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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 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 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.

Creating high-energy-density cathodes is crucial for building next-generation lithium-ion batteries. However, materials exploration along two main directions, namely Li-rich or Ni-rich oxides, has encountered bottlenecks. To get rid of the impasse, here a “Li-rich Ni-rich” route is consolidated by designing a new family of Li1+yNi(3-5y)/3W2y/3O2 oxides with high-voltage cycling stability up to 4.5 V and high capacities over 230 mAh g−1. It is discovered that W6+ is largely incorporated into the LiNiO2 lattice, forming W/Ni(Li) inverse honeycomb-ordered nano-domains. These Li-rich domains enable reversible anionic redox, clearly demonstrated by X-ray absorption spectroscopy, resonant inelastic X-ray scattering, transmission electron microscopy, and nuclear magnetic resonance, which is linked to improved electrochemical performance. Furthermore, the incorporation of W6+ into the lattice proves to be the key to generating electrochemically active Li-rich domains irrespective of Li stoichiometry given that a similar local structure is found in W-substituted non-Li-rich oxides. This therefore implies the underestimated role of high-valence cations in tuning the structure and electrochemistry of Ni-rich oxides. These results underline the necessity of a Li-rich composition in the request for reversible high capacity, reinforcing the promise of a “Li-rich Ni-rich” avenue for developing advanced cathodes.

Monitoring the chemical and physical processes during the initial charge of commercial-type cells is crucial for accelerating their optimization. In this study, operando optical calorimetry, pressure sensing, and infrared fiber evanescent wave spectroscopy (IR-FEWS) are harnessed as powerful diagnostic tools to investigate the first charge of the formation cycle of layered oxide-based sodium-ion cells composed of P2 or O3 cathode material and hard carbon (HC) anode. It is first revealed that the cathode composition significantly influences the initial charge behavior, showing that the O3 cathode triggers larger electrolyte decomposition than P2, which is associated with significant heat and gas generation at high states of charge. Then, the use of succinonitrile (SN) and prop-1-ene-1,3-sultone (PES) is explored as additives in the electrolyte, proving that while both additives raise the heat generation in P2/HC and O3/HC cells, they effectively suppress solvent and salt decomposition. These observations are further corroborated by online electrochemical mass spectrometry (OEMS) and X-ray photoelectron spectroscopy (XPS) analyses. Overall, this work underlines the importance of combining operando calorimetric and chemical studies in optimizing the cell chemistry and highlights the effectiveness of optical sensing techniques for investigating the interphase formation in commercial-type cells.

Organic materials demonstrate significant potential as electrodes for aqueous batteries, owing to their high theoretical capacity, structurally tunable frameworks, and sustainable material accessibility. Small-molecule organic electrode materials enable better active-site accessibility but remain challenged by the dissolution in aqueous electrolytes, which deteriorates cycling stability, and poor conductivity due to limited conjugation. Here, we designed an organic small-molecule cathode material (DPPZ-CN) featuring functional pyridine, pyrazine, and cyano groups. Its highly conjugated fused N-heteroaromatic structure provides strong intermolecular interactions and high reactivity, resulting in improved stability, capacity, and conductivity. The electron-withdrawing cyano group further modulates electron delocalization and molecular orbitals, enhancing electronic conductivity and operating voltage. Through combined theoretical and experimental studies, including operando synchrotron FT-IR, in situ Raman, ex situ XPS, and ¹H NMR, we demonstrate that DPPZ-CN facilitates efficient dual-cation storage (Al³⁺/H⁺), thereby reducing Al³⁺ cation repulsion and induced structural distortion. As a result, the Al//DPPZ-CN battery exhibits outstanding capacity, a well-defined voltage plateau, and an extended lifespan in organic aluminum batteries with aqueous and seawater electrolytes, highlighting its potential for operation in challenging environments.

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?

Sodium layered oxides, having either O3, P2 or P3 stacking, are extensively studied as low-cost cathode materials for high energy Na-ion batteries (NIBs). Previous efforts focused on the optimization of layered oxide compositions resulted in the O3-Na0.85Ni0.38Zn0.04Mn0.48Ti0.1O2 and P2-Na0.67Ni0.3Zn0.03Mn0.52Ti0.15O2 phases as potential candidates to establish prototype cylindrical 18650 cells with 120-150 Wh/kg specific cell energy. In this study, we focus particularly on the electrode-electrolyte reactivity of these phases, especially at high state of charge (∼70 % or more) and at high temperatures. Our results indicate that the end-of-charge phase, O1 and O2 formed during complete de-sodiation of O3 and P2, respectively, plays a major role in determining their reactivity. The O1 phase is particularly prone to transition metal migration and oxygen oxidation, having increased reactivity with electrolyte. On the other hand, the P2 layered oxide, while having lower capacity than O3, offers better cycling stability (90 % retention after 1000 cycles at 25 °C) due to the greater stability of the O2 end-of-charge structure. These results once again underline the fact that specific capacity should not be the sole metric for determining the most suitable electrode materials for Na-ion or other battery chemistries.

Gaseous molecules are inherent byproducts of (electro-)chemical reactions in lithium-ion battery cells during both formation cycles and long-term operation. While monitoring gas evolution can help understand battery chemistry and predict battery performance, the complex nature of gas dynamics makes conventional mass spectrometry approaches insufficient for real-time detection. Here, we present a radically different methodology for operando analysis of gas evolution in lithium-ion batteries using optical fiber photothermal spectroscopy. By placing an optical hollow-core fiber inside the battery cell, evolved gases can rapidly diffuse into the hollow core of the fiber, enabling photothermal spectroscopy which precisely and selectively quantifies their concentrations without altering the internal operation of the cell. This approach facilitates identification of individual gaseous species, thereby allowing for further clarification (electro-)chemical reaction pathways. Collectively, we show that the evolution paths of C₂H₄ and CO₂ are closely associated with the formation of the solid electrolyte interphase, the selection of electrolyte salts, and the inclusion of specific additives. Significantly, we confirm for the first time the spontaneous formation of CO₂, which occurs exclusively in the presence of LiPF₆ salt. Beyond the scope of batteries, the methodology presented here offers substantial potential for broader applications, particularly in characterizing electrocatalytic processes, providing unmatched precision, accuracy, and scalability compared to existing analytical techniques.

Lithium-rich manganese-based oxides are promising cathode materials for high-energy lithium-ion batteries but suffer from capacity deterioration due to oxygen release, irreversible structural changes, and detrimental secondary reactions—all of which are known to be exacerbated at elevated temperatures, leading to inferior high-temperature cycling performance. Here, we report the discovery of an unconventional temperature-dependent behavior in an O2-type Li0.75[Li0.25Mn0.75]O2 cathode, which exhibits significantly improved cycling stability at an elevated temperature (55°C) compared with room temperature (RT), delivering high capacities of up to 300 mAh g−1. Combined structural and electrochemical analyses reveal that an in situ-formed ramsdellite-like surface layer, with tunnels oriented parallel to the crystallite surface, effectively protects the O-redox activity within the layered core but impedes the Li+ diffusion into and out of the particle at RT. However, Li+ diffusion through this protective surface layer is kinetically unlocked at elevated temperatures, resulting in improved capacity and cycling stability.

Online acoustic emission (AE) sensing is a promising nondestructive technique for battery health monitoring. Herein, we report on the ability of AE sensing to differentiate among different chemomechanical degradation events in a TiS2-based model aqueous chemistry. Short and high-frequency AE signals primarily stem from fracture-related degradation of TiS2, such as layer delamination, exfoliation, and cracking. Long and lowfrequency signals originate from gas bubbles bursting when the cell is cycled outside the water stability window. The two processes demonstrate distinct AE features, allowing them to be semi-quantitatively distinguished from both time and frequency domains. Complementary physicochemical characterizations have been conducted to correlate with the AE observation, including online electrochemical mass spectrometry, operando synchrotron X-ray diffraction, and ex situ scanning electron microscopy. Our work indicates that online AE sensing holds the promise to identify complex chemomechanical degradation processes in batteries with liquid and potentially solid electrolytes.

Aqueous batteries are sustainable energy storage solutions for next-generation grid energy storage. However, their practical deployment is limited by the narrow electrochemical stability window of water, which constrains cell voltage and leads to persistent performance degradation. In this Perspective, online electrochemical mass spectrometry is highlighted as a powerful operando technique for detecting and quantifying gas evolution in aqueous batteries. The fundamental principle and historical development of the technique are briefly reviewed, followed by a systematic evaluation of recent advances in applying the technique to study common gassing events in aqueous chemistries. Perspectives on leveraging the technique for high-sensitivity, high-accuracy, and high-throughput investigations of key cell components are offered, with the goal of accelerating the development of robust and commercially viable aqueous batteries.