【摘要】：鋰離子電池正極材料Li_2MnSiO_4具有理論容量高(333.0 mAh g-1)、熱穩(wěn)定好、成本低以及對(duì)環(huán)境友好等特點(diǎn)。但是該材料也有很多缺點(diǎn),如電子導(dǎo)電性低、在循環(huán)過(guò)程中結(jié)構(gòu)坍塌以及Mn在電解液中溶解,從而導(dǎo)致其循環(huán)性能較差。本論文主要對(duì)Li_2MnSiO_4材料的制備以及改性進(jìn)行了系統(tǒng)性的研究。通過(guò)XRD、SEM、EDS、TEM等方法對(duì)合成的樣品進(jìn)行物理表征,恒流充放電測(cè)試、循環(huán)伏安曲線以及交流阻抗法對(duì)其進(jìn)行電化學(xué)表征。采用快速溶膠凝膠法合成了Li_2MnSiO_4/C材料,硅源為有機(jī)的硅酸四乙酯(TEOS)。研究了不同合成工藝對(duì)合成樣品的結(jié)構(gòu)和電化學(xué)性能的影響,探索出了合成Li_2MnSiO_4/C材料的最佳工藝:乙酸量為10 g,煅燒溫度為650 ℃,煅燒時(shí)間為6 h,碳含量為20 wt%。但是由于Li_2MnSiO_4材料在充放電過(guò)程中結(jié)構(gòu)坍塌的本質(zhì)缺陷以及Mn在電解液中的溶解,在最優(yōu)條件下合成的樣品循環(huán)性能仍不令人滿意。為了提高溶膠凝膠法合成的Li_2MnSiO_4/C材料電化學(xué)性能,我們分別對(duì)其在Mn位和Si位進(jìn)行離子摻雜。在Mn位摻雜共價(jià)離子(Zn~(2+)和Cu~(2+))和異價(jià)離子(Ag~+和Cr~(3+)),Li_2MnSiO_4/C樣品的電化學(xué)性能都有不同程度的提高。在硅位摻雜Al~(3+)離子可以使樣品中的鋰含量增加,合成的不同含量Al~(3+)離子摻雜的樣品中,Li2.02MnSi0.98Al0.02O4/C樣品呈現(xiàn)出了最優(yōu)的電化學(xué)性能。首次提出氧化物和碳共包覆來(lái)提高Li_2MnSiO_4材料的性能。本論文研究了三種不同的氧化物材料MoO_2,ZnO和TiO_2對(duì)Li_2MnSiO_4/C材料的結(jié)構(gòu)和性能的影響。一步溶膠凝膠法合成的不同含量MoO_2包覆的Li_2MnSiO_4/C材料中,包覆量為1wt%時(shí),材料呈現(xiàn)了最優(yōu)的電化學(xué)性能,在0.1 C倍率下的首次放電容量為184.9mAh g-1。包覆ZnO和TiO_2的最優(yōu)樣品在0.1 C倍率下的放電容量分別為182.8和186.4 mAh g-1。并且,包覆后的樣品都呈現(xiàn)出了較好的循環(huán)性能。通過(guò)非原位XRD分析可知,包覆氧化物可以在一定程度上抑制結(jié)構(gòu)的坍塌。ICP測(cè)試表明,氧化物可以減少M(fèi)n在循環(huán)過(guò)程中溶于電解液中的濃度。首次采用水熱法,使用無(wú)機(jī)的硅酸代替有機(jī)的TEOS作為硅源來(lái)合成Li_2MnSiO_4/C材料�？疾炝瞬煌暮铣蓷l件對(duì)最終樣品結(jié)構(gòu)和電化學(xué)性能的影響。得到該方法制備Li_2MnSiO_4/C材料的最優(yōu)條件為:水熱反應(yīng)溫度為180 ℃,水熱反應(yīng)時(shí)間為36 h,煅燒溫度為600 ℃,溶劑中添加20 ml的乙二醇,煅燒時(shí)間為10 h。最優(yōu)樣品在0.1 C和0.5 C倍率下的首次放電比容量分別為171.7和159.4 mAh g-1。
[Abstract]:Lithium ion battery cathode material Li_2MnSiO_4 has the advantages of high theoretical capacity (333.0 mAh g ~ (-1), good thermal stability, low cost and environmental friendliness. However, the material also has many disadvantages, such as low electrical conductivity, structure collapse during cycling and dissolution of Mn in electrolyte, which results in poor cycling performance. In this paper, the preparation and modification of Li_2MnSiO_4 materials were studied systematically. The samples were characterized by XRD,SEM,EDS,TEM, constant current charge-discharge test, cyclic voltammetry and AC impedance method. Li_2MnSiO_4/C materials were synthesized by a rapid sol-gel method with organic tetraethyl silicate (TEOS). As the source. The effects of different synthetic processes on the structure and electrochemical properties of the synthesized Li_2MnSiO_4/C materials were studied. The optimum conditions for the synthesis of Li_2MnSiO_4/C materials were found: the amount of acetic acid was 10 g, the calcination temperature was 650 鈩，

本文編號(hào)：2283367