導讀: 提起硅負極你想到的是什么呢?大容量、高體積膨脹?硅負極作為新一代的鋰離子電池負極材料,其容量*高可達4200mAh/g,是石墨負極材料的10倍以上,是*具希望的下一代鋰離子電池負極材料。
OFweek鋰(li)電網訊 提起硅負極你想到的是什么呢?大容量、高體積膨脹?硅負極作為新一代的鋰離子電池負極材料,其容量*高可達4200mAh/g,是石墨負極材料的10倍以上,是*具希望的下一代鋰離子電池負極材料。
在(zai)這(zhe)耀眼的光(guang)環(huan)下,硅(gui)(gui)(gui)負極(ji)(ji)也存在(zai)著(zhu)難以克服(fu)的缺點,這(zhe)主(zhu)要(yao)源于硅(gui)(gui)(gui)負極(ji)(ji)在(zai)嵌鋰過(guo)程中嚴重的體(ti)積膨脹,在(zai)完全嵌鋰狀態下,硅(gui)(gui)(gui)負極(ji)(ji)的體(ti)積膨脹可達300%,這(zhe)會造成材料顆(ke)粒的粉化和脫落,嚴重影(ying)響其電化學性能。人(ren)們竭(jie)力減少硅(gui)(gui)(gui)負極(ji)(ji)材料的體(ti)積膨脹,例如納米顆(ke)粒、薄(bo)膜電極(ji)(ji)、碳包覆處(chu)理等(deng)方(fang)法,都是(shi)(shi)人(ren)們為克服(fu)硅(gui)(gui)(gui)負極(ji)(ji)膨脹所做出的努力。體(ti)積膨脹對于鋰離(li)子電池是(shi)(shi)一個壞消息,但是(shi)(shi)讓我們換個角度(du)考慮一下,硅(gui)(gui)(gui)負極(ji)(ji)巨大的體(ti)積膨脹是(shi)(shi)不是(shi)(shi)還有一些特(te)使(shi)的用途呢?
清(qing)華大(da)學的(de)(de)Jialiang Lang等(deng)人就利用(yong)了(le)硅負極(ji)在(zai)充(chong)(chong)(chong)放電(dian)(dian)(dian)(dian)過(guo)(guo)程中的(de)(de)體積膨(peng)脹(zhang)開發了(le)一(yi)款“微型起重機(ji)”。該(gai)“微型起重機(ji)”實(shi)(shi)際上(shang)是一(yi)個軟包(bao)鋰(li)離子電(dian)(dian)(dian)(dian)池(chi)(chi)(chi),其正極(ji)采用(yong)了(le)體積變化(hua)(hua)(hua)很小(xiao)的(de)(de)LiFePO4材料,而負極(ji)使用(yong)了(le)硅負極(ji)材料,電(dian)(dian)(dian)(dian)池(chi)(chi)(chi)容量為2.1Ah。并利用(yong)該(gai)電(dian)(dian)(dian)(dian)池(chi)(chi)(chi)進行(xing)了(le)“舉水(shui)實(shi)(shi)驗”,在(zai)實(shi)(shi)驗中該(gai)電(dian)(dian)(dian)(dian)池(chi)(chi)(chi)通過(guo)(guo)充(chong)(chong)(chong)電(dian)(dian)(dian)(dian)“舉起”了(le)637.5g的(de)(de)水(shui),在(zai)完全充(chong)(chong)(chong)電(dian)(dian)(dian)(dian)狀(zhuang)態下電(dian)(dian)(dian)(dian)池(chi)(chi)(chi)膨(peng)脹(zhang)所產生(sheng)(sheng)的(de)(de)壓(ya)強達到了(le)25.8KPa,在(zai)后續(xu)的(de)(de)循(xun)環過(guo)(guo)程中產生(sheng)(sheng)了(le)平均(jun)21KPa的(de)(de)壓(ya)力(li)。后續(xu)的(de)(de)研(yan)究表明,該(gai)電(dian)(dian)(dian)(dian)池(chi)(chi)(chi)能(neng)夠產生(sheng)(sheng)的(de)(de)*高壓(ya)力(li)可(ke)達17MPa。在(zai)整個充(chong)(chong)(chong)放電(dian)(dian)(dian)(dian)電(dian)(dian)(dian)(dian)壓(ya)平臺期間,該(gai)電(dian)(dian)(dian)(dian)池(chi)(chi)(chi)可(ke)以持續(xu)產生(sheng)(sheng)10MPa以上(shang)的(de)(de)壓(ya)力(li)。在(zai)該(gai)過(guo)(guo)程中,充(chong)(chong)(chong)電(dian)(dian)(dian)(dian)產生(sheng)(sheng)的(de)(de)能(neng)量分(fen)為3部(bu)分(fen),一(yi)部(bu)分(fen)轉化(hua)(hua)(hua)為機(ji)械能(neng),一(yi)部(bu)分(fen)轉換為化(hua)(hua)(hua)學能(neng)儲存在(zai)電(dian)(dian)(dian)(dian)池(chi)(chi)(chi)中,一(yi)部(bu)分(fen)則(ze)轉化(hua)(hua)(hua)為熱能(neng)耗散了(le)。
當(dang)然對于(yu)一款意在(zai)將電(dian)(dian)(dian)能轉換為(wei)(wei)機(ji)械(xie)能的(de)(de)(de)(de)(de)(de)(de)(de)設備,快速的(de)(de)(de)(de)(de)(de)(de)(de)響應的(de)(de)(de)(de)(de)(de)(de)(de)能力自(zi)然是十(shi)分重要的(de)(de)(de)(de)(de)(de)(de)(de),Jialiang Lang對電(dian)(dian)(dian)池(chi)在(zai)快速充放(fang)電(dian)(dian)(dian)模式(shi)下(xia)(xia),體(ti)積膨(peng)脹(zhang)(zhang)的(de)(de)(de)(de)(de)(de)(de)(de)響應速度(du)(du)(du)進行了研(yan)(yan)究。研(yan)(yan)究表明(ming)電(dian)(dian)(dian)池(chi)膨(peng)脹(zhang)(zhang)對脈沖電(dian)(dian)(dian)流(liu)(liu)有著很好(hao)的(de)(de)(de)(de)(de)(de)(de)(de)響應速度(du)(du)(du)。并且(qie)膨(peng)脹(zhang)(zhang)距(ju)離(li)與充電(dian)(dian)(dian)時間基本呈(cheng)現線(xian)性關(guan)系(xi),在(zai)2A/g的(de)(de)(de)(de)(de)(de)(de)(de)電(dian)(dian)(dian)流(liu)(liu)密度(du)(du)(du)下(xia)(xia),膨(peng)脹(zhang)(zhang)速度(du)(du)(du)為(wei)(wei)1.6nm/s,因此(ci)(ci)該方案可以用于(yu)納米(mi)精度(du)(du)(du)的(de)(de)(de)(de)(de)(de)(de)(de)定位(wei)。電(dian)(dian)(dian)池(chi)的(de)(de)(de)(de)(de)(de)(de)(de)膨(peng)脹(zhang)(zhang)速度(du)(du)(du)主(zhu)要與硅負(fu)極的(de)(de)(de)(de)(de)(de)(de)(de)面密度(du)(du)(du)、電(dian)(dian)(dian)池(chi)厚度(du)(du)(du)和電(dian)(dian)(dian)流(liu)(liu)密度(du)(du)(du)相關(guan),因此(ci)(ci)在(zai)電(dian)(dian)(dian)池(chi)定型(xing)的(de)(de)(de)(de)(de)(de)(de)(de)前提下(xia)(xia),我們可以通(tong)過控制電(dian)(dian)(dian)流(liu)(liu)的(de)(de)(de)(de)(de)(de)(de)(de)方式(shi)來控制電(dian)(dian)(dian)池(chi)的(de)(de)(de)(de)(de)(de)(de)(de)膨(peng)脹(zhang)(zhang)速度(du)(du)(du),從而(er)達到我們所需(xu)要的(de)(de)(de)(de)(de)(de)(de)(de)控制精度(du)(du)(du)。在(zai)該研(yan)(yan)究中,Si負(fu)極的(de)(de)(de)(de)(de)(de)(de)(de)容量發揮僅為(wei)(wei)800mAh/g,因此(ci)(ci)該“微(wei)型(xing)起重機(ji)”還(huan)有很大的(de)(de)(de)(de)(de)(de)(de)(de)提升空間。該“微(wei)型(xing)起重器”能夠(gou)**的(de)(de)(de)(de)(de)(de)(de)(de)產(chan)生納米(mi)尺度(du)(du)(du)的(de)(de)(de)(de)(de)(de)(de)(de)位(wei)移,并能承受巨大的(de)(de)(de)(de)(de)(de)(de)(de)負(fu)載,因此(ci)(ci)可以應用在(zai)一些需(xu)要在(zai)納米(mi)級高精度(du)(du)(du)定位(wei)的(de)(de)(de)(de)(de)(de)(de)(de)領域,例如操作掃描隧(sui)道顯微(wei)鏡的(de)(de)(de)(de)(de)(de)(de)(de)探針等。反其道而(er)行之,往往能取得不錯的(de)(de)(de)(de)(de)(de)(de)(de)效果。