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Open Access Publications from the University of California

MgxMn2-xB2O5Pyroborates (2/3 ≤ x ≤ 4/3): High Capacity and High Rate Cathodes for Li-Ion Batteries

  • Author(s): Glass, HFJ
  • Liu, Z
  • Bayley, PM
  • Suard, E
  • Bo, SH
  • Khalifah, PG
  • Grey, CP
  • Dutton, SE
  • et al.

© 2017 American Chemical Society. MgMnB2O5, Mg2/3Mn4/3B2O5, and Mg4/3Mn2/3B2O5pyroborates have been prepared via a ceramic method. When charging MgMnB2O5vs Li, all of the Mg2+can be removed, and with subsequent cycles, 1.4 Li ions, corresponding to a capacity of 250 mAhg-1, can be reversibly intercalated. This is achieved at a C/25 rate with 99.6% Coulombic efficiency. Significant capacity is retained at high rates with 97 mAhg-1at a rate of 2C. Continuous cycling at moderate rates gradually improves performance leading to insertion of 1.8 Li, 314 mAhg-1with a specific energy of 802 Whkg-1, after 1000 cycles at C/5. Ex situ X-ray and neutron diffraction demonstrate the retention of the pyroborate structure on cycling vs Li and a small volume change (1%) between the fully lithiated and delithiated structures. Mg2/3Mn4/3B2O5and Mg4/3Mn2/3B2O5are also shown to reversibly intercalate Li at 17.8 and 188.6 mAhg-1, respectively, with Mn ions likely blocking Mg/Li transport in the Mg2/3Mn4/3B2O5material. The electrochemical ion-exchange of polyanion materials with labile Mg ions could prove to be a route to high energy density Li-ion cathodes.

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