Annealing-tuned sodium-ion transport in Na11Sn2PS12: Interfacial stabilization and degradation mechanisms for all-solid-state sodium batteries

Sodium-ion batteries (SIBs) hold significant promise in energy storage devices due to their low cost and abundant resources. Layered transition metal oxide cathodes (NaxTMO2, TM = Ni, Mn, Fe, etc.), owing to their high theoretical capacities and straightforward synthesis procedures, are emerging as the most promising cathode materials for SIBs. However, the practical application of the NaxTMO2 cathode is hindered by an unstable interface, causing rapid capacity decay. This work reviewed the critical factors affecting the interfacial stability and degradation mechanisms of NaxTMO2, including air sensitivity and the migration and dissolution of TM ions, which are compounded by the loss of lattice oxygen. Furthermore, the mainstream interface modification approaches for improving electrochemical performance are summarized, including element doping, surface engineering, electrolyte optimization, and so on. Finally, the future developmental directions of these layered NaxTMO2 cathodes are concluded. This review is meant to shed light on the design of superior cathodes for high-performance SIBs.

The rapid increase in the human population starting from the 20th century resulted in the excessive utilization of non-renewable energy sources. Environmental concerns caused by greenhouse gas emissions forced society to find renewable ways to produce energy. Their irregular nature, however, requires the development of large-scale energy storage technologies. While Li-ion batteries (LIBs) predominates the market, growing demand and increasing prices limit their large-scale application. As a cost-effective alternative, Na-ion batteries (NIBs) have gained attention from the research community. With similar chemical characteristics and no alloying with aluminum, existing LIB facilities can produce NIBs at a much lower cost while requiring minimal upgrades.1 Higher reactivity and the larger ionic radius of sodium creates mechanical and interfacial instabilities on the electrode materials due to sodium chemistry. Large and sudden changes in the lattice parameters of active materials originating from Na concentration may cause particle fracturing and eventually, capacity degradation with repeated sodium insertion/removal.2 Understanding the fundamentals of the mechanical deformation of the Na-ion active materials is crucial for the pursuit of better-performing NIBs.In our study, our goal was to investigate the effect of cycling rate on the mechanical response of sodium iron phosphate (NaFePO4, NFP) cathode material during sodium intercalation via galvanostatic cycling at different rates. We implemented digital image correlation (DIC) and galvanostatic intermittent titration technique (GITT), and a mathematical model to understand this phenomenon. Similar to our previous study on NFP electrodes, in situ DIC measurements showed that there is a linear relationship between Na concentration and strain regardless of cycling rate.3 It was also observed that the slower the scan rate, the rate of strain generation was also lower. A mathematical model was developed; using the in-situ XRD results, to estimate the strain evolution and concentration gradient in the composite electrode.4 Simulations suggested the nonuniform distribution of Na ions in the electrode particle, which can lead to the larger strain generation in the composite electrode. Effective utilization of in situ strain measurement system in conjunction with an analytical model helps us to understand the volumetric changes observed in NFP cathode during electrochemical reactions. Acknowledgment: The work was supported by the Department of Energy and we are thankful to Vijay Murugesan, Damien Saurel, and Monserrat Casas for fruitful discussions. References Kubota K, Dahbi M, Hosaka T, Kumakura S, Komaba S. Towards K-Ion and Na-Ion Batteries as “Beyond Li-Ion.” Chem Rec. 2018;18(4):459-479. doi:10.1002/tcr.201700057Moreau P, Guyomard D, Gaubicher J, Boucher F. Structure and stability of sodium intercalated phases in olivine FePO 4. Chem Mater. 2010;22(14):4126-4128. doi:10.1021/cm101377hÖzdogru B, Dykes H, Padwal S, Harimkar S, Çapraz Ö. Electrochemical strain evolution in iron phosphate composite cathodes during lithium and sodium ion intercalation. Electrochim Acta. 2020;353. doi:10.1016/j.electacta.2020.136594Galceran M, Saurel D, Acebedo B, et al. The mechanism of NaFePO4 (de)sodiation determined by in situ X-ray diffraction. Phys Chem Chem Phys. 2014;16(19):8837-8842. doi:10.1039/c4cp01089b

Coating and Interface Degradation of Coated steel, Part 2: Accelerated Laboratory Tests

Understanding the intricate surface chemistry and structural heterogeneity at the electrode-electrolyte interface (EEI) remains a central challenge in the development of high-performance and long-lasting sodium- and lithium-ion batteries. Conventional spectroscopic and microscopic tools often fall short in resolving these interfaces at the nanoscale, limiting insights into the mechanisms that govern interfacial stability and degradation. Tip-Enhanced Raman Spectroscopy (TERS), which synergistically combines scanning probe microscopy with the chemical specificity of Raman scattering, offers a unique capability for nanometer-scale chemical imaging. We present a TERS-focused exploration of various battery electrode systems, integrating key findings from sodium-ion battery interfaces, borate-coated disordered rock salt cathodes, and SiOx-coated graphite anodes.Focal point of this study is the illustration of nano-scale chemical heterogeneity of EEI in sodium‐ion batteries through TERS, which demonstrated the first application of TERS to spatially resolve nanoscale chemical inhomogeneities at the EEI in sodium-ion batteries. Through sub-20 nm spatial resolution, TERS enabled the direct mapping of organic and inorganic components within the solid electrolyte interphase (SEI), uncovering lateral heterogeneities that conventional techniques cannot resolve. These results provide critical insight into the role of electrolyte additives and local degradation pathways, offering guidelines to engineer more uniform and stable interphases.Complementing above, exploration on boron oxide based coating of cathode active materials provides perspective on interfacial stabilization. TERS revealed that, the synthesized borate layer is structurally disordered and doped with alkali ions leached from the active material. These dopants disrupt the “superstructural” borate units, leading to polymorphic species such as pyroborates and diborates. Notably, TERS allowed precise quantification of dopant incorporation (40–60 mol% relative to boron oxide), a level of detail unattainable through conventional analytical techniques.The capability of TERS to probe the interphase SiOx coated graphite with silicate based inorganic aqueous binders . TERS uncovered a synthesized hybrid interphase comprising polysilicate chains and cyclic silicate motifs, with spatially selective structural features across the graphite surface. This complex, symbiotic interaction between SiOx and binder species contributes to improved electrochemical performance—insights that were previously obscured using other bulk/surface characterization methods.Together, these case studies underscore TERS as a powerful tool for nanoscale probing of energy materials, offering chemically specific, high-resolution insights into heterogeneous interfacial phenomena. As battery technologies evolve toward more complex, multicomponent interfaces, TERS stands out as a critical technique for guiding the rational design of stable, high-performance electrodes. We conclude by outlining future directions for TERS, accurate tracking of interfacial chemical evolution upon successive electrochemical cycling. Figure 1

Tungsten and oxygen co-doped stable tetragonal phase Na3SbS4 with ultrahigh ionic conductivity for all-solid-state sodium batteries

Knowledge of interfacial mechanics and mechanisms of liquid exfoliation and stabilization of graphene in green solvents is vitally important in advancing preparation and characterization of graphene‐based materials. In this work, molecular dynamics simulations are performed to investigate exfoliation and stabilization of graphene from graphite with the assistance of urea and glycerol hybrid solvents. It is shown that the parallel exfoliation of graphene requires far less external forces as compared with the perpendicular exfoliation. Among different mediums, the 1:2 molar ratio of urea to glycerol solution presents the smallest or even negligible resistive force in both directions due to the less compressed steric hindrance to graphene exfoliation and the optimal hydrogen bonds formed between the binary solvents. During the dispersion process, the urea molecules first wedge into the graphene interlayer and then facilitate the glycerol to diffuse around or inside of the interstice due to hydrogen bonding. The confined solvents form stable layered structure to solvate and stabilize the exfoliated graphene. This work is believed to provide atomic scale understanding of interfacial mechanics and mechanisms of liquid‐phase exfoliation and dispersion of graphene and other 2D materials in low‐cost and environmental‐friendly hybrid solvents.

The increasing demand for carbon neutrality has accelerated the adoption of electric vehicles and large-scale energy storage systems, traditionally powered by lithium-ion batteries. However, concerns about the limited availability and rising cost of lithium resources have prompted growing interest in sodium-ion batteries, which offer advantages in abundance and cost-effectiveness.While hard carbon has been widely used as a commercial anode material for sodium-ion batteries, its limited capacity has driven the search for alternative high-capacity materials. Alloy-type materials, such as Sn and SnSb, are promising candidates due to their high theoretical capacities. Nonetheless, their practical application is hindered by challenges including severe volume changes, sluggish reaction kinetics, and interfacial instability during cycling.To overcome these issues, we developed heterostructured composite anodes by integrating active materials with a porous silicon oxycarbide (SiOC) matrix, which offers excellent mechanical robustness and surface capacitive properties. Through controlled dispersion of precursors in silicon oil followed by heat treatment, alloy-based high-capacity composites (Sn@SiOC and SnSb@SiOC) were successfully synthesized. Comprehensive structural, physicochemical, and electrochemical characterizations—including post-mortem analyses—revealed that the heterostructure effectively mitigates degradation and enhances sodium storage performance.Our findings demonstrate the potential of heterostructured anodes to significantly improve the energy density and cycling stability of sodium-ion batteries, contributing to the development of next-generation energy storage technologies.

The transition toward carbon neutrality has accelerated the adoption of electric vehicles and large-scale energy storage systems, predominantly powered by lithium-ion batteries. However, concerns over the limited lithium resources necessitate exploring alternative battery systems. Sodium-ion batteries stand out due to the abundant supply and economic feasibility of sodium compared to lithium.This study focuses on developing high-capacity anode materials for sodium-ion batteries through the design of heterostructured composites. By combining conversion- or alloy-based active materials with a porous silicon oxycarbide (SiOC) nanocoating layer, we aim to address challenges such as volume changes, sluggish kinetics, and interfacial instability during battery cycling. Heterostructured composite anodes with a SiOC-based nanocoating layer were synthesized via controlled dispersion of precursors in silicon oil followed by heat treatment. Comprehensive physicochemical and electrochemical characterization, along with post-mortem analysis, elucidated how the heterostructure influenced battery performance. Our findings demonstrate improved electrochemical stability and enhanced sodium storage capacity attributed to the unique architecture of the heterostructured composites.This novel approach offers promising prospects for developing advanced anode materials capable of significantly enhancing the energy density and overall performance of sodium-ion batteries, thereby contributing to sustainable energy storage solutions for future applications in electric vehicles and grid-scale energy storage systems.

The growing global demand for carbon neutrality has led to an increase in the use of electric vehicles and large-scale energy storage systems, which rely heavily on lithium-ion batteries. However, there are concerns about the limited availability of lithium resources, which may result in depletion and price increases in the near future. To solve this issue, researchers are actively exploring alternative next-generation secondary battery systems to replace current lithium-ion batteries. Sodium-ion batteries have received significant attention as one of promising candidates, as sodium is abundant in the earth's crust and economically viable compared to lithium.Although hard carbon has been considered a reversible anode material capable of sodium-ion insertion and extraction, high-capacity anode materials are required to increase the energy density of sodium-ion batteries. Among various candidates, conversion- and alloy-based materials are highly regarded due to their high theoretical capacity. However, challenges such as huge volume changes of active materials, sluggish reaction rates, and interfacial instability that occur during charging and discharging need to be overcome for these materials to be applied in high-performance sodium-ion batteries.To address these challenges, herein, we designed heterostructured anodes with a unique structure by combining conversion- or alloy-based materials with a porous silicon oxycarbide (SiOC) nanocoating layer, which possesses high surface capacitive reactivity and mechanical strength. We controlled the dispersion of the precursors in silicon oil and performed heat treatment to synthesize high-capacity heterostructured composites (MoS2@SiOC and Sn@SiOC). Subsequently, we conducted extensive physicochemical and electrochemical characterization as well as post-mortem analysis to investigate the properties of these composites, with a specific focus on the impact of the heterostructure on their battery performance. We anticipate that this heterostructure approach will pave the way for the development of novel, high-performance anode materials for sodium-ion batteries in the future.

Sodium-ion batteries are emerging as strong contenders for grid-scale energy storage applications due to the easy availability and affordability of sodium resources. However, their lower energy density compared to lithium-ion batteries poses a major challenge to their commercial scalability and limits the scope of applications. Enhancing the energy density of sodium-ion cells requires strategic material selection, particularly by integrating electrode materials with inherently high specific capacities. In this regard, layered transition metal oxides and hard carbon composites have been reported to have remarkably high specific capacities, presenting a unique opportunity for induction in sodium-ion battery systems. As elevated energy densities exacerbate interfacial degradation and thermal runaway, this study focuses on investigating the electrochemical performance and thermo-electrochemical stability of sodium-ion batteries composed of sodium iron manganese oxide cathode and micro-tin and hard carbon composite anode. This work highlights the anode-side dynamics, particularly sodium alloying behavior and solid electrolyte interphase progression under varied charging currents. Through electrochemical, morphological, surface, and chemical analyses, we elucidate the role of rate performance in interfacial nonuniformity, tin pulverization, and thermal stability.

The O3-type Na[Ni1-x-yCoxMny]O2 cathodes have received significant attention in sodium-ion batteries (SIBs) due to their high energy density. However, challenges such as structural instability and interfacial instability against an electrolyte solution limit their practical use in SIBs. In this study, the single-crystalline O3-type Na[Ni0.6Co0.2Mn0.2]O2 (SC-NCM) cathode has been designed and synthesized to effectively relieve the degradation pathways of the polycrystalline O3-type Na[Ni0.6Co0.2Mn0.2]O2 (PC-NCM) cathode for SIBs. The mechanically robust SC-NCM due to the absence of pores in the particles enhances tolerance to particle cracking, resulting in stable cycling performance with a cycle retention of 73% over 350 cycles. Moreover, the proposed SC-NCM is synthesized using a simple and cost-effective molten-salt synthetic route without the complex quenching process typically associated with PC-NCM synthesis methods, showing good practical applicability. This study will provide an innovative direction for the development of advanced cathode materials for practical SIBs.

Anion-derived cathode interface engineering enables ether-based electrolytes for sodium-ion batteries

Layered transition metal oxide (LTMO) cathode materials of sodium‐ion batteries (SIBs) have shown great potential in large‐scale energy storage applications owing to their distinctive periodic layered structure and 2D ion diffusion channels. However, several challenges have hindered their widespread application, including phase transition complexities, interface instability, and susceptibility to air exposure. Fortunately, an impactful solution has emerged in the form of a high‐entropy doping strategy employed in energy storage research. Through the implementation of high‐entropy doping, LTMOs can overcome the aforementioned limitations, thereby elevating LTMO materials to a highly competitive and attractive option for next‐generation cathodes of SIBs. Thus, a comprehensive overview of the origins, definition, and characteristics of high‐entropy doping is provided. Additionally, the challenges associated with LTMOs in SIBs are explored, and discussed various modification methods to address these challenges. This review places significant emphasis on conducting a thorough analysis of the research advancements about high‐entropy LTMOs utilized in SIBs. Furthermore, a meticulous assessment of the future development trajectory is undertaken, heralding valuable research insights for the design and synthesis of advanced energy storage materials.

Interfacial structure evolution and degradation are critical to the electrochemical performance of LiCoO2 (LCO), the most widely studied and used cathode material in lithium ion batteries. To understand such processes requires precise and quantitative measurements. Herein, we use well-defined epitaxial LCO thin films to reveal the interfacial degradation mechanisms. Through our systematical investigations, we find that surface corrosion is significant after forming the surface phase transition layer, and the cathode electrolyte interphase (CEI) has a double layer structure, an inorganic inner layer containing CoO, LiF, LiOH/Li2O and Li x PF y O z , and an outmost layer containing Li2CO3 and organic carbonaceous components. Furthermore, surface cracks are found to be pronounced due to mechanical failures and chemical etching. This work demonstrates a model material to realize the precise measurements of LCO interfacial degradations, which deepens our understanding on the interfacial degradation mechanisms.

With the advantages of similar theoretical basis to lithium batteries, relatively low budget and the abundance of sodium resources, sodium ion batteries (SIBs) are recognized as the most competitive alternative to lithium‐ion batteries. Among various types of cathodes for SIBs, advantages of high theoretical capacity, nontoxic and facile synthesis are introduced for layered transition metal oxide cathodes and therefore they have attracted huge attention. Nevertheless, layered oxide cathodes suffer from various degradation issues. Among these issues, interface instability including surface residues, phase transitions, loss of active transition metal and oxygen loss takes up the major part of the degradation of layered oxides. These degradation mechanisms usually lead to irreversible structure collapse and cracking generation, which significantly influence the interface stability and electrochemical performance of layered cathodes. This review briefly introduces the background of researches on layered cathodes for SIBs and their basic structure types. Then the origins and effects on layered cathodes of degradation mechanisms are systematically concluded. Finally, we will summarize various interface modification methods including surface engineering, doping modification and electrolyte composition which are aimed to improve interface stability of layered cathodes, perspectives of future research on layered cathodes are mentioned to provide some theoretical proposals.