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.

The integration of automation with data-driven methodologies represents a transformative approach to accelerating material discovery in the energy sector. In battery development, significant progress has been made in automating coin-cell assembly. However, these advancements remain largely disconnected from data-driven techniques, which have predominantly been applied to computational or multi-fidelity datasets. Addressing this gap, the present study introduces a self-driving laboratory framework to expedite aqueous electrolyte discovery, which combines automated coin-cell assembly, galvanostatic cycling of organic-aqueous full-cells, and Bayesian optimization for guiding experiment selection based on prior outcomes. The investigation centers on a water-organic hybrid electrolyte system with four co-solvents and two salts. By incorporating Bayesian optimization, the framework facilitates machine-intelligent decision-making and establishes a closed-loop experimentation and analysis workflow. Using this approach, the study successfully identified electrolyte formulations achieving a Coulombic efficiency of at least 94%. Furthermore, operando gas analysis was employed to quantify hydrogen evolution rate, revealing a direct relationship between the water content of the electrolyte and the kinetics of hydrogen evolution. These findings underscore the potential of integrating Bayesian optimization with autonomous experimentation for the design of sustainable and cost-effective aqueous batteries.

The integration of automation and data-driven methodologies offers a promising approach to accelerating materials discovery in energy storage research. Thus far, in battery research, coin-cell assembly has advanced to become nearly 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 LiFePO4jjLi4Ti5O12 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 an optimized electrolyte cycled with at least 94% Coulombic efficiency. Additionally, online electrochemical mass spectrometry revealed that the optimized organic co-solvents successfully mitigated the 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.

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.

Ethylene carbonate (EC) and vinylene carbonate (VC) are the archetypical electrolyte solvent and additive in Li-ion batteries (LIBs), respectively. However, our understanding of their reaction pathways remains incomplete. Herein, the reaction pathways of EC and VC are explored by using online electrochemical mass spectrometry complemented by nuclear magnetic resonance analysis. For EC, reduction occurs through two distinct pathways <0.8 V vs Li+/Li, one yielding C2H4 and the other yielding CO, depending on the electrode potential and the EC concentration. The CO-releasing pathway does not contribute to the solid electrolyte interphase formation. For VC, reduction commences at <1.9 V, but CO2 gas evolution proceeds through a chemical step via a nucleophilic attack and VC ring opening. Additionally, VC scavenges H2O and reduced protons via hydrolysis and via proton abstraction from the carbon electrode to form EC. Our study uncovers further reaction pathways and underscores the unique properties of EC and VC, both individually and in combination, and elucidates their roles in influencing the formation process in Li-ion batteries.

Anode-free zinc batteries offer reduced weight and simplified production compared to traditional zinc metal batteries, but challenges such as dendrite formation and parasitic reactions limit 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. Zinc plating/stripping processes were investigated using operando electrochemical quartz crystal microbalance with dissipation monitoring (EQCM-D) and hydrodynamic spectroscopy, combined with other ex situ techniques. Our findings demonstrate that the indium-containing electrolyte additive has three functions: it induces oriented zinc deposition through prenucleation, suppresses the hydrogen evolution reaction by forming an indium intermediate layer, and suppresses zinc hydroxide sulfate (ZHS) formation by consuming OH- with In2O3/InOOH formation. These advantages result in a decreased overpotential and higher Coulombic efficiency, enhancing the design of highly reversible anode-free zinc batteries.

Electrolyte additives are indispensable to enhance the performance of Li-ion batteries. Lithium bis(oxalato)borate (LiBOB) has been explored for many years, as it improves both cathode and anode performance. No consensus regarding its reaction mechanisms has, however, been established. A model operando study combining attenuated total reflection infrared spectroscopy (ATR-FTIR), electrochemical quartz crystal microbalance (EQCM), and online electrochemical mass spectrometry (OEMS) is herein presented to elucidate LiBOB reduction and electrode/electrolyte interphases thus formed. Reduction of the BOB- ion sets in at similar to 1.8 V with solid lithium oxalate and soluble oxalatoborates as the main products. The reduced BOB- ion also reacts with itself and its environment to evolve CO2, which in turn impacts the interphase formed on the negative electrode. This study provides further insights into the reduction pathways of LiBOB and how they contribute to the interphase formation.

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.

Two-dimensional TiS2 has been proposed as a versatile host material for various battery chemistries. Nevertheless, its compatibility with aqueous electrolytes has not been thoroughly understood. Herein, we report on a reversible hydration process to account for the electrochemical activity and structural evolution of TiS2 in a dilute electrolyte for sustainable aqueous Li-ion batteries. Solvated water molecules intercalate into TiS2 layers together with Li+ cations, forming a hydrated phase with a nominal formula unit of Li0.38(H2O)2 δTiS2 as the end product. We unambiguously confirm the presence of two layers of intercalated water by complementary electrochemical cycling, operando structural characterization, and computational simulation. Such a process is fast and reversible, delivering 60 mAh g-1 discharge capacity at a current density of 1250 mA g-1. Our work provides further design principles for high-rate aqueous Li-ion batteries based on reversible water co-intercalation.

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.

Herein the development and application of Electrochemical Quartz Crystal Microbalance (EQCM) sensing to study metal electroplating, especially for energy storage purposes, are reviewed. The roles of EQCM in describing electrode/electrolyte interface dynamics, such as the electric double-layer build-up, ionic/molecular adsorption, metal nucleation, and growth, are addressed. Modeling of the QCM sensor is introduced and its importance is emphasized. Challenges of metal electrode use, including side reactions and dendrite formation, along with their mitigation strategies are reviewed. Numerous factors affecting the electroplating processes, such as electrolyte composition, additives, temperature, and current density, and their influence on the electroplated metals’ mass, structural, and mechanical characteristics are discussed. Looking forward, the need for deeper fundamental understanding and advancing simulations of the QCM signal response as a result of electroplating metal nanostructures is stressed. Further development and integration of innovative EQCM-strategies will provide unique future means to fundamentally understand and optimize metal electroplating for energy storage and application alike.

Introducing small volumes of organosilicon-containing additives as part of lithium-ion battery (LIB) electrolyte engineering has been getting a lot of attention owing to these additives' multifunctional properties. Tris-(trimethylsilyl)-phosphate (TMSPa) is a prominent member of this class of additives and scavenges Lewis bases such as water, although the rate at which the reaction occurs and the fate of the resultant product in the battery system still remain unknown. Herein, we have employed complementary nuclear magnetic resonance and gas chromatography-mass spectrometry to systematically study the reactivity of TMSPa with water in conventional organic carbonate solvents mimicking the Li-ion cell environment. The reaction products are identified, and a working reaction pathway is proposed by following the chemical evolution of the products over varying time and temperatures. We found that the main reaction products are trimethylsilanol (TMSOH) and phosphoric acid (H3PO4); however, various P-O-Si-containing intermediates were also found. Similar to water, the Lewis base TMSOH can undergo reaction with TMSPa at room temperature to form hexamethyldisiloxane and can also activate ethylene carbonate (EC) ring-opening reactions at elevated temperatures (>= 40 degrees C), yielding a TMS derivative with ethylene glycol (TMS-EG). While the formation of TMS-EG at the expense of EC is in principle an unwanted parasitic reaction, it should be noted that this reaction is only activated at elevated temperatures in comparison to EC ring-opening by H2O, which takes place at >= 40 degrees C. Thus, the study underlines the advantages of organo-silicon compounds as electrolyte additives. Elucidating the reaction mechanism in model systems like this is important for future studies of similar additives in order to improve the accuracy of additive exploration in LIBs.

The spinel oxide LiNi0.5Mn1.5O4 (LNMO) currently competes to replace the conventional layered transition metal oxide active material in Li-ion batteries. The high average operating potential (4.70 V vs. Li+/Li) challenges the stability of the electrolyte, which in turn compromises the lifetime of the Li-ion cell. Online electrochemical mass spectrometry (OEMS) is herein implemented to study the degradation processes occurring at the cathode surface. Gases continuously evolve across subsequent cycles as a result of electrolyte oxidation, a process that is found to be only potential-activated and independent of electrode surface composition. The subsequent formation of protic species autocatalyzes electrolyte salt degradation, which in turn triggers the corrosion of active material, current collector, and conductive carbons. The effectiveness of several well-known electrolyte additives, previously claimed to act as cathode electrolyte interphase (CEI) formers, were explored revealing the efficacy of phosphorus-based additives. Our study provides a rapid and quantifiable approach to tackle the major challenge of high voltage cathode materials, namely its stabilisation towards the electrolyte, and how to identify and develop an efficient CEI.

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?

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 MgCl2, 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.

Vinylene carbonate (VC) is the most commonly applied performance-enhancing electrolyte additives in Li-ion batteries to date. Despite numerous studies, there is a lack of consensus regarding the various reaction pathways of VC and their implications. VC has primarily been observed to either polymerize forming poly(vinylene carbonate) (poly(VC)) or decompose releasing major amounts of CO2, two seemingly contradictory processes. Herein, we present evidence of additional reaction pathways of VC highlighting its role as a H2O scavenging agent. In contrast to the typical electrolyte solvent ethylene carbonate, VC reacts much more rapidly with water impurities, especially when in contact with hydroxides, forming products less likely to influence cell performance. Efficient removal of water and hydroxides is essential to preserve the stability of Li-ion electrolyte solvent and salt, hence guaranteeing a long lifetime of the battery. Model studies pinpointing reaction pathways of electrolytes and additives, as presented herein, are critical not only to improve modern Li-ion cells but also to establish design principles for future battery chemistries.

Optimization of cell formation during lithium-ion battery (LIB) production is needed to reduce time and cost. Operando gas analysis can provide unique insights into the nature, extent, and duration of the formation process. Herein we present the development and application of an Online Electrochemical Mass Spectrometry (OEMS) design capable of monitoring gas evolution and consumption in both model coin-cells (Q = 0.72 mAh) with a graphite/electrolyte weight-ratio of 1:12.5 and large-format Li-ion cells (Q = 72 Ah) with a graphite/electrolyte weight-ratio of 1:0.63 during operation. Although the composition and amounts of gas are highly comparable, even when validated against ex-situ analysis, the gas release rate is lower from the larger cell size and likely limited by gas bubble transport through the electrode stack of the cell during formation. Higher temperatures accelerate the formation process, but also alters the composition and extent of gas released. Apart from providing novel insights into the formation processes of large-format Li-ion cells, our OEMS setup offers an opportunity for the battery manufacturing and automotive industry to explore the impact of battery formation and/or operating conditions on gas evolution in next-generation Li-ion batteries of any size.

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. Here, we gain unique insights into the initial Mg plating and stripping cycles by comparing Mg bis(trifluoromethanesulfonyl)imide (Mg(TFSI)2)- and Mg tetrakis(hexafluoroisopropyloxy)borate (Mg[B(hfip)4]2)-based electrolytes, each with and without MgCl2, 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 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.

Advances in methodologies for real-time analysis of batteries have come a long way, especially with the development of Operando Electrochemical Mass Spectrometry (OEMS). These approaches allow for the determination of side reactions during battery cycling with unprecedented selectivity and sensitivity, providing vital information necessary for determination of lifetime-limiting processes. However, the work thus far has primarily been carried out on model battery systems, where cell atmospheres are largely altered (through open flow, closed cell, and intermittent sampling approaches) and operation conditions are therefore not comparable with real-life situations. Herein, the development and validation of an intermittently closed OEMS system adapted for readily available commercial batteries is showcased. We provide a detailed description of a unique analysis design for large-format PHEV2 cells, with subsequent pressure and gassing data. A qualitative analysis of the results shows that side reactions brought on by structural transitions within both electrodes can be clearly observed. Transitions causing large volume changes in graphite induce H2 and C2H4 as SEI reformation products while the c lattice collapse in NMC induces CO2 evolution (through O2 release). OEMS can therefore be used for the quick and effective study of commercially available rechargeable batteries without influencing the internal battery chemistry.

Ethylene carbonate (EC) is the archetype solvent in Li-ion batteries. Still, questions remain regarding the numerous possible reaction pathways of EC. Although the reaction pathway involving direct EC reduction and SEI formation is most commonly discussed, EC ring-opening is often observed, but seldomly addressed, especially with respect to SEI formation. By applying Online Electrochemical Mass Spectrometry, the EC ring-opening reaction on carbon is found to start already at ∼2.5 V vs Li+/Li as initiated by oxygenic carbon surface groups. Later, OH− generated from H2O reduction reaction at ∼1.6 V further propagates EC to ring-open. The EC reduction reaction occurs <0.9 V but is suppressed depending on the extent of EC ring-opening at higher potentials. Electrode/electrolyte impurities and handling conditions are found to have a significant influence on both processes. In conclusion, SEI formation is shown to be governed by several kinetically competing reaction pathways whereby EC ring-opening can play a significant role.