Difference in the Intercalation of Sodium Ions and Lithium Ions into Hard Carbon Electrodes
Na is in the same element group with Li and its diameter is only ~40% larger than a Li ion.1-2 Therefore, it is believed that it has very similar intercalation chemistry in Na-ion batteries as Li in Li-ion batteries. Hard carbon is a promising anode material for both Li-ion and Na-ion intercalation and has almost similar specific discharge capacity.3 Yet, it has been reported that the Na ions and Li ions are quite different when intercalating into hard carbon and the solid state interphase (SEI) on hard carbon anodes has different composition/morphology for Na and Li ions.4-5In this work, we further elucidate how the solid electrolyte interlayer can induce significant difference in the intercalation of Na-ion and Li-ion into hard carbon and hence lead to significant difference in the discharge capacity. Electrolyte additive effect was also investigated.
Results and Discussion
The same hard carbon electrode was cycled subsequently v.s. Li metal in Li-ion electrolyte and v.s. Na metal in Na-ion electrolyte. The capacity remains similar of ~200 mAh/g when it was switched back to Li-ion batteries. Yet, when the hard carbon electrode was cycled subsequently v.s. Na metal in Na-ion electrolyte and v.s. Li metal in Li-ion electrolyte, the capacity shows significant drop from ~200 mAh/g to ~40 mAh/g when it was switched back to Na-ion batteries. The electrolyte for Li-ion battery and Na-ion battery is only different for the alkali metal ion.
Fig. 1. Hard carbon electrodes cycled subsequently v.s. Li or Na metal in Li-ion or Na-ion electrolyte.
The authors would like to acknowledge financial support from the U.S. Department of Energy’s (DOE’s) Office of Electricity Delivery & Energy Reliability (OE) (under Contract No. 57558). (A portion of) The research was performed using EMSL, a national scientific user facility sponsored by the Department of Energy's Office of Biological and Environmental Research and located at Pacific Northwest National Laboratory.
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