Studies of Functional Defects for Fast Na‐Ion Conduction in Na_3−yPS_4−xCl_x with a Combined Experimental and Computational Approach

Abstract

All-solid-state rechargeable sodium (Na)-ion batteries are promising for inexpensive and high-energy-density large-scale energy storage. In this contribution, new Na solid electrolytes, Na 3−y PS 4−x Cl x , are synthesized with a strategic approach, which allows maximum substitution of Cl for S (x = 0.2) without significant compromise of structural integrity or Na deficiency. A maximum conductivity of 1.96 mS cm −1 at 25 °C is achieved for Na 3.0 PS 3.8 Cl 0.2 , which is two orders of magnitude higher compared with that of tetragonal Na 3 PS 4 (t-Na 3 PS 4 ). The activation energy (E a ) is determined to be 0.19 eV. Ab initio molecular dynamics simulations shed light on the merit of maximizing Cldoping while maintaining low Na deficiency in enhanced Na-ion conduction. Solid-state nuclear magnetic resonance (NMR) characterizations confirm the successful substitution of Cl for S and the resulting change of P oxidation state from 5+ to 4+, which is also verified by spin moment analysis. Ion transport pathways are determined with a tracer-exchange NMR method. The functional detects that promote Na -ion transport are maximized for further improvement in ionic conductivity. Full-cell performance is demonstrated using Na/Na 3.0 PS 3.8 Cl 0.2 /Na 3 V 2 (PO 4 ) 3 with a reversible capacity of ≈100 mAh g −1 at room temperature.

Light Generation in Lead Halide Perovskite Nanocrystals: LEDs, Color Converters, Lasers, and Other Applications

“…[4][5][6][7]59,[94][95][96][97][98][99][100][101][102][103][104][105][106][107][108][109][110][111] Electrical driving almost does not change the superior optical features of LHP-NCs as emitters in the resulting LEDs, including their high color purity, a wide color gamut, and a stable spectrum that is independent of the applied driving voltage. [4][5][6][7]59,[94][95][96][97][98][99][100][101][102][103][104][105][106][107][108][109][110][111] Under electrical excitation, LHP-NCs consisting of mixed halides would undergo spectral splitting; however, RGB primary color LEDs that use single-halide LHP-NC emitters still exhibit a wide color gamut that can display most natural colors in resulting full color displays.…”

“…The intrinsic EQE loss in LHP-NCs typically includes two contributions to nonradiative recombination: trap states and the Auger process. [4][5][6][7]59,[94][95][96][97][98][99][100][101][102][103][104][105][106][107][108][109][110][111] As a planar device structure limits the low photon outcoupling efficiency to ≈20%, the PLQY of the LHP-NC film plays an ultimate role in determining the maximum EQE that resulting LEDs can achieve. [4][5][6][7]59] A high defect tolerance does not correspond to the absence of the resulting EQE loss, which is consistent with a low initial EQE at a low driving current density level; [4][5][6][7]59,68,[94][95][96][97][98][99][100][101][102][103][104][105][106]…”

“…[4,59] In an LED with a low-quality LHP-NC film and charge carrier transport layers with many bandgap states, the injected charge carriers would flow across the device via these trap states even if the device is still in an off-state under a bias lower than the threshold. [4][5][6][7]59,[94][95][96][97][98][99][100][101][102][103][104][105][106][107][108][109][110][111] Nonuniformity in an LHP-NC film is another source of leakage current. The pinholes in a nonuniform LHP-NCs film act as a bypass that drains out charge carriers.…”

“…[5,7,96,97,99] The charge carrier balance in the recombination zone is another important factor in determining the EQE, which is consistent with the role played by the emissive film PLQY. [4][5][6][7]59,[94][95][96][97][98][99][100][101][102][103][104][105][106][107][108][109][110][111] For an LHP-NC LED driven by imbalanced charge carriers in the recombination zone, the excess carrier species are themselves the loss, and the resulting interaction with excitons leads to an additional loss, even at a low driving current density, via the Auger nonradiative process. The comparable mobilities of electrons and the holes of LHP-NCs are a good feature for realizing balanced opposite charge carriers in the recombination zone.…”

“…[4][5][6][7] However, it is difficult to eliminate the Auger nonradiative recombination of multiexcitons at a high driving current density, which plays a significant role in EQE roll-off. [4][5][6][7]59,[94][95][96][97][98][99][100][101][102][103][104][105][106][107][108][109][110][111]144] Thus, adjusting the charge carrier transport capabilities of the matched function layers can result in balanced charge carrier injections into the LHP-NC layer, and a higher maximum EQE can be reached by suppressing the Auger process at a low driving current density level in most devices. [4][5][6][7]59,[94][95][96][97][98][99][100][101][102][103][104][105][106][107]…”