【摘要】：鋰離子電池由于其具備較高的比能量、較寬的工作溫度、較長的儲存壽命等特點,在各能源板塊已經(jīng)得到廣泛的應(yīng)用,如手機、便攜式計算機、照相機、汽車、離微網(wǎng)及分布式電站等。本文主要聚焦于尖晶石型Li-Mn-O鋰離子電池正極材料的研究,從合成工藝、包覆、摻雜材料的包覆等方面改善極具市場前景的錳基高電壓正極材料的電化學(xué)性能,提升其市場競爭性,制備了球形多孔錳酸鋰、磷酸錳鋰包覆錳酸鋰、磷酸鈷鋰包覆鎳錳酸鋰,并對其結(jié)構(gòu)性能進行了測試表征,獲得了有一定的創(chuàng)新性意義和價值的研究結(jié)論。具體內(nèi)容如下:1、采用簡單快速的乳液法結(jié)合沉淀破乳法和高溫固相法制備了球形多孔錳酸鋰,并通過多種手段對其結(jié)構(gòu)、形貌、電化學(xué)性能進行了表征。通過XRD和SEM表明了合成前驅(qū)、中間體和成品的物相和形貌,探究了不同水相濃度對產(chǎn)物形貌的影響,再通過CV、EIS和電池循環(huán)性能測試探究了不同濃度水相對產(chǎn)物電化學(xué)性能的影響,得出如下結(jié)論:乳液中水相的Mn離子濃度會對成品的微觀形貌和性能有一定的影響,水相離子濃度越高,得到的組成球形顆粒的納米粒子越小,比表面積越大,對于材料的倍率性能有極大的改善,但是因為電解液與電極材料的接觸面積變大,使得Mn2+的溶出變得嚴(yán)重,從而使得其循環(huán)性能不佳。低水相離子濃度的產(chǎn)物雖然倍率性能不佳,但是其容量和循環(huán)性能有不錯的表現(xiàn)。2、通過常規(guī)沉淀法結(jié)合高溫固相制備了球形錳酸鋰,再通過一步水熱法對LiMn_2O_4進行表面LiMnPO_4材料的包覆,得到了一種富含Mn2+包覆層的LMO覆合材料。該包覆層能有效的阻止Mn2+溶出到電解液中,抑制了LiMn_2O_4中Mn~(3+)的歧化反應(yīng),從而有效的改善了LMO材料的循環(huán)性能。從電化學(xué)測試數(shù)據(jù)中可以看出,不同包覆比例的LiMn_2O_4@3wt%LiMnPO_4和LiMn_2O_4@10wt%LiMnPO_4在不同倍率循環(huán)測試的電化學(xué)性能都要優(yōu)于純的LiMn_2O_4。此外,由于低價錳在電極表面的存在,LiMn_2O_4的離子和電子導(dǎo)通能力得到改善,從而導(dǎo)致了材料的倍率性能得到改善。因此,穩(wěn)定的富含Mn2+的材料作為LiMn_2O_4的包覆層能有效的改善LiMn_2O_4的電化學(xué)性能。3、通過共沉淀結(jié)合高溫固相法制備球形多孔LiNi_(0.5)Mn_(1.5)O_4顆粒,再通過常規(guī)水熱法將LiCoPO_4生長在LiNi_(0.5)Mn_(1.5)O_4顆粒表面,借助SEM和HRTEM確定了材料的形貌及包覆結(jié)構(gòu)的形成,通過XRD和XPS確定了包覆層為LiCoPO_4。通過對四個樣品的XPS、CV和電池充放電分析,證實了包覆層LCP能在LCP和LNM界面上激發(fā)出Mn~(3+),Mn~(3+)含量隨著LCP量的增加而增加。而EIS和GITT測試則進一步說明了出現(xiàn)的Mn~(3+)對于材料導(dǎo)電性和鋰離子遷移能力的作用,其增加了LNM中Ni/Mn混排度從而極大的改善LNM的導(dǎo)電性和鋰離子遷移能力。從電池循環(huán)性能上看,Mn~(3+)的出現(xiàn)對于材料的倍率性能有著重要的提高。LCP作為包覆層的作用還體現(xiàn)在兩點:一是有效的阻止了Mn~(3+)歧化反應(yīng)生成的可溶性Mn2+溶出到電解液中,二是有效的減少了電解液中LiPF6的分解和在電極表面的副反應(yīng),這兩點確保了復(fù)合材料的循環(huán)性能得到了顯著的提高。在實驗中發(fā)現(xiàn),適量包覆層的LNM@5%LCP樣品呈現(xiàn)出最佳的電化學(xué)性能,在0.5C充放電倍率下,初始放電容量為128mAh g-1,循環(huán)100圈后,容量保持率為初始容量的96%。在20C的充放電倍率下,初始充放電容量為115 mAh g-1,遠(yuǎn)遠(yuǎn)高于純LNM的57 mAh g-1。
[Abstract]:As a result of its high specific energy, wide operating temperature and long storage life, Li-ion battery has been widely used in various energy sectors, such as mobile phone, portable computer, camera, automobile, off-grid and distributed power station. The paper mainly focuses on the research of the cathode material of the spinel Li-Mn-O lithium ion battery, and improves the electrochemical performance of the manganese-based high-voltage cathode material with the market prospect from the aspects of the synthesis process, the coating, the coating of the doping material and the like, improves the market competitiveness, and prepares the spherical porous lithium manganate, Lithium manganese phosphate, lithium nickelate and lithium cobalt phosphate are used to coat the lithium manganate, and the structural properties of the lithium manganese phosphate are tested and characterized, and the research conclusion with certain innovative significance and value is obtained. The following contents are as follows: 1. The spherical porous lithium manganate is prepared by a simple and rapid emulsion method in combination with a precipitation demulsification method and a high-temperature solid phase method, and the structure, the morphology and the electrochemical performance of the spherical porous lithium manganate are characterized by a plurality of means. The influence of different water phase concentration on the product morphology was investigated by means of XRD and SEM. The effects of different water phase concentration on the product morphology were investigated. The effects of different concentrations of water on the electrochemical performance of the product were investigated by CV, EIS and battery cycle performance test. The following conclusions were drawn: The Mn ion concentration of the water phase in the emulsion has a certain influence on the micro-morphology and the performance of the finished product, the higher the ion concentration of the water phase, the smaller the nano-particles of the obtained spherical particles, the larger the specific surface area, and greatly improves the rate performance of the material, However, because the contact area of the electrolyte and the electrode material becomes large, the dissolution of the Mn2 + becomes severe, so that the cycle performance thereof is not good. Although the product of low water phase ion concentration is not good, its capacity and cycle performance are good. 2. The spherical manganese acid lithium is prepared by conventional precipitation method in combination with high-temperature solid phase, and the surface LiMn _ 2O _ 4 is coated with LiMn _ 2O _ 4 by one-step hydrothermal method. and a LMO cladding material rich in Mn2 + cladding layer is obtained. The coating layer can effectively prevent Mn2 + from being dissolved in the electrolyte, and the disproportionation reaction of Mn to (3 +) in the LiMn _ 2O _ 4 is inhibited, so that the cycle performance of the LMO material is effectively improved. It can be seen from the electrochemical test data that the electrochemical performance of the LiMn_2O_4@3wt% LiMnPO _ 4 and the LiMn_2O_4@10wt% LiMnPO _ 4 with different coating ratios is better than that of the pure LiMn _ 2O _ 4. In addition, because of the presence of low-cost manganese on the electrode surface, the ion and electron-conduction ability of the LiMn _ 2O _ 4 is improved, resulting in an improvement in the rate performance of the material. Therefore, the stable Mn 2 +-rich material can effectively improve the electrochemical performance of LiMn _ 2O _ 4 as the coating of LiMn _ 2O _ 4. 3. The spherical porous LiNi _ (0.5) Mn _ (1.5) O _ 4 particles are prepared by co-precipitation and high-temperature solid phase method, and the LiCoPO _ 4 is grown on the surface of LiNi _ (0.5) Mn _ (1.5) O _ 4 particles by conventional hydrothermal method. The morphology of the material and the formation of the coating structure were determined by means of SEM and HRTEM, and the cladding layer was LiCoPO _ 4 by XRD and XPS. The content of Mn ~ (3 +) and Mn ~ (3 +) in the LCP and LNM interface can be increased with the increase of the LCP, by analyzing the XPS, CV and charge-discharge of the four samples. The EIS and GITT test further illustrate the effect of Mn ~ (3 +) on the conductivity of the material and the capacity of the lithium ion mobility, which increases the mixed degree of Ni/ Mn in the LNM so as to greatly improve the conductivity and the lithium ion mobility of the LNM. The appearance of Mn ~ (3 +) has an important effect on the rate performance of the material from the battery cycle performance. The effect of the LCP as the cladding layer is also shown at two points: one is effective to prevent the soluble Mn2 + dissolved in the Mn-(3 +) disproportionation reaction to be dissolved in the electrolyte, and the second is to effectively reduce the decomposition of the LiPF6 in the electrolyte and the side reaction on the surface of the electrode, These two points ensure a significant improvement in the cycle performance of the composite. In the experiment, the optimum electrochemical performance of the LNM@5% LCP sample was found, and the initial discharge capacity was 128mAh g-1 at the charge/ discharge rate of 0.5C, and the capacity retention rate was 96% of the initial capacity after 100 cycles. At the charge/ discharge rate of 20C, the initial charge/ discharge capacity was 115 mAh g-1, much higher than that of the pure LNM of 57 mAh g-1.
【學(xué)位授予單位】：江蘇大學(xué)
【學(xué)位級別】：碩士
【學(xué)位授予年份】：2017
【分類號】：TM912

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本文編號：2361267