Biotemplate Synthesis Of Carbon Coated Hierarchical Structure CO₃O₄ And Co₉S₈ For Their Lithium Storage Performance

As the increasing demand for high power density lithium-ion batteries（LIBs）,the low theoretical capacity(372 m A h g^-1)of commercial graphite anode material has severely limited its application fields.Thus,it is urgent to develop high-efficiency anode materials for LIBs to meet practical applications.Recently,Co₃O₄and Co₉S₈materials have been recognized as one of the hotspots in the research of next-generation LIBs as potential candidates for commercial graphite anode because of their unique mixed valence states and excellent electrochemical properties,as well as high theoretical capacity and reversible conversion reactions.Nevertheless,the Co₃O₄and Co₉S₈materials suffer from large volume changes,exhibiting rapid capacity decay and poor long-cycle performance.Mesoporous carbon-coated Co₃O₄and Co₉S₈heterostructures are an effective strategy to solve the above problems.However,most reports focus on artificial carbon materials（e.g.,graphene,carbon nanotubes,etc.）,and exists drawback of poor reproducibility.Therefore,it is still of practical significance to explore a simple,controllable and green method for preparing carbon-coated Co₃O₄and Co₉S₈anode materials and improve their long-cycle lithium storage performance.Based on the concept of environmental protection and social sustainability,we selected renewable and natural biomass as synthetic template and carbon source,and soaked them in Co（NO₃）₂aqueous solution,followed by carbonization,oxidation or sulfurization steps to controllably prepare Co₃O₄or Co₉S₈tubular structures composite with in-situ biomass-derived graphitized carbon（GC）.Meanwhile,they present good lithium storage performance and long-cycle stability as anode materials for LIBs.The main research contents are described below.（1）Three Co₃O₄-based materials were controllably in situ prepared by cobalt salt immersion,carbonization and oxidation methods using discarded scallion root（SR）as template and carbon source,respectively.The effect of SR-derived carbon content on their microstructures and lithium storage performance are also explored.Among,the Co₃O₄/G_CSR-2 hierarchical tubes obtained by air oxidation at 320°C are cross-linked by39.9 wt%GC and nanoparticles.As an anode material for LIBs,the capacity of Co₃O₄/GC_SR-2 electrode can maintain at 612 m A h g^-1after 1500 long cycles at 1 A g^-1,which indicates that it has good capacity retention and rate performance.（2）Three Co₃O₄-based biomorphic materials were simply and controllably in situ prepared through Co（NO₃）₂solution immersion,calcination,carbonization,as well as low-temperature oxidation method by using tractable waste willow catkins（WC）as template and carbon source,respectively,.The effect of WC-derived carbon content on their microstructures and lithium storage performance are explored.Among them,the Co₃O₄/GC_WC-2 monotube obtained by air oxidation at low 280℃is assembled from the cross-linkage of 15 wt%GC and hollow nanospheres.As an anode material for LIBs,the capacity of Co₃O₄/GC_WC-2 electrode can still stabilize at 647.3 m A h g^-1after 1800long cycles at 1 A g^-1,which is superior to that of Co₃O₄/GC_SR-2 and most reported Co₃O₄-based anode materials.（3）Three Co₉S₈-based biomorphic materials were controllably prepared by immersing t-SR in Co（NO₃）₂solution,followed by in situ calcination and sulfidation reactions under different atmospheres.The effects of SR-derived carbon content on their microstructures and lithium storage performance are investigated in detail.Among them,the Co₉S₈/GC_SR-1 hierarchical tubes are cross-linked by 43 wt%GC and small-size nanoparticles.As an anode material for LIBs,the capacity of Co₉S₈/GC_SR-1 electrode can still be stabilized to 471.3 m A h g^-1after 2000 long cycles at 1 A g^-1.Meanwhile,the capacity of assembled full cell maintains at～198 m A h g^-1after 800 cycles at 1 A g^-1.（4）Two Co₉S₈-based biomorphic materials were controllably prepared by immersing waste WC in Co（NO₃）₂solution,followed by in situ carbonization,oxidation and sulfidation reactions under different atmospheres.Among,the morphology of Co₉S₈/GC_WCis formed by nanoparticles（～30 nm）that are uniformly embedded in 18wt%GC monotubes,which in turn effectively alleviates the volume expansion of Co₉S₈.As an anode material for LIBs,the capacity of Co₉S₈/GC_WCelectrode can be stabilized to 510.3 m A h g^-1after 2000 cycles at room temperature and 1 A g^-1.Even at-20°C and1 A g^-1,its capacity can still maintain at 197.1 m A h g^-1after 150 cycles.In addition,the capacity of assembled full cell retains 289 m A h g^-1after 1800 cycles at 1 A g^-1.Therefore,these performance indexes are superior to currently reported Co₉S₈-based anode materials.