The large-voltage hysteresis remains one of the biggest barriers to optimizing Li/Na-ion cathodes using lattice anionic redox reaction, despite their very high energy density and relative low cost. Very recently, a layered sodium cathode Na2Mn3O7 (or Na4/7Mn6/7□1/7O2, □ is vacancy) was reported to have reversible lattice oxygen redox with much suppressed voltage hysteresis. However, the structural and electronic structural origin of this small-voltage hysteresis has not been well understood. In this article, through systematic studies using ex situ/in situ electron paramagnetic resonance and X-ray diffraction, we demonstrate that the exceptional small-voltage hysteresis (<50 mV) between charge and discharge curves is rooted in the well-maintained oxygen stacking sequence in the absence of irreversible gliding of oxygen layers and cation migration from the transition-metal layers. In addition, we further identify that the 4.2 V charge/discharge plateau is associated with a zero-strain (de)­intercalation process of Na+ ions from distorted octahedral sites, while the 4.5 V plateau is linked to a reversible shrink/expansion process of the manganese-site vacancy during (de)­intercalation of Na+ ions at distorted prismatic sites. It is expected that these findings will inspire further exploration of new cathode materials that can achieve both high energy density and efficiency by using lattice anionic redox.

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A novel P3-type Na2/3Mg1/3Mn2/3O2 cathode delivers a reversible capacity over 200 mA h g−1 mainly using lattice oxygen redox.

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 Fe O 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.

Although several principles have been recognized to fabricate a nominal "better" binder, there continues to be a lack of a rational design and synthesis approach that would meet the robust criteria required for silicon (Si) anodes. Herein, we report a synthetic polymer binder, i.e., catechol-functionalized chitosan cross-linked by glutaraldehyde (CS-CG+GA), that serves dual functionalities: (a) wetness-resistant adhesion capability via catechol grafting and (b) mechanical robustness via in situ formation of a three-dimensional (3D) network. A SiNP-based anode with a designed functional polymer network (CS-CG10%+6%GA) exhibits a capacity retention of 91.5% after 100 cycles (2144 ± 14 mAh/g). Properties that are traditionally considered to be advantageous, including stronger adhesion strength and higher mechanical robustness, do not always improve the binder performance. A clear relationship between these properties and ultimate electrochemical performance is established by assessing the rheological behavior, mechanical property, adhesion force, peel stress, morphology evolution, and semiquantitative evaluation. This study provides a clear path for the rational design of high-performance functional polymer binders for not only Si-based electrodes but also other types of alloy and conversion-based electrodes.

A sulfonamide-based electrolyte can greatly improve the cycling stability of the commercial LiCoO2 cathode at high cut-off voltages in Li metal||LCO batteries by stabilizing the electrode–electrolyte interfaces on both the anode and cathode.

We report an extensive study on fundamental properties that determine the functional electrochemistry of ZnFe2O4 spinel (theoretical capacity of 1000 mAh/g). For the first time, the reduction mechanism is followed through a combination of in situ X-ray diffraction data, synchrotron based powder diffraction, and ex-situ extended X-ray absorption fine structure allowing complete visualization of reduction products irrespective of their crystallinity. The first 0.5 electron equivalents (ee) do not significantly change the starting crystal structure. Subsequent lithiation results in migration of Zn2+ ions from 8a tetrahedral sites into vacant 16c sites. Density functional theory shows that Li+ ions insert into 16c site initially and then 8a site with further lithiation. Fe metal is formed over the next eight ee of reduction with no evidence of concurrent Zn2+ reduction to Zn metal. Despite the expected formation of LiZn alloy from the electron count, we find no evidence for this phase under the tested conditions. Additionally, upon oxidation to 3 V, we observe an FeO phase with no evidence of Fe2O3. Electrochemistry data show higher electron equivalent transfer than can be accounted for solely based on ZnFe2O4 reduction indicating excess capacity ascribed to carbon reduction or surface electrolyte interphase formation.

Doped motifs offer an intriguing structural pathway toward improving conductivity for battery applications. Specifically, Ca-doped, three-dimensional "flower-like" Li 4−x Ca x Ti 5 O 12 ("x" = 0, 0.1, 0.15, and 0.2) micrometer-scale spheres have been successfully prepared for the first time using a simple and reproducible hydrothermal reaction followed by a short calcination process. The products were experimentally characterized by means of X-ray diffraction (XRD), transmission electron microscopy (TEM), scanning electron microscopy (SEM), energy dispersive spectroscopy (EDS) mapping, inductively coupled plasma optical emission spectrometry (ICP-OES), X-ray photoelectron spectroscopy (XPS), cyclic voltammetry (CV), electrochemical impedance spectroscopy (EIS), and galvanostatic charge−discharge testing. Calcium dopant ions were shown to be uniformly distributed within the LTO structure without altering the underlying "flower-like" morphology. The largest lattice expansion and the highest Ti 3+ ratios were noted with XRD and XPS, respectively, whereas increased charge transfer conductivity and decreased Li + -ion diffusion coefficients were displayed in EIS for the Li 4−x Ca x Ti 5 O 12 ("x" = 0.2) sample. The "x" = 0.2 sample yielded a higher rate capability, an excellent reversibility, and a superior cycling stability, delivering 151 and 143 mAh/g under discharge rates of 20C and 40C at cycles 60 and 70, respectively. In addition, a high cycling stability was demonstrated with a capacity retention of 92% after 300 cycles at a very high discharge rate of 20C. In addition, first-principles calculations based on density functional theory (DFT) were conducted with the goal of further elucidating and understanding the nature of the doping mechanism in this study. The DFT calculations not only determined the structure of the Ca-doped Li 4 Ti 5 O 12 , which was found to be in accordance with the experimentally measured XPD pattern, but also yielded valuable insights into the doping-induced effect on both the atomic and electronic structures of Li 4 Ti 5 O 12 .