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Electrochimica Acta 108 (2013) 32– 38

Contents lists available at ScienceDirect

Electrochimica Acta

jou rn al hom ep age: www.elsev ier .com/ locate /e lec tac ta

haracterization of Li-rich xLi2MnO3·(1−x)Li[MnyNizCo1−y−z]O2 asathode active materials for Li-ion batteries

ong Nam Joa, K. Prasannaa, Suk Joon Parkb, Chang Woo Leea,∗

Department of Chemical Engineering, College of Engineering, Kyung Hee University, 1732 Deogyeong-daero, Gihung, Yongin, Gyeonggi 446-701, SouthoreaEcopro, 316-3 Songdae, Ochang, Cheongwon 363-883, South Korea

r t i c l e i n f o

rticle history:eceived 1 March 2013eceived in revised form 18 June 2013ccepted 22 June 2013vailable online 27 June 2013

a b s t r a c t

We have investigated the crystallographical, morphological, and electrochemical behaviors of synthe-sized four different compositions of xLi2MnO3·(1−x)Li[MnyNizCo1−y−z]O2 cathode active materials usingX-ray diffractometer (XRD), field emission scanning electron microscope (FE-SEM), and galvanostaticcycler. The four different compositions of cathode active materials demonstratea commonly angularshape of primary particles, but agglomerated spherical shape in appearance. All the attempted compo-sitions of xLi2MnO3·(1−x)Li[MnyNizCo1−y−z]O2 cathodes deliver a specific discharge capacity of between

eywords:i-ion batteryathode active materialsi-richverlithiated oxideycling properties

220 and 242 mAh/g at room temperature when cycled between 2.5 and 4.6 V versus Li/Li+ at C/10 rate.© 2013 Elsevier Ltd. All rights reserved.

ate capability

. Introduction

The Li-ion batteries have become an indispensable part of ourives from potable application such as mobile, digital camera andower tool to the large application, for example hybrid electricehicle (HEV), electric vehicle (EV), energy storage system (ESS)nd so on. During the last decades, plenty of materials have beenynthesized and estimated as cathode active materials for Li-ionechargeable batteries [1–4].

To increase the energy density of Li-ion batteries, it is necessaryo enlarge the capacity of the cathode because the usable capacityf graphite as an anode, about 350mAh/g, is much larger than thatf LiCoO2 as a cathode which has 150 mAh/g of practical specificischarge capacity, the LiCoO2 material that is widely used as theathode in Li-ion rechargeable batteries [5–9]. In order to increasehe energy density of cathode materials, recent researches haveocused on the Li-rich NCM compounds that have high specific dis-harge capacity. Electrodes based on Li-rich NCM compositions canrovide at high anodic potentials of 4.6 V vs. Li/Li+ and offer high

apacities(>200 mAh/g) [10,11].

In order to develop alternatives of LiCoO2 and/or conven-ional cathode materials, we investigated the different composition

∗ Corresponding author. Tel.: +82 31 201 3825; fax: +82 31 204 8114.E-mail address: cwlee@khu.ac.kr (C.W. Lee).

013-4686/$ – see front matter © 2013 Elsevier Ltd. All rights reserved.ttp://dx.doi.org/10.1016/j.electacta.2013.06.062

of xLi2MnO3·(1−x)Li[MnyNizCo1−y−z]O2 cathode active materials.Many researchers already studied that type of Li-rich cathode activematerials. In this research we tried to find out the optimum compo-sition of xLi2MnO3·(1−x)Li[MnyNizCo1−y−z]O2 for electric vehiclesand/or energy storage systems at room and elevated temperature.So as to study the electrochemical behavior, 2032-type coin cellsare assembled using four different compositions of cathode activematerials and carried out the intensive studies on potential pro-file, cycle life, and so on. Furthermore, crystallographies of theattempted cathode active materials were investigated.

2. Experimental

All the cathode active materials were synthesized by Ecoprousing the co-precipitation method. In order to fabricate the cathodeelectrode, each 90 wt% of Li-rich powder was mixed with 5 wt% ofconductive carbon agent, 5 wt% of polyvinylidene fluoride (PVDF)which acts as a binder and N-methyl-2-pyrrolidone (NMP). Themixed slurry was laminated on Al foil. The electrochemical prop-erties of Li-rich materials were evaluated using 2032-type coincells assembled in an argon filled glove box. The 2032-type coincell consisted of fabricated Li-rich cathode electrode, pure lithium

metal as the counter electrode, microporous membrane as theseparator and 1 M LiPF6 in ethylene carbonate (EC): diethylene car-bonate (DEC) (1:1 vol%) as the electrolyte. The morphology analysisof the each cathode active materials was observed using a field

Y.N. Jo et al. / Electrochimica

Fig. 1. XRD patterns of xLi2MnO3·(1−x)Li[MnyNizCo1−y−z]O2 cathode activem[0

eGwS(tccicta

3

3

sstsiSr

aterials: (a) 0.35Li2MnO3·0.65Li[Mn0.38Ni0.43Co0.19]O2; (b) 0.40Li2MnO3·0.60LiMn0.32Ni0.47Co0.21]O2; (c) 0.45Li2MnO3·0.55Li[Mn0.26Ni0.51Co0.23]O2; and (d).50Li2MnO3·0.50Li[Mn0.19Ni0.56Co0.25]O2.

missionscanning electron microscope (FE-SEM) (Leo Supra 55,enesis 2000, Carl Zeiss) and the crystalline phase of the powderas identified by X-ray diffractometer (XRD) (18 kW, M18XHF-

RA, Mac science). The cycling test was conducted using a cyclerBT2000, Arbin) in two electrodes 2032-type coin cells. The 2032-ype coin cells were cycled in a voltage range of 2.5–4.6 V usingonstant current plus constant voltage charge, namely chargingontinued at 4.6 V until the current reached a value correspond-ng to C/200 value. Discharge tests were performed using constanturrent mode at various rates to the 2.5 V cut-off voltage. All elec-rochemical characteristics were performed at room temperaturend/or 55 ◦C.

. Results and discussion

.1. X-Ray diffraction and morphological studies

The XRD patterns of the nanosized four samples are pre-ented in Fig. 1. All diffraction peaks can be indexed as a layeredtructure based on a hexagonal �-NaFeO2 structure. Sharp reflec-ions in the XRD patterns reveal the high crystallinity of the

amples. As seen from Fig. 1, the splits in the (1 0 8)/(1 1 0) doubletndicate the formation of a highly ordered layer structure [12,13].ome researchers [13,14] reported the high-integrated intensityatio of the I(0 0 3)/I(1 0 4) to indicate the cation mixing of the

Acta 108 (2013) 32– 38 33

layered structure. When I(0 0 3)/I(1 0 4)>1.2, the cation mixing issmall with good layered structure. In this work, the intensity ratioI(0 0 3)/I(1 0 4) of four materials was found at beyond of 1.2, so weauthors believed that the studied samples might have no undesir-able cation mixing and well synthesized as layered Li-rich cathodeactive materials.

Fig. 2 shows the morphologies and particle sizes of the four dif-ferent compositions of cathode active materials. As shown in theimage, the aggregated secondary particles are spherical in shapehaving a diameter ranging between 5 and 15 �m. The secondaryparticles comprise an angular shape of primary particles havingsizes between 50 and 180 nm. The particle size of four differentcathode active materials is not big different from each other. Andparticles form a dense and smoother surface for all cathode activematerials. It means that the particle size and shape could be lesseffect on electrochemical properties.

3.2. Electrochemical studies

Fig. 3 shows the initial potential profiles of0.35Li2MnO3·0.65Li[Mn0.38Ni0.43Co0.19]O2, 0.40Li2MnO3·0.60Li[Mn0.32Ni0.47Co0.21]O2, 0.45Li2MnO3·0.55Li[Mn0.26Ni0.51Co0.23]O20.50Li2MnO3·0.50Li[Mn0.19Ni0.56Co0.25]O2 cathodes in thevoltage range of 2.5–4.6 V under C/10 rate. It shows thatlayered xLi2MnO3·(1−x)Li[MnyNizCo1−y−z]O2 electrodes canprovide remarkably high specific capacities by activation of theLi2MnO3 component above 4.4 V. Especially, 0.35Li2MnO3·0.65Li[Mn0.38Ni0.43Co0.19]O2, 0.40Li2MnO3·0.60Li[Mn0.32Ni0.47Co0.21]O2showed more than specific discharge capacity of 240 mAh/g. Ascan be seen, all plots during charge are composed of a slope regionand a long plateau. The slope region is attributed to the extractionof Li+ ions from the lithium layer. After this process, the Ni2+ andCo3+ were oxidized to Ni4+ and Co4+, respectively [15]. The capacityafter 4.4 V at which is accompanied with Li and/or oxygen ionsextraction from the host, which is absent during the subsequentcharge, is consistent with the irreversible removal of Li2O fromthe Li2MnO3 component that occurs on the voltage plateau at4.5–4.6 V [16–18]. As shown in Fig. 4, from second cycling, theirreversible plateau during charging is disappeared for all samples.

The dQ/dV plots of the charge/discharge curves in Fig. 5. Dur-ing the initial charge to 4.6 V the four different compositions ofelectrodes showed much larger peak near 4.5 V corresponding tothe irreversible removal of Li2O from the structure. The occurrenceof an irreversible peak near 4.5 V is peculiar because it appeared inthe first charge process and then disappeared in subsequent cycling[19].

The electrochemical cycling results of four different cellsat C/10 rate and room temperature are presented in Fig. 6. Inall these experiments, charging was performed using CC/CVmode, while discharging was performed using CC mode.When these cells were cycled between 2.5 and 4.6 V, theinitial capacity of more than 220 mAh/g could be achieved.Before 11th cycle, 0.35Li2MnO3·0.65Li[Mn0.38Ni0.43Co0.19]O2and 0.45Li2MnO3·0.55Li[Mn0.26Ni0.51Co0.23]O2 had higherspecific discharge capacity than that of 0.40Li2MnO3·0.60Li[Mn0.32Ni0.47Co0.21]O2 and 0.50Li2MnO3·0.50Li[Mn0.19Ni0.56Co0.25]O2. However, with increase in the number of cycles up to25th cycle, 0.45Li2MnO3·0.55Li[Mn0.26Ni0.51Co0.23]O2 and0.50Li2MnO3·0.50Li[Mn0.19Ni0.56Co0.25]O2 showed highercapacities than those of the others. Therein, it seems thatthe cycling performance of the attempted cathode activematerials can be improved with the increase of x value in

xLi2MnO3·(1−x)Li[MnyNizCo1−y−z]O2 as long as the elec-trode structure is maintained in a certain level controllingremoval of Li2O from the structure. However, at elevatedtemperature, 55 ◦C, electrochemical cycling results were

34 Y.N. Jo et al. / Electrochimica Acta 108 (2013) 32– 38

Fig. 2. FE-SEM images of xLi2MnO3·(1−x)Li[MnyNizCo1−y−z]O2 cathode active materials: (a) 0.35Li2MnO3·0.65Li[Mn0.38Ni0.43Co0.19]O2; (b)0.40Li2MnO3·0.60Li[Mn0.32Ni0.47Co0.21]O2; (c) 0.45Li2MnO3·0.55Li[Mn0.26Ni0.51Co0.23]O2; and (d) 0.50Li2MnO3·0.50Li[Mn0.19Ni0.56Co0.25]O2.

Y.N. Jo et al. / Electrochimica Acta 108 (2013) 32– 38 35

0 50 100 150 200 250 3002.0

2.5

3.0

3.5

4.0

4.5

5.0

0.35Li2MnO3.0.65Li[Mn0.38Ni0.43Co0.19]O2

0.40Li2MnO3.0.60Li[Mn0.32Ni0.47Co0.21]O2

0.45Li2MnO3.0.55Li[Mn0.26Ni0.51Co0.23]O2

0.50Li2MnO3.0.50Li[Mn0.19Ni0.56Co0.25]O2

Vol

tage

, V v

s. L

i/Li+

Specific Capacity, mAh/g

F cath0 3]O2;

d0hwdctbc

F0

ig. 3. Initial potential profiles of xLi2MnO3·(1−x)Li[MnyNizCo1−y−z]O2

.40Li2MnO3·0.60Li[Mn0.32Ni0.47Co0.21]O2; (c) 0.45Li2MnO3·0.55Li[Mn0.26Ni0.51Co0.2

ifferent from room temperature results. As shown in Fig. 7,.35Li2MnO3·0.65Li[Mn0.38Ni0.43Co0.19]O2 demonstrated theighest specific discharge capacity on cycling when comparedith the others. In overall, with decreasing of x value, the specificischarge capacity was higher at initial cycling as well as extendedycling up to 25th cycle. These results show a tendency to be of

he opposite from the results at room temperature. We authorselieve that more amounts of the removed Li2O from the structureould accelerate damaging the electrode surface, particularly

ig. 4. The 2nd charge potential profiles of xLi2MnO3·(1−x)Li[MnyNizCo1−y−z]O2

.40Li2MnO3·0.60Li[Mn0.32Ni0.47Co0.21]O2; (c) 0.45Li2MnO3·0.55Li[Mn0.26Ni0.51Co0.23]O2;

ode active materials: (a) 0.35Li2MnO3·0.65Li[Mn0.38Ni0.43Co0.19]O2; (b)and (d) 0.50Li2MnO3·0.50Li[Mn0.19Ni0.56Co0.25]O2.

when exposed at elevated temperature during electrochemicalactivation above 4.4 V. Furthermore, for lower x value in thecomposition, it contains more amounts of Mn conventionallyable to serve for better thermal properties while Ni amounts arealmost identically maintained for all the attempted materials.Fig. 8 shows the capacity retention ratio of four different cathode

active materials at 55 ◦C. As shown in this figure, the retentionratio of cathode materials which have less x values were better.Actually the system xLi2MnO3·(1−x)Li[MnyNizCo1−y−z]O2 is so

cathode active materials: (a) 0.35Li2MnO3·0.65Li[Mn0.38Ni0.43Co0.19]O2; (b)and (d) 0.50Li2MnO3·0.50Li[Mn0.19Ni0.56Co0.25]O2.

36 Y.N. Jo et al. / Electrochimica Acta 108 (2013) 32– 38

2.5 3.0 3.5 4.0 4.5 5.0-500

0

500

1000

1500

2000

1st cycling 2nd cycling

dQ/d

V, m

Ah/

gV

Voltage, V vs. Li/Li+2.5 3.0 3.5 4.0 4.5 5.0

-500

0

500

1000

1500

2000

1st cycling 2nd cycling

dQ/d

V, m

Ah/

gV

Volt age , V vs. Li/Li+

2.5 3.0 3.5 4.0 4.5 5.0-500

0

500

1000

1500

2000

1st cycling 2nd cycling

dQ/d

V, m

Ah/

gV

Voltage, V vs. Li/Li+2.5 3.0 3.5 4.0 4.5 5.0

-500

0

500

1000

1500

2000

1st cycling 2nd cycling

dQ/d

V, m

Ah/

gV

Volt age , V vs. Li/Li+

(a) (b)

(c) (d)

F z]O2

0 3]O2;

cot[cs

ig. 5. The differential capacity profiles of xLi2MnO3·(1−x)Li[MnyNizCo1−y−.40Li2MnO3·0.60Li[Mn0.32Ni0.47Co0.21]O2; (c) 0.45Li2MnO3·0.55Li[Mn0.26Ni0.51Co0.2

omplicated and its electrochemical behaviors must be dependingn the x value and relative amounts of transition metals. Thus,

he Li2MnO3 plays an important role in stabilizing the structure16,20]. It contributes to give a high specific capacity (>200 mAh/g)aused by electrochemical activation above 4.4 V. Also, it serves totabilize LiMO2 (M = Ni, Co, Mn) structure. Whereas more amount

Fig. 6. The cycling performances of xLi2MnO3·(1−x)L

cathode active materials: (a) 0.35Li2MnO3·0.65Li[Mn0.38Ni0.43Co0.19]O2; (b)and (d) 0.50Li2MnO3·0.50Li[Mn0.19Ni0.56Co0.25]O2.

of Li2MnO3 may contribute to serve the high capacity performance,however, it also has an opposite side that the Li2MnO3 component

above 4.4 V may hinder transportation of Li+ and thereafter inducelower specific capacity and poor cycling stability. Accordingly, thecathode active materials with x = 0.45 and 0.50 show a relativelysignificant decay in cycling stability at elevated temperature.

i[MnyNizCo1−y−z]O2 cathode active materials.

Y.N. Jo et al. / Electrochimica Acta 108 (2013) 32– 38 37

0 50 100 15 0 20 0 25 0 30 02.0

2.5

3.0

3.5

4.0

4.5

5.0

1st

5th

10th

Vol

tage

, V v

s. L

i/Li+

Speci fic Capacity, mAh/g0 50 100 15 0 20 0 25 0 30 0

2.0

2.5

3.0

3.5

4.0

4.5

5.0

1st

5th

10th

Vol

tage

, V v

s. L

i/Li+

Speci fic Capac ity, mAh/g

0 50 100 15 0 20 0 25 0 30 02.0

2.5

3.0

3.5

4.0

4.5

5.0

1st

5th

10th

Vol

tage

, V v

s. L

i/Li+

Speci fic Capacity, mAh/g0 50 100 15 0 20 0 25 0 30 0

2.0

2.5

3.0

3.5

4.0

4.5

5.0

1st

5th

10th

Vol

tage

, V v

s. L

i/Li+

Speci fic Capac ity, mAh/g

(a) (b)

(c) (d)

F ode

0 3]O2;

xoist

Fx

ig. 7. The discharge potential profiles of four different Li-rich cath.40Li2MnO3·0.60Li[Mn0.32Ni0.47Co0.21]O2; (c) 0.45Li2MnO3·0.55Li[Mn0.26Ni0.51Co0.2

Fig. 9 shows the rate capability properties ofLi2MnO3·(1−x)Li[MnyNizCo1−y−z]O2 cells tested with vari-

us applied currents in room temperature. All samples werenitially operated for five cycles at C/10 rate and the C-rate wasubsequently changed to C/5 and C/3. As shown in Fig. 9, whenhe x value was decreased, the rate capability were improved.

ig. 8. Capacity retention ratio results of four differentLi2MnO3·(1−x)Li[MnyNizCo1−y−z]O2 cathode active materials at 55 ◦C.

active materials at 55 ◦C:(a) 0.35Li2MnO3·0.65Li[Mn0.38Ni0.43Co0.19]O2; (b)and (d) 0.50Li2MnO3·0.50Li[Mn0.19Ni0.56Co0.25]O2.

In all the attempted current rates, the capacity decline for0.50Li2MnO3·0.50Li[Mn0.19Ni0.56Co0.25]O2 was in noticeabledistinction from other samples. In this regard, the significant

capacity decline at higher current rates are in a good agreementwith the previous literature [16] and might be attributed to theextensive removal of Li2O from the structure.

Fig. 9. The rate capabilities of four different xLi2MnO3·(1−x)Li[MnyNizCo1−y−z]O2

cathode active materials.

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8 Y.N. Jo et al. / Electroch

. Conclusions

We studied crystallography, morphology, and electro-hemistry of four different composition of xLi2MnO3·(1−x)LiMnyNizCo1−y−z]O2 cathode active materials. The prepared Li-richathode active materials were well crystallized with ordered, lay-red structure. Their morphology using FE-SEM demonstrated thatost particles have a commonly angular shape as primary particles

nd spherical shape as secondary particles. Initial specific dischargeapacities for the 0.35Li2MnO3·0.65Li[Mn0.38Ni0.43Co0.19]O2,.40Li2MnO3·0.60Li[Mn0.32Ni0.47Co0.21]O2, 0.45Li2MnO3·0.55LiMn0.26Ni0.51Co0.23]O2, 0.50Li2MnO3·0.50Li[Mn0.19Ni0.56Co0.25]O2t the C/10 rate were 242 mAh/g, 241 mAh/g, 236 mAh/gnd 222 mAh/g. In other words, 0.35Li2MnO3·0.65LiMn0.38Ni0.43Co0.19]O2 and 0.40Li2MnO3·0.60Li[Mn0.32Ni0.47Co0.21]2 have higher capacity than that of the others at room tempera-

ure. With subsequent cycling up to 25th cycle, 0.45Li2MnO3·0.55LiMn0.26Ni0.51Co0.23]O2 and 0.50Li2MnO3·0.50Li[Mn0.19Ni0.56Co0.25]2 were more stable and showed higher specific discharge capacity.ith the increase of Li2MnO3 contents, rate capability of cathodeaterials was poor and the electrochemical ability was inferior at

levated temperature. In this study, we tried to find out a tailoredomposition of Li-rich cathode active material for large scale appli-ations. On balance, 0.35Li2MnO3·0.65Li[Mn0.38Ni0.43Co0.19]O2nd 0.40Li2MnO3·0.60Li[Mn0.32Ni0.47Co0.21]O2 are suggested to behe promising compositions of cathode electrodes for large scalepplications.

cknowledgements

This work was supported by the Energy Efficiency & Resourcesf the Korea Institute of Energy Technology Evaluation and Plan-ing (KETEP) grant funded by the Korea government Ministry ofnowledge Economy (MKE) (No. 2011201010016A).

eferences

[1] J.M. Tarascon, M. Armand, Issues and challenges facing rechargeable lithiumbatteries, Nature 414 (2001) 359.

[2] P.G. Bruce, Energy storage beyond the horizon: rechargeable lithium batteries,Solid State Ionics 179 (2008) 752.

[

Acta 108 (2013) 32– 38

[3] Y.G. Guo, J.S. Hu, L.J. Wan, Nanostructured materials for electrochemical energyconversion and storage devices, Advanced Materials 20 (2008) 2878.

[4] B. Scrosati, J. Garche, Lithium batteries: status, prospects and future, Journal ofPower Sources 195 (2010) 2419.

[5] W. Li, J.C. Currie, Morphology effects on the electrochemical performance ofLiNi1-xCoxO2, Journal of Electrochemical Society 144 (1997) 2773.

[6] J. Cho, G.B. Kim, H.S. Lim, Effect of preparation methods of LiNi1-xCoxO2 cathodematerials on their chemical structure and electrode performance, Journal ofElectrochemical Society 146 (1999) 3571.

[7] P. Barboux, J.M. Tarascon, F.K. Shokooshi, The use of acetates as precursorsfor the low-temperature synthesis of LiMn2O4 and LiCoO2 intercalation com-pounds, Journal of Solid State Chemistry 94 (1991) 185.

[8] J. Cho, H.S. Jung, Y.C. Park, G.B. Kim, H.S. Lim, Electrochemical properties andthermal stability of LiaNi1-xCoxO2 cathode materials, Journal of ElectrochemicalSociety 147 (2000) 15.

[9] A. Ito, K. Shoda, Y. Sato, M. Hatano, H. Horie, Y. Ohsawa, Direct observation of thepartial formation of a framework structure for Li-rich layered cathode mate-rial Li[Ni0.17Li0.2Co0.07Mn0.56]O2 upon the first charge and discharge, Journal ofPower Sources 196 (2011) 4785.

10] S.K. Martha, J. Nanda, G.M. Veith, N.J. Dudney, Electrochemical andrate performance study of high-voltage lithium-rich composition:Li1.2Mn0.525Ni0.175Co0.1O2, Journal of Power Sources 199 (2012) 220.

11] S.-H. Kang, D.P. Abraham, W.-S. Yoon, K.-W. Nam, X.-Q. Yang, First-cycleirreversibility of layered Li-Ni-Co-Mn- oxide cathode in Li-ion batteries, Elec-trochimica Acta 54 (2008) 684.

12] R. Snthanam, B. Rambabu, Improved high rate cycling of Li-richLi1.10Ni1/3Co1/3Mn1/3O2 cathode for lithium batteries, International Journal ofElectrochemical Science 4 (2009) 1770.

13] X. Luo, X. Wang, L. Liao, S. Gamboa, P.J. Sebastian, Synthesis and characteri-zation of high tap-density layered Li[Ni1/3Co1/3Mn1/3]O2 cathode material viahydroxide co-precipitation, Journal of Power Sources 158 (2006) 654.

14] Z.L. Liu, A.S. Yu, J.Y. Lee, Synthesis and characterization of LiNi1-x-yCoxMnyO2 asthe cathode materials of secondary lithium batteries, Journal of Power Sources81–82 (1999) 416.

15] J. Wang, G. Yuan, M. Zhang, B. Qiu, Y. Xia, Z. Liu, The structure, morphologyand electrochemical properties on Li1-xNi1/6Co1/6Mn4/6O2.25+x/2 (0.1 ≤ x ≤ 0.7)cathode materials, Electrochimica Acta 66 (2012) 61.

16] M.M. Thackeray, S.-H. Kang, C.S. Johnson, J.T. Vaughey, R. Benedeka, S.A. Hack-ney, Li2MnO3-stabilized LiMO2 (M = Mn, Ni, Co) electrodes for lithium-ionbatteries, Journal of Materials Chemistry 17 (2007) 3112.

17] P. Lanz, H. Sommer, M.S. -Dobrick, P. Novák, Oxygen release from high-energyxLi2MnO3·(1-x)LiMO2 (M = Mn, Ni, Co): electrochemical, differential elec-trochemical mass spectrometric, in situ pressure and in situ temperaturecharacterization, Electrochimica Acta 93 (2013) 114.

18] J.S. Kim, C.S. Johnson, J.T. Vaughey, M.M. Thackeray, Electrochemical andstructural properties of xLi2M’O3·(1-x)LiMn0.5Ni0.5O2 electrodes for lithiumbatteries (M’ = Ti, Mn, Zr; 0 ≤ x ≤ 0.3), Chemistry of Materials 16 (2004) 1996.

19] C.W. Lee, Y.-K. Sun, J. Prakash, A novel layered Li[Li0.12NizMg0.32-zMn0.56]O2

cathode material for lithium-ion batteries, Electrochimica Acta 49 (2004) 4425.20] C.J. Jafta, K.I. Ozoemena, M.K. Mathe, W.D. Roos, Synthesis, characterisation and

electrochemical intercalation kinetics of nanostructured aluminium-dopedLi[Li0.2Mn0.54Ni0.13Co0.13]O2 cathode material for lithium ion battery, Elec-trochimica Acta 85 (2012) 411.