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1. Layered Electrides as Fluoride Intercalation Anodes

   https://doi.org/10.1039/D0TA06162J  

   Hartman, Steven T.; Mishra, Rohan (January 2020, Journal of Materials Chemistry A)

   The fluoride ion is well suited to be the active species of rechargeable batteries, due to its small size, light weight, and high electronegativity. While existing F-ion batteries based on conversion chemistry suffer from rapid electrode degradation with cycling, those based on fluoride intercalation are currently less attractive then cation intercalation battery chemistries due to their low reversible energy densities. Here, using first-principles density-functional-theory calculations, we predict that layered electrides, such as Ca2N and Y2C — that have an electron occupying a lattice site — are promising hosts for fluoride intercalation, since their anionic electrons create large interstices. Our calculations indicate that anodes made from layered electrides can offer voltage up to –2.86 V vs. La2CoO4 cathode, capacity >250 mAh/g, and fast diffusion kinetics with migration barriers as low as 0.15 eV. These metrics compare favorably to popular Li-ion intercalation cathodes such as LiCoO2. Electrides open up a new space for designing fluorine intercalation batteries with good performance and cyclability. 

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2. High-throughput discovery of fluoride-ion conductors via a decoupled, dynamic, and iterative (DDI) framework

   https://doi.org/10.1038/s41524-022-00786-8  

   Sundberg, Jack D.; Druffel, Daniel L.; McRae, Lauren M.; Lanetti, Matthew G.; Pawlik, Jacob T.; Warren, Scott C. (May 2022, npj Computational Materials)

   Abstract Fluoride–ion batteries are a promising alternative to lithium–ion batteries with higher theoretical capacities and working voltages, but they have experienced limited success due to the poor ionic conductivities of known electrolytes and electrodes. Here, we report a high-throughput computational screening of 9747 fluoride-containing materials in search of fluoride-ion conductors. Via a combination of empirical, lightweight DFT, and nudged elastic band (NEB) calculations, we identified >10 crystal systems with high fluoride mobility. We applied a search strategy where calculations are performed in any order (decoupled), computational resources are reassigned based on need (dynamic), and predictive models are repeatedly updated (iterative). Unlike hierarchical searches, our decoupled, dynamic, and iterative framework (DDI) began by calculating high-quality barrier heights for fluoride-ion mobility in a large and diverse group of materials. This high-quality dataset provided a benchmark against which a rapid calculation method could be refined. This accurate method was then used to measure the barrier heights for 6797 fluoride–ion pathways. The final dataset has allowed us to discover many fascinating, high-performance conductors and to derive the design rules that govern their performance. These materials will accelerate experimental research into fluoride–ion batteries, while the design rules will provide an improved foundation for understanding ionic conduction. 

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3. Co-intercalation-free ether electrolytes for graphitic anodes in lithium-ion batteries

   https://doi.org/10.1039/D2EE01489K  

   Ma, Peiyuan; Mirmira, Priyadarshini; Eng, Peter J.; Son, Seoung-Bum; Bloom, Ira D.; Filatov, Alexander S.; Amanchukwu, Chibueze V. (November 2022, Energy & Environmental Science)

   Carbonate-based electrolytes are widely used in Li-ion batteries but are limited by a small operating temperature window and poor cycling with silicon-containing graphitic anodes. The lack of non-carbonate electrolyte alternatives such as ether-based electrolytes is due to undesired solvent co-intercalation that occurs with graphitic anodes. Here, we show that fluoroethers are the first class of ether solvents to intrinsically support reversible lithium-ion intercalation into graphite without solvent co-intercalation at conventional salt concentrations. In full cells using a graphite anode, they enable 10-fold higher energy densities compared to conventional ethers, and better thermal stability over carbonate electrolytes (operation up to 60 °C) by producing a robust solvent-derived solid electrolyte interphase (SEI). As single-solvent–single-salt electrolytes, they remarkably outperform carbonate electrolytes with fluoroethylene carbonate (FEC) and vinylene carbonate (VC) additives when cycled with graphite–silicon composite anodes. Our molecular design strategy opens a new class of electrolytes that can enable next generation Li-ion batteries with higher energy density and a wider working temperature window. 

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4. A Surface Modification Strategy Towards Reversible Na-ion Intercalation on Graphitic Carbon Using Fluorinated Few-Layer Graphene

   https://doi.org/10.1149/1945-7111/ac9c33  

   Sarbapalli, Dipobrato; Lin, Yu-Hsiu; Stafford, Sean; Son, Jangyup; Mishra, Abhiroop; Hui, Jingshu; Nijamudheen, A; Romo, Adolfo I.; Gossage, Zachary T.; van der Zande, Arend M.; et al (October 2022, Journal of The Electrochemical Society)

   Na-ion batteries (NIBs) are proposed as a promising candidate for beyond Li-ion chemistries, however, a key challenge associated with NIBs is the inability to achieve intercalation in graphite anodes. This phenomenon has been investigated and is believed to arise due to the thermodynamic instability of Na-intercalated graphite. We have recently demonstrated theoretical calculations showing it is possible to achieve thermodynamically stable Na-intercalated graphene structures with a fluorine surface modifier. Here, we present experimental evidence that Na + intercalation is indeed possible in fluorinated few-layer graphene (F-FLG) structures using cyclic voltammetry (CV), ion-sensitive scanning electrochemical microscopy (SECM) and in situ Raman spectroscopy. SECM and Raman spectroscopy confirmed Na + intercalation in F-FLG, while CV measurements allowed us to quantify Na-intercalated F-FLG stoichiometries around NaC 14–18 . These stoichiometries are higher than the previously reported values of NaC 186 in graphite. Our experiments revealed that reversible Na + ion intercalation also requires a pre-formed Li-based SEI in addition to the surface fluorination, thereby highlighting the critical role of SEI in controlling ion-transfer kinetics in alkali-ion batteries. In summary, our findings highlight the use of surface modification and careful study of electrode-electrolyte interfaces and interphases as an enabling strategy for NIBs. 

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5. Solvent-mediated oxide hydrogenation in layered cathodes

   https://doi.org/10.1126/science.adg4687  

   Wan, Gang; Pollard, Travis P; Ma, Lin; Schroeder, Marshall A; Chen, Chia-Chin; Zhu, Zihua; Zhang, Zhan; Sun, Cheng-Jun; Cai, Jiyu; Thaman, Harry L; et al (September 2024, Science)

   Self-discharge and chemically induced mechanical effects degrade calendar and cycle life in intercalation-based electrochromic and electrochemical energy storage devices. In rechargeable lithium-ion batteries, self-discharge in cathodes causes voltage and capacity loss over time. The prevailing self-discharge model centers on the diffusion of lithium ions from the electrolyte into the cathode. We demonstrate an alternative pathway, where hydrogenation of layered transition metal oxide cathodes induces self-discharge through hydrogen transfer from carbonate solvents to delithiated oxides. In self-discharged cathodes, we further observe opposing proton and lithium ion concentration gradients, which contribute to chemical and structural heterogeneities within delithiated cathodes, accelerating degradation. Hydrogenation occurring in delithiated cathodes may affect the chemo-mechanical coupling of layered cathodes as well as the calendar life of lithium-ion batteries. 

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