Synergistic Structure and Iron-Vacancy Engineering Realizing High Initial Coulombic Efficiency and Kinetically Accelerated Lithium Storage in Lithium Iron Oxide

Transition metal oxides with high capacity still confront the challenges of low initial coulombic efficiency (ICE, generally <70%) and inferior cyclic stability for practical lithium-storage. Herein, a hollow slender carambola-like Li_0.43 FeO_1.51 with Fe vacancies is proposed by a facile reaction of Fe³⁺ -containing metal-organic frameworks with Li₂ CO₃ . Synthesis experiments combined with synchrotron-radiation X-ray measurements identify that the hollow structure is caused by Li₂ CO₃ erosion, while the formation of Fe vacancies is resulted from insufficient lithiation process with reduced Li₂ CO₃ dosage. The optimized lithium iron oxides exhibit remarkably improved ICE (from 68.24% to 86.78%), high-rate performance (357 mAh g^-1 at 5 A g^-1 ), and superior cycling stability (884 mAh g^-1 after 500 cycles at 0.5 A g^-1 ). Paring with LiFePO₄ cathodes, the full-cells achieve extraordinary cyclic stability with 99.3% retention after 100 cycles. The improved electrochemical performances can be attributed to the synergy of structural characteristics and Fe vacancy engineering. The unique hollow structure alleviates the volume expansion of Li_0.43 FeO_1.51 , while the in situ generated Fe vacancies are powerful for modulating electronic structure with boosted Li⁺ transport rate and catalyze more Li₂ O decomposition to react with Fe in the first charge process, hence enhancing the ICE of lithium iron oxide anode materials.

Study on Oxygen Evolution Reaction Performance of Jarosite/C Composites

In the electrolysis of water process, hydrogen is produced and the anodic oxygen evolution reaction (OER) dominates the reaction rate of the entire process. Currently, OER catalysts mostly consist of noble metal (NM) catalysts, which cannot be applied in industries due to the high price. It is of great importance to developing low-cost catalysts materials as NM materials substitution. In this work, jarosite (AFe₃(SO₄)₂(OH)₆, A = K⁺, Na⁺, NH⁴⁺, H₃O⁺) was synthesized by a one-step method, and its OER catalytic performance was studied using catalytic slurry (the weight ratios of jarosite and conductive carbon black are 2:1, 1:1 and 1:2). Microstructures and functional groups of synthesized material were analyzed using XRD, SEM, FI-IR, etc. The OER catalytic performance of (NH₄)Fe₃(SO₄)₂(OH)₆/conductive carbon black were examined by LSV, Tafel, EIS, ECSA, etc. The study found that the OER has the best catalytic performance when the weight ratio of (NH₄)Fe₃(SO₄)₂(OH)₆ to conductive carbon black is 2:1. It requires only 376 mV overpotential to generate current densities of 10 mA cm⁻² with a small Tafel slope (82.42 mV dec⁻¹) and large C_dl value (26.17 mF cm⁻²).

Na doping into Li-rich layered single crystal nanoparticles for high-performance lithium-ion batteries cathodes

Lithium-rich layered manganese-based cathodes (LRLMOs) with first-class energy density (∼1000 W h kg^-1) have attracted wide attention. Nevertheless, the weak cycle stability and bad rate capability obstruct their large-scale commercial application. Here, single crystal Li_1.2-xNa_xNi_0.2Mn_0.6O₂(x = 0, 0.05, 0.1, 0.15) nanoparticles are designed and successfully synthesized due to the single crystal structure with smaller internal stress and larger ionic radius of Na. The synergistic advantages of single crystal structure and Na doping are authenticated as cathodes for Li ion batteries (LIBs), which can consolidate the crystallographic structure and be benefit for migration of lithium ion. Among all the Na doping single crystals, Li_1.1Na_0.1Ni_0.2Mn_0.6O₂cathode possesses supreme cycling life and discharge capacity at large current density. To be more specific, it exhibits a discharge capacity of 264.2 mAh g^-1after 50 charge and discharge cycles, higher than that of undoped material (214.9 mAh g^-1). The discharge capacity of Li_1.1Na_0.1Ni_0.2Mn_0.6O₂cathode at 10 C (1 C = 200 mA g^-1) is enhanced to 160.4 mAh g^-1(106.7 mAh g^-1forx = 0 sample). The creative strategy of Na doping single crystal LRLMOs might furnish an idea to create cathode materials with high energy and power density for next generation LIBs.

Green and Scalable Fabrication of Sandwich-like NG/SiOx/NG Homogenous Hybrids for Superior Lithium-Ion Batteries

SiOx is considered as a promising anode for next-generation Li-ions batteries (LIBs) due to its high theoretical capacity; however, mechanical damage originated from volumetric variation during cycles, low intrinsic conductivity, and the complicated or toxic fabrication approaches critically hampered its practical application. Herein, a green, inexpensive, and scalable strategy was employed to fabricate NG/SiOx/NG (N-doped reduced graphene oxide) homogenous hybrids via a freeze-drying combined thermal decomposition method. The stable sandwich structure provided open channels for ion diffusion and relieved the mechanical stress originated from volumetric variation. The homogenous hybrids guaranteed the uniform and agglomeration-free distribution of SiOx into conductive substrate, which efficiently improved the electric conductivity of the electrodes, favoring the fast electrochemical kinetics and further relieving the volumetric variation during lithiation/delithiation. N doping modulated the disproportionation reaction of SiOx into Si and created more defects for ion storage, resulting in a high specific capacity. Deservedly, the prepared electrode exhibited a high specific capacity of 545 mAh g-1 at 2 A g-1, a high areal capacity of 2.06 mAh cm-2 after 450 cycles at 1.5 mA cm-2 in half-cell and tolerable lithium storage performance in full-cell. The green, scalable synthesis strategy and prominent electrochemical performance made the NG/SiOx/NG electrode one of the most promising practicable anodes for LIBs.

Solid Solution of Bi and Sb for Robust Lithium Storage Enabled by Consecutive Alloying Reaction

Materials with alloying reactions have significant potential as electrodes for lithium-ion batteries (LIBs) due to its high theoretical capacity and appropriate lithiation potentials. Nonetheless, their cycling performance is inferior due to violent volume expansion and severe pulverization of active materials. Herein, solid solution of Bi_0.5 Sb_0.5 encapsulated with carbon is discovered to enable consecutive alloying reactions with manageable volume change, suitable for developing LIBs with high capacity and robust cyclability. A Sb-rich shell and Bi-rich core structure is formed in cycling since the alloying reaction between Sb and Li occurs first, followed by the alloying reaction between Bi and Li. Such a consecutive alloying reaction obeying the thermodynamic path is experimentally realized by the carbon capsulation, which acts as a protecting solid layer to avoid polarized reactions occurred when exposed directly to liquid electrolyte. The LIBs using Bi_0.5 Sb_0.5 @carbon run on the consecutive alloying reactions exhibits high capacity, prolonged lifespan (489.4 mAh g^-1 after 2000 cycles at 1 A g^-1 ) and fast kinetic, while those using bare Bi_0.5 Sb_0.5 suffer from worsened kinetic and thus a poor cycling performance owning to the polarized reactions. The work paves a way of developing alloy electrodes for alkaline-ion rechargeable batteries with potential industry applications.

Mn-Substituted Tunnel-Type Polyantimonic Acid Confined in a Multidimensional Integrated Architecture Enabling Superfast-Charging Lithium-Ion Battery Anodes

Given the inherent features of open tunnel-like pyrochlore crystal frameworks and pentavalent antimony species, polyantimonic acid (PAA) is an appealing conversion/alloying-type anode material with fast solid-phase ionic diffusion and multielectron reactions for lithium-ion batteries. Yet, enhancing the electronic conductivity and structural stability are two key issues in exploiting high-rate and long-life PAA-based electrodes. Herein, these challenges are addressed by engineering a novel multidimensional integrated architecture, which consists of 0D Mn-substituted PAA nanocrystals embedded in 1D tubular graphene scrolls that are co-assembled with 2D N-doped graphene sheets. The integrated advantages of each subunit synergistically establish a robust and conductive 3D electrode framework with omnidirectional electron/ion transport network. Computational simulations combined with experiments reveal that the partial-substitution of H3O+ by Mn2+ into the tunnel sites of PAA can regulate its electronic structure to narrow the bandgap with increased intrinsic electronic conductivity and reduce the Li+ diffusion barrier. All above merits enable improved reaction kinetics, adaptive volume expansion, and relieved dissolution of active Mn2+/Sb5+ species in the electrode materials, thus exhibiting ultrahigh rate capacity (238 mAh g-1 at 30.0 A g-1), superfast-charging capability (fully charged with 56% initial capacity for ≈17 s at 80.0 A g-1) and durable cycling performance (over 1000 cycles).

Synthesis of Hydronium-Potassium Jarosites: The Effect of pH and Aging Time on Their Structural, Morphological, and Electrical Properties

Structural and morphological properties of hydronium-potassium jarosite microstructures were investigated in this work, and their electrical properties were evaluated. All the microstructures were synthesized at a very low temperature of 70 °C with a reduced reaction time of 3 h. An increase in the pH from 0.8 to 2.1 decreased the particle sizes from 3 µm to 200 nm and an increase in the aging time from zero, three, and seven days resulted in semispherical, spherical, and euhedral jarosite structures, respectively. The Rietveld analysis also confirmed that the amount of hydronium substitution by potassium in the cationic site increased with an increase in pH. The percentages of hydronium jarosite (JH)/potassium jarosite (JK) for pH values of 0.8, 1.1, and 2.1 were 77.72/22.29%, 82.44/17.56%, and 89.98/10.02%, respectively. Microstructures obtained in this work were tested as alternative anode materials and the voltage measured using these electrodes made with hydronium-potassium jarosite microstructures and graphite ranged from 0.89 to 1.36 V. The results obtained in this work show that with reduced particle size and euhedral morphology obtained, modified jarosite microstructures can be used as anode materials for improving the lifetime of lithium-ion batteries.

The use of biochar for controlling acid mine drainage through the inhibition of chalcopyrite biodissolution

Although chalcopyrite biodissolution plays an important role in the formation of acid mine drainage (AMD), the control of AMD through inhibiting the biodissolution of chalcopyrite has not been studied until now. In order to fill this knowledge gap, a novel method for inhibiting chalcopyrite biodissolution using biochar was proposed and verified. The effects of biochar pyrolysis temperature and biochar concentration on the inhibition of chalcopyrite biodissolution in the presence of Acidithiobacillus ferrooxidans (A. ferrooxidans) were studied. The results indicate that biochar significantly inhibited chalcopyrite biodissolution, thus reducing the number of copper and iron ions and quantity of acid released. In turn, this suggests that AMD generation was suppressed under these conditions. Biochar pyrolyzed at 300 °C (Biochar-300 °C) was the most effective at inhibiting chalcopyrite biodissolution and reduced its biodissolution rate by 17.7%. A suitable concentration of biochar-300 °C enhanced its inhibition of chalcopyrite biodissolution. The optimal concentration of biochar-300 °C for inhibiting chalcopyrite biodissolution was 3 g/L. Biodissolution results, cyclic voltammetry, mineral surface morphology, mineralogical phase, and elemental composition analyses reveal that biochar inhibited the biodissolution of chalcopyrite by promoting the formation of passivation layer (jarosite and S_n^2-/S⁰) and adsorbing bacteria.

Facile Green Synthesis of Pseudocapacitance-Contributed Ultrahigh Capacity Fe2(MoO4)3 as an Anode for Lithium-Ion Batteries

The investigation into the use of earth-abundant elements as electrode materials for lithium-ion batteries (LIBs) is becoming more urgent because of the high demand for electric vehicles and portable devices. Herein, a new green synthesis strategy, based on a facile solid-state reaction with the assistance of water droplets' vapor, was conducted to prepare Fe₂(MoO₄)₃ nanosheets as anode materials for LIBs. The obtained sample possesses a two-dimensional stacked nanosheet construction with open gaps providing a much higher surface area compared to the bulk sample conventionally synthesized. The nanosheet sample delivers an ultrahigh reversible capacity (1983.6 mA h g^-1) at a current density of 100 mA g^-1 after 400 cycles, which could be related to the contribution of pseudocapacitance. The enhancement in cyclability and rated performance with an interesting increased capacity could be caused by the effect of electrochemical milling and the in situ formation of metallic particles in its lithium-ion storage mechanism.

H+ -Insertion Boosted α-MnO2 for an Aqueous Zn-Ion Battery

Rechargeable Zn/MnO₂ batteries using mild aqueous electrolytes are attracting extensive attention due to their low cost, high safety, and environmental friendliness. However, the charge-storage mechanism involved remains a topic of controversy so far. Also, the practical energy density and cycling stability are still major issues for their applications. Herein, a free-standing α-MnO₂ cathode for aqueous zinc-ion batteries (ZIBs) is directly constructed with ultralong nanowires, leading to a rather high energy density of 384 mWh g^-1 for the entire electrode. Greatly, the H⁺ /Zn²⁺ coinsertion mechanism of α-MnO₂ cathode for aqueous ZIBs is confirmed by a combined analysis of in situ X-ray diffractometry, ex situ transmission electron microscopy, and electrochemical methods. More interestingly, the Zn²⁺ -insertion is found to be less reversible than H⁺ -insertion in view of the dramatic capacity fading occurring in the Zn²⁺ -insertion step, which is further evidenced by the discovery of an irreversible ZnMn₂ O₄ layer at the surface of α-MnO₂ . Hence, the H⁺ -insertion process actually plays a crucial role in maintaining the cycling performance of the aqueous Zn/α-MnO₂ battery. This work is believed to provide an insight into the charge-storage mechanism of α-MnO₂ in aqueous systems and paves the way for designing aqueous ZIBs with high energy density and long-term cycling ability.

V3S4 Nanosheets Anchored on N, S Co-Doped Graphene with Pseudocapacitive Effect for Fast and Durable Lithium Storage

Construction of a suitable hybrid structure has been considered an important approach to address the defects of metal sulfide anode materials. V₃S₄ nanosheets anchored on an N, S co-coped graphene (VS/NSG) aerogel were successfully fabricated by an efficient self-assembled strategy. During the heat treatment process, decomposition, sulfuration and N, S co-doping occurred. This hybrid structure was not only endowed with an enhanced capability to buffer the volume expansion, but also improved electron conductivity as a result of the conductive network that had been constructed. The dominating pseudocapacitive contribution (57.78% at 1 mV s⁻¹) enhanced the electrochemical performance effectively. When serving as anode material for lithium ion batteries, VS/NSG exhibits excellent lithium storage properties, including high rate capacity (480 and 330 mAh g⁻¹ at 5 and 10 A g⁻¹, respectively) and stable cyclic performance (692 mAh g⁻¹ after 400 cycles at 2 A g⁻¹).

Sandwiching Defect-Rich TiO2-δ Nanocrystals into a Three-Dimensional Flexible Conformal Carbon Hybrid Matrix for Long-Cycling and High-Rate Li/Na-Ion Batteries

Developing flexible power sources is crucially important to fulfill the need for wearable electronic devices, but state-of-the-art flexible electrodes cannot meet the requirements of practical applications because of their heavy weight and unsatisfactory mechanical properties. Here, we highlight a design strategy for constructing a novel robust three-dimensional (3D) flexible electrode with a unique sandwichlike N-doped carbon sponge/TiO_2-δ/reduced graphene oxide (NCS/TiO_2-δ/RGO) configuration. In this electrode architecture, ultrafine defect-rich TiO_2-δ nanocrystals are spatially sandwiched by a 3D conformal carbon hybrid matrix, where the 3D porous NCS provides an interconnected open diffusion channel for efficient ionic accessibility while the conformal RGO coating layer serves as an additional upper current collector, resulting in a double continuous conductive network for fast electronic transport and guaranteeing excellent electrochemical reaction kinetics. Hence, the as-built NCS/TiO_2-δ/RGO flexible electrodes exhibit high-rate capabilities and long-cycling life in lithium-ion batteries (LIBs) and sodium-ion batteries (SIBs), and they also exhibit outstanding thermal stability under cycling at 55 °C. More remarkably, a flexible soft-package full battery based on a NCS/TiO_2-δ/RGO anode and a LiNi_1/3Co_1/3Mn_1/3O₂ (for LIBs) or Na_0.67Fe_0.3Mn_0.3Co_0.4O₂ (for SIBs) cathode shows stable electrochemical characteristics under bending and folding, holding great potential for flexible energy storage devices.

A Facile Synthesis of MoS2/g-C3N4 Composite as an Anode Material with Improved Lithium Storage Capacity

The demand for well-designed nanostructured composites with enhanced electrochemical performance for lithium-ion batteries electrode materials has been emerging. In order to improve the electrochemical performance of MoS2-based anode materials, MoS2 nanosheets integrated with g-C3N4 (MoS2/g-C3N4 composite) was synthesized by a facile heating treatment from the precursors of thiourea and sodium molybdate at 550 °C under N2 gas flow. The structure and composition of MoS2/g-C3N4 were confirmed by X-ray diffraction, scanning electron microscopy, transmission electron microscopy, infrared spectroscopy, X-ray photoelectron spectroscopy, thermogravimetric analysis and elemental analysis. The lithium storage capability of the MoS2/g-C3N4 composite was evaluated, indicating high capacity and stable cycling performance at 1 C (A·g-1) with a reversible capacity of 1204 mA·h·g-1 for 200 cycles. This result is believed the role of g-C3N4 as a supporting material to accommodate the volume change and improve charge transport for nanostructured MoS2. Additionally, the contribution of the pseudocapacitive effect was also calculated to further clarify the enhancement in Li-ion storage performance of the composite.