Solid Electrolyte Interphase Formation Research Articles

Stoichiometric Ti3C2Tx Coating for Inhibiting Dendrite Growth in Anode‐Free Lithium Metal Batteries

Lithium metal batteries (LMBs) and anode‐free LMBs (AFLMBs) present a solution to the need for batteries with a significantly superior theoretical energy density. However, their adoption is hindered by low Coulombic efficiency (CE) and rapid capacity fading, primarily due to the formation of unstable solid electrolyte interphase (SEI) layer and Li dendrite growth as a result of uneven Li plating. Here, we report on the use of a stoichiometric Ti3C2Tx (S‐Ti3C2Tx) MXene coating on the copper current collector to enhance the cyclic stability of an anode‐free lithium metal battery. The S‐Ti3C2Tx coating provides abundant nucleation sites, thereby lowering the overpotential for Li nucleation, and promoting uniform Li plating. Additionally, the fluorine (−F) termination of S‐Ti3C2Tx participates in the SEI formation, producing a LiF‐rich SEI layer, vital for stabilizing the SEI and improving cycle life. Batteries equipped with S‐Ti3C2Tx@Cu current collectors displayed reduced Li consumption during stable SEI formation, resulting in a significant decrease in capacity loss. AFLMBs with S‐Ti3C2Tx@Cu current collectors achieved a high initial capacity density of 4.2 mAh cm−2, 70.9% capacity retention after 50 cycles, and an average CE of 98.19% in 100 cycles. This innovative application of MXenes in the energy field offers a promising strategy to enhance the performance of AFLMBs and could potentially accelerate their commercial adoption.

Constructing LiF-Dominated Interphases with Polymer Interwoven Outer Layer Enables Long-Term Cycling of Si Anodes.

Constructing a robust solid electrolyte interphase (SEI) is extremely critical to developing high-energy-density silicon (Si)-based lithium-ion batteries. However, it is still elusive how to accurately manipulate the chemical composition and structure of the SEI layer. Herein, a LiF-dominated SEI film intertwined by a highly elastic polymer is achieved by regulating the defluorination mechanism of the fluorinated carbonate additive on the Si electrode surface. The experimental and computational results confirm that the decomposition route of trans-difluoroethylene carbonate (DFEC) molecules can be significantly altered in the presence of lithium difluoro(oxalato)borate (LiDFOB) additive. The induction of direct defluorination of DFEC step by LiDFOB, as opposed to the breaking of C-O bonds without LiDFOB addition, is crucial in ensuring the exclusive formation of LiF-dominated SEI and maintaining the cyclic structure of DFEC. The defluorinated DFEC easily polymerizes to form poly(vinylene carbonate), enhancing the elasticity of the SEI. The resulting LiF-dominated SEI film with a polymer interwoven outer layer shows enhanced ionic conductivity and mechanical stability, which can effectively accelerate electrode reaction kinetics and maintain the structural stability of the Si electrode. As a result, the Si electrode with the electrolyte containing the designed dual-additive exhibits superior cycling stability and excellent rate performance, delivering a high reversible capacity of 1487.3 mAh g-1 after 1000 cycles at 2 A g-1.

Ternary Eutectic Electrolyte-Assisted Formation and Dynamic Breathing Effect of the Solid-Electrolyte Interphase for High-Stability Aqueous Magnesium-Ion Full Batteries.

Aqueous rechargeable magnesium batteries hold immense potential for intrinsically safe, cost-effective, and sustainable energy storage. However, their viability is constrained by a narrow voltage range and suboptimal compatibility between the electrolyte and electrodes. Herein, we introduce an innovative ternary deep eutectic Mg-ion electrolyte composed of MgCl2·6H2O, acetamide, and urea in a precisely balanced 1:1:7 molar ratio. This formulation was optimized by leveraging competitive solvation effects between Mg2+ ions and two organic components. The full batteries based on this ternary eutectic electrolyte, Mn-doped sodium vanadate (Mn-NVO) anode, and copper hexacyanoferrate cathode exhibited an elevated voltage plateau and high rate capability and showcased stable cycling performance. Ex-situ characterizations unveiled the Mg2+ storage mechanism of Mn-NVO involving initial extraction of Na+ followed by subsequent Mg2+ intercalation/deintercalation. Detailed spectroscopic analyses illuminated the formation of a pivotal solid-electrolyte interphase on the anode surface. Moreover, the solid-electrolyte interphase demonstrated a dynamic adsorption/desorption behavior, referred to as the "breathing effect", which substantially mitigated undesired dissolution and side reactions of electrode materials. These findings underscore the crucial role of rational electrolyte design in fostering the development of a favorable solid-electrolyte interphase that can significantly enhance compatibility between electrode materials and electrolytes, thus propelling advancements in aqueous multivalent-ion batteries.

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

AbstractSodium‐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.

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.

In Situ Transmission Electron Microscopy Methods for Lithium-Ion Batteries.

In situ Transmission Electron Microscopy (TEM) stands as an invaluable instrument for the real-time examination of the structural changes in materials. It features ultrahigh spatial resolution and powerful analytical capability, making it significantly versatile across diverse fields. Particularly in the realm of Lithium-Ion Batteries (LIBs), in situ TEM is extensively utilized for real-time analysis of phase transitions, degradation mechanisms, and the lithiation process during charging and discharging. This review aims to provide an overview of the latest advancements in in situ TEM applications for LIBs. Additionally, it compares the suitability and effectiveness of two techniques: the open cell technique and the liquid cell technique. The technical aspects of both the open cell and liquid cell techniques are introduced, followed by a comparison of their applications in cathodes, anodes, solid electrolyte interphase (SEI) formation, and lithium dendrite growth in LIBs. Lastly, the review concludes by stimulating discussions on possible future research trajectories that hold potential to expedite the progression of battery technology.

Solid–electrolyte interphase formation during Li metal deposition in LiN(SO2F)2-based solvate ionic liquids

AbstractSolvate ionic liquids (SILs) are promising electrolytes for Li metal batteries. In this study, Li plating-stripping reactions in SILs were investigated using electrochemical quartz crystal microbalance measurements and X-ray photoelectron spectroscopy (XPS). SILs were prepared by mixing Li salt and glyme (triglyme or tetraglyme) in a 1:1 molar ratio. During the Li plating-stripping reaction, a reversible mass change was observed in LiN(SO2F)2 (LiFSA) based SILs. In contrast, a considerably higher mass change than the theoretical value calculated from the Faraday current was observed in the LiN(SO2CF3)2 (LiTFSA) based SILs, owing to the accumulation of decomposition products of electrolytes on the electrode surface. XPS depth profiling for the deposited Li suggested the formation of thin solid-electrolyte interphase (SEI) in the LiFSA-based SILs while considerably thicker SEI was formed in the LiTFSA-based SILs. The SEI formed in LiFSA-based SILs effectively suppressed the decomposition of electrolytes. Thus, LiFSA-based SILs are favorable for achieving highly reversible charge–discharge of Li electrodes in Li metal batteries.

Directing Fluorinated Solid Electrolyte Interphase by Solubilizing Crystal Lithium Fluoride in Aprotic Electrolyte for Lithium Metal Batteries

AbstractLithium fluoride (LiF) facilitates robust and fast‐ion‐transport solid electrolyte interphase (SEI) in lithium metal batteries. Fluorinated solvents/salts are ubiquitously employed to introduce LiF into SEI through electrochemical decomposition, but this approach is usually at the expense of their continuous consumption. A direct approach to fluorinate SEI that employs crystal LiF is limited by its poor solubility in the current battery electrolyte formulation. Dissolving crystal LiF in high‐dielectric‐constant solvents, like ethylene carbonate (EC) is nearly neglected. Herein, the feasibility of directly fluorinating SEI by the addition of crystal LiF in aprotic electrolyte with the assistance of EC is verified, and its mechanisms in fluorination of SEI and anti‐acidification of electrolyte are explored. The dissolved LiF is encapsulated by solvent‐/salt‐derived organic skins to promote the fluorinated SEI. Meanwhile, the presence of LiF in electrolyte alters hazardous thermodynamic equilibrium, suppressing the production of acid species to mitigate electrolyte acidification and SEI degradation. Such collective benefits yield a capacity retention ratio of ≈88% after 150 cycles at a high areal capacity (4.5 mAh cm−2) in Li||NCM622 cells. This facile and effective fluorination of SEI contributes to an in‐depth understanding of SEI formation and rational design of well‐performing lithium metal batteries.

Enhancing low-temperature electrolyte performance through intermittent discharge for improved LiODFB additive film formation

The challenge of improving low-temperature performance in lithium-ion batteries (LIBs) is attributed to the formation of an unstable solid electrolyte interphase (SEI) film. Lithium difluoro(oxalate)borate (LiODFB) has demonstrated potential in enhancing capacity retention and reducing impedance at low temperatures by establishing a high ion conductivity and stable SEI layer. Previous research indicates that the BOF2− anion, a soluble product of film formation additive of LiODFB hinder salt decomposition by aggregating on the electrode surface. This study presents a strategy to intensify the film formation process of LiODFB additives by introducing an optimal standing time during intermittent discharge processes. Three specific stages of soluble product diffusion are discussed. Diffusion starts from the outer layer of adsorption composed of soluble substances, gradually extends to the inner layer of adsorption, and finally establishes a new connection with the electrode. A brief standing time proves insufficient for inner adsorption layer diffusion, while excessively extended standing time fails to accelerate LiODFB decomposition. A standing time of 2300 s is selected to promote a stable SEI layer. This strategy elevates the capacity retention rate of cells at –20 °C from 66.59 % to 84.44 %. The study offers a method to address battery performance degradation in low-temperature conditions.

A Fluoride-Rich Solid-Like Electrolyte Stabilizing Lithium Metal Batteries.

To address the problems associated with Li metal anodes, a fluoride-rich solid-like electrolyte (SLE) that combines the benefits of solid-state and liquid electrolytes is presented. Its unique triflate-group-enhanced frame channels facilitate the formation of a functional inorganic-rich solid electrolyte interphase (SEI), which not only improves the reversibility and interfacial charge transfer of Li anodes but also ensures uniform and compact Li deposition. Furthermore, these triflate groups contribute to the decoupling of Li+ and provide hopping sites for rapid Li+ transport, enabling a high room-temperature ionic conductivity of 1.1 mS cm-1 and a low activation energy of 0.17eV, making it comparable to conventional liquid electrolytes. Consequently, Li symmetric cells using such SLE achieve extremely stable plating/stripping cycling over 3500h at 0.5mA cm-2 and support a high critical current up to 2mA cm-2. The assembled Li||LiFePO4 solid-like batteries exhibit exceptional cyclability for over 1 year and a half, even outperforming liquid cells. Additionally, high-voltage cylindrical cells and high-capacity pouch cells are demonstrated, corroborating much simpler processibility in battery assembly compared to all-solid-state batteries.

Electrophoretic Deposition as a Versatile Low-Cost Tool to Construct a Synthetic Polymeric Solid-Electrolyte Interphase on Silicon Anodes: A Model System Investigation.

The cycling of next-generation, high-capacity silicon (Si) anodes capable of 3579 mAh·g-1 is greatly hindered by the instability of the solid-electrolyte interphase (SEI). The large volume changes of Si during (de)lithiation cause continuous cracking of the SEI and its reconstruction, leading to loss of lithium inventory and extensive consumption of electrolyte. The SEI formed in situ during cell cycling is mostly composed of molecular fragments and oligomers, the structure of which is difficult to tailor. In contrast, ex situ formation of a synthetic SEI provides greater flexibility to deposit long-chain, polymeric, and elastomeric components potentially capable of maintaining integrity against the large ∼350% volume expansion of Si while also enabling electronic passivation of the surface for longer cycling and calendar life. Furthermore, polymers are amenable to structural modifications, and the desired elasticity can be targeted by selection of the SEI polymer feedstock. Herein, electrophoretic deposition (EPD) is used to apply chitosan as a synthetic SEI on model Si thin film electrodes. Comparison of synthetic SEIs obtained without (Si/Chit) and with CH3COOLi (Si/Chit+CH3COOLi) added during EPD is performed to demonstrate a facile route to tuning of the polymer SEI chemistry. Atomic force and scanning electron microscopy reveal that addition of CH3COOLi at EPD assists in conformal deposition of the synthetic SEI. During electrochemical cycling, the Chit+CH3COOLi coating nearly doubles the capacity retention versus the reference bare Si thin film. X-ray photoelectron and Fourier transform infrared spectroscopy reveal that CH3COOLi caps the -NH2 groups of chitosan through amidation during EPD, which suppresses the catalytic reduction of the electrolyte. The presented approach demonstrates and validates EPD as a low-capital route to achieving and chemistry-tuning synthetic SEIs on Si electrodes. More broadly, the method is a promising avenue toward controlled and tailored polymeric SEIs on various conversion-type electrodes with high particle volumetric expansion.

Interfacial structure changes between amorphous silicon anode/liquid electrolyte using a highly dense and flat model electrode

AbstractChanges in the interfacial structures of the amorphous silicon (a-Si) anode/organic electrolyte interfaces in lithium-ion batteries were investigated using highly dense a-Si films fabricated by cathodic arc plasma deposition as a model electrode. Raman spectroscopy, transmission electron microscopy (TEM), and X-ray reflectivity revealed that the Si films were grown in an amorphous state with an atomically flat surface. The a-Si films exhibited lithium alloying and de-alloying reactions, with a large irreversible capacity during the first cycle. The irreversible capacity was derived from the formation of a solid electrolyte interphase (SEI) along with an incompletely de-alloyed Li-Si phase, as confirmed by ex situ TEM and X-ray photoelectron spectroscopy observations. The discharge and charge capacities of the Si films gradually decreased in the subsequent cycles, despite the fact that no further SEI formation or cracking of the Si layer occurred. Scanning electron microscopy observations combined with energy-dispersive X-ray spectroscopy revealed the miniaturization of the a-Si film in the surface region to generate domains measuring less than a few hundred nanometers. These results suggest that delamination and miniaturization of the a-Si nanodomains from the electrode surface are partly responsible for degradation of the a-Si anode.

Electrochemical Signatures of Potassium Plating and Stripping

Alkali metal anodes can enable unmatched energy densities in next generation batteries but suffer from insufficient coulombic efficiencies. To deduce details about processes taking place during galvanostatic cycling, voltage profiles are commonly analyzed, however the interpretation is not straightforward as multiple processes can occur simultaneously. Here we provide a route to disentangle and interpret features of the voltage profile in order to build a mechanistic understanding on alkali metal stripping and deposition, by investigating potassium metal deposition as a model case where processes and reactions are exaggerated due to the high reactivity of potassium. In particular, the importance of separating SEI formation and nucleation to correctly estimate the energy barrier for nucleation is demonstrated. Further, we show how the native layer formed on alkali metal foils gives rise to strong features in the voltage profile and propose forming alkali metal electrode through electrodeposition to mitigate these effects.

Delineating the Effects of Transition-Metal-Ion Dissolution on Silicon Anodes in Lithium-Ion Batteries.

Silicon anode is an appealing alternative to enhance the energy density of lithium-ion batteries due to its high capacity, but it suffers from severe capacity fade caused by its fast degradation. The crossover of dissolved transition-metal (TM) ions from the cathode to the anode is known to catalyze the decomposition of electrolyte on the graphite anode surface, but the relative impact of dissolved Mn2+ versus Ni2+ versus Co2+ on silicon anode remains to be delineated. Since all three TM ions can dissolve from LiNi1-x-yMnxCoyO2 (NMC) cathodes and migrate to the anode, here a LiFePO4 cathode is paired with SiOx anode and assess the impact by introducing a specific amount of Mn2+ or Ni2+ or Co2+ ions into the electrolyte. It is found that Mn2+ ions cause a much larger increase in SiOx electrode thickness during cycling due to increased electrolyte decomposition and solid-electrolyte interphase (SEI) formation compared to Ni2+ and Co2+ ions, similar to previous findings with graphite anode. However, with a lower impedance, the SEI formed with Mn2+ protects the Si anode from excessive degradation compared to that with Co2+ or Ni2+ ions. Thus, Mn2+ ions have a less detrimental effect on Si anodes than Co2+ or Ni2+ ions, which is the opposite of that seen with graphite anodes.

Deciphering the Formation and Accumulation of Solid-Electrolyte Interphases in Na and K Carbonate-Based Batteries.

The continuous solid-electrolyte interphase (SEI) accumulation has been blamed for the rapid capacity loss of carbon anodes in Na and K ethylene carbonate (EC)/diethyl carbonate (DEC) electrolytes, but the understanding of the SEI composition and its formation chemistry remains incomplete. Here, we explain this SEI accumulation as the continuous production of organic species in solution-phase reactions. By comparing the NMR spectra of SEIs and model compounds we synthesized, alkali metal ethyl carbonate (MEC, M = Na or K), long-chain alkali metal ethylene carbonate (LCMEC, M = Na or K), and poly(ethylene oxide) (PEO) oligomers with ethyl carbonate ending groups are identified in Na and K SEIs. These components can be continuously generated in a series of solution-phase nucleophilic reactions triggered by ethoxides. Compared with the Li SEI formation chemistry, the enhancement of the nucleophilicity of an intermediate should be the cause of continuous nucleophilic reactions in the Na and K cases.

Sustainable Manufacturing of Graphitic Carbon from Bio‐Waste Using Flash Heating for Anode Material of Lithium‐Ion Batteries with Optimal Performance

AbstractTo address the fundamental challenge of resource sustainability and to effectively deal with issues pertaining to supply chain resilience, cost efficiency, environmental impact, and the ability to meet specific local needs; there is an urgent need for high‐grade battery anode materials produced locally from readily available raw materials. In this work, synthesis of high‐quality graphitic carbon (GH) derived from human hair is demonstrated using an in‐house engineered reactor based on Joule's Flash heating method. The GH is characterized using various techniques to examine its chemical composition, particle morphology, crystallinity, and demonstrate its usability as an anode material for lithium‐ion batteries. Fabricated coin cell with active material exhibits a gravimetric capacity of 320 mAh g−1 at a current density of 30 mA g−1 (equivalent to a C rate of ≈0.1C) over the 100 cycles. The in situ and ex situ studies using XRD, Raman, XPS, and UPS techniques conclude that during the initial charge cycle for GH, lithium ions diffused into the electrode during the resting period are effectively removed. This not only improves the lithium inventory to start with but also mitigates subsequent solvent degradation during solid electrolyte interphase (SEI) formation. Thus, these improvements ultimately enhance the capacity of the anode to 500mAh g−1 at a current density of 20 mA g−1. The study offers the potential to initiate a new realm of research by redirecting the focus to a material once considered as mere waste.

Interfacial polymerization mechanisms assisted flame retardancy process of low-flammable electrolytes on lithium anode

Thermal runaway is a hazardous risk, occurring more readily in high-energy–density lithium-ion batteries (LIBs), which leads to a rapid temperature rise and even combustion or explosion when using flammable electrolyte systems. Flame retardants (FRs), such as trimethyl phosphate (TMPa) and triethyl phosphate (TEP), are commonly utilized due to their effective flame suppression, low toxicity, and excellent thermal stability. However, the lack of in-depth understanding of the flame retardancy mechanism and solid electrolyte interphase (SEI) formation process has made the development of functional electrolytes difficult at present. In this study, we clarified the flame retardancy and interfacial reaction mechanisms of low-flammable TMPa localized high-concentration electrolytes (LHCE) using hybrid ab initio and reactive force field (HAIR) schemes. Long-term HAIR simulation reveals that phosphorous radicals produced by the decomposition of TMPa capture carbon radicals, encouraging their polymerization into low-flammable oligomers, while fluorine-containing solvents in the electrolyte capture hydrogen radicals and produce nonflammable hydrofluoric acid (HF). This synergistic flame retardancy mechanism provides essential atomic-level insights for the rational design of high-safety electrolytes in the future.

Borate-containing triblock copolymer electrolytes for improved lithium-ion transference number and interface stability

The electrolytes with high lithium-ion transference number (tLi+) can reduce the formation of concentration polarization during charge/discharge process and improve the electrochemical performance of lithium-ion batteries (LIBs). Herein, we report triblock copolymer electrolytes (PBOEE) containing borate. The sp2 hybridized boron atoms acting as Lewis acids can anchor the anions of lithium salts, enabling PBOEE to achieve high tLi+ of up to 0.53. Also, the borate groups can promote the formation of stable organic-rich solid electrolyte interphase (SEI) film, which enables the Li symmetric cell to cycle stably at 0.1 mA cm−2/0.1 mAh cm−2 for more than 3100 h with a low overpotential of 0.08 V under 50 °C. The optimized PBOEE_24 has an ionic conductivity of 1.41 × 10−4 S cm−1 and electrochemical stability window of 4.8 V vs. Li+/Li at 50 °C. Combining these advantages, the LiFePO4/PBOEE_24/Li cell exhibits an initial discharge specific capacity of 157.3 mA h g−1 at 0.5C with a capacity retention of 85 % after 600 cycles under 50 °C. At a higher current density of 1C, the discharge capacity maintains at 128.0 mA h g−1 after 400 cycles with a capacity retention of 84.88 %. These results suggest that block copolymer containing sp2 hybridized boron atoms is a promising all-solid-state polymer electrolyte.

Molecular Engineering Enabling High Initial Coulombic Efficiency and Rubost Solid Electrolyte Interphase for Hard Carbon in Sodium-Ion Batteries.

Hard carbon (HC) as a potential candidate anode for sodium-ion batteries (SIBs) suffers from unstable solid electrolyte interphase (SEI) and low initial Coulombic efficiency (ICE), which limits its commercial applications and urgently requires the emergence of a new strategy. Herein, an organic molecule with two sodium ions, disodium phthalate (DP), was successfully engineered on the HC surface (DP-HC) to replenish the sodium loss from solid electrolyte interphase (SEI) formation. A stabilized and ultrathin (≈7.4 nm) SEI was constructed on the DP-HC surface, which proved to be simultaneously suitable in both ester and ether electrolytes. Compared to pure HC (60.8 %), the as-designed DP-HC exhibited a high ICE of >96.3 % in NaPF6 in diglyme (G2) electrolyte, and is capable of servicing consistently for >1600 cycles at 0.5 A g-1 . The Na3 V2 (PO4 )3 (NVP)|DP-HC full-cell with a 98.3 % exceptional ICE can be cycled stably for 450 cycles, demonstrating the tremendous practical application potential of DP-HC. This work provides a molecular design strategy to improve the ICE of HC, which will inspire more researchers to concentrate on the commercialization progress of HC.

Molecular Engineering Enabling High Initial Coulombic Efficiency and Rubost Solid Electrolyte Interphase for Hard Carbon in Sodium‐Ion Batteries

AbstractHard carbon (HC) as a potential candidate anode for sodium‐ion batteries (SIBs) suffers from unstable solid electrolyte interphase (SEI) and low initial Coulombic efficiency (ICE), which limits its commercial applications and urgently requires the emergence of a new strategy. Herein, an organic molecule with two sodium ions, disodium phthalate (DP), was successfully engineered on the HC surface (DP‐HC) to replenish the sodium loss from solid electrolyte interphase (SEI) formation. A stabilized and ultrathin (≈7.4 nm) SEI was constructed on the DP‐HC surface, which proved to be simultaneously suitable in both ester and ether electrolytes. Compared to pure HC (60.8 %), the as‐designed DP‐HC exhibited a high ICE of >96.3 % in NaPF6 in diglyme (G2) electrolyte, and is capable of servicing consistently for >1600 cycles at 0.5 A g−1. The Na3V2(PO4)3 (NVP)|DP‐HC full‐cell with a 98.3 % exceptional ICE can be cycled stably for 450 cycles, demonstrating the tremendous practical application potential of DP‐HC. This work provides a molecular design strategy to improve the ICE of HC, which will inspire more researchers to concentrate on the commercialization progress of HC.