鋰離子充電電池的基礎知識
一般而言,鋰離子電池有三部分構成:
1.鋰離子電芯
2.保護電路(PCM)
3.外殼即膠殼
電池的分類
從鋰離子電池與手機配合情況來看,一般分為外置電池和內置電池,這種叫法很容易理解,外置電池就是直接裝在手上背面,如: MOTOROLA 191,SAMSUNG 系列等;而內置電池就是裝入手機后,還另有一個外殼把其扣在手機電池內,如:MOTOROLA 998,8088,NOKIA的大部分機型
1.外置電池
外置電池的封裝形式有超聲波焊接和卡扣兩種:
1.1超聲波焊接
外殼
這種封裝形式的電池外殼均有底面殼之分,材料一般為ABS+PC料,面殼一般噴油處理,代表型號有 :MOTOROLA 191,SAMSUNG 系列,原裝電池的外殼經噴油處理后長期使用一般不會磨花,而一些品牌電池或水貨電池用上幾天外殼噴油就開始脫落了.其原因為:手機電池的外殼較便宜,而噴油處理的成本一般為外殼的幾倍(好一點的),這樣處理一般有三道工序:噴光油(打底),噴油(形成顏色),再噴亮油(順序應該是這樣的,如果我沒記錯的話),而一些廠商為了降低成本就省去了第一和第三道工序,這樣成本就很低了.
超聲波焊塑機
其作用為:焊接,有了好的超聲波焊塑機不夠的,是否能夠焊接OK,還與外殼的材料和焊塑機參數設置有很大關系,外殼方面主要與生產廠家的水口料摻雜情況有關,而參數設置則需自己摸索,由于涉及到公司一些技術資料,在這里不便多講.
1.2卡扣式
卡(ka)扣(kou)式(shi)電池(chi)的原理為底面殼(ke)設計時形成卡(ka)扣(kou)式(shi),其一(yi)般為一(yi)次性,如果卡(ka)好后(hou)用戶強行折(zhe)開(kai)的話,就無(wu)法復原,不過這對于生產廠(chang)家來講不是很大的難度(卡(ka)好后(hou)再折(zhe)開(kai)),其代表(biao)型號有:愛立(li)信788,MOTOROLA V66.
2.內置電池
內置電池的封形式也有兩種,超聲波焊接和包標(使用商標將電池全部包起)
超聲波焊接的電池主要有:NOKIA 8210,8250,8310,7210等.
包標的電池就很多了,如前兩年很滸的MOTO998 ,8088了.
第二(er)節 鋰離子(zi)電(dian)芯的(de)基本(ben)知識
鋰離子電芯是一種新型的電池能源,它不含金屬鋰,在充放電過程中,只有鋰離子在正負極間往來運動,電極和電解質不參與反應。鋰離子電芯的能量容量密度可以達到300Wh/L,重量容量密度可以達到125Wh/L。
一、 電芯原理
鋰(li)離子電(dian)(dian)芯(xin)的(de)反應機(ji)理(li)是隨著充放電(dian)(dian)的(de)進(jin)行,鋰(li)離子在正負極之間嵌入脫(tuo)出,往返(fan)穿梭(suo)電(dian)(dian)芯(xin)內部而沒有金(jin)屬(shu)鋰(li)的(de)存在,因此鋰(li)離子電(dian)(dian)芯(xin)更(geng)加安全穩定(ding)。
二、 電芯的構造
電芯的正極是LiCoO2加導電劑和粘合劑,涂在鋁箔上形成正極板,負極是層狀石墨加導電劑及粘合劑涂在銅箔基帶上,目前比較先進的負極層狀石墨顆粒已采用納米碳。
根據上述的(de)反應機理,正(zheng)極(ji)采(cai)用(yong)LiCoO2、LiNiO2、LiMn2O2,其(qi)中(zhong)LiCoO2本是(shi)一(yi)(yi)種(zhong)層結構(gou)(gou)很(hen)(hen)穩定(ding)的(de)晶型(xing),但(dan)(dan)當(dang)從(cong)LiCoO2拿(na)走XLi后(hou),其(qi)結構(gou)(gou)可能(neng)發(fa)生(sheng)變化,但(dan)(dan)是(shi)否(fou)發(fa)生(sheng)變化取(qu)決于X的(de)大小。通(tong)過(guo)研究發(fa)現當(dang)X>0.5時Li1-XCoO2的(de)結構(gou)(gou)表現為(wei)極(ji)其(qi)不穩定(ding),會(hui)發(fa)生(sheng)晶型(xing)癱塌(ta),其(qi)外部表現為(wei)電(dian)(dian)芯的(de)壓(ya)(ya)倒(dao)終結。所(suo)以電(dian)(dian)芯在使用(yong)過(guo)程中(zhong)應通(tong)過(guo)限制充(chong)電(dian)(dian)電(dian)(dian)壓(ya)(ya)來控制Li1-XCoO2中(zhong)的(de)X值,一(yi)(yi)般充(chong)電(dian)(dian)電(dian)(dian)壓(ya)(ya)不大于4.2V那么(me)X小于0.5 ,這(zhe)時Li1-XCoO2的(de)晶型(xing)仍是(shi)穩定(ding)的(de)。負(fu)極(ji)C6其(qi)本身有自己的(de)特(te)點,當(dang)第一(yi)(yi)次化成后(hou),正(zheng)極(ji)LiCoO2中(zhong)的(de)Li被充(chong)到負(fu)極(ji)C6中(zhong),當(dang)放(fang)(fang)電(dian)(dian)時Li回到正(zheng)極(ji)LiCoO2中(zhong),但(dan)(dan)化成之(zhi)后(hou)必須(xu)有一(yi)(yi)部分Li留(liu)在負(fu)極(ji)C6中(zhong),心以保證(zheng)下次充(chong)放(fang)(fang)電(dian)(dian)Li的(de)正(zheng)常嵌入(ru),否(fou)則電(dian)(dian)芯的(de)壓(ya)(ya)倒(dao)很(hen)(hen)短(duan),為(wei)了(le)保證(zheng)有一(yi)(yi)部分Li留(liu)在負(fu)極(ji)C6中(zhong),一(yi)(yi)般通(tong)過(guo)限制放(fang)(fang)電(dian)(dian)下限電(dian)(dian)壓(ya)(ya)來實現。所(suo)以鋰電(dian)(dian)芯的(de)安全充(chong)電(dian)(dian)上限電(dian)(dian)壓(ya)(ya)≤4 .2V,放(fang)(fang)電(dian)(dian)下限電(dian)(dian)壓(ya)(ya)≥2.5V。
三、 電芯的安全性
電(dian)(dian)(dian)芯(xin)的(de)(de)(de)(de)安全性與電(dian)(dian)(dian)芯(xin)的(de)(de)(de)(de)設(she)計、材(cai)料(liao)及生(sheng)產(chan)工藝(yi)生(sheng)產(chan)過(guo)程(cheng)的(de)(de)(de)(de)控(kong)制等因素密(mi)切相關。在電(dian)(dian)(dian)芯(xin)的(de)(de)(de)(de)充放電(dian)(dian)(dian)過(guo)程(cheng)中(zhong),正(zheng)負(fu)極材(cai)料(liao)的(de)(de)(de)(de)電(dian)(dian)(dian)極電(dian)(dian)(dian)位(wei)(wei)(wei)均處于(yu)動態(tai)變化(hua)中(zhong),隨著充電(dian)(dian)(dian)電(dian)(dian)(dian)壓的(de)(de)(de)(de)增高,正(zheng)極材(cai)料(liao)(LixCoO2)電(dian)(dian)(dian)位(wei)(wei)(wei)不(bu)斷(duan)上(shang)升(sheng),嵌(qian)鋰的(de)(de)(de)(de)負(fu)極材(cai)料(liao)(LixC6)電(dian)(dian)(dian)位(wei)(wei)(wei)首先下(xia)降(jiang),然后出(chu)現一個較長(chang)的(de)(de)(de)(de)電(dian)(dian)(dian)位(wei)(wei)(wei)平臺,當充電(dian)(dian)(dian)電(dian)(dian)(dian)壓過(guo)高( >4.2V)或由于(yu)負(fu)極活性材(cai)料(liao)面(mian)密(mi)度(du)(du)相對于(yu)正(zheng)極材(cai)料(liao)面(mian)密(mi)度(du)(du)(C/A)比值不(bu)足(zu)時,負(fu)極材(cai)料(liao)過(guo)度(du)(du)嵌(qian)鋰,負(fu)極電(dian)(dian)(dian)位(wei)(wei)(wei)則迅速(su)下(xia)降(jiang),使金(jin)(jin)屬鋰析(xi)出(chu)(正(zheng)常情況下(xia)則不(bu)會有金(jin)(jin)屬鋰的(de)(de)(de)(de)的(de)(de)(de)(de)析(xi)出(chu)),這樣會對電(dian)(dian)(dian)芯(xin)的(de)(de)(de)(de)性能及安全性構成極大(da)的(de)(de)(de)(de)威(wei)脅。電(dian)(dian)(dian)位(wei)(wei)(wei)變化(hua)見下(xia)圖:
在材料已定的情況下,C/A太大,則會出現上述結果。相反,C/A太小,容量低,平臺低,循環特性差。這樣,在生產加工中如何保證設計好的C/A比成了生產加工中的關鍵。所以在生產中應就以下幾個方面進行控制:
1.負極材料的處理
1)將大粒徑及超細粉與所要求的粒徑進行徹底分離,避免了局部電化學反應過度激烈而產生負反應的情況,提高了電芯的安全性。
2)提高材料表面孔隙率,這樣可以提高10%以上的容量,同時在C/A 比不變的情況下,安全性大大提高。處理的結果使負極材料表面與電解液有了更好的相容性,促進了SEI膜的形成及穩定上。
2.制漿工藝的控制
1)制漿過程采用先進的工藝方法及特殊的化學試劑,使正負極漿料各組之間的表面張力降到了最低。提高了各組之間的相容性,阻止了材料在攪拌過程“團聚”的現象。
2)涂布時基材料與噴頭的間隙應控制在0.2mm以下,這樣涂出的極板表面光滑無顆粒、凹陷、劃痕等缺陷。
3)漿料應儲存6小時以上,漿料粘度保持穩定,漿料內部無自聚成團現象。均勻的漿料保證了正負極在基材上分布的均勻性,從而提高了電芯的一致性、安全性。
3.采用先進的極片制造設備
1)可以保證極片質量的穩定和一致性,大大提高電芯極片均一性,降低了不安全電芯的出現機率。
2)涂布機單片極板上面密度誤差值應小于±2%,極板長度及間隙尺寸誤差應小于2mm。
3)輥壓機的輥軸錐度和徑向跳動應不大于4μm,這樣才能保證極板厚度的一致性。設備應配有完善的吸塵系統,避免因浮塵顆粒而導致的電芯內部微短路,從而保證了電芯的自放電性能。
4)分切機應采用切刀為輥刀型的連續分切設備,這樣切出的極片不存在荷葉邊,毛刺等缺陷。同樣設備應配有完善的吸塵系統,從而保證了電芯的自放電性能。
4.先進的封口技術
目前國內外方形鋰離子電芯的封口均采用激光(LASER)熔接封口技術,它是利用YAG棒(釔鋁石榴石)激光諧振腔中受強光源(一般為氮燈)的激勵下發出一束單一頻率的光(λ=1.06mm)經過諧振折射聚焦成一束,再把聚焦的焦點對準電芯的筒體和蓋板之間,使其熔化后親合為一體,以達到蓋板與筒體的密封熔合的目的。為了達到密封焊,必須掌握以下幾個要素:
1)必須有能量大、頻率高、聚焦性能好、跟蹤精度高的激光焊機。
2)必須有配合精度高的適用于激光焊的電芯外殼及蓋板。
3)必須有高統一純度的氮氣保護,特別是鋁殼電芯要求氮氣純度高,否則鋁殼表面就會產生難以熔化的Al2O3(其熔點為2400℃)。
四、電芯膨脹原因及控制
鋰離子電芯在制造和使用過程中往往會有腫脹現象,經過分析與研究,發現主要有以下兩方面原因:
1鋰離子嵌入帶來的厚度變化
電芯充電時鋰離子從正極脫出嵌入負極,引起負極層間距增大,而出現膨脹,一般而言,電芯越厚,其膨脹量越大。
2. 工藝控制不力引起的膨脹
在制造過程中,如漿料分散、C/A比離散性、溫度控制都會直接影響電芯電芯的膨脹程度。特別是水,因為充電形成的高活性鋰碳化合物對水非常 敏感,從而發生激烈的化學反應。反應產生的氣體造成電芯內壓升高,增加了電芯的膨脹行為。所以在生產中,除了應對極板嚴格除濕外,在注液過程中更應采用除濕設備,保證空氣的干燥度為HR2%,露點(大氣中的濕空氣由于溫度下降,使所含的水蒸氣達到飽和狀態而開始凝結時的溫度)小于-40℃。在非常干燥的條件下,并采取真空注液,極大地降低了極板和電解液的吸水機率。
五、鋁殼電芯與鋼殼電芯安全性比較
鋁殼相對于鋼(gang)殼具有(you)很高的安全(quan)優勢,以下(xia)是不同的壓力實驗:
注(zhu):壓(ya)力(li)是電芯(xin)壓(ya)力(li)為電芯(xin)內(nei)部之壓(ya)力(li)(單(dan)位:Kg),表內(nei)數據為電芯(xin)之厚度(單(dan)位:mm)由此可(ke)見鋼殼對內(nei)壓(ya)反映十分遲鈍,而(er)鋁(lv)殼對內(nei)壓(ya)反應卻十分敏銳。因此從厚度上就基(ji)本能(neng)判斷出電芯(xin)的內(nei)壓(ya),而(er)鋼殼電芯(xin)往往隱含(han)著內(nei)壓(ya)帶(dai)來的不安全隱患(huan)。其(qi)中鋼殼電芯(xin)型(xing)號為063448。
第三(san)節 鋰離子電池保(bao)護線路(lu)(PCM)
由第二節鋰離子電芯的知識我們可以看出,鋰離子電池至少需要三重保護-----過充電保護,過放電保護,短路保護,那么就應而產生了其保護線路,那么這個保護線路針對以上三個保護要求而言:
過充電保護: 過充電保護 IC 的原理為:當外部充電器對鋰電池充電時,為防止因溫度上升所導致的內壓上升,需終止充電狀態。此時,保護 IC 需檢測電池電壓,當到達 4.25V 時(假設電池過充點為 4.25V)即啟動過度充電保護,將功率 MOS 由開轉為切斷,進而截止充電。
過(guo)(guo)放(fang)(fang)(fang)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)保(bao)(bao)護: 過(guo)(guo)放(fang)(fang)(fang)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)保(bao)(bao)護 IC 原理(li):為了防止鋰(li)(li)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)池(chi)的過(guo)(guo)放(fang)(fang)(fang)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian),假(jia)設鋰(li)(li)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)池(chi)接上負(fu)載,當(dang)鋰(li)(li)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)池(chi)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)壓(ya)低于(yu)其(qi)過(guo)(guo)放(fang)(fang)(fang)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)壓(ya)檢(jian)測點(假(jia)定為 2.5V)時(shi)(shi)將(jiang)啟動(dong)過(guo)(guo)放(fang)(fang)(fang)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)保(bao)(bao)護,使功率 MOSFET 由開轉(zhuan)變為切(qie)斷而截止放(fang)(fang)(fang)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian),以避免電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)池(chi)過(guo)(guo)放(fang)(fang)(fang)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)現象產生,并將(jiang)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)池(chi)保(bao)(bao)持在低靜態電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)流(liu)的待機模式(shi),此(ci)(ci)時(shi)(shi)的電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)流(liu)僅 0.1uA。 當(dang)鋰(li)(li)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)池(chi)接上充電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)器,且此(ci)(ci)時(shi)(shi)鋰(li)(li)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)池(chi)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)壓(ya)高(gao)于(yu)過(guo)(guo)度放(fang)(fang)(fang)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)壓(ya)時(shi)(shi),過(guo)(guo)度放(fang)(fang)(fang)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)保(bao)(bao)護功能方可解除(chu)。另外,考慮到脈沖放(fang)(fang)(fang)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)的情況,過(guo)(guo)放(fang)(fang)(fang)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)檢(jian)測電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)路(lu)設有(you)延遲時(shi)(shi)間以避免產生誤(wu)動(dong)作。