本文選題：鋰離子電池 + 磷酸鐵鋰　； 參考：《華南理工大學(xué)》2011年碩士論文

【摘要】：橄欖石結(jié)構(gòu)的磷酸鐵鋰(LiFePO_4)以其比容量高、價(jià)格低廉、熱穩(wěn)定性好和環(huán)境友好等優(yōu)點(diǎn)被認(rèn)為是一種最具有廣闊應(yīng)用前景的鋰離子電池正極材料。目前工業(yè)制備LiFePO_4所用的高溫固相法存在能耗高、難以得到高純產(chǎn)物、產(chǎn)物性能不穩(wěn)定等缺點(diǎn)。近年來,濕化學(xué)方法制備磷酸鐵鋰以其能耗低、結(jié)構(gòu)均勻穩(wěn)定、容易實(shí)現(xiàn)摻雜改性等重要優(yōu)點(diǎn)而越來越受到重視。 本文設(shè)計(jì)和提出了一種濕化學(xué)制備磷酸鐵鋰的新方法-混合沉淀法,該方法以(NH_4)_2Fe(SO_4)_2·6H_2O、LiOH·H_2O、H_3PO_4、(NH_4)_3PO_4·3H_2O為原料,先分別制得磷酸鐵和磷酸鋰的沉淀,經(jīng)過陳化和除去部分母液后,將兩種沉淀充分混合,繼續(xù)陳化,經(jīng)過過濾干燥,可得到磷酸鐵鋰的前驅(qū)體。該方法有效地解決了傳統(tǒng)的沉淀法及共沉淀法存在的鋰鹽同步沉淀困難、收率低、以及材料均勻性差等問題,可制備出純相的高性能LiFePO_4/C材料,產(chǎn)物的電化學(xué)性能遠(yuǎn)高于共沉淀法制備的樣品和工業(yè)樣品。本文考察了各種制備條件對于材料性能的影響,運(yùn)用恒電流充放電測試、循環(huán)伏安測試以及交流阻抗測試對產(chǎn)物的電化學(xué)性能進(jìn)行了分析,并采用XRD、SEM等表征手段對產(chǎn)物的結(jié)構(gòu)和形貌進(jìn)行了表征分析。 考察了原料中鋰鐵比、陳化溫度、焙燒溫度、液相中乙醇的添加量對產(chǎn)物性能的影響。研究結(jié)構(gòu)表明:鋰鐵比為1.0和1.1時(shí)能夠得到純相的LiFePO_4 ,鋰過多和過少都會(huì)產(chǎn)生雜質(zhì)相。鋰鐵比為1.1的樣品在0.1 C的放電比容量最高,為151.7 mAh·g~(-1) ,但是在2 C放電倍率下僅為109.2 mAh·g~(-1),不及鋰鐵比1.0的樣品的119.0 mAh·g~(-1)。所以鋰鐵比為1.0的樣品在大倍率下具有較好的電化學(xué)性能。50℃是比較適宜的陳化溫度,陳化溫度為50℃的樣品在不同倍率下的放電比容量都較高,在0.1 C和2 C倍率下分別為141.0 mAh·g~(-1)和125.7 mAh·g~(-1)。高溫焙燒溫度對產(chǎn)物的性能影響比較顯著,在考察范圍內(nèi),隨著焙燒溫度的升高,產(chǎn)物的結(jié)晶度越高,放電比容量越大。其中750℃焙燒的樣品的電化學(xué)性能最好,在0.1 C和2 C的放電比容量分別達(dá)到了155.9 mAh·g~(-1)和118.9 mAh·g~(-1)。 本文研究了不同碳源及碳含量對于LiFePO_4性能的影響。以聚乙烯醇(PVA)為包覆碳源具有非常好的改性效果,碳含量為8 wt.%的樣品在0.1 C和2 C的放電比容量分別為154.3 mAh·g~(-1)和134.5 mAh·g~(-1)。研究結(jié)果表明:采用葡萄糖包覆的樣品也具有非常好的電化學(xué)性能,當(dāng)碳含量為10 wt.%時(shí),其0.1 C放電的比容量可達(dá)148.1 mAh·g~(-1)。 實(shí)驗(yàn)發(fā)現(xiàn):碳含量少的樣品在小倍率放電時(shí)的電化學(xué)性能與碳含量多的樣品基本一樣,但在大倍率放電時(shí)比容量衰減非常明顯,如:碳含量為3 wt.%的樣品在2 C倍率時(shí)的容量僅為72.4 mAh·g~(-1),而碳含量為12 wt.%左右的樣品在2 C倍率下的放電比容量可高達(dá)125 mAh·g~(-1)。
[Abstract]:Olivine structure LiFePO4 (LiFePO4) is considered to be the most promising cathode material for lithium-ion batteries due to its high specific capacity, low price, good thermal stability and environmental friendliness.At present, the high temperature solid state method used in the industrial preparation of LiFePO_4 has the disadvantages of high energy consumption, difficulty in obtaining high purity products and unstable properties of the products.In recent years, more and more attention has been paid to the preparation of lithium iron phosphate by wet chemical method because of its advantages of low energy consumption, uniform structure stability and easy to achieve doping modification.A new wet chemical method for the preparation of lithium iron phosphate, mixed precipitation method, has been designed and proposed in this paper. The method is based on a new method, which is composed of a new method, which is composed of a mixture precipitation method. The method is based on the method of NH / NH _ 4 / S _ 2FeO _ 4 / S / S / T / T _ 6H _ 2OH _ 2O _ 4 / T _ 2H _ 2O _ 2H _ 2O _ 4 / s _ 4 3H_2O as raw material. The precipitation of Fe _ 2O _ 4 and Li _ 2PO _ 4 is prepared respectively after aging and removing part of the mother liquor.The precursor of lithium iron phosphate can be obtained by mixing the two precipitates and aging them through filtration and drying.This method can effectively solve the problems of simultaneous precipitation of lithium salt by traditional precipitation method and co-precipitation method, such as low yield and poor homogeneity of materials, and can be used to prepare pure phase high performance LiFePO_4/C materials.The electrochemical properties of the products are much higher than those prepared by coprecipitation and industrial samples.In this paper, the effects of various preparation conditions on the properties of the materials were investigated. The electrochemical properties of the products were analyzed by constant current charge-discharge test, cyclic voltammetry test and AC impedance test.The structure and morphology of the products were characterized by XRD SEM.The effects of the ratio of lithium to iron, aging temperature, calcination temperature and the amount of ethanol in liquid phase on the properties of the product were investigated.The results show that pure phase LiFePO_4 can be obtained when the ratio of lithium to iron is 1. 0 and 1. 1. The impurity phase can be produced by excessive lithium and too little lithium.The discharge capacity of the sample with Li / Fe ratio 1.1 is the highest at 0.1 C, which is 151.7 mAh / g ~ (-1), but at 2 C discharge rate is only 109.2 mAh / g ~ (-1), which is less than that of the sample with Li / Fe ratio of 151.7 mAh / g ~ (-1) ~ (-1).Therefore, the sample with Li / Fe ratio 1.0 has better electrochemical performance at large ratio. 50 鈩，

本文編號(hào)：1768068