Anindityo Arifiadi

Si‐based anodes (e.g., SiO _x ) can increase the specific energy of Li‐ion batteries but decrease cycle life due to volume change‐reasoned material stress, which requires continuous reformation of the solid electrolyte interphase (SEI) at the cost of active Li loss (ALL). Even in small ratios within a binary anode with graphite, Si can be exposed to a high state‐of‐charge as it can be stressed by transfer lithiation from lithiated graphite. SEI engineering via rational design of electrolyte additives can be an eligible measure, but is particularly challenging, as the SEI must effectively passivate and prevent detrimental SiO _x |LiPF ₆ contact in order to suppress failure cascades caused by generated HF (e.g., electrode crosstalk), while efficiently minimizing ALL. Also, theoretically, the recovery of the “SEI waste” stemming from the continuous SEI reformation can be advantageous and, for example, be realized via a designed and controlled electrolyte solubility, where the respective diffusion toward the cathode would compensate ALL by oxidation reactions. Here, an easily modifiable B‐based compound (dioxazaborole) is synthesized and exemplarily investigated. While it forms a partly effective SEI and can be suitable for “SEI‐waste” recovery, the remaining challenges of gassing and resistance require further design optimization, consequently highlighting the difficulty of an “allrounder” additive.

The specific energy of Li ion batteries with layered‐oxide‐based cathodes can be enhanced by enhancing charge cut‐off voltage, which increases both, mean discharge voltage and capacity. However, the increased delithiation capacity facilitates thermodynamically‐driven phase changes and increases transition metal (TM) dissolution, finally initiate a failure cascade, known as “electrode crosstalk”. This can trigger formation of high surface area lithium (HSAL), active Li/capacity loss, and consequently decrease the cycle life. Here, after screening of bio‐based additives, the maleimide (MI) is shown to be even superior compared to the effective and literature‐known TM‐scavenging additive lithium difluorophosphate (LiDFP). Although, the electrode crosstalk and the TM amount on the anode are not suppressed with MI, the anode surface remains intact, and is even free from HSAL deposits. The solid electrolyte interphase (SEI) is shown to consist from oligo and polymer‐based MI decomposition products and is concluded to scavenge TMs on the outer SEI layer via its characteristic coordinating chemistry. This way the TM diffusion toward the inner SEI layer is suppressed, where it otherwise would block the Li ⁺ pathway and initiate the well‐known failure cascades, that is, locally increase resistance, trigger HSAL formation and capacity fade, in worst case rollover failure.

Incorporating silicon‐based active materials, e.g., SiO _x , into the negative electrodes can increase the gravimetric/volumetric energy of Li ion batteries. Nevertheless, SiO _x shortens cycle life due to the large volume expansion during charge/discharge cycling. The mechanical stress on the solid electrolyte interphase (SEI) necessitates continuous SEI repair, which accelerates active lithium loss (ALL) over cycling. In this work, the impact of common lithium salts is investigated in electrolytes for LiNi _0.5 Co _0.2 Mn _0.3 O ₂ (NCM 523) || 10%SiO _x ‐graphite Li ion pouch cells. The end‐of‐life (EOL) with LiPF ₆ can be enhanced by anode passivation via fluoroethylene carbonate (FEC), which not only decreases ALL but also suppresses failure cascades (e.g., electrode crosstalk) initiated by HF over the course of SiO _x reactions with LiPF ₆ . Though ALL remains similar when adding FEC to lithium bis(oxalato)borate (LiBOB), it enhances the generation of active Li through oxidation reactions at the cathode, likely due to the inverse crosstalk of partly soluble SEI species. This “self‐healing” or “recovery” mechanism reactivates the apparently “wasted SEI” and formerly lost capacity, thereby enhancing cycle life. This positive effect is even more pronounced with LiDFOB. However, the accompanying gassing of the oxalato‐based salts remains an obstacle to practical applicability.

The mechanical stress resulting from volume changes during lithiation and delithiation cycles of silicon-containing anodes in high-energy-density lithium ion batteries (LIBs) causes continuous solid electrolyte interphase (SEI) breakdown. This results in constant SEI reformation and thus, loss of active lithium, ultimately reducing battery lifetime. To address these challenges, tailored electrolyte formulations incorporating molecular additives are being increasingly investigated to improve SEI stability and enhance electrochemical performance. In recent years, molecular electrolyte additives such as dioxazolones, ^[1,2] O -Carboxyanhydrides (OCAs), ^[3] and N -Carboxyanhydrides (NCAs) ^[4,5] have been introduced to enhance SEI robustness in LIBs. Herein, a novel and easily synthesizable class of compounds, dioxazaboroles – specifically, 2,5-diphenyl-1,3,4,2-dioxazaborole (DOB) – as an electrolyte additive for NCM 523 || 10%SiO _x -graphite lithium ion cells is presented. The effects of DOB on SEI formation, long-term cycling performance, self-discharge, gassing behavior, and interphase chemistry are investigated. This work demonstrates that DOB effectively enhances SEI durability, leading to a prolonged cycle life compared to cells with fluoroethylene carbonate (FEC) as a state-of-the-art additive. The improved performance is attributed to the DOB-derived SEI, which provides enhanced stabilization against the large volumetric fluctuations of the silicon-containing anode – thus contributing to the longevity of the cell. However, the instability of this SEI at elevated temperatures and high states of charge leads to increased self-discharge and more gassing compared to FEC-containing cells. This study highlights the critical role of rational electrolyte additive design and the necessity for comprehensive additive evaluations that go beyond cycle life improvements to ensure overall performance enhancements while maintaining practicability in terms of price and synthesis effort. References: [1] S. Röser, A. Lerchen, L. Ibing, X. Cao, J. Kasnatscheew, F. Glorius, M. Winter, R. Wagner, Chem. Mater. 2017 , 29 , 7733–7739. [2] D. S. Hall, T. Hynes, J. R. Dahn, J. Electrochem. Soc. 2018 , 165 , A2961–A2967. [3] R. Nölle, J.-P. Schmiegel, M. Winter, T. Placke, Chem. Mater. 2020 , 32 , 173–185. [4] J.-P. Schmiegel, R. Nölle, J. Henschel, L. Quach, S. Nowak, M. Winter, F. Glorius, T. Placke, Cell Rep. Phys. Sci. 2021 , 2 , 100327–100352. [5] L. Quach, E. Adhitama, ^§ V. Göldner, ^§ A. Das, F. Demelash, M. Winter, U. Karst, T. Placke, F. Glorius, ACS Appl. Energy Mater. 2023 , 6 , 9837–9850. This work: S. Heuvel, ^§ A. Arifiadi, ^§ L. Balke, ^§ N. M. Abke, A. Tsoufios, J. Buchmann, B. T. Manard, C. D. Quarles Jr., S. Novak, M. Winter, U. Karst, F. Glorius,* J. Kasnatscheew,* manuscript in preparation . Figure 1

Among different approaches, the prelithiation via sacrificing additives is at least technically readily applicable. In this work, lithium squarate (Li₂C₄O₄) as a literature-known representative is investigated in zero-excess lithium metal batteries. These batteries are simple in handling and have high active lithium loss (ALL), thus ideal for R&D of sacrificing additives. When incorporated via cathode, Li₂C₄O₄ oxidizes at a relatively low cathode potential (~4.5 V vs. Li|Li⁺) and provides the aimed active Li (= capacity). However, the gaseous evolution of CO and CO ₂ visually rupture the cathode composite. Interestingly, when incorporated via electrolyte, the additive oxidation is absent and is attributed to its reductive depletion in course of solid electrolyte interphase (SEI) formation. In line with computational analysis its reduction is indeed before the reduction of other electrolyte components according to lowest unoccupied molecular orbital (LUMO). Hence, the squarate is impractical as an additive in electrolytes combined with anodes, which in operando form the SEI ( e.g., graphite, Si). In Li metal cells, i.e., with an already existing “preformed” native SEI, the squarate oxidation can be seen again, but the oxidation onset sensitively depends on the cathode type and electrolyte formulation. Figure 1

Li/Mn‐rich layered oxide (LMR) cathode active materials offer a pathway towards high specific energy and low‐cost Li ion batteries (LIBs) due to their high practical specific discharge capacity (>250 mAh g ⁻¹ ) at moderate discharge voltages (≈3.5 V). However, oxygen redox requires electrochemical activation at high cathode potentials (> 4.5 V vs Li|Li ⁺ ), resulting in bulk degradation and surface reactivity. This perspective first summarizes the literature‐known efforts to elucidate the oxygen redox mechanism and then proposes strategies for systematic R&D of LMR, supported with techno‐economic analysis. Initially, bulk degradation should be addressed via compositional tuning and crystal modification. Subsequently, the microstructure, interphase, and electrolyte should be engineered, and finally, the charging protocol should be optimized. The various LMR chemistries with different Li to TM , Ni to Mn, and Co to Ni ratios are techno‐economically analyzed, and perspectives on the ideal LMR composition are presented. Ultimately, the specific energy, energy density, and costs of LMR || graphite cells are compared to state‐of‐the‐art cell chemistries.

The development of next‐generation Lithium‐ion batteries (LIBs) to meet the demands of advancing technology and energy storage requires focus on the formation of effective interphases on both the positive and negative electrodes. Different promising approaches to facilitate effective interphase formation are already known Out of these, the incorporation of film‐forming electrolyte additives is a straight‐forward strategy to achieve this goal. In the presented study, a bifunctional electrolyte additive, (5‐methyl‐2‐oxo‐1,3‐dioxol‐4‐yl)methyl thiophene‐3‐carboxylate composed of two functional motifs, vinylene carbonate (VC) and thiophene, is reported. Upon LIB operation, the additive undergoes in situ splitting, forming a VC‐assisted solid electrolyte interphase (SEI) and a polythiophene‐based cathode electrolyte interphase (CEI) simultaneously. The electrochemical performance of the proposed additive is studied in 250 mAh NMC811||AG + 20% SiO _x wound pouch cells, and shows considerable improvement in overall battery performance compared to cells with the baseline electrolyte. The additive's dual interphase formation is confirmed through a combination of advanced characterization techniques, including X‐ray photoelectron spectroscopy (XPS), scanning electron microscopy (SEM), and operando shell‐isolated nanoparticle‐enhanced Raman spectroscopy (SHINERS). This study introduces a new design strategy for a multifunctional electrolyte additive, providing a promising pathway to improve overall LIB's performance and lifetime by simultaneous stabilization of both electrodes through facilitated interphase formation.