Lithium Manganese Nickel Oxides Lix(MnyNi 1_) 2-x02
`I. Synthesis and Characterization of Thin Films and Bulk Phases
`
`B. J. Neudecker,* R. A. Zuhr, B. S. Kwak, * and J. B. Bates*
`Oak Ridge National Laboratory, Solid State Division, Oak Ridge, Tennessee 37831-6030, USA
`
`J. D. Robertson
`Department of Chemistry, University of Kentucky, Lexington, Kentucky 40502, USA
`
`ABSTRACT
`The series Lix(Mn Ni 1 _ ) 2_x02 for x::; 1.33 and 0.38 ::; y ::; 0.50 shows a very close relationship to its parent series
`LixNi2_x0 2• The refined lattice parameters for at least 0.93 ::; x ::; 1.26 are a linear function of the concentration ratio
`Li/(Mn + Ni) which in turn is proportional to the averaged valence state of the transition metals. Lix(MnyNi 1_y) 2_x02 is
`able to reversibly coprecipitate/reinsert Li20 and release/absorb 0 2• This self-regulation mechanism seems to always
`adjust the number of cations to an undisturbed oxygen sublattice according to the rule "cations/anions= 1," which holds
`true at least for temperatures up to 800°C and oxygen partial pressures above 10- 5 atm. Samples prepared in air and under
`0 2 did not show nucleation of Li 20, not eve!! for x > 1.0. The series LiAMnyNi1_y) 2_x02 where 0.38 ::; y ::; 0.50 crystallizes
`in a rhombohedral unit cell (space group R3m) for x < 1.15 and transforms into a single monoclinic phase (space group
`C2/c) for x > 1.25. The similarity between Li~i2_x02 and Lix(MnyNi1-yh-x02 strongly suggests a rhombohedral--+ cubic
`transition at x = 0.6 for the latter series. Derived from the linear aependence of the X-ray density on the stoichiometric
`parameter x, an equation was found with which the lithium concentration of Lix(MnyNi 1_yh-x02 thin film phases over the
`entire range 0 ::; x ::; 1.33 can be determined accurately without extensive ion-beam analysis. XPS measurements on a
`film with the bulk stoichiometry Liu 0Mn 0_39Ni 0 _510 2 gave evidence for Mn4+ and Mn3+, but no indication was found for
`nickel valence states other than Ni2+. In order to meet the above-given stoichiometry, the averaged nickel valence state
`had to increase with film depth.
`
`Introduction
`In recent years, LiNi02 has been used as a cathode mate(cid:173)
`rial in high-voltage lithium-ion and lithium batteries 1
`4
`-
`Electrochemical experiments, however, showed that a slight
`deviation from the ideal starting stoichiometry LiNi02 re(cid:173)
`sulted in a poor cell performance caused by NF+ defects on
`Li+ sites. 5 Moreover, upon extensive lithium deintercalation
`wherein x in Li_xNi02 approaches zero and the nickel
`valence state comes close to its maximum of +4, nickel ions
`migrate from their nickel layer sites into the vacancies of
`the lithium layers. Such nickel migration creates severe dif(cid:173)
`fusionallimitations to lithium reinsertion thereby reducing
`cell performance.6
`These drawbacks stimulated our research on the partial(cid:173)
`ly substituted manganese derivatives of LiNi02 , namely,
`Lix(MnyNi1_yh-x0 2 • In particular, it was felt that the intro(cid:173)
`duction of Mn4+ "buffer ions," which easily form under typ(cid:173)
`ical solid-state preparation conditions such as annealing at
`700°C in air, would lift the electrochemically detrimental
`effect Ni2+ -defects impose on chemically prepared LiNi02
`cathodes. That is, Mn4+ ions could help balance the two oxy(cid:173)
`gen anions without the need of Ni2+ occupying u+ sites.
`Although Li~i2_x02 for x < 1 can be chemically prepared,7
`attempts to synthesize single-phase compounds with x/(2 -
`x) > 1 were unsuccessful, 7 because the lithium excess always
`caused formation of Li2C03 or Li 20 as a second phase.
`Bronger et al. 8 and Migeon et al., 9 however, reported the
`preparation of single-phase Li0_65Ni 0_350 ( = Li130Ni 0 7o02) in
`dry 0 2 at 450°C and Li2Ni0 3 (= Li133Ni0_670 2) under 150 bar
`0 2 670°C, respectively. Therefore we were encouraged to
`attempt the synthesis of LUMnYNi1_yh-x02 films with x :S
`1.33 and to compare this series with the unsubstituted lithi(cid:173)
`um-nickel oxides. Furthermore, should single-phase
`Lix(MnyNi1_yh-x0 2 be obtained, we were interested in deter(cid:173)
`mining the extent of oxidation of manganese and nickel in
`subsequent electrochemical experiments upon lithium dein(cid:173)
`tercalation. These compounds could retain some u+ in the
`lithium layers, even when all manganese ions and all nickel
`ions have reached their maximal valence states of MnH and
`Ni4+, respectively. This idea is of particular interest with
`respect to possibly suppressing the detrimental Ni-migra(cid:173)
`tion into the lithium layers of highly charged cathodes.
`
`* Electrochemical Society Active Member.
`
`The purpose of this paper is to describe the synthesis
`and characterization of Lix(MnyNi 1_y) 2_x02 in thin-film and
`bulk forms. Our electrochemical studies of the thin films
`are reported in a companion. 10
`
`Experimental
`All of the lithium manganese nickel oxide thin films were
`deposited by planar rf magnetron sputtering from single
`disk-shaped targets, typically 50 mm in diam and 5 mm
`thick. These targets and the powder sample for the thermo(cid:173)
`gravimetric analysis (TGA) served as samples for studies on
`bulk phases.
`Preparation and characterization of bulk phases.(cid:173)
`Stoichiometric amounts of LiOH·HP (Alfa Aesar, min
`56.5 wt % LiOH), Mn02 (Alfa Aesar, Puratronic, 99.999%
`metals basis), and NiO (Alfa Aesar, Puratronic, 99.998%
`metals basis), leading to the nominal cation stoichiome(cid:173)
`tries Li~.24Mn0.37Ni0.39 and Liu 9Mn 0_33Ni 0 .. 8 , were thoroughly
`blended and ground in an Al20 3 mortar. The loose powders
`were placed in Al20 3 crucibles and heated at 600°C in air
`for 3 h. After regrinding, the powders were cold-pressed
`into disks (57.2 mm in diam) at 1 kbar and were subse(cid:173)
`quently fired in air at 9000C for 12 h. During cooling, the
`targets were held for 12 h at 500°C in order to minimize
`any possible lithium concentration gradients. This tem(cid:173)
`perature was low enough to ensure that no additional
`lithium evaporated from the targets, but it was still high
`enough for rapid u+ diffusion, thus equilibrating surface
`and bulk. The pellets shrank by 14% in diameter during
`the final firing at 9000C.
`Powder X-ray diffraction measurements (XRD) of the
`targets were performed on a PC-controlled Scintag Theta(cid:173)
`Theta XDS 2000 diffractometer using Cu K<X radiation.
`Data were acquired in the 2 6 range 10-90° at a continuous
`scan rate of 0.1°/min, and the peak positions were found
`after background removal by manual spline curve fitting
`and performing K<X2 (A. = 1.544390 A) stripping. Scraped(cid:173)
`off target powder samples were mixed and ground with
`mica powder11 which served as an internal standard.
`Lattice parameters were determined by weighted least(cid:173)
`squares refinement with the program LATCONY Because
`the targets consisted of two-phase mixtures belonging to
`the quaternary system Li-Mn-Ni-0, we did not attempt to
`apply Rietveld analysis.
`
`4148
`
`J. Electrochem. Soc., Vol. 145, No. 12, December 1998 ©The Electrochemical Society, Inc.
`
`
`
`108.31.169.173Downloaded on 2015-07-09 to IP
`
` address. Redistribution subject to ECS terms of use (see
`
`
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`
`SONY EXHIBIT 1010
`
`Page 1 of 21
`
`

`
`J. Electrochem. Soc., Vol. 145, No. 12, December 1998 ©The Electrochemical Society, Inc.
`
`4149
`
`The Li/Mn/Ni ratios of the powders scraped from the
`front and the back side of the targets were determined by
`inductively coupled plasma spectroscopy (ICP). Six inde(cid:173)
`pendent measurements were made on each sample and the
`results averaged. Assuming full occupancy of the oxygen
`sublattice (see Results and Discussion), the stoichiometries
`of the sputtered target surfaces were Liu8Mn0.39Ni 0.430 2 and
`Li 119Mn0.31Ni 0.500 2 for targets with the nominal cation start(cid:173)
`ing compositions Lit. 24Mn 0.37Ni 0.39 and Liu 9Mn0 .33Nio.4B•
`respectively. The unsputtered target back sides, representing
`the bulk stoichiometry, were Li 1.23Mn0.37Ni 0.400 2 and
`Liu 9Mn0.33Ni 0.480 2 , respectively, and, with respect to the
`cation ratios, were identical with the starting compositions
`within experimental error. The overall lithium oxide loss,
`which is commonly observed in lithium first-row transition
`metal oxides when annealed above 7oo•c under atmos(cid:173)
`pheres other than pure 0 2, appeared to be minimal. We
`assume that this can be attributed to a relatively large mass
`(-30 g) pressed into a target pellet with a relatively small
`geometrical surface area of about 55 cm2
`• The difference in
`stoichiometry between the target bulk and sputtered surface
`is a consequence of preferential sputtering. As can be seen
`from the results, the trend is not the same in both targets.
`The sample for TGA was prepared from LiOH·HzO,
`Mn0 2, and NiO by pressing a powder with the nominal
`cation composition Li1.45Mn0.45Ni0.45 into a pellet. The pellet
`was fired in air for 3 h intervals at 300, 600, and 75o•c.
`During cooling to room temperature, the pellet dwelled for
`12 h at 5oo•c. The pellet was ground to a fine powder
`which then was loaded into the Pt crucible of the balance.
`Alternate runs in air and flowing N2 were performed. The
`sample was heated at 10•c;min to 800°C and held at this
`temperature for 1 h before cooling to room temperature.
`At the conclusion of the TGA experiment, the powder was
`analyzed by ICP and XRD in the same way as the targets.
`Preparation and characterization of thin films.-Thin
`films were simultaneously deposited onto graphite disks,
`single-crystal silicon wafers, quartz glass slides, and gold
`foil substrates by rf magnetron sputtering of the lithium
`manganese nickel oxide targets in 20 mTorr of a 50:1 Ar/0 2
`gas mixture. The substrates and the thickness monitor
`were fixed at a distance of 5 em from the target, and the
`net applied rf power of 50 W yielded a deposition rate of
`typically 20 A;min. The films were deposited through an
`aluminum mask which defined a 12.5 X 3 mm area and
`ranged in thickness from 0.3 to 3.0 ,....m. The masses of the
`
`as-deposited films were estimated from the deposition
`time and the steady-state deposition rate measured with
`the thickness monitor before and after film preparation.
`Subsequent surface profile measurements (Dektak 3030)
`of the as-deposited films on smooth substrates (quartz
`glass slides or single-crystal silicon wafers) yielded geo(cid:173)
`metrical densities of approximately 4.2 g/cm 3
`• After depo(cid:173)
`sition, the films were annealed for 3 h in different atmos(cid:173)
`pheres (flowing 0 2 , N2 , or air) between 700 and 80o•c in
`order to investigate the influence of different oxygen par(cid:173)
`tial pressures on the film stoichiometry. Typical heating
`and cooling rates were 3•c;min. The geometrical density
`increased during the crystallization process, but the films
`maintained their black color regardless of the annealing
`temperature and atmosphere.
`Thin film analysis and characterization.-Powder X-ray
`diffraction (XRD) measurements of the 2-3 ,....m thick films
`were performed as described above for the targets. In these
`cases, the substrate materials (usually Au foil) served as
`internal standards. The as-deposited films were X-ray
`amorphous. Lattice parameters of the crystallized films
`were determined by least-squares refinement using the pro(cid:173)
`gram LATCON. Rietveld analysis was not applied because
`all of the films exhibited preferred orientation as demon(cid:173)
`strated in rocking curve scans 13 for the (101) and (104)
`reflection of a Liu0Mn0.45Nio. 450 2 and a Liu4Mno.4aNio.4a0 2
`films, respectively (Fig. 1).
`Rutherford backscattering spectrometry (RBS) was used
`to determine the Mn/Ni/0 ratios of the films. The meas(cid:173)
`ured energy spectra (Fig. 2) represent a convolution of
`both mass and depth information that was separated by an
`appropriate fitting program. Due to its low atomic number
`and mass, lithium could not be detected directly, but its
`presence was inferred from the stopping powers necessary
`to fit the Mn-Ni-0 data. The stoichiometry of as-deposit(cid:173)
`ed amorphous films was determined on graphite substrate
`disks whereas the annealed crystalline films were meas(cid:173)
`ured on Si wafers. We noticed a light SiOx tarnishing layer
`on the nondeposited area of the wafer when annealed in
`air at soo•c. Although this layer was much thinner than
`the films to be investigated, the presence of lithium ions at
`the film/silicon interface certainly enhanced its formation.
`The tarnishing layer was determined by X-ray diffraction
`to consist of Li2Si03 and an unidentified compound. Be(cid:173)
`cause of the presence of the SiOx and Li2Si03 layers, the
`measured (Mn + Ni)/0 ratio is smaller than the actual
`
`a)!\
`500 -
`I \ -
`-
`-
`tn
`tn 700
`Q.
`Q.
`(,) 400
`(,)
`>a 600
`>a
`.:!::::
`.:!::::
`c 300 I
`tn
`tn
`...
`...
`\ c 500
`Cl)
`Cl)
`-
`c
`c
`
`600
`
`200
`
`l
`
`\
`\
`
`l
`
`II •
`~
`~
`' \
`
`900
`
`800
`
`400
`
`300
`
`200
`15
`
`100
`10 15 20 25 30 35
`ro (Degrees)
`
`r; b)
`I \
`\
`\ er RBS, PIXE, PIGE, and XRD]
`
`(
`
`)
`
`Fig. 1 • XRD omega stefc scans
`0 rocking curves 0
`(a) or the
`(101) peak fixed at 29 •• ,on: =
`36.68• of a 2.6 11-m thick rhom-
`bohedral Li1.1Mn0.45Ni0.4502 [aft-
`er RBS, PIXE, PIGE, and XRD]
`film on Au foil annealed at
`750"C in air for 3 h and (b) for
`the (1 04) peak fix~ at 29""'"" =
`44.so• of a 9,000 A thick rhom-
`bohedral Li1.14Mno. 43Nio.4a02 [aft-
`
`film on Pt foil annealed at 750"C
`under 0 2 for 3 h. The appear-
`once of a peak in both omega
`scans aHirms the preferred ori-
`entation of these polycrystalline
`films. All other films gave similar
`scans due to film texture.
`
`20 25 30 35 40
`ro (Degrees)
`
`
`
`108.31.169.173Downloaded on 2015-07-09 to IP
`
` address. Redistribution subject to ECS terms of use (see
`
`
`
`) unless CC License in place (see abstract).(cid:160) ecsdl.org/site/terms_use
`
`Page 2 of 21
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`

`
`4150
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`J. E/ectrochem. Soc., Vol. 145, No. 12, December 1998 ©The Electrochemical Society, Inc.
`
`.-
`0
`::t
`0 ,...
`Fig. 2. Ja) RBS spectrum of a
`5,600 A
`thick
`crystalline
`........
`...
`Li1.11Mn0.39Nio.5002 [after RBS,
`tn
`PIXE, PIGE, and XRD] film on Si
`substrate. The RBS curve-fitting
`c:
`results in
`Li~.11 Mn0.41 Nio.41102.06
`::s
`substrate during the postanneal -
`with a thickness of 5,540 A. The
`0
`0.06 oxygen excess is attributed
`to oxygen taken up by the Si 0
`upper edge of the overlappin9 -
`treatment. The insets show the
`'t:J
`·-
`Cl)
`>
`
`energy scatter ranges of Mn an
`Ni and the Si substrate and oxy-
`gen, respectively.
`
`2500
`
`2000
`
`1500
`
`1000
`
`500
`
`0
`
`o Raw Data
`- - Simulation
`
`1480
`
`1520
`
`1560
`
`Mn, Ni
`
`Mn-Ni
`edge
`
`400
`
`800
`
`1600
`1200
`Energy (keV)
`
`2000
`
`ratio of the Li-Mn-Ni-0 film. However, we show below
`that the composition of all Li-Mn-Ni-0 films can be rep(cid:173)
`resented by Lix(MnyNi 1_y) 2_x0 2 and that the deviation of
`the true (Mn + Ni)/0 ratio from the measured ratio falls
`within the standard error of RBS measurements which is
`estimated to be less than 10 atom %.
`Particle-induced X-ray emission (PIXE) analysis14 was
`used to determine the Mn/Ni ratio in the films. The lithi(cid:173)
`um content could not be measured with this technique
`because the energy of the Li Kot X-ray emission line at
`0.052 keV is well below the detector threshold value. The
`areal masses of Mn and Ni in the films were analyzed by
`comparing the Mn and Ni X-ray yields to those obtained
`from thin-film standards (MicroMatter, Inc.). An example
`of a PIXE spectrum recorded from a crystalline sample is
`shown in Fig. 3. PIXE measurements confirmed that the
`Mn/Ni ratios were 0.76:!: 0.05 and 1.00:!: 0.07 for the films
`
`deposited from targets with the ratios Mn/Ni = 0.62 and
`0.91, respectively, at the sputter face. These ratios deter(cid:173)
`mined for the amorphous films did not change upon
`annealing, at least up to 800°C, independent of atmos(cid:173)
`phere. This is most likely due to the negligible volatility of
`the manganese and nickel oxides.
`The lithium and the manganese contents of the films
`were determined by particle-induced gamma-ray emission
`(PIGE) analysis. 15.t 6 The nuclear reactions 7Li(p,p''Y) 7Li
`E~ = 477 keV and 55Mn(p,n')') 55Fe E~ = 932 keV at a proton
`bombarding energy of 2.0 MeV were used. This low bom(cid:173)
`barding energy precluded the determination of the nickel
`content of the film, but had to be chosen in order to reduce
`the high ')'-ray count rate from the silicon substrate at 4
`MeV. An example of a PIGE spectrum which was taken
`from a postannealed crystalline Li~.26Mn037Ni0.3702 film on
`Si is shown in Fig. 4. Single measurements of the Li/Mn
`atom ratio in a film yielded results with uncertainties on
`
`160
`
`120
`
`100
`
`60
`
`40
`
`20
`
`- 140
`-c
`80 ->-
`-·;;;
`C1l -c
`
`N ._
`~en
`
`:::J
`0
`0
`
`c
`
`Si
`Ka
`
`Mn
`Ka
`
`Ni
`Ka
`
`~
`
`fn -c
`0 ->--'iii
`C1l -c
`
`:::J
`0
`
`c
`
`150
`
`100
`
`50
`
`0
`
`7Li(p,p'y)1Li
`Ey = 477 keV
`
`55Mn(p,ny)56Fe
`Ey = 932 keV
`
`I
`
`0
`
`1000
`Energy (keV)
`Fig. 4. PIGE spectrum of a 9,000 A thick crystalline
`Li1.26Mn0.37Ni0.370 2 [after RBS, PIXE, PIGE, and XRD] film on Si sub(cid:173)
`strate annealed at 750•C under 0 2 for 3 h. The relevant Li and Mn
`signals are marked with the appropriate nuclear reaction.
`
`2000
`
`0
`
`0
`
`2
`
`4
`
`6
`
`8
`
`10
`
`Energy (keV)
`Fig. 3. PIXE spectrum of a 9,000 A thick crystalline
`Liu6Mn0.37Ni0.370 2 [after RBS, PIXE, PIGE, and XRD] film on Si sub(cid:173)
`strate annealed at 750•c under 0 2 for 3 h. The sputter surface of
`the target had the composition Li1.18Mn0.39Ni0.4302 [after ICP and
`evaluating the oxygen stoichiometry].
`
`
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`Page 3 of 21
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`

`
`J. Electrochem. Soc. , Vol. 145, No. 12, December 1998 ©The Electrochemical Society, Inc.
`
`4151
`
`Fig. 5. SEM photograph of a 9,000 A thick as-deposited amor(cid:173)
`phous Liu1Mn0.36Ni0.1602 film on Si substrate. The average grain
`size is about 1 ,000 A.
`
`the order of 10%. As in the PIXE measurements, the 5%
`uncertainty in the certified concentration of each thin(cid:173)
`film standard from Micromatter, Incorporated, was the
`major source of experimental error.
`X-ray photoelectron spectra of the films were obtained
`with a Physical Electronics PHI 3057 Subsystem XPS
`equipped with a spherical capacitor energy analyzer and
`an Omni Focus III small area lens. The Mg anode was
`operated at 26.7 rnA and 15 kV (400 W) and emitted Mg Ka
`radiation of 1253.6 eV. High-resolution spectra at 11.75 eV
`pass energy were recorded in the C (1s), 0 (1s), Ni (2p),
`Mn (2p), Mn (3p), and Li (1s) regions. The specimens were
`analyzed at an electron takeoff angle of 45°, measured with
`respect to the surface plane. Measurements were made on
`a 2.6 ILm thick film prepared at 700°C in air which had the
`bulk stoichiometry of Liu 0Mn0.39Ni0.5 10 2 • The XPS peaks
`were deconvoluted into asymmetric Gaussian envelopes
`with the standard integral background subtraction
`method of Shirley." The spectra were corrected for the dif(cid:173)
`ference between the observed position of the C (1s) peak
`
`Fig. 6. SEM photograph of the film shown in Fig. 5, but now crys(cid:173)
`tallized after an anneal ot 700"C under 0 2 for 3 h. The stoichiometry
`Li~.2~n0.37Ni0.3702• The average grain diameter
`changed to
`increased to approximately 0.3 j.UII.
`
`(285.57 eV) and the reference position of adventitious
`hydrocarbons (285 eV).
`Scanning electron micrographs were obtained with a
`JEOL JSM-840 SEM equipped with a Tracor Northern
`5525 energy dispersive X-ray (EDX) analyzer. The as-de(cid:173)
`posited amorphous films had an average grain size of
`approximately 0.11J.m (Fig. 5). After the postanneal step at
`700°C in air, the crystalline films exhibited an enlarged
`grain size of about 0.3 ILm (Fig. 6). No elements other than
`Mn, Ni, 0, and elements of the underlying substrate were
`detected in the EDX measurements.
`Results and Discussion
`Structure studies.-Bulk phases from the targets.-At the
`sputter surfaces and at the back side surface, the gray-black
`targets were two-phase mixtures of a rhombohedral phase
`and a monoclinic phase which could be indexed to the space
`) and C2/c (Li 2Ni0 3 =
`groups R3m (LiNi0 2-related 18
`3/2 Li 133Ni 0 6P 2-related9
`) , respectively (Fig. 7 and Tables I-
`
`4000
`.-. 3200
`t/) a.
`._.
`(,)
`
`2400
`
`>-.., ·-t/) c 1600
`Q) ..,
`c -
`
`800
`
`0
`
`~~~~~~~~~~~1~
`
`100
`
`25
`
`Fig. 7. XRD powder pattern of
`the target sputter face with the
`overall
`stoichiometry
`Li1.19Mn0.31 Ni0.500 2• Arrows indi(cid:173)
`cate the peaks arising from the
`mica standard. 11 The pattern
`comprises
`a
`rhombohedral
`phase (!iNi02-related, space
`group R3m I and a monoclinic
`phase (Li 2Ni03-related, space
`group C2/c) which both belong
`to the series Li.(Mn~i1 -)2-.02•
`The inset shows the decisive 29
`range where only peaks origi(cid:173)
`nating
`from
`the monoclinic
`phase are expected to appear.
`
`60 70 80
`10 20 30. 40 50
`2 e (Degrees)
`
`90
`
`
`
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`
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`Page 4 of 21
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`

`
`4152
`
`J. Electrochem. Soc., Vol. 145, No. 12, December 1998 ©The Electrochemical Society, Inc.
`
`Table II. Experimental and refined X-ray data of the monoclinic
`phase (space group C2/c) spuHered from the two-phase target
`surface with the overall stoichioll)etry Li1.1~n0.31 Ni0.5002 displayed
`in Fig. 7 (Cu Ka 1 = 1.540562 A). Experimental 26 values after
`correction on the internal standard mica. Estimated stoichiometry
`(cf. Fig. 14 and 16) of the monoclinic phase:
`3/2Li1.2S(Mn~i1-)o.7s02 = Li1.ss(Mn~i1-yk1 203.
`a (A)
`(Exp.)
`
`28
`(Calc.)
`
`Relative
`intensity
`
`d(A)
`(Calc.)
`
`28
`(Exp.)
`
`h
`
`k
`
`Table I. Experimental anj:l refined X-ra~ data of the rhombohedral
`phase (space group RJm) spuHered om the two-phase target
`surface with the overall stoichioll)etry Li~.1 ~n0.31 Ni0.5002 displayed
`in Fig. 7 (Cu Ka 1 = 1.540562 A). Experimental 26 values after
`correction on the internal standard mica. Estimated stoichiometry
`(cf. Fig. 14 and 16) of the rhombohedral phase:
`Li1.1s(Mn~i1-ylo.ss02.
`
`28
`(Exp.)
`
`18.697
`36.572
`37.895
`38.195
`44.355
`48.535
`58.547
`64.348
`68.048
`81.812
`
`h
`
`0
`1
`0
`0
`1
`0
`1
`0
`1
`0
`
`k
`
`0
`0
`0
`1
`0
`1
`0
`1
`1
`2
`
`28
`(Calc.)
`
`Relative
`intensity
`
`d(Al
`(Exp.)
`
`d(Al
`(Calc.)
`
`3
`1
`6
`2
`4
`5
`7
`8
`3
`4
`
`18.702
`36.57 5
`37.927
`38.236
`44.351
`48.527
`58.570
`64.313
`68.036
`81.843
`
`100
`16
`5
`6
`45
`5
`6
`12
`3
`2
`
`4.7421
`2.4550
`2.3723
`2.3543
`2.0406
`1.8742
`1.57 53
`1.4466
`1.3766
`1.1763
`
`4.7407
`2.4548
`2.3703
`2.3519
`2.0408
`1.87 45
`1.5747
`1.4473
`1.3768
`1.1760
`
`, Hexagonal unit cell parameters: a= 2.8777(7) A), b = 14.222(4)
`A, volume = 102.0(0) A3
`, and Z = 3.
`
`III). The close structural relationship between LiNi02 and
`Li 2Ni03 discussed below, where in both cases the number of
`cations equals the number of oxygen anions, strongly sug(cid:173)
`gests that the overall target stoichiometries also adopt this
`ion ratio. Therefore, we can reasonably justify the stoichio(cid:173)
`metric parameters of oxygen given in the experimental sec(cid:173)
`tion. The targets showed approximately 70% of their theo(cid:173)
`retical density based on the amount and density of the two
`phases present in each target (see below).
`In order to understand the structure of lithium man(cid:173)
`ganese nickel oxide, we first demonstrate the structural
`(R3m) and
`resemblance between rhombohedral LiNi02
`19
`monoclinic Li2Ni03 (C2/c). Considering (i) that Li2Mn0 3
`crystallizes in the monoclinic space group C2jc with unit
`cell parameters close to those of Li2Ni03 and (ii) that the
`ionic radii20 of low-spin Ni3+ (r = 0.56 A) and low-spin Mn3+
`(r = 0.58 A) as well as Ni4+ (r = 0.48 A) and Mn4+ (r = 0.53 A)
`are very similar to each other within an octahedral environ(cid:173)
`ment, we propose that manganese ions occupy nickel sites in
`manganese-substituted lithium nickel oxides. This statement is
`supported by a neutron diffraction study on rhombohedral
`LiMn02Ni080 2 showing that Mn substituted for Ni only on the
`predominantly Ni-filled layers of the R3m structure.21 Thus,
`the structure of rhombohedral Lix(MnyNi1 _ylz-x02 can be
`derived from the respective rhombohedral parent com(cid:173)
`pound of the series Li~i2 _x02 • Judging from the cation radii
`given above, we believe that the structure of monoclinic
`Lix{MIIyNi1 _y) 2_x0 2 can be obtained by simply substituting
`manganese for nickel in monoclinic LixNi2_x02 •
`
`20.797
`20.958
`21.668
`24.258
`36.852
`44.596
`48.775
`58.708
`58.968
`60.454
`64.488
`68.628
`69.272
`77.492
`80.953
`81.812
`82.593
`82.815
`84.394
`
`0
`1
`-1
`1
`2
`-1
`1
`2
`-1
`3
`-3
`3
`-1
`-2
`-4
`-3
`1
`2
`0
`
`2
`1
`1
`1
`0
`3
`3
`0
`1
`1
`1
`3
`1
`2
`2
`5
`7
`6
`4
`
`0
`0
`1
`1
`0
`3
`3
`4
`6
`1
`4
`-3
`7
`7
`1
`0
`1
`2
`7
`
`20.808
`20.980
`21.646
`24.250
`36.864
`44.599
`48.784
`58.680
`58.954
`60.405
`64.487
`68.671
`69.240
`77.468
`80.947
`81.809
`82.586
`82.805
`84.385
`
`6
`4
`3
`4
`42
`100
`10
`21
`7
`7
`36
`8
`6
`7
`5
`5
`5
`6
`5
`
`4.2677
`4.2353
`4.0981
`3.6661
`2.4370
`2.0301
`1.8655
`1.5714
`1.5650
`1.5301
`1.4438
`1.3664
`1.3553
`1.2308
`1.1866
`1.1763
`1.1672
`1.1646
`1.1468
`
`4.2653
`4.2309
`4.1021
`3.6673
`2.4362
`2.0300
`1.8652
`1.5720
`1.5654
`1.5313
`1.4438
`1.3657
`1.3558
`1.2311
`1.1867
`1.1764
`1.1673
`1.1647
`1.1469
`
`Unit cell parameters: a = 4.9454(4) A), b = 8.53\(1) A, c
`9.6648(9) A, J3 = 99.96(1)". Volume = 401.6(1) A', Z = 8
`(X Li188(Mn"Ni,_y) 1120 3).
`
`The Li2Ni03 structure was determined following the mon(cid:173)
`22
`23 wherein the oxygen
`oclinic [1-Li2Sn03 structure (C2/c) 9
`•
`'
`anions form a cubic close-packed array with alternate lay(cid:173)
`ers occupied either by lithium ions only or by lithium and
`nickel ions in the ratio 1:2. Based on the similarities of nick(cid:173)
`el and manganese, the monoclinic unit cell of a hypothetical
`Li2MnyNi 1_y03 phase was constructed as shown in Fig. 8. If
`this monoclinic cell is extended by 150% inc direction, the
`hexagonal unit cell of LiNi02 can be seen as illustrated in
`Fig. 9 and 10 for the case wherein manganese has been par(cid:173)
`tially substituted for nickel. For better orientation, we
`marked an arbitrary lithium ion surrounded by six transi(cid:173)
`tion metal neighbors on one of the Li-Mn-Ni layers. The
`pseudo-hexagonal unit cell in Fig. 9 is almost identical with
`the hexagonal LiNi02 unit cell sketched in Ref. 24, except
`that in the case of Li2MnyNi1_y03 the nickel layer is partial(cid:173)
`ly occupied by Li+ and manganese ions, and the monoclinic
`c axis is inclined by [1-90° with respect to the hexagonal unit
`cell (Fig. 10). As far as the mixed cation layer is concerned,
`the lithium ion is assumed to be slightly off center within the
`hexagonal nickel-manganese environment (Fig. 11), as was
`
`Table Ill. Monoclinic (space group C/2c) and rhombohedral (space group RJm) target phases.
`
`Overall stoichiometry
`at the two-phase target surface
`
`Estimated phase stoichiometry•
`
`Unit cell parameters a, b, c, in (A)
`
`Li 118Mn0.39Ni0.43 0 2
`(Sputter surface)
`
`Li1.19Mn0.31Ni0.500 2
`(Sputter surface)
`
`Li 1.23Mn0.37Ni0.400 2
`(Back side)
`
`Li119Mn0 33Ni0.480 2
`(Back side)
`
`Li125(MI1yNi,_y),,,O,
`= 2/3Li, 88(MnyN. i,_y)u,O,
`Li115(MnyNi,_y)0 850 2
`Li125(MnyNi,_y) 0.,,0,
`= 2/3Li188MnyNi,::ll) 1120 3
`Li 1.15(MnyNi 1-y) 0.85 U2
`
`Li125(Mn"Ni,_y)o.,50,
`= 2. /3Li 188(MnyNi,_y) 11,0,
`Li115(MnyNi,_y) 0850 2
`
`Li,25(Mn,Ni,_y)o.,,O,
`= 2/3Li188 (Mn~Ni,_y) 11,03
`Li115(Mn.Ni,_yJ0.850,
`
`a= 4.946(1)
`b = 8.539(2)
`c = 9.658(4)
`a = 2.8717(3)
`a = 4.9454(4)
`b = 8.531(1)
`c = 9.6648(9)
`a = 2.8777(7)
`a = 4.9353(7)
`b = 8.527(2)
`c = 9.677(3)
`a = 2.8763(3)
`a = 4.9389(8)
`b = 8.544(2)
`c = 9.658(2)
`a = 2.881(1)
`
`J3 = 100.02(3)"
`
`c = 14.2244(3)
`
`J3 = 99.96(1)"
`
`c = 14.222(4)
`
`J3 = 99.97(2)"
`
`c = 14.239(2)
`
`J3 = 99.89(2)"
`
`c = 14.228(6)
`
`• For the Li/(Mn + Ni) ratio of each phase, cf. Fig. 16. Only the overall Mn/Ni ratio of a two-phase region is known, the Mn/Ni ratios
`of each phase may be different.
`
`
`
`108.31.169.173Downloaded on 2015-07-09 to IP
`
` address. Redistribution subject to ECS terms of use (see
`
`
`
`) unless CC License in place (see abstract).(cid:160) ecsdl.org/site/terms_use
`
`Page 5 of 21
`
`

`
`• Oxygen
`• Lithium
`
`0 Nickel,
`Manganese
`
`c
`
`b
`
`a
`F~g. 8. Monoclini~ u~it cell of Li~n,.Ni1 _,03 (space g~oup C2/c)
`denved from the Li2N103 structure.' The hexagonal rllckel-man(cid:173)
`ganese environment around an arbitrary lithium ion is highlighted
`for bener comparison with Fig. 9.
`
`9 in order to minimize the coulombic
`observed for Li2Ni03,
`repulsion between the Li+ ions and the Ni<+ and Mn<+ ions.
`When comparing the monoclinic unit cell of Li 2MnyN"i 1_p 3 ,
`which contains eight formula units
`[ = 8 X 3/2
`Li 1 33(MnyN'i 1-y)0670 2], with the hexagonal LiNi02 unit cell
`(three formula units), the following transformations Eq. 1-6
`are determined from Fig. 9-11
`
`[1]
`am= ./3 ah
`[2]
`bm = 3 ah
`ah = (am/./3 + bm/3)/2
`[3]
`[4]
`ch = 3/2 em sin ~
`[5]
`volm = 4Vh
`[6]
`~ = 'IT - arctan (ch/./3 ah
`where the indexes m and h stand for the monoclinic and
`hexagonal unit cells, respectively; a, b, c, and ~ are cell
`parameters, and V denotes the volume. The above trans(cid:173)
`formations are not limited to LiNi0 2 and Li2MnyNi 1_y0 3 ,
`
`I
`·c;; --.c
`
`co.
`r::::
`
`()
`II
`uE
`~ (t)
`
`l
`
`e Oxygen
`• Lithium
`
`0 Nickel,
`Manganese
`
`c
`
`b
`
`a
`
`J. Electrochem. Soc. , Vol. 145, No. 12, December 1998 ©The Electrochemical Society, Inc.
`
`4153
`
`ch = 3/2 Cm sin(180°-~)
`= 3/2 Cm sin~
`
`~----.,
`\
`\
`\
`\
`\
`\
`\
`\
`\
`\
`\
`\
`\
`\
`\
`\
`\
`\
`
`~lu-
`
`Fig. 1 0. Geometrical relationship between the monoclinic (space
`group C2/c) and the hexagonal (space group RJm) unit celt within
`the series Li.(MnyNi 1_) 2_.02 • The indexes m and h denote mono(cid:173)
`clinic and hexagonal, respectively. The relation of the a param(cid:173)
`eters is illustrated in Fig. 11.
`
`but hold true for the entire series Li:rNi 2_:r0 2 and
`Li:r(Mny-Ni 1 _)
`2-:r0 2 wherever a monoclinic unit cell (C2/c)
`is adopted tor x ~ 1.33 and the transition metal ions are
`octahedrally coordinated by oxygen ions. It appears that
`the monoclinic distortion of the rhombohedral structure
`occurs as soon as the lithium concentration on the pre(cid:173)
`dominantly filled transition metal layers reaches a
`8 and, in
`threshold value at a composition of Li 1 22Ni 0.780 2
`
`e Lithium
`0 Nickel, Manganese
`
`.c
`ccs
`('t)
`r
`II
`E
`ccs
`
`I<
`~1
`ah = 1/3 bm
`
`Fig. 9. The monoclinic unit cell of Li~,.Ni1 _y03 from Fig. 8 has
`been extended by 1 SO% in the c direction. ~or better orientation, the
`same six-membered ring as highlighted in Fig. 8 has been marked.
`Only that part of the extendec:l monoclinic unit cell is shown which
`corresponds ta the hex~l unit cell of LiMn,.Ni!:-.Y02 • This mono(cid:173)
`clinic (pseudo-hexagonal) cell becomes identical with the hexagonal
`cell when ~ = 90°.
`
`Fig. 11. Geometrical relationship between the a parameters and
`b parameters of the monoclinic (space group C2/c) and the hexag(cid:173)
`onal
`(space group R3m)
`unit cell within
`the
`series
`Li.MnyNi 1_j 2_.02• The indexes m and h signifv monoclinic and
`hexagonar, respectively. The highlighted nickel-manganese six(cid:173)
`membered ring around lithium is the same one as marked in Fig. 8
`and9.
`
`
`
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`
` address. Redistribution subject to ECS terms of use (see
`
`
`
`) unless CC License in place (see abstract).(cid:160) ecsdl.org/site/terms_use
`
`Page 6 of 21
`
`

`
`4154
`
`J. E/ectrochem. Soc., Vol. 145, No. 12, December 1998 ©The Electrochemical Society, Inc.
`
`the case of the manganese-substituted compounds, at
`Liu 5(MnyNi,_y) 0.850 2 , as will be shown below. We assume
`that substituting the larger Li+ ions (r = 0.76 A 20
`) for the
`smaller M3+ and M4+ ions on the octahedral sites belong(cid:173)
`ing to the same layer induces a sufficient stress to cause
`a hexagonal-to monoclinic distortion.
`Comparison of thin-film and bulk phases.-All of the
`films prepared in air or 0 2 atmosphere gave single-phase
`XRD patterns
`indicating phases of
`the
`series
`Lix(MnyNi1-y)2-x02 . As shown in Fig. 12, the film annealed at
`800oC under 0 2 having the stoichiometry Li~.26Mn0 s7Ni0.3702
`( = 2/3 Li,89Mn0.57Nio 560 3) crystal