Coordination Complex Pyrolyzation To Synthesize Nanostructured Electrodes For Lithium Ion Batteries

This paper has developed a new economic, effective and facile way to prepare eletrode materials with high specific capacity, by the selection of proper coordination compound precursor, and the pyrolysis of those coordination compounds under different atmosphere. Due to the escape of small-molecule gases, such as H2O, COx, the obtained electrode materials are usually nano-sized with homogeneous disctribution of pores. Furthermore, the synthetic route is friendly, low cost and so on. On the other hand, through the pyrolysis of coordination compounds containing carbon under inert gases, materials with uniform carbon coating will be obtained. At the same time, the synthetic route based on the pyrolysis of coordination compounds was extended to the preparation of other compounds successfully.The main research content of this paper includes the following several aspects:1. We present a new environmental benign and cost-effective approach for synthesis of nanostructured GeO2via (NH4)3H(Ge7O16)(H2O)2.72precursor-pyrolyzation. And the (NH4)3H(Ge7O16)(H2O)2.72precursor was obtained by the reaction between commercial bulk GeO2and NH4OH at150℃for6h. The designed synthetic route has been successful in avoiding the use of any toxic, expensive germanium compound or hazardous solvent (benzene, tetrahydrofuran, etc.). Furthermore, by changing the amount of tartaric acid and concentrations of reactants in the system, different shapes of GeO2nanostructures such as nanoparticles, nanocubes, and nanospindles can be obtained. The cycling performance and rate capability of the as-prepared different GeO2nanomaterials were investigated, and it was found that the electrochemical performance of GeO2nanoparticles was better than that of GeO2nanocubes and GeOa nanospindles. Significantly, the as-prepared GeO2nanoparticles exhibited excellent electrochemical storage properties with high specific reversible capacity of1340mA h g-1at0.1A g-1, with excellent rate performance (750mA h g-1at2A g-1).2. Benzfluorenone, one of commonly used chelating agent in the detection and enrichment of trace germanium, once coordinated with Ge(Ⅳ), a bright orange-red germanium chelate complex is formed (GeC38H20O10or GeC38H24O14). Through pyrolysis of such a chelate complex, germanium nanoparticles about30nm and uniform buffering carbon layers can be formed simultaneously. Homogenous mesoporous and carbon matrix are effectively formed after pyrolysis, due to the releasing of gas (H2O, COx) and the uniform dispersion of those elements (H, C, O, Ge) within the chelate complex matrix at molecular level. Furthermore, we used tannin, which can be solved both in water and ethanol, as chelating agent to reveal the liquid-liquid interface chelating reaction. The as-synthesized Ge/carbon hybrid nanoparticles exhibit outstanding electrochemical lithium-storage performance (high reversible capacity, excellent rate capability over64A g-1, and ultra long cycle life over2000cycles). Finally, the lithium ion battery system based on the prelithiated Ge/CHNs anode and LiCoO2cathode demonstrates a high energy density of370Wh kg-1after300cycles between2.7and4.4V at1C, with average capacity fading about0.018%per cycle.3. By the feature of C4H4MnO6precursor, such as appropriate proportion of elements, the different reducibility between carbon and metal, MnO@1-D carbon composites with MnO nanoparticles encapsulated or adhered to the surface of1-D carbon scaffold are obtained by annealing of the1-D C4H4MnO6precursor nanocomposites in argon atmosphere. In such synthetic route, due to the appropriate proportion of C, H, O, Mn, carbon coating can be finished during the MnO preparation, and Mn can not formed due to the weak reduction ability of carbon compared with MnO. MnO nanoparticles are encapsulated inside or adhered to the surface of1-D carbon scaffolds. With the presence of such1-D carbon scaffolds, the electrochemical properties of the MnO@1-D carbon composites are enhanced. The1-D carbon structure could ensure efficient electron transport along the longitude direction, and this is crucial to the rate performance of the electrode material. Second, though the collapse and reconstruction of the active MnO particles are inevitable during the cycling process, the reconstructed MnO particles can still loaded in the whole carbon network, which accommodate volume expansion/contraction during the Li+insertion/extraction processes because of its good mechanical stability. As an anode for lithium-ion batteries, MnO@1-D carbon composites exhibited a higher lithium storage capacity of1482mA h g-1at a current density of200mA g-1and when the current density rises to1460mA g-1, it still remains810mA h g-1even after1000cycles.4. Based on the MnO@1-D carbon composites obtained by annealing of the1-D precursor nanocomposites in argon atmosphere, we further expand such kind of coordination compounds in the preparation of lithium ion battery electrode materials. Here, we choose C4H4CuO6as precursor to prepare porous carbon materials, due to carbon can reduce the Cu2+in the precursor to Cu0. Porous nitrogen-doped carbon vegetable-sponges (N-DCSs) have been fabricated by chemical treatment of the Cu@C precursors using HNO3. The N doping in N-DCSs can enhance the electrochemical reactivity and electronic conductivity. The as-prepraed N-DCSs present significantly high capacity as the anode material for lithium ion batteries, delivering a reversible capacity of as high as870mA h g-1at a current density of0.5A g-1after300cycles. Furthermore, based on the carbonization of transition metal-tartaric acid complexes,3D porous carbon materials with different porous structure can be obtained. As supercapacitor electrodes, the prepared porous carbon materials exhibit good performance, with a distinguished specific capacitance (248F g-1) at current density of2A g-1.