Electrophoretically deposited ZnFe2O4-carbon black porous film as a

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Electrophoretically deposited ZnFe2O4-carbon black porous film as a superior negative electrode for lithium-ion battery Debasish Das, Arijit Mitra, Sambedan Jena, Subhasish B Majumder, and Rajendra Nath Basu ACS Sustainable Chem. Eng., Just Accepted Manuscript • DOI: 10.1021/ acssuschemeng.8b04332 • Publication Date (Web): 08 Nov 2018 Downloaded from http://pubs.acs.org on November 12, 2018

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ACS Sustainable Chemistry & Engineering

Electrophoretically deposited ZnFe2O4-carbon black porous film as a superior negative electrode for lithium-ion battery Debasish Dasa*, Arijit Mitrab, Sambedan Jenac, Subhasish B. Majumdera, Rajendra N. Basud a

Advanced Materials Processing Laboratory, Materials Science Centre, Indian Institute of Technology, Kharagpur, 721302, India

b

Structural Characterization of Materials Laboratory, Department of Metallurgical and Materials Engineering, Indian Institute of Technology, Kharagpur, 721302, India

c

School of Nano Science and Technology, Indian Institute of Technology, Kharagpur, 721302, India

d

Fuel Cell and Battery Division, CSIR-Central Glass and Ceramic Research Institute, Kolkata, 700032, India

Corresponding Author * [email protected], [email protected]

ACS Paragon Plus Environment

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.ABSTRACT

This manuscript reports ZnFe2O4 (ZFO) based negative electrodes for lithium-ion battery, which is synthesized using a simple auto-combustion technique and coated onto copper current collectors using the electrophoretic deposition technique. The use of electrophoretic deposition to manufacture the electrodes results in the significant improvement of electrochemical properties of ZFO, which is achieved without the use of any complex processing steps or costly additives like Graphene, CNT etc. The electrophoretically fabricated electrodes possess a porous microstructure with uniform carbon black distribution. Such a microstructure and carbon black distribution successfully tackles the issues related to the low electronic conductivity and volumetric fluctuation based delamination. These electrodes deliver a stable reversible specific capacity of 560mAhg-1 at a specific current rate of 0.5Ag-1, which is retained for 100 cycles. The electrodes also exhibit a specific capacity of 330mAhg-1 at a high specific current rate of 3.5Ag-1. Electrophoretic deposition, thus, represents a simple and cost-effective route to fabricate negative electrode coatings with superior electrochemical properties.

KEYWORDS: ZnFe2O4, Electrophoretic deposition, Negative electrode, Lithium-ion battery


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Introduction The increasing popularity of Lithium-ion battery in the past decades has seen numerous technological upgrades which deemed this technology to be a viable addition in many fields like consumer electronics and have pave their way into being a major contender as energy source in electric vehicles.

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However, recent reports indicate a need of high-capacity and/or high-power

lithium-ion batteries to meet the increasing market-requirements which conventional pristine graphite based negative electrodes fail to achieve.5-6 As a response, numerous efforts have been made in order to discover and establish novel, high-performance anode candidates to obtain high capacities, better cycleability and high-rate characteristics.7 Among them, mixed transition metal oxides with spinel structures are one of the most promising candidates due to their higher capacities compared to that of graphite, them being environmental benign, and low cost owing to their multiple oxidation states and synergistic properties.8-11 In the corresponding Fe family (ferrite based) spinels, zinc ferrite (ZnFe2O4) draws much attention owing to its low cost, natural abundance and high theoretical capacity of 1000mAhg-1.12-13 The lithium-ion storage mechanism of ZFO is attributed to the total storage of 9 Li+ per molecule of ZFO (ZnFe2O4 + 8Li+ + 8e-  Zn + 2Fe+ 4Li2O, Zn + Li+ + e-  Zn-Li).14 Despite such advantages, practical use of nascent ZFO particles is hindered due to their poor electronic conductivity and significant volumetric changes during Li+ insertion/extraction resulted in loss of electrical contact between the active material and current collector, leading to dramatic capacity fading during cycling. Hence, certain structural treatments are necessary during electrode fabrication in order to address such issues. These treatments include morphology tuning of the inherent ZFO particles, composite fabrication using conductive carbonaceous materials like CNT, graphene etc., followed by multi-step conventional electrode fabrication process which involves the use of volatile and toxic organic


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solvents like N-methyl-2-pyrrolidone.12,

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These treatments are often energy-intensive and

require complex processing thereby increasing the manufacturing costs. Hence, simpler alternatives with viable scope for industrial scalability needed to be explored. Electrophoretic deposition (EPD) featuring pronounced simplicity, reproducibity and scalability has immerged as suitable alternative route to fabricate porous/dense, thin particulate films with 1-50 μm thickness for different applications. Furthermore, high deposition rate, excellent thickness control, applicability for versatile materials, ability to deposit on complex shaped substrates and cost-effectiveness requiring simple apertures further increases the interest in EPD technique.20-21 It is a colloidal process where charged particulates dispersed in an electrostatically stabilized suspension are forced to move towards the oppositely charged electrode under the influence of an applied DC electric field and finally get deposited onto it to form a uniform film. Few reports are available in literature where EPD has been successfully used to fabricate in Li-ion battery cathodes such as LiCoO2-carbon black

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, LiNi0.5Mn1.5O4-

carbon black 23, LiFePO4/black-pearl carbon 24, as well as anodes like and SnO2 25, Fe2O3-CNTrGO

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, Co3O4-rGO

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MnOx-CNT

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etc. composite films. Ui et al. has reported a binder free

SnO2-carbon black composite film from an acetone based suspension bath.25 In a similar study, Benehkohal et al. fabricated TiO2-carbon black composite film using isopropanol as dispersing medium.29 However, they incorporate an additional control atmosphere sintering step in order to improve the adherence between the deposited film and current collector and achieved good electrochemical properties. Recently attempted have also been made to co-deposit the precursor ions of active materials along with rGO and/or CNT followed by high temperature control atmosphere calcination in order to achieve material synthesis and electrode assembling, simultaneously.30 Carbonaceous materials like rGO and CNT due to having several surface


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functional groups can easily be charged by adding dispersing agents. Again, in case of precursor ion-CNT and/or rGO co-deposition process, the metal salts themselves act as the charging agent. Therefore, fabrication of active material/CNT and or rGO composite can easily be carried out by EPD technique. On the other hand, owing to the lack of surface functional groups, conventional carbon black (CB) is difficult to disperse electrostatically in any non-aqueous medium to form a stable suspension. However, preparation of sufficiently stable suspension is one of the major prerequisite to obtain good quality deposition via EPD.31 Even though, various attempts exist in literature for synthesizing spinel based compounds viz. hydrothermal

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, micro-emulsion

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, reverse micelles

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, spray pyrolysis

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, etc. these have

complex schedules, low production rates and require extensive purification steps to obtain phase pure materials. In comparison, auto-combustion route is a more facile and industrially scalable route for producing such spinels.36 In this present research work, we have prepared sufficiently stable ZFO-carbon black composite suspension in isopropanol medium and demonstrate the efficacy of EPD route to fabricate highly porous ZFO-carbon black negative electrodes for Lithium-ion battery using conventional ZFO and carbon black powder. Such simple fabrication process eradicates the need of expensive structural treatment or the use of expensive carbonaceous material like CNT or rGO. The resulting EPD electrodes show promising electrochemical performance comparable, if not superior.


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Experimental Section Zinc Nitrate Hexahydrate (>99%), Ferric (III) Nitrate Nonahydrate (>99%), Glycine (>99%) and Ethylene Carbonate (98%) are procured from Sigma Aldrich. Iso-Propanol, Dimethyl Carbonate (≥99%), Nickel Nitrate Hexahydrate (≥98%) and Poly-acrylic Acid (average Mw250,000, 25% in water) are procured from Merck. All chemicals are used as received without further purification.

Auto-combustion synthesis of ZnFe2O4 powder:

The ZFO powder was synthesized via simple auto-combustion route. A solution having stoichiometric amounts of Zn(NO3)2.6H2O and Fe(NO)3.9H2O was prepared in de-ionized water followed by addition of glycine as fuel keeping NO3- : Glycine ratio as 1:1. The solution was stirred at 150oC, till the gel formation occurred. The temperature was increased to 250oC after the gel formation for the auto-combustion to occur. The as-synthesized auto-combustion product was finely grinded in an agate mortar-pestle, and subsequently calcined at elevated temperatures in air for 3 hr. The ZFO powder synthesis is briefly outlined in Scheme 1(a). The calcined powders was subjected to powder X-Ray Diffraction analysis (Bruker D8 Discover) within the range 2θ =10-80o, in Bragg-Brentano Geometry, at a scan speed of 0.3 s/step using Cu Kα radiation. Particle morphology of the calcined powders was ascertained via Scanning Electron Microscopy (Zeiss Merlin Gemini 2) and Transmission Electron Microscopy (FEI Tecnai G2).


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Suspension preparation and electrophoretic deposition of ZnFe2O4 and carbon black composite films: The calcined ZFO powders and carbon black particles were dispersed in Iso-propanol (IPA), containing Poly-acrylic Acid and Nickel Nitrate Hexahydrate as dispersants, using ultrasonic agitation for 30 minutes. The total solid loading was kept fixed at a concentration of 2.5g/l, with the weight ratio of ZFO: CB maintained at 9:1. Zeta Potential Measurements were carried out using a Zetasizer (Malvern Zetasizer Nano ZS90). Suspensions, thus prepared, were then used to fabricate ZFO, CB, and ZFO-CB films using electrophoretic deposition. In all the deposition experiments, the prepared suspension was placed in a 100ml beaker between Cu negative electrode and SS304L positive electrode. The exposed area of the positive electrode was kept larger than the negative electrode to streamline the electric field. The distance between the two electrodes was maintained at 2 cm for all deposition experiments. The suspension preparation procedure and EPD set-up used in this research work is schematically shown in Scheme 1(b). The electrophoretic deposition kinetics was performed by varying the applied potential and total deposition time, to optimize the deposition conditions. The EPD films were structurally characterized using Grazing Incidence X-ray diffraction (Bruker D8 Discover), and indexed as per JCPDS data. The surface morphology, homogeneity, pore distribution thickness etc. of the deposited films were identified using Scanning Electron Microscopy (Zeiss Merlin Gemini 2). EDS study (EDAX Octane T Plus) was performed in order to find out the ZFO and CB distribution in the deposited film. The electrical resistivity was measured using a home-made 4-probe setup connected to a Voltmeter (Keithley 2182a Nanovoltmeter), and a current source (Keithley 2400 Sourcemeter). The percentage of carbon


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black in the ZFO-CB composite films were identified using Thermogravimetric Analysis operated in air atmosphere (Q50, TA Instruments)

Scheme 1: (a) Schematic representation of the synthesis procedure for ZnFe2O4. (b) Schematic representation of the electrophoretic deposition technique used to prepare porous ZFO-CB coatings.

Electrochemical Characterization:

The electrophoretically deposited film on Cu foil was first air dried in hot air oven at 60oC, followed by vacuum drying at 80oC for 24 hrs. 15 mm diameter discs were punched out from the dried films for electrochemical testing (MSK-T06 MTI Corporation). CR2032 lithium-ion halfcells were fabricated in an argon filled glove box (Mbraun), maintained at

Electrophoretically deposited ZnFe2O4-carbon black porous film as a

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