Tin‐Containing Graphite for Sodium‐Ion Batteries and Hybrid Capacitors

Abstract

The limited Na‐storage capacity of graphite anodes for sodium‐ion batteries (∼110 mAh g−1) is significantly enhanced by the incorporation of nanosized Sn (17 wt%). The composite (SntGraphite), prepared by simple annealing of graphite with SnCl2, shows a specific capacity of 223 mAh g−1 (at 50 mA g−1) combined with excellent cycle life (i. e., 96 % of capacity retention after 2,200 cycles at 1 A g−1) and initial Coulomb efficiency (90 %). The combined storage of sodium in graphite (by solvent co‐intercalation) and Sn (by alloy formation) is followed by in situ X‐ray diffraction and in situ electrochemical dilatometry (ECD). While the additional tin almost doubles the electrode capacity, its contribution to the electrode expansion (∼3 %) is surprisingly small. The use of SntGraphite as anode for sodium‐ion hybrid capacitors with activated carbon as cathode provides a maximum energy and power density of ∼93 Wh kg−1 and 7.8 kW kg−1, with a capacity retention of ∼80 % after 8,000 cycles.

Strategies for Alleviating Electrode Expansion of Graphite Electrodes in Sodium‐Ion Batteries Followed by In Situ Electrochemical Dilatometry

“…[ 6 ] The ratio is still not completely clarified, but values of 1–2 and 15–22 for y and n are assumed. [ 2c − 4,7 ] The reaction has some characteristic properties: 1) the capacity so far is limited to around 110 mAh g −1 , [ 8 ] which is low compared with conventional battery electrodes (typically >150 mAh g −1 ), but high compared with supercapacitor electrodes; [ 9 ] 2) the initial Coulomb efficiency (ICE) is very high (≈ 90% or even higher [ 3,7a ] ); 3) the rate capability and cycle life are excellent (up to 6000 cycles with 100 mAh g −1 [ 10 ] ); 4) the concept requires an “SEI‐free” interface, [8a] and 5) the volume expansion/shrinkage during cycling is very large (70–100%) [8a] …”

In Situ (Operando) Electrochemical Dilatometry as a Method to Distinguish Charge Storage Mechanisms and Metal Plating Processes for Sodium and Lithium Ions in Hard Carbon Battery Electrodes

“…In this case, the electrode expansion is also significantly smaller compared to what would be expected from the alloy formation. [ 38 ]…”

“…In this case, the electrode expansion is also significantly smaller compared to what would be expected from the alloy formation. [38] To further support the hypothesis that sodium plating takes place in region III, reference measurements with ECD were made for lithium and sodium cells for which bulk plating was forced by taking the electrode potential below 0 V. Results can be seen in Figure 5. In line with the results discussed in the previous section, the sodium cells show a sudden thickness increase starting at around 0.03 V, the beginning of region III.…”

The Mystery from Tetragonal NaVPO4F to Monoclinic NaVPO4F: Crystal Presentation, Phase Conversion, and Na‐Storage Kinetics

“…[ 1a–c ] Up to now, great achievements including electrochemical performance and energy storage mechanism have been made in the anode side of SIBs. Specifically, Carbon based anode materials, such as hard carbon (HC), [ 2a,b ] soft carbon, [ 3a,b ] and graphene, [ 4a,b ] demonstrated excellent performance. Among which, HC has been recognized as one of the most potentially commercialized anode materials for SIBs attributed to the low cost, rich resources, and low voltage plateau.…”