【摘要】：鋰離子電池被廣泛應用在消費類電子產(chǎn)品、新能源汽車、儲能電網(wǎng)等領(lǐng)域,已經(jīng)為人們?nèi)粘Ｉ?經(jīng)濟發(fā)展不可或缺的能源產(chǎn)品。手機和新能源汽車是鋰離子電池主要的使用對象,兩者發(fā)展勢頭迅猛,這使鋰離子電池的需求非常巨大。所以加大對鋰離子電池的研發(fā),技術(shù)革新是非常必要的。而決定鋰離子電池性能最主要的部件就是正極材料。三元鋰電池由于具有更高的能量密度,相對較低的生產(chǎn)成本而受到企業(yè)和市場的重視。因此,選擇三元正極材料作為研究對象。石墨烯自2004年被發(fā)現(xiàn)以來由于其諸多優(yōu)異的性能而受到科研工作者的重視,石墨烯良好的導電性能不僅能用在負極材料上,同樣也可以應用在正極材料上,在提升容量的同時也可以提高倍率性能。本文采用物質(zhì)電中性的原理用溶膠凝膠法合成了5種不同元素配比的三元正極材料,分別為LiNi_(1/3)Co_(1/3)Mn_(1/3)O_2、LiNi_(1/2)Co_(1/3)Mn_(1/4)O_2、LiNi_(0.7)Co_(0.2)Mn_(0.25)O_2、LiNi_(1/4)Co_(1/2)Mn_(1/4)O_2、LiNi_(0.1)Co_(0.6)Mn_(0.25)O_2。通過對這5種材料分別進行XRD、SEM、恒流充放電測試、倍率測試、循環(huán)測試、循環(huán)伏安測試、電化學交流阻抗測試,來研究材料的結(jié)構(gòu)和電化學性能。從XRD衍射結(jié)果看出,這5種材料均具有層狀結(jié)構(gòu)。通過電化學測試表明,LiNi_(0.7)Co_(0.2)Mn_(0.25)O_2具有較高的可逆容量和穩(wěn)定的循環(huán)性能,在0.1C下首次放電容量達142mAh/g。然后將LiNi_(0.7)Co_(0.2)Mn_(0.25)O_2于700℃、800℃、900℃合成,考察不同合成溫度對材料的影響。測試結(jié)果表明,在700℃條件下合成的材料性能最優(yōu),材料經(jīng)過30個循環(huán)后,容量保持率為90%。隨著合成溫度的升高,材料的電化學性能越差。主要是因為合成溫度升高會使材料的粒徑變大,顆粒分布不均勻,影響了鋰離子的遷移過程,從而造成性能下降。將700℃條件下合成的LiNi_(0.7)Co_(0.2)Mn_(0.25)O_2分別與1%、2%、3%的石墨烯通過球磨法進行復合,同時以直接加入1%、2%、3%的石墨烯的正極材料做對比。在0.1C的電流密度下,2.0V到4.5V電壓區(qū)間內(nèi),經(jīng)過球磨的含量為2%的復合材料首次放電達166mAh/g,比單純的正極材料提升了近24mAh/g,倍率性能也有所提升。在確定了最佳的石墨烯摻量后,在氮氣的保護下通過熱處理工藝以進一步加工,處理溫度分別為200℃、300℃、400℃。實驗結(jié)果表明,經(jīng)過熱處理后材料的首次充放電并沒有得到提升,反而有點下降。原因可能是石墨烯與正極材料經(jīng)過熱處理后使正極材料的層狀結(jié)構(gòu)遭到一定程度的破壞,從而使電化學性能降低。但是通過電化學阻抗測試表明,300℃下得到的復合材料經(jīng)過50次循環(huán)后電荷轉(zhuǎn)移阻抗為70.68m?,低于任何材料循環(huán)50次后的電阻值,這說明經(jīng)過熱處理后能改善石墨烯與正極材料的結(jié)合性,增強復合材料的電子導電率。
[Abstract]:Lithium ion batteries are widely used in consumer electronics, new energy vehicles, energy storage grid and other fields, which have become indispensable energy products for people's daily life and economic development. Mobile phones and new energy vehicles are the main users of Li-ion batteries, and they are developing rapidly, which makes the demand of Li-ion batteries very great. So increasing the development of lithium ion batteries, technological innovation is very necessary. The main component that determines the performance of lithium ion battery is cathode material. Ternary lithium batteries have attracted much attention from enterprises and markets because of their higher energy density and lower production cost. Therefore, the ternary cathode material is chosen as the object of study. Since its discovery in 2004, graphene has been paid much attention by researchers because of its excellent properties. Graphene can be used not only in negative electrode materials, but also in positive electrode materials. While increasing the capacity, it can also improve the performance of the rate. In this paper, we have synthesized five kinds of ternary cathode materials by sol-gel method, which are LiNi_ (1 / 3) Co_ (1 / 3) Mn_ (1 / 3) O _ 2LiNi_ (1 / 2) Co_ (1 / 3) Mn_ (1 / 4) O _ (2) LiNi_ (0.7) Co_ (0.2) Mn_ (0.25) O _ 2LiNi _ (1 / 4) Co_ (1 / 2) Mn_ (1 / 4) O _ 2Li _ (0. 1) Co_ (0. 6) Mn_ (0. 25) O. The structure and electrochemical properties of the five materials were studied by XRD,SEM, constant current charge-discharge test, rate test, cyclic voltammetry test and electrochemical impedance test. The results of XRD diffraction show that all of the five materials have layered structure. Electrochemical measurements show that LiNi0.7 Co_ _ (0.2) Mn_ _ (0.25) O _ 2 has a high reversible capacity and stable cycling performance, and the initial discharge capacity at 0.1C is up to 142mAh/ g. Then LiNi_ _ (0.7) Co_ _ (0.2) Mn_ _ (0.25) O _ 2 was synthesized at 700 鈩，

本文編號：2222547