Study Of The Electrochemical Behavior At Low Temperature Of Li₃V₂（PO₄）₃ Cathode Material For Li-ion Batteries

In recent years, with the increasing rapid depletion of fossil fuels and environmental pollution, more and more researchers put their attentions to develop new energy. Lithium ion batteries have been developed as promising energy storage devices owing to their high capacity, high safety, fast charge-discharge rate and long lifespan. But the poor electrochemical performance of Li-ion batteries at low temperature is one of the major technical barriers to their application. The development of cathode materials is a key factor to improving the performance of lithium ion battery. Monoclinic Li3V2(PO4)3 has been proposed as one of the most promising cathode materials for lithium-ion batteries due to its good thermal stability, high security, wide working temperature range, large capacity. Electrolyte is also one of the major factors that affect the performance of battery, especially at low temperature. In this paper, the performance of electrochemical performance at low temperature is improved by modifying the materials and optimizing the electrolyte. Main contents are listed as follows:1. In this paper, we briefly reviewed the recent progress on lithium-ion battery and the corresponding materials, including cathode materials and electrolyte.2. With Li OH·H2O, NH4VO3, NH4H2PO4 as the raw materials and glucose as carbon source, the composite synthesized carbon-thermal reduction method at 700, 750, 800 ℃ for 8h. Compared with the three samples, there is no effect on the crystalline structure of the materials. But it can affect the particle size and the degree of uniformity of the material. The sample synthesized at 750 ℃ has much smaller and more homogeneous particles shows excellent electrochemical performance.3. We synthesized two samples; one is only used glucose as carbon source and the other one used glucose and CNTs. Then glucose and CNTs can not affect the crystalline structure of the materials. Glucose is the amorphous of residual carbon and CNTs is ordered carbon. The amorphous carbon coating on the surface of the LVP primary particles could limit the growth or gathering and further prevent re-gathering of LVP. CNTs can prevent the aggregation of the particles and provide electronic transmission network, which can effectively improve electronic conductivity. The LVP@C+CNT sample can still maintain excellent electrochemical performance even at-20 ℃.4. To improve the performance of electrolyte, diverse approaches combining multiple strategies are required. Firstly, electrolyte contains more than two solutions, such mixtures would permit an optimization of the electrolyte properties, like liquid range, viscosity, dielectric constant and so on. And it is likely to produce more highly conductive solutions, especially at low temperatures, due to a disordering effect in the lithium-ion coordination behavior of the solvent medium. Secondly, increasing the concentration of lithium salt ensure more Li+ ions transference number in the electrolyte. Finally, adding electrolyte additives, which is helpful to reduce electrode polarization improving the low temperature performance of electrolyte.