Degradation of an Ethylene Carbonate/Diethyl Carbonate Mixture by Using Ionizing Radiation

Radiolysis of Electrolytes in Batteries: A Quick and Efficient Screening Process for the Selection of Electrolyte-Additive Formulations

Understanding aging phenomena in batteries is crucial to the design of efficient, safe, and reliable energy storage devices as a part of the current green energy transition. Among the different aspects of a battery, the behavior of the electrolyte is a key parameter. Therefore, screening the aging characteristics of different electrolytes is of major interest. However, few screening studies exist because these are time-consuming and require the monitoring of numerous charge and discharge cycles. It has been demonstrated here that radiation chemistry, i.e., the interaction between ionizing radiation and matter, is a valuable tool to screen the behavior of various electrolytes within a few hours. Indeed, the rapid radiolysis of electrolytes leads to the production of the same gases as produced by electrochemical cycling (i.e., H₂ , CO₂ ), and the ranking of electrolytes by their H₂ production yields similar performance ratings to those reported in the literature. Therefore, this direct comparison of electrolytes alone, lasting a few hours without any manufacturing operations such as the fabrication of electrochemical cells, demonstrates that controlled irradiation makes it possible to predict battery cycling behavior. Additionally, mechanisms involved in the degradation processes of different electrolytes are proposed.

Probing the Electrode-Electrolyte Interface of a Model K-Ion Battery Electrode─The Origin of Rate Capability Discrepancy between Aqueous and Non-Aqueous Electrolytes

Li-ion batteries are the electrochemical energy storage technology of choice of today's electrical vehicles and grid applications with a growing interest for Na-ion and K-ion systems based on either aqueous or non-aqueous electrolyte for power, cost, and sustainable reasons. The rate capability of alkali-metal-ion batteries is influenced by ion transport properties in the bulk of the electrolyte, as well as by diverse effects occurring at the vicinity of the electrode and electrolyte interface. Therefore, identification of the predominant factor affecting the rate capability of electrodes still remains a challenge and requires suitable experimental and computational methods. Herein, we investigate the mechanistic of the K⁺ insertion process in the Prussian blue phase, Fe4III[FeII(CN)6]3 in both aqueous and non-aqueous electrolytes, which reveals drastic differences. Through combined electrochemical characterizations, electrochemical-quartz-crystal-microbalance and ac-electrogravimetric analyses, we provide evidences that what matters the most for fast ion transport is the positioning of the partially solvated cations adsorbed at the material surface in aqueous as opposed to non-aqueous electrolytes. We rationalized such findings by molecular dynamics simulations that establish the K⁺ repartition profile within the electrochemical double layer. A similar trend was earlier reported by our group for the aqueous versus non-aqueous insertion of Li⁺ into LiFePO₄. Such a study unveils the critical but overlooked role of the electrode-electrolyte interface in ruling ion transport and insertion processes. Tailoring this interface structuring via the proper salt-solvent interaction is the key to enabling the best power performances in alkali-metal-ion batteries.

Reaction Mechanisms of the Degradation of Fluoroethylene Carbonate, an Additive of Lithium-Ion Batteries, Unraveled by Radiation Chemistry

Numerous additives are used in the electrolytes of lithium-ion batteries, especially for the formation of an efficient solid electrolyte interphase at the surface of the electrodes. Understanding the degradation processes of these compounds is thus important; they can be seen through radiolysis. In the case of fluoroethylene carbonate (FEC), picosecond pulse radiolysis experiments evidenced the formation of FEC^.- . This radical is stabilized in neat FEC, whereas the ring opens to form more stable radical anions when FEC is a solute in other solvents, as confirmed by quantum chemistry calculations. In neat FEC, pre-solvated electrons primarily undergo attachment rather than solvation. On long timescales, the gases produced (H₂ , CO, and CO₂ ) were quantified. A reaction scheme for both the oxidizing and reducing pathways at stake in irradiated FEC is proposed. This work shows that the nature of the primary species formed in FEC depends on the amount of FEC in the solution.

Solution-Processable Thermally Crosslinked Organic Radical Polymer Battery Cathodes

Organic radical polymers are promising cathode materials for next-generation batteries because of their rapid charge transfer and high cycling stability. However, these organic polymer electrodes gradually dissolve in the electrolyte, resulting in capacity fade. Several crosslinking methods have been developed to improve the performance of these electrodes, but they are either not compatible with carbon additives or compromise the solution processability of the electrodes. A one-step post-synthetic, carbon-compatible crosslinking method was developed to effectively crosslink an organic polymer electrode and allow for easy solution processing. The highest electrode capacity of 104 mAh g^-1 (vs. a theoretical capacity of 111 mAh g^-1 ) is achieved by introducing 1 mol % of the crosslinker, whereas the highest capacity retention (99.6 %) is obtained with 3 mol % crosslinker. In addition, mass transfer was observed in situ by using electrochemical quartz crystal microbalance with dissipation monitoring. These results may guide future electrode design toward fast-charging and high-capacity organic electrodes.

Chromatographic Techniques in the Research Area of Lithium Ion Batteries: Current State-of-the-Art

Lithium ion batteries (LIBs) are widely used in numerous application areas, including portable consumer electronics, medicine, grid storage, electric vehicles and hybrid electric vehicles. One major challenge during operation and storage is the degradation of the cell constituents, which is called aging. This phenomenon drastically reduces both storage lifetime and cycle lifetime. Due to numerous aging effects, originating from both the individual LIB cell constituents as well as their interactions, a wide variety of instruments and methods are necessary for aging investigations. In particular, chromatographic methods are frequently applied for the analysis of the typically used liquid non-aqueous battery electrolytes based on organic solvents or ionic liquids. Moreover, chromatographic methods have also been recently used to investigate the composition of electrode materials. In this review, we will give an overview of the current state of chromatographic methods in the context of LIB cell research.

Picosecond Pulse Radiolysis Study on the Radiation-Induced Reactions in Neat Tributyl Phosphate

The ultrafast radiolytic behavior of tributyl phosphate, TBP, has been investigated using 7 ps electron pulses with 7 MeV kinetic energy, from which two key species have been observed and characterized: the TBP solvated electron (e_TBP^-) and the TBP triplet excited state TBP* (³a) or its fragmentation products. The e_TBP^- exhibits a broad absorption band in the visible and near-infrared (NIR) spectrum, with a maximum beyond our 1500 nm detection limit. Nitromethane was used to scavenge e_TBP^- to confirm its absorption spectrum and to determine its associated rate coefficient, 1.0 × 10¹⁰ M^-1 s^-1. The electron's molar extinction coefficients were found by an isosbestic method using biphenyl as a solvated electron scavenger. The time-dependent radiolytic yield of e_TBP^- was also determined directly from 7 ps to 7 ns and compared with those in water, tetrahydrofuran, and diethyl carbonate. In less than 10 ns, the decay is not due to the reaction with other solvent molecules and is instead predominantly due to the reactions with cations issued from the proton transfer by the TBP radical cation (TBP^•+). In addition to e_TBP^-, another absorption band, stable up to 7 ns, was identified in the visible range. This has been attributed mainly to the TBP triplet excited state, TBP*(³a), by a combination of molecular modeling methodologies. Interestingly, we did not observe any absorption band in the visible nor in the NIR range arising from TBP^•+. Calculations suggest that TBP^•+ undergoes rapid proton transfer to yield a UV-absorbing species, TBP(-H⁺). Experimental results and supporting molecular simulations provide detailed identification of the earliest species yielded from the radiolysis of neat TBP.