鋰離子電池論文：鋰離子電池正極材料氟磷酸釩鋰的合成及電化學(xué)性能研究

1、 鋰離子電池論文：鋰離子電池正極材料氟磷酸釩鋰的合成及電化學(xué)性能研究【中文摘要】近年來,氟磷酸釩鋰（LiVPO4F）因具有優(yōu)異的熱穩(wěn)定性、高放電平臺(tái)和較高的理論容量(156 mAh·g-1),被認(rèn)為是一種具有巨大潛力的鋰離子電池正極材料。然而,LiVPO4F較差的電導(dǎo)率導(dǎo)致其高倍率性能較差,從而限制了它的應(yīng)用。本文針對(duì)LiVPO4F電導(dǎo)率低的缺點(diǎn),通過改進(jìn)合成方法及離子摻雜制備LiVPO4F/C及其摻雜LiVPO4F/C復(fù)合材料,提高LiVPO4F的電導(dǎo)率,從而提高LiVPO4F的電化學(xué)性能。通過X射線衍射（XRD）、掃描電子顯微鏡（SEM）、循環(huán)伏安和充放電測(cè)試等測(cè)試技術(shù),研究合成

2、條件、摻雜鋁量對(duì)LiVPO4F的結(jié)構(gòu)及其電化學(xué)性能的影響,并優(yōu)化合成條件,制備出電化學(xué)性能優(yōu)異的LiV0.95Al0.05PO4F/C復(fù)合材料。以V2O5、NH4H2PO4、葡萄糖和LiF為原料,通過改變反應(yīng)原料的混合方式,改善傳統(tǒng)固相法原料混合不均勻的缺點(diǎn),改進(jìn)合成LiVPO4F/C復(fù)合正極材料的傳統(tǒng)固相法制備工藝,并比較由改進(jìn)固相法及傳統(tǒng)固相法合成LiVPO4F/C復(fù)合材料的物理和電化學(xué)性能。結(jié)果表明,兩種方法均可合成三斜結(jié)構(gòu)的LiVPO4F及碳組成的復(fù)合正極材料,但改進(jìn)固相法合成的LiVPO4F/C復(fù)合正極材料的放電比容量及循環(huán)性能均優(yōu)于傳統(tǒng)固相法合成的LiVPO4F/C復(fù)合材料。改進(jìn)固

3、相法合成的LiVPO4F/C復(fù)合正極材料的0.2C、0.5C和1C的放電比容量分別為133.7 mAh·g-1、124.9 mAh·g-1和118.7 mAh·g-1,而傳統(tǒng)固相法合成的LiVPO4F/C復(fù)合正極材料相應(yīng)倍率的放電比容量分別為131.2 mAh·g-1、121.4 mAh·g-1和104.9 mAh·g-1。以V2O5、H3PO4、檸檬酸和LiF為原料,通過溶膠凝膠法合成LiVPO4F/C復(fù)合正極材料并研究反應(yīng)條件對(duì)復(fù)合材料電化學(xué)性能的影響,確定合成的最佳條件:V2O5、H3PO4和檸檬酸的摩爾比為1:2:2.4,70

4、0焙燒干凝膠6h合成VPO4/C,750焙燒VPO4/C與LiF混合物1h合成LiVPO4F/C復(fù)合正極材料。最佳條件下合成LiVPO4F/C的放電比容量及循環(huán)性能均高于由固相法合成的復(fù)合材料,溶膠凝膠法合成的LiVPO4F/C復(fù)合材料1C和5C充放電倍率的放電比容量分別為123.7 mAh·g-1和104.4 mAh·g-1。在溶膠凝膠法成功合成LiVPO4F/C的基礎(chǔ)上,以V2O5、H3PO4、檸檬酸、硝酸鋁和LiF為原料,通過溶膠凝膠法合成LiV1-xAlxPO4F /C（x=0.03, 0.05, 0.07）復(fù)合材料。測(cè)試結(jié)果表明,LiV1-xAlxPO4F/C的放

5、電電壓平臺(tái)及循環(huán)性能隨著摻雜鋁量的增加而提高,放電比容量隨著鋁含量的增加而下降,其中LiV0.95Al0.05PO4F/C具有最高的能量密度,大電流充放電性能優(yōu)于LiVPO4F/C復(fù)合材料,其5C放電比容量高達(dá)110 mAh·g-1?！居⑽恼縍ecently, lithium vanadium fluorophosphates, LiVPO4F, has been considered as a potential cathode material for lithium ion batteries due to its excellent thermal stability,

6、high discharge voltage and high theoretic capacity of 156 mAh·g-1. However, the poor conductivity of LiVPO4F material results in poor high rate capability and limits its applications in lithium ion batteries.The study in this thesis mainly focuses on the improvement of electrochemical performan

7、ce of LiVPO4F by improving its poor conductivity. The conductivity of LiVPO4F was enhanced by improving the synthesis method and LiV0.95Al0.05PO4F/C with excellent performance was prepared by sol-gel method. The effects of preparation conditions and the content of dopped Al on the structure and elec

8、trochemical performance of LiVPO4F were investigated by X-ray diffraction （XRD）, scanning electron microscope （SEM）, cyclic voltammetry （CV） and charge-discharge tests.LiVPO4F/C composites were prepared by a traditional solid-state method and a modified solid-state method, respectively, using V2O5,

9、NH4H2PO4, glucose and LiF as raw materials. Defect of uneven mixing of raw materials resulted from traditional solid-state method was overcomed by modified solid-state method through the improved mixing procedure. Comparative study of physical and electrochemical properties of LiVPO4F/C composites p

10、repared by traditional and modified solid-state methods, respectively, was carried out. Results suggest that the two synthesis methods are effective to prepare composite cathode materials consisting of triclinic LiVPO4F and carbon. But the discharge capacity and cyclability of LiVPO4F/C composite sy

11、nthesized by modified solid-state method are better than that composite prepared by traditional solid-state method. The discharge capacities of LiVPO4F/C composite prepared by modified solid-state method at 0.2, 0.5 and 1C are 133.7, 124.9 and 118.7 mAh·g-1, respectively, while the LiVPO4F/C co

12、mposite prepared by traditional solid-state method exhibits 131.2, 121.4 and 104.9 mAh·g-1 at the corresponding above-mentioned current rates, respectively.LiVPO4F/C composite cathode materials were prepared by a sol-gel method using V2O5, H3PO4, citric acid and LiF as raw materials and the eff

13、ects of preparation conditions on the electrochemical performance of composites were investigated. The results reveal the optimum preparation conditions as follows: mole ratios of V2O5, H3PO4 and citric acid are 1:2:2.4; VPO4/C was prepared by calcination of dried gel at 700for 6h; preparation of Li

14、VPO4F/C by sintering mixture of VPO4/C and LiF at 750for1 h. The discharge capacity and cyclability of LiVPO4F/C composite prepared by sol-gel method at optimum conditions are better than that of LiVPO4F/C composite prepared by solid-state method. The discharge capacities of LiVPO4F/C composite prep

15、ared by sol-gel method are 123.7 and 104.4 mAh·g-1 at 1C and 5C, respectively.Based on the preparation of LiVPO4F/C composite by sol-gel method, LiV1-xAlxPO4F/C （x=0.03, 0.05 and 0.07） composites were synthesized by sol-gel method using V2O5, H3PO4, citric acid, Al（NO3）3·9H2O and LiF as ra

16、w materials, and the electrochemical performance was investigated. The discharge voltage plateau and cyclability of LiV1-xAlxPO4F/C are improved with the increase in doped-Al content, while the discharge capacity decreases with the increase of doped-Al content and LiV0.95Al0.05PO4F/C exhibits highes

17、t energy density among the above-mentioned LiV1-xAlxPO4F/C composites. The high rate discharge capacity of LiV0.95Al0.05PO4F/C is higher than that of LiVPO4F/C composite and displays high capacity of 110 mAh·g-1 at 5C.【關(guān)鍵詞】鋰離子電池 正極材料 氟磷酸釩鋰 LiVPO4F Al摻雜【英文關(guān)鍵詞】Li-ion batteries cathode material li

18、thium vanadium fluorophosphate LiVPO4F Al doped【目錄】鋰離子電池正極材料氟磷酸釩鋰的合成及電化學(xué)性能研究摘要4-5Abstract5-6第1章 緒論9-221.1 引言91.2 鋰離子電池概述9-121.2.1 鋰離子電池的結(jié)構(gòu)9-101.2.2 鋰離子電池的工作原理10-111.2.3 鋰離子電池的特點(diǎn)和存在的問題11-121.3 鋰離子電池正極材料的研究進(jìn)展12-171.3.1 過渡金屬氧化物正極材料12-151.3.2 聚陰離子型正極材料15-171.4 氟磷酸釩鋰LiVP0_4F 正極材料的研究進(jìn)展17-201.4.1 氟磷酸釩鋰的結(jié)構(gòu)與

19、特點(diǎn)17-181.4.2 氟磷酸釩鋰的制備方法18-191.4.3 LiVP0_4F 材料的缺點(diǎn)和改進(jìn)的方法19-201.5 本論文研究的意義及內(nèi)容20-22第2章 實(shí)驗(yàn)22-272.1 主要實(shí)驗(yàn)儀器與藥品22-232.1.1 主要實(shí)驗(yàn)儀器22-232.1.2 主要實(shí)驗(yàn)藥品232.2 實(shí)驗(yàn)方法23-242.2.1 高溫固相法制備LiVP0_4F/C232.2.2 改進(jìn)的固相法制備LiVP0_4F/C23-242.2.3 溶膠凝膠法制備LiVP0_4F/C242.2.3.1 溶膠凝膠法制備LiV_(1-x)Al_xP0_4F/C242.3 LiVP0_4F 正極材料的表征24-252.3.1 物相分析242.3.2 形貌分析242.3.3 熱重分析24-252.3.4 碳含量分析252.4 扣式模擬電池的組裝252.5 材料的電化學(xué)性能測(cè)試252.