Lithium ion transport in self-assembled zwitterionic nanochannels containing ionic liquids

下一代电化学储能技术，如锂金属电池，将需要先进的电解质材料。这些电解质应促进目标离子（如Li+）的快速、选择性传导，同时还提供强大的机械性能，以抑制枝晶生长并消除电解质泄漏。共聚物自组装可以促进两种化学性质不同的单体自发形成互穿结构域和导电域，是实现这类材料的有力工具。然而，到目前为止，仅限盐共聚物电解质在很大程度上未能达到实际应用所需的离子电导率水平。具有导电纳米通道的双连续结构尤其具有吸引力，因为可以利用两个结构域之间独特的界面效应来促进选择性离子传输。本项目的目的是研究由两亲性梳状共聚物自组装形成的两性离子（ZI）导电纳米通道内Li+离子的传输。为了确保在环境温度下具有足够高的离子电导率，富锌通道将被一定量的含有锂盐的非挥发性离子液体（IL）膨胀。由此产生的材料被称为纳米结构电解质（nse）。本研究的主要目的是验证这样一个假设，即约束在带有弱相互作用ZI界面的纳米通道中，将选择性地增强nse内Li+离子的输运。所提出的实验计划旨在研究当NSE中il膨胀的纳米通道尺寸（即导电畴的通道直径）被系统调节时ZI侧基对Li+离子传输的影响。约束的调制将通过仔细调整：(i)共聚物结构，（ii） IL膨胀程度，以及（iii）结构域的刚度来实现。nse中的整体离子传输将通过交流阻抗谱和直流极化测量来表征，用于确定Li+转移数值。使用7Li， 19F和1H脉冲场梯度核磁共振波谱来探测单个离子的扩散。电泳核磁共振（eNMR）光谱将首次应用于nse，直接测量Li+的选择性传导。nse的物理表征将包括：DSC、TEM、SAXS/WAXS和流变学。所提出的具有ZI导电纳米通道的nse有望为电解质材料设计提供有价值的新策略，以实现电化学储能系统中靶向离子传输的增强。虽然这项研究将重点放在Li+的传输上，但这种NSE材料也可以为其他应用（如“超锂”电池和燃料电池）中增强其他阳离子（Na+, H+）和/或阴离子的传输提供平台。

Next-generation electrochemical energy storage technologies, such as lithium metal batteries, will require advanced electrolyte materials. These electrolytes should promote fast, selective conduction of a target ion (e.g. Li+) while also providing robust mechanical properties to inhibit dendrite growth and eliminate electrolyte leakage. Copolymer self-assembly, which can facilitate the spontaneous formation of interpenetrating structural domains and conducting domains from two chemically distinct monomers, is a powerful tool for realizing such materials. However, confined salt-in-copolymer only electrolytes have so far largely failed to reach the levels of ionic conductivity that are necessary for practical applications. Bicontinuous structures that exhibit conducting nanochannels are especially attractive, as unique interfacial effects between the two domains that may promote selective ion transport can be exploited. The aim of this project is to study Li+ ion transport within zwitterionic (ZI) conducting nanochannels formed by the self-assembly of amphiphilic comb copolymers. To ensure sufficiently high ionic conductivity at ambient temperatures, the ZI-rich channels will be swollen with controlled amounts of a nonvolatile ionic liquid (IL), containing Li salt. The resulting materials are referred to as nanostructured electrolytes (NSEs). The primary objective of this study is to test the hypothesis that confinement into nanochannels decorated with weakly interacting ZI interfaces will selectively enhance Li+ ion transport within NSEs. The proposed experimental plan is designed to examine the effect of ZI side-groups on Li+ ion transport as the IL-swollen nanochannels size (i.e. channel diameter of the conducting domain) in a NSE is systematically modulated. Modulation of confinement will be achieved by carefully tuning: (i) copolymer architecture, (ii) degree of IL swelling, and (iii) rigidity of the structural domain. Overall ion transport in NSEs will be characterized by AC impedance spectroscopy and DC polarization measurements used to determine Li+ transference number values. Diffusion of individual ion species will be probed using 7Li, 19F, and 1H pulsed field gradient NMR spectroscopy. Electrophoretic NMR (eNMR) spectroscopy will be applied to NSEs for the first time to measure selective Li+ conduction directly. Physical characterization of NSEs will include: DSC, TEM, SAXS/WAXS, and rheology. The proposed NSEs featuring ZI conducting nanochannels are expected to provide a valuable new strategy for electrolyte materials design to realize an enhancement of targeted ion transport within electrochemical energy storage systems. While this study will focus on Li+ transport, such NSE materials may also provide a platform for enhancing the transport of other cations (Na+, H+) and/or anions in other applications such as “beyond-lithium” batteries and fuel cells.