An optimized solid electrolyte interphase is the key to stabilization of microparticle anodes.

No abstract

Transitional metal dichalcogenides represent one important type of anodes for emerging K-ion batteries. K ions are stored through both intercalation and conversion reactions, but the detailed phase transition is not clear. It is believed that deep potassiation would trigger the conversion reaction, which induces the fracture of particles and leads to fast capacity degradation. By utilizing MoS2 as a model material, the competition between intercalation and conversion is revealed, which shows a rate-dependent behavior. The crystal structure of several newly discovered intermediate phases including K0.5MoS2 and K1.0MoS2 is disclosed by complementary experimental and calculational approaches. It shows that intercalation takes place even discharge down to 0 V, differing from the cases in Li-ion and Na-ion batteries. The intercalated compound preserves the layered structure of MoS2, which avoids the structural collapse and maintains the integrity of the electrode for stable cyclic performance. This finding opens up a new opportunity in the exploration of high capacity anode among layered transitional metal dichalcogenide families.

Black phosphorus (BP) shows superior capacity toward K ion storage, yet it suffers from poor reversibility and fast capacity degradation. Herein, a BP-graphite (BP/G) composite with a high BP loading of 80 wt % is synthesized and stabilized via the utilization of a localized high concentration electrolyte (LHCE), i.e., potassium bis­(fluorosulfonyl)­imide in trimethyl phosphate with a fluorinated ether as the diluent. We reveal the benefits of high concentration electrolytes rely on the formation of an inorganic component rich solid electrolyte interphase (SEI), which effectively passivates the electrode from copious parasite reactions. Furthermore, the diluent increases the electrolyte’s ionic conductivity for achieving attractive rate capability and homogenizes the elemental distribution in the SEI. The latter essentially improves the SEI’s maximum elastic deformation energy for accommodating the volume change, resulting in excellent cyclic performance. This work promotes the application of advanced potassium-ion batteries by adopting high-capacity BP anodes, on the one hand. On the other hand, it unravels the beneficial roles of LHCE in building robust SEIs for stabilizing alloy anodes.

Alloy anodes composed of microsized particles receive increasing attention recently, which outperform the nanostructured counterparts in both the manufacturing cost and volumetric energy density. However, the pulverization of particles and fracture of solid electrolyte interphase (SEI) during cycling brings about fast capacity degradation. Herein, it is shown how normally considered fragile SEI can become highly elastic through electrolyte chemistry regulation. Compared to the SEI constructed in classic carbonate electrolyte, the atomic force microscopy tests reveal that the one built in ether‐based electrolyte doubles the maximum elastic strain to accommodate the repeated swelling‐contracting. Such an SEI effectively encapsulates the microsized Sb anodes to prevent the capacity loss from particle isolation. Coupled with an intercalation‐assisted alloying reaction mechanism, a sustained capacity of ≈573 mAh g−1 after 180 cycles at 0.1 A g−1 with outstanding initial Coulombic efficiency is obtained, which is among the highest values achieved in K‐ion batteries. This study emphasizes the significance of building robust SEI, which offers the opportunity to enable stable microsized alloy anodes.