High Gravimetric Capacity Research Articles

A Dithiin-Linked Covalent Organic Polymer for Ultrahigh Capacity Half-Cell and Symmetric Full-Cell Sodium-Ion Batteries.

Sodium ion-batteries (SIBs) are considered as a class of promising alternatives to lithium-ion batteries (LIBs) to overcome their drawbacks of limited sources and safety problems. However, the lack of high-performance electrode materials hinders the wide-range commercialization of SIBs. Comparing to inorganic counterparts, organic electrode materials, which are benefitted from flexibly designable structures, low cost, environmental friendliness, and high theoretical gravimetric capacities, should be a prior choice. Here, a covalent organic polymer (COP) based material (denoted as CityU-9) is designed and synthesized by integrating multiple redox motifs (benzoquinone and thioether), improved conductivity (sulfur induction), and intrinsic insolubility (rigid skeleton). The half-cell SIBs exhibit ultrahigh specific capacity of 1009mAhg-1 and nearly no capacity drop after 650 cycles. The first all-COP symmetric full-cell shows high specific capacity of 90mAhg-1 and excellent rate capability. This work can extend the selection of redox-active moieties and provide a rational design strategy of high-performance novel organic electrode materials.

Electrical bridging effects of dual-carbon microsphere frameworks in Si-based composite anodes for high-performance Li-ion batteries

Herein, the successful fabrication of a high-performance Si-based composite Li-ion battery (LIB) anode, comprising a dual-carbon framework of reduced graphene oxide (r-GO) and oxidized single-walled carbon nanohorns (o-NHs), was demonstrated using a simple and scalable spray-drying process followed by heat treatment (h-s-GO/Si/NH). The r-GO nanosheets in the h-s-GO/Si/NH anode acted as a robust spherical framework that facilitated the mechanical and electrical connection between the carbon-coated Si (c-Si) nanoparticles, homogeneous dispersion of c-Si and o-NH nanoparticles, and suppression of the volume expansion and pulverization that occur during lithiation/delithiation. Additionally, the o-NH nanoparticles incorporated in the h-s-GO/Si/NH composite served as electrical bridges between the r-GO nanosheets, resulting in enhanced electrical conductivity and effortless Li-ion shuttling. The h-s-GO/Si/NH composite anode exhibited high electrochemical performance with a very high initial gravimetric charge capacity (2961 mAh g−1 at 0.1 A g−1), stable initial Coulombic efficiency (80.6% at 0.2 A g−1), and high cycling stability (983 mAh g−1 at 0.2 A g−1 after 50 cycles). This study highlights the importance of the effective design of electrically conductive three-dimensional frameworks in Si-based composite anodes, which may contribute to the development of high-performance LIB anode materials.

A new 3D porous metallic carbon allotrope composed of 5–7 nanoribbons as an anode material for sodium-ion batteries

Motivated by the successful synthesis of three-dimensional (3D) graphene monoliths, tremendous effort has been devoted to the design of 3D porous metallic carbon allotropes with rich topology by assembling various nanoribbons for the anode materials of metal-ion batteries in recent years. Going beyond the allotropes reported so far we propose a new 3D carbon monolith, Hex-C57, by using 5–7 nanoribbons observed in the experiment as the building block. Hex-C57 is found to be dynamically, thermally, and mechanically stable, and electronically metallic. An analysis based on the tight-binding model reveals that the metallicity originates from the pz-orbitals of the sp2-hybridized carbon atoms, forming the conducting channels along the axial direction. With the advantages of intrinsic metallicity, mechanical ductility, and ordered pores, Hex-C57 is a highly promising anode material for sodium-ion batteries (SIBs). Calculations of the electrochemical properties show that Hex-C57 possesses a high reversible gravimetric capacity (334.69 mAhg−1) and volumetric capacity (314.61 mAhcm−3), a small volume change (1.45%), very low diffusion barriers (0.046–0.070 eV), and a low average open-circuit voltage (0.18 V). This work not only expands the 3D porous carbon family with different nanoribbons as the building blocks, but also demonstrates the functionality of unconventional 5–7 carbon rings-assembled materials.

Anti-Shedding Nickel-Protection-Layer Boosting an Ultrahigh Loading Carbon Fiber@Co-NiSx Electrode to Deliver Superior Areal/Volumetric/Gravimetric Capacitance.

Challenges remain to show good capacitive performance while achieving high loadings of active materials for supercapacitors. Trying to realize this version, a nickel-protecting carbon fiber paper@Co-doped NiSx (Ni-CP@Co-NiSx) electrode with high specific gravimetric, areal, and volumetric capacitance is reported in this work. This free-standing electrode is prepared by an electroplating-hydrothermal-electroplating (EHE) three-step method to achieve a high loading of almost 26.7 mg cm-2. The cobalt-doping and nickel-protection strategies effectively decrease the impedance and inhibit the active material dropping from the electrode resulting from the expansion stress, which endows the Ni-CP@Co-NiSx electrode with a high rate and good cycling performance, especially with an ultrahigh specific areal/volumetric/gravimetric capacitance of 53.3 F cm-2/2807 F cm-3/1997 F g-1 at 5 mA cm-2, respectively. Employing activated carbon functionalized with riboflavin (AC/VB2) as a negative electrode, the asymmetric supercapacitor device delivers a very high energy density of up to 60.4 W h kg-1. This work demonstrates that electrodes with a high loading density and excellent performance can be obtained by the combination of the EHE method to adjust the internal conductivity and external structural stability.

Walnut shell derived N, S co-doped activated carbon for solid-state symmetry supercapacitor device

The kernel of the walnut constitutes a nutrient-dense food source. However, the walnut shell is useless and was thrown away. Therefore, as a small initiative towards waste-to-wealth, herein we developed walnut shell-derived highly porous heteroatom (nitrogen and sulfur) doped activated carbon (NS-WAC) via KOH activation and post-processing treatment by thioacetamide (TAA). The NS-WAC exhibits a high specific surface area (SSA) and various particle size distribution (PSD) involving micropores, mesopores, and macropores, conferring substantial supercapacitor advantages. The NS-WAC possesses a significant proportion of mesopores, which can decrease the ion diffusion path length and improve ion transport efficiency. Hence, NS-WAC demonstrates promising electrochemical performance achieving a high gravimetric specific capacitance of 271.4 Fg−1 at 0.5 Ag−1 in 3 M KOH aqueous electrolyte. Furthermore, the solid-state symmetric supercapacitor (SSC) device exhibited a gravimetric specific capacitance of 52 Fg−1 and volumetric specific capacitance of 74.36F cm−3 at a current density of 0.5 Ag−1. This SSC device also exhibited a gravimetric energy density of 23.4 Wh Kg−1 at a power density of 250 W Kg−1 at a current density of 0.5 Ag−1. It showed superior cycle stability of 91.8% after 10,000 cycles at 5 Ag−1.

Impact of Coin Cell Preparation and Testing Protocols on Coulombic Efficiency Measurements

The lithium (Li) metal anode holds great promise for high energy-density rechargeable batteries due to its high gravimetric capacity (3860 mAh/g), an order of magnitude larger than graphite at a similar electrochemical potential (-3.040 V vs SHE for Li). However, limited Coulombic efficiency (CE), caused by the thermodynamic instability of conventional Li-ion electrolyte solvents and salts with Li that leads to unstable solid-electrolyte interphase (SEI) during repeated plating and stripping, has hindered the commercialization of Li metal batteries. Research efforts have focused on tuning the electrolyte composition to promote a stable SEI that simultaneously blocks continuous side reactions and electronic conductivity while facilitating Li+ transport [1], with coin cells being by far the most preferred form factor for evaluating these electrolyte designs.Coin cells enable accessible and rapid testing of diverse electrolyte compositions. Their preparation requires no specialized equipment beyond an inert chemical environment, a crimping mechanism to seal the cell, and modest quantities of Li metal (~50 - 100 μm thickness) and electrolyte (~50 - 100 μL volume) [2]. Despite these attractive features, the procedures for preparing and techniques for measuring CE in coin cells are not fully standardized. In this presentation, we examine the impact on measured CE from preparation and testing procedures, including the internal coin cell stack consisting of components such as the electrodes, current collectors / spacers, and separators, and the cycling protocol. While the cycling protocol and cycling capacity are known to affect capacity loss mechanisms in Li metal batteries [3], we show that variances in CE can additionally be attributed to specific details of cell preparation. In particular, the working electrode area and stack thickness affect the pressure magnitude and uniformity inside the cell. We demonstrate that standardizing the procedures for preparing coin cells reduces variation due to nonuniformities and edge effects and hence improves the reproducibility of CE measurements.[1] Hobold, G. M., et al. Nature Energy 2021 6 (10), 951-960.[2] Xiao, J., et al. Nature Energy 2020 5 (8), 561-568.[3] Adams, B. D., et al. Advanced Energy Materials 2018 8 (7), 1702097. Figure 1

Enhancing the Cycle Life of Solid-State Batteries by Restraining the Volume Change of Silicon Anodes

The high gravimetric and volumetric capacity of silicon makes it an attractive anode material for lithium-ion solid-state batteries (SSBs). [1,2] However, silicon suffers from high volume changes during cycling and requires high stack pressures to stabilize the interfaces. [3-5] Herein, we present different approaches to minimize the breathing of silicon-based anodes leading to stabilized cycling.Silicon carbon void structures (Si-C) obtain a void between the silicon nanoparticle and the surrounding carbon matrix to compensate the volume changes already within the anode structure. As a result, excellent cycling performance in solid-state cells with areal loadings as high as 7.4 mAh cm-2 can be demonstrated. Thereby, Si-C composite electrodes show higher lithiation capacities, better rate stability and higher capacity retentions than pristine silicon nanoparticles (SiNPs), which rapidly degrade due to the immense mechanical stress upon charging and discharging. Hence, the volume changes of the SiNPs are well compensated by the carbon matrix, which also stabilizes the entire electrode. In full cells with nickel-rich NCM (LiNi0.9Co0.05Mn0.05O2, 210 mAh g-1) as cathode, higher initial discharge capacities and coulombic efficiencies (72.7 % vs. 31.0 %) can be achieved compared to the liquid system. The solid electrolyte (Li6PS5Cl, 3 mS cm-1) does not penetrate the whole carbon matrix of the Si-C particles resulting in less side reactions. Consequently, prelithiation of the Si-C anodes is not required in SSBs. By applying either a low (1.1) or rather high n/p ratio (2.0) capacity retentions of up to 87.7 % after 50 cycles can be reached. [6]Especially for industrial fabrication of SSB anodes other procedures than the complex multi-step synthesis of e.g. Si-C composites are needed. [7] Consequently, we evaluated low-cost silicon microparticles (µm-Si) as partially lithiated electrode material (800 mAh g-1) in SSB half- and full cells. By reducing the utilized fraction of silicon, the breathing during cycling is reduced from 300 % to 66 %, which reduces the armorphization of the active material. In addition, the grain boundaries of silicon are connected by a matrix of solid electrolyte and carbon additive, which drastically reduces the need for a high stack pressure. After limiting the charge cut-off potential of NCM|SE|µm-Si full cells, significant increased capacity retentions from 32 % to 71 % after 50 cycles can be reached. In addition, similar performance compared to the Si-C electrodes can be demonstrated making it to an auspicious alternative. [8]Overall, the herein presented silicon materials achieved decent electrochemical performance without active pressure control on the cells being beneficial for electric vehicle and other applications. Hence, both Si-C and µm-Si particles are promising concepts for stable, high-capacity SSB anodes.Literature:[1] A. Mukanova, A. Jetybayeva, S.-T. Myung, S.-S. Kim, Z. Bakenov, Mater. Today Energy 2018, 9, 49.[2] N. Nitta, G. Yushin, Part. Part. Syst. Charact. 2014, 31, 317.[3] X. Su, Q. Wu, J. Li, X. Xiao, A. Lott, W. Lu, B. W. Sheldon, J. Wu, Adv. Energy Mater. 2014, 4, 1300882.[4] D. H. S. Tan, Y.-T. Chen, H. Yang, W. Bao, B. Sreenarayanan, J.-M. Doux, W. Li, B. Lu, S.-Y. Ham, B. Sayahpour et al., Science (N.Y.) 2021, 373, 1494.[5] S. Cangaz, F. Hippauf, F. S. Reuter, S. Doerfler, T. Abendroth, H. Althues, S. Kaskel, Adv. Energy Mater. 2020, 3, 2001320.[6] S. Poetke, F. Hippauf, A. Baasner, S. Dörfler, H. Althues, S. Kaskel, Batteries Supercaps 2021, 4, 1323.[7] D. Jantke, R. Bernhard, E. Hanelt, T. Buhrmester, J. Pfeiffer, S. Haufe, J. Electrochem. Soc. 2019, 166, A3881.[8] S. Poetke, S. Cangaz, F. Hippauf, S. Haufe, S. Dörfler, H. Althues, S. Kaskel, Energy Technol. 2022 submitted.

Cathode Development for All Solid-State Lithium-Sulfur Batteries

With higher demand for alternative energy sources that are cleaner and more sustainable, research has shifted towards various lithium metal-based batteries with higher capacities than lithium-ion (LIBS). The study of lithium-sulfur energy storage systems has been heavily influenced due to the high gravimetric capacity of sulfur (1672 mA h g−1) and its abundance in the Earth’s crust. To increase the safety of lithium-sulfur batteries, solid state systems have been developed. These systems are also advantageous as the polysulfide shuttle effect normally seen in organic liquid electrolytes (OLEs) is eliminated, decreasing degradation due the irreversible reactions. Some of the most successful electrolytes found for lithium-sulfur all solid-state batteries (ASSLSBs) are ceramic based electrolytes. These electrolytes have high ionic conductivities (ranging 10-3-10-4 S cm-1) and do not pose any safety risks. However, one of the biggest bottlenecks of ASSLSBs is the utilization and accessibility of sulfur during cycling.To ensure these attributes are met, carbon materials have been used as supports; additionally, carbon also aids in electron transport due sulfur’s low electrical conductivity (10 -15 S m-1).Sulfur is typically dispersed or deposited on these carbon supports in different approaches before a full cathode composition is developed. Varying synthesis methods of sulfur deposition onto reduced graphene oxide are studied to determine which synthesis method provides the most accessibility for sulfur utilization. Utilization and accessibility will be analyzed through cyclic voltammetry, galvanostatic charge and discharge and impedance measurements to obtain characteristic voltammograms, specific capacity curves and Nyquist plots. Cells are assembled in PEEK Split cells using ceramic based electrolyte and lithium metal for the development of a noble ASSLSB.

Investigating the Electrolyte Degradation of Lithium-Ion Cells with Silicon-Containing Anodes

Silicon with a high gravimetric capacity of 3579 mAh g-1 of the pure material becomes increasingly common in the anode of lithium-ion batteries to increase energy density on the full cell level. However, silicon changes its volume excessively during (de-)lithiation making it prone to ageing. In commercial cells, it is typically applied as SiOx in small quantities in a composite anode together with graphite.Gas analytical studies of Gr/SiOx||NMC622 cells with varying silicon content and carbonate-based electrolyte are presented. The electrolyte consists of 1M LiPF6 in EC:DEC (1:1, v/v) + 5 wt-% FEC. The focus of this study is on investigations of ageing processes such as electrolyte decomposition during formation cycling. All measurements were carried out using specially developed multifunctional test setups and accordingly modified test cells. The different cell specifications were examined by operando mass spectrometry (MS) and post-mortem gas chromatography-mass spectrometry (GC-MS).Strong gas formation leads to a loss of electrolyte, which can cause the cell to dry out and consequently limit the cycle life. Gas analysis is a suitable method to identify decomposition products as well as to illustrate degradation reactions. Operando MS can be used to detect gaseous substances produced by (electro)chemical processes as a function of the state of charge. Furthermore, a post-mortem GC-MS analysis was performed to identify the individual substances qualitatively.The cyclic formation of several degradation products can be determined. Among others, carbon dioxide, hydrogen as well as ethane are identified as characteristic decomposition products of the electrolyte. In addition, the decomposition path of the conducting salt can be detected. Another main result is the evidence of the presence of silicon-containing gaseous fragments as a function of the Si-content in the composite anode.These gas analytical studies of silicon graphite composite anodes provide an important contribution to the understanding of the degradation reactions taking place. The results shown help to illustrate them and give information about the influence of the silicon content on electrolyte degradation. Figure 1

Grand Canonical Monte Carlo simulations of hydrogen and methane storage capacities of two novel Al-nia MOFs at room temperature

Novel materials capable of storing hydrogen or/and methane at high gravimetric and volumetric densities are required for hydrogen vehicles to be widely employed as a clean alternative to fossil-based vehicles. Metal-Organic Frameworks (MOFs) are considered as promising candidates to achieve the Department Of Energy (DOE) targets for both, hydrogen and methane storage. Using Grand Canonical Monte Carlo (GCMC) simulations, the hydrogen and methane gravimetric and volumetric storage capacities of two recently synthesized Al-nia MOFs have been studied. Their storage capacities have been compared with the storage capacities of other Al-based MOFs and classical and well-known MOFs, such as IRMOF-5. The two novel Al-nia MOFs have shown high hydrogen and methane gravimetric and volumetric storage capacities at room temperature and moderate pressures, 25–35 MPa, comparable or higher than the storage capacities of classical and Al-based MOFs.

Rationalizing the impact of oxygen vacancy on polysulfide conversion kinetics for highly efficient lithium-sulfur batteries

The “shuttle effect” of lithium polysulfides (LiPSs) is a huge challenge for practical use of high-energy-density lithium-sulfur (Li-S) batteries, and one of the main reasons is the sluggish kinetics of sulfur conversion. Metal oxides are able to expedite the sulfur electrochemistry, and the structural defects enhance the adsorption-conversion ability of metal oxides for polysulfides. However, a significant research gap still remains regarding the relationship between the oxygen vacancy concentration and the adsorptive-catalytic performance of metal oxides. Herein, we establish a correlation between oxygen vacancy concentration and adsorptive-catalytic properties by using tungsten oxide (WOx) as model catalysts. It is revealed that high-concentration oxygen vacancy is beneficial for enhancing the binding between tungsten oxide and LiPSs, reducing the energy barrier of Li2S decomposition, and promoting polysulfide conversion kinetics. Consequently, the Li-S batteries using the tungsten oxide with high-concentration oxygen vacancies deliver high initial discharge capacity of 1169 mA h g−1 at 0.2 C and 865 mA h g−1 at 2 C, low attenuation rate of 0.064% per cycle over 1100 cycles at 2 C. With a high sulfur area loading of 5.34 mg cm−2, the Li-S batteries still exhibit high initial gravimetric capacity of 982 mA h g−1 at 0.1 C and areal capacity of 5.92 mA h cm−2. This work promotes the feasibility of defect engineering on metal oxides as an effective mean to enhance the practicality of Li-S batteries.

Corn-straw-converted activated carbons with tunable porosity and N/O functionalities as high-performance supercapacitors electrode at commercial-level mass loading

With the scientific importance and industrial need for low-cost but high-performance activated carbons (ACs) for supercapacitors (SCs), ACs with tailorable porous texture and heteroatom doping are turned from corn straw via hydrothermal and activation processes. Porous texture is mainly adjusted by KOH/biochar mass ratio. O and N surface functionalities are tuned by a subsequent high-temperature treatment by H2O or ammonia. The influences of porosity in the amounts of the introduced N contents are investigated. With symmetric SC cells, the electrochemical performances of the corn-straw-derived ACs are examined at commercial-level mass loading. For aqueous electrolyte, the ACs prepared without KOH activation but with high-temperature treatment by ammonia exhibit high gravimetric capacitance of 192 F/g and volumetric capacitance of 150 F/cm3 due to their high compact density and N atomic fraction. For organic system, the optimum ACs are activated with KOH/biochar ratio of 1:1 and a subsequent ammonia high-temperature treatment, which deliver high gravimetric capacitance of 258 F/g and volumetric capacitance of 167 F/cm3. Balanced porosity and density, low O fraction but high N fraction are found to be favored for organic system. The cost-effective technique route may provide guidance for the design and preparation of biomass-derived ACs with tunable porosity and heteroatom functionalities for practical applications in SCs.

Converting renewable saccharides to heteroatom doped porous carbons as supercapacitor electrodes

Supercapacitors have a high-power throughput and large cycle life, so designing a suitable electrode material is crucial. Saccharide-derived carbons have been explored as sustainable anodes for supercapacitor applications. Mono- and polysaccharides were analyzed with pre-treatment of precursors and activation to understand the critical roles of heteroatom(s) in the precursors and the functionalized architecture in the charge storage mechanism. Acid-base synergistic pre-treatment/activation resulted in an almost 10-fold enhancement in the surface area with multifaceted pore distribution, rendering enhanced charge storage. A dual effect of heteroatom functionalization and activation of saccharide precursors resulted in a high gravimetric capacitance of 172 F/g at 1 A/g in a symmetric two-electrode configuration of chitin polysaccharide samples with a power density of 5000 W/kg at 3.5 W h/kg. It showed capacity retention of up to 100% for over 10,000 cycles. The results widen the current understanding of the electrochemical behaviour of carbons using chemically treated modifications at precursor levels. It unravels the impacts of hierarchical pore size distribution achieved by pre-treatment resulting in higher energy/power density and cycling stability.

Zn2TiO4 synthesized via solid-state method and its effects on dehydrogenation properties of LiAlH4

Lithium alanate (LiAlH4) has high gravimetric capacity but its practical application is still severely constrained by poor reversibility and sluggish kinetics. In this study, the dehydrogenation behaviour of LiAlH4 was modified with the inclusion of Zn2TiO4. The initial temperature for the dehydrogenation of LiAlH4 was downshifted to 111 °C (first dehydrogenation) and 151 °C (second dehydrogenation) with the inclusion of 10 wt% Zn2TiO4. The as-milled LiAlH4 released only 0.1 wt% H2 while the LiAlH4–10 wt% Zn2TiO4 sample released 3.6 wt% H2 in 60 min at 90 °C which is 36 times faster than undoped LiAlH4. The dehydrogenation activation energies for the first two dehydrogenation process was also reduced by 24.1 and 21.0% than as-milled LiAlH4. The X-ray diffraction analysis revealed that the Zn2TiO4 reacts with LiAlH4 and the formed Al–Ti and Ti–Zn during the dehydrogenation leading to the superior dehydrogenation behaviour of LiAlH4.

Fe-doped densely stacked graphene for compact capacitive energy storage

Herein, we present iron oxide (α-Fe2O3) etching and simultaneous hydrothermal reduction approach to prepare densely stacked defect-rich graphene with abundant pseudocapacitive heteroatoms (18.1 wt% O and 1.2 wt% Fe). Electrochemical measurements were conducted in acidic (1 M H2SO4) and neutral (1 M Na2SO4) aqueous media. The Fe-doped densely stacked graphene (Fe-rGO) with a low specific surface area (32.9 m2 g−1) and high particle density (1.84 g cm−3) displayed high gravimetric and volumetric capacitances of 425 F g−1 and 780 F cm−3 at 0.25 A g−1, respectively, as well as outstanding rate performance (71 % capacitance retention at 20 A g−1 in 1 M H2SO4). Moreover, Fe-rGO exhibited high electrochemical and structural stability over 5000 cycles at 10 A g−1 without any loss in capacitance. An asymmetric supercapacitor (ASC) with Fe-rGO negative electrode and MnO2/PEDOT:PSS positive electrode was assembled with aqueous 1 M Na2SO4 electrolyte. The device exhibited 17.3 Wh kg−1 specific energy and a long cyclic stability (10,000 cycles at 1 A g−1). A practical application of the device was demonstrated by powering a light emitting diode.

Hydrogen storage properties of Mg0.10Ti0.30V0.25Zr0.10Nb0.25 lightweight high entropy alloy: A theoretical study

In the past several years, Mg-based high entropy alloys (HEAs) have attracted great attention in high gravimetric hydrogen storage capacity. In this work, the hydrogen storage properties of Mg0.10Ti0.30V0.25Zr0.10Nb0.25 HEA are investigated by first-principles calculations. With increasing hydrogen concentration, the structural stability of BCC and FCC hydrides decreases and increases, respectively. By comparing the lattice constants, number of hydrogenation-induced abnormal short hydrogen-hydrogen bonds and radial distribution functions of BCC and FCC hydrides, it is found that the hydrogen accommodation ability of BCC phase is weaker than that of FCC phase, and a BCC to FCC phase transformation occurs during hydrogenation process. Further total energy calculations suggest that the threshold hydrogen content of phase transformation for Mg0.10Ti0.30V0.25Zr0.10Nb0.25 is around H/M = 1.16. By phonon spectra calculation, the maximum gravimetric hydrogen storage capacity of Mg0.10Ti0.30V0.25Zr0.10Nb0.25 is predicated to be as high as 3.16 wt%, demonstrating that Mg0.10Ti0.30V0.25Zr0.10Nb0.25 HEA is a potential hydrogen storage material.

Cascade Defluorination of Perfluoroalkylated Catholytes Unlocks High Lithium Primary Battery Capacities

AbstractExceeding the energy density of lithium−carbon monofluoride (Li−CFx), today's leading Li primary battery, requires an increase in fluorine content (x) that determines the theoretical capacity available from C−F bond reduction. However, high F‐content carbon materials face challenges such as poor electronic conductivity, low reduction potentials (<1.3 V versus Li/Li+), and/or low C−F bond utilization. This study investigates molecular structural design principles for a new class of high F‐content fluoroalkyl‐aromatic catholytes that address these challenges. A polarizable conjugated system—an aromatic ring with an alkene linker—functions as electron acceptor and redox initiator, enabling a cascade defluorination of an adjacent perfluoroalkyl chain (RF = −CnF2n+1). The synthesized molecules successfully overcome premature deactivation observed in previously studied catholytes and achieve close‐to‐full defluorination (up to 15/17 available F), yielding high gravimetric capacities of 748 mAh g−1fluoroalkyl‐aromatic and energies of 1785 Wh kg−1fluoroalkyl‐aromatic. The voltage compatibility between fluoroalkyl‐aromatics and CFx enables design of hybrid cells containing C−F redox activity in both solid and liquid phases, with a projected enhancement of Li–CFx gravimetric energy by 35% based on weight of electrodes+electrolyte. With further improvement of cathode architecture, these “liquid CFx” analogues are strong candidates for exceeding the energy limitations of today's primary chemistries.

The Structural and Electronic Engineering of Molybdenum Disulfide Nanosheets as Carbon-Free Sulfur Hosts for Boosting Energy Density and Cycling Life of Lithium-Sulfur Batteries.

The compact sulfur cathodes with high sulfur content and high sulfur loading are crucial to promise high energy density of lithium-sulfur (Li-S) batteries. However, some daunting problems, such as low sulfur utilization efficiency, serious polysulfides shuttling, and poor rate performance, are usually accompanied during practical deployment. The sulfur hosts play key roles. Herein, the carbon-free sulfur host composed of vanadium-doped molybdenum disulfide (VMS) nanosheets is reported. Benefiting from the basal plane activation of molybdenum disulfide and structural advantage of VMS, high stacking density of sulfur cathode is allowed for high areal and volumetric capacities of the electrodes together with the effective suppression of polysulfides shuttling and the expedited redox kinetics of sulfur species during cycling. The resultant electrode with high sulfur content of 89wt.% and high sulfur loading of 7.2mgcm-2 achieves high gravimetric capacity of 900.9 mAh g-1 , the areal capacity of 6.48mAh cm-2 , and volumetric capacity of 940 mAh cm-3 at 0.5 C. The electrochemical performance can rival with the state-of-the-art those in the reported Li-S batteries. This work provides methodology guidance for the development of the cathode materials to achieve high-energy-density and long-life Li-S batteries.

Salt template strategy to P doped honeycomb-like carbon with high zinc ion storage performance

As one of the energy storage devices, aqueous zinc ion hybrid capacitors (AZHCs) have been intensively investigated because of their characteristics of high gravimetric capacity, excellent safety and environmental compatibility. Yet, the preparation of highly active electrode materials for AZHCs is still a huge defiance. Herein, the superior energy density and anti-self-discharge AZHCs are achieved based on the P doped honeycomb-like carbons (PHCs) with high surface area, total pore volume and O/P functionalities, which prepared from the triphenyl phosphate by the salt template strategy. The unique structural characteristics of the PHC cathodes not only offer abundant active sites for Zn2+ ion storage, but also supply lots of channels for ion transfer, resulting in rapid ion transport kinetics. Interestingly, the PHC3 cathode presents high capacity of 150.1 mAh g−1 at 0.1 A g−1, big energy and power output of 126.8 Wh kg−1 and 12.19 kW kg−1 and excellent cycle stability with capacity retention of 98.56% after 30,000 cycles. Moreover, the capacity keeps 87.77% of the initial capacity after rested for 250 h. This study offers a facile strategy to prepared carbon cathodes with the heteroatoms for high performance AZHCs.

High well‐matched energy gravimetric–volumetric symmetric super‐capacitor derived from hollow paper stack‐like biomass‐based functional carbon

AbstractBACKGROUNDTwo‐ and three‐dimensional porous activated carbon (C)‐based symmetrical supercapacitors show great potential for extraordinary gravimetric performance as sustainable energy storage. However, the applications of portable and microdimensional supercapacitors are limited by their low volumetric performance stemming from reduced density resulting from increased porosity and high fabrication costs. This study aimed to demonstrate the high gravimetric–volumetric performance of symmetrical supercapacitors from biomass‐based porous carbon‐sources materials through an environmentally benign development method. Unique porous C sourced from TENERA‐type palm oil stick waste was prepared using potassium hydroxide (KOH) as an activating agent. The electrode set resembled a solid plate with an encapsulation density of ≈1.40 g cm−3.RESULTThe study used superior gravimetric–volumetric electrode materials, including an adjusted specific surface area of 934 m2 g−1, single‐doped optimization, and a hollow paper‐stack‐like morphological structure with a high C content of 91%. The results showed that the best electrode in the 1 mol L−1 H2SO4 electrolytes exhibited a high gravimetric capacitance of 233 F g−1 and an extraordinary volumetric capacitance of 326 F cm−3 at 1 A g−1. Furthermore, their coulombic efficiency was ≈99.1% at 10 A g−1. The symmetrical electrode device performed a high gravimetric–volumetric energy density of 19.03 Wh kg−1 and 26.6 Wh L−1 at a maximum output power density of 1.7 kW kg−1 and 1.9 kW L−1, respectively.CONCLUSIONThese results indicate that the applied method development and the C‐biomass‐based electrode material design could achieve a high, well‐matched gravimetric–volumetric performance balance in symmetric supercapacitor devices. © 2023 Society of Chemical Industry.