Anode Design Research Articles

An experimental investigation on the performance of direct methanol fuel cell using new anode and cathode flow field designs

This is a comprehensive study of the DMFC through the introduction of new channel designs. A traditional serpentine design with a rib and channel width of 0.8mm on an area of 50mm×50mm is designated as design-1 and used as the reference channel design. Three other new designs are fabricated and tested in comparison with design-1. A 4-outlet, 1-inlet, 4-zone serpentine with 0.8mm of rib and channel width, is designated as design-2. A 4-outlet, 1-inlet, 4-zone serpentine with a converging channel width is designated as design-3. A 4-outlet, 1-inlet, 4-zone zigzag serpentine with a converging channel width is designated as design-4. The study was done in three stages. The first stage investigates the effect of anode channel designs by fixing the cathode design to design-1 and varying the anode designs from design-1 to design-4. The second stage investigates the effect of cathode designs by fixing the anode design to design-1 and varying the cathode designs from design −1 to −4. The third stage investigates the effect of using the same designs at both the anode and cathode sides. All the stages were tested using three anode flowrates (2,5, and 8mL/min) and three methanol concentrations (1, 2, and 3mol/L). Higher concentrations perform better than lower concentrations while lower flowrates perform better than higher flowrates. The percentage improvement by the new designs in comparison to the reference design is: 142%, 94%, and 136% for the first stage; 74%, 125%, and 40% for the second stage; and 16%, -33% and -45% for the third stage, and the order being design −2, −3 and −4 respectively. Design −3 and −4 underperform in the third stage due to the availability of direct paths that boost methanol crossover when using the same design of anode and cathode. The new designs evacuate the CO2 bubbles and byproduct water faster and more efficiently than the reference design.

Ultrahigh Pyridinic/Pyrrolic N Enabling N/S Co-Doped Holey Graphene with Accelerated Kinetics for Alkali-Ion Batteries.

Carbonaceous materials hold great promise for K-ion batteries due to their low cost, adjustable interlayer spacing, and high electronic conductivity. Nevertheless, the narrow interlayer spacing significantly restricts their potassium storage ability. Herein, hierarchical N, S co-doped exfoliated holey graphene (NSEHG) with ultrahigh pyridinic/pyrrolic N (90.6at.%) and large interlayer spacing (0.423nm) is prepared through micro-explosion assisted thermal exfoliation of graphene oxide (GO). The underlying mechanism of the micro-explosive exfoliation of GO is revealed. The NSEHG electrode delivers a remarkable reversible capacity (621 mAhg-1 at 0.05 Ag-1), outstanding rate capability (155 mAhg-1 at 10 Ag-1), and robust cyclic stability (0.005% decay per cycle after 4400 cycles at 5 Ag-1), exceeding most of the previously reported graphene anodes in K-ion batteries. In addition, the NSEHG electrode exhibits encouraging performances as anodes for Li-/Na-ion batteries. Furthermore, the assembled activated carbon||NSEHG potassium-ion hybrid capacitor can deliver an impressive energy density of 141 Whkg-1 and stable cycling performance with 96.1% capacitance retention after 4000 cycles at 1 Ag-1. This work can offer helpful fundamental insights into design and scalable fabrication of high-performance graphene anodes for alkali metal ion batteries.

Multi boron-doping effects in hard carbon toward enhanced sodium ion storage

Hard carbon (HC) has been considered as promising anode material for sodium-ion batteries (SIBs). The optimization of hard carbon’s microstructure and solid electrolyte interface (SEI) property are demonstrated effective in enhancing the Na+ storage capability, however, a one-step regulation strategy to achieve simultaneous multi-scale structures optimization is highly desirable. Herein, we have systematically investigated the effects of boron doping on hard carbon’s microstructure and interface chemistry. A variety of structure characterizations show that appropriate amount of boron doping can increase the size of closed pores via rearrangement of carbon layers with improved graphitization degree, which provides more Na+ storage sites. In-situ Fourier transform infrared spectroscopy/electrochemical impedance spectroscopy (FTIR/EIS) and X-ray photoelectron spectroscopy (XPS) analysis demonstrate the presence of more BC3 and less B–C–O structures that result in enhanced ion diffusion kinetics and the formation of inorganic rich and robust SEI, which leads to facilitated charge transfer and excellent rate performance. As a result, the hard carbon anode with optimized boron doping content exhibits enhanced rate and cycling performance. In general, this work unravels the critical role of boron doping in optimizing the pore structure, interface chemistry and diffusion kinetics of hard carbon, which enables rational design of sodium-ion battery anode with enhanced Na+ storage performance.

Defect-driven ion storage on hexagonal boron nitride for fire-safe and high-performance lithium-ion batteries

The mass market adoption of electric vehicles has increased the risk of safety concerns, such as overheating and flammability. Rational design of fire-safe and high-capacity anodes with thermal tolerance, capable of fast-charging and long cycle-life, is crucial for the development of next generation Li-ion batteries operating under extreme conditions. Here we report a defect engineered hexagonal boron nitride (hBN) anode to mediate the safety dilemma. We demonstrate that the defects generated via cryomilling catalyze the reversible LiF formation and enable the pseudocapacitive type Li-ion storage on hBN. The non-flammability and excellent thermal tolerance of hBN allows high specific capacity (880 mAh/g @ 25 mA/g), rate performance (480 mAh/g @ 5 A/g) and stable cycling (5000 cycles) at 60 °C. The Li-ion full-cell with the defective hBN anode and the conventional cathode (LiNiMnCoO2) delivers significantly higher energy (400 Wh kg−1) and power density (1 kW kg−1) when compared to graphite/LiNiMnCoO2 full-cells (121 Wh kg−1 and 250 W kg−1). First-principles calculations confirm that nitrogen antisite (NBVN) defects are responsible for the electrochemical activation of otherwise inactive hBN. The strategy of defect-induced electrochemical activation opens up new avenues in the design of high-performance electrode materials for numerous secondary batteries.

Revealing the sodium storage mechanism of cellulose separator-derived hard carbon anode materials for sodium-ion batteries

Hard carbon (HC) shows significant promise as a material for sodium-ion batteries (SIB). Cellulose-derived carbon is considered one of the most promising high-performance anode materials for sodium-ion batteries. In this study, waste cellulose separator-derived HC anode materials were rationally developed using the pre-oxidation-carbonization pyrolysis method. The as-prepared HC possessed advantageous characteristics for Na+ storage, including a unique fibrous structure, a reasonable space layer, and a small specific surface area (SSA). The optimal sample demonstrated a substantial reversible capacity of 361.29 mAh/g at 0.1C, an impressive high-rate performance with a reversible capacity of 272.93 mAh/g at 10C, and an initial coulombic efficiency of 84.85 %. Following 500 cycles at 1C, the capacity retained 96.38 % of its initial value. The sodium storage process was identified as the “adsorption-insertion-pore filling mechanism” through ex-situ XRD and in-situ Raman experiments. Moreover, the as-prepared HCs demonstrated better rate and cycle capability when evaluated as anodes in full-cell sodium-ion batteries (SIBs). This research provides valuable insights into the rational design of high-performance HC anodes for SIBs and other applications.

Layered double hydroxide assembled on a metal–organic framework coupled with polyaniline as pseudocapacitive anode for phosphorus capture

Excessive phosphorus is detrimental to supporting the proper function of aquatic ecosystems. Capacitive deionization (CDI) is an emerging, highly efficient, eco-friendly electrochemical technology that eliminates phosphorus from wastewater. In this work, a novel LDH@MOF/PANI composite was successfully fabricated by utilizing polyaniline (PANI) as a conductive substrate and metal–organic framework (MOF) as a self-sacrificial template for layered double hydroxide (LDH). The results demonstrated that LDH and PANI are favorable for improving the pore structure features, enriching the phosphorus binding sites, and strengthening the electrochemical performance of the electrode materials. Accordingly, the LDH@MOF/PANI electrode presented a superior phosphorus capture capacity than LDH@MOF and MOF. The isotherm and kinetic experiments revealed that the phosphorus capture by LDH@MOF/PANI is a chemisorption-dominated process associated with heterogeneous adsorption. The potential interference with phosphorus uptake was also assessed by focusing on several vital factors. Eventually, the possible mechanism suggested that ligand exchange, anion exchange, hydrogen bond, electrostatic attraction, and electric field assistance participate in the phosphorus uptake process. This work presents promising insight into the assembly design and rational construction of LDH-based pseudocapacitive anode for phosphorus capture.

Homogeneous Deposition of Zinc on N-Doped Carbon Fibers Interconnected with Sn Nanoparticles for Advanced Aqueous Zinc Batteries.

Currently, inhomogeneous distribution of Zn2+ on the surface of the Zn anode is still the essential reason for dendrite formation and unsatisfactory stability of zinc ion batteries. Given the merits of strong interaction between Sn and Zn, as well as a low nucleation barrier during Zn deposition, the combination of metallic Sn with carbon material is expected to improve the deposition of zinc ions and inhibit the growth of zinc dendrites by guiding the homogeneous plating/stripping of zinc on the electrode surface. In this article, zincophilic Sn nanoparticles with low nucleation barriers and strong interaction with Zn2+ were embedded into 3D N-doped carbon nanofibers using a simple electrostatic spinning technique. Accordingly, when serving as an artificial coating layer for the zinc metal anode, an ultrastable Sn@NCNFs@Zn||Sn@NCNFs@Zn symmetric cell can be achieved for over 3500 h with a low nucleation overpotential of 29.1 mV. Significantly, the full cell device assembled with the as-prepared anode and MnO2 cathode exhibits desirable electrochemical behaviors. Moreover, this simple method could be extended to other metal-carbon composites, and to ensure ease in scaling up as required. Such significant approach can provide an effective strategy for the design of high-performance zinc anodes.

Se-vacancy porous ultrathin ZnSe nanosheet/carbon composite for sodium storage via electron beam irradiation strategy

Zinc selenide (ZnSe) is a next-generation anode material due to its high sodium storage capacity. However, the poor conductivity and volume expansion lead to its capacity attenuation and short cycle life. Herein, Se-vacancy porous ultrathin ZnSe nanosheet/carbon composite (ZnSe@NC/N-GQD) is reported as a high-performance anode material for sodium-ion batteries. Organic-inorganic hybrid ZnSe(en)0.5 ultrathin nanosheets with abundant Se vacancies are rapidly prepared by electron beam irradiation for the first time. Using it as a precursor, Se-vacancy carbon-coated porous ultrathin ZnSe nanosheets loaded with nitrogen-doped graphene quantum dots (N-GQDs) are synthesized via carbonization and electrodeposition process. Through the design of ZnSe@NC/N-GQD, the sodium storage performance can be effectively improved by implementing nanostructure engineering (porous ultrathin nanosheet) via organic–inorganic hybrid, defect engineering (Se vacancy) via electron beam irradiation, and carbon composite (amorphous carbon and N-GQD). Consequently, ZnSe@NC/N-GQD delivers a high capacity of 483 mA h g−1 after 200 cycles at 0.5 A g−1, shows an outstanding rate capability of 381 mA h g−1 at 10.0 A g−1, and exhibits an excellent cycling stability of 86 % retention after 2800 cycles at 5.0 A g−1. This work develops a new method to rapidly prepare organic–inorganic nanohybrids, and proposes an innovative design of high-performance ZnSe-based anodes.

Uncovering and preventing polytellurides dissolution enables stable sodium-ion storage: A case study of SnTe

Metal tellurides (MTes) have emerged as promising candidates for high-specific energy sodium-ion batteries owing to their superior volumetric capacity and exceptional intrinsic conductivity. Nevertheless, their practical application faces challenges associated with pronounced capacity degradation associated with unclear decay mechanisms. In this study, we uncover, for the first time, that the dissolution and shuttling of intermediates (NaxTey) are responsible for the rapid capacity decay in alloy- and conversion-type MTe anodes. Based on this discovery, we propose a novel structural engineering strategy that involves confining ultrafine SnTe nanoparticles within a fibrous carbon matrix, facilitating the smooth immobilization and highly reversible conversion of NaxTey. State-of-the-art in-/ex-situ tests and density functional theory calculations elucidate the evolution and shuttling mechanisms of NaxTey, highlighting the van der Waals barrier of the carbon matrix and the remarkable chemisorption of N and S dopant sites towards Na2Te2 and Na2Te intermediates. Significantly, the chemisorption capacity of NaxTey is enhanced through the optimization of doping content and bonding type of N and S, resulting in excellent stability of SnTe embedded in a high-content N and S co-doped carbon fiber matrix (SnTe@SHNC). The elaborate SnTe@SHNC composites demonstrate exceptional performance, enduring over 1000 cycles at 1.0 A g−1 with an ultraslow capacity decay rate of 0.028 % per cycle. This work provides valuable insight into the pivotal role of controlling NaxTey in the design of durable MTe anodes for advanced SIBs.

Rational design of 2D blue phosphorene/Ti2BT2 (T=Se, Te) heterostructures as high-performance anode materials for alkali-metal ion batteries: A first principles study

Blue phosphorene (BlueP) is extensively regarded as an attractive anode for the next generation of metal-ion batteries (MIBs) owing to the rapid ion diffusion and high storage capacity; however, its electrochemical performance is still seriously impeded by the intrinsically low conductivity and poor mechanical stiffness. To overcome the above obstacles, we theoretically designed BlueP/Ti2BSe2 and BlueP/Ti2BTe2 heterostructures, and explored their potential as the anodes of MIBs using first principles calculations. The computational results demonstrate that the resulting heterostructures have excellent thermal and mechanical stability. Moreover, the designed two heterostructures show low ion diffusion barrier (<0.30 eV) with inherent metallicity, which greatly contributes to the rate performance of MIBs. Remarkably, the BlueP/Ti2BSe2 (BlueP/Ti2BTe2) anode delivers high Li/Na/K storage capacities of 492.68 (379.54)/410.54 (379.54)/191.59 mA h/g, and suitable averaged open circuit voltages (OCVs) of 0.56 (0.33)/0.33 (0.10)/0.42 V. This work not only broadens the BlueP-based 2D heterostructures, but also lays a solid foundation for the theoretical design of exceptional anodes.

Concentrated Chloride Electrolyte Enabling SEI for Fe Metal Anode

Iron is one of the most abundant metal elements in the Earth’s crust and has been widely used worldwide since ancient times. Due to this natural abundance and well-established mass production methods, iron is a promising candidate as a battery electrode for cost-effective large-scale energy storage systems. Edison’s Ni-Fe battery, invented in 1900, used an alkaline electrolyte without ferrous or ferric ions that eventually limited its anode design using iron oxide. More recent Fe redox flow batteries and the newly suggested Fe-ion batteries that use an acidic electrolyte containing ferrous ions (Fe2+) can utilize iron foil as an anode. Combining iron foil with Fe2+ electrolyte enables a simple design and faster kinetics on the anode side. However, introducing acidic electrolytes accelerates hydrogen evolution reaction (HER) on the iron surface. Severe HER affects cell performance in various ways, including lower Coulombic efficiency (CE), drying out of the electrolyte by water consumption, and precipitation of Fe2+ ions due to increased pH of the electrolyte. In this work, a concentrated chloride-based electrolyte was introduced to Fe-ion batteries to suppress HER and achieve a high-CE Fe2+/Fe electrode. With the help of nonpolar [ZnCl4]2- which enables low-polarity organic additives to be soluble in the aqueous solution, an organic solid electrolyte interface (SEI) can be formed on top of the electrode while plating iron. Fe anode protected by the SEI shows a noticeable decrease in HER during cycling, which leads to higher CE of more than 98% and twice longer cycle life.

(Battery Division Postdoctoral Associate Research Award Sponsored by MTI Corporation and the Jiang Family Foundation) Science of Multiphysics Behavior of Si/C Composite Anodes in High-Energy-Density Lithium-Ion Batteries

The rapidly growing demands on energy storage technologies over the last decade have imposed further requirements for the high energy/power density, safety, and durability of lithium-ion batteries (LIBs). Si/C composite materials have attracted enormous research interest as the most promising candidates for the anodes of next-generation lithium-ion batteries, owing to their high energy density and mechanical buffering property. However, the major disadvantage of materials with ultra-high capacities, such as Si-based materials, is the significant volume change during cycling, which further leads to mechanical and electrochemical degradation. However, a sophisticated and quantitative understanding of the highly electrochemical-mechanical coupling behaviors is still lacking.A comprehensive computational model is indispensable in the developing process of the excellent performance of anode material due to the low-realizability, inconvenience, and high-cost of experiments, which also provides powerful tools for fabrication guidance of novel Si/C composites designs. Hence, a multiphysics modeling framework is established with a detailed geometric description to quantitatively reveal the underlying governing mechanisms of Si/C composite anode behaviors. We studied the effects of the Si weight percentage, the Si-related particle distribution, the Si-related particle size, the mechanical constraint, and the binder domain gradient on the battery performance regarding the potential behavior, capacity delivery, mechanical stress/strain, Li plating, and polarization evolution. In our study, we used silicon monoxide (SiO) as the Si element source and graphite (Gr) as the C element source. Results discover that an 8-10 wt% of SiO would be an optimal choice regarding capacity delivery and minimizing Li plating under 1C constant current charging condition. Positioning SiO particles near the separator and reducing the sizes of SiO particles are also demonstrated to be beneficial for electrochemical performance with trivial influence on mechanical mismatch. In addition, the mechanical constraint demonstrates a balanced effect on the overall performance of cells and the local behaviors of particles. Our findings also indicate that reducing the proportion of carbon-binder domain (CBD) in the upper domain (near the anode surface) compared to the lower domain (near the current collector) positively influences electrochemical performance, particularly in terms of capacity and Li plating. However, such an arrangement introduces potential risks of mechanical failures and we recommend to incorporate a higher proportion of CBD alongside the SiO particles. Finally, an anode design with a lower CBD proportion in the upper domain exhibits superior rate performance.This study explores the multiphysics behavior of Si/C anodes material using a comprehensive methodology combining experimental and FEA techniques, systematically revealing the coupling mechanism among various physical fields, as well as providing efficient and powerful tools in the design, development, and evaluation of high energy density lithium-ion batteries.

The Range of Influence across Commercial Glass Fiber Separators on the Cycling of the Zinc Metal Anode

Aqueous zinc-ion batteries (AZIBs) have attracted significant research attention due to their promising potential for large-scale energy storage applications in support of the rapid global growth of renewable wind and solar energy generation. However, challenges associated with the limited cycling life and low energy density of AZIBs persist as the critical limiting factors preventing their practical use in utility-scale energy storage applications [1]. Throughout zinc-ion research working to address these challenges, commercial glass fiber (GF) membranes are often used as the separator in studies investigating cathode, electrolyte, and anode designs [2]. Nevertheless, commercial GF membranes are available with a range of physicochemical properties, and the specific details of the selected membrane are often missing in published studies. In our work, we systematically compare Whatman™ GF separators (GF/A, GF/B, GF/C, GF/D, and GF/F) to assess the influence of the separator’s physicochemical properties (i.e., pore size and thickness) on the cycling life and cell-to-cell variability across multiple trials of Zn|Zn cells. Under constant current cycling, significant differences were observed in the cycling life and cell-to-cell consistency depending on the pore size and thickness of the GF separator [3]. In addition, our use of micro-computed X-ray tomography explores the associations between the separator’s pore size and zinc deposition morphology and provides visual identification of the failure mechanism corresponding with an overpotential collapse. The results of this work clarify the importance of GF separator selection and the separator’s influence to support the improvement of other cell components.

(Invited) Design Criteria of Ether Electrolytes and Stable Interphase Toward Reversible Intercalation Chemistry of Graphite Anode in Li-Ion Batteries

To date, it is extensively believed that ether electrolytes are incompatible with graphite anode in Li-ion batteries due to detrimental solvent co-intercalation and exfoliation. Here, we provide design criteria of ether electrolytes for reversible graphite anode without the high salt concentration. In short, for ether electrolytes, the reductive stability of anions (or their solvated complex) and the solid-electrolyte interphase (SEI) govern the reversibility of graphite anode. Exfoliation and co-intercalation are not the root cause of as-documented cell failures using graphite anodes. While reductive-instable lithium bis(fluorosulfonyl)imide (LiFSI) is the optimal salt paired with DOL, reductive-stable LiBF4 finds applications with DME. Individual 1,3-dioxolane (DOL) and 1,2-dimethoxyethane (DME) based electrolytes can enable ~99.9% Coulombic efficiency with excellent capacity retention and fast-charge capability using natural graphite. In DOL electrolytes, weakened Li-solvent interaction and preferential reduction of FSI anion coordinated with Li-ion contribute to homogeneous SEI enriched with inorganic species, for example, LiF. Therefore, electrolyte reduction and Li-DOL co-intercalation are inhibited. In DME electrolytes, we show that LiBF4 has limited reduction, majorly on the edge site. We discover that a self-terminating, heterogeneous interphase based on grainy LiF proves to be desirable for operating Li-solvent co-intercalation. Taking advantage of the anisotropic characteristics of natural graphite, we conducted a holistic investigation into the nature, function, and formation of the heterogeneous SEI. In these studies, we clarify a long-lasting confusing issue in LIBs community-that is, the compatibility between ether electrolytes and graphite anode. Our findings not only shed light on the enigmatic interphase formed by ether electrolytes but also offer critical insights into future electrolyte design for graphite anodes operated under extreme conditions.

Design of Lithium Metal Anode and Other High-Capacity Alloy Anodes Solid-State Batteries in Context of Contact Loss between Anode and Solid Electrolyte Separator

Cyclic volume changes and non-uniform electrodeposition/stripping, among other cycling-induced chemo-mechanical degradation of lithium metal and lithium-alloy solid state batteries, lead to contact loss between the anode and the solid electrolyte separator[1, 2]. In-operando experiments have shown ac-celerated short-circuiting behavior due to contact loss in “anode-free” solid-state batteries[2]. Simulations reveal the relationship between active area fraction and the ratio of effective conductivities in made-up active area configurations[3]. Through modeling experiments using imputed active con-tact area of lithium-metal anode batteries, we quantify the effects of this contact loss in terms of accelerated chemo-mechanical degradation and de-creased rate capability. Specifically, we (1) quantify the interfacial resistance due to this contact loss, (2) show non-uniform local current density distribution such that local current densities could exceed lithium filament growth critical current densities, (3) show uniaxial stress inhomogeneity due to non-uniform reaction at the anode/separator interface, and (4) show non-uniform reaction distribution at the positive electrode.Besides allowing for the optimization of designs to minimize contact loss, our work sheds light on tradeoffs in the design of solid electrolyte separators.

Deciphering the Impact of Current, Composition, and Potential on the Lithiation Behavior of Graphite in Silicon-Graphite Anodes

Graphite is the most used anode material for current-generation lithium-ion batteries due to its beneficial cycle life, availability and reasonable rate capability. Still, the modest capacity of 372 mAhg-1 represents a bottleneck in the pursuit of high-energy density anodes. Enabling much higher theoretical capacities of 3600 mAhg-1 [1], silicon represents a promising candidate as anode material for next generation batteries. However, the alloying-based lithiation mechanism of silicon is accompanied by a large volumetric change of up to 300% upon cycling, leading to fast degradation due to electrode pulverization, continuous SEI formation and extensive electrolyte consumption. Even though shallow cycling of silicon anodes has been demonstrated in laboratory scale cells [2], the mixing of silicon with graphite is considered the most viable approach to lift energy density while maintaining appropriate cycle life.Due to the fundamentally different kinetics and potentials of Li insertion and extraction of both materials, the development of silicon-graphite composite electrodes is not straightforward. One of the key questions for optimization is how the incorporation of silicon impacts the (de)lithiation behavior of graphite as a function of the silicon:graphite mass ratio, operating current and electrode potential. While lithiation of graphite in composite electrodes of 15 wt% silicon has been shown to occur in a similar manner as pure graphite, higher fractions of silicon are expected to exert more stress on the graphite and represent kinetic barriers for Li diffusion. This study presents results from in-situ X-ray diffraction experiments (XRD) of silicon-graphite/Li half cells conducted at the European Synchrotron Radiation Facility (ESRF). Serving as a reference, the current-dependent (de)lithiation behavior of a pure graphite/Li half cell has been thoroughly investigated and systematically compared to the (de)lithiation behavior of two selected silicon-graphite composite anodes (silicon:graphite ratio of 30:70 and 70:30, respectively) exposed to the same formation cycle and C-rate protocol. An optimized and novel measurement setup was used, based on a perforated current collector of the anode, providing a complete picture of the graphite in-plane and interplanar structural changes as well as the evolution of semicrystalline silicon peaks which would usually be obscured by the current collector signal.By correlating the electrochemical features (voltage curve and differential capacity plot) with the in-situ diffraction data, it was possible to identify and assign the occurrence and absence of dilute-stage and ordered graphite intercalation compounds (GICs) for the respective electrodes, yielding an in-depth insight into the graphite state of charge upon (de)lithiation and how it is influenced by the silicon content and applied C-rate.As expected, the silicon is (de)lithiated within the entire potential range, whereas graphite is most electrochemically active at potentials lower than 260 mV. In both composite electrodes, graphite attains a lower lithiation degree compared to pure graphite. This is because the high theoretical capacity of silicon results in high specific currents, ultimately challenging the rate capability of graphite. Moreover, the high delithiation overpotential encountered in the composite electrodes results in a highly asymmetrical lithiation/delithiation behavior of graphite. Also, graphite lithiation is less uniform in the composite anodes, indicated by the coexistence of dilute GICs upon (de)lithiation, compared to pure graphite where dilute phases are fully consumed (formed) as (de)lithiation progresses. Surprisingly, the in-situ XRD studies did not reveal signs of structural degradation and strain of graphite as a result of mechanical interaction with silicon. Instead, the volume change of graphite is well correlated with the amorphization of crystalline, unreacted silicon and the volume evolution of silicon crystallites upon charge-discharge.To mitigate the observed effects, the work suggests nanostructuring and advanced electrode architectures towards higher utilization and more homogeneous lithiation of graphite. Overall, the study provides a demonstration of a suitable operando cell for studies of anodes for Li-based systems, and aids the rational design of silicon-graphite composite anodes.

(Invited) Catalyst and Anode Design for Durable Alkaline-Membrane Electrolysis

Commercialized membrane electrolyzers use acidic proton exchange membranes (PEMs). These systems offer high performance but require the use of expensive precious-metal catalysts such as IrO2 and Pt that are nominally stable under locally acidic conditions. Alkaline-exchange-membrane (AEM) electrolyzers in principle offer the performance of PEM electrolyzers with the ability to use earth-abundant catalysts and inexpensive bipolar plate materials. I will highlight our fundamental work in understanding the chemical and electrochemical processes in earth-abundant water-oxidation catalysts over the past decade and we are using that understanding to drive progress in high-performance AEM electrolyzers.Baseline systems operate at 1 A·cm-2 in pure water feed at < 1.9 V at a moderate temperature of ~70 °C using either IrO2 or Co3O4 anode catalyst layers, PiperION alkaline ionomers, and stainless-steel porous transport layers. These devices, however, degrade rapidly compared to PEM electrolyzers which we link to chemical and structural changes in the ionomer-catalyst reactive zone using a combination of integrated reference-electrode device architectures, impedance, and cross-sectional and post-mortem materials analysis. We further discover that dynamic Fe-based OER catalysts – that have world-record performance in traditional liquid alkaline electrolyzer systems – perform poorly with enhanced degradation rates in alkaline membrane electrolysis, illustrating fundamentally different chemical design principles for OER catalysts.Given this baseline understanding, I will end with new chemical strategies we have developed to mitigate degradation and enhance performance using novel ionomers, passivated electrolyte-catalyst interfacial architectures, and specifically designed multicomponent anode oxygen catalysts to target stable performance without supporting soluble electrolyte: <10 μV/h degradation at currents > 2 A cm-2 and cell voltages < 2V.

Designing Better Li Metal Anodes for Next-Generation Batteries

Li metal batteries have the potential to significantly advance battery technology due to their substantially higher energy densities. However, robust high-capacity Li metal anodes are necessary to realize this approach, and current Li metal anode designs suffer from significant degradation over time due to non-uniform Li plating/stripping during cycling, which can lead to dead Li and/or Li dendrite growth. Carbon scaffold hosts can help mitigate this problem by creating a uniform electric field and providing abundant Li nucleation sites, but the relationship between the host architecture and performance is not well understood. We investigated the effect of scaffold architecture and chemistry on the resulting Li morphology and electrochemical performance using a combined experiment/theory approach. Carbon scaffolds with well-controlled geometries and varied porosities were fabricated using 3D printing and then characterized by SEM, Raman, and XPS before cycling in cells to evaluate their performance as hosts for uniform Li plating/stripping with both liquid and solid electrolytes. Atomistic and mesoscale modeling were used to predict how scaffold chemistry and microstructure affect Li nucleation probability and the formation of current density/stress hotspots that can lead to dendrite growth, and these results were used to help guide scaffold design. This work provides further insight into the relationship between anode architecture and Li metal cycling stability, which will facilitate the development of high-energy-density batteries in the future.Lawrence Livermore National Laboratory is operated by Lawrence Livermore National Security, LLC, for the U.S. Department of Energy, National Nuclear Security Administration under Contract DE-AC52-07NA27344.

High-Energy-Density High-Power-Density Micro Aluminum-Air Batteries for Small Scale Quadcopters

Small-scale quadcopters are increasingly used in various fields, including rescue, surveillance and precision agriculture. The predominant energy storage system for such quadcopters has been the micro lithium-ion battery (mLIB). Two of the most important design metrics for power sources used in quadcopters are specific power and specific energy. The specific energy determines the flight duration of the quadcopters, while specific power is necessary for maneuverability and takeoff. The mLIB can easily meet the power requirement of small scale quadcopters; however, the limited energy density of mLIBs (exacerbated by the packaging overhead of these batteries as scales shrink) constrains their flight duration. To increase the flight time, aluminum-air batteries (AABs), with a theoretical energy density twenty times greater than conventional lithium-ion batteries, are being explored. [1] Despite AAB’s high theoretical energy density, the conventional AAB lacks the high-power performance of LIBs. [2] To fulfill the demanding power requirements of small scale quadcopters, the AAB cell has been re-engineered to enhance power capability while maintaining high energy density.To maximize AAB energy and power density at the cell level, it is imperative to address the issue of battery packages that add weight without contributing to electrochemical performance. A light-weight battery packaging approach is developed for the micro-AAB (mAAB). In the context of AABs, the primary function of the battery package is to retain the aqueous electrolyte within the cell. Typically, the cathode of an AAB is constructed using a carbon cloth, doped with a layer of polytetrafluoroethylene (PTFE). This hydrophobic carbon cloth cathode effectively retains the aqueous electrolyte. In order to increase the mechanical integrity of mAAB pouch cells, 3D printed polypropylene is utilized as the body frame of mAABs, providing a robust and lightweight structure. The carbon cloth cathode is affixed to the 3D printed polypropylene using epoxy, as shown in Figure 1A. An image of an assembled 2-gram mAAB pouch cell is shown in Fig 1B. Remarkably, the electrochemically inactive packaging materials contribute to less than 13% of the total cell weight, achieving the goal of minimizing packaging material to enhance battery performance. As a comparison, the packaging material of gram-scale mLIBs can contribute to over 30% of total cell weight. Furthermore, in contrast to traditional aluminum-air battery designs, the pouch cell architecture optimizes cathode area exposure, which is advantageous for high-power applications.The anode structure is also engineered for high power capability. Figure 2A shows that increasing the anode/cathode area ratio can augment areal power density. Therefore, a multi-layer anode structure, supported by 3D printed polypropylene, is developed for mAAB pouch cells. This design effectively increases the anode/cathode surface area ratio and enables rapid ion and electron transport within the multi-layer anode, optimizing power performance. A schematic of a 3D printed polypropylene supported multi-layer anode structure is shown in Figure 2B.The electrochemical performance of assembled mAAB pouch cells is evaluated to assess their suitability for the demanding requirements of small scale quadcopter applications. Figure 3A provides a comparative analysis of power densities between mAABs and commercial micro-quadcopter mLIBs. Notably, mAABs exhibit a peak power density exceeding 1500 Wh/kgbattery at 4 Amp, surpassing that of mLIBs. Battery weight encompasses anode, cathode, electrolyte and all necessary battery packaging, confirming that mAABs can meet the power demands of micro-quadcopters. In Figure 3B, the energy density of mAABs is compared to commercial mLIBs. When the power density is above 500 W/kgbattery, a threshold sufficient to lift a quadrotor drone, mAABs exhibit an energy density of 320 Wh/kgbattery, which is multiple times higher than that of mLIBs. [3] Notably, the anode utilization of the mAAB exceeds 85%, underscoring the effectiveness of the multi-layer anode design. This superior electrochemical performance emphasizes the superior capability of mAABs, indicating their potential as an advanced power source for long flight duration small scale quadcopters.

Dual plating zinc foam of three-dimensional reconstruction as a high-flux and stable zinc metal anode for aqueous zinc-ion batteries

The practical utilization of zinc-metal anodes is primarily hindered by the restricted lifespan and diminished Coulombic efficiency (CE) arising from the growth of zinc dendrites and concurrent side reactions. To tackle these challenges, numerous 3D hosts have been thoroughly investigated, although there is still a need to address concerns related to high-flux deposition and electrode corrosion resistance. In a pioneering effort, a double-coated material derived from foamed zinc (denoted as FZn@Cu) has been developed for utilization as an anode in high-performance zinc-metal batteries. FZn@Cu originates from a three-dimensional reconstruction of a zinc electrode (foam Zn) in a porous and layered structure with a dense Cu coating on the surface and a solid CuZn5 at the interface. Experimental observations, density-functional theory calculations and phase-field simulations indicate that zincphilic Cu and CuZn5 can induce homogeneous deposition of Zn. The results show that FZn@Cu has low voltage hysteresis (25.1 mV), long cycling stability (exceeding 1800 h) and the ability to inhibit electrode corrosion. In addition, the full cell based on FZn@Cu composite anode and MnO2 cathode exhibits excellent multiplicity performance and stable cycle life (133.9 mAh g−1 at 1 A g−1 after 1000 cycles). This study introduces an innovative and scalable zinc-based anode material, offering a new strategy for the design of dendrite-free zinc anodes.