More Like this

1. Ion Coordination and Transport in Magnesium Polymer Electrolytes Based on Polyester-co-Polycarbonate

   https://doi.org/10.34133/2021/9895403  

   Park, Bumjun; Andersson, Rassmus; Pate, Sarah G; Liu, Jiacheng; O’Brien, Casey P; Hernández, Guiomar; Mindemark, Jonas; Schaefer, Jennifer L (January 2021, Energy Material Advances)

   Magnesium-ion-conducting solid polymer electrolytes have been studied for rechargeable Mg metal batteries, one of the beyond-Li-ion systems. In this paper, magnesium polymer electrolytes with magnesium bis(trifluoromethane)sulfonimide (Mg(TFSI)₂) salt in poly(ε-caprolactone-co-trimethylene carbonate) (PCL-PTMC) were investigated and compared with the poly(ethylene oxide) (PEO) analogs. Both thermal properties and vibrational spectroscopy indicated that the total ion conduction in the PEO electrolytes was dominated by the anion conduction due to strong polymer coordination with fully dissociated Mg²⁺. On the other hand, in PCL-PTMC electrolytes, there is relatively weaker polymer–cation coordination and increased anion–cation coordination. Sporadic Mg- and F-rich particles were observed on the Cu electrodes after polarization tests in Cu|Mg cells with PCL-PTMC electrolyte, suggesting that Mg was conducted in the ion complex form (Mg_xTFSI_y) to the copper working electrode to be reduced which resulted in anion decomposition. However, the Mg metal deposition/stripping was not favorable with either Mg(TFSI)₂in PCL-PTMC or Mg(TFSI)₂in PEO, which inhibited quantitative analysis of magnesium conduction. A remaining challenge is thus to accurately assess transport numbers in these systems. 

   more » « less
2. Self-discharge of magnesium–sulfur batteries leads to active material loss and poor shelf life

   https://doi.org/10.1039/D0EE01578D  

   Ford, Hunter O.; Doyle, Emily S.; He, Peng; Boggess, William C.; Oliver, Allen G.; Wu, Tianpin; Sterbinsky, George E.; Schaefer, Jennifer L. (February 2021, Energy & Environmental Science)

   null (Ed.)

   Due to its high theoretical energy density and relative abundancy of active materials, the magnesium–sulfur battery has attracted research attention in recent years. A closely related system, the lithium-sulfur battery, can suffer from serious self-discharge behavior. Until now, the self-discharge of Mg–S has been rarely addressed. Herein, we demonstrate for a wide variety of Mg–S electrolytes and conditions that Mg–S batteries also suffer from serious self-discharge. For a common Mg–S electrolyte, we identify a multi-step self-discharge pathway. Covalent S 8 diffuses to the metal Mg anode and is converted to ionic Mg polysulfide in a non-faradaic reaction. Mg polysulfides in solution are found to be meta-stable, continuing to react and precipitate as solid magnesium polysulfide species during both storage and active use. Mg–S electrolytes from the early, middle, and state-of-the-art stages of the Mg–S literature are all found to enable the self-discharge. The self-discharge behavior is found to decrease first cycle discharge capacity by at least 32%, and in some cases up to 96%, indicating this is a phenomenon of the Mg–S chemistry that deserves focused attention. 

   more » « less
3. Mapping mechanisms and growth regimes of magnesium electrodeposition at high current densities

   https://doi.org/10.1039/c9mh01367a  

   Davidson, Rachel; Verma, Ankit; Santos, David; Hao, Feng; Fincher, Cole D.; Zhao, Dexin; Attari, Vahid; Schofield, Parker; Van Buskirk, Jonathan; Fraticelli-Cartagena, Antonio; et al (March 2020, Materials Horizons)

   The utilization of metallic anodes holds promise for unlocking high gravimetric and volumetric energy densities and is pivotal to the adoption of ‘beyond Li’ battery chemistries. Much of the promise of magnesium batteries stems from claims regarding their lower predilection for dendrite growth. Whilst considerable effort has been invested in the design of novel electrolytes and cathodes, detailed studies of Mg plating are scarce. Using galvanostatic electrodeposition of metallic Mg from Grignard reagents in symmetric Mg–Mg cells, we establish a phase map characterized by disparate morphologies spanning the range from fractal aggregates of 2D nanoplatelets to highly anisotropic dendrites with singular growth fronts and nanowires entangled in the form of mats. The effects of electrolyte concentration, applied current density, and coordinating ligands have been explored. The study demonstrates a complex range of electrodeposited morphologies including canonical dendrites with shear moduli conducive to penetration through typical polymeric separators. We further demonstrate a strategy for mitigating Mg dendrite formation based on the addition of molecular Lewis bases that promote nanowire growth through selective surface coordination. 

   more » « less
4. Reversible Insertion of Mg‐Cl Superhalides in Graphite as a Cathode for Aqueous Dual‐Ion Batteries

   https://doi.org/10.1002/anie.202009172  

   Kim, Keun‐il; Guo, Qiubo; Tang, Longteng; Zhu, Liangdong; Pan, Changqing; Chang, Chih‐hung; Razink, Joshua; Lerner, Michael M.; Fang, Chong; Ji, Xiulei (August 2020, Angewandte Chemie International Edition)

   Abstract Oxidative anion insertion into graphite in an aqueous environment represents a significant challenge in the construction of aqueous dual‐ion batteries. In dilute aqueous electrolytes, the oxygen evolution reaction (OER) dominates the anodic current before anions can be inserted into the graphite gallery. Herein, we report that the reversible insertion of Mg‐Cl superhalides in graphite delivers a record‐high reversible capacity of 150 mAh g⁻¹from an aqueous deep eutectic solvent comprising magnesium chloride and choline chloride. The insertion of Mg‐Cl superhalides in graphite does not form staged graphite intercalation compounds; instead, the insertion of Mg‐Cl superhalides makes the graphite partially turbostratic. 

   more » « less
5. Chemistry‐Performance Relationships of Polymer Gel‐Electrolytes for Mg−S and Li−S Batteries: Influence of Network Cation Solvation Capacity on Polymer‐Polysulfide Interactions

   https://doi.org/10.1002/cphc.202100881  

   Ford, Hunter_O; He, Peng; Schaefer, Jennifer_L (February 2022, ChemPhysChem)

   Abstract Metal‐sulfur batteries are a promising next‐generation energy storage technology, offering high theoretical energy densities with low cost and good sustainability. An active area of research is the development of electrolytes that address unwanted migration of sulfur and intermediate species known as polysulfides during operation of metal‐sulfur batteries, a phenomenon that leads to low energy efficiency and short life‐spans. A particular class of electrolytes, gel polymer electrolytes, are especially attractive for their ability to repel polysulfides on the basis of structure, electrostatics, and other polymer properties. Herein, within the context of magnesium‐ and lithium‐sulfur batteries, we investigate the impact of gel polymer electrolyte cation solvation capacity, a property related to network dielectric constant and chemistry, on sulfur/polysulfide‐polymer interactions, an understudied property‐performance relationship. Polymers with lower cation solvation capacity are found to permanently absorb less polysulfide active material, which increases sulfur utilization for Li−S batteries and significantly increases charge efficiency and life‐span for Li−S and Mg−S batteries. 

   more » « less