| This dissertation involves the following four parts: The first part describes some background materials which include mineral fast ion conductors and their application in full solid state cell; gel polymer electrolytes; lithium-water primary batteries; lithium ion battery and corresponding cathode materials. The second part describes the solid electrolytes containing water. Two kinds of electrolytes are introduced, one is poly(methyl methacrylic acid)(PMAA) based gel polymer electrolyte membrane. PMAA was prepared by free radical polymerization, and the solvent casting method was used to manufacture gel electrolyte membrane. The ionic conductivity at room temperature is 1.63×10-7S.cm-1 for the newly produced PMAA with 19.2% water amount. Interaction between polymer chains can be lowered by the presentation of water. PMAA membrane lost water when exposed in air, so its ionic conductivity decreases. When Poly(methyl methacrylic lithiumate)(Li-PMAA) was added in PMAA whose ionic conductivity increases first and then decreases with increasing the weigh ratio(Li-PMAA:PMAA). The ionic conductivity reaches maximum at the weigh ratio of Li-PMAA:PMAA=1:1. When glycerol was added to PMAA membrane, its ionic conductivity lowers down slightly first then increases fast, the maximum conductivity occurs at the weigh ratio of ( PMAA: Li-PMAA: glycerol=3:2:3), the maximum conductivity is 2.3×10-4S.cm-1. When aluminum oxide is added into membrane, it gets stiff, when weigh percent of Al2O3 exceeds 0.2%, the ionic conductivity of membrane decreases. AC Impedance Spectra show that there are stiff micro-area and soft micro-area in the gel membrane, the resistance of both stiff section and soft section decreases with increasing water amount of membrane. It proved that water molecule can disperse in the gel membrane. Steady Polarization Curve of GPW when use graphite as electrode show that hydrogen ion can be reduced to hydrogen at the surface of graphite, this procedure is just like water electrolysis. The plot of ionic conductivity vs. temperature showed that water molecule plays a major role in the course of GPW's conduction, glycerol is also helpful for the hydrogen ion migration because it can lower the interaction between polymer chains. The equilibrium potential of GPW is –90mV, exchange current is 1.182μA. The electrode consists of GPW and graphite is irreverse electrode. The direct Current conductivity of GPW is 2.25 ×10-7S.cm-1 ,DC conductivity : AC conductivity <0.1%. The other kind of solid electrolyte containing water is Li-PMAA composited Montmorillonite(Mont.), Weigh percent of Li-PMAA is smaller than 50%. Two methods are employed to prepare composite Mont.. One is by solution, the other is by heat. X Ray Powder Diffraction Patterns indicated that when Li-PMAA is mixed with Mont., the pure phase can't be obtained even weigh ratio of Li-PMAA:Mont. smaller than 1:10. Composite Mont. by solution method gives a new diffraction peak at 2θ=0-10o, it means that a new phase of composite Mont. occurs at the presence of water molecule. The analysis program of X'Pert Plus show that although composite Mont. isn't pure phase, some Li-PMAA molecule embeds into Mont. which were prepared by solution method and heat method. It makes spacing of Mont. crystal change at c axis. Both IR Spetra and DTA analysis showed that Li-PMAA molecule embeds into Mont. AC Impedance Spetra showed that ionic conductivity of composite Mont. is smaller than pure Mont., composite Mont. by heat method smaller than that by solution method. Also, the ionic conductivity of composite Mont. containing higher weigh percent of Li-PMAA are smaller than that of lower weigh percent. The third part is solid-state cell by using water as oxidation agent. The cell assembly is Re| SE| GPW| graphite, Me stands for negative electrode which is lithium or magnesium, SE is solid electrolyte; GPW is gel polymer containing water. Principle of cell reaction is (a) reaction at negative electrode: Me+nOH-=Me(OH)n+ne-…(1)or Me=Men++ne-…(2),n=1 for lithium, n=2 for magnesium. Both of reaction (1) and (2) are occurred in the process of cell reaction, the ratio of (1) : (2) depends on the solid electrolyte. (b) Reaction at positive electrode: RH+H2O+e=RH+OH-+1/2H2,RH stands for PMAA ,and R stands for PMAA anion. Hydrogen ion of PMAA in GPW embeds into the graphite, it combines with one electron to produce hydrogen atom, PMAA anion seizes one hydrogen ion, it makeswater molecule disaggregate to produce hydroxide anion. Hydroxide anion migrate through GPW layer, solid electrolyte layer and reach the surface of metal, combines with metal ion to produce metal hydroxide. The results of cell reaction is to make surface of metal covered with metal hydroxide, so the internal resistance of cell increases. When magnesium was used as negative electrode, the cell is called magnesium water cell. The cell using Mont as solid electrolyte, the open circuit voltage (OCV) is 1.45V, the discharging time is 30 hours when constant load (51KΩ) discharging at voltage plateau above 1.0V, the discharge capacity is 2mAh/g. The cell using reformed Mont as solid electrolyte, the discharging time is 90 hours when constant load(51KΩ) discharging at voltage plateau above 1.0V, the discharge capacity is 6mAh/g. Discharging time of cell using sintering gaolinite disc, sintering magnesium oxide disc, gel polymer electrolyte (LiClO4-PMMA), cross-linking GPW as solid electrolyte is 6 days, 40 hours, 48 hours and 14 hours respectively at the same discharging condition. Store property of cell is poor; the utilization rate of magnesium is 2.8%. When the negative electrode is lithium, the cell is lithium water cell. The solid electrolyte employed is gel polymer electrolyte (GPE) LiClO4-PMMA of weigh ratio(LiClO4:PMMA= 3:2), OCV of cell is 3.2V, discharge capacity is 1.4mAh/g when constant current 0.05mA discharge. Negative electrode can be eroded by electrolyte, the OCV decreases when cell was storaged. When solid electrolyte is LiClO4-PEG20,000, negative electrode can also be eroded by the electrolyte with even a little amount water, the short current is 12.5mA, average short current 7mA can maintain one hour, discharge capacity 7mAh. Discharging time is 7 hours when constant load 51KΩat voltage plateau above 2.8V with discharge capacity 2.1mAh/g. The fourth part is primary study on cerium dioxide base embedded compound, lithium ion doped cerium dioxide was synthesized by high temperature solid phase reaction, lithium oxide and cerium dioxide can be molted together to get molten solid solution at about 950℃.DTA analysis at the synthetic process and XRD patterns showed that lithium oxide and cerium dioxide can turn into fluorite type solid solutionat mole ratio 0.4-1.0(Li+:Ce4+), a new phase is occurred at mole ratio below 0.3. Intensity of new phase peak decreases with increasing the mole ratio of Li+:Ce4+. When lithium ion doped into cerium dioxide, unit-cell shrinks slightly, unit-cell parameters decrease from 5.4124? to 5.4034?,d-spacing for(1,1,1)shrinks from 3.1248? to 3.12268?.Charge discharge examination indicated that the OCV of lithium ion cell assembly by using lithium ion doped cerium dioxide as cathode material is 3.26V, discharge capacity at 2.5V plateau is 10.5mAh when 0.2mA constant current discharge. It proved that lithium doped cerium dioxide can be embedded and unimpeded by lithium ion, and it is a potential cathode material for the lithium ion battery.
|
PDF Full Text Request