High-capacity Electrode Materials Research Articles

Casein As a Novel Binder for Silicon-Based Electrodes for Li-Ion Batteries

High capacity electrode material has been studied over the years due to the constant demand for high energy density applications in li ion batteries. Among others, silicon has been considered a more promising candidate for its high theoretical capacity of ~ 3600 mAh/g, abundant resources, low cost and low toxicity. However, silicon-based electrodes face rapid degradation due to the extensive volume variation (~300%) in the charge discharge process. Binders used in the electrode fabrication plays a crucial role in these high-performance electrodes since it can reduce the mechanical fracture in the cycling process. Utilization of polymeric material as binders to hold the active material has been the most common approach used in the li ion battery electrode preparation. Recent studies carried out by Nguyen et. al have shown the use of small molecular carboxylic acids as binders which showed an improvement in the cell performance for silicon electrodes. In this study we introduce a cheap and environmentally friendly alternative that could be used as a non-polymeric binder for silicon electrodes. Further, the electrode preparation can be done in water medium which reduces the introduction of toxic organic solvents such as NMP to the environment. Casein is a milk protein found in bovine milk rich in amine groups and carboxylic acid groups which can form bonds with the silanol groups in silicon. A comparative study conducted between PVDF and Casein as binders have shown that when casein was used as binder, it shows better performance compared to PVDF. It has 12% higher capacity retention compared to PVDF with a 2200 mAh/g capacity after 50 cycles. Surface morphology and Solid electrolyte interface was analyzed using electron microscopy techniques and spectroscopic methods and the results will be discussed.

The Effect of Electrolyte Additives on High Cut-Off Voltage Electrochemical Performances of LiNi0.5Mn0.3Co0.2O2/Graphite Full

As the demand for electric vehicles and energy storage systems expands, it is essential to increase the capacity of Li-ion batteries (LIBs) applied to mid- and large-sized devices. High voltage operation of LIB and the use of high capacity electrode materials are common ways to increase the battery capacity. However, there are several problems caused by structural instability, when these electrodes are operated at high voltage. The approach of using functional additives in electrolyte is one of the effective way to improving performances. In this study, the effect of adding the functional additives in electrolyte on full cell performance at high voltage was investigated. The cycle performance of the cell operated at cut-off voltage of 4.5 V with the additives showed improvement than that of coin cell without additives. SEM image of the cycled electrodes surface with additives showed more clear morphology. It can be observed that the introduction of new functional additives effectively reduces the cell resistance by inhibiting formation of by-products during the cycling which was confirmed from the result of AC impedance and SEM images. Furthermore, the XRD patterns of the electrodes after cycling exhibited improved stability with the addition of functional additive used in this work. Our results clearly indicate the significance of additive selection for promising high voltage operation of lithium-ion batteries.

Prediction of MoO2 as high capacity electrode material for (Na, K, Ca)-ion batteries

Na, K and Ca-ion battery electrode materials with appropriate electrochemical properties are desirable candidates for replacing lithium-ion batteries (LIBs) because of their natural richness and low cost. Recently, MoO2 has been reported as the anode material in LIBs, but so far not received attention in Na and other ion batteries. In this paper, the behaviors of Na, K, and Ca on MoO2 are investigated by first-principles calculations. These metal atoms strongly absorb on the hexagonal center of MoO2 and the adsorption results in semiconducting-metallic transition. The low diffusion barrier, 0.13, 0.08, 0.22 eV for Na, K, Ca, respectively, leads to an ultrahigh diffusivity. Importantly, the maximum metal-storage phases of MoO2 monolayer correspond to Na4MoO2, K2.5MoO2 and Ca3MoO2, with considerable theoretical specific capacities of 837, 523 and 1256 mAh g−1. The electrode materials exhibit moderate average voltage of 0.30, 0.75, 0.35 V, respectively. Our findings suggest that MoO2 monolayer can be utilized as a promising anode material with high capacities and high rate performance for next generation ion batteries.

Spinel (Ni0.4Co0.4Mn0.2)3O4 nanoparticles as conversion-type anodes for Li- and Na-ion batteries

High-capacity electrode materials are needed for electrochemical energy storage. Spinel (Ni0.4Co0.4Mn0.2)3O4 nanoparticles have been prepared by simplified and efficient coprecipitation in combination with thermal decomposition. As conversion-type anodes for lithium ion batteries (LIBs), the materials exhibit high capacities of 779 mAh g−1 after 600 cycles at the optimal current density of 0.5 A g−1. The enhanced cycling performance of (Ni0.4Co0.4Mn0.2)3O4 electrodes benefits from multiple metal species providing synergic effects in electrical processes, nanosize favorable for releasing stress and optimal rate lithiation for generating unique solid electrolyte interphase (SEI) with reactivation ability. And, the SEI layer is critical for the cycling properties. Optimal rate lithiation offers in designing long-lived electrodes. Additionally, the spinel materials are evaluated in sodium systems. The different capacity fading behaviors of the (Ni0.4Co0.4Mn0.2)3O4 electrodes between lithium and sodium ion cells are concerned.

Sb2Se3 nanorods with N-doped reduced graphene oxide hybrids as high-capacity positive electrode materials for rechargeable aluminum batteries.

For substantially promoting the unexpected rechargeable capability induced from the dissolution of Sb2Se3 positive electrode materials in aluminum batteries, here a novel prototype of a cell assembled by a hybrid of single-crystalline Sb2Se3 nanorods and N-doped reduced graphene oxide (SNG) coupled with a modified separator has been developed. With this specific cell design, the hybrid positive electrode material exhibits a high discharge potential (∼1.8 V) with a considerably high initial discharge capacity of up to 343 mA h g-1 at a current density of 500 mA g-1. Owing to the alleviation of active material loss from the positive electrode, the cell having the modified separator exhibits much enhanced cycling stability. Besides, nitrogen-doping on the reduced graphene oxide is found to boost the active sites in SNG, and thus the cycling performance has been largely improved. The strategy used in this work offers a universal plateau for designing long-life cycle aluminum batteries.

Influences of nanoscale particles and interparticle compression in electrodes on voltage hysteresis of lithium ion batteries

As one of high capacity electrode materials of lithium ion battery, silicon suffers significant stress effects, which further affects the voltage performance of battery. In this paper, a reaction-diffusion-stress coupled model is established, and the stress induced voltage hysteresis with consideration of diffusion induced stress, surface effects and interparticle compression under potentiostatic operation are investigated. It is found that stress and stress induced voltage hysteresis are dependent on particle size. For big particles, the diffusion induced stress is dominant and further aggravates the hysteresis of both stress and the overpotential consumed by it, indicating that more energy dissipates due to the stress effects. For small particles, especially ones with radius of a few nanometers, surface effects play a more prominent role than diffusion induced stress and the stress evolves into the state of compressive stress on the whole, leading the hysteresis of overpotential to be consumed by stress shrink and making the hysteresis plot of overpotential used to drive electrochemical reaction move downward. The electrode potential first reaches a cutoff voltage and finally the capacity of lithium ion battery decays. Therefore, too large or too small particle size in the electrode can both have a negative effect on the performance of lithium ion batteries, which indicates that an optimal size of the electrode particles must be designed in terms of electrode structure. Based on the calculation, particles with around 9 nm in radius are an appropriate option for electrode design in consideration of both diffusion induced stress and surface effect. In addition, for silicon electrodes, the silicon particles inevitably squeeze each other in a charge and discharge cycle. Therefore, interparticle compression is considered in this case. In detail, interparticle compression pushes the plot of stress hysteresis to the compressive state and leads to lower lithiation capacity, which makes the overpotential plot consumed by stress move downward and accordingly the overpotential plot used to drive the electrochemical reaction move upward. Denser electrode would strengthen this effect due to higher particle compression. It is indicated that for electrode design, the minimum of porosity ratio of electrodes should be adopted because higher interparticle compressive stress would reduce the battery capacity. Our results reveal that the voltage hysteresis of lithium ion batteries is related to the active particle size and the porosity ratio of the electrode, which is of great significance for guiding one in designing the lithium ion batteries.

Enhancing the high voltage interface compatibility of LiNi0.5Co0.2Mn0.3O2 in the succinonitrile-based electrolyte

A stable electrolyte system with wide electrochemical window and excellent interface compatibility is the key to successfully obtaining higher power and energy density of lithium ion batteries. Here we report that cycle life and rate performance of LiNi0.5Co0.2Mn0.3O2 (NCM) at a high charge cutoff voltage of 4.7 V can be greatly extended by manipulating the electrode/electrolyte interphases with succinonitrile (SN) and fluoroethylene carbonate (FEC) simultaneously as solvents. Remarkably, NCM//Li cells can retain extraordinary capacity retention up to 73.6% after 100 stable cycles, which far surpasses the commercial electrolyte counterpart (35.5%). It also delivers a high discharge capacity of >80 mA h g−1 at 5 C, significantly higher than that of commercial electrolytes (20 mA h g−1). Meanwhile, the characteristics of interface layer on NCM are investigated in detail using scanning electron microscopy, transmission electron microscopy, electron diffraction images, X-ray diffraction, X-ray photoelectron spectroscopy with and without Ar ion etching technology, and electrochemical impedance spectroscopy. This is mainly attributed to a stable, uniform, N-containing and high ionic conductive electrolyte interphase layer on the surface of NCM positive material using this optimized electrolyte. So it reveals the importance of controlling electrode/electrolyte interphases through manipulation of electrolyte compositions, and opens a new avenue for developing NCM as high-capacity electrode materials for lithium ion batteries.

Understanding the role of conductive polymer in thermal lithiation and battery performance of Li-Sn alloy anode

There is an urgent demand to develop high-capacity electrode materials for electric vehicles. LixSn alloy is one promising anode due to its pre-stored lithium and high capacity, but faces several challenges, especially high chemical reactivity and huge volume variation. Here, we conformally coated a conductive polypyrrole on the Sn nanoparticle, and first time studied the protection effect of the polymer on thermal lithiation process of the Sn nanoparticles. By tuning the thickness of polypyrrole from 8 to 40 nm, we find that the optimized coating layer (20 nm) keeps intact during the thermal lithiation, and ensures LixSn nanoparticles a very high stability in dry air condition. Moreover, the flexible and conductive polypyrrole accommodates huge volume variation of LixSn nanoparticles and enhances the electronic connections of interparticles. As a result, the LixSn@PPy (20 nm) composite maintains 75% of its prelithiated capacity after exposure to dry air for 5 days and delivers a stable reversible capacity of 534 mA h g-1 for 300 cycles. This anode material is also paired with traditional LiFePO4 cathode to achieve a stable full cell cycling.

The novel P3-type layered Na0.65Mn0.75Ni0.25O2 oxides doped by non-metallic elements for high performance sodium-ion batteries

Due to the attractive advantage of safety and cost of sodium-ion batteries, lithium-ion batteries can be replaced by sodium-ion batteries with the ever-increasing demand of large-scale energy storage systems. However, short cycle life and poor rate performance restrict sodium-ion batteries further commercial application. Cathode materials are one of the most important components of sodium-ion batteries, which have an unparalleled effect on the electrochemical performance of sodium-ion batteries. Herein, the novel P3-Na0.65Mn0.75Ni0.25O2 cathode material doped by non-metal elements is synthesized via hydrothermal method and subsequent low temperature annealing process. The as-prepared P3-Na0.65Mn0.75Ni0.25O2 shows excellent electrochemical performance due to doping of non-metal elements. It can be found that fluorine doped Na0.65Mn0.75Ni0.25F0.1O1.9 can distinctly suppress P3-O1 phase transition and deliver a higher reversible capacity of 163.7 mAh g−1 at 0.1 C, while boron doped Na0.65Mn0.75Ni0.25B0.1O2 transforms from P3 phase to a more stable P2 phase and exhibits remarkable cycle life and rate performance. Therefore, this new strategy doping by means of non-metal elements provides a significant exploration for the development of the high capacity electrode materials of sodium-ion batteries.

Na2SeO3: A Na-Ion Battery Positive Electrode Material with High Capacity

Recent experimental and theoretical studies on the family of Li-rich layered materials show that they can deliver much higher capacities than traditional Li-transitional metal oxides. This also leads to great interests in Na-rich layered oxides as alternative positive electrode materials for sodium-ion batteries for large-scale energy storage. Herein, we report a Na-rich material, Na2SeO3 with an unconventional layered structure as a positive electrode material in NIBs for the first time. This material can deliver a discharge capacity of 232 mAh g−1 after activation, one of the highest capacities from sodium-based positive electrode materials. X-ray photoelectron spectroscopy indicates the oxidation state of selenium remains unchanged during the charge process. Theoretical simulation shows that after removal of Na, spin is situated around oxygen atoms near the Na vacancy, and the projected density of state of oxygen electron is close to the Fermi level. These suggest the involvement of oxygen during charge-discharge. This work will propel new searches of high-capacity sodium-based positive electrode materials.

Yolk-Shell Germanium@Polypyrrole Architecture with Precision Expansion Void Control for Lithium Ion Batteries

SummaryThe key properties of yolk-shell architecture in improving electrochemical performance lies in its uniformity and the appropriate void space, which can expand/contract freely upon lithium alloying and leaching without damaging the outer shell, while being achievable with minimal sacrifice of volumetric energy density. Therefore, we developed a highly controllable strategy to fabricate a uniform porous germanium@polypyrrole (PGe@PPy) yolk-shell architecture with conformal Al2O3 sacrificial layer by atomic layer deposition (ALD) process. The PGe@PPy yolk-shell anode fabricated with 300 ALD cycles delivers excellent electrochemical performance: high reversible capacity (1,220 mA hr g−1), long cycle performance (>95% capacity retention after 1,000 cycles), and excellent rate capability (>750 mA hr g−1 at 32 A g−1). Electrodes with high areal capacity and current density were also successfully fabricated, opening a new pathway to develop high-capacity electrode materials with large volume expansion.

Ultrastable Graphene-Encapsulated 3 nm Nanoparticles by In Situ Chemical Vapor Deposition.

Nanoscale materials offer enormous opportunities for catalysis, sensing, energy storage, and so on, along with their superior surface activity and extremely large surface area. Unfortunately, their strong reactivity causes severe degradation and oxidation even under ambient conditions and thereby deteriorates long-term usability. Here superlative stable graphene-encapsulated nanoparticles with a narrow diameter distribution prepared via in situ chemical vapor deposition (CVD) are presented. The judiciously designed CVD protocol generates 3 nm size metal and ceramic nanoparticles intimately encapsulated by few-layer graphene shells. Significantly, graphene-encapsulated Co3 O4 nanoparticles exhibit outstanding structural and functional integrity over 2000 cycles of lithiation/delithiation for Li-ion battery anode application, accompanied by 200% reversible volume change of the inner core particles. The insight obtained from this approach offers guidance for utilizing high-capacity electrode materials for Li-ion batteries. Furthermore, this in situ CVD synthesis is compatible with many different metal precursors and postsynthetic treatments, including oxidation, phosphidation, and sulfidation, and thus offers a versatile platform for reliable high-performance catalysis and energy storage/conversion with nanomaterials.

MoS2 nanosheets@N-carbon microtubes: A rational design of sheet-on-tube architecture for enhanced lithium storage performances

Transition metal dichalcogenides (TMDs, typically MoS2) have shown great promise as anodes for high-performance lithium-ion batteries (LIBs) due to the layered structure. However, the low electric and ionic conductivities and the large volume expansion of MoS2 during lithiation inevitably result in a fast capacity decrease and limited cycling life. In this work, a unique sheet-on-tube micro/nanostructure was designed and realized to tackle the above mentioned drawbacks. In detail, MoS2 nanosheets are perpendicularly anchored on the N-doped carbon microtubes (NCMs) by a facile approach. NCMs was selected as the support to prevent aggregation of MoS2 nanosheets, and serve as the pathway for electron conduction, as well as a media to alleviate the volume change of MoS2 during lithiation/delithiation. Due to the advantageous structure, the MoS2@NCMs show significantly enhanced lithium storage properties in comparison to pure MoS2. The design strategy and mechanism demonstrated in this work is potentially useful for developing high-capacity electrode materials for LIBs.

Material Design Concept of Lithium-Excess Electrode Materials with Rocksalt-Related Structures for Rechargeable Non-Aqueous Batteries.

Dependence on lithium-ion batteries for automobile applications is rapidly increasing, and further improvement, especially for positive electrode materials, is indispensable to increase energy density of lithium-ion batteries. In the past several years, many new lithium-excess high-capacity electrode materials with rocksalt-related structures have been reported. These materials deliver high reversible capacity with cationic/anionic redox and percolative lithium migration in the oxide/oxyfluoride framework structures, and recent research progresses on these electrode materials are reviewed. Material design strategies for these lithium-excess electrode materials are also described. Future possibility of high-energy non-aqueous batteries with advanced positive electrode materials is discussed for more details.

Hetero-interface constructs ion reservoir to enhance conversion reaction kinetics for sodium/lithium storage

Developing high-capacity electrode materials is most vital to high-energy rechargeable batteries. The conversion reaction-based anode materials deliver substantially higher theoretical capacities in respect to intercalation-based materials. However, the sluggish conversion reaction kinetics is a big obstacle to deliver high practical capacity and rate capability, which is particularly severe for sodium storage. Herein, we implement an interface engineering approach by designing hetero-interfaces to enhance conversion reaction. As a proof of concept, Sb2S3-SnS2 hetero-nanostructures are synthesized and show greatly improved electrochemical performance in terms of specific capacity and rate capability. The DFT calculations reveal that the hetero-interfacial electric field prompts sodium ions pump into the interfaces, which greatly reduces the activation barrier and hence accelerates reaction kinetics. The Sb2S3-SnS2 hetero-interface serves therefore as a “reservoir” and fast diffusion channel for sodium or lithium ions. The obtained results provide important insights into engineering efficient hetero-nanostructures towards fast conversion reaction kinetics for rechargeable batteries.

Synergistic Role of Electrolyte and Binder for Enhanced Electrochemical Storage for Sodium-Ion Battery.

Sodium-ion batteries are promising futuristic large-scale energy-storage devices because of the abundance and low cost of sodium. However, the development and commercialization of the sodium-ion battery solely depends on the use of high-capacity electrode materials. Among the various metal oxides, SnO2 has a high theoretical specific capacity for sodium-ion battery. However, the enormous volume expansion and low electrical conductivity of SnO2 hinder its capability to reach the predicted theoretical value. Although different nanostructured designs of electrode materials like SnO2 nanocomposites have been studied, the effects of other cell components like electrolyte and binder on the specific capacity and cyclic stability are yet to be understood. In the present study, we have investigated the synergistic effect of electrolyte and binder on the performance enhancement of SnO2 supported on the intertwined network structure of reduced graphene oxide partially open multiwalled carbon nanotube hybrid as anode in sodium-ion battery. Our result shows that sodium carboxyl methyl cellulose and ethylene carbonate/diethyl carbonate as the electrolyte solvent offers a high specific capacity of 688 mAh g–1 and a satisfactory cyclic stability for 500 cycles. This is about 56% enhancement in specific capacity compared to the use of poly(vinylidene fluoride) binder and propylene carbonate as the electrolyte solvent. The present study provides a better understanding of the synergistic role of electrolyte and binder for the development of metal-oxide-based electrode materials for the advancement of the commercialization of sodium-ion battery.

Synthesis of Ternary Blended Materials of Li1.2Mn0.4Ni0.16Co0.24O2, the Li2MnO3-Stabilized Compound, and Olivine Fluorides (Li2MPO4F) As a High Capacity Cathode Materials for Lithium Ion Batteries

The area of blended cathode materials is still evolving and there are very few research on the subject. The blending parent cathode materials typically involves high capacity electrode materials; layered oxides compounds with spinel cathode compounds that are lower in cost, more environmentally benign and higher operating voltage. These blended cathode materials are expected to be resilient in terms of storage capacity, cycle life, cheaper and environmentally safer. However, chemically, there are exist challenges in pairing a high- operating voltage material and high capacity material and still achieving less resistance, greater storage and cycle life may be difficult to achieve, since high voltages are likely to enable more degradation pathways. This paper seeks to explore a composite systems made of three different cathode materials involving lithium rich compounds Li1.2Mn0.4Ni0.16Co0.24O2, the Li2MnO3-stabilized compounds, spinel, or Olivine fluorides (Li2MPO4F). This study aims to design a better ternary system that meets the high energy density demand for hybrid electric vehicles and at the same time, minimizes the salient but important material properties like the thermal stability, longer life, high capacity and yet meet bottom line. The paper therefore explores a thorough understanding of the various interaction of each of the compounds so as to tailor their properties to have that synergy, conducting basic scientific analysis of the particle-to particle interaction at the atomic level, as well as the chemical interaction of the constituents in the ternary system to achieve the synergistic effect.

In situ fabrication of Ni(OH)2/Cu2O nanosheets on nanoporous NiCu alloy for high performance supercapacitor

The rapid depletion of fossil fuels along with critical environmental pollution has put forward urgent demands for advanced energy storage devices such as high-performance supercapacitors (SCs). Nickel hydroxides (Ni(OH)2) have been proved to be a high capacity electrode material for SCs, however, the preparation method and stability of Ni(OH)2 structures are unsatisfactory. In this work, via a low cost and one-step hydrothermal method in H2O2 aqueous solution without other reagents, vertically arranged Ni(OH)2/Cu2O nanosheets can be facilely fabricated on three-dimensional nanoporous NiCu alloy (NPNC), which exhibits large surface area and high electrical conductivity. Being the source of Ni and Cu, NPNC acts as the matrix of active materials as well. Thus, the strong combination and electron transportation between the active materials and NPNC can be achieved. Furthermore, the uniform distribution of Cu2O in the hybrids enhances the electrochemical stability of electrode. As a result, the binder-free Ni(OH)2/Cu2O/NPNC electrode materials exhibit a high capacity (8234 mC cm−2 or 823.4 C cm−3 at 20 mA cm−2) with excellent cycling stability (112.8% capacity retention after 10,000 cycles at 200 mA cm−2) and rate capability. Such desirable properties signify that the Ni(OH)2/Cu2O/NPNC composites hold great promise for the high-performance supercapacitors.

Coordination Polymers for High-Capacity Li-Ion Batteries: Metal-Dependent Solid-State Reversibility

Electrode materials exploiting multielectron-transfer processes are essential components for large-scale energy storage systems. Organic-based electrode materials undergoing distinct molecular redox transformations can intrinsically circumvent the structural instability issue of conventional inorganic-based host materials associated with lattice volume expansion and pulverization. Yet, the fundamental mechanistic understanding of metal-organic coordination polymers toward the reversible electrochemical processes is still lacking. Herein, we demonstrate that metal-dependent spatial proximity and binding affinity play a critical role in the reversible redox processes, as verified by combined 13C solid-state NMR, X-ray absorption spectroscopy, and transmission electron microscopy. During the electrochemical lithiation, in situ generated metallic nanoparticles dispersed in the organic matrix generate electrically conductive paths, synergistically aiding subsequent multielectron transfer to π-conjugated ligands. Comprehensive screening on 3d-metal-organic coordination polymers leads to a high-capacity electrode material, cobalt-2,5-thiophenedicarboxylate, which delivers a stable specific capacity of ∼1100 mA h g-1 after 100 cycles.

Highly conductive carbon nanotube micro-spherical network for high-rate silicon anode

We report on a highly conductive CNT micro-spherical network for high-rate silicon anode materials prepared by one-pot spray drying for lithium-ion batteries. The anode material contains silicon nanoparticles bound to CNTs through a small amount of sucrose-derived carbon. The first charge and discharge capacities of the Si/CNT/C microsphere electrode are measured to be 3152 and 2302 mA h g−1 of the composite, respectively, at 0.1 A g−1. The Si/CNT/C microsphere electrode exhibits an initial capacity of 1989 mA h g−1 at current density of 1.0 A g−1 and retains ∼70% of the initial capacity after 100 cycles. Even at a high current density of 10 A g−1, the Si/CNT/C microsphere electrode exhibits a capacity of 784 mA h g−1 with a stable charge/discharge behavior. The superior rate capability of the Si/CNT/C microsphere composites can be attributable to the unhindered Li-ion transport through the highly conductive CNT buffer matrix, to which Si NPs are strongly bound by the sucrose-derived carbon. These salient results give further impetus to the study of CNTs for use as a buffer matrix to improve the rate capability of high-capacity electrode materials with large volume changes during charge storage.