Improving the Cycling Stability of SnO₂–Graphite Electrodes

Abstract

The combination of SnO 2 and graphite in a composite electrode allows obtaining a Li-ion battery negative electrode with enhanced specific charge. However, the reported cycling stability of these electrodes is often rather poor. Here we report conditions under which long-term cycling for these electrodes can be achieved, determined by studying the effects of the electrode and electrolyte composition as well as of the cycling protocol on the cycling stability of SnO 2 −graphite electrodes. The amount and type of binder, in combination with an optimized amount of electrolyte additive and applied limitation to the delithiation cutoff potential, play a major role in stabilizing performance of these electrodes. A specific charge retention of 81.5% after 300 cycles was obtained for electrodes prepared with 50 wt % SnO 2 , KS6L graphite, and PAA:CMC binder cycled with FEC electrolyte additive by using a 1.0 V delithiation cutoff potential.

Potential and Limitations of Research Battery Cell Types for Electrochemical Data Acquisition

“…In these systems, complete consumption of FEC is marked by a distinct drop in capacity retention [27,36,37] . However, from a material testing perspective, excess electrolyte volumes “turn off” some of the undesired side reactions described above and therefore allow the investigation of other degradation phenomena [38,39] . Lastly, insufficient drying of cell components (electrodes, separators or coin cell parts) or high moisture levels within the electrolyte can lead to electrolyte and electrolyte salt decomposition reactions (e. g., electrolytes containing LiPF 6 as conducting salt), resulting in aging effects.…”

Graphite Particle-Size Induced Morphological and Performance Changes of Graphite–Silicon Electrodes

“…Regarding the use of FEC, it should be noted that the consumption of the electrolyte additive is strongly dependent on the active material content (and consequently the electrode loading) of the expanding alloying or conversion material, 8,15 and (absolute) FEC content, 24,25 which correlates with electrolyte volume 39 used. The specific active material contents of the electrode formulations shown in Figs.…”

“…Even small differences in mass loading can have an profound effect on the onset of capacity fading in these electrodes, as the FEC electrolyte additive is used up at different times. 8,15,24,25,39 More important than the actual mass loading is the effective electrode SSA, that is, the electroactive surface area (EASA). It determines how much electrode surface needs to be covered by the SEI layer and, therefore, how much of the additive it will consume for its formation.…”

“…1 An obvious parameter is the electrode capacity, which can be improved by substituting the standard active material, graphite, partly or fully with alternative materials, possessing higher specific charge, for instance Si, 2-6 Sn 7 or SnO 2 . 8 However, while the theoretical specific charge of these materials is promising, they generally lack stability in terms of capacity retention when used in their pure form. 9 Therefore, a partial substitution of graphite seems to be more realistic and, according to recent energy-density estimations, 10 sufficient to significantly increase the energy density of state-ofthe-art batteries on the cell level.…”

“…As a consequence, considerable consumption of the electrolyte additive fluoroethylene carbonate (FEC) has been observed in several studies. 8,[24][25][26] We have recently investigated the impact of the Si content in these electrodes on cycle life, using 5-20 wt% Si. 15 In this previous study, small graphite particles (d 90 < 6.9 μm) were used, which overall led to a good dispersion as long as the Si content remained below 10 wt%.…”