Preparation And Performance Of Carbon-based Nano Anode Materials For Lithium/Potassium-ion Batteries

Lithium-ion batteries（LIBs）with outstanding energy and power density have been extensively investigated in recent years,rendering them the most suitable energy storage technology for application in emerging markets such as electric vehicles and stationary storage.The ever-increasing demand for large-scale energy storage systems requires novel battery technologies with low-cost and sustainable properties.Due to earth-abundance and cost effectiveness,the development of rechargeable potassium ion batteries（PIBs）has recently attracted much attention.Potassium exhibiting similar physicochemical properties as lithium,has been gaining increasing attention for the development of PIBs in order to address the concern about Li availability and cost.Carbon can be used as elastic buffer carrier to increase the stability of electrode materials during cycling,and its pore structure is rich and the conductivity is high.It has excellent performance as protective material,loading material and electrode material,which are potential anode materials of for LIBs/PIBs.The specific research content and results are as follows:（1）Uniform pomegranate-like nanoclusters（NCs）organized by ultrafine transition metal oxides@nitrogen-doped carbon subunits（diameter ca.4 nm）are prepared for the first time through a facile,novel and one-pot approach.Taking pomegranate-like Fe3O4@N-C NCs as an example,this unique structure provides short Li⁺/electron diffusion pathways for electrochemical reactions,structural stability during cycling and high electrical conductivity,leading to superior electrochemical performance.The resulting pomegranate-like Fe3O4@N-C NCs possess a high specific capacity(1204.3 m A h g^-1 at 0.5 Ag^-1 over 100 cycles),a stable cycle life(1063.0 m A h g^-1 at 1 Ag^-1,98.4%retention after 1000 cycles)and excellent rate capacities(606.0 m A h g^-1 at 10 Ag^-1,92.0%retention;417.1 m A h g^-1 at 20 Ag^-1,91.7%retention after 1000 cycles).（2）Red phosphorus is a promising anode material for LIBs because of its low cost and higher theoretical capacity compared with transition metal oxides.However,tremendous volume variation and low conductivity limit its widespread applications.Hence,we design and synthesize uniformly distributed honeycomb-like hierarchical micro-mesoporous carbon nanospheres（HHPCNSs）with ultralarge pore volume(3.258 cm³ g^-1)through a facile way.The large pore volume provides enough space for loading of P and the expansion of P,and the uniform distribution of the micro-mesopores makes the red P loaded uniformly.The HHPCNSs/P composite exhibits extremely high capacity(2463.8 m A h g^-1 at 0.1 Ag^-1),splendid rate performance(842.2 m A h g^-1 at 10 Ag^-1)and superior cycling stability(1201.6 and938.4 m A h g^-1 at 2 and 5 Ag^-1 after 1000 cycles).More importantly,when coupled with Li Fe PO4 cathode,lithium-ion full batteries display high capacity,superior rate and cycling performances,revealing the practicability of HHPCNSs/P composite.The exceptional electrochemical performance is caused by the honeycomb-like carbon network with ultralarge pore volume,uniformly distributed hierarchical micro-mesoporous nanostructure,outstanding electronic conductivity and excellent nanostructural stability.（3）PIBs are considered as a promising alternative to LIBs for low cost and large-scale application.However,owing to the large size of K ions,traditional carbon materials still undergo poor rate performance,low capacity and unsatisfied cycling life.Herein,we design and synthesize highly ordered microporous carbon nanospheres（OMCNSs）through a simple method.In PIBs,OMCNSs negative electrode deliver an ultrahigh capacity of 256.9 m A h g^-1 at 0.5 Ag^-1 after 500 cycles,outstanding rate performance of 156.6 m A h g^-1 at 5 Ag^-1 after 2000 cycles.Furthermore,when coupled with potassium Prussian blue positive electrode,the potassium-ion full cells also display outstanding electrochemical performance,highlighting the practicability of OMCNSs.The excellent electrochemical performance is ascribed to the highly ordered micropores,which increase the action of physical adsorption and trap K⁺stably.（4）Because the radius of potassium ion is too large,hard carbon materials such as porous carbon have limited potassium storage sites,and can not obtain satisfactory electrochemical performance of PIBs.Ultrafine hollow nanoparticles-based（7 nm）carbon nanoclusters（HNPCNCs）are developed by a facile and novel method.Benefiting from the ultrafine nanostructure,we have achieved close-packed storage of K metallic clusters and a close-packed K metallic clusters with a diameter of 7 nm has been observed for the first time through ex TEM.In K-ion batteries,HNPCNCs anodes deliver an ultrahigh reversible capacity of 269.8 m A h g^-1 after 200 cycles at0.5 Ag^-1,excellent rate performance of 150.5 m A h g^-1 at 5 Ag^-1 after 5000 cycles.Moreover,when coupled with potassium Prussian blue cathode,the potassium-ion full cells also display outstanding electrochemical performance,highlighting the practicability of HNPCNCs.