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Kandhasamy, S., Singh, P., Thurgate, S., Ionescu, M., Appadoo,

D. and Minakshi, M. (2012) Olivine-type cathode for rechargeable batteries: Role of chelating agents. Electrochimica

Acta, 82 . pp. 302-308

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Accepted Manuscript

Title: Olivine-type cathode for rechargeable batteries: role ofchelating agents

Authors: Sathiyaraj Kandhasamy, Pritam Singh, StephenThurgate, Mihail Ionescu, Dominique Appadoo, ManickamMinakshi

PII: S0013-4686(12)00949-8DOI: doi:10.1016/j.electacta.2012.05.129Reference: EA 18830

To appear in: Electrochimica Acta

Received date: 12-12-2011Revised date: 29-5-2012Accepted date: 29-5-2012

Please cite this article as: S. Kandhasamy, P. Singh, S. Thurgate, M. Ionescu, D.Appadoo, M. Minakshi, Olivine-type cathode for rechargeable batteries: role ofchelating agents, Electrochimica Acta (2010), doi:10.1016/j.electacta.2012.05.129

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dx.doi.org/doi:10.1016/j.electacta.2012.05.129dx.doi.org/10.1016/j.electacta.2012.05.129

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Olivine-type cathode for rechargeable batteries: role of chelating agents Sathiyaraj Kandhasamy1, Pritam Singh1, Stephen Thurgate2, Mihail Ionescu3, Dominique

Appadoo4, Manickam Minakshi1*

1Faculty of Minerals and Energy, Murdoch University, Murdoch, WA 6150, Australia

2Faculty of Science, Macquarie University, Sydney, NSW 2109, Australia

3Institute of Environmental science, ANSTO, Lucas Heights, NSW 2234, Australia 4Australian Synchrotron Company Ltd., Blackburn Road, Clayton, VIC 3168, Australia

Abstract

Olivine (LiCo1/3Mn1/3Ni1/3PO4) powders were synthesised at 550 – 600 °C for 6 h in air

by a sol-gel method using multiple chelating agents and used as a cathode material for

rechargeable batteries. Range of chelating agents like a weak organic acid (Citric acid - CA),

emulsifier (Triethanolamine - TEA) and non-ionic surfactant (Polyvinylpyrrolidone - PVP) in

sol-gel wet chemical synthesis were used. The dependence of the physicochemical properties of

the olivine powders such as particle size, morphology, structural bonding and crystallinity on the

chelating agent was extensively investigated. Among the chelating agents used, unique cycling

behavior (75 mAh/g after 25 cycles) is observed for the PVP assisted olivine. This is due to

volumetric change in trapped organic layer for first few cycles. The trapped organic species in

the electrode - electrolyte interface enhances the rate of lithium ion diffusion with better capacity

retention. In contrast, CA and TEA showed a gradual capacity fade of 30 and 38 mAh/g

respectively after multiple cycles. The combination of all the three mixed chelating agents

showed an excellent electrochemical behavior of 100 mAh/g after multiple cycles and the

synergistic effect of these agents are discussed.

Keywords: Olivine; sol-gel synthesis; chelating agents; aqueous battery.

E-mail: [email protected]; [email protected]

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1. IntroductionThe reversible Li+ extraction/insertion behavior in olivine phosphates and its suitability

as a cathode material in rechargeable battery was first demonstrated by Padhi et al. in 1997 [1].

However, the low electrical conductivity and lack of suitable high voltage electrolytes, limits the

olivine phosphates for high energy applications [1-2]. Further, lithium-ion battery that uses non-

aqueous solvents as an electrolyte has safety concerns due to their highly toxic and flammable

organic solvents. Aqueous rechargeable batteries may solve the safety problem associated with

the currently available lithium-ion batteries and the poor cycling life associated with lead-acid

and nickel-metal hydride systems. Recently, we showed [3-4] LiOH aqueous electrolyte found to

be an alternate to perform the electrochemical behavior of olivine cathodes. It was reported [5]

that the electrical conductivity of the olivine can be improved and is strongly dependent on the

synthetic method of the materials that influences superior physical properties i.e. smaller particle

size, conductive coatings and transition-metal ion doping.

Considerable improvements have been made in the preparation of high-performance

materials that includes the use of preparation methods like hydrothermal [6], co-precipitation [7],

and microwave-assisted [8] that yield narrow particle size distribution, unique morphology,

enhanced conductivity and lower calcination temperature. Among the synthesis methods, sol-gel

method can produce particles in smaller size with homogeneous distribution, good stoichiometric

control and in-situ carbon coatings [9]. Sol-gel method is a wet chemical synthesis in which

chelating agents form a percolated homogeneous metal matrix, yielding well crystalline particles

of reduced size. Above the decomposition temperature, the chelating agent decomposes and the

carbon atoms appear as residual carbon to form carbon composites. This simple method can

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produce homogenous powders of increased surface area that enhance the performance of the

electrochemical activity of the battery [9-10].

Although a variety of organic solvents and polymers are available as chelating agents,

citric acid (CA) was widely used as chelating agent due to its carboxylic group [10]. During

gelation, it is believed that CA provides a strong bonding with the metal ion through its

carboxylic group that led to obtain a homogeneous precursor gel with finer particle size. But the

degradation of CA during synthesis leave randomly coated residual carbon over the cathode that

does not show any superior quality in terms of electrochemical performance to that of the

uncoated cathode [11]. In this context, the chelating agents like triethanolamine (TEA) and

polyvinylpyrrolidone (PVP) have unique properties [11-13]. One of the unique properties of

TEA is the presence of nitrogen atoms which act as a fuel in producing internal heat and

performs a combustion reaction. The resulted heat accelerates remarkably the decomposition of

the remaining constituents that results in smaller particle size with higher crystallinity [12]. In

the case of PVP, the unique strong pyrrolidine ring (with nitrogen and carbon atoms) in PVP

decomposes and forms a new organic trap over the material that increases the conductivity of the

olivine [11, 13]. Hence, the physicochemical properties of olivine powders strongly depend on

the chelating agent used in the sol-gel method. This prompted us to investigate this range of

chelating agents and to determine their role in achieving a higher energy density battery in a safe

environment using aqueous electrolyte.

With this as an objective, in this paper, the olivine phosphate containing mixed transition

metal cations i.e. LiCo1/3Mn1/3Ni1/3PO4 was synthesized by a sol-gel method using a range of

chelating agents. The chelating agents used in this study are Citric acid (CA), Triethanolamine

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(TEA), Polyvinylpyrrolidone (PVP) and a mixture of these three agents in equal ratio (33.3)

(CA+TEA+PVP). The interest of this work is to investigate the influence and synergistic effect

of chelating agents to the physicochemical properties and electrochemical behaviour (cyclic

voltammetry and charge-discharge characteristics) of olivine phase LiCo1/3Mn1/3Ni1/3PO4

synthesized by sol-gel route. The battery was constructed with the synthesized composite

cathode and zinc anode using LiOH electrolyte.

2. Experimental

2.1.MaterialsandSynthesis

LiCo1/3Mn1/3Ni1/3PO4 was synthesized from stoichiometric precursors containing Lithium

acetate, Cobalt acetate, Manganese acetate, Nickel acetate, Ammonium dihydrogen phosphate

and chelating agents (citric acid, triethanolamine, polyvinylpyrrolidone). All chemicals were

purchased from Sigma Aldrich. Primarily, the metal and phosphate reactants were dissolved in

water at 80°C with an effective stirring to obtain a homogeneous solution. Then the chelating

agent was added in 1:1 weight ratio to the metal ions. In the case of CA, PVP and mixed

chelating agents, pH of the solution was adjusted to 3.5. The process of stirring and heating were

continued until getting a thick transparent gel and the gel was dried at 110°C in a hot air oven for

12 h. Then, the precursors were heated at 300oC for 8 h and 550oC for 5 h (600oC for 5 h in PVP

sol-gel alone) with an intermediate grinding. The olivine phase LiCo1/3Mn1/3Ni1/3PO4 powder

obtained was collected and ground. All the synthesized LiCo1/3Mn1/3Ni1/3PO4 powders were

subjected to systematic physical and electrochemical studies.

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2.2.Instrumentalmethods

Thermogravimetric analysis (TGA) and differential scanning calorimetry (DSC) studies for

the precursors were conducted using a TA instruments (SDT 2960). The structural determination

of all the synthesized LiCo1/3Mn1/3Ni1/3PO4 was done by Siemens D500 X-ray diffractometer

5635 using Cu-Ka radiation and a scan speed of 1 degree per minute. The FTIR spectrum was

recorded in transmittance at the Australian Synchrotron using IR synchrotron radiation as the

source coupled to an IFS 125/HR spectrometer. LiCo1/3Mn1/3Ni1/3PO4 (5 mg) powder was mixed

with KBr (95 mg) powder for these FTIR transmission studies. The surface analysis of the

materials was conducted using a scanning electron microscope (Philips Analytical XL series 20).

Elemental concentration of the olivine powders were analyzed through proton induced x-ray

emission (PIXE) and proton induced Gamma-ray emission (PIGE) techniques for elements

heavier than Al, and lighter than Al, respectively, with both techniques being non-destructive

[14]. This ion beam measurement was performed at ANSTO using the 2 MV tandem ion beam

accelerator with 2.6 MeV protons.

2.3.Electrochemicalmeasurements

An EG&G Princeton Applied Research Versa Stat III model was used to scan the potential

at 25 μV/s in all cyclic voltammetric (CV) experiments. The standard reference electrode was

Hg/HgO purchased from Koslow Scientific. The cell design and its experimental procedures for

the galvanostatic and slow scan cyclic voltammetric studies were made in a similar way to that

described in our earlier report [15]. An electrochemical cell was constructed with a disk-like

pellet of cathode (pellet was prepared by mixing 75 wt. % synthesized material, 15 wt. %

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acetylene black (A-99, Asbury, USA) and 10 wt. % poly (vinylidene difluoride) (Sigma Aldrich)

binder), metallic zinc foil as anode and whatman filter paper as separator. The electrolyte was a

saturated solution of lithium hydroxide (LiOH) containing 1 molL-1 zinc sulphate (ZnSO4) with a

pH equal to 10.5. For galvanostatic experiments, the cell was discharged/ charged

galvanostatically at a constant current of 0.2 mA (on mass density 8 mA/g) using an 8 channel

battery analyzer from MTI Corp., USA, operated by a battery testing system (BTS).

3.ResultsandDiscussion

3.1. Structural,morphological characterizations and elemental analysis ofas‐

preparedLiCo1/3Mn1/3Ni1/3PO4cathodematerial

Fig. 1 shows the TGA/DSC curves of the olivine LiCo1/3Mn1/3Ni1/3PO4 precursors. The

TGA curves (Fig. 1a) for all set of precursors with different chelating agents shows major weight

loss only in the region between 150 and 450°C. The TG curves show a weight loss mechanism of

a fairly similar fashion for all the chelating agents but the DSC curves displayed (Fig. 1b) are

very different illustrating thermal sequences with endothermic and exothermic peaks in this

region which strongly depend on the chelating agent used. For CA sample the weight loss region

extending up to 405°C may be ascribed to the decomposition of CA benzene ring (six carbon

atoms) and the formation of the olivine compound, which is displayed by the predominant

exothermic peak observed [13, 16] in the DSC profile around 400oC. Small endothermic peak in

the region 150 to 250°C for all samples is attributed to the release of physically adsorbed water

from the precursor mix and ammonia as by-product [17]. The CA and PVP samples show only

the exothermic peaks, whereas TEA sample shows two endothermic peaks at 350°C and 425°C.

This is ascribed to the nitrogen atom present in TEA that functions as a fuel in producing internal

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heat and combustion reaction. In the case of PVP sample, although an exothermic peak is seen at

lower temperature (350°C) than that observed for CA sample, the strong pyrrolidone ring in PVP

with nitrogen atom was not decomposed up to 450°C. The DSC curve for the mixed chelating

agents shows the synergetic effect in the thermal behavior, which has well pronounced

endothermic peaks at lower temperature (180 and 220°C), and was attributed to the release of

ammonia and physically adsorbed water. A sharp exothermic peak observed at 310°C is due to

decomposition of acetate precursor and a broad exothermic peak at 450°C is due to the

decomposition of carbon atom and combustion of nitrogen atoms in chelating agents. However,

this exothermic peak at 450°C is broad and extends up to 600°C, but no significant weight loss

was found in TGA curve beyond 410°C, and this is ascribed to a reorganization of the crystal

lattice [5]. The flattening of the DSC curve indicates the thermal reaction was completed after

the formation of olivine phase compounds.

Fig. 2 shows the XRD patterns of sol-gel synthesized olivine LiCo1/3Mn1/3Ni1/3PO4 phase

compound containing all different chelating agents. All the observed XRD peak reflections can

be assigned to a pure phase with olivine-type orthorhombic structure Pmna (JCPDS: 01-085-

0002). A small peak split was observed in all the major peak reflections for PVP and mixed

chelating agents samples, but no additional impurity peaks were observed. The polymer ligand

and metal ion complex formation depends on the oxidation state and ionic radii of the metal

cation substitution. As Co, Ni and Mn are in the same oxidation state (2+), the complex

formation depends on the ionic radius [18]. Here, Co and Ni have smaller ionic radii than the Mn

ion and a smaller ionic radius can facilitate faster interaction with the polymer and hence the

peak splitting can be related to the Mn bigger ionic radius i.e. LiMnPO4 phase. This peak

splitting and absence of any other phase than olivine confirms the resultant crystal was pure

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phase with small lattice tilt without affecting the solid phase [19, 20]. This peak splitting was not

observed for CA and TEA precursors this may be due to the nature of the gel formation.

The FT-IR spectra of sol-gel derived olivine LiCo1/3Mn1/3Ni1/3PO4 phase compound are

shown in Fig. 3. IR spectral bands have been observed at wavelengths around 500 cm-1 and 650

cm-1 for the fundamental modes of PO43- vibrations [21, 22] that are ascribed to the Li–O

bending vibration and Li– M (metal cations) – O stretching vibration, respectively. A few minor

differences are observed between the spectra due to the effect of chelating agents. The IR

spectral band observed at 642 cm−1 for PVP is a well resolved doublet, whereas, this is not well

identified for other chelating agents. On a closer examination, a small decrease in intensity and

band broadening for the spectral band at 510 cm−1 to 460 cm−1 are observed respectively for CA

and mixed chelating agents samples. The difference observed in the stretching mode for PVP

suggests the presence of a trapped organic layer in the local structure [22]. The low energy

spectral bands at below 530 cm−1 is due to the symmetrical bending modes and Li+ lattice

vibrations, and the change in the band intensity for CA and mixed chelating agents are attributed

to differences seen in cation mixing and particle size.

Fig. 4 shows the microstructural (SEM) images of synthesized olivine

LiCo1/3Mn1/3Ni1/3PO4 powders. The SEM analyses show the nature of the chelating agents in

good stoichiometric control and production of smaller sized particles. It is clear that the size of

the obtained powder with CA as precursor is about 10-12 µm. It shows a large particle size with

inhomogeneous particles distribution. However, with TEA as precursor, the size of particles was

reduced dramatically to 1-2 µm. It seems that the introduction of TEA in the sol-gel process is

helpful due to increased amount of combustion heat the obtained product resulted in finer

particles with even size distribution. The smaller particle size of the LiCo1/3Mn1/3Ni1/3PO4 with

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TEA means the shorter diffusion distance for lithium ions. For PVP as a chelating agent, the

precursor decomposes and forms as a trapped organic layer over LiCo1/3Mn1/3Ni1/3PO4 and

provides a strong contact between the subsequent particles (agglomeration) and improves

conductivity between the particle to particle contacts [11]. Hence, a diverse range of properties

such as residual carbon (for CA), fine particles (for TEA) and organic trap layer (for PVP) are

observed for the chelating agents. This clearly shows that the physicochemical properties of the

synthesized material strongly depend on the chelating agent chosen. To avail these entire merits

in a single cathode material, LiCo1/3Mn1/3Ni1/3PO4 was synthesized with all of these chelating

agents in an equivalent ratio (0.33). As expected the LiCo1/3Mn1/3Ni1/3PO4 synthesized by mixed

chelating agents (CA+TEA+PVP) shows unique morphology comprising of sub-micron particles

size, uniform particle size distribution, a low degree of agglomeration, with a primary particle

size of ≤ 3 µm. This conclusion is also confirmed by the particle size distribution histogram (Fig.

5) for the samples synthesized with a range of chelating agents. The histogram for the multiple

chelating agents showed a narrow particle distribution with particle size of around 3 µm. The

elemental concentration was evaluated by proton induced x-ray and Gamma-ray emission (PIXE

and PIGE) analysis (Fig. 6) for the synthesized olivine powders. These techniques are capable of

multi-elemental analysis for samples with a minimum detectable concentration of parts per

million (ppm). Nearly equal amount of element concentrations (in Fig. 6) of the transition metal

cations (Co; Ni and Mn) confirm the stoichiometric ratio is preserved for all the chosen chelating

agents in performing homogeneous matrix formation. The mixed chelating agents shows the

highest homogenous distribution of the transition metals in the preferred olivine phase as

compare with the distribution of the transition metals for the synthesis with individual chelating

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agents CA, TEA or PVP. Since the atomic distribution depends on the particle size, higher

concentration was observed for CA due to larger particle size [23].

3.2.ElectrochemicalcharacterizationofLiCo1/3Mn1/3Ni1/3PO4electrode

The reduction/oxidation mechanisms of the synthesized olivine LiCo1/3Mn1/3Ni1/3PO4

powders were investigated by slow scan cyclic voltammetry (CV) in the voltage range from 0.2

to -0.4 V vs. Hg/HgO. In fig. 7, presence of redox peaks (A1 and C1) for all the samples

confirms the reversible redox behaviour (Li+ extraction/insertion) of the synthesized cathode in

aqueous LiOH electrolyte and the peaks A2 and C2 are due to proton/hydrated H2O intercalation

[4]. As seen from the cyclic voltammetry experiments, electrochemical properties are strongly

depending on the chelating agents used. Hence, influence of these chelating agents is not only

seen in particle morphology but also in the reduction/oxidation behaviour. The shifts observed in

redox peak positions are related to difference in cation matrix formation, degree of crystallinity

and lattice parameters. The CA and TEA samples showed broad oxidation peaks, but the

reduction peak in CA was not well defined as in TEA, and this indicates that a lower amount of

Li+ are re-inserted back into the olivine structure, due to larger particle size observed in CA. The

peaks C1 and C2 are merged in the TEA sample indicating lithium and proton/hydrated H2O

insertion are inseparable and the exact identification of these peaks is more complex. In the case

of PVP sample, narrow and well defined oxidation/reduction peaks are observed. This excellent

performance could be due to the improvement in the electrolyte-electrode interface via the

trapped organic layer. The broader oxidation peak of CA and TEA cathodes showed a larger

number of Li ions are extracted during oxidation than from the PVP cathode. To utilize all these

advantages, CA and TEA along with the unique behavior of PVP, olivine LiCo1/3Mn1/3Ni1/3PO4

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cathode was synthesized for the first time in combining all these chelating agents. As expected,

cathode synthesized by mixed chelating agents (CA+TEA+PVP) resulted in broad and well

defined redox peaks which are attributed to the synergistic effect of all these additives.

The typical charge-discharge characteristics and its trend in discharge capacities upon

multiple cycles for all the synthesized cathodes are shown in Figs. 8-9. The charge-discharge

curves are characterized by one charged plateau and two discharged plateaus are identified in

Fig. 8. The lower discharged plateau around 1.0 V is not well accessed for CA and TEA as

chelating agents and hence the poor capacity. While for PVP and mixed chelating agents the

plateau is quite long implying the insertion/de-insertion behavior is improved. Unusual charge-

discharge behavior and the increase in specific capacity upon cycling, was observed for PVP

(from 64 to 75 mAh/g) and for mixed chelating agents (from 69 to 100 mAh/g) cathodes upon

successive cycling. A similar trend of charge-discharge behavior was also observed in the

literature for PPy/LiFePO4 composite [24] using non-aqueous solvents as an electrolyte. It is

reported in the literature that this unique behavior is observed due to the change in volume of

trapped polymer layer for an initial oxidation and then the structure is stabilized [24]. Also,

Sasaki et al [25] reported that the trapped organic between electrode-electrolyte interface

increase the lithium ion diffusion rate with better capacity retention. The direct evidences of

trapped polymer layer formations in PVP are reported by the authors in a separate publication

[26]. On the other hand, chelating agents CA (from 40 to 30 mAh/g) and TEA (from 68 to 38

mAh/g) cathodes showed drastic loss of 23 % and 45 % in their capacities respectively on

subsequent cycles. The inhomogeneous particle distribution and random carbon coating are

attributed to a poor capacity for CA cathode. Very fine particles caused by an additional

combustion heat and its low conductivity led to a severe capacity fade for TEA cathode. In the

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case of combining all the three chelating agents within one compound, the mixed performances

(synergistic effect) of CA, TEA and PVP resulted in an improved discharge capacity of 30 %

increment with high capacity retention after the 25th cycle than the PVP cathode by itself. The

oxidation of the trapped organic species leads to volumetric changes, allowing for effective

electrolyte penetration into the bulk cathode, thereby increasing the ionic conductivity and hence

the unusual enhanced electrochemical performance is seen in Fig. 9. This is reflected in

increasing capacity during multiple cycling. The role of anodic zinc dissolution in aqueous LiOH

solution during electrochemical discharge /charge cycles is reported by us earlier [27] which

could inhibit the cycleability. To be suitable for practical applications, further work is needed to

improve the specific capacity together with the cycle life of the olivine cathode mixed with all

the three chelating agents (CA+ TEA+ PVP).

4.Conclusions The influence of chelating agents in synthesizing olivine LiCo1/3Mn1/3Ni1/3PO4 cathodes

in rechargeable battery was investigated via sol-gel route. The battery was fabricated with

synthesized cathodes, Zn anode and aqueous LiOH as electrolyte. A diverse range in properties

such as residual carbon (for CA), fine particles (for TEA) and organic trap layer (for PVP) are

observed for the chelating agents. The physical and electrochemical properties of the olivine

powders strongly depend on the chelating agent used in the sol-gel method. The low degree of

agglomeration and the organic trapped layer are the key issues attained by PVP as chelating

agent that lead to enhanced electrochemical behavior. In the case of CA and TEA a quick fade in

capacity was observed upon cycling, 23 % and 45 % loss respectively, although a larger amount

of lithium was extracted from the structure. For the mixed chelating agents, a synergistic effect

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of all these additives (CA+TEA+PVP; 0.33 ratio) led to an excellent electrochemical behavior of

100 mAh/g after successive cycling.

Acknowledgements

The author (M. M) wishes to acknowledge the Australian Research Council (ARC). This

research was supported under Australian Research Council (ARC) Discovery Project funding

scheme (DP1092543). The views expressed herein are those of the author (M. M) and are not

necessarily those of the ARC. M. M. would also like to thank the Australian Institute of Nuclear

Science and Engineering (AINSE) for providing financial assistance (Award 11133) for access to

Ion beam analysis at ANSTO. The Infrared analysis was undertaken in the FRIR beamline at the

Australian Synchrotron, Victoria, Australia through the grant no. AS113/HRIR 4065.

References

[1] A.K. Padhi, K.S. Nanjundaswamy, J.B. Goodenough, J. Electrochem. Soc. 144 (1997) 1188.

[2] M. Minakshi, P. Singh, N. Sharma, M. Blackford, M. Ionescu, Ind. Eng. Chem. Res. 50

(2011) 1899.

[3] M. Minakshi, P. Singh, D. Appadoo, D.E. Martin, Electrochim. Acta. 56 (2011) 4356.

[4] M. Minakshi, A. Pandey, M. Blackford, M. Ionescu, Energy & Fuels 24 (2010) 6193.

[5] A.F. Liu, Z.H. Hu, Z.B. Wen, L. Lei, J. An, Ionics 16 (2010) 311.

[6] H. Nakano, K. Dokko, S. Koizumi, H. Tannai, K. Kanamura, J. Electrochem. Soc. 155

(2008) A909.

[7] D. Shanmukaraj, R. Murugan, Ionics 10 (2004) 88.

of 26

Acce

pted

Man

uscr

ipt

14

[8] A. Vadivel Murugan, T. Muraliganth, P.J. Ferreira, A. Manthiram, Inorg. Chem. 48 (2009)

946.

[9] J. Yang, J. J. Xu, J. Electrochem. Soc. 153 (2006) A716.

[10] H. Liu, Y.P. Wu, E. Rahm, R. Holze, H.Q. Wu, J. Solid State Electrochem. 8 (2004) 450.

[11] S.H. Lim, J. Cho, Electrochem. Commun. 10 (2008) 1478.

[12] S. Soltanmohammad, S. Asgari, J. Nanomater. 2010 (2010) 104012.

[13] Y.K. Du, P. Yang, Z.G. Mou, N.P. Hua, L. Jiang, J. Appl. Polym. Sci. 99 (2006) 23.

[14] R. Siegele, A.G. Kachenko, M. Ionescu and D.D. Cohen, Nucl. Instr. and Meth. B 267

(2009) 2054.

[15] M. Minakshi, Electrochim. Acta. 55 (2010) 9174.

[16] V. Koleva, E. Zhecheva, R. Stoyanova, Eur. J. Inorg. Chem. 2010 (2010) 4091.

[17] V.M. Bogatyrev, N.V. Borisenko, V.A. Pokrovskii, Russ. J. App. Chem.74 (2001) 839.

[18] N. Pekel, O. Guven, Colloid Polym. Sci. 277 (1999) 570.

[19] R.S. Okojie, T. Holzheu, X.R. Huang, M. Dudley, Appl. Phys. Lett. 83 (2003) 1971.

[20] T. Nagasaki, K. Kok, A.H. Yahaya, N. Igawa, K. Noda, H. Ohno, Solid State Ionics

96 (1997) 61.

[21] M. Minakshi, N. Sharma, D. Ralph, D. Appadoo, K. Nallathamby, Electrochem.

Solid-State Lett. 14 (2011) A86.

[22] N.S. Norberg, R. Kostecki, Electrochim. Acta. 56 (2011) 9168.

[23] A.P. Marques, M.C. Freitas, H.T. Wolterbeek, T.G. Verburg, J.J.M. De Goeij, Nucl.

Instr. and Meth. B 255 (2007) 380.

[24] K.S. Park, S.B. Schougaard, J.B. Goodenough, Adv. Mater. 19 (2007) 848.

of 26

Acce

pted

Man

uscr

ipt

15

[25] H. Sasaki, K. Takada, T. Inada, A. Kajiyama, S. Kondo, M. Watanabe, J. Power

Sources 119-121 (2003) 774.

[26] S. Kandhasamy, A. Pandey and M. Minakshi, Electrochim. Acta 62 (2010) 170.

[27] M. Minakshi, D. Appadoo and D. E. Martin, Electrochim. Solid State let. 13 (2010)

A77.

of 26

Acce

pted

Man

uscr

ipt

16

Figure Captions

Fig. 1 Thermogravimetric and differential scanning calorimetry analysis (TG/DSC) of

LiCo1/3Mn1/3Ni1/3PO4 olivine precursors with chelating agents (CA, TEA, PVP and

CA+TEA+PVP; 0.33 ratio).

Fig. 2 XRD diffraction patterns of as-synthesized olivine LiCo1/3Mn1/3Ni1/3PO4 powders with

chelating agents (CA, TEA, PVP and CA+TEA+PVP; 0.33 ratio).

Fig. 3 Far-IR spectra (using synchrotron source) of as-synthesized olivine LiCo1/3Mn1/3Ni1/3PO4 powders with chelating agents (CA, TEA, PVP and CA+TEA+PVP; 0.33 ratio).

Fig. 4 Scanning electron micrographs of as-synthesized olivine LiCo1/3Mn1/3Ni1/3PO4 powders

with chelating agents (CA, TEA, PVP and CA+TEA+PVP; 0.33 ratio).

Fig. 5 Particle size distribution histogram of as-synthesized olivine LiCo1/3Mn1/3Ni1/3PO4 powders


Fig. 6 Concentration of elements present in the as-synthesized olivine LiCo1/3Mn1/3Ni1/3PO4 powders with chelating agents (CA, TEA, PVP and CA+TEA+PVP; 0.33 ratio) determined by

PIXE technique.

Fig. 7 Cyclic voltammogram of as-synthesized olivine LiCo1/3Mn1/3Ni1/3PO4 powders with

chelating agents (CA, TEA, PVP and CA+TEA+PVP; 0.33 ratio) in LiOH electrolyte. Potential

scanned at 25 µV.s-1 from + 0.2 to - 0.35 V and back.

Fig. 8 Typical charge-discharge characteristics of as-synthesized olivine LiCo1/3Mn1/3Ni1/3PO4 cathodes with chelating agents (CA, TEA, PVP and CA+TEA+PVP; 0.33 ratio) in LiOH

electrolyte.

Fig. 9 Discharge capacities of as-synthesized olivine LiCo1/3Mn1/3Ni1/3PO4 cathodes with

chelating agents (CA, TEA, PVP and CA+TEA+PVP; 0.33 ratio) in aqueous battery upon

successive cycling at a constant current 0.2 mA.

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100 200 300 400 500 600 7000

20

40

60

80

100

CA TEA PVP CA+TEA+PVP

TGA

Temperature / οC

Wei

ght (

%)

100 200 300 400 500 600 700

250

125

0

-125

-250

Temperature / ο

C

Hea

t Flo

w /

mW

Endo

CA TEA PVP CA+TEA+PVP

DSC

Fig. 1 Thermogravimetric and differential scanning calorimetry analysis (TG/DSC) of

LiCo1/3Mn1/3Ni1/3PO4 olivine precursors with chelating agents (CA, TEA, PVP and

CA+TEA+PVP; 0.33 ratio).

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15 20 25 30 35 4022

110

200

2121

311

3010

20111

01121

0

101

200

2θ / degree

CA

TEA

PVP

Inte

nsity

/ a.

u.

CA+TEA+PVP

Fig. 2 XRD diffraction patterns of as-synthesized olivine LiCo1/3Mn1/3Ni1/3PO4 powders with

chelating agents (CA, TEA, PVP and CA+TEA+PVP; 0.33 ratio).

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750 700 650 600 550 500 450 400

CA+TEA+ PVP

PVP

TEA

Tra

nsm

ittan

ce /

a.u.

Wavenumber / cm-1

CA

Fig. 3 Far-IR spectra (using Synchrotron source) of as-synthesized olivine LiCo1/3Mn1/3Ni1/3PO4

powders with chelating agents (CA, TEA, PVP and CA+TEA+PVP; 0.33 ratio).

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Fig. 4 Scanning electron micrographs of as-synthesized olivine LiCo1/3Mn1/3Ni1/3PO4 powders


CA TEA

PVP CA+TEA+PVP

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Size / μm

CA

TEA

PVP 0 50 100 150 200 250 300

CA+TEA+PVP

Fig. 5 Particle size distribution histogram of as-synthesized olivine LiCo1/3Mn1/3Ni1/3PO4 powders


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CA TEA PVP CA+TEA+PVP0

50

100

150

200

Mas

s per

uni

t are

a / µ

g cm

-2

Elements present in Olivine compound

Li P Mn Co Ni

Fig. 6 Concentration of elements present in the as-synthesized olivine LiCo1/3Mn1/3Ni1/3PO4

powders with chelating agents (CA, TEA, PVP and CA+TEA+PVP; 0.33 ratio) determined by

PIXE technique.

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-0.001

0.000

0.001

0.002

-0.4 -0.3 -0.2 -0.1 0.0 0.1 0.2

-0.001

0.000

0.001

0.002

-0.4 -0.3 -0.2 -0.1 0.0 0.1 0.2

A2

A1

C2

CA

C1

A1 TEA

C1

A2

A1

C2

Cur

rent

/ A

PVP

C1

A2

A1

C2

Potential vs. Hg/HgO / V

CA+TEA+PVP

C1

Fig. 7 Cyclic voltammogram of as-synthesized olivine LiCo1/3Mn1/3Ni1/3PO4 powders with

chelating agents (CA, TEA, PVP and CA+TEA+PVP; 0.33 ratio) in 5 M LiOH electrolyte.

Potential scanned at 25 µV.s-1 from + 0.2 to - 0.35 V and back.

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0 20 40 60 80 1000.0

0.5

1.0

1.5

2.0

Discharge

Cel

l pot

entia

l / V

Specific capacity / mAh g-1

Charge

125

CA

0 20 40 60 80 1000.0

0.5

1.0

1.5

2.0

25Discharge

Cel

l pot

entia

l / V


Charge TEA

1

0 20 40 60 80 1000.0

0.5

1.0

1.5

2.0

Discharge

Cel

l pot

entia

l / V


ChargePVP

1 25

0 20 40 60 80 1000.0

0.5

1.0

1.5

2.0

25

Discharge

Cel

l pot

entia

l / V


ChargeCA+TEA+PVP

1

Fig. 8 Typical charge-discharge characteristics of as-synthesized olivine LiCo1/3Mn1/3Ni1/3PO4

cathodes with chelating agents (CA, TEA, PVP and CA+TEA+PVP; 0.33 ratio) in LiOH

electrolyte

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0 5 10 15 20 250

20

40

60

80

100CA+TEA+PVP

PVP

TEA

Dis

char

ge c

apac

ity /

mA

h g-

1

Cycle Number

CA

Fig. 9 Discharge capacities of as-synthesized olivine LiCo1/3Mn1/3Ni1/3PO4 cathodes with

chelating agents (CA, TEA, PVP and CA+TEA+PVP; 0.33 ratio) in aqueous battery upon

successive cycling at a constant current 0.2 mA.

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Research Highlights

Olivine phosphate containing mixed transition metal cations i.e. LiCo1/3Mn1/3Ni1/3PO4 was synthesized by a sol‐gel method for the first time using a range of chelating agents.

The role of chelating agents in synthesizing olivine LiCo1/3Mn1/3Ni1/3PO4 cathodes in rechargeable battery was investigated.

The battery was fabricated with synthesized cathodes, Zn anode and aqueous LiOH as electrolyte.

Synergistic effect of all the additives (CA+TEA+PVP; 0.33 ratio) led to an excellent electrochemical behaviour of 100 mAh/g after successive cycling.

Cover page author's versionolivine-type cathode for rechargeable batteries

murdoch research repository · 2013. 2. 12. · and microwave-assisted [8] that yield narrow...

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