Synergizing Conformal Lithiophilic Granule and Dealloyed Porous Skeleton toward Pragmatic Li Metal Anodes

Dendrite-Free Dual-Phase Li-Ba Alloy Anode Enabled by Ordered Array of Built-in Mixed Conducting Microchannels

The development and application of lithium (Li) anode is hindered by volumetric variation, dendritic Li growth, and parasitic reactions. Herein, a dual-phase Li-barium (Ba) alloy with self-assembled microchannels array is synthesized through a one-step thermal fusion method to investigate the inhibition effect of lithiophilic composite porous array on Li dendrites. The Li-rich Li-Ba alloy (BaLi24) as composite Li electrode exhibits an ordered porous structure of BaLi4 intermetallic compound after delithiation, which acts as a built-in 3D current collector during Li plating/striping process. Furthermore, the lithiophilic BaLi4 alloy scaffold is a mixed conductor, featuring with Li+ ions diffusion capability, which can efficiently transport the reduced Li to the interior of the electrode structure. This unique top-down growth mode can effectively prohibit Li dendrites growth and improve the space utilization of 3D electrode structure. The spin-polarized density functional theory (DFT) calculations suggest that the absorption capability of BaLi4 benefits the deposition of Li metal. As a result, the cell performance with the dual-phase Li-Ba alloy anode is significantly improved.

Suppressed charge recombination via defect engineering of confined semiconducting quantum dots for photoelectrocatalysis

Confined semiconducting CuSe quantum dots with abundant Se vacancies are synthesized by pulsed laser deposition with in situ vacuum annealing. With the presence of Se vacancies, the photogenerated charge recombination is suppressed by the self-introduced in-gap trapping states, thus enhancing the photoelectrocatalytic activity under solar illumination.

Vanadium fluorophosphates: advanced cathode materials for next-generation secondary batteries

Next-generation secondary batteries including sodium-ion batteries (SIBs) and potassium-ion batteries (PIBs) are considered the most promising candidates for application to large-scale energy storage systems due to their abundant, evenly distributed and cost-effective sodium/potassium raw materials. The electrochemical performance of SIBs (PIBs) significantly depends on the inherent characteristics of the cathode material. Among the wide variety of cathode materials, sodium/potassium vanadium fluorophosphate (denoted as MVPF, M = Na and K) composites are widely investigated due to their fast ion transportation and robust structure. However, their poor electron conductivity leads to low specific capacity and poor rate capacity, limiting the further application of MVPF cathodes in large-scale energy storage. Accordingly, several modification strategies have been proposed to improve the performance of MVPF such as conductive coating, morphological regulation, and heteroatomic doping, which boost the electronic conductivity of these cathodes and enhance Na (K) ion transportation. Furthermore, the development and application of MVPF cathodes in SIBs at low temperatures are also outlined. Finally, we present a brief summary of the remaining challenges and corresponding strategies for the future development of MVPF cathodes.

Diagnosing and Correcting the Failure of the Solid-State Polymer Electrolyte for Enhancing Solid-State Lithium-Sulfur Batteries

Solid-state polymer electrolytes (SPEs) attract great interest in developing high-performance yet reliable solid-state batteries. However, understanding of the failure mechanism of the SPE and SPE-based solid-state batteries remains in its infancy, posing a great barrier to practical solid-state batteries. Herein, the high accumulation and clogging of "dead" lithium polysulfides (LiPS) on the interface between the cathode and SPE with intrinsic diffusion limitation is identified as a critical failure cause of SPE-based solid-state Li-S batteries. It induces a poorly reversible chemical environment with retarded kinetics on the cathode-SPE interface and in bulk SPEs, starving the Li-S redox in solid-state cells. This observation is different from the case in liquid electrolytes with free solvent and charge carriers, where LiPS dissolve but remain alive for electrochemical/chemical redox without interfacial clogging. Electrocatalysis demonstrates the feasibility of tailoring the chemical environment in diffusion-restricted reaction media for reducing Li-S redox failure in the SPE. It enables Ah-level solid-state Li-S pouch cells with a high specific energy of 343 Wh kg^-1 on the cell level. This work may shed new light on the understanding of the failure mechanism of SPE for bottom-up improvement of solid-state Li-S batteries.

A Multifunctional Interphase Layer Enabling Superior Sodium-Metal Batteries under Ambient Temperature and -40 °C

The sodium (Na)-metal anode with high theoretical capacity and low cost is promising for construction of high-energy-density metal batteries. However, the unsatisfactory interface between Na and the liquid electrolyte induces tardy ion transfer kinetics and dendritic Na growth, especially at ultralow temperature (-40 °C). Herein, an artificial heterogeneous interphase consisting of disodium selenide (Na₂ Se) and metal vanadium (V) is produced on the surface of Na (Na@Na₂ Se/V) via an in situ spontaneous chemical reaction. Such interphase layer possesses high sodiophilicity, excellent ionic conductivity, and high Young's modulus, which can promote Na-ion adsorption and transport, realizing homogenous Na deposition without dendrites. The symmetric Na@Na₂ Se/V cell exhibits outstanding cycling life span of over 1790 h (0.5 mA cm^-2 /1 mAh cm^-2 ) in carbonate-based electrolyte. More remarkably, ab initio molecular dynamics simulations reveal that the artificial Na₂ Se/V hybrid interphase can accelerate the desolvation of solvated Na⁺ at -40 °C. The Na@Na₂ Se/V electrode thus exhibits exceptional electrochemical performance in symmetric cell (over 1500 h at 0.5 mA cm^-2 /0.5 mAh cm^-2 ) and full cell (over 700 cycles at 0.5 C) at -40 °C. This work provides an avenue to design artificial heterogeneous interphase layers for superior high-energy-density metal batteries at ambient and ultralow temperatures.

Enhanced Moisture Stability of Lithium-Rich Antiperovskites for Sustainable All-Solid-State Lithium Batteries

Lithium-rich antiperovskites (LiRAPs) solid electrolytes have attracted extensive interest due to their advantages of structural tunability, mechanical flexibility, and low cost. However, LiRAPs are instinctively hygroscopic and suffer from decomposition in air, which not only diversifies their electrochemical performances in present reports but also hinders their application in all-solid-state lithium batteries (ASSLBs). Herein, the origin of the hygroscopicity, and also the effect of the hygroscopicity on the electrochemical performances of Li_3-x (OH_x )Cl are systematically investigated. Li_3-x (OH_x )Cl is demonstrated to be unstable in the air and prone to decompose into LiOH and LiCl. Nevertheless, with fluorine doping on chlorine sites, the hygroscopicity of LiRAPs is suppressed by weakening the intermolecular hydrogen bond between LiRAPs and H₂ O, forming a moisture-resistive Li_3-x (OH_x )Cl_0.9 F_0.1 . Taking advantage of its low melting point (274 °C), two prototypes of ASSLBs are assembled in the ambient air by means of co-coating sintering and melt-infiltration. With LiRAPs as the solder, low-temperature sintering of the ASSLBs with low interfacial resistance is demonstrated as feasible. The understanding of the hygroscopic behavior of LiRAPs and the integration of the moisture-resistive LiRAPs with ASSLBs provide an effective way toward the fabrication of the ASSLBs.

Dual-Functional Hosts for Polysulfides Conversion and Lithium Plating/Stripping towards Lithium-Sulfur Full Cells

The practical application of lithium-sulfur (Li-S) batteries is greatly hindered by the shuttle effect of dissolved polysulfides in the sulfur cathode and the severe dendritic growth in the lithium anode. Adopting one type of effective host with dual-functions including both inhibiting polysulfide dissolution and regulating Li plating/stripping, is recently an emerging research highlight in Li-S battery. This review focuses on such dual-functional hosts and systematically summarizes the recent research progress and application scenarios. Firstly, this review briefly describes the stubborn issues in Li-S battery operations and the sophisticated counter measurements over the challenges by dual-functional behaviors. Then, the latest advances on dual-functional hosts for both cathode and anode in Li-S full cells are catalogued as species, including metal chalcogenides, metal carbides, metal nitrides, heterostuctures, and the possible mechanisms during the process. Besides, we also outlined the theoretical calculation tools for the dual-functional host based on the first principles. Finally, several sound perspectives are also rationally proposed for fundamental research and practical development as guidelines.

Single-Atom Vanadium Catalyst Boosting Reaction Kinetics of Polysulfides in Na-S Batteries

The practical application of the room-temperature sodium-sulfur (RT Na-S) batteries is hindered by the insulated sulfur, the severe shuttle effect of sodium polysulfides, and insufficient polysulfide conversion. Herein, on the basis of first principles calculations, single-atom vanadium anchored on a 3D nitrogen-doped hierarchical porous carbon matrix (denoted as 3D-PNCV) is designed and fabricated to enhance sulfur reactivity, and adsorption and catalytic conversion performance of sodium polysulfide. The 3D-PNCV host with abundant and active V sites, hierarchical porous structure, high electrical conductivity, and strong chemical adsorption/conversion ability of V-N bonding can immobilize the polysulfides and promote reversibly catalytic conversion of polysulfides toward Na₂ S. Therefore, as-fabricated RT Na-S batteries can achieve a high reversible capacity (445 mAh g^-1 over 800 cycles at 5 A g^-1 ) and excellent rate capability (224 mAh g^-1 at 10 A g^-1 ). The electrocatalysis mechanism of sodium polysulfides is further experimentally and theoretically revealed, which provides a new strategy to develop the highly stable RT Na-S batteries.

Ultralight Porous Cu Nanowire Aerogels as Stable Hosts for High Li-Content Metal Anodes

Using porous copper (Cu) as the host is one of the most effective approaches to stabilize Li metal anodes. However, the most widely used porous Cu hosts usually account for the excessive mass proportion of composite anodes, which seriously decreases the energy density of Li metal batteries. Herein, an ultralight porous Cu nanowire aerogel (UP-Cu) is reported as the Li metal anode host to accommodate a high mass loading of Li content of 77 wt %. Specifically, the Li/UP-Cu electrode displays a satisfactory gravimetric capacity of 2715 mAh g^-1, which is higher than that of the most reported Li metal composite anodes. The UP-Cu host achieves a high Coulombic efficiency of ∼98.9% after 250 cycles in the half cell and exceptional electrochemical stability under high-current-density and deep-plating-stripping conditions in the symmetrical cell. The Li/UP-Cu|LiFePO₄ battery displays a specific capacity of 102 mAh g^-1 at 5 C for 5000 cycles. The Li/UP-Cu|LiFePO₄ pouch cell achieves a significantly high capacity of 146.3 mAh g^-1 with a high capacity retention of 95.83% for 360 cycles. This work provides a lightweight porous host to stabilize Li-metal anodes and maintain their high mass-specific capacity.

Isotropic Amorphous Protective Layer with Uniform Interfacial Zincophobicity for Stable Zinc Anode

Aqueous zinc-ion batteries (AZIBs) have drawn the attention of numerous researchers owing to their high safety and cost-effectiveness. However, the dendrite growth and side reactions of the zinc (Zn) anodes limit their further practical applications. Herein, a porous amorphous silicon nitride protective layer with high zincophobicity is constructed on the Zn anode surface, which can guide the uniform stripping/plating of Zn²⁺ underneath the protective layer through its isotropic Zn affinity to alleviate the growth of dendrites and by-products. As a result, the amorphous silicon nitride-protected Zn anode can maintain a stable Coulombic efficiency (CE) of 98.8% and low voltage hysteresis for 710 cycles in the half cell. The full cell with the as-prepared Zn anode can deliver excellent electrochemical performances (89.0% capacity retention and 144.4 mAh g^-1 discharge capacity after 1000 cycles at 4 A g^-1 ). This work reveals the key role of uniform metal affinity induced by the amorphous materials in the interface modification of metal anodes, which is instructive for the design of stable metal anodes.

Revisiting the Role of Physical Confinement and Chemical Regulation of 3D Hosts for Dendrite-Free Li Metal Anode

Lithium metal anode has been demonstrated as the most promising anode for lithium batteries because of its high theoretical capacity, but infinite volume change and dendritic growth during Li electrodeposition have prevented its practical applications. Both physical morphology confinement and chemical adsorption/diffusion regulation are two crucial approaches to designing lithiophilic materials to alleviate dendrite of Li metal anode. However, their roles in suppressing dendrite growth for long-life Li anode are not fully understood yet. Herein, three different Ni-based nanosheet arrays (NiO-NS, Ni₃N-NS, and Ni₅P₄-NS) on carbon cloth as proof-of-concept lithiophilic frameworks are proposed for Li metal anodes. The two-dimensional nanoarray is more promising to facilitate uniform Li⁺ flow and electric field. Compared with the NiO-NS and the Ni₅P₄-NS, the Ni₃N-NS on carbon cloth after reacting with molten Li (Li-Ni/Li₃N-NS@CC) can afford the strongest adsorption to Li⁺ and the most rapid Li⁺ diffusion path. Therefore, the Li-Ni/Li₃N-NS@CC electrode realizes the lowest overpotential and the most excellent electrochemical performance (60 mA cm^-2 and 60 mAh cm^-2 for 1000 h). Furthermore, a remarkable full battery (LiFePO₄||Li-Ni/Li₃N-NS@CC) reaches 300 cycles at 2C. This research provides valuable insight into designing dendrite-free alkali metal batteries.

Efficient Charge Transfers in Highly Conductive Copper Selenide Quantum Dot-Confined Catalysts for Robust Oxygen Evolution Reaction

Defective quantum dots (QDs) are the emerging materials for catalysis by virtue of their atomic-scale size, high monodispersity, and ultra-high specific surface area. However, the dispersed nature of QDs fundamentally prohibits the efficient charge transfer in various catalytic processes. Here, we report efficient and robust electrocatalytic oxygen evolution based on defective and highly conductive copper selenide (CuSe) QDs confined in an amorphous carbon matrix with good uniformity (average diameter 4.25 nm) and a high areal density (1.8 × 10¹² cm^-2). The CuSe QD-confined catalysts with abundant selenide vacancies were prepared by using a pulsed laser deposition system benefitted by high substrate temperature and ultrahigh vacuum growth conditions, as evidenced by electron paramagnetic resonance characterizations. An ultra-low charge transfer resistance (about 7 Ω) determined by electrochemical impedance spectroscopy measurement indicates the efficient charge transfer of CuSe quantum-confined catalysts, which is guaranteed by its high conductivity (with a low resistivity of 2.33 μΩ·m), as revealed by electrical transport measurements. Our work provides a universal design scheme of the dispersed QD-based composite catalysts and demonstrates the CuSe QD-confined catalysts as an efficient and robust electrocatalyst for oxygen evolution reaction.

Direct-Chemical Vapor Deposition-Enabled Graphene for Emerging Energy Storage: Versatility, Essentiality, and Possibility

The direct chemical vapor deposition (CVD) technique has stimulated an enormous scientific and industrial interest to enable the conformal growth of graphene over multifarious substrates, which readily bypasses tedious transfer procedure and empowers innovative materials paradigm. Compared to the prevailing graphene materials (i.e., reduced graphene oxide and liquid-phase exfoliated graphene), the direct-CVD-enabled graphene harnesses appealing structural advantages and physicochemical properties, accordingly playing a pivotal role in the realm of electrochemical energy storage. Despite conspicuous progress achieved in this frontier, a comprehensive overview is still lacking by far and the synthesis-structure-property-application nexus of direct-CVD-enabled graphene remains elusive. In this topical review, rather than simply compiling the state-of-the-art advancements, the versatile roles of direct-CVD-enabled graphene are itemized as (i) modificator, (ii) cultivator, (iii) defender, and (iv) decider. Furthermore, essential effects on the performance optimization are elucidated, with an emphasis on fundamental properties and underlying mechanisms. At the end, perspectives with respect to the material production and device fabrication are sketched, aiming to navigate the future development of direct-CVD-enabled graphene en-route toward pragmatic energy applications and beyond.