 輸出電壓的穩定精度
   為了盡(jin)可能(neng)地充分利用電(dian)(dian)池容量(liang)，輸(shu)出(chu)電(dian)(dian)壓(ya)(ya)穩(wen)壓(ya)(ya)精(jing)(jing)度非(fei)常關鍵。輸(shu)出(chu)電(dian)(dian)壓(ya)(ya)精(jing)(jing)度的(de)小(xiao)幅(fu)(fu)度下降也(ye)會(hui)導致電(dian)(dian)池容量(liang)的(de)大幅(fu)(fu)減少。然(ran)而(er)出(chu)于安(an)全和可靠性(xing)方面的(de)考慮(lv)，輸(shu)出(chu)電(dian)(dian)壓(ya)(ya)也(ye)不能(neng)隨意設(she)置得過高。圖2顯示(shi)出(chu)了輸(shu)出(chu)電(dian)(dian)壓(ya)(ya)穩(wen)定(ding)精(jing)(jing)度的(de)重(zhong)要性(xing)。

3 充電終止方法

  毋庸置(zhi)疑(yi)，過充(chong)始(shi)終(zhong)是鋰(li)離(li)子電(dian)池充(chong)電(dian)的(de)心頭大患。準確的(de)充(chong)電(dian)終(zhong)止方法對于安全可靠(kao)的(de)充(chong)電(dian)系統(tong)來(lai)說非常關(guan)鍵。

3 .1 電池溫度監控
  一般情況下，鋰離子電(dian)(dian)(dian)(dian)(dian)池(chi)(chi)充(chong)電(dian)(dian)(dian)(dian)(dian)時(shi)的(de)溫度范(fan)圍(wei)應當在(zai)0℃至45℃。在(zai)此(ci)溫度范(fan)圍(wei)之(zhi)外對電(dian)(dian)(dian)(dian)(dian)池(chi)(chi)充(chong)電(dian)(dian)(dian)(dian)(dian)會(hui)(hui)導(dao)致(zhi)電(dian)(dian)(dian)(dian)(dian)池(chi)(chi)過熱。在(zai)充(chong)電(dian)(dian)(dian)(dian)(dian)周期(qi)中(zhong)，電(dian)(dian)(dian)(dian)(dian)池(chi)(chi)內的(de)壓力上(shang)升還會(hui)(hui) 導(dao)致(zhi)電(dian)(dian)(dian)(dian)(dian)池(chi)(chi)膨脹。隨著(zhu)溫度上(shang)升，壓力也(ye)會(hui)(hui)過大，這可能(neng)會(hui)(hui)導(dao)致(zhi)電(dian)(dian)(dian)(dian)(dian)池(chi)(chi)內部(bu)的(de)機械破裂(lie)或(huo)材料(liao)泄漏，嚴(yan)重時(shi)還有可能(neng)導(dao)致(zhi)爆炸。在(zai)此(ci)溫度范(fan)圍(wei)之(zhi)外 對電(dian)(dian)(dian)(dian)(dian)池(chi)(chi)充(chong)電(dian)(dian)(dian)(dian)(dian)還會(hui)(hui)損害(hai)電(dian)(dian)(dian)(dian)(dian)池(chi)(chi)的(de)性(xing)能(neng)，或(huo)縮短電(dian)(dian)(dian)(dian)(dian)池(chi)(chi)的(de)預期(qi)壽命。

  通常鋰離子電(dian)(dian)池包(bao)內都(dou)采用了熱敏電(dian)(dian)阻(zu)來準確測(ce)量電(dian)(dian)池溫度。充電(dian)(dian)器(qi)檢測(ce)熱敏電(dian)(dian)阻(zu)的阻(zu)值，當(dang)阻(zu)值超出規定工(gong)作范圍，即溫度超過規定范圍時(shi)，充電(dian)(dian)被禁止(zhi)。

3.2 電池放電電流或反向泄漏電流
  在許多應(ying)用中，即使輸(shu)(shu)入電源不存(cun)在，充(chong)電系統(tong)仍然與電池(chi)相連。充(chong)電系統(tong)必須保證輸(shu)(shu)入電源不存(cun)在時，從電池(chi)汲取(qu)的電流極小。最(zui)大(da)泄漏(lou)電流應(ying)當(dang)小于(yu)幾個(ge)微安，通常應(ying)小于(yu)一個(ge)微安。

4 鋰離子充電--應用實例

  將(jiang)以(yi)上幾點系(xi)統(tong)注意事項事先充分(fen)考(kao)慮，就能(neng)開發出適合的充電管(guan)理系(xi)統(tong)。

4.1 線性解決方案
  當存在(zai)(zai)穩壓良好的輸(shu)入電源時(shi)，通(tong)常采用線(xian)性(xing)充(chong)(chong)電解(jie)決(jue)方(fang)案。在(zai)(zai)此類應用中，線(xian)性(xing)解(jie)決(jue)方(fang)案的優點包括易用、尺寸小以(yi)及成本低。由于線(xian)性(xing)充(chong)(chong)電解(jie)決(jue)方(fang)案 效率低因此影響(xiang)設計的最(zui)重(zhong)要因素就是(shi)散(san)(san)熱設計。最(zui)糟的情況是(shi)器(qi)件從(cong)涓流充(chong)(chong)電階段向 恒流充(chong)(chong)電階段轉換時(shi)，在(zai)(zai)此情況下，傳(chuan)輸(shu)晶體管必(bi)(bi)須散(san)(san)發最(zui)大(da)的熱能(neng)，必(bi)(bi)須在(zai)(zai)充(chong)(chong)電電流、系統尺寸、成本和散(san)(san)熱要求之間進行權衡。

  例如，應用中需(xu)(xu)要利(li)用一個(ge)5V ±5%的(de)(de)輸(shu)入電(dian)(dian)源以0.5C或1C的(de)(de)恒(heng)(heng)定電(dian)(dian)流(liu)對一個(ge)1000mAh的(de)(de)單節鋰離子電(dian)(dian)池充(chong)(chong)電(dian)(dian)。圖(tu)3顯示了如何利(li)用Microchip的(de)(de) MCP73843構成(cheng)一個(ge)低成(cheng)本的(de)(de)獨立(li)解決(jue)方案，只需(xu)(xu)要極少量的(de)(de)外部元器件，就(jiu)可(ke)以實現所(suo)需(xu)(xu)要的(de)(de)充(chong)(chong)電(dian)(dian)算法。MCP73843完美地結合(he)了高精度恒(heng)(heng)流(liu)充(chong)(chong)電(dian)(dian)、 恒(heng)(heng)壓穩壓以及自動充(chong)(chong)電(dian)(dian)終(zhong)止(zhi)等功(gong)能。

  為進一步減小(xiao)線(xian)性解決(jue)方案的(de)尺寸、降低其成(cheng)本和復雜性，許多外(wai)部元器(qi)件都可以集成(cheng)到(dao)充(chong)電(dian)(dian)管(guan)理控(kong)制(zhi)器(qi)中。先進的(de)封(feng)裝可以提供(gong)更高的(de)集成(cheng)度(du)，當然也會犧(xi)牲一定的(de)靈活性。此外(wai)此類充(chong)電(dian)(dian)管(guan)理控(kong)制(zhi)器(qi) 還會實(shi)現一定的(de)熱調節(jie)功能。熱調節(jie)功能可根(gen)據器(qi)件管(guan)芯溫度(du)來限制(zhi)充(chong)電(dian)(dian)電(dian)(dian)流，從而可在(zai)保證(zheng)器(qi)件可靠(kao)性的(de)情況下優(you)化充(chong)電(dian)(dian)周期時間，熱調節(jie)功能大大降低了散熱設 計的(de)工作量。

  基于Microchip MCP73861的全集(ji)成線性(xing)解決方案如(ru)圖4所示。MCP73861包含了MCP73843的所有功能，另(ling)外(wai)還包括電流檢測、傳輸晶體管、反向放電保護以(yi)及電池溫度監測。

4.2 充電周期波形
  利用(yong)MCP73843在1C和0.5C恒流充(chong)電(dian)速率(lv)下的整個充(chong)電(dian)周期如(ru)圖5.以(yi)0.5C而不是1C速率(lv)充(chong)電(dian)時，充(chong)電(dian)結束的時間(jian)大約(yue)晚了一個小(xiao)時。充(chong)電(dian)終(zhong)止電(dian)流從(cong)0.07C降(jiang)到0.035C,使得最終(zhong)電(dian)池(chi)容(rong)量從(cong)~98%增長到~100%.系統(tong)設(she)計師(shi)必須在充(chong)電(dian)時間(jian)、功率(lv)損耗和可(ke)用(yong)電(dian)池(chi)容(rong)量之間(jian)進行權衡。

4.3 開關式充電解決方案
  輸(shu)入電(dian)壓波動范圍寬(kuan)或輸(shu)入輸(shu)出電(dian)壓差大的(de)應(ying)用通(tong)常采用開關式充(chong)電(dian)解決(jue)(jue)方案。例如應(ying)用中需要利(li)用汽車適配器以0.5C或1C的(de)恒定電(dian)流(liu)對一個(ge)2200mAh的(de)單(dan)節(jie)鋰離子電(dian)池充(chong)電(dian)，由于(yu)散熱(re)等(deng)問題(ti)，利(li)用線性解決(jue)(jue)方案實現(xian)極為(wei)困難，當然(ran)也可以采用支持(chi)熱(re)調節(jie)的(de)線性解決(jue)(jue)方案，但降低充(chong)電(dian)電(dian)流(liu)造成的(de)充(chong)電(dian)周(zhou)期延長是(shi)無法接受的(de)。

  成功設計(ji)開關式(shi)(shi)充電(dian)(dian)(dian)(dian)解(jie)決方案(an)的第一(yi)(yi)步是(shi)選擇(ze)設計(ji)結(jie)構：降壓式(shi)(shi)、升壓式(shi)(shi)、升/降壓式(shi)(shi)、反激式(shi)(shi)、單端(duan)初級(ji)電(dian)(dian)(dian)(dian)感式(shi)(shi)或者其他形式(shi)(shi)。SEPIC拓撲結(jie)構的優點是(shi)低端(duan)柵極驅(qu)動(dong)和電(dian)(dian)(dian)(dian)流(liu)(liu)檢測、持續輸(shu)(shu) 入電(dian)(dian)(dian)(dian)流(liu)(liu)以及輸(shu)(shu)入和輸(shu)(shu)出間的直流(liu)(liu)隔(ge)離(li)，其主要(yao)缺點是(shi)需要(yao)兩個電(dian)(dian)(dian)(dian)感和一(yi)(yi)個能量(liang)傳輸(shu)(shu)電(dian)(dian)(dian)(dian)容。

  MCP1630是一款可配合單片機使用的高速脈寬調制器，配合單片機，MCP1630可控制電源系統占空比，提供輸出電壓或電流穩定 功能。PIC16F684單片機可用于輸出穩壓或穩流，以及開關頻率和最大占空比的調整。MCP1630產生占空比，并可根據不同外部輸入提供快速過流保 護。充電器采用的電(dian)(dian)(dian)源結(jie)構(gou)是SEPIC.單片機提供(gong)了極(ji)大的設計靈(ling)活 性。此外單片機還可以與電(dian)(dian)(dian)池(chi)包內(nei)的電(dian)(dian)(dian)池(chi)監控器通信，從(cong)而大大縮短充電(dian)(dian)(dian)周(zhou)期時間。

  利(li)用開(kai)關式充電(dian)(dian)解(jie)決方案的(de)整個充電(dian)(dian)周(zhou)期(qi)如(ru)圖6所示。通過在充電(dian)(dian)系統中采用電(dian)(dian)池(chi)監(jian)控(kong)器，可以(yi)大大縮短充電(dian)(dian)周(zhou)期(qi)，使用電(dian)(dian)池(chi)監(jian)控(kong)器就不必(bi)再(zai)檢測(ce)電(dian)(dian)池(chi)包保(bao)護電(dian)(dian)路(lu)兩端的(de)電(dian)(dian)壓以(yi)及充電(dian)(dian)電(dian)(dian)流的(de)接觸電(dian)(dian)阻(zu)。

5 結論

  在目前的(de)便攜(xie)式產(chan)品中，要(yao)正確地實現電(dian)池充(chong)電(dian)需(xu)要(yao)仔(zi)細地設(she)計考(kao)慮。本文討(tao)論了鋰離子電(dian)池的(de)線性和開關式充(chong)電(dian)解決方案(an)，本文所探討(tao)的(de)指導原則和設(she)計考(kao)慮要(yao)素，實際(ji)上(shang)也(ye)是(shi)所有電(dian)池充(chong)電(dian)系統設(she)計都需(xu)要(yao)考(kao)慮的(de)。