Construction Of Quinone Polymer Interfacial Membrane With High Ion Conductivity For Alkali Metal Anode Protection

Alkali metals are promising anode materials due to their superior theoretical specific capacities and low electrochemical potentials.However,the high reducing activity of the alkali metal anodes leads to a series of side reactions with the electrolyte,then a layer of solid electrolyte interface film（SEI）with slow ion transport and unstable structure is generated,resulting in the growth of metal dendrites,which eventually leads to short circuits inside the battery and even leads to safety problems such as fire and explosion.Therefore,SEI,which has a uniform and stable structure with high ionic conductivity is conducive to maintaining the interfacial stability of the alkali metal anode.It is essential to improve the cycling performance of alkali metal batteries.Based on the research background,we propose to construct a polymer-based SEI film rich in lithiophilic/natrilophilic functional groups on the surface of lithium/sodium metal.The functional groups guide the rapid conduction of ions along the polymer and improve the conductivity of SEI membrane ions while realizing the uniform distribution of its surface ions,finally realizes the uniform deposition of metal anode and its cycling performance.The specific research content and research results are as follows:（1）In view of the problems of uncontrollable dendrite growth and serious side reactions faced by the anode of lithium metal battery during the cycling process,we developed a method for constructing SEI membrane by in-situ reaction and construct a polymer SEI film with high ion transport rate,then improved the cycle stability of lithium metal battery.By exploring the effects of the addition of poly（2,5-dihydroxy-1,4-benzoquinone-3,6-methylene）（PDBM）quinone polymer on the cycle stability of the battery in SEI,we realize that compared with traditional SEI,the addition of polymer interface films rich in-OLigroups promotes the rapid conduction of Li⁺and uniform deposition of lithium metal.This operation realizes the homogenization of Li⁺flux on the surface of lithium metal,which also avoids the problems of dendrite growth and side reactions caused by uneven ion deposition.In addition,the organic salts of PDBM are insoluble in LiTFSI/DME electrolyte,which proves that the polymer interface film can effectively isolate the direct contact between lithium metal and electrolyte,so as to avoid increasing the interface impedance of lithium metal battery due to the side reaction between highly reactive lithium metal and electrolyte.The electrochemical test data show that under the test conditions of 1 mA cm^-2-1 mAh cm^-2,the lithium-metal symmetrical battery under the modification of PDBM can be stably cycled for more than 1500 h at an ultra-low polarization voltage（9 mV）.In contrast,the blank lithium-metal symmetrical cells have an increase in polarization voltage（25 mV）under the same conditions after 200 h of cycling.Even in the absence of LiNO₃,the PDBM-modified lithium-metal symmetrical batteries stably cycle for more than 1100 h under the test conditions of 0.5 mA cm^-2-0.5 mAh cm^-2,and the voltage polarization is 11 mV.The life of battery is extended by 10 times.In the system of Li|S battery,PDBM-modified lithium metal that is after 260 battery cycles promotes the capacity retention rate up to 96.8%.These results show that the construction of PDBM-based SEI film effectively improves the cycle stability of lithium metal batteries,indicating that polyliphilic group polymer materials have great application potential in lithium metal anode protection.（2）In the work introduced earlier,the construction of PDBM polymer film effectively improves the SEI interface stability of lithium metal anode,while the long cycle performance of the lithium metal battery system at high current density was not good,this limites the commercial application of alkali metal batteries.Considering that the highly reactive sodium metal anode faces more serious problems of side reactions and dendrite growth,we further introduce PDBM polymer membranes to the surface of sodium metal anodes,we also explore the influence of PDBM and interionic dipole interactions between different alkali metal ions on the interface stability and uniformity of metal deposition of SEI membranes.In order to solve the problem of poor cycle stability of sodium anode,an quinone polymer SEI membrane with high ion transport rate was also constructed on the surface of sodium metal by in-situ reaction.Under the modification of PDBM,PDBM@Na|PDBM@Na symmetrical cells exhibit excellent long-term cycle stability（4000 h）and very low polarization voltage（8 mV）.Even in the test conditions of high current density of 5 mA cm^-2 and high area capacity of 5 mA h cm^-2,PDBM@Na|PDBM@Na symmetrical cells can still be stable for 1000 h.Combined with density functional theory calculation,COMSOL simulation and ex situ XPS spectroscopic characterization,the natrisophilic groups in the SEI membrane effectively improved the binding energy of Na⁺and ion flow distribution uniformity on the surface of the PDBM@Na electrode.The dissociation energy of Na⁺is lower than PDBM@Li,which shows that the addition of PDBM envoies sodium metal possess a more uniform Na⁺flux and faster Na⁺conduction,which effectively improves the cycle stability of sodium anode under high current density conditions.Also,PDBM@Na|Na₃V₂（PO₄）₃ full cells can cycle stably for2400 cycles at a current density of 5 C,showing a capacity retention rate of 92.97%.At a current density of20 C,the battery can achieve a specific capacity of 83 mAh g^-1,when the current density is reduced to 0.1C,it can still exhibit a capacity retention rate of 98.4%,all of these show the excellent cycle stability and excellent rate performance.In summary,by constructing a layer of quinone-type polymer interface film rich in-OLiand-ONa groups on the surface of the alkali metal anode,this thesis realizes the rapid conduction of Li⁺and Na⁺and the homogenization of Li⁺and Na⁺fluxes,effectively inhibits the problems of dendrite growth and frequent side reactions faced by alkali metals.It also significantly improves the cycle performance of lithium metal batteries and sodium metal batteries,which provides new ideas for the research of alkali metal anode protection.