本文選題：納米Si　切入點(diǎn)：多壁碳納米管　出處：《南昌大學(xué)》2017年碩士論文

【摘要】：硅由于其極高的理論比容量(4200mAh/g)、較低的嵌鋰電壓、資源豐富等優(yōu)勢(shì)成為新一代最有潛力的鋰離子電池負(fù)極活性材料。但是其電導(dǎo)率低和充放電過(guò)程中高達(dá)4倍的體積效應(yīng)導(dǎo)致的循環(huán)性能差問(wèn)題嚴(yán)重阻礙了硅在鋰離子電池中的商業(yè)應(yīng)用。本文選用粒徑為100 nm的納米Si粉為硅源,采用人造石墨(G)或多壁碳納米管(MWCNTs)與納米Si粉復(fù)合、以CNT導(dǎo)電紙代替?zhèn)鹘y(tǒng)銅箔集流體、預(yù)鋰化處理等手段對(duì)硅基鋰離子電池進(jìn)行改性,觀察其形貌和結(jié)構(gòu),組裝成扣式半電池后,通過(guò)恒流充放電、電化學(xué)阻抗等方法研究其電化學(xué)性能。主要研究成果如下:(1)將比容量高,循環(huán)穩(wěn)定性、導(dǎo)電性差的納米Si與循環(huán)穩(wěn)定性、導(dǎo)電性好,比容量低的人造石墨(G)復(fù)合涂于銅箔集流體,發(fā)現(xiàn)石墨片間搭筑的空間可為納米Si的體積膨脹提供良好地緩沖作用。Si-G復(fù)合電極在低電流密度下放電比容量高,材料利用率最高可達(dá)85%。但是電池在較大電流密度下循環(huán)時(shí),電池比容量衰減迅速。(2)將MWCNTs與紙纖維通過(guò)抽濾制備的CNT導(dǎo)電紙代替銅箔集流體負(fù)載MWCNTS-納米Si復(fù)合材料。CNT導(dǎo)電紙具有導(dǎo)電性良好,面密度低,接觸面積大,吸液性強(qiáng)等一系列優(yōu)點(diǎn),以CNT導(dǎo)電紙為集流體的硅基鋰離子電池在80mA/g電流密度下比容量穩(wěn)定在約1000mAh/g;1000mA/g電流密度下電池比容量達(dá)500mAh/g。尤其值得關(guān)注的是,對(duì)比銅箔硅基電池循環(huán)后電化學(xué)阻抗的急劇升高,導(dǎo)電紙電池的電化學(xué)阻抗在循環(huán)后不升反降。因此CNT導(dǎo)電紙作為集流體代替銅箔可有效改善Si的體積膨脹效應(yīng)。(3)采用穩(wěn)定金屬鋰粉(SMLP)預(yù)嵌鋰的方法改善硅基導(dǎo)電紙電池不可逆容量大的問(wèn)題。預(yù)鋰化的電池在靜置過(guò)程中可自發(fā)完成SEI膜的形成,且由于其自發(fā)緩慢的SEI膜形成過(guò)程,形成的SEI膜更為致密和穩(wěn)定,不但有效減少電池的不可逆容量,還使得電池的整體容量略高于未鋰化的硅電池。
[Abstract]:Due to its extremely high theoretical specific capacity of 4200mAh / g, low lithium intercalation voltage and abundant resources, silicon has become the most promising anode active material for lithium-ion batteries.However, the low conductivity and the volume effect of up to 4 times during charge and discharge lead to poor cycling performance, which seriously hinders the commercial application of silicon in lithium ion batteries.In this paper, silicon based lithium-ion battery was modified by using 100nm nano-Si powder as silicon source, using artificial graphite (G) or multi-walled carbon nanotube (MWCNTs) as composite with nano-Si powder, using CNT conductive paper instead of traditional copper foil to collect fluid, pre-lithiation treatment and so on.The morphology and structure of the cells were observed, and the electrochemical properties of the cells were studied by constant current charge / discharge and electrochemical impedance.The main research results are as follows: (1) Nanocrystalline Si with high specific capacity, cyclic stability and poor electrical conductivity is coated on copper foil with high specific capacity, good electrical conductivity and low specific capacity.It is found that the space between graphite sheets can provide a good buffer for volume expansion of nanocrystalline Si. Si-G composite electrode has a high discharge capacity at low current density and the highest material utilization ratio can reach 85.However, when the battery circulates at a high current density, the specific capacity of the battery decreases rapidly. (2) the CNT conductive paper prepared by MWCNTs and paper fiber, instead of copper foil collector loaded MWCNTS- nanocrystalline silicon composite, has good conductivity and low surface density.There are a series of advantages such as large contact area and strong liquid absorption. The specific capacity of silicon-based lithium-ion battery with CNT conductive paper as a fluid collector at 80mA/g current density is stable at about 1000mAh/ g ~ 1000mA-1 路g / g current density, and the specific capacity of the battery is 500mAh/ g.In particular, compared with the rapid increase of electrochemical impedance of copper foil silicon based cells, the electrochemical impedance of conductive paper cells does not rise but drop after the cycle.The formation of SEI film can be completed spontaneously in the static process of pre-lithiated battery, and because of its spontaneous slow formation of SEI film, the formed SEI film is denser and more stable, which not only reduces the irreversible capacity of the battery, but also reduces the irreversible capacity of the battery.The overall capacity of the battery is slightly higher than that of the non-lithium silicon cell.
【學(xué)位授予單位】：南昌大學(xué)
【學(xué)位級(jí)別】：碩士
【學(xué)位授予年份】：2017
【分類(lèi)號(hào)】：TM912;TB332

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