Bismuth (Bi) has been demonstrated as a promising anode
for Na-ion
batteries (NIBs) because it has high gravimetry (386 mA h g–1) and volumetric capacity (3800 mA h cm–3). However,
Bi suffers from large volume expansion during sodiation, leading to
poor electrochemical performance. The construction of a nanostructure
with sufficient void space to accommodate the volume change has been
proven effective for achieving prolonged cycling stability. However
the excessive void space will definitely decrease the volumetric energy
density of the battery. Herein, we design optimized Bi@Void@C nanospheres
(Bi@Void@C-2) with yolk–shell structure that exhibit the best
cycling performance and enhanced volumetric energy density. The optimized
void space not only could buffer the volume change of the Bi nanosphere
but also could keep the high volumetric energy density of the battery.
The Bi@Void@C-2 shows an excellent rate capacity of 173 mA h g–1 at ultrahigh current density of 100 A g–1 and long-cycle life (198 mA h g–1 at 20 A g–1 over 10 000 cycles). The origin of the superior
performance is achieved through in-depth fundamental studies during
battery operation using in situ X-ray diffraction
(XRD) and in situ transmission electron microscope
(TEM), complemented by theoretical calculations and ex situ TEM observation. Our rational design provides insights for anode
materials with large volume variation, especially for conversion type
and alloying type mechanism materials for batteries (i.e., Li-ion
batteries, Na-ion batteries).
The sodium (potassium)‐metal anodes combine low‐cost, high theoretical capacity, and high energy density, demonstrating promising application in sodium (potassium)‐metal batteries. However, the dendrites’ growth on the surface of Na (K) has impeded their practical application. Herein, density functional theory (DFT) results predict Na2Te/K2Te is beneficial for Na+/K+ transport and can effectively suppress the formation of the dendrites because of low Na+/K+ migration energy barrier and ultrahigh Na+/K+ diffusion coefficient of 3.7 × 10−10 cm2 s−1/1.6 × 10−10 cm2 s−1 (300 K), respectively. Then a Na2Te protection layer is prepared by directly painting the nanosized Te powder onto the sodium‐metal surface. The Na@Na2Te anode can last for 700 h in low‐cost carbonate electrolytes (1 mA cm−2, 1 mAh cm−2), and the corresponding Na3V2 (PO4)3//Na@Na2Te full cell exhibits high energy density of 223 Wh kg−1 at an unprecedented power density of 29687 W kg−1 as well as an ultrahigh capacity retention of 93% after 3000 cycles at 20 C. Besides, the K@K2Te‐based potassium‐metal full battery also demonstrates high power density of 20 577 W kg−1 with energy density of 154 Wh kg−1. This work opens up a new and promising avenue to stabilize sodium (potassium)‐metal anodes with simple and low‐cost interfacial layers.
Thermochromic phosphors are intriguing materials for realizing thermochromic behaviors of light‐emitting diodes. Here a highly luminescent and stable thermochromic phosphor based on one‐dimensional Cu4I6(4‐dimethylamino‐1‐ethylpyridinium)2 is reported. This unique ionic copper‐iodine chain‐based hybrid exhibits near‐unity photoluminescence efficiency owing to the through‐space charge‐transfer character of relevant electronic transitions. More importantly, an alternative mechanism of thermochromic phosphorescence was unraveled, supported by a first principles simulation of concerted copper atom migration in the copper‐iodine chain. Furthermore, we successfully fabricate a bright thermochromic light‐emitting diode using this Cu4I6(4‐dimethylamino‐1‐ethylpyridinium)2 thermochromic phosphor. Our reported flexible ionic copper‐iodine chain‐based thermochromic luminescent material represents a new type of cost‐effective functional phosphor.
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