Redox Couple Strategy for Improving the Oxygen Redox Activity and Reversibility of Li- and Mn-Rich Cathode Materials.

The specific capacity of Li- and Mn-rich layered oxide (LMROs) cathodes can be enhanced by the oxidation of lattice oxygen at high voltages. Nevertheless, an irreversible oxygen loss emerges with cycling, which triggers interlocking surface/interface issues and results in the fast deterioration of cycling performance. Herein, we prepare a surface modified LMRO electrode by one step doctor-blade casting and introducing a benzoquinone species DBBQ redox couple. The electrochemical test shows that the DBBQ-modified electrode has a high reversible capacity (>320 mAh g-1) and excellent rate performance, while the cyclic stability has been significantly improved as well. The capacity retention reaches as high as 93.3% after 500 cycles at 1 C. Mechanism analysis shows that DBBQ can not only play a redox couple in LMROs which achieves the adsorption and reduction of surface oxygen gas but also significantly enhance anionic redox in the bulk, thus realizing extraordinary capacity.

Local Electronic Structure Regulation Enabling Fluorophosphates Cathode with Improved Redox Potential and Reversible Capacity for Sodium-Ion Batteries.

Mn-based fluorophosphates have attracted much attention as cathodes for sodium-ion batteries owing to their high cost effectiveness, considerable capacity, and stable framework. However, the fascinating Mn3+/2+ redox couple suffers from inadequate activation due to the Mn-O covalent character and poor electronic conductivity, impeding its further applications. Herein, a local electronic structure regulation strategy is proposed to improve the Mn3+/2+ redox potential and reversible capacity simultaneously through introducing elements with low-energy 3d orbitals to expand the energy gap between the eg orbitals and Fermi energy of Na. Moreover, the 3d element substitution serves to narrow the band gap toward the improved intrinsic electronic conductivity. In comparison with pristine Na2Fe0.45Mn0.55PO4F, the as-prepared Na2Fe0.45Mn0.4V0.1PO4F cathode achieves an increase from 3.5 to 3.6 V in the high-voltage platform and an improvement in energy density from 330 to 361 Wh kg-1. This work inspires new ideas in adjusting the redox potential of polyanionic cathodes through deliberate regulation of the local electronic structure.

A Na-Free Surface Enables "Three-In-One" Enhancement of Structural, Interfacial and Air Stability for Sodium-Ion Battery Cathodes.

O3-type layered oxides are regarded as one of the most promising cathode materials for sodium-ion batteries. However, the multistep phase transitions, severe electrode/electrolyte parasitic reactions, and moisture sensitivity are challenging for their practical application because of the highly active Na+. Here, a Na-free layer is built on the surface of NaNi1/3Mn1/3Fe1/3O2 (NMF111) via a leaching treatment and the subsequent surface reconstruction. Accordingly, both the structural degradation from bulk to surface and the overgrowth of the solid electrolyte interface (SEI) are greatly ameliorated, which results in the improved capacity retention of modified NMF111 from 58.3% to 89.6% after 400 cycles at 1 C. Besides, the Na-free surface with rock-salt structure prevents the H+/Na+ exchange and then enables good reversibility and low polarization of the optimal NMF111 when exposed to wet air (50% RH) for 4 days. This work opens a new avenue for the comprehensive cyclability improvement of layered oxides via surface reconstruction.

A Novel 4-Fluorophenyl Isocyanate Additive Constructing Solid Cathodes-Electrolyte Interface for High-Performance Lithium-Ion Batteries.

Building a stable cathode-electrolyte interface (CEI) is crucial for achieving high-performance layered metal oxide cathode materials LiNixCoyMn1-x-yO2 (NCM). In this work, a novel 4-fluorobenzene isocyanate (4-FBC) electrolyte additive that contains isocyanate and benzene ring functional groups is proposed, which can form robust and homogeneous N-rich and benzene ring skeleton CEI film on the cathode surface, leading to significant improvement in the electrochemical performance of lithium-ion batteries. Taking LiNi0.5Co0.2Mn0.3O2 (NCM523) as an example, the NCM523/SiO@Graphite pouch full cells with electrolytes containing a mass fraction of 1% 4-FBC additives demonstrate improved capacity retention after 200 cycles, retaining capacity retention rates of 81.3%, which is much higher than that of 39.1% without additive. The improvement can be ascribed to the mitigation of electrolyte decomposition and inhibition of transition metal ions the dissolution from the cathode material due to the stable CEI film. Moreover, the electrochemical performance enhancement can also be achieved in high voltage and Ni-rich cathode materials, indicating the universality and effectiveness of this strategy for the practical applications of high energy density lithium-ion batteries.

Transient Zwitterions Dynamics Empowered Adaptive Interface for Ultra-Stable Zn Plating/Stripping.

A highly reversible zinc anode is crucial for the commercialization of zinc-ion batteries. However, the change in the microstructure of the electric double layer originated from the dynamic change in charge density on the electrode greatly impacts anode reversibility during charge/discharge, which is rarely considered in previous research. Herein, the zwitterion additive is employed to create an adaptive interface by coupling the transient zwitterion dynamics upon the change of interfacial charge density. Ab initio molecular dynamics simulations suggest the molecular orientation and adsorption groups of zwitterions will be determined by the charging state of the electrode. ZnSO4 electrolyte with zwitterion fulfills a highly reversible Zn anode with an average Coulombic efficiency of up to 99.85%. Zn/Zn symmetric cells achieve greatly enhanced cycling stability for 700 h with extremely small voltage hysteresis of 29 mV under 5 mA cm-2 with 5 mAh cm-2 . This study validates the adaptive interface based on transient dynamics of zwitterions, which sheds new light on developing highly reversible metal anodes with a high utilization rate.

Critical Review of Emerging Pre-metallization Technologies for Rechargeable Metal-Ion Batteries.

Low Coulombic efficiency, low-capacity retention, and short cycle life are the primary challenges faced by various metal-ion batteries due to the loss of corresponding active metal. Practically, these issues can be significantly ameliorated by compensating for the loss of active metals using pre-metallization techniques. Herein, the state-of-the-art development in various pr-emetallization techniques is summarized. First, the origin of pre-metallization is elaborated and the Coulombic efficiency of different battery materials is compared. Second, different pre-metallization strategies, including direct physical contact, chemical strategies, electrochemical method, overmetallized approach, and the use of electrode additives are summarized. Third, the impact of pre-metallization on batteries, along with its role in improving Coulombic efficiency is discussed. Fourth, the various characterization techniques required for mechanistic studies in this field are outlined, from laboratory-level experiments to large scientific device. Finally, the current challenges and future opportunities of pre-metallization technology in improving Coulombic efficiency and cycle stability for various metal-ion batteries are discussed. In particular, the positive influence of pre-metallization reagents is emphasized in the anode-free battery systems. It is envisioned that this review will inspire the development of high-performance energy storage systems via the effective pre-metallization technologies.

An Active Strategy to Reduce Residual Alkali for High-Performance Layered Oxide Cathode Materials of Sodium-Ion Batteries.

Residual alkali is one of the biggest challenges for the commercialization of sodium-based layered transition metal oxide cathode materials since it can even inevitably appear during the production process. Herein, taking O3-type Na0.9Ni0.25Mn0.4Fe0.2Mg0.1Ti0.05O2 as an example, an active strategy is proposed to reduce residual alkali by slowing the cooling rate, which can be achieved in one-step preparation method. It is suggested that slow cooling can significantly enhance the internal uniformity of the material, facilitating the reintegration of Na+ into the bulk material during the calcination cooling phase, therefore substantially reducing residual alkali. The strategy can remarkably suppress the slurry gelation and gas evolution and enhance the structural stability. Compared to naturally cooled cathode materials, the capacity retention of the slowly cooled electrode material increases from 76.2% to 85.7% after 300 cycles at 1 C. This work offers a versatile approach to the development of advanced cathode materials toward practical applications.

In Situ Fast Construction of Ni3S4/FeS Catalysts on 3D Foam Structure Achieving Stable Large-Current-Density Water Oxidation.

By increasing the content of Ni3+, the catalytic activity of nickel-based catalysts for the oxygen evolution reaction (OER), which is still problematic with current synthesis routes, can be increased. Herein, a Ni3+-rich of Ni3S4/FeS on FeNi Foam (Ni3S4/FeS@FNF) via anodic electrodeposition to direct obtain high valence metal ions for OER catalyst is presented. XPS showed that the introduction of Fe not only further increased the Ni3+ concentration in Ni3S4/FeS to 95.02%, but also inhibited the dissolution of NiOOH by up to seven times. Furthermore, the OER kinetics is enhanced by the combination of the inner Ni3S4/FeS heterostructures and the electrochemically induced surface layers of oxides/hydroxides. Ni3S4/FeS@FNF shows the most excellent OER activity with a low Tafel slope of 11.2 mV dec-1 and overpotentials of 196 and 445 mV at current densities of 10 and 1400 mA cm-2, respectively. Furthermore, the Ni3S4/FeS@FNF catalyst can be operated stably at 1500 mA cm-2 for 200 h without significant performance degradation. In conclusion, this work has significantly increased the high activity Ni3+ content in nickel-based OER electrocatalysts through an anodic electrodeposition strategy. The preparation process is time-saving and mature, which is expected to be applied in large-scale industrialization.

Se-p Orbitals Induced "Strong d-d Orbitals Interaction" Enable High Reversibility of Se-Rich ZnSe/MnSe@C Electrode as Excellent Host for Sodium-Ion Storage.

The heterostructure of transition-metal chalcogenides is a promising approach to boost alkali ion storage due to fast charge kinetics and reduction of activation energy. However, cycling performance is a paramount challenge that is suffering from poor reversibility. Herein, it is reported that Se-rich particles can chemically interact with local hexagonal ZnSe/MnSe@C heterostructure environment, leading to effective ions insertion/extraction, enabling high reversibility. Enlightened by theoretical understanding, Se-rich particles endow high intrinsic conductivities in term of low energy barriers (1.32 eV) compared with those without Se-rich particles (1.50 eV) toward the sodiation process. Moreover, p orbitals of Se-rich particles may actively participate and further increase the electronegativity that pushes the Mn d orbitals (dxy and dx2-y2) and donate their electrons to dxz and dyz orbitals, manifesting strong d-d orbitals interaction between ZnSe and MnSe. Such fundamental interaction will adopt a well-stable conducive electronic bridge, eventually, charges are easily transferred from ZnSe to MnSe in the heterostructure during sodiation/desodiation. Therefore, the optimized Se-rich ZnSe/MnSe@C electrode delivered high capacity of 576 mAh g-1 at 0.1 A g-1 after 100 cycles and 384 mAh g-1 at 1 A g-1 after 2500 cycles, respectively. In situ and ex situ measurements further indicate the integrity and reversibility of the electrode materials upon charging/discharging.

Cu-N Synergism Regulation to Enhance Anionic Redox Reversibility and Activity of Li- and Mn-Rich Layered Oxides Cathode.

Anionic redox chemistry enables extraordinary capacity for Li- and Mn-rich layered oxides (LMROs) cathodes. Unfortunately, irreversible surface oxygen evolution evokes the pernicious phase transition, structural deterioration, and severe electrode-electrolyte interface side reaction with element dissolution, resulting in fast capacity and voltage fading of LMROs during cycling and hindering its commercialization. Herein, a redox couple strategy is proposed by utilizing copper phthalocyanine (CuPc) to address the irreversibility of anionic redox. The Cu-N synergistic effect of CuPc could not only inhibit surface oxygen evolution by reducing the peroxide ion O2 2- back to lattice oxygen O2-, but also enhance the reaction activity and reversibility of anionic redox in bulk to achieve a higher capacity and cycling stability. Moreover, the CuPc strategy suppresses the interface side reaction and induces the forming of a uniform and robust LiF-rich cathode electrolyte, interphase (CEI) to significantly eliminate transition metal dissolution. As a result, the CuPc-enhanced LMRO cathode shows superb cycling performance with a capacity retention of 95.0% after 500 long-term cycles. This study sheds light on the great effect of N-based redox couple to regulate anionic redox behavior and promote the development of high energy density and high stability LMROs cathode.

Thickness-Controlled Synthesis of Compact and Uniform MOF Protective Layer for Zinc Anode to Achieve 85% Zinc Utilization.

Zinc anode-based aqueous batteries have attracted considerable interest for large-scale energy storage and wearable devices. Unfortunately, the formation of Zn dendrite, parasitic hydrogen evolution reaction (HER), and irreversible by-products, seriously restrict their practical applications. Herein, a series of compact and uniform metal-organic frameworks (MOFs) films with precisely controlled thickness (150-600 nm) are constructed by a pre-oxide gas deposition (POGD) method on Zn foil. Under the protection of MOF layer with optimum thickness, the corrosion of zinc, the side reaction of hydrogen evolution, and the growth of dendrites on the zinc surface are suppressed. The symmetric cell based on Zn@ZIF-8 anode exhibits exceptional cyclicality for over 1100 h with low voltage hysteresis of≈38 mV at 1 mA cm-2 . Even at current densities of 50 mA cm-2 with an area capacity of 50 mAh cm-2 (85% Zn utilization), the electrode can keep cycling for >100 h. Besides, this Zn@ZIF-8 anode also delivers a high average CE of 99.4% at 1 mA cm-2 . Moreover, a rechargeable Zn ion battery is fabricated based on the Zn@ZIF-8 anode and MnO2 cathode, which presents an exceptionally long lifespan with no capacity attenuation for 1000 cycles.

Ion Hopping: Design Principles for Strategies to Improve Ionic Conductivity for Inorganic Solid Electrolytes.

Solid electrolytes are considered as an ideal substitution of liquid electrolytes, avoiding the potential hazards of volatilization, flammability, and explosion for liquid electrolyte-based rechargeable batteries. However, there are significant performance gaps to be bridged between solid electrolytes and liquid electrolytes; one with a particular importance is the ionic conductivity which is highly dependent on the material types and structures. In this review, the general physical image of ion hopping in the crystalline structure is revisited, by highlighting two main kernels that impact ion migration: ion hopping pathways and skeletons interaction. The universal strategies to effectively improve ionic conductivity of inorganic solid electrolytes are then systematically summarized: constructing rapid diffusion pathways for mobile ions; and reducing resistance of the surrounding potential field. The scoped strategies offer an exclusive view on the working principle of ion movement regardless of the ion species, thus providing a comprehensive guidance for the future exploitation of solid electrolytes.

Cobalt Single Atoms Enabling Efficient Methanol Oxidation Reaction on Platinum Anchored on Nitrogen-Doped Carbon.

Developing efficient platinum (Pt)-based electrocatalysts with high tolerance to CO poisoning for the methanol oxidation reaction is critical for the development of direct methanol fuel cells. In this work, cobalt single atoms are introduced to enhance the electrocatalytic performance of N-doped carbon supported Pt (N-C/Pt) for the methanol oxidation reaction. The cobalt single atoms are believed to play a critical role in accelerating the prompt oxidation of CO to CO2 and minimizing the CO blocking of the adjacent Pt active sites. Benefitting from the synergistic effects among the Co single atoms, the Pt nanoparticles, and the N-doped carbon support, the Co-modified N-C/Pt (Co-N-C/Pt) electrocatalyst simultaneously delivers impressive electrocatalytic activity and durability with lower onset potential and superb CO poisoning resistance as compared to the N-C/Pt and the commercial Pt/C electrocatalysts.

Latticed-Confined Conversion Chemistry of Battery Electrode.

The electrochemical conversion reaction, usually featured by multiple redox processes and high specific capacity, holds great promise in developing high-energy rechargeable battery technologies. However, the complete structural change accompanied by spontaneous atomic migration and volume variation during the charge/discharge cycle leads to electrode disintegration and performance degradation, therefore severely restricting the application of conventional conversion-type electrodes. Herein, latticed-confined conversion chemistry is proposed, where the "intercalation-like" redox behavior is realized on the electrode with a "conversion-like" high capacity. By delicately formulating the high-entropy compounds, the pristine crystal structure can be preserved by the inert lattice framework, thus enabling an ultra-high initial Coulombic efficiency of 92.5% and a long cycling lifespan over a thousand cycles after the quasistatic charge-discharge cycle. This lattice-confined conversion chemistry unfolds a ubiquitous insight into the localized redox reaction and sheds light on developing high-performance electrodes toward next-generation high-energy rechargeable batteries.

Atomic-Level Modulation of the Interface Chemistry of Platinum-Nickel Oxide toward Enhanced Hydrogen Electrocatalysis Kinetics.

Precise manipulation of the interactions between different components represents the frontier of heterostructured electrocatalysts and is crucial to understanding the structure-function relationship. Current studies, however, are quite limited. Here, we report targeted modulation of the atomic-level interface chemistry of Pt/NiO heterostructure via an annealing treatment, which results in substantially enhanced hydrogen electrocatalysis kinetics in alkaline media. Specifically, the optimized Pt/NiO heterostructure delivers by far the highest specific exchange current density of 8.1 mA cmPt-2 for hydrogen oxidation reaction. X-ray spectroscopy results suggest Pt-Ni interfacial bonds are formed after annealing, inducing more significant electron transfer from NiO to Pt. Also, the regulated interface chemistry, as proven by theoretical calculations, optimizes the binding behaviors of hydrogen and hydroxyl species. These findings emphasize the importance of interface engineering at the atomic level and inspire further explorations of heterostructured electrocatalysts.

Single-Atom Electrocatalysts for Multi-Electron Reduction of CO2.

The multi-electron reduction of CO2 to hydrocarbons or alcohols is highly attractive in a sustainable energy economy, and the rational design of electrocatalysts is vital to achieve these reactions efficiently. Single-atom electrocatalysts are promising candidates due to their well-defined coordination configurations and unique electronic structures, which are critical for delivering high activity and selectivity and may accelerate the explorations of the activity origin at atomic level as well. Although much effort has been devoted to multi-electron reduction of CO2 on single-atom electrocatalysts, there are still no reviews focusing on this emerging field and constructive perspectives are also urgent to be addressed. Herein recent advances in how to design efficient single-atom electrocatalysts for multi-electron reduction of CO2 , with emphasis on strategies in regulating the interactions between active sites and key reaction intermediates, are summarized. Such interactions are crucial in designing active sites for optimizing the multi-electron reduction steps and maximizing the catalytic performance. Different design strategies including regulation of metal centers, single-atom alloys, non-metal single-atom catalysts, and tandem catalysts, are discussed accordingly. Finally, current challenges and future opportunities for deep electroreduction of CO2 are proposed.

Conversion-Alloying Anode Materials for Sodium Ion Batteries.

The past decade has witnessed a rapidly growing interest toward sodium ion battery (SIB) for large-scale energy storage in view of the abundance and easy accessibility of sodium resources. Key to addressing the remaining challenges and setbacks and to translate lab science into commercializable products is the development of high-performance anode materials. Anode materials featuring combined conversion and alloying mechanisms are one of the most attractive candidates, due to their high theoretical capacities and relatively low working voltages. The current understanding of sodium-storage mechanisms in conversion-alloying anode materials is presented here. The challenges faced by these materials in SIBs, and the corresponding improvement strategies, are comprehensively discussed in correlation with the resulting electrochemical behavior. Finally, with the guidance and perspectives, a roadmap toward the development of advanced conversion-alloying materials for commercializable SIBs is created.

A Novel Perovskite Electron-Ion Conductive Coating to Simultaneously Enhance Cycling Stability and Rate Capability of Li1.2 Ni0.13 Co0.13 Mn0.54 O2 Cathode Material for Lithium-Ion Batteries.

Poor cycling stability and rate capability are two key issues needing to be solved for Li- and Mn-rich oxide cathode material for lithium-ion batteries (LIBs). Herein, a novel perovskite electron-ion mixed conductor Nd0.6 Sr0.4 CoO3 (NSCO) is used as the coating layer on Li1.2 Ni0.13 Co0.13 Mn0.54 O2 (LNCMO) to simultaneously enhance its cycling stability and rate capability. By coating 3 wt% NSCO, LNCMO-3NSCO exhibits an optimal cycling performance with a capacity retention of 99% at 0.1C (1C = 200 mA g-1 ) after 60 cycles, 91% at 1C after 300 cycles, and 54% at 20C after 1000 cycles, much better than 78%, 63%, and 3% of LNCMO, respectively. Even at a high charge and discharge rate of 50C, LNCMO-3NSCO exhibits a discharge capacity of 53 mAh g-1 and a mid-point discharge voltage of 2.88 V, much higher than those of LNCMO (24 mA h g-1 and 2.40 V, respectively). Benefiting from the high electronic conductivity (1.46 S cm-1 ) and ionic conductivity (1.48 × 10-7  S cm-1 ), NSCO coating not only suppresses transition metals dissolution and structure transformation, but also significantly enhances electronic conductivity and Li+ diffusion coefficient of LNCMO by an order of magnitude.

Hexagonal Boron Nitride as a Multifunctional Support for Engineering Efficient Electrocatalysts toward the Oxygen Reduction Reaction.

Developing heterostructures with well-defined interfaces is attracting ever-increasing interest toward the development of advanced electrocatalysts. Herein, hexagonal boron nitride (h-BN) nanosheets are reported as a multifunctional support for constructing efficient electrocatalysts for the oxygen reduction reaction (ORR). h-BN/Pd heterostructured electrocatalysts with decent activity and long-term durability are designed and synthesized by confining Pd nanoparticles (NPs) on ultrathin h-BN nanosheets. The robust h-BN serves as a durable platform to maintain the structural integrity of the heterostructured catalysts. Both experimental findings and theoretical calculations reveal that the strong interaction between h-BN and Pd downshifts the Pd d-band center and hence optimizes the affinity with the reaction intermediates. Meanwhile, h-BN also endows the heterostructured catalysts with superhydrophobic surfaces, promoting the diffusion kinetics of O2. These findings open a new avenue for the rational design and development of heterostructured catalysts by interface engineering toward electrocatalysis applications.

Low-Coordinate Iridium Oxide Confined on Graphitic Carbon Nitride for Highly Efficient Oxygen Evolution.

Highly active and durable electrocatalysts for the oxygen evolution reaction (OER) is greatly desired. Iridium oxide/graphitic carbon nitride (IrO2 /GCN) heterostructures are designed with low-coordinate IrO2 nanoparticles (NPs) confined on superhydrophilic highly stable GCN nanosheets for efficient acidic OER. The GCN nanosheets not only ensure the homogeneous distribution and confinement of IrO2 NPs but also endows the heterostructured catalyst system with a superhydrophilic surface, which can maximize the exposure of active sites and promotes mass diffusion. The coordination number of Ir atoms is decreased owing to the strong interaction between IrO2 and GCN, leading to lattice strain and increment of electron density around Ir sites and hence modulating the attachment between the catalyst and reaction intermediates. The optimized IrO2 /GCN heterostructure delivers not only by far the highest mass activity among the reported IrO2 -based catalysts but also decent durability.