Single-Ion Polymer Electrolytes For High-Performance Lithium Metal Batteries Research

The renewable clean energy requires efficient energy storage systems because of its intermittent nature,and demand for portable electronics and electric cars has grown in recent years.traditional lithium-ion batteries can no longer meet people's demand for high energy and large capacity batteries due to its limited theoretical energy density.Lithium metal has been regarded as the most promising electrode material and received extensive research attention because of their extremely high capacity(3860 m Ah g^-1,almost 10 times of graphite electrode),lowest electrochemical potential?-3.04 V?and extremely low density(0.59 g cm^-3).However,a series of problems caused by lithium dendrite growth,such as poor cycle performance,overheat or even explosion,have prevented the development of lithium metal batteries.Thus,in this paper,according to the Space-Charge theory proposed by Chazalviel and the Sand's time model,we designed poly?lithium 4-styrenesulfonate?single-ion polymer electrolyte?SIPE?and another single-ion polymer electrolyte containing boron group capable of trapping anion to increase the lithium-ion transference number and suppress the growth of lithium dendrites.The physical and chemical properties were characterized by thermogravimetric analysis,FIIR and scanning electron microscopy?SEM?.By the way,the cycling performance and electrochemical properties such as ionic conductivity,lithium-ion transference number,along with electrochemical stability window were also measured.Firstly,poly?lithium 4-styrenesulfonate??Li PSS?was synthesized via a simple acid–base neutralization reaction,and the SIPEs with semi-interpenetrating polymer network?semi-IPN?structure were synthesized by compounding Li PSS and polymethylmethacrylate?PMMA?.The Li PSS@PMMA SIPE which the mass fraction of crosslinking agent is 2%exhibits an outstanding liquid-absorption capacity of 494%,excellent ionic conductivity of 0.94?10^-3 S cm^-1 at room temperature,and wide electrochemical window of 4.7 V.Thus,the SIPEs meet the basic electrochemical performance requirements for lithium batteries.Moreover,lithium-ion transference number of the SIPEs is extremely high?0.91?.The voltage of Li/Li PSS@PMMA SIPE/Li cell remains stable throughout the entire 550 h charge and discharge cycles.And the smooth surface morphology of lithium anode after cycles shows the uniform deposition of lithium.Then,in order to get a SIPE with higher ionic conductivity,a boron-containing group capable of trapping anion was introduced into polymer backbone containing ethylene oxide chain segmer.When the mass ratio of poly?ethylene glycol?methacrylate?PEGMA?to allylboronic acid pinacol ester?ABAPE?is 3:7,the boron-containing SIPE?BC-SIPE?has the optimal ionic conductivity of 2.4×10^-3 S cm^-1,close to that of commercial liquid electrolyte.Meanwhile,the BC-SIPE shows wide electrochemical window?4.7V?,high lithium-ion transference number?0.71?,and excellent interface stability with lithium metal.Furthermore,the SEM photographs of lithium anode after cycles show that the growth of lithium dendrites was well inhibited.In addition,cells assembled with Li Fe PO₄ show excellent cycling performance,with a capacity retention rate of 90%after 100 cycles.In conclusion,by designing SIPEs,we can improve the lithium-ion transference number and get the dendrite-free lithium anode,which provides a new approach for the research of lithium metal battery.