Abstract Leveraging physicochemical advantages over lithium hexafluorophosphate (LiPF6), lithium bis(fluorosulfonyl)imide (LiFSI) is being investigated as a conducting salt for lithium manganese‐rich cathodes (LMR) and micro‐crystalline silicon anodes (μ‐Si). Nevertheless, its behavior towards the aluminum (Al) current collector and stainless‐steel (SUS) coin cell parts limits its application under operating conditions requiring potentials higher than 3.9 V vs. Li|Li+. Using a mixture of organic carbonate‐based solvents, various functional additives, and LiPF6 lithium salt concentrations up to 1.0 M, the instability issue of the Al current collector in the presence of LiFSI is avoided. However, stainless‐steel dissolution remains, being confirmed by both potentiodynamic measurements and SEM morphology investigations of the coin cell components after linear sweep voltammetry measurements carried out to 5.0 V. The results also indicate that the amount of stainless‐steel dissolution is influenced by both the LiFSI amount in the electrolyte and the quality (grade) of stainless‐steel used. Using Al‐coated SUS 316L coin cell parts and/or high concentration electrolytes (HCE) with LiFSI (≈4 M LiFSI), the observed stainless‐steel dissolution process can be fully avoided, allowing the evaluation of the electrochemical performance of LMR cathodes with μ‐Si anodes in LiFSI‐based electrolytes.

Solid-state batteries based on lithium metal anodes, solid electrolytes, and composite cathodes constitute a promising battery concept for achieving high energy density. Charge carrier transport within the cells is governed by solid-solid contacts, emphasizing the importance of well-designed interfaces. A key parameter for enhancing the interfacial contacts among electrode active materials and electrolytes comprises externally applied pressure onto the cell stack, particularly in the case of ceramic electrolytes. Reports exploring the impact of external pressure on polymer-based cells are, however, scarce due to overall better wetting behavior. In this work, the consequences of externally applied pressure in view of key performance indicators, including cell longevity, rate capability, and limiting current density in single-layer pouch-type NMC622||Li cells, are evaluated employing cross-linked poly(ethylene oxide), xPEO, and cross-linked cyclodextrin grafted poly(caprolactone), xGCD-PCL. Notably, externally applied pressure substantially changes the cell's electrochemical cycling performance, strongly depending on the mechanical properties of the considered polymers. Higher external pressure potentially enhances electrode-electrolyte interfaces, thereby boosting the rate capability of pouch-type cells, despite the fact that the cell longevity may be reduced upon plastic deformation of the polymer electrolytes when passing beyond intrinsic thresholds of compressive stress. For the softer xGCD-PCL membrane, cycling of cells is only feasible in the absence of external pressure, whereas in the case of xPEO, a trade-off between enhanced rate capability and minimal membrane deformation is achieved at cell pressures of ≤0.43 MPa, which is considerably lower and more practical compared to cells employing ceramic electrolytes with ≥5 MPa external pressure.

Single lithium-ion conducting polymers represent a promising class of electrolytes that potentially enable the utilization of lithium metal anodes in next-generation batteries. The immobilization of anions within the polymer's structure in principle mitigates issues related to localized ion depletion, resulting in decreased cell polarization when compared to common dual-ion conductors comprising poly(ethylene oxide) and lithium salt. However, the intrinsic rigidity of these materials often necessitates incorporation of flowable components and blending with other polymers, such as poly(vinylidene fluoride-co-hexafluoropropylene) (PVdF-HFP), to enhance the mechanical flexibility of the resulting polymer membranes. Within polymer blends, distinct phases may be present, and the distribution of plasticizers among these phases is highly crucial as they act as carrier molecules for Li+ transport. In this study, we thus explored the impact of polymer chain modification from a rigid aromatic single-ion conducting polymer to a more flexible polymer by introducing ethylene glycol units into the backbone. Notably, this alteration yielded a substantial decrease of 100 degrees C of the glass transition temperature and a 6-fold increase in ionic conductivity (0.5 mS cm(-1) @ 40 degrees C) after blending with PVdF-HFP and addition of ethylene carbonate/dimethyl carbonate. Atomistic molecular dynamics simulations suggest that this enhancement can be attributed to a high concentration of plasticizer within the Li+ containing phase. In symmetric Li||Li cells, exceptional performance was achieved, demonstrating operation at high limiting current density and successful plating/stripping for 1000 h at 0.2 mA cm(-2). When paired with high-voltage NMC cathodes, the introduced polymer structures exhibited noteworthy capacity retention after 800 cycles, emphasizing advantages brought forth by flexible and adapted polymer architecture.

Polymer electrolytes are attractive candidates to boost the application of rechargeable lithium metal batteries. Single-ion conducting polymers may reduce polarization and lithium dendrite growth, though these materials could be mechanically overly rigid, thus requiring ion mobilizers such as organic solvents to foster transport of Li ions. An inhomogeneous mobilizer distribution and occurrence of preferential Li transport pathways eventually yield favored spots for Li plating, thereby imposing additional mechanical stress and even premature cell short circuits. In this work, we explored ceramic-in-polymer hybrid electrolytes consisting of polymer blends of single-ion conducting polymer and PVdF-HFP, including EC/PC as swelling agents and silane-functionalized LATP particles. The hybrid electrolyte features an oxide-rich layer that notably stabilizes the interphase toward Li metal, enabling single-side lithium deposition for over 700 h at a current density of 0.1 mA cm-2. The incorporated oxide particles significantly reduce the natural solvent uptake from 140 to 38 wt % despite maintaining reasonably high ionic conductivities. Its electrochemical performance was evaluated in LiNi0.6Co0.2Mn0.2O2 (NMC622)||Li metal cells, exhibiting impressive capacity retention over 300 cycles. Notably, very thin LiNbO3 coating of the cathode material further boosts the cycling stability, resulting in an overall capacity retention of 78% over more than 600 cycles, clearly highlighting the potential of hybrid electrolyte concepts.

Silicon (Si) is one of the most promising candidates for application as high-capacity negative electrode (anode) material in lithium ion batteries (LIBs) due to its high specific capacity. However, evoked by huge volume changes upon (de)lithiation, several issues lead to a rather poor electrochemical performance of Si-based LIB cells. The Coulombic efficiency (C-Eff) during the first cycle(s), especially when using nano-sized Si, is relatively low, due to the formation of the solid electrolyte interphase (SEI). Pre-lithiation approaches can increase the C-Eff by compensating active lithium losses during the first cycle(s). Here, we evaluate the beneficial impact of pre-lithiated Si/C electrodes for their application in NCM111 parallel to Si/C cells by comparing two approaches, i. e., electrochemical pre-lithiation and pre-lithiation by direct contact to Li metal foil. The SEI composition and surface morphology of pre-lithiated Si/C electrodes as well as the impact of reducing active Li losses on individual electrode potentials over cycling are revealed. For long-term cycling, both pre-lithiation techniques lead to a distinct improvement of the overall capacity as well as the C-Eff for the first 40 cycles due to i) the pre-formed SEI and ii) a Li reservoir within the anode. Depletion of the active Li from NCM111 is significantly reduced and we can confirm that both pre-lithiation techniques improve the cycling performance of NCM111 parallel to Si/C cells in an almost equal manner.

Due to its low cost, high abundance and non-toxicity zinc metal is a very promising electrode material for rechargeable batteries. The main drawback of using zinc in aqueous alkaline solutions is the formation of zinc dendrites, which lead to cell failure, and a low coulombic efficiency. In this study the suppression of dendritic zinc growth by applying either pure 1-ethylimidazolium trifluoromethane sulfonate or 1-ethylimidazolium trifluoromethane sulfonate / water mixtures with zinc trifluoromethane sulfonate as electrolyte formulations was examined. The surface morphology of the deposited zinc is significantly influenced by the amount of water present in the electrolyte. Cyclic voltammetry measurements showed a less negative reduction potential of zinc with increasing water content. Additionally, the presence of air in the electrolyte proved to be another factor influencing the cyclic voltammetry results. Furthermore, galvanostatic cycling data showed a lowering of the overpotential and constant potentials during long-term cycling of 100 cycles if water is present in the electrolyte, and SEM micrographs confirmed that the surface structure remains compact even after long-term cycling. (C) 2019 The Electrochemical Society.