High Gravimetric Capacity Research Articles

Crystal Facet and Architecture Engineering of Metal Oxide Nanonetwork Anodes for High-Performance Potassium Ion Batteries and Hybrid Capacitors.

Metal oxides are considered as prospective dual-functional anode candidates for potassium ion batteries (PIBs) and hybrid capacitors (PIHCs) because of their abundance and high theoretic gravimetric capacity; however, due to the inherent insulating property of wide band gaps and deficient ion-transport kinetics, metal oxide anodes exhibit poor K+ electrochemical performance. In this work, we report crystal facet and architecture engineering of metal oxides to achieve significantly enhanced K+ storage performance. A bismuth antimonate (BiSbO4) nanonetwork with an architecture of perpendicularly crossed single crystal nanorods of majorly exposed (001) planes are synthesized via CTAB-mediated growth. (001) is found to be the preferential surface diffusion path for superior adsorption and K+ transport, and in addition, the interconnected nanorods gives rise to a robust matrix to enhance electrical conductivity and ion transport, as well as buffering dramatic volume change during insertion/extraction of K+. Thanks to the synergistic effect of facet and structural engineering of BiSbO4 electrodes, a stable dual conversion-alloying mechanism based on reversible six-electron transfer per formula unit of ternary metal oxides is realized, proceeding by reversible coexistence of potassium peroxide conversion reactions (KO2↔K2O) and BixSby alloying reactions (BiSb ↔ KBiSb ↔ K3BiSb). As a result, BiSbO4 nanonetwork anodes show outstanding potassium ion storage in terms of capacity, cycling life, and rate capability. Finally, the implementation of a BiSbO4 nanonetwork anode in the state-of-the-art full cell configuration of both PIBs and PIHCs shows satisfactory performance in a Ragone plot that sheds light on their practical applications for a wide range of K+-based energy storage devices. We believe this study will propose a promising avenue to design advanced hierarchical nanostructures of ternary or binary conversion-type materials for PIBs, PIHCs, or even for extensive energy storage.

Rapeseed meal-derived N,S self-codoped porous carbon materials for supercapacitors

N,S self-doped porous carbon with high specific surface area and gravimetric specific capacitance from rapeseed meal was successfully synthesized.

Densified HKUST-1 Monoliths as a Route to High Volumetric and Gravimetric Hydrogen Storage Capacity

Densified HKUST-1 Monoliths as a Route to High Volumetric and Gravimetric Hydrogen Storage Capacity

Mxene Enabled Binder-Free Feof Cathode with High Volumetric and Gravimetric Capacities for Flexible Lithium Ion Batteries

Mxene Enabled Binder-Free Feof Cathode with High Volumetric and Gravimetric Capacities for Flexible Lithium Ion Batteries

Module-Designed Carbon-Coated Separators for High-Loading, High-Sulfur-Utilization Cathodes in Lithium-Sulfur Batteries.

Lithium–sulfur batteries have great potential as next-generation energy-storage devices because of their high theoretical charge-storage capacity and the low cost of the sulfur cathode. To accelerate the development of lithium–sulfur technology, it is necessary to address the intrinsic material and extrinsic technological challenges brought about by the insulating active solid-state materials and the soluble active liquid-state materials. Herein, we report a systematic investigation of module-designed carbon-coated separators, where the carbon coating layer on the polypropylene membrane decreases the irreversible loss of dissolved polysulfides and increases the reaction kinetics of the high-loading sulfur cathode. Eight different conductive carbon coatings were considered to investigate how the materials’ characteristics contribute to the lithium–sulfur cell’s cathode performance. The cell with a nonporous-carbon-coated separator delivered an optimized peak capacity of 1112 mA∙h g−1 at a cycling rate of C/10 and retained a high reversible capacity of 710 mA∙h g−1 after 200 cycles under lean-electrolyte conditions. Moreover, we demonstrate the practical high specific capacity of the cathode and its commercial potential, achieving high sulfur loading and content of 4.0 mg cm−2 and 70 wt%, respectively, and attaining high areal and gravimetric capacities of 4.45 mA∙h cm−2 and 778 mA∙h g−1, respectively.

High-Efficiency Hybrid Sulfur Cathode Based on Electroactive Niobium Tungsten Oxide and Conductive Carbon Nanotubes for All-Solid-State Lithium-Sulfur Batteries.

All-solid-state lithium-sulfur batteries (ASSLSBs) have become a promising candidate because of their high energy density and safety. To ensure the high utilization and electrochemical capacity of sulfur in all-solid-state batteries, both the electronic and ionic conductivities of the sulfur cathode should be as high as possible. In this work, an intercalation-conversion hybrid cathode is proposed by distributing sulfur evenly on electroactive niobium tungsten oxide (Nb18W16O93) and conductive carbon nanotubes (CNTs) for achieving high performance ASSLSBs. Herein, Nb18W16O93 shows good electrochemical lithium storage in the hybrid cathode, which could serve as an effective Li-ion/electron conductor for the conversion of sulfur in the discharge/charge processes to achieve a high utilization of sulfur. However, CNTs could further increase the electronic conductivity of the hybrid cathode by constructing good conductive frameworks and suppress the volumetric fluctuation during the interconversion of sulfur and Li2S. With this strategy, the S/Nb18W16O93/CNT cathode achieves a high sulfur utilization of 91% after one cycle activation with a high gravimetric capacity of 1526 mA h g-1. In addition, excellent rate performance is also obtained at 0.5 C with a reversible capacity of 1262 mA h g-1 after 1000 cycles. This work offers a new perspective to develop ASSLSBs.

Superior pseudocapacitive performance and mechanism of self-assembled MnO2/MXene films as positive electrodes for flexible supercapacitors

Two-dimensional (2D) MXene materials have significant potential applications in electrochemical energy storage. A Ti3C2Tx MXene film can be used as a high-performance electrode for a flexible supercapacitor owing to its flexibility and excellent rate capability. However, Ti3C2Tx is usually only used as a negative electrode material because it can be easily oxidized under positive (anodic) potential. Herein, we report a simple filtration method to fabricate a hybrid cathode by mixing a colloidal solution of 2D Ti3C2Tx nanosheets and 1D MnO2 nanobelts to form an alternating MnO2/Ti3C2Tx stacked structure. Compared with pure Ti3C2Tx, the hybrid cathode has higher electrochemical stability toward anodic oxidation. The MnO2/Ti3C2Tx hybrid cathode delivers a high gravimetric capacitance of 315 F g−1 at 10 mV s−1 and a good rate capability of 166 F g−1 at 100 mV s−1. The high stability of the MnO2/Ti3C2Tx hybrid cathode is mainly attributed to the charge transfer-induced work function enlargement at the Ti3C2Tx and MnO2 heterointerface. Furthermore, a flexible asymmetric supercapacitor assembled using MnO2/Ti3C2Tx as the cathode and alkalized Ti3C2Tx as the anode delivers a high-voltage window up to 1.9 V. This work provides new insights for designing high-performance MXene-based cathode materials and devices for wearable electronics.

Bi@C Nanospheres with the Unique Petaloid Core-Shell Structure Anchored on Porous Graphene Nanosheets as an Anode for Stable Sodium- and Potassium-Ion Batteries.

Bismuth (Bi) has emerged as a prospective candidate as Na-ion and potassium-ion battery anodes because of its unique advantages of low cost, high theoretical gravimetric capacity (386 mAh g-1), and superior volumetric capacity (3800 mAh cm-3). However, the low electronic conductivity and the huge volume expansion of Bi during the alloying/dealloying reactions are extremely detrimental to cycling stability, which seriously hinder its practical application. To overcome these issues, we propose a rational design: Bi@C nanospheres with the unique petaloid core-shell structure are synthesized in one step for the first time and then combined with different contents of graphene (GR) nanosheets to form the composites Bi@C@GR. The Bi@C nanospheres with a core-shell structure are beneficial to shortening the transmission path of electrons/ions and reducing the risk from structural rupture of the particles during cycling. In addition, the combination of Bi@C nanospheres and porous GR could greatly improve the conductivity and prevent the aggregation of particles, which is conducive to better cycling stability and rate performance. Consequently, Bi@C@GR-2 presents a superior reversible capacity for sodium storage (300 mAh g-1 over 80 cycles) and potassium storage (200 mAh g-1 over 70 cycles) at 0.1 A g-1. Furthermore, in situ electrochemical impedance spectroscopy and ex situ transmission electron microscopy are carried out to analyze and reflect the kinetic reaction mechanism and the phase change of the Bi@C@GR-2 electrode during the charge/discharge processes.

Spontaneous nanominiaturization of silicon microparticles with structural stability as flexible anodes for lithium ion batteries

Silicon (Si) is an ideal anode material for lithium ion batteries (LIBs) because of its high gravimetric capacity (3579 mAh g−1). However, Si anode undergoes sharp volume expansion during the charge/discharge process and then easily fragments to forfeit electronic contact, thereby forming dead Si, especially for micron-sized Si particles. We prepared a free-standing Si-based film anode, in which the micron Si particles are embedded by a coupled network of carbon nanotubes and the micro-nano structure is anchored by a carbon nanocoating layer. The networks can catch the nanominiaturized Si particles and provide continuous electrical contact during long cycling, thereby reviving the fragmented Si and maintaining lithium storage properties. This Si anode exhibits an ultra-high specific capacity of 3385.2 mAh g−1. The excellent cycling performance of 2345.3 mAh g−1 remained after 100 cycles at a current density of 0.3 A g−1. The pouch LIB based on the Si anode showed outstanding rate capacity and flexibility. This strategy is expected to solve the volume expansion and promote the application of the micron Si-based materials.

Atomic layer deposited aluminum oxynitride coating for high-performance Si anode in lithium-ion batteries

Silicon (Si) has received great attention as a promising anode material for lithium-ion batteries (LIBs) due to its high gravimetric capacity and large abundance. However, the use of Si anodes in LIBs has been hindered by their inferior electrochemical performance, resulting from its vast volume expansion and unstable solid electrolyte interphase (SEI). To address these problems, a novel surface coating material, aluminum oxynitride (AlOxNy), was developed using a plasma-enhanced atomic layer deposition technique with trimethylaluminum and plasma N2/H2 as the precursors. The effects of AlOxNy surface coatings on the electrochemical properties of Si electrodes were investigated. With the optimal AlOxNy coating (∼2 nm), the reversible capacity after 140 cycles was improved from 331 mAh g−1 for bare Si electrode to 1297 mAh g−1 for AlOxNy-coated one, and the capacity retention was elevated from 13% to 72%. Post-cycling analysis revealed that the AlOxNy coating significantly suppressed the charge transfer and SEI resistances and maintained the structural integration of Si electrodes by suppressing continuous electrolyte decomposition and electrode delamination from the current collector. This study provides a new perspective on designing advanced functional coating materials for atomic layer deposition for lithium-ion batteries.

Stability, Electronic Structure and Thermodynamic Properties of Nanostructured MgH2 Thin Films

Magnesium is an attractive hydrogen storage candidate due to its high gravimetric and volumetric storage capacities (7.6 wt.% and 110 gH2/l, respectively). Unfortunately, its use as a storage material for hydrogen is hampered by the high stability of its hydride, its high dissociation temperature of 573–673 K and its slow reaction kinetics. In order to overcome those drawbacks, an important advancement toward controlling the enthalpy and desorption temperatures of nano-structured MgH2 thin films via stress/strain and size effects is presented in this paper, as the effect of the nano-structuring of the bulk added to a biaxial strain on the hydrogen storage properties has not been previously investigated. Our results show that the formation heat and decomposition temperature correlate with the thin film’s thickness and strain/stress effects. The instability created by decreasing the thickness of MgH2 thin films combined with the stress/strain effects induce a significant enhancement in the hydrogen storage properties of MgH2.

Fine-Tuning a Robust Metal-Organic Framework toward Enhanced Clean Energy Gas Storage.

The development of adsorbents with molecular precision offers a promising strategy to enhance storage of hydrogen and methane─considered the fuel of the future and a transitional fuel, respectively─and to realize a carbon-neutral energy cycle. Herein we employ a postsynthetic modification strategy on a robust metal-organic framework (MOF), MFU-4l, to boost its storage capacity toward these clean energy gases. MFU-4l-Li displays one of the best volumetric deliverable hydrogen capacities of 50.2 g L-1 under combined temperature and pressure swing conditions (77 K/100 bar → 160 K/5 bar) while maintaining a moderately high gravimetric capacity of 9.4 wt %. Moreover, MFU-4l-Li demonstrates impressive methane storage performance with a 5-100 bar usable capacity of 251 cm3 (STP) cm-3 (0.38 g g-1) and 220 cm3 (STP) cm-3 (0.30 g g-1) at 270 and 296 K, respectively. Notably, these hydrogen and methane storage capacities are significantly improved compared to those of its isoreticular analogue, MFU-4l, and place MFU-4l-Li among the best MOF-based materials for this application.

Metal hydroborates: From hydrogen stores to solid electrolytes

The last twenty years of an intense research on metal hydroborates as solid hydrogen stores and solid electrolytes are reviewed. It is shown that from the most promising application in hydrogen storage due to their high gravimetric and volumetric capacities, the focus has moved to solid electrolytes due to high cation mobility in disordered structures with rotating or tumbling anions-hydroborate clusters. Various strategies of overcoming the strong covalent bonding of hydrogen in hydroborates for hydrogen storage and disordering their structures at room temperature for solid electrolytes are discussed. The important role of crystal chemistry and crystallography knowledge in material design can be read in the cited literature.

High performance and long cycle life neutral zinc-iron flow batteries enabled by zinc-bromide complexation

Zinc-based flow batteries have attracted tremendous attention owing to their outstanding advantages of high theoretical gravimetric capacity, low electrochemical potential, rich abundance, and low cost of metallic zinc. Among which, zinc-iron (Zn/Fe) flow batteries show great promise for grid-scale energy storage. However, they still face challenges associated with the corrosive and environmental pollution of acid and alkaline electrolytes, hydrolysis reactions of iron species, poor reversibility and stability of Zn/Zn2+ redox couple. In this work, bromide ions are used to stabilize zinc ions via complexation interactions in the cost-effective and eco-friendly neutral electrolyte. Cyclic voltammetry results reveal that the redox reversibility between Zn and stabilized Zn2+ is greatly improved. The results of spectrum characterizations and density functional theory calculations verify that the formation of Zn[Brn(H2O)6-n]2-n (1 ≤ n ≤4, n is integer.) ions accounts for the increased electrochemical reversibility of Zn/Zn2+pair. Moreover, to overcome the bottleneck of slow kinetics of the coordination interactions between Zn2+ and Br−, ZnBr2 is judiciously selected as the electrolyte additive to promote the complexation process. Adopting K3Fe(CN)6 as the positive redox species to pair with the zinc anode with ZnBr2 modified electrolyte, the proposed neutral Zn/Fe flow batteries deliver excellent efficiencies and superior cycling stability over 2000 cycles (356 h), shedding light on their great potential for large scale energy storage.

La1-x K x FeO3-δ: An Anion Intercalative Pseudocapacitive Electrode for Supercapacitor Application.

The green energy alternative to a fossil fuel-based economy can be provided only by coupling renewable energy solution solutions such as solar or wind energy plants with large-scale electrochemical energy storage devices. Enabling high-energy storage coupled with high-power delivery can be envisaged though high-capacitive pseudocapacitor electrodes. A pseudocapacitor electrode with multiple oxidation state accessibility can enable more than 1e– charge/transfer per molecule to facilitate superior energy storage. K-doped LaFeO3 (La1–xKxFeO3−δ) is presented here as an electrode having a high pseudocapacitance storage, equivalent to 1.32e– charge/transfer per molecule, resulting in a capacity equivalent of 662 F/g at 1 mV/s scan rate by introduction of a layered potential over the Fe-ion octahedral to utilize higher redox state energies (Fe4+→ Fe2+). La/K ordering in orthorhombic perovskite (La1–xKxFeO3−δ) made the Fe4+ oxidation state accessible, and a systematic shift in the redox energies of Fe4+/3+ and Fe3+/2+ redox couples was observed with K+ ion doping in the A site of the LaFeO3 perovskite, which resulted in a high faradic contribution to the capacitance, coupled with anionic intercalation of H2O/OH– in the host perovskite lattice. The surface capacitive and diffusion control contributions for capacitance are about 42 and 58%, respectively, at −0.6 V, with a scan rate of 1 mV/s. A high gravimetric capacitance, equivalent to 619, 347, 188, 121, and 65 F/g, respectively, at 1, 2, 3, 5, and 10 A/g constant current, was observed for the La0.5K0.5FeO3−δ electrode. Up to 88.9% capacitive retention and 97% Coulombic efficacy were obtained for continuous 5000 cycles of charge/discharge for the La0.5K0.5FeO3−δ electrode. The gravimetric capacitance values of ASCs (activated carbon//La0.5K0.5FeO3−δ) are 348, 290, 228, and 147 F/g at current densities of 1, 2, 3, and 5 A/g, respectively. A maximum specific power of ∼3594 W/kg was obtained when the specific energy reached ∼117 Wh/kg at 5 A/g of current density.

Potential reversible and high-capacity hydrogen storage medium: Li-decorated B3S monolayers

The potential application of the B3S monolayer with and without Li decorated as hydrogen storage materials (HSMs) were studied using DFT calculations. We found that the interactions between H2 molecule and the pure B3S monolayer is too tiny to meet the requirements of optimal HSMs. The large binding energy (3.00–3.30 eV) of Li atoms on the B3S monolayer effectively hinders Li clustering. The adsorption energy per H2 for H2 molecules on the Li-decorated B3S monolayer is as moderate as between 0.167 and 0.208 eV, and the electrostatic nature of the interactions between H2 and Li-decorated monolayers is found. The Li-decorated B3S monolayers have high gravimetric and volumetric capacity of 7.7 wt% and 94.8 g/L, respectively. The desorption temperature indicates that the Li-decorated B3S monolayers as HSMs have high reversibility over the temperature of 224 K, and AIMD simulations show that H2 molecules have no kinetic hindrance for desorption. Therefore, the Li-decorated B3S monolayers are reversible and high capacity materials for hydrogen storage meeting the targets of U.S. DOE.

The influence of LiH and TiH2 on hydrogen storage in MgB2 I: Promotion of bulk hydrogenation at reduced temperature

Mg(BH4)2 is an attractive hydrogen storage material, owing to its high gravimetric capacity of 14.9 wt %. However, the dehydrogenated material MgB2 is very difficult to rehydrogenate, requiring excessive pressures and temperatures. Here we report the influence of LiH and TiH2 on hydrogen storage reactions involving Bulk MgB2 using XRD, XAS, FTIR and NMR. In ball-milled mixtures of LiH/MgB2, the LiH loses crystallinity but remains undissociated, forming a weakly bound complex with MgB2. The weak interactions produce minor variations in the local electronic structure at B and Mg, but do not markedly affect the underlying MgB2 hexagonal crystal structure. No evidence is found for a mixed-metal boride Mg1-xLixB2 in the as-prepared LiH/MgB2 materials. The presence of LiH dramatically improves the hydrogenation of MgB2 at 700 bar, forming borohydride 100 °C below the minimum hydrogenation temperature of pure MgB2 and without the formation of undesirable intermediates such as [B3H8]-, [B10H10]2- or [B12H12]2-. Evidence is reported for a mixed-metal borohydride of the type Mg(3-x)/2Lix(BH4)3 produced by the hydrogenation. Subsequent desorption is also improved compared to pure Mg(BH4)2 and LiBH4, showing single-step hydrogen release up to ∼8 wt% by 380 °C, whereas Mg(BH4)2 and LiBH4 still retain significant amounts of hydrogen at this temperature. The material produced by desorption contains both MgB2 and Mg metal, revealing the original LiH/MgB2 system is not fully reversible. In contrast to LiH, TiH2 is essentially inert when ball-milled with MgB2, and high-pressure hydrogenation leaves only unreacted TiH2 and MgB2. Thus, added TiH2 provides no benefit to MgB2 hydrogenation.

In-situ constructed destabilization reaction of LiBH4 wrapped with graphene toward stable hydrogen storage reversibility

Building destabilization reaction of LiBH4 with high gravimetric and volumetric capacity has been regarded as one of the most effective ways to improve its hydrogen storage performance. These destabilization reactions, however, suffer from low efficiency and severe phase separation upon hydrogen storage, resulting in poor reversibility of LiBH4. Herein, the construction of LiBH4 destabilized by Al wrapped by graphene is realized by an in-situ solid–gas reaction of LiH and Al resulting from the dehydrogenation of LiAlH4 and diborane. Owing to the uniform formation of LiH around Al nanoparticles on a molecular level, the homogeneous distribution of LiBH4 around Al nanoparticles with intimate contact could be achieved, which, coupled with the significant decrease of their particle sizes down to the nanometer size, effectively promotes the destabilization reaction between LiBH4 and Al. As a result, a single-step dehydrogenation reaction between LiBH4 and Al towards the complete dehydrogenation of LiBH4 with the formation of AlB2 and AlLi is demonstrated at 400°C. More importantly, induced by the enhanced destabilization reaction efficiency between LiBH4 and Al, the complete dehydrogenation and hydrogenation of LiBH4 with a reversible capacity of 4.49 wt% after 5 cycles could be well preserved owing to the structural support role of graphene.

Programmable coating of polyaniline on hemispherical nitrogen-doped mesoporous hollow carbon as high performance material for supercapacitor

Miniaturized electronic and wearable devices require energy storage systems, which can store a large amount of energy in a very narrow space/volume. Supercapacitors are considered as promising devices for portable electronics due to their robust performance and ultra-high cycling stability; however, their volumetric capacitance is far from the reality. Herein, we have developed a hybrid of nitrogen-doped hemispherical structured carbon (HNC) and polyaniline (PANI). Synergistic contribution of pseudocapacitive PANI and electric double layer capacitive HNC results in remarkably improved electrochemical properties. An optimized HNC/PANI-0.05 composite displayed 16.19 times improvement in the volumetric capacitance (1263 F cm−3) and seven times in gravimetric capacitance (547 F g−1) than that of pure HNC. The composite also showcases improved energy, power density, and cyclic stability. Hence, in the HNC/PANI-0.05 composite achievement of a balance between the mesoporosity and high value density imparts a high gravimetric capacitance together with an excellent volumetric capacitance.

The preparations of nanoporous carbon with multi-heteroatoms co-doping from black liquor powders for supercapacitors

Abstract A green and economically viable route without any additional activation agents and templates has been developed to synthesize biomass-derived nanoporous carbon for superior electric double-layer capacitors via direct pyrolysis of dried black liquor powders, which is the main waste in pulping and paper-making industry. The resulting carbon materials present hierarchical porosity and moderate specific surface area of 1134 m 2 g − 1 {\text{m}^{2}}\hspace{0.1667em}{\text{g}^{-1}} , as well as multi-heteroatoms co-doping such as N, S, Na and K, which exist originally in black liquor. When evaluated as electrode materials for supercapacitors in 6 M KOH aqueous electrolyte, the-prepared carbon samples deliver a significantly high gravimetric capacitance of 331 F g − 1 \text{F}\hspace{0.1667em}{\text{g}^{-1}} at 0.5 A g − 1 \text{A}\hspace{0.1667em}{\text{g}^{-1}} in a three-electrode system. Moreover, the fabricated symmetric supercapacitor also possesses a gravimetric capacitance of 211 F g − 1 \text{F}\hspace{0.1667em}{\text{g}^{-1}} at 0.5 A g − 1 \text{A}\hspace{0.1667em}{\text{g}^{-1}} , with an impressive long-term cycling stability of 92 % capacitance retention after 3000 cycles. This work explores a suitable and scalable approach for mass production of high-performance electrode materials with industrial wastes on the base of cost-efficiency and environment-friendship.