Metal organic frameworks to transform the cyclability of metal-sulfur batteries

金属硫电池具有很高的潜在能量密度，比现有的摇椅式金属离子电池的能量密度高5倍，因此作为电池有很大的前景。然而，金属硫电池，如Li/S材料，其可循环性受到影响，因为容量迅速衰减，因为多硫化物物种攻击金属阳极，然后与硫磺阴极反应，导致金属硫化物物种毒害电池。隔膜(通常是玻璃纤维)不能消除物种从阴极到阳极的迁移；然而，我们提出了一个重要的双重策略修改来缓解这一问题。在这项工作中，我们将寻求在分离器上涂覆金属有机骨架(MOF)，以精确控制物种(S42--S82-)的流动，并另外使用金属有机骨架内表面(特别是不协调的金属位置)来捕获不稳定的聚合硫化物物种(特别是S2--S32-)。我们相信，这种新颖的双管齐下的攻击提供了一种高度可实现的机制，可以显著提高金属硫电池的寿命，这与EPSRC在电化学科学以及计算和理论化学方面的关键挑战密切相关。我们将使用理论方法的组合来指导实验室工作，期望在理论和实验之间建立反馈回路。我们将重点研究Na/K-S和Na/K-Se电池以及电池循环过程中的多硫化物物种，通过模拟，我们将使用现有的力场(如MOF-UFF或QuickFF)确定在玻璃纤维隔膜上有希望的MOF膜组合。我们已经在挖掘和筛选MOF数据库方面拥有丰富的经验3，这将被用来识别具有窄孔的MOF，这将阻碍聚合物SN2-(特别是S42-S82-)、NaxSy或KxSy物种通过涂层分离器的迁移。学生将进行实验，以评估寡聚体Sn2-在无MOF的细胞中的分布，将MOF分散在溶液中，然后涂覆分离器，然后真空过滤器产生涂覆的分离器。然后将涂覆的分离器放置在电池中，并进行循环实验以评估材料的性能，并将模拟结果反馈给预测。在工作的后期阶段，我们将利用筛选和密度泛函理论(DFT)寻找配位位置不佳的MOF来捕获多硫化物物种。一旦确定了候选者的排名名单，将在现场评估涂层隔膜的有效性和寿命。总体而言，我们的目标是制造一种能量密度超过当前典型金属离子电池的原型金属硫电池，其寿命远远超过目前通常只能持续几个循环的金属硫电池。原则上，该项目可能会对电池领域产生戏剧性的影响，并有助于摆脱相对稀缺的金属，这些金属将在几十年内耗尽。

Metal sulfur batteries hold much promise as batteries due to their high potential energy density that are up to 5 times more energy dense than established "rocking chair" metal-ion batteries. However, metal-sulfur batteries, such as Li/S materials are compromised by their cyclability, as capacity fades quickly due to polysulfide species that attack the metal anode and then react with the sulfurous cathode, leading to metal sulfide species that poison the battery. Separators (typically glass fiber) are unable to eliminate the migration of species from cathode to anode; however we propose an important dual strategy modification to mitigate this. In this work, we will seek to coat separators with a metal organic framework (MOF) to precisely control the flow of species (S42- - S82-) and additionally use the MOF internal surface (specifically, undercoordinated metal sites) to trap labile polymeric sulphide species (especially S2- - S32-). We believe this novel dual-pronged attack provides a highly achievable mechanism for dramatically improving the lifetime of metal-sulfur batteries which is closely aligned to key EPSRC challenges in electrochemical sciences and computational and theoretical chemistry.We will use a combination of theoretical approaches, to guide laboratory work with the expectation of a feedback loop between theory and experiment. We will focus on Na/K-S and Na/K-Se batteries and the polysulfide species during battery cycling, where using simulation, we will identify promising combinations of MOF films on glass fibre separators using established forcefields such as MOF-UFF or QuickFF. We already have extensive experience of mining and screening MOF databases3 and this will be used to identify MOFs that have narrow pores, that will hinder the migration of polymeric Sn2-(especically S42- - S82-) , NaxSy or KxSy species through the coated separator. The student will perform experiments to assess the distribution of oligomeric Sn2- in a MOF-free cell disperse MOFs in solution and then coat the separator and then vacuum filter to generate the coated separator. The coated separator will then be placed in the cell and cycling experiments will be undertaken to assess the performance of the material, feeding back to the predictions from simulation. In the latter stages of the work, we will seek to identify MOFs with undercoordinated sites to trap polysulphide species using screening and density functional theory (DFT). Once a ranked list of candidate has been identified, the coated separator will be assessed for its effectiveness and longevity in situ. Overall the aim is build a protype metal sulfur battery with an energy density that surpasses current typical metal-ion batteries with lifetime that greatly exceeds current metal sulfur batteries which typically last for just a few cycles. In principle, this project could have a dramatic effect on the battery field and help to get away from relatively scarce metals that will be exhausted in a few decades.