Ge-Doped Hematite with FeCoNi-Bi as Cocatalyst for High-Performing Photoelectrochemical Water Splitting.

Hematite is a promising photoanode material for photoelectrochemical water-splitting technology. However, the low current density associated with the low conductivity, low charge carrier mobility, and poor oxygen evolution catalytic activity is a challenging issue for the material. In this study, the challenge is addressed by introducing Germanium (Ge) doping, coupled with the use of FeCoNi-Bi as a co-catalyst. Ge doping not only increases the conductivity and charge carrier concentration of the hematite photoanode, but also induces nanopores, thereby expanding its electrochemical reactive surface area to facilitate the oxygen evolution reaction. In the meantime, the FeCoNi-Bi cocatalyst electrodeposited onto the surface of Ge-doped hematite, improves the oxygen evolution reaction performance. As a result, the obtained photoanode achieves a photocurrent density of 2.31 mA cm-2 at 1.23 VRHE, which is three times higher than that of hematite (0.72 mA cm-2). Moreover, a new analytical method is introduced to scrutinize both the positive and negative effects of Ge doping and FeCoNi-Bi cocatalyst on the photoanode performance by decoupling the photoelectrochemical process steps. Overall, this study not only enhances the performance of hematite photoanodes but also guides their rational design and systematic assessment.

Pressure-Induced Defects and Reduced Size Endow TiO2 with High Capacity over 20 000 Cycles and Excellent Fast-Charging Performance in Sodium Ion Batteries.

Anatase TiO2 as sodium-ion-battery anode has attracted increased attention because of its low volume change and good safety. However, low capacity and poor rate performance caused by low electrical conductivity and slow ion diffusion greatly impede its practical applications. Here, a bi-solvent enhanced pressure strategy that induces defects (oxygen vacancies) into TiO2 via N doping and reduces its size by using mutual-solvent ethanol and dopant dimethylformamide as pressure-increased reagent of tetrabutyl orthotitanate tetramer is proposed to fabricate N-doped TiO2 /C nanocomposites. The induced defects can increase ion storage sites, improve electrical conductivity, and decrease bandgap and ion diffuse energy barrier of TiO2 . The size reduction increases contact interfaces between TiO2 and C and shortens ion diffuse distance, thus increasing extra ion storage sites and boosting ion diffusion rate of TiO2 . The N-doped TiO2 possesses highly stable crystal structure with a slightly increase of 0.86% in crystal lattice spacing and 3.2% in particle size after fully sodiation. Consequently, as a sodium-ion battery anode, the nanocomposite delivers high capacity and superior rate capability along with ultralong cycling life. This work proposes a novel pressure-induced synthesis strategy that provides unique guidance for designing TiO2 -based anode materials with high capacity and excellent fast-charging capability.

Highly Efficient Aligned Ion-Conducting Network and Interface Chemistries for Depolarized All-Solid-State Lithium Metal Batteries.

Improving the long-term cycling stability and energy density of all-solid-state lithium (Li)-metal batteries (ASSLMBs) at room temperature is a severe challenge because of the notorious solid-solid interfacial contact loss and sluggish ion transport. Solid electrolytes are generally studied as two-dimensional (2D) structures with planar interfaces, showing limited interfacial contact and further resulting in unstable Li/electrolyte and cathode/electrolyte interfaces. Herein, three-dimensional (3D) architecturally designed composite solid electrolytes are developed with independently controlled structural factors using 3D printing processing and post-curing treatment. Multiple-type electrolyte films with vertical-aligned micro-pillar (p-3DSE) and spiral (s-3DSE) structures are rationally designed and developed, which can be employed for both Li metal anode and cathode in terms of accelerating the Li+ transport within electrodes and reinforcing the interfacial adhesion. The printed p-3DSE delivers robust long-term cycle life of up to 2600 cycles and a high critical current density of 1.92 mA cm-2. The optimized electrolyte structure could lead to ASSLMBs with a superior full-cell areal capacity of 2.75 mAh cm-2 (LFP) and 3.92 mAh cm-2 (NCM811). This unique design provides enhancements for both anode and cathode electrodes, thereby alleviating interfacial degradation induced by dendrite growth and contact loss. The approach in this study opens a new design strategy for advanced composite solid polymer electrolytes in ASSLMBs operating under high rates/capacities and room temperature.

Macroporous Directed and Interconnected Carbon Architectures Endow Amorphous Silicon Nanodots as Low-Strain and Fast-Charging Anode for Lithium-Ion Batteries.

Fabricating low-strain and fast-charging silicon-carbon composite anodes is highly desired but remains a huge challenge for lithium-ion batteries. Herein, we report a unique silicon-carbon composite fabricated by uniformly dispersing amorphous Si nanodots (SiNDs) in carbon nanospheres (SiNDs/C) that are welded on the wall of the macroporous carbon framework (MPCF) by vertical graphene (VG), labeled as MPCF@VG@SiNDs/C. The high dispersity and amorphous features of ultrasmall SiNDs (~ 0.7 nm), the flexible and directed electron/Li+ transport channels of VG, and the MPCF impart the MPCF@VG@SiNDs/C more lithium storage sites, rapid Li+ transport path, and unique low-strain property during Li+ storage. Consequently, the MPCF@VG@SiNDs/C exhibits high cycle stability (1301.4 mAh g-1 at 1 A g-1 after 1000 cycles without apparent decay) and high rate capacity (910.3 mAh g-1, 20 A g-1) in half cells based on industrial electrode standards. The assembled pouch full cell delivers a high energy density (1694.0 Wh L-1; 602.8 Wh kg-1) and an excellent fast-charging capability (498.5 Wh kg-1, charging for 16.8 min at 3 C). This study opens new possibilities for preparing advanced silicon-carbon composite anodes for practical applications.

Spin-Polarized Surface Capacitance Effects Enable Fe3 O4 Anode Superior Wide Operation-Temperature Sodium Storage.

Fe3 O4 is widely investigated as an anode for ambient sodium-ion batteries (SIBs), but its electrochemical properties in the wide operation-temperature range have rarely been studied. Herein, the Fe3 O4 nanoparticles, which are well encapsulated by carbon nanolayers, are uniformly dispersed on the graphene basal plane (named Fe3 O4 /C@G) to be used as the anode for SIBs. The existence of graphene can reduce the size of Fe3 O4 /C nanoparticles from 150 to 80 nm and greatly boost charge transport capability of electrode, resulting in an obvious size decrease of superparamagnetic Fe nanoparticles generated from the conversion reaction from 5 to 2 nm. Importantly, the ultra-small superparamagnetic Fe nanoparticles (≈2 nm) can induce a strong spin-polarized surface capacitance effect at operating temperatures ranging from -40 to 60 °C, thus achieving highly efficient Na-ion transport and storage in a wide operation-temperature range. Consequently, the Fe3 O4 /C@G anode shows high capacity, excellent fast-charging capability, and cycling stability ranging from -40 to 60 °C in half/full cells. This work demonstrates the viability of Fe3 O4 as anode for wide operation-temperature SIBs and reveals that spin-polarized surface capacitance effects can promote Na-ion storage over a wide operation temperature range.

Growth of Vertical Graphene Sheets on Silicon Nanoparticles Well-Dispersed on Graphite Particles for High-Performance Lithium-Ion Battery Anode.

With rapidly increasing demand for high energy density, silicon (Si) is greatly expected to play an important role as the anode material of lithium-ion batteries (LIBs) due to its high specific capacity. However, large volume expansion for silicon during the charging process is still a serious problem influencing its cycling stability. Here, a Si/C composite of vertical graphene sheets/silicon/carbon/graphite (VGSs@Si/C/G) is reported to address the electrochemical stability issues of Si/graphite anodes, which is prepared by adhering Si nanoparticles on graphite particles with chitosan and then in situ growing VGSs by thermal chemical vapor deposition. As a promising anode material, due to the buffering effect of VGSs and tight bonding between Si and graphite particles, the composite delivers a high reversible capacity of 782.2 mAh g-1 after 1000 cycles with an initial coulombic efficiency of 87.2%. Furthermore, the VGSs@Si/C/G shows a diffusion coefficient of two orders higher than that without growing the VGSs. The full battery using VGSs@Si/C/G anode and LiNi0.8 Co0.1 Mn0.1 O2 cathode achieves a high gravimetric energy density of 343.6 Wh kg-1 , a high capacity retention of 91.5% after 500 cycles and an excellent average CE of 99.9%.

A review of vertical graphene and its energy storage system applications.

The pursuit of advanced materials to meet the escalating demands of energy storage system has led to the emergence of vertical graphene (VG) as a highly promising candidate. With its remarkable strength, stability, and conductivity, VG has gained significant attention for its potential to revolutionize energy storage technologies. This comprehensive review delves deeply into the synthesis methods, structural modifications, and multifaceted applications of VG in the context of lithium-ion batteries, silicon-based lithium batteries, lithium-sulfur batteries, sodium-ion batteries, potassium-ion batteries, aqueous zinc batteries, and supercapacitors. The review elucidates the intricate growth process of VG and underscores the paramount importance of optimizing process parameters to tailor VG for specific applications. Subsequently, the pivotal role of VG in enhancing the performance of various energy storage and conversion systems is exhaustively discussed. Moreover, it delves into structural improvement, performance tuning, and mechanism analysis of VG composite materials in diverse energy storage systems. In summary, this review provides a comprehensive look at VG synthesis, modification, and its wide range of applications in energy storage. It emphasizes the potential of VG in addressing critical challenges and advancing sustainable, high-performance energy storage devices, providing valuable guidance for the development of future technologies.

Dead-zone-compensated design as general method of flow field optimization for redox flow batteries.

One essential element of redox flow batteries (RFBs) is the flow field. Certain dead zones that cause local overpotentials and side effects are present in all conventional designs. To lessen the detrimental effects, a dead-zone-compensated design of flow field optimization is proposed. The proposed architecture allows for the detection of dead zones and their compensation on existing flow fields. Higher reactant concentrations and uniformity factors can be revealed in the 3D multiphysical simulation. The experiments also demonstrate that at an energy efficiency (EE) of 80%, the maximum current density of the novel flow field is 205 mA cm-2, which is much higher than the values for the previous ones (165 mA cm-2) and typical serpentine flow field (153 mA cm-2). Extensions of the design have successfully increased system EE (2.7 to 4.3%) for a variety of flow patterns. As a result, the proposed design is demonstrated to be a general method to support the functionality and application of RFBs.

3D hierarchical graphene matrices enable stable Zn anodes for aqueous Zn batteries.

Metallic zinc anodes of aqueous zinc ion batteries suffer from severe dendrite and side reaction issues, resulting in poor cycling stability, especially at high rates and capacities. Herein, we develop two three-dimensional hierarchical graphene matrices consisting of nitrogen-doped graphene nanofibers clusters anchored on vertical graphene arrays of modified multichannel carbon. The graphene matrix with radial direction carbon channels possesses high surface area and porosity, which effectively minimizes the surface local current density, manipulates the Zn2+ ions concentration gradient, and homogenizes the electric field distribution to regulate Zn deposition. As a result, the engineered matrices achieve a superior coulombic efficiency of 99.67% over 3000 cycles at 120 mA cm-2, the symmetric cells with the composite zinc anode demonstrates 2600 h dendrite-free cycles at 80 mA cm-2 and 80 mAh cm-2. The as-designed full cell exhibits an inspiring capacity of 16.91 mAh cm-2. The Zn capacitor matched with activated carbon shows a superior long-term cycle performance of 20000 cycles at 40 mA cm-2. This strategy of constructing a 3D hierarchical structure for Zn anodes may open up a new avenue for metal anodes operating under high rates and capacities.

Single-Layered MoS2 Fabricated by Charge-Driven Interlayer Expansion for Superior Lithium/Sodium/Potassium-Ion-Battery Anodes.

Single-layered MoS2 is a promising anode material for lithium-ion batteries (LIBs), sodium-ion batteries (SIBs), and potassium-ion batteries (PIBs) due to its high capacity and isotropic ion transport paths. However, the low intrinsic conductivity and easy-agglomerated feature hamper its applications. Here, a charge-driven interlayer expansion strategy that Co2+ replaces Mo4+ in the doping form to endow MoS2 layers with negative charges, thus inducing electrostatic repulsion, together with the insertion of gaseous groups, to drive interlayer expansion which once breaks the confinement of interlayer van der Waals force, single-layered MoS2 is obtained and uniformly dispersed into carbon matrix arising from the transformation of carbonaceous gaseous groups under high vapor pressure, is proposed. Co atom doping helps enhance the intrinsic conductivity of single-layered MoS2 . Carbon matrix effectively prevents agglomeration of single-layered MoS2 . The doped Co atoms can be fully transformed into ultrasmall Co nanoparticles during conversion reaction, which enables strong spin-polarized surface capacitance and thus significantly boosts ion transport and storage. Consequently, the prepared material delivers superb Li/Na/K-ion storage performances, which are best in the reported MoS2 -based anodes. The proposed charge-driven interlayer expansion strategy provides a novel perspective for preparing single-layered MoS2, which shows huge potential for energy storage.

Thermodynamically Stable Dual-Modified LiF&FeF3 layer Empowering Ni-Rich Cathodes with Superior Cyclabilities.

Pushing the limit of cutoff potentials allows nickel-rich layered oxides to provide greater energy density and specific capacity whereas reducing thermodynamic and kinetic stability. Herein, a one-step dual-modified method is proposed for in situ synthesizing thermodynamically stable LiF&FeF3 coating on LiNi0.8 Co0.1 Mn0.1 O2 surfaces by capturing lithium impurity on the surface to overcome the challenges suffered. The thermodynamically stabilized LiF&FeF3 coating can effectively suppress the nanoscale structural degradation and the intergranular cracks. Meanwhile, the LiF&FeF3 coating alleviates the outward migration of Oα- (α<2), increases oxygen vacancy formation energies, and accelerates interfacial Li+ diffusion. Benefited from these, the electrochemical performance of LiF&FeF3 modified materials is improved (83.1% capacity retention after 1000 cycles at 1C), even under exertive operational conditions of elevated temperature (91.3% capacity retention after 150 cycles at 1C). This work demonstrates that the dual-modified strategy can simultaneously address the problems of interfacial instability and bulk structural degradation and represents significant progress in developing high-performance lithium-ion batteries (LIBs).

Atomic-Scale Laminated Structure of O-Doped WS2 and Carbon Layers with Highly Enhanced Ion Transfer for Fast-Charging Lithium-Ion Batteries.

WS2 anode materials show huge potential for fast-charging lithium-ion batteries (LIBs) due to the naturally good 2D diffusion pathways but suffer from large Li+ diffusion barrier energy and poor intrinsic electrical conductivity. Here, a defect-rich atomic-scale laminated structure of WS2 and C (D-WS2 -C) with O doping and enlarged interlayer distance from 0.62 to 1.06 nm of WS2 is first fabricated, which is assembled into micron-sized spheres to prepare WS2 /C composite microspheres. D-WS2 -C with maximized molecular layer contact area between WS2 and carbon and large interlayer spacing greatly enhances the electrical conductivity of WS2 and reduces Li-ion diffusion energy barrier, confirmed by density functional theory calculations. Besides, the unique D-WS2 -C enables the formation of vast superfine W nanoparticles (1-2 nm) during the conversation reaction, resulting in the construction of a space charge zone on W surface. Based on these characteristics of D-WS2 -C, the prepared WS2 /C composite microspheres show superior fast-charging capability with a high capacity of 647.8 mAh g-1 at 20 C in half cells. For full cells, a high-energy density of 100.9 Wh kg-1 is achieved at a charge time of only 8.5 min at 5 C, representing the best fast-charging performances in WS2 -based anode materials to date.

Nitrogen, Oxygen-Codoped Vertical Graphene Arrays Coated 3D Flexible Carbon Nanofibers with High Silicon Content as an Ultrastable Anode for Superior Lithium Storage.

Free-standing and foldable electrodes with high energy density and long lifespan have recently elicited attention on the development of lithium-ion batteries (LIBs) for flexible electronic devices. However, both low energy density and slow kinetics in cycling impede their practical applications. In this work, a free-standing and binder-free N, O-codoped 3D vertical graphene carbon nanofibers electrode with ultra-high silicon content (VGAs@Si@CNFs) is developed via electrospinning, subsequent thermal treatment, and chemical vapor deposition processes. The as-prepared VGAs@Si@CNFs electrode exhibits excellent conductivity and flexibility because of the high graphitized carbon nanofiber network and abundant vertical graphene arrays. Such 3D all-carbon architecture can be fabulous for providing a conductive and mechanically robust network, further improving the kinetics and restraining the volume expansion of Si NPs, especially with an ultra-high Si content (>90 wt%). As a result, the VGAs@Si@CNFs composite demonstrates a superior specific capacity (3619.5 mAh g-1 at 0.05 A g-1 ), ultralong lifespan, and outstanding rate capability (1093.1 mAh g-1 after 1500 cycles at 8 A g-1 ) as a free-standing anode for LIBs. It is believed that this work offers an exciting method for developing free-standing and high-energy-density electrodes for other energy storage devices.