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MgxMn2-xB2O5 Pyroborates (2/3 ≤ x ≤ 4/3): High Capacity and High Rate Cathodes for Li-Ion Batteries

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Liu, Z 
Bayley, PM 
Suard, E 
Bo, SH 


MgMnB2O5, Mg2/3Mn4/3B2O5, and Mg4/3Mn2/3B2O5 pyroborates have been prepared via a ceramic method. When charging MgMnB2O5 vs 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-1 at a rate of 2C. Continuous cycling at moderate rates gradually improves performance leading to insertion of 1.8 Li, 314 mAhg-1 with 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. Mg2/3Mn4/3B2O5 and Mg4/3Mn2/3B2O5 are 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 Mg2/3Mn4/3B2O5 material. The electrochemical ion-exchange of polyanion materials with labile Mg ions could prove to be a route to high energy density Li-ion cathodes.



40 Engineering, 4016 Materials Engineering, 34 Chemical Sciences, 3406 Physical Chemistry, 7 Affordable and Clean Energy

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Chemistry of Materials

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American Chemical Society (ACS)
Engineering and Physical Sciences Research Council (EP/G037221/1)
Engineering and Physical Sciences Research Council (EP/M000524/1)