【作者】 王莹；

【导师】 赵亮；

【作者基本信息】 东北师范大学 ， 物理化学， 2021， 硕士

【摘要】 锂氧气电池由于其极高理论能量密度被认为是最有前途的能量存储系统之一。虽然科研工作者对锂氧气电池的研究已经获得了一些成果,但是锂氧气电池仍然处于初级阶段,要想实现真正的产业化还有很长的路要走。目前,锂氧气电池的面临最大难题就是绝缘的Li₂O₂会导致反应动力学缓慢,过电位高,从而造成能量效率低和电化学稳定性差。虽然加入氧化还原介质（Redox Mediator,RM）在很大程度上降低了充电过电位,但部分氧化后的RM(RM^ox)或还原后的(RM^re)会自发扩散到Li负极,与之发生副反应（称之为“穿梭效应”）。这不仅导致了RM的降解,而且不可避免地造成Li负极的持续腐蚀,从而导致锂氧气电池的可持续性较差。基于以上问题,我们制备了功能性隔膜用来减缓/抑制穿梭效应,继而保护Li负极,提高电池的循环稳定性。基于此,本论文开展了如下工作:1.我们采用简单滴涂法制备了聚（3,4-乙烯二氧噻吩）-聚苯乙烯磺酸（PEDOT:PSS）修饰的功能性隔膜（PEDOT:PSS-decorated隔膜）,将其应用于含有2,2,6,6-四甲基哌啶-1-氧自由基（TEMPO）和2,5-二叔丁基-1,4-苯醌（DBBQ）作为混合型RM的锂氧气电池中。PEDOT:PSS是一种导电的高分子复合物,其PSS中的负电荷和PEDOT中的正电荷通过库仑相互作用与TEMPO⁺和DBBQ^-相互作用,从而抑制了穿梭效应。为了研究PEDOT:PSS负载量对电池性能的影响,我们制备了不同PEDOT:PSS负载量的隔膜（PEDOT:PSS负载量分别为1、2、3和4 mg,即26、41、51和59 wt%PEDOT:PSS-decorated隔膜）。研究发现,含有51 wt%PEDOT:PSS-decorated隔膜的电池具有最好的循环稳定性。在电流密度为200 m A g^-1,限制容量为500 m Ah g^-1以及电压范围2.2-4.2 V vs.Li/Li⁺的条件下,电池可以稳定循环170次。我们对循环后电池的负极进行表征后发现,其仍然保持良好。这说明PEDOT:PSS-decorated隔膜可以有效抑制穿梭效应,保护Li负极,从而大大提高了电池的循环寿命。此外,我们也对PEDOT:PSS-decorated隔膜抑制穿梭效应的机理进行了深入探究。我们期待这个工作可以为功能性隔膜的设计提供了一个新的思路。2.我们首次设计了一种新型功能性复合隔膜—聚环氧乙烷（PEO）/TiO₂/PE隔膜,将其应用于含有Li I作为RM的锂氧气电池中。PEO具有良好的致密性,所以有利于减缓/抑制RM^ox或RM^re的扩散。TiO₂具有优良的导电性和化学稳定性,其有利于降低PEO的结晶度,保证隔膜良好的Li⁺迁移率。通过探讨PEO与TiO₂配比对电池性能的影响,系统地研究了PEO与TiO₂之间的协同作用。研究结果表明,当PEO和TiO₂的质量比为1:1时,电池具有最好的循环稳定性。与含有PE隔膜的锂氧气电池相比,含有PEO/TiO_2/PE隔膜的电池具有的更低的过电势,更稳定的循环性以及更良好的可逆性。此外,我们还提出了该复合型隔膜抑制穿梭效应的机理。这将为功能性复合隔膜的设计做出一定贡献。更多还原

【Abstract】 Li-O₂ battery is considered to be one of the most promising energy storage systems due to its high theoretical specific energy density.Although some achievements for Li-O₂ battery have been made,Li-O₂ battery is still in the primary stage,and there is still a long way to go before it can be truly industrialized.One of the fundamental problems for Li-O₂ battery is the sluggish reaction kinetics due to the insulate nature of Li₂O₂,resulting to a high overpotential,which thus causes a low energy efficiency and a poor electrochemical stability.Although redox mediator（RM）largely decreases the charge overpotential in Li-O₂ battery,the shuttle effect leads to a RM degradation and a serious corrosion of Li metal,which results in a poor sustainability.Based on the above problems,we develop functional separators which protect Li anode,resulting in the stability of Li-O₂ battery improvement.Therefore,the main research works are mainly focused on:1.we develop a novel（3,4-ethylenedioxythiophene）:poly（styrenesulfonate）（PEDOT:PSS）-decorated separator（PEDOT:PSS-decorated separator）by a simple drip coating method,which is applied in a Li-O₂ battery containing DBBQ and TEMPO as a mixture RM.PEDOT:PSS is a conductive interpolymer complex,the negative charge in PSS and the positive charge in PEDOT can interact with TEMPO⁺and DBBQ^-by coulombic interactions,thus inhibiting shuttle effect.In order to investigate the influence of PEDOT:PSS amount on battery performance,we prepare separators with different amount of PEDOT:PSS coating 26,41,51,and 59 wt%.On the basis of the experimental results,a cell with 51 wt%PEDOT:PSS-decorated separator（i.e.,3 mg PEDOT:PSS loading）exhibits a best cyclability and a lowest overpotential.The cell with PEDOT:PSS-decorated separator shows a considerable cyclability of 170 cycles at a constant current density of 200 m A g^-1 under a capacity limit of 500 m Ah g^-1.In addition,the mechanism for inhibition of shuttle effect by PEDOT:PSS-decorated separator is proposed.We expect that this work will provide a promising process in the design of functional separators.2.We firstly develop a novel polyethylene oxide/TiO₂/polypropylene（PEO/TiO₂/PE）separator,which contributes to inhibiting the redox shuttling for Li-O₂ battery containing Li I.Owing to compactness of PEO and considerable electrical conductivity of TiO₂,a PEO/TiO₂/PE separator can suppress RM shuttle and promote Li⁺migration.The influences for TiO₂nanoparticles and PEO on battery performance are systematically investigated.A cell with PEO/TiO₂/PE separator（i.e.,PEO:TiO₂=1:1 w/w）exhibits a better cycling stability.Moreove,compared to a cell with PE separator,a cell with PEO/TiO₂/PE separator shows a lower overpotential,more stable cyclability and more excellent reversibility.Furthermore,the mechanism of suppressing shuttle effect by this composite separator is also proposed.This work contributes to the development of functional separator to inhibit shuttle effect in Li-O₂battery.更多还原