Solid Electrolyte Interface Layer Research Articles

Formation of Solid–Electrolyte Interfaces in Aqueous Electrolytes by Altering Cation‐Solvation Shell Structure

AbstractAqueous lithium/sodium‐ion batteries (AIBs) have received increasing attention because of their intrinsic safety. However, the narrow electrochemical stability window (1.23 V) of the aqueous electrolyte significantly hinders the development of AIBs, especially the choice of electrode materials. Here, an aqueous electrolyte composed of LiClO4, urea, and H2O, which allows the electrochemical stability window to be expanded to 3.0 V, is developed. Novel [Li (H2O)x(organic)y]+ primary solvation sheath structures are developed in this aqueous electrolyte, which contribute to the formation of solid–electrolyte interface layers on the surfaces of both the cathode and anode. The expanded electrochemical stability window enables the construction of full aqueous Li‐ion batteries with LiMn2O4 cathodes and Mo6S8 anodes, demonstrating an operating voltage of 2.1 V and stability over 2000 cycles. Furthermore, a symmetric aqueous Na‐ion battery using Na3V2(PO4)3 as both the cathode and anode exhibits operating voltage of 1.7 V and stability over 1000 cycles at a rate of 5 C.

A bilayer interface formed in high concentration electrolyte with SbF3 additive for long-cycle and high-rate sodium metal battery

The applications of sodium metal batteries are limited due to the strong reducing property of sodium, and its electrolyte design is quite challenging because of the decomposition of the solvents. In this paper, a small amount of SbF3 as an electrolyte additive is combined with high concentration electrolyte of 4 mol L−1 sodium bis(fluorosulfonyl) imide (NaFSI) in 1,2-dimethoxyethane (DME) for building a bilayer solid electrolyte interface (SEI) for long-cycle and high-rate sodium metal batteries. The SbF3 additive leads to an adamant Na-Sb alloy layer, and the 4 mol L−1 NaFSI/DME electrolyte contributes to a compact NaF-rich SEI layer on the sodium metal surface. The bilayer structure realizes the fast ion transport of sodium ions and effective suppression on the growth of sodium dendrites. The increased solvent coordination and the bilayer interface on sodium metal result in enhanced stable cycling of a Na||Na symmetric battery about 1000 h at 0.5 mA cm−2. Moreover, the Na|| Na3V2(PO4)3 battery delivers stable cycling at 2 C nearly 1400 cycles (82.6% capacity retention), and it also exhibits superior rate capability of 80 mAh g−1 at 40 C. These results demonstrate that the new electrolyte holds large potential for sodium metal battery applications.

Nano-ordered structure regulation in delithiated Si anode triggered by homogeneous and stable Li-ion diffusion at the interface

Abstract The huge volume change of silicon anode during cycling results in unstable solid electrolyte interface (SEI), causing rapid performance degradation. Natural SEI layer has a heterogeneous structure, results in the inhomogeneous Li+ diffusion. The repeated destruction and regeneration of SEI aggravate the inhomogeneity of Li+ diffusion at the interface, leading to non-uniform alloy reaction in the Si bulk. In this work, the silicon surface is passivated by an ultrathin uniform chitosan layer with abundant lithiophilic groups. The capacity of chitosan-coated Si (Si@CS) could reach 1500 mAh g−1 at a current density of 1 A g−1, and the capacity retention remains 91% after 400 cycles. It is demonstrated that the oxygen and nitrogen atoms in chitosan are coordinated with Li+, providing uniformly distributed Li+ transfer sites, results in a homogeneous Li+ flux in the surface layer. Interestingly, a nano-scale ordered atomic arrangement is observed in the delithiated Si@CS, which contributes to more stable and reversible lithiation/delithiation reaction of the Si@CS electrode. It is proposed that optimizing the reaction interface on the Si surface is able to alter the Li-ion diffusion kinetics and structure transition behavior of silicon, which can improve the structure reversibility and stability during cycling.

Thin solid electrolyte interface on chemically bonded Sb2Te3/CNT composite anodes for high performance sodium ion full cells

Nanostructured metal chalcogenides (MCs) and their composites are studied for high performance sodium-ion batteries (SIBs). Herein, we report the assembly of an emerging MC, Sb2Te3, with functionalized carbon nanotubes (CNTs) to form composite anodes. The role of oxygenated functional groups on CNTs in fostering the chemical interactions with Sb2Te3 for enhanced structural integrity of electrodes is elucidated by density functional theory combined with ab-initio molecular dynamics simulations and X-ray photoelectron spectroscopy analysis. Remarkably, cryogenic transmission electron microscopy (TEM) analysis reveals a uniform and thin solid electrolyte interface (SEI) layer of ~19.1 nm on the Sb2Te3/CNT composite while the neat Sb2Te3 presents an irregular and ~67.3 nm thick SEI. The ex-situ X-ray diffraction (XRD) and ex-situ/in-situ TEM analyses offer mechanistic explanations of phase transition and volume changes during sodiation. The Sb2Te3/CNT composite electrode with an optimal content of 10 wt% CNTs delivers excellent reversible gravimetric and volumetric capacities of 422 mA h g−1 and 1232 mA h cm−3, respectively, at 100 mA g−1 with ~97.5% capacity retention after 300 cycles. The excellent high-rate capability of 318 mA h g−1 at 6400 mA g−1 corroborates the structural robustness of the composite electrode. Sodium-ion full cells (SIFCs) are assembled by pairing the above anode with a Na3V2(PO4)2F3 cathode, which exhibit remarkable energy density of ~229 Wh kg−1 at 0.5 C and excellent cyclic stability of over 71% and 66% capacity retention at 5 C and 10 C, respectively, after 200 cycles. Even at 40 C, an ultrahigh power density of 5384 W kg−1 is delivered. Furthermore, the pouch-type SIFCs prove excellent flexibility with ~85% capacity retention after 1000 bending cycles and satisfactory operation under temperatures ranging from 40 to −20 °C. The design strategy developed here can also be employed to other electrode materials to achieve better SEI stability and excellent Na storage performance.

A Combined Theory‐Experiment Analysis of the Surface Species in Lithium‐Mediated NH3 Electrosynthesis

AbstractElectrochemical processes for ammonia synthesis could potentially replace the high temperature and pressure conditions of the Haber‐Bosch process, with voltage offering a pathway to distributed fertilizer production that leverages the rapidly decreasing cost of renewable electricity. However, nitrogen is an unreactive molecule and the hydrogen evolution reaction presents a major selectivity challenge. An electrode of electrodeposited lithium in tetrahydrofuran solvent overcomes both problems by providing a surface that easily reacts with nitrogen and by limiting the access of protons with a nonaqueous electrolyte. Under these conditions, we measure relatively high faradaic efficiencies (ca. 10 %) and rates (0.1 mA cm−2) toward NH3. We observe the development of a solid electrolyte interface layer as well as the accumulation of lithium and lithium‐containing species. Detailed DFT studies suggest lithium nitride and hydride to be catalytically active phases given their thermodynamic and kinetic stability relative to metallic lithium under reaction conditions and the fast diffusion of nitrogen in lithium.

Cascading use of barley husk ash to produce silicon for composite anodes of Li-ion batteries

Silicon is a promising alternative anode material for LIBs because it has ten times higher capacity than the currently used graphite giving the possibility to even double to capacity of the total battery cell. The high specific capacity is essential in the electric vehicles and portable electronic devices. However, silicon anodes are unstable during the charge/discharge cycles due to the large volume change of silicon leading to cracking of the silicon particles, which results in poor conductivity between the particles and unstable solid electrolyte interface layer. Mesoporous silicon structures can solve the stability issue and provide stable high capacity anodes for LIBs. In the present study, porous silicon anode material was prepared from barley husk ash, an agricultural residue. The production of the silicon material was carried out through a simple magnesiothermic reduction process, which is a cost-effective method compared with the conventional production method. To improve the performance of the biogenic silicon as anode material, carbon nanotubes were conjugated on the particles to connect the particles to each other. The developed porous silicon composite delivered the average discharge capacity of 2049 mAh g−1 and 472 mAh g−1 at the rate of 0.1 C and 1 C, respectively.

Chemically Prelithiated Hard-Carbon Anode for High Power and High Capacity Li-Ion Batteries.

Hard carbons (HC) have potential high capacities and power capability, prospectively serving as an alternative anode material for Li-ion batteries (LIB). However, their low initial coulombic efficiency (ICE) and the resulting poor cyclability hinder their practical applications. Herein, a facile and effective approach is developed to prelithiate hard carbons by a spontaneous chemical reaction with lithium naphthalenide (Li-Naph). Due to the mild reactivity and strong lithiation ability of Li-Naph, HC anode can be prelithiated rapidly in a few minutes and controllably to a desirable level by tuning the reaction time. The as-formed prelithiated hard carbon (pHC) has a thinner, denser, and more robust solid electrolyte interface layer consisting of uniformly distributed LiF, thus demonstrating a very high ICE, high power, and stable cyclability. When paired with the current commercial LiCoO2 and LiFePO4 cathodes, the assembled pHC/LiCoO2 and pHC/LiFePO4 full cells exhibit a high ICE of >95.0% and a nearly 100% utilization of electrode-active materials, confirming a practical application of pHC for a new generation of high capacity and high power LIBs.

Electrode/Electrolyte Interface Study of LiCoO2/Graphite Cell Using Carbonate-Free Electrolytes Based on Lithium Bis(fluorosulfonyl)imide and Sulfolane

LiCoO2/graphite full-cells with a carbonate-free electrolyte based on lithium bis(fluorosulfonyl)imide and sulfolane (LiFSI/SL) show excellent cycle stability at high temperatures. In this study, we used X-ray photoelectron spectroscopy to investigate the composition of the solid electrolyte interface (SEI) layer on the surface of the positive and negative electrodes of a cell containing LiFSI/SL cycled at high temperature. Inorganic species, such as LiF and sulfonyl compounds, were observed in the SEI on the surface of both the positive and negative electrodes of cells with LiFSI/SL. The SEI derived from LiFSI on the positive electrode suppressed not only oxidative electrolyte decomposition but also crystal structure change of LiCoO2. Moreover, the SEI on the negative electrode controlled severe reductive decomposition of the electrolytes.

Revealing Principles for Design of Lean-Electrolyte Lithium Metal Anode via In Situ Spectroscopy

Lean electrolyte conditions are highly pursued for the practical lithium (Li) metal batteries. The previous studies on the Li metal anodes, in general, exhibited good stability with a large excess of electrolyte. However, the targeted design of Li hosts under relatively low electrolyte conditions has been rarely studied so far. Herein, we have shown that the electrolyte con-sumption severely affects the cycling stability of Li metal anode. Considering carbon hosts as typical examples, we innova-tively employed the in-situ synchrotron X-ray diffraction, in-situ Raman spectroscopy and theoretical computations to ob-tain better understanding of the Li nucleation/deposition processes. Besides, we showed the usefulness of in-situ electro-chemical impedance spectra to analyze interfacial fluctuation at the Li/electrolyte interface, and together with the nuclear magnetic resonance data to quantify electrolyte consumption. We have found that uneven Li nucleation/deposition and the crack of surface-area-derived solid-electrolyte-interface (SEI) layer both leads to a great consumption of electrolyte. Then, we suggested a design principle for Li host to overcome the electrolyte loss, that is, uneven growth of Li structure and the crack of SEI layer must be simultaneously controlled. As a proof of concept, we demonstrated the usefulness of a 3D low-surface-area defective graphene host (L-DG) to control Li nucleation/deposition and stabilize SEI layer, contributing to a highly reversible Li plating/stripping. As a result, such a Li host can achieve stable cycles (e.g., 1.0 mAh cm-2) with a low elec-trolyte loading (10 μL). This work demonstrates the necessity to design Li metal anodes under lean electrolyte conditions and brings the Li metal batteries a step closer to their practical applications.

Electrolyte solvation structure manipulation enables safe and stable aqueous sodium ion batteries

A multi-component aqueous electrolyte with a composite solvent sheath can widen the voltage window to 2.8 V and inhibit side reactions. A solid electrolyte interface layer containing Na2CO3 and organic compounds suppresses the reaction of water with the discharged anode.

The rational design of carbon coated Fe2(MoO4)3 nanosheets for lithium-ion storage with high initial coulombic efficiency and long cycle life.

Binary metal oxides are potential anode materials for lithium-ion storage due to their high theoretical specific capacities. However, the practical applications of metal oxides are limited due to their large volume changes and sluggish reaction kinetics. Herein, carbon coated Fe2(MoO4)3 nanosheets are prepared via a simple method, adopting urea as the template and carbon source. The carbon coating on the surface helps to elevate the conductivity of the active material and maintain structural integrity during the lithium storage process. Combining this with a catalytic effect from the generated Fe, leading to the reversible formation of a solid electrolyte interface layer, a high initial coulombic efficiency (>87%) can be obtained. Based on this, the carbon coated Fe2(MoO4)3 nanosheets show excellent rate capability (a reversible discharge capacity of 983 mA h g−1 at 5 A g−1) and stable cycling performance (1376 mA h g−1 after 250 cycles at 0.5 A g−1 and 864 mA h g−1 after 500 cycles at 2 A g−1). This simple in situ carbonization and template method using urea provides a facile way to optimize electrode materials for next-generation energy storage devices.

Design of a LiF-rich solid electrolyte interface layer through salt-additive chemistry for boosting fast-charging phosphorus-based lithium ion battery performance.

A robust and conductive LiF-rich solid electrolyte interface layer was generated at the phosphorus surface through salt-additive chemistry, and it then served as a high-performance fast-charging lithium ion battery anode, delivering a high reversible capacity of 450 mA h g-1 after 450 cycles with a high charging current density of 8 A g-1 (about 3 min).

Porosity‐ and Graphitization‐Controlled Fabrication of Nanoporous Silicon@Carbon for Lithium Storage and Its Conjugation with MXene for Lithium‐Metal Anode

AbstractSilicon (Si) and lithium metal are the most favorable anodes for high‐energy‐density lithium‐based batteries. However, large volume expansion and low electrical conductivity restrict commercialization of Si anodes, while dendrite formation prohibits the applications of lithium‐metal anodes. Here, uniform nanoporous Si@carbon (NPSi@C) from commercial alloy and CO2 is fabricated and tested as a stable anode for lithium‐ion batteries (LIBs). The porosity of Si as well as graphitization degree and thickness of the carbon layer can be controlled by adjusting reaction conditions. The rationally designed porosity and carbon layer of NPSi@C can improve electronic conductivity and buffer volume change of Si without destroying the carbon layer or disrupting the solid electrolyte interface layer. The optimized NPSi@C anode shows a stable cyclability with 0.00685% capacity decay per cycle at 5 A g−1 over 2000 cycles for LIBs. The energy storage mechanism is explored by quantitative kinetics analysis and proven to be a capacitance‐battery dual model. Moreover, a novel 2D/3D structure is designed by combining MXene and NPSi@C. As lithiophilic nucleation seeds, NPSi@C can induce uniform Li deposition with buffered volume expansion, which is proven by exploring Li‐metal deposition morphology on Cu foil and MXene@NPSi@C. The practical potential application of NPSi@C and MXene@NPSi@C is evaluated by full cell tests with a Li(Ni0.8Co0.1Mn0.1)O2 cathode.

Constructing a liquid-metal based self-healing artificial solid electrolyte interface layer for Li metal anode protection in lithium metal battery

Uncontrollable Li dendrite growth and unstable SEI during repetitive Li deposition–dissolution processes severely impede the practical application of lithium metal batteries (LMBs). Herein, we create a novel artificial SEI layer by using liquid metal with self-healing property. The liquid metal could effectively facilitate the stable SEI layer formation by virtue of its self-healing property and regulate Li ion flus and inhibit the Li dendrite growth in the deposition process of Li. Electrochemical studies show that the LMNP-Li|LTO full-cell exhibits a superb rate capability and an excellent long-term cycling stability. This work offers a novel approach to achieve a stable Li metal anode with long cycle life.

A bio-inspired nanofibrous Co3O4/TiO2/carbon composite as high-performance anodic material for lithium-ion batteries

A bio-inspired nanofibrous Co3O4/TiO2/carbon composite was fabricated using natural cellulose substrate (laboratory filter paper) as both the carbon source and the structural scaffold. Employing a surface sol–gel process to form a thin TiO2 gel layer coating on each cellulose nanofiber of the filter paper, the resulted composite sheet was successively carbonized in inert atmosphere to give a nanofibrous TiO2/carbon composite; afterwards, nano-sized Co3O4 particles (10–30 nm) were uniformly deposited onto the yielded composite fibers via a simple hydrothermal method, resulting in the Co3O4/TiO2/carbon hybrid. The ternary composite possessed a unique hierarchically three-dimensional porous structure which inherited precisely from the initial filter paper. This special structure with the internal conductive carbon fiber and the external nano-sized Co3O4 particles offered the nanocomposite with an excellent electrochemical performance as anodic material for lithium-ion batteries. The optimal sample with a Co3O4 mass content of 50.6% delivered an initial discharge capacity of 1239 mAh g−1 at a current density of 100 mA g−1, which was far exceeded the theoretical capacity of Co3O4. The extra capacity is ascribed to the additional lithium storage sites provided by the large specific surface area of the composite, and the formation of the solid electrolyte interface (SEI) layer in the initial discharge process causing a large consumption of Li+ which results in some irreversible capacity. And after 200 discharge/charge cycles, a high reversible capacity of 764 mAh g−1 was maintained, which is higher than most of the Co3O4/carbon hybrid materials reported. This work provided a simple and efficient strategy for designing and preparing nanoscale metal-oxide/carbon composite material with considerable potential in energy storage and conversion.

Self‐Stabilized and Strongly Adhesive Supramolecular Polymer Protective Layer Enables Ultrahigh‐Rate and Large‐Capacity Lithium‐Metal Anode

AbstractConstructing a solid electrolyte interface (SEI) is a highly effective approach to overcome the poor reversibility of lithium (Li) metal anodes. Herein, an adhesive and self‐healable supramolecular copolymer, comprising of pendant poly(ethylene oxide) (PEO) segments and ureido‐pyrimidinone (UPy) quadruple‐hydrogen‐bonding moieties, is developed as a protection layer of Li anode by a simple drop‐coating. The protection performance of in‐situ‐formed LiPEO–UPy SEI layer is significantly enhanced owing to the strong binding and improved stability arising from a spontaneous reaction between UPy groups and Li metal. An ultrathin (approximately 70 nm) LiPEO–UPy layer can contribute to stable and dendrite‐free cycling at a high areal capacity of 10 mAh cm−2 at 5 mA cm−2 for 1000 h. This coating together with the promising electrochemical performance offers a new strategy for the development of dendrite‐free metal anodes.

Self-Stabilized and Strongly Adhesive Supramolecular Polymer Protective Layer Enables Ultrahigh-Rate and Large-Capacity Lithium-Metal Anode.

Constructing a solid electrolyte interface (SEI) is a highly effective approach to overcome the poor reversibility of lithium (Li) metal anodes. Herein, an adhesive and self-healable supramolecular copolymer, comprising of pendant poly(ethylene oxide) (PEO) segments and ureido-pyrimidinone (UPy) quadruple-hydrogen-bonding moieties, is developed as a protection layer of Li anode by a simple drop-coating. The protection performance of in-situ-formed LiPEO-UPy SEI layer is significantly enhanced owing to the strong binding and improved stability arising from a spontaneous reaction between UPy groups and Li metal. An ultrathin (approximately 70 nm) LiPEO-UPy layer can contribute to stable and dendrite-free cycling at a high areal capacity of 10 mAh cm-2 at 5 mA cm-2 for 1000 h. This coating together with the promising electrochemical performance offers a new strategy for the development of dendrite-free metal anodes.

Co-guiding the dendrite-free plating of lithium on lithiophilic ZnO and fluoride modified 3D porous copper for stable Li metal anode

Lithium metal battery is considered to be the most promising energy storage technologies due to its ultra-high theoretical capacity and extremely low standard potential. However, the infinite volume change during uneven deposition/dissolution process and the growth of lithium dendrite resulting in severe capacity decay and high safety hazards, which hinders the application in next generation secondary batteries. In this paper, the three dimensional (3D) porous copper is prepared through an electrochemical etching CuZn alloy, and the pore walls are modified with lithiophilic layer of ZnO and fluorine. The as-prepared 3D Cu/ZnO/F can inhibit the growth of Li dendrite and mitigate the huge volume change of Li metal anode during cycling process, resulting in stable solid electrolyte interface (SEI) layer and electrode structure. The Li|3D Cu/ZnO/F cell can be stably cycled over 300 cycles with 98% of coulomb efficiency at 0.5 mA cm−2, 1 mAh cm−2. The synergistic effects of both ZnO and fluorine on inducing the uniform deposition of lithium by providing bonding sites can inhibit the generation of lithium dendrites and thus improve the electrochemical performance of lithium metal batteries.

Towards a stable Li–CO2 battery: The effects of CO2 to the Li metal anode

Rechargeable Li–CO2 batteries are very attractive energy storage devices because of their high theoretical energy density and unique CO2 capture capability. Unfortunately, Li metal anode is unstable to the widely used ethers-based electrolytes, and the related Coulombic efficiency is low. Here, in the ethers-based electrolyte, the effects of CO2 to the Li metal anode was studied. Using a porous electrode, the reduced CO2 will be replenished from outside upon cycling. We found that, sufficient CO2 contributed to the formation of stable solid electrolyte interface (SEI) layers and protected the Li metal anode from rapid consumption. Under a current density of 1.0 ​mA ​cm−2, the Coulombic efficiency of Li metal reached 99.0% after 200 cycles. Our work helps the researchers better understand the effects of CO2 crossover on anode and also provides a promising method to develop a stable Li metal anode for Li–CO2 battery.

Hollow Boron-Doped Si/SiOx Nanospheres Embedded in the Vanadium Nitride/Nanopore-Assisted Carbon Conductive Network for Superior Lithium Storage.

SiOx-based anode materials with high capacity and outstanding cycling performance have gained numerous attentions. Nevertheless, the poor electrical conductivity and non-negligible volume change hinder their further application in Li-ion batteries. Herein, we propose a new strategy to construct a hollow nanosphere with boron-doped Si/SiOx decorated with vanadium nitride (VN) nanoparticles and embedded in a nitrogen-doped, porous, and partial graphitization carbon layer (B-Si/SiOx@VN/PC). Benefiting from such structural and compositional features, the B-Si/SiOx@VN/PC electrode exhibits a stable cycling capacity of 1237.1 mA h g-1 at a current density of 0.5 A g-1 with an appealing capacity retention of 87.0% after 300 cycles. Additionally, it delivers high-rate capabilities of 1139.4, 940.7, and 653.4 mA h g-1 at current densities of 2, 5, and 10 A g-1, respectively, and ranks among the best SiOx-based anode materials. The outstanding electrochemical performance can be ascribed to the following reasons: (1) its hollow structure makes the Li+ transportation length decreased. (2) The existing nanopores facilitate the Li+ insertion/desertion and accommodate the volume variation. (3) The nitrogen-doped partial graphitization carbon enhances the electrical conductivity and promotes the formation of stable solid electrolyte interface layers during the repetitive Li+ intercalation/extraction process.