Facile synthesis and electrochemical performance of Mg-substituted Ni1-xMgxCo2O4 mesoporous nanoflakes for energy storage applications

Accepted Manuscript Facile synthesis and electrochemical performance of Mg-substituted Ni1-xMgxCo2 O4 mesoporous nanoflakes for energy storage applications

Meenu Sharma, Shashank Sundriyal, Amrish K. Panwar, Anurag Gaur PII:

S0013-4686(18)32324-7

DOI:

10.1016/j.electacta.2018.10.085

Reference:

EA 32882

To appear in:

Electrochimica Acta

Received Date:

21 February 2018

Accepted Date:

13 October 2018

Please cite this article as: Meenu Sharma, Shashank Sundriyal, Amrish K. Panwar, Anurag Gaur, Facile synthesis and electrochemical performance of Mg-substituted Ni1-xMgxCo2O4 mesoporous nanoflakes for energy storage applications, Electrochimica Acta (2018), doi: 10.1016/j.electacta. 2018.10.085

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ACCEPTED MANUSCRIPT Facile

synthesis

and

electrochemical

performance

of

Mg-substituted

Ni1-xMgxCo2O4 mesoporous nanoflakes for energy storage applications Meenu Sharma1, Shashank Sundriyal2, Amrish K. Panwar3, Anurag Gaur1* 1Department

of Physics, National Institute of Technology, Kurukshetra 136119, India

2CSIR-Central 3Department

Scientific Instrument Organisation (CSIR-CSIO), Chandigarh-160030, India of Applied Physics, Delhi Technological University, New Delhi-110042, India

GRAPHICAL ABSTRACT

Ni0.5Mg0.5Co2O4

Flexible Electrode

ABSTRACT The specific surface area and pore size of illustrative electrode material is a promising task to achieve better performance of energy storage devices. In this respect, Mg-substituted Ni1xMgxCo2O4

(x=0.0, 0.1, 0.2, 0.3, 0.4, 0.5) samples were synthesized by cost-effective and facile

hydrothermal method. As-prepared samples were evaluated as the electrode material for a battery application. The structural and electrochemical characterization analysis has been carried out systematically. Among different samples, NMC50 (x=0.5) exhibit highest BET surface area of 61 m2g-1 with a suitable pore volume of 0.3029 cm3g-1 and narrow pore size distribution of 2−10 nm. It is verified that the special features of the NMC50 including uniformity of the surface texture and porosity bring significant effect on the electrochemical performances. Consequently, the excellent specific capacity of 302 mAhg-1 is observed for NMC50 sample at a current density of 1.1 Ag-1 and a remarkable cyclic stability of ~95% is maintained over 2000 continuous charge-discharge cycles. The improved electrochemical performance of NMC50, undoubtedly makes it worth as an excellent electrode material for high-performance energy storage applications. 1

ACCEPTED MANUSCRIPT Keywords: Mg-substitution, Electrochemical reaction, Battery material, Cyclic stability. *Author to whom correspondence should be addressed. Phone: +91 1744 233496 E-mail: [email protected] 1. Introduction The exhaustion of global energy will soon become unavoidable in the near future at current consumption rates. It is reported that our global energy needs will roughly double by mid-century and triple by 2100. Thus, there has been an ever-increasing and urgent demand for the vigorous development of not only clean, renewable, and sustainable alternative energies (solar, wind, and tide), but also advanced, low-cost, and environmentally friendly energy conversion and storage devices. This satisfies the needs of modern society and emerging ecological concerns while the continuous

advancement

in

electrochemical

energy

storage

(EES)

technology

[1-6].

Electrochemical energy storage technologies, including supercapacitors and lithium-ion batteries, have attracted significant attention for applications such as portable electronics and hybrid electric vehicles (HEVs). Rechargeable batteries have been considered as one of the most capable nextgeneration energy storage devices, because of advances in characteristics such as long cycling life, and higher specific capacity (Cs) [7-10]. Transition metal (Ni, Mn, Co, Ru, etc.) oxides and hydroxides are used as batteries, electrochemical supercapacitors, magnetic devices and gas sensors due to its numerous redox properties, morphologies, structural identities, and higher surface area [11,12]. Recently NiCo2O4, a cobalt– nickel spinel oxide is gaining much attention as one of the most promising electrode material because of its high theoretical capacity, it has been reported that NiCo2O4 has a much higher electrical conductivity and electrochemical performances. Additionally, this binary metal oxide of nickel and cobalt has been regarded as a desirable electrode material due to its high safety, environmental friendliness and relatively higher specific capacity compared to their individual counterparts’ viz. cobalt oxide and nickel oxide. NiCo2O4 has been widely studied as an electrode material for supercapacitors; however, there have been only a few reports on the application of NiCo2O4 as an electrode material for batteries. Generally, the term pseudo-capacitive is used for metal oxide electrodes, whereas these electrodes do not exhibit the linear relationship between potential and current like an ideal capacitor except the RuO2 and MnO2 [13-15]. Therefore, such a non-capacitive faradaic type charge storage process should be excluded from discussions on pseudo-capacitive faradaic processes. Due to the misconception of the term pseudo-capacitance,

2

ACCEPTED MANUSCRIPT these materials are considered as the electrode for supercapacitor, which shows battery like redox process [16]. In this paper, we developed a facile approach to synthesize Mg-doped NiCo2O4 based nanoflakes which can be utilized as a high-performance electrode. In this approach, we have utilized a very simple hydrothermal route in order to prepare Mg-doped NiCo2O4 binary metal oxide, which facilitates the formation of nanoflakes like morphology. This doping and morphology facilitate the physicochemical and electrochemical properties of NiCo2O4 based electrodes. Various optimizations are undergone in this study to obtain the best electrochemical properties by the doping of Mg in NiCo2O4 at Ni site. It is found that 50% Mg-doped (abbreviated as NMC50) among all the synthesized samples show an excellent electrochemical performance in terms of the high specific capacity of 302 mAhg-1 at a current density of 1.1 Ag-1 using 6M KOH as an aqueous electrolyte. Also, the optimized fabricated electrode exhibits an excellent cyclic stability of ~95% even after 2000 continuous charge-discharge cycles. 2. Materials and Methods 2.1 Material synthesis NiCo2O4 and Mg-substituted Ni1-xMgxCo2O4 (x=0.0, 0.1, 0.2, 0.3, 0.4, 0.5) samples were synthesized by the facile hydrothermal method. The entire set of chemicals used in the experiment was of analytical grade and used without further purification. The stoichiometric ratio of Ni(NO3).6H2O, Co(NO3).6H2O and urea was dissolved in 80ml of DI water. After stirring for 1 hour a light pink colour solution is obtained and this solution is sealed in 100ml Teflon lined stainless steel autoclave bottle and heated to 120ºC for 6h. After cooling down to room temperature, precipitates were collected and washed with DI water and ethanol several times and dried in an oven at 80ºC for 10h. The obtained precursors were calcinated in a tubular furnace at 400◦C for 2 hours with a ramping rate of 2ºC min-1 to get the phase of Ni1-xMgxCo2O4 (x=0.0, 0.1, 0.2, 0.3, 0.4, 0.5). The final samples were abbreviated as NC, NMC10, NMC20, NMC30, NMC40 and NMC50 corresponding to x=0.0, 0.1, 0.2, 0.3, 0.4, 0.5 respectively. 2.2 Material Characterization All synthesized samples were characterized using X-ray powder diffractometer (Rigaku, CuKα, =1.54 Å) in the angular range of 2=10-80º with a step scan of 0.02º for phase and crystal structure analysis. The observed XRD data were matched with the JCPDS data (ref 40-1191). The surface morphology of all the samples was studied by Scanning Electron Microscope (SEM) operated at 10kV. The Brunauer Emmett-Teller (BET) surface area measurements were carried out 3

ACCEPTED MANUSCRIPT on a Belsorp Max system from Microtracusing nitrogen gas adsorption/desorption isotherms at room temperature. The FTIR spectra were recorded for determination of the functional group with a Fourier-Transform infrared spectrometer in the range of 1400-500 cm-1.

2.3 Electrode Preparation and Electrochemical Characterization For electrochemical analysis, the working electrodes were prepared by taking 80 wt.% of the synthesized active material, 10 wt.% of activated carbon and 10 wt.% of Polyvinylidene fluoride (PVDF) as a binder in N-methyl 2-pyrrolidone (NMP) as a solvent. To make a homogeneous slurry, precursor mixture was stirred for 2h and the resulting slurry was uniformly coated on (1×1cm2) nickel foil having no oxide layer (cleaned with HCl) using tape casting method. The working electrode is then dried at 600C in a vacuum oven to remove the solvent for 10h and weighed before and after coating. The Electrochemical measurements of as prepared electrodes are carried out at room temperature in a three-electrode configuration using 6 M KOH as an aqueous electrolyte with platinum (Pt) wire and Ag/AgCl as the counter and a reference electrode, respectively. The electrochemical performance of fabricated electrodes is tested using Cyclic Voltammetry (CV) (performed in the potential window of 0-0.6V at different scan rates), Galvanostatic Charge/Discharge (GCD) (at different current densities) and Electrochemical Impedance Spectroscopy (EIS) using AC voltage pulse of 10 mV in the frequency range of 100 kHz-10Hz. All the electrochemical measurements were performed using a Biologic SP-240 potentiostat instrument with EC Lab software. 3. Results and Discussion 3.1 Structural and Morphological Analysis The structure information and the crystal phase of the samples are obtained by XRD measurements. Fig. 1 presents XRD spectra of as-synthesized samples, including bare NiCo2O4 and its doped counterparts. The crystal structure obtained from the XRD pattern confirms the pure phase formation of all samples. There are nine broad peaks corresponding to (111), (2 2 0), (3 1 1), (2 2 2), (4 0 0), (4 2 2), (5 1 1), (4 4 0) and (7 3 1) crystalline planes which have been indexed to the standard pattern of NiCo2O4. No second phase is observed within the limit of the XRD measurement which ensures that there is no impurity phase. The results of XRD patterned for all the samples demonstrate the formation of single phase spinal cubic structure, indicating that Mg was substituted into the crystal lattice of nickel cobaltite. Additionally, it is also observed that 4

ACCEPTED MANUSCRIPT absorption of Mg ion via doping does not affect the crystal structure of NiCo2O4 up to definite concentrations. The crystalline size for Ni1-xMgxCo2O4 (x=0.0, 0.1, 0.2, 0.3, 0.4, 0.5) samples is calculated 𝑘𝜆

using Scherrer formula, 𝛽𝑐𝑜𝑠𝜃 , where β is full width at half maximum (FWHM), k=0.94 is the shape factor, 𝜆 is the wavelength of X-rays, and 𝜃 is Bragg angle. It has been observed that the crystalline size decreases from 32 to 15 nm by increasing doping content from x=0.0 to 0.5. This is attributed due to the difference of atomic radius of Mg ions which may decrease the tendency for the agglomeration and leads to decrease in crystalline size. The decreasing particle size enhances the high surface to volume ratio, which is also being noticed through BET results, presented ahead in this manuscript. The improvement in the surface to volume ratio is a good sign for enhancing the charge storing capacity of this compound. The value of lattice parameter (a=b=c) is varying from 8.192 to 8.114 Å with a doping concentration of Mg from x=0 to 0.5 into the NiCo2O4 structure at the Ni site. Lattice parameter is calculated from XRD by equation (1) 2

2

2

1 ℎ +𝑘 +𝑙 = 2 𝑑2 𝑎

(1)

The unit cell volume has been determined by the formula 𝑉=𝑎

3

(2)

The strain (𝜖) induced peak broadening due to crystal imperfection and distortion are calculated by 𝛽𝑠

(3)

𝜖 = 4𝑡𝑎𝑛𝜃

The structural properties of samples such as crystalline size, lattice strain, lattice parameter, and cell volume have been calculated using the above equations through XRD data and listed in Table 1. Furthermore, lattice parameters are also calculated through Rietveld analysis and reported in Table 1. The scanning electron microscopy (SEM) images of the Mg-doped Ni1-xMgxCo2O4 (x= 0.0, 0.1, 0.3, 0.5) samples are shown in Figure 2. It can be seen from these images that interconnected nanoflakes are uniformly present within the material and agglomeration in the interconnected flakes is decreasing continuously with an increase in the concentration of Mg doping. The morphology of NiCo2O4 nanoflakes Fig. 2 (a-d) indicates the existence of a large number of mesopores as confirmed through BET results also. This helps for better charge storage and improved charge transport of electrolyte ions onto the pores of Mg-doped NiCo2O4 electrode material. 5

ACCEPTED MANUSCRIPT Fig. 3 represents the FT-IR spectra of NiCo2O4 and Ni1-xMgxCo2O4 (x=0.1, 0.2, 0.3, 0.4, 0.5) samples. Two strong peaks have been observed at about 602 and 550 cm−1 in the FT-IR spectra of the synthesized samples corresponds to the stretching vibrations of the Ni-O and Co-O bands, respectively [17] and there is no absorption related to oxygen-containing groups. The nitrogen adsorption and desorption isotherms of the Ni1-xMgxCo2O4 nanoflakes with x=0 and 0.5 are shown in Fig.4 (a) and (c). The N2 adsorption of the pure NiCo2O4 nanoflakes and the NMC50 material shows typical type-IV isotherms surface area profile with a contribution of both micropores and mesopores. The calculated value of the BET surface area and pore volume for NC and NMC50 samples are 50, 61 m2g-1 and 0.3041, 0.3029 cm3g-1, respectively. This result shows that the specific surface area is more for NMC50 samples (61m2g-1) as compared to the NC sample (50 m2g-1). This increase in surface area of NMC50 sample might be attributed to Mg ion doping, which provides better ionic transport and thus able to access more number of mesopores with few micropores. Fig. 4 (b) and (d) displays the pore size distribution using Barrett-JoynerHalenda (BJH) curves (Using Barrett−Joyner−Halenda (BJH) method) which indicates the narrow pore size distribution with an average pore size of (~ 2.5 nm) and (~ 8.1 nm) for NMC50and NC, respectively. It has also been observed, the narrow pore size distribution of NMC50 (~1-10 nm) which further verify the uniform mesoporous surface morphology that will provide large active size for transportation of ions. 3.2 Electrochemical Studies The specific capacity, energy density and power density of the fabricated electrodes are determined using Cyclic Voltammetry (CV) and Galvanostatic Charge Discharge (GCD) measurements. Further, the impedance is evaluated using the Nyquist plot via electrochemical impedance spectroscopy (EIS) and cyclic stability is calculated using GCD curves. 3.2.1 Cyclic Voltammetry studies Fig. 5 (a-d) shows the CV curves of NC, NMC10, NMC30, NMC50 samples at different scan rates of 5, 20, 30, 40 and 50 mVs-1 in the potential window of 0.0-0.6 V using 6M KOH as an aqueous electrolyte. The CV measurements for NiCo2O4 and Mg-doped NiCo2O4 samples show reversible redox reactions in KOH electrolyte. It is clear from fig. 5 that all the CV curves exhibit redox peaks indicating faradaic behaviour. The negligible change in the shape of CV curves is observed, as the scan rate increases from 5 to 50 mVs-1, which indicates the excellent rate capability for all the fabricated electrodes. The anodic and cathodic peaks in the CV curves are due to the oxidation and reduction of the material, which exhibits the redox nature of the samples. With an increase in scan rate, the anodic peak shift towards the higher potential and cathodic peaks shift towards the lower potential side of the curve. The anodic peak shifts from 0.383 to 0.406 V and cathodic peak shifts 6

ACCEPTED MANUSCRIPT from 0.299 V to 0.293V at 5 mVs-1 as we move from NC to NMC50 electrodes, respectively. This peak shift may arise due to the addition of dopant ions or might be due to kinetic irreversibility in the redox process. Further, the broadening of both anodic and cathodic peak at variable scan rates is primarily because of the diffusion controlled charge transfer process [17-19]. Among all four fabricated electrodes, the large area under NMC50 electrode reflects enhanced electrode conductivity. It can be seen that the peak current increases approximately linear with the square root of the scan rate, indicating diffusion controlled faradaic reactions [20, 21]. 3.2.2. Chronopotentiometry/Galvanostatic Charge Discharge (GCD) Studies Galvanostatic charging-discharging analysis has been performed to further examine the electrochemical performance of the fabricated electrode. Fig. 6 (a-d) shows the galvanostatic charge-discharge plots of the four fabricated electrodes, performed at various current densities of 1.1, 1.3, 1.5 and 2 Ag-1 within a potential window of 0-0.43 V using 6M KOH as an aqueous electrolyte. It is seen that all GCD deviate from the predictable triangular shapes with the appearance of clear plateaus in both charge and discharge curves indicating significant faradaic behaviour supporting the observations of CV results [15]. Therefore, gravimetric Specific capacities (Cs) of pristine and Mg-doped samples have been calculated by using following equation applicable for battery type materials [22, 23]. The charging-discharging curves of the samples show voltage plateaus between 2.5 and 3.1 V. Since the discharge time is controlled by the rate of electrolyte ions diffusion rate, the electrochemical performance can be described with their discharge time. The NMC50 electrode exhibits a much longer discharge time than others fabricated electrodes, which can be attributed to increased redox reactions. Further, specific capacity values calculated using Eq. 4 for NC, NMC10, NMC30, and NMC50 electrodes are given in Table 2. 𝐶𝑠 =

𝐼𝛥𝑡 𝑚

(4)

Where I is the discharge current, m is the mass of the active material in gram, and 𝛥𝑡 is the discharge time [24]. The calculated specific capacity values for the pure and Mg-doped NMC10, NMC30, NMC50 samples are 249, 260, 278, 302 mAhg-1, respectively at a constant current density of 1.1 Ag-1. It has been observed from the calculated data that NMC50 electrode exhibits the highest specific capacity at all current densities. This could be due to a large surface area for NMC50 electrode, which is favourable for high specific capacity. Furthermore, the large numbers of mesoporous on the surface of NMC50 electrode are effectively accessible by electrolyte ions and provide better utilization of material. The variation of specific capacity with various current densities for Ni1-xMgxCo2O4 (x=0.0, 0.1, 0.3, 0.5) samples is shown in Fig. 7(a). The higher specific capacity is observed at 1.1 Ag-1 for all the samples and it gradually decreases while increasing the 7

ACCEPTED MANUSCRIPT current density. This is because of the fact that at high current density, electrolyte ions does not get enough time to access all the inner microstructures of the electrode material, and thus the transport of ions is limited (due to their slow diffusion), thus higher utilization of electro-active material in surface redox process is at low current density [25, 26]. It can be seen from the graphs that among the all synthesized samples, NMC50 delivers the highest specific capacity at each current density. The energy efficiency of the electrode in energy storage systems is of crucial importance [26]. It has been seen from figure 7 (b) that the NMC50 attain maximum energy efficiency of about ~ 99 % for NMC50, NMC30, NMC10 and NC at 2 Ag–1 current density. The efficiency decreases at a lower current density where ~ 97 efficiency was observed for 1.1 Ag–1 current density. The decrease in energy efficiency could be due to a slower rate of charge-discharge at low energy density [27]. Beside the above discussions, the cycling stability is a serious issue and long-term retention of capacity is another crucial parameter to confirm the practical applicability of electrodes. Therefore, the cyclic stability test was performed using the Galvanostatic charge/discharge over 2000 cycles for NC and NMC50 samples as shown in Fig. 8 (a). It can be observed from Fig. 8 (a) that the value of a specific capacity for NMC50 decreases from 174 to 160.5 mAhg-1 up to 2000 charge-discharge cycles at a constant current density of 10 Ag-1. Figure 8(b) shows that NMC50 retain 95% of initial capacity even after 2000 continuous charge-discharge cycles, however, NC sample exhibits 92 % capacity retention, which is indicative of a good stability of NMC50 electrode. 3.2.3. Electrochemical Impedance Spectroscopy (EIS) Studies EIS has been performed to further analyze the influence of Mg substitution on the impedance of NiCo2O4 electrode. Fig. 9 shows the Nyquist plot in the frequency range of 100 kHz to 10 Hz with an AC amplitude of 10 mV. In the high-frequency region, the intercept at the real axis represents the solution resistance, which indicates the resistance of the electrolyte and electrode material (Rs). The semicircle observed in the middle-frequency region represents the charge transfer resistance (Rct), which is observed because of the electrochemical reaction occurring at the electrode and electrolyte interface. In the lower frequency range, a straight line corresponds to Warburg impedance is observed because of the solid state-state diffusion process within electrode active material [28-30]. Table 3 compares the Rct and Rs values of the pure and Mg-doped samples. It clearly shows that NMC50 samples have the lowest value of Rct and Rs which indicates the low charge transfer resistance during the redox process. This also points out that electrolyte ions can be easily moved from the bulk solution to the surface of the electrode material, which makes it suitable to be used as an efficient electrode material for energy storage applications. 8

ACCEPTED MANUSCRIPT 4. Conclusions In summary, Pristine NiCo2O4 and Ni1-xMgxCo2O4 (0≤ x≤0.5) samples were successfully synthesized using a facile hydrothermal method. It has been observed that NMC50 sample possess abundant mesoporous of 2-15 nm range, which exhibits superior electrochemical performance with a high specific capacity of 302 mAhg-1 at the current density of 1.1Ag-1 with excellent cycling stability of about 95% over 2000 charge/discharge cycles. The enhanced electrochemical performance of NMC50 could be attributed to mesoporous morphology with high a surface area of 61 m2g-1. The low cost and abundance of metal oxides may render this Mg-doped NiCo2O4 as a promising candidate for high-performance energy storage applications. Acknowledgements Authors thank Director, N.I.T. Kurukshetra to provide the research facilities to accomplish this work. Authors also acknowledge Dr. Akash Deep and Dr. Sunita Mishra from CSIO, Chandigarh for providing BET measurement facility. References: [1] A.K. Mondal, D. Su, S. Chen, K. Kretschmer, X. Xie, H.J. Ahn, G. Wang, A Microwave Synthesis of Mesoporous NiCo2O4 Nanosheets as Electrode Materials for Lithium‐Ion Batteries and Supercapacitors, ChemPhysChem, 16 (2015) 169-175. [2] S. Zhang, N. Pan, Supercapacitors performance evaluation, Advanced Energy Materials, 5 (2015) 1401401. [3] G. Zhang, X.W.D. Lou, General Solution Growth of Mesoporous NiCo2O4 Nanosheets on Various Conductive Substrates as High‐Performance Electrodes for Supercapacitors, Advanced Materials, 25 (2013) 976-979. [4] Q. Wei, F. Xiong, S. Tan, L. Huang, E.H. Lan, B. Dunn, L. Mai, Porous one dimensional nanomaterials: design, fabrication and applications in electrochemical energy storage, Advanced Materials, 29 (2017) 1602300. [5] S. Chu, A. Majumdar, Opportunities and challenges for a sustainable energy future, nature, 488 (2012) 294. [6] S. Sundriyal, M. Sharma, A. Kaur, S. Mishra, A. Deep, Improved electrochemical performance of rGO/TiO 2 nanosheet composite based electrode for supercapacitor applications, Journal of Materials Science: Materials in Electronics, 29 (2018) 12754-12764. [7] A.S. Arico, P. Bruce, B. Scrosati, J.-M. Tarascon, W. Van Schalkwijk, Nanostructured materials for advanced energy conversion and storage devices, Materials For Sustainable Energy: A Collection of PeerReviewed Research and Review Articles from Nature Publishing Group, World Scientific2011, pp. 148-159. [8] H.-J. Qiu, L. Liu, Y.-P. Mu, H.-J. Zhang, Y. Wang, Designed synthesis of cobalt-oxide-based nanomaterials for superior electrochemical energy storage devices, Nano Research, 8 (2015) 321-339. [9] S. Zheng, X. Li, B. Yan, Q. Hu, Y. Xu, X. Xiao, H. Xue, H. Pang, Transition‐Metal (Fe, Co, Ni) Based Metal‐Organic Frameworks for Electrochemical Energy Storage, Advanced Energy Materials, 7 (2017) 1602733. [10] A. Eftekhari, P. Corrochano, Electrochemical energy storage by aluminium as a lightweight and cheap anode/charge carrier, Sustainable Energy & Fuels, 1 (2017) 1246-1264. 9

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ACCEPTED MANUSCRIPT Table and Figure captions Table 1 Variations of lattice parameters, unit cell volume, average crystallite size, lattice strain for NMC50, NMC40, NMC30, NMC20, NMC10 and NC samples. Table 2 Specific capacity values of NMC50, NMC30, NMC10 and NC with a different current density of 1.1, 1.3, 1.5 and 2 Ag-1. Table 3 Variation of Rs and Rct parameters for NC, NMC10, NMC30 and NMC50 samples. Fig. 1. XRD patterns of as-synthsisedNMC50, NMC40,NMC30,NMC20,NMC10 and NC samples. Fig. 2. SEM images of (a) NMC50 (b) NMC30 (c) NMC10 (d) NC samples. Fig. 3. FTIR spectrum of NMC50, NMC40,NMC30,NMC20,NMC10 and NC samples at 530 to 2000 cm−1. Fig. 4. N2 Adsorption-Desorption isotherms of (a) NMC50, (c) NC and Pore size distribution plot of (b) NMC50 (d) NC. Fig. 5. Cyclic voltammetry (CV) curves of (a) NMC50, (b) NMC30, (c) NMC20, (d) NC in potential range of 0-0.6 V at a scan rate from 5-50 mVs-1. Fig. 6. Galvanostatic charging-discharging curves of (a) NMC50 (b) NMC30 (c) NMC10 (d) NC at different current densities (2,3,4,5,6 Ag-1). Fig. 7.(a).Variation of specific capacity of NMC50,NMC30, NMC10 and NC samples at current densities of 1.1,1.3, 1.5,2 Ag-1, (b) Energy efficiency of NMC50, NMC30, NMC10 and NC samples at current density of 1.1, 1.3, 1.5, 2 Ag-1. Fig. 8. (a) The cycling performance of NC and NMC50 at a constant current density of 10 Ag-1 for 2000 cycles, (b) Variation of capacity retention versus cycle number for NC and NMC50 samples. Fig. 9. Nyquist Plot of NMC50, NMC30, NMC10 and NC samples in the frequency range of 1 kHz to 0.1 MHz at ac amplitude of 10 mV.

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ACCEPTED MANUSCRIPT Table 1 Sample Name

𝜷𝑫

Lattice

Crystallize

Lattice

Lattice

Unit Cell

(Degree)

strain

Size (nm)

parameter

parameter

Volume

calculated

calculated

(Å)3

through

through

equation (1)

Rietveld's

(Å)

analysis

(𝝐)

(Å) NC

0.2730

0.0036

~32

8.192

8.1342

549.75

NMC10

0.2814

0.0037

~31

8.245

8.1842

560.49

NMC20

0.3008

0.0040

~29

8.192

8.1327

549.75

NMC30

0.3102

0.0041

~28

8.114

8.0546

534.22

NMC40

0.3224

0.0042

~27

8.114

8.0531

534.22

NMC50

0.6297

0.0068

~ 15

8.114

8.0528

534.22

Table 2 Samples

Specific Capacity (mAhg-1) at different current densities 1.1 A g-1

1.3 A g-1

1.4 A g-1

2 A g-1

NMC50

302

299

292

225

NMC30

278

267

260

200

NMC10

260

254

250

172

NC

249

245

240

165

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ACCEPTED MANUSCRIPT Table 3 Resistance

Electrode Samples

(Ω)

NMC50

NMC30

NMC10

NC

Rct

1.53

1.76

1.98

2.3

Rs

0.82

0.83

0.87

0.93

Figure 1

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ACCEPTED MANUSCRIPT

Figure 2

Figure 3

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ACCEPTED MANUSCRIPT

Figure 4

15

Current (mA)

Current (mA)

Current (mA)

(a) Current (mA)

ACCEPTED MANUSCRIPT

(c)

Figure 5

16

(b)

9 (d)

ACCEPTED MANUSCRIPT

(a)

(b)

Time(s)

Time(s)

(d)

(c) Time(s)

Time(s) Figure 6

(a)

(b)

Figure 7

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ACCEPTED MANUSCRIPT

(a) (a)

Figure 8

Figure 9

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