| The theoretical energy density(200?300 Wh kg-1)of existing commercial lithium-ion batteries is low,and it is difficult to meet the future demand for long battery life of mobile devices.In recent years,lithiumoxygen batteries(?3500 Wh kg-1)with higher theoretical energy density have attracted much attention from researchers and are considered to be a new type of battery that is expected to replace lithium-ion batteries.However,lithium-oxygen batteries still face many problems in the development process,such as poor battery rate performance,high charge overpotential,decomposition of electrolyte and carbon positive electrode,lithium anode dendrite and lithium anode corrosion,etc.Among them,the corrosion and poor stability of lithium anodes are included in lithium-oxygen batteries,and one of the main problems faced in the development of lithium metal-based batteries.During the cycle of the lithium-oxygen battery,redox molecules or side reaction factors such as oxygen,water,carbon dioxide,etc.continue to shuttle and come into contact with the lithium anode,causing it to undergo a side reaction with the strongly reducing lithium metal,which in turn causes the lithium anode to corrode and generates by-product.The poor ionic conductivity of the by-products will cause the battery charge-discharge potential difference to increase continuously,which will lead to the decomposition of the electrolyte and the carbon cathode,which will eventually cause the battery to stop prematurely and the battery cycle stability is poor.The existing main way to solve the problem of corrosion of lithium anodes in lithium-oxygen batteries is to protect the lithium anodes by blocking the side reaction factors,so as to improve the cycle stability of lithium-oxygen batteries.In current research,in situ SEI membrane and artificial SEI membrane are mainly used to isolate side reaction factors.Among them,the inorganic artificial SEI film is mainly prepared by physical pressing or bonding.Although this type of protective film has a certain barrier effect,the inorganic substances in the SEI film are changing in potential during the charge and discharge cycle of the lithium-oxygen battery.It gradually reacts with the lithium anode,causing contact consumption.Another method is to use artificial polymer SEI membranes to suppress the shuttle of side reaction factors.Although this type of SEI membrane has a good barrier effect,the polymer often has insufficient ion conduction and a large internal impedance,which is easy to cause internal loss during the battery cycle.In view of the shortcomings of the existing methods,inspired by the "salt effect" and electrostatic effects,we propose a strategy to construct a high-ion lithium ion membrane through a lithiated polymer.On the one hand,by increasing the amount of lithium ion in the membrane to ensure the rapid conduction of lithium ions.On the other hand,by the electrostatic effect of the charged functional groups of the polymer,the shuttle of side reaction factors is inhibited.The lithiated graphene oxide and lithium polystyrene sulfonate contained in the membrane component provide a high concentration of lithium ions,which reduces the dissolution of side reaction factors in the membrane,and at the same time improves the lithium ion conductivity and overcomes the problem of insufficient lithium ion conductivity of the traditional protective film;in addition,the lithium polystyrene sulfonate in the membrane component contains a large number of negatively charged sulfonate groups,and the electrostatic effect further inhibits the shuttle of the side reaction factor,thereby better protecting the lithium anode,which improves the cycle stability of lithium oxygen battery.The details are as follows:1.By synthesizing a lithiated polymer,the concentration of lithium ions in the membrane is increased,the conduction of lithium ions is promoted and the diffusion and dissolution of the side reaction factors are blocked.Through the lithiation reaction treatment,the surface of the membrane contains a large amount of lithium ions,thereby significantly reducing the dissolution of redox molecules or side reaction factors?water,oxygen,carbon dioxide,etc.?in the membrane.In the demonstration experiment of using a high lithium ion content membrane to block redox molecules?2,2,6,6-tetramethylpiperidine oxide?,the blocking effect is significantly improved compared to the non-lithiated membrane,blocking the above molecules,the diffusion time is increased by nearly 5 times.The assembled lithium symmetrical battery can be stably cycled for 1000 h.In addition,the lithium ion migration number?t+ = 0.74?of high lithium ion content membrane is close to that of ordinary glass fiber membrane?t+ = 0.75?.The above results indicate that the high lithium ion content membrane effectively improves its blocking effect on side reaction factors while maintaining lithium ion conduction.2.The continuous loss of electrolyte seriously affects the cycle stability of lithium oxygen battery.Based on the first part of the research work,we further optimized and modified the membrane with high lithium ion content.Gel electrolytes with nanofiber network structure were prepared by quaternion reaction.A high lithium content gel membrane was prepared by compounding the high lithium content membrane and gel electrolyte.On the one hand,the introduction of gel promoted the gel solidification of electrolyte,reduced the loss of electrolyte,and stabilized the overall lithium ion concentration of the membrane.On the other hand,the filling of gel fibers made the membrane more compact,and increased the flatness of the membrane surface,thus enhancing the wettability of the lithium membrane to the electrolyte.In the demonstration experiment of using high lithium content gel membrane to block redox molecules?2,2,6,6-four methyl piperidine oxide?,the blocking time is 2.5 times higher than that of the first part of the high lithium ion content membrane.The lithium ion battery with 2,2,6,6-four methyl piperidine oxide was assembled and the cycle stability test was carried out.The results showed that the cycle stability was 3 times higher than that of the lithium oxygen battery assembled by ordinary glass fiber membrane.In conclusion,through the construction and optimization of the membrane barrier in the lithium oxygen battery,this paper solves the problems such as the original barrier is easy to react with the lithium anode,the barrier effect is not good,and the lithium ion conduction is insufficient.After the reaction of graphene oxide and polystyrene sulfonic acid with lithium,the membrane with high lithium ion content was obtained.The lithium ion enriched on its surface inhibited the dissolution and shuttle of redox molecules or side reaction factors?such as oxygen,water,carbon dioxide,etc.?through the effect of "salt effect",which played a role of barrier and provided better lithium ion conductivity.The introduction of gel electrolyte in the membrane not only reduces the flow loss of the electrolyte,but also improves the barrier capacity and interface wettability of the gel electrolyte.The barrier time of the high ion content gel membrane for the side reaction factor is further extended,and the lithium anode of the lithium oxygen battery is effectively protected during the circulation process?the stability of the circulation is increased by more than 3 times?.The construction of the composite membrane with high lithium ion content provides an effective solution and technical means for the protection of lithium anode in lithium oxygen battery. |
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