Solution Combustion Preparation And Electrochemical Performance Of Metal Oxides-carbon Composite Materials

Lithium-ion batteries show advantages such as high energy density, highworking voltage, environment-friendliness, but its energy density and powerdensity still cannot meet the performance requirements for the field of greentransportation. Supercapacitors with features of high power density and long lifeare commonly used as energy storage devices with high power density butshort-time charge and discharge ability, which render excellent complement forlithium ion-batteries. Therefore, rational microstructure design and achievementof high-performance electrode materials, which can effectively combine theadvantages of both lithium-ion batteries and supercapacitors, is one of the hottopic for the electrochemical energy storage devices.Transition metal oxides show simultaneously high lithium-ion storagecapacity and pseudo-capacitance characteristics, endowing important candidatesfor lithium-ion and supercapacitors electrode systems. For transition metaloxide, low electrical conductivity and weak mechanical strength result in thelow usage affectivity of the active material, along with poor cycle stability. Construction of metal-oxide/carbon nano-composite has been identified as auniversal and effective strategy for the enhancement of the electrochemicalperformance, which not only shorten the ion migration distance down tonanoscale, reduce the absolute expansion of electrode materials duringcharge-discharge cyclings, but also improve the conductivity of the compositesystem. Although traditional nanotechnology (such as electrospinning,hydrothermal, chemical bath deposition methods) could effectively regulate themicrostructure features of oxides (for example, their phase, particle shape, size,morphology of aggregates), the synthesis approaches are alwaystime-consuming and the required equipment is complex and highly-costed. Withthe assistance of rapid redox reactions between oxidants and reductants, a facileand cheap method is developed for the preparation of transition metaloxide/carbon composites.The resulting products exhibit good electrochemicalproperties, showing promise for the potential practical application. The maincontents and conclusions are as follows:1. Fe2O3/C nano-composite was prepared by a one-step route from aFe(NO3)39H2O solution containing citric acid at only350°C in air, in which thecarbon content could be regulated by the used dosage of citric acid.Electrochemical tests showed that the optimized Fe2O3/C nano-compositeexhibited a high reversible capacity of419mAh g1after200thcycles with acurrent density of125mA g1, which are12%higher than the theoreticalcapacity of graphite (372mAh g1). 2. Carbon nanotubes/Fe2O3/C (CNTs/Fe2O3/C) ternary nano-compositeshave been fabricated by simply adding certain amount of acid-treated carbonnanotubes (CNTs) into the precursor solution, while keeping other experimentalconditions the same with those of for Fe2O3/C. The ternary compositespossessed192.6F·g1specific capacitance at1A·g1much, obviously higherthan that of Fe2O3/C (139.7F·g1at1A·g1). When the current density increasesto3.5A·g1, its capacitance remains still116.6F·g1.3. To void the potential nitrogen oxide pollution caused by nitrates rawmaterials, low-cost, non-toxic and high performance K2Mn4O9andK2Mn4O9/CNTs composites were synthesized with a clean oxidant, KMnO4. In1M KOH electrolyte, the K2Mn4O9electrode shows a high specific capacitanceof603F·g-1at1A·g-1. Meanwhile, the electrode retains90.1%of its initialcapacitance after5000cycles. With the addition of high conductive CNTs, thecapacitance of K2Mn4O9/CNTs electrode was further increased by23%(corresponding a capacity of743F·g-1)4. To show its potential application, a K2Mn4O9/CNTs//activated carbonasymmetric supercapacitor (ASC) was prepared with K2Mn4O9/CNTs andactivated carbon working as the positive and negative electrodes, respectively.The electrochemical results showed the the prepared ASC device possessed aspecific capacitance of153F·g1at1A·g1, corresponding to a high energydensity of62Wh·kg1at a power density of852W·kg-1, along with a decentcycling stability (capacitance retention of～85%after1000cycles), suggesting its promise application potential in low-cost high energy density storagesystems.