| At present,lithium ion battery and electrochemical capacitor are two kinds of important energy storage equipments.On account of high working voltage,large energy density,long cycle life,low self discharge rate and green environmental conservation,lithium ion battery has attracted much attention and has been widely applied in mini-type electric instruments presently.Meanwhile,the lithium ion batteries are developing toward the fields of space technology,national defense industry,electromotive vehicle and UPS actively.Electrochemical capacitor is a new type of energy storage equipment,which combines the advantages of both dielectric capacitors that can deliver high power within a very small period and conventional rechargeable batteries that have high energy densities.Therefore,electrochemical capacitors also have a wide range of applications and have already become one of the research interests related to new chemical energy sources studies.In this thesis,we have reviewed the newest development in the research of electrode materials of both lithium ion battery and electrochemical capacitor devices, prepared relevant electrode materials and explored their applications in these two kinds of devices in detail.The main content is as follows:1.The improvement of the performance of LiMn2O4 cathode materials by doping the spinel with different cations have been studied in detail.A series of LiM0.05Mn1.95O4(M=Al,Cr,Fe) materials are prepared by the sol-gel method.The experimental results indicated that metal-doping could improve the cycle performance of LiMn2O4 due to the inhibition of Jahn-Teller distortion and could enhance the atomic cohesive force in the cathode hosts to strengthen their stability.Compare these doped LiMn2O4,it is clear to see that different metal ions have different improving effect to the LiMn2O4.Among these Al,Cr and Fe doped materials,the substituted chromium manganese oxide spinel(LiCr0.05Mn1.95O4) had the best cycle performance, and the capacity loss was only 5%of its initial capacity after 30 cycles.Besides,we have also investigated the influence of Cr doping content on the structure and electrochemical properties of the LiCrxMn2-xO4 cathode materials.It is evident that, the lattice parameter and crystal volume decrease with increasing the Cr content, which is beneficial to the stability of the spinel structure and could improve the cyclability of the material.However,the initial capacitance decreases to some extent with increasing the Cr doping content due to the loss of Mn3+.According to the results, it is found that when X(Cr doping content)=0.05,the doping material has the best battery performance.2.A series of Ag/LiMn2O4 composites with different Ag additive contents were prepared by thermal decomposition of AgNO3 added to the pure LiMn2O4 powders. Because of the high electronic conductivity of metal Ag,Ag additive could significantly increase the electronic conductivity of Ag/LiMn2O4 composites,make the transfer rate of Li-ion in Ag/LiMn2O4 composites higher,lower the resistance of the cell,reduce the irreversible capacity loss and f'mally improve the cycling stability and rate capability.The electrochemical tests results indicate that Ag/LiMn2O4 composites have very good battery properties and capacity retention rate.At the discharge rate of C/3,the initial discharge capacitance of Ag(0.1)/LMO composite is 114.6 mAh/g,after 30 cycles,its capacitance retention rate is still as high as 97.6%. The initial discharge capacity ratio of(1C)/(C/3) is 92%.Besides,the influence of the Ag additive contents on the electrochemical properties of the Ag/LiMn2O4 composites is also investigated in detail.3.Spinel-type LiAl0.05Mn1.95O4 cathode materials have been firstly synthesized by a simple ultrasonic assisted rheological phase(UARP) method.The experiments results reveal that using this novel method to deal with the precursor is beneficial to the complete dispersion of the reactant.Compared with the solid-state reaction(SSR) method,the UARP method could shorten the calcination time to some extent.The LiAl0.05Mn1.95O4 product prepared via this new method has a good crystallinity with fine cubic spinel structure and exhibits a regular morphology with homogeneous particle size distribution.The electrochemical properties focused on the LiAl0.05Mn1.95O4 by this new method have also been investigated in detail.According to these tests results,it is obviously to see that the newly prepared sample delivers a relatively high initial discharge capacity of 111.6 mAh/g,presents excellent rate capability and reversibility,and shows good cycling stability with capacity retention of 90.6%after 70 cycles.Meanwhile,the electrochemical impedance spectroscopy (EIS) investigations were employed to study the electrochemical process of Li+ ions with the synthesized LiAl0.05Mn1.95O4 electrode detailedly.4.A novel ordered mesoporous cobalt hydroxide film(designated HI-e Co(OH)2) has been successfully electrodeposited on titanium substrate from the hexagonal lyotropic liquid crystalline phase using surfactant Brij 56 as the structure-directing agent.Low-angle X-ray diffraction(XRD) and transmission electron microscopy (TEM) studies indicate that the film electrodeposited from liquid crystal template has a regular nanostructure consisting of a hexagonal array of cylindrical pores with a repeat center-to-center spacing of about 7 nm.This special ordered nanoporous structure creates the fast electrochemical accessibility of the electrolyte and OH- ions not only to the surface of the electrode materials but also to the bulk of the Co(OH)2 phase,which is very helpful for making full use of the electroactive sites to take place the faradic reaction,providing an important morphological foundation for a high specific capacitance.Cyclic voltammeter(CV) and galvanostatic charge/discharge measurements show that the ordered mesoporous HI-e Co(OH)2 film electrode has excellent electrochemical capacitance between potential range of -0.1-0.45 V,and a maximum specific capacitance as high as 1084 F/g could be achieved in 2 M KOH solution at a charge-discharge current density of 4 A/g.Meanwhile,the properties of Co(OH)2 film electrodeposited from aqueous solution without templates(designated Aq-e Co(OH)2) are also discussed for comparison.Preliminary studies show that the film has many merits such as low-cost,high special capacitance and good cycle properties,suggesting its potential application in electrochemical capacitors.5.Experimental electrodeposition parameters such as deposition potentials, deposition temperatures and deposition substrates are varied to analyze their influences on the electrochemical capacitor behavior systematically.The films are physically characterized by X-ray diffraction(XRD),scanning electron microscopy (SEM) and transmission electron microscopy(TEM) to determine the effects of deposition potentials,temperatures and substrates on the surface morphology. Electrochemical techniques such as cyclic voltammetry(CV) and chronopotentiometry are used to systematically study the effects of deposition potentials,temperatures and substrates on the capacitance of the films.The investigation show that the deposition potentials and temperatures have obvious influence on the HI-e Co(OH)2 film.The capacitive performance of the HI-e Co(OH)2 film achieved the highest value of 1084 F/g at a discharge current density of 4 A/g when it is electrodeposited at -0.75 V under the deposition temperature of 50℃. Meanwhile,different deposition substrates also have great influence on the films,the ordered mesoporous Co(OH)2 film on foamed Ni mesh has much higher specific capacitance(maximum:2646 F/g) than that of the film on Ti plate(maximum:1018 F/g) at the same discharge current density of 8 A/g.,which is mainly because that the foamed Ni mesh substrate with much larger surface area than Ti plate could enhance the utilization and the capacitance of Co(OH)2 film greatly.
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