本文選題：鋰離子電池　切入點(diǎn)：隔膜　出處：《武漢理工大學(xué)》2014年碩士論文

【摘要】：鋰離子電池具有能量密度高和循環(huán)壽命長(zhǎng)等優(yōu)點(diǎn)，，被大量應(yīng)用于移動(dòng)電子設(shè)備和動(dòng)力裝置當(dāng)中，但是頻繁發(fā)生的安全事故引起了廣泛關(guān)注。隔膜對(duì)鋰離子電池的安全性具有非常重要的影響，本文制備了兩種高穩(wěn)定性的復(fù)合隔膜。 首先是對(duì)聚烯烴隔膜進(jìn)行表面改性，聚烯烴隔膜是目前使用最廣泛的鋰電池隔膜，但是聚烯烴隔膜存在熱收縮率太高和電解液浸潤(rùn)性不足的問(wèn)題。本文通過(guò)簡(jiǎn)單的浸漬和萃取步驟，在聚烯烴隔膜上涂覆高孔隙率的乙基纖維素涂層。研究了乙基纖維素涂層對(duì)隔膜熱收縮率、電解液浸潤(rùn)性、拉伸強(qiáng)度和電化學(xué)性能的影響。利用纖維素較高的熱穩(wěn)定性，使涂覆后聚烯烴隔膜的熱收縮率明顯降低，減少了鋰離子電池因隔膜熱縮導(dǎo)致內(nèi)部短路的可能，提高其熱安全性。同時(shí)因?yàn)橐一w維素涂層帶有較多的極性基團(tuán)和具有互相貫通的孔結(jié)構(gòu)，可以被電解液快速浸潤(rùn)，解決了聚烯烴隔膜因電解液浸潤(rùn)性差而導(dǎo)致的循環(huán)性能下降的問(wèn)題。單層PE隔膜在涂覆后，熱閉孔時(shí)（132℃）的收縮率從20％降低到9％，最大熱收縮率從42％降低到23％，升溫測(cè)試發(fā)現(xiàn)開路電壓降為0的溫度從130℃推遲到160℃。不僅如此，因?yàn)橐一w維素具有更好的電解液親合力，涂覆后PP/PE/PP隔膜的電解液浸潤(rùn)性顯著提高，使循環(huán)后的容量保持率從28%提升至99%。 其次，本文制備了一種高孔隙率的PVDF-HFP/ePTFE復(fù)合鋰離子電池隔膜。其中，多孔的PVDF-HFP可以吸納大量的電解液，并且在溫度達(dá)到其熔點(diǎn)時(shí)發(fā)生熱閉孔而切斷電流，防止因溫度進(jìn)一步上升而發(fā)生熱失控反應(yīng)。同時(shí)以耐高溫的ePTFE作為骨架，不但能夠提高機(jī)械強(qiáng)度，還能夠在隔膜熱閉孔后保持結(jié)構(gòu)穩(wěn)定，避免發(fā)生熔化短路。該復(fù)合隔膜不僅具有良好的離子電導(dǎo)率和電解液浸潤(rùn)性，還可以在升溫時(shí)保持較低的熱收縮率，防止因?yàn)闊崾湛s導(dǎo)致正負(fù)極接觸短路。實(shí)驗(yàn)顯示，該隔膜在室溫下的離子電導(dǎo)率為1.29mS· cm-1，在162℃時(shí)的熱收縮率為8.8％。隔膜在162℃時(shí)發(fā)生熱閉孔并迅速切斷電流，在溫度升至329℃之前依然可以保持結(jié)構(gòu)完整。使用該復(fù)合隔膜的扣式電池表現(xiàn)出了良好的倍率和循環(huán)性能。
[Abstract]:Li-ion batteries are widely used in mobile electronic devices and power devices because of their high energy density and long cycle life. However, frequent safety accidents have aroused widespread concern. Diaphragm has a very important impact on the safety of lithium-ion batteries. In this paper, two kinds of composite membranes with high stability have been prepared. The first is to modify the surface of polyolefin separator, which is the most widely used lithium battery membrane. However, the polyolefin membrane has the problems of too high thermal shrinkage and insufficient electrolyte wettability. The effects of ethylcellulose coating with high porosity on thermal shrinkage, electrolyte wettability, tensile strength and electrochemical properties of polyolefin membranes were studied. The thermal shrinkage rate of the coated polyolefin membrane was obviously reduced, and the possibility of short circuit caused by the thermal shrinkage of the membrane was reduced. Improve its thermal safety. Also because the ethylcellulose coating has more polar groups and interpenetrating pore structures, it can be rapidly infiltrated by the electrolyte, It solves the problem that the cycle performance of polyolefin separator is decreased due to poor electrolyte wettability. The shrinkage rate decreased from 20% to 9%, the maximum thermal shrinkage rate decreased from 42% to 23%, and the temperature at which the open circuit voltage dropped to 0 was delayed from 130 鈩

本文編號(hào)：1699694