Huge Volume Variation Research Articles

Reversible silicon anodes enabled by fluorinated inorganic-organic hybrid coating

Silicon anodes deliver batteries with energy densities much higher than those based on today’s dominant graphite anodes. However, they commonly exhibit huge volume variations and unfavorable interface stability, causing a gradually diminishing capacity on extended cycling. Most Si-based batteries consisting Si/C composites in industry can only use a very limited amount of Si (<30 % by weight). Exploiting molecular layer deposition (MLD) technique, a fluorine-rich flexible inorganic–organic hybrid alucone (AlFHQ) shell is controllably deposited onto Si electrodes. Employing ex situ XPS and AFM, the AlFHQ film presents reversible electrochemical evolutions in terms of composition and morphology. The interactions the between Li+ and −O−2,3,5,6-fluorobenzene functional groups help to construct a mechanically-chemically robust LiF-rich hybrid solid electrolyte interphase (SEI) on Si anode, delivering enhanced interfacial stability and integrity of electrode. An optimized coating thickness (≈5 nm) for interfacial stabilization and Li+ transport kinetics is demonstrated, namely, Si@AlFHQ-20. The reported fluorine-rich hybrid modification technique endows (a), stable cycling of Si anode (≈3.8 mAh cm−2) with an ultrahigh initial Coulombic efficiency (ICE) of 92.3 %; (b), enhanced rate capability of 1468 mAh/g at 2.0 A g−1 and good cycling performance; and (c), overall cell (Si@AlFHQ-20//LiCoO2@Al2O3) operational stability for more than 100 cycles under stringent cathode conditions (2.68 mAh cm−2, high cutoff voltage at 4.55 V).

Anchored Bi with cobalt polyphthalocyanine enhances the reversibility of Bi2Te3 anode for endurable lithium-ion storage

As an intermetallic material, Bi2Te3 possesses great potential in lithium-ion batteries due to its attractive layered structure, intrinsic excellent conductivity and impressive theoretical specific capacity. However, the phase decomposition and the huge volume variation leading to rapid capacity fading hinder the further application of Bi2Te3 in lithium-ion batteries. In this study, two dimensional Bi2Te3 encapsulated in cobalt polyphthalocyanine (CoPPc) is synthesized by a facile recrystallization method, and its electrochemical properties and lithium storage mechanism are comprehensively studied. The Bi2Te3@CoPPc electrodes exhibit outstanding cycling stability with a specific capacity of 551.9 mAh g−1 at 100 mA g−1 and 628.5 mAh g−1 at 500 mA g−1 after 500 cycles, benefiting from the configured composite layered structure and the amiable interaction of Bi2Te3 and CoPPc. Our experimental and theoretic results demonstrate that the electron redistribution induced by the incorporation of CoPPc with charge accumulation around Bi2Te3 and low potential region around Co efficiently facilitates the fast lithium-ion transportation resulting in outstanding rate performance. Our explorative strategy of electron redistribution proposes a new avenue to enhance the catalysis activity and durability of alloy anodes in metal-ion batteries.

Amorphous titanium dioxide and polyaniline dual modifying silicon for highly enhanced lithium-ion storage

Silicon (Si) anode material is promising in the next generation of lithium-ion batteries (LIBs) with high energy densities for its much higher capacity (4200 mAh/g) than that of commercial graphite (372 mAh/g). However, silicon anode material with low electronic conductivity suffers a huge volume variation and accompanies side reactions during alloyed and de-alloyed process. Here, we design an inner amorphous titanium dioxide (TiO2) and an outer flexible conductive polyaniline (PANI) network dual modified Si@TiO2@PANI material for LIBs, where the TiO2 avoids the side reactions and the PANI network layer buffers the volume expansion and increases the electronic conductivity. The as-prepared Si@TiO2@PANI exhibits a high initial discharge capacity of 3050 mAh/g and maintains 1583 mAh/g after 200 cycles at 0.5 A/g. It even delivers the discharge capacity of 1002 mAh/g after 600 cycles at 1 A/g, as well as an excellent rate ability with discharge capacity of 1890, 1260 and 432 mAh/g at the high current density of 1, 2 and 5 A/g, respectively. Our strategy shows that the innovative design of double buffer layers on Si can synergistically promote stability and accelerate kinetics of Li+ transport, offering novel resolution strategy to enhance the performance of Si-based anodes for LIBs.

Facile Galvanic Replacement Construction of Bi@C Nanosheets Array as Binder‐Free Anodes for Superior Sodium‐Ion Batteries

AbstractBismuth (Bi) possesses an ultrahigh theoretical volume capacity (3800 mAh cm−3) and low embedding potential stimulated considerable attention as anodes for sodium‐ion batteries (SIBs). However, its practical application is still hampered by the huge volume variation during the charge/discharge process. To settle this issue, Bi@C nanosheet arrays (Bi@C‐NSA) are fabricated on copper foam via a facile galvanic replacement followed by in situ polymerization of dopamine and an annealing procedure. The carbon‐coated nanosheet array structure not only accommodates the volume expansion during cycling and maintains electrode stability, but also facilitates rapid electron/ion transport. Due to the unique structural design, this Bi@C‐NSA exhibits an impressive capacity of 315.72 mAh g−1 after 1500 cycles under 1 A g−1. Furthermore, a series of in situ/ex situ techniques reveal that this Bi@C‐NSA possesses superior reaction kinetics and undergoes a typical alloying/dealloying storage mechanism. Furthermore, Bi@C‐NSA also achieves commendable reversible capacity and cycling stability in a wide temperature range (0 °C–60 °C). Notably, the assembled Na3V2(PO4)3//Bi@C‐NSA full cell demonstrates a capacity of 325 mAh g−1 after 50 cycles at 0.05 A g−1, which promises for practical applications. This galvanic replacement strategy spearheads a way to prepare nanoarray electrodes and will accelerate the development of sodium‐ion batteries.

Enhanced redox kinetics in hierarchical tubular FeSe2 by incorporating Se quantum dots towards high-performance sodium-ion batteries

Metal selenides have emerged as promising Na-storage anode materials owing to their substantial theoretical capacity and high cost-effectiveness. However, the application of metal selenides is hindered by inferior electronic conductivity, huge volume variation, and sluggish kinetics of ionic migration. In response to these challenges, herein, a hierarchical hollow tube consisting of FeSe2 nanosheets and Se quantum dots anchored within a carbon skeleton (HT-FeSe2/Se/C) is strategically engineered and synthesized. The most remarkable feature of HT-FeSe2/Se/C is the introduction of Se quantum dots, which could lead to high electron density near the Fermi level and significantly enhance the overall charge transfer capability of the electrode. Moreover, the distinctive hollow tubular structure enveloped by the carbon skeleton endows the HT-FeSe2/Se/C anode with robust structural stability and fast surface-controlled Na-storage kinetics. Consequently, the as-synthesized HT-FeSe2/Se/C demonstrates a reversible capacity of 253.5 mAh/g at a current density of 5 A/g and a high specific capacity of 343.9 mAh/g at 1 A/g after 100 cycles in sodium-ion batteries (SIBs). Furthermore, a full cell is assembled with HT-FeSe2/Se/C as the anode, and a vanadium-based cathode (Na3V2(PO4)2O2F), showcasing a high specific capacity of 118.1 mAh/g at 2 A/g. The excellent performance of HT-FeSe2/Se/C may hint at future material design strategies and advance the development and application of SIBs.

Inorganic/organic composite binder with self-healing property for silicon anode in lithium-ion battery

Silicon (Si) has garnered significant attention as a high-capacity anode material in high-energy density lithium-ion batteries (LIBs). Nevertheless, the huge volume variation of Si (>300%) during cycling results in rapid capacity deterioration, thereby impeding its commercial application. To confront this challenge, inorganic binder has been identified as a highly promising solution for Si anode due to its high bonding strength. Despite its effectiveness, the inorganic binder's limited elasticity hinders the rejuvenation of the impaired electrode structure. Hence, we devised an elasticity and self-healing composite binder, incorporating both inorganic and organic binders. The inorganic lithium metasilicate not only offers ample adhesion sites to Si but also establishes a protective coating layer on SiNPs. Simultaneously, the organic poly (vinyl alcohol) featuring a low glass transition temperature (72 °C) furnishes elasticity and a self-healing framework. Consequently, the Si anode shows exemplary cycling and rate performances. Additionally, the Si||NCM811 full cell attains a reversible capacity of 1.86 mAh/cm2 with a capacity retention of 67% after 50 cycles, indicating the commercial application potential of the composite binder. This study thus explores design strategies for composite binders, paving the way for high-performance Si anode.

Fe2O3 nanoparticles encapsulated in the inner walls of integrated 3D carbon tube grid as high-performance anode for lithium-ion batteries

Ferric oxide (Fe2O3) holds huge potential as a promising anode material for lithium-ion batteries (LIBs) due to its high theoretical capacity and low cost, however, its battery performance is still limited by the intrinsic poor conductivity and huge volume variation during lithiation and de-lithiation processes. Herein, we developed a self-standing 3D interconnected vertical and lateral carbon tube (3D-CT) grid with Fe2O3 nanoparticles (NPs) encapsulated in the wall of CT (denoted as 3D-CT@Fe2O3-NPs@C), as structurally-integrated anode without any inactive components. The 3D-interconnected vertical and lateral CTs with open channels not only provide plenty of attachment sites for the Fe2O3 NPs and accommodate the strain generated by the volume variation of Fe2O3, but also facilitate the fast ions and electrons transfer. Therefore, the self-supported 3D-CT@Fe2O3-NPs@C electrode delivers superior cycling and high-rate performance with a high stable specific capacity of 896.2 mAh g−1 at the current density of 1.0 A g−1 after 700 cycles. Even at the high current density of 4.0 A g−1, a reversible capacity of 488.1 mAh g−1 can be reached based on the mass of the electrode. This study provides a facile and efficient strategy to improve the electrochemical performance of LIBs through the design of structurally-integrated grid electrode.

Nanocomposites of Conducting Polymers and 2D Materials for Flexible Supercapacitors.

Flexible supercapacitors (FSCs) with high electrochemical and mechanical performance are inevitably necessary for the fabrication of integrated wearable systems. Conducting polymers with intrinsic conductivity and flexibility are ideal active materials for FSCs. However, they suffer from poor cycling stability due to huge volume variations during operation cycles. Two-dimensional (2D) materials play a critical role in FSCs, but restacking and aggregation limit their practical application. Nanocomposites of conducting polymers and 2D materials can mitigate the above-mentioned drawbacks. This review presents the recent progress of those nanocomposites for FSCs. It aims to provide insights into the assembling strategies of the macroscopic structures of those nanocomposites, such as 1D fibers, 2D films, and 3D aerogels/hydrogels, as well as the fabrication methods to convert these macroscopic structures to FSCs with different device configurations. The practical applications of FSCs based on those nanocomposites in integrated self-powered sensing systems and future perspectives are also discussed.

Graphene–Encapsulated Si@C with Dual Carbon Layer Structure as High‐Performance Anode Materials for Lithium–Ion Batteries

AbstractSilicon–based materials are among the highly promising anode candidates for Li–ion batteries owing to their excellent theoretical energy density. However, the huge volume variation makes the application of silicon anode in lithium–ion batteries be full of challenge. Herein, high–performance Si@C@rGO composites anode for lithium–ion batteries are successfully prepared by graphene oxide (GO) uniformly encapsulating resorcinol–formaldehyde resin (RF) coated silicon nanoparticles. The RF‐derived carbon layer can prevent the silicon from direct contact with the electrolyte. Furthermore, the continuous conductive graphene network not only improves the overall electrical conductivity of the composite material, but also can be reversibly deformed with the volume change of silicon during the charging and discharging process, thus greatly improving the structural stability of the anode. The optimal Si@C@rGO‐2 composite provides a high specific capacity of 743.9 mAh g−−1 after 300 cycles at a current density of 1 A g−1. Meanwhile, the material also exhibits good rate performance, showing a good reversible capacity of 719.5 mAh g−1 even at a high current density of 2 A g−1. In addition, this simple and low‐cost strategy of Si@C@rGO anode can provide a design reference for the further development of anode materials in lithium–ion batteries.

Peapod-Like Structured B/N Co-Doped Carbon Nanotube Array Encapsulating MxPy (M = Fe, Co, and Ni) Nanoparticles for High-Rate Potassium Storage.

Potassium-ion batteries (PIBs) have become the desirable alternatives for lithium-ion batteries (LIBs) originating from abundant reserves and appropriate redox potential, while the considerable radius size of K+ leading to poor reaction kinetics and huge volume expansion limits the practical application of PIBs. Hybridization of transition-metal phosphides and carbon substrates can effectively optimize the obstacles of poor conductivity, sluggish kinetics, and huge volume variation. Thus, the peapod-like structural MxPy@BNCNTs (M = Fe, Co, and Ni) composites as anode materials for PIBs were synthesized through a facile strategy. Notably, the unique architecture of B/N codoped carbon nanotube array as fast ion/electron transfer pathways effectively improves the electronic conductivity of composites. The MxPy nanoparticles (NPs) are encapsulated in BNCNTs with an amorphous carbon layer (5-10 nm), which discernibly alleviate the volume changes during potassiation/depotassiation. In conclusion, the composites show a commendable cycling performance, possessing reversible capacities of 111, 152, and 122 mA h g-1 after 1000 cycles at 1.0 A g-1 with a negligible capacity loss for FeP@BNCNT, CoP/Co2P@BNCNT, and Ni2P@BNCNT electrodes, respectively. Especially, after 1000 cycles at 2.0 A g-1, the CoP/Co2P@BNCNT electrode still possesses a capacity of 87.9 mA h g-1, demonstrating excellent rate performance and long-term life. This work may offer an innovative and viable route to construct a stable architecture for solving the issue of poor stability of TMP-based anodes at a high current density.

(Invited) Binder Investigation for Silicon Electrode of Lithium-Ion Batteries

Though the binder is not an active material and does not contribute capacity to lithium ion batteries (LIBs), it is an important ingredient for maintaining the integrity of the electrode, which helps to improve electrical contact between the active materials and conductive carbon black, improves the Li+ transport efficiency, reduces the internal resistance of Li-ion batteries and effectively depresses the crack formations and phase separation.Polyvinylidene fluoride (PVDF) is a polymer that is commonly used as a binder for both anode and cathode materials in LIBs. However, it is not suitable for Si electrode due to its poor binding capability and stability. Viewed as a next generation anode material, Si has been extensively studied due to its extremely high theoretical specific capacity of 3578 mAh/g (assuming Li15Si4 as intermediate product). However, silicon undergoes huge volume variations during repeated discharge and charge, which requires a strong binder to maintain the electrode mechanical integrity. Developing a high strength binder for silicon anodes has been considered as an efficient pathway to alleviate various capacity decay pathways.Polyacrylic acid (PAA) and its lithiated version (LiPAA), rich with carboxy function group, can provide stronger binding and are widely used as binder for Si electrode. In this work, we optimized Si electrode formulation by varying the binder composition. The optimized Si electrodes were electrochemically tested in both half cells and full cells. With improvement in electrochemical performance, cracks at the electrode level can still be observed for the cycled electrodes, which suggests that a stronger binder is required to mitigate volume expansion of Si electrodes and hold the particles together.We further studied the polyimide (PI) materials as binders for Si anodes in an attempt to achieve more stable cycling performance. In this work, we explore various PI crosslinking conditions and their effects on electrochemical performance. The optimized silicon electrode exhibits a higher tensile strength than that of conventional PAA binder. The strong adhesion of the PI binder suppresses the structural collapse of the Si negative electrode during lithiation/delithiation, enabling good capacity retention and stable cycle life.

Carbon coated Bi2S3 microwires as anode for enhanced lithium storage

As a typical metal sulfide, Bi2S3 is intensively explored for its high capacity. However, the capacity decays quickly because of its intrinsic poor conductivity and huge volume variation. Therefore, carbon coated Bi2S3 microwires (Bi2S3@C) are synthesized via facile hydrothermal and subsequent annealing procedure to improve lithium storage. The composite manifests a high capacity of 661 mAh g−1 at 0.1 A g−1 after 100 cycles. It exhibits excellent rate capability, delivering the capacity of 757 mAh g−1 at 0.1 A g−1 and 331 mAh g−1 even at the high current density of 10 A g−1. The composite also shows good cycling stability. It delivers a high capacity of 456 mAh g−1 at 2 A g−1 after 1000 cycles. The good lithium storage capability is ascribed to the synergistic effect of dwindled size and amorphous carbon coating layer. The carbon layer not only improves the electronic conductivity but also relaxes the strain upon cycling.

Fast and Long‐Lasting Potassium‐Ion Storage Enabled by Rationally Engineering Strain‐Relaxation Bi/Bi2O3 Nanodots Embedded in Carbon Sheets

AbstractBismuth (Bi)‐based materials merit high theoretical volumetric specific capacity (3800 mAh mL⁻1) but suffer from huge volume variations and sluggish reaction kinetics during cycling. Herein, the optimal framework of Bi/Bi2O3 nanodots enriched in suitable outer amorphous carbon sheets (Bi/Bi2O3 NDs@CSs) is first proposed to alleviate volume variations and accelerate stable charge transport to boost K+ storage performance. The introduction of proper Bi2O3 not only provides an efficient K+ adsorption path, but also effectively buffers volume changes via conversion reaction. Accordingly, the as‐prepared anode exhibits a remarkable rate capability (149.3 mAh g−1 at 60 A g−1, 42% capacity retention with a 120‐fold current‐density increase) and extraordinary durability (1800 cycles at 5.0 A g−1, 95% capacity retention), among the best rate and cycling performance to date in potassium ion batteries (PIBs) anodes. Theoretical calculations reveal the feasible structures of Bi/Bi2O3 NDs@CSs with double protection of carbon sheets and Bi2O3 are conducive to enhance charge transfer and efficiency of electrochemical reaction. Substantial in situ/ex situ characterizations and finite element simulation further unveil high reversibility and robust mechanical behavior of Bi/Bi2O3 NDs@CSs, favorable for the reinforcement of structural stability. This study provides new insights into developing high‐performance and durable Bi‐based anodes for PIBs.

Advanced inorganic lithium metasilicate binder for high-performance silicon anode

Silicon (Si) is considered a high-capacity anode material with potential for next-generation lithium-ion batteries. However, the commercial application of Si anode is seriously hindered by huge volume variation (>300%) and limited Li+ diffusion ability. Herein, lithium metasilicate (LS), a novel inorganic binder, was innovatively developed to accommodate these challenges. Favorable compatibility is observed between the LS binder and Si nanoparticles (SiNPs) due to the existence of Si element within the LS skeleton. The interaction of the LS binder and SiNPs leads to a strong adhesion effect, enhancing the cycling stability of Si anode. The Si electrode with the LS binder presented an average discharge capacity of 2123 mAh/g at 0.84 A/g after 100 cycles. Furthermore, the presence of the Li+ transport channel within the LS binder enhances Li+ diffusion ability within Si anode. As a result, the average discharge capacity reaches 663 mAh/g at 8.4 A/g. This work thus explored new inorganic binder design approaches for Si anode, contributing to the advancement of high-performance Si anode.

Layer stacked SiOx microparticle with disconnected interstices enables stable interphase and particle integrity for lithium-ion batteries

Severe mechanical fracture and unstable interphase, associated with the large volumetric expansion/contraction, significantly hinder the application of high-capacity SiOx materials in lithium-ion batteries. Herein, we report the design and facile synthesis of a layer stacked SiOx microparticle (LS-SiOx) material, which presents a stacking structure of SiOx layers with abundant disconnected interstices. This LS-SiOx microparticle can effectively accommodate the volume expansion, while ensuring negligible particle expansion. More importantly, the interstices within SiOx microparticle are disconnected from each other, which efficiently prevent the electrolyte from infiltration into the interior, achieving stable electrode/electrolyte interface. Accordingly, the LS-SiOx material without any coating delivers ultrahigh average Coulombic efficiency, outstanding cycling stability, and full-cell applicability. Only 6 cycles can attain >99.92% Coulombic efficiency and the capacity retention at 0.05 A g−1 for 100 cycles exceeds 99%. After 800 cycles at 1 A g−1, the thickness swelling of LS-SiOx electrode is as low as 0.87%. Moreover, the full cell with pure LS-SiOx anode exhibits capacity retention of 91.2% after 300 cycles at 0.2 C. This work provides a novel concept and effective approach to rationally design silicon-based and other electrode materials with huge volume variation for electrochemical energy storage applications.

Cobalt-doping-induced ultrathin solid-electrolyte interphase construction and shuttle effect inhibition in Cu3PS4-carbon nanotube hybrid enabling superior potassium-ion storage

Ternary transition-metal phosphorus chalcogenides have intriguing properties as anodes for K-ion batteries, such as diverse compositions, abundant resources, high theoretical capacities, and multiplex redox reactions. However, they mostly suffer from intermediate polysulfides shuttling, huge volume variations, sluggish kinetics, and poor conductivity, leading to rapid decay of electrochemical performance. To efficiently exploit their advantages, we introduce a simple heteroatom transition-metal (Co, Fe, Ni) doping strategy to a Cu3PS4-carbon nanotube heterostructure for the first time. The doping of Co particles into Cu3PS4-carbon nanotube (CPSC/Co) hybrid concurrently alleviates volumetric changes, causes the formation of a thin solid-electrolyte interphase film, suppresses the dissolution of soluble potassium polysulfides into the electrolyte, hinders the agglomeration of discharging/recharging products, and boosts the reversibility of redox reactions during potassiation/depotassiation processes. The CPSC/Co hybrid thus delivers an excellent initial Coulombic efficiency (86.1%), outstanding cyclic stability (489 mAh g−1 after 300 cycles at 0.2 A g−1), and high rate capability (291 mAh g−1 at 2 A g−1). Our findings demonstrate that transition-metal doping can rationally modulate the morphology and composition of solid-electrolyte interphase films and alter the discharging/charging reactions in metal-ion batteries.

Lithium Azides Induced SnS Quantum Dots for Ultra-Fast and Long-Term Sodium Storage.

Tin sulfide (SnS) is an attractive anode for sodium ion batteries (NIBs) because of its high theoretical capacity, while it seriously suffers from the inherently poor conductivity and huge volume variation during the cycling process, leading to inferior lifespan. To intrinsically maximize the sodium storage of SnS, herein, lithium azides (LiN3 )-induced SnS quantum dots (QDs) are first reported using a simple electrospinning strategy, where SnS QDs are uniformly distributed in the carbon fibers. Taking the advantage of LiN3 , which can effectively prevent the growth of crystal nuclei during the thermal treatment, the well-dispersed SnS QDs performs superior Na+ transfer kinetics and pseudocapacitive when used as an anode material for NIBs. The 3D SnS quantum dots embedded uniformly in N-doped nanofibers (SnS QDs@NCF) electrodes display superior long cycling life-span (484.6mAhg-1 after 5800 cycles at 2Ag-1 and 430.9mAhg-1 after 7880 cycles at 10Ag-1 ), as well as excellent rate capability (422.3mAhg-1 at 20Ag-1 ). This fabrication of transition metal sulfides QDs composites provide a feasible strategy to develop NIBs with long life-span and superior rate capability to pave its practical implementation.

Constructing strain-alleviated structures in ultrathin FeS/C composites for durable lithium and sodium storage

Iron sulfide (FeS) is a competitive anode material for Li-/Na-ion batteries (LIBs/SIBs) with high specific capacity and excellent environmental benignity. Nevertheless, its practical application is greatly hindered by the sluggish charge transfer dynamics and large volume variations upon cycling. Herein, by constructing a strain-alleviated (bubble film-like) structure in an ultrathin FeS/C composite, the sluggish transfer kinetics and huge volume variations of FeS were fundamentally solved. The bubble film-like carbon matrix serves as the protective shell to alleviate the huge volume changes of FeS and enhance its electronic conductivity, as verified by finite element simulation and ex-situ transmission electron microscopy results. Benefiting from this unique design, the as-designed electrode exhibited a significantly enhanced performance with a high discharge capacity of 469 mA h g−1 at 5 A g−1 for LIBs and 354 mA h g−1 after 1500 cycles at 1 A g−1 for SIBs. Moreover, the full cell with this electrode and LiFePO4 cathode can deliver outstanding cycling stability of 558 mA h g−1 even after 100 cycles. We expect that this strategy can also be applied to other anode materials plagued by poor conductivity and huge volume changes and remarkably spur the development of batteries with high rate capability and long lifespan.

Structure and Interface Engineering of Ultrahigh-Rate 3D Bismuth Anodes for Sodium-Ion Batteries.

Sodium-ion batteries (SIBs) have attracted tremendous attention as promising low-cost energy storage devices in future grid-scale energy management applications. Bismuth is a promising anode for SIBs due to its high theoretical capacity (386mAhg-1 ). Nevertheless, the huge volume variation of Bi anode during (de)sodiation processes can cause the pulverization of Bi particulates and rupture of solid electrolyte interphase (SEI), resulting in quick capacity decay. It is demonstrated that rigid carbon framework and robust SEI are two essentials for stable Bi anodes. A lignin-derived carbonlayer wrapped tightly around the bismuth nanospheres provides a stable conductive pathway, while the delicate selection of linear and cyclic ether-based electrolytes enable robust and stable SEI films. These two merits enable the long-term cycling process of the LC-Bi anode. The LC-Bi composite delivers outstanding sodium-ion storage performance with an ultra-long cycle life of 10 000 cycles at a high current density of 5Ag-1 and an excellent rate capability of 94% capacity retention at an ultrahigh current density of 100Ag-1 . Herein, the underlying origins of performance improvement of Bi anode are elucidated, which provides a rational design strategy for Bi anodes in practical SIBs.

Restraining volume expansion via ultra-elastic polydimethylsiloxane/carbon nanotubes coatings toward high performance FeS2 cathode

Pyrite FeS2 is considered a promising conversion cathode material due to its high energy density, low cost, and environmental benignity. However, its huge volume variation induced particle pulverization and slow kinetic properties during cycling are the main obstacles to further commercial applications. In this work, a dual-functional polydimethylsiloxane/carbon nanotubes(PDMS/CNTs) coating layer is introduced to overcome these drawbacks. The ultra-elastic PDMS layer can hold the drastic volume change and protect FeS2 from pulverization. Meanwhile, the carbon nanotubes dispersed in PDMS can function as highways to facilitate electron transport kinetics. As a result, FeS2@PDMS-CNTs display a better discharge specific capacity of 559 mAh·g−1, while bare FeS2 only shows an inferior discharge specific capacity of 235 mAh·g−1 after 100 cycles. This work provides a straightforward coating strategy for the formation of a conductively elastic core-shell composite to improve electrochemical performances for the conversion-type reaction materials.