Superior Long-term Cyclability Research Articles

Molecular-Level Interfacial Chemistry Regulation of MXene Enables Energy Storage beyond Theoretical Limit.

Ti3C2Tx MXene often suffers from poor lithium storage behaviors due to its electrochemically unfavorable OH terminations. Herein, we propose molecular-level interfacial chemistry regulation of Ti3C2Tx MXene with phytic acid (PA) to directly activate its OH terminations. Through constructing hydrogen bonds (H-bonds) between oxygen atoms of PA and OH terminations on Ti3C2Tx surface, interfacial charge distribution of Ti3C2Tx has been effectively regulated, thereby enabling sufficient ion-storage sites and expediting ion transport kinetics for high-performance energy storage. The results show that Li ions preferably bind to H-bond acceptors (oxygen atoms from PA), and the flexibility of H-bonds therefore renders their interactions with adsorbed Li ions chemically "tunable", thus alleviating undesirable localized geometric changes of the OH terminations. Meanwhile the H-bond-induced microscopic dipoles can act as directional Li-ion pumps to expedite ion diffusion kinetics with lower energy barrier. As a result, the as-designed Ti3C2Tx/PA achieves a 2.4-fold capacity enhancement compared with pristine Ti3C2Tx (even beyond theoretical capacity), superior long-term cyclability (220.0 mAh g-1 after 2000 cycles at 2.0 A g-1), and broad temperature adaptability (-20 to 50 °C). This work offers a promising interface engineering strategy to regulate microenvironments of inherent terminations for breaking through the energy storage performance of MXenes.

Al3+ intercalated NH4V4O10 nanosheet on carbon cloth for high-performance aqueous zinc-ion batteries

Ammonium vanadium bronze (NH4V4O10) with open crystal structures and superior theoretical capacity is promising cathode for aqueous zinc-ion batteries (AZIBs). However, the sluggish intrinsic ion/electron kinetics and unsatisfied structural stability remain bottlenecks that limit their further development. Herein, we report a facile synthesis of Al+-intercalated NH4V4O10 nanosheet grown on carbon cloth (Al-NVO@CC) via a one-step hydrothermal reaction. The expanded lattice spacing of the synthesized Al-NVO@CC not only facilitates the Zn2+ ion intercalation/deintercalation but also improves the electrochemical stability in AZIBs. As a result, the cathode shows high reversible capacity (475.8 mA h g-1 at 0.2 A g-1), superior long-term cyclability (152.8 mA h g-1 over 2500 cycles at 5.0 A g-1), as well as excellent rate performance. Moreover, the zinc storage process of Al-NVO@CC and underlying mechanism of the enhanced performance are revealed by ex-situ X-ray powder diffraction (XRD), X-ray photoelectron spectra (XPS) and Transmission electron microscope (TEM) analyses. This study provides a reasonable strategy to promote V-based nanomaterials on CC for the development of AZIBs.

2D V10O24·nH2O sheets as a high-performance cathode material for aqueous zinc-ion batteries

In this work, 2D V10O24·nH2O sheets are synthesized via a facile solvothermal method. When used as a cathode material for aqueous rechargeable zinc ion batteries (ZIBs), the as-prepared V10O24·nH2O sheets show high reversible capacity (408 mA h g−1 at 0.1 A g−1), superior long-term cyclability (with a stable capacity of 314 mA h g−1 over 1000 cycles at 2.0 A g−1), as well as excellent rate performance. The impressive electrochemical performance can be attributed to the 2D morphology composed of staked nanosheets and the existence of V4+, which enhances the structural stability, promotes the electrochemical activity and improves the reaction kinetics as demonstrated by electrochemical tests and ex-situ characterizations. This study provides a viable and promising cathode material for practical ZIBs.

Surface modification enabling 4.7 V Nickel-rich layered cathode with superior long-term cyclability via novel functional polyimide binders

High voltage operation of LiNi0.8Co0.1Mn0.1O2 (NCM) for high energy density lithium-ion batteries has poor cycling performance, due to the unstable cathode-electrolyte interface. Herein, two functional polyimides (PIs), one polyimide with hydroxyl group is abbreviated as PI-OH and the other polyimide with carboxyl group is abbreviated as PI-COOH, are designed to contain hydroxyl, carboxyl, trifluoromethyl and ether groups and used as cathode binder, which allows a strong hydrogen bond interaction, abundant chemical bonding sites, superior electrochemical oxidation resistance, and excellent flexibility. Experimental results reveal that both PI-OH and PI-COOH binders show the impressive efficiency on improving the cathode-electrolyte interface stability and long-term cyclability. Especially, the NCM cathode using PI-COOH binder exhibits the highest cyclability (205 mAh g−1 at 40 mA g−1 with 73% capacity retention after 100 cycles at 4.7 V), contrasting to NCM cathode with commonly-used polyvinylidene fluoride (PVDF) binder (208 mAh g−1 with 34% capacity retention). Furthermore, the fully-charged NCM cathode with PI-COOH binder releases the less heat than the NCM/PVDF cathode during high-temp treatment to 300 °C, demonstrating the superiority of polyimide binders in improving the safety of the cathode materials.

Preparation of mesocarbon microbeads as anode material for lithium-ion battery by co‑carbonization of FCC decant oil and conductive carbon black

Low yield and unremarkable electrochemical performance of MCMB prepared from conventional thermal polymerization are inevitable, which limits its large-scale application as anode material for lithium-ion batteries. Hence, in this work, MCMBs were prepared by co‑carbonization of low-valued FCC decant oil and conductive carbon black (CCB). CCB can enhance the nucleation, inhibit the growth of the mesophase spheres and adhere on the surface of spheres, thereby increasing the yields (38.9 wt%), influencing the microstructure and subsequent electrochemical performance of MCMB. The MCMBs prepared by doping with 3 wt% CCB exhibited a small particle size (15.0 μm) and moderate structural disorder degree with wide interlayer spacing (AD3/Aall = 18.15%, d002 = 3.5342 Å), which shortened the transport pathway of Li+ inside the microbeads. Besides, chain-like conductive carbon black connected to the surface of the MCMBs, forming a continuous and developed conductive network, which was benefit for increasing of electron conduction and enhancing the Li+ transport rate outside the microbead. Such MCMB delivered the superior long-term cyclability with specific capacity of 394.5 mAh g−1 at 0.5 A g−1 (over 400 cycles) and presented a high-rate capability with reversible capacity of 276.0 mAh g−1 at an ultra-high current density of 3 A g−1.

Mo2 N-W2 N Heterostructures Embedded in Spherical Carbon Superstructure as Highly Efficient Polysulfide Electrocatalysts for Stable Room-Temperature Na-S Batteries.

Room-temperature sodium-sulfur (RT Na-S) batteries are highly desirable for a sustainable large-scale energy-storage system due to their high energy density and low cost. Nevertheless, practical applications of RT Na-S batteries are still prevented by the shuttle effect of sodium polysulfides (NaPS), slow reaction kinetics of S, and incomplete conversion process of NaPS. Here, Mo2 N-W2 N heterostructures embedded in a spherical carbon superstructure (Mo2 N-W2 N@PC) are designed to efficiently suppress the "polysulfide shuttle" and promote NaPS redox reactions. The designed Mo2 N-W2 N@PC heterostructure with abundant heterointerfaces, high conductivity, and porosity can facilitate electron/ion diffusion and provide high catalytic activity for efficient NaPS conversion. The obtained Na-S battery delivers high reversible capacity with superior long-term cyclability (517 mAh g-1 at 1 A g-1 after 400 cycles) and unprecedented rate capability (417 mAh g-1 at 2 A g-1 ). Furthermore, the electrocatalysis mechanism is revealed by combining in situ X-ray diffraction (XRD), ex situ X-ray photoelectron spectroscopy (XPS), UV-vis spectra, and precipitation experiments. This work demonstrates a novel heterostructure design strategy that enables high-performance Na-S batteries.

3D-Assembled rutile TiO2spheres withc-channels for efficient lithium-ion storage

Three-dimensional (3D) TiO2 architectures have attracted significant attention recently as they can improve the electrochemical stability and realize the full potential of TiO2-based anodes in lithium ion batteries. Here, flower-like rutile TiO2 spheres with radially assembled nanorods (c-channels) were fabricated via a simple hydrothermal method. The 3D radial architecture affords massive active sites to fortify the lithium storage. Moreover, the presence of c-channels facilitates electrolyte infiltration and offers facile pathways for efficient Li+ transport. As a result, this flower-like rutile TiO2 anode gives significantly enhanced specific capacities (615 mA h g-1 at 1 C and 386 mA h g-1 at 2 C after 400 cycles) and a superior long-term cyclability (up to 10 000 cycles with a specific capacity of 67 mA h g-1 at 100 C). Kinetic analysis reveals that the enhanced diffusion-controlled and surface capacitive storage leads to the excellent electrochemical behavior. This work not only exhibits the enormous advantages of 3D architectures with c-channels, but also provides access to structural design and crystal phase selection for TiO2-based anode materials.

Electrophoretic Deposition of Binder-Free MOF-Derived Carbon Films for High-Performance Microsupercapacitors.

Recently, miniaturized power supplies have become essential components of micro-electromechanical systems (MEMS) and portable microdevices due to their high-power density, moderate specific energy, and superior long-term cyclability. In this study, microsupercapacitors with ZIF-8-derived carbons as active materials were successfully fabricate by electrophoretic deposition method. The carbon materials on microsupercapacitors, which are directly deposited or obtained by pyrolyzing predeposited ZIF-8 particles, play a crucial role in achieving outstanding electrochemical performances. The microsupercapacitor of 16 interdigital finger electrodes, prepared by electrophoretic deposition of ZIF-8 particles and subsequent pyrolysis, shows maximum specific power 687.6 mW cm-3 , specific energy 2.87 mWh cm-3 , and 97.8 % capacitance retention rate after 10 000 cycles. The simple and facile process of electrophoretic deposition and subsequent pyrolysis of ZIF-8 particles generates a film of densely populated microporous carbon particles on microsupercapacitor, leading to superior capacitive performances.

2D Titania-Carbon Superlattices Vertically Encapsulated in 3D Hollow Carbon Nanospheres Embedded with 0D TiO2 Quantum Dots for Exceptional Sodium-Ion Storage.

Two-dimensional (2D) superlattices offer promising technological opportunities in tuning the intercalation chemistry of metal ions. Now, well-ordered 2D superlattices of monolayer titania and carbon with tunable interlayer-spacing are synthesized by a molecularly mediated thermally induced approach. The 2D superlattices are vertically encapsulated in hollow carbon nanospheres, which are embedded with TiO2 quantum dots, forming a 0D-2D-3D multi-dimensional architecture. The multi-dimensional architecture with the 2D superlattices encapsulated inside exhibits a near zero-strain characteristic and enriched electrochemical reactivity, achieving a highly efficient Na+ storage performance with exceptional rate capability and superior long-term cyclability.

From sand to fast and stable silicon anode: Synthesis of hollow Si@void@C yolk–shell microspheres by aluminothermic reduction for lithium storage

As an alloying type anode material, silicon is a promising alternative of graphitic carbon due to its high theoretical capacity and natural abundance. Developing an industrially viable silicon anode, however, is still a huge challenge because of several problems: First of all, the common process to synthesize a silicon anode is complicated, costly, and energy-intensive. Besides, the huge volume expansion, inevitable side reactions with the electrolyte, and low intrinsic conductivity of silicon are eventually responsible for the poor cyclability and unsatisfactory rate capability. Herein, we aim to address these issues by proposing synthesis of hollow Si@void@C yolk–shell microspheres from sand by low-temperature aluminothermic reduction, which energetically combines a cost-effective silicon source with an energy-efficient, high-yield methodology. The hollow Si@void@C yolk–shell microspheres effectively accommodate the diffusion-induced stress by providing the hollow interior and the void space. Moreover, the carbon shell not only functions as an electrolyte-blocking layer to protect the silicon yolk from undesirable side reactions and SEI formation, but also acts as a conductive framework to reduce the resistance to electron and Li+ ion transport. Benefiting from these synergistic effects, the hollow Si@void@C yolk–shell microspheres exhibit superior long-term cyclability and rate capability.

Superior long-term cyclability of a nanocrystalline NiO anode enabled by a mechanochemical reaction-induced amorphous protective layer for Li-ion batteries

Herein, we demonstrate a novel amorphous composite layer-protected nanocrystalline NiO with superior long-term cyclability as an anode material for Li-ion batteries. Amorphous nickel and lithium carbon oxides form on nickel oxide (NiO nanoparticulate crystals with d < 15 nm) at room-temperature by mechanically milling a mixture of NiO and LiH under a CO2 atmosphere. The amorphous composite layer on the surface of NiO nanocrystal contains lithium carbonate (Li2CO3), nickel carbonate (NiCO3) and nickel acetate (NiC2O4). The NiO-0.4LiH sample milled under an atmosphere of 3 bar of CO2 delivers 770 mAh g−1 of specific capacity with nearly no capacity decrease from 2nd to 565th cycle at 100 mA g−1. Even operating at a high rate of 2 A g−1, the specific capacity remains at 530 mAh g−1, which is remarkably superior to that of pristine NiO (∼393 mAh g−1). The cycling stability is attributed to the amorphous carbon oxide layer effectively buffering the volume expansion of the anode during lithiation and stabilizing the solid electrolyte interphase (SEI) film during cycling of the NiO anode. The facile preparation process and favourable electrochemical performance of the composite NiO anode indicate this is a promising anode for a Li-ion battery.

Hierarchical MoO2@TiO2-Carbon Nanostructure Enable Ultrafast and High-Capacity Na-Ion Storage By Enhanced Pseudocapacitance

Over the past few decades, tremendous efforts have been focused on the development of lithium ion batteries (LIBs) used in portable electronics and electric vehicles because of their high energy density and long cycle life. However, the large-scale application of LIBs is hindered by the high cost and the scarcity of lithium resources. In contrast, sodium ion batteries (SIBs) represent potential alternatives for large-scale energy storage due to low-cost and abundant resources. Nevertheless, the sluggish Na-ion transport and severe volume expansion currently limit the rate performance and stability of the SIBs respectively. To address these issues, one effective approach is to utilize the incorporation of pseudocapacitive charge storage into SIBs. Pseudocapacitive charge storage is based on the faradic reaction that occurs on or near the surface of the electrode materials. Some of the materials exhibit pseudocapacitive features in nature, for example, RuO2, MnO2 and Nb2O5. In addition, other materials display the capacitive characteristics with nanoscale morphologies such as TiO2, MoO2 and V2O5. Previous studies1-2 showed great promise towards high-rate electrodes in LIBs and SIBs driven by a pseudocapacitive mechanism. Inspired by this, it is highly expected to achieve superior rate capability and long cycle life of SIBs by introducing pseudocapacitive charge storage in electrodes. In order to take advantage of fast pseudocapacitive charge storage kinetics, we report a sandwich composite anode material where the ultrafine TiO2 and MoO2 nanoparticles are embedded between the layers of carbon nanotube (CNT) and amorphous carbon. (referred to as CNT-TiO2@MoO2-C). The unique sandwich nanoarchitecture and the ultrafine TiO2 and MoO2 nanoparticle can not only significantly decrease the ion diffusion length but also effectively accommodate the volume expansion. Fig.1 shows the long-term cycling performance of the CNT-TiO2@MoO2-C electrode for over 8000 cycles at a current rate of 10A g–1. After a slow capacity fading in the initial dozens of cycles, a reversible capacity of 200 mAhg–1 was maintained during the subsequent cycles, indicating a superior long-term cyclability. In summary, we reported an innovative design of sandwich nanoscale architecture. Based on this rational and unique morphology, the CNT-TiO2@MoO2-C shows an excellent cycling stability up to 8 000 cycles.

Morphology changes and long-term cycling durability of Si flake powder negative electrode for lithium-ion batteries

Silicon flake powder (Si LeafPowder®, Si-LP) with the thickness and lateral dimension of 100 nm and 3–5 μm, respectively, demonstrated superior cycle performance as a negative electrode in lithium-ion batteries. A multi-folded layered structure with many voids was spontaneously formed in Si-LP composite electrodes by morphology changes of Si-LP sheets in repeated charge and discharge cycles. The multi-folded layered structure accommodated volumetric changes of the Si active material and prevented exfoliation of the active material from the current collector, which led to the superior long-term cyclability of the Si-LP electrode. The main factor for capacity fading in long-term cycling was a gradual loss of conduction pathways between Si-LP sheets due to the accumulation of electrolyte reduction products in the electrode. The film-forming additives, vinylene carbonate and fluoroethylene carbonate, effectively suppressed the electrolyte decomposition and remarkably improved the cycle performance of the Si-LP electrode.

Nanograin tungsten oxide with excess oxygen as a highly reversible anode material for high-performance Li-ion batteries

Nanogranular tungsten oxide (WO3) with excess oxygen is synthesized and its battery performance is evaluated as an anode material for the Li-ion battery (LIB). The formation of a monoclinic WO3 phase is confirmed using X-ray diffraction (XRD) and micro (µ)-Raman spectroscopy analyses. The Rutherford back scattering results confirm the existence of excess oxygen in the film. The charge discharge processes are associated with the conversion of the WO3 from the oxide state to the metallic state, and vice versa, and it shows a maximum specific capacity of 778.8 mAh g−1 at a current density of 0.1 Ag−1 in the first discharge. Even at a very high current density of 1 Ag−1, the sample retains the capacity of 228.6 mAh g−1. It shows excellent rate capability and a long-term cycling stability over 500 charge–discharge cycles, with capacity retention of 217%. The observed high discharge capacity and superior long-term cyclability of the nanograin WO3 anode are attributable to the synergetic effect of the excess-oxygen induced increased donor density and enhanced electrical conductivity.

Pyrite FeS2 nanobelts as high-performance anode material for aqueous pseudocapacitor

To push energy and power limits of aqueous pseudocapacitors, advanced anode materials are highly desirable. In this work, pyrite FeS2 nanobelts are fabricated through a soft-template-assisted one-pot method. The high electrical conductivity and nanostructured morphology of this anode material facilitate charge transports, thus considerably improving pseudocapacitive performance compared to Fe2O3 and FeS2 contrast samples. This material can deliver a high capacitance of 308.3Fg−1/317.8Fg−1 at 5mVs−1/3Ag−1. It also exhibits good rate capability that 64.2% and 42.0% of the above capacitance can be retained when the scan rate and current density are increased to 10-fold, respectively, and superior long-term cyclability that 81.1% capacitance retention can be obtained after 1000 cycles. The results demonstrate great potential of pyrite FeS2 anode material for aqueous pseudocapacitors.

High-Performance Li-S Batteries with an Ultra-lightweight MWCNT-Coated Separator.

A bifunctional separator consisting of a layer of multiwall carbon nanotubes (MWCNTs) on the cathode-side of a Celgard polypropylene sheet has been investigated to overcome the challenges of Li-S cells. The conductive/porous MWCNT-coating functions (i) as an upper current collector to facilitate electron transport and high active-material utilization and (ii) as a filter to intercept/absorb the migrating polysulfides and thereby suppress the polysulfide diffusion. Also, the access to the electrolyte through the porous network of MWCNT along with its fast electronic transport facilitates the reutilization of the trapped active material and superior long-term cyclability. The MWCNT-coating is lightweight (0.17 mg cm(-2)), yet allows the successful use of regular sulfur cathodes (high sulfur content of 70 wt %) with high discharge capacity, excellent rate performance, and long cycle life, demonstrating that the MWCNT-coated separator is a viable solution to practical Li-S batteries.