3 V manganese oxide electrode materials for lithium batteries. Page: 7 of 20
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Li coin cells (size 1225) were constructed with cathode laminates cast from a PVDF
(Kynar; Elf Atochem) slurry mix onto Al foil current collectors with a doctor blade in an NMP (N-
methylpyrrolidone, Aldrich 99+%) solvent. The final laminates consisted of 8% Kynar, 10%
carbon, and 82% active oxide. After oven drying at 70 C in air, final punched laminates were
dried at 80*C in vacuo prior to cell rolling and assembly in either a dry room with <200 ppm H20
or a helium glovebox with <5 ppm 02 and H20.
RESULTS AND DISCUSSION
The redox stability of many manganese systems is related to how well the structure can
resist the Jahn-Teller crystallographic distortion caused by a high concentration of Mn3.(d4) ions
within the structure at the end of discharge. The number of Mn3+ ions produced increases when
cells operate at voltages below 3 V, and this imposes a serious impediment to long-term cycle life.
In the search for MnO materials, a-MnO2 has been found to maintain a tetragonal
structure upon lithiation . A small, 6.5% volume increase was observed in its approximately
half-reduced state (discharged condition) from LioMnO2 to Li0 48Mn02 [71. The retention of
tetragonal symmetry ensures that the Jahn-Teller effect is accommodated in two dimensions, as
opposed to one dimension in the case of Li1+XMn204 (0<x<1) spinel electrodes . Lattice
imaging and convergent beam electron diffraction have confirmed that structural changes take
place in lithiated a-MnO2products; the structural changes are believed to be associated with
manganese and oxygen diffusion from the a-Mn02framework into the (2x2) tunnels and a possible
ordering of the electro-inserted Li ions . This results in a modified structure that has greater
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Johnson, C. S. & Thackeray, M. M. 3 V manganese oxide electrode materials for lithium batteries., article, June 20, 2000; Illinois. (digital.library.unt.edu/ark:/67531/metadc711713/m1/7/: accessed November 15, 2018), University of North Texas Libraries, Digital Library, digital.library.unt.edu; crediting UNT Libraries Government Documents Department.