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The practical application of high-capacity Li-rich cathode materials is hindered by capacity fading and voltage decay. The capacity fading and voltage decay could be effectively overcome by using water-soluble guar gum (GG) binder instead of traditional polyvinylidene fluoride (PVDF). However, the specific role of the GG binder is not clear yet, though the GG binder can significantly improve the electrochemical performance of Li-rich cathode. To understand the effect of GG binder on the morphology, microstructure of electrode and electrode/electrolyte interfaces, ex-situ scanning electron microscope (SEM), transmission electron microscope (TEM), X-ray adsorption near edge spectroscopy (XANES), in-situ electrochemical impedance spectroscopy (EIS) were applied to comparatively study the charge-discharge processes of Li-rich Li1.2Ni0.2Mn0.6O2 cathode when using GG and PVDF as binders. The results indicate that the GG binder can prevent electrode crack and active material loss, ascribing to the strong mechanical adhesion of GG binder with active material particles and current collector. It has found that the GG binder can also induce the formation of a uniform layer on Li1.2Ni0.2Mn0.6O2 particles’ surface. As a consequence, both the electrolyte decomposition and the electrode corrosion were significantly inhibited. The strong chelation between Mn2+ and polar OH group restrain Mn ion dissolution, which contributes to surface structural transformation mitigation. The present study reveals the role of water-soluble GG binder in reducing capacity fading and voltage decay of Li-rich material and is of great importance in design functional binders for high-performance Li-rich electrodes.

We report an investigation of the pseudo-photocatalytic behavior of rutile TiO2 nanorods for water splitting observed with liquid cell transmission electron microscopy (TEM). The electron beam serves as a “light” source to initiate the catalytic reaction and a “water-in-salt” aqueous solution is employed as the electrolyte. The observation reveals that bubbles are generated preferentially residing near the {110} facet of a rutile TiO2 nanorod under a low electron dose rate (9.3–18.6 e-/Å2·s). These bubbles are ascribed to hydrogen gas generated from the pseudo-photocatalytic water splitting. As the electron beam current density increases to 93 e-/Å2 ·s, bubbles are also found at the {001} and {111} facets as well as in the bulk liquid solution, demonstrating the dominant effects of water electrolysis by electron beam under higher dose rates. The facet-dependent pseudo-photocatalytic behavior of rutile TiO2 nanorods is further validated using density functional theory (DFT)calculation. Our work establishes a facile liquid cell TEM setup for the study of pseudo-photocatalytic water splitting and it may also be applied to investigation of other photo-activated phenomena occurring at the solid-liquid interfaces.

Rational design and synthesis of transition metal sulfide complex nanostructures are significant for achieving desired materials properties for a variety of applications. Herein, we synthesized nickel sulfide (NiS) nanostructures using laser irradiation in an aqueous solution and under the ambient condition. Crystalline nanostructures with high phase-purity were achieved without further calcination. Other transition metal sulfides, such as CuS and ZnS, were also successfully synthesized using the laser irradiation approach, suggesting the practical application of this method. The hydrogen evolution reaction (HER) measurements show the NiS nanostructures synthesized for 4h (NiS-4h) not only exhibited competitive overpotential (−159 mV vs. RHE at 10 A/g), lower Tafel slope (218 mV/dec) but also delivered long-term stability (14 A/g at −250 mV vs. RHE for 12h). Moreover, the NiS-4h functioned as the electrode for supercapacitor with excellent specific capacitance (3761 F/g at 10 mV/s), reversibility and rate capability (1152 F/g at 100 mV/s). These superb electrochemical performances are attributed to the remarkable value of electrochemically active surface area (ECSA) and synergistic effect of Ni3+OOH for HER electrocatalytic activities, while the co-existence of Ni2+ and Ni3+ facilitates the rich redox reactions of NiS for supercapacitor.

The first-cycle behavior of layered Li-rich oxides, including Li2MnO3 activation and cathode electrolyte interphase (CEI) formation, significantly influences their electrochemical performance. However, the Li2MnO3 activation pathway and the CEI formation process are still controversial. Here, the first-cycle properties of xLi2MnO3·(1- x) LiNi0.3Co0.3Mn0.4O2 ( x = 0, 0.5, 1) cathode materials were studied with an in situ electrochemical quartz crystal microbalance (EQCM). The results demonstrate that a synergistic effect between the layered Li2MnO3 and LiNi0.3Co0.3Mn0.4O2 structures can significantly affect the activation pathway of Li1.2Ni0.12Co0.12Mn0.56O2, leading to an extra-high capacity. It is demonstrated that Li2MnO3 activation in Li-rich materials is dominated by electrochemical decomposition (oxygen redox), which is different from the activation process of pure Li2MnO3 governed by chemical decomposition (Li2O evolution). CEI evolution is closely related to Li+ extraction/insertion. The valence state variation of the metal ions (Ni, Co, Mn) in Li-rich materials can promote CEI formation. This study is of significance for understanding and designing Li-rich cathode-based batteries.

Localized high‐concentration electrolyte (LHCE) is considered to be a promising substitution for the conventional carbonate electrolytes in fast‐charging Li‐ion batteries. However, the rate‐determining steps (RDS) for fast‐charging electrodes (i.e., graphite anode) in LHCE remain unclear. Herein, a typical localized high‐concentration electrolyte consisting of lithium bis(fluorosulfonyl)imide in dimethoxyethane with 1,1,2,2‐tetrafluoroethyl‐2,2,3,3‐tetrafluoropropyl ether as a diluent is selected to investigate the RDS of lithiation process in graphite anode, including the diffusion of solvated Li+ in the electrolyte, the desolvation behavior of solvated Li+, the Li+ transfer in solid electrolyte interphase (SEI) on the graphite surface, and the Li+ diffusion in bulk graphite. The results indicated that the rate performance of graphite anode in LHCE lies in the balance between Li+ desolvation process and Li+ migration in SEI. Through the regulation of solvated Li+ structure and SEI component, excellent fast‐charging performance can be obtained in the LHCE. The present studies not only offer fresh insights in the mechanistic understanding of fast‐charging batteries, but also provide new clues to the performance improvement of graphite anodes. [ABSTRACT FROM AUTHOR]

Sulfide‐based all‐solid‐state lithium‐ion batteries (ASSLIBs) are the widely recognized approach toward high safety owing to excellent ionic conductivity and nonflammable nature of solid‐state electrolytes (SSEs). However, narrow potential window of SSEs brings about serious interfacial parasitic reactions, resulting in fast degradation of the battery. Herein, a glassy/ceramic analogous solid electrolyte interface (SEI) is constructed on LiCoO2 (LCO) to enhance interfacial stability between LCO and the Li10GeP2S12 (LGPS) SSEs. In which, ceramic Li2TiO3 guarantees good mechanical toughness of analogous SEI, while glassy LixByOz reinforces the coverage to avoid parasitic reactions. Analogous SEI endows ASSLIBs with excellent cycling and rate performance under an upper charge voltage of 4.3 V with 82.3% capacity retention after 300 cycles at 0.2 C. When pushing charge voltage to 4.5 V, analogous SEI also enables desirable performance with an initial capacity of 172.7 mAh g−1 and long lifespan of 200 cycles at 0.2 C. Both experiments and theoretical computation reveal excellent stability between analogous SEI and LGPS, which endows ASSLIBs with small polarization and improved performance. This work provides an insight on glassy/ceramic analogous SEI strategy to boost the interfacial stability of ASSLIBs. [ABSTRACT FROM AUTHOR]

Aqueous zinc‐ion battery (AZB) is a promising candidate for next‐generation energy storage owing to inherent safety and low cost. However, AZBs are currently plagued by Zn dendrite growth and undesirable side‐reactions, leading to poor cycling stability and premature failure. To restrain the uncontrollable Zn growth, a unique separator is developed based on polyacrylonitrile/graphene oxide (abbreviated as PG) composite nanofibers, which contain abundance of zincophilicity functional groups to regulate the migration and distribution of Zn2+ ions in the separator. It is demonstrated that the cyano ligands on PG not only facilitate the dehydration of solvated Zn2+ ions prior to deposition, but also form fast lanes to enable homogenous scattering of deposition spots. Benefiting from these features, the PG separator offers a high ionic conductivity of 7.69 mS cm‐1 and a transference number of 0.74 for Zn2+. The Zn||Zn symmetrical cells with PG separators achieve an ultra‐stable cycle life over 13 000 h. Zn||Zn0.27V2O5 full batteries with PG separators retain 71.5% of the original capacity after 2800 cycles at a high current density of 2 A g‐1. This study offers future research directions toward the design of multifunctional separators to overcome the limits of Zn metal anode in AZBs. [ABSTRACT FROM AUTHOR]

As a powerful tool for chemical compositional analyses, electron energy loss spectroscopy (EELS) can reveal an abundance of information regarding the atomic‐level electron state in a variety of materials, including the elemental types as well as their valence and concentration distributions, and the structure‐related atom radial distribution. Benefiting from its unique capabilities and the newly developed advanced transmission electron microscope (TEM) configurations (i.e., in situ bias, in situ heating, cryo‐TEM, etc.), EELS has facilitated the battery studies in various aspects. Here, a brief introduction of EELS is provided. Thereafter, a description of the recent progress in studying battery materials using EELS is provided, and finally a look ahead on the future development of EELS techniques and their applications in battery studies is provided. [ABSTRACT FROM AUTHOR]

As one of the most promising cathodes for Li‐ion batteries, Li‐rich layered oxides suffer from low Coulombic efficiency, severe capacity fading, and voltage decay, which are related to the aggregated Li@Mn6 superstructure units. Herein, a Co‐free Li‐rich oxide Li[Li1/4Mn1/2Ni1/6Al1/12]O2 through Al substitution of Co in Li[Li1/4Mn1/2Ni1/6Co1/12]O2, is designed. Combining the average structural refinement with the detailed local structural/chemical analysis, it is found that the introduced Al ions occupy the Mn sites in Li@Mn6 superstructure units, which further induces the partial replacement of the central Li ions in Li@Mn6 units by Ni2+. The modified superstructure units stabilize the anionic framework and suppress structural degradation during long‐term cycling. A superior cyclability (a capacity retention of 91.4% after 500 cycles at 1 C) is achieved. This work not only deepens the understanding into the mechanism of Al substitution, but also provides a novel route to design high‐performance Li‐rich cathodes by modifying the local functional units. [ABSTRACT FROM AUTHOR]