Characteristics of LiNi 1/3 Co 1/3 Mn 1/3 O 2 Cathode Powder Prepared by Different Method in Lithium Rechargeable Batteries

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1 Int. J. Electrochem. Sci., 3 (28) Interntionl Journl of ELECTROCHEMICAL SCIENCE Chrcteristics of LiNi 1/3 Co 1/3 Mn 1/3 O 2 Cthode Powder Prepred by Different Method in Lithium Rechrgeble Btteries Sung-Keun Kim 1, Woon-Te Jeong 2, Hong-Ki Lee3, Joongpyo Shim 1,* 1 Deprtment of Chemicl Engineering, Kunsn Ntionl University, Jeonbuk, , Kore 2 Umicore Kore Ltd, Chungnm, 33-2, Kore 3 Fuel Cell Regionl Innovtion Center, Woosuk University, Jeonbuk, , Kore * E-mil: jpshim@kunsn.c.kr Received: 1 September 28 / Accepted: 25 October 28 / Published: 17 November 28 LiNi 1/3 Co 1/3 Mn 1/3 O 2 mterils were synthesized by different synthetic routes; through spry-drying, combustion, or solid-stte rections. The LiNi 1/3 Co 1/3 Mn 1/3 O 2 powders were exmined by X-ry diffrction (XRD), scnning electron microscopy (SEM), prticle size nlysis, nd chrge/dischrge cycling. All the prepred LiNi 1/3 Co 1/3 Mn 1/3 O 2 powders were identified s hexgonl structures nd exhibited dischrge cpcities of c mah/g t V. The LiNi 1/3 Co 1/3 Mn 1/3 O 2 powder prepred through the spry-drying method showed better electrochemicl properties, such s dischrge cpcity, rte cpbility, nd constnt cycling, over those synthesized from combustion nd solid-stte rection. Keywords: Lithium-ion btteries, spry-drying, cthode, LiNi 1/3 Co 1/3 Mn 1/3 O 2, combustion 1. INTRODUCTION Rechrgeble lithium-ion btteries hve been developed nd LiCoO 2 hs been widely used s cthode mteril becuse of its high cyclebility. [1] However, its cpcity is limited due to structurl chnge bove 4.3V nd coblt is reltively expensive nd toxic compred to nickel, mngnese nd iron which cn form vrious lyered oxides with lithium. Mny reserchers hve tried to develop low cost nd less toxic mterils such s nickel (LiNiO 2 ), mngnese (LiMn 2 O 4 or LiMnO 2 ) nd iron (LiFePO 4 )-bsed mterils. LiNi 1/3 Co 1/3 Mn 1/3 O 2 compounds hve thus been studied s the most promising cthode mteril for lithium-ion btteries due to their good cyclebility, no structurl trnsformtion during cycling, nd

2 Int. J. Electrochem. Sci., Vol. 3, reltively low cost compred to lyered oxides such s LiCoO 2. [2] LiNi 1/3 Co 1/3 Mn 1/3 O 2 hs been prepred by solid-stte rection which hs severl disdvntges, such s inhomogeneous composition, irregulr morphology, lrge prticle size, nd long heting times followed by severl grinding nd nneling processes. [3] In this work, we report on the synthesis nd electrochemicl chrcteristics of LiNi 1/3 Co 1/3 Mn 1/3 O 2 mterils prepred from three different methods; spry-drying, combustion nd solid-stte rection. 2. EXPERIMENTAL PART For the spry-drying (SD) method, the LiNi 1/3 Co 1/3 Mn 1/3 O 2 precursors were prepred using LiCH 3 COO 2H 2 O, Ni(CH 3 COO) 2 4H 2 O, Co(CH 3 COO) 2 4H 2 O, Mn(CH 3 COO) 2 4H 2 O with molr rtio of Li/Me = 1.1 (Me=Ni, Co nd Mn). These metl cettes were dissolved in deionized wter. The resulting solution ws spryed to form homogeneous mixture of precursors t 15 o C. The mixed precursor powder ws heted to 4 o C for 4 h in ir. Then the obtined powder ws ground in mortr nd re-nneled t 9 o C for 15 h in ir. [4] For the combustion method (CB), Li(NO 3 ) 2 4H 2 O, Ni(CH 3 COO) 2 4H 2 O, Co(CH 3 COO) 2 4H 2 O, nd Mn(CH 3 COO) 2 4H 2 O were dissolved in deionized wter with molr rtio of Li/Me = 1.1 (Me=Ni, Co nd Mn). The dissolved solution ws heted t 8-9 o C to mke green-colored gel. It ws then burned nd trnsformed into blck sponge-like fluffy mteril. The powder ws dditionlly sintered t 9 o C for 15 h. LiNi 1/3 Co 1/3 Mn 1/3 O 2 mterils were prepred by the solid-stte rection (SS) of precursors. The precursors were prepred in the sme mnner s in the spry-drying method bove. The metl cette precursors were well-mixed in mortr nd pressed into pellet. The pellet ws preheted t 4 o C in ir for 4 h nd then sintered t 9 o C for 15 h. The thermo grvimetric nlysis (TGA) for the mixture of precursors ws conducted in ir tmosphere to observe the temperture for precursor decomposition nd clcintion. The LiNi 1/3 Co 1/3 Mn 1/3 O 2 powders were chrcterized by X-ry diffrction (XRD) using n X-ry diffrctometer (Bruker M18XCE) with Cu-Kα rdition. The prticle morphology nd size distribution were observed by scnning electron microscopy (SEM) nd prticle size nlyzer (Anlysette 22, Fritsch). Cthodes were mde by coting mixture of 88% of LiNi 1/3 Co 1/3 Mn 1/3 O 2, 6% crbon blck, nd 6% polyvinylidene fluoride (PVdF) binder onto luminum foil. The electrode ws dried under vcuum t 12 for 12 h nd then pressed. The loding mount of ctive mteril ws 8-1 mg/cm 2. The electrolyte ws 1 M LiPF 6 in mixture of ethylene crbonte (EC) nd diethyl crbonte (DEC) in 1:1 volume rtio. The Swgelok-type cell ws ssembled in n Ar-filled glove box nd tested t room temperture. Positive nd negtive electrodes were seprted by polypropylene membrne (Celgrd 24). A metllic lithium foil ws used s the counter electrode. This cell ws dischrged until 2.8V nd chrged up to 4.3 ~ 4.7V by bttery cycler (WonA Tech, WBCS 3).

3 Int. J. Electrochem. Sci., Vol. 3, RESULTS AND DISCUSSION The temperture for the decomposition of precursors, metl cettes contining lithium, nickel, mngnese nd coblt, ws observed using by thermo-grvimetric nlysis (TGA), s shown in Fig. 1. Most of hydrte in precursor ws vporized round 13 o C nd then, the decomposition of cette strted round 3 o C nd finished before 5 o C. Therefore, we decided tht the temperture nd time for preheting ws 4 o C nd 4hours to decompose the cette fully nd then form the lyered oxide o C 396 o C Weight loss (%) o C 4-4 DTA (uv) Temperture ( o C) -12 Figure 1. TGA of the mixture of precursors in ir. Intensity (c) (b) () thet Figure 2. X-ry diffrction ptterns of LiNi 1/3 Co 1/3 Mn 1/3 O 2 compounds prepred by () spry-drying method, (b) combustion method, nd (c) solid-stte rection.

4 Int. J. Electrochem. Sci., Vol. 3, The powder XRD ptterns of LiNi 1/3 Co 1/3 Mn 1/3 O 2 compounds prepred from different synthetic methods re shown in Fig. 2. All the prepred mterils could be identified s α-nfeo 2 structures with spce group of R 3m. This ws determined by the fct tht ll of the XRD ptterns ccorded well with typicl hexgonl pttern nd showed cler split between (18) nd (11) peks. [6] Tble 1 shows the lttice prmeters nd the unit cell volume clculted from the XRD results. The lttice prmeters, = 2.862Å nd c = Å, nd the unit cell volume, V = 1.77Å 3, of LiNi 1/3 Co 1/3 Mn 1/3 O 2 powder (SD) re very consistent with the vlues reported by Ohzuku. 1,7 Other mterils (CB nd SD) show slightly lower vlue. Tble 1. Lttice prmeter, men prticle size of the mterils prepred from different method. Method (Å) c(å) c/ V(Å 3 Men prticle ) size (µm) SD CB SS Smple NA N. Ybuuchi, T. Ohzuku, J. Power Sources, (23) 171 () (b) (c) Figure 3. SEM imges of LiNi 1/3 Co 1/3 Mn 1/3 O 2 powders prepred by () spry-drying method, (b) combustion, (c) solid-stte rection

5 Int. J. Electrochem. Sci., Vol. 3, Fig. 3 shows SEM imges of LiNi 1/3 Co 1/3 Mn 1/3 O 2 powders. Although the prticle morphology is not clerly shown, ll the imges show the lrge gglomertion of smll prticle with size of ~1 µm. The prticle size distribution in Fig. 4 shows tht two of the powders (SD nd CB) hve more uniform size distribution in the rnge of.2 to 3 µm thn tht with brod distribution (SS) from.2 to 1 µm. However, Tble 1 shows very similr men prticle size for ll three mterils. Prticle size distribution (%) Spry-drying Combustion Solid stte rection Prticle size (µm) Figure 4. Prticle size distribution of LiNi 1/3 Co 1/3 Mn 1/3 O 2 powders Fig. 5 shows the initil chrge nd dischrge curves of LiNi 1/3 Co 1/3 Mn 1/3 O 2 electrodes t 6. ma/g in the rnge from 2.8 to 4.3 V t 25 o C. LiNi 1/3 Co 1/3 Mn 1/3 O 2 electrodes (SD, CB nd SS) show the initil chrge/dischrge cpcities of 171/139 (~81% of coulombic efficiency), 17/128 (~75% of coulombic efficiency) nd 174/134 mah/g (~79% of coulombic efficiency), respectively. All of the mterils were prepred from different methods shown by very similr initil cpcity. However, the irreversible cpcity observed in the first cycle ws bout 3-4 mah/g which is slightly higher thn tht reported by Ohzuku. 1 The dq/dv plots of LiNi 1/3 Co 1/3 Mn 1/3 O 2 electrodes in Fig. 5 (d) show one redox pek t V. Ohzuku s group nd Chng s group proposed tht the Ni 2+ /Ni 4+ couple occurs t V nd the oxidtion of Co 3+ to Co 4+ follows bove 4.5V. 8, 9 As shown in Fig. 6, the rte cpbility tests were crried out to exmine the lithium-ion trnsfer in the solid stte. The cell ws chrged t.2 C (1 C = 16 mah/g) 7 until it ws t 4.3 V nd then dischrged to 2.8 V t different C rtes from.2 C to 5 C. Fig. 6 () shows the dischrge curves of LiNi 1/3 Co 1/3 Mn 1/3 O 2 (SD) with different C rtes. The dischrge cpcity rpidly decreses with incresing C rte nd those re 73 nd 16 mah/g t 2 nd 5 C which re ssigned to 51% nd 11% cpcity retention for the initil cpcity, respectively. As shown in Fig. 6, LiNi 1/3 Co 1/3 Mn 1/3 O 2 (SD) exhibits better rte cpbility thn the other two powders (CB nd SS). Poor rte cpbility of this mteril compred to the results reported in literture might be due to less crystllinity of the powder, low crbon content in the electrode, or lck of skill in electrode preprtion. The skill to mke uniform electrodes should be improved for further study. Fig. 7 shows specific cpcity s function of cycle number for LiNi 1/3 Co 1/3 Mn 1/3 O 2 cell cycled through vrious voltge rnges t.2 C (32

6 Int. J. Electrochem. Sci., Vol. 3, ma/g) nd 25 o C. The LiNi 1/3 Co 1/3 Mn 1/3 O 2 cells showed very similr cyclebility up to 4.5V of chrging voltge. From 4.6V, the electrode (SS) showed fster cpcity fding rther thn those (SD nd CB). The dischrge cpcity (SD) showed slightly higher thn tht (CB) E vs. Li/Li + (V) () Spry-drying (b) Combustion (c) Solid-stte rection b c Specific cpcity (mah/g) 8 6 (d) b c () Spry-drying (b) Combustion (c) Solid-stte rection dq/dv (mah/gv) b c E vs Li/Li + (V) Figure 5. Initil chrge/dischrge curves of differentil LiNi 1/3 Co 1/3 Mn 1/3 O 2 electrodes prepred by () spry-drying method, (b) combustion method, nd (c) solid-stte rection. (d) dq/dv plot

7 Int. J. Electrochem. Sci., Vol. 3, Specific cpcity (mah/g) Spry-drying Combustion Solid-stte rection C rte Figure 6. Dischrge cpcity curves t different dischrge rtes t C/5, C/2, 1C, 2C, 5C for the LiNi 1/3 Co 1/3 Mn 1/3 O 2 electrodes rnging from 2.8 to 4.3 V. 16 Specific cpcity (mah/g) V V V V V Spry-drying Combustion Solid stte rection Cycle Number Figure 7. Dischrge cpcities s function of cycle number in vrious voltge rnges t.2c.

8 Int. J. Electrochem. Sci., Vol. 3, CONCLUSIONS LiNi 1/3 Co 1/3 Mn 1/3 O 2 mterils were synthesized from three different methods; spry-drying, combustion, nd solid-stte rection. The results from XRD showed tht the crystl structure of ll the powders ws hexgonl structure nd the unit cell volume ws different ccording to the synthetic method used. The SEM nd prticle size nlysis of the prepred mterils showed uniform size distribution round ~1 µm. The LiNi 1/3 Co 1/3 Mn 1/3 O 2 electrodes delivered dischrge cpcity of c mah/g between 2.8 nd 4.6 V nd showed good cyclebility until the chrge voltge reched to 4.6 V. It ws found tht the LiNi 1/3 Co 1/3 Mn 1/3 O 2 mteril prepred through the spry-drying method showed the lrgest unit cell volume nd better cyclebility over those obtined from the combustion nd solid-stte rection methods. ACKNOWLEDGEMENT This work ws finncilly supported by the Kore Reserch Foundtion Grnt funded by the Koren Government (MOEHRD) (KRF D17). References 1. N. Ybuuchi, T. Ohzuku, J. Power Sources (23) N. Ybuuchi, Y. Mkimur, T. Ohzuku, J. Electrochem. Soc 154 (27) Y.M. Hon, S.P. Lin, K.Z. Fung, M.H. Hon, J. Eur. Cerm. Soc 22 (22) S.H. Prk, C.S. Yoon, S.G. Kng, H.-S. Kim, S.-I. Moon, Y.-K. Sun, Electrochim. Act 49 (24) H.J. Bng, V.S. Donepudi, J Prksh, Electrochim. Act 48 (22) J.-M. Kim, N. Kumgi, S. Komb, Electrochim. Act 52 (26) I. Belhrouk, Y.-K. Sun, J. Liu, K. Amine, J. Power Sources 123 (23) N. Ybuuchi, Y. Mkimur, T. Ohzuku, J. Electrochem. Soc. 154 (27) A Y.J. Shin, W.-J. Choi, Y.-S. Hong, S. Yoon, K.S. Ryu, S.H. Chng, Solid Stte Ionics 177 (26) by ESG (