| Monoclinic Li3V2(PO4)3 is a polyanion cathode material for lithium ion batteries, which is famous for high theory capacity, low cost and high safety. Tremendous efforts have been made in recent years to study the Li3V2(PO4)3 materials. In this thesis, we have focused on investigating synthesis methods, structure characteristic and electrochemical performance of Li3V2(PO4)3 material, understanding the performance and characteristic of Li3V2(PO4)3 as cathode material. Some fruitful results are obtained, which are favorable for research and development of Li3V2(PO4)3. The goal of the thesis is finding a facile and effective approach to prepare Li3V2(PO4)3 with enhanced performance. Main contents as following:(1) In this chapter, we introduce an improved rheological phase reaction (RPR) method to prepare Li3V2(PO4)3/C with different phosphoric sources, such as 1-Hydroxy Ethylidene-1,1-Diphosphonic Acid (HEDP), Polyvinyl alcohol ammonium phosphate (PVAN) and Tributyl phosphate (TBP). The phosphoric sources contain both phosphorus and organic function groups, which can inhibit Li3V2(PO4)3 grains growth with conductive carbon formation in pyrolysis. This strategy can be used as a safe and straightforward method to prepare LVP/C composite, which the phosphoric introduction, V5+ reduction and carbon doping can be achieved in one step. The TBP is used as not only a reagent but also a rheological body. Effects of phosphoric sources on crystal structure and electrochemical properties such as capacities and rate capabilities of the composite materials have also been discussed.(2) In this chapter, ascorbic acid (C6H8O6) was used as reducing agent and organic carbon source. Firstly, V5+ was reduced to V4+ or V3+ with ascorbic acid addition in the mixture solution; secondly, the in-situ carbon was formed from organic residue carbonization under heat treatment. Compared to the reported methods, this strategy not only shortened the period (only 1h) of material preparation and lowered energy cost, but also obtained Li3V2(PO4)3/C with enhanced performance. As a matter of the fact, our approach allowed us to obtain new insights into the synthesis of Li3V2(PO4)3/C materials. The reversible capacity of Li3V2(PO4)3/C prepared with LiOH and H3PO4 is 141.2 mAhg?1 after 100 cycles at 1C discharge rate in the range of 3-4.8V, and the retention rate of discharge capacity is 93.4%. Furthermore, the effects of different reactant (such as LiOH, Li2CO3, H3PO4 and NH4H2PO4) on the electrochemical performance of Li3V2(PO4)3 cathode material were also evaluated.(3) The electrochemical performance of the Li3V2(PO4)3 is inhibited by the low electronic and ionic conductivity, especially limited high rate performance. The particle size of Li3V2(PO4)3 obtained from traditional solid state and carbon thermal reduction methods is large, leading to low Li+ diffusion coefficient.. Li3V(2-2x/3)Mgx(PO4)3/C (x=0, 0.15, 0.30, 0.45) composites have been synthesized by the sol-gel assisted solid state method, using adipic acid C6H10O4 (Hexanedioic acid) as carbon source. The particle size of the composites is 1μm. During the pyrolysis process, Li3V(2-2x/3)Mgx(PO4)3/C network structure is formed. Compared to the Li3V2(PO4)3 material, its specific capacity and rate capability is significantly enhanced. XRD results indicate that the structure stability is enhanced after charge and discharge.(4) We present here a microwave-assisted method to synthesis of carbon-decorated Li3V2(PO4)3 materials. While the conventional process relies on convective heating that leads to sharp thermal gradients and nonuniform reaction conditions. The microwave-assisted method utilizes the dielectric microwave heating of the entire volume of reactants, which not only provides uniform reaction condition and monodisperse nanoparticles with controlled size but also offers significant energy and cost savings for large-scale industrial manufacturing. The lithium ion diffusion coefficients (DLi+) of prepared carbon-decorated Li3V2(PO4)3 materials are investigated by CV and EIS technology.
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