Fabrication Of Cobalt-based Nanocomposites And Study On The Anode Performance Of Lithium/sodium Ion Batteries

With the deployment of national strategies,the market for electricity used such as new energy cars,large energy storage power plants is continuously expanding.The stable cycling performance and high energy density make lithium-ion batteries（LIBs）to be one of the major energy storage devices.Additionally,sodium ion batteries（SIBs）have also gradually become one of the candidates for future energy storage devices due to the abundant sodium storage resources and low price.At the moment,carbon based materials remain the case for anode materials used in commercial LIBs or SIBs.Although carbon based anode materials have good cycling stability,the carbon based anode cannot provide higher energy density in view of the development of new energy markets that require them.Therefore,the exploration of new anode materials with higher energy density needs to be accelerated.Transition metal compounds（TMCs）,which consist of one metal cation and one non-metal anion,undergo conversion reactions during cycling to endow the material with high capacity for lithium and sodium storage,and gradually become one of the candidates for new high energy density anode materials.Representative among transition metal compounds are cobalt based compounds,whose high theoretical capacity and excellent physicochemical characteristics become one of the research hot spots for anode materials.In this paper,nitrogen doped carbon encapsulated cobalt chloride particles were prepared by nanostructure design and carbon recombination based on Co based compounds（Co Cl2@CHCB）.In situ growth of phosphorus cobalt selenide in carbon nanocages（Co PSe@C nanoboxes）and Co glycerol spheres@Fe-Co Prussian blue yolk shell structured nanospheres（Co-G@Fe-Co PBA）nanocomposites with different structures to improve the performance of lithium/sodium-ion batteries,the main research content is as follows:（1）Preparation of Co-Co Prussian blue analogues（Co-Co PBA）by simple ion exchange reaction and polymerization of dopamine（PDA）layer on the surface of the square（Co-Co PBA@PDA）.It is decomposed into particles of Co Cl2·2H2O and Co Cl2·6H2O encapsulated in a carbon hollow nanoboxes（Co Cl2@CHCB）,by carbonized and chlorinated.Prepared Co Cl2@CHCB small sized particles with freestanding cuboidal morphology,unique multi-core shell structure as well as dispersibility.As lithium-ion battery anode materials,this composite provides an appreciable discharge capacity of 406 m Ah g^-1 after 1500 cycles at 2 A g^-1 current density,exhibiting excellent cycling performance.The average discharge capacities of1282 m Ah g^-1 and 123 m Ah g^-1 can be delivered at 0.2 A g^-1 and 10 A g^-1,demonstrating excellent electrochemical activity and excellent rate capability.The fast and stable lithium-ion diffusion capacity,low reaction impedance,and good structural integrity during cycling benefit from the electrochemical reaction kinetics of the materials.The synergetic effects of the strong coupling effect between the freestanding closed carbon nanocages and Co Cl2 particles,the ultrahigh electronic conductivity of carbon nanocages,the fast lithium-ion diffusion ability,and the wide internal space lead to the superior lithium storage performance.The freestanding hollow carbon nanocages form a multi-core shell structure with the particles of Co Cl2 2H2O and Co Cl2 6H2O,and such a structure provides storage space for the electrolyte and also buffer space for the volume change caused upon lithium-ion intercalation/exfoliation.（2）Co-Co PBA@PDA is synthesized by coating the Co-Co PBA（600-900 nm）with dopamine.The metal organic framework was transformed into Co metal particles and carbon nanoboxes（Co@C nanoboxes）by high-temperature carbonization under argon atmosphere.Finally,a single-phase ternary cobalt phosphorus selenide enclosed inside a carbon hollow box（Co PSe@C nanoboxes）was successfully synthesized by synchronous gaseous phosphorization and selenization treatment.Co PSe@C Carbon hollow cubic nanocages of nanoboxes possess abundant hollow inner cavity space,and their inner in situ grown copse nanoparticles are only 50-120 nm in size.Co PSe@C as a negative electrode material for lithium-ion batteries,nanoboxes can provide discharge capacity of 989 m Ah g^-1 at a current density of 0.2 A g^-1 for 200 cycles,and 885 m Ah g^-1 for 1000 cycles at a current density of 1 A g^-1,even if 200 cycles at a current density of 5 A g^-1 can provide a discharge capacity of 315 m Ah g^-1.As an anode material for sodium-ion batteries,it can provide a discharge capacity of 438 m Ah g^-1（1000 cycles）,309 m Ah g^-1（700 cycles）,and 200 m Ah g^-1（500 cycles）at 0.5 A g^-1,1 A g^-1,and 5 A g^-1 current densities,respectively.The nanoscale size of Co PSe has enhanced reaction kinetics,while the atomic level hybridization of Se and P changes the physical and chemical properties of the material.Hollow carbon nanoboxes improve the electronic conductivity of Co PSe and effectively limit Co PSe to enclosed micro spaces.The rich internal void space in the nanobox is conducive to electrolyte storage,promoting ion diffusion,and well adapting to the volume changes of Co PSe.The nanoscale size of Co PSe has enhanced reaction kinetics,while the atomic level hybridization of Se and P changes the physical and chemical properties of the material.Hollow carbon nanoboxes improve the electronic conductivity of Co PSe and effectively limit Co PSe to enclosed micro spaces.The rich internal void space in the nanobox is conducive to electrolyte storage,promoting ion diffusion,and well adapting to the volume changes of Co PSe.（3）Synthesis of solid Co glycerol sphere（Co-G）by a simple hydrothermal reaction.Then the size of the Co-G sphere is gradually reduced by the etching reaction of water.The ion exchange reaction between the etched Co ion and K3[Fe（CN）6]generates Prussian blue shell（Fe-Co PBA）.A small size Co-G core（300 nm）and a Fe-Co PBA shell（approximately 50 nm）form a typical core-shell structure（Co-G@Fe-Co PBA）,on which 50 nm sized Fe-Co PBA cubes are grown.With such a composite structure,Prussian Blue and Co-G were ingeniously combined to obtain core shell microspheres with uniform size.When Co-G@Fe-Co as a negative electrode material for lithium ion batteries,PBA exhibits high discharge capacity and excellent cycle stability.After 200 cycles at a current density of 0.2 A g^-1,the discharge capacity can be stabilized at 1100 m Ah g^-1.At a current density of 1 A g^-1,the discharge capacity can also be stabilized at 600 m Ah g^-1（300 cycles）.Co-G@Fe-Co PBA has excellent multiplying power,and even if the current density returns from 5 A g^-1 to 0.1 A g^-1,the discharge capacity remains stable at 820 m Ah g^-1.The outer shell of Fe-Co PBA significantly improves the cycle stability of Co-G,while the unique ion channel of PBA is conducive to the diffusion of lithium-ions.The space of 100 nm between the shell and Co-G provides sufficient variation space for the volume deformation of the core,promoting the storage of electrolytes in the material.