Co2SiO4/SiO2/RGO nanosheets: Boosting the lithium storage capability of tetravalent Si by using highly-dispersed Co element

Tetravalent Si materials (SiO 2 and transition metal silicates) are receiving tremendous attentions for lithium storage, whereas a troublesome problem is how to improve the content of active Si. This work reports a novel method to boost their lithium storage capabilities by using highly-dispersed Co element in the form of nanofilm-like Co 2 SiO 4 /SiO 2 powder on the surface of reduced graphene oxide (RGO) that promotes the electronic diffusion and accommodates the volume changes. As a result, the Co 2 SiO 4 /SiO 2 /RGO exhibits over 20 times higher reversible capacity and better rate performance than the SiO 2 /RGO counterpart. In comparison, the Co 2 SiO 4 /SiO 2 /RGO shows the highest reversible capacity (1382 mAh g −1 at 500 mA g −1 ) and longest life span (500 cycles) in all known silicates-based materials and higher power/energy density than both of commercial graphite and Li 4 Ti 5 O 12 materials. Ex-situ X-ray photoelectron spectra and electrochemical tests at different voltage windows are conducted to illustrate the reason for the significantly improved performances. It demonstrates that tetravalent Si is gradually activated to lower-valence form by highly-dispersed Co generated with cycling. This observation provides new evidence for the electrochemical catalytic mechanism in transition metal silicates for lithium storage.