Bohui Xu,Pifu Gong,Fan Liu,Xingyu Zhang,Hao Huo,Zheshuai Lin
The search for new ultraviolet (UV) or deep-UV nonlinear optical (NLO) crystals would greatly prompt the development of laser science and technology. As the NLO performance of these crystals is mainly determined by the anionic groups, herein the (SO 3 CF 3 ) − group is highlighted as a promising non-π-conjugated NLO-active motif with excellent deep-ultraviolet (DUV) transmission and good NLO properties. First-principles studies reveal that this group possesses the largest HUMO-LOMO gap among the (SO 4 ) 2− -based units, as well as a relatively large NLO response. The further experiments demonstrate that the CsSO 3 CF 3 compound containing the (SO 3 CF 3 ) − motif exhibits th UV cutoff edge below 200 nm and an NLO effect ≈0.8× KH 2 PO 4 , confirming the potentials of this new motif for UV and DUV NLO applications.
Mg(SO 3 CF 3 ) 2 (Mg(OTf) 2 ) is a simple and cost-effective magnesium salt, which can promote the future applications of rechargeable magnesium batteries (RMBs). However, the simple Mg(OTf) 2 /ether electrolytes suffer from poor electrochemical properties due to the low solubility of Mg(OTf) 2 and the serious decomposition passivation of the [Mg 2+ -OTf − ] ion pair on Mg. Herein, the OTf − anion is successfully grafted on low-cost fluoride boronic esters (B(OC x H y F 2x-y+1 ) 3 ) to obtain the asymmetric and weak-coordination boron-center [B(OC x H y F 2x-y+1 ) 3 OTf] − anion in ether electrolytes. The -OCH 2 CF 3 (TFE) groups in B(TFE) 3 effectively realize the charge delocalization of the OTf − and B-O plane, restraining the independent decomposition of the [Mg 2+ -OTf − ] ion pair. The co-decomposition of the asymmetric [B(TFE) 3 OTf] − induces the formation of the B-containing organic/inorganic interphase, thus achieving a reversible Mg plating/stripping. After the further solubilization reaction, the obtained electrolyte exhibits a high average coulombic efficiency of 98.13% and long-term cycling stability (1000 h). Notably, the long cycling life (capacity retention of 90.2% after 600 cycles at 1 C) and high-rate capacity (43.0 mAh g −1 at 5 C) of the Mg/Mo 6 S 8 full cell demonstrate a favorable electrolyte/cathode compatibility. This work brings new insights to design the new-type and low-cost Mg-salts and high-performance electrolytes for commercial RMBs.
Ma Jing,Yamaguchi Toshio,Tseng Jochi,Yamada Hiroki,Yu Zhiwu,Zhou Yongquan
The concentration-dependent local
structure and ion solvation behavior
in sodium triflate NaOTf/dimethoxyethane (DME) electrolytes were systematically
investigated by integrating large-angle X-ray scattering (LAXS) with
atomic modeling, IR, and density functional theory (DFT) calculations
across a range of salt concentrations ( x (NaOTf) =
0, 0.05, 0.1, and 0.2). LAXS data-driven all-atomic modeling reveals
that Na + ions preferentially induce DME to adopt the trans–gauche–trans
(TGT) conformation, with each DME molecule coordinating to Na + in a bidentate chelation mode via both oxygen atoms. Quantitative
analysis of center-of-mass radial distribution functions shows that
the average number of DME molecules coordinating to Na + decreases from 2.2 at x (NaOTf) = 0.05 to 1.1 at x (NaOTf) = 0.2, while the average number of associated OTf – anions per Na + increases from 0.9 to 2.3
over the same concentration range. Pair distribution functions combined
with DFT-optimized cluster geometries indicate that Na + maintains a total coordination number of 5.4–5.8, with concentration-dependent
contributions from the oxygen atoms in both DME and OTf – . The Na + -OTf – contact ion pairs exhibit
two distinct configurations: bidentate (CIPB) with a Na–S distance
of 2.94 Å and monodentate (CIPM) with a Na–S distance
of 3.69 Å. The fraction of CIPB decreases from 56% at x (NaOTf) = 0.05 to 28% at x (NaOTf) = 0.2,
while the fraction of CIPM increases correspondingly from 44% to 72%.
Speciation analysis based on coordination number distributions reveals
that at x (NaOTf) = 0.05, 49% of Na + exists
as [Na-3DME] + , 44% as neutral [Na-1OTf-2DME] 0 , and 7% as anionic [Na-2OTf-1DME] − ; at x (NaOTf) = 0.2, the dominant species becomes [Na-2OTf-1DME] − (35%), followed by [Na-3OTf] 2– (29%),
with only 20% remaining as neutral [Na-1OTf-2DME] 0 . This
systematic evolution from solvent-separated ions to contact ion pairs
and higher-order ionic aggregates with increasing salt concentration
provides a quantitative structural basis for understanding the nonlinear
ionic conductivity behavior in glyme-based sodium electrolytes.
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