Despite the theoretically high energy density, the practical energy density of Li-S batteries at the moment does not meet the demand due to low sulfur (S) loading (<2 mg cm −2 ), large electrolyte amount (electrolyte/sulfur ratio >20 µL mg −1 ), and excess lithium (Li) metal use (>10 times excess). [5] In particular, large electrolyte usage (flooding) greatly diminishes the practical energy density of Li-S batteries. Due to the intrinsic solution-based redox chemistry, however, many of the challenges arise from minimizing the electrolyte/ sulfur ratio (E/S ratio). Since soluble lithium polysulfide (LiPS, Li 2 S x when 2 < x ≤ 8) intermediates are self-redox mediating, the decrease in the LiPS dissolution causes a sluggish sulfur conversion and high polarization. [6] Next, the morphology of lithium sulfide (Li 2 S) electrodeposition and the kinetics of the re-oxidation are affected by the sulfur species solubility as well. [7] Hence, uncontrolled precipitation and continual accumulation of Li 2 S limit the discharge capacity and further passivate the cathode interface throughout the cycling. [8] Reducing the electrolyte volume exacerbates not only the cathode performance but also the anode stability. A high reactivity and an infinite volume change of the Li metal anode cause the incessant decomposition of the electrolyte. Therefore, the lean electrolyte condition accelerates the increase of the cell resistance and provokes earlier performance failure compared to the flooding electrolyte system. [9] Manipulating electrolyte materials (solvents, salt anions, and additives) has a considerable impact on the electrochemical performance of Li-S batteries. There have been studies in which solvents with high Gutmann donor numbers (DNs) form strong interactions with lithium ions (Li + ) and promote the solvation of polysulfide (PS) anions. The increased LiPS solubility facilitates the solution-mediated reaction pathway, enabling fast reaction kinetics and high sulfur utilization. [10] Furthermore, the same merits can also be achieved with salt anions having high-DNs [11] or additives promoting ionic solvation. [12] Under a lean electrolyte regime, the role of highly solvating electrolytes becomes more prominent because of the limited solubility of sulfur species. For example, high-DN solvents can enhance the sulfur utilization under the reduced electrolyte amount by promoting the charge/discharge reactions. [13] Despite this fact, the Minimizing electrolyte use is essential to achieve high practical energy density of lithium-sulfur (Li-S) batteries. However, the sulfur cathode is more readily passivated under a lean electrolyte condition, resulting in low sulfur utilization. In addition, continuous electrolyte decomposition on the Li metal anode aggravates the problem, provoking rapid capacity decay. In this work, the dual functionalities of NO 3 − as a high-donor-number (DN) salt anion is presented, which improves the sulfur utilization and cycling stability of lean-electrolyte Li-S batteries. The NO 3 − anion eleva...
A series of methoxy-bridged diamidotitanium dimers have been synthesized and fully characterized. Treatment of the Grignard reagent MeMgBr with (cycl)Si(NBu t ) 2 TiCl 2 (2; cycl ) C n H 2n , n ) 3-5) in 2:1 or 1:1 stoichiometry yielded four-coordinate dimethyltitanium (cycl)Si(NBu t ) 2 TiMe 2 (3) and monomethyltitanium (CH 2 ) 3 Si(NBu t ) 2 TiMeCl (5) complexes, respectively. Subsequent reaction of these complexes with dioxygen proceeds by insertion of an oxygen molecule into the Ti-C bond of 3 and 5, generating the respective methoxybridged titanium dimers [(cycl)Si(NBu t ) 2 Ti(µ-OMe)Me] 2 (4) and [(cycl)Si(NBu t ) 2 Ti(µ-OMe)Cl] 2 (6). In contrast, the reaction of the titanium(IV) dichloride complex (CH 2 ) 3 Si(NBu t ) 2 TiCl 2 (2a) with O 2 gives the hydrazido species [{(NBu t NBu t )(CH 2 ) 3 SiO}TiCl 2 ] 2 (7a) as a result of facile Si-O-Ti bond formation upon autoxidation. To our knowledge, these complexes are the first examples of methoxy-bridged diamidotitanium(IV) dimers. Reaction of 2 with 2 equiv of PhCH 2 MgBr yielded the corresponding dibenzyl (Bn 2 ) derivatives of titanium (cycl)Si(NBu t ) 2 TiBn 2 (9). When these dibenzyl complexes were used as precursors for the conversion of monomeric to dimeric alkoxy-bridged species, oxo insertion did not occur, presumably because formation of the alkoxy-bridged dimer was hampered by the presence of bulky dibenzyl units.
In this article, a novel anode material with high electrochemical performance, made of elements abundant on the Earth, is reported for use in lithium ion batteries. A chemically synthesised material (SiO 2 /ZrO 2 ) containing Si-O-Zr bonds, exhibits as much as 2.1 times better electrochemical performance at the 10 th cycle than a physically mixed material (SiO 2 +ZrO 2 ) of the same elements. When compared to synthesized SiO 2 or conventional graphite-based electrodes, the SiO 2 /ZrO 2 anode shows superiorcapability and cycling performance. This superior performance is ascribed to the effect of ternary compounds, which contributes not only to increasing the packing density, but also to creating the Si-O-Zr bond that makes additional reactions between SiO 2 /ZrO 2 and lithium ions possible. The Si-OZr bond also contributes to improved conductivity for SSZ and provides facile paths for charge transfer at the electrode/electrolyte interface. Therefore, the overall internal resistance in a battery would be decreased and better performance could thus be obtained, with this type of anode. In every result, the positive influence of the Si-O-Zr bonds in the anode of a lithium ion battery was confirmed.
In article number 2000493, Hee‐Tak Kim and co‐workers demonstrate the dual functionality of lithium nitrate in lean‐electrolyte lithium–sulfur batteries. Based on its high electron donicity, the nitrate anion enhances sulfur utilization and prevents electrolyte decomposition, enabling both high cycling capacity and long‐term stability of lean‐electrolyte lithium‐sulfur batteries.
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