Synthesis and Electrochemistry of LiNiMn2_O4

Synthesis and Electrochemistry of LiNiMn2_O4Qiming Zhong,*a Arman Bonakclarpour, Meijie Zhang,0b Yuan 01s,b,c and J. R. Dahn'

aMoli Energy (1990) Limited, Maple Ridge, British Columbia V2X 9E7, Canada6Department of Physics, Simon Fraser University, Burnaby, British Columbia V5A 1S6, Canada

ABSTRACTLiNiMn2_104 has been synthesized using sol-gel and solid-state methods for 0

206 J. Electrochem. Soc., Vol. 144, No. 1, January 1997 The Electrochemical Society, Inc.

Table I. Summary of the samples studied.

Samplex in

LiNiMn,O4Preparati

methodon Temp.

(C)Coolingmethod ,a (A) Atmosphere

Mn oxidationstate

1 0.0 S-S 750 Furnace 8.243 air 2 0.05 5-5 750 Furnace 8.234 air 3 0.1 S-S 750 Furnace 8.228 air 4 0.15 S-S 750 Furnace 8.222 air 5 0.2 S-S 750 Furnace 8.215 air 6 0.3 S-S 750 Furnace 8.200 air 7 0.4 S-S 750 Furnace 8.187 air 8 0.5 S-S 800 Furnace 8.176 air .9

101112

0.50.50.50.5

sol-gelsol-gelsol-gelsol-gel

250300400500

3C/mm3C/mm3C/mm3C/mm

8.18868.18408.18058.1772

airairairair

3.8693.9273.9353.962

13 0.5 sol-gel 600 3C/mm 8.1716 air 3.9671415

0.50.5

sol-gelsol-gel

700800

3C/mm3C/mm

8.17808.1857

airair

3.9193.855

16171819202122

0.50.50.50.10.20.30.4

sol-gelsol-gelsol-gelsol-gelsol-gelsol-gelsol-gel

250800800600600600600

3C/mm3C/mm

0.8C/mm0.8C/mm0.8C/mm--0.8C/mm0.8C/mm

8.18068.17598.17448.21968.20808.19158.1730

oxygenoxygenoxygen

airairairair

3.891

3.6633.7713.907

23 0.5 sol-gel 600 0.8C/mm 8.1678 air 3.98724252627282930

0.20.30.40.50.50.50.5

sol-gelsol-gelsol-gelsol-gelsol-gelsol-gelsol-gel

850850850850850850850

0.8C/mm0.8C/mm0.8C/mm0.8C/mm

650q750qBSOq

8.21768.20348.18188.17228.17458.18408.2183

airairairairairairair

s-s means solid-state synthesis.

determined by the single-point nitrogen sorption Bru-nauer-Emmett-Teller (BET) method using a MicromeriticsFlowsorb 112300 surface area analyzer.

The electrochemical properties of the LiNirMfl2_x04samples were evaluated using coin-type cells (size 2320)containing a lithium metal foil anode, a Celgard 2502microporous polypropylene separator, together with anelectrolyte of 1 M LiBF4 dissolved in a 30/70 volume per-centage mixture of ethylene carbonate and diethyl car-bonate (EC/DEC). Composite cathode electrodes weremade from the spmnel sample powders, Super S carbonblack (10% by weight) (Chemetals Incorporated), andpolyvmnylidene fluoride (PVDF) binder, uniformly coatedon aluminum foil. The sample powder and carbon blackwere added to a solution of 9.4% PVDF in n-methyl pyrro-lidinone (NMP) such that 5% of the final electrode mass isPVDF. Excess NMP was then added until the slurryreached a syrupy viscosity, and then the slurry was spreadon the Al foil with a doctor blade spreader, and dried at110C in air. Dried electrodes were then compressedbetween two flat plates at about 60 bar pressure. Test elec-trodes 1.2 >( 1.2 cm were then cut using a precision cuttingjig. Electrode squares were weighed, and the combinedweight of foil, carbon black, and PVDF was subtracted toobtain the active electrode mass. Fabrication of the coincells was carried out in an argon-filled glove box.

The electrochemical measurements were conductedunder thermostatic conditions at 3 0C. Cells were cycledgalvanostatically in a potential range of 3.0 to 4.9 V usinga Moli cycler [Moli Energy (1990) Limited, Maple Ridge,BC, Canada] with 1% current stability. Currents wereadjusted to be either 14.7, 3.7, or 3.0 mA/g of active elec-trode material, which corresponds to a discharge or chargetime of 10, 40, or 50 h, respectively, assuming that one Liatom per formula unit can be extracted.

Results and DiscussionFigure 1 shows diffraction profiles for samples 19, 21,

and 23 which have x = 0.1, 0.3, and 0.5, respectively Thesesamples were made at 600C and are single-phase spinelsamples. The insets in the figures show an expanded viewof the spinel (400) peak. When LiNi1O is present as animpurity, an impurity peak appears to the left of the (400)

peak, as we see later. Figure 2 shows the variation of thelattice constant with nickel content for the samples pre-pared by both the solid-state and sol-gel methods. Datafor all samples, except samples 9-18 and 28-30, are includ-ed in the figure. The linear variation of the lattice con-stants coupled with the single-phase patterns in Fig. 1show that a solid-solution series has been prepared.

Figure 3 shows potential profiles of representative sol-gel and solid-state materials. The solid-state materialswere cycled two times to 4.3 V before they were charged to4.9 V. The currents used were 3.7 mA/g. The sol-gel mate-rials were cycled directly to 4.9 V, and the data shown arefor the third cycle of these materials. The currents usedwere 3.0 mA/g for these samples. It is clear that the 4.1 Vplateau moves upward to 4.7 V as the Ni content increas-es. There is a sharp step between the plateaus. We haverecently shown that the cause of potential step stems fromthe position of the Ni 3d e5 levels with respect to the Mn 3de5 levels. The former have an electron binding energywhich is about 0.5 eV larger than the latter.

As Li is removed from the solid, the Li and a corre-sponding electron are removed. The electron comes fromthe top of the valence band, which is shown in Ref. 16 tobe made up of metal 3d levels. In LiMn2O4 (high-spin con-figuration) there is one electron per formula unit in thelowest e5 level and three electrons in the lowest tig level. Niin this compound has an exchange splitting which issmaller than the crystal field splitting and is in the lowspin configuration. There are six electrons in the nearlydegenerate t2g levels. The lowest eg level, which can holdtwo electrons, is about 0.5 eV below the filled Mn e5 level.Since the other exchange split Ni e5 level is above the filiedMn e5 level, it remains empty Thus, as Ni is added to thecompound, d electrons from Mn e5 "dump" into the lowestNi eg level, which can hold two electrons, giving a total ofeight on the Ni. Thus, the Ni in this compound takes oxi-dation state + 2 (as experimentally confirmed by Amineet al.ii) and there are 1 2x Mn atoms in oxidation state+3 and 1 + x Mn atoms in oxidation state +4 inLiNiMn2O4 per formula uhit. Therefore we write the oxi-dation state of this compound as LiNit2MntMnixO_.

Since there are 1 2xMn eg electrons per LiNiMn2_O4formula unit, the length of the 4.1 V plateau should vary

) unless CC License in place (see abstract). ecsdl.org/site/terms_use address. Redistribution subject to ECS terms of use (see 130.237.29.138Downloaded on 2014-06-04 to IP

Fig. 1. Powder x-ray diffrac-tion patterns for LiNi,Mn1_,04samples 19, 21, and 23, with

= 0.1 (a), 0.3 (b), and 0.5 (c)prepared by the sal-gel methadat 600C. The inset shows theregion near the spinel (400)peak.

as 1 2x Li per formula unit. Once all the Mn 3d e5 elec-trons are removed, the next electrons available are from Ni3d e5, which has a 0.5 eV higher binding energy. Thus, thepotential of the cell steps up by about 0.5 V. The length ofthe 4.7 V plateau should be 2x Li per formula unit becausethere are two electrons per nickel atom in the lowest eglevel. Thus, in the fully charged state (4.9 V), the Ni shouldbe in oxidation state +4.

When x = 0, the capacity of Li/LiMn2O4 cells appears at4.1 V. Figure 4 shows that as x increases, the discharge

0.10 0.20 0.30 0.40 0.50x in LiNiMn2O4

Fig. 2. Lattice constant vs. x for LiNiMn1_O4 samples as indicat-ed in the legend. All the samples in Table I, except samples 9-18and 28-30 are included in the figure.

capacity of the 4.1 V plateau decreases approximately as1 2x Li per formula unit (1 Li per formula unit is about148 mAh/g). The discharge capacity of the 4.7 V plateauincreases approximately as 2x Li per formula unit, so thatthe total capacity of the samples (both the 4.1 and 4.7 Vplateaus) is constant. This agrees well with the argumentsabove and proves that the electron energy level locationsproposed in Ref. 16 are correct. In simple terms, the 4.1 Vplateau is related to the oxidation of Mn3 to Mn" and the4.7 V plateau to the oxidation of Ni2 to Ni".

The cells made from the sol-gel materials described inFig. 3 suffered from parallel electrolyte decomposition aLthese high potentials. The net effect of this is that theeffective current used to deintercalate lithium duringcharge is smaller than the set current, because some frac-tion of the current is used to decompose electrolyte.During discharge, the effective current is higher than theset current. This leads to a charge imbalance betweencharge and discharge which is particularly severe for thex = 0.5 sample in Fig. 3a. Since the capacities used in Fig.4a are the discharge capacities from Fig. 3, these are sys-tematically lower than would be attained in the absence ofelectrolyte decomposition. On the other hand, electrolytedecomposition is much less severe for the solid-state mate-rials as shown in Fig. 3f-j, and hence Fig. 4b is more reli-able than Fig. 4a. The sol-gel materials made at 600Chave specific surface areas near 10 m2/g as we see later,while the solid-state materials have surface areas near1 m2/g. This is a possible explanation why electrolytedecomposition is more severe for the sol-gel materials.Alternatively, differences in surface chemistry between thesol-gel and solid-state materials could be responsible forthe difference.

According to our model for the length of the plateaucapacities, materials with x = 0.5 should show no 4.1 Vplateau. This is true for the sol-gel material (sample 23)shown in Fig. 3a, but not for the solid-state material (sam-ple 8) shown in Fig. 3f. The presence of the 4.1 V plateauin Fig. 3f, suggests that this sample may be nickel defi-cient. Figure 2 shows that sample 8 has a larger latticeconstant than sample 23, again consistent with less nickelin the spinel phase. AAS analysis shows that both speci-mens have the same desired overall Ni composition of x =0.5. In order to understand the origin of the 4.1 V plateauin sample 8, we noted that it had been prepared at higher

J. Electrochem. Soc., Vol. 144, No. 1, January 1997 The Electrochemical Society, Inc. 207

S

10 20 30 40 50 60 70 80 90SCA I I tRING ANGLE (deg.)

A+.

600 Sol-Gel

850 Sol-Gel

750 Solid State

CCD

C0C-)

CD-J

' I ' I I

8.24d

8.220-

8.200 -A

.8.180 - +

A8.160 I I I I

0.00


208 J. Electrochem. Soc., Vol. 144, No. 1, January 1997 The Electrochemical Society, Inc.

temperature than sample 23. We now consider the effect ofan increase to the synthesis temperature.

Figure 5 shows the TGA curve for sample 10 (sol-gel, x =0.5, 300C) heated and cooled in air. There is a reversibleweight loss associated with oxygen loss during heating

>(0.

and weight gain due to reincorporation during cooling. Ina recent paper of ours, we identified the reactions whichoccurred during similar weight loss events in the beatingsof Li1Mn2_O4. ' There we used diffraction studies ofsamples quenched from temperatures above the onset of

SOL-GEL SOLID-STATE

Fig. 3. Potential vs. capacityfor Li/LiNi,,Mn1_O4 cells. Thesamples presented are: (a) sam-pie 23, (b) sample 22, (c) sample21, (d) sample 20, (e) sample19, (f) sample 8, (gJ no dataavailable, (h) sample 6, Ci) sam-ple 5, (j) sample 3.

0 40 80Capacity (mA.hr/g)

120 160 0 40Capacity (mA.hr/g)

120 160


J. Electrochem. Soc., Vol. 144, No. 1, January 1997 The Electrochemical Society, Inc.

!rap-,t

209

a) SOL-GELI low V plateauA high V plateauD total

117 mAhr/g.2x 117 mAhr/g.(1-2x)

b) SOLID-STATE

Fig. 4. Discharge capacity ofthe 4.1 V plateau, 4.7 Vplateau, and total dischargecapacity between 3.0 and 4.9 Vfor Li/LiNiMn1.O4 cells. (a)Samples 19-23 prepared by sol-gel methods; (b) samples 2, 3, 5,6, and 8 prepared by solid-statemethods. A demarcation line at43 V was used to partition thecapacity into the two regions.The solid and dashed lines in thefigures are linear fits as indicat-ed in the legends.

weight loss to determine the reaction occurring duringweight loss. We use the same strategy here.

Figure 6 shows the diffraction patterns of samples 28,29, and 30 (all x = 0.5), quenched from 650, 750, and850C. The latter two samples have been quenched wellabove the onset of weight loss in Fig. 5. An extra set of dif-fraction lines appears in samples 29 and 30. Peaks from arock-salt related structure near 37.5, 43.8 (see inset in thefigure), and 63.8 are clearly visible. In addition, the latticeconstant of the spinel phase itself increases with quench-ing temperature, as shown in Fig. 7. The peaks of theimpurity phase can be indexed on a rock-salt structure,and a cubic lattice constant of 4.140 A was found for thisphase from two-phase Rietveld refinement. Since the lat-tice constants of NiO and MnO are 4.18 and 4.44 A, respec-tively,'8 it is unlikely that this phase contains Mn. The lat-tice constant of LiNi50 decreases with z, and is 4.140 Aat z 0.18. We propose that the impurity phase isLiNi1_0 with z near 0.18. The increase of the lattice con-stant of the spinel phase with quenching temperature isdue to the removal of Ni from it (see Fig. 2).

We propose that the following disproportionation reac-tion occurs above the weight loss onset

LiNi05Mn1 504 5 qLiNi10+ rLiNj55 ,,,Mn1 5+,o04 + s 02 [1]

This reaction can be balanced by equating the Ni, Mn, Li,and 0 amounts on the right and left sides of the equation,s is obtained from the weight loss vs. temperature. Thisqualitatively explains the observed data. Figure 5 showsthat as the temperature increases above 650C, s increases,necessitating the formation of a phase with a larger cationto anion ratio than the 3:4 found in spinel. Since LiNi10has a cation to anion ratio of 1:1, q and w increase, and rdecreases while s increases. Further work is needed to ver-ify Eq. 1 quantitatively, and this will be the subject offuture investigations.

Now that we have learned that the oxygen loss in sam-ples heated above 650C reduces the amount of Ni in thespinel phase, the 4.1 V plateau in sample 8 (Fig. 3f) is dueto Ni deficiency probably caused by excessively fast cool-ing and insufficient oxygen uptake during cooling of the

sample. Indeed, x-ray diffraction on this sample does showthe presence of the rock-salt LiNi1_0 phase. The amountof Ni deficiency is easily estimated from the length of the4.1 V plateau (Fig. 3f) for sample 8. We estimate a Ni con-centration of x = 0.43, not x = 0.5, in this sample. Theadvantage of the sol-gel method is that it allows the pro-duction of materials at lower synthesis temperatures thanthe solid-state method, for example, entirely below 650C,where oxygen loss occurs.

At this point, it is worth discussing the results present-ed in Ref. 13, Amine et al. claim that NiO, not LiNi10,coexists with LiNi05Mn15O4 when sol-gel samples arerecalcined at 650C. (See their Fig. 2.) Since they did notcarefully measure the lattice constant of their impurityphase, it is likely that they really have LiNi1_,0, with znear 0.2, just like us. Figure 4 in Ref. 13, shows the varia-tion of the spinel lattice constant with x in LiNi.Mn204.The data show substantial upward curvature near x 0.5,unlike our data in Fig. 2. This suggests that Amine et al's

0)

E>.C)

0

140.0.

a120.0 -

100.0 -

80.0 -

60.0 -

40.0 -

20.0 - S.I . I I I _._I

0.1 0.2 0.3 0.4x in LiNiMn2,O4

0.5 0.0 0.1 0.2 0.3 0.4 0.5x in LiNiMn2.04

101

100

I,rM0.z. 98

97

96

95100 300 500 700 900

Temperature C

Fig. 5. TGA measurement on sample 10 (x = 0.5 in LiNiMn1OJin air.


210 1 Electrochem. Soc., Vol. 144, No. 1, January 1997 The Electrochemical Society, Inc.

Fig. 6. X-ray diffraction pro-files of (a) sample 28, (b) sample29, (c) sample 30, quenchedfrom 650, 750, and 850C,respectively. All samples hadx = 0.5 in LiNi,,Mn1.O4. Theinsets show the region near thespinel (400) peak. The (peak)from a U,Ni1.Z0 phase appearsto the left of the spinel (400)peak in the samples quenchedfrom higher temperature.

samples with large x are Ni deficient. This suggestion isfurther supported by an examination of the potential pro-files in Ref. 13, shown in Fig. 10a of that reference. A sub-stantial 4.1 V plateau is still observed for Amine's x =0.5sample, unlike our sol-gel sample shown in Fig. 3a. Thisfurther proves that Amine's x = 0.5 samples have lessincorporated Ni than ours.

Now we examine the effect of heating temperature onsol-gel LiNi55Mn1504 samples. Figure 8 shows the diffrac-tion patterns of samples 10, 13, and 15 (x = 0.5, sol-gel)heated at 300, 600, and 800C. Only in the sample heatedto 800C is evidence of LiNi1O observed. Figure 9 showsthe lattice constant and average Mn oxidation state ofsamples 9-15 (x = 0.5, sol-gel) plotted vs. heating temper-ature. The lattice constant is minimum, and the Mn oxida-tion state is maximum, near 600C heating temperature.The increase of lattice constant and decrease of Mn oxida-tion state above 600C is explained by the disproportiona-tion reaction 1. The reasons for the variations below 600Care now explored.

In the sol-gel method, the reactants used do not containenough oxygen for the final product, once that needed forthe gaseous decomposition products is accounted for. Theextra oxygen needed must come from the atmosphere. Insamples heated at low temperatures, this oxygen uptakemay be slow and hence incomplete for samples heated forshort times in air. Then the samples will contain excessMn3, and their lattice constants should be larger (asobserved) since Mn3 is larger than Mn4t Figure 10 showsthe manganese oxidation state and the lattice constant forsamples heated at 250C in air (sample 9) and in pure oxy-gen (sample 16) compared to the optimum sol-gel samplemade at 600C (sample 13). Heating in pure oxygenimproves the sample, as its lattice constant decreases andMn oxidation state increases..

It is possible to make LiNi55Mn5 504 at 80 0C which isapproximately single phase. This is done with a combina-tion of slow cooling and an oxygen atmosphere. Figure 11shows the lattice constant of sol-gel samples 15, 17, and18. These were made in air, in oxygen, and in oxygen withslow cooling, respectively. They are compared to the sam-ple (sample 13) made at 600C. Figure 12 shows the poten-tial profiles for samples 15, 17, and 18, measured with acurrent of 14.8 mA/g. The 4.1 V plateau is almost absent insamples 17 and 18, proving that they contain almost all the

desired nickel. Thus slow cooling and an oxygen atmos-phere help eliminate the LiNi1.0 impurity.

Figure 13 shows the differential capacity, dy/dy ofLi/LiiyNirMns..x04 cells plotted vs. potential. The sol-gelsamples are samples 19-23, respectively, and the solid-state samples are samples 3, 5, 6, and 8. Figure 13 showsthe shift of the capacity to higher potential as x increases,and the complete elimination of the 4.1 V plateau for sam-ple 23. The dy/dy data for the sol-gel sample suffers dueto the simultaneous electrolyte decomposition reactions.The data for the solid-state samples are particularly beau-tiful. The solid-state sample with x = 0.5 (Fig. 13f) showsa double-peaked feature centered at 4.7 V, which looksalmost identical to that of Li/LiMn2O4 cells19 but shiftedup in potential from 4.1 to 4.7 V. This helps to demonstratethat the double-peaked feature is not due to some struc-ture in the electronic density of states, because it is unlike-ly that the Mn e5 and Ni e9 levels would show the samestructure. Instead, this feature is most likely due to theordering of lithium on 8a sites at 50% filling as we have

8.22C , I

8.210

8.200 . -

8.190

8.180.

I I I I500 600 700 800 900

Quench Temperature (C)

Fig. 7. The lattice constant of the quenched samples (28, 29, 30)planed vs. quenching temperature. Each of the samples had x =0.5 in liNi,,Mn1.,04 before quenching.

p6000400002000

40 50 60 70 80 90SCM iuzRING ANGLE (deg.)

'CC(0(I)C0

C-)a)0tCa-J

8.1 CSlowCool

1


J. Electrochem. Soc., Vol. 144, No. 1, January 1997 The Electrochemicat Society, Inc. 211

1800

1200600

0C/) 12008004oo

0800600400200

0

ato-C0?

a0?a0?5500to.0?

c)8ocLxNAj.4243444546i.

-I

600C,.42 43 44 45 46

. 1.LL1Fig. 8. Selected diffraction

patterns of the sd-gel sampleswith x = 0.5 in LiNiMn1O4 asa function of heating tempera-ture as indicated. The insetshows the region of the spine1(400) peak. The samples are (a)sample 10, (b) sample 13, Cc)sample 15.a) 300C

Il 42 43 44 45 46

10 20 30 40 50 60 70 80 90SCM rRJNG ANGLE (deg.)

discussed thoroughly elsewhere.2 Since the lattice of 8a present when x = 0 shifts to 4.7 V when x = 0.5. At inter-sites is not changed by the addition of nickel, this is rea- mediate compositions, the 4.1 V plateau has a length givensonable. The details of dy/dV for samples with intermedi-ate x are more difficult to explain, and further work isneeded to do so.

As a final result, Fig. 14 shows the discharge capacity vs.cycle number for sample 13 (501-gel, x = 0.5, 600C) for acell cycled at 14.8 mA/g. The cell was cycled between 4.9and 3.0 V. The recharge capacity is always about 10 mAhlonger than the discharge capacity due to electrolytedecomposition, but the cell maintains its discharge capac-ity quite well, suggesting that the material itself is quitestable to cycling.

ConclusionsThe structure and electrochemistry of LiNirMni_O4

have been studied for 30 samples prepared by two routesunder a variety of synthesis conditions. The 4.1 V plateau

8.190

8.186a

8.182to,a

8.1784?. 8.174

8.170

200 300 400 500 600 700 800

200 300 400 500 600 700 800Heating temperature (C)

Fig. 9. Comparison of the lattice constant of the unit cell and theaverage valence of Mn for sal-gel LiNi0 5Mn 504 samples 9-15 heat-ed at different temperatures: (a) lattice constant vs. synthesis tem-perature, (b) oxidation state of Mn vs. synthesis temperature.

24 hrs, air 24 hrs, air 24 hrs, air250C /24hrs, 02, 250C 600C

(a)

Fig. 10. Variation of both the lattice constant and the averagevalence of Mn with synthesis conditions for L1Ni05Mn15O5 samples9, 16, and 13. Synthesis conditions are given in the figure.

800C 800C 800C, 02 6000air 02 slow cool air

Fig. 11. Lattice constant for sal-gel samples 15, 17, and 18 com-pared to sample 13. The preparation conditions are given in thefigure.


212 J. Elect rochem. Soc., Vol. 144, No. 1, January 1997 The Electrochemical Society, Inc.

5.3

5.1

4.9

4.74.5.144.1

3.9

3.7

3.5

Fig. 12. Potential profiles of samples 15, 17, and 18, measuredat C/1O (14.7 mA/g). The preparation conditions are given in thelegend to the figure.

by 1 to 2x Li per formula unit, and the 4.7 V plateau has alength given by 2x Li per formula unit. The shift of the

plateau potential is caused by the 0.6 eV higher bindingenergy of the Ni e5 electrons compared to the Mn eg electrons.

LiNi.Mn1O4 loses oxygen and disproportionates to aspinel with a smaller Ni content and LiNi1_,O when it isheated over about 650C. The reaction is reversible if slowcooling rates are used, but samples which are rapidlycooled end up with less nickel in the spinel phase thandesired. The importance of a careful understanding of thesolid-state chemistry of these complex spinels is critical tothe successful interpretation of their electrochemicalbehavior.

It is our opinion that similar careful studies of otherLiMMn1_O4 materials are warranted, even though therehave been numerous works on such materials before. Thisis because most of the early workers did not pay attentionto the oxygen loss from spinels at high temperatures andhence may have had impure samples, and also becausemuch of the electrochemistry was limited to potentialsbelow 4.3 V

AcknowledgmentOne of the authors (M.Z.) would like to thank the

Natural Sciences and Engineering Research Council ofCanada (NSERC) for the award of an NSERC PostdoctoralFellowships. The useful comments of Ulrich von Sackenand Jan Reimers are gratefully acknowledged.

Manuscript submitted May 24, 1996; revised manuscriptreceived Sept. 2, 1996.

Fig. 13. Differential capacityof Li/LiNiMn1.O4 cells vs.potential. The samples studiedhave the same nomenclature asin Fig. 3. Notice that the verticalaxes on the left and right panelsfor each sample are different.

0 2 4 6 8 10 12 14 16Time

I>V>1.9


J. Electrochem. Soc., Vol. 144, No. 1, January 1997 The Electrochemical Society, Inc. 213

I

Fig. 14. Capacity vs. cycle number for an Li/LiNi05Mn15O4 cellusing sample 13 as the cathode. The cell was cycled at 14.7 mA/g.

Daihousie University assisted in meeting the publicationcosts of this article.

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20Cycle number


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Synthesis and Electrochemistry of LiNiMn2_O4