Structural Design And Surface Chemical Regulation Of Metal Anode

With the gradually scarce of traditional energy sources and the deteriorating of earth environment,an efficient,green and environmentally friendly energy storage device was urgently needed.At present,the mainstream lithium-ion secondary batteries on the market gradually tend to their theoretical capacity,which has been unable to meet people’s increasing energy density requirements.Some metals such as lithium and zinc have excellent theoretical specific capacities and extremely low redox potentials,making them ideal anode materials for next-generation energy storage batteries.However,like most metal anodes,they are inevitably plagued by dendrite growth and side reactions.In this article,two different protection strategies are designed according to the characteristics of lithium anode and zinc anode,and the following two experiments are carried out:1.Research on 3D structure design and super-filling mechanism of lithium metal anode.Through a simple multi-step process,a large number of nano-sized pores are modified on the surface of commercial foamed copper,and this porous foamed copper is used as the skeleton of the lithium anode.Its porous framework helps reduce current density.And its stable porous structure can also reduce the volume expansion of the anode.More importantly,after adding thiourea to the electrolyte,the "super-filling" effect of thiourea can guide the preferential deposition of lithium in the small pores on the surface of the framework to achieve initial uniform nucleation,thereby inhibiting the growth of lithium dendrites.The symmetrical battery using this collaborative strategy can cycle stably for 500 hours under the conditions of 1 mA cm^-2 and 1 mAh cm^-2;at the same time,a full battery was assembled by this anode and the lithium iron phosphate cathode and it behaved a capacity retention rate of 94%,which exhibits excellent cycle stability.2.Study on the surface protection of zinc metal anode and the performance of zinc ion secondary battery.According to the diffusion barrier theory and the problems of water-based batteries,an artificial protective layer composed of polyvinyl butyral ester（PVB）and nano-copper-zinc alloy is designed on the surface of the zinc anode.The protective layer is very dense,has good adhesion and mechanical strength,can effectively block the contact between the zinc anode and the electrolyte,thereby inhibiting the occurrence of side reactions;at the same time,due to the presence of copper-zinc alloy particles,the zinc diffusion barrier at the interface is greatly reduced and the diffusion rate of adsorbed atoms on the surface is increased so the tendency to form dendrites is reduced.The symmetric battery coated with this protective layer can cycle stably for more than 1000 h under the conditions of 0.5 mA cm^-2 and 0.5 mAh cm^-2,which exhibits excellent negative electrode protection capabilities.In a word,aiming at the problems of dendrite growth and surface side reactions existing in metal anode and starting from the electrode structure design and surface chemistry,the preparation and electrochemical performance of lithium metal anode and zinc metal anode are carried out respectively.Porous foamed copper is prepared as the anode framework,and thiourea is used as the electrolyte additive to realize the non-dendritic cycle of the lithium anode through the synergistic effect of the two;the surface of the zinc anode is coated with an artificial protective layer of PVB and copper-zinc alloy which inhibited the occurrence of side reactions and achieved uniform deposition of zinc anode.This work provides new ideas and new strategies for the protection of metal anode,which is conducive to promoting the practical application of secondary metal batteries.