Large Volume Change Research Articles

A composite phase change material with large volume change rate for thermal underwater glider

The thermal underwater glider (TUG) is an important device currently used for exploring ocean resources and monitoring ocean temperature. The TUG harvests ocean thermal energy (OTE) through working medium and converts into net buoyancy variation for propulsion. The phase change material (PCM) filled in the thermal engine is the key working fluid for the TUG to harvest OTE. A large volume change rate of PCM at ocean temperature difference is important for improving the TUG's efficiency and performance. Previous studies focus on N-hexadecane for OTE conversion with limited performance. This paper proposes N-hexadecane (C16) based composite PCM for an improved thermal-to-mechanical conversion process. The experimental test results show that the composite PCM (C16:C24 = 9:1 wt%) exhibits a similar phase transition temperature (17.8–18.4℃) with C16 (18.2–18.6℃). As compared to pure C16, the volume shrinkage of this composite PCM was 26.67% higher than that of C16 and the volume expansion rate was 30.74% higher than that of C16, indicating that the composite PCM based TUG could output more net buoyancy variation and propulsion power. Following experimental test, molecular dynamics simulation of the composite PCM is carried out. The reason for this volume expansion/shrinkage improvement was revealed as the larger C–C bond length and H–C–C bond angle variations. The composite materials provided in this paper could potentially improve the propulsion performance of TUG.

In Situ Raman Mapping of Si Island Electrodes and Stress Modeling as a Function of Lithiation and Size.

Si is known for cracking and delamination during electrochemical cycling of a battery due to the large volume change associated with Li insertion and extraction. However, it has been found experimentally that patterned Si island electrodes that are 200 nm thick and less than 7 μm wide can deform in a purely elastic manner. Inspired by this, we performed in situ Raman stress characterization of model poly-crystalline Si island electrodes using an electrochemical cell coupled with an immersion objective lens and designed for a short working distance. A 5 μm wide Si island electrode showed a parabolic stress profile during lithiation, while for a 15 μm Si island electrode, a stress plateau in the center of the electrode was observed. A continuum model with coupled electro-chemo-mechanical (ECM) physics was established to understand the stress measurement. A qualitative agreement was reached between modeling and experimental data, and the critical size effect could be explained by the Li diffusive flux as governed by competition between the Li concentration and hydrostatic stress gradients. Below the critical size, the stress gradient drives Li toward the edges, where the electrode volume is free to expand, while above the critical size, the stress plateau inhibits Li diffusion to the edge and forces destructive stress relief by cracking. This work represents a promising methodology for in situ characterization of ECM coupling in battery electrodes, with suggestions provided for further improvement.

Ti3C2Tx MXene wrapped, carbon-coated porous Si sheets for improved lithium storage performance

Si-based materials have shown great potential as lithium-ion batteries (LIBs) anodes due to their natural reserves and high theoretical capacity. However, the large volume changes during cycles and poor conductivity of Si lead to rapid capacity decay and poor cycling stability, ultimately limiting their commercial applications. Herein, we have skillfully utilized the microporous MCM-22 zeolite as the unique silicon source to produce porous Si (pSi) sheets by a simple magnesiothermic reduction, followed by a carbon coating and further Ti3C2Tx MXene assembly, obtaining the ternary pSi@NC@TNSs composite. In the design, porous Si sheets provide more active sites and shorten Li-ion transport paths for electrochemical reactions. The N-doped carbon (NC) layer serves as a bonding layer to couple pSi and Ti3C2Tx. The conductive network formed by 2D Ti3C2Tx and medium NC layer effectively enhances the overall charge transport of the electrode material, and helps to stabilize the electrode structure. Therefore, the as-made pSi@NC@TNSs anode delivers an improved lithium storage performance, exhibiting a high reversible capacity of 925 mAh/g at 0.5 A/g after 100 cycles. This present strategy provides an effective way towards high-performance Si-based anodes for LIBs.

Synthesized Fe-doped Co3O4 nanoparticles-based anode for high-performance lithium-ion batteries application

ABSTRACT Co3O4 has been considered a promising anode material because of its high theoretical capacity (890 mAh/g) and remarkable energy density. Unfortunately, it suffers from low initial coulombic efficiency, rapid capacity fading, poor electronic conductivity, large volume changes, and aggregation during the lithium ion intercalation/deintercalation process. In this work, a series of Fe2+-doped Co3O4 nanostructured materials Co3(1-x)Fe3xO4 (x = 0, 0.01, 0.02 and 0.03) were produced by a simple chemical co-precipitation method. The Fe doping led to a slight increase of the lattice parameter, which is beneficial to the rapid diffusion of Li+ ion during the lithiation/delithiation process. Meanwhile, the Fe-doped Co3O4 sample exhibited an excellent rate capability of 886.47 mAh/g at 500 mA/g, and outstanding cyclic stability (1156.91 mAh/g for 50 cycles, with the capacity retention rate of 83.53% at the current density of 100 mA/g), demonstrating improved electrochemical performance, compared with that of pure Co3O4. The good electrochemical performance profited from the formation of oxygen vacancies by Fe doping, which provided more space for Li+ diffusion and improved the electronic conductivity of the anode material. This work provides a simple way to improve the comprehensive electrochemical performance of the transitional metal oxide Co3O4 anode electrodes for lithium-ion batteries.

Constructing Hierarchical Porous MoO2 @Mo2 N@C Composite via a Confined Pyrolysis Synthetic Strategy Towards Lithium-Ion Battery Anodes.

Molybdenum dioxide (MoO2 ) demonstrates a big potential toward lithium-ion storage due to its high theoretical capacity. The sluggish reaction kinetics and large volume change during cycling process, however, unavoidably lead to inferior electrochemical performance, thus failing to satisfy the requirements of practical applications. Herein, we developed a molybdenum-based oxyacid salt confined pyrolysis strategy to achieve a novel hierarchical porous MoO2 @Mo2 N@C composite. A two-step successive annealing process was proposed to obtain a hybrid phase of MoO2 and Mo2 N, which was used to further improve the electrochemical performance of MoO2 -based anode. We demonstrate that the well-dispersed MoO2 nanoparticles can ensure ample active sites exposure to the electrolyte, while conductive Mo2 N quantum dots afford pseudo-capacitive response, which conduces to the migration of ions and electrons. Additionally, the interior voids could provide buffer spaces to surmount the effect of volume change, thereby avoiding the fracture of MoO2 nanoparticles. Benefiting from the aforesaid synergies, the as-obtained MoO2 @Mo2 N@C electrode demonstrates a striking initial discharge capacity (1760.0 mAh g-1 at 0.1 A g-1 ) and decent long-term cycling stability (652.5 mAh g-1 at 1.0 A g-1 ). This work provides a new way for the construction of advanced anode materials for lithium-ion batteries.

Enhanced Lithium Storage Performance of α-MoO3/CNTs Composite Cathode.

Orthorhombic molybdenum oxide (α-MoO3), as a one-layered pseudocapacitive material, has attracted widespread attention due to its high theoretical lithium storage specific capacity (279 mAh/g) for lithium-ion batteries' cathode. Nevertheless, low conductivity, slack reaction kinetics, and large volume change during Li+ ions intercalation and deintercalation seriously limit the practical application of α-MoO3. Herein, we added a small number of CNTs (1.76%) to solve these problems in a one-step hydrothermal process for preparing the α-MoO3/CNTs composite. Because of the influence of CNTs, the α-MoO3 nanobelt in the α-MoO3/CNTs composite had a larger interlayer spacing, which provided more active sites and faster reaction kinetics for lithium storage. In addition, CNTs formed a three-dimensional conductive network between α-MoO3 nanobelts, enhanced the electrical conductivity of the composite, accelerated the electron conduction, shortened the ion transport path, and alleviated the structural fragmentation caused by the volume expansion during the α-MoO3 intercalation and deintercalation of Li+ ions. Therefore, the α-MoO3/CNTs composite cathode had a significantly higher rate performance and cycle life. After 150 cycles, the pure α-MoO3 cathode had almost no energy storage, but α-MoO3/CNTs composite cathode still retained 93 mAh/g specific capacity.

The role, formation and characterization of LiC6 in composite lithium anodes

To solve the problems of large volume changes and the formation of lithium dendrites in lithium metal batteries, the incorporation of carbon into the lithium metal anodes has gained considerable attention due to its excellent chemical and electrochemical stability, as well as its exceptional mechanical strength that allows repeated cycling. This review provides a comprehensive overview of the formation of lithiated graphite (LiC6) and its role in both bulk and electrode-electrolyte interface regions during lithium plating and stripping. In bulk form, LiC6 has excellent lithiophilic properties, reducing the overpotential for lithium nucleation and promoting uniform lithium deposition. Additionally, when LiC6 is introduced at the electrode-electrolyte interfaces, it improves contact between the electrode and electrolyte by acting as a buffering layer, thereby reducing interfacial impedance. Finally, prospects and challenges for the development of Li/C composite anodes are discussed.

Constructing Pure Si Anodes for Advanced Lithium Batteries.

ConspectusWith the escalating demands of portable electronics, electric vehicles, and grid-scale energy storage systems, the development of next-generation rechargeable batteries, which boasts high energy density, cost effectiveness, and environmental sustainability, becomes imperative. Accelerating these advancements could substantially mitigate detrimental carbon emissions. The pursuit of main objectives has kindled interest in pure silicon as a high-capacity electroactive material, capable of further enhancing the gravimetric and volumetric energy densities compared with traditional graphite counterparts. Despite such promising attributes, pure silicon materials face significant hurdles, primarily due to their drastic volumetric changes during the lithiation/delithiation processes. Volume changes give rise to severe side effects, such as fracturing, pulverization, and delamination, triggering rapid capacity decay. Therefore, mitigating silicon particle fracture remains a primary challenge. Importantly, nanoscale silicon (below 150 nm in size) has shown resilience to stresses induced by repeated volume changes, thereby highlighting its potential as an anode-active material. However, the volume expansion stress not only affects the internal structure of the particle but also disrupts the solid-electrolyte interphase (SEI) layer, formed spontaneously on the outer surface of silicon, causing adverse side reactions. Therefore, despite silicon nanoparticles offering new opportunities, overcoming the associated issues is of paramount importance.Thus, this Account aims to spotlight the significant strides made in the development of pure silicon anodes with particular attention to feature size. From the emergence of nanoscale silicon, the following nanotechnology played a crucial role in growing the particle through nano/microstructuring. Similarly, bulk silicon microparticles gradually surfaced with the post-engineering methods owing to their practical advantages. We briefly discuss the special characteristics of representative examples from bulk silicon engineering and nano/microstructuring, all aimed at overcoming intrinsic challenges, such as limiting large volume changes and stabilizing SEI formation during electrochemical cycling. Subsequently, we outline guidelines for advancing pure silicon anodes to incorporate high mass loading and high energy density. Importantly, these advancements require superior material design and the incorporation of exceptional battery components to ensure compatibility and yield synergistic effects. By broadening the cooperative strategies at the cell and system levels, we anticipate that this Account will provide an insightful analysis of pure silicon anodes and catalyze their practical applications in real battery systems.

Symmetry Breaking and Cooperative Spin Crossover in a Hofmann-Type Coordination Polymer Based on Negatively Charged {FeII(μ2-[MII(CN)4])2}n2n- Layers (MII = Pd, Pt).

We report herein the synthesis and characterization of two unprecedented isomorphous spin-crossover two-dimensional coordination polymers of the Hofmann-type formulated {FeII(Hdpyan)2(μ2-[MII(CN)4])2}, with MII = Pd, Pt and Hdpyan is the in situ partially protonated form of 2,5-(dipyridin-4-yl)aniline (dpyan). The FeII is axially coordinated by the pyridine ring attached to the 2-position of the aniline ring, while it is equatorially surrounded by four [MII(CN)4]2- planar groups acting as trans μ2-bidentate ligands defining layers, which stack parallel to each other. The other pyridine group of Hdpyan, being protonated, remains peripheral but involved in a strong [MII-C≡N···Hpy+] hydrogen bond between alternate layers. This provokes a nearly 90° rotation of the plane defined by the [MII(CN)4]2- groups, with respect to the average plane defined by the layers, forcing the observed uncommon bridging mode and the accumulation of negative charge around each FeII, which is compensated by the axial [Hdpyan]+ ligands. According to the magnetic and calorimetric data, both compounds undergo a strong cooperative spin transition featuring a 10-12 K wide hysteresis loop centered at 220 (Pt) and 211 K (Pd) accompanied by large entropy variations, 97.4 (Pt) and 102.9 (Pd) J/K mol. The breaking symmetry involving almost 90° rotation of one of the two coordinated pyridines together with the large unit-cell volume change per FeII (ca. 50 Å3), and subsequent release of significantly short interlayer contacts upon the low-spin → high-spin event, accounts for the strong cooperativity.

Tight Binding and Dual Encapsulation Enabled Stable Thick Silicon/Carbon Anode with Ultrahigh Volumetric Capacity for Lithium Storage.

Silicon (Si) is regarded as one of the most promising anode materials for high-performance lithium-ion batteries (LIBs). However, how to mitigate its poor intrinsic conductivity and the lithiation/delithiation-induced large volume change and thus structural degradation of Si electrodes without compromising their energy density is critical for the practical application of Si in LIBs. Herein, an integration strategy is proposed for preparing a compact micron-sized Si@G/CNF@NC composite with a tight binding and dual-encapsulated architecture that can endow it with superior electrical conductivity and deformation resistance, contributing to excellent cycling stability and good rate performance in thick electrode. At an ultrahigh mass loading of 10.8mg cm-2 , the Si@G/CNF@NC electrode also presents a large initial areal capacity of 16.7mA h cm-2 (volumetric capacity of 2197.7mA h cm-3 ). When paired with LiNi0.95 Co0.02 Mn0.03 O2 , the pouch-type full battery displays a highly competitive gravimetric (volumetric) energy density of ≈459.1Wh kg-1 (≈1235.4Wh L-1 ).

In-situ embedding of ultrasmall MnO nanoparticles into pollen biomass-derived hollow porous N heteroatoms enriched carbon microspheres as high-performance anode for lithium-ion batteries

The transition manganese monoxide (MnO) is investigated as the one of the most promising candidates of anode nanomaterials for lithium-ion batteries (LIBs) due to its irreplaceable advantages of higher theoretical capacity, restricted voltage hysteresis and favorable electrochemical kinetics. Nevertheless, it still remains a big challenge to simultaneously resolve the nonideal properties of the relatively low dispersion of MnO, the structural metastability as well as the undesirable permeability of electrolyte. Herein, the ultrasmall MnO nanoparticles/sulfuric-acid-pretreated camellia pollen carbon (MnO/SCPC) composites are successfully fabricated by a facile bio-templating method of carbonization hydrolysis of camellia pollen, wet-impregnation treatment of Mn/SCPC precursor and followed by thermal annealing, which delivers hollow porous microspheres structure where the shell components are formed by orderly stacking of multiple ultrasmall-size MnO-loaded nanocarbon spheres. This advantageous nano-structures not only allow for a large volume change during the lithiation/delithiation process, a large accessible contact area with electrolyte and a short transport path for Li+ ions, but also enhance the amounts of electrochemically active sites while simultaneously endow them with a superior structural stability through robust interfacial interaction. These clever designs enable the MnO/SCPC composites to perform exceptionally well electrochemically. More specifically, the MnO/SCPC-600 anode possesses a high initial discharge capacity (1490 mAh·g−1) at a current density of 0.1 A·g−1, and still retains 60% of the initial capacity (894 mAh·g−1) after 100 cycles. Besides, it also exhibits a high discharge capacity of 612 mAh·g−1 at a current density of 2.0 A·g−1 and an ultralong cycling life of 584 mAh·g−1 at 1.0 A·g−1 for long period of 1000 cycles. This work also paves up a facile direction for the application of MnO/biomass-derived carbonaceous nanomaterials in LIBs.

Mechano-Electrochemically Promoting Lithium Atom Diffusion and Relieving Accumulative Stress for Deep-Cycling Lithium Metal Anodes.

Lithium metal batteries (LMBs) can double the energy density of lithium-ion batteries. However, the notorious lithium dendrite growth and large volume change are not well addressed, especially under deep cycling. Here, an in-situ mechanical-electrochemical coupling system is built, and it is found that tensile stress can induce smooth lithium deposition. Density functional theory (DFT) calculation and finite element method (FEM) simulation confirm that the lithium atom diffusion energy barrier can be reduced when the lithium foils are under tensile strain. Then tensile stress is incorporated into lithium metal anodes by designing an adhesive copolymer layer attached to lithium in which the copolymer thinning can yield tensile stress to the lithium foil. Elastic lithium metal anode (ELMA) is further prepared via introducing a 3D elastic conductive polyurethane (CPU) host for the copolymer-lithium bilayer to release accumulated internal stresses and resist volume variation. The ELMA can withstand hundreds of compression-release cycles under 10% strain. LMBs paired with ELMA and LiNi0.8 Co0.1 Mn0.1 O2 (NCM811) cathode can operate beyond 250 cycles with 80% capacity retention under practical condition of 4 mAh cm-2 cathode capacity, 2.86g Ah-1 electrolyte-to-capacity ratio (E/C) and 1.8 negative-to-cathode capacity ratio (N/P), five times of the lifetime using lithium foils.

Using Highly Flexible SbSn@NC Nanofibers as Binderless Anodes for Sodium-Ion Batteries

Flexible and binderless electrodes have become a promising candidate for the next generation of flexible power storage devices. However, developing high-performance electrode materials with high energy density and a long cycle life remains a serious challenge for sodium-ion batteries (SIBs). The main issue is the large volume change in electrode materials during the cycling processes, leading to rapid capacity decay for SIBs. In this study, flexible electrodes for a SnSb alloy–carbon nanofiber (SnSb@NC) membrane were successfully synthesized with the aid of hydrothermal, electrospinning and annealing processes. The as-prepared binderless SnSb@NC flexible anodes were investigated for the storage properties of SIBs at 500 °C, 600 °C and 700 °C (SnSb@NC-500, SnSb@NC-600 and SnSb@NC-700), respectively. And the flexible SnSb@NC-700 electrode displayed the preferable SIB performances, achieving 240 mAh/g after 100 cycles at 0.1 A g−1. In degree-dependent I-V curve measurements, the SnSb@NC-700 membrane exhibited almost the same current at different bending degrees of 0°, 45°, 90°, 120° and 175°, indicating the outstanding mechanical properties of the flexible binderless electrodes.

The Deformation Behavior and Failure Modes of Surrounding Rock after Excavation: A Experimental Study

The deformation and failure of the surrounding rock during roadway excavation often determine the choice of supporting methods. To study the deformation behavior and failure modes of the surrounding rock after excavation under unloading stress, structural model tests were carried out with a novel experimental device. The present structural model test using partial hollow thick-walled cylinder cement mortar specimen φ200 mm × 280 mm with a horizontal central circular hole of 60 mm diameter and the hollow height of 160 mm was conducted to investigate the deformation, failure characteristics, and AE response of a whole testing process from excavation to postunloading state. Experimental results revealed that the amount of deformation behind the surface is significantly higher than that in front of the surface, and the radial strain increases with the increase of the distance from the surface within the range affected by unloading. Furthermore, the unloading rate has a little effect on the radial deformation of the surrounding rock in front of the surface, but has a substantial effect on the radial deformation behind the excavation surface. The peak value of the strain rate at the unloading rate of 2 MPa/s is much higher than that at the unloading rate of 0.1 MPa/s. According to AE results and the failure of opening the boundary, the increase of unloading rate triggers and exacerbates the damage of the specimen under high in situ stress conditions. The surrounding rock expanded to the inner hollow, accompanied by large dilation and volume changes, and it resulted in the shrinkage of the hole diameter. A large number of rock slices are generated at the opening curved free surface and then fell off, whose morphology is similar to the rock blocks that fell off after caving failure and rock burst in situ field. The results show that the system can accurately simulate the mechanical response and acoustic emission response of the excavated surrounding rock, which provides a new experimental method for further study of the unloading response of the surrounding rock.

A solution-to-solid conversion chemistry enables ultrafast-charging and long-lived molten salt aluminium batteries

Conventional solid-to-solid conversion-type cathodes in batteries suffer from poor diffusion/reaction kinetics, large volume changes and aggressive structural degradation, particularly for rechargeable aluminium batteries (RABs). Here we report a class of high-capacity redox couples featuring a solution-to-solid conversion chemistry with well-manipulated solubility as cathodes—uniquely allowed by using molten salt electrolytes—that enable fast-charging and long-lived RABs. As a proof-of-concept, we demonstrate a highly reversible redox couple—the highly soluble InCl and the sparingly soluble InCl3—that exhibits a high capacity of about 327 mAh g−1 with negligible cell overpotential of only 35 mV at 1 C rate and 150 °C. The cells show almost no capacity fade over 500 cycles at a 20 C charging rate and can sustain 100 mAh g−1 at 50 C. The fast oxidation kinetics of the solution phase upon initiating the charge enables the cell with ultrafast charging capability, whereas the structure self-healing via re-forming the solution phase at the end of discharge endows the long-term cycling stability. This solution-to-solid mechanism will unlock more multivalent battery cathodes that are attractive in cost but plagued by poor reaction kinetics and short cycle life.

Enhanced Lithium Storage Performance in Si/MXene Porous Composites

As a potential negative electrode material for lithium-ion batteries (LIBs), silicon has a relatively high specific lithium storage capacity. However, the large volume change during the cycle may result in the isolation with the current collector and therefore the rapid capacity decay during cycling. The poor electric conductivity of the silicon limits the high-power density application in LIBs. To meet the above challenges, a stable Si/Ti3C2Tx composite material was designed. Si nanoparticles are bonded with -NH2 group so that the silicon surface has a positive charge, which can then be electrostatic self-assembly with negatively charged MXene nanosheets in a facile freeze-drying method. Silicon nanoparticles were anchored on the surface or inside the interspace of the MXene nanosheets, which could improve the conductivity of the composites. The composite material (NH2-Si/MXene) presented a stable and porous structure with extra room for silicon expansion and plentiful channels for carrier transportation. Benefiting from the improved structural stability and enhanced charge storage dynamics, the discharge capacity of NH2-Si/MXene is 1203.3 mAh g−1 after 100 cycles at 200 mA g−1. These results provide new insights for the application of silicon-based negative electrode materials in high-energy-density LIBs.

Topology-enhanced mechanical stability of swelling nanoporous electrodes

Materials like silicon and germanium offer a 10-fold improvement in charge capacity over conventional graphite anodes in lithium-ion batteries but experience a roughly threefold volume increase during lithiation, which challenges ensuring battery integrity. Nanoporous silicon, created by liquid-metal-dealloying, is a potentially attractive anode design to mitigate this challenge, exhibiting both higher capacity and extended cycle lifetimes. However, how nanoporous structures accommodate the large volume change is unknown. Here, we address this question by using phase-field modeling to produce nanoporous particles and to investigate their elastoplastic swelling behavior and fracture. Our simulations show that enhanced mechanical stability results from the network topology consisting of ligaments connected by bulbous, sphere-like nodes. The ligaments forcefully resist elongation while the nodes, behaving like isolated spherical particles, experience large stresses driving fracture. However, being smaller compared to a sphere of the same volume as the entire nanoporous particle, the nodes are more protected against fracture.

Revealing the size effect of FeS2 on solid-state battery performances at different operating temperatures

FeS2 shows significant potential as cathode material for all-solid-state lithium batteries (ASSLBs) due to its high theoretical specific capacity, low cost, and environmental friendliness. However, the poor ion/electron conductivity and large volume variation effect of FeS2 inhibit its practical applications. Here, the influence of particle size of FeS2 on the corresponding sulfide-based solid-state batteries is carefully investigated by tuning FeS2 size. Moreover, low operating temperature is chosen to mitigate the large volume changes during cycling in the battery. S-FeS2 with smaller particle sizes delivers superior electrochemical performances than that of the larger L-FeS2 in Li5.5PS4.5Cl1.5-based ASSLBs under different operating temperatures. S-FeS2 shows stable discharge capacities during 50 cycles with a current density of 0.1 mA/cm2 under -20 °C. When the current density rises to 1.0 mA/cm2, it delivers an initial discharge capacity of 146.9 mAh/g and maintains 63% of the capacity after 100 cycles. This work contributes to constructing ASSLBs enables excellent electrochemical performances under extreme operating temperatures.

Multilevel carbon architecture of subnanoscopic silicon for fast‐charging high‐energy‐density lithium‐ion batteries

AbstractSilicon (Si) is widely used as a lithium‐ion‐battery anode owing to its high capacity and abundant crustal reserves. However, large volume change upon cycling and poor conductivity of Si cause rapid capacity decay and poor fast‐charging capability limiting its commercial applications. Here, we propose a multilevel carbon architecture with vertical graphene sheets (VGSs) grown on surfaces of subnanoscopically and homogeneously dispersed Si–C composite nanospheres, which are subsequently embedded into a carbon matrix (C/VGSs@Si–C). Subnanoscopic C in the Si–C nanospheres, VGSs, and carbon matrix form a three‐dimensional conductive and robust network, which significantly improves the conductivity and suppresses the volume expansion of Si, thereby boosting charge transport and improving electrode stability. The VGSs with vast exposed edges considerably increase the contact area with the carbon matrix and supply directional transport channels through the entire material, which boosts charge transport. The carbon matrix encapsulates VGSs@Si–C to decrease the specific surface area and increase tap density, thus yielding high first Coulombic efficiency and electrode compaction density. Consequently, C/VGSs@Si–C delivers excellent Li‐ion storage performances under industrial electrode conditions. In particular, the full cells show high energy densities of 603.5 Wh kg−1 and 1685.5 Wh L−1 at 0.1 C and maintain 80.7% of the energy density at 3 C.

Surface Deposition of Ni(OH)2 and Lattice Distortion Induce the Electrochromic Performance Decay of NiO Films in Alkaline Electrolyte

NiO, an anodic electrochromic material, has applications in energy‐saving windows, intelligent displays, and military camouflage. However, its electrochromic mechanism and reasons for its performance degradation in alkaline aqueous electrolytes are complex and poorly understood, making it challenging to improve NiO thin films. We studied the phases and electrochemical characteristics of NiO films in different states (initial, colored, bleached and after 8000 cycles) and identified three main reasons for performance degradation. First, Ni(OH)2 is generated during electrochromic cycling and deposited on the NiO film surface, gradually yielding a NiO@Ni(OH)2 core–shell structure, isolating the internal NiO film from the electrolyte, and preventing ion transfer. Second, the core–shell structure causes the mode of electrical conduction to change from first‐ to second‐order conduction, reducing the efficiency of ion transfer to the surface Ni(OH)2 layer. Third, Ni(OH)2 and NiOOH, which have similar crystal structures but different b‐axis lattice parameters, are formed during electrochromic cycling, and large volume changes in the unit cell reduce the structural stability of the thin film. Finally, we clarified the mechanism of electrochromic performance degradation of NiO films in alkaline aqueous electrolytes and provide a route to activation of NiO films, which will promote the development of electrochromic technology.