Erik Jaemstorp Berg

Cycling NMC cathodes to high voltage causes a severe c -lattice contraction, which leads to poor capacity retention and cycle life. Limiting the upper cut-off voltage (UCV) mitigates this degradation. In this study, we examine whether overlithiation can serve as a strategy to stabilize the c -lattice while allowing operation at higher voltage. We choose NMC 532 as a model system and synthesize both standard NMC 532 and overlithiated NMC 532 (Li-rich 532) from the same precursor to compare their performance. We find that Li-rich 532 achieves superior capacity retention and, after extended cycling, delivers a specific capacity comparable to NMC 532 cycled to 4.4 V. Furthermore, the Li-rich 532 exhibits fewer anti-site defects, resulting in enhanced rate capability. These findings suggest that strategic overlithiation of NMC cathode materials coupled with a moderate UCV cycling is a viable method for improving NMC cathode performance, particularly for applications requiring both high stability and fast-charging capabilities.

Despite the lack of fundamental understanding of their operating mechanisms, layer‐forming electrolyte additives are key to stabilizing modern Li‐ion cells. Herein, the reduction mechanism of sulfur‐containing additive prop‐1‐ene‐1,3‐sultone (PES) is investigated using a model inert electrode/electrolyte system to isolate additive‐driven reactions. Attenuated total reflection fourier‐transform infrared spectroscopy, online electrochemical mass spectrometry, electrochemical quartz crystal microbalance with dissipation monitoring, and electrochemical impedance spectroscopy (EIS) are applied operando along with ex situ X‐ray photoelectron spectroscopy. PES satisfies the main criteria for layer‐forming additives, to reduce at higher potentials than typical carbonate ester‐based electrolytes and to suppress further electrolyte decomposition. Inclusion of PES in the electrolyte significantly reduced gas evolution, forming a thin, dense, and Li ⁺ ‐conductive SEI. Despite significant charge passed already at 1.4 V vs. Li ⁺ /Li, no major interfacial change is observed until 1.0 V, where a high‐resistance, low‐capacitance interphase forms containing sulfur–oxygen species, such as ROSO ₂ Li, RSO ₃ Li, and Li ₂ SO ₃ . Such species primarily form in chemical steps after PES reduction, which in turn continue the layer growth long after the electrochemical PES reduction has ended. The combined operando methodology applied herein provides unique insights into electrode layer formation in batteries and thereby guides understanding and development of future electrolyte additives.

The integration of automation and data-driven methodologies offer a promising approach to accelerating materials discovery in energy storage research. Thus far, in battery research, coin-cell assembly has advanced to become near fully-automated but remains largely disconnected from data-driven methods. To bridge the disconnect, this work presents a self-driving laboratory framework to accelerate electrolyte discovery by integrating automated coin-cell assembly, galvanostatic cycling of LiFePO4||Li4Ti5O12 organic-aqueous full-cells, and Bayesian optimization for selecting subsequent experiments based on prior results. The study explored an organic-aqueous hybrid electrolyte system comprising four co-solvents and two lithium-conducting salts. Using this framework, cells with optimized electrolyte cycled with at least 94% Coulombic efficiency. Additionally, online electrochemical mass spectrometry revealed the optimized organic co-solvents successfully mitigated parasitic hydrogen evolution reaction. The results highlight the potential of combining Bayesian optimization with autonomous full-cell experimentation, while contributing new electrolyte design insights for next-generation aqueous batteries.

Wieder aufladbare Magnesium Batterien sind vielversprechend für die zukünftige Energiespeicherung. Ihre praktische Anwendung wird jedoch unter anderem durch niedrige Coulomb'sche Effizienzen bei der Magnesiumabscheidung und ‐auflösung behindert. Grundlegende Prozesse wie die Bildung, Struktur und Stabilität von Passivierungsschichten und der Einfluss verschiedener Elektrolytbestandteile auf diese sind immer noch nicht vollständig verstanden. In dieser Studie erhalten wir einzigartige Einblicke in die ersten Magnesiumabscheidungs‐ und auflösungszyklen, indem wir Magnesium bis(trifluoromethansulfonyl)imid (Mg(TFSI)₂)‐ und Magnesium tetrakis(hexafluoroisopropyloxy)borat (Mg[B(hfip)₄]₂)‐basierte Elektrolyte, jeweils mit und ohne MgCl₂, operando auf Goldelektroden mittels hochempfindlicher elektrochemischer Quarzmikrowaage mit Dissipationsmessung (EQCM−D) unter Anwendung hydrodynamischer Spektroskopie vergleichen. Mit den stabilen Mg[B(hfip)₄]₂‐basierten Elektrolyten ist hocheffizientes und Interphasen‐freies Zyklieren möglich, während die Bildung von Passivierungsschichten Elektrolytverunreinigungen zugerechnet werden kann. Diese bilden sich und degradieren während des sogenannten Konditionierungsprozesses. Mit dem reaktiveren Mg(TFSI)₂‐basierten Elektrolyten wachsen während des Zyklierens dicke Passivierungsschichten mit kleinen Poren. Wir zeigen, dass die Zugabe von MgCl₂ bei diesen Elektrolyten die Menge an passiviertem Mg verringert und die stromlose Auflösung der Passivierungsschicht beschleunigt. Dies hat einen positiven Effekt, da wir das effizienteste Zyklieren und die gleichmäßigste Abscheidung beobachten, wenn sich keine Interphase auf der Elektrode befindet.

Rechargeable magnesium batteries are promising for future energy storage. However, among other challenges, their practical application is hindered by low coulombic efficiencies of magnesium plating and stripping. Fundamental processes such as the formation, structure, and stability of passivation layers and the influence of different electrolyte components on them are still not fully understood. In this work, we gain unique insights into the initial Mg plating and stripping cycles by comparing magnesium bis(trifluoromethanesulfonyl)imide (Mg(TFSI) ₂ )‐ and magnesium tetrakis(hexafluoroisopropyloxy)borate (Mg[B(hfip) ₄ ] ₂ )‐based electrolytes, each with and without MgCl ₂ , on gold electrodes by highly sensitive operando electrochemical quartz crystal microbalance with dissipation monitoring (EQCM−D) applying hydrodynamic spectroscopy. With the stable Mg[B(hfip) ₄ ] ₂ ‐based electrolytes, highly efficient and interphase‐free cycling is possible and passivation layers are attributed to electrolyte contaminants. These are forming and degrading during the so‐called initial conditioning process. With the more reactive Mg(TFSI) ₂ ‐based electrolyte, thick passivation layers with small pores are growing during cycling. We demonstrate that the addition of chloride lowers the amount of passivated Mg deposits in these electrolytes and accelerates the currentless dissolution of the passivation layer. This has a positive effect since we observe the most efficient cycling and uniform deposition when no interphase is present on the electrode.

Prussian blue analogues (PBAs) for sodium ion battery (SIB) cathodes are growing in popularity as next generation energy storage devices. Prussian White (PW) with formula NaxFe[Fe(CN)6]y•nH2O is leading the trend, having already been commercialized. However, capacity fade (PW/electrolyte degradation) and safety concerns (cyanide/cyanogen release) still raise concerns. Online electrochemical mass spectrometry (OEMS), supported by both operando Fourier transform infrared spectroscopy (FTIR) and Mössbauer spectroscopy (MöS), is herein used to analyse degradation processes in PW based Na-ion full cells. Apart from the typical cell formation reactions, hydrogen is observed to evolve during cell discharge and evidenced to stem from oxidation of NaH, accumulated upon charge. Over-oxidation of PW after full desodiation releases CN, which not only forms (CN)2 but also degrades the electrolyte. Loss of CN likely results in a nanometric (~4 nm) surface-reconstructed passivation layer on PW thus inhibiting further degradation. Fundamental understanding of degradation reactions in PW full-cells, as gathered herein, shows that the aforementioned capacity fade and safety concerns are wholly addressable and hence guides the further development of Na-ion batteries for wider ranges of applications.

Advanced aqueous batteries are promising solutions for grid energy storage. Compared with their organic counterparts, water‐based electrolytes enable fast transport kinetics, high safety, low cost, and enhanced environmental sustainability. However, the presence of protons in the electrolyte, generated by the spontaneous ionization of water, may compete with the main charge‐storage mechanism, trigger unwanted side reactions, and accelerate the deterioration of the cell performance. Therefore, it is of pivotal importance to understand and master the proton activities in aqueous batteries. This Perspective comments on the following scientific questions: Why are proton activities relevant? What are proton activities? What do we know about proton activities in aqueous batteries? How do we better understand, control, and utilize proton activities?

Anode-free Zn batteries are gaining significant interest due to their reduced weight and simplified production compared to traditional Zn metal batteries. However, challenges such as zinc dendrite formation and parasitic reactions continue to impact their efficiency and cycle life. In this study, we present an effective strategy to form a zincophilic interphase in situ via indium co-deposition during cycling, using InCl3 as an electrolyte additive. We investigated the zinc plating/stripping processes with and without InCl3 using operando electrochemical quartz crystal microbalance with dissipation monitoring (EQCM-D). Structural changes from zinc deposition and dissolution were quantified using hydrodynamic spectroscopy (HS) and validated by ex-situ scanning electron microscopy (SEM) and X-ray photoelectron spectroscopy (XPS). Our findings demonstrate that the indium-containing electrolyte additive has triple functions: it induces oriented zinc deposition through pre-nucleation, suppresses hydrogen evolution reaction by forming an indium intermediate layer, and suppresses zinc hydroxide sulfate (ZHS) by consuming OH- with In2O3/InOOH formation. These advantages result in decreased overpotential and higher Coulombic efficiency, enhancing the design of highly reversible anode-free zinc batteries.