在(zai)有些應用中，較(jiao)長的電(dian)池(chi)壽命、較(jiao)多的充電(dian)次數(shu)或較(jiao)安全的電(dian)池(chi)比(bi)電(dian)池(chi)容(rong)量更重要。本文介紹幾(ji)種(zhong)可以極大延(yan)長電(dian)池(chi)壽命的鋰離子電(dian)池(chi)充電(dian)和(he)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(shi)因為與其他可(ke)再充(chong)電電池相比，鋰離子電池有較(jiao)(jiao)高的(de)能量密(mi)度(du)、較(jiao)(jiao)高的(de)電池電壓、自放電少(shao)、周期壽命非(fei)常長，而且(qie)環保，且(qie)充(chong)電和維護簡(jian)單。另外(wai)，由(you)于其具有相對(dui)高的(de)電壓（2.9V至4.2V），因此(ci)很多便攜式產品都能用(yong)單節電池工作，從而簡(jian)化(hua)了產品總體設計。C速率等于特定條件(jian)下的(de)充(chong)電或放電電流，定義(yi)如下：I=M×Cn

  其(qi)中：I = 充電或放電電流，單位為(wei)(wei)A；M = C的(de)倍數或分數；C = 額定(ding)容量的(de)數值，單位為(wei)(wei)Ah；N = 小時(shi)數（對應于C）。

  以1倍(bei)C速(su)率(lv)放(fang)(fang)電(dian)的(de)電(dian)池將在一個小時內(nei)釋放(fang)(fang)標稱的(de)額定(ding)容量(liang)。例如(ru)，如(ru)果標稱容量(liang)是1000mAhr,那(nei)么1C的(de)放(fang)(fang)電(dian)速(su)率(lv)對(dui)應于(yu)1000mA的(de)放(fang)(fang)電(dian)電(dian)流(liu)，C/10的(de)速(su)率(lv)對(dui)應100mA的(de)放(fang)(fang)電(dian)電(dian)流(liu)。

  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。
 

  給鋰離子(zi)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)池(chi)(chi)(chi)充(chong)(chong)(chong)(chong)(chong)(chong)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)的(de)(de)推(tui)薦方法是(shi)，向電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)池(chi)(chi)(chi)提供一(yi)個(ge)±1%限壓的(de)(de)恒定(ding)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)流(liu)(liu)(liu)(liu)(liu)，直到電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)池(chi)(chi)(chi)充(chong)(chong)(chong)(chong)(chong)(chong)滿(man)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)，然(ran)后停止充(chong)(chong)(chong)(chong)(chong)(chong)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)。用來決定(ding)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)池(chi)(chi)(chi)何(he)時(shi)(shi)充(chong)(chong)(chong)(chong)(chong)(chong)滿(man)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)的(de)(de)方法包括：給總的(de)(de)充(chong)(chong)(chong)(chong)(chong)(chong)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)時(shi)(shi)間(jian)定(ding)時(shi)(shi)、監(jian)視充(chong)(chong)(chong)(chong)(chong)(chong)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)流(liu)(liu)(liu)(liu)(liu)或(huo)兼(jian)用這兩種(zhong)(zhong)(zhong)方法。第(di)一(yi)種(zhong)(zhong)(zhong)方法采用限壓恒定(ding)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)流(liu)(liu)(liu)(liu)(liu)，變化范圍從C/2到1C,持續2.5至(zhi)(zhi)(zhi)3小時(shi)(shi)，使電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)池(chi)(chi)(chi)達(da)到100%充(chong)(chong)(chong)(chong)(chong)(chong)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)。也(ye)可(ke)以使用較(jiao)低的(de)(de)充(chong)(chong)(chong)(chong)(chong)(chong)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)流(liu)(liu)(liu)(liu)(liu)，但是(shi)將需要(yao)(yao)更長時(shi)(shi)間(jian)。第(di)二種(zhong)(zhong)(zhong)方法與(yu)第(di)一(yi)種(zhong)(zhong)(zhong)方法類似，只是(shi)需要(yao)(yao)監(jian)視充(chong)(chong)(chong)(chong)(chong)(chong)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)流(liu)(liu)(liu)(liu)(liu)。隨(sui)著(zhu)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)池(chi)(chi)(chi)的(de)(de)充(chong)(chong)(chong)(chong)(chong)(chong)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)，電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)壓上升，這與(yu)采用第(di)一(yi)種(zhong)(zhong)(zhong)方法時(shi)(shi)完全相同。電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)池(chi)(chi)(chi)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)壓達(da)到編程限壓值（也(ye)稱為浮動電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)壓）時(shi)(shi)，充(chong)(chong)(chong)(chong)(chong)(chong)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)流(liu)(liu)(liu)(liu)(liu)開始下降。電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)流(liu)(liu)(liu)(liu)(liu)一(yi)開始下降時(shi)(shi)，電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)池(chi)(chi)(chi)約充(chong)(chong)(chong)(chong)(chong)(chong)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)至(zhi)(zhi)(zhi)容(rong)量的(de)(de)50%至(zhi)(zhi)(zhi)60%.浮動電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)壓繼續提供，直到充(chong)(chong)(chong)(chong)(chong)(chong)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)流(liu)(liu)(liu)(liu)(liu)降至(zhi)(zhi)(zhi)足夠低的(de)(de)水平（C/10至(zhi)(zhi)(zhi)C/20），這時(shi)(shi)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)池(chi)(chi)(chi)約充(chong)(chong)(chong)(chong)(chong)(chong)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)至(zhi)(zhi)(zhi)容(rong)量的(de)(de)92%至(zhi)(zhi)(zhi)99%,充(chong)(chong)(chong)(chong)(chong)(chong)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)周期終止。目(mu)前(qian)，要(yao)(yao)為標準(zhun)鋰離子(zi)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)池(chi)(chi)(chi)快速充(chong)(chong)(chong)(chong)(chong)(chong)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)（不(bu)到1小時(shi)(shi)）至(zhi)(zhi)(zhi)容(rong)量的(de)(de)100%,還沒有(you)一(yi)種(zhong)(zhong)(zhong)安(an)全的(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)曲線(xian)，圖中(zhong)顯示(shi)了充(chong)(chong)(chong)電(dian)(dian)電(dian)(dian)流(liu)(liu)、電(dian)(dian)池(chi)電(dian)(dian)壓(ya)和電(dian)(dian)池(chi)容量隨時間的(de)(de)變化。那么(me)怎樣(yang)才(cai)能正確地為(wei)鋰離子電(dian)(dian)池(chi)充(chong)(chong)(chong)電(dian)(dian)呢？鋰離子電(dian)(dian)池(chi)最適合的(de)(de)充(chong)(chong)(chong)電(dian)(dian)過(guo)程可以分(fen)為(wei)四個階段：涓流(liu)(liu)充(chong)(chong)(chong)電(dian)(dian)、恒流(liu)(liu)充(chong)(chong)(chong)電(dian)(dian)、恒壓(ya)充(chong)(chong)(chong)電(dian)(dian)以及充(chong)(chong)(chong)電(dian)(dian)終(zhong)止(zhi)。參考圖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續(xu)涓(juan)流(liu)充電(dian)(dian)。連續(xu)涓(juan)流(liu)充電(dian)(dian)會導(dao)致金屬鋰(li)出現極板電(dian)(dian)鍍效(xiao)應。這會使電(dian)(dian)池不(bu)穩定，并且有可能(neng)導(dao)致突然(ran)的自(zi)動快(kuai)速(su)解(jie)體(ti)。

  有兩種(zhong)典型(xing)的(de)充(chong)(chong)(chong)(chong)電(dian)(dian)(dian)終止(zhi)(zhi)(zhi)方法：采用最小充(chong)(chong)(chong)(chong)電(dian)(dian)(dian)電(dian)(dian)(dian)流(liu)判(pan)斷或(huo)采用定時(shi)器（或(huo)者兩者的(de)結合）。最小電(dian)(dian)(dian)流(liu)法監視(shi)恒壓(ya)充(chong)(chong)(chong)(chong)電(dian)(dian)(dian)階段的(de)充(chong)(chong)(chong)(chong)電(dian)(dian)(dian)電(dian)(dian)(dian)流(liu)，并在充(chong)(chong)(chong)(chong)電(dian)(dian)(dian)電(dian)(dian)(dian)流(liu)減小到0.02C至0.07C范圍時(shi)終止(zhi)(zhi)(zhi)充(chong)(chong)(chong)(chong)電(dian)(dian)(dian)。第二種(zhong)方法從(cong)恒壓(ya)充(chong)(chong)(chong)(chong)電(dian)(dian)(dian)階段開始時(shi)計時(shi)，持續充(chong)(chong)(chong)(chong)電(dian)(dian)(dian)兩個小時(shi)后(hou)終止(zhi)(zhi)(zhi)充(chong)(chong)(chong)(chong)電(dian)(dian)(dian)過程(cheng)。

  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。高級充電器還采(cai)用(yong)了更多安全措施。例如(ru)(ru)如(ru)(ru)果電池溫度超出指定(ding)窗口（通常為0℃至45℃），那么充電會暫停。

  1 決定鋰離子(zi)電池周期壽(shou)命或服務(wu)壽(shou)命的因素

  不存在任何(he)延(yan)長或縮短(duan)電池(chi)(chi)壽(shou)命(ming)的單一因(yin)素，而常(chang)常(chang)是幾(ji)種因(yin)素合起來發揮作用。就延(yan)長周期壽(shou)命(ming)而言有以下(xia)方法(fa)可以延(yan)長電池(chi)(chi)壽(shou)命(ming)：

1).采用部(bu)分(fen)放(fang)(fang)電(dian)(dian)(dian)的做法(fa)。在再充電(dian)(dian)(dian)前僅使用20%或30%的電(dian)(dian)(dian)池(chi)(chi)容量會(hui)極大延長周(zhou)(zhou)期壽命(ming)。作為一個(ge)(ge)一般性的規(gui)則(ze)，5至(zhi)10個(ge)(ge)淺放(fang)(fang)電(dian)(dian)(dian)周(zhou)(zhou)期等于(yu)(yu)1個(ge)(ge)滿(man)放(fang)(fang)電(dian)(dian)(dian)周(zhou)(zhou)期。盡管部(bu)分(fen)放(fang)(fang)電(dian)(dian)(dian)周(zhou)(zhou)期可能達(da)到數千次，但是(shi)保持電(dian)(dian)(dian)池(chi)(chi)處于(yu)(yu)滿(man)充電(dian)(dian)(dian)狀態也縮短電(dian)(dian)(dian)池(chi)(chi)壽命(ming)。如果可能，應該(gai)避免滿(man)放(fang)(fang)電(dian)(dian)(dian)周(zhou)(zhou)期（降至(zhi)2.5V或3V,取(qu)決于(yu)(yu)化學材料(liao)）。

2).避免充電(dian)至容量(liang)的100%.選(xuan)擇一(yi)個較低的浮(fu)動(dong)(dong)(dong)電(dian)壓(ya)可(ke)以做到這一(yi)點。降低浮(fu)動(dong)(dong)(dong)電(dian)壓(ya)將提高周(zhou)期壽命和服(fu)務壽命，代價是降低電(dian)池(chi)容量(liang)。浮(fu)動(dong)(dong)(dong)電(dian)壓(ya)降低100mV至300mV可(ke)以將周(zhou)期壽命延(yan)長2至5倍或更(geng)長。與(yu)其(qi)他化學(xue)材料相比，鋰(li)離(li)子鈷化學(xue)材料對較高浮(fu)動(dong)(dong)(dong)電(dian)壓(ya)更(geng)敏(min)感。磷酸鋰(li)離(li)子電(dian)池(chi)一(yi)般(ban)比更(geng)常見(jian)的鋰(li)離(li)子電(dian)池(chi)的浮(fu)動(dong)(dong)(dong)電(dian)壓(ya)低。

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(tong)過不(bu)充電(dian)(dian)到容量(liang)的100%,也(ye)可以延長電(dian)(dian)池(chi)壽(shou)(shou)命(ming)。例如，電(dian)(dian)流降至C/5時結(jie)束充電(dian)(dian)周期與將(jiang)浮動電(dian)(dian)壓降至4.1V的效(xiao)果類(lei)似。在(zai)這兩(liang)種情況下，電(dian)(dian)池(chi)都只充電(dian)(dian)至約為容量(liang)的85%,這是決定電(dian)(dian)池(chi)壽(shou)(shou)命(ming)的一個重要因(yin)素。

4).限(xian)制(zhi)電(dian)(dian)(dian)池(chi)(chi)溫度。限(xian)制(zhi)電(dian)(dian)(dian)池(chi)(chi)的極限(xian)溫度可以延長電(dian)(dian)(dian)池(chi)(chi)壽命，尤其是禁止(zhi)在(zai)(zai)0℃以下(xia)充(chong)電(dian)(dian)(dian)。在(zai)(zai)0℃以下(xia)充(chong)電(dian)(dian)(dian)促進金(jin)屬(shu)在(zai)(zai)電(dian)(dian)(dian)池(chi)(chi)陽極上的鍍(du)敷(fu)，這可能造成內部短路(lu)，產生熱量并使電(dian)(dian)(dian)池(chi)(chi)不穩定和不安全。很多電(dian)(dian)(dian)池(chi)(chi)充(chong)電(dian)(dian)(dian)器(qi)都有測量電(dian)(dian)(dian)池(chi)(chi)溫度的裝置(zhi)，以確保不會在(zai)(zai)極限(xian)溫度時充(chong)電(dian)(dian)(dian)。

5).避免(mian)大(da)(da)的充(chong)電和放電電流，因(yin)為這(zhe)會(hui)縮(suo)短周(zhou)期(qi)壽命。有(you)些(xie)化學材料更(geng)適合較大(da)(da)電流，如鋰離(li)(li)子(zi)錳(meng)和磷酸鋰離(li)(li)子(zi)電池。大(da)(da)電流給電池施(shi)加了過(guo)大(da)(da)的壓力。

6).避免低(di)(di)于2V或(huo)2.5V的深度放電(dian)(dian)，因(yin)為這會(hui)迅速永久性損壞鋰離子(zi)電(dian)(dian)池(chi)(chi)(chi)。可能發生內部(bu)金屬鍍敷，這會(hui)引起(qi)短(duan)路(lu)，使電(dian)(dian)池(chi)(chi)(chi)不可用或(huo)不安(an)全。大(da)多數鋰離子(zi)電(dian)(dian)池(chi)(chi)(chi)在電(dian)(dian)池(chi)(chi)(chi)組內部(bu)都(dou)有電(dian)(dian)子(zi)電(dian)(dian)路(lu)，如果(guo)充電(dian)(dian)或(huo)放電(dian)(dian)時電(dian)(dian)池(chi)(chi)(chi)電(dian)(dian)壓低(di)(di)于2.5V、超(chao)過(guo)(guo)4.3V或(huo)如果(guo)電(dian)(dian)池(chi)(chi)(chi)電(dian)(dian)流(liu)超(chao)過(guo)(guo)預(yu)定門(men)限(xian)值(zhi)，該(gai)電(dian)(dian)子(zi)電(dian)(dian)路(lu)就(jiu)會(hui)斷(duan)開(kai)電(dian)(dian)池(chi)(chi)(chi)連接。

  2 鋰離子(zi)充電--系統注意事(shi)項

  要(yao)快速可靠地完成(cheng)充電過程需要(yao)一個(ge)高(gao)性能的充電系(xi)統(tong)。為實現可靠且(qie)經濟(ji)高(gao)效的解決方案，設計時應當考慮(lv)到(dao)以下(xia)系(xi)統(tong)參數：

2.1 輸入源
  許多應用都采用極廉價的墻式適配器(qi)作為輸(shu)入電源。其(qi)輸(shu)出電壓(ya)主要依賴于(yu)交流輸(shu)入電壓(ya)和從墻式適配器(qi)流出的負載電流。

  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是次級(ji)繞組的(de)電阻與初級(ji)繞組反(fan)射(she)電阻的(de)和。RPTC是PTC的(de)電阻，VFD是橋式整流(liu)器(qi)的(de)前向壓(ya)降。此外變壓(ya)器(qi)磁芯損失也會使輸(shu)出(chu)電壓(ya)略有降低。

  利用汽(qi)車(che)(che)適配(pei)(pei)器充電的(de)應用也(ye)會遇到類似的(de)問題。汽(qi)車(che)(che)適配(pei)(pei)器的(de)輸出(chu)電壓典型范圍為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
   為了盡可能地充分利(li)用電(dian)池(chi)容量(liang)，輸(shu)出(chu)(chu)電(dian)壓(ya)穩(wen)壓(ya)精度(du)(du)(du)非(fei)常關鍵。輸(shu)出(chu)(chu)電(dian)壓(ya)精度(du)(du)(du)的(de)小幅度(du)(du)(du)下降也(ye)會導致電(dian)池(chi)容量(liang)的(de)大幅減少。然而(er)出(chu)(chu)于安(an)全和可靠性(xing)方面的(de)考(kao)慮(lv)，輸(shu)出(chu)(chu)電(dian)壓(ya)也(ye)不能隨(sui)意設置得過高。圖2顯示(shi)出(chu)(chu)了輸(shu)出(chu)(chu)電(dian)壓(ya)穩(wen)定精度(du)(du)(du)的(de)重要(yao)性(xing)。

3 充電終止方法

  毋(wu)庸(yong)置疑，過充(chong)始終是鋰(li)離(li)子電(dian)(dian)池充(chong)電(dian)(dian)的(de)心(xin)頭大患。準(zhun)確的(de)充(chong)電(dian)(dian)終止方(fang)法對于安全可靠的(de)充(chong)電(dian)(dian)系統來說非常關鍵。

3 .1 電池溫度監控
  一般情況下(xia)，鋰離子(zi)電(dian)(dian)池(chi)(chi)充(chong)電(dian)(dian)時的溫(wen)(wen)度范(fan)圍(wei)應當在0℃至45℃。在此溫(wen)(wen)度范(fan)圍(wei)之外對電(dian)(dian)池(chi)(chi)充(chong)電(dian)(dian)會(hui)導致(zhi)(zhi)電(dian)(dian)池(chi)(chi)過熱(re)。在充(chong)電(dian)(dian)周期中，電(dian)(dian)池(chi)(chi)內的壓力(li)上(shang)升還會(hui) 導致(zhi)(zhi)電(dian)(dian)池(chi)(chi)膨脹。隨著溫(wen)(wen)度上(shang)升，壓力(li)也會(hui)過大，這可(ke)能會(hui)導致(zhi)(zhi)電(dian)(dian)池(chi)(chi)內部的機械(xie)破(po)裂(lie)或材料泄漏，嚴重(zhong)時還有可(ke)能導致(zhi)(zhi)爆炸(zha)。在此溫(wen)(wen)度范(fan)圍(wei)之外 對電(dian)(dian)池(chi)(chi)充(chong)電(dian)(dian)還會(hui)損(sun)害電(dian)(dian)池(chi)(chi)的性(xing)能，或縮短(duan)電(dian)(dian)池(chi)(chi)的預期壽命。

  通常鋰離(li)子(zi)電(dian)(dian)池包內都采用了熱敏(min)電(dian)(dian)阻來準確測量電(dian)(dian)池溫度(du)。充(chong)電(dian)(dian)器檢測熱敏(min)電(dian)(dian)阻的阻值(zhi)，當(dang)阻值(zhi)超(chao)出規(gui)(gui)定(ding)工(gong)作范圍(wei)，即溫度(du)超(chao)過規(gui)(gui)定(ding)范圍(wei)時，充(chong)電(dian)(dian)被禁止。

3.2 電池放電電流或反向泄漏電流
  在(zai)許(xu)多應用(yong)中，即使輸(shu)入電(dian)(dian)源不存在(zai)，充電(dian)(dian)系統(tong)(tong)仍然與電(dian)(dian)池(chi)相連。充電(dian)(dian)系統(tong)(tong)必須保證輸(shu)入電(dian)(dian)源不存在(zai)時(shi)，從(cong)電(dian)(dian)池(chi)汲取的電(dian)(dian)流極(ji)小。最大(da)泄(xie)漏電(dian)(dian)流應當小于幾個微安，通常應小于一個微安。

4 鋰離子(zi)充電--應(ying)用(yong)實例

  將以上(shang)幾點系(xi)統注(zhu)意事項事先充分(fen)考慮(lv)，就(jiu)能開(kai)發出適合的充電管理系(xi)統。

4.1 線性解決方案
  當存在穩壓良好的(de)輸(shu)入電(dian)(dian)源時，通(tong)常(chang)采用線(xian)(xian)性充電(dian)(dian)解決(jue)(jue)方(fang)案。在此(ci)類(lei)應用中(zhong)，線(xian)(xian)性解決(jue)(jue)方(fang)案的(de)優點包括(kuo)易用、尺寸小(xiao)以及成(cheng)本(ben)低。由于線(xian)(xian)性充電(dian)(dian)解決(jue)(jue)方(fang)案 效率低因此(ci)影響設計的(de)最重要(yao)因素就是(shi)散(san)(san)熱設計。最糟(zao)的(de)情況(kuang)是(shi)器件從涓流充電(dian)(dian)階段向 恒(heng)流充電(dian)(dian)階段轉換時，在此(ci)情況(kuang)下，傳(chuan)輸(shu)晶體管必須(xu)散(san)(san)發最大的(de)熱能，必須(xu)在充電(dian)(dian)電(dian)(dian)流、系統尺寸、成(cheng)本(ben)和(he)散(san)(san)熱要(yao)求(qiu)之間(jian)進行(xing)權(quan)衡。

  例(li)如(ru)，應用(yong)(yong)中需(xu)要(yao)利用(yong)(yong)一(yi)(yi)個5V ±5%的(de)輸入(ru)電(dian)源以(yi)(yi)0.5C或1C的(de)恒定電(dian)流(liu)對(dui)一(yi)(yi)個1000mAh的(de)單節鋰(li)離子電(dian)池充(chong)電(dian)。圖3顯(xian)示了(le)如(ru)何利用(yong)(yong)Microchip的(de) MCP73843構成一(yi)(yi)個低成本的(de)獨立(li)解決方案，只需(xu)要(yao)極少(shao)量(liang)的(de)外部元器件(jian)，就可以(yi)(yi)實現所需(xu)要(yao)的(de)充(chong)電(dian)算法。MCP73843完(wan)美(mei)地結(jie)合了(le)高精度(du)恒流(liu)充(chong)電(dian)、 恒壓(ya)穩(wen)壓(ya)以(yi)(yi)及自(zi)動充(chong)電(dian)終止(zhi)等(deng)功能。

  為進一(yi)步減小(xiao)線性(xing)(xing)解決方案的(de)(de)尺寸、降低其成本和復雜性(xing)(xing)，許多外(wai)部(bu)元器(qi)件(jian)都(dou)可以集成到充(chong)電(dian)(dian)管理控(kong)制器(qi)中。先(xian)進的(de)(de)封裝可以提供(gong)更高的(de)(de)集成度，當(dang)然也會犧牲一(yi)定的(de)(de)靈(ling)活性(xing)(xing)。此外(wai)此類充(chong)電(dian)(dian)管理控(kong)制器(qi) 還會實現一(yi)定的(de)(de)熱(re)(re)調節(jie)功能。熱(re)(re)調節(jie)功能可根據(ju)器(qi)件(jian)管芯溫度來限(xian)制充(chong)電(dian)(dian)電(dian)(dian)流，從而可在保證(zheng)器(qi)件(jian)可靠性(xing)(xing)的(de)(de)情(qing)況下優化充(chong)電(dian)(dian)周期(qi)時間，熱(re)(re)調節(jie)功能大(da)大(da)降低了(le)散(san)熱(re)(re)設 計的(de)(de)工作量。

  基于Microchip MCP73861的(de)全集成線性(xing)解決方案如圖4所示。MCP73861包含了MCP73843的(de)所有(you)功能，另外還包括(kuo)電流(liu)檢測、傳輸晶體管(guan)、反向(xiang)放電保護(hu)以(yi)及(ji)電池溫度(du)監測。

4.2 充電周期波形
  利用MCP73843在1C和0.5C恒流充(chong)電(dian)(dian)速率(lv)(lv)下的整個(ge)充(chong)電(dian)(dian)周期(qi)如(ru)圖5.以0.5C而不是(shi)1C速率(lv)(lv)充(chong)電(dian)(dian)時(shi)，充(chong)電(dian)(dian)結(jie)束(shu)的時(shi)間(jian)(jian)大約晚了一個(ge)小時(shi)。充(chong)電(dian)(dian)終止電(dian)(dian)流從(cong)0.07C降到0.035C,使得最終電(dian)(dian)池容(rong)量(liang)從(cong)~98%增長到~100%.系統設計師必(bi)須在充(chong)電(dian)(dian)時(shi)間(jian)(jian)、功率(lv)(lv)損耗和可用電(dian)(dian)池容(rong)量(liang)之間(jian)(jian)進行權(quan)衡(heng)。

4.3 開關式充電解決方案
  輸(shu)入電(dian)(dian)(dian)(dian)(dian)壓波動(dong)范圍寬或輸(shu)入輸(shu)出電(dian)(dian)(dian)(dian)(dian)壓差(cha)大的(de)應(ying)用(yong)通常采用(yong)開關式充(chong)電(dian)(dian)(dian)(dian)(dian)解決方(fang)案(an)(an)。例如應(ying)用(yong)中需(xu)要(yao)利用(yong)汽(qi)車適(shi)配(pei)器以0.5C或1C的(de)恒定電(dian)(dian)(dian)(dian)(dian)流對(dui)一個2200mAh的(de)單節(jie)鋰離子電(dian)(dian)(dian)(dian)(dian)池充(chong)電(dian)(dian)(dian)(dian)(dian)，由于散熱等問題，利用(yong)線性(xing)解決方(fang)案(an)(an)實現(xian)極(ji)為困難，當然也可以采用(yong)支持熱調(diao)節(jie)的(de)線性(xing)解決方(fang)案(an)(an)，但(dan)降低充(chong)電(dian)(dian)(dian)(dian)(dian)電(dian)(dian)(dian)(dian)(dian)流造成的(de)充(chong)電(dian)(dian)(dian)(dian)(dian)周期延長是無法(fa)接受的(de)。

  成功設(she)計(ji)開關式充電解決(jue)方案的(de)第一步是選(xuan)擇設(she)計(ji)結(jie)構：降(jiang)壓式、升壓式、升/降(jiang)壓式、反激(ji)式、單端(duan)初(chu)級電感(gan)式或者其他形式。SEPIC拓撲結(jie)構的(de)優點是低(di)端(duan)柵極驅動(dong)和(he)電流檢(jian)測、持續輸(shu) 入(ru)電流以(yi)及輸(shu)入(ru)和(he)輸(shu)出間的(de)直(zhi)流隔(ge)離，其主要缺點是需(xu)要兩個電感(gan)和(he)一個能量傳輸(shu)電容。

  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。充電器采用的電源結(jie)構(gou)是SEPIC.單(dan)片(pian)機提供了極大(da)的設計靈活 性。此外單(dan)片(pian)機還可(ke)以與電池(chi)包內的電池(chi)監控器(qi)通(tong)信，從而大(da)大(da)縮短充(chong)電周期時(shi)間。

  利用開(kai)關式充(chong)電(dian)(dian)(dian)解決(jue)方案(an)的(de)整個充(chong)電(dian)(dian)(dian)周期如圖6所示。通過在(zai)充(chong)電(dian)(dian)(dian)系(xi)統中采用電(dian)(dian)(dian)池(chi)(chi)監控器，可以(yi)大大縮短充(chong)電(dian)(dian)(dian)周期，使用電(dian)(dian)(dian)池(chi)(chi)監控器就不必再檢測電(dian)(dian)(dian)池(chi)(chi)包保護電(dian)(dian)(dian)路兩端的(de)電(dian)(dian)(dian)壓以(yi)及充(chong)電(dian)(dian)(dian)電(dian)(dian)(dian)流的(de)接觸電(dian)(dian)(dian)阻(zu)。

5 結論

  在目前的便攜式(shi)產品(pin)中，要(yao)(yao)(yao)正確地實現電(dian)池(chi)充電(dian)需要(yao)(yao)(yao)仔細(xi)地設計考慮。本文(wen)討論了鋰離子(zi)電(dian)池(chi)的線(xian)性(xing)和開(kai)關式(shi)充電(dian)解決方案，本文(wen)所探討的指(zhi)導原(yuan)則(ze)和設計考慮要(yao)(yao)(yao)素，實際上(shang)也是所有電(dian)池(chi)充電(dian)系統設計都需要(yao)(yao)(yao)考慮的。