Anode for Sodium-Ion Batteries

DOI: 10.1002/aenm.201500174 The continuous pulverization of alloy anodes during repeated sodiation/desodiation cycles is the major reason for the faster capacity decay. However, if these elements can form a compound (such as Sn 4 P 3 ) after each Na extraction, the pulverization of these elements can be partially repaired and the accumulation of pulverization can be terminated. Therefore, we can use the reversible conversion reaction (Sn 4 P 3 + 9Na ↔ 3Na 3 P + 4Sn) to terminate the continuous pulverization and aggregation of Sn in alloy reaction (4Sn + 15Na ↔ Na 15 Sn 4 ) in the sodiation/desodiation cycles. Therefore, the pulverization of Sn and P during alloy process can be partially self-healed (recovered) by the conversion reaction process. The drastic enhancement in cycle stability of Sn 4 P 3 /C composites compared to individual Sn and P anodes has been reported, [ 6,22 ] where the reversible conversion reaction of Sn 4 P 3 during sodiation/desodiation has been identifi ed. [ 6 ] The reversible conversion reaction can only self-heal the pulverization and aggregation induced in followed alloy reaction by recombining the cracked Sn and P back to P–Sn compounds in each cycle to avoid the crack propagation and Sn and P aggregation, thus improving the cycle stability of alloy reaction anodes to the cycling life of conversion reaction anodes with much high capacity. Since P has much higher capacity (2596 mA h g −1 ) than Sn (847 mA h g −1 ), SnP 3 exhibits much higher theoretical mass capacity (1616 mA h g −1 ) than reported Sn 4 P 3 (1133 mA h g −1 ), the highest volumetric capacity of 6890 mA g cm −3 among the reported anode materials for SIBs ( Figure 1 and Table S1, Supporting Information). Due to the self-healing mechanism through conversion reaction, SnP 3 should also have much better cycling stability than P and Sn anodes. Herein, for the fi rst time, we reported a novel self-healing SnP 3 anode for the SIBs. The SnP 3 /C composites synthesized by simple ball milling deliver a high capacity of 810 mA h g −1 at current density of 150 mA g −1 over 150 cycles without noticeable capacity decay, and retain a high capacity of ≈400 mA h g −1 even at 2560 mA g −1 current density. The SnP 3 shows comparable cycling stability to and higher capacity than reported Sn 4 P 3 (460–718 mA h g −1 ) at the similar current (100 mA g −1 ) [ 6,22,23 ]