Electrochemical Cycling Research Articles

Lignin‐Derived Functional Carbon Framework for Homogeneous Sodium Deposition

AbstractSodium metal batteries have become popular owing to their low redox potential, high theoretical capacity, and superior energy density. But the formation of sodium dendrites during electrochemical cycles diminishes the security and longevity of these batteries. In response to this challenge, we employ lignin as a carbon source to fabricate a three‐dimensional (3D) carbon framework current collector. This framework boosts an expansive specific surface area and a wealth of oxygen‐rich functional groups. These components serve to cushion the volume fluctuations of sodium metal throughout the electrochemical cycle, directing the even deposition of sodium ions. The as‐prepared anode displays a low overpotential of −7 mV and a stable cycling life of 400 hours at 0.5 mA cm−2. When coupled with Na3V2(PO4)3 cathode, the full cell can achieve a capacity of 97.6 mAh g−1 and a capacity retention of 94.7 % after 60 cycles. This research shows that using lignin as a carbon source to prepare a 3D carbon framework current collector is an effective mean to inhibit the harmful effects of sodium dendrites on batteries.

Oxygen Transport through Amorphous Cathode Coatings in Solid-State Batteries.

All solid-state batteries (SSBs) are considered the most promising path to enabling higher energy-density portable energy, while concurrently improving safety as compared to current liquid electrolyte solutions. However, the desire for high energy necessitates the choice of high-voltage cathodes, such as nickel-rich layered oxides, where degradation phenomena related to oxygen loss and structural densification at the cathode surface are known to significantly compromise the cycle and thermal stability. In this work, we show, for the first time, that even in an SSB, and when protected by an intact amorphous coating, the LiNi0.5Mn0.3Co0.2O2 (NMC532) surface transforms from a layered structure into a rocksalt-like structure after electrochemical cycling. The transformation of the surface structure of the Li3B11O18 (LBO)-coated NMC532 cathode in a thiophosphate-based solid-state cell is characterized by high-resolution complementary electron microscopy techniques and electron energy loss spectroscopy. Ab initio molecular dynamics corroborate facile transport of O2- in the LBO coating and in other typical coating materials. This work identifies that oxygen loss remains a formidable challenge and barrier to long-cycle life high-energy storage, even in SSBs with durable, amorphous cathode coatings, and directs attention to considering oxygen permeability as an important new design criteria for coating materials.

A green and cost-effective zinc-biphenol hybrid flow battery with eutectic electrolyte

Eutectic electrolytes have been widely used in redox flow batteries (RFBs) due to their unique features such as abundant availability, biodegradability, and low cost, as well as their excellent dissolution ability for redox-active substances. Despite these advantages, eutectic electrolytes still have some limitations in important aspects such as reaction kinetics, mass transport and ionic conductivity due to their relatively high intrinsic viscosity. In this work, we explore a green and cost-effective zinc-based eutectic electrolyte containing small molecules additives, which not only has elevated ionic conductivity, but also can dissolve organic cathode materials 3,3′,5,5′-tetramethylaminemethylene-4,4′-biphenol (TABP) at high concentrations. In this zinc-based eutectic electrolyte, TABP exhibits a highly positive redox potential (1.50 V versus Zn/Zn2+), quasi-reversible redox reaction kinetics and good redox stability. When operated in a practical hybrid flow battery, the Zn-TABP cell based on this eutectic electrolyte exhibits excellent rate performance, high capacity utilization, and low capacity decay rate (0.119 % per cycle). Post-analysis for the TABP catholyte suggests that the Michael side reaction rate of TABP in electrochemical cycling appears to depend upon its concentration.

Protective Nanosheet Coatings for Thiophosphate‐Based All‐Solid‐State Batteries

AbstractSuperionic sulfide solid electrolytes (SEs) are of considerable interest for application in solid‐state batteries, but suffer from limited stability. When in combination with state‐of‐the‐art cathode active materials (CAMs), severe degradation at the CAM/SE interface occurs during electrochemical cycling. To improve upon the interfacial stability, inert coatings can be applied to the CAM particles, with the goal of preventing direct contact to the SE. In this study, different methods of depositing coatings, including hexagonal boron nitride, tungsten sulfide and exfoliated ((CH3(CH2)3)4N)4Nb6O17, in the form of nanosheets onto the free surface of a Ni‐rich LiNixCoyMnzO2 (NCM) CAM are examined and compared with one another. While dry coating is shown to produce relatively uniform coatings (good surface coverage), the secondary particle morphology of the NCM makes ball milling as a mechanical deposition method less attractive. In contrast, deposition from dispersions in organic solvents yields protective coatings with a lower degree of surface coverage. The different materials are electrochemically tested in liquid‐ and solid‐electrolyte‐based lithium‐ion batteries. A stabilizing effect from nanosheet coating is only observed for the cells with lithium thiophosphate SE.

Selectively etched inhomogeneous metal-organic framework-derived CoS/N-codoped hierarchical hollow carbon for long-cycling lithium sulfur batteries

Owing to high theoretical energy density and potentially low cost, lithium sulfur (Li–S) batteries have become a viable alternative for use in future energy storage devices. However, practical applications of this battery type are limited by the significant volume change of S and the undesired shuttle effect of polysulfides during cycling, ultimately causing rapid capacity decay. Herein, we developed a novel method to fabricate a N-doped hollow carbon composite (CoS/HNC) embedded with well-dispersed CoS nanoparticles (NPs) through inheritable carbonization of functionalized hollow metal-organic frameworks (MOFs). Specifically, the hollow UiO-66-NH2 is created by a sequence involving (1) use of non-uniform nucleation-growth approach to generate inhomogeneous UiO-66-NH2 that has more defects in the core, and (2) selective etching of the less stable core to obtain hollow structure. The CoS/HNC composite has advantages associated with not only hollow nanostructure that buffers the volume expansion of S species during cycling, but also CoS that prevents the shuttle effect. More importantly, both experimental and calculated results reveal that CoS/HNC could catalyze the reduction of LiPSs more effectively and CoS/HNC heterostructure enables the short-chain polysulfide that obtained from the catalytic conversion of soluble long-chain polysulfide by CoS NPs to be deposited on HNC. This process avoids passivation of the catalytic site and ensures continuity of the catalytic conversion. Benefiting from integration of its intriguing composition and morphology advantages, an as-prepared CoS/HNC–S cathode exhibits significantly improved electrochemical performance and cycling stability associated with a low capacity decay of 0.05% per cycle over 800 cycles at 1 C.

Improving the electrochemical performance of LiNi0.5Mn1.5O4 by ZnO nanocrystals coating

The cathodic material LiNi0.5Mn1.5O4 was produced by the Solution Combustion Synthesis method (SCS). The as-made crystalline nanoparticles were annealed at 900 °C, obtaining micron-sized particles, and then coated with ZnO nanocrystals at a weight relation between 0.5 and 2.5 wt%, also using the SCS method. The nanocrystalline porous coating was confirmed by XRD, SEM and TEM. Electrochemical measurements verified that all materials coated with ZnO nanoparticles improved their electrochemical properties concerning the uncoated material, preventing degradation over the cycles, and stability along cyclic voltammetry cycles. It was observed that a 1 wt% ZnO coating presents the best improvement in discharge capacity and rate capability, and that the charge transfer resistance of the coated material is reduced to 1/3 of the uncoated one after 100 electrochemical cycles. In this work, the simple, time and energy saving SCS method was verified to obtain nanoshell-coated LNMO microparticles with improved electrochemical performance.

Unraveling the New Role of Manganese in Nano and Microstructural Engineering of Ni‐Rich Layered Cathode for Advanced Lithium‐Ion Batteries

AbstractSubstantial endeavors are dedicated to advance the electrochemical performance of Ni‐rich Li[Ni1−x−yCoxMny]O2 (NCM) and Li[Ni1−x−yCoxAly]O2 (NCA) cathode, with a particular focus on doping, aimed at addressing cycling durability and thermal stability of the cathodes. Mn is widely considered an attractive dopant because of its abundance and considerably lower cost than other dopant candidates. However, despite the long history of research, the role of Mn doping remains poorly understood, confined to the historical level, and associated with crystal structural and chemical aspects. Herein, the role of Mn doping beyond its classical role is redefined, particularly in terms of cathode microstructure. Introducing excess Mn during calcination significantly engineers the nano‐ and micro‐level structural features of the peripheral grains of the Li[Ni0.910Co0.079Al0.011]O2 cathode. The microstructural modification achieved by doping with 4 mol% Mn significantly improves the electrochemical cycling performance of the cathode, extending the capacity retention up to 76.5% after 1000 cycles under fast charging conditions (3 C and 45 °C). Hence, by providing an alternative approach to redesign the structural features of the cathode, Mn doping offers a significant step toward the sustainable development of high‐performance Ni‐rich Li[Ni1−x−y−zCoxMnyAlz]O2 (NCMA) cathodes for next‐generation lithium‐ion batteries.

Improving the electrochemical cycle stability of LiNi0.8Co0.1Mn0.1O2 via Al(H2PO4)3 treatment on its precursor

Ni-rich layered transition-metal oxides are important cathodes for lithium-ion batteries (LIBs). Unfortunately, they still suffer from capacity fading arising from structure transformation and side reactions. Cation doping and surface coating with a protective layer can alleviate the problem. Herein, a synergistic strategy of Al3+ doping near the surface and Li3PO4-LiAlO2 coating is adopted to modify LiNi0.8Co0.1Mn0.1O2 (NCM811), and it is carried out by using a simple Al(H2PO4)3 wet deposition method on its precursor. Structure and surface analysis show that Li3PO4-LiAlO2 is formed on the NCM surface and some Al3+ ions enter the near-surface lattice of cathode particles. Compared to NCM811, the modified-NCM811 exhibits slower impedance growth and better capacity retention (from 55.55 % to 75.09 % after 100 cycles) during cycling, which shows the strategy can effectively stabilize the interface and crystal structure.

Cryo-Electron Microscopy Reveals Na Infiltration into Separator Pore Free-Volume as a Degradation Mechanism in Na Anode:Liquid Electrolyte Electrochemical Cells.

Batteries utilizing a sodium (Na) metal anode with a liquid electrolyte are promising for affordable large-scale energy storage. However, a deep understanding of the intrinsic degradation mechanisms is limited by challenges in accessing the buried interfaces. Here, cryogenic electron microscopyof intact electrode:separator:electrode stacks is performed and degradation and failure of symmetric Na||Na coin cells occurs through the infiltration of Na metal through thepores of the separator rather than by mechanical puncturing by dendrites is revealed. It is shown the interior structure of the cell (electrode:separator:electrode) must be preserved anddeconstructing the cell into different layers for characterization results in artifacts. In intact cell stacks, minimal liquid is found between the electrodes and separator, leading to intimate electrode:separator interfaces. After electrochemical cycling, Na infiltrates into the pore free-volume, growing through the separator to create electrical shorts and degradation. The Na infiltration occurs at interfacial regions devoid of solid-electrolyte interphase (SEI), revealing SEI plays an important role in preventing Na from growing into the separator by being a physical barrier that the plated Na cannot penetrate. These results shed new light on the fundamental failure mechanisms in Na batteries and demonstrate the importance of preserving the cell structure and buried interfaces.

Healable and conductive sulfur iodide for solid-state Li-S batteries.

Solid-state Li-S batteries (SSLSBs) are made of low-cost and abundant materials free of supply chain concerns. Owing to their high theoretical energy densities, they are highly desirable for electric vehicles1-3. However, the development of SSLSBs has been historically plagued by the insulating nature of sulfur4,5 and the poor interfacial contacts induced by its large volume change during cycling6,7, impeding charge transfer among different solid components. Here we report an S9.3I molecular crystal with I2 inserted in the crystalline sulfur structure, which shows a semiconductor-level electrical conductivity (approximately 5.9 × 10-7 S cm-1) at 25 °C; an 11-order-of-magnitude increase over sulfur itself. Iodine introduces new states into the band gap of sulfur and promotes the formation of reactive polysulfides during electrochemical cycling. Further, the material features a low melting point of around 65 °C, which enables repairing of damaged interfaces due to cycling by periodical remelting of the cathode material. As a result, an Li-S9.3I battery demonstrates 400 stable cycles with a specific capacity retention of 87%. The design of this conductive, low-melting-point sulfur iodide material represents a substantial advancement in the chemistry of sulfur materials, and opens the door to the practical realization of SSLSBs.

Endogenous Interfacial Mo-C/N-Mo-S Bonding Regulates the Active Mo Sites for Maximized Li+ Storage Areal Capacity.

Active sites, mass loading, and Li-ion diffusion coefficient are the benchmarks for boosting the areal capacity and storage capability of electrode materials for lithium-ion batteries. However, simultaneously modulating these criteria to achieve high areal capacity in LIBs remains challenging. Herein, MoS2 is considered as a suitable electroactive host material for reversible Li-ion storage and establish an endogenous multi-heterojunction strategy with interfacial Mo-C/N-Mo-S coordination bonding that enables the concurrent regulation of these benchmarks. This strategy involves architecting 3D integrated conductive nanostructured frameworks composed of Mo2C-MoN@MoS2 on carbon cloth (denoted as C/MMMS) and refining the sluggish kinetics in the MoS2-based anodes. Benefiting from the rich hetero-interface active sites, optimized Li adsorption energy, and low diffusion barrier, C/MMMS reaches a mass loading of 12.11mgcm-2 and showcases high areal capacity and remarkable rate capability of 9.6mAhcm-2@0.4mAcm-2 and 2.7mAhcm-2@6.0mA cm-2, respectively, alongside excellent stability after 500 electrochemical cycles. Moreover, this work not only affirms the outstanding performance of the optimized C/MMMS as an anode material for supercapacitors, underscoring its bifunctionality but also offers valuable insight into developing endogenous transition metal compound electrodes with high mass loading for the next-generation high areal capacity energy storage devices.

Enhancing Durability and Capacity Retention of Ultrafine-Grained Aluminum Foil Anodes in Lithium-Ion Batteries.

In this study, we present our successful fabrication of commercial-grade pure aluminum anode foil (99.5%, 2NAl) with an ultrafine-grained (UFG) microstructure and high hardness, achieved through cold rolling. Under identical rolling conditions, a coarse-grained microstructure with a low hardness was attained from the high-purity Al foil (99.99%, 4NAl). The UFG 2NAl foil exhibited enhanced lithium-ion diffusivity and reduced nucleation and activation overpotentials for forming the β-LiAl phase compared to the 4NAl foil. The high-density grain boundaries in the UFG 2NAl foil facilitated the rapid formation of a uniform β-LiAl phase layer on its surface, thereby mitigating mechanical damage within the β-LiAl phase layer caused by volume changes during the lithiation and delithiation processes. The high hardness of the UFG 2NAl sample effectively prevented macroscopic plastic deformation during cycling, thus preserving the integrity of the β-LiAl phase layer and inhibiting the formation of cracks within the unreacted Al matrix. The collective advantages of reduced overpotential, enhanced Li-ion diffusivity, and high resistance to mechanical damage and plastic deformation in UFG 2NAl contribute to its superior durability and capacity retention compared to the high-purity Al in electrochemical cycling.

Heterostructure Engineering of NiCo-LDHs for Enhanced Energy Storage Performance in Aqueous Zinc-Ion Batteries.

Aqueous zinc-ion batteries (AZIBs) are considered a promising device for next-generation energy storage due to their high safety and low cost. However, developing high-performance cathodes that can be matched with zinc metal anodes remains a challenge in unlocking the full potential of AZIBs. In this study, a typical transition metal layered double hydroxides (NiCo-LDHs) can be in situ reconstructed to NiCo-LDHs/Ni(Co)OOH heterostructure using an electrochemical cycling activation (ECA) method, serving as a novel cathode material for AZIBs. The optimized ECA-NiCo-LDHs cathode demonstrates a high capacity of 181.5 mAh g-1 at 1 A g-1 and retains 75% of initial capacity after 700 cycles at 5 A g-1. The abundant heterointerfaces of the NiCo-LDHs/Ni(Co)OOH material can activate additional active sites for zinc-ion storage and accelerate ion diffusion. Theoretical calculations also suggest the heterostructure can boost charge transfer and regulate ion-adsorption capability, thereby improving the electrochemical performance. Additionally, the flexible AZIBs device exhibits good service performance. This study on interface engineering introduces a new possibility for utilizing LDHs in AZIBs and offers a novel strategy for designing electrode materials.

Phase Engineering via Aluminum Doping Enhances the Electrochemical Stability of Lithium-Rich Cobalt-Free Layered Oxides for Lithium-Ion Batteries.

Lithium-rich, cobalt-free oxides are promising potential positive electrode materials for lithium-ion batteries because of their high energy density, lower cost, and reduced environmental and ethical concerns. However, their commercial breakthrough is hindered because of their subpar electrochemical stability. This work studies the effect of aluminum doping on Li1.26Ni0.15Mn0.61O2 as a lithium-rich, cobalt-free layered oxide. Al doping suppresses voltage fade and improves the capacity retention from 46% for Li1.26Ni0.15Mn0.61O2 to 67% for Li1.26Ni0.15Mn0.56Al0.05O2 after 250 cycles at 0.2C. The undoped material has a monoclinic Li2MnO3-type structure with spinel on the particle edges. In contrast, Al-doped materials (Li1.26Ni0.15Mn0.61-xAlxO2) consist of a more stable rhombohedral phase at the particle edges, with a monoclinic phase core. For this core-shell structure, the formation of Mn3+ is suppressed along with the material's decomposition to a disordered spinel, and the amount of the rhombohedral phase content increases during galvanostatic cycling. Whereas previous studies generally provided qualitative insight into the degradation mechanisms during electrochemical cycling, this work provides quantitative information on the stabilizing effect of the rhombohedral shell in the doped sample. As such, this study provides fundamental insight into the mechanisms through which Al doping increases the electrochemical stability of lithium-rich cobalt-free layered oxides.

Boosting the performance enhancement of short-process regenerated Ni-rich cathode via antimony doping and modification

Currently, the short-process regeneration of cathode materials in spent lithium-ion batteries has attracted wide attention from researchers because of its short process flow, less waste liquid discharge and the cascade utilization of recycled materials. However, the performance of short-process regenerated electrode materials is generally difficult to comparable with the commercial materials, especially for lithium nickel cobalt manganese oxide (NCM). Herein, antimony (Sb) doping, and modification is proposed to boost the performance enhancement of short-process regenerated NCM in our work. Spent NCM is first selectively leached by oxalic acid, and then directly dried to obtain the precursor without separation and filtration. Finally, NCM is regenerated by lithium supplement and Sb doping modification. The regenerated NCM with optimal Sb doping modification (R-Sb10) has better electrochemical performance and cycle stability. It delivers an initial specific discharge capacity of 152.3 mAh/g, and the capacity retention maintains 86.3 % after 200 cycles at 0.5C, which can be comparable to the commercial NCM. The Sb element can be evenly distributed in the interior of short-process regenerated NCM, especially with a protective Li3SbO4 film on the surface. Through theoretical calculation, the R-Sb10 has a lower energy for material formation, higher energy barrier for cation disorder and decreasing diffusion energy barrier for Li+. The doping modification method provides a new idea to improve the performance of regenerated materials and is expected to meet the needs of industrial applications in the future.

Probing the account of phase transition upon electrochemical cycling of the P2-Na0.67Ni0.15Fe0.2Mn0.65O2 layered oxide cathodes for sodium-ion batteries

Layered P2-Na0.67Ni0.15Fe0.2Mn0.65O2 (P2-NFM) cathode material has attracted great attention in sodium-ion batteries due to its high theoretical capacity, low cost, and environmental friendliness. However, P2-NFM exhibits irreversible phase transition and slip of transition metal layers in the high voltage range during charging process, leading to a gradually declined performance of the cathode material. It is therefore necessary to investigate the mechanism of phase transition of P2-NFM as well as the effect of phase transition on its performance. Herein, utilizing ex situ x-ray diffraction spectroscopy and x-ray photoelectron spectroscopy, the crystal structure and TM (transition-metal) bonding changes caused by phase transition are elucidated. It is found that P2-NFM is prone to undergo an irreversible P2-O2 phase transition at high voltage, causing changes in lattice parameters and rapid capacity decay. The irreversible phase transition is mainly due to he dynamic transformation of valence states of Fe and Ni in P2-NFM materials at high voltage. It is this process that results in irreversible fluctuations in the bond lengths between these elements and oxygen, consequently instigating interlayer slip within the material. Besides, the charge compensation mechanism of P2-NFM has been elucidated based on the study of its initial charging process. Results show that the charge compensation is mainly contributed by Ni and Fe in the high voltage range, while by a small amount of Mn in the low voltage range. It reveals the essential cause of the adverse phase transition of P2-NFM materials and points out the direction for improving the cycling stability of these layered oxide materials.

Li3V2(PO4)3 Cathode Material: Synthesis Method, High Lithium Diffusion Coefficient and Magnetic Inhomogeneity.

Li3V2(PO4)3 cathodes for Li-ion batteries (LIBs) were synthesized using a hydrothermal method with the subsequent annealing in an argon atmosphere to achieve optimal properties. The X-ray diffraction analysis confirmed the material's single-phase nature, while the scanning electron microscopy revealed a granular structure, indicating a uniform particle size distribution, beneficial for electrochemical performance. Magnetometry and electron spin resonance studies were conducted to investigate the magnetic properties, confirming the presence of the relatively low concentration and highly uniform distribution of tetravalent vanadium ions (V4+), which indicated low lithium deficiency values in the original structure and a high degree of magnetic homogeneity in the sample, an essential factor for consistent electrochemical behavior. For this pure phase Li3V2(PO4)3 sample, devoid of any impurities such as carbon or salts, extensive electrochemical property testing was performed. These tests resulted in the experimental discovery of a remarkably high lithium diffusion coefficient D = 1.07 × 10-10 cm2/s, indicating excellent ionic conductivity, and demonstrated impressive stability of the material with sustained performance over 1000 charge-discharge cycles. Additionally, relithiated Li3V2(PO4)3 (after multiple electrochemical cycling) samples were investigated using scanning electron microscopy, magnetometry and electron spin resonance methods to determine the extent of degradation. The combination of high lithium diffusion coefficients, a low degradation rate and remarkable cycling stability positions this Li3V2(PO4)3 material as a promising candidate for advanced energy storage applications.

Top-down nanostructured multilayer MoS2 with atomically sharp edges for electrochemical hydrogen evolution reaction

Cost-efficient and readily scalable platinum-free electrocatalysts are crucial for a smooth transition to future renewable energy systems. Top-down activation of MoS2 promises the production of sustainable hydrogen evolution electrocatalysts from the Earth-abundant molybdenite ore. Here, the deterministic nanopatterning of multilayer MoS2 with numerous zigzag edges is explored as a pathway to enhance hydrogen evolution reaction (HER). Nanopatterned single-nanosheet MoS2 electrodes are assessed by two highly localized electrochemical techniques: selected area voltammetry (with lithography-defined regions of electrode-electrolyte contact) and Scanning ElectroChemical Microscopy (SECM). The nanopatterning effect is the most pronounced after prolonged electrochemical cycling in an acidic electrolyte. The electrocatalytic hydrogen evolution activity of edge-enriched electrodes is dramatically enhanced: the maximum electrochemical current density (jmax) achieved at -510 mV vs. reversible hydrogen electrode (mVRHE) is increased by two orders of magnitude, reaching >300 mA⋅cm−2. Both the η10 and η100 overpotentials are significantly reduced as well. Meanwhile, pristine MoS2 shows just ≈6 times jmax increase (≈30 mA⋅cm−2) after the very same cycling. The increased electrocatalytic activity comes with electrode morphology degradation, evidenced by ex-situ scanning electron microscopy. SECM directly visualizes stronger HER activity in the regions with densely located zigzag edges. Intense white light illumination significantly boosts HER on MoS2 electrodes due to the photo-enhanced MoS2 conductivity. These results improve the understanding and reveal the limitations of MoS2-based electrocatalytic water splitting.

CoS2/Ni3S4 − N − C heterostructured electrode materials derived from Prussian-blue analogs for supercapacitors

Prussian blue analogues (PBAs) have the advantages of dependable electrochemical performance and long service life when used as energy storage materials because of their face-centered cubic structure. In this case, the appropriate metal sulfide derivatives were created using NiCo prussian blue analogue nano units as a precursor, which took on the precursor's structural traits. More reaction sites are exposed by this distinctive structural design, and a little quantity of nitrogen-doped carbon is produced, which improves charge transfer. The box-like structure has a buffer effect on the stress of the active material during charging and discharging, and the heterostructure of mixed metal sulfides and nitrogen-doped carbon composite cubic can both significantly increase the electrode's electrochemical capacitance and cycling stability. The CoS2/Ni3S4–N–C offers a capacitance of 817C g−1 at 3 A g−1 and 556C g−1 at 20 A g−1. The CoS2/Ni3S4–N–C electrode also has outstanding cycle stability (98.2 % capacitance retention after 10,000 cycles). An asymmetric supercapacitor (ASC) device made of CoS2/Ni3S4–N–C with activated carbon electrodes exhibits exceptional cycle stability. With a retention rate of 103.7 % after 10,000 cycles at 10 A g−1 and an energy density of 40 Wh kg−1. Using density functional theory (DFT), the electron characteristics of Co2NiO4 and CoS2/Ni3S4–N–C are compared. CoS2/Ni3S4–N–C detected more state densities at the Fermi level, which causes more charge to accumulate. This shows that the heterojunction's electron conductivity is significantly greater than the oxide's, and ultimately leads to quicker reaction kinetics.

Correlation between surface/bulk properties and electrochemical cycling performance of pure silicon anode materials

State-of-the-art lithium-ion batteries (LIBs) employ silicon (Si)-graphite composite anode with just a few percentages of Si active material, whose cycle-life relies on a stable solid electrolyte interphase (SEI) layer. As a number of various types of industrial Si active materials are currently available, an informative guideline based on the material properties and resultant cycling performance of different pure Si (i.e., without graphite) anode materials is strongly needed for material selection. The present study provides for the first time the correlation among material's surface and bulk properties, the SEI formation behavior, and cycling behavior of highly loaded pure Si anodes (2.3 mAh cm−2) prepared from four different industrial active materials, which are SiOx, carbon-coated Si, and bare Si with submicron and micron sizes. Commercial electrolyte with 10 wt% fluoroethylene carbonate additive is used for electrochemical performance evaluation. Based on solid-state NMR, XPS, and electrochemical analysis results, SiOx is determined to be relatively beneficial for practical applications beyond Si materials, in the aspects of high structural and particle morphology stability, cycling stability and suppressed interfacial resistance. This is mainly because of more effective accommodation of volume change of Si and oxygen-enriched surface (SEI) stability. The data give insight into the rational design of well-working Si-dominant or pure Si anodes for high energy density LIBs.