Kinetics of the Thermally-Induced Structural Rearrangement of 纬-MnO2

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• 作者：Wesley M. Dose ; Neeraj Sharma ; Nathan A. S. Webster ; Vanessa K. Peterson ; Scott W. Donne
• 刊名：Journal of Physical Chemistry C
• 出版年：2014
• 出版时间：October 23, 2014
• 年：2014
• 卷：118
• 期：42
• 页码：24257-24265
• 全文大小：557K
• ISSN：1932-7455

文摘

This work presents a temperature-dependent and time-resolved X-ray and neutron diffraction study of the thermally induced structural rearrangement of 纬-MnO₂. Here, we study electrochemically prepared 纬-MnO₂, the manganese dioxide phase used in the majority of battery applications, which we find to be 鈭?4% ramsdellite [a = 4.4351(6) 脜, b = 9.486(2) 脜, c = 2.8128(7) 脜, and V = 118.33(3) 脜³] and 鈭?6% pyrolusite [a = 4.718(3) 脜, c = 2.795(2) 脜, and V = 62.22(8) 脜³]. Taking a deeper look at the kinetics of the structural rearrangement, we find two steps: a fast transition occurring within 4鈥? min with a temperature-dependent ramsdellite to pyrolusite transformation (rate constant 0.11鈥?.74 min^鈥?) and a slow transition over 4 h that densifies (with changes in unit cell and volume) the ramsdellite and pyrolusite phases to give structures that appear to be temperature-independent. This effectively shows that 纬/尾-MnO₂ prepared in the range of 200鈥?00 掳C consists of temperature-independent structures of ramsdellite, unit cell a = 4.391(1) 脜, b = 9.16(5) 脜, c = 2.847(1) 脜, and V = 114.5(6) 脜³, and pyrolusite, unit cell a = 4.410(2) 脜, c = 2.869(2) 脜, and V = 55.79(4) 脜³, with a temperature-dependent pyrolusite fraction between 0.45 and 0.77 and increasing with temperature. Therefore, we have linked the temperature and time of heat treatment to the structural evolution of 纬-MnO₂, which will aid the optimization of 纬/尾-MnO₂ as used in Li-primary batteries.