Study On Stabilization Strategies For Alkali Metal Anodes Of Secondary Batteries

The new energy industry is currently in a state of rapid development and lithium-ion batteries are widely used in many industries,especially in the electric vehicles.However,the graphite-based lithium-ion batteries have reached a bottleneck in energy density.It is difficult to fully meet the increasing demand from the higher energy densities.Therefore,there is an urgent need to develop higher capacity electrode materials which is used to construct higher energy density battery systems.Among the various anodes,lithium metal is considered the"holy grail"of anode materials,owing to the highest specific capacity and the lowest redox potential.That makes lithium metal anode a good alternative product to the conventional one.However,the use of lithium metal as anode material faces the lithium dendrite growth problems.The formed dendrite will puncture the separator which leads to a battery short circuit and other safety hazards.To address these issues,the research contents in this paper focus on the following two aspects.1.A carbon nanotubes（CNTs）-doped porous polypyrrole（PPy）material was prepared by using calcium carbonate as a hole template.A lithophilic PPy was distributed on the outside of the material structure.Another lithophilic CNTs on the inside of the structure were exposed by etching the hole template.Here the CNTs at the holes severe as a lithophilic site to guide the uniform lithium nucleation and deposition which can retard the formation of the lithium dendrite.The electrochemical measurements showed that the lithium nucleation overpotential of porous CNTs@PPy material was reduced from 57.59 m V to 26 m V in compared with the non-porous one.In addition,the porous CNTs@PPy material has lower charge transfer resistance and higher lithium ion diffusion coefficient.In the half-cell test,more than 420 cycles（1700 h）can be stably cycled at 0.5 m A cm^-2 current density and 1 m Ah cm^-2 capacity,and the porous CNTs@PPy material has good lithium metal deposition and stripping ability.The mechanism of inhibition of lithium dendrite by porous CNTs@PPy material was supplemented by DFT simulation,and it was inferred that porous CNTs@PPy material could be applied to sodium and potassium metal anode by calculating the binding energy of porous CNTs@PPy material with sodium and potassium.2.The CoO/PPy tube composites were prepared by hydrothermal method.The hollow PPy tube substrate can accommodate more lithium metal than the dense one.The PPy tube surface is loaded with good lithophilic CoO particles as the lithophilic sites,which can guide the homogeneous nucleation and deposition of lithium,and then delay the formation of lithium dendrites.The CoO/PPy tube material has a low lithium nucleation overpotential（14.06 m V）.In the half-cell test,more than 550 cycles（2200 h）with stable Coulombic efficiency above 98%were achieved at a current density of 0.5 m A cm^-2 and a capacity of 1 m Ah cm^-2.The symmetric cell assembled with Li@CoO/PPy tube was cycled stably for more than 1000 h at 0.5 m A cm^-2and 0.5 m Ah cm^-2.Li@CoO/PPy tube-LFP full cell exhibits superior long cycle stability and multiplicity performance.The mechanism of lithium dendrite inhibition by CoO/PPy tube material was supplemented by DFT theoretical calculations,and it was inferred that CoO/PPy tube material could be applied in sodium metal anode by calculating the adsorption energy of sodium atoms with PPy tube and CoO.