Regulation of anion-Na+ coordination chemistry in electrolyte solvates for low-temperature sodium-ion batteries

Electrolyte Solvation Structure Regulation for Low-Temperature Sodium-Ion Battery

The development of high-performance sodium-ion batteries (SIBs) that can operate effectively in low-temperature environments is essential for large-scale energy storage systems. Due to the sluggish kinetics of Na+ desolvation at the electrode-electrolyte interface, the capacity of SIBs decays rapidly at low temperatures, which is one of the main challenges SIBs are facing at present. On the basis of diethylene glycol dimethyl ether (DEGDME) electrolyte, 1,3-dioxane (DOL) with a low melting point and low solvation energy is used as a cosolvent, and trimethylsilyl isocyanate (Si-NCO) with a low LUMO level is used as an additive to optimize the solvation structure. This optimization facilitates greater participation of PF6- anions in the inner shell of the solvation structure, thereby improving its stability over a certain temperature range. The designed electrolyte enables the Na||HC half-cell to maintain 88.57% of its room-temperature capacity at -40 °C, with a capacity retention of 94.50% after 100 cycles. Additionally, in the full cell composed of O3-type layered oxide sodium nickel iron manganese (NFMN) and hard carbon (HC), the capacity retention is 83.73% after 100 cycles at -40 °C. This work provides new insights into the development of electrolyte formulations for enhancing the electrochemical stability of SIBs at low temperatures.

Cation-Anion Regulation Engineering in a Flame-Retardant Electrolyte toward Safe Na-Ion Batteries with Appealing Stability

Great electrochemical stability and intrinsic safety are of critical significance in realizing large-scale applications of Na-ion batteries (NIBs). Unfortunately, the notorious decomposition of the electrolyte and undesirable side reactions on the cathode-electrolyte interphase (CEI) pose major obstacles to the practical implementation of NIBs. Besides, the flammability of traditional carbonate-based electrolytes raises increasing safety concerns about the batteries. Herein, a flame-retardant all-fluorinated electrolyte is proposed to achieve an anion-aggregated inner solvation shell by modulating cation-anion interactions through a low-coordination number cosolvent. The more electrochemically antioxidant fluorinated solvents and anion-dominated interfacial chemistry contribute to the construction of both mechanically and chemically stable F-rich CEI. Such thin, homogeneous interphase effectively inhibits the parasitic reaction, strengthens the interfacial stability, and enables fast Na+ diffusion kinetics on the interface. When employing this electrolyte, the Na0.95Ni0.4Fe0.15Mn0.3Ti0.15O2 (NFMT) cathode delivers remarkable discharge capacity up to 169.7 mAh g-1, with stable cycling at 1C for 500 cycles. Impressively, NFMT//hard carbon pouch cells with such electrolyte also achieve a steady operation for 100 cycles at 0.5C with 86.8% capacity remaining. This study offers a practical reference for developing high-performance and flame-retardant electrolytes.

Temperature-Inert Weakly Solvating Electrolytes for Low-Temperature Lithium-Ion Batteries with Micro-Sized Silicon Anodes

Cost-effective micro-sized silicon (μSi) anodes with high specific capacity are promising for high-energy-density lithium-ion batteries but face significant volume changes during cycling. Constructing anion-derived, inorganic-rich solid-electrolyte interphase by electrolyte engineering is considered a viable strategy for stabilizing μSi anodes. However, at low temperatures, temperature-dependent anion-dominated solvation and sluggish Li+ desolvation hinder cyclability and capacity retention. Here we introduce a unique temperature-inert weakly solvating electrolyte (TIWSE) that preserves the anion-dominated solvation sheath and has weak solvent coordination capability, enabling stable cycling of μSi anodes in subzero environments. The crucial role of NO3 - anions with a high donor number in regulating competitive coordination in TIWSE is unveiled. As a result, μSi||LiNi0.8Co0.1Mn0.1O2 full cells with TIWSE demonstrate impressive capacity retention of 91.8 % at -20 °C and 80.8 % at 30 °C after 100 cycles, along with a high specific capacity of 137.4 mAh g-1 at 6 C. Furthermore, a 1-Ah pouch cell of Si-C||LiNi0.8Co0.1Mn0.1O2 shows remarkable cycling stability with 89.3 % capacity retention over 300 cycles at 30 °C and 77.3 % retention at -20 °C, demonstrating the practical applicability. This work highlights the importance of solvation chemistry in addressing low-temperature challenges and offers new insights into high-energy μSi-based lithium-ion batteries operating under harsh conditions.

Evaluations of Highly Stable Derivatives of Polycyanated Tricyclic[10]annulene Anions as Efficient Halogen-Free Electrolyte for Lithium- and Sodium-Ion Batteries

Polycyanated tricyclic[10]annulene and the benzene derivatives, namely polycyanated Rees hydrocarbons, exhibit properties of organic superacids in the gas phase because they generate highly stable anions after deprotonation. Stable anions can prospectively be used as electrolytes in lithium- and sodium-ion batteries (LIBs and NIBs, respectively). This study investigates the stability of polycyanated benzo-fused tricyclic[10]annulene anion and polycyanated tricyclic[10]annulene anion and discusses their potential as halogen-free electrolytes in LIBs and NIBs using density functional theory calculations. The calculated energy for binding of an electron to the polycyanated Rees hydrocarbon anions in the gas phase is larger than that of recently developed, efficient, halogen-free electrolytes. The binding energy of Li+ and Na+ with the polycyanated Rees hydrocarbon anions is smaller than that of the electrolyte B12H12 2-, as well as the currently used electrolytes, but is comparable to that of the electrolytes B12(CN)12 2- and CB11(CN)12 2-. The present calculations suggest that polycyanated Rees hydrocarbon anions can be used as halogen-free electrolytes in LIBs and NIBs. This study paves the way for the synthesis of stable anions derived from organic superacids with potential applications as halogen-free electrolytes in metal-ion batteries.

Sole-Solvent High-Entropy Electrolyte Realizes Wide-Temperature and High-Voltage Practical Anode-Free Sodium Pouch Cells

Anode-free sodium batteries (AFSBs) hold great promise for high-density energy storage. However, high-voltage AFSBs, especially those can stably cycle at a wide temperature range are challenging due to the poor electrolyte compatibility toward both the cathode and anode. Herein, high-voltage AFSBs with cycling ability in a wide temperature range (-20-60 °C) are realized for the first time via a sole-solvent high-entropy electrolyte based on the diethylene glycol dibutyl ether solvent (D2) and NaPF6 salt. The sole-solvent high-entropy electrolyte with unique solvent-ions effect of strong anion interaction and weak cation solvation enables entropy-driven electrolyte salt disassociation and high-concentration contact ion pairs, thus simultaneously forming stable anion-derived electrode-electrolyte interphases on cathode and anode. Moreover, the wide liquid range of D2 further extends the temperature extremes of the battery. Consequently, ampere-hour (Ah)-level anode-free sodium pouch cells with cyclability in a wide temperature range of -20-60 °C are realized. Impressively, the pouch cell achieves a leadingly high cell-level energy density of 209 Wh kg-1 and a high capacity retention of 83.1% after 100 cycles at 25 °C. This work provides inspirations for designing advanced electrolytes for practical AFSBs.

Topological Design of Highly Conductive Weakly Solvating Electrolytes for Ultrastable Sodium Metal Batteries Operating at -60 °C and Below

Weakly solvating electrolytes (WSE) can favor reversible Na batteries at -40 °C for some extreme applications because of the low desolvation energy. However, it is challenging to enable reversible Na batteries at lower temperatures. Herein, we uncover that the low ionic conductivity of WSE reduces reaction kinetics at -60 °C. Accordingly, a highly conductive weakly solvating electrolyte (HCWSE) is designed by introducing additives of strongly solvating solvents and the dilution of NaPF6. The additive can dominate the solvation sheath, increase the dissociation of NaPF6 and the fluidity of the electrolyte, and thus greatly improve the ionic conductivity. Furthermore, the binding energy between Na+ and solvents is proposed as a descriptor to determine the solvating power of solvents, based on which a series of ultralow-temperature HCWSEs have been topologically designed by facilely introducing strong-solvation ether additives into the weak-solvation solvents. As a demonstration, the HCWSE showcases the long cycling of Na||Na cell at -60 °C with an overpotential of 42 mV under 1 mA cm-2 for 1200 h. The Na||NNFM (Na0.75Ni0.25Fe0.25Mn0.5O2) cell exhibits a reversible capacity of 79.2 mAh g-1 after 160 cycles. The cells also achieve impressive performances at -70 °C.

Advances in Anion Chemistry in the Electrolyte Design for Better Lithium Batteries

Electrolytes are crucial components in electrochemical energy storage devices, sparking considerable research interest. However, the significance of anions in the electrolytes is often underestimated. In fact, the anions have significant impacts on the performance and stability of lithium batteries. Therefore, comprehensively understanding anion chemistry in electrolytes is of crucial importance. Herein, in-depth comprehension of anion chemistry and its positive effects on the interface, solvation structure of Li-ions, as well as the electrochemical performance of the batteries have been emphasized and summarized. This review aims to present a full scope of anion chemistry and furnish systematic cognition for the rational design of advanced electrolytes for better lithium batteries with high energy density, lifespan, and safety. Furthermore, insightful analysis and perspectives based on the current research are proposed. We hope that this review sheds light on new perspectives on understanding anion chemistry in electrolytes.

Deciphering and Enhancing Rate-Determining Step of Sodium Deposition towards Ultralow-Temperature Sodium Metal Batteries

Achieving high ionic conductivity and stable performance at low temperatures remains a significant challenge in sodium-metal batteries (SMBs). In this study, we propose a novel electrolyte design strategy that elucidates the solvation structure-function relationship within mixed solvent systems. A mixture of diglyme and 1,3-dioxolane was developed to optimize the solvation structure towards superior low-temperature electrolyte. Molecular dynamics simulations and Raman spectra results reveal the solvent-separated ion pairs and contact ion pairs dominated solvation structure in the designed electrolyte, displaying a superior ionic conductivity of 1.78×10-3 S cm-1 at -40 °C. Besides, comprehensive kinetic analysis shows Na+ transportation in the electrolyte shows a greater impact on sodium plating than Na+ transport through the solid electrolyte interphase or charge transfer. As a result, the electrolyte enables stable operation for over 12,000 hours in Na ∥ ${\parallel }$ Na cells at -40 °C. In Na ∥ ${\parallel }$ Na2/3Ni1/4Cu1/12Mn2/3O2 full cells, it maintains a high capacity retention of 92.4 % over 600 cycles with an initial specific capacity of 89.4 mAh g-1 at -40 °C, and achieves 81.7 % capacity retention after 50 cycles with an initial specific capacity of 75.3 mAh g-1 at -78 °C. These results pave the way for the development of high-performance SMBs capable of operating under ultralow temperatures.

Dual-Anionic Coordination Manipulation Induces Phosphorus and Boron-Rich Gradient Interphase Towards Stable and Safe Sodium Metal Batteries

High-voltage sodium metal batteries (SMBs) present a viable pathway towards high-energy-density sodium-based batteries due to the competitive cost advantage and abundant supply of sodium resources. However, they still suffer from severe capacity decay induced by the notorious decomposition of the electrolyte under high voltage and unstable cathode/electrolyte interphase (CEI). In addition, the high reactivity of Na metal and flammable electrolytes push SMBs to their safety limits. Herein, a special dual-anion aggregated Na+ solvation structure is designed in a nonflammable trimethyl phosphate-based localized high-concentration electrolyte, and a gradient CEI enriched with phosphorus and boron compounds is formed on the cathode. This thin and stable interphase effectively suppresses the parasitic reaction, improves the interfacial stability of the cathode, and facilitates Na+ transport through the interface by the synergistic effect of multi-components, thus optimizing the cycling stability and safety of SMBs. The Na0.95Ni0.4Fe0.15Mn0.3Ti0.15O2//Na batteries employing such electrolyte provide a discharge capacity of 167.5 mAh g-1 and high retention in the capacity of 85.2 % after 800 cycles at 1 C. This approach offers a general strategy for the design of flame-retardant high-voltage electrolytes and the practical application of SMBs.

Dual-Steric Hindrance Modulation of Interface Electrochemistry for Potassium-Ion Batteries

Electrolyte chemistry regulation is a feasible and effective approach to achieving a stable electrode-electrolyte interface. How to realize such regulation and establish the relationship between the liquid-phase electrolyte environment and solid-phase electrode remains a significant challenge, especially in solid electrolyte interphase (SEI) for metal-ion batteries. In this work, solvent/anion steric hindrance is regarded as an essential factor in exploring the electrolyte chemistry regulation on forming ether-based K+-dominated SEI interface through the cross-combination strategy. Theoretical calculation and experimental evidence have successfully indicated a general principle that the combination of increasing solvent steric hindrance with decreasing anion steric hindrance indeed prompts the construction of an ideal anion-rich sheath solvation structure and guarantees the cycling stability of antimony-based alloy electrode (Sb@3DC, Sb nanoparticles anchored in three-dimensional carbon). These confirm the critical role of electrolyte modulation based on molecular design in the formation of stable solid-liquid interfaces, particularly in electrochemical energy storage systems.

Electrolyte Solvation Engineering Stabilizing Anode-Free Sodium Metal Battery With 4.0 V-Class Layered Oxide Cathode

Anode-free sodium metal batteries (AFSMBs) are regarded as the "ceiling" for current sodium-based batteries. However, their practical application is hindered by the unstable electrolyte and interfacial chemistry at the high-voltage cathode and anode-free side, especially under extreme temperature conditions. Here, an advanced electrolyte design strategy based on electrolyte solvation engineering is presented, which shapes a weakly solvating anion-stabilized (WSAS) electrolyte by balancing the interaction between the Na+-solvent and Na+-anion. The special interaction constructs rich contact ion pairs (CIPs) /aggregates (AGGs) clusters at the electrode/electrolyte interface during the dynamic solvation process which facilitates the formation of a uniform and stable interfacial layer, enabling highly stable cycling of 4.0 V-class layered oxide cathode from -40 °C to 60 °C and excellent reversibility of Na plating/stripping with an ultrahigh average CE of 99.89%. Ultimately, industrial multi-layer anode-free pouch cells using the WSAS electrolyte achieve 80% capacity remaining after 50 cycles and even deliver 74.3% capacity at -30 °C. This work takes a pivotal step for the further development of high-energy-density Na batteries.

Electrolyte Design Strategies for Aqueous Sodium-Ion Batteries: Progress and Prospects

Sodium-ion batteries (SIBs) have emerged as one of today's most attractive battery technologies due to the scarcity of lithium resources. Aqueous sodium-ion batteries (ASIBs) have been extensively researched for their security, cost-effectiveness, and eco-friendly properties. However, aqueous electrolytes are extremely limited in practical applications because of the narrow electrochemical stability window (ESW) with extremely poor low-temperature performance. The first part of this review is an in-depth discussion of the reasons for the inferior performance of aqueous electrolytes. Next, research progress in extending the electrochemical stabilization window and improving low-temperature performance using various methods such as "water-in-salt", eutectic, and additive-modified electrolytes is highlighted. Considering the shortcomings of existing solid electrolyte interphase (SEI) theory, recent research progress on the solvation behavior of electrolytes is summarized based on the solvation theory, which elucidates the correlation between the solvation structure and the electrochemical performance, and three methods to upgrade the electrochemical performance by modulating the solvation behavior are introduced in detail. Finally, common design ideas for high-temperature resistant aqueous electrolytes that are hoped to help future aqueous batteries with wide temperature ranges are summarized.

Eliminating Charge Transfer at Cathode-Electrolyte Interface for Ultrafast Kinetics in Na-Ion Batteries

Sodium-ion batteries suffer from kinetic problems stemming from sluggish ion transport across the electrode-electrolyte interface, causing rapid energy decay during fast-charging or low-temperature operation. One exciting prospect to enhance kinetics is constructing neuron-like electrodes that emulate fast signal transmission in a nervous system. It has been considered that these bioinspired designs enhance electron/ion transport of the electrodes through carbon networks. However, whether they can avoid sluggish charge transfer at the electrode-electrolyte interface remains unknown. By connecting the openings of carbon nanotubes with the surface of carbon-coated Na3V2O2(PO4)2F cathode nanoparticles, here we use carbon nanotubes to trap Na+ ions released from the nanoparticles during charge. Therefore, Na+ movement is confined only inside the neuron-like cathode, eliminating ion transport between the electrolyte and cathode, which has been scarcely achieved in conventional batteries. As a result, a 14-fold reduction in interfacial charge transfer resistance is achieved when compared to unmodified cathodes, leading to superior fast-charging performance and excellent cyclability up to 200C, and surprisingly, reversible operation at low temperatures down to -60 °C without electrolyte modification, surpassing other Na3V2O2(PO4)2F-based batteries reported to date. As battery operation has relied on charge transfer at the electrode-electrolyte interface for over 200 years, our approach departs from this traditional ion transport paradigm, paving the way for building better batteries that work under harsh conditions.

Entropy-Assisted Anion-Reinforced Solvation Structure for Fast-Charging Sodium-Ion Full Batteries

Anion-reinforced solvation structure favors the formation of inorganic-rich robust electrode-electrolyte interface, which endows fast ion transport and high strength modulus to enable improved electrochemical performance. However, such a unique solvation structure inevitably injures the ionic conductivity of electrolytes and limits the fast-charging performance. Herein, a trade-off in tuning anion-reinforced solvation structure and high ionic conductivity is realized by the entropy-assisted hybrid ester-ether electrolyte. Anion-reinforced solvation sheath with more anions occupying the inner Na+ shell is constructed by introducing the weakly coordinated ether tetrahydrofuran into the commonly used ester-based electrolyte, which merits the accelerated desolvation energy and gradient inorganic-rich electrode-electrolyte interface. The improved ionic conductivity is attributed to the weakly diverse solvation structures induced by entropy effect. These enable the enhanced rate performance and cycling stability of Prussian blue||hard carbon full cells with high electrode mass loading. More importantly, the practical application of the designed electrolyte was further demonstrated by industry-level 18650 cylindrical cells.

Ethyl Isopropyl Sulfone Modulating to Achieve Stable High-Voltage Electrolyte for Lithium-Ion Batteries

The demand for efficient large-scale energy storage necessitates high-energy-density batteries, making research on high-voltage electrolytes particularly important. In this article, ethyl isopropyl sulfone (ES), which has a high dielectric constant, is added to traditional carbonate-based electrolyte solvents and analyzed. Based on calculated and analyzed results, different proportions of ES are added to the conventional carbonate-based electrolyte. The high-voltage performance, the influence on the surface of the electrode, the active material structure after cycling, the electrochemical behavior, and the impedance of the electrode were studied systematically. As a result, ES addition is applied in high-voltage lithium-ion batteries and exhibits excellent electrochemical properties. These results will provide support for the research and application of sulfone additives in increasing the decomposition voltage of lithium-ion battery electrolytes and improving battery cycle stability.

Aggregate-Dominated Dilute Electrolytes with Low-Temperature-Resistant Ion-Conducting Channels for Highly Reversible Na Plating/Stripping

Developing rechargeable batteries with high power delivery at low temperatures (LT) below 0 °C is significant for cold-climate applications. Initial anode-free sodium metal batteries (AFSMBs) promise high LT performances because of the low de-solvation energy and smaller Stokes radius of Na+, nondiffusion-limited plating/stripping electrochemistry, and maximized energy density. However, the severe reduction in electrolyte ionic conductivity and formation of unstable solid electrolyte interphase (SEI) hinder their practical applications at LT. In this study, a 2-methyltetrahydrofuran-based dilute electrolyte is designed to concurrently achieve an anion-coordinated solvation structure and impressive ionic conductivity of 3.58 mS cm-1 at -40 °C. The dominant aggregate solvates enable the formation of highly efficient and LT-resistant Na+ hopping channels in the electrolyte. Moreover, the methyl-regulated electronic structure in 2-methyltetrahydrofuran induces gradient decomposition toward an inorganic-organic bilayer SEI with high Na+ mobility, composition homogeneity, and mechanical robustness. As such, a record-high Coulombic efficiency beyond 99.9% is achieved even at -40 °C. The as-constructed AFSMBs sustain 300 cycles with 80% capacity maintained, and a 0.5-Ah level pouch cell delivers 85% capacity over 180 cycles at -25 °C. This study affords new insights into electrolyte formulation for fast ionic conduction and superior Na reversibility at ultralow temperatures.

Anionic Solvation Transition at Low Temperatures for Reversible Anodes in Lithium-Oxygen Batteries

Li-O2 batteries provide a novel technology for electric energy storage due to their high energy density. However, the strong solvent coordination with Li+ at low temperatures impacts their performance and triggers irreversible interfacial reactions on the Li anode. Herein, cyclopentyl methyl ether (CME) is incorporated in a dimethoxyethane (DME)-based electrolyte to realize an anionic solvation transition at low temperatures in Li-O2 batteries. CME featuring a single O coordination site substitutes highly solvating DME in the first solvation sheath, and it induces more anion coordination to Li+ across the room- and low-temperature ranges. The low residence time of CME (66 ps at 25 °C, 382 ps at -40 °C.) in the solvation structures leads to the fast exchange of coordinated CME molecules with Li+ in comparison with DME and facilitates Li+ desolvation at low temperatures. The simultaneously generated inorganic-rich solid electrolyte interphase promotes Li+ transport to improve Li deposition and suppress Li dendrite formation. These enable the Li-O2 battery to present a good cycling stability of 110 cycles with a fixed capacity of 1000 mA h g-1 at -40 °C. This work paves the way for designing novel electrolytes in low-temperature batteries.

Solvation Effect: The Cornerstone of High-Performance Battery Design for Commercialization-Driven Sodium Batteries

Sodium batteries (SBs) emerge as a potential candidate for large-scale energy storage and have become a hot topic in the past few decades. In the previous researches on electrolyte, designing electrolytes with the solvation theory has been the most promising direction is to improve the electrochemical performance of batteries through solvation theory. In general, the four essential factors for the commercial application of SBs, which are cost, low temperature performance, fast charge performance and safety. The solvent structure has significant impact on commercial applications. But so far, the solvation design of electrolyte and the practical application of sodium batteries have not been comprehensively summarized. This review first clarifies the process of Na+ solvation and the strategies for adjusting Na+ solvation. It is worth noting that the relationship between solvation theory and interface theory is pointed out. The cost, low temperature, fast charging, and safety issues of solvation are systematically summarized. The importance of the de-solvation step in low temperature and fast charging application is emphasized to help select better electrolytes for specific applications. Finally, new insights and potential solutions for electrolytes solvation related to SBs are proposed to stimulate revolutionary electrolyte chemistry for next generation SBs.

Strategies to boost the electrochemical performance of bismuth anodes for potassium-ion batteries

Potassium-ion batteries (PIBs) are considered potential candidates for large-scale energy storage systems due to the abundant resources of potassium. Among various reported anode materials, bismuth anodes with the advantages of high theoretical specific capacity, low cost, and nontoxicity have attracted widespread attention. However, bismuth anodes experience significant volume changes during the charge/discharge process, leading to unsatisfactory cycling stability and rate performance. In this review, we focus on summarizing the research progress of bismuth anodes in PIBs. We discuss in detail the modification strategies for bismuth anodes in PIBs, including electrolyte optimization, morphology design, and hybridization with carbon materials. In addition, we attempt to propose possible future directions for the development of bismuth anodes in PIBs, aiming to expedite their practical application. It is believed that this review can assist researchers in more efficiently designing high-performance bismuth anode materials for PIBs.

Anion-Reinforced Solvation Structure Enables Stable Operation of Ether-Based Electrolyte in High-Voltage Potassium Metal Batteries

Electrolytes with anion-dominated solvation are promising candidates to achieve dendrite-free and high-voltage potassium metal batteries. However, it's challenging to form anion-reinforced solvates at low salt concentrations. Herein, we construct an anion-reinforced solvation structure at a moderate concentration of 1.5 M with weakly coordinated cosolvent ethylene glycol dibutyl ether. The unique solvation structure accelerates the desolvation of K+, strengthens the oxidative stability to 4.94 V and facilitates the formation of inorganic-rich and stable electrode-electrolyte interface. These enable stable plating/stripping of K metal anode over 2200 h, high capacity retention of 83.0 % after 150 cycles with a high cut-off voltage of 4.5 V in K0.67MnO2//K cells, and even 91.5 % after 30 cycles under 4.7 V. This work provides insight into weakly coordinated cosolvent and opens new avenues for designing ether-based high-voltage electrolytes.

Nonflammable Succinonitrile-Based Deep Eutectic Electrolyte for Intrinsically Safe High-Voltage Sodium-Ion Batteries

Intrinsically safe sodium-ion batteries are considered as a promising candidate for large-scale energy storage systems. However, the high flammability of conventional electrolytes may pose serious safety threats and even explosions. Herein, a strategy of constructing a deep eutectic electrolyte is proposed to boost the safety and electrochemical performance of succinonitrile (SN)-based electrolyte. The strong hydrogen bond between S═O of 1,3,2-dioxathiolane-2,2-dioxide (DTD) and the α-H of SN endows the enhanced safety and compatibility of SN with Lewis bases. Meanwhile, the DTD participates in the inner Na+ sheath and weakens the coordination number of SN. The unique solvation configuration promotes the formation of robust gradient inorganic-rich electrode-electrolyte interphase, and merits stable cycling of half-cells in a wide temperature range, with a capacity retention of 82.8% after 800 cycles (25 °C) and 86.3% after 100 cycles (60 °C). Correspondingly, the full cells deliver tremendous improvement in cycling stability and rate performance.

Challenges and Breakthroughs in Enhancing Temperature Tolerance of Sodium-Ion Batteries

Lithium-based batteries (LBBs) have been highly researched and recognized as a mature electrochemical energy storage (EES) system in recent years. However, their stability and effectiveness are primarily confined to room temperature conditions. At temperatures significantly below 0 °C or above 60 °C, LBBs experience substantial performance degradation. Under such challenging extreme contexts, sodium-ion batteries (SIBs) emerge as a promising complementary technology, distinguished by their fast dynamics at low-temperature regions and superior safety under elevated temperatures. Notably, developing SIBs suitable for wide-temperature usage still presents significant challenges, particularly for specific applications such as electric vehicles, renewable energy storage, and deep-space/polar explorations, which requires a thorough understanding of how SIBs perform under different temperature conditions. By reviewing the development of wide-temperature SIBs, the influence of temperature on the parameters related to battery performance, such as reaction constant, charge transfer resistance, etc., is systematically and comprehensively analyzed. The review emphasizes challenges encountered by SIBs in both low and high temperatures while exploring recent advancements in SIB materials, specifically focusing on strategies to enhance battery performance across diverse temperature ranges. Overall, insights gained from these studies will drive the development of SIBs that can handle the challenges posed by diverse and harsh climates.

Emerging high voltage V4+/V5+ redox reactions in Na3V2(PO4)3-based cathodes for sodium-ion batteries

Na3V2(PO4)3 (NVP) cathode materials with the advantages of long cycle life and superior thermal stability have been considered promising cathode candidates for SIBs. However, the unsatisfactory energy density derived from low theoretical capacity and operating voltage (3.35 V vs. Na+/Na, based on the V3+/V4+ redox couple) inevitably limits their practical application. Therefore, the activation of the V4+/V5+ redox couple (∼4.0 V vs. Na+/Na) in NVP-based cathode materials to boost the energy density of SIBs has attracted extensive attention. Herein, we first analyze the challenges of activation of the V4+/V5+ redox couple in NVP-based cathode materials. Subsequently, the recent achievement of NVP-based cathode materials with activated V4+/V5+ redox reactions for SIBs is overviewed. Finally, further research directions of high voltage V4+/V5+ redox reactions in NVP-based cathodes are proposed. This review provides valuable guidance for developing high energy density NVP-based cathode materials for SIBs.

Weakly Coordinating Diluent Modulated Solvation Chemistry for High-Performance Sodium Metal Batteries

Diluents have been extensively employed to overcome the disadvantages of high viscosity and sluggish kinetics of high-concentration electrolytes, but generally do not change the pristine solvation structure. Herein, a weakly coordinating diluent, hexafluoroisopropyl methyl ether (HFME), is applied to regulate the coordination of Na+ with diglyme and anion and form a diluent-participated solvate. This unique solvation structure promotes the accelerated decomposition of anions and diluents, with the construction of robust inorganic-rich electrode-electrolyte interphases. In addition, the introduction of HFME reduces the desolvation energy of Na+, improves ionic conductivity, strengthens the antioxidant, and enhances the safety of the electrolyte. As a result, the assembled Na||Na symmetric cell achieves a stable cycle of over 1800 h. The cell of Na||P'2-Na0.67MnO2 delivers a high capacity retention of 87.3 % with a high average Coulombic efficiency of 99.7 % after 350 cycles. This work provides valuable insights into solvation chemistry for advanced electrolyte engineering.

Interfacial Engineering for Oriented Crystal Growth toward Dendrite-Free Zn Anode for Aqueous Zinc Metal Battery

Zn deposition with a surface-preferred (002) crystal plane has attracted extensive attention due to its inhibited dendrite growth and side reactions. However, the nucleation and growth of the Zn(002) crystal plane are closely related to the interfacial properties. Herein, oriented growth of Zn(002) crystal plane is realized on Ag-modified surface that is directly visualized by in situ atomic force microscopy. A solid solution HCP-Zn (~1.10 at. % solubility of Ag, 30 °C) is formed on the Ag coated Zn foil (Zn@Ag) and possesses the same crystal structure as Zn to reduce its nucleation barrier caused by their lattice mismatch. It merits oriented Zn deposition and corrosion-resistant surface, and presents long cycling stability in symmetric cells and full cells coupled with V2O5 cathode. This work provides insights into interfacial regulation of Zn anodes for high-performance aqueous zinc metal batteries.

Regulating Ion-Dipole Interactions in Weakly Solvating Electrolyte towards Ultra-Low Temperature Sodium-Ion Batteries

Sodium-ion batteries (SIBs) are recognized as promising energy storage devices. However, they suffer from rapid capacity decay at ultra-low temperatures due to high Na+ desolvation energy barrier and unstable solid electrolyte interphase (SEI). Herein, a weakly solvating electrolyte (WSE) with decreased ion-dipole interactions is designed for stable sodium storage in hard carbon (HC) anode at ultra-low temperatures. 2-methyltetrahydrofuran with low solvating power is incorporated into tetrahydrofuran to regulate the interactions between Na+ and solvents. The reduced Na+-dipole interactions facilitate more anionic coordination in the first solvation sheath, which consistently maintains anion-enhanced solvation structures from room to low temperatures to promote inorganic-rich SEI formation. These enable WSE with a low freezing point of -83.3 °C and faster Na+ desolvation kinetics. The HC anode thus affords reversible capacities of 243.2 and 205.4 mAh g-1 at 50 mA g-1 at -40 and -60 °C, respectively, and the full cell of HC||Na3V2(PO4)3 yields an extended lifespan over 250 cycles with high capacity retention of ~100 % at -40 °C. This work sheds new lights on the ion-dipole regulation for ultra-low temperature SIBs.