Maximilian Becker

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Becker

First Name

Maximilian

ORCID

0000-0001-8379-4771

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Publications 1 - 9 of 9

Niobium oxide anode materials with suppressed activity toward hydrogen evolution reaction for aqueous batteries
Becker, Maximilian; Bernasconi, Francesco; Egorov, Konstantin; et al. (2024)
Energy Storage Materials
The hydrogen evolution reaction is the most prominent parasitic reaction for aqueous battery chemistries. Although water-in-salt electrolytes show greatly enhanced electrochemical stability, increasing the voltage of aqueous batteries further by lowering the potential of the negative electrode remains a major challenges due to reductive water splitting. Here, we systematically investigate twelve niobium-based anode materials that show much lower activity towards hydrogen evolution reaction than classic titanium-based anode materials such as lithium titanate (Li4Ti5O12) or titanium dioxide and are therefore a much better choice for aqueous batteries. We confirm Zn2Nb34O87 to be the most suitable anode material for aqueous batteries among these niobates and present full-cell cycling data with LiMn2O4 and LiNi0.8Mn0.1Co0.1O2 cathodes in a water-in-salt/ionic liquid hybrid electrolyte. Furthermore, we compare the catalytic activities of Zn2Nb34O87 and Cu2Nb34O87, with the latter being incompatible with aqueous batteries, and discuss the origin of the large difference in activity toward hydrogen evolution reaction.
Stability of highly soluble ferrocyanides at neutral pH for energy-dense flow batteries
Reber, David; Thurston, Jonathan R.; Becker, Maximilian; et al. (2023)
Cell Reports
Ferrocyanides and ferricyanides are among the most employed positive electrolyte materials in aqueous flow battery research, but the limited solubility of commonly available sodium and potassium salts is a critical factor limiting application at scale. Here, we systematically study the cation-dependent solubility of these materials and, importantly, the cation-dependent stability of the anion in aqueous solution. For Li4Fe(CN)6, we report a maximum solubility of 2.3 M and show stable cycling of a 2 M symmetric cell, corresponding to electrolyte capacities of 54 Ah L−1, over 200 days. We also demonstrate solubilities of 1.6 M for ammonium and calcium salts and investigate the pronounced anion decomposition observed in the presence of ammonium cations. Our observations lead to a discussion of challenges associated with the osmotic strength of concentrated electrolytes that employ ions with high charge states, such as ferrocyanide.
Multifunctional Additive Ethoxy(pentafluoro)cyclotriphosphazene Enables Safe Carbonate Electrolyte for SiOx-Graphite/NMC811 Batteries
Liu, Sufu; Becker, Maximilian; Huang-Joos, Yuanye; et al. (2023)
Batteries & Supercaps
The silicon (Si) or silicon monoxide (SiOx)-graphite (Gr)/nickel-rich LiNixMnyCozO2 (NMC, x+y+z=1, with x >= 80 %) cell chemistry is currently regarded as a promising candidate to further improve the energy density of rechargeable lithium-ion batteries, but is confronted with safety and cycling stability issues. Here, the flame retardant ethoxy(pentafluoro)cyclotriphosphazene (PFPN) is studied as electrolyte additive in the SiOx-Gr/NMC811 full cell system. We find that PFPN in combination with an increased lithium hexafluorophosphate (LiPF6) concentration renders carbonate-based electrolytes non-flammable based on a very low self-extinguishing time of 3.1 s g(-1) while the electrolyte maintains a high ionic conductivity of 8.4 mS cm(-1) at 25 degrees C. Importantly, PFPN in combination with fluoroethylene carbonate (FEC) also stabilizes the solid-electrolyte interphase of Si-based anodes beyond the level achieved only with FEC. Furthermore, PFPN improves the wetting property of the electrolyte, rendering it a multifunctional additive. As a result, excellent capacity retention of 87 % after 200 cycles at 1 C was achieved for SiOx-Gr/NMC811 pouch cells with a relatively high SiOx content of 20 %. Our work provides a promising avenue for developing safe and high-performance electrolytes for lithium-ion batteries with silicon-based anodes.
Towards Stable High-Voltage Aqueous Lithium-Ion Batteries Based on Water-In-Salt Electrolytes
Becker, Maximilian (2022)
Mediating anion-cation interactions to improve aqueous flow battery electrolytes
Reber, David; Thurston, Jonathan R.; Becker, Maximilian; et al. (2022)
Applied Materials Today
The limited solubility of electrolyte active materials has impeded the development of energy dense aqueous redox flow batteries. Here, we report on the solubilizing effect urea has on metal-organic complexes chelated by aminopolycarboxylate ligands. Upon addition of urea, solubility enhancements of up to 60% or 125% are observed for chromium ethylenediaminetetraacetate (CrEDTA) and chromium 1,3-propylenediaminetetraacetate (CrPDTA) salts, respectively, resulting in maximum solubilities of e.g., 1.5 м for KCrPDTA and 2.2 м for NaCrEDTA. We investigate the mechanism behind enhanced solubility of aminopolycarboxylate chelates, revealing strong hydrogen bonding between urea and anions, resulting in eutectic-like destabilization of the solid phase. We study the impact of urea on the electrochemical performance of near neutral pH flow batteries and demonstrate 50% higher anolyte capacities, up to 40 Ah L−1, than previously reported for this promising class of materials. In capacity balanced full cells, using ferrocyanide catholytes, we observe excellent Coulombic efficiencies >99.6% and voltage efficiencies >78% at average discharge voltages of ca. 1.5 V when cycling at 100 mA cm−2. Peak discharge power densities of >400 mW cm−2 further highlight the potential of our facile and cost-effective approach. Finally, we discuss avenues for future work to further exploit the solubilizing effect described herein.
Precipitation in lean Mg–Zn–Ca alloys
Schäublin, Robin; Becker, Maximilian; Cihova, Martina; et al. (2022)
Acta Materialia
While lean Mg–Zn–Ca alloys are promising materials for temporary implants, questions remain on the impact of Zn and Ca on the microstructure. In this context, the precipitation of Zn and Ca in Mg-1.5Zn-0.25Ca (in wt.%), initially extruded at 330°C, towards Mg–Ca binary precipitates or Ca–Mg–Zn ternary precipitates was probed in a multiscale correlative approach using atom probe tomography (APT) and analytical transmission electron microscopy (TEM). Particular focus was set on the ternary precipitate phase whose structure is debated. In the as-extruded material, the binary precipitates are made of hexagonal C14 Mg2Ca containing up to about 3 at.% of Zn. The ternary ones are based on the hexagonal Ca2Mg5Zn5 prototype structure with a composition close to Ca3Mg11Zn4, as deduced from atomically resolved EDS mapping and scanning TEM imaging, supported by simulations. The precipitation sequence was scrutinized upon linear heating from room temperature to 375°C, starting from the solutionized material. Three exothermic differential scanning calorimetry (DSC) peaks were observed, at respectively 125, 250 and 320°C. Samples were taken after the peak decays, at respectively 205, 260 and 375°C for structural analysis. At 205°C, APT analysis revealed Ca-rich, Zn-rich and Zn‒Ca-rich clusters of about 3 nm in size and with a number density of 5.7 × 1023 m−3. At 260°C, APT and TEM showed mono-layered Zn‒Ca-rich Guinier‒Preston (GP) zones of about 8 nm in size and with a number density of 1.3 × 1023 m−3. At 375°C, larger and highly coherent elongated precipitates were found, with a size of about 50 nm. They occur as binary Mg–Ca precipitates or ternary Ca2Mg6Zn3 precipitates, as deduced from scanning TEM-based energy dispersive X-ray spectroscopy (EDS) and nanodiffraction in TEM. Here, the binary precipitates outnumber the ternary ones, while in the as-extruded material the ternary precipitates outnumber the binary ones, which corresponds well to the calculated phase diagram. We correlated the microstructure to hardness probed by Vickers testing. The largest hardening relates to the end of the 125°C DSC peak and thus to GP zones, which outperform the hardening induced by the nanometer-sized clusters and the larger intermetallic particles. The complexity of the precipitation sequence in lean Mg–Zn–Ca alloys is discussed.
Toward an Autonomous Robotic Battery Materials Research Platform Powered by Automated Workflow and Ontologized Findable, Accessible, Interoperable, and Reusable Data Management
Svaluto-Ferro, Enea; Kimbell, Graham; Kim, Yeonju; et al. (2025)
Batteries & Supercaps
The discovery of novel battery materials has been accelerated by advanced modeling and machine learning. However, their integration into battery cells remains constrained by the necessity for experimental validation. The status of development and validation of the automated robotic battery materials research platform Aurora is presented, enabling rapid testing of scientific hypotheses and validation of physical models. Aurora integrates electrolyte formulation, battery cell assembly, and battery cell cycling into a stepwise automated application-relevant workflow. The different features of the Aurora platform can be leveraged to design experiments elucidating the impact of cycling parameters, electrode composition, and balancing, and electrolyte formulation on battery performance and long-term cycling stability with the example of NMC||graphite and LFP||graphite cells with carbonate-based electrolytes, which serve as benchmark battery cell chemistries. A large, structured, dataset with ontologized metadata detailing cell assembly and cycling protocols, alongside corresponding time series cycling data for all cells is provided as open research data. This study establishes Aurora as a powerful research platform for accelerating battery materials research.
The Hydrotropic Effect of Ionic Liquids in Water-in-Salt Electrolytes**
Becker, Maximilian; Rentsch, Daniel; Reber, David; et al. (2021)
Angewandte Chemie. International Edition
Water-in-salt electrolytes have successfully expanded the electrochemical stability window of aqueous electrolytes beyond 2 V. Further improvements in stability can be achieved by partially substituting water with either classical organic solvents or ionic liquids. Here, we study ternary electrolytes composed of LiTFSI, water, and imidazolium ionic liquids. We find that the LiTFSI solubility strongly increases from 21 mol kg−1 in water to up to 60 mol kg−1 in the presence of ionic liquid. The solution structure is investigated with Raman and NMR spectroscopy and the enhanced LiTFSI solubility is found to originate from a hydrotropic effect of the ionic liquids. The increased reductive stability of the ternary electrolytes enables stable cycling of an aqueous lithium-ion battery with an energy density of 150 Wh kg−1 on the active material level based on commercially relevant Li4Ti5O12 and LiNi0.8Mn0.1Co0.1O2 electrode materials.
Understanding the Stability of NMC811 in Lithium-Ion Batteries with Water-in-Salt Electrolytes
Becker, Maximilian; Zhao, Wengao; Pagani, Francesco; et al. (2022)
ACS Applied Energy Materials
The high practical capacity and high average de-/lithation potential of LiNi0.8Mn0.1Co0.1O2 (NMC811) renders it one of the most prominent cathode materials for lithium-ion batteries. Here, we investigate the compatibility of NMC811 with non-flammable water-in-salt electrolytes. These highly concentrated aqueous solutions possess a much extended electrochemical stability window compared to common dilute aqueous electrolytes and can comfortably accommodate 4 V-class cathodes. We find that common degradation phenomena observed when cycling NMC811 in organic electrolytes such as surface phase transformation, transition metal dissolution, and particle cracking, also occur in water-in-salt electrolytes, but the enhanced salt concentration of a water-in-salt/ionic-liquid hybrid electrolyte effectively diminishes these effects. Furthermore, we find that self-discharge reactions of NMC811 at a high state of charge with aqueous electrolytes lead to NMC811 protonation and irreversible capacity losses. Protonation represents an additional challenge that needs to be overcome when combining NMC811 with non-flammable aqueous electrolytes.

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Maximilian Becker

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