Nanostructured Anode Research Articles

A high-power and fast charging Li-ion battery with outstanding cycle-life

Electrochemical energy storage devices based on Li-ion cells currently power almost all electronic devices and power tools. The development of new Li-ion cell configurations by incorporating innovative functional components (electrode materials and electrolyte formulations) will allow to bring this technology beyond mobile electronics and to boost performance largely beyond the state-of-the-art. Here we demonstrate a new full Li-ion cell constituted by a high-potential cathode material, i.e. LiNi0.5Mn1.5O4, a safe nanostructured anode material, i.e. TiO2, and a composite electrolyte made by a mixture of an ionic liquid suitable for high potential applications, i.e. Pyr1,4PF6, a lithium salt, i.e. LiPF6, and standard organic carbonates. The final cell configuration is able to reversibly cycle lithium for thousands of cycles at 1000 mAg−1 and a capacity retention of 65% at cycle 2000.

Long Cycle Life Rutile TiO2 Inverse Opal Anodes for Li-Ion Batteries

With the ever advancing improvements in electronics and display technologies, it is crucial that Li-ion batteries will be able to rise to the challenge of powering future consumer electronics. Consumers are all too aware of the challenges facing next generation Li-ion batteries with issues such as poor cycle life and the requirement to charge devices everyday becoming commonplace. Consequently, in recent years there has been a tremendous amount of research into developing materials which are capable of delivering long cycle-life with suitable stability in terms of capacity values, capacity retention and voltage. (1-3) In order to significantly advance Li-ion battery technology, it is crucial to identify electrode materials that are capable of delivering stable capacities over a large number of cycles, instead of materials which offer high initial capacities and then significantly fade over the course of a relatively low number of cycles. In this work we detail the preparation of rutile TiO2 inverse opal (IO) structured samples and their application as an anode material for Li-ion batteries. We present X-ray diffraction, electron diffraction and Raman analysis to confirm that the IOs are pure rutile TiO2. The electrochemical performance of the TiO2 IOs is evaluated via cyclic voltammetry, rate capability testing and long cycle life galvanostatic tests. We demonstrate stable cycling of TiO2 IOs over 1000 and 5000 cycles, at specific currents of 75 and 450 mA g-1, respectively. The capacity values obtained when cycled at a specific current of 75 mA g-1 are greater than previously reported values for other TiO2 nanostructures, achieving an impressive capacity of ~ 140 mAh g-1 after 1000 cycles. (4-6) We demonstrate that our TiO2 IO anodes are capable of delivering high specific capacities with stable capacity rentention, achieving a capacity retention of ~ 82.4% between the 100th and 1000th cycles. We present SEM images of TiO2 IO samples after cycling showing that the IO morphology is retained after thousands of galvanostatic cycles. Previous reports for anode materials such as Si and Ge nanowires have shown that volume expansion during cycling can lead to substantial capacity fading due to significant changes in nanostructure morphology.(7, 8) However, the porosity of the IO structure is able to accommodate volume changes to the TiO2 nanoparticles that make up the walls of the IO material. The 3D porous structure and morphology is retained via expansion of the IO walls into the pores. The level of structural integrity retained after 5000 cycles is not only a first for TiO2 nanostructures but also for nanostructured oxide anode materials in general. Acknowledgements This work was also supported by Science Foundation Ireland (SFI) through an SFI Technology Innovation and Development Award under contract no. 13/TIDA/E2761. This publication has also emanated from research supported in part by a research grant from SFI under Grant Number 14/IA/2581.

High Areal Capacity Si/LiCoO2 Batteries from Electrospun Composite Fiber Mats.

Freestanding nanofiber mat Li-ion battery anodes containing Si nanoparticles, carbon black, and poly(acrylic acid) (Si/C/PAA) are prepared using electrospinning. The mats are compacted to a high fiber volume fraction (≈0.85), and interfiber contacts are welded by exposing the mat to methanol vapor. A compacted+welded fiber mat anode containing 40 wt % Si exhibits high capacities of 1484 mA h g-1 (3500 mA h g-1Si ) at 0.1 C and 489 mA h g-1 at 1 C and good cycling stability (e.g., 73 % capacity retention over 50 cycles). Post-mortem analysis of the fiber mats shows that the overall electrode structure is preserved during cycling. Whereas many nanostructured Si anodes are hindered by their low active material loadings and densities, thick, densely packed Si/C/PAA fiber mat anodes reported here have high areal and volumetric capacities (e.g., 4.5 mA h cm-2 and 750 mA h cm-3 , respectively). A full cell containing an electrospun Si/C/PAA anode and electrospun LiCoO2 -based cathode has a high specific energy density of 270 Wh kg-1 . The excellent performance of the electrospun Si/C/PAA fiber mat anodes is attributed to the: i) PAA binder, which interacts with the SiOx surface of Si nanoparticles and ii) high material loading, high fiber volume fraction, and welded interfiber contacts of the electrospun mats.

Large-scale synthesis of ternary Sn5SbP3/C composite by ball milling for superior stable sodium-ion battery anode

Alloy-based materials (i.e. Sn, Sb, P) are promising candidates for sodium-ion battery (SIB) anodes, but they suffer from capacity decay during charge/discharge cycling due to the pulverization caused by their huge volume change. Nanostructures can slow down the capacity fade, but most of the synthesis methods of such nanostructured anodes are difficult to scale-up. Herein, a ternary Sn5SbP3/C composite was fabricated by a green, low cost, one-step and easily scalable ball-milling of elementary Sn, Sb, P, and C. The microstructure of the ball-milled powders consists of micrometric agglomerates of active nano Sn4P3 and SnSb and Sn particles. Carbon in the composite acts as a conducting matrix, and it does not only benefit to the ball milling efficiency, but also benefit to the cycle life of the electrode. Each of the active Sn4P3 and SnSb and Sn phases in the composite functions mutually as a buffer for the others. As a result, this ternary composite anode delivers a good capacity of 352mAhg−1 at the current density of 2Ag−1, which is notably higher than that of the binary Sn4P3/C and SnSb/C composites produced under the same conditions.

Na-ion batteries based on the inorganic BN nanocluster anodes: DFT studies

It has been recently indicated that the Li-ion batteries may be replaced by Na-ion batteries because of their low safety, high cost, and low-temperature performance, and lack of the Li mineral reserves. Here, using density functional theory calculations, we studied the potential application of B12N12 nanoclusters as anode in Na-ion batteries. Our calculations indicate that the adsorption energy of Na+ and Na are about −23.4 and −1.4kcal/mol, respectively, and the pristine BN cage to improve suffers from a low cell voltage (∼0.92V) as an anode in Na-ion batteries. We presented a strategy to increase the cell voltage and performance of Na-ion batteries. We showed that encapsulation of different halides (X=F−, Cl−, or Br−) into BN cage significantly increases the cell voltage. By increasing the atomic number of X, the Gibbs free energy change of cell becomes more negative and the cell voltage is increased up to 3.93V. The results are discussed based on the structural, energetic, frontier molecular orbital, charge transfer and electronic properties and compared with the performance of other nanostructured anodes.

Fast, Scalable Synthesis of Micronized Ge3N4@C with a High Tap Density for Excellent Lithium Storage

Nanostructuring has significantly contributed to alleviating the huge volume expansion problem of the Ge anodes. However, the practical use of nanostructured Ge anodes has been hindered due to several problems including a low tap density, poor scalability, and severe side reactions. Therefore, micrometer‐sized Ge is desirable for practical use of Ge‐based anode materials. Here, micronized Ge3N4 with a high tap density of 1.1 mg cm−2 has been successfully developed via a scalable wet oxidation and a subsequent nitridation process of commercially available micrometer‐sized Ge as the starting material. The micronized Ge3N4 shows much‐suppressed volume expansion compared to micrometer‐sized Ge. After the carbon coating process, a thin carbon layer (≈3 nm) is uniformly coated on the micronized Ge3N4, which significantly improves electrical conductivity. As a result, micronized Ge3N4@C shows high reversible capacity of 924 mAh g−1 (2.1 mAh cm−2) with high mass loading of 3.5 mg cm−2 and retains 91% of initial capacity after 300 cycles at a rate of 0.5 C. Additionally, the effectiveness of Ge3N4@C as practical anodes is comprehensively demonstrated for the full cell, showing stable cycle retention and especially excellent rate capability, retaining 47% of its initial capacity at 0.2 C for 12 min discharge/charge condition.

A Well-Defined Silicon Nanocone-Carbon Structure for Demonstrating Exclusive Influences of Carbon Coating on Silicon Anode of Lithium-Ion Batteries.

Nanotechnology and carbon coating have been applied to silicon anodes to achieve excellent lithium-ion batteries, but the exclusive influence of carbon coating on solid-electrolyte interphase (SEI) formation is difficult to exhibit distinctly because of the impurity and morphological irregularity of most nanostructured anodes. Here, we design a silicon nanocone-carbon (SNC-C) composite structure as a model anode to demonstrate the significant influences of carbon coating on SEI formation and electrochemical performance, unaffectedly as a result of pure electrode component and distinctly due to regular nanocone morphology. As demonstrated by morphological and elemental analysis, compared to the SNC electrode, the SNC-C electrode maintains a thinner SEI layer (∼10 nm) and more stable structure during cycling as well as longer cycle life (>725 cycles), higher Coulombic efficiency (>99%), and lower electrode polarization. This well-defined structure clearly shows the interface stability attributed to carbon coating and is promising in fundamental research of the silicon anode.

Rational Construction of Multivoids-Assembled Hybrid Nanospheres Based on VPO4 Encapsulated in Porous Carbon with Superior Lithium Storage Performance.

The design of a new nanostructured anode material with high tap density while still keeping the common advantages of the hollow structure is a great challenge for future lithium-ion batteries (LIBs). Here, multivoids-assembled hierarchically meso-macroporous nanospheres based on VPO4 encapsulated in porous carbon (MVHP-VPO4@C NSs) were designed and fabricated. This unique structure can evidently decrease the excessive interior space in hollow spheres or multishelled hollow spheres to gain high volumetric energy density and at the same time can alleviate the large mechanical strain during the cycling process. As expected, MVHP-VPO4@C NSs show good lithium storage behavior with gravimetric discharge capacity of 628 mAh g-1 after 100 cycles at a current density of 100 mA g-1. Furthermore, the full cell (LiFePO4 cathode//MVHP-VPO4@C NSs anode) also exhibits outstanding lithium storage performance. The insight obtained from this structure may provide guidance for the design of other electrode materials experiencing large volume variation during the lithiation-delithiation process.

SnO<sub>2</sub> Nanoparticles for Lithium-Ion Batteries Prepared by Sol-Gel Method

Nanostructured SnO2 is an attractive anode material for high-energy-density lithium-ion batteries because of the fourfold higher theoretical charge capacity than commercially used graphite. However, the poor capacity retention at high rates and long-term cycling have intrinsically limited applications of nanostructured SnO2 anodes due to large polarization and ~300% volume change upon lithium insertion/extraction. Here we report the design of SnO2 nanoparticles, which are synthesized by sol-gel method, with an aim at overcome the above problems for the high-performance reversible lithium storage. The results showed that the mean sizes of SnO2 particles treated with 6 wt.% ammonia were less than 30 nm, which can store charge with a capacity density as high as ~1888 mAh/g. Even when the discharge rate was increased to 0.5 C, it still retained ~1017 mAh/g.

Carbon supported Rh nanoparticles for the production of hydrogen and chemicals by the electroreforming of biomass-derived alcohols

An electrolyzer assembled with a Rh/C nanostructured anode electrode, promotes the partial oxidation of alcohols and high-purity hydrogen evolution in alkaline media at low energy input.

Enabling the study of stress states using in situ µSXRD in the silicon nanowire anode during electrochemical lithiation in a specially designed Li-ion battery test cell

Synchrotron X-ray microdiffraction has proven to be effective in revealing insights of mechanical stress and other mechanics considerations in small scale crystalline structures in many important technological applications, such as microelectronics, nanotechnology and energy systems. In the present study, a special Li-ion battery test cell was designed to enable an in situ synchrotron X-ray microdiffraction experiment to elucidate the mechanical stress states during the first electrochemical cycle of lithiation in single-crystalline silicon nanowires (SiNWs). Silicon is considered as a promising anode material for the next generation lithium-ion battery due to its high capacity at nanoscale. However, silicon expands up to 300% during lithiation, which induces high stresses and leads to fractures. To design silicon nanostructures that could minimize fracture, it is important to understand and characterize stress states in the silicon nanostructures during lithiation. The stress of the crystalline core of the SiNWs during electrochemical lithiation was determined (at different levels of the electrochemical lithiation) using the in situ synchrotron X-ray microdiffraction technique. We found that the crystalline core of the SiNWs became highly compressive (up to -~325.5 MPa) once lithiation started. This finding helps unravel insights about mechanical stress states in the SiNWs during the electrochemical lithiation, which could potentially pave the path to fracture-free design of silicon nanostructure anode materials in the next generation lithium-ion battery.

Atomic layer deposition of ZnO on carbon black as nanostructured anode materials for high-performance lithium-ion batteries

Although zinc oxide (ZnO), a low-cost and naturally abundant material, has a high theoretical specific capacity of 987 mA h g-1 for hosting lithium ions, its application as an anode material has been hindered by its rapid capacity fading, mainly due to a large volume change (around 228%) upon repeated charge-discharge cycles. Herein, using carbon black (CB) powder as a support, ZnO-carbon black (denoted as ZnO-CB) nanocomposites were successfully fabricated using the atomic layer deposition (ALD) method. This method was able to produce strong interfacial molecular bindings between ZnO nanoclusters and the carbon surface that provide stable and robust electrical contact during lithiation and delithiation processes, as well as ZnO nanoclusters rich in oxygen vacancies (OVs) for faster Li-ion transport. Overall, the nanocomposites were able to deliver a high discharge specific capacity of 2096 mA h g-1ZnO at 100 mA g-1 and stable cyclic stability with a specific capacity of 1026 mA h g-1ZnO maintained after 500 cycles. The composites also have excellent rate capability, and a reversible capacity at a high 1080 mA h g-1ZnO at 2000 mA g-1. The facile but unique synthesis method demonstrated in this work for producing nanostructures rich in OVs and nanocomposites with strong coupling via interfacial molecular bindings could be extended to the synthesis of other oxide based anode materials and therefore could have general significance for developing high energy density lithium ion batteries.

Improved Electrochemical Performance of Nanostructured Fe2O3 Anode Synthesized by Chemical Precipitation Method for Lithium-ion Batteries

Fe2O3 nanoparticles (Fe2O3-NPs) with spherical morphology were synthesized by a facile chemical precipitation method followed by post-annealing treatment. The as-synthesized NPs have a uniform particle size with a diameter of about 20–200 nm with an average particle size of 80 nm. The NPs showed an improved electrochemical performance in terms long cycle life as well as rate capability. The observed reversible capacities after 200 cycles are 776, 445 and 343 mA h g−1 at the current densities of 150, 500 and 1000 mA h g−1, respectively. These excellent electrochemical properties can be attributed to the nanometer dimension of anode materials which offers smooth charge-transport pathway, short diffusion paths of lithium ions and adequate spaces for volume expansion during Li+ insertion.

Influence of the ZnO nanoarchitecture on the electrochemical performances of binder-free anodes for Li storage

Zinc oxide nanoarchitectures may be employed as binder-free, high specific capacity anodes for lithium batteries. By means of simple and low-impact wet chemistry approaches, we synthesized 1D (nanorods), 2D (single- and multi-layered nanosheets), and 3D (nanobrushes) ZnO arrays. These nanoarchitectures were compared as far as concerns their electrochemical properties and the structural modifications upon lithiation/delithiation. The best results were offered by 2D nanosheets, which showed reversible capacity of the order of 400mAhg−1 after 100 cycles at 1Ag−1. This was due to: i) small nanoparticles, with average diameter of about 10nm, which maximize the array specific surface area and favor the formation of the LiZn alloy; ii) the presence of a mesoporous texture, which allows larger space for accommodating the volume changes upon lithiation/delithiation. However, also these 2D structures showed large irreversible capacity losses. Our work highlights the need for more efficient buffering solutions in ZnO binder-free nanostructured anodes.

Nanoporous Tin with a Granular Hierarchical Ligament Morphology as a Highly Stable Li-Ion Battery Anode.

Next generation Li-ion batteries will require negative electrode materials with energy densities many-fold higher than that found in the graphitic carbon currently used in commercial Li-ion batteries. While various nanostructured alloying-type anode materials may satisfy that requirement, such materials do not always exhibit long cycle lifetimes and/or their processing routes are not always suitable for large-scale synthesis. Here, we report on a high-performance anode material for next generation Li-ion batteries made of nanoporous Sn powders with hierarchical ligament morphology. This material system combines both long cycle lifetimes (more than 72% capacity retention after 350 cycles), high capacity (693 mAh/g, nearly twice that of commercial graphitic carbon), good charging/discharging capabilities (545 mAh/g at 1 A/g, 1.5C), and a scalable processing route that involves selective alloy corrosion. The good cycling performance of this system is attributed to its nanoporous architecture and its unique hierarchical ligament morphology, which accommodates the large volume changes taking place during lithiation, as confirmed by synchrotron-based ex-situ X-ray 3D tomography analysis. Our findings are an important step for the development of high-performance Li-ion batteries.

Effects of binders on electrochemical properties of the SnS2 nanostructured anode of the lithium-ion batteries

Binders play a significant role in enhancing the electrochemical performance of tin disulfide (SnS2) as the anode for lithium-ion batteries (LIBs) because of their excellent dispersion and cohesion in the electrodes. In the present work, flake-like SnS2 nanoparticles with a hexagonal structure were synthesized by a facile one-step hydrothermal method with a mean grain size of 7.7 nm. When sodium alginate (SA), carboxymethyl cellulose (CMC), poly acrylic acid (PAA), and CMC-PAA (1:1, wt%) are applied as binders for the SnS2 anode electrode (the obtained electrodes are denoted as SnS2-S, SnS2-C, SnS2-CP, and SnS2-P, respectively) in LIBs, the electrodes exhibited high reversible lithium-ion storage capacities of 762.00 mA h g−1, 891.65 mA h g−1, 913.94 mA h g−1, and 930.36 mA h g−1 at the current densities of 100 mA g−1, respectively. Importantly, the SnS2-P electrode exhibited excellent rate capacity and cycling performance. The –COOH of PAA attached to SnS2 can increase the amount of free radicals, which can prevent the detachment of SnS2 from the current collector, and the carboxyl group can effectively inhibit the volume expansion and pulverization of particles of the electrode. Undoubtedly, PAA binder significantly improves the cycling and rate performances of SnS2 anode material for LIBs.

Growth of ultrafine CuCo2O4 nanoparticle on graphene with enhanced lithium storage properties

Nanosized anode materials have been shown to be successful in addressing the problems of metal oxide anodes during electrochemical reactions. However, issues with low Coulombic efficiencies and poor cyclability of nanostructured metal oxide anodes still need to be resolved. Ultrafine CuCo2O4 nanoparticles of 6∼9nm uniformly anchored on graphene have been synthesized. CuCo2O4/graphene (CuCo2O4/G) composites show superior lithium-storage performances. A high reversible capacity of 1040mAhg−1 is achieved at 0.1C after 80 cycles, and can retain 211mAhg−1 at a current density of 2C. Furthermore, the lithiation process of CuCo2O4/G was recorded by TEM. It suggests the Li+ diffuse through an individual CuCo2O4 nanoparticle consists of three stages: (1) the insertion of Li+ without crystalline structure change, (2) the nanoparticle’s crystalline lattice collapses, and (3) nanograins grow and reform from the collapsed nanoparticle. The lithium conversion resulting in the formation of a network of many ultrafine nanograins (2nm) embedded in the Li2O matrix; also these ultrafine nanograins are confined in a layer of crystal, which is beneficial for the improved electrochemical performance. The macroscopic electrochemical performance of CuCo2O4/G was further correlated with the microcosmic in situ TEM results.

Nanostructured ZnO-TiO2 thin film oxide as anode material in electrooxidation of organic pollutants. Application to the removal of dye Amido black 10B from water.

Electrochemical oxidative degradation of diazo dye Amido black 10B (AB10B) as model pollutant in water has been studied using nanostructured ZnO-TiO2 thin films deposited on graphite felt (GrF) substrate as anode. The influence of various operating parameters, namely the current intensity, the nature and concentration of catalyst, the nature of electrode materials (anode/cathode), and the adsorption of dye and ambient light were investigated. It was found that the oxidative degradation of AB10B followed pseudo first-order kinetics. The optimal operating conditions for the degradation of 0.12mM (74mgL-1) dye concentration and mineralization of its aqueous solution were determined as GrF-ZnO-TiO2 thin film anode, 100mA current intensity, and 0.1mM Fe2+ (catalyst) concentration. Under these operating conditions, discoloration of AB10B solution was reached at 60min while 6h treatment needed for a mineralization degree of 91%. Therefore, this study confirmed that the electrochemical process is effective for the degradation of AB10B in water using nanostructured ZnO-TiO2 thin film anodes.

Ambient-Air Stable Lithiated Anode for Rechargeable Li-Ion Batteries with High Energy Density.

An important requirement of battery anodes is the processing step involving the formation of the solid electrolyte interphase (SEI) in the initial cycle, which consumes a significant portion of active lithium ions. This step is more critical in nanostructured anodes with high specific capacity, such as Si and Sn, due to their high surface area and large volume change. Prelithiation presents a viable approach to address such loss. However, the stability of prelithiation reagents is a big issue due to their low potential and high chemical reactivity toward O2 and moisture. Very limited amount of prelithiation agents survive in ambient air. In this research, we describe the development of a trilayer structure of active material/polymer/lithium anode, which is stable in ambient air (10-30% relative humidity) for a period that is sufficient to manufacture anode materials. The polymer layer protects lithium against O2 and moisture, and it is stable in coating active materials. The polymer layer is gradually dissolved in the battery electrolyte, and active materials contact with lithium to form lithiated anode. This trilayer-structure not only renders electrodes stable in ambient air but also leads to uniform lithiation. Moreover, the degree of prelithiation could vary from compensating SEI to fully lithiated anode. With this strategy, we have achieved high initial Coulombic efficiency of 99.7% in graphite anodes, and over 100% in silicon nanoparticles anodes. The cycling performance of lithiated anodes is comparable or better than those not lithiated. We also demonstrate a Li4Ti5O12/lithiated graphite cell with stable cycling performance. The trilayer structure represents a new prelithiation method to enhance performance of Li-ion batteries.

Inorganic-Organic Ionic Liquid Electrolytes Enabling High Energy-Density Metal Electrodes for Energy Storage

It has recently been shown, in the case of the bis(fluorosulfonyl)amide (FSI) based ionic liquids, that as the concentration of the alkali metal salt (LiFSI or NaFSI) is increased, the alkali metal cation transference number increases, despite an increase in viscosity and decrease in conductivity. At the same time significant enhancements in electrochemical stability and rate performance of devices are also observed. Here we overview some of the recent findings already in the literature and in addition demonstrate the feasibility of stable, high rate room temperature lithium battery cycling in an electrolyte comprised of 60 mol% LiFSI in a trimethyl, isobutyl phosphonium FSI ionic liquid using a high voltage NMC cathode. We also demonstrate that the high rate cycling of lithium and sodium metal in these phosphonium FSI electrolytes leads to a nanostructured anode deposit and a lowering of the interfacial impedance, suggesting a stable SEI layer formation. Finally, we propose a hypothesis that may explain some of the observations thus made, by which the high alkali ion concentration in these mixed electrolyte systems leads to the effective elimination of the mass transport limitations that are chiefly responsible for the formation of dendrites in traditional electrolytes. This work suggests that a new type of ionic liquid consisting of a mixture of metal cations with organic cations can provide a solution to the instability of the reactive alkali metal anodes and hence enable higher energy density technologies.