Single Ion Conducting Polymers of Boron Rich Nanoclusters: Synthesis and Fundamental Electrochemical Properties

非技术总结：锂离子电池（LIB）之外的创新电化学储能技术对于信息和通信技术的新时代至关重要。智能电网、电信和物联网等新兴应用需要具有低成本、高安全性和优异循环稳定性的新型可充电电池。可充电镁（Mg）离子电池可以潜在地满足这些要求，并且由于其与LIB中已知的电化学机制明显不同而具有科学吸引力。镁离子电池的关键瓶颈是缺乏提供优异的Mg 2+导电性、化学和电化学稳定性的Mg 2+离子电解质。在该项目中，由材料研究部门的固态和材料化学计划支持，研究人员开发了一种全新的固体聚合物电解质（SPE），具有高Mg 2+离子电导率和优异的稳定性。研究人员通过将阴离子物种共价连接到聚合物主链上来实现这一点，聚合物主链在聚合物网络中吸引和运输Mg 2+阳离子。该项目中的特定阴离子是富硼纳米团簇（BRN），它是由碳和硼原子组成的笼状庞大分子结构，并携带负电荷。这些BRN阴离子的独特性和优势在于它们与Mg 2+阳离子的键合相对较弱，使得Mg 2+可以在固态下在电场内解离和移动。BRN SPE由于强的碳-硼和硼-硼键也表现出优异的稳定性。此外，该项目直接涉及来自代表性不足群体的研究生、本科生和高中生的参与。已为高中学生津贴拨款，以继续PI和Co-PI制定的外联方案。这些活动将为社会提供更多急需的STEM教育人员进入劳动力市场。富硼纳米团簇（BRN）是由硼和碳组成的弱配位多原子阴离子。它们的盐在低温下表现出非凡的固态离子导电性和无与伦比的（电）化学稳定性。通过该项目，由材料研究部门的固态和材料化学计划支持，研究团队将镁（Mg）BRN盐的有利特性转化为Mg 2+单离子导电离聚物，作为可充电镁离子电池的固体聚合物电解质（SPE）。中心假设是，一类新的单离子Mg 2+导电聚合物可以通过共价连接BRN阴离子到聚合物主链。所获得的Mg 2+离聚物保持高的离子电导率和（电）化学稳定性观察其结晶粉末。据推测，Mg 2+离子的传输在建议的BRN SPEs遵循一个新的机制上级传统的离子跳跃由于弱配位性质的BRN阴离子。还研究了BRN的表面官能化以微调其电化学性质，这对于传统的多原子阴离子是不可能的或非常有限的。提出了两种方法，即（1）碱引发环氧开环聚合法和（2）开环烯烃易位聚合法合成Mg BRN SPE。系统地研究了合成的SPE的物理、化学和电化学性质。电化学性能的研究主要集中在离子导电性、与镁金属阳极的界面稳定性以及与阴极的电化学反应。该奖项反映了NSF的法定使命，并通过使用基金会的知识价值和更广泛的影响审查标准进行评估，被认为值得支持。

Non-Technical Summary: Innovative electrochemical energy storage technologies beyond lithium-ion batteries (LIBs) are essential for a new era of information and communication technologies. Emerging applications such as smart grid, telecommunications, and the Internet of Things demand new rechargeable batteries characterized with low costs, high safety, and excellent cycle stability. Rechargeable magnesium (Mg) ion batteries can potentially fulfill these requirements and are scientifically intriguing due to their distinctly different electrochemical mechanisms from those known in LIBs. The key bottleneck for Mg-ion batteries is the lack of Mg2+ ion electrolytes that offer excellent Mg2+ conductivity, chemical and electrochemical stability. In this project, supported by the Solid State and Materials Chemistry Program in the Division of Materials Research, researchers develop a completely new class of solid polymer electrolytes (SPEs) that have high Mg2+ ion conductivity and excellent stability. The researchers achieve this by covalently tethering anionic species to the polymer backbones, which attract and transport Mg2+ cations within the polymer network. The specific anions in this project are boron rich nanoclusters (BRNs), which are cage-like bulky molecular structures composed of carbon and boron atoms and carrying a negative charge. The uniqueness and advantage of these BRN anions is their relatively weak bonding with Mg2+ cations so that Mg2+ can be dissociated and moved within the electric field in solid state. The BRN SPEs also exhibit excellent stability due to the strong carbon-boron and boron-boron bonds. Additionally, this project directly involves the participation of graduate, undergraduate, and high school students from underrepresented groups. Funds have been allocated for high school student stipends to continue an outreach program the PI and Co-PI developed. These activities will provide society with more greatly needed STEM educated people to enter the workforce. Technical Summary: Boron Rich Nanoclusters (BRNs) are weakly coordinating polyatomic anions composed of boron and carbon. Their salts exhibit extraordinary solid-state ionic conductivity at low temperature and unmatched (electro)chemical stability. With this project, supported by the Solid State and Materials Chemistry Program in the Division of Materials Research, the research team translates the favorable properties of magnesium (Mg) BRN salts into Mg2+ single ion conducting ionomers as solid polymer electrolytes (SPEs) for rechargeable Mg-ion batteries. The central hypothesis is that a new class of single ion Mg2+ conducting polymers can be created by covalently linking BRNs anions to polymer backbones. The obtained Mg2+ ionomers maintain the high ionic conductivity and (electro)chemical stability observed for their crystalline powders. It is also hypothesized that the Mg2+ ion transport in the proposed BRN SPEs follows a new mechanism superior to the conventional ion hopping due to the weakly coordinating nature of the BRN anions. Surface functionalization of BRNs is also investigated to fine tune their electrochemical properties, which is not possible or very limited with traditional polyatomic anions. Two methods including (1) base initiated epoxide ring opening polymerization and (2) ring opening olefin metathesis polymerization are proposed to synthesize the Mg BRN SPEs. The physical, chemical, and electrochemical properties of the synthesized SPEs are systematically investigated. The investigations on the electrochemical properties focus on ion conductivity, interfacial stability with Mg metal anodes, and electrochemical reactions with the cathodes.This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.