The Application Of Mg₃N₂ And Quaternary Ammonium In-Situ Polymer In Lithium Anode Protection

Due to the limitation of fossil resources,the utilization of renewable energy has become a hotspot in the scientific community.In order to improve the utilization efficiency,energy storage and conversion devices should be used during the energy conversion process of renewable energy.As a "transfer station" of electric energy,battery has been widely concerned and studied.Since the successful commercialization of lithium ion batteries,the scientific community has set off a research upsurge of lithium ion batteries.People are urgently looking for next generation batteries with higher efficiency and energy density.Ascribed to the high theoretical energy density(3860 mAh/g)and low reduction potential(-3.040 V VS SHE),lithium metal serves as one of the future anode materials.However,in the practical process of lithium anode,there are a series of urgent problems to be solved.Among those issues,the problem of dendrite growth is particularly serious.The penetration of lithium dendrite even causes the separator punctured and batteries’ short circuit,which leads to serious safety problems.Therefore,the current research on lithium anode is mainly focused on modifying lithium anode structure,optimizing lithium ion deposition,reducing the generation of dendrites,enhancing the cyclic stability of lithium anode and so on.Among those modification methods,coating protection has been widely utilized due to ease of operation.In this thesis,we come up with two kinds of coating protection methods and conduct a preliminary study on these two lithium protection strategies.In the first work,we use Mg3N2-PVDF coating for the assistance of lithium metal deposition.With strong polarity surface on Mg3N2 coating layer,we can realize uniform lithium ions flux distribution and homogenously lithium deposition.This method can protect lithium metal from side reactions between electrolyte and lithium during long time repeated deposition and stripping.At the same time,the overpotential of symmetric batteries kept at a relatively low level.In addition,the capacity retention rate of batteries using LiFePO4 or NCM81 1 as cathode have been obviously improved.In second work,we use Ethylbutyl-hexafluorophosphate to achieve in-situ polymerization on the surface of lithium metal.This protective film can reduce the overpotential and prolong the cycle life of lithium anode in carbonate-based electrolyte.The performance of symmetric batteries and high mass loading LiFePO4 and NCM811 batteries are significantly improved after protection.At the same time,the mechanism on film formation and electrochemical performance of protected lithium anode were investigated.These two methods have realized long-term protection of lithium anode at the same time.By means of constructing protective film and exploring electrochemical protection mechanism,we have further in-depth understanding of this method.Therefore,we have developed new methods for long-term and durable protection of lithium anode.Both of the strategies have high scientific meaning and great practical application prospect.