Thermal stability of Fe–Mn binary olivine cathodes for Li rechargeable batteries

다국어 초록 (Multilingual Abstract)

<P>The phase stability of binary Fe and Mn olivine materials is extensively studied with temperature-controlled <I>in situ</I> X-ray diffraction (XRD) for various Fe/Mn ratios and state of charges (SOCs). We identify that the thermal behavior of partially charged olivine materials is sensitively affected by the Fe/Mn ratio in the crystal. While Fe-rich binary olivine materials readily formed a solid solution phase of Li<SUB>1−<I>y</I></SUB>Fe<SUB>1−<I>x</I></SUB>Mn<SUB><I>x</I></SUB>PO<SUB>4</SUB> near room temperature or with only slight heating, the Mn-rich binary olivine retained its two-phase characteristic up to <I>ca.</I> 250 °C before decomposition into non-olivine phases. The thermal stability and decomposition mechanism of fully delithiated olivine materials are more sensitively affected by the Fe/Mn ratio in the crystal. The decomposition temperature varies from 200 °C to 500 °C among the different Fe/Mn ratios. It is generally observed that the Mn-rich binary olivine materials are inferior to the Fe-rich ones with respect to the thermal stability in the delithiated state.</P>

<P>Graphic Abstract</P><P>The phase stability of Fe–Mn binary olivine cathodes was investigated as a function of the temperature and the Li composition in the structure with temperature-controlled in situ XRD. Fully lithiated LiFe<SUB>1-x</SUB>Mn<SUB>x</SUB>PO<SUB>4</SUB> (0 ≤ x < 1) remained stable up to high temperatures (> 700 °C). However, the thermal stability of delithiated Li<SUB>1-y</SUB>Fe<SUB>1-x</SUB>Mn<SUB>x</SUB>PO<SUB>4</SUB> (0 ≤ x, y ≤ 1) was influenced sensitively by the Fe/Mn content in the structure.
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