Strong interplay between dopant and SnO2 in amorphous transparent (Sn, Nb)O2 anode with high conductivity in electrochemical cycling

Abstract

The loss of structure integrity and intrinsic poor conductivity of SnO2 anode are regarded as the main origination of capacity decay. In this work, a serious phase separation of β → α during cycling was confirmed and related with the capacity decaying closely. To address these challenges, an amorphous transparent (Sn, Nb)O2 with high conductivity was fabricated. The Nb dopant with a full oxidation state endows SnO2 with high conductivity of 211.42 S/cm by increasing its carrier concentration to the level of 3.02 × 10−20 cm−3. At a rate of 20C (about 30 A g−1), discharge capacity of (Sn, Nb)O2 with Nb content of 6 at. % can still remain 658 mA h g−1 and the specific capacity of NTO6 sample nearly got back to its original capacity when the rate returned back to 0.1C, maintaining at 986 mA h g−1 after 90 cycles. During the electrochemical cycling, the strong interplay of Nb dopant with host SnO2 was verified. Nb with an optimized content of 6 at.% can suppress the allotropy transformation from β to α - tin and sustain a capacity of 982.7 mA h g−1 till to 200 cycles. At the same time, Nb doped amorphous SnO2 crystallized into rutile structure, which would help to release stress during electrochemical reaction. The improved cycling performance is closely related with a persistence of Nb+5 valence, which will help to keep high conductivity of the host SnO2 materials. As a result, NTO6 remained crack-free, with a low electrical impedance within 200 cycles.