Conversion Anode Materials Research Articles

Tracking the confinement effect of highly dispersive carbon in a tungsten oxide/carbon nanocomposite: conversion anode materials in lithium ion batteries

A variety of transition metal binary compounds, whose reaction mechanism involves intercalation-initiated conversion, have been extensively studied as anode materials in lithium ion batteries (LIBs).

Versatile electrochemical cell for Li/Na-ion batteries and high-throughput setup for combined operando X-ray diffraction and absorption spectroscopy

A fundamental understanding of de/intercalation processes (single phase versus multi-phase), structural stability and voltage–composition profiles is pivotal for optimization of electrode materials for rechargeable non-aqueous batteries. A fully operational setup (electrochemical cells, sample changer and interfacing software) that enables combined quasi-simultaneous operando X-ray diffraction (XRD) and absorption (XANES and EXAFS) measurements coupled with electrochemical characterization is presented. Combined XRD, XANES and EXAFS analysis provides a deep insight into the working mechanisms of electrode materials, as shown for the high-voltage Li insertion cathode material LiMn1.5Ni0.5O4 and the high-capacity sodium conversion anode material Bi2S3. It is also demonstrated that the cell design can be used for in-house XRD characterization. Long-term cycling experiments on both Li and Na electrode materials prove the hermeticity and chemical stability of the design as a versatile operando electrochemical cell.

Co3O4 negative electrode material for rechargeable sodium ion batteries: An investigation of conversion reaction mechanism and morphology-performances correlations

Abstract Transition metal oxides have recently aroused a renewed and increasing interest as conversion anode materials for sodium ion batteries. Being their electrochemical performances strongly dependent on morphological aspects, has been here proposed a straightforward approach to modulate morphological characteristics of a transition metal oxide (Co3O4) using a low cost synthetic route. The as obtained optimized morphology allows the realization of high practical specific capacities, higher than 500 mAh g−1 after 50 cycles, and represents a valid candidate for further optimization. In addition to the morphology-performance correlations, the reaction mechanism beyond the electrochemical behavior was also investigated revealing the role of the CoO phase in the charge/discharge process. Finally, an electrode pre-sodiation treatment for conversion materials is presented: it has been indeed demonstrated that it sensibly decreases the irreversible capacity correlated to the first cycle and improves cycle ability.

Facile synthesis of CoFe2O4 nanoparticles anchored on graphene sheets for enhanced performance of lithium ion battery

Recently, metal oxides as high capacity anode materials had been investigated for lithium ion batteries. However, the fast capacity fading upon cycling leaded poor durability, which hindered their application as higher energy density of lithium ion battery. In this paper, a nanostructured nanocomposite with graphene supported CoFe2O4 nanoparticles (NPs) was prepared via simple hydrothermal reaction. The uniform CoFe2O4 NPs were anchored on graphene sheets, which brought a good performance on cyclability. Combined with the optimization of graphene content, the anode delivered a better capacity retention of 944mAhg−1 over 50 cycles at current density of 100mAg−1 and the good reversible capacity as 990mAh g−1 when the rate returned from 5Ag−1 to 0.1Ag−1 after 60 cycles. The present work provided a desired structure for conversion anode materials or other electrode materials of large volume change.

Activation of Al3+ Ion Redox in the Conversion Type Anode Material for Lithium Ion Battery

A new conversion type anode material for lithium ion battery utilizing the redox activity of aluminum (III) ion has developed. Conversion type materials are known to have a serious weak point as anode materials, that is the high reaction voltage in spite of its high capacity (over 600 mAh/g). This high reaction voltage originates in high redox potential of transition metal oxide such as NiO or CoO, those are known as representative conversion anode materials for lithium ion battery. In order to improve this high reaction voltage, it is effective to use oxides of light metal with lower redox potentials such as aluminum oxides, titanium oxide and so on. However, aluminum oxides are difficult to use as the electrode materials owing to the low electric and ionic conductivity. We have synthesized solid solution of nickel oxide and aluminum oxide with nano level particle size by calcination of Ni-Al layered double hydroxides (LDH). In the previous studies, we have investigated the structure and electrochemical properties for the solid solution of NiO with TiO2 or V2O5. [1-3] The fine structure of calcinated materials are determined by XRD and XAFS: Ni2+ and Al3+ ions are randomly locating metal ion sites of NiO with rock salt structure and cation vacancies are introduced to compensate the excessive charges brought by the aluminum ions. In this structure, electron and lithium ion are expected to be supplied via NiO type host structure and cation vacancies, respectively. The charging capacity of the half cell with lithium metal counter electrode from 0.03 V to I.5 V, that corresponds to the discharge capacity or the full cell was improved to 600 mAh/g, where as that for pristine NiO was 230 mAh/g. (Fig. 1) This improvement of capacity in the lower voltage region is expected to originate in redox of aluminum ion. The redox activity of aluminum ion was confirmed by ex-situ XANES measurement at Al K edge. The absorption edge of aluminum ion shifted to lower energy direction with discharge from 1560 keV to 1556 keV. With charging, the absorption edge of aluminum shifted back to the initial position. This dearly indicates the redox activity of aluminum ion during charge- discharge. This is the first report of anode material for lithium battery that utilizes redox of aluminum ion as far as we know. In order to investigate the detailed reaction mechanism, ex-situ XRD and XAFS measurements were carried out. On the basis of these results, the reaction mechanism of Ni-Al binary metal oxide was concluded as follows. In the higher voltage discharge process (OCV-1.0 V), lithium intercalation into the cation vacancy and lithium ion adsorption to the surface of Ni-Al binary metal oxide with the partial redaction of nickel ion is proceeding. [1] In the lower voltage discharge (1.0-0.03 V), the conversion reaction proceeds with the reduction of Ni and Al ions. In the lower voltage charge process (0.03-1.0 V), only aluminum ion is oxidized to form an intermediate state, where aluminum ion makes complex with surrounding oxide ions. In the higher voltage charge process, nickel metal is oxidized to re-form the Ni-Al binary metal oxide with the rock salt structure.

Biogenous Iron Oxide(BIOX)-As a High-Capacity Anode Material for Lithium Ion Batteries

1.Introduction Biogenous iron oxide(BIOX) is produced by Leptothrix ochracea, aquatic bacteria living in the world. BIOX is amorphous Fe3+-based oxide containing Si and P, and takes tube-formed structure. In recent years, lithium-ion batteries have been widely used and intensively studied to meet an increasing variety of application in the future. Especially exploitation of high-capacity lithium-ion batteries is very important. The capacity of BIOX is approximately three times larger than that of graphite, so that BIOX is expected as a new high-capacity anode material for lithium ion batteries. BIOX belongs to the category of conversion anode materials and shows superior cycle and rate performance beyond normal conversion anode; however, the large first irreversible capacity remains in disadvantage for the practical use. In this study, we applied lithium pre-doping to BIOX electrode to eliminate the first irreversible capacity, and succeeded to provide the lithium ion battery with high capacity and high cycle performance.< 2.Experimental The BIOX cultured in Okayama university was firstly mixed with CNF (Carbon nanofiber) as a conductive agent, SBR (styrene-butadiene rubber) / CMC (carboxymethyl acid) as a binder (80:10:10 wt%) and water as a viscosity adjustor in an agate mortar. The slurry was coated on a copper foil, dried in air at 80ºC and vacuum-dried at 120ºC for 3h. The punched out electrode was pressed under the pressure of 2t. The first irreversible capacity was eliminated by contacting a lithium metal sheet to the electrode in an electrolyte (LiPF6in EC / DEC (1:1)). The charge-discharge behavior was measured in a coin type cell (2025) with Li metal as a counter electrode. The current rate was 0.1 C (the theoretical capacity of BIOX: 666mAh / g) and the voltage range was set between 50 and 3000mV 3.Results Figure 1 shows the voltage profiles of the first cycle for the as-prepared and Li- contacted electrodes. The former showed the first discharge capacity of 984mAh/g, and the following charged one of 712mAh/g. The first irreversible capacity is considerably large; the coulomb efficiency is only 72.0%. After the second cycle, almost 100% efficiency was obtained. On the other hand, the Li pre-doping by the contact of Li metal brought the high coulomb efficiency. The electrode of 30 s contacting of Li metal showed discharged capacity of 972mAh/g and charged one of 818mAh/g(coulomb efficiency:84.1% ). The first irreversible capacity due to the SEI formation on the nano-particles in BIOX may be compensable with the reaction of Li metal in advance. Figure 1

Triggering the in Situ Electrochemical Formation of High Energy Density Cathode Material from MnO

High energy density electrode materials are in pressing needs for next generation Li-ion batteries. While the stellar, laboratory-wise, is intercalation-type layered oxides involving both cationic and anionic redox processes,1 conversion-type fluorine-based materials are also demonstrating attractive performances owning to the multi-electron transfer and high electronegativity of fluorine. Compared to pure fluorides, metal oxyfluorides possess higher conductivity and better electrochemical activity.2 However, their performances are overwhelmingly dependent on several parameters, such as nominal composition, synthesis conditions, particle size and morphology. Recently, Kang and co-workers proposed a “redox composite” model, where a redox center (transition metal oxide/fluoride, MO/MF) and a Li+ reservoir (LiF) were blended by ball milling and directly used as the cathode.3This allows in principle countless pairs of composite electrodes to be explored as high energy density positive electrodes. Herein, we report that manganese monoxide (MnO), who has long been believed as a promising conversion anode material based on the Mn2+/Mn0 redox couple, can indeed turn into a high energy density cathode material delivering over 200 mAh g-1 capacity with an average potential around 3 V (Fig. 1). A one-step high energy ball milling method is adopted to trigger the reactivity of nanosized MnO particles. This process does not require any sophisticated synthesis routes, and can be easily scaled up for volume production. Interestingly, this encouraging result is achieved without any LiF addition, thus calling for further exploration and understanding of the reaction paths. Based on various characterization techniques, it is found that the electrochemical activity is deeply rooted in the electrode-electrolyte interfacial reactions, and is strongly correlated with the stability of LiPF6-based organic electrolyte. This finding raises the practical utility of such electrochemically made high capacity electrodes. Reference: 1 M. Sathiya, G. Rousse, K. Ramesha, C. P. Laisa, H. Vezin, M. T. Sougrati, M. L. Doublet, D. Foix, D. Gonbeau, W. Walker, A. S. Prakash, M. Ben Hassine, L. Dupont and J. M. Tarascon, Nature Mater., 2013, 12, 827–835. 2 N. Pereira, F. Badway, M. Wartelsky, S. Gunn and G. G. Amatucci, J. Electrochem. Soc., 2009, 156, A407. 3 S.-W. Kim, K.-W. Nam, D.-H. Seo, J. Hong, H. Kim, H. Gwon and K. Kang, Nano Today, 2012, 7, 168–173. Fig. 1 First three cycles of MnO electrode cycled in LiPF6-based electrolyte. Figure 1

New Conversion Anode Material Utilizing Redox of Al3+ Ion

A new conversion type anode material for lithium ion battery utilizing the redox activity of aluminum (III) ion has developed. Conversion type materials are known to have a serious weak point as anode materials, that is the high reaction voltage in spite of its high capacity (over 600 mAh/g). This high reaction voltage originates in high redox potential of transition metal oxide such as NiO or CoO, those are known as representative conversion anode materials for lithium ion battery. In order to improve this high reaction voltage, it is effective to use oxides of light metal with lower redox potentials such as aluminum oxides. However, aluminum oxides are difficult to use as the electrode materials owing to the low electric and ionic conductivity. We have synthesized solid solution of nickel oxide and aluminum oxide with nano level particle size by calcination of Ni-Al layered double hydroxides (LDH). The fine structure of calcinated materials are determined by XRD and XAFS: Ni2+ and Al3+ ions are randomly locating metal ion sites of NiO with rock salt structure and cation vacancies are introduced to compensate the excessive charges brought by the aluminum ions. In this structure, electron and lithium ion are expected to be supplied via NiO type host structure and cation vacancies, respectively. The charging capacity of the half cell with lithium metal counter electrode from 0.03 V to I.5 V, that corresponds to the discharge capacity or the full cell was improved to 600 mAh/g, where as that for pristine NiO was 230 mAh/g. This improvement of capacity in the lower voltage region is expected to originate in redox of aluminum ion. The redox activity of aluminum ion was confirmed by ex-situ XANES measurement at Al K edge. The absorption edge of aluminum ion shifted to lower energy direction with discharge from 1560 keV to 1556 keV. With charging (the absorption edge of aluminum shifted back to the initial position. This dearly indicates the redox activity of aluminum ion during charge- discharge. This is the first report of anode material for lithium battery that utilizes redox of aluminum ion as far as we know. In order to investigate the detailed reaction mechanism, ex-situ XRD and XAFS measurements were, carried out. On the basis of these results, the reaction mechanism of Ni-Al binary metal oxide was concluded as follows. In the higher voltage discharge process (OCV-1.0 V), lithium intercalation into the cation vacancy and lithium ion adsorption to the surface of Ni-Al binary metal oxide with the partial redaction of nickel ion is proceeding. In the lower voltage discharge (1.0-0.03 V), the conversion reaction proceeds with the reduction of Ni and Al ions. In the lower voltage charge process (0.03-1.0 V), only aluminum ion is oxidized to form an intermediate state, where aluminum ion makes complex with surrounding oxide ions. In the higher voltage charge process, nickel metal is oxidized to re-form the Ni-Al binary metal oxide with the rock salt structure.

Using New Quasi in-Situ TEM Technique to Study Structural Changes of Electrode Materials for Li-Ion and Na-Ion Batteries

In this poster, we report the development of a quasi in-situ TEM technique to study structural changes of electrode materials for Li-ion and Na-ion batteries. Some preliminary results about structural (ir)reversibility of NiO conversion anode materials relating to the materials’ size and morphology will be discussed as an example. Using a quasi in-situ TEM setup, we were able to track the structural changes of electrode materials in marked locations on a TEM grid repeatedly before and after electrochemical lithiation/delithiation in LiPF6/EC/DEC electrolyte. This method is a further development of the TEM grid-in-a-coin cell method reported in the literature (F Lin et al, Nat. Comms.,5, 3356 (2014)) with much improved capability to locate the same materials on the TEM grid before and after charging/discharging. Our results show that upon lithiation, NiO is converted into a three-dimensional nanoporous network of metallic Ni. However, we found that the structural reversibility of NiO upon delithiation is highly dependent on the initial size and morphology of the materials. Particularly in our 10 nm-thick NiO nanoplate materials, the nanoporous structure can be removed and the solid-form palette structure can be fully recovered when the material is delithiated. This study shows that that size effect can be an important parameter in dictating the structural reversibility of transition metal oxide conversion materials. Acknowledgements This work was supported by the U.S. Department of Energy, the Assistant Secretary for Energy Efficiency and Renewable Energy, Office of Vehicle Technologies under Contract Number DE-SC0012704. This research used resources of the Center for Functional Nanomaterials, which is a U.S. DOE Office of Science Facility, at Brookhaven National Laboratory under Contract No. DE-SC0012704.

Revealing Corrosion Chemistry in Lithium Ion Battery and Beyond--a Tale of Two "Cities"

Tailoring the surface chemistry to enhance corrosion resistance lies at the heart of materials processing for corrosion control of structural materials. This conventional wisdom, however, can fail miserably when the underlying materials’ function(s) involves chemical reactions. In this talk, I will introduce the concepts of surface passivation and passivity breakdown. I will show that, by tuning the surface composition, passivation can lead to successful optimization of intercalation cathode materials in lithium ion batteries (LIBs).[1,2] On the other hand, self-passivation in anode materials can significantly alter the rate performance of LIBs.[3,4] I will show that the rate capacity of a large family of phase conversion anode materials, i.e. transition metal oxides, is dependent on the stochastic process of passivity breakdown which can be described by a Poisson model.[5] This model can answer the long standing question—why transition metal oxides conversion materials perform much more poorly in sodium ion batteries than in LIBs, even though sodium ions can diffuse equally fast as lithium does in these materials.[6] Reference [1] Metal segregation in hierarchically structured cathode materials for high-energy lithium batteries, Feng Lin, et al, Yijin Liu*, H L Xin*, M Doeff*, Nature Energy, 1, 15004 (2016) [2] Surface reconstruction and chemical evolution of stoichiometric layered cathode materials for lithium-ion batteries, Feng Lin, Isaac Markus, Dennis Nordlund, Tsu-Chien Weng, Mark Asta, H. L. Xin*, M. M. Doeff, Nature Communications, 5, 3529 [3] Phase Evolution for Conversion Reaction Electrodes in Lithium-ion Batteries, Feng Lin, Dennis Nordlund, Tsu-Chien Weng, Ye Zhu, Chunmei Ban, Ryan Richards, and H L Xin*, Nature Communications, 5, 3356 [4] Three-dimensional hollow-structured binary oxide particles as an advanced anode material for high-rate and long cycle life lithium-ion batteries, Deli Wang, et al, H L Xin*, Nano Energy, 20, 212 (2016) [5] Transitions from Near-Surface to Interior Redox upon Lithiation in Conversion Electrode Materials, Kai He et al, Nano Letters, 15, 1437 (2015) [6] Sodiation Kinetics of Metal Oxide Conversion Electrodes: a Comparative Study with Lithiation, Kai He, et al H L Xin*, Dong Su*, Nano Letters, 15, 5755 Acknowledgement HLX acknowledges contributions from all coauthors, to name a few, Feng Lin, Kai He, Dong Su, Marca Doeff, Yijin Liu, Eric Stach, Ryan Richards, Xiqian Yu, Xiao-Qing Yang, Dennis Nordlund, and Deli Wang. This research is supported in part by the Center for Functional Nanomaterials, which is a U.S. DOE Office of Science Facility, at Brookhaven National Laboratory under Contract No. DE-SC0012704, and by Assistant Secretary for Energy Efficiency and Renewable Energy, Office of Vehicle Technologies of the U.S. Department of Energy under Contract No. DE-AC02-05CH11231. This research made use of resources of Stanford Synchrotron Radiation Lightsource, SLAC National Accelerator Laboratory, which is supported by the U.S. Department of Energy, Office of Science, Office of Basic Energy Sciences under Contract No. DE-AC02-76SF00515.

MnO Conversion in Li-Ion Batteries: In Situ Studies and the Role of Mesostructuring

Complex manganese oxides have been extensively studied as intercalation Li-ion battery electrodes. The simple oxide MnO has been proposed as a conversion anode material with a theoretical capacity of 756 mAh g(-1) for full reduction to the metal. We report the reaction of MnO with Li using in situ X-ray diffraction and find no sign of crystalline products upon either discharge or charge. However, the absence of reflections, paired with electrochemical impedance spectroscopy, suggests disordered discharge products. We also examine composite electrodes with porous particles of MnO as the active component, with pores generated through the reductive heating of Mn3O4. We compare the behavior of these with more dense MnO powders, including studies of the electrode morphologies pre- and postcyling. We find differences in the first discharge relevant to the utility of such mesostructuring in conversion reaction materials. Specifically, we find this type of mesostructure, which gives advantage in intercalation and pseudocapacitive storage, does not yield the same benefits for conversion reaction systems.

Carbon-Nanofibers Encapsulated Metal Oxide Nanocomposite and Its Application as Conversion Anode Material for Lithium Ion Batteries

Functional metal oxide/C-fibers composites were synthesized by a simple pyrolysis-oxidation process and have been investigated as promising conversion anode materials for Li-ion batteries. Metallocene was used as precursor and acts as both metal and carbon source. No templates or solvents were involved in the fabrication process. Three different composites of Fe3O4/C, Co3O4/C and CoFe2O4/C were synthesized by applying this method and tentatively studied as active anode materials. The synergistic effects by combining metal oxide nanoparticles and carbon fibers and also their intimate contact developed in the synthetic process are suggested to be crucial for the observed good cycling performance of the composites. This work offers a facile and broadly applicable way for fabrication and utilization of metal oxide/mixed metal oxide-C composites as electrode materials for Li-ion batteries.

Structural and Chemical Evolution of Amorphous Nickel Iron Complex Hydroxide upon Lithiation/Delithiation

Development of novel electrode materials is essential to achieve high-performance lithium ion batteries. Here, we demonstrate that amorphous nickel iron complex hydroxides (Ni–Fe–OH) synthesized by a laser–chemical method can be used as a potential conversion anode material for lithium storage. Complementary characterizations, including ensemble-averaged X-ray absorption spectroscopy, spatially resolved electron energy-loss spectroscopy, and energy dispersive X-ray spectroscopy in a scanning transmission electron microscope, were performed to reveal the chemical and structural evolutions of the active hydroxide particles undergoing electrochemical cycling. The solid–electrolyte interphase (SEI) layer with a primary component of lithium fluoride (LiF) was found and remained robust on the particle surface during the charge/discharge processes, which suggests that the LiF-containing SEI layer plays a critical role in maintaining the stable capacity retention and good reversibility of the Ni–Fe–OH anode.

Facile Synthesis of a Carbon Encapsulated Metal Oxide Nanocomposite and Its Application As Conversion Anode Material for Lithium Ion Batteries

Metal oxide has been reported to be an active conversion anode material in lithium-ion-batteries (LIBs) owing to its high specific capacity. The large volume change and the poor electronic conductivity during the Li+ insertion/extraction process limited its application, leading to capacity fade and poor cycling performance. Great efforts have been devoted on the combination of nanosized metal oxide with versatile carbon materials of special forms, such as carbon nanotubes, graphene, or fibers, in order to improve the cycling behavior. Most strategies to fabricate such functional composite structure involve multi-step processes or the use of certain templates, surfactants, or special solvents, removal of which in the post treatment complicates their practical applications. Thus, it is desirable to develop a facile straightforward synthetic strategy to generate such functional composite materials.In our work, a simple pyrolysis-oxidation process has been developed to produce metal oxide/C-fiber composite in a solvent-free and template-free way. Metal oxide nanoparticles anchored onto in-situ formed carbon nanofibers were synthesized and have been investigated as promising conversion anode materials for Li-ion batteries. In the fabrication process, metallocene was used as precursor and acts as both metal and carbon source. As an example, Fe3O4 encapsulated into helical carbon nanofiber structure was fabricated by pyrolysis of ferrocene and subsequent oxidation of the pyrolysed product. The as-obtained Fe3O4/C composite shows a high and reversible capacity, good cycling and rate capability. The synthetic strategy has been further applied to a binary metal oxide CoFe2O4/C system through pyrolysis of the mixture of ferrocene and cobaltocene and further oxidation. The final composite shows a high and stable capacity. More than 700 mAhg-1 based on the total mass of the as-prepared composite was obtained in the composite after long-term cycling of 250 cycles. The synergistic effects by combining metal oxide nanoparticles and carbon and also their intimate contact developed in the synthetic process are suggested to be the major contribution to the observed superior electrochemical properties. This work opens a facile and broadly applicable way for fabrication and utilization of metal oxide/mixed metal oxide-C composites as anode materials for Li-ion batteries.

Surface film formation on TiSnSb electrodes: Impact of electrolyte additives

X-ray photoelectron spectroscopy (XPS), scanning electron microscopy (SEM), and electrochemical impedance spectroscopy (EIS) have been performed to study the formation of surface film on TiSnSb, a promising conversion anode material for lithium ion battery. TiSnSb electrodes were cycled using a standard EC/PC/3DMC (1 M LiPF6) electrolyte containing vinylene carbonate (VC) as a primary filming agent. Fluoroethylene carbonate (FEC) was added as an additional additive intended to improve the stability of the surface film and, hence, the cyclability of the electrode. Surface analysis was performed by a combined XPS core peaks and quantification data analysis to establish the main components of the solid electrolyte interphase film (SEI) were identified. The key observation is that the thickness and the chemical nature of the SEI layer is strongly related to the nature of the electrolyte additives. From XPS and EIS results, the role of FEC as an effective SEI improver in alkylcarbonate based electrolyte has been enlighten.

Bacterial Nanometric Amorphous Fe-Based Oxide: A Potential Lithium-Ion Battery Anode Material

Amorphous Fe(3+)-based oxide nanoparticles produced by Leptothrix ochracea, aquatic bacteria living worldwide, show a potential as an Fe(3+)/Fe(0) conversion anode material for lithium-ion batteries. The presence of minor components, Si and P, in the original nanoparticles leads to a specific electrode architecture with Fe-based electrochemical centers embedded in a Si, P-based amorphous matrix.

LiMn2O4-based materials as anodes for lithium-ion battery

LiMn 2 O 4-based materials such as LiMn 2 O 4 and LiMn 1.53 Ni 0.47 O 3.67 were synthesized by both conventional-hydrothermal (CH), microwave-hydrothermal (MH) methods and calcination route. Both reaction temperature and reaction time during MH routes were lower than those of CH routes. LiMn 2 O 4 electrode materials were assembled into lithium-ion battery anodes and their electrochemical performances were studied. The results proved that these LiMn 2 O 4 electrodes can be served as conversion anode materials, and show electrochemical activity during the potential range of 0.01–3.0 V versus Li +/ Li . For LiMn 1.53 Ni 0.47 O 3.67 materials when used as lithium-ion battery anodes, we found that the introduction of Ni can change their electrochemical reaction and thus improve their electrochemical performances.

Unfolding the role of iron in Li-ion conversion electrode materials by 57Fe Mössbauer spectroscopy

57Fe Mossbauer spectroscopy is particularly useful in the study of oxide and oxalate conversion anode materials for Li-ion batteries. After reduction in lithium test cells, all these materials showed Mossbauer spectra ascribable to iron atoms in two different environments with superparamagnetic relaxation. The spectra recorded at 12 K revealed the ferromagnetic character in agreement with particle sizes of ca. 5 nm. The two types of iron can be ascribed then to surface and core atoms. Core iron atoms play an important role to retain high faradic capacity values for a large number of cycles. These atoms are preserved from irreversible reactions with the electrolyte and hence they promote a high reversibility and rate capability.

NiMn 2− xFe xO 4 prepared by a reverse micelles method as conversion anode materials for Li-ion batteries

Synthesis by reverse micelles was used to produce NiMn 2− x Fe x O 4 with nanometric particle sizes for their use as conversion anode materials for lithium ion batteries. The hydroxide precursor was characterized by infrared spectroscopy and the decomposition was followed by thermal analysis. Cation distribution in the spinel structure of pristine samples was evaluated by Mössbauer spectroscopy evidencing that octahedral Fe 3+ is substituted by Mn 3+ ions in NiMnFeO 4. Capacity values of 750 mA h g −1 were retained for 50 cycles for NiMnFeO 4 and NiFe 2O 4, respectively. A good kinetic response was observed in NiMnFeO 4 at 2C.