Study On The Performance Of Polymer Electrolyte And Lithium Anode

More and more serious global power and environmental crisis have become the two main problems which the human being has to face during the process of continuous development for the society. It is an inevitable tendency to develop a new kind of green chemical power source with good performance, long cycling life, no pollution and low price.Polymer lithium ion battery not only has the higher specific energy than liquid lithium ion battery, but also can resolve the problems of leakage and unsafety in liquid electrolyte lithium ion battery, and the shape of polymer lithium ion battery can be designed flexibly as well.Solid polymer lithium battery is one of the most promising kind of batteries. Poly(ethylene oxide)(PEO) is regarded as one of the most excellent polymer matrix. But its conductivity at room temperature is very low. Therefore the principal duty is to enhance the ambient ionic conductivity of PEO electrolyte.Lithium metal is the most promising anode material because of its most negative normal electrode potential and the highest specific energy. However, the dendritic lithium and lithium powderization will be produced during the charge process, therefore the potential safety problem confines the commercial application for lithium anode. Resolution of this problem will help the secondary lithium battery come into the market.With the development of novel cathode materials, the future lithium battery or lithium ion battery will possess much higher specific energy density and higher potential, which requires the higher electrochemical stability for the current collectors. Therefore, it has practical meaning to increase the corrosion resistance of the current collectors.In this work, much effort has been devoted to investigating the problems above, and the results as follows:1. Two kinds of mesoporous materials containing lithium, LiAlSBA and Li-FER, are used as fillers to PE0/LiC104 polymer electrolytes. Compared with barePE0/LiC104 sample, the ionic conductivities at 30"C for composite electrolytes with LiAlSBA and Li-FER are both enhanced three orders, and exhibit good performance in temperature range of 30°C ~ 80°C. In addition, other electrochemical performances are also increased greatly, including the cation transference number (t+) representing the effective ion transference number, the diffusion coefficient (Ds) and the cation and anion diffusion coefficients (D+, D.). The electrochemical windows and the compatibility between lithium metal anode and the composite polymer electrolytes are improved as well.We analyse and discuss the intrinsic mechanism for the enhancement of ionic conductivity of PEO composite electrolytes by adding mosoporous materials containing lithium ions using XREK TGA, DSC, IR and PLM methods. The crossed polarizers microscope (PLM) is employed to investigate the crystal micrographs of PEO polymer electrolytes for the first time. The results show that the mesoporous grains not only hinder the ordered arrange of PEO chains, but also have the ability to fine crystal and increase the fraction of the amorohous phase in solid polymer electrolyte. The decrease of the glass-transition temperature (Tg) and melting temperature (Tm) indicates the increase of the polymer chains flexibility.It was proposed that the affect between Li+ in mesoporous fillers and CIO4' can promote the dissociation of Li+-C104' in PEO polymer electrolyte , and result in the increase of transference number of Li+, therefore enhance the ionic conductivity. 2 For the first time lithium anode was charged by bi-directional pulse current instead of traditional direct current (DC) to suppress the formation of lithium dendrites. When the lithium electrode was charged by pulse current (0.2mA/cm2), there was no dendrite formed in 7 h and the lithium surface kept smooth. However, obvious dendrites formed on the surface of lithium electrode when it was charged by DC at the same current density for 30 min. Additionally, the lithium anode charged by pulse current had better coulombic efficiency than that of lithium anode charged by DC. The EIS was used to confirm the phenomena from the view of the lithium surface area changes during these processes. This result exhibits it is a new way to suppress the lithium dendrites during the charging process, and it is beneficial to...