Optimized Electrode/Electrolyte Interface of MWCNT/SnO Composite through Gas-Solid Fluorination.

The benefit of enriching solid-electrolyte interface with fluorine atoms through the use of fluorinated additives into the electrolyte composition has recently gained popularity for anode materials used in secondary lithium-ion batteries. Another strategy is to provide these fluorine atoms via surface fluorination of the electrode material, particularly for multiwalled carbon nanotube (MWCNT)/SnO-based composites where fluorination must act selectively on SnO. Our study presents two methods of surface fluorination applied on MWCNT/SnO, one using F(g) and the other XeF(s). These fluorinating agents are known for their different particle penetration depths. An ultrathin and very dense fluorinated layer achieved by the action of F(g) allows to form a very stable interface leading to gravimetric capacities of 789 mA h g after 50 cycles. A thin and porous fluorinated layer made by the action of XeF(s) favors the formation of a new Sn-based fluorinated phase, never reported in the literature, which also stabilizes capacities over 50 cycles. In any case, the value of adding fluorine atoms to the surface of the electrode material to improve cycle stability is demonstrated.