A new strategy for developing superior electrode materials for advanced batteries: using a positive cycling trend to compensate the negative one to achieve ultralong cycling stability

Ordered SnO2 nanotube arrays of tuneable geometry as a lithium ion battery material with high longevity

Ordered arrays of straight, parallel SnO₂ nanotubes are prepared by atomic layer deposition (ALD) on inert 'anodic' aluminum oxide porous membranes serving as templates. Various thicknesses of the SnO₂ tube walls and various tube lengths are characterized in terms of morphology by scanning electron microscopy (SEM), chemical identity by X-ray photoelectron spectroscopy (XPS) and phase composition by X-ray diffraction (XRD). Their performance as negative electrode ('anode') materials for lithium-ion batteries (LIBs) is quantified at different charge and discharge rates in the absence of additives. We find distinct trends and optima for the dependence of initial capacity and long-term stability on the geometric parameters of the nanotube materials. A sample featuring SnO₂ tubes of 30 µm length and 10 nm wall thickness achieves after 780 cycles a coulombic efficiency of >99% and a specific capacity of 671 mA h g^-1. This value represents 92% of the first-cycle capacity and 86% of the theoretical value.

Interfacial Superassembly of Grape-Like MnO-Ni@C Frameworks for Superior Lithium Storage

Despite the excellent electrochemical performance of MnO-based electrodes, a large capacity increase cannot be avoided during long-life cycling, which makes it difficult to seek out appropriate cathode materials to match for commercial applications. In this work, a grape-like MnO-Ni@C framework from interfacial superassembly with remarkable electrochemical properties was fabricated as anode materials for lithium-ion batteries. Electrochemical analysis indicates that the introduction of Ni not only contributes to the excellent rate capability and high specific capacity but also prevents further oxidation of MnO to the higher valence states for ultrastable long-life cycling performance. Furthermore, thermodynamic calculation proves that the ultrastable long cycling life of the Ni-Mn-O system originated from a buffer composition region to stabilize the MnO structure. Because of the unique grape-like structure and performance of the Ni-Mn-O system, the MnO-Ni@C electrode displayed an invertible specific capacity of 706 mA h g^-1 after 200 cycles at a current density of 0.1 A g^-1 and excellent cycling stability maintained a capacity of 476.8 mA h g^-1 after 2100 cycles at 1.0 A g^-1 without obvious capacity change. This new nanocomposite material could offer a novel fabrication strategy and insight for MnO-based materials and other metal oxides as anodes for improved electrochemical performance.

Achieving High Lithium Storage Capacity and Long-Term Cyclability of Novel Cobalt Germanate Hydroxide/Reduced Graphene Oxide Anodes with Regulated Electrochemical Catalytic Conversion Process of Hydroxyl Groups

To develop ternary transition-metal germanate anodes with superior lithium storage performances for lithium-ion batteries, a novel capacity counterbalance approach in one compound is designed by introducing an electrocatalytic conversion-type component with a positive cycling trend to compensate the negative cycling trend of the GeO₂ component. Novel cobalt germanate hydroxide (CGH) nanoplates chemically bonded on reduced graphene oxide (RGO) sheets are thus synthesized with a mild one-pot hydrothermal approach, constructing maximal face-to-face contact interfaces with interfacial bonds to boost the electrochemical conversion reactions. Furthermore, the hydroxyl groups (Co-OH) of CGH nanoplates are regulated by thermal annealing treatments, thus controlling the capacity contribution resulting from the electrocatalytic conversion reaction of LiOH to exactly offset the capacity fading of GeO₂. The results on the CGH electrodes at different cycling potentials confirm the stepwise electrochemical reactions of Co, GeO₂, and LiOH. The equilibrium of these electrochemical reactions ensures a stable cycling capacity without obvious fluctuations. Consequently, the optimal CGH/RGO hybrid anode delivers a reversible capacity as high as 1136 mA h g^-1 at 0.1 A g^-1 until 100 cycles. It also exhibits a long cyclability with a retained capacity of 560 mA h g^-1 at 1 A g^-1 until 1000 cycles. This work demonstrates a general and efficient capacity counterbalance method to highly boost lithium storage performances in terms of high capacity and long-term cyclability.

A Flexible Si@C Electrode with Excellent Stability Employing an MXene as a Multifunctional Binder for Lithium-Ion Batteries

Silicon is a promising anode material with high capacity for lithium-ion batteries (LIBs) but suffers from poor conductivity and large volume change during charge/discharge. Herein, by using two-dimensional conductive MXene as a multifunctional binder instead of conventional insulating polymer binders such as poly(vinylidene fluoride) or carboxymethylcellulose sodium (PVDF and CMC, respectively), a free-standing, flexible Si@C film was fabricated by simple vacuum filtration and directly used as anode for LIBs. In the MXene-bonded Si@C film, MXene constructed a three-dimensional conductive framework in which Si@C nanocomposites were embedded. Its loose and porous structure provided much space to buffer the large volume expansion of Si@C nanoparticles and thus led to significantly superior cycle stability compared with conventional CMC- and PVDF-bonded Si@C electrodes. Moreover, the porous structure and the metallically conductive MXene offered fast ion transport and outstanding conductivity of the MXene-bonded Si@C film, which were favorable for its rate performance. These results promise good potential of the MXene-bonded Si@C film electrode for LIBs.

Synergic effects of the decoration of nickel oxide nanoparticles on silicon for enhanced electrochemical performance in LIBs

Significant efforts continue to be directed toward the construction of anode materials with high specific capacity and long cycling stability for lithium-ion batteries (LIBs). In this context, silicon is preferred due to its high capacity even though it has a problem of excessive volume expansion during electrochemical reactions as well as poor cyclability due to a reduction in conductivity. Hence, the hybridization of silicon with suitable materials could be a promising approach to overcome the abovementioned problems. Herein, we demonstrate the uniform decoration of nickel oxide (NiO) nanoparticles (15-20 nm) on silicon nanosheets using bis(cyclopentadienyl) nickel(ii) (C₁₀H₁₀Ni) at low temperatures, taking advantage of the presence of two unpaired electrons in an antibonding orbital in the cyclopentadienyl group. The formation and growth mechanism are discussed in detail. The electrochemical study of the nanocomposite revealed an initial delithiation capacity of 2507 mA h g^-1 with a reversible capacity of 2162 mA h g^-1, having 86% retention and better cycling stability for up to 500 cycles. At the optimum concentration, NiO nanoparticles facilitate Li⁺-ion adsorption, which in turn accelerates the transport of Li⁺-ions to active sites of silicon. The Warburg coefficient and Li⁺-ion diffusion at the electrodes confirm the enhancement in the charge transfer process at the electrode/electrolyte interface with NiO nanoparticles. Further, the NiO nanoparticles with uniform distribution suppress the agglomeration of Si nanosheets and provide sufficient space to accommodate a volume change in Si during cycling, which also reduces the diffusion path length of the Li-ions. It also helps to strengthen the mechanical stability, which might be helpful in preventing the cracking of silicon due to volume expansion and maintains the Li-ion transport pathway of the active material, resulting in enhanced cycling stability. Due to the synergic effect between NiO nanoparticles and Si sheets, the nanocomposite delivers high reversible capacity.

High-Lithium-Affinity Chemically Exfoliated 2D Covalent Organic Frameworks

Covalent organic frameworks (COFs) with reversible redox behaviors are potential electrode materials for lithium-ion batteries (LIBs). However, the sluggish lithium diffusion kinetics, poor electronic conductivity, low reversible capacities, and poor rate performance for most reported COF materials limit their further application. Herein, a new 2D COF (TFPB-COF) with six unsaturated benzene rings per repeating unit and ordered mesoporous pores (≈2.1 nm) is designed. A chemical stripping strategy is developed to obtain exfoliated few-layered COF nanosheets (E-TFPB-COF), whose restacking is prevented by the in situ formed MnO₂ nanoparticles. Compared with the bulk TFPB-COF, the exfoliated TFPB-COF exhibits new active Li-storage sites associated with conjugated aromatic π electrons by facilitating faster ion/electron kinetics. The E-TFPB-COF/MnO₂ and E-TFPB-COF electrodes exhibit large reversible capacities of 1359 and 968 mAh g^-1 after 300 cycles with good high-rate capability.

A hierarchical porous architecture of silicon@TiO2@carbon composite novel anode materials for high performance Li-ion batteries

The excellent electrochemical properties are attributed to the synergistic action of hierarchical porous TiO₂ and carbon layers.

Tin nanoparticles embedded in an N-doped microporous carbon matrix derived from ZIF-8 as an anode for ultralong-life and ultrahigh-rate lithium-ion batteries

A carbon matrix with abundant micropores derived from ZIF-8 can confine Sn particles in an ultrasmall nanosize, contributing to the buffering of the huge volume changes.

3D Hierarchical Microballs Constructed by Intertwined MnO@N-doped Carbon Nanofibers towards Superior Lithium-Storage Properties

MnO is a promising high-capacity anode material for lithium-ion batteries (LIBs), but pristine material suffers short cycle life and poor rate capability, thus hindering the practical application. In this work, a new type of porous MnO microballs stringed with N-doped porous carbon (3DHB-MnO@NC) with a well-connected hierarchical three-dimensional network structure was prepared by the facile self-template method. The 3DHB-MnO@NC electrode can effectively promote the ion/electron transfer and buffer the large volume change of electrode during the electrochemical reaction. As the anode for LIBs, the 3DHB-MnO@NC possesses outstanding cycling performance (1247.7 mA h g^-1 after 90 cycles at 200 mA g^-1 ) and good rate capabilities (949.6 mA h g^-1 after 450 cycles at 1000 mA g^-1 ). The facile self-template method of the prepared 3DHB-MnO@NC composite paves a new way for practical applications of MnO in high performance LIBs.

MnWO4 nanoparticles as advanced anodes for lithium-ion batteries: F-doped enhanced lithiation/delithiation reversibility and Li-storage properties

F-Doped MnWO4 nano-particles were synthesized by a one-pot hydrothermal reaction. When evaluated as an electrode material for a Li ion battery, the F-doped nano-MnWO4 delivers a theoretical capacity of 708 mA h g-1 and a long cycle life, as demonstrated by more than 85% capacity retention when cycled for 150 cycles.

Uniform MnCo2O4 Porous Dumbbells for Lithium-Ion Batteries and Oxygen Evolution Reactions

Three-dimensional (3D) binary oxides with hierarchical porous nanostructures are attracting increasing attentions as electrode materials in energy storage and conversion systems because of their structural superiority which not only create desired electronic and ion transport channels but also possess better structural mechanical stability. Herein, unusual 3D hierarchical MnCo₂O₄ porous dumbbells have been synthesized by a facile solvothermal method combined with a following heat treatment in air. The as-obtained MnCo₂O₄ dumbbells are composed of tightly stacked nanorods and show a large specific surface area of 41.30 m² g^-1 with a pore size distribution of 2-10 nm. As an anode material for lithium-ion batteries (LIBs), the MnCo₂O₄ dumbbell electrode exhibits high reversible capacity and good rate capability, where a stable reversible capacity of 955 mA h g^-1 can be maintained after 180 cycles at 200 mA g^-1. Even at a high current density of 2000 mA g^-1, the electrode can still deliver a specific capacity of 423.3 mA h g^-1, demonstrating superior electrochemical properties for LIBs. In addition, the obtained 3D hierarchical MnCo₂O₄ porous dumbbells also display good oxygen evolution reaction activity with an overpotential of 426 mV at a current density of 10 mA cm^-2 and a Tafel slope of 93 mV dec^-1.

A novel bismuth-based anode material with a stable alloying process by the space confinement of an in situ conversion reaction for a rechargeable magnesium ion battery

Due to the space confinement of in situ conversion, the BiOF electrode shows superior magnesium storage performance.

High Lithium Storage Capacity and Long Cycling Life Fe3S4 Anodes with Reversible Solid Electrolyte Interface Films and Sandwiched Reduced Graphene Oxide Shells

Increasing demands for lithium-ion batteries (LIBs) with high energy density and high power density require highly reversible electrochemical reactions to enhance the cyclability and capacities of electrodes. As the reversible formation/decomposition of the solid electrolyte interface (SEI) film during the lithiation/delithiation process of Fe₃S₄ could bring about a higher capacity than its theoretical value, in the present work, synthesized Fe₃S₄ nanoparticles are sandwich-wrapped with reduced graphene oxide (RGO) to fabricate highly reversible and long cycling life anode materials for high-performance LIBs. The micron-sized long slit between sandwiched RGO sheets effectively prevents the aggregation of intermediate phases during the discharge/charge process and thus increases cycling capacity because of the reversible formation/decomposition of the SEI film driven by Fe nanoparticles. Furthermore, the RGO sheets interconnect with each other by a face-to-face mode to construct a more efficiently conductive network, and the maximum interfacial oxygen bridge bonds benefit the fast electron hopping from RGO to Fe₃S₄, improving the depth of the electrochemical reactions and facilitating the highly reversible lithiation/delithiation of Fe₃S₄. Thus, the resultant Fe₃S₄/RGO hybrid shows a highly reversible charge capacity of 1324 mA h g^-1 over 275 cycles at a current density of 100 mA g^-1, even retains 480 mA h g^-1 over 500 cycles at 1000 mA g^-1, which are much higher than reported values.

Porous and Low-Crystalline Manganese Silicate Hollow Spheres Wired by Graphene Oxide for High-Performance Lithium and Sodium Storage

Herein, a graphene oxide (GO)-wired manganese silicate (MS) hollow sphere (MS/GO) composite is successfully synthesized. Such an architecture possesses multiple advantages in lithium and sodium storage. The hollow MS structure provides a sufficient free space for volume variation accommodation; the porous and low-crystalline features facilitate the diffusion of lithium ions; meanwhile, the flexible GO sheets enhance the electronic conductivity of the composite to a certain degree. When applied as the anode material for lithium-ion batteries (LIBs), the as-obtained MS/GO composite exhibits a high reversible capacity, ultrastable cyclability, and good rate performance. Particularly, the MS/GO composite delivers a high capacity of 699 mA h g^-1 even after 1000 cycles at 1 A g^-1. The sodium-storage performance of MS/GO has been studied for the first time, and it delivers a stable capacity of 268 mA h g^-1 after 300 cycles at 0.2 A g^-1. This study suggests that the rational design of metal silicates would render them promising anode materials for LIBs and SIBs.

Metal-Organic Framework Template Synthesis of NiCo2S4@C Encapsulated in Hollow Nitrogen-Doped Carbon Cubes with Enhanced Electrochemical Performance for Lithium Storage

Owing to its richer redox reaction and remarkable electrical conductivity, bimetallic nickel cobalt sulfide (NiCo₂S₄) is considered as an advanced electrode material for energy-storage applications. Herein, nanosized NiCo₂S₄@C encapsulated in a hollow nitrogen-doped carbon cube (NiCo₂S₄@D-NC) has been fabricated using a core@shell Ni₃[Co(CN)₆]₂@polydopamine (PDA) nanocube as the precursor. In this composite, the NiCo₂S₄ nanoparticles coated with conformal carbon layers are homogeneously embedded in a 3D high-conduction carbon shell from PDA. Both the inner and the outer carbon coatings are helpful in increasing the electrical conductivity of the electrode materials and prohibit the polysulfide intermediates from dissolving in the electrolyte. When researched as electrode materials for lithium storage, owing to the unique structure with double layers of nitrogen-doped carbon coating, the as-obtained NiCo₂S₄@D-NC electrode maintains an excellent specific capacity of 480 mAh g^-1 at 100 mA g^-1 after 100 cycles. Even after 500 cycles at 500 mA g^-1, a reversible capacity of 427 mAh g^-1 can be achieved, suggesting an excellent rate capability and an ultralong cycling life. This remarkable lithium storage property indicates its potential application for future lithium-ion batteries.

Flexible P-Doped Carbon Cloth: Vacuum-Sealed Preparation and Enhanced Na-Storage Properties as Binder-Free Anode for Sodium Ion Batteries

In this work, a flexible and self-supporting P-doped carbon cloth (FPCC), which is composed of interwoven mesh of hollow microtubules with porous carbon walls, is prepared via a vacuum-sealed doping technology by employing the commercially available cotton cloth as sustainable and scalable raw material. When directly used as binder-free anode for sodium-ion batteries, the as-prepared FPCC delivers superior Na-storage properties in terms of specific capacity up to 242.4 mA h g^-1, high initial Coulombic efficiency of ∼72%, excellent rate capabilities (e.g., 123.1 mA h g^-1 at a high current of 1 A g^-1), and long-term cycle life (e.g., ∼88% capacity retention after even 600 cycles). All these electrochemical data are better than the undoped carbon cloth control, demonstrating the significance of P-doping to enhance the Na-storage properties of cotton-derived carbon anode. Furthermore, the technologies of electrochemical impedance spectroscopy and galvanostatic intermittent titration technique are implemented to disclose the decrease of charge transfer resistance and improvement of Na-migration kinetics, respectively.

Electrochemical Performance and Storage Mechanism of Ag2 Mo2 O7 Micro-rods as the Anode Material for Lithium-Ion Batteries

Ag₂ Mo₂ O₇ micro-rods are prepared by one-step hydrothermal method and their lithium electrochemical properties, as the anode for lithium-ion batteries, are comprehensively studied in terms of galvanostatic charge-discharge cycling, cyclic voltammetry, and rate performance measurements. The electrode delivers a high reversible capacity of 825 mAh g^-1 at a current density of 100 mA g^-1 and a superior rate capability with a discharge capacity of 263 mAh g^-1 under the high current density of 2 Ag^-1 . The structural transition and phase evolution of Ag₂ Mo₂ O₇ were investigated by using ex situ XRD and TEM. The Ag₂ Mo₂ O₇ electrode is likely to be decomposed into amorphous molybdenum, Li₂ O, and metallic silver based on the conversion reaction. Silver nanoparticles are not involved in the subsequent electrochemical cycles to form a homogeneous conducting network. Such in situ decomposition behavior provides an insight into the mechanism of the electrochemical reaction for the anode materials and would contribute to the design of new electrode materials in future.

Low-Cost and Novel Si-Based Gel for Li-Ion Batteries

Si-based nanostructure composites have been intensively investigated as anode materials for next-generation lithium-ion batteries because of their ultra-high-energy storage capacity. However, it is still a great challenge to fabricate a perfect structure satisfying all the requirements of good electrical conductivity, robust matrix for buffering large volume expansion, and intact linkage of Si particles upon long-term cycling. Here, we report a novel design of Si-based multicomponent three-dimensional (3D) networks in which the Si core is capped with phytic acid shell layers through a facile high-energy ball-milling method. By mixing the functional Si with graphene oxide and functionalized carbon nanotube, we successfully obtained a homogeneous and conductive rigid silicon-based gel through complexation. Interestingly, this Si-based gel with a fancy 3D cross-linking structure could be writable and printable. In particular, this Si-based gel composite delivers a moderate specific capacity of 2711 mA h g^-1 at a current density of 420 mA g^-1 and retained a competitive discharge capacity of more than 800.00 mA h g^-1 at the current density of 420 mA g^-1 after 700 cycles. We provide a new method to fabricate durable Si-based anode material for next-generation high-performance lithium-ion batteries.

Metastable Marcasite-FeS2 as a New Anode Material for Lithium Ion Batteries: CNFs-Improved Lithiation/Delithiation Reversibility and Li-Storage Properties

Marcasite (m-FeS₂) exhibits higher electronic conductivity than that of pyrite (p-FeS₂) because of its lower semiconducting gap (0.4 vs 0.7 eV). Meanwhile, as demonstrates stronger Fe-S bonds and less S-S interactions, the m-FeS₂ seems to be a better choice for electrode materials compared to p-FeS₂. However, the m-FeS₂ has been seldom studied due to its sophisticated synthetic methods until now. Herein, a hierarchical m-FeS₂ and carbon nanofibers composite (m-FeS₂/CNFs) with grape-cluster structure was designed and successfully prepared by a straightforward hydrothermal method. When evaluated as an electrode material for lithium ion batteries, the m-FeS₂/CNFs exhibited superior lithium storage properties with a high reversible capacity of 1399.5 mAh g^-1 after 100 cycles at 100 mA g^-1 and good rate capability of 782.2 mAh g^-1 up to 10 A g^-1. The Li-storage mechanism for the lithiation/delithiation processes of m-FeS₂/CNFs was systematically investigated by ex situ powder X-ray diffraction patterns and scanning electron microscopy. Interestingly, the hierarchical m-FeS₂ microspheres assembled by small FeS₂ nanoparticles in the m-FeS₂/CNFs composite converted into a mimosa with leaves open shape during Li⁺ insertion process and vice versa. Accordingly, a "CNFs accelerated decrystallization-recrystallization" mechanism was proposed to explain such morphology variations and the decent electrochemical performance of m-FeS₂/CNFs.

Graphene enhanced silicon/carbon composite as anode for high performance lithium-ion batteries

Silicon-based anode materials for lithium ion batteries (LIBs) have become a hot research topic due to their remarkably high theoretical capacity (4200 mA h g⁻¹).

Engineering the Li Storage Properties of Graphene Anodes: Defect Evolution and Pore Structure Regulation

A general and mild strategy for fabricating defect-enriched graphene mesh (GM) and its application toward the anode of Li-ion batteries (LIBs) has been reported. The GM with a pore size of 60-200 nm is achieved by employing Fe₂O₃ as the etching reagent that is capable of locally etching the graphene basal plane in a relatively mild manner. Upon different drying technologies, that is, oven drying and freeze-drying, GMs with different porous structure are obtained. The electrochemical Li storage properties of GMs in comparison with graphene aerogels (GAs) disclose that both defect sites and porous structure are crucial for the final anodic performances. We show that only when merged with rich porosity, the GM anode can achieve a better Li storage performance than that of GA. Moreover, we further fabricated nitrogen-doped GM (NGM) using urea as the nitrogen source with a freeze-drying process. Benefiting from the unique structural characteristics, that is, plentiful defects, abundant pores, and nitrogen doping, the NGM anode exhibits high Li storage capacity with good cyclic stability (1078 mAh g^-1 even after 350 continuous cycles at a current density of 0.2 C) and outstanding rate capability. Our finding provides fundamental insights into the influence of defects and pore structure on the Li storage properties of graphene, which might be helpful for designing advanced graphene-based anodes for LIBs.

Carbon-Free Porous Zn2GeO4 Nanofibers as Advanced Anode Materials for High-Performance Lithium Ion Batteries

In this work, carbon-free, porous, and micro/nanostructural Zn₂GeO₄ nanofibers (p-ZGONFs) have been prepared via a dissolution-recrystallization-assisted electrospinning technology. The successful electrospinning to fabricate the uniform p-ZGONFs mainly benefits from the preparation of completely dissolved solution, which avoids the sedimentation of common Ge-containing solid-state precursors. Electrochemical tests demonstrate that the as-prepared p-ZGONFs exhibit superior Li-storage properties in terms of high initial reversible capacity of 1075.6 mA h g^-1, outstanding cycling stability (no capacity decay after 130 cycles at 0.2 A g^-1), and excellent high-rate capabilities (e.g., still delivering a capacity of 384.7 mA h g^-1 at a very high current density of 10 A g^-1) when used as anode materials for lithium ion batteries (LIBs). All these Li-storage properties are much better than those of Zn₂GeO₄ nanorods prepared by a hydrothermal process. The much enhanced Li-storage properties should be attributed to its distinctive structural characteristics including the carbon-free composition, plentiful pores, and macro/nanostructures. Carbon-free composition promises its high theoretical Li-storage capacity, and plentiful pores cannot only accommodate the volumetric variations during the successive lithiation/delithiation but can also serve as the electrolyte reservoirs to facilitate Li interaction with electrode materials.