Electrode Materials For Ion Batteries Research Articles

Synthesis of Co-Free Ni-Rich Single Crystal Positive Electrode Materials for Lithium Ion Batteries: Part I. Two-Step Lithiation Method for Al- or Mg-Doped LiNiO2

Increasing the Ni content of a Ni-rich layered positive electrode material is one common way to improve energy density of Li-ion cells but normally leads to shorter cell lifetimes. Single crystalline materials have been shown to improve the cell lifetime by reducing the degree of material degradation. This first study in a two part series investigates the synthesis of Co-free single crystalline LiNi0.95Al0.05O2 and LiNi0.975Mg0.025O2 via a two-step lithiation method. This method consists of a first step heating of the precursors at high temperatures but with deficient Li to grow crystalline particles and then a second step at lower temperature to fully lithiate the material. The synthesized materials were characterized by scanning electron microscopy and X-ray diffraction to understand the impact of synthesis conditions. Single crystal materials were successfully synthesized, and Mg-containing single crystal materials achieved micron-sized particles with as low as 2% Ni in the Li layer. Al-containing single crystal materials could not avoid the formation of Li5AlO4 impurity for all conditions tested. The presence of Li or Mg and high temperatures were identified as factors that promote crystallite growth. Selected samples were characterized electrochemically and compared to their polycrystalline counterparts. Mg-containing single crystal materials are not yet competitive with their polycrystalline counterparts yet, and further understanding and development is needed.

A Thorough Analysis of Two Different Pre‐Lithiation Techniques for Silicon/Carbon Negative Electrodes in Lithium Ion Batteries

AbstractSilicon (Si) is one of the most promising candidates for application as high‐capacity negative electrode (anode) material in lithium ion batteries (LIBs) due to its high specific capacity. However, evoked by huge volume changes upon (de)lithiation, several issues lead to a rather poor electrochemical performance of Si‐based LIB cells. The Coulombic efficiency (CEff) during the first cycle(s), especially when using nano‐sized Si, is relatively low, due to the formation of the solid electrolyte interphase (SEI). Pre‐lithiation approaches can increase the CEff by compensating active lithium losses during the first cycle(s). Here, we evaluate the beneficial impact of pre‐lithiated Si/C electrodes for their application in NCM111||Si/C cells by comparing two approaches, i. e., electrochemical pre‐lithiation and pre‐lithiation by direct contact to Li metal foil. The SEI composition and surface morphology of pre‐lithiated Si/C electrodes as well as the impact of reducing active Li losses on individual electrode potentials over cycling are revealed. For long‐term cycling, both pre‐lithiation techniques lead to a distinct improvement of the overall capacity as well as the CEff for the first 40 cycles due to i) the pre‐formed SEI and ii) a Li reservoir within the anode. Depletion of the active Li from NCM111 is significantly reduced and we can confirm that both pre‐lithiation techniques improve the cycling performance of NCM111||Si/C cells in an almost equal manner.

Enhancing the understanding of the redox properties of lithium-inserted anthraquinone derivatives by regulating molecular structure

The reductional potentials of AQ is positive correlation with the number of EWGs, and the overall effect ability of substituents on redox potentials of AQ is -C 2 F 5 >-CF 3 >-F>-Cl >-Br under the condition of the same number of EWGs. • The effect of -CF 3 and -C 2 F 5 on redox properties of AQ are firstly investigated by DFT. • Overall influence ability of substituents on redox potentials of AQ is -C 2 F 5 > -CF 3 > -F > -Cl > -Br. • Full -C 2 F 5 substituted EWGs on AQ exhibits the highest reductional potential in five types EWGs. Organic compounds, such as quinone compounds, are promising renewable electrode materials for lithium ion batteries (LIBs) with redox stability and structural diversity. However, quinone electrode materials (QEMs) have low redox potentials as cathode and high solubility. In particular, low redox potentials result in low energy density and power density of QEMs. In this work, the substituent influence on anthraquinone (AQ) are studied by density-functional theory calculations to predict redox properties of potential positive materials for LIBs. The calculated results indicate a positive correlation between the redox potentials and the number of substituent, and the full substitution groups with electron-withdrawing groups (EWGs) gain the highest redox potentials, which is borne out by lowest unoccupied molecular orbital (LUMO). Mono-substitution, however, bring the highest specific capacity. Also, the different substituent sites on AQ can influence the redox potentials of AQ. Moreover, the calculation of molecular electrostatic potential (MESP) reveal carbonyl groups with local minima of MESP easily tend to bind lithium. AQ with Li binding carbonyl groups is more stable than the bare AQ, which is confirmed by the calculation of nucleus-independent chemical shift. At the same time, lithium atoms also easily bind electronegative atoms of EWGs and form intramolecular lithium bonds, which improve the thermodynamic stabilization of the lithiation AQ. The present study provide the new understanding with guidelines to design potential organic cathode materials with efficiency for LIBs.

WS2 nanosheets@ZIF-67-derived N-doped carbon composite as sodium ion battery anode with superior rate capability

Devising novel composite electrodes with particular structural/electrochemical characteristics becomes an efficient strategy to advance the performance of rechargeable battery. Herein, considering the homogeneous transition metal sulfide with N-doped carbon derived from zeolitic imidazolate framework-67 (ZIF-67) and WS2 with large interlayer spacing, a laurel-leaf-like Co9S8/WS2@N-doped carbon bimetallic sulfide (Co9S8/WS2@NC) is engineered and prepared via a step-by-step method. As an electrode material for sodium ion batteries (SIBs), Co9S8/WS2@NC composite delivers high capacities of 480 and 405 mA h g−1 at 0.1 and 1.0 A g−1, respectively. As the current density increases from 0.1 to 5.0 A g−1, it provides specific capacity of 359 mA h g−1 with a capacity retention rate of 78.0%, which is higher than that of Co9S8@NC (63.5%) and WS2 (58.6%). The Co9S8/WS2@NC composite anode maintains a stable specific capacity (354 mA h g−1 at 2.0 A g−1). It also exhibits a high capacitive contribution ratio of 90.8% at 1.0 mV s−1. This study provides a new and reliable insight for designing bimetallic sulfide with two-dimensional nanostructure for energy storage.

NH4V3O8 Rectangular Nanotube: A Novel High-Performance Cathode Material for Lithium Ion Batteries

The morphology and nanosize of cathode materials play a crucial role in the improved electrochemical properties of the electrode material for lithium ion batteries. Herein, we report the synthesis of a novel NH4V3O8 rectangular nanotube via a facile one-pot solvothermal protocol with the use of the mixing solvent containing glycerol, ethanol, and ethylene glycol. The morphology and nanosize evolution of the as-prepared NH4V3O8 materials from the addition of different solvents has been systematically investigated. The electrochemical properties of these materials are closely related to their structure. Compared with other synthesized counterparts with three different morphologies (nanoparticle, ultra-small nanoparticle, and hierarchical microsheet), the resultant NH4V3O8 rectangular nanotube exhibited high reversible capacity with a maximum discharge capacity of 253.8 mAh g−1at 15 mA g−1, and the capacity retention rate is 75% after 50 cycles. This work reveals the relationship between the morphology and electrochemical performance of NH4V3O8 and provides a feasible method for the synthesis of high-performance electrode materials.

Sulfur vacancies and morphology dependent sodium storage properties of MoS2-x and its sodiation/desodiation mechanism

Creating rich vacancies and designing distinct micro-morphology are considered as effective strategies for boosting the electrochemical performances of sodium ion battery (SIB) electrode materials. In this paper, a variety of MoS2 nanostructures with different sulfur vacancies concentration and morphologies are successfully constructed by a hydrothermal method combined with various-temperature calcination treatment in a Ar/H2 mixed atmosphere. Employed as a free-standing anode for SIBs, the flower-like MoS2-x microspheres assembled by the intertwined nanosheet arrays (MoS2-x-800) delivers highest specific capacity of 525.3 mAh g−1 and rate capability, as well as extraordinarily stable cycle life with almost no loss of capacity after 420 cycles. The favorable sodium storage properties are mainly ascribed to the cooperated effects of superior intrinsic conductivity and richer active sites generated by sulfur vacancies, and numerous interspace achieved by the intersection of neighbouring nanosheets. Meanwhile, through ex situ analyses, the reversible charge/discharge mechanism of the obtained MoS2-x-800 is revealed reasonably. This work not only brings new insights into the design of high-performance electrode materials for SIBs, but also makes a great step forward in the practical applications of transition metal sulfides in energy storage systems.

Elucidating the charge storage mechanism of carbonaceous and organic electrode materials for sodium ion batteries.

Sodium ion batteries (SIB) have received much research attention in the past decades as they are considered to be one alternative to the currently prevalent lithium ion batteries, and carbonaceous and organic compounds present two promising classes of SIB electrode materials advantaged by abundance of their constituent elements and reduced environmental footprints. To accelerate the development of these materials for SIB applications, future research directions must be guided by a thorough understanding of the charge storage mechanism. This review presents recent efforts in mechanism elucidation for these two classes of SIB electrode materials since, compared to their inorganic counterparts, they have unique challenges in material analysis. Topics covered will include characterization techniques and analytical frameworks for mechanism elucidation, emphasizing the advantages and limitations of individual experimental methodologies and providing a commentary on scientific rigor in result interpretation.

Preparation and application of LiSiC-oxide for low temperature solid oxide fuel cells

Semiconductors are well known as excellent materials in the field of exploring novel avenues which combine various fields in electronics, electrochemistry, etc for new functional device concepts. Lithium silicon carbide (LiSiC) is a well-known electrode material for Lithium ion batteries but relatively new for solid oxide fuel cells (SOFCs) and electrolyte-layer free fuel cells (EFFCs). In the present work, we have explored three categories of fuel cells based on mixed LiSiC-SDC (samarium doped ceria) in SOFC and LiSiC as a single component material with type (I) and without coating of a layer of 3CSiC as EFFC type (II). All of three cells are sandwiched between Ni foams coated with NCAL (Ni0.8Co0.15Al0.05Li-oxide). The electrochemical performances of as prepared fuel cells are tested at 550°C, which is substantially lower than in conventional fuel cell materials. The LiSiC based EFFC type (II) demonstrates better performance because of less ohmic resistance as compared to type (I) have more layers. This indicates that the LiSiC-SDC system has potential for fuel cell development in accordance with energy band structure and alignment.

Theoretical study of electrode materials for sodium ion batteries based on Graphether/Graphene heterostructure

The graphether/graphene vdW heterostructure has been systematically studied as an electrode material for sodium batteries based on density functional theory. We predict that the graphether/graphene heterostructure exhibits low diffusion barrier and large capacity. All these calculation results suggest that the graphether/graphene heterostructure can be used as a future commercial anode material for sodium ion batteries.

Functionalized M2TiC2Tx MXenes (M = Cr and Mo; T = F, O, and OH) as high performance electrode materials for sodium ion batteries.

First-principles calculations were performed to study the electrochemical performance of M2TiC2 (M = Cr or Mo) and M2TiC2Tx (T = O, F or OH) used as anode materials for sodium ion batteries (SIBs). The O functionalized MXenes (Cr2TiC2O2 and Mo2TiC2O2) are found to be more stable than F and OH terminated systems. The diffusion performance of sodium in MXene materials is mainly affected by the functional groups. The lowest diffusion barrier of functionalized MXenes is about one order larger in magnitude than that of bare MXenes. Although the introduction of O-groups hinders the diffusion of sodium, it can greatly improve the theoretical storage capacities. Meanwhile, the diffusion paths and diffusion energy barriers of Na are affected by Na concentration effects, while the interactions between terminations have little effect. Furthermore, multiple layers of sodium atoms are found to be adsorbed between the layers of M2TiC2O2, thus significantly increasing the theoretical capacities. The theoretical sodium storage capacities of M2TiC2O2 monolayers reach 515.70 mA h g-1 (M = Cr) and 362.46 mA h g-1 (M = Mo) and the OCVs can approach 0.034 V (M = Cr) and 0.042 V (M = Mo). Therefore, Cr2TiC2O2 and Mo2TiC2O2 are expected to be promising anode materials for SIBs due to their excellent properties, such as good electronic conductivity, low sodium diffusion barrier, and high theoretical sodium storage capacity.

M-Site Vacancy-Mediated Adsorption and Diffusion of Sodium on Ti2CO2 MXene

MXenes is a promising electrode material for Na ion batteries. To achieve better electrode performance in different aspects, we provide theoretical insight into vacancy engineering of a common MXen...

Reduced graphene oxide thin layer induced lattice distortion in high crystalline MnO2 nanowires for high-performance sodium- and potassium-ion batteries and capacitors

The large-radius of both K- and Na-ions gives rise to a serious concern towards exploring high-performance electrode materials for potassium ion batteries (KIBs) and sodium ion batteries (SIBs), respectively. Herein, MnO2 nanowires coated with reduced graphene oxide (denoted MnO2@rGO) are demonstrated as excellent anode materials in KIBs and SIBs. The coating of rGO not only facilitates a lattice distortion in the spacing of high crystallinity MnO2 nanowires allowing the faster transfer of K- and Na-ions, but also creates an interfacial structure between rGO and MnO2. Both enhance the electronic conductivity and further protect the nanowires from degradation. As an anode for KIBs and SIBs, the MnO2@rGO nanowires deliver a stable cycling performance with capacity retention of 81.7% over 400 cycles and 75% after 500 cycles, respectively. The potassiation and depotassiation reaction mechanisms are also revealed. Furthermore, the uniqueness of our hybrid designs allows high crystallinity MnO2@rGO nanowires to be used as anodes for both K-ion capacitors (KICs) and Na-ion capacitors (SICs). Considering their easy synthesis, environmental benignity and low cost, MnO2@rGO nanowires are potential anode materials for Na- and K-ion based energy storage devices.

Controlled synthesis of Li1.17Ni0.21Mn0.54Co0.08O2 as a cathode material for Li ion batteries

Abstract Li-rich layered oxides Li1+xMO2 (M: Ni, Co, Mn) being a combination between Li2MnO3 and LiMO2, are considered as attractive high-capacity electrode materials for Lithium ion batteries. Here, we present the composition Li1.17Ni0.21Mn0.54Co0.08O2 with low cobalt content. The synthesis process was optimized by varying the pH of the co-precipitation step and pure phase was obtained only for pH = 11.3. The morphology of the material consists on the agglomeration of quasi-spherical particles an average particle size of 157 nm. The electrochemical properties of this electrode material were investigated, and a specific capacity of 250 mAh/g was recorded in the voltage range of 2–4.8 V. While the first charge process evidenced a potential plateau at 4.5 V corresponding to the oxygen redox activity, the subsequent electrochemical behavior is governed by Ni2+/Ni4+ and Co3+/Co4+ redox couples. When cycled for 40 charge/discharge cycles at 0.1C rate, the capacity retention is still good and remains around 85% with a coulombic efficiency of around 98%. The comparison of the obtained performances with those of existing Li-rich electrode materials show the excellent features of the studied Li-rich material for the next generation Lithium-ion batteries.

Flower-like spherical FeCoS2 coated by reduced graphene oxide as anode for high performance potassium ion storage

Bimetallic sulfides are regarded as promising electrode materials for potassium ion batteries owing to their attractive theoretical specific capacity, high redox activity, and environmental friendliness. However, undesirable agglomeration and inferior structural reversibility might result in their poor electrochemical performance and block their practical application. In this work, flower-like spherical FeCoS2 coated with reduced graphene oxide was prepared by a one-step hydrothermal synthesis method. As an anode material of potassium ion batteries, this flower-like spherical structure with extensive mesopores is conducive to the rapid penetration of electrolyte, thereby accelerating the transmission of potassium ions. Meanwhile, the encapsulation of reduced graphene oxide not only effectively reduces the structural deformation during the reaction, but also limits the aggregation of FeCoS2, which provides favorable conditions for improving the reversibility of the electrode material. As a result, it exhibits promising cycling stability (maintions 371 mAh g–1 at 100 mA g–1 after 150 cycles) and attractive rate performance (428 mAh g–1 at 50 mA g–1 and 248 mAh g–1 at 1000 mA g–1).

(Invited) Interface Engineering in Transition-Metal Oxide Electrode Materials for Sodium Ion Batteries

Sodium ion batteries (SIBs) are attractive alternative energy storage technology to lithium-ion batteries due to its low-cost. There has been growing attention in developing new electrode materials for sodium ion batteries. Compared to lithium ion batteries, SIBs suffer from more issues in long-term stability, resulted from the sluggish kinetics, large volume change due to the much larger Na+ ion (~ two times the size of Li+) as well as multiple phase transitions upon cycling. Several approaches to enhance the electrode performance have been explored such as doping, nanostructuring, and carbon coating. Here, we will discuss our recent work on developing advanced electrode materials for SIBs through interfacial engineering. We have developed a coaxial core-shell nanostructured negative composite electrode composed of carbon nanotube (CNT) as the core and TiO2@MoO2@C as shells. The 1D tubular nanostructure can effectively reduce ion diffusion path, increase electrical conductivity, accommodate the stress due to volume change upon cycling, and provide additional interfacial active sites for enhanced charge storage and transport properties. Significantly, a synergistic effect between TiO2 and MoO2 nanostructures is investigated through ex-situ solid state nuclear magnetic resonance. We also developed multi-phased transition metel oxide positive electrodes, which exhibits enhanced capacity and cycling stability.

Hard Carbon Ethylene Carbonate Interfaces – Atomic Scale Insight into Surface Termination, Defects, Functional Groups, and Roughness on Electrolyte Breakdown, Metal Adsorption, Intercalation and Nucleation

In the search for post lithium ion batteries (LIBs), sodium ion batteries (NIBs) are gaining traction, but fundamental understanding of the atomic scale interactions at the anode electrolyte interfaces in NIBs remains poorly understood. In moving from LIBs, the LIB anode material graphite was found to be unsuitable for NIBs. Instead, hard carbon anode materials have arisen as one of the most promising electrode materials for sodium ion batteries (NIBs), which are also suitable for use with carbonate based electrolyte solvents. Hard carbons are complex amorphous carbon structures with randomly orientated, defective, and curved graphene nanosheets, and turbostratically stacked graphitic layers. This complex structure leads to a plethora of carbon structural motifs being present in the anode, leading to a large number of potential morphologies having to be taken into account when investigating the anode electrolyte interface.In this study, we use ab initio molecular dynamics to investigate the effect of surface roughness, disorder, defects, and termination on the electrolyte anode interactions in the EC (electrolyte solvent) | hard carbon (anode) system. These simulations show that EC intercalation and breakdown is directly influenced by the carbon surface termination and surface roughness. Furthermore, defects were found to be more probable to form in terms of defect formation energies at strained and curved carbon morphologies. These defects were also found to have a direct impact on the sodium binding to the anode. The effect of all these different structural motifs on sodium adsorption, intercalation, and diffusion were simulated to form an understanding of the anode electrolyte interfacial reactions. One consequence of electrolyte molecule breakdown, but could also be an effect of anode synthesis method, is the presence of functional groups at the carbon surface. From density functional theory simulations of functional groups O, OH, NH2, and COOH at different carbon motifs (planar basal plane, H-terminated edges, and curved morphologies) we could show that O-functional groups from an energetical perspective are highly probable to form on these surfaces, and can act as favourable sodium storage sites. The hydroxyl group on the other hand were found to form inorganic NaOH compounds, which could contribute to irreversible capacity.AcknowledgmentThe financial support from EPSRC (Engineering and Physical Sciences Council) under the grant number EP/M027066/1, and EP/R021554/2, is acknowledged.

Synthesis and Electrochemical Properties of Mg-Substituted Ni/Mn-Based High-Voltage Spinel Oxides

1. Introduction Currently, research on layered and rocksalt Li-rich materials is being actively conducted as a high-capacity positive electrode material for lithium ion batteries, and now it is widely accepted that large capacity originates from oxygen redox reaction.[1] Oxygen redox is proposed to be activated for oxygen ions with a Li-O-Li configuration.[2] It was also reported that oxygen redox is activated for Li-rich manganese spinel-type oxides, i.e., Li[Li x Mn2–x ]O4.[3] Nevertheless, its origin of activation of anionic redox for spinel-type oxides is not known. In this study, LiMg y Ni0.5-y Mn1.5O4, which is solid solution samples between LiNi0.5Mn1.5O4 and LiMg0.5Mn1.5O4, is targeted as positive electrode materials with anionic redox for spinel-type oxides. Mg ions have a high ionic bonding nature with oxygen, and thus better reversibility for anionic redox is anticipated.[1] We report the impact of Mg substitution on reversibility of Ni cationic and O anionic redox in the spinel framework structure, and the possibility of 5 V-class high-voltage electrode materials with excellent capacity retention is discussed. 2. Experimental LiMg y Ni0.5-y Mn1.5O4 (0 ≤ y ≤ 0.5) were synthesized from mixtures of Li2CO3, Mg(OH)2, Ni(OH)2 and Mn2O3 by two-step solid-state reaction at 950 oC for 6 h to 700 °C for 48 h in air atmosphere. Characterization of LiMg y Ni0.5-y Mn1.5O4 were conducted by X-ray diffraction (XRD) and scanning electron microscopy (SEM). For the evaluation of electrochemical properties, composite electrodes consisting of 80 wt% active material, 10 wt% AB, and 10 wt% PVdF, and were casted on aluminum foil. 1.0 M LiPF6 dissolved in ethylene carbonate (EC)/dimethyl carbonate (DMC) (3/7 by volume) solution was used as electrolyte. 3. Results and Discussion XRD patterns of LiMg y Ni0.5-y Mn1.5O4 (0 ≤ y ≤ 0.5) are assigned into the spinel structure with space group of Fd-3m. From SEM images, particle sizes of LiMg y Ni0.5-y Mn1.5O4 are estimated to be ~4 μm. No difference in particle sizes regardless of chemical compositions is observed. Figure 1 compares charge/discharge curves of LiMg y Ni0.5-y Mn1.5O4. After 5 cycles, the non Mg-substituted sample, LiNi0.5Mn1.5O4, delivers 135 mAh g−1 of the discharge capacity in a lithium cell when the cut-off voltage is set to 5.3 V. After 50 cycles test, discharge capacity of LiNi0.5Mn1.5O4 is decreased to 125 mAh g-1. On the other hand, significant improvement of cyclability is evidenced for the partially Mg-substituted samples. No capacity fading and no increase in polarization is observed for LiMg0.06Ni0.44Mn1.5O4 even charge to 5.3 V vs. Li for 50 cycles at a rate of 10 mA g-1. On the basis of these findings, Mg substitution is proposed to be effective to reduce electrolyte decomposition and improve structural stability upon high-voltage exposure. Nevertheless, the further enrichment of Mg ions in the structure results in loss of reversible capacity, and anionic redox seems to be inactive for LiMg0.5Mn1.5O4. From these results, factors affecting electrode performance of high voltage spinel with cationic/anionic redox will be discussed in detail.References(1) N. Yabuuchi, Chem. Rec., 19, 703 (2019).(2) D.-H. Seo, Nature Chem., 8, 692 (2016).(3) E. Iwata et al., and T. Ohzuku, Electrochemistry, 71,1187 (2003). Figure 1

Factors Affecting on Electrochemical Properties of O3-Type NaFeO2 for Sodium Ion Batteries

LiCoO2 is generally used as a positive electrode material for lithium ion batteries. However, the abundance of cobalt in the Earth’s crust is limited to be less than 100 ppm, and therefore cobalt is expensive element. Iron-based electrode materials would be attractive as positive electrode materials for battery applications because iron is the most abundant transition metal ion. However, as a counterpart of LiCoO2, layered LiFeO2 is electrochemically inactive.[1] In contrast, layered NaFeO2 is electrochemically active, but cyclability is not enough associated with the irreversible structural change upon charge.[2, 3] In this study, we examine different factors affecting the electrode properties of NaFeO2 and discuss possibility as the positive electrode material for sodium ion batteries.O3-type NaFeO2 was prepared by solid-state reaction from stoichiometric amount of Na2O2 and Fe2O3 as described by Takeda et al.[4] These starting materials were mixed using a mortar and pestle in an argon-filled globe box, and then pressed into a pellet. The pellet was heated at 650 oC for 12 h in O2. After the sample was prepared, the sample was mixed with acetylene black (NaFeO2: acetylene black = 90: 10 wt%) by using the planetary ball mill.Figure 1 shows the XRD patterns and SEM images of O3-type NaFeO2 before and after mixing with acetylene black (denoted as as-prepared and carbon-composite NaFeO2, respectively). The as-prepared sample crystallizes into an O3-type layered structure as previously reported, and, from the XRD patterns, no change in the structure is found after milling with carbon. However, the particle size of the sample is clearly reduced by milling with carbon. Charge/discharge curves of O3-type NaFeO2 before and after milling with carbon are compared in Fig 2. A voltage profile of the as-prepared sample with a well-defined voltage plateau at 3.3 V is similar to that of the previous reports, and capacity degradation on electrochemical cycles is clearly observed. In contrast, carbon-composited NaFeO2 delivers a reversible capacity of over 100 mA h g-1 with much improved capacity retention.From these results, we will discuss factors affecting electrode reversibility of O3-type NaFeO2 and possibility of rechargeable batteries made from only abundant elements.

Creep Deformation of Lithium Foil at Moderate Pressures (< 2 MPa) and Temperatures (30-50°C)

Lithium metal is receiving significant research attention as a potential next generation negative electrode material in lithium ion batteries because it can offer a ~50% increase in cell energy density compared to conventional graphite electrodes. There are, however, a number of mechanical challenges using lithium metal electrodes. Mechanical stack pressure is required to ensure good contact between solid-state electrodes and electrolytes. Moderate to high stack pressures (e.g. < 10 MPa) can also supress void formation during fast charging and discharging.1 Creep, the plastic deformation of a material under constant pressure, improves battery performance by preventing and filling voids, but can also lead to decreased performance if lithium is unable to sustain the required stack pressure, and potentially cell shorting if lithium is e.g. extruded beyond the current collectors.Creep deformation rates are highly dependent on homologous temperature and pressure. Lithium metal has a relatively low melting point (181°C) / high homologous temperature at common cell temperatures which should result in substantial lithium creep deformation. Previous studies have characterized both the tensile creep properties of lithium foils2 and compressive creep properties of bulk lithium rods.3 Significant barrelling of the high aspect ratio lithium rods (initial height:width of 4:1 to 1:1) during compression made it difficult to determine the applied pressure on the lithium, obscuring the relationship between pressure and creep rate.3 These important studies increased our collective understanding of the mechanical properties of lithium, but are not necessarily reflective of the compressive creep of lithium foils in a cell environment. Here, we report on the compressive creep of lithium foil within an electrochemical cell at commercially relevant stack pressures and temperatures.Compressive creep deformation of low aspect ratio (1:40 to 1:10; initially 0.3 – 2.5 mm thick, 13 mm diameter) lithium metal foils was measured in hermetically sealed, rigid but flexible cells at temperatures between 30 - 110°C and applied pressures between 1 - 2 MPa. Creep testing was performed by integrating a Conflat-style electrochemical cell4 featuring welded bellows and an optical window with an Instron 5966 Universal Testing System (which measures / controls force and displacement). Creep rates were determined using the time-dependent displacement data after reaching a constant applied force. Two methods to convert force to pressure will be described, including the use of an inline camera to measure the lithium-compressive piston contact area.Creep deformation was observed at all tested temperatures, and all pressures above 1 MPa. Creep rates were on the order of a few tenths of a micron per hour, which while small, implies very limited device lifetime with thin lithium layers. Lithium metal may not be physically strong enough for use in high energy density all solid-state devices. Figure 1

Self-Assembled Hybrid of Microwave-Exfoliated V2O5 Nanoribbons and Reduced Graphene Oxide Nanosheets As a Sustainable Electrode Material for Zinc Ion Batteries

Rechargeable aqueous zinc ion batteries are an emerging topic in the battery research due to its high volumetric capacity (5855 mAh/cm3), low cost, environmental friendliness and safety. But the development of the zinc ion batteries have been seriously hindered by the slow insertion/extraction kinetics of the multivalent Zn2+ ions in the host structure. Two-dimensional (2D) transition metal oxides are intensely studied for various energy storage applications such as batteries and supercapacitors but controlled synthesis and tunable nanoscale properties are still a challenge. Herein we present and discuss the self-assembly of a hybrid material of microwave-exfoliated Vanadium pentoxide (V2O5) nanoribbons (NRs) on graphene oxide (GO) nanosheets as a potential host for zinc ion storage. Vanadium pentoxide have several advantages such as high discharge capacity (294 mAhg-1) and large abundance but suffers from low electrical conductivity and poor stability. Using a thermal treatment, the GO template is converted to reduced graphene oxide (rGO) which improves the electrical conductivity of the hybrid. Multiple divalent cations such as Zn2+ and Mn2+ have been used in the self-assembly process to bind the negatively charged V2O5 NRs and GO nanosheets to improve the stability of the hybrid and accommodate the intercalation/deintercalation of the Zn2+ ions. Incorporation of 0.0357 M Mn2+ along with 0.10 M Zn2+ in the assembly process has been found to form a stoichiometric composition of Mn0.15Zn0.08V2O5 by XPS, which provides the high specific capacity of 295 mAh g-1 at 0.5 A g-1 and a high stability with the capacity retention of ~81.3% after 500 cycles at 4 A g-1.