The propensity of metals to form irregular and nonplanar electrodeposits at liquid-solid interfaces has emerged as a fundamental barrier to high-energy, rechargeable batteries that use metal anodes. ...We report an epitaxial mechanism to regulate nucleation, growth, and reversibility of metal anodes. The crystallographic, surface texturing, and electrochemical criteria for reversible epitaxial electrodeposition of metals are defined and their effectiveness demonstrated by using zinc (Zn), a safe, low-cost, and energy-dense battery anode material. Graphene, with a low lattice mismatch for Zn, is shown to be effective in driving deposition of Zn with a locked crystallographic orientation relation. The resultant epitaxial Zn anodes achieve exceptional reversibility over thousands of cycles at moderate and high rates. Reversible electrochemical epitaxy of metals provides a general pathway toward energy-dense batteries with high reversibility.
This study develops a tunable 3D nanostructured conductive gel framework as both binder and conductive framework for lithium ion batteries. A 3D nanostructured gel framework with continuous electron ...pathways can provide hierarchical pores for ion transport and form uniform coatings on each active particle against aggregation. The hybrid gel electrodes based on a polypyrrole gel framework and Fe3O4 nanoparticles as a model system in this study demonstrate the best rate performance, the highest achieved mass ratio of active materials, and the highest achieved specific capacities when considering total electrode mass, compared to current literature. This 3D nanostructured gel‐based framework represents a powerful platform for various electrochemically active materials to enable the next‐generation high‐energy batteries.
A tunable 3D nanostructured gel framework with continuous electron pathways can provide hierarchical pores for ion transport and form uniform coatings on each active particle against aggregation. The hybrid gel electrodes based on a polypyrrole gel framework and Fe3O4 nanoparticles demonstrate one of the best rate performances and the highest achieved specific capacities when considering total electrode mass.
Controlling architecture of electrode composites is of particular importance to optimize both electronic and ionic conduction within the entire electrode and improve the dispersion of active ...particles, thus achieving the best energy delivery from a battery. Electrodes based on conventional binder systems that consist of carbon additives and nonconductive binder polymers suffer from aggregation of particles and poor physical connections, leading to decreased effective electronic and ionic conductivities. Here we developed a three-dimensional (3D) nanostructured hybrid inorganic-gel framework electrode by in situ polymerization of conductive polymer gel onto commercial lithium iron phosphate particles. This framework electrode exhibits greatly improved rate and cyclic performance because the highly conductive and hierarchically porous network of the hybrid gel framework promotes both electronic and ionic transport. In addition, both inorganic and organic components are uniformly distributed within the electrode because the polymer coating prevents active particles from aggregation, enabling full access to each particle. The robust framework further provides mechanical strength to support active electrode materials and improves the long-term electrochemical stability. The multifunctional conductive gel framework can be generalized for other high-capacity inorganic electrode materials to enable high-performance lithium ion batteries.
Spinel transition metal oxides (TMOs) have emerged as promising anode materials for lithium-ion batteries. It has been shown that reducing their particle size to nanoscale dimensions benefits overall ...electrochemical performance. Here, we use in situ transmission electron microscopy to probe the lithiation behavior of spinel ZnFe
O
as a function of particle size. We have found that ZnFe
O
undergoes an intercalation-to-conversion reaction sequence, with the initial intercalation process being size dependent. Larger ZnFe
O
particles (40 nm) follow a two-phase intercalation reaction. In contrast, a solid-solution transformation dominates the early stages of discharge when the particle size is about 6-9 nm. Using a thermodynamic analysis, we find that the size-dependent kinetics originate from the interfacial energy between the two phases. Furthermore, the conversion reaction in both large and small particles favors {111} planes and follows a core-shell reaction mode. These results elucidate the intrinsic mechanism that permits fast reaction kinetics in smaller nanoparticles.
Some types of batteries contain both a transition metal reducible metal, such as the cathode material Ag2VP2O8. During operation, both Ag and V ions are reduced, and the Ag atoms can form wires to ...enhance the internal conductivity. Kirshenbaum et al. probe the discharge of a battery at different rates and track the formation of Ag atoms using in situ energy-dispersive x-ray diffraction (see the Perspective by Dudney and Li). They show how the discharge rate affects whether the Ag or V is preferentially reduced and also the distribution of the Ag atoms, and then correlate this to the loss of battery capacity at higher discharge rates. Science, this issue p. 149; see also p. 131 The functional capacity of a battery is observed to decrease, often quite dramatically, as discharge rate demands increase. These capacity losses have been attributed to limited ion access and low electrical conductivity, resulting in incomplete electrode use. A strategy to improve electronic conductivity is the design of bimetallic materials that generate a silver matrix in situ during cathode reduction. Ex situ x-ray absorption spectroscopy coupled with in situ energy-dispersive x-ray diffraction measurements on intact lithium/silver vanadium diphosphate (Li/Ag2VP2O8) electrochemical cells demonstrate that the metal center preferentially reduced and its location in the bimetallic cathode are rate-dependent, affecting cell impedance. This work illustrates that spatial imaging as a function of discharge rate can provide needed insights toward improving realizable capacity of bimetallic cathode systems.
LiNi0.6Mn0.2Co0.2O2 (NMC622) is one of the most promising Li-ion battery cathodes as it delivers high capacity at high potentials. However, high potentials also lead to decreases in capacity ...retention where the disintegration of the secondary particles has been implicated as a major driving force of this capacity fade. This has been attributed to anisotropic lattice changes and increased microstrain during cycling. To probe how these factors affect capacity fade, Li/NMC622 batteries were cycled from 3 to 4.3 or 4.7 V and probed with operando X-ray diffraction (XRD) over the 1st, 2nd, and 101st cycles. Further characterization with scanning electron microscopy and inductively coupled plasma-optical emission spectroscopy was also performed. The use of operando XRD over many cycles allowed for the collection of detailed structural information in real time over a time frame in which fading can be observed. During the first two cycles, the cells charged to 4.7 V exhibit increased anisotropic lattice changes as compared to the cells charged to 4.3 V. Upon the 101st cycle, when significant fade has been observed, the cells charged to 4.3 and 4.7 V show identical lattice changes to one another, while the 4.7 V charge limit induces more microstrain. This shows that elevated microstrain at high charge limits is a major driver for particle disintegration in NMC622 cathodes. This study provides important insights into the mechanisms of particle disintegration and capacity fade in NMC/Li-ion batteries, which will enable the design of NMC electrodes that deliver both higher capacities and exhibit better capacity retention.
Peierls stresses (τP) of dislocations of 66 slip systems in 52 crystals were estimated from experimental data either by direct extrapolation of the critical resolved shear stress (τc) vs. temperature ...curve to absolute zero temperature, or from the T0 value at which the temperature dependence of τc vanishes, based on the kink-pair formation enthalpy, which is a function of τP, described by the line tension model of the dislocation. The normalized τP/G (G is the shear modulus) values are distributed over four orders of magnitude, but τP/G values for a group of crystals with the same crystal structure are within an order of magnitude, indicating a homologous nature of τP in crystals. In order to compare the results with the Peierls–Nabarro (P–N) formula generalized to any dislocation character, log(τP/G) values were correlated with crystal parameters. In this generalized P–N plot, most of the plots deviate downwards from the Huntington relation (a revised, original P–N relation) and the results of the discretized P–N models of Ohsawa et al. (Ohsawa K, Koizumi H, Kirchner HOK, Suzuki T. Philos Mag A 1994;69:171), with the deviation becoming larger at large h/δ value, where h is the lattice spacing of the glide plane, and δ is the period of the lattice in the direction of the dislocation glide. In the plot, there is a tendency that the stronger the covalent character, the higher the τP/G value, reflecting the general tendency of the normalized theoretical shear strength of crystals.
In times of crisis, including the current COVID-19 pandemic, the supply chain of filtering facepiece respirators, such as N95 respirators, are disrupted. To combat shortages of N95 respirators, many ...institutions were forced to decontaminate and reuse respirators. While several reports have evaluated the impact on filtration as a measurement of preservation of respirator function after decontamination, the equally important fact of maintaining proper fit to the users' face has been understudied. In the current study, we demonstrate the complete inactivation of SARS-CoV-2 and preservation of fit test performance of N95 respirators following treatment with dry heat. We apply scanning electron microscopy with energy dispersive X-ray spectroscopy (SEM/EDS), X-ray diffraction (XRD) measurements, Raman spectroscopy, and contact angle measurements to analyze filter material changes as a consequence of different decontamination treatments. We further compared the integrity of the respirator after autoclaving versus dry heat treatment via quantitative fit testing and found that autoclaving, but not dry heat, causes the fit of the respirator onto the users face to fail, thereby rendering the decontaminated respirator unusable. Our findings highlight the importance to account for both efficacy of disinfection and mask fit when reprocessing respirators to for clinical redeployment.
PDF
