Galvanostatic Cycling Experiments Research Articles

Investigation of Electrolyte Salts in Non‐Flammable Triethyl Phosphate for Sodium‐Ion Batteries

Five different electrolyte salts, namely NaBF4, NaClO4, NaDFOB, NaFSI and NaPF6, were evaluated in non‐flammable triethyl phosphate (TEP) based electrolyte solutions in sodium‐ion full‐cells using high‐mass loading Prussian white and hard carbon electrodes. Their impact on the viscosity, ionic conductivity and solvation structure was analyzed, revealing that NaFSI‐based electrolytes exhibited a stronger interaction with TEP and less ion‐pairing than the other salts, resulting in the highest ionic conductivity at a concentration of 0.8 m (mol/kg). Galvanostatic cycling experiments showed that none of the electrolyte salts dissolved in TEP forms an efficient passivation layer. However, adding 1 wt.% vinylene carbonate (VC) significantly improved cycling performance for the cells with NaBF4, NaDFOB or NaFSI, but not with NaClO4 or NaPF6. Additionally, NaFSI in TEP with 1 wt.% VC electrolyte solution showed minimal gas evolution during the formation cycling (< 8 mbar). In a 1 Ah multilayer pouch cell, 0.8 m NaFSI in TEP with 1 wt.% VC showed promising results with 88% capacity retention after 200 cycles. X‐ray photoelectron spectroscopy analysis revealed that the addition of VC results in the formation of a thin SEI and minimized TEP decomposition on hard carbon, especially for 0.8 m NaFSI TEP with 1 wt.% VC.

Exploring Sodium Gadolinium Silicate as a Solid Electrolyte for Next-Generation Sodium Batteries

Sodium-ion batteries (SIBs) represent a promising alternative to commercially prevalent Lithium-ion batteries (LIBs), primarily attributed to the economic feasibility and widespread availability of sodium resources. Solid-State Sodium Batteries (SSSBs) have garnered significant attention owing to their capacity to mitigate safety risks associated with organic liquid electrolytes by utilizing solid electrolytes. Additionally, they offer higher energy density and wide operational temperature for next-generation, cost-effective battery technology.[ 1 ] Sodium rare-earth silicates are emerging as a solid electrolyte with enhanced ionic conductivity of 10-3 S cm-1 at room temperature (RT), alongside notable mechanical stability and a wide electrochemical window, attributed to their three-dimensional framework structure.[ 2 ] In this study, sodium gadolinium silicates were synthesized through a conventional solid-state method followed by high-temperature sintering. The highest ionic conductivity of 7.25 x 10-4 S cm-1 at room temperature was achieved through sintering at 1075 °C. Galvanostatic cycling experiments were conducted to assess the compatibility of Na metal with the silicate solid electrolyte, achieving a critical current density (CCD) of 0.4 mA cm-2 and long-term stability for 6000 h at 0.1 mA cm-2. Charge-discharge studies employed a battery configuration comprising Na metal anode, silicate solid electrolyte, and Na3V2(PO4)3 cathode, demonstrating excellent capacity retention of 98% after 100 charge-discharge cycles at 0.1 C.[ 3 ] These findings highlight the potential of sodium gadolinium silicate as a promising solid electrolyte for next-generation sodium batteries, characterized by its high ion conductivity and stable interface compatibility.

Electrochemical Signatures of Potassium Plating and Stripping

Alkali metals are attractive anodes for high energy density batteries, but practical utilization of these materials in rechargeable cells has so far been hindered by safety concerns, limited Coulombic efficiencies and short cycle lives. These issues are all connected to the uneven electrodeposition and stripping of alkali metals; dendritic metal deposits can short circuit the cell and deposits with large surface areas consume more electrolyte and active material in side reactions.[1] To circumvent these problems, one of the approaches which have been attempted is electrolyte engineering. For instance, electrolytes with higher salt concentration, so called highly concentrated electrolytes, have been shown to suppress both dendrite growth and increase the Coulombic efficiency of metal anodes.[2,3] When different metal anode stabilization strategies are evaluated, it is common to perform galvanostatic cycling experiments in symmetric or asymmetric cells. This allows the cycling stability and Coulombic efficiency of the plating/stripping to be analyzed. Additionally, it is common to use features of the voltage profile as signatures on the mechanisms responsible for changes in electrochemical performance. For instance, a sharp decrease in (over)voltage during plating/stripping is a sign of a short circuit. A gradually increasing overvoltage during cycling on the other hand can be a result of continuous solid electrolyte interphase (SEI) buildup. However, several processes often occur in parallel when symmetric/asymmetric cells are cycled galvanostatically, each giving different contributions to the voltage profile which need to be deconvoluted to make sense of the data. In this contribution, we use three-electrode cells in combination with simple electrochemical experiments like cyclic voltammetry, chronoamperometry and chronopotentiometry to disentangle the contributions to different features in the galvanostatic voltage profiles of alkali metal anodes.In particular, we dissect the voltage profiles of potassium-copper (K-Cu) cells with highly concentrated electrolytes. Due to the higher reactivity of K compared to other alkali metals, certain features in the voltage profiles of these cells become exaggerated compared to lithium or sodium metal cells. We show that during galvanostatic deposition on a fresh Cu substrate, SEI formation and nucleation occur partly in parallel. If an SEI-formation step is performed prior to the galvanostatic deposition, a much sharper ‘nucleation peak’ in the voltage profile can be observed, indicative of the higher rate of nucleation that needs to occur in this case. Further, the potassium metal anode exhibits a steplike voltage profile from the second cycle and onwards. We confirm that this feature arises because bulk K is covered by a resistive native layer, whereas another type of, less resistive, interphase covers the freshly deposited K. This inhomogeneous interphase will inevitably promote preferential and inhomogeneous plating/stripping.

Deflecting Dendrites by Introducing Compressive Stress in Li7La3Zr2O12 Using Ion Implantation.

Lithium dendrites belong to the key challenges of solid-state battery research. They are unavoidable due to the imperfect nature of surfaces containing defects of a critical size that can be filled by lithium until fracturing the solid electrolyte. The penetration of Li metal occurs along the propagating crack until a short circuit takes place. It is hypothesized that ion implantation can be used to introduce stress states into Li6.4La3Zr1.4Ta0.6O12 which enables an effective deflection and arrest of dendrites. The compositional and microstructural changes associated with the implantation of Ag-ions are studied via atom probe tomography, electron microscopy, and nano X-ray diffraction indicating that Ag-ions can be implanted up to 1µm deep and amorphization takes place down to 650-700nm, in good agreement with kinetic Monte Carlo simulations. Based on diffraction results pronounced stress states up to -700MPa are generated in the near-surface region. Such a stress zone and the associated microstructural alterations exhibit the ability to not only deflect mechanically introduced cracks but also dendrites, as demonstrated by nano-indentation and galvanostatic cycling experiments with subsequent electron microscopy observations. These results demonstrate ion implantation as a viable technique to design "dendrite-free" solid-state electrolytes for high-power and energy-dense solid-state batteries.

Glass Fiber Reinforced Epoxy-Amine Thermosets and Solvate IL: Towards New Composite Polymer Electrolytes for Lithium Battery Applications.

To effectively use (Li) lithium metal anodes, it is becoming increasingly necessary to create membranes with high lithium conductivity, electrochemical and thermal stabilities, as well as adequate mechanical properties. Composite gel polymer electrolytes (CGPE) have emerged as a promising strategy, offering improved ionic conductivity and structural performance compared to polymer electrolytes. In this study, a simple and scalable approach was developed to fabricate a crosslinked polyethylene oxide (PEO)-based membrane, comprising two different glass fiber reinforcements, in terms of morphology and thickness. The incorporation of a solvated ionic liquid into the developed membrane enhances the ionic conductivity and reduces flammability in the resulting CGPE. Galvanostatic cycling experiments demonstrate favorable performance of the composite membrane in symmetric Li cells. Furthermore, the CGPE demonstrated electrochemical stability, enabling the cell to cycle continuously for more than 700 h at a temperature of 40 °C without short circuits. When applied in a half-cell configuration with lithium iron phosphate (LFP) cathodes, the composite membrane enabled cycling at different current densities, achieving a discharge capacity of 144 mAh·g-1. Overall, the findings obtained in this work highlight the potential of crosslinked PEO-based composite membranes for high-performance Li metal anodes, with enhanced near room temperature conductivity, electrochemical stability, and cycling capability.

An Insight into the Mechanisms of Energy Storage in a Double Layer Capacitor with ILs and a Microporous Carbon: Experimental Evidences of Ion-Swapping by Electrochemical Impedance Spectroscopy

The energy storage mechanism operating in carbon-based supercapacitors using ionic liquids as electrolytes is not yet fully understood. In this paper, the interactions of ions of two widely used ionic liquids, i.e. EMImTFSI and EMImBF4, with a high specific surface area microporous carbon are investigated. Galvanostatic cycling experiments performed on each electrode and in the full cell demonstrate that a specific energy close to 46 Wh kg−1 can be achieved with this carbon. More interestingly, impedance spectroscopy studies reveal the presence of some unusual behavior, such as the presence of inductive elements in some of the electrodes, either in the positive or in the negative electrode. These inductive elements are identified, for the first time, as another type of possible experimental evidences of some phenomena previously proposed, such as ion-swapping or co-ions desorption, both phenomena leading to the formation of the superionic state.

Macroporous carbon coatings through carbonization of emulsion-templated poly(dicyclopentadiene) on metal substrates

In this article, we demonstrate the fabrication of thin and macroporous carbon coatings that adhere to various metal substrates such as nickel- or aluminum-based foils or meshes. The coating process is a combination of emulsion-templating and the doctor-blade method, which allows to prepare up to 350 µm thick poly(dicyclopentadiene) membranes with a polyHIPE (polymerized high internal phase emulsions) architecture. Carbonization of these poly(dicyclopentadiene) membranes directly on the metal substrates resulted in up to 30-µm-thick foamy carbon coatings that retain the highly porous architecture and flexibility. Subsequently, carbon foam-coated Ni-foils were filled with elemental sulfur by a melt diffusion technique. A macroporous carbon coating supported sulfur loadings up to 65 wt%, obtaining cathodes for galvanostatic cycling experiments in Li–S cells. The latter revealed discharge capacities higher than 800 mA h−1 according to the sulfur mass. With our approach, the final assembly of the electrodes is greatly simplified because no binders or conductive fillers are required.Graphical abstract

Assembly of Two-Dimensional δ-V2O5-Ti3C2Tx Heterostructure Electrodes for Li-Ion Batteries

The bilayered phase of vanadium oxide (δ-V2O5∙nH2O or BVO) synthesized via sol-gel synthesis method is an attractive candidate to be used as a cathode material for Li-ion batteries (LIBs) due to its expanded interlayer spacing, and high theoretical capacity. However, poor electrical conductivity and rapid capacity fade present challenges for achieving high-rate performance and good cycle life during cycling in LIBs. A viable solution to mitigating these drawbacks is to fabricate two-dimensional (2D) heterostructures comprised of vanadium oxide and an additional selected 2D material. Titanium carbide (Ti3C2Tx) MXenes are particularly of interest for their high electronic conductivity (103 S cm-1) and well developed delamination protocols. Herein, we present a wet-based approach for assembling BVO and MXene nanoflakes into 2D heterostructures in suspension.In this study, we first demonstrate a simple liquid phase exfoliation technique utilizing probe ultrasonication to exfoliate bulk -LixV2O5·nH2O (LVO). Previous experiments from our group showed the exfoliation technique in n-methyl-2-pyrrolidone, an organic solvent that is toxic, flammable, and resulted in low yield during exfoliation. Here, for the first time, we have successfully performed exfoliation of LVO in aqueous media and obtained few layered nanoflakes with high yield after centrifugation. Despite the partial solubility of vanadium oxide in water, these nanoflakes suspended in aqueous media maintained chemical stability and readily assembled into a free-standing film using vacuum filtration. The LVO nanoflake films have a two-dimensional (2D) layered morphology as confirmed by SEM and maintain the bilayered structure as confirmed by XRD.Due to the hydrated nature of LVO, we also highlight the importance of controlling interlayer water content with vacuum drying for achieving better cycling stability. The comparison of a 105°C and 200°C vacuum drying temperature and corresponding interlayer water content was carried out using XRD, TGA, and Raman spectroscopy characterization methods. The 200°C vacuum dried LVO nanoflake cathode achieved an initial ion storage capacity of 212 mAh g-1 which was 32.5% higher than the sample dried at 105°C. In addition, galvanostatic cycling experiments conducted for the 200°C vacuum dried LVO nanoflake cathode show there were significant improvements in capacity retention by ~35%, compared to the 105°C dried sample, after 100 cycles at a current density of 20 mA g-1.Subsequently, dispersions of LVO and Ti3C2Tx flakes in water were combined in different weight ratios of 9:1, 4:1, and 1:1 LVO to Ti3C2Tx. The heterostructure electrostatic assembly was facilitated by the introduction of a cationic species into the mixed suspensions. Resistivity measurements showed that heterostructure films achieved electronic conductivities as high as ~105 higher than pristine LVO. Through electrochemical testing, the 9:1 heterostructure cathodes delivered the highest ion storage capacity of 167 mAh g-1. At the cost of lower capacity (125.3 mAh g-1), the 4:1 heterostructures maintain a superior capacity retention of ~96% after 10 cycles. Furthermore, rate capability experiments for the 9:1 heterostructure cathodes demonstrate that the addition of 10 wt % Ti3C2Tx to LVO enables greater tolerance to high current densities with a capacity retention of ~90% after cycling through increasing current densities. In this work we also show that increased capacities can be acquired upon the extension of the potential window below 2V covering where Ti3C2Tx exhibits redox activity.These results demonstrate an environmentally friendly and safe approach to obtaining 2D LVO nanoflakes and offers pathways to constructing novel vanadium oxide based 2D heterostructures for improving electrochemical performance in energy storage devices.

Toward Li-ion Graphite Anodes with Enhanced Mechanical and Electrochemical Properties Using Binders from Chemically Modified Cellulose Fibers

Cellulose nanofibers (CNFs) are bio-sourced nanomaterials, which, after proper chemical modification, exhibit a unique ability to disperse carbon-rich micro- and nanomaterials and can be used in the design of mechanically strong functional nanocomposites. When used in the preparation of graphite anodes for Li-ion batteries, they have the potential to outperform conventional binders such as carboxymethyl cellulose (CMC) and styrene–butadiene rubber (SBR) both electrochemically and mechanically. In this study, cellulose-rich fibers were subjected to three different chemical modifications (including carbonyl-, carboxyl-, and aldehyde-functionalization) to facilitate their fibrillation into CNFs during the preparation of aqueous slurries of graphite and carbon black. Using these binders, graphite anodes were prepared through conventional blade coating. Compared to CMC/SBR reference anodes, all anodes prepared with modified cellulosic fibers as binders performed better in the galvanostatic cycling experiments and in the mechanical cohesion tests they were subjected to. Among them, the aldehyde- and carboxyl-rich fibers performed the best and resulted in a 10% increase in specific capacity with a simultaneous two- and three-fold increase of the electrode material’s stress-at-failure and strain-at-break, respectively. In-depth characterizations attributed these results to the distinctive nanostructure and surface chemistry of the composites formed between graphite and these fiber-based binders.

Efficient, Selective Sodium and Lithium Removal by Faradaic Deionization Using Symmetric Sodium Titanium Vanadium Phosphate Intercalation Electrodes.

NASICON (sodium superionic conductor) materials are promising host compounds for the reversible capture of Na+ ions, finding prior application in batteries as solid-state electrolytes and cathodes/anodes. Given their affinity for Na+ ions, these materials can be used in Faradaic deionization (FDI) for the selective removal of sodium over other competing ions. Here, we investigate the selective removal of sodium over other alkali and alkaline-earth metal cations from aqueous electrolytes when using a NASICON-based mixed Ti-V phase as an intercalation electrode, namely, sodium titanium vanadium phosphate (NTVP). Galvanostatic cycling experiments in three-electrode cells with electrolytes containing Na+, K+, Mg2+, Ca2+, and Li+ reveal that only Na+ and Li+ can intercalate into the NTVP crystal structure, while other cations show capacitive response, leading to a material-intrinsic selectivity factor of 56 for Na+ over K+, Mg2+, and Ca2+. Furthermore, electrochemical titration experiments together with modeling show that an intercalation mechanism with a limited miscibility gap for Na+ in NTVP mitigates the state-of-charge gradients to which phase-separating intercalation electrodes are prone when operated under electrolyte flow. NTVP electrodes are then incorporated into an FDI cell with automated fluid recirculation to demonstrate up to 94% removal of sodium in streams with competing alkali/alkaline-earth cations with 10-fold higher concentration, showing process selectivity factors of 3-6 for Na+ over cations other than Li+. Decreasing the current density can improve selectivity up to 25% and reduce energy consumption by as much as ∼50%, depending on the competing ion. The results also indicate the utility of NTVP for selective lithium recovery.

Combining ReaxFF Simulations and Experiments to Evaluate the Structure-Property Characteristics of Polymeric Binders in Si-Based Li-Ion Batteries.

High energy capacity silicon (Si) anodes in Li-ion batteries incorporate polymeric binders to improve cycle life, which is otherwise limited by large volume and stress fluctuations during charging/discharging cycles. Several properties of the polymeric binder play a role in achieving optimal battery performance, including interfacial adhesion strength, mechanical elasticity, and lithium-ion conduction rate. In this work, we utilize atomistic simulations with the ReaxFF force field and complementary experiments to investigate how these properties dictate the performance of Si/binder anodes. We study three C/N/H-based polymer binders with varying structures (pyrolyzed polyacrylonitrile (PPAN), polyacrylonitrile (PAN), and polyaniline (PANI)) to determine how the structure-property characteristics of the binder affect performance. The Si/binder adhesion analysis reveals some counter-intuitive results: although an individual PANI chain has a stronger affinity to Si compared to PPAN, the PANI bulk binds weaker to the Si surface. Interfacial structural analyses from simulations of the bulk phase show that PANI chains have poor stacking at the interface, while PPAN chains exhibit dense and highly ordered stacking behavior, leading to stronger adhesion. PPAN also has a lower Young's modulus compared to PANI and PAN owing to its ordered and less entangled bulk structure. This added elasticity better accommodates volume changes associated with cycling, making it a more suitable candidate for Si anodes. Finally, both simulations and experimental measurements of Li-ion diffusion rates show higher Li mobility through PPAN than PAN and PANI because the ordered stacking of PPAN chains creates channels that are favorable for Li diffusion to the Si surface. Galvanostatic charge-discharge cycling experiments show that PPAN is indeed a highly promising binder for Si anodes in Li-ion batteries, retaining a capacity of ∼1400 mAh g-1 for 150 cycles. This work demonstrates that the orientation and structure of the polymer at and near the interface are essential for optimizing binder performance as well as showcases the initial steps for binder evaluation, selection, and application for electrodes in Li-ion batteries.

From solid electrolyte to zinc cathode: vanadium substitution in ZnPS3

Development of next generation batteries is predicated on the design and discovery of new, functional materials. Divalent cations are promising options that go beyond the canonical Li-based systems, but the development of new materials for divalent ion batteries is hindered due to difficulties in promoting divalent ion conduction. We have developed a family of cathode materials based on the divalent cation conductor ZnPS3. Substitution of V for Zn in the lattice concomitant with vacancy introduction yields isostructural but redox-active materials that can reversibly store Zn2 + in the vacancies. A range of voltammetry and galvanostatic cycling experiments along with x-ray photoelectron spectroscopy support that redox is indeed centered on V and that capacity is dependent on the V content. The voltage of the materials is limited by the irreversible decomposition of the polyanion above 1.4 V vs. Zn/Zn2 + . The reversible capacity before anion decomposition is limited to half the vacancies and is due to the relative ratios of oxidized and reduced V centers. Such observations provide useful design rules for cathode materials for divalent cation based battery technologies, and highlight the necessity for a holistic interpretation of physical and electronic structural changes upon cycling.

Draining Over Blocking: Nano-Composite Janus Separators for Mitigating Internal Shorting of Lithium Batteries.

Catastrophic battery failure due to internal short is extremely difficult to detect and mitigate. In order to enable the next-generation lithium-metal batteries, a "fail safe" mechanism for internal short is highly desirable. Here, a novel separator design and approach is introduced to mitigate the effects of an internal short circuit by limiting the self-discharge current to prevent cell temperature rise. A nano-composite Janus separator-with a fully electronically insulating side contacting the anode and a partially electronically conductive (PEC) coating with tunable conductivity contacting the cathode-is implemented to intercept dendrites, control internal short circuit resistance, and slowly drain cell capacity. Galvanostatic cycling experiments demonstrate Li-metal batteries with the Janus separator perform normally before shorting, which then results in a gradual increase of internal self-discharge over >25 cycles due to PEC-mitigated shorting. This is contrasted by a sudden voltage drop and complete failure seen with a single layer separator. Potentiostatic charging abuse tests of Li-metal pouch cells result in dendrites completely penetrating the single-layer separator causing high short circuit current and large cell temperature increase; conversely, negligible current and temperature rise occurs with the Janus separator where post mortem electron microscopy shows the PEC layer successfully intercepts dendrites.

Experimental and Theoretical Analysis of Li-Stuffed Garnet-Type Electrolytes

Rechargeable lithium-ion batteries (LIBs) are one of the dominant technologies for electrochemical energy storage. They are widely used in portable electronics, electrical vehicles, and large-scale energy storage systems. Current LIBs use organic polymer based electrolytes and they have several problems such as dendrite formation, flammability and leakage.1 Therefore, there is much attention on developing a solid-state Li-ion electrolyte that is thermally and chemically stable. Among the various inorganic solid Li-ion conducting electrolytes, garnet structured compounds have shown great promise as potential electrolytes for all-solid-state lithium batteries due to their high ionic conductivities (10-4 S/cm), compatibility with Li metal anode, and wide electrochemical window (~ 6V vs Li/Li+).2 The present study reports a comparison of the experimental and theoretical data of garnet type Li-ion solid electrolytes. The solid electrolytes, Li6.5La2.9A0.1Ta0.6Zr1.4O12 (A = Ca, Sr, Ba) were prepared by conventional solid state sintering and spark plasma sintering method. The formation of the ‘‘single-phase’’ garnet-type structure was analysed by powder X-ray diffraction (PXRD). Li-ion conductivity was determined using electrochemical impedance spectroscopy (EIS) and all the members have exhibited ionic conductivity in the order of 104 S/cm at 25 °C. Interfacial resistance of the garnet samples and Li metal was measured using EIS and the interfacial stability of the same was confirmed by DC galvanostatic cycling experiments. Li-ion conductivity and activation energy of the prepared compounds were also calculated using a statistical mechanical approach and the estimated values are in good agreement with the experimental values.

A nanowire-nanoparticle double composite polymer electrolyte for high performance ambient temperature solid-state lithium batteies

Development of solid-state electrolytes that can allow corresponding lithium-ion batteries (LIBs) to perform excellent room temperature cell performance is very meaningful, and also is still a great challenge. One effective measure to solve the above problem is to reduce the interface resistance of the cells via special methods. In this study, a novel double composite polymer electrolyte using polyethylene oxide-polypropylene oxide-polyethylene oxide (PEO-PPO-PEO)/LiTFSI, ceramic nanowires and nanoparticles is designed and prepared (the composite electrolyte is named as CPE) for the first time, which combines the advantages of polymer electrolyte, ceramic nanowires and nanoparticles (different from the related works about only using ceramic nanopartices or ceramic nanowires as fillers). Compared with the composite electrolyte without adding ceramic nanoparticles (named as CPE-0), CPE presents higher ionic conductivity (4.58 × 10−5 S cm−1 at ambient temperature), much higher lithium-ion transference number (0.28), which likely because nanoparticles can promote the formation of more continuous ion channels at the interface of polymer and ceramic fillers. In addition, the CPE shows much wider electrochemical window (5.6 V) than that of the CPE-0 (4.2 V), which can be attributed to the extra nanoparticles can further scavenge trace impurities. Especially, the galvanostatic cycling experiments confirm that CPE has much better stability against Li metal than that of CPE-0, while the Li/CPE/Li symmetric cell also shows a low and stable interface resistance of ∼800 Ω from day 1 to day 25. Therefore, the LiFePO4/Li cell using the CPE shows good cycle performance at 28 °C. Specifically, the cell exhibits a discharge capacity of 154 mAh g−1 with coulombic efficiency of 100% at the 100 cycles. Our work indicates that the interface resistance of the corresponding batteries can be significantly reduced by preparation of CPE with specific polymer electrolytes and ceramic fillers. Thus, the solid-state cells can be well run at ambient temperature.

Characterization of Carbon Felt Materials As Negative Electrode Material for Flow-Assisted Zn-Air Batteries

Secondary alkaline Zinc-Air batteries hold several distinct advantages over other large-scale systems for energy storage. Such batteries use materials that are low cost: Zn is abundant in the earth’s crust and alkaline aqueous solutions are cheap and well understood. They also have low toxicity and high chemical stability. To make Zn-air batteries viable for large scale use, issues at the Zn electrode need to be addressed. Allowance must be made to prevent dendrite growth that eventually leads to cell shorting during charging. During the oxidation of Zn occurring in the discharge process in the battery, a sequence of chemical steps occurs producing a passive layer of ZnO on the electrode. Additionally, electrode morphology changes between each cycle produce inconsistent performance. These issues can be improved by using a three-dimensional support structure on which Zn is deposited. Carbon felt electrodes provide an ideal structure for the Zn anode in Zn-air systems as they are porous and highly conductive. These features allow for high surface area for deposition to occur, low mass transport constraints and low internal IR losses of the electrode. Furthermore, the carbon structure provides a consistent structure to return to minimize Zn morphology changes. These structures have been explored for their potential as the anode in Zn electrodes and showed significant promise. No issues with dendrite growth and passivation have been observed in the electrode during cycling. They can achieve 100mA/cm2 of current density at 20mV of overpotential during deposition and dissolution at a flow rate of 15ml/min of electrolyte through the electrode. Additionally, they have been shown to be stable for 100 cycles of cycling in a symmetric cell at 50mA/cm2 while maintain an average overpotential of less than 50mV during each step. Cycling at high flow rates improves the performance of the felt with an average step overpotential of 16mV at 28 ml/min and 28mV overpotential average at 10ml/min, all also at 4M NaOH saturated with Zincate. Increased state of charge of the electrode appears to increase the efficiency of the electrode. During charging steps in 10ml/min cycling experiments overpotential starts out near 40mV and trends towards 20mV during the step. Further, a 50mV CA step at 30ml/min shows current density increase from 100mA/cm2 at the start of the test to 400mA/cm2 at the end of 30 min. This is the result of the increased amount of Zn in the felt system providing more surface area of Zn for deposition to occur directly on. The potential during galvanostatic cycling experiments appears to be somewhat unstable indicating that the basic electrochemical performance of the electrode needs more study. Nucleation of Zn deposits occurs throughout the felt thickness regardless of the applied overpotential or current. As deposition progresses, the location of Zn growth depends on the current applied. At higher currents or overpotentials growth localizes near the membrane separator. It then begins to fill in back towards the current collector. The reverse occurs during discharge of the electrode, material is removed preferentially from the parts of the electrode near the current collector then proceeds towards the membrane separator. Experiments show that this is based on overpotential in the cell and under both potentiostatic and galvanostatic conditions; at low observed or applied potentials growth occurs throughout the cell felt and at higher overpotentials the growth becomes localized. IR drop measurements through the felt indicate that only 20% of the electrode is active during the growth phase of a 1hour, 40mA/cm2 deposition test. This suggests migration of the negatively charged zincate towards the membrane separator is dominant in these conditions. This ultimately reduces the efficiency of the electrode as it increases the overpotential required to achieved the desired current. Methods to counteract this effect with be discussed. Optimized electrode performance including flow rate, electrolyte conditions, and preconditioning of the electrode for cycling of symmetric and full cell setups will also be discussed further. We gratefully acknowledge the support of Dr. Imre Gyuk and the DOE Office of Electricity Delivery and Reliability. Figure 1

Plasticized Hybrid Network Solid Polymer Electrolytes for Lithium‐Metal Batteries

AbstractIncorporating solid polymer electrolyte (SPE) into lithium metal batteries has the benefit of employing the electrolyte as the electrode separator while inhibiting the growth of lithium dendrites. The two main models on lithium dendrite growth show that either ionic conductivity or mechanical property affect lithium dendrite nucleation and growth rate. In this work, with a well‐controlled hybrid network SPE as the model system, the modulus and conductivity of the hybrid SPEs are systematically tuned by plasticizing the network with low molecular with diluents. This systematic property control allows for establishing the correlation between mechanical/electrochemical properties of the SPEs with their propensity of lithium dendrite resistance using galvanostatic polarization and cycling experiments. It is further demonstrated that lithium metal batteries can be operated at 30 °C for the plasticized SPEs due to the dramatically improved conductivity.

Characterization of carbon-coated LiFe0.3Mn0.7PO4 particles produced using a colloidal method for lithium batteries

A convenient colloidal process for the preparation of LiFe0.3Mn0.7PO4/C nanocomposite cathode material for lithium batteries is reported. The process involves the use of lithium dihydrogen phosphate (LiH2PO4), ferrous chloride (FeCl2) and manganese chloride (MnCl2) as starting materials, with anhydrous N-methylimidazole (NMI) as the solvent and carbon source, followed by a 3 h annealing step at 650 °C. Carbonization of the molten salt NMIH+Cl− derived from NMI resulted in 3.0 wt% carbon content in the LiFe0.3Mn0.7PO4/C with 3–6 nm thick carbon coating. The material was characterized by thermogravimetric and differential thermal analysis, differential scanning calorimetry, powder X-ray diffraction, field-emission scanning electron microscopy, transmission electron microscopy, atomic absorption spectroscopy, Raman spectroscopy, four-point probe method, cyclic voltammetry and galvanostatic cycling experiments in coin cells. SEM analysis of the LiFe0.3Mn0.7PO4/C material revealed non-spherical agglomerates with average width and length of 50–70 nm and 120–150 nm, respectively. The electronic conductivity of carbon-coated LiFe0.3Mn0.7PO4 was found to be 9.7 × 10−2 S cm−1 at room temperature, and the discharge capacity reached 137 mAh g−1 measured at C/20 when the cell was cycled between 2.2 V and 4.2 V vs. Li+/Li, and 124 mAh g−1 at C/10 for the first cycle. The capacity dropped to 122 mAh g−1 at C/10 after the first 25 cycles and then stayed constant at 121 mAh g−1 until the 100th discharge cycle, making this cell to exhibit excellent cycling stability with only a 2.4% decrease.

A novel low-cost and simple colloidal route for preparing high-performance carbon-coated LiFePO4 for lithium batteries

Abstract Nanosized carbon-coated lithium iron phosphate (LiFePO4/C) particles were synthesized using a novel low-cost colloidal process with LiH2PO4, FeCl2 and anhydrous N-methylimidazole (NMI) as starting materials, following by a short annealing step at 600 °C. The ∼3–5 nm thick carbon coating comes from the carbonization of molten salt NMIH+Cl− derived from NMI; the resulting carbon contents of the LiFePO4/C powder is 2.53 wt.%. The materials were characterized by thermogravimetric and differential thermal analysis, differential scanning calorimetry, powder X-ray diffraction, field-emission scanning electron microscopy, transmission electron microscopy, atomic absorption spectroscopy, Raman spectroscopy, four-point probe method, cyclic voltammetry and galvanostatic cycling experiments in coin cells. The LiFePO4 phase reveals agglomeration of semi-spherically particles with an average individual size of 35 ± 4 nm. Carbon-coated LiFePO4 posseses electronic conductivity of 1.4 × 10−3 S cm−1 at room temperature causing a markable increase in rate capability. Cycling the cells between 2.2 and 4.2 V vs. Li+/Li resulted in a discharge capacity of 164 mAh g−1 at the first cycle of C/20 and 162 mA hg−1 after 35 cycles, which corresponds to over 95% of the theoretical capacity of olivine LiFePO4.

Reversible Delithiation of Disordered Rock Salt LiVO2

AbstractA rigid crystal lattice, in which cations occupy specific positions, is generally regarded as a critical requirement to enable Li+ diffusion in the bulk of conventional cathode materials, whereas disorder is generally considered as detrimental. Herein, we demonstrate that facile and reversible insertion and extraction of Li+ is possible with LiVO2, a new cation‐disordered rock salt compound (space group: Fm m), which is, to the best of our knowledge, described for the first time. This new polymorph of LiVO2 is synthesized by mechanical alloying. Rietveld refinements of the X‐ray diffractions patterns and SAED (selected‐area electron diffraction) patterns attested the formation of the disordered LiVO2 rock salt phase. Galvanostatic cycling experiments were employed to characterize the electrochemical performance of the material, demonstrating that reversible cycling over 100 cycles with a discharge capacity around 100 mAh g−1 is possible.