Stable SEI Film Research Articles

Hydrothermal synthesis of SnO2/MoO3-x/rGO ternary nanocomposites as a high-performance anode for lithium ion batteries

The theoretical specific capacity of tin dioxide (SnO2) as a lithium-ion batteries (LIBs) anode material is up to 1494 mAh·g−1, far exceeding that of graphite. However, the low conductivity, volume expansion, crushing failure and particles agglomeration during charge/discharge cycles limit its application in LIBs. In this work, the SnO2/MoO3-x/rGO composite material was synthesized by one-step hydrothermal method, with SnO2 and amorphous MoO3-x tightly and uniformly anchored at the surface of reduced graphene oxide (rGO). The results of structural characterization and electrochemical performance evaluation show that amorphous MoO3-x can increase the reactive active sites, inhibit Sn particles aggregation, and promote the reversible reaction of SnO2. rGO effectively improves the electrical conductivity of the composite and buffers the volume change of Li-Sn alloying/dealloying during cycles. In addition, due to introduction of MoO3-x and rGO a stable SEI film can be formed at the material's surface to improve the cycle stability. SnO2/MoO3-x/rGO exhibits excellent rate performance and cycle performance. When the rGO content is 10.9 wt%, the reversible capacity of the composite reach 813 mAh·g−1 after 800 cycles at current density of 1.0 A·g−1, and 450.6 mAh·g−1 after 1000 cycles at current density of 5.0 A·g−1, with the capacity retention rate of 96.9%.

The nanofiber gel electrolytes with ultra-high ionic conductivity regulated by different acid radical ions for lithium batteries

A nanofiber gel electrolytes with excellent physical properties, electrochemical properties, and cycle life based on poly(vinylidene fluoride)-hexafluoropropylene copolymer modified by magnesium–aluminum bilayered nanosheets (MgAl-LDs) intercalated with different acidic roots ions is prepared by electrostatic spinning. The electrolytes exhibit the best elongation at break of 166 % and tensile strength of 6.59 MPa, and the electrochemical windows are all higher than 5 V. Meanwhile, the ionic conductivity number of nano-GPE intercalated with CO32–, ClO4−, and NO3– reach 5.55*10−3 S/cm, 5.04*10−3 S/cm, and 6.93*10−3 S/cm, respectively. The Li//Li symmetric battery can be stably cycled for more than 1000 h at 1 mA/cm2 with an overpotential of less than 50 mV. The LiFePO4// Li batteries assembled with nano-GPE modified by MgAl-LDs (s = NO3–) show better 0.1-2C multiplicity performance than CO32– and ClO4−, accompanied by an optimal discharge capacity of up to 155 mAhg−1 at 0.1C as well as a high reversible capacity of 135 mAhg−1 and a capacity retention rate of 90 % after 100 cycles at 0.5C. In addition, the results of polarization, X-ray photoelectron spectroscopy (XPS), Computed Tomography (CT), and scanning electron microscope (SEM) tests show that a stable SEI film is formed between nano-GPE and Li anode.

Cross-Linkable Binders for Si Anodes in High-Energy-Density Lithium-Ion Batteries.

Although silicon (Si) has a high theoretical capacity, the large volume expansion during lithiation has greatly hindered its application in high-energy-density lithium-ion batteries (LIBs). Among the strategies for improving the performance of Si anode, the role of binders should not be underestimated. Here, a novel strategy for designing a cross-linkable binder for Si anode has been proposed. The binder with hydroxyl and nitrile groups can be in situ covalently cross-linked through the amide group in the batteries. The cross-linked binder (c-POAH) shows high elasticity and strong adhesion to Si particles and the current collector. Si||Li half coin cells using the c-POAH binder have excellent cycle performance and the capacity retention ratio is 67.1% after 100 cycles at 0.2 C. Scanning electronic microscopy images show that the c-POAH binder can contribute to suppressing the pulverization of the Si anode. Moreover, the investigation with X-ray photoelectronic spectrum demonstrates that the decomposition of the liquid electrolyte on Si anode has been mitigated and the c-POAH binder can promote the formation of a more stable SEI film. Our strategy of endowing the binder with good elasticity through in situ cross-linking has opened up a new route for developing binders, which will definitely promote the application of Si anodes in high-energy-density LIBs.

Cross-linkable binder for composite silicon-graphite anodes in lithium-ion batteries

Silicon (Si) is a promising substitute for graphite anode due to the high theoretical specific capacity (4200 mAh g−1). However, too large volume change exists during the lithiation/delithiation process. Composite anode, prepared by mixing Si with graphite, can realize higher specific capacity than graphite and much better cycle performance than Si anode. However, the capacity decay caused by pulverization of Si particles is still a great challenge. Here, a cross-linkable binder rich in nitrile, carboxyl and hydroxyl groups is designed for composite silicon-graphite (Si-C) anode. The nitrile and hydroxyl groups can be in situ cross-linked in the batteries through Ritter reaction. The cross-linked binder has excellent resilience and good adhesion to the active materials and current collector. The cycle performance of the cell with cross-linked binder is much better than the counterpart. Scanning electron microscopy results of the cycled Si-C anode show that the cross-linked binder can suppress the volume expansion and pulverization. Moreover, the investigation with X-ray photoelectronic spectrum and density function theory calculation demonstrate that the decomposition of ester solvent and LiPF6 on Si anode has been mitigated and more stable SEI film is formed on the Si-C anode. Our strategy of in situ cross-linking binder in the batteries has provided a feasible way for designing the next generation of silicon-based anodes with higher specific capacity and longer cycling life.

A three-dimensional Ge@C anode with a hollow and micro/nano structure for high-capacity lithium-ion battery

Aiming at the key issues of low intrinsic conductivity and large volume expansion during the cycling existed in high-capacity Ge anode material system, a micro/nano structured Ge@C hybrid material was designed and prepared through a facile and controllable method. The as-prepared micron conductive cage with a dodecahedral structure is composed of interconnected ultra-thin walled Ge nanotubes encapsulated in the porous N-containing carbon network, which can not only reserve more buffer space for the volume expansion of Ge and assist in building a stable SEI film during the cycling, improves the conductivity and stability of the material, but also provide a rich and penetrating channel for the transmission of ions, realizing high dynamics. When applied to the anode of lithium-ion battery, the three-dimensional micro/nano structured germanium-based hybrid material (Ge-3D@C) delivers a high initial specific capacity of 1500 mAh g−1 at 0.2 A g−1, and after 350 cycles, it can still maintain a high reversible specific capacity of 1147 mAh g−1. Even at high current densities of 1 A g−1 and 2 A g−1, high reversible specific capacities of 752 and 631 mAh g−1 can still be obtained. Importantly, the rational design can be used to prepare Ge hybrids doped with other metals or metal oxides, as well as different structures, by adjusting the layer materials and the types of germanates, so as to adapt to different application environments.

Coral-like CoSe2@N-doped carbon with a high initial coulombic efficiency as advanced anode materials for Na-ion batteries.

Na-ion batteries (NIBs) have attracted great interest as a possible technology for grid-scale energy storage for the past few years owing to the wide distribution, low cost and environmental friendliness of sodium resources and similar chemical mechanisms to those of established Li-ion batteries (LIBs). Nonetheless, the implementation of NIBs is seriously hindered because of their low rate capability and cycling stability. This is mainly because the large ionic size of Na+ can reduce the structural stability and cause sluggish reaction kinetics of electrode materials. Herein, three-dimensional nanoarchitectured coral-like CoSe2@N-doped carbon (CL-CoSe2@NC) was synthesized through solvothermal and selenizing techniques. As a result, CL-CoSe2@NC for NIBs at 2 A g-1 exhibits an ultrahigh specific capacity of 345.4 mA h g-1 after 2800 cycles and a superhigh initial coulombic efficiency (ICE) of 93.1%. Ex situ XRD, HRTEM, SAED and XPS were executed to study the crystal structure evolution between Na and CoSe2 during sodiation/de-sodiation processes. The aforementioned results indicate that the improved sodium storage property of CL-CoSe2@NC could be attributed to better electrode kinetics and a stable SEI film because of the 3D nanoarchitecture and the existence of the NC layer.

Solvation structure fine-tuning enables high stability sodium metal batteries

2-Propyn-1-ol methanesulfonate (PMS) preferentially undergoes reduction decomposition on sodium metal anodes and actively induces FEC solvation behavior, thereby forming a stable SEI film enriched with sulfide compounds and NaF.

Insight into the probability of ethoxy(pentafluoro)cyclotriphosphazene (PFPN) as the functional electrolyte additive in lithium-sulfur batteries.

Enhancing the flame retardancy of electrolytes and the stability of lithium anodes is of great significance to improve the safety performance of lithium-sulfur (Li-S) batteries. It is well known that the most commonly used ether based electrolyte solvents in Li-S batteries have a lower flash point and higher volatility than the ester electrolyte solvents in Li-ion batteries. Hence, lithium-sulfur batteries have greater safety risks than lithium-ion batteries. Herein, ethoxy(pentafluoro)cyclotriphosphazene (PFPN), which is commonly used as a flame retardant for ester electrolytes in lithium-ion batteries, is utilized as both a film-forming electrolyte additive and a flame retardant additive for the ether electrolyte to investigated its applicability in Li-S batteries. It is found that the ether electrolyte containing PFPN not only has good flame retardant properties and a wide potential window of about 5 V, but also can form a stable SEI film on the surface of a lithium anode. As a result, with the ether-based electrolyte containing 10 wt% PFPN, Li-Cu and Li-S batteries all delivered a stable cycling performance with a high coulombic Efficiency and a long-lifespan performance, which were all superior to the batteries using the ether-based electrolyte without PFPN. This study demonstrates an effective solution to solve the problems of flammable ether-based electrolytes and reactive lithium anodes, and it may contribute to the development of safe Li-S batteries.

Mitigating the volume expansion and enhancing the cycling stability of ferrous fluorosilicate-modified silicon-based composite anodes for lithium-ion batteries

This study introduces an FeSiF6 additive synthesized via the reaction of HF with Si–Fe alloys. It prevents crystalline Li15Si4 formation and promotes stable SEI film, significantly enhancing the cycling stability of silicon-based anodes.

In-situ construction of cellulose acetate propionate-based hybrid gel polymer electrolyte for high-performance lithium metal batteries

Quasi-solid-state gel polymer electrolytes (GPEs) have a great deal of promise for usage in future energy systems due to their high safety. However, ex-situ prepared GPEs still suffer from interfacial incompatibility. Herein, to create stable electrolyte-electrode interfaces and ensure adequate contact, a novel GPE was prepared by in-situ polymerization using pentaerythritol tetraacrylate (PETEA) and cellulose acetate propionate (CAP) as raw materials. PETEA and CAP with a certain mass ratio were added into liquid electrolyte, and the in-situ polymerization of PETEA and CAP was initiated by azobisisobutyronitrile (AIBN). The multi-side chain structure of PETEA and the hydrogen bonding interaction between PETEA and CAP contributed to a robust cross-linked framework, while CAP improved Li+ transport through its polar oxygen-containing groups. The obtained GPE 1:1 exhibited high ionic conductivity (1.03 ×10−3 S/cm at 25 ℃), superior Li+ transference number (0.73), and good stability to Li metal. Meanwhile, a stable SEI film with rich LiF was established, ensuring a long-term cycling lifespan. After 500 cycles at 1 C, the assembled LiFePO4/GPE 1:1/Li cell revealed a high capacity retention of 90.6%. These results provide a guideline for the future design of novel cellulose-based GPEs for high performance lithium metal batteries.

Regulating anion chemistry with F-containing bonds enable superior potassium ions storage in hard carbon

The high reactivity of potassium metal and the large potassium ion radius lead to increased side reactions and poor stability at the electrode/electrolyte interface. Constructing a stable electrode/electrolyte interface is essential to develop high-performance potassium ion storage devices. Herein, we propose an anion chemistry strategy to enhance interfacial stability by modulating the F-containing bonds in electrolyte potassium salts. Compared to C-F and P-F bonds, the experimental results, together with theoretical calculations, revealed that the S-F bonds are more likely to break to facilitate the formation of dense, robust, stable and KF-rich SEI films with high ionic conductivity. Meanwhile, the electrochemical impedance spectroscopy reveals the unique role of S-F-containing potassium bis(fluorosulfonyl)imide (K((FSO2)2N), KFSI) electrolytes in stabilizing potassium metal, which inhibits electrolyte decomposition and potassium dendrite formation. The synergistic stabilization of electrode and potassium metal by KFSI electrolyte effectively boosts the Coulomb efficiency, rate capability (4.7 and 1.8 times higher than those obtained with P-F and C-F-containing electrolytes) and cycling performance (capacity retentions of 80.4%, 1.4% and 47.7% for S-F, P-F and C-F-containing electrolytes after 1000 cycles at 1 A g−1, respectively) of hard carbon anode. This work reveals the importance of anion chemistry in regulating interfacial properties and provides a valuable insight into the rational design of interfacial chemistry.

Double-Layer Electrolyte Boosts Cycling Stability of All-Solid-State Li Metal Batteries.

All-solid-state lithium metal batteries (ASSLMBs), as a candidate for advanced energy storage devices, invite an abundance of interest due to the merits of high specific energy density and eminent safety. Nevertheless, issues of overwhelming lithium dendrite growth and poor interfacial contact still limit the practical application of ASSLMBs. Herein, we designed and fabricated a double-layer composite solid electrolyte (CSE), namely, PVDF-LiTFSI-Li1.3Al0.3Ti1.7(PO4)3/PVDF-LiTFSI-h-BN (denoted as PLLB), for ASSLMBs. The reduction-tolerant PVDF-LiTFSI-h-BN (denoted as PLB) layer of the CSE tightly contacts with the Li metal anode to avoid the reduction of LATP by the electrode and participates in the formation of a stable SEI film using Li3N. Meanwhile, the oxidation-resistance and ion-conductive PVDF-LiTFSI- LATP (denoted as PLA) layer facing the cathode can reduce the interfacial impedance by facilitating ionic migration. With the synergistic effect of PLA and PLB, the Li/Li symmetric cells with sandwich-type electrolytes (PLB/PLA/PLB) can operate for 1500 h with ultralong cycling stability at 0.1 mA cm-2. Additionally, the LiFePO4/Li cell with PLLB maintains satisfactory capacity retention of 88.2% after 250 cycles. This novel double-layer electrolyte offers an effective approach to achieving fully commercialized ASSLMBs.

The effect of AlF3 as an electrolyte additive on Li anode in Li-O2 batteries

Li metal is considered as an ideal anode for Li-O2 batteries because of its unbeatably theoretical specific capacity and low electrode potential. Unfortunately, the growth of Li dendritic and the sensitivity to electrolyte and O2 hinder the practical applications of Li anode. Herein, AlF3 as an electrolyte additive is firstly employed in a Li-O2 battery, which can boost the formation of LiF@Al-Li@Al2O3-rich SEI film via in-situ spontaneous reactions of AlF3 with Li anode in O2 atmosphere. The generated SEI film contributes to inducing the homogeneous nucleation of Li and reducing the disgusting side reactions, which can suppress the growth of Li dendrite and improve the cyclability of Li anode. Benefiting from the rational design, both the Li-O2 and the Li|Li symmetric batteries with AlF3 electrolyte exhibit low overpotential and good cycling stability. We hope this work could provide a facile way to in-situ construct a stable SEI film to alleviate the uneven Li nucleation for Li-O2 batteries.

Ultrathin CuF2‐Rich Solid‐Electrolyte Interphase Induced by Cation‐Tailored Double Electrical Layer toward Durable Sodium Storage

AbstractSolid‐electrolyte interphase (SEI) seriously affects battery's cycling life, especially for high‐capacity anode due to excessive electrolyte decomposition from particle fracture. Herein, we report an ultrathin SEI (3–4 nm) induced by Cu+‐tailored double electrical layer (EDL) to suppress electrolyte consumption and enhance cycling stability of CuS anode in sodium‐ion batteries. Unique EDL with SO3CF3‐Cu complex absorbing on CuS in NaSO3CF3/diglyme electrolyte is demonstrated by in situ surface‐enhanced Raman, Cyro‐TEM and theoretical calculation, in which SO3CF3‐Cu could be reduced to CuF2‐rich SEI. Dispersed CuF2 and F‐containing compound can provide good interfacial contact for formation of ultrathin and stable SEI film to minimize electrolyte consumption and reduce activation energy of Na+ transport. As a result, the modified CuS delivers high capacity of 402.8 mAh g−1 after 7000 cycles without capacity decay. The insights of SEI construction pave a way for high‐stability electrode.

Room temperature solid-state deformation induced high-density lithium grain boundaries to enhance the cycling stability of lithium metal batteries.

Due to its high theoretical capacity and low anode potential advantages, lithium is becoming the ideal high-capacity anode of next generation batteries. Nevertheless, the satisfactory long-term cyclability of lithium metal batteries is still not achieved. Inspired by the intrinsic soft nature of the lithium metal, we have developed a simple room temperature solid-state deformation route to overcome the lithium dendrite issue, and the cycle life of the deformation treated lithium anode is 5 times that of the untreated lithium anode. It is demonstrated that microscale lithium grains are divided into nanoscale lithium grains by directional friction forces of solid-state deformation. The lithium grain boundaries are lithiophilic active sites towards Li ions, which regulate homogeneous deposition of Li ions to form a thin and stable SEI film, eventually overcoming the lithium dendrite issue and enhancing the cyclability of lithium batteries. Overcoming the challenges in conventional tedious chemical routes to grow high-density grain boundary active sites for catalysis, the room temperature solid-state deformation route will pave a new road to grow high-density grain boundaries for fuel cells and metal-based batteries.

A yolk-shell eGaSn@Void@SiO2 nanodroplet design for high-performance cathodes in room temperature liquid metal batteries

Gallium-based liquid alloys that exhibit high capacity and self-healing properties have been demonstrated to be promising cathodes for room temperature liquid metal batteries (RTLMBs). However, the electrochemical performances of these alloys are poor due to severe volume expansion and an unstable solid electrolyte interface layer during the lithiation process. Here, a sol-gel strategy was performed to construct yolk-shell structure nanodroplets (eGaSn@Void@SiO2) that contain sufficient void space by amorphous silicon oxide, which generated a liquid metal electrode with a high performance. The amorphous SiO2 shells not only play an important role in building stable SEI films, providing efficient electron/ion conduction channels and preventing agglomeration of active substances, but exhibit good elastic behavior during charging/discharging. Due to the appropriate voids in the yolk-shell structure, the eGaSn nanodroplets can expand freely without breaking or disrupting the electrode structure; thus, the resulting eGaSn@Void@SiO2 NDs exhibited high capacities of 538, 454, and 338 mA h g−1 at current rates of 0.2, 1 and 5 C, respectively. No obvious decay was observed with more than 500 cycles and a capacity of 377 mA h g−1 at 2 C. Interestingly, the density functional theory (DFT) calculations revealed that the effective chemisorption between the discharge products and SiO2 provides sufficient electrical contact sites with a significant drop in electrochemical impedance during cycling. The causes of the superior electrodes performance were investigated in depth using in situ X-ray diffraction and theoretical calculations. Our rational design may shed unprecedented light on the development of liquid alloy-based cathodes for high-performance RTLMBs.

Electrolyte manipulation enhanced pseudo-capacitive K-storage for TiO2 anode

Titanium dioxide (TiO2) has been developed as a popular anode candidate beyond carbonaceous materials for potassium-ion batteries (PIBs). However, the serious lack of understanding of the electrolyte chemistry as well as the interfacial electrochemistry over TiO2-based materials during the K-storage process significantly limited their rational design as well K-storage applications. Herein, the K-storage performance of MOF-derived TiO2@C anode materials via optimizing structure and manipulating electrolyte chemistry was systematically investigated. A significantly improved K-storage performance was achieved in the optimized 4.0 M KFSI/EC+DEC electrolyte attributed to the formation of stable and thin SEI film induced by the unique solvation structures of the high concentrated electrolyte, which remarkably enhanced the K-storage kinetics via strengthening the pseudo-capacitive mechanism. These discoveries provide new insight into the electrolyte design principles for TiO2-based anode materials and will promote the development of advanced K-storage system for next-generation energy storage applications.

Homogeneously distributed heterostructured interfaces in rice panicle-like SbBi-Bi2Se3-Sb2Se3 nanowalls for robust sodium storage

Antimony-based materials offer great potential for sodium-ion battery application owing to their high capacity and suitable Na alloying potential. However, their practical application is hampered by the rapid capacity decay resulting from serious volume change during cycling. Herein, we report a template-free electrodeposition method to grow SbBi-Bi2Se3-Sb2Se3 (SbBi-Se) self-supported nanowall array with a rice-panicle-like top surface directly on Cu substrates. During the electrodeposition, Bi, Sb, and Se have been simultaneously incorporated into the nanowalls, giving rise to an array structure with uniformly dispersed phases of SbBi alloy, and metal selenides Bi2Se3 and Sb2Se3. As a result, the heterostructured interfaces amongst these phases are also homogeneously distributed throughout the entire structure. The density functional theory calculation results indicate that these interfaces facilitate Na+ diffusion and promote electronic conduction, and the sample also demonstrates enhanced high-rate performance and superior cyclic retention with almost no capacity decay after 100 cycles at 0.7 A/g. More importantly, in-situ temperature sensing suggests that such a unique heterostructured material exhibits high thermal stability during charge/discharge, while ex-situ analysis confirms that this electrode material induces the formation of a highly stable SEI film, and verifies the high durability of these alloy and selenide phases allowing the interfaces to keep functioning during charge/discharge process.

Artificial SEI Film via Synchronous Reaction‐Diffusion‐Assembly on Li Liquid Metal

AbstractSolid electrolyte interphase (SEI) is considered as an effective way to suppress Li dendrite. However, most of the constructed SEI films are usually nonuniform and incompact due to the uncertain interface between Li and electrolyte, finally resulting in failure to Li anode protection. To overcome such disadvantage, a stable pristine SEI film is formed successfully by self‐diffusion and assembly when the surface reaction occur between the molten Li and the substrate, benefitting from the ultra‐high chemical activity, atomic level smoothness, and flowability of liquid lithium. It is an inside–outside process via the obtained Li composites migrating from reaction interface to the Li liquid metal surface. Then, the obtained SEI can lead to a stable and long‐lifespan Li integrated electrode, showing the self‐diffusion/assembly strategy upon liquid Li‐metal is a promising way for practical dendrite‐free anode.

Ultrathin 2D hexagon CoP/N-doped carbon nanosheets for robust sodium storage

Due to the natural abundance and potential price advantage, sodium-ion batteries (SIBs) have attracted increasing attention as promising alternatives to lithium-ion batteries (LIBs). However, the development of SIBs is severely hampered due to the poor cycling stability and low rate capability resulting from the larger ionic size of Na+ than that of Li+. Herein, 2D hexagon CoP/N-doped carbon (H-CoP@NC) nanosheets have been prepared via solvothermal method combined with the upper gas phase phosphating. Benefiting from the synergistic effect of N-doped carbon layer and ultrathin 2D hexagonal nanosheet structure, the H-CoP@NC as anode materials exhibit superior electrochemical performances in terms of rate capability and cyclic stability, delivering specific capacity of 209.9 mAhg−1 at 2 Ag−1 after 1100 cycles for SIBs, and high Coulombic effciency of approximately 100% over 1100 cycles. Ex-situ XRD were performed to research the structural evolution between Na and CoP during cycling processes. Analysis from the Ex-situ XPS and work function indicates that the enhanced electrochemical property H-CoP@NC might be attributed to the stable SEI film, lower charge-transfer resistance and better electrode kinetics as a result of thinner nanosheet and the presence of carbon layer.