The
development of high-performance potassium ion battery (KIB)
electrodes requires a nanoengineering design aimed at optimizing the
construction of active material/buffer material nanocomposites. These
nanocomposites will alleviate the stress resulting from large volume
changes induced by K+ ion insertion/extraction and enhance
the electrical and ion conductivity. We report the synthesis of phosphorus-embedded
ultrasmall bismuth–antimony nanocrystals (Bi
x
Sb1–x
@P, (0 ≤ x ≤ 1)) for KIB anodes via a facile
solution precipitation at room temperature. Bi
x
Sb1–x
@P nanocomposites can
enhance potassiation–depotassiation reactions with K+ ions, owing to several attributes. First, by adjusting the feed
ratios of the Bi/Sb reactants, the composition of Bi
x
Sb1–x
nanocrystals can be
systematically tuned for the best KIB anode performance. Second, extremely
small (diameter ≈ 3 nm) Bi
x
Sb1–x
nanocrystals were obtained after
cycling and were fixed firmly inside the P matrix. These nanocrystals
were effective in buffering the large volume change and preventing
the collapse of the electrode. Third, the P matrix served as a good
medium for both electron and K+ ion transport to enable
rapid charge and discharge processes. Fourth, thin and stable solid
electrolyte interface (SEI) layers that formed on the surface of the
cycled Bi
x
Sb1–x
@P electrodes resulted in low resistance of the overall battery
electrode. Lastly, in situ X-ray diffraction analysis
of K+ ion insertion/extraction into/from the Bi
x
Sb1–x
@P electrodes
revealed that the potassium storage mechanism involves a simple, direct,
and reversible reaction pathway: (Bi, Sb) ↔ K(Bi, Sb) ↔
K3(Bi, Sb). Therefore, electrodes with the optimized composition, i.e., Bi0.5Sb0.5@P, exhibited excellent
electrochemical performance (in terms of specific capacity, rate capacities,
and cycling stability) as KIB anodes. Bi0.5Sb0.5@P anodes retained specific capacities of 295.4 mA h g–1 at 500 mA g–1 and 339.1 mA h g–1 at 1 A g–1 after 800 and 550 cycles, respectively.
Furthermore, a capacity of 258.5 mA h g–1 even at
6.5 A g–1 revealed the outstanding rate capability
of the Sb-based KIB anodes. Proof-of-concept KIBs utilizing Bi0.5Sb0.5@P as an anode and PTCDA (perylenetetracarboxylic
dianhydride) as a cathode were used to demonstrate the applicability
of Bi0.5Sb0.5@P electrodes to full cells. This
study shows that Bi
x
Sb1–x
@P nanocomposites are promising carbon-free anode
materials for KIB anodes and are readily compatible with the commercial
slurry-coating process applied in the battery manufacturing industry.