發(fā)布時間：2018-04-04 22:31

  本文選題：鋰離子電池　切入點：鎂摻雜　出處：《湘潭大學(xué)》2014年碩士論文

【摘要】：單斜結(jié)構(gòu)的Li3V2(PO4)3材料因其具有高理論容量、高鋰離子擴散率、優(yōu)異的熱穩(wěn)定性和較好的循環(huán)穩(wěn)定性，而成為最有潛力的鋰離子電池正極材料。然而，，較低的電子電導(dǎo)率（2.010-8S cm-1）成為阻礙LVP發(fā)展的致命缺陷。因此，提高LVP材料的電子遷移率和離子遷移率是改善其電化學(xué)性能的有效對策。為了克服LVP材料的上述缺點，本論文通過改進(jìn)合成方法和對LVP材料進(jìn)行鋰位金屬離子摻雜等手段提高其電化學(xué)性能。在本論文中分別合成了Li3V2(PO4)3/C、Li3-2xMgxV2(PO4)3/C(x=0、x=0.01、x=0.03和x=0.05)和Li3-3xMgxNaxV2(PO4)3/C(x=0、x=0.03、x=0.05和x=0.07)復(fù)合材料。通過掃描電鏡(SEM)、X-射線衍射(XRD)、電子衍射光譜(EDS)、交流阻抗(EIS)以及循環(huán)伏安(CV)和恒電流充放電等電化學(xué)測試手段，研究最優(yōu)合成條件、鎂離子以及鈉鎂離子在鋰位摻雜對材料電化學(xué)性能的影響規(guī)律，優(yōu)化合成條件并確定鋰位摻雜離子的最佳含量。 采用溶膠凝膠法制備Li3V2(PO4)3/C復(fù)合材料，通過XRD、SEM、CV、EIS和恒流充放電等測試方法，研究焙燒溫度、碳源及釩源對復(fù)合材料的物理性能及電化學(xué)性能影響規(guī)律，并優(yōu)化合成條件，確定合成材料的最佳合成條件，即最佳焙燒溫度為800℃，最佳焙燒時間為8h，最佳碳源為檸檬酸和最佳釩源為V2O5。 以LiAc、NH4H2PO4、Mg(NO3)2·6H2O、30%(v/v)H2O2和檸檬酸為原材料，采用溶膠凝膠法合成Li3-2xMgxV2(PO4)3/C(x=0.01、x=0.03和x=0.05)復(fù)合材料,討論不同鎂含量在鋰位摻雜對材料物理性能及電化學(xué)性能的影響。結(jié)果表明，在0.01≤x≤0.05范圍內(nèi)，LVP在鋰位引入摻雜Mg2+的條件下，仍然維持其單斜結(jié)構(gòu)，但摻雜樣品的晶胞體積大于未摻雜樣品。所有摻雜樣品的電化學(xué)性能均優(yōu)于未摻雜樣品，其中，Li2.94Mg0.03V2(PO4)3/C具有最好的電化學(xué)性能。其在3.0-4.8V電壓范圍及0.1C充放電倍率的條件下，Li3V2(PO4)3/C材料的首次放電容量僅為170mAh g-1，而Li2.94Mg0.03V2(PO4)3/C材料的首次放電容量高達(dá)192mAh g-1。30次循環(huán)后Li3V2(PO4)3/C材料的放電容量僅為144mAh g-1，而Li2.94Mg0.03V2(PO4)3/C材料的放電容量為170mAh g-1，其容量保持率分別為85%和89%。采用循環(huán)伏安法測定材料的鋰離子擴散系數(shù)，結(jié)果表明在鋰位摻雜少量Mg2+可以顯著提高鋰離子擴散系數(shù)，擴散系數(shù)的增大有利于提高鋰離子在活性材料顆粒中的擴散速率，從而有利于提高活性材料的電化學(xué)性能。 以LiAc、NH4H2PO4、Mg(NO3)2·6H2O、NaNO3、30%(v/v)H2O2和檸檬酸為原材料，采用溶膠凝膠法合成Li3-3xMgxNaxV2(PO4)3/C(x=0、x=0.03、x=0.05和x=0.07)復(fù)合材料，研究鈉鎂離子在鋰位共摻雜對材料電化學(xué)性能的影響規(guī)律。結(jié)果表明，所有摻雜樣品的電化學(xué)性能均優(yōu)于未摻雜樣品，其中，Li2.85Mg0.05Na0.05V2(PO4)3/C具有最好的電化學(xué)性能。在3.0-4.8V電壓范圍及0.1C的充放電條件下，Li3V2(PO4)3/C材料的首次放電容量僅為170mAh g-1，30次循環(huán)后其容量保持率為85%， Li2.85Mg0.05Na0.05V2(PO4)3/C的首次放電容量為190mAh g-1，30次循環(huán)后其容量保持率為88%。采用循環(huán)伏安法測試鋰離子擴散系數(shù)，結(jié)果表明，鈉鎂離子共摻雜材料的鋰離子擴散系數(shù)均比未摻雜材料要高，，這可能是共摻雜提高材料電化學(xué)性能的主要原因
[Abstract]:Monoclinic Li3V2 (PO4) 3 materials because of its high theoretical capacity, high lithium ion diffusion rate, excellent thermal stability and good cycle stability, and has become the most promising cathode materials for lithium ion batteries. However, low electronic conductivity (2.010-8S cm-1) become a fatal flaw hindering the development of LVP. Therefore, to improve the electron mobility of LVP materials and ion mobility are effective measures to improve its electrochemical performance. In order to overcome the disadvantages of LVP materials, this paper improved the synthesis methods and materials of LVP lithium metal ions doped in a better electrochemical performance. The Li3V2 were synthesized in this paper (PO4 3/C), Li3-2xMgxV2 (PO4) 3/C (x=0, x=0.01, x=0.03 and x=0.05) and Li3-3xMgxNaxV2 (PO4) 3/C (x=0, x=0.03, x=0.05 and x=0.07) composite materials. By scanning electron microscopy (SEM), X- ray diffraction (XRD), electron diffraction spectroscopy (EDS), AC Impedance (EIS), cyclic voltammetry (CV) and galvanostatic charge discharge method were used to study the optimal synthesis conditions, the influence of magnesium ion and sodium magnesium ion on the electrochemical performance of lithium doped materials, optimize the synthesis conditions and determine the optimum content of lithium doped ions.
Preparation of Li3V2 by sol gel method (PO4) 3/C composites by XRD, SEM, CV, EIS and galvanostatic charge discharge test method, the effects of calcination temperature, carbon source and vanadium source physical properties and electrochemical performance of composite materials, and optimize the synthesis conditions, determine the optimum conditions of the synthesis of materials synthesis that is, the best calcination temperature is 800 DEG C, the best roasting time is 8h, the best carbon source for citric acid and the best source of vanadium V2O5.
In LiAc, NH4H2PO4, Mg (NO3) 2 - 6H2O, 30% (v/v) H2O2 and citric acid as raw materials by sol gel method for synthesis of Li3-2xMgxV2 (PO4) 3/C (x=0.01, x=0.03 and x=0.05) composites, discussed different magnesium content in lithium doping on the physical properties of materials and electrochemical properties were studied. Results show that in x = 0.01 ~ 0.05 range, LVP introduced Mg2+ doped in lithium a condition, still maintain the monoclinic structure, but the cell volume is greater than the doped samples of undoped samples. The electrochemical properties of all doped samples are better than that of the undoped samples, among them, Li2.94Mg0.03V2 (PO4) 3/C has the best electrochemical performance. In the voltage range of 3.0-4.8V and the charge discharge rate of 0.1C under the condition of Li3V2 (PO4) 3/C materials and the initial discharge capacity is only 170mAh g-1, and Li2.94Mg0.03V2 (PO4) 3/C material for the first time a high discharge capacity of 192mAh after g-1.30 cycles of Li3V2 (PO4) 3/C discharge material Capacity is only 144mAh g-1 Li2.94Mg0.03V2 (PO4), and the discharge capacity of 3/C material is 170mAh g-1, the capacity retention rate was 85% 89%. and lithium ion diffusion coefficient were determined by cyclic voltammetry. The results show that the Li doped Mg2+ can significantly improve the lithium ion diffusion coefficient, diffusion coefficient increases in favor of improve the diffusion rate of lithium ion in the particles in the active material, which helps to improve the electrochemical performance of the active material.
In LiAc, NH4H2PO4, Mg (NO3) 2 - 6H2O, NaNO3,30% (v/v) H2O2 and citric acid as raw materials by sol gel method for synthesis of Li3-3xMgxNaxV2 (PO4) 3/C (x=0, x=0.03, x=0.05 and x=0.07) composite materials, research of sodium magnesium ion in Li Co doped on the electrochemical properties of materials were investigated. The results show that the electrochemical properties of all doped samples are better than that of the undoped samples, among them, Li2.85Mg0.05Na0.05V2 (PO4) 3/C has the best electrochemical performance. The discharge conditions and the voltage range of 3.0-4.8V 0.1C, Li3V2 (PO4) 3/C materials the first discharge capacity is only 170mAh g-1,30 cycles, the capacity retention rate was 85% Li2.85Mg0.05Na0.05V2 (PO4) 3/C, the initial discharge capacity was 190mAh after g-1,30 cycles the capacity retention rate was 88%. by cyclic voltammetry of lithium ion diffusion coefficient, the test results show that the lithium magnesium sodium ion Co doped material diffusion coefficients Higher than undoped materials, this may be the main reason for CO doping to improve the electrochemical properties of the materials.

【學(xué)位授予單位】：湘潭大學(xué)
【學(xué)位級別】：碩士
【學(xué)位授予年份】：2014
【分類號】：TM912

【參考文獻(xiàn)】

相關(guān)期刊論文 前3條

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3 劉潔群;鐘勝奎;伍凌;萬康;呂凡;;不同方法合成的LiVPO_4F/C的電化學(xué)性能(英文)[J];Transactions of Nonferrous Metals Society of China;2012年S1期

本文編號：1712006