Gravimetric Energy Density Research Articles

Band Structure Engineering and Orbital Orientation Control Constructing Dual Active Sites for Efficient Sulfur Redox Reaction.

The kinetics difference among multistep electrochemical processes leads to the accumulation of soluble polysulfides and thus shuttle effect in lithium-sulfur (Li-S) batteries. While the interaction between catalysts and representative species has been reported, the root of the kinetics difference, interaction change among redox reactions, remains unclear, which significantly impedes the catalysts design for Li-S batteries. Here, this work deciphers the interaction change among electrocatalytic sulfur reactions, using tungsten disulfide (WS2 ) a model system to demonstrate the efficiency of modifying electrocatalytic selectivity via dual-coordination design. Band structure engineering and orbital orientation control are combined to guide the design of WS2 with boron dopants and sulfur vacancies (B-WS2- x ), accurately modulating interaction with lithium and sulfur sites in polysulfide species for relatively higher interaction with short-chain polysulfides. The modified interaction trend is experimentally confirmed by distinguishing the kinetics of each electrochemical reaction step, indicating the effectiveness of the designed strategy. An Ah-level pouch cell with B-WS2- x delivers a gravimetric energy density of up to 417.6 Wh kg-1 with a low electrolyte/sulfur ratio of 3.6µL mg-1 and negative/positive ratio of 1.2. This work presents a dual-coordination strategy for advancing evolutionarily catalytic activity, offering a rational strategy to develop effective catalysts for practical Li-S batteries.

SU8 polymer derived high capacity and performance anode material for secondary and flexible Li-ion batteries: Experimental and first principle study

This study provides a novel and sustainable protocol for the synthesis of SU8 polymer-based pattern, un-pattern carbon nanofibers (CNF) using an electrospinning process followed by a photolithography technique. Scanning electron microscopy (SEM) analysis of pattern, un-pattern CNFs shows that the average diameter of CNF is within the range of 60–140 nm. Transmission electron microscopy (TEM) studies disclose the average size of CNF exists within the range of 40–150 nm. The first-principle calculations predict that the gravimetric energy and power densities of Li/CNF half cells are 26.96 kW h g−1 and 26.96 kW g−1, respectively. The corresponding theoretical volumetric energy and power densities are 0.07 W h cm−3 and 0.07 W cm−3, respectively. Electrochemical analysis demonstrates the initial discharge capacities of pattern, un-pattern Li/CNF half cells at 100 mA g−1 are 3450 and 2429.8 mA h g−1, respectively. The gravimetric energy density of pattern, un-pattern Li/CNF half cells are within the range of 1800–1366.76 W h kg−1, and subsequent power densities are in the span of 519.63–434.22 kW g−1. The theoretical gravimetric energy and power densities of CNF/LiMn0.33Ni0.33Co0.33 (LMNC) full cells are 2.9 kWh kg−1 and ∼ 2.9 kW kg−1, respectively. Their theoretical volumetric energy and power densities are 1.96 W h cm−3 and 1.96 W cm−3, respectively. Electrochemical analysis discloses that the gravimetric energy and power densities of pattern CNF/LMNC full cells are in the range of 43.18–42.4 kW h kg−1 and 51.82–50.90 kW kg−1, respectively. The gravimetric energy and power densities of un-pattern CNF/LMNC full cells are 42.07–41.59 W h kg−1 and 50.48–49.92 kW kg−1, respectively.

Crystal Engineering of Silica Anode Achieving Intrinsic Zero-Strain.

Si-based anodes have large intrinsic volume expansion, which hinders their practicality and commercialization. To address this challenge, the design principle of intrinsic zero-strain anodes (① large intracrystalline cavities and ② strong bonds) is proposed, and silica with large intracrystalline cavities (SLIC) established by strong Si─O bonds ([SiO4 ] coordinate structures) is obtained and acts as an anode, achieving the intrinsic zero-strain feature first in silicon-based anodes. The phase structure of SLIC is maintained and the [SiO4 ] coordinate structure merely shows slight disorder during cycling. The feature stems from lithiation taking place by the solid-solution insertion reaction rather than the conventional conversion/alloying addition reactions, because the solid-solution insertion reaction for the SLIC has the lowest change in the Gibbs free energy. The SLIC anode demonstrates excellent cycling stability and high initial Coulombic efficiency (≈85%). Moreover, owing to the low working voltage (≈0.28V) and relatively high specific capacity, the SLIC anode presents the highest gravimetric energy density among reported zero-/quasi-zero-strain anodes and high volumetric energy density (around twice as much as graphite). The universality of the designing principle is also validated. This work provides design guidelines for zero-strain anodes in next-generation batteries.

Rugby-ball-like Zinc molybdate electrodes for Li-ion battery anode applications

ZnMoO4 nanostructures with varying morphologies were synthesized using a simple hydrothermal technique, employing different Zn to Mo ratios. Various analytical techniques were employed to characterize both the structure and morphology of the ZnMoO4 nanostructures. As the Zn concentration in the reaction mixture was systematically increased, a transformation in morphology from non-uniform particles to uniform rugby-ball-like structures occurred. Additionally, there was a notable phase transition from predominantly α-ZnMoO4 phase to primarily β-ZnMoO4 phase. At a current density of 0.1 A g−1, the β-ZnMoO4 exhibited an initial discharge capacity of 2249 mAh g−1, while maintaining remarkable reverse rate capacity of 883 mAh g−1 even at a high current density of 0.2 A g−1. This uniform rugby-ball-like morphology favors Li-ion diffusion and ease of ion transfer from the electrode surface to electrolyte. The estimated gravimetric energy density LiCoO2//ZnMoO4 is 511 Wh kg−1, which is better than that of conventional LiCoO2//graphite (398 Wh kg−1). These findings underscore the exceptional properties of ZnMoO4, positioning it as a highly promising anode material for lithium-ion battery applications.

Cell teardown and characterization of an automotive prismatic LFP battery

A key challenge in lithium-ion battery research is the need for more transparency regarding the cell design and production processes of battery as well as vehicle manufacturers. This study comprehensively benchmarks a prismatic hardcase LFP cell that was dismounted from a state-of-the-art Tesla Model 3 (Standard Range). The process steps and manufacturing peculiarities were traced by disassembling the cell and analyzing the characteristics on the material level. A butterfly-design with two jelly rolls was found for the cell design in order to minimize the void volume (6.4%). Cross-sections and microscopy analyses from the cell cap revealed the application of multiple laser-welding processes that are needed to provide a high stability and tightness. The coatings of the approximately 22m long electrodes showed a high homogeneity with thickness fluctuations less than 2µm. Scanning electron microscopy images revealed a pure graphite anode and a bimodal particle distribution within the lithium iron phosphate cathode, whereby the edges of the cathode were covered in a 27µm thick aluminum oxide (Al2O3) insulation layer. Electrochemical analyses were performed showing the improved performance of the inherent electrolyte over a common LP572 electrolyte. A gravimetric energy density of 163Wh/kg and a volumetric energy density of 366Wh/l was determined based on a nominal cell capacity of 161.5Ah. Overall, the purpose of this work is to demonstrate which design decisions and manufacturing challenges are addressed in industrial cell production, so that the focus of academic research can align with the state-of-the-art.

Influence of blending cycloalkanes on the energy content, density, and viscosity of Jet-A

This work focuses on the influence of addingvarious cyclohexanes on the volumetric and gravimetric energy content, density, and kinematic viscosity of Jet A. Mixtures of Jet-A and alkylcyclohexanes with varying alkyl-chain lengths, degrees of branching, and number of rings at 5, 10, 15, 30, and 60 % wt./wt. were examined. Among the alkylcyclohexanes under study, addition of the compounds with the longest alkyl chains, i.e., n-hexylcyclohexane and n-heptylcyclohexane, were identified as compounds with the potential to increase both the specific and energy density of the mixtures. Contrasting results obtained for 1,2,3-trimethylcyclohexane (decreasing specific energy and increasing density) and 1,3,5-trimethylcyclohexane (decreasing energy density and kinematic viscosity) revealed the importance of the relative position of the substituents in cycloalkanes. More sterically hindered isomers and less symmetrical structures were associated to higher density and kinematic viscosity values. C9-cycloalkanes were identified as potential molecules to decrease the kinematic viscosity of blending mixtures. Branched structures in C12-cycloalkanes, such as 1,3-diisopropylcyclohexane and 1,4-diisopropylcyclohexane, were found to decrease gravimetric energy. However, additions higher than 15 % wt./wt. of branched cycloalkanes were also associated with increments of the volumetric energy content to values similar when linear alkyl-chain cycloalkanes of the same carbon number were added into the mixture. Decalin withcis-stereochemistry exhibited greater energy density, density, and kinematic viscosity thantrans-stereochemistry. JP-10 additions provided slightly higher energy densities but lower specific energies thancis-decalin. At low mass additions (<10 % wt./wt.), tricyclic compounds, such as tetradecahydroanthracene and adamantane, caused the largest increases in the energy density and density of the mixtures. Tetradecahydroanthracene increased the specific energy by +0.26 % and the volumetric energy by +1.40 % when added at 5 and 10 % wt./wt., respectively. However, larger mass additions (>10 % wt./wt.) of adamantane into Jet-A are not possible due to solubility conditions. Additions of JP-10 (28 % wt./wt.), cis-decalin (40 % wt./wt.), or trans-decalin (50 % wt./wt.) into Jet-A are proposed to maximize energy content (∼+3.5 %) while meeting density and kinematic viscosity requirements. These results broaden the understanding of cycloalkanes as potential key compoundsof sustainable aviation fuels withhigher energy content and minimal environmental impact.

Non‐Carbon‐Dominated Catalyst Architecture Enables Double‐High‐Energy‐Density Lithium–Sulfur Batteries

AbstractThe commonly used “catalyst on carbon” architecture as a sulfur host is difficult to jointly achieve high gravimetric and volumetric energy densities for lithium–sulfur (Li–S) batteries due to the contradiction between low tap density/poor catalytic activity of carbon and the easy agglomeration of metal‐based compounds without carbon. Here, a non‐carbon‐dominated catalytic architecture using macroporous nickel/cobalt phosphide (NiCoP) is reported as the sulfur host for Li–S batteries. The macroporous framework, which accommodates a large amount of sulfur, can accelerate the electrochemical reaction kinetics by accelerated e− transport, Li+ diffusion, and superior adsorption and catalytic activity of inherent Ni2P/CoP heterostructures. The high tap density (0.45 g cm−3) and mechanically hard features contribute to the excellent structural and physicochemical stability of the NiCoP@S electrode after the pressing and rolling process. These features enable the Li–S coin cell to exhibit excellent electrochemical performance under conditions of high sulfur loading (10.2 mg cm−2) and lean electrolyte (electrolyte/sulfur of 2 µL mg−1). Inspiringly, the assembled pouch cell can simultaneously deliver a gravimetric energy density of 345.2 Wh kg−1 and an impressive volumetric energy density of 952.7 Wh L−1 based on the entire device configuration.

Parametric Analysis for Hybrid–Electric Regional Aircraft Conceptual Design and Development

This paper proposes a conceptual analysis of the limitations related to the development (and integration) of hybrid–electric propulsion on regional transport aircraft, with the aim to identify a feasibility space for this innovative aircraft concept. Hybrid–electric aircraft have attracted the interest of aeronautical research as these have the potential to reduce fuel consumption and, thus, the related greenhouse gas emissions. Nevertheless, considering the development of such an aircraft configuration while keeping the constraints deriving from technological and/or operating aspects loose could lead to the analysis of concepts that are unlikely to be realised. In this paper, specifically to outline the boundaries constraining the actual development of such aircraft, the influence on overall aircraft design and performance of the main technological, operating, and design factors characterising the development of such a configuration is analysed and discussed at a conceptual level. Specifically, the current achievable gravimetric battery energy density (BED) is identified as the main limiting factor for the development of regional hybrid–electric aircraft, and a sensitivity analysis shows the correlation of this important technological parameter with aircraft performance in terms of both fuel consumption and energy efficiency. In this context, minimum technological development thresholds are therefore identified to enable the effective development of this type of aircraft; namely, a minimum of BED = 500 Wh/kg at battery pack level is identified as necessary to provide tangible benefits. From an operating point of view, flight distance is the most limiting design requirement, and a proper assessment of the design range is necessary if a hybrid–electric aircraft is to be designed to achieve lower emissions than the state of the art; flight ranges equal to or lower than 600 nm are to be considered for this type of aircraft. As a bridging of both of the previous constraints, a change in the design paradigm with respect to established practices for state-of-the-art aircraft is necessary. More specifically, penalisations in maximum take-off weight and overall aircraft energy efficiency may be necessary if the aim is to reduce direct in-flight consumption by means of integration of hybrid–electric powertrains.

Nitrogen-doped carbon/graphitic CQDs composites with 98.8% microporosity as a highly stable electrocatalyst for oxygen reduction

Designing micropore-rich carbon materials with large specific surface area (SSA) as a carbon-based oxygen reduction reaction (ORR) electrocatalyst is still frontier but remains challenging in catalysis of zinc-air batteries. Here we propose a new strategy for synthesis of nitrogen atoms co-doped carbon sheets and carbon quantum dots (N-C@CQDs) with an SSA of 1485.3 m2 g−1 and 98.8 % micro-porosity from α-cellulose via using a complex salt (ZnCl2-NH4Cl) with low eutectic point (179 °C) as a pore regulator and K2FeO4 as a graphitization catalyst, which can serve as an active and stable carbon-based ORR electrocatalyst. The role of K2FeO4 not only promotes graphitization but also oxidizes the large-sized graphitic carbon particles into a huge amount of uniformly distributed CQDs. This catalyst has exhibited a comparable ORR activity and superior stability to the Pt/C, but a Zn-air battery assembled with the former has delivered a higher peak power density (214 mW cm−2) and a larger gravimetric energy density (ED) of (959 Wh kgZn-1), especially in which it also displays an outstanding catalytic durability with 98.7 % ED retention during a ∼110 h continuous discharge. This work provides a new pathway for design of high-performance carbon-based ORR catalysts in various energy devices.

Preparation of High‐Power Lithium Fluoride Carbon Battery via Microstructural Modulation of Ketjen Black

Ketjen black fluoride (KBF‐2) material, a novel carbon fluoride cathode nanomaterial, is fabricated through a pregrinding treatment followed by a fluorination process for lithium primary batteries. The ketjen black material as the carbon precursors provides a 3D spherical structure with a high‐specific surface area. In addition, the pregrinding treatment results in several cracks in the spherical KBF‐2 particles. The effects of cracks on the fluorine content ratio under the same fluorination process conditions, diffusion coefficient of lithium ions, rate performance, and power density performance are investigated. At an extremely high current density of 4.5 A g−1(at a 6 C rate), the discharge capacity retention is 52.09%, which is a breakthrough for the series of fluoride cathode materials. Moreover, the KBF‐2 cathode is evaluated in a 10 Ah KBF‐2/Li primary pouch cell and demonstrated a high gravimetric energy density of 573.70 Wh kg−1 at a 0.5 C rate, and the discharge duration time reached 624 s under a constant specific power of 1,500 W kg−1. These factors contribute to the remarkable energy density performance and power output stability, particularly at high current densities.

Magnesium-Induced Strain and Immobilized Radical Generation on the Boron Oxide Surface Enhances the Oxidation Rate of Boron Particles: A DFTB-MD Study.

Despite their high gravimetric and volumetric energy densities, boron (B) particles suffer from poor oxidative energy release rates as the boron oxide (B2O3) shell impedes the diffusivity of O2 to the particle interior. Recent experiemental studies have shown that the addition of metals with a lower free energy of oxidation, such as Mg, can reduce the oxide shell of B and enhance the energetic performance of B by ∼30-60%. However, the exact underlying mechanism behind the reactivity enhancement is unknown. Here, we performed DFTB-MD simulations to study the reaction of Mg vapor with a B2O3 surface. We found that the Mg becomes oxidized on the B2O3 surface, forming a MgBxOy phase, which induces a tensile strain in the B-O bond at the MgBxOy-B2O3 interface, simultaneously reducing the interfacial B and thereby developing dangling bonds. The interfacial bond straining creates an overall surface expansion, indicating the presence of a net tensile strain. The B with dangling bonds can act as active centers for gas-phase O2 adsorption, thereby increasing the adsorption rate, and the overall tensile strain on the surface will increase the diffusion flux of adsorbed O through the surface to the particle core. As the overall B particle oxidation rate is dependent on both the O adsorption and diffusion rates, the enhancement in both of these rates increases the overall reactivity of B particles.

Facile Synthesis of a SiOx-Graphite Composite toward Practically Accessible High-Energy-Density Lithium-Ion Battery Anodes.

SiOx-based material is a promising candidate for lithium-ion batteries (LIBs) owing to its high theoretical capacity. The inherent disadvantages of poor electronic conductivity and large volume variation can be solved by constructing the outermost carbon layer and reserving internal voids. However, the practical application of SiOx/C composites remains a great challenge due to the unsatisfactory energy density. Herein, we propose a facile synthetic approach for fabricating SNG/H-SiOx@C composites, which are constructed by amorphous carbon, hollow SiOx (H-SiOx), and spherical natural graphite (SNG). H-SiOx alleviates volume expansion, while amorphous carbon promotes Li+ migration and stable solid electrolyte interphase (SEI) formation. The as-prepared SNG/H-SiOx@C demonstrates a high reversible capacity (465 mAh g-1), excellent durability (93% capacity retention at 0.5C after 500 cycles), lower average delithiation potential than SNG (0.143 V after 500 cycles), and a 14% gravimetric energy density improvement at a loading level of 4.5 mg cm-2. Even at a compacted density of 1.5 g cm-3, the SNG/H-SiOx@C anode presents a modest volume deformation of 14.3% after 100 cycles at 0.1C.

Ag nanodots-induced interfacial fast electronic/ionic diffusion kinetics of carbon capsule supported CoMn2O4 for high-voltage supercapacitors

The low energy density of SCs (<10 Wh kg−1) severely limits their commercial application, increasing either specific capacitance or broadening the potential window of the device is the effective pathway to improve the device energy density. Herein, nitrogen-doped carbon capsule (NC) supported Ag nanodots-decorated CoMn2O4 nanoflower (NC/CoMn2O4/Ag) electrode material has been successfully designed and synthesized. NC/CoMn2O4/Ag exhibits superior discharge capacity of 1806.4C/g, superior to NC/CoMn2O4 electrode (without Ag nanodots, 1319.2C/g at 1 A g−1). Theoretical calculations analysis demonstrates that decorated Ag nanodots on CoMn2O4 plays a fundamental role in improving the band gap, electrical conductivity, diffusion and transfer of electrolyte ions. In addition, asymmetric gel electrolytes of PVA-Na2SO4//PVA-KOH were designed for the assembly of asymmetric devices. This device delivers gravimetric energy density up to 89.9 Wh kg−1 at 894 W kg−1. The device can reach a large electrochemical voltage of up to 2.3 V, which could drive a remote-controlled toy easily. This work showcases a promising approach to rationally design conductive nanodots-decorated transition metal oxide-based materials towards high energy density supercapacitors. And it also sheds light on an in-depth understanding of their charge storage mechanisms.

Engineering of carbon anodes by laser irradiation for advanced sodium-ion batteries

Sodium-ion batteries (NIBs) represent an attractive alternative to Li-ion batteries due to sodium-abundant sources, lower cost, and better safety characteristics. However, the limited sodium-ion intercalation into graphite anodes has motivated researchers to search for new anode materials of NIBs. Herein, we demonstrate that laser-irradiated fly ash carbon (FAC), which is a waste by-product of the oil-burning process, can be a promising carbon anode of NIBs. The laser irradiation approach yields three synergistic benefits: (1) introducing carbonyl and carboxylic functional groups that increase adsorption capacity, (2) structurally transforming amorphous carbon into graphitic nanoplatelets to boost dynamic intercalation, and (3) enabling an additive and binder-free electrode to increase gravimetric energy density. The laser-irradiated fly ash carbon (LFAC) anode exhibits an excellent specific charge capacity of 356 mAh/g at 0.1 A/g, which is significantly higher than that of the FAC anode (119 mAh/g). At the end of the cycling measurement, the LFAC anode delivers a capacity of 250 mAh/g, which is three times higher than the untreated FAC anode (80 mAh/g).

Direct growth of MnCoSe2 nanoneedles on 3D nickel foam for supercapacitor application

The present work reports the fabrication and performance studies of supercapacitors using MnCoSe2 nanoneedles-based electrodes. The MnCoSe2 nanoneedles-based supercapacitor electrode with a unique nanostructure exhibits an enhanced specific capacitance of 820 F g−1 and 386 F g−1 at 1 A g−1 in three-electrode and symmetric two-electrode configurations, respectively. The MnCoSe2 nanoneedles-based supercapacitor device has a specific energy of 54 Wh kg−1 at a specific power of 1 kW kg−1 and a superior cyclic stability of 95% retention after 10,000 charge-discharge cycles at 5 A g−1. Additionally, an asymmetric supercapacitor (ASC) device has been developed employing an anode based on rGO and a cathode based on MnCoSe2 nanoneedles. The asymmetric supercapacitor demonstrates an excellent gravimetric capacitance of 71 F g−1 at 1 A g−1 and an exceptional cycle life of 96% after 10,000 cycles. At a gravimetric power density of 227 W kg−1, the device produces a gravimetric energy density of 32 W h kg−1. The increased electrochemical performance can be ascribed to the three-dimensional nanowire-like surface morphology with a large electroactive site for enhanced redox reaction. Furthermore, high conductivity due to the presence of selenium provides rapid electron transfer and improves the electrochemical properties of supercapacitors. Accordingly, the present work indicates that the MnCoSe2 nanoneedles can be used as a potential electrode material for electrochemical energy storage applications.

High capacity rechargeable coin cells using all active material electrodes and percolated networks of LiCoO2 blended with LiNi0.8Co0.15Al0.05O2

Lithium-ion batteries have become a popular rechargeable energy storage technology due to high volumetric and gravimetric energy density. One route to increase energy density at the cell level is to increase electrode thickness. All active material (AAM) electrodes, fabricated via hydraulic compression and mild sintering of only electroactive material (no polymer binder or conductive additives) provide a robust route to thick lithium-ion electrodes. However, depending on the materials chosen, AAM electrodes can have high matrix electronic conductivity resistance due to low intrinsic electronic conductivity of the electroactive materials. Herein, a multicomponent AAM was constructed using a blend of electroactive material with high electronic conductivity to facilitate matrix electronic transport and high energy density to increase overall cell capacity. The electrode thicknesses were matched within the geometry of a 2032-type coin cell, resulting in high overall reversible capacity for these AAM electrode cells.

Zeolite Coated Separators for Improved Performance and Safety of Lithium Metal Batteries

Lithium (Li) metal batteries are attractive due to their high gravimetric and volumetric energy densities. However, they can fail catastrophically due to dendritic nucleation, growth, and penetration through the polypropylene (PP) or polyethylene (PE) separators. Poor electrolyte wetting and non-uniform Li ion flux are known to affect Li dendrite formation, especially since the PP/PE separators have non-uniform pore size distribution and typical organic electrolytes do not wet them well. In this work, we demonstrate that a porous zeolite coating on a commercial PP separator can improve electrolyte wettability and through plane ionic conductivity, giving rise to more uniform Li flux. Consequently, coated separator can delay dendrite penetration and enhance cell performance and safety. We tested Celgard 2400 (uncoated) and zeolite-coated separator (coated) in high energy NMC||Li cells for their rate capability and cycle life performance. Rate capability test for these cells shows that the additional resistance due to the zeolite coating can negatively impact the cell performance at high C-rates. However, cells with the coated separator outperform those with uncoated separator in the cycle life test with improved capacity retention. Symmetric cell studies performed to understand the differences in Li plating morphology indicate initial lower overpotential for the coated separator cells, revealing improved electrolyte wetting and relatively uniform Li flux. Scanning electron microscopy (SEM) reveals zeolite-coating microstructure with evenly distributed zeolite particles and cycled Li metal electrode morphologies. SEM images show much smoother Li plating morphology on Li metal surface in the cells with coated separators. This study highlights the potential of using zeolite-coated separators to enhance lithium metal battery (LMB) performance and safety.

Influence of different anode active materials and blends on the performance and fast-charging capability of lithium-ion battery cells

To further extent the driving range of battery electric vehicles, an increase of the energy density of lithium-ion battery cells is necessary. One way to increase the energy density is the use of high-capacity electrodes. The challenges for this kind of electrodes are transport limitations, like the long lithium-ion diffusion path to the layers near the substrate of the electrode, leading to performance degradation during cycling. To get a better understanding on how the material selection influences the battery cell performance, various active materials (graphite, silicon, and hard carbon) are investigated, both, pure and in blends and the relation between material, structure and performance is studied. On material level pure silicon active material has a very high electric resistance compared to carbon-based materials. Nevertheless, on electrode level, the high gravimetric energy density, and the round-shaped particle morphology of silicon result into a lower tortuosity and layer thickness, hence, ionic resistance of the electrode. With respect to cell performance, the ionic resistance seems to have a greater impact compared to the charge-transfer and electric resistance. Therefore, silicon-based electrodes show the best performance.

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.

Ultrathin, Smooth Li-Metal Anode Via Electrodeposition for Stable Cycling of Li-Betal Batteries Under Practical Conditions

Lithium (Li) metal anodes (LMAs) with high specific capacity (3860 mAh g–1) and lowest redox voltage (–3.04 V vs SHE) are considered superlative candidates for high energy batteries. Ultra-thin, large-area LMA is crucial for building Li-metal batteries (LMBs) that can deliver high volumetric and gravimetric energy density in practice. As the charging and discharging continue, the growth of Li dendrite is regarded as one of the significant challenges. The surface nature of LMAs is the main aspect of Li dendrite formation and interface reaction. However, most studies overlooked the initial condition of LMA surface. Native passivation layer (NPL) of commercial Li foils is inherently uneven composed of Li2CO3, LiOH, and Li2O, and its chemical nature is mostly determined under manufacturing conditions. Incomplete passivation at an initial stage can trigger sporadic Li dendrite growth and chemical/structural deterioration of LMAs, adversely affecting the cycling stability of LMBs.This work presents the electrochemical pre-passivation to build an electrolyte-derived native layer (electro-native layer, E-NPL) through Li electrodeposition method. Electrodeposited LMA (ed-LMA) was prepared by pre-deposition at the Cu foil using localized high-concentration electrolyte (LHCE) and post calendaring for smooth LMA surface. As-prepared ed-LMA has 4.13 mAh cm-2 of areal capacity with ~22 µm, and reduced roughness, which is much lower than that of manufactured LMA (m-LMA). Particularly, the E-NPL derived by LHCE can tailor the LMA surface by enriching the inorganic SEI compounds such as LiF, and N-SOx. In addition, decreased amount of passivated components such as Li2CO3, LiOH, and hydroxide were found in XPS analysis of the anodes. Compared to manufactured LMA (m-LMA), the ed-LMA exhibited lower overpotential for Li plating/stripping cycles and enhanced capacity retention. Benefiting from better compatibility with newly plated Li, it showed higher plating density without electric isolation from beneath Li surface, mitigating the anode swelling during subsequent cycling. We successfully demonstrated battery cycling stability of Li||NMC622 cells exploiting ed-LMA (195 cycle at 80% retention), superior to m-LMA (110 cycle at 80% retention) under stringent conditions.