發(fā)布時(shí)間：2018-06-20 12:31

  本文選題：層狀富鋰正極材料 + 表面修飾�。� 參考：《湘潭大學(xué)》2017年碩士論文

【摘要】：近年來(lái),層狀富鋰正極材料xLi_2MnO_3·(1-x)LiMO_2(M=Ni,Co,Mn等過(guò)渡金屬)因其具有高的放電比容量(250 mAh/g)和工作電壓(4.6 V vs.Li/Li+),吸引了國(guó)內(nèi)外研究人員的興趣,并被視為最具前景的下一代高性能鋰離子電池正極材料。盡管層狀富鋰正極材料擁有高放電比容量和能量密度,但是在其大規(guī)模商業(yè)化應(yīng)用之前,層狀富鋰正極材料存在的幾個(gè)固有缺陷必須要得到解決,如首次不可逆容量損失大以及差強(qiáng)人意的循環(huán)性能和倍率性能。針對(duì)以上問(wèn)題,本文通過(guò)表面修飾,微納結(jié)構(gòu)設(shè)計(jì)以及形貌尺寸優(yōu)化等策略,旨在改善層狀富鋰正極材料的電化學(xué)性能,主要研究?jī)?nèi)容如下:(1)首先采用共沉淀法及后續(xù)的高溫固相反應(yīng)合成了球形層狀富鋰正極材料Li1.5Ni_(0.25)Mn_(0.75)O_2+δ,然后用水熱法在球形層狀富鋰正極材料的表面均勻地包覆了一層Li Ti_2(PO_4)_3(LTP)。系統(tǒng)地研究了不同量的LTP包覆材料物理及電化學(xué)性能之間的差異。結(jié)果表明,LTP主要是以納米粒子的形式均勻地包覆在材料的表面,沒(méi)有改變?cè)牧系慕Y(jié)構(gòu)。另外,LTP包覆層不僅有效提高了富鋰正極材料的首次庫(kù)倫效率,其循環(huán)性能和倍率性能也得到了顯著的改善。包覆量為3 wt%樣品展示了最好的電化學(xué)性能,在0.5 C電流密度下,其首次可逆容量為232.8mAh/g,循環(huán)100次后容量保持率為95.9%,10 C大倍率下的放電容量高達(dá)103.2mAh/g。同時(shí),LTP包覆層為無(wú)定形態(tài)的電化學(xué)活性材料,能夠有效地抑制材料在循環(huán)過(guò)程中SEI膜的形成并降低了電荷轉(zhuǎn)移阻抗,有助于鋰離子和電子的傳輸。(2)采用簡(jiǎn)單而溫和的共沉淀法通過(guò)自組裝制備了一種新型的梭形多孔微納結(jié)構(gòu)富鋰正極材料0.5Li_2MnO_3·0.5LiNi_(1/3)Co_(1/3)Mn_(1/3)O_2。由納米初級(jí)粒子堆積而成的微米材料能夠穩(wěn)定材料的結(jié)構(gòu),為材料的循環(huán)性能提供保障;多孔結(jié)構(gòu)不僅可以顯著地增大活性材料的比表面積,使其能與電解液更充分的接觸,而且可以縮減Li+/電子的傳輸距離,顯著改善材料的倍率特性。恒電流充放電測(cè)試表明該材料在0.1 C倍率,2.0~4.6 V條件下的初始可逆容量為294.8 mAh/g,0.5 C電流密度下循環(huán)200次后其容量依然保持在220.6 mAh/g,容量保持率高達(dá)87.1%。得益于這種獨(dú)特的結(jié)構(gòu)特征,該材料同樣展示了卓越的倍率性能,在10 C大倍率下,其放電容量可高達(dá)139.5 mAh/g。(3)為了進(jìn)一步提高層狀富鋰正極材料各方面的性能,設(shè)計(jì)并成功制備了一系列形貌和尺寸可控的微納結(jié)構(gòu)Li_(1.2)Ni_(0.13)Co_(0.13)Mn_(0.54)O_2正極材料。通過(guò)合理調(diào)節(jié)乙二醇在水/醇混合溶液中的體積比,在CTAB的輔助下,該材料的形貌可由棒狀逐漸轉(zhuǎn)變成橄欖狀,繼而演變成梭子狀。研究結(jié)果表明,富鋰正極材料的形貌和尺寸對(duì)它的電化學(xué)性能影響較大,相比于棒狀和梭子狀正極材料,橄欖狀正極材料因其均一的形貌和合適的尺寸在首次可逆容量(0.1 C,297.0 mAh/g),循環(huán)性能(0.5 C循環(huán)100次,保持率為95.4%)以及倍率性能(10 C,142.8 mAh/g)等方面均顯現(xiàn)出了更為優(yōu)異的電化學(xué)性能。其卓越的電化學(xué)性能主要是得益于良好的形貌和適當(dāng)?shù)某叽缫约拔⒓{結(jié)構(gòu)之間的協(xié)同作用。
[Abstract]:In recent years, layered lithium rich cathode material xLi_2MnO_3 (1-x) LiMO_2 (M=Ni, Co, Mn and other transition metals) has attracted the interest of researchers both at home and abroad because of its high discharge specific capacity (250 mAh/g) and working voltage (4.6 V vs.Li/Li+), and is considered as the most promising next generation of high performance lithium ion battery positive electrode. The material has high discharge ratio and energy density, but before its large-scale commercial application, several inherent defects in the layered lithium rich cathode material must be solved, such as the first irreversible capacity loss and the poorly intended cycle performance and multiplying performance. In order to improve the electrochemical performance of layered lithium rich cathode materials, the main research contents are as follows: (1) first, spherical lamellar lithium rich cathode materials Li1.5Ni_ (0.25) Mn_ (0.75) O_2+ delta are synthesized by co precipitation method and subsequent high temperature solid state reaction, and then the hydrothermal method is used in spherical lithium rich cathode material A layer of Li Ti_2 (PO_4) _3 (LTP) was uniformly coated on the surface of the material. The differences between the physical and electrochemical properties of different amounts of LTP coated materials were systematically studied. The results showed that LTP was coated on the surface of the material evenly in the form of nanoparticles, and the structure of the raw material was not changed. In addition, the LTP coating not only improved the rich of the LTP coating effectively. The first Kulun efficiency of lithium-ion cathode material has been greatly improved for its cycle performance and multiplying performance. The coating volume of 3 wt% shows the best electrochemical performance. Under the 0.5 C current density, its first reversible capacity is 232.8mAh/g, the capacity retention rate is 95.9% after 100 cycles, and the discharge capacity of 10 C ratio is as high as 103.2mAh/g. At the same time, the LTP coating is an amorphous electrochemical active material, which can effectively inhibit the formation of the SEI film during the cycle process and reduce the charge transfer impedance, which is helpful for the transfer of lithium ions and electrons. (2) a new type of shuttle shaped porous micro nano structure is prepared by self assembly by a simple and mild coprecipitation method. Micron materials, 0.5Li_2MnO_3. 0.5LiNi_ (1/3) Co_ (1/3) Mn_ (1/3) O_2., which are deposited by nanometer primary particles, can stabilize the structure of materials and provide a guarantee for the cycling performance of the materials. The porous structure can not only significantly increase the specific surface area of the active material, make it contact more fully with the electrolyte, but also reduce the Li+/. The transmission distance of the electron significantly improves the ratio of the material. The constant current charge discharge test shows that the initial reversible capacity of the material at 0.1 C ratio and 2.0~4.6 V is 294.8 mAh/g, and the capacity remains 220.6 mAh/g after 200 cycles of 0.5 C current density, and the capacity retention rate is as high as 87.1%. benefits from this unique structural feature. The material also shows excellent multiplier performance. Under 10 C large ratio, the discharge capacity can be as high as 139.5 mAh/g. (3). In order to further improve the properties of layered lithium rich cathode materials, a series of morphology and size controlled micro nano structure Li_ (1.2) Ni_ (0.13) Co_ (0.13) Mn_ (0.54) O_2 positive electrode has been prepared and successfully prepared. By adjusting the volume ratio of ethylene glycol in water / alcohol mixed solution, with the aid of CTAB, the morphology of the material can be transformed from bar shape to olive shape and then into a shuttle shape. The results show that the morphology and size of the lithium rich cathode material have great influence on the electrochemical properties of the material, compared with the bar like and the shuttle shaped positive material, the olive shape. Due to its homogeneous morphology and suitable size, the cathode material has more excellent electrochemical properties, such as the first reversible capacity (0.1 C, 297 mAh/g), cycling performance (0.5 C cycle 100, retention rate 95.4%), and multiplying performance (10 C, 142.8 mAh/g). Its excellent electrochemical performance is mainly due to good morphology and adaptation. The synergy between the size and micro nano structure.
【學(xué)位授予單位】：湘潭大學(xué)
【學(xué)位級(jí)別】：碩士
【學(xué)位授予年份】：2017
【分類號(hào)】：TM912;TQ131.11

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