Solid Electrolyte Interface Layer Research Articles

Core-Shell Sn@Sioc Nanocomposite Synthesized Via Spray Pyrolysis for LIBs

Lithium-ion batteries (LIBs) have become promising energy storage devices for the consumer electronics and electric vehicles due to their high energy and power density. Anode materials such as Si, Sn and Ge which are alloying with Li+ ions have been attracted as alternatives to conventional graphite due to their very high theoretical capacities. Among the possible candidates, Sn has been thought to be a great anode material that shows high theoretical Li ion storage capacity of 994mAh g-1 and high electrical conductivity. However, the major drawback of tin based anode is their poor cycling stability because of large volme changes (260% for Li22Sn5) during lithiation resulting in pulverization and loss of electrical contact within the electrode. Especially, the repetitive formation and rupture of solid electrolyte interface (SEI) layer continuously deplete the electrolyte. Nanocrystallization can effectively decrease the absolute volume change of every single particle and mitigated the strain improving the cycling stability of Sn anodes. However, preparation methods of nano-Sn have some negative factors, such as the high cost, complex process and reaggregation after cycling. In order to take full advantage of nano-Sn, many studies introduce suitable matrix. These matrix acts as a buffer agents and avoids side reactions by preventing the direct contact of Sn and electrolyte. The common one is carbon matrix works as a conducting medium and enhances the rate performance of electrode. Another one is active metals including Ge-Sn, Sb-Sn and Ag-Sn that can contribute to the overall capacity of the electrodes and long cycling life. Yet these comes with loss of charge storage capacity or large volume expansion. The quest for suitable matrix with high Li ion storage, low volume expansion and sufficient electronic conductivity is important. In this study, silicon oxycarbide (SiOC) was adapted for Sn based anodes. The SiOC consists of silica tetrahedral SiO2, SiOC glass phase and free carbon. This matrix features a high charge storage capacity (~800mAh g-1), low voulme expansion (~7%) and sufficient mechanical strength contributed by SiO2 domains to accommodate the high volume expansion without capacity fading of Sn anode. In particular, the SiOC can suppress the aggreation of metallic Sn at high temperature remaining nano size. First, we obtained the Sn@SiOC nanocomposite with uniformly coated SiOC layer containing metallic Sn nanoparticle by spray pyrolysis and a subsequent carbonization process. The spray pyrolysis is scalable and facile method to synthesize various nanostructure functional materials via one-pot process. Also it can be easily scaled up for mass production. During the spray pyrolysis process, the tin(II) acetate and diphenylsilanediol (DPSD), the starting materials of Sn and SiOC, can be easily vaporized due to its low boiling point. The tin acetate nucleates first due to lower boiling point than DPSD and formates many clusters. Subsequently, DPSD vapors can be deposited onto the Sn clusters via aerosol assisted chemical vapor depsition (AACVD) mechanism. The deposited DPSD vapors lead to formation of coating layer by nucleation, growth and coagulation. Then, the spray pyrolyzed Sn@SiOC nanocomposite thermally treated at the inert atmosphere for growth of carbon network. This approach yields unifomly coated SiOC matrix with Sn nanoparticles of sizes on the order of 40-50nm. Anodes of the Sn@SiOC nanocomposite demonstrate high capacities and better stability against volume change during lithiation and delithiation cycling.

In Situ Detecting Lithium-Ion Batteries Thermal Runaway with Resistance Temperature Detector

Advanced next-generation lithium-ion batteries (LIBs) can only be realized when the thermal safety-related incidents, which have been the roadblocks for development, are mitigated. A variety of advanced works have been proposed for safety enhancement viz., isolating shutdown separators, protective electrode coatings, electrolyte additives. However, they have been stalled from further developments on account of their narrow range in working voltage window, stability, performance, and response time. Also, to date in situ safety devices are known to drastically affect LIBs’ performance. Novel temperature measurement schemes have been developed to help battery management systems (BMS) for improved prediction such as Thermocouples, Thermistors, Fiber Bragg-grating (FBG) sensors, etc. but each has its limitation. Hence, this points towards developing an effective temperature management system that is capable of quick detections, compact, cost-effective, and light-weighted. Here, we are reporting in operando thermal runaway detection for LIBs, from beneath the anode current collector, using an internal resistance temperature detector (RTD). Sensing temperature fluctuations from the anode is more critical compared to the cathode is that it has a solid electrolyte interface (SEI) layer, which is comprised of reduced electrolytic compounds like ROCO2Li, (CH2OCO2Li)2 and ROLi and has lithium stored in graphitic interlayers. During thermal runaway events, decomposition of these compounds and reactions of the charged anode with electrolyte leads to the generation of an enormous amount of heat, which can induce fire, smoke, or explosion. Hence, sensing the anode becomes critical and gives direct access to this heat.Here, we studied three such thermal runway events, viz, external short circuit (ESC), overcharging, and overheat using multiple module calorimetry (MMC) to elucidate the thermal detection capabilities and presence of RTD inside the LIB. During ESC and overcharge tests, temperatures of around 36°C and 48°C were recorded using internal RTDs, respectively. These temperatures were about 9°C and 20°C more than the external RTDs. An interesting statistic about the internal RTD was its detection ability, which for 90% temperature rise was about 14 times faster than compared to the external RTD. RTD embedded mesocarbon microbeads (MCMB) anode half-cell was cycled at 0.25C rate giving a stable average capacity of 238 mAh g-1 over 200 cycles with voltage profile congruent to those reported in the literature. Modeling simulated tests elucidated the prevalence of different regions during thermal runaway events initialed by ESC and overcharge. Additionally, Multimode Calorimetry (MMC) for LIB with embedded internal RTD produced more endothermic peaks beyond 150°C and overall heat generated was 1.75 kJ g-1, which is significantly lower than conventional LIB. RTD assembly has another role of being a passive safety device while placed inside the LIB. Using thermal signatures from internal RTD, future BMS can provide a conducive environment for the LIBs, which would deliver power for high energy density applications such as in the grid-storage and EVs industries.

In-Situ Electrochemical Dilatometry Study for Understanding Volume Changes of the Graphite Electrodes for Lithium-Ion Battery

In-situ electrochemical dilatometry is applied as an analytical technique to investigate the effect of both solid electrolyte interface (SEI) formation and the microstructure of the electrode on the dilation behavior of the graphite electrodes during lithium ion intercalation at the same time. It was found that the dilation and contraction behavior of the graphite electrode was dependent on the microstructure of the graphite electrode. The relationship between the microstructure, such as preferred orientation of graphite particles and the pore structure, and the volume changes of the graphite electrode were investigated by half-cell type in-situ electrochemical dilatometer during cycling. Dilation behavior of graphite electrodes monitored by in-situ dilatometer clearly showed the volume changes of the graphite electrodes induced by Li ion intercalation/de-intercalation as well as the SEI layer formation, and how the microstructure of the electrodes affects their volume expansion upon lithium ion intercalation. It was also found that differential dilation plots of the graphite electrodes upon lithiation and delithiation gave us more detailed information of dilation and contraction behaviors with respect to the amount of Li ion intercalated into graphite.

Vanadium diphosphide as a negative electrode material for sodium secondary batteries

The abundance of sodium resources has sparked interest in the development of sodium-ion batteries for large-scale energy storage systems, amplifying the need for high-performance negative electrodes. Although transition metal phosphide electrodes have shown remarkable performance and great versatility for both lithium and sodium batteries, their electrochemical mechanisms in sodium batteries, particularly vanadium phosphides, remain largely elusive. Herein, we delineate the performance of VP2 as a negative electrode alongside ionic liquids in sodium-ion batteries. The polycrystalline VP2 is synthesized via one-step high energy ball-milling and characterized using X-ray diffraction, X-ray photoelectron spectroscopy, and transmission electron microscopy. Electrochemical tests ascertained improved performance at intermediate temperatures, where the initial cycle was conducted at 100 mA g−1 yielded a significantly higher discharge capacity of 243 mAh g−1 at 90 °C compared to the limited capacity of 49 mAh g−1 at 25 °C. Enhanced rate and cycle performance are also achieved at 90 °C. Electrochemical impedance spectroscopy and scanning electron microscopy further reveal a reduced charge transfer resistance at 90 °C and the formation of a uniform and stable solid electrolyte interface (SEI) layer after cycling. X-ray diffraction and nuclear magnetic resonance spectroscopy are used to confirm the conversion-based mechanism forming Na3P after charging.

The identification of specific N-configuration responsible for Li-ion storage in N-doped porous carbon nanofibers: An ex-situ study

Nitrogen (N)-doped carbon is widely used as an anode material for Li-ion battery (LIB). However, the identification of a specific type of N-configuration responsible for Li-ion storage in N-doped carbon is an elusive topic for LIB. Herein, the N-doped porous carbon nanofibers (N-pCNFs) with various atomic percentages of N and different types of N-configurations are prepared by carbonization of polyacrylonitrile-Zeolitic imidazolate framework-8 fibres at 800, 900, and 1000 °C in N2 atmosphere. The N content of pCNFs-800, N-pCNFs-900, and N-pCNFs-1000 samples are found to be 12.9, 9.4, and 4.8% atomic percentage, respectively. The free-standing/binder-free N-pCNFs-800, N-pCNFs-900, and N-pCNFs-1000 anode electrodes deliver the reversible Li storage capacity of 650, 805, and 520 mAh g−1, respectively at 0.1 C-rate. The ex-situ X-ray diffraction, scanning electron, and transmission electron microscopic results of N-pCNFs-900 indicate the formation of the solid electrolyte interface (SEI) layer. Further, the ex-situ X-ray photoelectron spectroscopy (XPS) analysis of N-pCNFs-900 identifies the presence of LiF, LixPF5-x, LixPOF5-x, Li-O-C, and R-COOLi constituents of the SEI layer and the deconvoluted XPS N1s spectra confirms that the pyridinic-N is responsible for Li-ion storage sites in N-pCNFs.

Boosting Coulombic Efficiency of Conversion‐Reaction Anodes for Potassium‐Ion Batteries via Confinement Effect

AbstractPotassium‐ion battery anode materials with high capacity always hold one or more K ions and are companied by large volume swelling, which threatens the stability of solid‐electrolyte‐interface (SEI) layers, and results in low coulombic efficiency as well as inferior cycling stability. Herein, an avenue that induces the rapid formation of continuous SEI layers by the confinement effect to boost K ions storage property is proposed. CuS nanoplates are dispersed on the core layer of carbon nanofibers and further confined by the Nb2O5‐C shell layer, constructing core–shell structure CuS‐C@Nb2O5‐C nanofibers (NFs). The shell layer protects the CuS nanoplates from immediate contact with the electrolyte and brings about volume expansion, assisting the rapid formation of continuous SEI layers. As a result, the capacity retention of the CuS‐C@Nb2O5‐C NFs electrode remains at 93.1% after 100 cycles, much larger than that of the CuS‐C NF electrode (74.6%); the process that coulombic efficiency stabilized above 99.0% shortens to 5 cycles from 30 cycles. This progress is also found in the CoS2‐C@Nb2O5‐C and NiS2‐C@Nb2O5‐C NFs electrodes. The improved coulombic efficiency and cycling stability brought about by the confinement effect offer a facile approach to boost the K ion storage property of conversion reaction anodes.

Role of SEI layer growth in fracture probability in lithium‐ion battery electrodes

SummaryUnderstanding of degradation mechanisms in batteries is essential for the widespread use of eco‐friendly vehicles. Degradation mechanisms affect battery performance not only individually but also in a coupled manner. Solid electrolyte interface (SEI) formation deteriorates battery capacity through consuming available lithium ions. On the other hand, as the SEI layer grows over multiple cycles, the level of mechanical constraints is changed, which can affect the fracture behavior of the active particles. We investigate the effect of the SEI layer growth on the fracture probability of the electrode particles. The simulations show that as the SEI layer grows, tensile stress inside the active particles turns into compressive stress, reducing the probability of particle fracture. Once the SEI layer is fractured, the particle fracture is sequentially more likely to happen because the SEI constraint is removed. The study emphasizes that the stability of SEI layers is important because it helps in alleviating electrochemical performance fade as well as mechanical failure probability. In addition, the SEI layer on small particles tends to be more fractured than that on large particles, suggesting that the particle size uniformity is essential for reducing the fracture probability of the SEI layers at the electrode.

Surface chemistry of LiFePO4 cathode material as unraveled by HRTEM and XPS

During the first cycle of lithium-ion batteries, a passivation layer is formed on the surface of electrode due to electrolyte decomposition, which is called solid electrolyte interface (SEI). In this study, the evolution of LiFePO4 cathode surface and components of SEI layer are investigated in different states by high-resolution transmission electron microscopy and X-ray photoelectron spectroscopy. The results suggest that SEI layer is mainly formed during the first cycle and remains stable in the following cycles. Furthermore, SEI layer can be divided into two parts, and components of these two parts are different. The outer layer that is near to electrolyte is composed of organic components, and the inner layer that is near to active material is composed of inorganic components. Taken together, the study reveals SEI layer formation process on LiFePO4 cathode surface, which is of significance for understanding the influence of SEI layer on electrochemical performance.

Abnormal Overcharging during Lithium-Ether Co-Intercalation in a Graphite System: Formation of Shuttling Species by the Reduction of the TFSI Anion.

Materializing an ultrafast charging system is one of the crucial technologies for next-generation Li-ion batteries (LIBs). Among many studies aimed at achieving fast charging systems, Li-ether solvent cointercalation into the graphite electrodes in LIB has been identified as a novel concept for achieving high power performance because this system does not consist of the sluggish desolvation step and a resistive solid-electrolyte interface (SEI) layer. Interestingly, while studying the Li-ether solvent cointercalation into graphite electrodes, employing lithium bis-trifluoromethane sulfonimide (LiTFSI) as the Li salt, we observed an abnormal overcharging phenomenon. Here, we screened the specific conditions, under which the abnormal overcharging occurred, and revealed that this abnormal overcharging was attributable to the shuttling mechanism. The formation of shuttling species could have been derived by the reduction of TFSI- anion. With this understanding of the underlying mechanism, we efficiently suppressed the abnormal overcharging by adding LiNO3 to the electrolyte. The shuttling and resulting overcharging could be prevented by the synergistic contributions of LiNO3 and SxOy, dissolved in the electrolyte, to the formation of a dense solid LiSxOy SEI layer on Li-metal. We expect that this work could be a great reference in analyzing many unsolved phenomena in systems utilizing TFSI-.

Design of quadruple-layered metal oxides/nitrogen, oxygen-doped carbon nanotube arrays as binder-free electrodes for flexible lithium-ion batteries

Designing flexibly binder-free metal oxide electrodes, which could effectively alleviate the mechanical stress and maintain the structural integrity during the lithiation/delithiation process, is still a major challenge. Here we report a facile strategy for successfully synthesizing free-standing quadruple-layered metal oxides/nitrogen, oxygen-doped carbon nanotube array electrodes. In the quadruple-layered structure, metal oxides are protected by carbon layer to minimize the direct exposure to the electrolyte and accommodate the huge volume change during cycling, and thus form the solid-electrolyte interface layer. Besides that, the abundant oxygen and nitrogen-containing functional groups of carbon layer shows a strong interaction with metal oxides to prevent the electrode pulverization during charging and discharging. Meanwhile, carbon layer is introduced to facilitate the stable and fast electrons mobility. As a result, the as-prepared quadruple-layered electrodes show excellent electrochemical performance in terms of high reversible capacity, good rate capability, and stable cyclability. This work may pave the way for the construction of flexible binder-free lithium ion batteries with superior lithium storage properties.

An optimal charging algorithm to minimise solid electrolyte interface layer in lithium-ion battery

This article presents a novel control algorithm for online optimal charging of lithium-ion battery by explicitly incorporating degradation mechanism into control, to reduce the degradation process. The health of battery directly relates to degradation and capacity fade in cycles of charging. We mainly focus on the growth of the solid electrolyte interface (SEI) layer, which is the primary source of degradation of batteries. This article addresses the challenge of minimising SEI layer growth during charging by incorporating the first-order SEI layer growth rate model into a non-linear model predictive control approach. A single particle model (SPM) is used for optimal charging using orthogonal projection-based model reformulation. Gauss pseudo-spectral method is used for the optimisation of charging trajectories. Results of the optimal algorithm are compared with the traditional constant current constant voltage (CCCV) approach without considering SEI layer growth. It is ensured that overpotential caused by lithium plating remains in a healthy regime which is another feature of the proposed strategy. Simulation results are presented to demonstrate the advantages of the proposed charging method.

Self‐Regulating Organic Polymer Coupled with Enlarged Inorganic SnS2 Interlamellar Composite for Potassium Ion Batteries

AbstractTin (Sn)‐based alloy SnS2 has attracted significant attention as a promising candidate for potassium ion storage due to the high theoretical capacity, however, it seriously suffers from the huge volume variation and the growth of potassium dendrites during the repeated cycling process. Herein, hierarchical polyaspartic acid (PASP) modified SnS2 nanosheets embedded into hollow N doped carbon fibers (CN) derived from setaria glauca (PASP@SnS2@CN) are fabricated for potassium storage. PASP cross‐linkers provide the enlarged interlamellar spacing of 6.8 Å (against 5.9 Å for the pristine SnS2), the higher ion transportation channels as well as the self‐regulating dendrite‐free K plating. Consequently, a high reversible capacity (564 mAh g−1 at 50 mA g−1) and a prominent rate performance of 273 mAh g−1 at 2 A g−1 are delivered. Both the experimental data and computational models confirm that a thin and robust solid electrolyte interface (SEI) layer is formed over the dendrite free PASP@SnS2@CN due to the strong interactions (K–N and H+/K+ proton exchange) between the PASP and the electrolyte (KFSI). The deformable and self‐ regulating organic–inorganic configuration is promising for the basis construction of transition metals, has practical applications for K storage.

Unveiling solid electrolyte interface morphology and electrochemical kinetics of amorphous Sb2Se3/CNT composite anodes for ultrafast sodium storage

Sb2Se3 based anodes are widely studied for advanced Na-ion batteries. However, their Na storage performance at high rates is limited to 2000 mA g−1 because of poor kinetics of redox reactions. Here, the heterointerfacial interactions taking place between Sb2Se3 and functionalized CNTs are probed to understand the formation of Sb–O–C and Se–C bonds in the amorphous a-Sb2Se3/CNT composite using the density functional theory and ab-initio molecular dynamics simulations. The distinct morphologies and thicknesses of solid electrolyte interface layers formed on crystalline c-Sb2Se3 and a-Sb2Se3/CNT composite electrodes are revealed by advanced cryogenic transmission electron microscopy and their influences on the kinetics of redox reactions in the corresponding electrodes are identified. The structurally robust a-Sb2Se3/CNT composite electrode exhibits four orders of magnitude higher Na-ion diffusion coefficient than the crystalline c-Sb2Se3 counterpart, giving rise to an exceptional high-rate capacity of 454 mA h g−1 at 12800 mA g−1 and capacity retention of over 62% after 200 cycles at 10000 mA g−1. The full cells containing the composite electrodes present energy and power densities of ∼175 Wh kg−1 at 0.5C and ∼5784 W kg−1 at 80C, respectively, and stable cyclic performance up to 120 cycles.

Bi-Sb Nanocrystals Embedded in Phosphorus as High-Performance Potassium Ion Battery Electrodes.

The development of high-performance potassium ion battery (KIB) electrodes requires a nanoengineering design aimed at optimizing the construction of active material/buffer material nanocomposites. These nanocomposites will alleviate the stress resulting from large volume changes induced by K+ ion insertion/extraction and enhance the electrical and ion conductivity. We report the synthesis of phosphorus-embedded ultrasmall bismuth-antimony nanocrystals (BixSb1-x@P, (0 ≤ x ≤ 1)) for KIB anodes via a facile solution precipitation at room temperature. BixSb1-x@P nanocomposites can enhance potassiation-depotassiation reactions with K+ ions, owing to several attributes. First, by adjusting the feed ratios of the Bi/Sb reactants, the composition of BixSb1-x nanocrystals can be systematically tuned for the best KIB anode performance. Second, extremely small (diameter ≈ 3 nm) BixSb1-x nanocrystals were obtained after cycling and were fixed firmly inside the P matrix. These nanocrystals were effective in buffering the large volume change and preventing the collapse of the electrode. Third, the P matrix served as a good medium for both electron and K+ ion transport to enable rapid charge and discharge processes. Fourth, thin and stable solid electrolyte interface (SEI) layers that formed on the surface of the cycled BixSb1-x@P electrodes resulted in low resistance of the overall battery electrode. Lastly, in situ X-ray diffraction analysis of K+ ion insertion/extraction into/from the BixSb1-x@P electrodes revealed that the potassium storage mechanism involves a simple, direct, and reversible reaction pathway: (Bi, Sb) ↔ K(Bi, Sb) ↔ K3(Bi, Sb). Therefore, electrodes with the optimized composition, i.e., Bi0.5Sb0.5@P, exhibited excellent electrochemical performance (in terms of specific capacity, rate capacities, and cycling stability) as KIB anodes. Bi0.5Sb0.5@P anodes retained specific capacities of 295.4 mA h g-1 at 500 mA g-1 and 339.1 mA h g-1 at 1 A g-1 after 800 and 550 cycles, respectively. Furthermore, a capacity of 258.5 mA h g-1 even at 6.5 A g-1 revealed the outstanding rate capability of the Sb-based KIB anodes. Proof-of-concept KIBs utilizing Bi0.5Sb0.5@P as an anode and PTCDA (perylenetetracarboxylic dianhydride) as a cathode were used to demonstrate the applicability of Bi0.5Sb0.5@P electrodes to full cells. This study shows that BixSb1-x@P nanocomposites are promising carbon-free anode materials for KIB anodes and are readily compatible with the commercial slurry-coating process applied in the battery manufacturing industry.

A superb 3D composite lithium metal anode prepared by in-situ lithiation of sulfurized polyacrylonitrile

Lithium metal has been regarded as the most promising anode for the next generation high energy- density batteries. However, detrimental side reactions with electrolyte, uncontrollable lithium dendrite growth, distinct volume expansion and fragile solid electrolyte interface (SEI) layer lead to low coulombic efficiency (CE), rapid battery failure and even safety hazards, which hinders its practical application. Herein, we propose a novel composite anode which embeds Li metal particles into a Li+/electron hybrid conductive framework and is reinforced by CNTs. Sulfurized pyrolyzed poly(acrylonitrile) (S@pPAN), which is extensively studied as superior cathode materials, is creatively adopted to render abundant Li3N and Li2S on the surface of the Li particles and in the free-space. The in-situ formed hybrid framework not only provides a rapid Li+ transfer channel throughout the electrode, but also suppresses the Li dendrite growth and inhibits the volume expansion. With further assistance of lithiophilic nano-MgO, the composite anode achieved dense and reversible Li plating/striping. As a result, a long cycle life of more than 800 hours with 10 mAh cm−2 and excellent electrode kinetics are obtained for symmetric cells. Moreover, the full cells coupled with S@pPAN and LiFePO4 cathodes deliver a long and stable cycle life. The rational 3D composite anode design provides a feasible strategy to build high performance Li metal batteries.

Mirror-Like Electrodeposition of Lithium Metal under a Low-Resistance Artificial Solid Electrolyte Interphase Layer.

Nonuniform electrodeposition and dendritic growth of lithium metal coupled to its chemical incompatibility with liquid electrolytes are largely responsible for poor Coulombic efficiency and safety hazards preventing the successful implementation of energy-dense Li metal anodes. Artificial solid electrolyte interface (ASEI) layers have been proposed to address the morphological evolution and chemical reactions in Li metal anodes. In this study, an ASEI layer consisting of a lithium phosphorus oxynitride (LiPON) thin film electrolyte and gold-alloying interlayer was developed and shown to promote the electrodeposition of smooth, homogeneous, mirror-like Li metal morphologies. The Au layer alloyed with Li, reducing the nucleation overpotential and resulting in a more spatially uniform metal deposit, while the LiPON layer provided a physical barrier between the Li metal and aprotic liquid electrolyte. The effectiveness and integrity of the LiPON protective layer was assessed using in operando impedance spectroscopy and ex situ SEM/EDS characterization. Smooth, homogeneous Li morphologies were realized in capacities up to 3 mAh cm-2 plated at 0.1 mA cm-2. At higher current densities up to 1 mA cm-2 or increased deposition capacities of 6 mAh cm-2, the LiPON coating fractured due to the localized, nonuniform lithium deposits and rough, dendritic Li morphologies were observed. This approach represents a new strategy in the design of artificial SEIs to enable Li metal anodes with practical areal capacities.

Sodiophilic Zn/SnO2 porous scaffold to stabilize sodium deposition for sodium metal batteries

Sodium is regarded as a promising electrode material in the post lithium ion battery era due to its high theoretical specific capacity of 1166 mAh g−1, low electrochemical potential (−2.71 V vs standard hydrogen electrode), low cost and high natural abundance. However, similar to lithium metal anode, sodium metal anode also shares the problems of uncontrollable dendrites growth, formation of unstable solid electrolyte interface and large volume change during repeated plating/stripping. Herein, a porous sodiophilic zinc metal framework modified with SnO2 surface layer is introduced on copper substrate and used as 3D current collector for sodium metal batteries in order to realize even deposition of Na, moderate the volume change and construct a stable solid electrolyte interface layer simultaneously. Theoretical calculations based on density functional theory are used to interpret the deposition behavior of the metallic Na on different current collectors. The electrochemical performance results show that the Cu/Zn/SnO2@Na symmetric cell can deliver an extremely low nucleation overpotential (0 mV), outstanding long-term rate performance over 1000 h and also can be cycled for around 700 h even at a high current density of 5 mA cm−2 for total capacity of 5 mAh cm−2. Cu/Zn/SnO2@Na//Na3V2(PO4)3 full cell is also constructed to display the feasible application of the designed Cu/Zn/SnO2 porous current collector in advanced sodium metal anode.

Lithium Dendrite Suppression with a Silica Nanoparticle-Dispersed Colloidal Electrolyte.

Developing a safe and long-lasting lithium (Li) metal battery is crucial for high-energy applications. However, its poor cycling stability due to Li dendrite formation and excessive Li pulverization is the major hurdle for its practical applications. Here, we present a silica (SiO2) nanoparticle-dispersed colloidal electrolyte (NDCE) and its design principle for suppressing Li dendrite formation. SiO2 nanoclusters in the NDCE play roles in enhancing the Li+ transference number and increasing the Li+ diffusivity in the vicinity of the Li-plating substrate. The NDCE enables less-dendritic Li plating by manipulating the nucleation-growth mode and extending Sand's time. Moreover, SiO2 can interplay with the electrolyte components at the Li-metal surface, enriching fluorinated compounds in the solid electrolyte interface layer. The initial control of the Li plating morphology and SEI structure by the NDCE leads to a more uniform and denser Li deposition upon subsequent cycling, resulting in threefold enhancement of the cycle life. The efficacy of the NDCEs has been further demonstrated by the practical battery design, featuring a commercial-level cathode and thin Li-metal (40 μm) anode.

Visualizing the growth process of sodium microstructures in sodium batteries by in-situ 23Na MRI and NMR spectroscopy

The growth of sodium dendrites and the associated solid electrolyte interface (SEI) layer is a critical and fundamental issue influencing the safety and cycling lifespan of sodium batteries. In this work, we use in-situ 23Na magnetic resonance imaging (MRI) and nuclear magnetic resonance (NMR) techniques, along with an innovative analytical approach, to provide space-resolved and quantitative insights into the formation and evolution of sodium metal microstructures (SMSs; that is, dendritic and mossy Na metal) during the deposition and stripping processes. Our results reveal that the growing SMSs give rise to a linear increase in the overpotential until a transition voltage of 0.15 V is reached, at which point violent electrochemical decomposition of the electrolyte is triggered, leading to the formation of mossy-type SMSs and rapid battery failure. In addition, we determined the existence of NaH in the SEI on sodium metal with ex-situ NMR results. The poor electronic conductivity of NaH is beneficial for the growth of a stable SEI on sodium metal.

Coupling a Sponge Metal Fibers Skeleton with In Situ Surface Engineering to Achieve Advanced Electrodes for Flexible Lithium-Sulfur Batteries.

Lithium-sulfur batteries (LSBs) are regarded as promising next-generation energy storage systems, however, the uncontrollable dendrite formation and serious polysulfide shuttling severely hinder their commercial success. Herein, a powerful 3D sponge nickel (SN) skeleton plus in situ surface engineering strategy, to address these issues synergistically, is reported, and a high-performance flexible LSB device is constructed. Specifically, the rationally designed spray-quenched lithium metal on the SN matrix (solid electrolyte interface (SEI)@Li/SN), as dendrite inhibitor, combines the merits of the 3D lithiophilic SN skeleton and the in situ formed SEI layer derived from the spray-quenching process, and thereby exhibits a steady overpotential within 75 mV for 1500 h at 5 mA cm-2 /10 mA h cm-2 . Meanwhile, in situ surface sulfurization of the SN skeleton hybridizing with the carbon/sulfur composite (SC@Ni3 S2 /SN) serves as efficient lithium polysulfide adsorbent to catalyze the overall reaction kinetics. COMSOL Multiphysics simulations and density functional theory calculations are further conducted to explore the underlying mechanisms. As a proof of concept, the well-designed SEI@Li/SN||SC@Ni3 S2 /SN full cell shows excellent electrochemical performance with a negative/positive ratio in capacity of ≈2 and capacity retention of 99.82% at 1 C under mechanical deformation. The novel design principles of these materials and electrodes successfully shed new light on the development of flexible LSBs.