【摘要】：鋰離子電池具有高能量密度、長循環(huán)壽命和價格低廉等優(yōu)點,因此在各個領(lǐng)域被廣泛應(yīng)用。但是,當(dāng)前常用的鋰離子電池負(fù)極材料主要是石墨類材料,由于其理論容量較低,不能滿足人們?nèi)找嬖鲩L的需求。因此,尋找新型具有高充放電容量和較好循環(huán)性能的負(fù)極材料至關(guān)重要。相較于石墨類負(fù)極材料,三元過渡金屬氧化物由于具有高的理論比容量,受到了人們的廣泛研究。本論文以提高鋰離子電池電化學(xué)性能為目的,主要以三元過渡金屬氧化物為中心,通過對材料納米化、構(gòu)筑空心結(jié)構(gòu)和復(fù)合這些方法來提高其電化學(xué)性能,具體的研究為如下三個方面:1.通過一步水熱法成功合成出了多孔空心CuCo_2O_4納米微球和空心MgCo_2O_4納米微球,研究了構(gòu)筑空心結(jié)構(gòu)對其作為鋰離子電池負(fù)極材料的電化學(xué)性能影響。與實心CuCo_2O_4納米微球比較,多孔空心CuCo_2O_4納米微球表現(xiàn)出了優(yōu)異的電化學(xué)性能,在電流密度為0.1 Ag~(-1)時,多孔空心CuCo_2O_4納米微球經(jīng)過150圈的循環(huán)后其可逆容量仍然保持在930 mAh g~(-1),對于實心CuCo_2O_4納米微球而言僅僅經(jīng)過70圈的循環(huán)后已經(jīng)衰減到了430 mAh g~(-1)。該結(jié)果表明,空心結(jié)構(gòu)的構(gòu)筑使其儲鋰性能有了明顯的提高,主要原因是空心結(jié)構(gòu)具有較大的比表面積,有助于增大電解液與電極的接觸面積同時可以提供更多的存儲鋰的電化學(xué)活性位點。2.利用水熱法原位復(fù)合的方法合成了 CuCo_2O_4/rGO復(fù)合材料。相較于單純的CuCo_2O_4,與石墨烯進(jìn)行復(fù)合后的電極材料表現(xiàn)出了更好的循環(huán)和倍率性能。在電流密度為0.5 Ag~(-1)時,CuCo_2O_4/rGO復(fù)合材料經(jīng)過200圈循環(huán)以后其容量仍然可以保持在900 mAh g~(-1),其優(yōu)異的電化學(xué)性能得益于石墨烯的引入可以緩解材料在充放電過程中的體積膨脹同時也可以克服納米粒子的團(tuán)聚。3.以空心碳微球為模板,然后通過水熱法成功合成出了空心HC@NiCo_2O_4復(fù)合材料。經(jīng)過熱重分析,所合成的復(fù)合材料中的碳含量為23.1%,獨特的結(jié)構(gòu)使其作為鋰離子電池負(fù)極材料的時候展現(xiàn)出了優(yōu)越的電性能,在100圈循環(huán)以后其放電比容量仍然可以保持在810 mAhg~(-1)(0.5 Ag~(-1))。材料呈現(xiàn)出空心納米花狀的結(jié)構(gòu),在充放電的時候有助于電解液與電極材料的接觸,可以形成較大的固液接觸面,這樣可以縮短電子和離子的傳輸路徑,進(jìn)而提高了其電化學(xué)性能。
[Abstract]:Lithium ion batteries are widely used in many fields because of their high energy density, long cycle life and low cost. However, graphite is the main anode material of lithium ion battery, which can not meet the increasing demand due to its low theoretical capacity. Therefore, it is very important to find new negative materials with high charge and discharge capacity and good cycling performance. Compared with graphite anode materials, ternary transition metal oxides have been widely studied because of their high theoretical specific capacity. In order to improve the electrochemical performance of lithium-ion batteries, the electrochemical properties of the lithium-ion batteries were improved by nanocrystalline materials, hollow structures and composite methods, focusing on the ternary transition metal oxides. The specific research is as follows: 1. Porous hollow CuCo_2O_4 nanospheres and hollow MgCo_2O_4 nanospheres were successfully synthesized by one-step hydrothermal method. The effect of hollow structure on the electrochemical properties of hollow CuCo_2O_4 nanospheres as anode materials for lithium ion batteries was studied. Compared with solid CuCo_2O_4 nanospheres, porous hollow CuCo_2O_4 nanospheres exhibit excellent electrochemical properties. When the current density is 0.1 Ag~ (-1), the porous hollow CuCo_2O_4 nanospheres exhibit excellent electrochemical properties. The reversible capacity of porous hollow CuCo_2O_4 nanospheres remains at 930 mAh g ~ (-1) after 150 cycles. For solid CuCo_2O_4 nanospheres, it has been attenuated to 430 mAh g ~ (-1) only after 70 cycles. The results show that the structure of hollow structure has greatly improved the lithium storage performance, which is mainly due to the large specific surface area of hollow structure. It can increase the contact area between electrolyte and electrode and provide more electrochemical active sites of lithium storage. CuCo_2O_4/rGO composites were synthesized by hydrothermal in-situ recombination. Compared with the composite of CuCo_2O_4, and graphene, the electrode material showed better cycling and rate performance. When the current density is 0. 5 Ag~ (-1), the volume of cuCo _ 2O _ 4 / r go composite can still be maintained at 900 mAh g ~ (-1) after a 200th cycle. Its excellent electrochemical performance is due to the introduction of graphene, which can alleviate the volume expansion of the material during charging and discharging. Expansion can also overcome the agglomeration of nanoparticles. Hollow HC@NiCo_2O_4 composites were successfully synthesized by hydrothermal method using hollow carbon microspheres as template. The thermogravimetric analysis shows that the carbon content of the composite is 23.1.The unique structure makes it exhibit excellent electrical properties when it is used as cathode material for lithium ion battery. The specific discharge capacity of the composite can be maintained at 810 mAhg~ (-1) (0.5 Ag~ (-1).) after 100th cycle. The material shows hollow nanoscale structure, which is helpful to the contact between electrolyte and electrode material during charge and discharge, and can form a large solid-liquid contact surface, which can shorten the transmission path of electron and ion. Furthermore, the electrochemical performance was improved.
【學(xué)位授予單位】：西北大學(xué)
【學(xué)位級別】：碩士
【學(xué)位授予年份】：2017
【分類號】：TB383.1;TM912

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本文編號：2199911