Galvanostatic Cycling Research Articles

Pillar[5]arene-supported viologen networks with enhanced rate capability and cycling stability for rechargeable organic batteries

Organic redox-active compounds are promising alternatives to traditional inorganic counterparts because of their sustainable resources and highly tunable properties. However, their solubility in organic electrolyte solvents and the sluggish electrode reactions hinder their further development. Herein, an intrinsically microporous decabromopropyl pillar[5]arene (P5Br) was used to support the methyl viologen (MV) functionality to yield two non-crosslinked and crosslinked organic electrode materials, namely MV-P5Br and CMV-P5Br, respectively. When evaluating against Li metal counter electrode, the MV-P5Br and CMV-P5Br electrodes delivered high discharge capacities of 87.9 and 92.7 mAh g−1 at 0.1 C, respectively, which are close to their theoretical values. After galvanostatic cycling at 0.1 C for 100 cycles, the CMV-P5Br electrode maintained a discharge capacity of 82.3 mAh g−1, much higher than the 43.7 mAh g−1 of the MV-P5Br electrode. When the current rate was increased to 10 C, the CMV-P5Br electrode delivered a discharge capacity of 60.7 mAh g−1, also higher than the 41.3 mAh g−1 of the MV-P5Br electrode. The increased cycling stability and rate performance of the CMV-P5Br electrode were attributed to the diminished solubility and the enhanced ion diffusion coefficient of the active material. When the counter electrode was changed to Na metal, similar results were obtained, suggesting that the CMV-P5Br electrode can also be used in Na-ion systems. This study demonstrates that the combination of crosslinked and microporous structure is highly effective to boost the electrochemical performance of organic redox-active compounds for rechargeable batteries.

High conductive poly(1,8-diaminonaphthalene)/graphene nanocomposite as a cathode for zinc ion batteries

Recently, aqueous zinc ion batteries (AZIBs) are experiencing rapid development benefiting to their high safety and increasing electrochemical performance. Among all kinds of AZIB electrode materials, organic materials have attracted attentions due to their unique advantages such as structural flexibility, small volume expansion, abundant Zn2+ storage sites and environmental friendliness. However, issues involving electrode dissolution, sluggish electrochemical kinetics etc. still hampered the prior choice of organic electrodes. Herein, we designed a poly(1,8-diamino-naphthalene)/ graphene composite aiming to improve the availability of organic electrodes in AZIBs. By means of constructing high conducting graphene network and the synergetic effect between the two components, the electronic transfer kinetics and overall electrochemical performance of PDAN organic electrode have been fully improved. The organic-inorganic composite exhibited an initial specific capacity of 240 mA·h·g−1 and stable galvanostatic cycling after 1000 cycles, exceeding the original polymer.

Role of Co Content on the Electrode Properties of P3-Type K0.5Mn1-xCoxO2 Potassium Insertion Materials.

Potassium-ion batteries are widely being pursued as potential candidates for stationary (grid) storage, where energy dense K+ insertion cathodes are central to economic and energy efficient operation. To develop robust K-based cathodes, it is key to correlate their underlying electronic states to the final electrochemical performance. Here, we report the synthesis and structure-electrochemical property correlation in P3-type K0.5Mn1-xCoxO2 binary layered oxide cathodes. Spectroscopic analyses revealed a random distribution of Mn and Co in transition metal layers in the oxygen anion framework. In this solid-solution family, Co substitution improved the electronic conductivity and structural stability of P3 phases by minimizing local lattice distortion. Co substitution led to a systematic shift of the Co4+/Co3+ and Mn4+/Mn3+ redox potentials. Galvanostatic cycling showed that the Co substitution reduced the initial capacity while improving the cycling stability. The role of Co on final electrochemical properties of P3-layered oxides has been elucidated as a design tool to develop practical potassium-ion batteries.

Nano Scale Poly(vinylidene chloride-co-acrylonitrile) Protection for Reversible and Stable Mg Anode Interface

This study investigates the efficacy of a polymer coating, PVdC-co-AN, in enhancing the stability and reversibility of the electrochemical Mg anode interface. Coated electrodes, immersed in a 0.25 M Mg(TFSI)2−0.50 M MgCl2/dimethoxyethane (DME) electrolyte, exhibit notable improvements. Cyclic voltammetry demonstrates consistent behavior with the coated electrode, while the uncoated electrode changes dramatically. During extended open circuit potential conditions, the coated electrode maintains much higher coulombic efficiency (93%) compared to the uncoated electrode (62%). Galvanostatic cycling test over 200 cycles further show the benefits of the PVdC-co-AN coating, decreasing the overpotential of Mg plating and improving long-term stability. The coated electrodes also demonstrate improved rate capability at higher current densities. Surface analysis reveals differences in the formation of byproducts between the coated and uncoated electrodes, indicating a more stable and uniform interface in the former. Nuclear magnetic resonance (NMR) spectroscopy suggests that the polymer influences ion mobility through tuning the solvation environments which results in better kinetics and fewer byproducts. In summary, the study affirms that the PVdC-co-AN coating significantly improves the stability and performance of Mg electrochemistry, offering a promising advancement for practical battery applications.

Tailored Yolk-Shell Design to Silicon Microparticles via Scalable and Template-Free Synthesis for Superior Lithium Storage.

Micrometer-sized Si particles are beneficial to practical lithium-ion batteries in regard to low cost and high volumetric energy density in comparison with nanostructured Si anodes. However, both the issues of electrical contact loss and overgrowth of solid electrolyte interface for microscale Si induced by colossal volume change still remain to be addressed. Herein, a scalable and template-free method is introduced to fabricate yolk-shell structured Si anode from commercially available Si microparticles. The void is created via a one-step alkali etching process with the remaining silicon core as the yolk, and a double-walled shell is formed from simultaneous in situ growth of the conformal native oxide layer and subsequent carbon coating. In this configuration, the well-defined void spaces allow the Si core to expand without compromising structural integrity, while the double-walled shell acts as a static capsule to confine silicon fragments despite likely particle fracture. Therefore, electrical connectivity is maintained on both the particle and electrode level during deep galvanostatic cycling, and the solid-electrolyte interface is stabilized on the shell surface. Owing to the benefits of tailored design, excellent cycling stability (capacity retention of 95% after 100 cycles) and high coulombic efficiency (99.5%) are realized in a practical full-cell demonstration.

Pseudocapacitive Kinetics in Synergistically Coupled MoS2-Mo2N Nanowires with Enhanced Interfaces toward All-Solid-State Flexible Supercapacitors.

Pseudocapacitive kinetics in rationally engineered nanostructures can deliver higher energy and power densities simultaneously. The present report reveals a high-performance all-solid-state flexible symmetric supercapacitor (FSSC) based on MoS2-Mo2N nanowires deposited directly on stainless steel mesh (MoS2-Mo2N/SSM) employing DC reactive magnetron co-sputtering technology. The abundance of synergistically coupled interfaces and junctions between MoS2 nanosheets and Mo2N nanostructures across the nanocomposite results in greater porosity, increased ionic conductivity, and superior electrical conductivity. Consequently, the FSSC device utilizing poly(vinyl alcohol)-sodium sulfate (PVA-Na2SO4) hydrogel electrolyte renders an outstanding cell capacitance of 252.09 F·g-1 (44.12 mF·cm-2) at 0.25 mA·cm-2 and high rate performance within a wide 1.3 V window. Dunn's and b-value analysis reveals significant energy storage by surface-controlled capacitive and pseudocapacitive mechanisms. Remarkably, the symmetric device boosts tremendous energy density ∼10.36 μWh·cm-2 (59.17 Wh·kg-1), superb power density ∼6.5 mW·cm-2 (37.14 kW·kg-1), ultrastable long cyclability (∼93.7% after 10,000 galvanostatic charge-discharge cycles), and impressive mechanical flexibility at 60°, 90°, and 120° bending angles.

Porous MCM‐41 Silica Materials as Scaffolds for Silicon‐based Lithium‐ion Battery Anodes

AbstractAiming for specific energy improvements, lithium‐ion battery (LIB) research explores Si based materials as potential alternatives for the negative electrode/anode. Si exhibits a high specific capacity when lithiated, accompanied by a large volumetric expansion. To mitigate expansion induced failures, composite materials with finely distributed Si inside a scaffold have been established. Potential scaffolds to create such Si composites are nano porous SiO2 materials, such as MCM‐41. MCM‐41 exhibits a fine nanostructure, and the synthesis allows precise tuning of the pore properties and thus, after filling with Si, of Si morphology and Si content in the composite. In this work, insights into relevant MCM‐41 synthesis parameters are acquired, with special attention towards specific pore volumes and pore sizes of the SiO2 powders. Materials characterization is performed using nitrogen sorption analysis, X‐ray scattering, electron microscopy and thermogravimetric analysis. Selected MCM‐41 scaffolds are processed to Si composites and integrated into LIB electrodes. The specific capacity and the stability of the Si−SiO2 composites are evaluated by PITT and galvanostatic cycling. They show capacities above 800 mAh g−1, i. e. more than twice the specific capacity of industry standard graphite, and last over 200 charge/discharge cycles before their capacity loss exceeds 25 %.

Superior compatibility of silicon nanowire anodes in ionic liquid electrolytes

Silicon nanowire anodes were investigated in lithium-metal cells using different electrolyte formulations based on 1-ethyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide, 1-ethyl-3-methylimidazolium bis(fluorosulfonyl)imide and N -trimethyl-N -butyl-ammonium bis(fluoro sulfonyl)imide ionic liquids. The lithium insertion process in the silicon anode was analyzed by cyclic voltammetry measurements, performed at different scan rates and for prolonged cycles, combined with impedance spectroscopy analysis. A galvanostatic charge-discharge cycling test was performed to analyze the electrochemical performances using different types of ionic liquids. A study of the Solid Electrolyte Interphase layer on the silicon nanowire electrode surface was carried out through X-ray photoelectron spectroscopy. In general, the silicon anodes in 1-ethyl-3-methylimidazolium bis(fluorosulfonyl)imide-based electrolytes show very good reversibility, reproducibility, and efficiency in the lithiation process, even at high scan rates, and exhibit a reversible capacity exceeding 1,000 mA h g-1 after 2,000 charge-discharge cycles, corresponding to 46% of the initial value.

Win-Win on both ion-conducting and mechanical properties achieved in PEO-based solid electrolytes through microstructure regulation

Solid state electrolytes are of great importance in the design of all-solid-state lithium metal batteries (ASLMBs) that with excellent properties and glorious working stability. And solid polymer electrolytes (SPEs) are the attention-getting candidate, because of its flexibility lightweight and suitable ionic transportation ability. However, current SPEs always need balance between ionic conductivity (σ) and the mechanical strength. To this end, organic-inorganic composite solid-state electrolytes (CSEs) are designed by introduction of BN nanosheets into the polymer matrix, coupled with using the electrospinning technique. It is proved show that the PEO crystallinity in the fibrous electrolyte is significantly suppressed, with only 1 wt% BN adding. And the σ of the designed sample is raised to 1.93×10−4 S∙cm−1 at 40 ℃, on account of that the BN layered structure and three-dimensional fibrous framework help to provide dual channels for Li+ transport. Also better interfacial miscibility with Li metal is realized in the obtained fibrous CPEs and the Galvanostatic cycling of the symmetric Li//Li cell sustains as long as 850 h with 0.1 mA·cm−2 current density. Compared with the solution-casted sample with the same composition, the tensile strength (0.88 MPa) and electrochemical stability of the electrospun membrane (5.1 V) are both significantly enhanced. In addition, the obtained LiFePO4|PEO/LiClO4/BN CSE|Li all solid state coin cells exhibit excellent cycling and rate performances. The initial discharge specific capacity reaches to 144.1 mAhg−1. And coin cells cycled at 1 C current and at 80℃ give a capacity retention ratio of 81.1% after 200 cycles. It demonstrates that thin and flexible CSEs with excellent electrochemical performance can be accomplished through electrospining technique.

Methylene Blue in a High-Performance Hydrogen-Organic Rechargeable Fuel Cell.

A hydrogen-organic hybrid flow battery (FB) has been developed using methylene blue (MB) in an aqueous acid electrolyte with a theoretical positive electrolyte energy storage capacity of 65.4 A h L-1. MB paired with the versatile H2/H+ redox couple at the negative electrode forms the H2-MB rechargeable fuel cell, with no loss in capacity (5 sig. figures) over 30 100% discharge cycles of galvanostatic cycling at 50 mA cm-2, which shows excellent stability. A peak power density of 238 mW cm-2 has also been demonstrated by utilizing 1.0 M MB electrolyte. This represents a type of scalable electrochemical energy storage system with favorable properties in terms of material cost, stability, crossover management, and energy and power density, overcoming many typical limitations of organic-based redox FBs.

Evaluation of electrochemical performance of supercapacitors from equivalent circuits through cyclic voltammetry and galvanostatic charge/discharge

Conventional methods used to analyze electrochemical performance of supercapacitors are complex and cannot illustrate the asymmetrical behavior of charge and discharge curves and the variation of resistance with scan rate and current density. In this work, we propose a simple method to calculate total capacitance and internal resistance of supercapacitors with equivalent circuits and discuss the mechanisms responsible for the asymmetry of galvanostatic charge discharge (GCD) curves. Using the equivalent circuits, we demonstrate the feasibility of analyzing electrochemical performance of supercapacitors from the current-voltage curve for cyclic voltammetry (CV) and the GCD curves for galvanostatic cycling. A series of supercapacitors are constructed, in which the electrodes are pre-compressed under a compressive stress in a range of 1– 7.5 MPa. The experimental results reveal that the total capacitance of the supercapacitors increases with increasing the pre-compressive stress and validated the proposed method. Increasing the pre-compressive stress likely can improve the electrochemical performance of supercapacitors. The results from the analysis with the analytical relations for the resistance of the resistor in parallel connection in the three-element circuit approaching infinity exhibit similar trends to the corresponding ones from the conventional methods in contrast to the results from the three-element circuit, which exhibit different trends. The three-element circuit with the resistor in parallel connection approaching infinity can be used to analyze the electrochemical performance of supercapacitors for both the CV and GCD operational conditions.

Phase Engineering via Aluminum Doping Enhances the Electrochemical Stability of Lithium-Rich Cobalt-Free Layered Oxides for Lithium-Ion Batteries.

Lithium-rich, cobalt-free oxides are promising potential positive electrode materials for lithium-ion batteries because of their high energy density, lower cost, and reduced environmental and ethical concerns. However, their commercial breakthrough is hindered because of their subpar electrochemical stability. This work studies the effect of aluminum doping on Li1.26Ni0.15Mn0.61O2 as a lithium-rich, cobalt-free layered oxide. Al doping suppresses voltage fade and improves the capacity retention from 46% for Li1.26Ni0.15Mn0.61O2 to 67% for Li1.26Ni0.15Mn0.56Al0.05O2 after 250 cycles at 0.2C. The undoped material has a monoclinic Li2MnO3-type structure with spinel on the particle edges. In contrast, Al-doped materials (Li1.26Ni0.15Mn0.61-xAlxO2) consist of a more stable rhombohedral phase at the particle edges, with a monoclinic phase core. For this core-shell structure, the formation of Mn3+ is suppressed along with the material's decomposition to a disordered spinel, and the amount of the rhombohedral phase content increases during galvanostatic cycling. Whereas previous studies generally provided qualitative insight into the degradation mechanisms during electrochemical cycling, this work provides quantitative information on the stabilizing effect of the rhombohedral shell in the doped sample. As such, this study provides fundamental insight into the mechanisms through which Al doping increases the electrochemical stability of lithium-rich cobalt-free layered oxides.

Synthesis and Characterization of Modified Centrifuged-Electrospun Carbon Nanofibers for High-Performance Supercapacitor Electrodes

Background: Incorporating novel multifunctional effective materials into supercapacitors electrode is an ongoing requirement for hybrid supercapacitors with enhanced electrochemical performance. Methods: Herein, modified plasma-grafted multiwalled carbon nanotubes (CMS) with improved dispersion are embedded within centrifugal-spun carbon nanofibers as a hierarchical template (CNFs-CMS) to facilitate the growth of subsequent active materials. CNFs-CMS is then electroless plated with acicular nickel (Ni) balls, followed by one-step hydrothermal co-deposition to grow Ni(OH)2-MnO2 hybrid nanosheets. Significant findingsA binder-free, 3D interconnected nanostructures of CNFs-CMS@Ni@Ni(OH)2-MnO2 electrode material is employed for an all-in-one hybrid supercapacitor that exhibits excellent electric double layer (EDLC), battery-like and pseudocapacitance (PC) properties, along with a high surface area (665 m2 g−1) and conductivity (2.96 S cm−1). The as-fabricated electrode demonstrates specific capacitance (Cs) of 1063.33 F g−1 at a high current density of 20 A g−1 in 3M KOH electrolyte, maintaining capacitance retention of 92.5 % after 10,000 galvanostatic charge-discharge cycles. An asymmetric supercapacitor pairing CNFs-CMS@Ni@Ni(OH)2-MnO2 with CNFs-CMS is established, attributes comparably high energy density (52.54 Wh kg−1) and power density (59 kW kg−1) across a potential window of 1.2 V.

High‐performance symmetric supercapacitor using cost‐efficient iron oxide (Fe3O4) nanoparticles

AbstractWe investigated Fe3O4 nanoparticles (NPs) for a symmetric supercapacitor (SSC) under ambient conditions from synthesizing material to device fabrication. The prepared Fe3O4 NPs are characterized using different characterization, X‐ray diffraction, Raman and FTIR spectroscopy. The electrochemical performance of supercapacitor (SC) is measured in two electrode systems using coin‐cell assembly at various scan rates varying from 10–100 mV s−1, and cyclic voltammetry measurements are investigated from −0.8 to 0.6 V window. The Fe3O4 NPs based SSC shows an energy density of 24.99 Wh kg−1 with the high specific capacitance of 91.82 F g−1 at 10 mV s−1 scan rate. At a current rate of 4 A g−1, the power density reaches 2000 W kg−1. The Fe3O4 NPs based SSC exhibits a quick charge and discharge mechanism at various current rates and is stable over 500 galvanostatic chargingdischarging cycles at a current rate of 4 A g−1. The fabricated SSC showed >60% capacitance retention even after operating for 1000 cyclic voltammetry cycles at a scan rate of 100 mV s−1. A reasonable choice for SSC electrodes with high power density, and the outstanding resilience of electrodes is further shown by cyclic stability and impedance study exhibiting a negligible change in the different impedance elements. The potential of the fabricated SSC is demonstrated by lightening a light emitting diode (LED) light as a practical aspect for future applications.

Mechanically Robust and Highly Conductive Poly(ionic liquid)/Polyacrylamide Double-Network Hydrogel Electrolytes for Flexible Symmetric Supercapacitors with a Wide Operating Voltage Range.

Flexible electronic devices, such as supercapacitors (SCs), place high demands on the mechanical properties, ionic conductivity, and electrochemical stability of electrolytes. Hydrogels, which combine flexibility and the advantages of both solid and liquid electrolytes, will meet the demand. Here, we report the synthesis of novel poly(ionic liquid)/polyacrylamide double-network (DN) (PIL/PAM DN) hydrogel electrolytes containing different metal salts via a two-step γ-radiation method. The resultant Li2SO4-1.0/PIL/PAM DN hydrogel electrolyte possesses excellent mechanical properties (tensile strength of 3.64 MPa, elongation at break of 446%) and high ionic conductivity (24.1 mS·cm-1). The corresponding flexible SC based on the Li2SO4-1.0/PIL/PAM DN hydrogel electrolyte (SC-Li2SO4) presents improved ion diffusion, ideal electrochemical double-layer capacitor behavior, good rate capability, and excellent cyclic stability. Moreover, symmetric SC-Li2SO4 achieves a wide operating voltage range of up to 1.5 V, with a maximum energy density of 26.0 W h·kg-1 and a capacitance retention of 94.1% after 10,000 galvanostatic charge-discharge cycles, owing to the deactivation of free water molecules by the synergistic effect of PIL, PAM, and SO42-. Above all, the capacitance of SC-Li2SO4 is well-maintained after overcharge, overdischarge, short circuit, extreme temperature, compression, and bending tests, indicating its high security and flexibility. This work reveals the enormous application potential of PIL-based conductive hydrogel electrolytes for flexible electronic devices.

Ionogel hybrid polymer electrolytes encompassing room-temperature ionic liquids for 4V-class Li-metal batteries operating at ambient temperature

ABSTRACT In this study, we prepare ionogels composed of bisphenol A ethoxylate dimethacrylate, poly(ethylene glycol) methyl ether methacrylate, lithium bis(trifluoromethanesulfonyl)imide, and 1-butyl-1-methylpyrrolidinium bis(fluorosulfonyl)imide or 1-ethyl-3-methylimidazolium bis(fluorosulfonyl)imide ionic liquids via rapid, scalable, solvent-free UV-induced polymerization. The various hybrid polymer electrolyte formulations are thoroughly characterized using a comprehensive set of physico-chemical and electrochemical methods, including gel content, FTIR, rheology, DTMA, TGA, SEM, cycling voltammetry, impedance spectroscopy, and galvanostatic cycling in laboratory-scale Li-metal cells. We particularly focus on the influence of using two different ionic liquids as reaction medium on the properties of the resulting materials and their electrochemical behaviors. Our results indicate that viscosity affects the polymerization kinetics of the ionogels, which in turn might affect their thermal stability and galvanostatic cycling behavior. In the purpose of promoting overall performance of solid-state batteries, we also present the results of composite electrolytes obtained by introducing Li7La3Zr2O12 (LLZO) into ionogels and following in-situ UV-polymerisation. The addition of LLZO ceramic results in more porous solid networks, leading to enhanced charge/discharge stability at ambient temperature and higher C-rates featuring 4V-class NMC cathodes, enlightening the promising prospects of the developed materials to be successfully implemented as stable, durable, and efficient electrolytes in next-generation Li-metal cells.

Fabrication of new Mn-based MXene structure from MnO2 for electrochemical energy storage applications

MXene compound of Mn7C3 was successfully prepared using combined mechanical, thermal, and leaching processes. A mixture of MnO2, Al, and black C with stoichiometric ratios 3:5:2 was mechanically activated in the ball mill for 5 h. Thermal treatment at 1000 °C was applied to this mixture. Magnetic separation was used to separate Mn3AlC2 from Al2O3. After that, Al was leached from Mn3AlC2 using 15% HF. SEM investigation indicated the formation of Mxene (Mn7C3) particles as aligned sheet-like structure and particle size distribution range of 110–145 nm. The obtained MXene compounds were used as an active material vs. lithium metal and assembled in a coin cell. The electrochemical assessment of this cell was carried out using galvanostatic cycling, electrochemical impedance spectroscopy, and cyclic voltammetry techniques. MXene (Mn7C3) cell showed better performance with charge capacity by preserving about 150 mAh g−1 after 100 cycles. The coulombic efficiency of the cell is approaching 99.2% after long cycles.Graphical abstract

Prompt Molten Na Infusion and Fluidic Transport by Virtue of Versatile Nano Canal Defects on Tin Oxide Sodiophilic Hosts

AbstractIntrinsically weak metal affinity and sluggish sodium (Na) nucleation/molten fluidic transport of conventional hosts impede the fabrication of high‐capacity Na anodes. Mediating surface free energies (SFEs) of hosts and reinforcing their intermolecular attraction to viscous Na fluids can radically solve these problems. Herein, “canaled” tin oxide nanorod arrays grown on a 3D carbon cloth (CC) matrix exhibit distinct polar/nonpolar SFE components that markedly elevate the solid–liquid wettability for molten Na is reported. Such nanocanal defects render strong capillary forces for spontaneous molten Na imbibition and help to instantly activate Na─Sn alloying and Na nucleation reactions. Furthermore, sodiophilic Na15Sn4 interlayers evolved in former alloying procedures also aid in reducing Na nucleation energy barriers and guide the planar electro‐deposition/dispersion, alleviating the uncontrolled Na dendrite growth. The derived Na/Na15Sn4/CC anodes can thus keep stable after 2000 h of galvanostatic cycling at 1 mA cm−2 or high‐rate testing, without notable dendritic formation. The packed full cells also show superior rate capability and cyclability (capacity retention over 91.5% after all cycling at 1 C). This work provides a smart nano‐engineering way to trigger a fast infusion of molten metals into hosts and synergistically facilitate Na fluidic transport, which may push forward the scalable application of Na metal batteries.

Imidazole-Based Lithium Salt LiHDI as a Solid Electrolyte Interphase-Stabilising Additive for Lithium-Conducting Electrolytes.

Lithium salt LiHDI (lithium 4,5-dicyano-2-(n-heptafluoropropyl)imidazolide) is proposed as a solid electrolyte interphase-stabilising additive for lithium-ion batteries, which can be added in a smaller amount than fluoroethylene carbonate (FEC) and vinylene carbonate (VC) additives. Electrolytes containing either lithium 4,5-dicyano-2-(trifluoromethyl)imidazolide (LiTDI) or battery-standard LiPF6 were tested with various amounts of LiHDI additive. Chemical stability in the presence of water and the thermal stability of LiHDI are on par with LiTDI. LiHDI additive does not negatively affect the properties of electrolytes. Conductivity measurements of solutions, galvanostatic cycling of graphite-LiFePO4 cells at room temperature, cells' cycling at 60 °C, internal cell resistance monitoring during cycling, and XPS analysis of electrodes' surfaces after cycling have been performed. LiHDI, unlike the FEC-VC mixture, does not negatively affect the properties of the electrolyte. Cycling showed improved capacity retention with LiHDI additive with both graphite and LiFePO4 as capacity-limiting electrodes over samples without additives. At elevated temperatures, samples with LiHDI exhibited better capacity retention during cycling than those with FEC-VC. Internal cell resistance can be correlated with capacity retention. XPS results show changes in the composition of SEI depending on the composition of the electrolyte and the duration of cycling.

Electrochemical Signatures of Potassium Plating and Stripping

Alkali metal anodes can enable unmatched energy densities in next generation batteries but suffer from insufficient coulombic efficiencies. To deduce details about processes taking place during galvanostatic cycling, voltage profiles are commonly analyzed, however the interpretation is not straightforward as multiple processes can occur simultaneously. Here we provide a route to disentangle and interpret features of the voltage profile in order to build a mechanistic understanding on alkali metal stripping and deposition, by investigating potassium metal deposition as a model case where processes and reactions are exaggerated due to the high reactivity of potassium. In particular, the importance of separating SEI formation and nucleation to correctly estimate the energy barrier for nucleation is demonstrated. Further, we show how the native layer formed on alkali metal foils gives rise to strong features in the voltage profile and propose forming alkali metal electrode through electrodeposition to mitigate these effects.