`
`LETTERS TO THE EDITOR
`
`Synthesis and Structural Characterization of a Novel Layered
`Lithium Manganese Oxide, Liu6Mn0.910 2 , and Its Lithiated
`Derivative, Li1.09Mn0,g10 2
`
`M. H. ROSSOUW, D. C. LILES, AND M. M. THACKERAY
`
`Divi,fiorr of Materials Science and Teclrllology, CSIR, P.O. Box 395,
`Pretoria 0001, Sowll Africa
`
`Communicated by J. M. Honig, January IS, 1993
`
`!1. novel layered lithium manganese oxide, Lio . .!6Mn0.91 0 2, has been prepared from Li2Mn03 by acid
`digc~tion. The structure oflhe producl consists of alternate layers of trigonal prisms, partially occupied
`hy Li • ions. and cJge-~hnrcd I)Ciahedrn , occupied almost completely by MnH ions. Lithia lion of this
`f!rnducl with Lil nt 80"C forms II ro~k·snft pha~e. Lit09Mnn.910z, in which the cubic close-packed
`oxygen array of the parent Li1Mn01 structure is regenerated. c 1993 Acad•mic Press, Inc.
`
`Introduction
`
`Layered compounds such as LiCo02 (I)
`and LiNi0 2 (2) are of interest as insertion
`electrodes for rechargeable lithium cells be(cid:173)
`cause lithium can be extracted from andre(cid:173)
`introduced into their structures with a con(cid:173)
`comitant change in I he oxidation slate of the
`lransition-mctul cation. Although an iso(cid:173)
`structural LiMn02 compound is not known,
`a recent report has indicated that it might
`be possible to synthesize related layered
`Li,.(MntLi 1_z)02 structures (0 s: y < 1,
`0.67 < z :s; 1) by leaching Li20 from the
`rock-salt phase Li 2Mn03 (3). In this commu(cid:173)
`nication the synthesis and structural fea(cid:173)
`tures of a novel Li0.36Mn0.91 0 2 (or alterna(cid:173)
`tively, Li 0,21(Mno.91Li0•09)0z, y = 0.27, z =
`0.91) compound and its lithiatcd derivative
`Liu19Mn 0.91 0 2 (Li(Mn0.9,Lio.09)02, Y = 1,
`z = 0.91) al'e reported.
`
`at 400°C in air by reacting electrolytic man(cid:173)
`ganese dioxide (EMD) with a stoichiometric
`quantity of Li 2CO) for 2 weeks. A long
`reaction time was required to obtain a
`single-phase product at this temperature.
`Single-phase Li0.36Mn0 .910 2 was prepared by
`digesting Li2 Mn0~ in 2.25 M H2S04 at 25°C
`for M hr. The sample was hcutcd at IOU°C
`for 24 hr to remove Slllfacc water. A H+(cid:173)
`ion analysis of the heated sample showed
`that Li0.36Mn0.910 2 contained a small amount
`of residual occluded water associated with
`grain boundaries and possibly some ion(cid:173)
`exchanged protons within the structure
`(LH +] = 0.5% by mass). It has not been
`possible as yet to obtain anhydrous materi(cid:173)
`als because of their thermal instability at
`higher
`temperatures. Nevertheless,
`the
`presence of the occluded water did not pre(cid:173)
`vent the structure analysis of the lithium(cid:173)
`manganese-oxide component.
`Samples were analyzed for lithium and
`Experimental
`manganese by atomic absorption spectros(cid:173)
`copy to determine the Li: Mn ratio in the
`Li2Mn03 , or alternatively, Li(Mn0,t\7
`Li0•33)02 (y "" I, z = 0.67), was prepared
`compounds. Liu19Mn0.910 2 was synthesized
`0022-4596/93 $5.00
`464
`Cop~ri[lht (> 199) hy Academic Pre ... Inc .
`Nl rli/lts ol' reproduelion In any fonn reserved.
`
`Page 1 of 3
`
`SONY EXHIBIT 1019
`
`
`
`LEITERS TO THE EDITOR
`
`465
`
`a
`
`b
`
`10
`
`20
`
`30
`
`40
`
`50
`
`60
`
`70
`
`2e (CuKa.)
`
`FJG, I. The powder X-ray diffraction patterns of(a)
`(b)
`(c)
`Li2Mn03
`Li0.~Mno.•n02, and
`(400.C),
`Li1.09 Mno.9102 •
`
`by reacting a slight excess of Lil with
`Li0.36Mn0,91 0 2 in acetonitrile at sooc ac(cid:173)
`cording to the reaction
`Li0,36Mn0.91 0 2 + 1. lOLil ~
`Li1.09Mn0.9P2 + 0.37Lil3 ,
`in which the occluded water has been omit(cid:173)
`ted for simplicity. Li0.36 +xM"o.910 2 com(cid:173)
`pounds with intermediate values of x could
`be obtained by using lesser amounts of Lil.
`
`Results and Discussion
`
`The powder X-ray diffraction patterns of
`Li2Mn03, Li0,36Mn0.9P 2 , and Liu19Mn0_91 02
`are shown in Figs. la-lc. The pattern of
`Li0.36Mn0_91 0 2 (Fig. 1 b) differs significantly
`from that of the parent Li2Mn03 (Fig. ta) in
`both peak positions and peak intensities; the
`pattern is also significantly different from
`that of well-known layered birnessite com(cid:173)
`pounds which have a hexagonally close(cid:173)
`packed oxygen array (4). Li2Mn03 has a
`rock-salt-type structure in which the oxy(cid:173)
`gen-ion array is slightly distorted from cubic
`close packing and in which layers of Li +
`
`ions alternate with layers containing Mn4+
`ions and Li+ ions in a 2: 1 ratio (5). Al(cid:173)
`though the lack of high quality X-ray data
`and the small number of strong reflections
`prevented satisfactory structural refine(cid:173)
`ments using the monoclinic symmetry (C2/
`c) of the parent Li2Mn03 compound, the
`gross structural features of Li0.36Mn0.9P 2
`and Li1.09Mn0.91 0 2 were obtained by profile
`refinement of their X-ray patterns (Figs. Jb
`and lc, respectively) using the higher sym(cid:173)
`metry space group R3m that characterizes
`the layered LiCo02 and LiNi02 structures.
`The structure refinements demonstrated
`that:
`I. Removal of Li20 from Li2 Mn03 causes
`a shearing of the dose-packed oxygen
`planes
`to yield an oxygen array
`in
`L\o_36 Mno.91 0 2 comprised of alternate layers
`of trigonal prisms and sheets of edge-shared
`octahedra (Fig. 2a).
`
`a
`
`b
`
`FIG. 2. The layered structures of (a) Li0 36Mn0_91 0 1
`(RJtn, a = 2.9()3(1) A., c = \3.803(5) A) and (b)
`Li1.09 Mno.9P2 (RJm, a = 2.851(1) A, c = 14.259(6) A).
`The partially shaded octahedra are mostly occupied
`by manganese ions; the fully shaded polyhedra are
`occupied by lithium ions.
`
`Page 2 of 3
`
`
`
`466
`
`LEITERS TO THE EDITOR
`
`2. The manganese ions remain in alternate
`layers and do not migrate to the lithium lay(cid:173)
`ers during the leaching process. The u+(cid:173)
`ion positions could not be located because
`of the weak scattering power of lithium; it
`was presumed that they resided in the small
`fraction of octahedral sites that were not
`occupied by manganese, and partially occu(cid:173)
`pied the trigonal prismatic sites. With this
`arrangement the structural notation would
`be [L~_27 ltrpr(MI1o.9J Lio.oo)oct 02 ·
`3. Lithiation ofLio.Jt>Mno_91 0 2 with Lii re(cid:173)
`generates the close-packed oxygen array of
`the parent Li2Mn03
`structure. Liu19
`Mn0_910 1 (Fig. 2b), like Li2Mn03 , has the
`ideal rock-salt stoichiometry; the structure
`differs only in the Li: Mn ratio in the manga(cid:173)
`nese-rich layer. It closely approximates the
`layered structures of LiCo02 and LiNi02 •
`Preliminary investigations have shown
`that layered L~.(Mn,Li1 _z)02 compounds
`derived from Li2Mn03 exhibit promising
`
`electrochemical properties for use as elec(cid:173)
`trodes in rechargeable lithium cells (3). Fur(cid:173)
`ther work is in progress to synthesize anhy(cid:173)
`drous materials and
`to gather more
`information about the structural stability of
`these layered structures on cycling. A de(cid:173)
`tailed description of the structural refine(cid:173)
`ments of Lio_ 36 Mno_91 Oz and Li~_09 Mno_91 0 2
`will be reported elsewhere.
`
`References
`
`1. K. MIZUSHIMA, P. C. JONES, P. I. WISEMAN, AND
`J. B. GooDENOUGH , Mater. Res. Bull. IS, 783
`(1980).
`2. J. R. DAHN, U. VON SACKEN, M. W. JUZKOW,
`AND H. AL-JANABY, J. Electrochem. Soc. 138,
`2207 (1991}.
`3. M. H. Rossouw AND M. M. THACKERAY, Mater.
`Res. Bull. 26, 463 (1991).
`4. S. BACH, J. P. PEREIRA-RAMOS, N. BAFFlER, AND
`R. MESSINA, Eleclrochim. Acta 36, 1595 (1991).
`5. A. Rmu, A. LECERF, Y. GERAULT, AND Y.
`CUDENNEC, Mater. Res. Bull. 2.1, 269 (1992) .
`
`Page 3 of 3