Polymorph Engineering for Boosted Volumetric Na-Ion and Li-Ion Storage

Building Robust Manganese Hexacyanoferrate Cathode for Long-Cycle-Life Sodium-Ion Batteries

Manganese Hexacyanoferrate (Mn─HCF) is a preferred cathode material for sodium-ion batteries used in large-scale energy storage. However, the inherent vacancies and the presence of H2O within the imperfect crystal structure of Mn─HCF lead to material failure and interface failure when used as a cathode. Addressing the challenge of constructing a stable cathode is an urgent scientific problem that needs to be solved to enhance the performance and lifespan of these batteries. In this review, the crystal structure of Mn─HCF is first introduced, explaining the formation mechanism of vacancies and exploring the various ways in which H2O molecules can be present within the crystal structure. Then comprehensively summarize the mechanisms of material and interfacial failure in Mn─HCF, highlighting the key factors contributing to these issues. Additionally, eight modification strategies designed to address these failure mechanisms are encapsulated, including vacancy regulation, transition metal substitution, high entropy, the pillar effect, interstitial H2O removal, surface coating, surface vacancy repair, and cathode electrolyte interphase reinforcement. This comprehensive review of the current research advances on Mn─HCF aims to provide valuable guidance and direction for addressing the existing challenges in their application within SIBs.

Strain Self-Adaptive Iron Selenides Toward Stable Na+-Ion Batteries with Impressive Initial Coulombic Efficiency

High tap density electrodes play a vital role in developing rechargeable batteries with high volumetric capacities, however, developing advanced electrodes with satisfied capacity, excellent structural stability, and achieving the resulted batteries with a high initial Coulombic efficiency (ICE) and good rate capability with long lifespan simultaneously, are still an intractable challenge. Herein, an ultrahigh ICE of 94.1% and stable cycling of carbon-free iron selenides anode is enabled with a high tap density of 2.57 g cm-3 up to 4000 cycles at 5 A g-1 through strain-modulating by constructing a homologous heterostructure. Systematical characterization and theoretical calculation show that the self-adaptive homologous heterointerface alleviates the stress of the iron selenide anodes during cycling processes and subsequently improves the stability of the assembled batteries. Additionally, the well-formed homologous heterostructure also contributes to the rapid Na+ diffusion kinetic, increased charge transfer, and good reversibility of the transformation reactions, endowing the appealing rate capability of carbon-free iron selenides. The proposed design strategy provides new insight and inspiration to aid in the ongoing quest for advanced electrode materials with high tap densities and excellent stability.

Fast-Charging Anode Materials for Sodium-Ion Batteries

Sodium-ion batteries (SIBs) have undergone rapid development as a complementary technology to lithium-ion batteries due to abundant sodium resources. However, the extended charging time and low energy density pose a significant challenge to the widespread use of SIBs in electric vehicles. To overcome this hurdle, there is considerable focus on developing fast-charging anode materials with rapid Na⁺ diffusion and superior reaction kinetics. Here, the key factors that limit the fast charging of anode materials are examined, which provides a comprehensive overview of the major advances and fast-charging characteristics across various anode materials. Specifically, it systematically dissects considerations to enhance the rate performance of anode materials, encompassing aspects such as porous engineering, electrolyte desolvation strategies, electrode/electrolyte interphase, electronic conductivity/ion diffusivity, and pseudocapacitive ion storage. Finally, the direction and prospects for developing fast-charging anode materials of SIBs are also proposed, aiming to provide a valuable reference for the further advancement of high-power SIBs.

Interior-Confined Vacancy in Potassium Manganese Hexacyanoferrate for Ultra-Stable Potassium-Ion Batteries

Metal hexacyanoferrates (HCFs) are viewed as promising cathode materials for potassium-ion batteries (PIBs) because of their high theoretical capacities and redox potentials. However, the development of an HCF cathode with high cycling stability and voltage retention is still impeded by the unavoidable Fe(CN)6 vacancies (VFeCN) and H2O in the materials. Here, a repair method is proposed that significantly reduces the VFeCN content in potassium manganese hexacyanoferrate (KMHCF) enabled by the reducibility of sodium citrate and removal of ligand H2O at high temperature (KMHCF-H). The KMHCF-H obtained at 90 °C contains only 2% VFeCN, and the VFeCN is concentrated in the lattice interior. Such an integrated Fe-CN-Mn surface structure of the KMHCF-H cathode with repaired surface VFeCN allows preferential decomposition of potassium bis(fluorosulfonyl)imide (KFSI) in the electrolyte, which constitutes a dense anion-dominated cathode electrolyte interphase (CEI) , inhibiting effectively Mn dissolution into the electrolyte. Consequently, the KMHCF-H cathode exhibits excellent cycling performance for both half-cell (95.2 % at 0.2 Ag-1 after 2000 cycles) and full-cell (99.4 % at 0.1 Ag-1 after 200 cycles). This thermal repair method enables scalable preparation of KMHCF with a low content of vacancies, holding substantial promise for practical applications of PIBs.

Metal Selenides Find Plenty of Space in Architecting Advanced Sodium/Potassium Ion Batteries

The rapid evolution of smart grid system urges researchers on exploiting systems with properties of high-energy, low-cost, and eco-friendly beyond lithium-ion batteries. Under the circumstances, sodium- and potassium-ion batteries with the semblable work mechanism to commercial lithium-ion batteries, hold the merits of cost-effective and earth-abundant. As a result, it is deemed a promising candidate for large-scale energy storage devices. Exploiting appropriate active electrode materials is in the center of the spotlight for the development of batteries. Metal selenides with special structures and relatively high theoretical capacity have aroused broad interest and achieved great achievements. To push the smooth development of metal selenides and enhancement of the electrochemical performance of sodium- and potassium-ion batteries, it is vital to grasp the inherent properties and electrochemical mechanisms of these materials. Herein, the state-of-the-art development and challenges of metal selenides are summarized and discussed. Meanwhile, the corresponding electrochemical mechanism and future development directions are also highlighted.

Solvent-Free Ultrafast Construction of Se-Deficient Heterojunctions of Bimetallic Selenides toward Flexible Sodium-Ion Full Batteries

Flexible quasi-solid-state sodium ion batteries featuring their low-cost, high safety and excellent mechanical strength have attracted widespread interest in the field of wearable electronic devices. However, the development of such batteries faces great challenges including the construction of interfacial compatible flexible electrode materials and addressing the high safety demands of electrolyte. Here selenium-vacancies regulated bimetallic selenide heterojunctions anchored on waste cotton cloth-derived flexible carbon cloth (FCC) with robust interfacial C-Se-Co/Fe chemical bonds as a flexible anode material (CCFSF) is proposed by ultrafast microwave pyrolysis method. Rich selenium vacancies and CoSe2 /FeSe2-x heterostructures are synchronously formed that can significantly improve ionic and electronic diffusion kinetics. Additionally, a uniform carbon layer coating on the surface of Se-deficient heterostructures endows it with outstanding structural stability. The flexible cathode (PB@FCC) is also fabricated by directly growing Prussian blue nanoparticles on the FCC. Furthermore, an advanced flexible quasi-solid-state Na-ion pouch cell is assembled by coupling CCFSF anode, PB@FCC cathode with P(VDF-HFP)-based gel polymer electrolyte. The full cell not only demonstrates excellent energy storage performance but also robust mechanical flexibility and safety. The present work offers an effective avenue to achieve high safety flexible energy storage device, promoting the development of flexible wearable electronic devices.

Small Things Make a Big Difference: Conductive Cross-Linking Sodium Alginate@MXene Binder Enables High-Volumetric-Capacity and High-Mass-Loading Li-S Battery

Binders are crucial for maintaining the integrity of an electrode, and there is a growing need for integrating multiple desirable properties into the binder for high-energy batteries, yet significant challenges remain. Here, we successfully synthesized a new binder by cross-linking sodium alginate (SA) with MXene materials (Ti3C2Tx). Besides the improved adhesion and mechanical properties, the integrated SA@Ti3C2Tx binder demonstrates much improved electronic conductivity, which enables ruling out the fluffy conductive additive from the electrode component with enhanced volumetric capacity. When SA@Ti3C2Tx is used to fabricate sulfur (S) cathodes, the conductive-additive-free electrode demonstrates extremely high capacity (1422 mAh cm-3/24.5 mAh cm-2) under an S loading of 17.2 mg cm-2 for Li-S batteries. Impressively, the SA@Ti3C2Tx binder shows remarkable feasibility in other battery systems such as Na-S and LiFePO4 batteries. The proposed strategy of constructing a cross-linking conductive binder opens new possibilities for designing high-mass-loading electrodes with high volumetric capacity.

Binary Metallic CuCo5 S8 Anode for High Volumetric Sodium-Ion Storage

With the rapid improvement of compact smart devices, fabricating anode materials with high volumetric capacity has gained substantial interest for future sodium-ion batteries (SIBs) applications. Herein, a novel bimetal sulfide CuCo5 S8 material is proposed with enhanced volumetric capacity due to the intrinsic metallic electronic conductivity of the material and multi-electron transfer during electrochemical procedures. Due to the intrinsic metallic behavior, the conducting additive (CA) could be removed from the electrode fabrication without scarifying the high rate capability. The CA-free CuCo5 S8 electrode can achieve a high volumetric capacity of 1436.4 mA h cm-3 at a current density of 0.2 A g-1 and 100 % capacity retention over 2000 cycles in SIBs, outperforming most metal chalcogenides, owing to the enhanced electrode density. Reversible conversion reactions are revealed by combined measurements for sodium systems. The proposed new strategy offers a viable approach for developing innovative anode materials with high-volumetric capacity.

Metal Selenides Anode Materials for Sodium Ion Batteries: Synthesis, Modification, and Application

The powerful and rapid development of lithium-ion batteries (LIBs) in secondary batteries field makes lithium resources in short supply, leading to rising battery costs. Under the circumstances, sodium-ion batteries (SIBs) with low cost, inexhaustible sodium reserves, and analogous work principle to LIBs, have evolved as one of the most anticipated candidates for large-scale energy storage devices. Thereinto, the applicable electrode is a core element for the smooth development of SIBs. Among various anode materials, metal selenides (MSe_x ) with relatively high theoretical capacity and unique structures have aroused extensive interest. Regrettably, MSe_x suffers from large volume expansion and unwished side reactions, which result in poor electrochemistry performance. Thus, strategies such as carbon modification, structural design, voltage control as well as electrolyte and binder optimization are adopted to alleviate these issues. In this review, the synthesis methods and main reaction mechanisms of MSe_x are systematically summarized. Meanwhile, the major challenges of MSe_x and the corresponding available strategies are proposed. Furthermore, the recent research progress on layered and nonlayered MSe_x for application in SIBs is presented and discussed in detail. Finally, the future development focuses of MSe_x in the field of rechargeable ion batteries are highlighted.

A Review of Performance Prediction Based on Machine Learning in Materials Science

With increasing demand in many areas, materials are constantly evolving. However, they still have numerous practical constraints. The rational design and discovery of new materials can create a huge technological and social impact. However, such rational design and discovery require a holistic, multi-stage design process, including the design of the material composition, material structure, material properties as well as process design and engineering. Such a complex exploration using traditional scientific methods is not only blind but also a huge waste of time and resources. Machine learning (ML), which is used across data to find correlations in material properties and understand the chemical properties of materials, is being considered a new way to explore the materials field. This paper reviews some of the major recent advances and applications of ML in the field of properties prediction of materials and discusses the key challenges and opportunities in this cross-cutting area.

In-situ fabrication of active interfaces towards FeSe as advanced performance anode for sodium-ion batteries

Transition metal selenides have gained enormous interest as anodes for sodium ion batteries (SIBs). Nonetheless, their large volume expansion causing poor rate and inferior cycle stability during Na⁺ insertion/extraction process hinders their further applications in SIBs. Herein, a confined-regulated interfacial engineering strategy towards the synthesis of FeSe microparticles coated by ultrathin nitrogen-doped carbon (NC) is demonstrated (FeSe@NC). The strong interfacial interaction between FeSeand NC endows FeSe@NC with fast electron/Na⁺ transport kinetics and outstanding structural stability, delivering unexceptionable rate capability (364 mAh/gat 10 A/g) and preeminent cycling durability (capacity retention of 100 % at 1 A/g over 1000 cycles). Furthermore, variousex situcharacterization techniques and density functional theory (DFT) calculations have been applied to demonstrate the Na⁺ storage mechanism of FeSe@NC. The assembled Na₃V₂(PO₄)₂F₃@rGO//FeSe@NC full cell also displays a high capacity of 241 mAh/gat 1 A/g with the capacity retention of nearly 100 % over 2000 cycles, and delivers a supreme energy density of 135 Wh kg^-1 and a topmost power density of 495 W kg^-1, manifesting the latent applications of FeSe@NC in the fast charging SIBs.

Honeycomb-like 3D carbon skeletons with embedded phosphorus-rich phosphide nanoparticles as advanced anodes for lithium-ion batteries

Phosphorus-rich iron phosphides (FeP₂) have been regarded as excellent anode candidates for lithium storage owing to their low cost, high natural abundance, high theoretical capacity, and reasonable redox potential. However, FeP₂ suffers from a few challenging problems such as low reversibility, fast capacity degradation, and big volume variation. Herein, we have designed and synthesized a 3D honeycomb-like carbon skeleton with embedded FeP₂ nanoparticles (denoted as FeP₂ NPs@CK), which can significantly promote the kinetics and maintain the structural stability during the cycling, resulting in an excellent electrochemical performance reflected by high reversibility and long-term cycling stability. FeP₂ NPs@CK shows high reversibility, delivering a reversible capacity as high as 938 mA h g^-1 at 0.5 A g^-1. It also shows excellent cycling stability, delivering a capacity of 620 mA h g^-1 after 500 cycles at 1 A g^-1. Moreover, the fast kinetics and lithium storage mechanism of FeP₂ NPs@CK are investigated by quantitative analysis and in situ X-ray diffraction. Such superior performance demonstrates that FeP₂ NPs@CK could be a promising and attractive anode candidate for lithium storage.

Ether-Based Electrolyte Chemistry Towards High-Voltage and Long-Life Na-Ion Full Batteries

Although ether-based electrolytes have been extensively applied in anode evaluation of batteries, anodic instability arising from solvent oxidability is always a tremendous obstacle to matching with high-voltage cathodes. Herein, by rational design for solvation configuration, the fully coordinated ether-based electrolyte with strong resistance against oxidation is reported, which remains anodically stable with high-voltage Na₃ V₂ (PO₄ )₂ O₂ F (NVPF) cathode under 4.5 V (versus Na⁺ /Na) protected by an effective interphase. The assembled graphite//NVPF full cells display superior rate performance and unprecedented cycling stability. Beyond that, the constructed full cells coupling the high-voltage NVPF cathode with hard carbon anode exhibit outstanding electrochemical performances in terms of high average output voltage up to 3.72 V, long-term cycle life (such as 95 % capacity retention after 700 cycles) and high energy density (247 Wh kg^-1 ). In short, the optimized ether-based electrolyte enriches systematic options, the ability to maintain oxidative stability and compatibility with various anodes, exhibiting attractive prospects for application.

Cobalt Selenide Hollow Polyhedron Encapsulated in Graphene for High-Performance Lithium/Sodium Storage

Owing to the high specific capacities, high electrochemical activity, and various electronic properties, transition metal selenides are considered as promising anodes for lithium- and sodium-ion storage. However, poor electronic conductivity and huge volume expansion during cycling are still responsible for their restricted electrochemical performance. Herein, CoSe hollow polyhedron anchoring onto graphene (CoSe/G) is synthesized by self-assembly and subsequent selenization. In CoSe/G composites, the CoSe nanoparticles, obtained by in situ selenization of metal-organic frameworks (MOFs) in high temperature, are distributed among graphene sheets, realizing N element doping, developing robust heterostructures with a chemical bond. The unique architecture ensures the cohesion of the structure and endorses the reaction kinetics for metal ions, identified by in situ and ex situ testing techniques, and kinetics analysis. Thus, the CoSe/G anodes achieve excellent cycling performance (1259 mAh g^-1 at 0.1 A g^-1 after 300 cycles for lithium storage; 214 mAh g^-1 at 2 A g^-1 after 600 cycles for sodium storage) and rate capability (732 mAh g^-1 at 5 A g^-1 for lithium storage; 290 mAh g^-1 at 5 A g^-1 for sodium storage). The improved electrochemical performance for alkali-ion storage provides new insights for the construction of MOFs derivatives toward high-performance storage devices.