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Electrochemical Energy Laboratory, Depart

and National Centre for Solar Photovoltaic

of Technology Bombay, Mumbai 400076, In

+91-22-25767849

† Electronic supplementary information (characterization: Fig. S1–S3. See DOI: 10.1

Cite this: RSC Adv., 2013, 3, 25058

Received 30th July 2013Accepted 16th September 2013

DOI: 10.1039/c3ra44001j

www.rsc.org/advances

25058 | RSC Adv., 2013, 3, 25058–25

Nickel ferrite as a stable, high capacity and high rateanode for Li-ion battery applications†

P. Ramesh Kumar and Sagar Mitra*

Conversion electrodes based on binary or ternary metal oxides are known to suffer from a slow electrode

kinetic problem that is related to solid-state lithium diffusion, electrochemical stability and loss of

coulombic efficiency in the initial cycles. The solid-state diffusion problem is mainly governed by the

grain boundary effect during the conversion reaction but the reason behind the electrochemical

stability is still unknown. To overcome the issues related to solid-state diffusion, electrodes are

nanoarchitectured and made in nano-dimensions but it is still not clear how to solve the stability

problem, which is very acute when electrodes perform at a high rate. To attempt solving this problem

for the ternary based conversion anode, we have carried out this study. The current study describes the

use of a nanosized NiFe2O4-based conversion anode along with an alginate binder as an excellent high

rate (for instance, 20 C rate) electrode. In this study, more than 98% of the initial charge storage

capacity of a nickel ferrite electrode is restored over a large number of cycles. Galvanostatic tests on

such electrodes show that NiFe2O4 nanoparticles can deliver 740 mA h g�1 capacity at 1 C current rate

with very good capacity retention. The observed outstanding electrochemical performance, stability and

coulombic efficiency will help us to design a ternary metal oxide based electrode as an anode for future

generation lithium-ion batteries.

Introduction

In the case of lithium-ion battery electrode design, the choice ofanode properties, including, fast electrode kinetics, low costand safety of the material and a very low redox potential vs. Li/Li+ compared to cathode materials. In the early stage of lithiumbattery development, the anode materials were low potentialinsertion compounds such as Li2WO2.1 Later on these metaloxides were replaced by low density carbon-based materials,which are currently enjoying widespread commercial successand have been for over two decades.2

Despite advances being made on carbon-based anodes, it iswell understood that new anode materials are required becauseof the energy demands of the modern age. There are disad-vantages of carbon anodes, rstly carbon materials can sufferfrom solvent co-intercalation resulting in large interlayerexpansion, which exfoliates when reactions have a high rate ofcharge–discharge. Secondly, carbon materials suffer fromfundamental drawbacks in terms of gravimetric and volumetriccapacity, which affect the development of high energy densitylithium batteries. It is noteworthy that a large number of

ment of Energy Science and Engineering

Research and Education, Indian Institute

dia. E-mail: sagar.mitra@iitb.ac.in; Tel:

ESI) available: Experimental details and039/c3ra44001j

064

alternative possibilities have been proposed recently as negativelithium battery electrodes, which may give us new directions inmeeting the challenges faced by anode materials. One impor-tant aspect of anode development concerns the conversionreaction. The very rst report of a conversion anode was basedon an iron oxide and cobalt oxide material, which was deepdischarged to achieve the desired capacity.3 Later on fewcomplex oxides including LiMVO4, RVO4, MV2O6 and MMoO3

were used as conversion anodes.4–6 However, in the initial stagethe lithium storage mechanism and the origin of the revers-ibility was not clear to the battery community. Later on thereaction mechanism and problems associated with theconversion reactions were understood and a large number ofreports reected this in the literature.7–15 Among all of thereported metal and mixed metal oxides, less expensive ironoxides (Fe2O3, Fe3O4) have gained much interest as anodesbecause they are eco friendly, abundant and can accommodatemore than six lithium ions during deep discharge.16–18 However,a large volume change can occur during the conversion reac-tion, which can lead to capacity fading and cause mechanicalfailure in the battery electrode. The volume expansion andpulverization problem can be neutralized by optimisingmorphology and size.16,19,20

At the same time, pure Fe2O3 can react with divalent metaloxides (MO) and form stable MFe2O4. Basically, these ternaryoxide spinels were crystallized into either normal, inverse orpartially inverse structures depending on the site preference

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energy, ionic radius of the metal ions, and possibility ofdifferent valency states. Tirado et al., have reported on theinverse spinel with the formula of MFe2O4 (M ¼ Co and Ni). ForNiFe2O4, the initial reversible capacity was found to be 920mA hg�1 depending on the temperature of the synthesis, when cycledin the voltage range of 0.005–3 V vs. Li at a 1 C rate. But, capacityfading was observed to a large extent during the rst 20 cycles.21

This was ascribed to the optimized particle size and macroporous structure of the phase, in comparison to those preparedat lower or higher temperatures. Aerwards, the same authorsexplained that the electrochemical grinding effect producedduring cycling would disaggregate the Li2O–Ni–Fe agglomera-tions, which might be the reason behind the capacity fading.Capacity fading is still a problem in the case of metal ferrites tobe considered as effective anodes. It is known that when theparticles of electrodes expand/contract during conversion, alarge interparticle motion occurs, which may result in binderbonds being broken unless the polymer binder is highlyextensible and reversible. Obviously, the binder may also play avery important role in stabilizing the electrode materials. Inlithium ion battery technology, researchers have preparedelectrodes using different binders like polyvinylidene uoride(PVDF), polyvinyl pyrrolidone (PVP), poly acrylic acid (PAA),carboxymethyl cellulose (CMC) and alginate.22–24 Yushin et al.,introduced alginate as a binder for LIBs. They have carried outindentation studies of electrodes with a Na alginate binder in adry state and it has exhibited �6 times higher stiffness than drylms of polyvinylidene diuoride (PVDF), the binder used inLi-ion battery electrodes.25 Alginate (alginic acid) is a copolymerof 1/ 4 linked b-D-mannuronic acid (M) and a-L-guluronic acid(G) residues. Different compositions and sequences of M and Gmonoblocks in alginates yield a plethora of physical and bio-logical properties.26

The aim of this work is to avoid the capacity fading in inversespinel ternary oxides by using high surface area nanoparticlesand improving the interface between the active material andbinder. In this study, NiFe2O4 nanoparticles were prepared by asol–gel combustion technique to obtain pure nano size parti-cles. The prepared NiFe2O4 nanoparticles were characterizedusing various techniques such as XRD, FTIR, FESEM, TEM andRaman spectroscopy. The electrochemical response of theprepared nanoparticles was studied using cyclic voltammetryand galvanostatic charge–discharge measurements. TheseNiFe2O4 nanoparticles with sodium alginate binders couldexhibit promising electrochemical performance such as a highreversible capacity, excellent cycling performance and good ratecapability, which are reported for the rst time here.

Experimental

Nanocrystalline nickel ferrite (NiFe2O4) particles were synthe-sized by a sol–gel combustion route. In the sol–gel combustionprocess, nickel nitrate (Sigma Aldrich), iron nitrate (SigmaAldrich), citric acid (Qualigence, Analar grade) and urea (Qual-igence, Analar grade) were used as precursors to synthesizenanocrystalline NiFe2O4 particles. First, the solutions of all therequired precursors weremixed with continuous stirring at 80 �C

This journal is ª The Royal Society of Chemistry 2013

to form a gel, which was then heated up to 180 �C. The gelexpanded into a foam with a volume 20 times that of the gel.Pure nano crystalline NiFe2O4 particles were obtained on furtherheating of the foam up to 600 �C for 12 h. The synthesizednanocrystalline NiFe2O4 particles were characterized by using anX-ray diffractometer (XRD, X'pert PRO MPD, PANalytical, Phi-lips) with Cu Ka radiation (l ¼ 1.54 A at 40 kV and 30 mA). Thesize and shape of the synthesized samples were examined with aeld emission gun (FEG) scanning electron microscope-EDX(Zeiss, Ultra 55 model with Oxford EDX system). A transmissionelectron microscope with energy dispersive spectroscopy (TEM),JEOL 2010F HRTEM, Japan, with a 200 kV operating voltage wasused to capture the morphology and crystallinity of the NiFe2O4

sample. Raman measurements were carried out in the backscattered geometry using an Ar+ laser excitation source emittingat 514 nm with 20 mW power, coupled with a Labram-HR800micro-Raman spectrometer (equipped with an appropriate edgelter and a Peltier-cooled charge coupled device detector). Theelectrochemical studies of nanocrystalline NiFe2O4 particleswere analyzed in a CR2032 coin cell in a half-cell conguration.The composite electrode was prepared by mixing 70 wt% of theactive material with 20 wt% Super P carbon black (Timcal superP) and 10 wt% sodium alginate (Sigma Aldrich) or carboxymethylcellulose (CMC) and PVDF binders (Sigma Aldrich) in a suitablesolvent. The obtained slurry was cast on a piece of Cu-foil andcut into circular electrodes. Lithium foil was used as the anodeand a 1 M solution of LiPF6 in ethylene carbonate and dimethylcarbonate (1 : 1) was used as the electrolyte [LP 30, Merck Ger-many]. Swagelok-type cells were assembled in an argon-lled dryglove box (Mbraun, MB10 compact) using a Whatman GF/Dborosilicate glass–ber separator. The cyclic voltammetry and insitu electrochemical impedance spectroscopy were recorded atvarious potentials during the rst discharge–charge cycles usinga frequency range between 1 MHz and 1 mHz with 5 mV ofamplitude (Model: VMP-3, Biologic, France). The cells were gal-vanostatically cycled between 3 V and 0.02 V vs. Li/Li+ using anArbin Instrument (model BT 2000, USA).

Results and discussion

The XRD pattern of the nanocrystalline NiFe2O4 sample alongwith the JCPDS data (no. 862267) is shown in Fig. 1. Theobserved XRD peaks were indexed to a face centered cubic phase(space group Fd�3m) of NiFe2O4. The crystallite size (D) wascalculated using the Scherrer formula: b cos(q)¼ kl/D, where b isthe full width-at-half-maximum length of the reection.27 Thecalculated crystallite size of the pure NiFe2O4 nanoparticlesample was approximately 22 nm. The schematic representationof a NiFe2O4 unit cell is shown as an inserted image in Fig. 1.

Fig. 2 shows the FEG-SEM images of the polymeric interme-diate (foam) and pure nanocrystalline NiFe2O4 samples. Fig. 2(a)and (b), show the polymeric intermediate (as synthesized mate-rial) at different magnications. Fig. 2(c) and (d), show the pureNiFe2O4 nanoparticle sample, which was heated up to 600 �C for12 h in air. Fig. 3(a)–(d) show the TEM images of the NiFe2O4

nanoparticles at different magnications. The size investigationand selected area electron diffraction (SAED) patterns of the

RSC Adv., 2013, 3, 25058–25064 | 25059

Fig. 2 FEG-SEM images of (a) and (b) polymeric intermediate and (c) and (d)pure NiFe2O4 nanoparticles.

Fig. 3 (a–c) HRTEM images and (d) SAED patterns for pure nanocrystallineNiFe2O4 nanoparticles.

Fig. 4 Cyclic voltammetry graphs for NiFe2O4 nanoparticles with (a) PVDF and(b) alginate binders.

Fig. 1 XRD patterns for (a) the pure NiFe2O4 nanoparticles along with (b)respective JCPDS data.

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prepared NiFe2O4 nanoparticles were observed using HRTEM.The HRTEM images of the NiFe2O4 nanoparticles shown inFig. 3(a) and (b) indicate the formation of agglomerates withspherical morphology�15 nm in diameter, which is close to whatwas observed with SEM. The SAED patterns were recorded andDebye–Scherrer rings were obtained. These are shown in Fig. 3(d)and represent the (111), (220), (311), (222), (400), (331) and (422)lattice planes and they are supported by the XRD analysis. TheXRD, FTIR (see ESI, Fig. S1†), SEM and TEM results conrmedthat the NiFe2O4 nanoparticles are phase pure and can besuccessfully prepared by using the sol–gel combustion process.

Electrochemical properties

Fig. 4(a) and (b) show the cyclic voltammetry prole for NiFe2O4/Li (PVDF) and NiFe2O4/Li (alginate) respectively. For these thinlm electrodes, substantial differences between the rst and thesubsequent cycles are observed. As shown in Fig. 4(a) and (b), inthe rst cycle, a large cathodic peak located around 0.6 V vs. Li/

25060 | RSC Adv., 2013, 3, 25058–25064

Li+ is probably associated with the reduction reactions of Fe3+

and Ni2+ with Li and the formation of Li2O. In the subsequentcathodic scans, the NiFe2O4/Li (PVDF) sample (Fig. 4(a)) shows acathodic peak and anodic peak at 0.5 V and 1.9 V, respectively.The intensity of the peaks changes with cycle numbers, whichindicates poor stability against lithium. As shown in Fig. 4(b),the two cathodic peaks located at 0.83 V and 1.6 V vs. Li/Li+ canbe attributed to the reductive reaction of Fe2O3 and NiO to Feand Ni metal, respectively.28 The decrease of the redox peakintensity implies that the electrode stability is a major issueaer the rst cycle. In the rst anodic cycle, a main broad peakcentred at 1.6 V vs. Li/Li+ is related to the oxidation of metalliciron and nickel to Fe3+ and Ni2+, which shis towards a higherpotential, about 1.9 V vs. Li/Li+, aer the second cycle due to thechange in the ionic environment.

It should be noted that the peak intensity during the anodicand cathodic polarization process remained unchanged for 20scanning cycles in the case of the alginate binder, indicating agood electrochemical reversibility of the NiFe2O4/Li (alginate)electrode. The observed conversion redox mechanism mayoccur in the following steps

NiFe2O4 + 8Li+ + 8e 4 Ni + 2Fe + 4Li2O8Li 4 8Li+ + 8e

NiFe2O4 + 8Li / Ni + 2Fe + 4Li2O

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Table 1 Impedance parameters of the Li/NiFe2O4 cell with an alginate binderduring the 1st discharge–charge cycles at various voltages

Voltage (V) Re (Ohm) R(SF+CT) (Ohm)Warburgelement

Discharging2.9 3.28 57.38 0.8972 3.13 68.63 0.79621.5 3.3 69.02 0.99630.8 3.1 71.5 0.75390.5 3.7 71.1 0.72880.2 3.6 84.5 0.8215

Charging0.5 3.76 92.25 0.82351 4.023 94.24 0.8341.5 4.727 92.3 0.77192 4.2 93.9 0.8406

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At the cathode (in the present case the working electrode),NiFe2O4 started reacting with the Li ions and was converted toNi and Fe nanoparticles along with an amorphous Li2O phaseduring the deep reduction cycle. However, in the reverseoxidation process, Ni and Fe nanoparticles are oxidized to NiOand Fe2O3 phases respectively, which is conrmed by thevibrational spectroscopy study and shown in a later stage of thediscussion.

The sodium alginate has carboxyl groups on its surface,which allow bonding between the outer surface of the NiFe2O4

nanoparticles and the binder. The proposed redox mechanismof ion transport through the alginate lm occurs via hopping ofLi ions between the adjacent carboxylic sites. Furthermore, thealginate binder will provide a very weak binder–electrolyteinteraction, which is needed for the long-term anode stability bypreventing the rapid anode degradation.29 The kinetic responseof the current electrode material can be evaluated from the insitu impedance spectra measured from the samples in the 1stdischarge and charge cycle (Fig. 5(a)). Fig. 5(a) and (b) show theNyquist plots typically recorded at different onset voltages. Theimpedance data were analyzed by using the equivalent electricalcircuit model shown in Fig. 5(c), similar to the circuit employedfor other oxide electrodes.30,31 It consists of electrolyte (Re),surface lm (RSF), and charge transfer (RCT) resistances, aconstant phase element (CPE) instead of pure capacitance,

Fig. 5 In situ electrochemical impedance spectroscopy plots for the NiFe2O4–

alginate cathode in (a) discharging state, (b) charging state and (c) equivalentelectrical circuit.

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along with a suitable diffusional component like Warburgimpedance (WS) and the intercalation capacitance (Cint).

From Fig. 5, we can observe that there is one depressedsemicircle, which consists of two semi circles convoluted intoone semicircle. The rst one is located in the high frequencyrange and can be tentatively ascribed to the migration oflithium ions through an inorganic surface lm (SF), mainlycomposed of lithium carbonate and alkyl carbonate. Thesemicircle observed in the intermediate frequency region andcan be ascribed to a charge-transfer (CT) reaction occurring atthe particle–electrolyte surface. The observed depressed semi-circle was tted by using an R(SF+CT) combination. From the rstdispersed semicircle, R(SF+CT) resistance values could be esti-mated from tted data. In Fig. 5, we can observe that the R(SF+CT)

increases slightly as the voltage is decreased in the dischargestate; however there is no change in the charging state, evenwhen the voltage is increased. The reason for the increase ofR(SF+CT) during the charging state might be due to thesuppression of the reaction between the Li ions and electrons atthe electrode/electrolyte interface due to the formation of largegrain boundaries affecting the efficient mass transfer process.32

The values of Re and R(SF+CT) at different voltages are shown inTable 1. Furthermore, nano-sized electrode materials offer goodcharge transfer kinetics due to their shorter diffusion pathlengths. Therefore, the better performance of NiFe2O4 must beascribed to the stability of the interfaces providing constantcapacity values in long-term cycling.

Fig. 6 shows the EDX line scan spectrum of the cathode lmaer 20 cycles (at a fully charged state). We have chosen onespecic grain of active material of 2 mm width that protrudesslightly and used for the EDX map (in line scanning mode) tond out which elements are present on the surface of the grain.It can be seen from Fig. 6 that the oxygen content is higher onthe surface of the agglomerated particle than in its interior. But,the content of Fe and Ni is almost constant throughout thegrain. This conrmed the formation of Li2O, Fe2O3 and NiOnanoparticles on the surface of the cathode lm (present casew.r.t. Li anode) during the charge–discharge in the conversionreaction.

RSC Adv., 2013, 3, 25058–25064 | 25061

Fig. 6 EDX line scanning spectra for NiFe2O4–alginate cathode after 20 charge–discharge cycles.

Fig. 7 Raman spectra of (a) pure NiFe2O4 and (b) NiFe2O4 electrode after 20cycles along with the Lorentzian line shape fitting.

Fig. 8 a) Capacity versus cycle number plot and b) Galvanostatic charge–discharge curves of NiFe2O4 with PVDF binder.

Fig. 9 (a) Capacity versus cycle number plot and (b) galvanostatic charge–discharge curves of NiFe2O4 with the alginate binder at a 0.1 C rate.

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Fig. 7 shows the Raman spectra of the pure NiFe2O4 andNiFe2O4–alginate electrodes aer 20 cycles in the charge statealong with the Lorentzian line shape tting. As shown inFig. 7(a), the ve bands conrm the formation of inverse spinelNiFe2O4 nanoparticles. NiFe2O4 crystallizes in a spinel structurewith the space group Fd�3m and group theoretical calculationsresult in ve Raman active bands namely A1g + Eg + 3T2g.33 Asshown in Fig. 7(b), the four peaks on the lower wavenumber sidebelong to the a g-Fe2O3 phase.34,35 The bands at 925 cm�1and1100 cm�1, belong to two-phonon (TO + LO & 2LO) excitations.One band at 1500 cm�1 belongs to the two magnon excitationsof nickel oxide.36–38 Furthermore, two broad bands at 1350 and1580 cm�1 belong to the super P carbon, which is used as aconductive additive in the electrode preparation. Hence, theRaman spectrum shows the formation of a g-Fe2O3 phase andNiO aer 20 cycles, which is strong evidence in support of theconversion reaction mechanism described in an earlier section.

The electrochemistry of the NiFe2O4 electrode is inter-esting and Fig. 8 shows the discharge capacity versus cyclenumber of NiFe2O4/Li (PVDF). The discharge capacity of theNiFe2O4 electrode at the 0.1 C (91.5 mA g�1) rate during the1st cycle was observed as 1440 A h�1, while at the 50th cycle itwas 180 mA h g�1.

25062 | RSC Adv., 2013, 3, 25058–25064

The discharge capacity loss in the Li/NiFe2O4 nanoparticlecell was around 85% between the 1st and the 50th cycles. InFig. 8(b), the 1st discharge curve shows a large plateau, whichindicates the reduction of metal ions and formation of Li2O.Aerwards, the discharge curves do not show any plateau, so itcan be concluded that the prepared electrode thin lm with thePVDF binder experiences rapid capacity fading due to inade-quate interfacial stability.39 At the same time, the cycle perfor-mance of NiFe2O4/Li (CMC) at 91 mA g�1 (1 C) for 30 cycles isshown in Fig. S2 (see ESI†). The rate performance curves ofNiFe2O4/Li (CMC) were recorded at various discharge currentdensities, from 915 mA g�1 to 18 300 mA g�1 and are shown in

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Fig. S3 (see ESI†). The specic capacity of NiFe2O4/Li (CMC)dropped dramatically, but still the CMC binder shows bettercyclic performance compared to the conventional PVDF binder.Finally, we prepared an electrode with an alginate binder and toevaluate the cycling behavior of NiFe2O4 nanoparticles with thealginate binder up to 30 cycles were performed, using the 0.1 C(91.5 mA g�1) current rate. The discharge capacity of theNiFe2O4 nanoparticles with the alginate binder shows very goodcapacity retention as represented in Fig. 9(a).

From Fig. 9(a), the NiFe2O4 nanoparticles with the alginatebinder show a stable discharge capacity of 880mAh g�1 at a 0.1 Crate with excellent coulombic efficiency. The enhanced capacitywas attributed to the highly stable interface between the activematerials and binder. Signicantly the NiFe2O4/Li (alginate) hadan increased capacity at 0.1 C compared to recently reportedternary nanocomposites.21,29 From Fig. 9(b), several plateaus canbe observed during the rst discharge, which were ascribed to thesequential reduction of nickel and iron, according to the lengthof the plateaus. Also, the lithium insertion into the nano-sizedternary samples and the atom ordering during the NiO reductionwere believed to be responsible for the appearance of newplateaus at the beginning of the rst discharge stage.40

Fig. 10 (a) Discharge capacity as a function of cycle numbers and (b) galvano-static charge–discharge curves of NiFe2O4 with an alginate binder at differentC rates.

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Fig. 10 shows the rate capability plots of the NiFe2O4/Li(alginate) electrode cycled at different rates starting from 915mA g�1 (1 C), 1830 mA g�1 (2 C), 4575 mA g�1 (5 C), 9150 mA g�1

(10 C), 18 300 mA g�1 (20 C) and then reverting back to the 1 Crate. At each rate, ten cycles were tested to assess the material’sretention capacity. The rate capability of the electrodes is alsoshown in Fig. 10(a). At the very high rate of 18 300 mA g�1

(20 C), 42.5% of the original capacity was retained with highcycleability. It was observed that the discharge capacity of theNiFe2O4 nanoparticle anode decreases to 740, 620, 504, 420 and380 mA h g�1 when the current rate is increased to 1, 2, 5, 10and 20 C, respectively. The prepared NiFe2O4 nanoparticleswere shown to have a stable high capacity along with goodcycleability compared to previous reports.21,41 From Fig. 10(b),the plateaus corresponding to Li uptake and extraction canclearly be seen even at high current rates. Such impressivelithium storage at high current rates may be attributed to betteradherence between the active material surfaces with the algi-nate binder. While charge and discharge processes werecarried out at a high rate (20 C), we still observed good speciccapacities with 99% coulomb efficiency. As the current rateincreases, the pseudo-plateaus of each discharge curve movedownwards. The observation can be explained as follows, at ahigh rate the electrode overpotentials and the internal IRdrops, mainly due to the low conductive organic electrolyte,thus decreasing the operating voltage of the cell. At high rates,the intercalation/de-intercalation of Li+ ions happens only atthe surface of the particles, and hence the observed capacity islow.42 As per our documentation, the current capacity retentionand specic capacity value are higher compared to previouslyreported ternary anode materials at low as well as at high rates.Therefore, we can say here that this is the rst report of NiFe2O4

nanoparticles that are cycled at very high current rates for usein high power energy storage applications.

Conclusions

The nanocrystalline nickel ferrite particles were successfullysynthesized using a sol–gel combustion technique. The phase,structure and microstructure of the prepared NiFe2O4 nano-particles were conrmed by XRD, SEM-EDX, and HRTEMstudies. The present work has a few important points to shareincluding (1) without any template we could synthesize electrodematerials based on the conversion reaction, which can showexcellent electrochemical performance at a high rate; (2) thebetter electrochemical stability of the NiFe2O4 nanoparticleswith an alginate binder. The NiFe2O4/Li (alginate) seem to have ahigher capacity and better stability than the earlier reportedresults of other NiFe2O4 materials. The main reason could bedue to the use of high surface area of the particles and highstable interface between the active material and alginate binder.The nanocrystalline NiFe2O4 with the alginate binder delivers astable maximum discharge capacity of 880 mA h g�1 at 0.1 C,which is nearer to the theoretical capacity (915mA h g�1) limit ofthis material. It has a high rate performance as at 18 300 mA g�1

(20 C) it also exhibits a discharge capacity of about 380 mA h g�1

under similar conditions. Hence, we suggest that the ternary

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nickel ferrite nanocrystalline particle is an important class ofanode material for next generation Li-ion battery applications.

Acknowledgements

The authors are grateful to NCPRE (National Centre for Photo-voltaic Research and Education) for nancial support to carryout this research work. We also express our thanks to SAIF, IITBombay and Research Scholars for providing adequate instru-ments and facilities to meet the characterizations of thesematerials.

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