Preparation Of Nano-Structured Copper Particles For Ultra-Stable Silicon Anode In Lithium-Ion Batteries

Lithium-ion batteries（LIBs）are widely used in portable electronic devices as well as electric and hybrid electric vehicles.However,the energy density of LIBs is still not high enough to satisfy the need from supporting further development of those devices and systems,causing problems like the short range,long charging time and safety hazards of electric vehicles.Therefore,replacing the traditional graphite anode with a high-capacity material is considered a promising method to obtain higher energy density lithium-ion batteries.Silicon is believed to be one of the most attractive anode materials for next-generation LIBs due to its natural abundance,environmental friendliness,relatively low lithiation potential（<0.4 V vs Li⁺/Li）,and high theoretical specific capacity of 4200 m Ah·g^-1(more than 10 times that of conventional graphite anodes(372 m Ah·g^-1)).Nonetheless,the huge volume expansion of silicon（up to 300～400%）in the process of charging and discharging will cause expansion and pulverization of the electrode material,thereby detaching from the current collector.The rapid decay of capacity,continuous growth of solid electrolyte interface（SEI）and consumption of a large amount of electrolyte and lithium sources,jointly results in irreversible capacity loss and low coulomb efficiency.In addition,its inherent low electrical conductivity(10^-5～10^-3S·cm^-1)and ion diffusivity(10^-14～10^-13 cm²·S^-1)and other problems also hinder the further development of silicon based anode materials.At present,the solutions adopted by researchers mainly start from nano-silicon,surface engineering strategies,and interface engineering strategies.In view of the above problems,a new three-dimensional current collector was designed and constructed to build high-performance silicon anodes in this thesis.The specific surface area was increased,and a suitable buffer space was provided for the volume expansion of silicon by the three-dimensional frames.Moreover,the metal network skeleton could increase the conductivity and ion transport rate,thereby improving the cycle stability of silicon anode.The main research contents are as follows:（1）The three-dimensional current collector composed of flower-like copper oxide nanoparticles was designed to increase the specific surface area of current collector and electric contact for silicon.The flower-like structure with nano-copper oxide surface was synthesized by simple thermochemical synthesis.The three-dimensional assembly of copper oxide material created lots of pore spaces,which help accommodate more nano-silicon,and leaves sufficient buffer volume for the expansion of silicon material during the cycle process.（2）The preparation of coral-like copper nanoparticels and fabrication of three-dimensional current collector was carried out to further improve the conductivity and specific surface area of silicon anode.The coral-like copper nanoparticles with different content of copper oxide was obtained by reduction reaction at different temperatures in a hydrogen atmosphere.The nanosilicon was confirmed uniformly embedded on the branches of coral-like copper,which guaranteed the constant electric contact with the conductive network of the connected coral-like copper.At present,the solution strategies adopted by researchers mainly start from nano-silicon,surface engineering strategies,and interface engineering strategies.