Gradient Interphase Research Articles

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

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

Trinitarian Design of Gradient Artificial Interphase Enables Colossal Granular Li Deposits for Stable Li-Metal Batteries.

The cycling lifespan of Li-metal batteries is compromised by the unstable solid electrolyte interphase (SEI) and the continuous Li dendrites, restricting their practical implementations. Given these challenges, establishing an artificial SEI holds promise. Herein, a trinitarian gradient interphase is innovatively designed through composite coatings of magnesium fluoride (MgF2), N-hexadecyltrimethylammonium chloride (CTAC), and polyvinylidene fluoride-hexafluoropropylene copolymer (PVDF-HFP) on Li-metal anode (LMA). Specifically, the MgF2/CTAC/PVDF-HFP SEI spontaneously forms a lithium fluoride (LiF)-rich PVDF-HFP-based SEI, along with lithium-magnesium (Li-Mg) alloy substrate as lithiophilic electronic conductor and positively charged CTAC during plating. Noticeably, the Li-Mg alloy homogenizes the distribution of electric field and reduce the internal resistance, while the electronically insulated LiF/PVDF-HFP composite SEI offers fast ion-conducting and mechanical flexibility, accommodating the volumetric expansion and ensuring stable Li-ion flux. Additionally, CTAC at the dendritic tip is pivotal for mitigating dendrites through its electrostatic shield mechanism. Innovatively, this trinitarian synergistic mechanism, which facilitates colossal granular Li deposits, constructs a dendrite-free LMA, leading to stable cycling performances in practical Li||LFP, popular Li||NCM811, and promising Li||S full cells. This work demonstrates the design of multifunctional composite SEI for comprehensive Li protection, thereby inspiring further advancements in artificial SEI engineering for alkali-metal batteries.

Unlocking 4.9 V Quasi-Solid-State Lithium Metal Battery via Solvent Screening and Interfacial Manipulation.

Parlous structure integrity of the cathode and erratic interfacial microdynamics under high potential take responsibility for the degradation of solid-state lithium metal batteries (LMBs). Here, high-voltage LMBs have been operated by modulating the polymer electrolyte intrinsic structure through an intermediate dielectric constant solvent and further inducing the gradient solid-state electrolyte interphase. Benefiting from the chemical adsorption between trimethyl phosphate (TMP) and the cathode, the gradient interphase rich in LiPFxOy and LiF is induced, thereby ensuring the structural integrity and interface compatibility of the commercial LiNi0.8Co0.1Mn0.1O2 (NCM811) cathode even at the 4.9 V cutoff voltage. Eventually, the specific capacity of NCM811|Li full cell based on TMP-modulated polymer electrolyte increased by 27.7% from 4.5 to 4.9 V. Such a universal screening method of electrolyte solvents and its derived electrode interfacial manipulation strategy opens fresh avenues for quasi-solid-state LMBs with high specific energy.

A promising solution for highly reversible zinc metal anode chemistry: Functional gradient interphase

A promising solution for highly reversible zinc metal anode chemistry: Functional gradient interphase

Synergy in bio-inspired hybrid composites with hierarchically structured fibrous reinforcements

In response to the global energy crisis, high-performance transportation sectors are rapidly embracing lightweight materials to enhance energy efficiency and sustainability, while grappling with the persistent challenges of developing structural materials that meet stringent safety standards with robust mechanical performance and ease of scalability. Thus, this work presents a combined experimental and theoretical framework to develop a profound understanding of the synergistic effect in hybrid composites with bio-inspired fibrous reinforcements, by elucidating the interfacial interactions across multiple length-scales, encompassing atomic covalent bonding to micro-morphology. A model hybrid composite system, containing a self-assembled fibrous reinforcement consisting of nano-sized Graphene Nanoplatelets (GnP) covalently bonded onto chemically-modified micro-sized Glass Fibers (GF), was utilized to showcase the synergistic effect and highlight its associated mechanisms. The interfacial interactions of the reinforcement were optimized by obtaining the maximum density of covalent bonds, which was achieved with 0.5 wt% GnP for the hybrid composites containing 10 wt% GF, increasing the work of adhesion by 33 %, compared to the biphasic GF composites. The composite’s morphology contains minimal agglomeration with ∼68 % of GnPs oriented with the melt flow, supressing high-stress concentration areas, while the formed crystalline microstructure, with ∼18 % β-crystals, allows the matrix to absorb substantial energy. Furthermore, the increased trans-crystallization encapsulating the hierarchical reinforcement induced nanoscale stiffness variations, increasing rigidity, and forming an ∼16 µm gradient interphase that facilitates load transfer. The greatest synergistic effect observed was ∼54 %, ∼37 %, and ∼75 % for the tensile modulus, tensile strength, and impact strength, respectively. Additionally, a theoretical framework accounting for the synergistic effect was formulated, using a two-step core/shell homogenization model, which shows great potential in expediting the design and optimization of innovative hybrid composite materials.

Gradient Interphase Engineering Enabled by Anionic Redox for High-Voltage and Long-Life Li-Ion Batteries.

Intelligent utilization of the anionic redox reaction (ARR) in Li-rich cathodes is an advanced strategy for the practical implementation of next-generation high-energy-density rechargeable batteries. However, due to the intrinsic complexity of ARR (e.g., nucleophilic attacks), the instability of the cathode-electrolyte interphase (CEI) on a Li-rich cathode presents more challenges than typical high-voltage cathodes. Here, we manipulate CEI interfacial engineering by introducing an all-fluorinated electrolyte and exploiting its interaction with the nucleophilic attack to construct a gradient CEI containing a pair of fluorinated layers on a Li-rich cathode, delivering enhanced interfacial stability. Negative/detrimental nucleophilic electrolyte decomposition has been efficiently evolved to further reinforce CEI fabrication, resulting in the construction of LiF-based indurated outer shield and fluorinated polymer-based flexible inner sheaths. Gradient interphase engineering dramatically improved the capacity retention of the Li-rich cathode from 43 to 71% after 800 cycles and achieved superior cycling stability in anode-free and pouch-type full cells (98.8% capacity retention, 220 cycles), respectively.

Interface Ionic/Electronic Redistribution Driven by Conversion-Alloy Reaction for High-Performance Solid-State Sodium Batteries.

NASICON-type Na+ conductors show a great potential to realize high performance and safety for solid-state sodium metal batteries (SSSMBs) owing to their superior ionic conductivity, high chemical stability, and low cost. However, the interfacial incompatibility and sodium dendrite hazards still hinder its applications. Herein, a conversion-alloy reaction-induced interface ionic/electronic redistribution strategy, constructing a gradient sodiophilic and electron-blocking interphase consisting of sodium-tin (Na-Sn) alloy and sodium fluoride (NaF) between NASICON ceramic electrolyte and Na anode is proposed. The NaxSny alloy-rich layer near the side of the sodium electrode acts as a superior conductor to enhance the anodic sodium-ion transport dynamics while the NaF-rich layer near the side of the ceramic electrolyte serves as an electron insulator to confine the interfacial electron turning ability, achieving uniform and dendrite-free Na deposition during the cycling. Profiting from the synergistic effect of the gradient interphase, the critical current density (CCD) of the assembled Na symmetric cell is significantly increased to 1.7mAcm-2 and the cycling stability of that is as high as 1200h at 0.5mAcm-2. Moreover, quasi-solid-state sodium batteries with both Na3V2(PO4)3 and NaNi1/3Fe1/3Mn1/3O2 cathode display outstanding electrochemical performance.

Impact of coating and curing temperature on the formation of CFRP/sealant gradient interphase

Flexible sealant joints are extensively utilized for sealing aircraft wing fuel tanks due to the excellent stress transfer release of gradient interphase. This study investigates the impact of coating and curing temperature on the formation of CFRP/sealant gradient interphase. The interphase quality was identified using SEM equipped with EDS, and a detailed analysis of element concentration transition was performed to understand the interplay between different mechanisms. Contact angle calculation and FTIR-XPS combined spectral analysis were conducted to determine the interfacial physicochemical state. The results showed that coating enhances compatibility and broadens interphase, whereas opposite results were observed at higher temperatures. The improvement of surface energy and wettability, chemical groups, and molecular bonding sites provided by coating promotes interfacial reactivity and molecular mobility. Elevated cure temperature accelerates the formation of cross-linked networks that restricts sealant chain mobility, indicating that vulcanization dominates over diffusion under high cure temperature.

Fluoride-Rich, Organic-Inorganic Gradient Interphase Enabled by Sacrificial Solvation Shells for Reversible Zinc Metal Batteries.

Zinc metal batteries are strongly hindered by water corrosion, as solvated zinc ions would bring the active water molecules to the electrode/electrolyte interface constantly. Herein, we report a sacrificial solvation shell to repel active water molecules from the electrode/electrolyte interface and assist in forming a fluoride-rich, organic-inorganic gradient solid electrolyte interface (SEI) layer. The simultaneous sacrificial process of methanol and Zn(CF3SO3)2 results in the gradient SEI layer with an organic-rich surface (CH2OC- and C5 product) and an inorganic-rich (ZnF2) bottom, which combines the merits of fast ion diffusion and high flexibility. As a result, the methanol additive enables corrosion-free zinc stripping/plating on copper foils for 300 cycles with an average coulombic efficiency of 99.5%, a record high cumulative plating capacity of 10 A h/cm2 at 40 mA/cm2 in Zn/Zn symmetrical batteries. More importantly, at an ultralow N/P ratio of 2, the practical VO2//20 μm thick Zn plate full batteries with a high areal capacity of 4.7 mAh/cm2 stably operate for over 250 cycles, establishing their promising application for grid-scale energy storage devices. Furthermore, directly utilizing the 20 μm thick Zn for the commercial-level areal capacity (4.7 mAh/cm2) full zinc battery in our work would simplify the manufacturing process and boost the development of the commercial zinc battery for stationary storage.

Tailored flexibility in inherently brittle epoxy-based composites through gradient interphase formation with bio-based thermoplastic elastomer grades

Tailored flexibility in inherently brittle epoxy-based composites through gradient interphase formation with bio-based thermoplastic elastomer grades

Domino Reactions Enabling Sulfur-Mediated Gradient Interphases for High-Energy Lithium Batteries.

Silicon (Si)-based anodes are currently considered a feasible solution to improve the energy density of lithium-ion batteries owing to their sufficient specific capacity and natural abundance. However, Si-based anodes exhibit low electric conductivities and large volume changes during cycling, which could easily trigger continuous breakdown/reparation of the as-formed solid-electrolyte-interphase (SEI) layer, seriously hampering their practical application in current battery technology. To control the chemoelectrochemical instability of the conventional SEI layer, we herein propose the introduction of elemental sulfur into nonaqueous electrolytes, aiming to build a sulfur-mediated gradient interphase (SMGI) layer on Si-based anodes. The SMGI layer is generated through the domino reactions (i.e., electrochemical cascade reactions) involving the electrochemical reductions of elemental sulfur followed by nucleophilic substitutions of fluoroethylene carbonate, which endows the corresponding SEI layer with strong elasticity and chemomechanical stability and enables rapid transportation of Li+ ions. Consequently, the prototype Si||LiNi0.8Co0.1Mn0.1O2 cells attain a high-energy density of 622.2 W h kg-1 and a capacity retention of 88.8% after 100 cycles. Unlike previous attempts based on sophisticated chemical modifications of electrolyte components, this study opens a new avenue in interphase design for long-lived and high-energy rechargeable batteries.

Regulating interfacial reaction through electrolyte chemistry enables gradient interphase for low-temperature zinc metal batteries

In situ formation of a stable interphase layer on zinc surface is an effective solution to suppress dendrite growth. However, the fast transport of bivalent Zn-ions within the solid interlayer remains very challenging. Herein, we engineer the SEI components and enable superior kinetics of Zn metal batteries under harsh conditions through regulating the sequence of interfacial chemical reaction. With the differences in chemical reactivity of trimethyl phosphate co-solvent and trifluoromethanesulfonate anions in the Zn2+-solvation shell, Zn3(PO4)2 and ZnF2 are successively generated on Zn metal surface to form a gradient ZnF2–Zn3(PO4)2 interphase. Mechanistic studies reveal the outer ZnF2 facilitates Zn2+ desolvation and inner Zn3(PO4)2 serves as channels for fast Zn2+ transport, contributing to long-term cycling at subzero temperatures. Impressively, the gradient SEI enables a high lifespan over 7000 hours in Zn symmetric cell and a capacity retention of 86.1% after 12000 cycles in Zn–KVOH full cell at –50 °C.

Tailored rigid-flexible interphase of M40X composites via block copolymers: A combined method of experimental analysis and molecular dynamic simulation

The rigid-flexible interphase was constructed by polyamide acid-polyether amine block copolymer with various ratios of rigid/flexible segments (PAE20, PAE10, PAE5), and the correlation of rigid/flexible proportion with interfacial properties of M40X composites was explored via the combined method of experiments and molecular dynamic (MD) simulation. As the proportion of flexible segments increased, the PAE-CF surface exhibited improved chemical activity and uniform coverage. The interfacial simulation presented a distribution plateau of rigid backbones in the interphase of PAE10-CF/EP composite, corresponding to the experimentally-verified double transit-modulus platform, which indicated that the spatial homogeneity of the stable crosslinked networks facilitated the gradient interphase stiffening. The graduated interfacial structures contributed to 55.25%, 179.31% increment of simulated interfacial shear stress (ISS), and 7.96%, 19.03% enhancement in interfacial shear strength (IFSS) in comparison with those of PAE20-CF/EP and PAE5-CF/EP composites. The interphase reinforcing mechanisms were investigated by interfacial residual stress and toughness via experimental analysis and theoretical calculation. Compared with the pristine CF composite, the interfacial residual stress and interfacial toughness were improved by 26.4% and 165.6% in PAE10-CF/EP composite, respectively. The integration of stress transfer capacity with energy dissipation efficiency was achieved by the optimal rigid/flexible ratio, which contributed to the balance between the interfacial stiffness and toughness of M40X composites.

Armoring lithium metal anode with soft–rigid gradient interphase toward high-capacity and long-life all-solid-state battery

Solid polymer electrolytes (SPEs) are highly promising for realizing high-capacity, low-cost, and safe Li metal batteries. However, the Li dendritic growth and side reactions between Li and SPEs also plague these systems. Herein, a fluorinated lithium salt coating (FC) with organic-inorganic gradient and soft–rigid feature is introduced on Li surface as an artificial protective layer by the in-situ reaction between Li metal and fluorinated carboxylic acid. The FC layer can improve the interface stability and wettability between Li and SPEs, assist the transport of Li ions, and guide Li nucleation, contributing to a dendrite-free Li deposition and long-lifespan Li metal batteries. The symmetric cell with FC-Li anodes exhibits a high areal capacity of 1 mAh cm−2 at 0.5 mA cm−2, and an ultra-long lifespan of 2000 h at a current density of 0.1 mA cm−2. Moreover, the full cell paired with the LiFePO4 cathode exhibits improved cycling stability, remaining 83.7% capacity after 500 cycles at 1 C. When matching with the S cathode, the FC layer can prevent the shuttle effect, contributing to stable and high-capacity Li–S battery. This work provided a promising way for the construction of stable all-solid-state lithium metal batteries with prolonged lifespan.

Fast-Tracking of the Segmental Orientation in Poly(ethylene oxide)-based Polyurethane Urea by Mechano-optical (Infrared Dichroism and Birefringence) Properties: Degree of the Soft-Segment Ordering Effect

The orientation behavior of segment-specific chemical groups of NH and CH was investigated for poly(ethylene oxide) (PEO)-based polyurethane urea (PUU) during uniaxial stretching using a uniaxial stretching system integrated with spectral birefringence and ultrafast IR spectrometers that capture two polarization states simultaneously. PUUs with 30% by-weight urethane-urea hard segment content were prepared using PEO oligomers with number average molecular weights of 2000, 4600, and 8000 g/mol. High-molecular weight PEO-based PUUs exhibited microphase morphologies with sharp interfaces between the PEO matrix and urethane-urea hard segments, while low-molecular weight PEO-2000 (2000 g/mol)-based PUU exhibited a gradient interphase. This is primarily due to substantial hydrogen-bonding interactions between the urea hard segments and ether groups of highly amorphous PEO-2000 compared with highly crystalline soft segments in PEO-4600 and PEO-8000, which lack significant hydrogen-bonding interactions with urea groups and hence a sharper interface and improved microphase separation. The segment-specific chemical group orientation study revealed that the relaxation and reorganization behaviors are closely dependent on the initial morphology. In microphase-separated PUU with a gradient interphase, responses of the hard and soft segments to deformation are similar even at lower strain levels. For the microphase-separated PUUs with a sharp interface, the low-strain level orientation is localized in the soft-segment regions until the connection with the hard segments drive the orientation in the chain axis toward the stretching direction. This network transition is also reflected in the mechano-optical behavior as a change from a high-strain optical constant to a lower-strain optical constant.

In-situ forming lithiophilic-lithiophobic gradient interphases for dendrite-free all-solid-state Li metal batteries

Solid polymer electrolytes offer a promise for all-solid-state Li batteries due to their low cost and good processability. However, dendrites and the associated contact loss occurring at the undesirable Li/electrolyte interface during repeated plating and stripping remain a challenge. To address the issue, here, we propose to coat a thin layer containing Al/Li dual-salt onto the polyethylene oxide (PEO) electrolyte. When cycled with the Li metal anode, the salts are sequentially reduced, in-situ forming a lithiophilic Li-Al alloy-rich layer near the anode and a lithiophobic LiF-rich layer close to the electrolyte. The former improves the interfacial adhesion and regulates the Li nucleation, while the latter contributes to dendrite suppression due to its high interface energy against Li. As a result, the gradient interphase enables a Li/Li symmetrical cell to be stably cycled for over 1000 h without short circuits. Moreover, the full cell paired with the LiFePO4 cathode shows enhanced cyclability, retaining 89.1% capacity after 350 cycles at 0.5 C. A pouch cell using the dual-salt coated electrolyte demonstrates good performance and safety. This work provides a facile yet effective approach to construct functional interphase for achieving stable batteries using solid polymer electrolytes.

In Situ Characterization of the Reaction-Diffusion Behavior during the Gradient Interphase Formation of Polyetherimide with a High-Temperature Epoxy System.

This study presents two novel methods for in situ characterization of the reaction-diffusion process during the co-curing of a polyetherimide thermoplastic interlayer with an epoxy-amine thermoset. The first method was based on hot stage experiments using a computer vision point tracker algorithm to detect and trace diffusion fronts, and the second method used space- and time-resolved Raman spectroscopy. Both approaches provided essential information, e.g., type of transport phenomena and diffusion rate. They can also be combined and serve to elucidate phenomena occurring during diffusion up to phase separation of the gradient interphase between the epoxy system and the thermoplastic. Accordingly, it was possible to distinguish reaction-diffusion mechanisms, describe the diffusivity of the present system and evaluate the usability of the above-mentioned methods.

A self-regulated gradient interphase for dendrite-free solid-state Li batteries

A functional gradient lithium anode (FGLA), where a LiF-rich layer faces garnet side and gradually changes to a LiAl-rich layer facing Li side, effectively prevents solid-state electrolytes from dendrite penetration at high current densities.

Constructing a Rigid-and-Flexible Twin-Stage Gradient Interphase through Starlike Copolymer Coating on Carbon Fibers: A Route for Enhancing Interfacial Properties of Composites.

A rigid-and-flexible interphase was established by a starlike copolymer (Pc-PGMA/Pc) consisting of one tetraaminophthalocyanine (TAPc) core with four TAPc-difunctionalized poly(glycidyl methacrylate) (PGMA) arms through the surface modification of carbon fibers (CFs) and compared with various interphases constructed by TAPc and TAPc-connected PGMA (Pc-PGMA). The increase in the content of N-C═O showed that PGMA/Pc branches were successfully attached onto the CF-(Pc-PGMA/Pc) surface, exhibiting concavo-convex microstructures with the highest roughness. Through adhesive force spectroscopy by atomic force microscopy (AFM) with peak force quantitative nanomechanical mapping (PF-QNM) mode and visualization of the relative distribution of TAPc/PGMA via a Raman spectrometer, a rigid interphase with highly cross-linked TAPc and a flexible layer from PGMA arms as the soft segment were separately detected in CF-TAPc/EP and CF-(Pc-PGMA)/EP composites. The rigid-and-flexible interphase in the CF-(Pc-PGMA/Pc)/EP composite provided excellent stress-transfer capability by the rigid inner modulus intermediate layer and energy absorption efficiency from the flexible outer layer, which contributed to 64.6 and 61.8% increment of transverse fiber bundle test (TFBT) strength, and 33.8 and 40.6% enhancement in interfacial shear strength (IFSS) in comparison with those of CF-TAPc/EP and CF-(Pc-PGMA)/EP composites. Accordingly, schematic models of the interphase reinforcing mechanism were proposed. The interfacial failures in CF-TAPc/EP and CF-(Pc-PGMA)/EP composites were derived from the rigid interphase without effective relaxation of interfacial stress and soft interphase with excessive fiber-matrix interface slippage, respectively. The cohesive failure in the CF-(Pc-PGMA/Pc)/EP composite was attributed to the crack deflection through the balance of the modulus and deformability from the twin-stage gradient intermediate layer.

A nanostructured cellulose-based interphase layer to enhance the mechanical performance of glass fibre-reinforced polymer composites

In this study, we report the effect of sizing glass fibres (GFs) with tetramethylpiperidine-1-oxyl (TEMPO)-mediated cellulose nanocrystals (t-CNC) to improve the interfacial mechanical performance of glass fibre reinforced polymer composites (GFRP). These nanoparticles are introduced at different concentrations to yield a coating of t-CNCs which are (1) sparsely deposited at low concentrations, and (2) uniformly self-assembled over the glass fibre at a higher concentration. The mechanical, morphological and interphase results show that self-assembled CNC coating around a fibre provides better strengthening than sparsely deposited CNCs. Experimental results confirmed that GFs coated with self-assembled t-CNCs yielded a ~30% increase in the interlaminar shear strength (ILSS), 43% increase in flexural strength and 40% increase in flexural modulus of the GFRP composite. Strong nanoscale interactions between the t-CNC and GF, coupled with the formation of a high modulus gradient interphase layer, contributed to the significant improvement in the mechanical performance of t-CNC/GFRP composites.